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Monotonic and cyclic pullout resistance of geosynthetics Raju, Muthu 1995

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MONOTONIC AND CYCLIC PULLOUT RESISTANCE OFGEOSYNTHETICSbyMUTHU RAJUB.E., Bangalore University, 1986M.E., Indian Institute of Science, Bangalore, 1988M.A.Sc., The University ofBritish Columbia, 1991A THESIS SUBMITTED IN PARTIAL FULFILMENT OFTHE REQUIREMENTS FOR THE DEGREE OFDOCTOR OF PHILOSOPHYinTHE FACULTY OF GRADUATE STUDIESDEPARTMENT OF CIVIL ENGINEERINGWe accept this thesis as conformingto the required standardTHE UNIVERSITY OF BRITISH COLUMBIAMarch 1995©MuthuRaju, 1995In presenting this thesis in partial fulfilment of the requirements for an advanceddegree at the University of British Columbia, I agree that the Library shall make itfreely available for reference and study. I further agree that permission for extensivecopying of this thesis for scholarly purposes may be granted by the head of mydepartment or by his or her representatives. It is understood that copying orpublication of this thesis for financial gain shall not be allowed without my writtenpermission.(Signature)Department of QYIL 4i,J€e4Ji1The University of British ColumbiaVancouver, CanadaDate 2.o 9’DE-6 (2188)ABSTRACTAn evaluation of soil-geosynthetic interface strength for different types of loading isimportant to the design of any anchorage detail of a reinforced soil structure or membrane-lined waste containment facility. The imposed loadings may be classified as static, repeatednon-dynamic or cyclic, and dynamic. The test method best suited to model the anchoragebehaviour is the pullout test.A large scale pullout apparatus was designed that accommodates a soil sample 1.30 mlong x 0.64 m wide x 0.60 m thick. Samples of a uniformly-graded medium sand wereprepared by air pluviation. A stress-controlled top boundary was used and tests performedfor normal stresses in the range 4 to 30 kPa. Tests were performed on five types ofgeosynthetics: three geogrids, a smooth geomembrane and a textured geomembrane. Asophisticated electro-hydraulic control system was developed and two modes of testing wereused to evaluate pullout resistance.The response of the geosynthetic is characterized by a non-linear variation of tensileforce along the specimen. Consequently the profile of shear stress variation is non-linear andis dependent on the magnitude of pullout displacement: interpretation of the pullout test toobtain an interaction factor for design should account for this extensible behaviour. Ageneralized method is proposed for use with independent measurements of force and strain.The application of the generalized method is demonstrated: it describes very well the variationof interaction factor with pullout displacement and suggests a unique value that is independentof normal stress.Cyclic loading of the test specimen in most cases reveals that an interaction factormobilized is equal to or slightly exceeds the value mobilized in corresponding DC test. A loadIIABSTRACT(continued)ratio is defined as the ratio of the measured pullout load in cyclic pullout test to thecorresponding DC test. A conceptual model is proposed that links a load ratio to stable andunstable behaviour in cyclic pullout, and identifies a threshold ratio above which an unstablebehaviour results. The threshold ratio is observed to be influenced by the specimencharacteristic, being >1 for a grid specimen with a relatively rigid bearing member, and =1 forall other test specimens except a few tests where a value <1 was observed. This implies thatusing a reduced value of interaction factor for dynamic loads in all cases is inappropriate, inthat it does not properly describe the mobilized response.mTABLE OF CONTENTSABSTRACT iiLIST OF ‘I’ABI.ES xiiLIST OF FIGURES xiii1. IrTRODIJT’IOI 11.1 Use of Geosynthetics 11.2 Current Design Practice 11.3 Objectives 21.4 Thesis Organization 42. 52.1 Introduction 52.2 Soil Reinforcement using Geosynthetics 52.3 Fluid/Gas Containment using Geosynthetics 62.4 Types of Imposed Loading 72.4.1 Construction Loading 82.4.2 Static Loading 82.4.3 Repeated Non-Dynamic Loading 82.4.4 Dynamic Loading 92.5 Analytical Methods used in Design 92.5.1 Limit Equilibrium Method 102.5.2 Strain Compatibility Design Method 112.5.3 Finite Element Method 122.5.4 Seismic Design 13ivTABLE OF CONTENTS(continued)2.5.4.1 A Pseudo-Static Analysis.132.5.4.1.1 The Displacement-Controlled Design 162.6 Evaluation of Soil-Geosynthetic Interaction 162.6.1 Direct Shear Tests 172.6.2 Pullout Tests 192.6.2.1 Factors Influencing Pullout Resistance 252.6.2.1.1 Soil Characteristics 252.6.2.1.2 Test Specimen Characteristics 262.6.2.1.3 Test Apparatus and Procedure 272.6.2.1.3.1 Normal Stress 272.6.2.1.3.2 Boundary Effects 282.6.2.1.4 Loading Characteristics 312.6.2.2 Methods for Interpretation of the Pullout Test 342.6.2.2.1 Monotomc Pullout Tests 342.6.2.2.2 Cyclic Pullout Tests 352.6.2.3 Finite Element Modelling 372.6.3 Model Shake Table Tests 382.6.4 Behaviour of Field Structures 392.6.4.1 Pullout Tests 392.6.4.2 Dynamic Tests 402.7 Research Needs 413. APPARATUS 52VTABLE OF CONTENTS(continued)3.1 Introduction 523.2 Large Pullout Apparatus 523.2.1 Pullout Box 523.2.2 Hopper 553.2.3 Pullout Control Assembly 563.2.3.1 Clamp 573.2.4 Surcharge Pressure 583.2.4.1 Reaction 583.3 Instrumentation 593.3.1 Pullout Force 593.3.2 Pullout Displacement 593.3.3 Pressure on the Front Wall 603.3.4 Water Pressure Transducer 603.3.5 Strain Gauges 613.4 Data Acquisition System 614. MATERIAL PROPERTIES 714.1 Introduction 714.2 Sand 714.2.1 Angle ofFriction 724.2.1.1 Direct Shear Tests 724.3 Geosynthetic Test Specimens 734.3.1 Geogrids 74viTABLE OF CONTENTS(continued)4.3.1.1 TensarUX-1500 .744.3.1.2Miragrid 15T 744.3.1.3 Stratagrid 700 754.3.2 Geomembranes 764.4 Aluminum Sheet Test Specimen 764.5 Direct Shear Tests on the Sand and Test Specimens 775 PRODEDIJRE 835.1 Introduction and Test Program 835.2 Test Preparation 845.2.1 Preparation of the Test Apparatus 845.2.2 Preparation of the Test Specimen 855.2.3 Placement of the Sand Sample and the Test Specimen 855.2.4 Application of Surcharge Load 865.2.5 Clamping of the Test Specimen 875.3 Test Procedure 875.4 Post Test Procedure 886. E.ESI’ REStT[4T 916.1 Introduction 916.2 Displacement-Controlled Pullout Tests 916.2.1 Influence ofFront Boundary 926.2.2 Influence of Rate ofDisplacement 946.2.3 Aluminum Test Specimen 94viiTABLE OF CONTENTS(continued)6.2.3.1 Rough Aluminum Sheet .956.2.4 Geosynthetic Test Specimens 956.2.4.lGeogrid 976.2.4.1.1 Pullout Resistance 976.2.4.1.2 Rib Strain 996.2.4.2 Geomembranes 1016.2.4.2.1 Pullout Resistance 1026.2.4.2.2Local Strain 1026.3 Load-Controlled Tests 1036.3.1 Aluminum Test Specimen 1046.3.1.1 Pullout Resistance 1046.3.1.1.1 Displacement of the Embedded End 1056.3.2 Geosynthetic Test Specimens 1056.3.2.1 Geogrids 1066.3.2.1.1 Pullout Resistance 1066.3.2.1.2 Influence ofLoading Frequency 1076.3.2.1.3 Rib Strain 1076.3.2.1.4 Displacement of the Embedded End 1096.3.2.2 Geomembranes 1096.3.2.2.1 Pullout Resistance 1096.3.2.2.2 Local Strain 1116.3.2.2.3 Displacement of the Embedded End 111VIIITABLE OF CONTENTS(continued)7. ANALYSIS OF THE TEST RESULTS.1387.1 Introduction 1387.2 Displacement-Controlled Pullout Tests 1387.2.1 Influence oftheFrontBoundary 1397.2.2 Mobilization of Pullout Resistance 1417.2.3 Experimental Interaction Factors 1447.2.3.1 Average Resistance Method 1447.2.3.1.1 Total Area 1457.2.3.1.2EffectiveArea 1467.2.3.1.3 Maximum Slope 1477.2.3.1.4 Mobiising Process Method 1477.2.3.2 Generalized Method 1487.2.3.3 Application of the Generalized Method 1527.2.3.3.1 Displacement of the Embedded End 1537.2.3.3.2 Tensile Force 1537.2.3.3.3 Shear Stress 1557.2.3.3.4 Interaction Factors 1577.2.3.3.4.1 Peak and Limiting Interaction Factors 1597.2.4 Comparison of Interaction Factors With and Without Bearing Elements 1617.2.5 Comparison of Theoretical and Experimental Interaction Factors 1627.2.6 Comparison of Geogrid Interaction Factors with Other Laboratory andField Data 164ixTABLE OF CONTENTS(continued)7.3 Load-Controlled Pullout Tests.1697.3.1 Incremental Displacement Response 1707.3.2 Strain Response 1727.3.3 Interaction Factors for Cyclic Loading 1747.4 Comparison of Interaction Factors from DC and LC Tests 1758. SUMMARY AND CONCLUSIONS 2288.1 Summary 2288.2 On the Pullout Test 2298.2.1 Apparatus and Instrumentation 2298.2.2 Materials and Test Procedure 2308.2.3 Test Results and Interpretation 2318.3 Implications for Selection of a Pullout Interaction Factor in Design 2338.4 Recommendations for Future Studies 234236A. TECHNIQUE OF STRAIN GAUGING PLASTICS 246A. 1 Introduction 246A.2 Characteristics of the Strain Gauge 247A.3 Strain Gauging Procedure 247A.3. 1 Chemicals for Surface Preparation 247A.3.2 Adhesive Selection and Preparation 248A.3.3 Geosynthetic Surface Preparation 248A.3.4 Gauge Preparation 249xTABLE OF CONTENTS(continued)A.3.5 Application of the Gauge 250A.3.6 Gauge Soldering 251A.3.7 Gauge Protection 252A.3.8 Analysis of Strain Data 253B. RAW DATA OF PULLOUT RESISTANCE AND STRAIN 254xiLIST OF TABLESTable 2.1: Summary of the pullout test apparatus and testing characteristics 29Table 4.1: Properties of the geogrid test specimens 75Table 4.2: Properties of the geomembrane test specimens 76Table 6.1: Summary of displacement-controlled tests on the geogrids 93Table 6.2: Summary of displacement-controlled tests on the geomembrane andaluminum sheets 94Table 6.3’: Summary of the load-controlled pullout tests 104Table 7.1: Geometric and interface friction characteristics of the test specimens 163Table 7.2: Theoretical interaction factor for the grid specimens, USFIIWA guidance. 163Table 7.3: Stress ratio GbIGn from pullout tests on the geogrid 165Table 7.4: Typical properties of the geogrid specimens 166Table 7.5: Properties of soil used in the laboratory studies and field structure 166xliLIST OF FIGURESFigure 2.1: Typical examples of soil reinforcement applications (after Palmeira, 1987). 43Figure 2.2: Failure mechanisms of reinforced soil structures (after Palmeira, 1987) 43Figure 2.3: Section showing the components of a liner system (after Udwari andKittridge, 1986) 44Figure 2.4: Schematic illustration of potential failure modes in a containment facility(after Mitchell and Mitchell, 1992) 45Figure 2.5: Forces acting on a reinforced soil wall (after Christopher et al., 1990) 46Figure 2.6: Schematic illustration of the multilayer liner system used in the KettlemanHills landfill (after Seed et al., 1990) 46Figure 2.7: Mechanisms of load transfer (after Jewell et al., 1984) 47Figure 2.8: Bearing stresses on a grid reinforcement (after Jewell et al., 1984) 48Figure 2.9: Comparison of test results with predicted values of stress ratio (after Jewell,1990) 49Figure 2.10: Relationship between efficiency factor and confining stress for variousgeogrids (after Juran et al., 1988) 50Figure 2.11: Effect of front wall roughness on pullout test results (after Palmeira andMilligan, 1989) 51Figure 2.12: A schematic ofvarious interpretation methods for the pullout test 51Figure 3.1: Components of the pullout apparatus 63Figure 3.2: Photograph illustrating components of the pullout apparatus 64Figure 3.3: Slot arrangement on the front wall of the apparatus 65Figure 3.4: Top and side view of the hopper assembly 66xliiFigure 3.5:Figure 3.6:Figure 3.7:Figure 3.8:Figure 3.9:Figure 3.10Figure 4.1:Figure 4.2:Figure 4.3:Figure 4.4:Figure 4.5:Figure 4.6:Figure 4.7:Figure 4.8:Figure 4.9:Figure 4.10:Figure 5.1:Figure 5.2:Figure 6.1:LIST OF FIGURES(continued)Principle components of closed-loop control 67Schematic illustration of the closed-loop control system 67Details of the clamp 68Reaction frame and the pressurizing system 69Location of pressure transducers on the front wall of the pullout box 70Strain gauge locations with respect to the front wall of the apparatus 70Grain size distribution curve of the sand before and after testing 78Normalized shear stress relationship with shear displacement for directshear tests on the sand 78Relationship between normal displacement and shear displacement for thesand 79Plane strain friction angle for the sand 79Variation of constant volume plane strain ffiction angle with normal stress. 80Measured dimensions of Tensar UX-1500 80Instrumented Tensar UX- 1500 test specimen with strain gauges 81Photograph and measured dimensions of Miragrid 15T 81Photograph and measured dimensions of Stratagrid 700 82Shear stress and normal stress relationship of various interfaces fromdirect shear tests 82Demand signal in the displacement-controlled mode 90Demand signal in the load-controlled mode 90Reference code for tests on the geogrids 112xivLIST OF FIGURES(continued)Figure 6.2: Reference code for tests on the geomembranes and aluminum sheets 112Figure 6.3: Pullout resistance of the Tensar grid with an aluminum or arborite surfaceonthefrontwall 113Figure 6.4: Pullout resistance of the smooth and textured geomembranes with analuminum or arborite surface on the front wall 113Figure 6.5: Influence of displacement rate on mobilized pullout resistance for theTensar grid 114Relationship between d and de for the aluminum rough sheet 114Pullout resistance of the aluminum rough sheet at a=4 to 12 kPa 115Relationship between d and d for the Tensar grid at a4 to 30 kPa 115Relationship between d and de for the Stratagrid at a=4 to 17 kPa 116Relationship between d and de for the Miragrid at a=10 and 17 kPa 116Relationship between d and cL for the smooth and textured geomembraneat a=4 to 12 kPa 117Pullout resistance of the Tensar grid at a=4 to 30 kPa 117Pullout resistance of the Miragrid at a4 to 17 kPa 118A photograph illustrating the displacement pattern of transverse elementsfortheMiragrid 118Pullout resistance of the Miragrid when tested in the cross-machinedirection at a=4 to 17 kPa 119Figure 6.16: Pullout resistance of the Stratagrid at a=4 to 17 kPa 119Figure 6.6:Figure 6.7:Figure 6,8:Figure 6.9:Figure 6.10:Figure 6.11:Figure 6.12:Figure 6,13:Figure 6.14:Figure 6.15:xvLIST OF FIGURES(continued)Figure 6.17: Mobilization of strain with d for the Tensar grid at a=10 kPa 120Figure 6.18: Mobilization of strain with d for the Stratagrid at o10 kPa 120Figure 6.19: Mobilization of strain with d for the Miragrid at a=10 kPa 121Figure 6.20: Mobilization of strain with dfor the Miragrid at a=17 kPa 121Figure 6.21: Characteristic variation of strain with displacement d 122Figure 6.22: Variation of strain with rate of pullout for the Tensar grid at a20 kPa. 122Figure 6.23: Pullout resistance of the smooth geomembrane at a=4 to 12 kPa 123Figure 6.24: Pullout resistance of the textured geomembrane at a4 to 12 kPa 123Figure 6.25: Mobilization of strain with dfor the smooth geomembrane at a4 kPa 124Figure 6.26: Mobilization of strain with d for the smooth geomembrane at a8 kPa 124Figure 6.27: Mobilization of strain with d for the smooth geomembrane ata=12kPa 125Figure 6.28: Pullout resistance of the rough aluminum sheet at a=8 kPa andf=0.01 Hz 125Figure 6.29: Detailed response at small displacement, from Figure 6.28 126Figure 6.30: Relationship between d and de for the rough aluminum sheet in the LCtests at a=8 kPa and f=0.01 Hz 126Figure 6.31: Pullout resistance of the Tensar grid in the DC and LC tests at a=4 to 17kPaandf=0.OlHz 127xviLIST OF FIGURES(continued)Figure 6.32: Pullout resistance of the IVliragrid in the DC and LC tests at vr4 to 17kPaandf=0.OlHz 127Figure 6.33: Pullout resistance of the Stratagrid in the DC and LC tests at a4 to 17kPaandf=0.OlHz 128Figure 6.34: Pullout resistance of the Stratagrid in the DC and LC tests at a=17 kPaandf=0.01I{z 128Figure 6.35: Pullout resistance of the Tensar grid in the DC and LC tests at a=10 kPaandf=0.1I{z 129Figure 6.36: Mobilization of strain for the Tensar grid in the LC tests at a=10 kPa andf0.O1 Hz 129Figure 6.37: Mobilization of strain for the Miragrid in the LC test at a1O kPa andf=O.O1 Hz 130Figure 6.38: Mobilization of strain for the Stratagrid in the LC tests at a= 10 kPaandf0.OlHz 130Figure 6.39: Mobilization of strain for the Tensar grid in the LC tests at a=17 kPa andf=0.01 Hz 131Figure 6.40: Mobilization of strain for the Miragrid in the LC tests at a=17 kPa andf=0.OlHz 131Figure 6.41: Mobilization of strain for the Stratagrid in the LC tests at a17 kPa andf=0.01 Hz 132xviiLIST OF FIGURES(continued)Figure 6.42: Relationship between d and defor the Tensar grid in the LC tests at (T4,lOandl7kPa 132Figure 6.43: Relationship between d and de for the Ivliragrid in the LC tests at = 4kPaandlOkPa 133Figure 6.44: Relationship between d and de for the Stratagrid in the LC tests at a 4,lOandl7kPa 133Figure 6.45: Pullout resistance of the smooth geomembrane in the DC and LC tests.. 134Figure 6.46: Pullout resistance of the textured geomembrane in the DC and LC test atc=8 kPa and f=O.O1 Hz 134Figure 6.47: Pullout resistance of the textured geomembrane in the DC and LCtests at a=8 kPa and f=O.lHz 135Figure 6.48: Mobilization of strain for the smooth geomembrane in the LC test at8kPa 135Figure 6.49: Mobilization of strain d for the smooth geomembrane in the LC test at12kPa 136Figure 6.50: Relationship between d and d for the smooth geomembrane in the LCtests at a=8 and 12 kPa 136Figure 6.51: Relationship between d and de for the textured geomembrane in the LCtests at a=8 and 12 kPa 137Figure 7.1: Measured lateral stress and applied normal stresses at TPT- 1 and TPT-6locations 178xviiiLIST OF FIGURES(continued)Figure 7.2: Measured lateral stress and pullout resistance for the Stratagrid at o10kPa 178Figure 7.3: Incremental lateral stress on the front wall for the smooth geomembraneand Tensar grid at similar normal stress 179Figure 7.4: Variation of normalised lateral stress ratio with depth ratio for the smoothgeomembrane and Tensar grid at similar normal stress 179Figure 7.5: Variation of normalised lateral stress ratio with depth ratio for the Tensargrid at a=4 to 30 kPa 180Figure 7.6: Variation of normalised lateral stress ratio with depth ratio for theStratagrid at a=4 to 17 kPa 180Figure 7.7: Variation of normalised lateral stress ratio with depth ratio for the Miragridtested in the machine direction at a=4 to 17 kPa 181Figure 7.8: Variation of normalised lateral stress ratio with depth ratio for the Miragridtested in the cross-machine direction at a=4 to 17 kPa 181Figure 7.9: Variation of normalised lateral stress ratio with depth ratio for the smoothgeomembrane at a=4 to 12 kPa 182Figure 7.10: Variation of normalised lateral stress ratio with depth ratio for the texturedgeomembrane at a=4 to 12 kPa 182Figure 7.11: Relationship between d and de for the Tensar grid in the DC test at 183Figure 7.12: Strain profile for the Tensar grid in the DC test at a10 kPa 183xixLIST OF FIGURES(continued)Figure 7.13: Relationship between d and de for the Tensar grid in the DC test at a3OkPa 184Figure 7.14: Strain profile for the Tensar grid in the DC test at a=30 kPa 184Figure 7.15: Strain profile for the Tensar grid in the DC test at a=20 kPa and rdO.50mmlmin 185Figure 7.16: Relationship between d and de for the Stratagrid in the DC test at a10kPa 185Figure 7.17: Strain profile for the Stratagrid in the DC test at a1O kPa 186Figure 7.18: Strain profile for the Stratagrid in the DC test at a=17 kPa 186Figure 7.19: Relationship between d and de for the Miragrid in the DC test at a17kPa 187Figure 7.20: Strain profile for the Miragrid in the DC test at a17 kPa 187Figure 7.21: Relationship between d and d for the smooth geomembrane in the DCtest at a11=8 kPa 188Figure 7.22: Strain profile for the smooth geomembrane in the DC test at a8 kPa.. 188Figure 7.23: A schematic illustration of the interpretation of data by various resistingarea methods (modified after Ochiai et al., 1992) 189Figure 7.24: Schematic illustration of nodes and elements for a) smooth geomembrane,b) Tensar grid and c) Stratagrid and Miragrid 190Figure 7.25: Flow chart of the generalized method for interpretation of a pullout test 191xxLIST OF FIGURES(continued)Figure 7.26: Comparison of measured and calculated displacements of the embeddedend of the Tensar grid in the DC test at a=10 kPa 192Figure 7.27: Relationship between strain and tensile force per unit width for the Tensargrid 192Figure 7.28: Relationship between tensile force at the clamped end and the measuredstrain at location SG-2 (X/LejO. 106) for the Stratagrid 193Figure 7.29: Relationship between tensile force at the clamped end and the measuredstrain at location SG- 1 (X/LejO.O43) for the Miragrid 193Figure 7.30: Relationship between tensile force at the clamped end and the measuredstrain at location SG-1 (x/Le=0.074) for the smooth geomembrane in theDC tests 194Figure 7.31: Profile of deduced tensile force/width and the generated polynomial fit forthe Tensar grid at a=10 kPa 194Figure 7.32: Profile of deduced tensile force/width and the generated polynomial fit forthe Tensar grid at a20 kPa and rd=O.5 mm/mm 195Figure 7.33: Profile of deduced tensile force/width and the generated polynomial fit forTensar grid at =30 kPa 195Figure 7.34: Shear stress variation along the embedded length of the Tensar grid ata=10kPa 196Figure 7.35: Shear stress variation along the embedded length of the Tensar grid ata=20kPa 196xdLIST OF FIGURES(continued)Figure 7.36: Shear stress variation along the embedded length of the Tensar grid ata=30kPa 197Figure 7.37: Shear stress variation along the embedded length of the Stratagrid ata=10kPa 197Figure 7.38: Shear stress variation along the embedded length of the Miragrid at a=17kPa 198Figure 7.39: Shear stress variation along the embedded length of the smoothgeomembrane at a=8 kPa 198Figure 7.40: Interaction factors for the Tensar grid: corrected total area method andgeneralized method 199Figure 7.41: Interaction factors for the Tensar grid: generalized method 199Figure 7.42: Interaction factor for the Stratagrid and Miragrid: corrected total areamethod and generalized method 200Figure 7.43: Interaction factor for smooth geomembrane using the corrected area andgeneralized method 200Figure 7.44: Relationship between average shear stress and nonnal stress for the gridsand rough aluminum sheet 201Figure 7.45: Influence of grid orientation on pullout behaviour of the Miragrid 201Figure 7.46: Relationship between average shear stress and normal stress for thegeomembranes and rough alumimun sheet 202XxiiLIST OF FIGURES(continued)Figure 7.47: Relationship between average shear stress and normal stress for the Tensargrid and Miragrid with and without bearing elements 202Figure 7.48: Details of the geogrid specimen (after Fannin et al,, 1994) 203Figure 7.49: Comparison of Tensar grid interaction factors from laboratory pullouttests 203Figure 7.50: Comparison of interaction factors from Figure 7.39 for smalldisplacement 204Figure 7.51: Comparison of interaction factor for Conwed G9027/Stratagrid 700 204Figure 7.52: Strain profile deduced from the reported nodal displacements of Conwedgrid at a=48.2 kPa from Farrag et al. (1993) 205Figure 7.53: Reinforcement in the field structure (after Fannin et al., 1994) 205Figure 7.54: A schematic diagram showing strain gauge locations(after Farmin, 1990) 206Figure 7.55: Strain in layer No. 7 of the field structure (after Fannin andHermann, 1990) 206Figure 7.56: Relationship between M and Me for the Tensar grid ata1,10 kPa andf0.OlHz 207Figure 7.57: Relationship between M and M for the Tensar grid at a10 kPa andf0.lHz 208Figure 7,58: Relationship between zd and Ad for the Stratagrid at a=10 kPa andf0.OlHz 209xxiiiLIST OF FIGURES(continued)Figure 7.59: Relationship between Ad and Ade for the Miragrid at a17 kPa andf=0.OlHz 210Figure 7.60: Relationship between M and Me for the smooth geomembrane ata=8 kPa and f=0.OlHz 211Figure 7.61: Relationship between Ad and Ade for the textured geomembrane ata=8 kPa and f=0.OlHz 212Figure 7.62: A conceptual model for the modes of behaviour observed in cyclic pullouttesting 213Figure 7.63: Mobilization of rib strain with number of cycles and increasing load ratiofor the Tensar grid at a=10 kPa and f=0.01 Hz 214Figure 7.64: Strain profile with loading ratio at the end of the loading series for theTensar grid at a=10 kPa and f=0.01 Hz 214Figure 7.65: Mobilization of rib strain with number of cycles and increasing load ratiofor the Tensar grid at a=17 kPa and f=0.01 Hz 215Figure 7.66: Strain profile with loading ratio at the end of the loading series for theTensar grid at a=17 kPa and f=0.0l Hz 215Figure 7.67: Mobilization of rib strain with number of cycles and increasing load ratiofor the Miragrid at a=10 kPa and f=0.01 Hz 216Figure 7.68: Strain profile with loading ratio at the end of the loading series for theMiragrid at a=10 kPa and f=0.01 Hz 216xxivLIST OF FIGURES(continued)Figure 7.69: Mobilization of rib strain with number of cycles and increasing load ratiofor the Miragrid at G=17 kPa and f=0.01 Hz 217Figure 7.70: Strain profile with loading ratio at the end of the loading series for theMiragrid at a=17 kPa and f=0.01 Hz 217Figure 7.71: Mobilization of rib strain with number of cycles and increasing load ratiofor the Stratagrid at c=10 kPa and f0.O1 Hz 218Figure 7.72: Strain profile with loading ratio at the end of the loading series for theStratagrid at a=1O kPa and f=0.O1 Hz 218Figure 7.73: Mobilization of rib strain with number of cycles and increasing load ratiofor the Stratagrid at a=17 kPa and f=0.01 Hz 219Figure 7.74: Strain profile with loading ratio at the end of the loading series for theStratagrid at a=17 kPa and f=0.01 Hz 219Figure 7.75: Cyclic pullout interaction factor from the generalized and corrected totalarea methods for the Tensar grid at a=10 kPa and f=0.01 Hz 220Figure 7.76: Comparison of interaction factors in the LC and DC tests for the Tensargrid at a=4 kPa and f=0.01 Hz 220Figure 7.77: Comparison of interaction factors in LC and DC tests for the Tensar gridat o 10 kPa and f0. 01 Hz 221Figure 7.78: Comparison of interaction factors in the LC and DC tests for the Tensargrid at a=10 kPa and f=0.1 Hz 221X2WLIST OF FIGURES(continued)Figure 7.79: Comparison of interaction factors in the LC and DC tests for the Tensargrid at a=17 kPa and f=0.01 Hz 222Figure 7.80: Comparison of interaction factors in the LC and DC tests for the Miragridat a=4 kPa and f0.01 Hz 222Figure 7.81: Comparison of interaction factors in the LC and DC tests for the Miragridata1=1O kPa and f=0.O1 Hz 223Figure 7.82: Comparison of interaction factors in the LC and DC tests for the Miragridat a=17 kPa and f=0,O1 Hz 223Figure 7.83: Comparison of interaction factors in the LC and DC tests for theStratagrid at a=4 kPa and f=0.01 Hz 224Figure 7.84: Comparison of interaction factors in the LC and DC tests for theStratagrid at a=10 kPa and f=0.01 Hz 224Figure 7.85: Comparison of interaction factors in the LC and DC tests for theStratagrid at a=17 kPa and f=0.01 Hz 225Figure 7.86: Comparison of interaction factors in the LC and DC tests for the smoothgeomembrane at a=8 kPa and f=0.01 Hz 226Figure 7.87: Comparison of interaction factors in the LC and DC tests for the smoothgeomembrane at a=12 kPa and f=0.01 Hz 226Figure 7.88: Comparison of interaction factors in the LC and DC tests for the texturedgeomembrane at a=8 kPa and f=0,01 Hz 227LIST OF FIGURES(continued)Figure 7.89: Comparison of interaction factors in the LC and DC tests for the texturedgeomembrane at a=8 kPa and f=0. 1 Hz 228Figure 7.90: Comparison of interaction factors in the LC and DC tests for the texturedgeomembrane at a=12 kPa and f=0.01 Hz 228Figure B. 1: Mobilization of pullout resistance and strain with pullout displacement forthe Tensar grid at a=4 kPa 254Figure B.2: Mobilization of pullout resistance and strain with pullout displacement forthe Tensar grid at a=10 kPa 254Figure B.3: Mobilization of pullout resistance and strain with pullout displacement forthe Tensar grid at a=10 kPa: smooth arborite front boundary 255Figure B.4: Mobilization of pullout resistance and strain with pullout displacement forthe Tensar grid without bearing elements at a=4 kPa 255Figure B .5: Mobilization of pullout resistance and strain with pullout displacement forthe Tensar grid without bearing elements at a=10 kPa 256Figure B.6: Mobilization of pullout resistance and strain with pullout displacement forthe Tensar grid without bearing elements at a=17 kPa 256Figure B.7: Mobilization of pullout resistance and strain with pullout displacement forthe Tensar grid without bearing elements at a=20 kPa and rd=O.25mm/mm 257LIST OF FIGURES(continued)Figure B.8: Mobilization of pullout resistance and strain with pullout displacement forthe Tensar grid without bearing elements at a=2O kPa and rdO.5Omm/mm 257Figure B.9: Mobilization of pullout resistance and strain with pullout displacement forthe Tensar grid without bearing elements at a=2O kPa and rd=l .00mm/mm 258Figure B. 10: Mobilization of pullout resistance and strain with pullout displacement forthe Stratagrid without bearing elements at a=17 kPa 258Figure B. 11: Relationship between Ad and Me for Tensar grid at a=4 and 17 kPa... 259Figure B. 12: Relationship between Ad and M for Stratagrid at a=4 and 17 kPa 260xxviiiLIST OF SYMBOLSa Factoram Maximum wall acceleration at the centroid of the active massa0 Reference accelerationB Thickness of the bearing memberC CohesionC Effective unit perimeter, for sheets and grids it is 2C Coefficient of curvatureC Coefficient of unifonnityCRD Constant rate of displacementCRL Constant rate of loadingdai average displacement of ith elementd Clamped end displacement of the test specimende Embedded end displacement of the test specimend Displacement of the ith noded10 Particle size at 10 percent finerd50 Particle size at 50 percent finer or mean particle sizeD Depth of the pullout test apparatusDC Displacement-controlled testing modeD I Degree of interferenceem Maximum void ratioemin Minimum void ratioxxixLIST OF SYMBOLS(continued)f Frequency of cyclic loadingfb Generalized bond coefficientF* Pullout resistance (friction-bearing-interaction) factorF Non-dimensional stress factorg Gravitational acceleration (9.81 mIs2)H Height of the retaining wallh Half thickness of soil sampleK Ratio of the actual normal stress to the applied effective normal stressK0 Coefficient of lateral earth pressure at restK Material constantL Length of the reinforcement in the retaining wallLe Embedment or adherence length in the resisting zone behind the failure surfaceLea Actual embedment length of the test specimenLei Initial embedment length of the test specimenLr Length of the test specimenLength of the specimen between front wall of the apparatus and the section xLC Load-controlled testing modeLR Load ratioLVDT Linear variable differential transformerN Number of cyclesn Number of bearing membersp Corrected pullout resistance of the test specimenxxxLIST OF SYMBOLS(continued)Pm Maximum pullout resistance of the test specimen in CRDPAE Horizontal dynamic thrustPb Maximum pullout force for a grid with n bearing membersP0 Maximum pullout force for an isolated bearing memberP1 Horizontal inertia force acting at the centroid of the reinforced soil massP1p, Inertia forcePr,max Pullout force measured at the clamped end of the specimenPr,x Pullout force measured or estimated at a point x on the specimenP Skin friction component of the pullout resistancerd Rate of displacementr1 Rate of loadingS Spacing between bearing memberst1, t2, t3 RealtimeT Tensile forceTmax Pullout force measured at the clamped end of the specimenT Pullout force measured or estimated at the section x of the test specimenTPT Total pressure transducerVRL Variable rate of loadingW Width of the test specimenx Distance of a point on the test specimen from the front wall of the apparatusy Distance of a point on the front wall from the middle of the slotScale effect correction factorxdLIST OF SYMBOLS(continued)Fraction of the bearing area available for bearingcf, o Fraction of the plan area of the test specimen that is solidcx Structural geometric factor for bearing resistanceYr Unit weight of the reinforced massYb Unit weight of the retained soil6 Friction angle between soil and specimen surface6av Average interface friction angle mobilized along the test specimen6peak Peak interface ffiction angle mobilized along the test specimenLocal strain in the element iEgi Global strain in the element iEr Rib strainAngle of internal frictionConstant volume friction angleØds Direct shear friction anglePlane strain friction angleLarge displacement plane strain friction angle)pps Peak plane strain friction angleApparent friction coefficientrh Normalised distance of the strain gauge from the front wall of the apparatusEffective normal stress at the soil-test specimen interfaceLIST OF SYMBOLS(continued)a’b Bearing stress acting on the embedded anchora Normal stresst Shear stresstav Average interface shear stress mobilized along the test specimentpeak Peak interface shear stress mobilized along the test specimenIncremental displacement of the clamped endAde Incremental displacement of the embedded end‘Pm, APmi Ap Amplitude of cyclic loadingAah Incremental lateral (horizontal) stressxxdiiACKNOWLEDGEMENTSI am deeply indebted to my thesis supervisor Dr. Jonathan Fannin for his unfailingsupport, advice and engineering judgement throughout the study. Without his advice andunderstanding this research project would not have been possible.I would like to express my sincere gratitude to Mr. Art Brookes, a technician in thecivil engineering workshop, for his help in the fabrication of the large pullout test apparatus. Iwould also like to thank Mr. Harold Schemp for his assistance in modifying some parts of theapparatus, and Mr. Dick Postgate, chief technician in the civil engineering workshop, for hishelpful suggestions. I wish to thank Mr. John Wong and Ron Dolling, electronic techniciansfor their help in the commissioning of the servo-hydraulic control system and the dataacquistion testing system, often at short notice.This research is funded by a Research Grant from the Natural Sciences andEngineering Research Council of Canada. I wish to express my thanks for the financialsupport provided. Thanks are also due to Nilex Geotechnical Products Inc., ArmtecConstruction Products, Gundle Lining Systems Inc., and Mirafi Inc., for providing materialsused in the testing program.Finally, I wish to express my sincere gratitude to my wife Suneetha for her constantsupport, patience and understanding throughout the thesis work.xxxivCHAPTER 1INTRODUCTION1.1 Use of GeosyntheticsPolymeric materials such as geotextiles, geogrids and geomembranes that are used ingeotechnical engineering applications are collectively termed “geosynthetics”. Five primaryfunctions of geosynthetics are recognized (C. G. S., 1992): separation, filtration, drainage,reinforcement and fluid/gas containment. The last decade has seen a tremendous growth inthe use of geosynthetics in engineering practice, and given recognition to these materials as analternative to conventional solutions in design. Various factors, such as cost savings, ease ofconstruction and quality control have made the use of geosynthetics attractive in foundationengineering. The increasing use has been supported by advances in analytical methods, andmay be attributed to:• research to evaluate design methodologies and fundamental behaviour;• Standard Test methods that facilitate material specifications;• regulatory guidance for construction practice.Design using geosynthetics requires that consideration be given to appropriateanalytical methods, material properties, material tests, interpretation of the manufacturer’stechnical literature, and soil-geosynthetic interaction. The latter consideration of soilgeosynthetic interaction is the subject of this research study.1.2 Current Design PracticeIn the design of reinforced soil structures and membrane-lined containment facilities,an internal stability analysis includes examination of:1Chapter 1. Introduction• a tensile failure of the geosynthetic;• a tensile failure of any connections;• a pullout failure of the geosynthetic.Pullout failure of the geosynthetic is governed by the limiting soil-geosyntheticinterface shear strength. A proper understanding of the development of interface resistanceunder different loading conditions is essential for computing the required embedment length ofa geotextile or a geogrid in a reinforced soil structure, and of a geomembrane in theanchorage trench of a waste containment facility. Several parameters influence themobilization of soil-geosynthetic interaction. In laboratory studies using a pullout apparatus,these parameters relate to the soil type, the type of geosynthetic, configuration of the testapparatus, nature of the loading characteristics, and the testing procedure. Although manytest methods have been standardized for determining the material properties of geosynthetics,at the time of writing no standard test method has been approved for the pullout test.Notwithstanding some significant research contributions on the subject ofsoil/geosynthetic interaction in pullout, there is a need for quality test data on behaviour inpullout at small relative displacements and under different types of loading. This need arisesbecause most of the available pullout test data are from monotonic tests performed under adisplacement-controlled mode.1.3 ObjectivesThe objectives of this study were to:2Chapter]. Introduction• Design and commission a large pullout test apparatus, and associated controls toperform pullout tests under displacement-control and load-control;• Develop a routine for cyclic loading of the test specimen, taking into account thecurrent method for monotonic loading in pullout tests;• Comprehensively describe the development of pullout resistance frominstrumentation on the test specimen and on the test apparatus;• Establish a method of interpretation for the response of the test specimen basedon measurements of pullout load, and strain along the embedded length, thataccounts for the extensible behaviour of geosynthetic test specimens;• Compare and contrast the behaviour in pullout of grids and sheets;• Contrast the results of this work with the limited experimental database forlaboratory testing;• Assess experimental and theoretical interaction factors for geosynthetic;• Compare the behaviour in pullout testing with that for “in-service” conditions;and• Compare values of interaction factor for static and dynamic loading, andcritically evaluate the current approach used in design for selection of aninteraction factor.To achieve these objectives, a large scale pullout apparatus was designed andcommissioned at the University of British Columbia. The apparatus is used to replicate sandsamples to a targeted density. Pullout tests were performed on embedded geosyntheticspecimens confined at different values of normal stress. A sophisticated control system3Chapter]. Introductionallowed tests to be performed in a displacement-controlled or load-controlled mode. Theapparatus and test specimen were instrumented to allow an examination of behaviour at smallstrains less than 0.5% that are representative of in-service conditions. Based on theexperimental results, a generalized method is presented for interpretation of pullout test data.Implications of the results for design practice are discussed.1.4 Thesis OrganizationThe state of the art for pullout testing and interpretation of the test results is reviewedin Chapter 2. Chapter 3 describes the design and fabrication of the pullout test apparatus usedin this research study. Properties of the materials used in the program of testing are reportedin Chapter 4. In Chapter 5 the experimental procedure followed in the pullout testpreparation and performance is described. Pullout test results are reported in Chapter 6. InChapter 7 an analysis and discussion of the results are presented. Some conclusions on theuse and interpretation of the pullout test are drawn in Chapter 8, and recommendations madefor further study.4CHAPTER 2LITERATURE REVIEW2.1 IntroductionIn this chapter the literature is reviewed with an emphasis placed on: geosyntheticapplications; various types of loading; current design practice; approaches used in thelaboratory evaluation of design parameters; and behaviour of thu scale structures. Inconcluding, a statement is made of the research needs arising from the state of the art and thestate of the practice.2.2 Soil Reinforcement using GeosyntheticsThe technique of reinforcing soils with natural fibres is many thousands of years old,but the use of materials such as steel and plastic is more recent. Initially, galvanized steelstrips and a granular backfill material were used in construction, though today geogrids andgeotextiles are routinely used as reinforcing elements as well. In the analysis and design ofsuch structures, a distinction is made between steel and polymeric materials because of theirdifferent stifihess: steel strips are considered to be inextensible inclusions, and polymericmaterials are considered to be extensible inclusions. Typical examples of soil reinforcementapplications are shown in Figure 2.1.Placing reinforcement in a region of tensile strain, and orienting it in the direction ofprincipal tensile strain, will best restrain the tensile stresses and increase the shear strengthcharacteristics of the soil (McGown et al., 1978). The direction of principal strain isdependent on geometry, construction technique and type of load acting on the structure. The5Chapter 2. Literature Reviewaction of the reinforcement is mobilized by the stress field in operation, invoking a compositebehaviour in which the “active zone” and the “restrained zone” in the soil mass are bonded(Schiosser, 1978).The potential mechanism of failure that develops in a structure will determine whichmode of soil-reinforcement interaction is critical (Palmeira, 1987), see Figure 2.2. Tn the caseof failure along surface 1-2, sliding of soil on the plane of reinforcement occurs at A, and thetest method best suited to model this behaviour is the direct shear test. If failure occurs alongsurface 3-4, then soil and reinforcement are sheared and the direct shear test, with properorientation of reinforcement, best models the behaviour. In the case of failure along thesurface 5-6, due to insufficient anchorage, sliding of the reinforcement inside the soil matrixtakes place, and the test best suited to model this behaviour is the pullout test.2.3 Fluid/Gas Containment using GeosyntheticsGeomembranes are used in the liner systems of waste containment facilities because oftheir low permeability and chemical resistance to many waste material leachates. In somecountries, and for certain types of waste, their use is mandated by regulatory requirements.The facilities are designed and constructed to comply with US EPA regulations in the UnitedStates (US EPA, 1989) and B.C. Provincial Regulations (Waste Management Act, 1988) inthe province of British Columbia. Emphasis in both the B.C. Provincial regulations and theUS EPA guidance is placed firmly on two parameters for design: cross-plane permeability ofthe liners to prevent migration of leachates; and in-plane permeability of the drainage layers tofacilitate collection of the leachate.6Chapter 2. Literature ReviewTypically the geomembrane liner is taken up the side slope of a facility and anchored atthe top in a trench, see Figure 2.3. A common failure mechanism of geomembrane lined sideslopes of impoundments and reservoirs is by slippage between components of the liner system,Martin et al. (1984), or of the cover soil itself, Seed et al. (1990). A schematic illustration ofthe potential failure modes is given in Figure 2.4.An analysis of slope stability requires:(i) data on limiting shear strength along the interface between soil and geosyntheticand between different geosynthetic layers;(ii) an understanding of tension in the liner system and its influence on overall slopestability;(iii) an understanding of slippage between soil, geomembrane and other constructionmaterials, and its relationship to the general stress-strain behaviour of thematerials.The type of failure in a geomembrane-lined structure will determine the mechanism ofsoil-geosynthetic interaction that is developed. In the case of failure at the cover soil surface,or a geosynthetic-geosynthetic surface, the test method best suited to model the materialinteraction is the direct shear test. If failure occurs at the anchor trench, then the test bestsuited to model the interaction is the pullout test.2.4 Types of Imposed LoadingThe geosynthetic element in a structure may be subjected to various loading conditionsduring construction and its service life. The imposed loads are typically a result ofconstruction techniques, self-weight of the structure and any live loading. Loads may be7Chapter 2. Literature Reviewclassified as static, repeated or dynamic in nature. The following sections describe these loadson the structure.2.4.1 Construction LoadingThe construction sequence in a typical application is to place the geosynthetic on aprepared surface, and then cover it with the soil, Placement and compaction of soil inducelateral spreading and invoke strain in the geosynthetic, and lead to a ‘locking-in’ of stresses(McGown et al., 1990). Consequently the rate and path of loading of an element aredependent on a number of factors, but during a particular stage of construction the loadapplied to the reinforcement will be either constant or changing monotonically at a reasonablyslow rate (McGown et al., 1992).2.4.2 Static LoadingThe static loads acting on a structure are the permanent loads due to self-weight of thestructure and any imposed load from the superstructure. They are essentially constant andindependent of time. Load sharing between elements is governed by their arrangement andspacing. The stress distribution from imposed loads is computed by elastic theory or byassuming a load spread angle (Christopher et al., 1990).2.4.3 Repeated Non-Dynamic LoadingA load is said to be repeated when there is an increase and decrease of magnitude withtime. When inertia forces are negligible the load is termed non-dynamic. Some examples ofrepeated non-dynamic loads are: transient loads due to traffic on reinforced soil structures;variations of waste or water level in an impoundment; and severe wave loading on coastalstructures.8Chapter 2. Literature ReviewIn reinforced soil structures that support highways and railways, the effect of atransient surcharge is to cause a simultaneous increase of vertical stress on the reinforcementand the horizontal stress within the structure. Wave loading on a reinforced structure imposeshorizontal forces that vary in a cyclic manner. The additional increments of horizontal stressare resisted by shear stress mobilized at the soil-geosynthetic interface. Similarly, thevariation of waste level in an impoundment induces varying tension in the geosynthetic liner,as well as a repeated loading and unloading sequence to the soil-geosynthetic interface in theanchorage trench.2.4.4 Dynamic LoadingDynamic loads are imparted to the geosynthetic element by a seismic event, blastloading or man- or machine- induced vibrations. A seismic event induces accelerations in thehorizontal as well as the vertical direction. The horizontal component of the accelerationincreases the lateral thrust on the soil geosynthetic structure due to acceleration of the activemass and the retained soil. The vertical component of the acceleration increases anddecreases the normal stresses in a cyclic manner at the soil-geosynthetic interface. Blastloading or man- or machine- induced vibrations affect a structure by subjecting it toinstantaneous transient loads (Yegian and Lahiaf, 1992). Again, the consequence of dynamicloading is to superimpose an increment of load on an element already loaded by self-weight.2.5 Analytical Methods used in DesignApproaches used in design of geosynthetic structures may be classified as: limitequilibrium methods; strain compatibility design methods; and finite element methods, Thelimit equilibrium methods are simple and inexpensive, and consequently form the basis of most9Chapter 2. Literature Reviewdesign. The current practice to account for dynamic loading is to perform a conventionalpseudo-static analysis.2.5.1 Limit Equilibrium MethodMany variations on the limit equilibrium method are proposed for design of walls andslopes, (Schneider and Holtz, 1986; Leschinsky and Perry, 1987; Schmertmann et al., 1987;Bonaparte et al., 1987; Bathurst and Simac, 1993). Reinforced soil structures are checked fortwo general modes of failure: external stability; and internal stability. In general, the externalstability will govern the length of the reinforcement and internal stability will govern thevertical spacing of layers. A failure surface through the reinforced mass is assumed forinternal stability analysis that establishes an active zone and a resistant zone. Reinforcementlayers that extend beyond the postulated failure surface are considered to act as tension-resistant tiebacks for the failing mass. Force and moment equilibriums are used to calculatethe mobilized tensile force in each layer of reinforcement. Limit equilibrium methods do notaddress wall deformations directly, and an empirical chart has been proposed for use in design(Christopher et al., 1990).Claybourn and Wu (1993) compare several available methods when designing twowalls, 3.6 m and 9.1 m high, with three different types of reinforcement. They conclude thatthe various design methods yield widely varying results. For the case of a 9.1 m high wallreinforced with the similar reinforcement, the ratio of largest design quantity (requiredreinforcement) to smallest design quantity was 12.5. However, this ratio was 2.5 when safetyfactors were not considered. Although some variation was attributed to differences in the10Chapter 2. Literature Reviewanalytical methods used in each design, significant variation was attributed to selection of anallowable reinforcement strength and appropriate factors of safety.2.5.2 Strain Compatibility Design MethodThe strain compatibility design method was proposed by Juran et al. (1990) toovercome limitations of the limit equilibrium method which (1) does not consider thefundamental requirements of strain compatibility between soil and reinforcement; and (2) doesnot allow for the influence of soil dilatancy, and extensibility of the reinforcement, onmobilized tension and stability of the structure.The main assumptions in the strain compatibility design method are:(1) constitutiveequations for the soil; (2) stress-strain relationships for the reinforcement; (3) soil-reinforcement interaction; (4) the strain path of elements on the potential sliding surfaceduring construction; and (5) effects of the construction process on the initial state of strain.Deutsch (1993) has presented a quantitative procedure for distributing the tensile loadamong the various geosynthetics within a lining system which assumes that there is noslippage between geosynthetic “sandwich” components. When designing a geosynthetic liningsystem, the usual practice is to assume that the most rigid material within the geosynthetic“sandwich” carries the developed tensile load. The assumption that the individualgeosynthetic components act as a single block mass implies that the strain in each of thecomponents is the same as the most rigid material. The consideration of strain compatibilitybetween individual components within the lining system allows for distribution of load to eachof the components based on the stress-strain relationships. Thus, the strain compatibilitydesign method promotes an economical design.11Chapter 2. Literature Review2.5.3 Finite Element MethodIn comparison with the limit equilibrium method, the finite element method is a morepowerful analytical tool for boundaiy value problems. A proper account of straincompatibility may only be made using a deformation analysis, and the finite element method iswell suited for this purpose (Chan et al., 1993). It provides information such as thedeformation, and stress-strain distribution in the structure and accounts for complexgeometries and loading conditions.Segrestin and Bastick (1988) modelled reinforced earth retaining walls using dynamicfinite elements. The program used was SUPERFLUSH, a modification of the LUSH programof University of California, Berkeley. The elasto-plastic behaviour of soil is simulated byvarying the modulus of elasticity as a function of observed deformations, this process beingrepeated until moduli and deformations are compatible.Chalturnyk et al. (1990) performed nonlinear finite element analyses on anunreinforced embankment and a polymeric reinforced embankment, with 1:1 side slopes, on asimulated competent foundation. The soil behaviour was idealized as a hyperbolic nonlinearelastic material. The load-strain relationship for the reinforcement was defined by a nonlinearquadratic model. They conclude that significant reductions occur in shear, horizontal, andvertical strains within the slope because of the presence of the reinforcement, Also, for theexample studied a circular-shaped slip surface was found to best represent the probable failuremechanism within the slope.Yogendrakumar et al. (1992) review two methods used in current engineering practicefor the dynamic response analysis of reinforced-soil retaining walls. The predictive capability12Chapter 2. Literature Reviewof the iterative equivalent linear elastic approach, and the incremental elastic approach, iscontrasted with reported field test data. The incremental elastic approach was reported topredict dynamic stress increments and accelerations at various locations that are similar to themeasured values.2.5.4 Seismic DesignTwo approaches used in the design of reinforced soil structures to resist seismic forcesare the conventional pseudo-static analysis and the displacement-controlled design. Atpresent the displacement-controlled design is applied only to retaining walls.2.5.4,1 A Pseudo-Static AnalysisThe pseudo-static approach of the USFHWA for retaining walls (Christopher et al.,1990) proposes that the seismic forces be modelled as equivalent static forces using theMononobe-Okabe approach.During an earthquake the retained fill exerts a dynamic horizontal thrust on thereinforced soil wall, PAE, that acts in addition to other lateral earth pressures, see Figure 2.5.A peak horizontal ground acceleration is selected based on the design earthquake. Due to theflexibility of the structure, an acceleration of greater magnitude is anticipated at the top of thewall. Based on finite element studies, Segrestin and Bastik (1988) recommend an expressionfor computing the maximum wall acceleration coefficient at the centroid of the active mass:= (L45—(2.1)g ggwhere am is the maximum wall acceleration at the centroid of the active mass, and a0 is areference acceleration between 0.05g and 0.5g13Chapter 2. Literature ReviewFor analysis of external stability, the horizontal inertial force P1 acting at the centroidof the reinforced soil mass is given by, Christopher et al. (1990):=ay.HL (2.2)I gwhere Yr is the unit weight of the reinforced mass; H is the height of the wall; and L is thelength of the reinforcement.The horizontal dynamic thrust PAE is calculated using the Mononobe-Okabe pseudo-static expression:= 0.375.i1iybH2 (2.3)gwhere Yb is the unit weight of the retained soil. The force PAE is assumed to act at the level0.6H above the base of the wall, see Figure 2.5. The seismic thrust PAE and 60% of theinertia force P1 are added to the static forces on the structure. The reduction of inertia forceis justified by the fact that these two forces are unlikely to peak simultaneously. Externalstability is evaluated for sliding and overturning, taking the required minimum factors of safetyto be 75% of the static factors of safety.For analysis of internal stability, it is assumed the horizontal inertia force is taken up asan increment of dynamic load in each layer of geosynthetic. The inertia force acting on thereinforced soil mass is distributed between each layer of reinforcement in proportion to theresistant areas beyond the postulated failure surface. The increments of dynamic load areadded to the existing static loads, and a check made for tensile failure of the geosynthetic andany connections for pullout failure. Again the minimum factors of safety are 75% of the14Chapter 2. Literature Reviewcorresponding factors for static loading. In addressing soil-geosynthetic interaction, it isproposed that the interaction factor in dynamic loading be taken as 80% of that for staticloading (Segrestin and Bastik, 1988; Christopher et al. 1990). However, there is noexperimental evidence to justify this assumption. Clearly, additional data are required toestablish interaction factors for dynamic loading.This issue of soil-geosynthetic interaction was also recognized by Bonaparte et al.(1986) in their pseudo-static analysis of slopes and embankments subjected to earthquakeloading. In preparing a series of charts that compare the required tensile strength and lengthof reinforcement for seismic and gravity loading conditions, they concluded:• Few additional layers of reinforcement are necessary to resist earthquakeinduced loads on slopes because(1) the visco-elastic properties of geosynthetics permit the use of a higheravailable strength under conditions of rapid loading; and(2) lower factors of safety are adopted for seismic design;• The resultant dynamic increment of force should be distributed uniformly overthe height of the slope;• The allowable reinforcement tensile force for seismic design should: (1)consider the rapid rate of strain which occurs over a short duration; (2) ensurethat brittle rupture of the reinforcement is precluded; and (3) result in workingstrains compatible with mobilization of soil strength at large displacement;15Chapter 2. Literature Review• Few data are available on the influence of cyclic loading and deformation rateson the soil-geosynthetic interface.2.5.4.1.1 The Displacement-Controlled DesignThe displacement-controlled design method applied to gravity retaining walls wasproposed to address the over-conservatism of conventional methods, Richards and Elms(1979). The analysis was based on the Mononobe-Okabe equations for active seismicpressures, and the Newmark sliding-block analysis for displacement of a block with a givencoefficient of friction. More recently, Richards and Elms (1992) proposed an extension of themethod to the design of tied-back walls based on model experiments. They observed that theacceleration response corresponding to the formation of a failure surface showed a patternexpected by the sliding-block model at a level roughly the same as that predicted by theMononobe-Okabe equations using the residual friction angle. The method should be usedwith caution because the result is sensitive to wall friction, which is difficult to estimateaccurately.2.6 Evaluation of Soil-Geosynthetic InteractionThe common parameters for designing the geosynthetic structure using methodsdescribed in previous section are soil strength (cohesion, c, and angle of internal friction, 0),interface strength factors, and the allowable tensile strength of the geosynthetic. Soil strengthparameters are typically obtained by performing conventional direct shear tests and/or triaxialtests. Interface strength factors are governed by the postulated failure mode in the structure,and measured in the shear test or pullout test. In 1992 the American Society for Testing andMaterials established a test method for measurement of geosynthetic interface strength in16Chapter 2. Literature Reviewdirect shear (ASTM D532 1-92). A standard test method for the pullout test is currentlyunder development by ASTM.2.6.1 Direct Shear TestsDirect shear tests are used to model the failure behaviour observed along surface 1-2and 3-4 of Figure 2.2. Martin et al. (1984) conducted modified direct shear tests on variousgeosynthetic-geosynthetic and geosynthetic-sand interfaces and concluded that the interfacefriction mobilized was between 65% and 90% of the peak friction angle for medium-densesand samples. Eigenbrod and Locker (1987) report the results of direct shear tests on variousgeosynthetics and sand samples, performed on both dense and loose samples. Dilation of thedense samples was indicated by mobilization of a distinct peak and residual shear stress.Interface friction mobilized was between 55% and 85% of peak friction angle. Negussey Ctal. (1989) observed that interface sliding between a geomembrane and granular soils exhibits apeak and residual value, whereas sliding between a geomembrane and geotextile interfacedoes not result in any such peak. Rinnie (1989), using the same ring shear apparatus, testeddifferent types of geomembrane using an angular quartz sand and a rounded sand at highconfining stresses. Geomembranes used in testing were polyvinyichioride (PVC), smooth highdensity polyethylene (HDPE) and textured HDPE. The soft PVC and textured HDPEmobilized a value of interface friction equal to the shear resistance of the sand, for both theangular and the rounded sand. In contrast, the smooth HDPE mobilized approximately 65%of the peak resistance of the rounded sand, and 90% of that for the angular sand.O’Rourke et al. (1990) summarize the results of an experimental program involvingover 450 direct shear tests of sand-polymer interfaces. Their results indicate that the interface17Chapter 2. Literature Reviewffictional strength increases with soil density, but decreases with the Shore D Hardness of thepolymer. The shear strength characteristics were found to vary as a flinction of the type ofsand, but were independent of repeated loading, at least for polyethylene piping and linings.They expressed the shear strength characteristics of a polymer interface as the ratio of theinterface angle of friction and the angle of ffiction in direct shear of the soil itself, in bothcases at the residual state. It was observed that this ratio was relatively constant at 0.55-0.65along high- and medium density polyethylene surfaces for different types of sand at variousdensities.Takasumi et al. (1991) present a review of state-of-the-art testing procedures for soilgeosynthetic interface strength characteristics. Their review revealed that there is a widerange of interface strength characteristics reported and that there are significant variations inhow interface testing is performed. Based on their study, they conclude that more testing isrequired to understand the influence of type and size of the apparatus on interface strengthcharacteristics.The importance of conditioning of the test specimen was emphasized in aninvestigation of the Kettleman Hills landfill failure, Seed et al. (1990). Failure developed bysliding along interfaces within the composite, multilayered geosynthetic-compacted clay linersystem beneath the waste fill, see Figure 2.6. The materials used to construct the lowpermeability liner system at the facility involved contact surfaces between variousgeosynthetics including sheets of HDPE geomembrane, geonet and geotextile; and betweenthese materials and the compacted clay liner. Based on a comprehensive series of testing itwas concluded that the frictional resistance was affected by various properties, including the18Chapter 2. Literature Reviewdegree of polishing, whether the surfaces were wet or dry, and in some cases the relativeorientation of the layers to the direction of shear-stress application. A decrease in frictionalresistance was observed with an increase in degree of polishing. A wet interface gave areduced interface friction when compared to dry condition. Also an increase in frictionalresistance was exhibited when the relative orientation changed from aligned shear totransverse shear.In discussion of the Kettleman Hills investigation and testing, Yegian and Lahlaf(1991) present data which illustrate the importance of specimen preparation. Static loadingtests were performed to determine interface friction between two layers of HDPEgeomembrane. Specimens were cleaned by two methods prior to testing: hand-wiping andtowel-wiping. Results indicated that the residual friction angle was 110 when towel-wipedand about 6° when hand-wiped. This observation was attributed to a “dry” or “lubricated”condition of the geomembrane. They also noticed that when a geotextile was used with aHDPE geomembrane, the effect of hand-wiping the geomembrane was insignificant.2.6.2 Pullout TestsSoil-geosynthetic interaction in pullout is an important parameter in the design of areinforced soil structure or a low permeability barrier. Jewell et al. (1984) refer to themechanism of interaction for a grid structure in soil as “bond”, and propose the use of a bondcoefficient. In a similar approach, Martin et al. (1984) and Eigenbrod and Locker (1987) usean efficiency factor when describing interaction of geomembranes and geotextiles. Soilreinforcement interaction in pullout involves some or all the following general mechanisms ofload transfer, see Figure 2.7.19Chapter 2. Literature Review• lateral friction, where shear occurs on plane surface areas of the geosynthetic;• passive earth pressure on transverse elements of geogrids, welded wire meshes,bar mats and woven geotextiles, as a result of soil bearing against surfaces normalto the direction of relative movement; and• soil shearing over soil in the apertures of a grid.The transfer of load between soil and geosynthetic in pullout is by mobilization of thefirst two components only, since there is no relative displacement between soil particles oneither side of the element: the two components are lateral friction and passive resistance orbearing.Jewell et a!. (1984) derived an expression to describe pullout interaction between gridreinforcement and soil, so that a bond capacity could be calculated from the fundamentalproperties of the reinforcement geometry and angle of friction of the soil. The skin frictioncomponent of pullout resistance for a geosynthetic specimen is given by:Ps2csLrWrantafl8 (2.4)where:a is the fraction of the specimen plan area that is solid,Lr and Wr are the length and width of the specimen,a is the effective normal stress at the soil-inclusion surface, andis the angle of interface friction20Chapter 2. Literature ReviewEquation 2.4 is valid for geomembranes and planar geosynthetics without significant asperitiesout of the plane of the specimen.Passive soil resistance developed against bearing surfaces normal to the direction ofrelative movement is similar to the pressure developed on deep foundations in soil. Jewell etal. (1984) modified an expression for deeply-embedded anchors to establish a theoreticalcontribution from bearing stresses. A lower bound to the expression is associated with apunching shear failure mode in the soil, (see Figure 2.8), is:F= e(9)tantan(45+ (2.5)2where:3b is the effective bearing stress acting on the embedded anchor; andFis a stress ratio.An upper bound value is estimated by taking the conventional characteristic stress fieldfor a footing rotated to the horizontal, and a horizontal boundary stress in the soil, where:= F = ent tan2 (45 + (2.6)It was suggested by Jewell et al. (1984) that the stress ratio be established directlyfrom pullout tests, or estimated from curves summarizing test results in the literature. Acomparison of the theoretical expressions with experimental data, Jewell (1990), shows goodagreement despite the large spread and variability of the test results, see Figure 2.9. Thestress ratio is used in the following expression to determine the bond coefficient, where:Pr2LrWrGnfbtaI (2.7)21Chapter 2. Literature Reviewandrtanol EGb1B 1fb=0s[ tanØj [_j 2tanØ (2.8)where:Pr is the total pullout resistance,fb is the bond coefficient,ab is the fraction of the specimen bearing member width available for bearing,B is the thickness of the bearing member, andS is the spacing between bearing membersThe effect of interference between transverse bars of a grid on the bond capacity inpullout has been analyzed for grid reinforcement by Palmeira (1987). A comparison of thevalue of the pullout load for a given grid (Pb) with the value obtained for an ideal grid (nP0),defined as one having the sum of bearing pressure of a single isolated member (P0) undersimilar conditions without interference, led to a parameter for degree of interference beingdefined as:DI=1—j-- (2.9)where:Pb is the maximum pullout load for a grid with n bearing members, andP0 is the maximum pullout load for an isolated bearing member of the same grid.Thus an expression to calculate bond coefficient is proposed as follows:Etan6l FBi FGb1F 1—DI 1fbaI IXbIILII I (2.10)LtanOJ LSJLaJL2tan0J22Chapter 2. Literature ReviewJewell (1990) suggests fhrther modification to the above relation to account for the firstbearing member which acts undisturbed on the sand, and subsequent bearing members forwhich interference can occur. For a grid with n bearing members, this gives:DI=[1_*][1_(BJ ] (2.11)abB •where the ratio is defined as the grid geometry required to achieve a fully roughab B),bond.The FHWA manual of the U.S Department of Transportation (Christopher et al. 1990)for the design of reinforced soil structures recommends the following expression:PrF*0GnLeC (2.12)where:Le is the embedment or adherence length in the resisting zone behind the failure surface,C is the effective unit perimeter of the geosynthetic, which is 2 for planar sheets,F’ is the pullout resistance (or friction-bearing-interaction) factor,x is a scale effect correction factor, anda is the effective normal stress at the soil-geosynthetic interface.It is recommended that tests be performed to determine the pullout resistance factor F*, whichis very similar to the bond coefficient proposed by Jewell et al. (1984), and is given by:F’=Fo+K.L OCt (2.13)23Chapter 2. Literature Reviewwhere:Fis the stress ratio,K is a ratio of the actual normal stress to the effective normal stress; and is influenced by thegeometry of the specimen,a is a structural geometric factor for bearing resistance, where = [-]; andis an apparent friction coefficient for the specimen.A value of 20 has been suggested for F based on limited experimental data (see also Figure2.9). For geogrids, geomembranes and geotextiles, K=1 and = tan & Recognising that theextensibility of geosynthetics leads to an interface shear stress that may not be uniformlymobilized along the total length of the geosynthetic, a scale effect correction factor a isintroduced defined as:a= tanav (2.14)tpeak tan öpeakwhere tav and tpeak are the average and ultimate interface shear stresses respectively, mobilizedalong the inclusion,6av and speak are the average and peak interface friction angles respectively.The value of the scale effect correction factor is influenced by strain softening of thecompacted granular backfill, extensibility of the geosynthetic material and the embedmentlength. The manual recommends a value of 0.6 in the absence of test results for extensiblereinforcement; a realistic value may be in the range 0.6 to 1, with 1 being appropriate for aninextensible material. The factor can be obtained from pullout tests performed with different24Chapter 2. Literature Reviewlengths of geosynthetic or derived using analytical or numerical load transfer models whichhave been “calibrated” against physical tests.2.6.2.1 Factors Influencing Pullout ResistanceTypically the pullout resistance of a geosynthetic in laboratory testing is influenced bythe type of soil, the material properties and geometry of the specimen, and the configurationof the test apparatus. Soil parameters of interest are: the particle size, shape and gradation;relative density; dilatancy; and water content. Test specimen parameters of interest are thegeometry of the specimen (such as in-plane or out-of-plane transverse elements), orientation,tensile strength, extensibility, and creep behaviour. The influence of the test apparatus is aresult of the loading system, the sample dimensions and its preparation, the boundaryconditions and the testing procedure. A comparitive summary of pullout test equipment andtest materials is given in Table 2.1.2.6.2.1.1 Soil CharacteristicsIn construction practice a well-graded free draining granular material is commonlyspecified for permanent reinforced soil structures because these soils develop a greater bondwith the reinforcement. Since a high fines content will tend to restrict the free drainingbehaviour of a soil, an upper limit to the percentage of fines permitted in the backfill materialis usually recommended, Brown et al. (1979). This is not to suggest that other soils cannot beused successfully in construction: Murray et al. (1979) used a silty clayey sand as backfillmaterial for a reinforced soil wall and concluded that, despite construction difficulties andpore pressure development, cost savings could be achieved over granular backfills importedover substantial distances.25Chapter 2. Literature ReviewDense soils dilate during shearing, but with confinement from the surrounding soil theyexperience a restrained dilatancy. The dilatancy characteristics of dense sand and its effect onpullout resistance have been demonstrated for metallic reinforcements (Schiosser and Elias,1978), where restrained dilatancy caused an increment of normal stress to act on the element,increasing its pullout resistance. The effect of such dilatancy is dependent on the magnitudeof normal stress, surface texture of the reinforcement and the density of the soil.Johnston (1985) evaluated the effect of dilatancy by placing pressure cells within thesoil sample of a large pullout apparatus to monitor the applied normal stress on a Tensar SR-2geogrid. A normal pressure on dense samples (at peak pullout load) some 1.5 to 3 timeshigher than the applied normal stress was measured. It was a result of the top boundary of theapparatus being rigid and restrained against upward displacement. In contrast pullout testsperformed on loose samples (Figure 2.10) show efficiency factors to be independent of normalstress with tan4=tan6.2.6.2.1.2 Test Specimen CharacteristicsCharacteristics of a test specimen which influence pullout resistance are: geometry,tensile strength and stiffness, and creep behaviour. Geosynthetics are thermo-viscoelasticmaterials, hence the load-strain characteristics are dependent not only on strain magnitude butalso on strain rate and temperature. Creep is defined as continued strain at constant load, andthe phenomenon is well-recognized in polymeric materials. The magnitude of any creep strainis influenced by:• type of polymer;• geosynthetic macro-structure;26Chapter 2. Literature Review• manufacturing technique;• magnitude of loading;• temperature;• time.Therefore, an evaluation of long-term performance over the service life of a structurerequires data describing the load-strain-time behaviour of the geosynthetic. Such data aretypically presented as isochronous load-strain curves, from laboratory constant load-extensiontests on unconfined samples, following an approach reported by McGown et al. (1984) andfurther described by Jewell (1985). The test method involves loading a series of testspecimens in a rapid, smooth manner. Load is maintained throughout the test at ±1% of thetargetted constant load, at a controlled temperature and humidity, and specimen elongationmeasured over time. The tests are performed for at least 10, 000 hrs or until failure,whichever is less. Data obtained from each test are plotted as strain against logarithm of timefor each magnitude of load. A long-term design strength is selected based on a value ofperformance limit strain (identified from a plot of strain versus logarithm of strain rate) andextrapolation of the data from 1 x 1 hrs to 1 x 106 hrs, which is equivalent to a service lifeof 120 years.2.6.2.1.3 Test Apparatus and Procedure2.6.2.1.3.1 Normal StressThe normal stress imposed on the test specimen strongly influences pullout, and theeffect of any increase in stress is to increase the pullout resistance, while causing the length ofthe test specimen that is mobilized to decrease (Palmeira, 1987). At relatively high normal27Chapter 2. Literature Reviewstresses, tests will tend toward a failure of the test specimen in tension, (Fannin and Raju,1993). Pullout tests performed at high normal stresses may also cause particle breakage insome sands, and result in a small change in grain size distribution, (Raju, 1991).. In testing,the magnitude of normal stress is used as a control to promote a pullout failure, to simulatefield conditions, or to develop very large strains in the test specimen if it tends towards atensile failure rather than pulling out.2.6.2.1.3.2 Boundary EffectsTypically a soil sample for pullout testing is prepared in a rectangular box with a rigidbase and side walls. The top boundary may be rigid or flexible. The influence of a rigidboundary that was free to displace, and a flexible boundary, was examined by Palmeira(1987). A flexible top boundary, typically a surcharge bag filled with water, eliminatesboundary shear stresses and for otherwise similar test conditions, leads to a smaller maximumpeak pullout load. This behaviour is attributed to no restrained dilatancy.Some experiences are reported in the literature regarding the influence of the rigidfront wall of the apparatus on the measured pullout resistance. As the specimen is beingpulled out from the box, lateral pressures develop against the front wall. Juran et al. (1988)postulate that arching of the soil over the specimen will reduce the normal stress on the testspecimen close to the front boundary and, consequently decrease the pullout resistance.Tests performed to examine the influence of roughness of the front wall showed a markedeffect, with a dramatic increase in pullout resistance attributed to an increase in normal stresson the sample caused by shear stresses developed on the front wall during pullout, Palmeira(1987), see Figure 2.11.28Chapter2.LiteratureReview1’)Table2.1:SummaryofthepuilouttestapparatusandtestingcharacteristicsDimensionsSoilTestSpecimenBoundarySampleTestModeInterpreResearchInstitutionICompanyincmPropertiesPreparationPreparationtationMethodLxWxDUnifonnfmesandGeogrids andLubricatedtaperedSandplacedatConstantTotalarea,TheReinforcedEarthCo.,152,6130.4withsilttraces;Geotextiles;wovenmetalsleeveonfront95%ofstandarddisplacement rateofEffectiveareaC,,=2.2,C,=l.23,fromhightenacitywall;Proctor drydensity1mm/mmd100.1imnpolyester yamsandwithin2%of(CowellandSprague,1993)optimummoisturecontentFine-grainedsand;NonwovenheatMetalclampburiedinStoppedatregularTotal area,Instituteof Soils,RocksandFoundations,80x55x20moistsiltbondedsandtoavoidrigidintervals toenableEffectiveareaSwitzerland.polypropylenefrontwalltakingX-RayshotscontinuousifiamentTYPARgeotextiles(KharchafiandDysli,1993)Blastingsand,Geogrids -TensarMetalsleeveonfrontSandplacedinConstantrateofMobilising process152x90x761..ouisianastateUniversityd10=0.26mm,SR-2andConwedwall;minimumfourlayersanddisplacement-varyingdensity9027distanceof15cmofeachlayer6n/mm;Stepsidestoreducesidecompactedusingloadinginload(Farragetal.1993)frictionvibratingelectriccontrolledmode.hammerToyourasand,Geogrids TensarCompactedtoConstantrateofTotal area60x40x40KyushuUniversity, JapanDr30and80;SR-2andSS-2achieverequireddisplacement of1Twootherwelldensitiesmm/mincyclicgradedsoilat85toloadingbycycling(Ochiaietal.1992;Yasudaetal.1992))90%ofProctoroverburdenpressuremaximumdensityoraddingcyclicloads overstaticWell gradedsandyGeogridTensarSR-Loadcontrolled:Netlon,U.K.200x100100gravel,C,=28,80dynamicloadmaximumgrainsuperposedonstaticsize=3Ommloadat5Hz(NimmesgemandBush, 1991frequencyLeightonBuzzardMetallicgrids,Sides andfront:-AirpluviationConstantrateofTotal areaOxfordUniversity100,100100Sand14/25,TensarSR-landDoublelayer ofwithspeciallydisplacement 0.5unifonri coarseSR-2, Geolon,polyethylenewithdesignedhoppernun/mmwitharelativeStabilenka400greaseinbetween(Palmeira andMilligan, 1989)density87%Chapter 2.LiteratureReviewDimensionsSoilTestSpecimenBoundarySampleTestModeInterpreResearchInstitutionICompanyPropertiesPreparationPreparationtationMethodLxWxDAir-driedToyouraConstantrateof120x60x60PublicWorksResearchInstitute,Tsukuba,Sand;d50=0.16TensarSR2-displacementJapan100x80x50mm:relativelmnihnin; stageddensity20%andloadcontrolled test60%withO.Stflmforl2(Kutaraeta!.1988)hoursFinesandandPlacedusingV-ConstantrateofUniversityofMissouri-Rolla76.2x29.2xl 0CoarsesandTensarSSIandshapedhopperanddisplacement2.5sieachlayervibratedmnifmintodensi1,(LentzandPyatt,1988)Light brownCompactedtoConstantrateofAsianInstituteofTechnology100x80x90clayeySSIidandTensarSR2and95%ifstandarddisplacementweatheredclayBambootripaproctoratOMC,1mm/mmeachlayer15cm(Bergadoetal.1987)FontainbleausandAslotintroducedtoCompactedusingConstantrateofTotalarea,STSConsultantsLtd.,Illinois,USA134x70x38(SP);densesampleTensarSS2andtransfertherigidfrontvibratoryplatedisplacementEffectiveareasiuboundaryintothebox1mm/mm(Bonczkiewiczeta!.1986)TullingsandToreducethesideTotalarea,SwedishGeotechnicalInstitute190x70x70(Stockholm)Wovenpolyestereffects,the—-—--Effectivearea0-12sandgeotextile5ped1ieh1W5S5cm(Denmark);narrowerthanthe(Holtz,1977)mediumdensewidthofthebox.sandChapter 2. Literature ReviewVarious techniques have been tried to reduce or control the influence of the frontboundary of the apparatus. Polyethylene sheets with grease in between have been used tocreate a low friction boundary (Palmeira, 1987; Lo, 1990). The influence of such anarrangement is to reduce boundary shear stresses, and hence the complimentary shear stresseson the specimen close to the front wall of the apparatus. In another approach the frontboundary was essentially transferred into the soil mass by embedding a sleeve into the soilacross the width of the pullout box, through which the specimen is pulled, Bonczkiewicz et al.(1986). To further address the issue, Juran et al. (1991) clamped the test specimen within thesoil sample. Mthough the introduction of a sleeve mitigates the problem of front wall friction,it complicates the stress distribution within the soil mass at the edge of the sleeve, and theintroduction of the clamp into the soil leads to further complexity. A rational understandingof the influence of the front wall will best be obtained through measurement of the distributionof lateral stress acting on it.2.6.2.1.4 Loading CharacteristicsPullout tests on reinforcement installed in an experimental wall constructed with auniformly graded sand, are reported by Murray et al. (1979). The tests were carried outunder both static and dynamic loading conditions. Results showed a significant reduction inpullout resistance when vibration was applied to the surface of the fill. The measurement ofvertical stress in close proximity to the reinforcement showed reductions of the overburdenstress acting at the level of the interface: the observed reduction in pullout resistance wasattributed to the temporary reduction of normal stress.31Chapter 2. Literature ReviewWhen designing a structure to resist repeated non-dynamic loads, a knowledge of thematerial behaviour and load transfer characteristics of the interface is essential. At present,very few studies have addressed this issue. A1-Ashou and Hanna (1990) studied the effect ofrepeated loading on the life-span of metallic (inextensible) reinforcement. Displacement andstress distributions along the reinforcement element were measured after application of severalseries of load cycles. Results showed that a considerable amount of residual load was locked-in along the reinforcement, and a reversal of shear stress was generated during the loadingcycles. Pullout behaviour was greatly influenced by the loading amplitude. Further, for thesame amplitude of load, the static loading level was found to be the primary factor governingthe pullout resistance.Hanna and Touahmia (1991) performed static and slow repeated load tests on 4 mlong smooth steel and polymeric grid reinforcing strips. A medium dense sand was placed bythe air pluviation method to a relative density of 53%. Tests were performed at three levels ofnormal stress: 50, 75 and 100 kPa. On the basis of these results they conclude that the rateof accumulation of displacement of the test specimen increases with an increase in the numberof load repetitions, load amplitude and load level. Failure by pullout occured only with thesmooth strip, despite testing to 1 load applications. The polymeric grid exhibited a greaterpullout efficiency than either of smooth or ribbed steel strips under both static and repeatedloading; it failed in tensile rupture.In a limited study of the effects of transient surcharge loading due to traffic onreinforced soil structures, Nimmesgern and Bush (1991) devised a dynamic pullout test tosimulate in-situ conditions. The tests were carried out at low confining stress on polymeric32Chapter 2. Literature Reviewgrids in a large (1 m x 2 m in plan) pullout box, using a well-graded sandy gravel. In additionto a static surcharge pressure of 57 kPa, a dynamic surcharge pressure of 10 kPa was imposedat a frequency of 5 Hz. Results showed that the grid efficiently resisted the dynamic loads.To simulate the loading regime prevalent during a seismic event, Yasuda et al. (1992)performed pullout tests on polymeric grids. Three types of soils were used in the testingseries: a uniformly graded air-dried Toyoura sand at relative densities of 30% and 80%, andtwo well-graded volcanic ashes compacted to 85 to 90% of maximum density at optimummoisture content. Test specimens used were polymeric grids. Two types of loading wereimposed. In the first mode, cyclic pullout loads were applied to the test specimen byincreasing the amplitude of pullout load in stages until the specimen failed either in pullout orin tension. In the second mode, the normal stress was cycled, and simultaneously thespecimen was pulled monotonically out of the box until it failed either in pullout or in tension.From the results they conclude:• the maximum pullout loads under both modes of loading are affected by soil typeand overburden pressure;• the maximum pullout load under cyclic loading is greater than the load undermonotonic loading; and• the maximum pullout load under cyclic overburden pressure decreases with anincrease of the amplitude of the cyclic pressure.33Chapter 2. Literature Review2.6.2.2 Methods for Interpretation of the Pullout Test2.6.2.2.1 Monotonic Pullout TestsJuran and Chen (1988) present a soil-reinforcement load transfer model forinterpreting pullout tests on extensible reinforcement. The model combines a constitutiveequation for the reinforcement with interaction laws relating the shear stress mobilized at anypoint on the interface to the soil-reinforcement shear displacement. The procedure is derivedfrom the “t-z” method that is commonly used in design of friction piles. They conclude that,for a meaningful interpretation of pullout test results on geosynthetics, an adequate estimationof the in-soil (confined) properties of the reinforcement is required. In addition, theextensibility of the specimen affects soil-reinforcement interaction, and extrapolation of testresults to specimens of different dimensions requires a careful evaluation of scale effects.More recently, to account for the non-uniform and non-linear shear stress distributionalong the specimen length, three methods have been proposed based on the area of thespecimen active in resistance (Ochiai et al., 1992, Bonczkiewicz et al., 1986), see Figure 2.12.The profile of shear stress distribution at any value of pullout resistance is used to evaluate theinteraction factor in pullout using a value of average shear stress, hence the approach istermed the average resistance method. It may be classified into three methods:1. Total Area Method, in which the pullout force at the front end and the whole areaof the geogrid inside the pullout box are used;2. Effective Area Method, in which the pullout force and effective area only areused; and34Chapter 2. Literature Review3. Maximum Slope Method, in which the slope of an appropriate tangent to the loaddistribution curve is used.The total area and effective area methods of evaluating pullout resistance proposed byOchiai et al. (1992) are similar to the total area and corrected area method proposed byBonczkiewicz et al. (1986). A determination of the mobilized length of the specimen by directmeasurement during testing is utilized to calculate the corrected area. Analysis has shownthat at low normal stresses both the effective area and total area methods give similar results.In the mobilizing process method, the profile of tensile force along the embeddedlength of the specimen is determined indirectly from the strain measurements (Juran, 1991;and Ocbiai, 1992). A common method used to obtain the strain distribution along thespecimen is to attach a tell-tale to various nodes. This method of deducing strain isappropriate for specimens with well defined nodes, A generalized technique for measuringstrain and an appropriate method for interpreting pullout data are necessary for tests at lownormal stress and small strain.2.6.2.2.2 Cyclic Pullout TestsHanna and Touahmia (1991) observed a deterioration in the pullout resistance ofmetallic strips subjected to repeated loads. The test data demonstrated a complex reponse toloading, and the authors attributed the behaviour to several partly understood factorsincluding, (i) changes in load transfer along the embedded length, (ii) changes in the normalstress along the specimen with increase in the number of load repetitions, (iii) “compaction” ofthe sand due to local shear reversals causing a breakdown of particles, (iv) locked-in stresseschanging after each load cycle. To better understand these complex and interrelated factors,35Chapter 2. Literature Reviewthey identif,r a need for further development of a unified theory to explain and interpret resultsfrom cyclic pullout loading.The interface behaviour under cyclic loading depends on the surface characteristics ofthe specimen. If the surface is a planar surface the relevant theory for predicting theperformance would be that used for soil-pile interaction under cyclic loading. Swinianski andSawicki (1992) proposed a model for a soil-pile system subjected to vertical cyclic loading.This model, based on the classical t-z concept and compaction of granular materials, was usedto study the reduction of shearing resistance around a shaft owing to cyclic loading. Theredistribution of loads carried by the shaft and tip of a pile was predicted by the model.Turner and Kulhawy (1990) present results from an experimental study illustrating the effectsof repeated axial loading on the drained uplift capacity of drilled shafts in granular soils. Theirresults indicate that changes in the uplift capacity depend primarily upon the magnitude ofcyclic displacement. Critical levels of repeated loading (CLRL) are established, above whichshafts fail in uplift and below which failure under repeated loading does not occur.If a bearing component, rather than skin friction component, is predominant in themeasured pullout resistance of the geosynthetic, consideration must be given to bearingcapacity and rate effects. The effects of variation of the loading rate on the bearing capacityof footings on sand were studied by Vesic et al. (1965). Observations showed a limited effectof variation of rate of displacement on the bearing capacity of dry sand: there was somedecrease, as the rate increases to moderate values of about 0.05 mm/mm, followed by anincrease for faster tests.36Chapter 2. Literature Review2.6.2.3 Finite Element ModellingChan et al. (1993) used the finite element method to simulate pullout tests andinvestigated the effect of progressive shearing on the calculation of the shear stifihess of thesoil-reinforcement interface. The reinforcing elements were 3 noded elements capable ofsustaining only tensile stress. The interface was modelled by 6 node elements. Eight nodeisoparametric elements were used to simulate the soil. The numerical simulation performed at51 kPa normal stress reproduced the highly non-uniform shear stress distribution along thespecimen. A discrepancy between true stiffness and apparent stiffness was evident when theforce-displacement response of the pullout test was used to obtain a value of tensile shearstiffness. This discrepancy was found to depend on the relative stiffness between the interfaceand the specimen. It was concluded that an appropriate stifihess correction was necessary toobtain true values of stiffness from the pullout test data.Wilson-Fahmy and Koerner (1993) modelled the pullout test by deriving anincremental finite-element formulation to simulate the non-linear response of a geogrid topullout. Polynomial and hyperbolic functions were used to represent the load-extensionbehaviour of the geogrid and the soil-geogrid interaction properties in friction and bearing.Three models were used in the analysis to simulate the deformation of the transverse ribs inbearing. Highly flexible transverse ribs were assumed to take a parabolic shape and to act asstrings, whereas short stiff ribs were considered not to deflect during puffing. Intermediatecases were analyzed by assuming the ribs to behave as beams deflecting under load. Typicalresults indicated that the contribution of the transverse ribs to pullout resistance was greatlyaffected by their flexibility, especially at low normal stress.37Chapter 2. Literature ReviewYogarajah and Yeo (1994) measured load and strain distributions along a geogridreinforcement during a pullout test by experiments and numerically modeled the responseusing the CRISP finite element program. Load and strain along the test specimen weremeasured using load cells and strain gauges respectively. They used variable elastic modulifor the test specimen and conclude that the use of a single elastic modulus over the entirelength is inappropriate due to the visco-elastic nature of the polymeric reinforcement, which isto be expected.2.6.3 Model Shake Table TestsSeveral investigators have attempted to simulate dynamic loading in the laboratoryusing the shaking table for: reinforced embankments, Koga et al. (1988); reinforced retainingwalls, Richards and Elms (1992), Sommers and Wolfe (1988); and to study the interfacebehaviour of geomembranes and geotextiles, Yegian and Lahlaf (1992).Sommers and Wolfe (1988) investigated the effects of different input motions on themeasured amplification ratios and displacements of model gravity walls. The experimentsshowed that at low levels of excitation, the model walls behaved as damped elastic structures.Magnification factors were found to be somewhat higher for input motions near the naturalfrequency of the model. All displacements were shown to be a function of the level of baseacceleration with a minimum level of input acceleration required to induce permanentdisplacement. For all walls tested, a minimum acceleration of approximately O.25g had to beexceeded before any measurable relative movement between the top of the wall and its basewas observed. This yield acceleration was seen to be relatively insensitive to a specific type orfrequency of base motion.38Chapter 2. Literature ReviewYegian and Lahiaf (1992) performed shaking table tests to measure the dynamicinterface shear strength properties between geotextiles and geomembranes. From the testresults it was observed that there was a limiting shear stress, that can be transmitted from onegeosynthetic to another. Thereafter a relative displacement occurs along the geosyntheticinterface. They conclude that the primary concern about the dynamic response of ageotechnical facility that incorporates geosynthetics should be the permanent relativedisplacement that may accumulate along the geosynthetic interfaces. The measured dynamicfriction angles at the onset of relative displacement between the geosynthetics were notappreciably different from those obtained from static tests.2.6.4 Behaviour of Field Structures2.6.4.1 Pullout TestsField pullout tests were performed by Ochiai et al. (1988) on polymer grids embeddedin an embankment. Based on a comparison of the results with laboratory tests they concludethat the basic characteristics of pullout resistance observed in each case are very similar.Bonczkiewicz et al. (1991) performed laboratory and field pullout tests on Mirafi 5T(a continuous ifiament polyester yarn formed into a biaxial grid by a knitting process) toevaluate stress transfer in geogrids exhibiting a low junction strength. Resistance straingauges were mounted on geogrid sections to obtain strain data. A pullout rate of 1 mm/mmwas used in testing. Grid displacement was measured using a dial gauge near the face of thewall, and eight strain gauges were used to measure local strains. Again, the behaviourobserved during pullout tests in the field was similar to that observed in the laboratory.39Chapter 2. Literature ReviewIn comparing the laboratory and field pullout tests Bergado et al. (1992) noted that theinfluence of arching effects on the field response was more pronounced.2.6.4.2 Dynamic TestsRichardson et a!. (1975, 1977) conducted dynamic tests by subjecting a full-scaleinstrumented reinforced soil wall to random excitations at the University of California, LosAngeles. The test wall was 6.1 m high and reinforced with steel strips 4.88 m long placed atequal vertical spacings of 0.76 m. Instrumentation in the wall measured acceleration-timehistories at selected locations in the wall and dynamic force histories along the steel strips.The input acceleration to the base of the wall was measured by an accelerometer placed at thetoe of the wall. They conclude that the Mononobe-Okabe pseudo-static seismic coefficientwas found to give reasonable predictions of the location of the postulated failure plane in thebackfill, but seriously underestimated the magnitude of the maximum tie forces developed inreinforced earth walls during seismic loading.Qualitative observations of the field performance of geosynthetic structures, whensubjected to a seismic event, are reported by Collin et al. (1992). The performance of fivereinforced slopes and walls that experienced the Loma Prieta earthquake of 1989 wereevaluated. In the Watsonville wall, a uniaxial Tensar geogrid was used as a primaryreinforcement and a biaxial grid used to stabilize the soil at the face of the slope betweenprimary layers. The wall was designed for a maximum horizontal acceleration of 0.1-0.2g.The estimated horizontal acceleration at the site was 0.4g. Visual observations at the siteindicated no sign of movement or cracks in the wall, and similar observations are reported atthe other sites where very little if any distress occurred in the composite structures.40Chapter 2. Literature Review2.7 Research NeedsFrom the literature review it is evident that the field response of geosyntheticstructures to seismic loading is excellent. This fact makes the use of geosynthetics in practiceattractive. However, the available data on soil-geosynthetic interaction under various loadingconditions are very limited. Moreover the use and understanding of the pullout apparatus tocharacterize soil-geosynthetic response in anchorage is an essential requirement.White and Holtz (1992) review current methods for the analysis of geosyntheticreinforced earth slopes that are subjected to earthquake shaking and conclude that seismicdesign procedures are very limited. They also observe that despite design procedures beingconservative, building code officials are hesitant to approve the technology of steepgeosynthetic earth slopes. This was attributed to a lack of published research regarding theseismic stability of steep geosynthetic reinforced slopes. Therefore, they conclude that theseismic design of geosynthetic reinforced slopes and walls are among the “high priority”research needs.The review of literature reveals that there is a need for a better understanding of soilgeosynthetic interaction, and the following specific research needs are identified:• comprehensively describe the development of pullout resistance frominstrumentation on the test specimen and on the test apparatus;• describe soil-geosynthetic interaction under monotonic loading, and at smallstrain;41Chapter 2. Literature Review• develop a procedure for load-controlled (cyclic) loading on specimens, takinginto account the current method for displacement-controlled (monotonic)loading in pullout tests;• study the influence of an instantaneous increase of load due to a dynamic eventon mobilized pullout resistance, and characterize soil-geosynthetic interactionunder cyclic loading;• account for the extensible behaviour of geosynthetic specimens, which arevisco-elastic materials by establishing a method of interpretation based onmeasurements of pullout load, and strain along the test specimen;• adopt a strain gauging technique for use in pullout testing on grids and sheets;• compare laboratory derived interaction factors with theoretical factorsproposed for design, for both static and dynamic loading conditions;• assess experimental and theoretical interaction factors; and• compare pullout test behaviour with in-service conditions.The present study of monotonic and cyclic pullout resistance of geosynthetics isundertaken to better understand soil-geosynthetic interaction when geosynthetics aresubjected to various loading conditions, and make recommendations for both materials testingand design practice.42Chapter 2. Literature Reviewunpaved roadsnfiflfoundationsretaining walls::. ‘//reinforcementFigure 2.1: Typical examples of soil reinforcement applications (after Palmeira, 1987)3; ‘I1._—..potenHaL faib.ire surfacesreinforcnentFigure 2.2: Failure mechanisms of reinforced soil structures (after Palmeira, 1987)F’‘x’ 6/43Chapter2.LiteratureReview____ZZZEEJSecondaryLeakDetectionPiping10cmDii.Perforated,WrappedPEFabric(WhereRequired)DikeCrestAnchorExistingExcavationandRefeenceLine’PlasticDrainageNets(2Layers),CoveredwithSingleLayerof.BeddingFabric.13mmCompositeThickness(InstalledonSlopesBetweenPrimaryandSecondaryHDPELiners)inSituSoilorAsh,__1.5mm(60Md)/PrimaryLiner-HDPE/1—PrimaryLeakDetectionPiping//10cmDii.Perforated,WrappedPENominal3%Slope4’!1.5mm(60Mu)Liner-HDPE—DrainageVentFabricClayLinerFigure2.3:Sectionshowingthecomponentsof alinersystem(afterUdwanandKittridge,1986)Chapter 2. Literature ReviewFALJJ1Ea) Sld.wal Stop. and 8aa. Faux.tJ%1ER CO9Ole4Tb) Pullout of Un.r Syst.m Compen.nts from Anchor rr.neh.sc) Faikr. flwough th Wast. PS.WkSTE FLL/ t3SOFT FOUAT)ONd) Psiur. T)wough th Wast., Un.r and Fowid.t)enLATIL77 CO.4POStTE tIER SYSTEM•) FaHur. By Slldtng Asong th Lsndflfl Un.r SystemFigure 2.4: Schematic illustration of potential failure modes in a containment facifity (afterMitchell and Mitchell, 1992)OP4500 aCM I z.0oga.;—14 40 0 ‘400••o0 —I4ftOV0ITImpfli;llzm N m8(amrzIn0z In0 0 z (ft r in0 a)Chapter 2. Literature Review—Ia. shear between soil and planereinforcement surfacesb. soil bearing on grid reinforcementbearing surfaces— —-:.V. ::-:. :;:.•:‘6C. soil shearing over soil through thereinforcement grid aperturesFigure 2.7: Mechanisms of load transfer (after Jewell et aL, 1984)47U.1’I.Iz. ii IICl)a, U 0 U 41111I I) .: Cl) Cl) 0U 0 0+‘U‘U Ui+t1 0 0ICDChapter2.LiteratureReviewJewel!ata!.(1984)DOvesen8Strocnan(1972)*Ovesen&Stroman(1972)Huekel&Kwasniewski(1961)Changetal.(1977)OJewell(1980)Palnieira&Miltigan(1989)PresentworkAkinmusuru(1978)Audrbert&Nyman(1977)xDickin8Leung(1983)oDyer(1985)•Peterson(1980)ATrautmann&ORourke(1985)OWang8Wu(1980)1000b’Q’n.Mbetan’((.‘T14)+(c/2))100C a10xxV +01tan((3114)+(/2))40,:degrees60Figure2.9:Comparisonof testresultswithpredictedvaluesofstressratio(afterJeweIl,1990)Chapter 2. Literature Review5.0— 4.5t 3.5C,-LL>- 2.3C-,2.0Li 1.50.50NOR)4AL STRESS (PSi)Figure 2.10: Relationship between efficiency factor and confining stress for various geogrids(after Juran et al., 1988)6.05.5rIb o1 Li (irece Li in (arcr Soil type.io.n..stac Te.nisr Doge ienA. (1983) 51—2Ingold Tez.iir DDse ti• (1983) 51—1 fi —3.L°-33’Ingold )tJo Do..e iz.nf0 (1983) 1168 f —)L-35°,to4rn.Ir Teo.iar ti’eo.ee ia.n(1986) 51—2 0’ — ‘.4°Looee, Tine,• ‘°‘•‘ ‘C *1 Thusrsend(1985) 51—2Tv+v1I 2 2 2 1 i__ 2 I I I t I 1. I t01234567 8 9 10 H 12 13 14 15 16 1750Chapter 2. Literature ReviewGrd1.L-75mmL.on Bard sand 14/25a,—25kPaFigure 2.11: Effect of front wall roughness on pullout test results (after Palmeira andMilligan, 1989)/TotalAreaAverage ResistanceMethodEffective7AreaMaximumLloPeMobilizing ProcessMethodFigure 2.12: A schematic of various interpretation methods for the pullout test4.0j200 20 40Interpretation Methods51CHAPTER 3APPARATUS3.1 IntroductionA large pullout apparatus that was designed and constructed at the University ofBritish Columbia a preliminary study, Raju (1991), was modified substantially for the presentstudy. The apparatus is used to evaluate the development of pullout resistance withincreasing displacement of the geosynthetic specimen, and is described in section 3.2.Instrumentation is used to measure pullout force, pullout displacement at the clamped end andembedded end of the test specimen, lateral pressure on the front wall of the apparatus, and thestrain in the geosynthetic specimen. The instrumentation scheme and data acquisition systemare described in section 3.3.3.2 Large Pullout ApparatusThe apparatus comprises several components: a pullout box which contains the soilsample and geosynthetic test specimen; a hopper for controlled placement of soil in the box toa targeted density; ; a clamp assembly for gripping the geosynthetic test specimen; a servocontrolled, electro-hydraulic system to mobilize pullout resistance through control ofdisplacement or load on the specimen; and a reaction frame. They are described in detailbelow.3.2.1 Pullout BoxThe internal dimensions of the pullout box were selected to meet the followingcriteria:52Chapter 3. Apparatus(1) the box should be long enough to accommodate a geosynthetic test specimenrepresentative of the material used in field structures;(2) the box should accept test specimens of length to width ratio up to 2; and(3) the width and the depth of the pullout box should be large enough to minimize theeffect of boundary shear stresses.The first two criteria help establish the dimensions of the test specimen: a minimumlength of the reinforcement in the resistant or anchorage zone beyond any postulated slipsurface in a reinforced soil structure is commonly taken as 1 m or 3 ft (Christopher et al.,1990). Therefore, a test specimen of dimension 1 m in length and 0.5 m in width was selectedas a basis for testing. The third criterion implies that the pullout box dimensions in plan viewshould be sufficiently larger than the test specimen and the box deep enough to reduce theinfluence of the side, top and bottom boundaries respectively. Little experience was availableon this matter of clearance at the time of design and fabrication. In the absence of specificguidance the internal dimensions of the pullout box were chosen to be: 1.3 m long, 0.64 mwide and 0.63 m deep, and the influence of specimen dimensions assessed in the program oftesting. The box accommodates a soil sample 1.3 m long, 0.64 m wide and 0.6 m deep, andprovides a clearance of 7.5 cm between the specimen and the side wall of the apparatus. Itgives a clearance of 0.03 m to seat a surcharge bag on top of the soil sample that is in contactwith the top plate of the pullout box. In a recent ASTM draft proposal for pullout testing, theminimum dimension for the pullout box is proposed to be: 0.76 m long, 0.46 m wide and0.305 m deep. Also a minimum clearance on the sides is proposed to be 7.5 cm or 15 cmwhen the side wall friction is minimized, or not minimized, respectively. Based on aparametric study Farrag et al. (1993) concluded that a minimum clearance of 150 mm is53Chapter 3. Apparatusnecessary in their pullout box to reduce the effect of the side boundary friction. The ASTMdraft proposal further recommends the use of a metal sleeve to minimize the influence of thefront boundary. The pullout apparatus used in this research meets the requirements of theASTM draft proposal except for the metal sleeve recommendation: this was to permitmeasurements of horizontal stress on the front wall of the pullout box.The pullout box comprises a base frame, base plate, two side frames, and two endplates with supporting frame work, see Figures 3.1 and 3.2. The base frame is made of 76mm x 76 nmi mild steel tube. It supports the pullout box and provides a reaction for thepullout force and the applied normal stress on the test specimen. The base plate of the pulloutbox is made of 13 mm thick aluminum plate. It provides a rigid lower boundary for thesample, and supports the two side frames and two end frames. The side frames are also madeof 7.6 cm x 7.6 cm mild steel tube. A 2.5 cm thick plexiglas sheet, that is fixed to the sideframe, forms the side walls of the test box. A 0.3 cm thick glass sheet is glued to the insideface of the plexiglas to minimize friction between the sand sample and side walls. The frontwall of the apparatus is made of two 13 mm thick aluminum plates mounted on the end framewith a 12 mm slot between them at the mid-height of the soil sample, through which the testspecimen is pulled. Details of the slot arrangement are illustrated in Figure 3.3, The backwall of the apparatus is a 13 mm thick aluminum plate: a small hole of diameter 16 mm iscentrally located through which wires from the instrumentation on the test specimen are takenout of the box.The pullout reaction frame of the apparatus is made of mild steel flats and bars, andbolts to the base frame. It supports the pullout assembly used to load the test specimens.54Chapter 3. ApparatusBending restraint to the pullout frame is provided by a pair of stiffeners at450to the baseframe, see Figure 3.2. Two hollow circular tubes, connected between the pullout frame andthe side frame of the apparatus, are used to transfer bending stresses to the side frames.3.2.2 HopperA hopper is used for controlled placement of the sand sample to a targeted density inthe pullout box. Characteristics of the hopper are shown in Figure 3.4. Icomprises analuminum frame that supports two perforated mild steel plates that are overlapped to create aregular pattern of apertures of constant size. The opening size can be altered to suit the typeof sand, and therefore grain size used in testing.Selection of height of fall, and the size of aperture, was based on a study reported byVaid and Negussey (1988) of factors influencing the maximum achievable density of auniformly graded Ottawa sand by air pluviation. The rate of placement was varied by adjustingthe diameter of aperture, and an optimum value established to minimize interference betweenfalling particles. It was also recognized that a critical height of fall exists for a given particleof sand to impart a terminal velocity and hence achieve a maximum increase in density.Consequently a series of trials were performed in which the sand for testing was air pluviatedinto a small mould, and variations of the sieve opening size and the height of fall used todetermine an optimum configuration. As a result the hopper is fixed on legs above the pulloutbox to give a height of fall in the range 1.4 m to 0.8 m for the 0.6 m thick sand sample. Twomild steel plates, with apertures of 6 mm diameter on a triangular spacing of 13 mm, areoverlapped to give approximately 50% openings. Pneumatically operated cylinders control a55Chapter 3. Apparatustrap door beneath the perforated plates and initiate pluviation. Dispersion of any dust isprevented by thin plexiglas curtain walls on the hopper assembly.3.2.3 Puliout Control AssemblyThe pullout load assembly comprises a double-acting hydraulic actuator with anassociated electro-hydraulic servo-controlled system, and a clamp that connects the rod of theactuator to the test specimen. The hydraulic actuator is bolted to the longitudinal cross-pieceof the pullout frame, such that the centre of the piston is in alignment with the slot in thepullout box. The hydraulic system comprises a pump and several control valves that are usedto control delivery of oil to the actuator. The hydraulic power supply, manufactured by theMTS systems corporation, operates at 3 gallons per minute and is capable of delivering oil atpressures in the range 20.7 to 34.5 MPa (3000 to 5000 psi). The hydraulic actuator,manufactured by the Cunnigham Cylinder Co., has a 82.5 mm diameter rod with a stroke of152.4 mm. A servo valve, model 760-912A manufactured by Moog Hydraulics, mountsdirectly on the actuator and interfaces between the electric and hydraulic control.A closed-loop servo-controlled system is used for control of the movement of theactuator: the principle components are illustrated in Figure 3.5. In closed-loop control, thefunction to be controlled is continuously measured and used as a feedback for comparisonwith the demand signal for that function. The difference between feedback and demand,termed error, is then used to correct the system.Pullout tests are performed under displacement or load control. For displacementcontrolled (DC) tests, the feedback signal comes from a displacement transducer monitoringthe position of the actuator rod. Tests performed under load-control (LC) use a feedback56Chapter 3. Apparatussignal from a load cell measuring the tensile force imposed on the test specimen. The twoclosed-loop control options are illustrated schematically in Figure 3.6. The demand signal forthe control system, in either displacement or load control, is generated from software on a3 86-SX personal computer, see section 3.4. For tests in which a constant rate of displacement(CRD) or a constant rate of load (CRL) is applied to the test specimen, the demand signalgenerated is a ramp fhnction. If the requirement of testing is to impose a repeated load, thenthe demand signal is a waveform. Digital to analog conversion of the demand signal is madeusing a D/A board in the computer, and the signal is then output to a controller. Thecontroller, manufactured by the MTS systems corporation, is used to amplif,r the feedbacksignal, compare it with the demand signal, and generate the error signal for the servo valve.The entire control system was specifically designed and commissioned for this study.3.2.3.1 ClampThe clamp used to connect the actuator rod to the test specimen is made of aluminumand comprises three pieces: a lower jaw, an upper jaw and a central insert, see Figure 3.7.The lower jaw is connected to the actuator rod by a self aligning swivel joint, which eliminatesany transfer of moment. The inside surface of the lower jaw, which grips the test specimenduring testing, is serrated to provide a good grip. The upper jaw fixes to the lower jaw withfour screws.The central insert is a wedge shaped bar that bears against a stainless steel rodmounted in the inside face of the upper jaw. Serrations on the lower face of the insert grip thetest specimen. To increase the efficiency of clamping for some test specimens, the centralinsert was drilled and tapped to accept a series of studs that seat into the apertures of the57Chapter 3. ApparatusTensar geogrid specimens or pre-drilled holes in the aluminum test specimen. During testingthe upper and the lower jaw move as a rigid piece: any attempt by the jaws to open isprevented by 0-clamps placed at four locations across the clamp.The clamp moves on a support table, see Figure 3.1. It rests directly on a mild steelroller plate, 25,4 mm x 152.4 mm, which translates on ball bearings located at a triangularpitch of 25.4 mm. This roller plate mounts between two arborite surfaces: one glued to thelower jaw of the clamp, and the other to the support table.3.2.4 Surcharge PressureSurcharge pressure is applied to the sand sample by pressurizing a flexible bag filledwith water, see Figure 3.8. The bag is 1300 mm long, 640 mm wide and 25.4 mm thick, andis made of PVC. It is pressurized by maintaining a constant head of water for low surchargepressures (8 to 25 kPa), and by use of an air-water interface chamber for higher pressure.The air-water interface chamber, modified from a triaxial cell, has two ports on the topand bottom plates. One of the ports on the top plate serves as a vent to the atmosphere whilefilling the bag with water, whereas the other port acts as a pressure inlet to the reservoirduring testing. A regulator on the pressure inlet from the laboratory air supply is used tomaintain a constant pressure during testing.3.2.4.1 ReactionReaction to the applied surcharge pressure on the sand sample is provided by a 25.4mm thick top plate resting on the pullout box, which is held in place by two cross-beams andfour tie bars attached to the base frame of the apparatus. The top plate, 147 mm x 777 mm,58Chapter 3. Apparatusseats on the pullout box and is bolted in position prior to the application of surchargepressure. The cross beams are fabricated using 76 mm x 76 mm channel sections placed back-to back, and welded together at the ends using 13 mm thick mild steel plates. Four 25.4 mmdiameter high yield steel bars are used to connect the base frame and the top plate.3.3 InstrumentationInstrumentation is used to measure pullout force, pullout displacement at the clampedand the embedded end, total pressure on the front wall of the pullout box, water pressure inthe surcharge bag and strain in the geosynthetic test specimen.3.3.1 Pullout ForcePullout force is measured using a load cell connected between the clamp and thehydraulic actuator. Three load cells were used in the program of testing, all manufactured byInterface Inc.: model 121OAF and 121OAF-1K with a capacity of 44.5 kN (10,000 lbs) and22.25 kN (5000 lbs) respectively, and S type with 4.45 kN (l000lbs) capacity. All three loadcells are powered with a 1OV DC supply.3.3.2 Pullout DisplacementPullout displacement of the clamped end of geosynthetic specimen is measured using alinear variable differential transformer (LVDT) mounted on each end of the central insert ofthe clamp. They are both DC-DC types SE 373/100, manufactured by SE LABS, with a 100mm stroke. They are mounted independently of the base frame using a separate frame thatrests on the floor. Displacement of the insert is taken as the mean of these two measurements.59Chapter 3. ApparatusDisplacement of the embedded end of the specimen is monitored by a tell-tale cableconnected to a LVDT that is mounted outside the back wall of the box, see Figure 3.1. TheLVDT, a DC-DC type, manufactured by Transtek, has a total stroke of 100 mm. The otherend of the tell-tale cable is connected to some test specimens with a screw (aluminum sheetsand Tensar geogrid) and to all others using glue.3.3.3 Pressure on the Front WallSix total pressure transducers (TPT) were used to measure the distribution of lateralstress on the front wall of the pullout box: their locations are shown in Figure 3.9. Thetransducers, type AB/TIP manufactured by Data Instruments, are bonded semiconductor straingauge pressure transducers. Three transducers are mounted above the slot and three below italong a vertical axis through the centre line of the sample. Two transducers have a range 0-100 kPa; three have a range 0-50 kPa; and one has a range 0-25 kPa. They are mounted flushwith the inside surface of the front wall of the pullout box. Transducers at locations TPT-3and TPT-4 are of the 0 to 100 kPa range, while those at locations TPT-2, TPT-4 and TPT-5are 0 to 50 kPa. The most sensitive transducer, with a range 0 to 25 kPa, was used atlocation TPT-1. Each transducer was calibrated in contact with soil using a separate devicethat applies air pressure via bellofram to small chanber in which the transducer is mounted.3.3.4 Water Pressure TransducerA gauge pressure transducer, type SP100-15G, manufactured by MagnetekTransducer Products, was used to monitor the pressure in the surcharge bag during theexperiment. The range of the transducer is 0 to 100 kPa. The transducer is mounted on abracket that is fixed at the same level as the surcharge bag. The body of the transducer was60Chapter 3. Apparatusdismantled, and connected by immersing in water, to ensure that the cavity is free of air. Fullsaturation of connecting tubing was ensured by using a hypodermic syringe to fill theconnecting hoses.3.3.5 Strain GaugesStrain gauges were fixed on the geosynthetic specimen to measure tensile strain duringtesting. A full description of the gauges, type EP-08-250BF-350 OPTION E, manufacturedby the Micro-Measurements Division of Measurements Group Inc., and the procedure forbonding them was developed after Bathurst (1990) and is reported in Appendix-A. The wiresconnect to the data acquisition system through a circuit completion box, where dummygauges are used to complete a full Wheatstone bridge.A schematic illustration of the strain gauge locations (SG- 1 to SG-5) is given in Figure3.10. The mounting locations of the gauges on a test specimen are dependent on the type ofspecimen. Hence, in the reporting of a gauge location, the distance from the front wall isnormalized with respect to the initial embedded length of the geosynthetic test specimen(X!Lei).3.4 Data Acquisition SystemThe data acquisition system consists of a DAS-16 board, a 386-SX desktopmicrocomputer, a signal conditioning unit, and a data acquisition program. The DAS-16board is a multifunction, high speed A/D (analog/digital), I/O (input/output) expansion board,manufactured by the Metrabyte Corp. It includes a 12-bit successive approximation converterand user-selectable gain, and accommodates 16 single-ended channels or 8 double-ended(differential) channels. The signal conditioning unit was designed and built at UBC. It61Chapter 3. Apparatussupplies DC. input to the transducers, and amplifies the output using a variable gain on eachchannel. The transducer signals from the signal conditioning unit are taken to the DAS-16that converts the signal from analog to digital. A digital to analog converter channel of theDAS-16 board is used to apply a demand signal to the servo-control valve.A data acquisition program was written using Quick Basic to support the programof testing. Features of the program are:• Program input:- The test initialization file is read before starting the program.The input parameters include: test name, length and width of the test specimen,and calibration coefficients of all the transducers. For cyclic loading tests,additional input parameters are: frequency of loading and expected maximumpullout resistance of the test specimen from a CRD test.• Scan before testing:- Continuous scanning of all channels before testing, andrecording of initial readings of the transducers.• Scan during testing:- Continuous scanning of all channels during testing. Thedemand and the measured displacement or load are written to the computer screenas a real time plot, together with displacement of the clamped end, to allowmonitoring of test progression.The test is terminated automatically when actuator travel distance exceeds 76 mm inthe case of displacement-controlled tests, In load-controlled tests, the test continues until thespecimen fails in pullout or in tension. A data reduction program was developed to reduce theresults to engineering units.62Chapter3.Apparatus1Soilsample2Testspecimen3Baseframe4Supporttableforclamp5Clamp6Surchargebag7Topplate8ReactionframeServovalveLVDTHydraulicactuatorPulloutframeLoadcellLVDT9 10 11 12 13 14C’814Figure3.1:Componentsof thepulloutapparatusChapter 3.ApparatusFigure3,2:PhotographillustratingcomponentsofthepulloutapparatusChapter 3. ApparatusmmH12.7mm•Front wall of the pulloutboxmm thick neoprenestrippingFigure 3.3: Slot arrangement on the front wall of the apparatus65Chapter 3. ApparatusSide viewTop viewFigure 3.4: Top and side view of the hopper assembly66Chapter 3. ApparatusError measuringDisturbancefunctionControlledvariableDemandreference)signalFigure 3.5: Principle components of closed-loop controlControllerDemandsigialFeedbacksigialPullout boxfront eHFigure 3.6: Schematic illustration of the closed-loop control system67Section A-AFigure 3.7: Details of the clampChapter 3. ApparatusPlan00A00r125I_A 645125Upper jaw Central insertLower jawAll dimensions in mm68Chapter 3. Apparatus1474ConstantwaterheadA_A:Regulator____Air supplyAir-water interface chamber5Flexible bagfilled withwater SoilsampleSection A-AAll dimensions in mmPressure transducerTest specimen77PlanFigure 3.8: Reaction frame and the pressurizing system69Chapter 3. Apparatus*480Figure 3.9: Location of pressure transducers on the front wall of the pullout boxFigure 3.10: Strain gauge locations with respect to the front wall of the apparatus8297976328097Base frame MI dmensions in mm-x56-4. LSOIL SAMPLE70CHAPTER 4MATERIAL PROPERTIES4.1 IntroductionMaterials used in the program of pullout testing are the soil, and the pullout testspecimens which are classified as either extensible inclusions, or inextensible inclusions. Theextensible inclusions are the geosynthetic specimens: geogrids and geomembranes. Theinextensible inclusion is a rough aluminum sheet that was used for comparative purposes.Some material properties that are relevant to the present study are reported in the followingsections based on laboratory testing and the manufacturers’ technical literature.4.2 SandThe soil used in the present study is a rounded silica sand, supplied from a source inMinnesota, USA, by the Badger Mining Corporation. This sand was chosen because of itshigh crush strength and gradation, based on experiences with degradation of an angular sandused in earlier work (Muthu, 1991). Grain size distribution curves determined for samplesprior to, and at the end of the program of testing are presented in Figure 4.1. It is a uniformlygraded sand (C=1 .5) with little or no fines. Particle size diameters are in the range 0.1 mm to2 mm, with a value of d50 between 0.8 and 0.9 mm. Inspection showed the particles to besubrounded to rounded. The similarity of grain size distribution curves indicates there was nosignificant particle breakage or crushing during testing. Determinations of a minimum andmaximum void ratio according to ASTM D 4253-93 and ASTM D 4254-9 1 gave e= 0.49and emax 0.62 respectively.71Chapter 4. Material Properties4.2.1 Angle of FrictionDirect shear tests were performed to establish the angle of internal friction of the sand(Øds). A plane strain friction angle (%) for the sand is determined knowing the angle ofdilation during shearing as shown in the following section. The plane strain friction angle atlarge displacement corresponds to the constant volume friction angle of the sand.4.2.1.1 Direct Shear TestsA small scale laboratory shear box, 76 mm x 76 mm in plan, was used to studybehaviour of the sand in direct shear at large displacement. Sand samples were prepared byair pluviation which resulted in relative densities between 40 and 60%. Although lower thanthe initial relative density of the pullout tests (85-90%), the objective was to allow acomparison of residual strength values. Tests were performed at normal stresses between 5kPa and 30 kPa, a range chosen to encompass that applied to the soil samples during pullouttesting. Results are reported as a normalized stress ratio (t/a) against shear displacement inFigure 4.2. A maximum stress ratio for the densities tested is observed at all stress levels at asimilar shear displacement of approximately 1.4 mm. As shearing continues, the stress ratiodecreases to a constant value. The magnitude of stress ratio at large displacement appears tobe dependent on stress level: a higher value is observed at the lower stresses (4 and 10 kPa).The relationship between normal displacement and shear displacement shows a similarresponse for all tests, see Figure 4.3. An initial, slight tendency to contract changes rapidly toa dilative behaviour at a shear displacement of 0.6 mm. Dilation continues to a sheardisplacement of 3 mm, and thereafter shearing takes place at essentially constant volume.72Chapter 4. Material PropertiesConsidering the stress ratio and the dilatancy characteristics, a plane strain frictionangle for the sand, (%), is obtained using the following expression, after Jewell and Wroth(1987):tansinØ = S (4.1)coslI(1+tandS tan)where:‘v is the angle of dilation in the soil; andtan Øds =t/a is the normalized stress ratio in direct shear.The change in plane strain friction angle with increased shear displacement is shown inFigure 4.4. Residual values at large displacement are in the range 29° to 36°: the variation isattributed to slight stress dependency, see Figure 4.5.43 Geosynthetic Test SpecimensGeosynthetics are polymeric materials, and exhibit a marked visco-elastic behaviour.Consequently the load-extension behaviour is governed by temperature, strain magnitude andrate of strain. Common polymers used in the manufacture of geosynthetics are polyethylene,polypropylene, polyester and polyvinylchloride. Carbon black is added to protect againstdegradation in the presence ofUV radiation.Five types of geosynthetic specimens were used in the testing program to investigatethe influence of structural geometry and tensile strength of the specimen. They are broadlyclassified in two categories: geogrids and geomembranes.73Chapter 4. Material Properties4.3.1 GeogridsThe three geogrids used in testing are termed uniaxial grids because the materialproperties vary with the machine direction (MD) and cross machine direction (CMD) due tothe manufacturing process. All of them comprise longitudinal ribs and tranverse bars. Somephysical and mechanical properties of the geogrids are reported in Table 4.1 frommanufacturers’ technical literature.4.3.1.1 Tensar UX-1500Tensar UX-1500, manufactured by the Tensar Earth Technologies Corp. of Atlanta,Georgia, is a uniaxial grid that is formed by punching small holes in a solid sheet of extrudedHDPE and stretching it preferentially in one direction. This action causes the holes toelongate and form the apertures of the grid which exhibits a monolithic structure with highjunction strength. Measured dimensions of the geogrid are as shown in Figure 4.6; a testspecimen with strain gauges mounted is illustrated in Figure 4.74.3.1.2 Miragrid 15TMiragrid 15T, manufactured by the Mirafi Inc. (now NicolonllVlirafi Inc.) is a bidirectional grid made of polyester multifilament yams which are interlocked by weaving tocreate a stable network such that the yams retain their relative position. In contrast to theTensar geogrid this product is more flexible in bending and exhibits a relatively lower junctionstrength. Measured dimensions of the grid are as shown in Figure 4.8.74Chapter 4. Material Properties4.3.1.3 Stratagrid 700Stratagrid 700, manufactured by Strata Systems Inc., of Atlanta, Georgia, is alsoproduced from a polyester yarn. Measured dimensions of the geogrid are illustrated in Figure4.9. The yarns are bonded, and interwoven at the junctions to form a dimensionally stablestructure, with a uniform network of apertures providing significant tensile strength in oneprincipal direction.Table 4.1: Properties of the geogrid test specimensProperty Unit TENSAR MIRAGRU) STRATAGRIDIJX-1500 15T 700Test code GT GM GSInterlockApertures:Machine Direction (MD) cm 14.478 2.286 5.766Cross Machine Direction (CM])) cm 1.676 2.16 1.981Open area % 60 60 46Thickness:Ribs cm 0.127 0.16 0.185Junctions cm 0.432 0.16 0.205Tensile strengthWide width strip tensile strength(D4595-86):(i) at 5% strain kN/m 52.4 34.0 32.0(ii) Ultimate strength kN/m 86.0 124,0 146.0Long term design load in MD (GRI kN/m 29.2 50.0 68.1GGR)MaterialHigh Density Polyethylene (HDPE) % 97.5Polyester (PET) % 100 100Carbon Black % 2.0 coating coatingCreep Reduction Factor (CRF)Manufacturer’s Test Results ratio .35 - .39 .55 - .65 .55 - .65AASHTO Default Values ratio .20 .40 .40DimensionsRoll length 29.87 45.72 45.72Roll width m 1.0 & 1.31 4.05 1.83Weight/unit area kN/m2 0.00746 0.005 16 0.0065475Chapter 4. Material Properties4.3.2 GeomembranesTwo types of geomembranes were used in testing. The smooth membrane was aNovex IIDPE sheet, 1.5 mm thick, supplied by Nilex Geotechnical Products mc: the texturedgeomembrane was a Gundline HDT, 2 mm thick, manufactured by Gundle Li!Iing SystemsInc., from high density polyethylene. Some physical and mechanical properties of thegeomemebranes are reported in Table 4.2 from the manufacturers’ technical literature.Table 4.2: Properties of the geomembrane test specimensProperty Test Method Unit Novex- GundleSmooth TexturedTest code MS MTDensity (mm) ASTM D1505 g/cc 0.94 0.94Minimum Tensile Properties:Tensile Strength at Break (mm) ASTM D638 kN/m 41 6Tensile Strength at Yield (mm) kN/m 20.7 29Elongation at Break (mm) % 700 --Elongation at Yield (mm) % 10 13Modulus of Elasticity IviPa 770 —Tear Strength ASTM D1004, Die C kN 0.2 0.274.4 Aluminum Sheet Test SpecimenTests were performed on a rigid test specimen to allow a comparison of behaviour inpullout with that of the extensible geosynthetics. The specimen was a fully roughenedaluminum sheet 1.5 mm thick, 0.5 m wide and placed to an embedment length of 0.965 m.The rough texture was acheived by gluing particles of the sand used in testing to its surface.76Chapter 4. Material Properties4.5 Direct Shear Tests on the Sand and Test SpecimensThe same small scale laboratory shear box referred to in secton 4.2.1.1 was used, withmodifications to the bottom half, to study the behaviour of the sand-test specimen interface indirect shear. The objective was to obtain some data for comparison with results from themain program of pullout testing. Coupons of the test specimens were placed on an aluminumblock in the lower half of the shear box. Sand was placed by air pluviation in the top half ofthe shear box. Normal stresses applied were in the range 5 to 20 kPa. The relationshipbetween applied normal stress and the interface shear stress at large displacement is presentedin Figure 4.10.Similar values are obtained for both the sand-sand and sand-textured geomembraneinterface (MT). The response is attributed to the shearing surface being transferred into thesoil mass from the geosynthetic leading to shearing between sand particles. The interfacefriction angle for the sand-aluminum interface is 1 50 A characteristic value for the arboritesand, glass-sand, and smooth geomembrane-sand (MS) interfaces is 12.50 at largedisplacement.77Chapter 4. Material Properties10-00.01Figure 4.1: Grain size distribution curve of the sand before and after testing1.0 —0.9 —0.8 _:0.7 —0.6tla 0.5_:0.40.3 —E0.20.111111 rITE, I I I III0 1 2 3 4 5 6 7 SShear displacement (mm)Figure 4.2: Normalized shear stress relationship with shear displacement for direct shear testson the sandjill90- -e—C-Pncr to test programEnd o test program80100.J70:50—--40__3o__.20—-.0.10 1.00Particle diameter (mm) 10.00Aied ssso)Q4• 20• 25+ 300.078Chapter 4. Material Properties1.0—__________08(kPa)QQ4U 10E 0.6— 154-’-C •200.4 • 25: + 300.2—0.0 —__ ______________________-0.2 —-0.4III II IjiII I III III liii I I0 1 2 3 4 5 6 7 aShear displacement (nTrI)Figure 43: Relationship between normal displacement and shear displacement for the sand45040 0 000030_Z025Applied stress-20—(kPa): Q415— U 1015iozci)A 25Cu+ 300 _:_______ __ _ __ __ __ __ __ __ _fl F I I II 11111 II I0 1 2 3 4 5 6 7 8Shear displacement (niii)Figure 4.4: Plane strain friction angle for the sand794035 —30 —25 —20—15 —10 —5—I I I I I I I I I I I I10 20 30Normal stress, o, (kPa)Figure 4.5: Variation of constant volume plane strain friction angle with normal stressPlan viewMD1.3Section viewAll dimensions in mmTransverseh/barFigure 4.6: Measured dimensions of Tensar IJX-150080Chapter 4. Material Properties00 40162LongitudinalribVChapter 4. Material Properties.J.* 7HEE:.E:.: .......,‘\,‘< \ \ait:>>//h:///: iz/// ,v/ e ‘*‘tA4 >/4+’/ Z’V/_,W;t&/S//4’o4t4ø %ewa ‘ g.I eer /47//A 6/::::........Z ..7€//M at4 ///a4nAfl ai”x=/A’= e><trt47 /7 //WW ea’>3/ *v< / / /\‘SG# /75< 9/ / / $2’/ %%“#“ 5, /7/ <5<<’/ / // ,/Figure 4.7: Instrumented Tensar UX-1SOO test specimen with strain gaugesSectionviewAll dimensions inmmFigure 4.8: Photograph and measured dimensions of Miragrid 1ST81— aIi_ -.atfl—ei n...SPlanview{1.6Chapter 4. Material PropertiesSection viewAll dimensions inmmI I I I I I I I I I5 10 15 20Normal stress, a, (kPa)Figure 4.10: Shear stress and normal stress relationship for various interfaces from direct sheartestsRibIDMDacco(.a. 4Q9.2%. ‘.‘CQ5j....,.. - t.-4GW*. *—“— _w.Plan view1.7Figure 4.9: Photograph and measured dimensions of Stratagrid 700.ii.0>(a(0)U)2.031°15°12.5201510 —5—0—0 Sand-SandArborite-SandGlass-SandK’ MS-Sand7 MT-Sand>< Aluminum-Sand0082CHAPTER 5TEST PROCEDURE5.1 Introduction and Test ProgramIn this chapter the procedure for performing a pullout test, including both preparationof the sand sample and the test specimen is described. The pullout resistance of extensibleand inextensible specimens was studied using the large scale laboratory pullout test apparatusdescribed in Chapter 3. Pullout resistance was mobilized in one of two modes of control -displacement or load. In a displacement controlled test, the test specimen was pulled at aconstant rate of displacement (CRD) until the specimen exhibited tension failure or pulloutfailure defined as displacement in excess of 76 mm. The demand signal in the CRD test is aramp function that varies linearly with time, see Figure 5.1: the rate of displacement (rd) wastypically 0.5 mm/mm, although some tests were performed at rd =0.25 and 1.00 mm/mm. Themonotonic pullout resistance per unit width established in these tests is termed Pm.In the second type of control, the test specimen was pulled out at a constant rate ofloading (CRL) until a certain ratio of the monotonic pullout resistance (apm) was achieved,after which series of cyclic loading were imposed, see Figure 5.2: the rate of loading was 0.25kN/m/min. The constant rate of loading (ri) in the initial monotonic phase of loading is givenby equation 5.1:(5.1)where:a is a constant,83Chapter 5. Test Procedureti is time, andPm is the maximum pullout resistance of the test specimen in the CRD test.Several series of cyclic loading, in which the amplitude of loading (APm) was increasedwith each series, were applied until the test specimen failed either in tension or pullout.Pullout failure of the specimen is defined as the condition corresponding to a substantialaccumulation of displacements with little or no increase in pullout resistance. In each series ofcyclic loading, the number of cycles (N=10) and frequency (f) are kept constant. Typicallytesting frequency was 0.01 Hz, although some tests were performed at 0.1 Hz. In contrast tothe initial part of the test, the cyclic loading phase is characterised by a variable rate of loading(VRL). The behaviour in pullout, for both modes of testing, is interpreted frommeasurements of pullout resistance, displacement of the clamped and embedded ends of thetest specimen, tensile strain along the specimen, lateral pressure on the front wall of thepullout box, and the surcharge pressure imposed on the sample.5.2 Test PreparationThe preparation of each test involved air pluviation of the sand sample, placement ofthe test specimen and application of the surcharge pressure to the sand sample. Proceduresfollowed in the preparation of each test are described in the following sections.5.2.1 Preparation of the Test ApparatusPrior to each test, the pullout box was thoroughly cleaned. The total pressuretransducers were then connected to the data acquisition system and a series of baselinereadings taken with the box empty before pluviation of the sand. The hopper was then lifted84Chapter 5. Test Procedureand seated on the pullout box with the pnuematically controlled trap doors closed. Thelaboratory apparatus was then ready for sample preparation.5.2.2 Preparation of the Test SpecimenTypically each geosynthetic specimen was cut to a width of 0.5 m and length 1.135 m,but some were also 0.5 and 0.65 m in length. The embedded length of a 1.135 m longspecimen was 0.965 m leaving a protruding length of 0.17 m for clamping. Prior to placementin the box the test specimen was strain-gauged. The same routine, see Appendix-A, was usedfor fixing gauges to a geogrid and geomembrane. Five gauges were mounted, typically alongthe centreline of the specimen.5.2.3 Placement of the Sand Sample and the Test SpecimenSand was placed in several layers to a targeted relative density in excess of 85% by airpluviation from the hopper. The hopper was filled with sand from a storage drum that waslifted using an overhead crane. Using a straight edge, the sand in the hopper tray was levelledto form a loose layer, approximately 10 cm thick. A 10 cm layer in the hopper was found togive a finished thickness of 7 to 8 cm in the pullout box. The density variaton of the sandsample in a layer was determined by placing small tins at six locations. Pluviation wasinitiated by the release of pressure to two pneumatic cylinders that support the trap doors onthe hopper, causing them to retract, and the doors to open. A uniform thickness of loose sandin the hopper was found to give a uniform layer in the box.Four pluviated layers brought the sand sample to the mid-height of the slot on thefront wall of the apparatus. At this point the surface of the sand was levelled to receive thetest specimen. Care was taken not to disturb the sand in any significant way. Excess material85Chapter 5. Test Procedureat any location was removed carefully by hand, and any low pockets filled by manuallypouring additional sand through the hopper.The instrumented test specimen was placed on the surface of the sand with the gaugesfacing upwards. Three wires from each strain gauge were passed through a nylon tube (seeFigure 4.7) that served two purposes: (1) protection of the wires, and (2) provision ofunrestrained movement of the wire during the experiment. All wires were taken out of thebox through a 16 mm hole in the back wall of the test apparatus and connected to aWheatstone bridge circuit. A tell-tale cable attached to the rear end of the specimen was alsotaken out of the box in the same way and connected to the LVDT mounted outside the box.Four more layers of sand were then placed following the procedure describedpreviously. A determination of density was made from the mass of sand collected in tinsplaced at six locations on the sample before pluviation of the first and the penultimate layers.The local density thus measured establishes the spatial variation for each test. Followingplacement of the final layer of sand, the hopper was removed and the top surface levelled offas before, in preparation for surcharge loading.5.2.4 Application of Surcharge LoadThe sand sample was surcharge loaded using a pressurized PVC bag. It was placedempty, and care was required to avoid pinching it between the top plate and side frames of thebox. The top plate and cross-beams were then positioned and bolted to the main reactionframe.86Chapter 5. Test ProcedureA reading of the total pressure transducers on the front wall of the apparatus wastaken before filling the bag with water. The bag was then back-filled with water. Thesurcharge loading assembly and the pressurizing system are illustrated in Figure 3.8. For testsat low normal stress (a<25 kPa), a stand pipe was used to maintain a constant head, andtherefore a uniform normal stress, on the test specimen. In tests at a higher normal stress, thewater level in the air-water interface chamber was brought to mid-height; during this processthe chamber was vented to atmosphere. The water pressure transducer that is mounted inalignment with the surcharging bag was then connected and an initial reading taken. At thispoint the venting hose was disconnected from the chamber, and surcharge pressure wasapplied with control from a pressure regulator on the laboratory air supply. A constantsurcharge pressure was maintained during a test by manual adjustment of this regulator or bymaintaining a constant head in the standpipe. This was necessary because of pressure changescaused by changes in volume of the sand sample during pullout.5.2.5 Clamping of the Test SpecimenFollowing application of surcharge loading, the test specimen was attached to thepullout assembly. The lower jaw of the clamp was advanced to align with the test specimen,the clamp insert and upper jaw were placed on the test specimen, and the upper jaw was thenbolted to the lower jaw. G-clamps placed on the clamp assembly at four locations to preventthe jaws from opening during pullout loading.5.3 Test ProcedureThe pullout test in a displacement-controlled (DC) mode or a load-controlled (LC)mode was carried out by specifying a demand signal as illustrated in Figures 5.1 and 5.2. A87Chapter 5. Test Proceduretest is started by sending a demand signal to the electro-hydraulic servo-controlled valve. Theprocess of controlling displacement or load, and acquiring data is carried out entirely bysoftware.Fifteen channels of data were monitored during a test: six total pressure transducerson the front wall; five strain gauges on the test specimen; a load cell on the hydraulic actuator;two LVDTs on the clamp; a LVDT attached to embedded end of the test specimen; and apressure transducer connected to the surcharge bag. The digital output of the A/D board isscanned continuously and stored at regular intervals throughout a test. Pressure in thesurcharge bag is adjusted as necessary during testing by manually operating a pressureregulator or by maintaining a constant head in the stand pipe. Typically a displacementcontrolled test is continued to a displacement of 76 mm, which at a rate of displacement of 0.5mmlmin, takes 2 hours and 32 minutes. However, a load controlled test was continued untilthe test specimen failed in pullout or an accumulated displacement of 100 mm was recorded.The total duration of testing depends on several factors and typically ranged from 30 minutesto 3 hours.5.4 Post-Test ProcedureAt the end of the test the hydraulic supply was switched off, the data acquisitionprogram stopped, the surcharge pressure released, and water allowed to drain out of the bag.All the instrumentation cables were disconnected from the data acquisition unit. The reactionframe was then dismantled, the top plate lifted off the box, and the surcharge bag removed.Sand was removed from the box using a modified vacuum cleaner. A measurement of themass of the storage drums before and after emptying the box was used to determine the mass88Chapter 5. Test Procedureof sand in the box, and hence calculate the mean density of the sample knowing the volume ofthe box.A typical routine for testing was to clean the box and strain gauge a geosyntheticspecimen on day 1. On day 2 the box was filled and instrumentation connections made.Surcharge load was applied and the test carried out on day 3. On day 4 the sand wasremoved from the box. Thus a typical testing routine requires 4 days ofwork for each test.89:‘z-G)0Cu4-.Cl)Cl)ci)4-,D00Time (mm)Chapter 5. Test ProcedureIFigure 5.1: Demand signal in the displacement-controlled modeapmFigure 5.2: Demand signal in the load-controlled modeti t2 t3Time (mm)90CHAPTER 6TEST RESULTS6.1 IntroductionResults are presented for pullout tests on extensible and inextensible test specimens.Variables examined in the program of testing include: normal stress, geometry and stiffness ofthe test specimen, embedment length, roughness of the front wall of the pullout box and modeof testing. Most tests were performed on specimens 0.5 m wide and with an embedmentlength of 0.965 m: a shorter embedment length (0.5 m and 0.65 m) was used in a few tests.The testing mode was either displacement-control (DC) or load-control (LC). In the LCtests, a constant rate of loading (CRL) was applied to a targeted value and a variable rate ofloading (VRL) then imposed that was dependent on the amplitude and frequency of loading.A reference code is used to identify each test configuration, see Figures 6.1 and 6.2. Thefourth column is a suffix which identifes, for example, whether a test was repeated to assessthe reproducibility of the results.6.2 Displacement-Controlled Pullout TestsThe displacement-controlled tests were typically performed at a constant rate ofdisplacement, rd=0. 5 mmlmin. The applied normal stress (as,) at the interface of soil and testspecimen was in the range 4 to 30 kPa, and was selected to promote development of a pulloutfailure. Test specimens evaluated in the monotonic series of tests are: (1) geogrids (Tensargrid, Stratagrid, and Miragrid), (2) geomembranes (smooth and textured) and (3) a roughaluminum sheet. The following section presents the results for these specimens of differing91Chapter 6. Test Resultsgeometry and stiffness. The influence of rate of displacement on the measured pulloutresistance was examined by performing some tests on the Tensar grid at rd=0.25 and 1.0mm/mm. Roughness of the front wall was examined in tests using an arborite surface fixed tothe aluminum wall of the pullout box.Characteristics of all displacement-controlled tests performed on geogrids aretabulated in Table 6.1 and in Table 6.2 for the geomembranes and aluminum sheets.6.2.1 Influence of Front BoundaryTo evaluate the influence of the front boundary, and more specifically the surfaceroughness of the front wall, on the measured pullout resistance, some tests were performedwith two different front boundary materials. As fabricated, the front wall of the pullout box ismade of aluminum, and most tests were performed with this arrangement. Direct shearboxtests gave a value of &=150 for the sand/aluminum at large displacement. However, in sometests an arborite sheet was fixed to the front wall to provide a lower friction boundary: directshearbox tests for the sand/arborite gave &=1 2. 50•The variation of pullout resistance with displacement for the Tensar grid at a10 kPa(GT 10) exhibits little difference at small displacement, see Figure 6.3. With increasingdisplacement and as the pullout resistance reached a maximum value, the test with the arboritesurface gave a lower resistance. Finally, at large displacement, both curves appear to beconverging. A very similar response is obtained with the textured geomembrane at a=8 kPa(MTO8), see Figure 6.4. The equivalent smooth geomembrane, test MSO8, develops a peakpullout resistance that is slightly greater with the aluminum surface, and again, both curvesconverge at large displacement. It appears that tests with the arborite surface, which has a92Chapter 6. Test Resultsrelatively smaller value of interface friction with the sand, exhibit a maximum pulloutresistance that is lower. The results imply the ideal front boundary that will give a lowerbound to the pullout resistance is a smooth, frictionless material. Since the results with eachmaterial are not significantly different and there was a desire, in this study, to measure lateralpressures on the front wall of the pullout box, the aluminum surface was adopted for use intesting. All of the following data are presented for this configuration.Table 6.1: Summary of displacement-controlled tests on geogrid specimensApplied Initial Rate ofTest code normal embedded Width displacement, rstress, a length, Lei (m) (mm/mm)(kPa) (m)GTO4 3.9 0.965 0.50 0.50GT1O 10.0 0.965 0.50 0.50GT1OR 10.5 0.965 0.50 0.50GT17 17.0 0.965 0.50 0.50GT17R 17.0 0.965 0.50 0.50GT2O 19.9 0.965 0.50 0.50GT2O 19.8 0.965 0.50 0.25GT2O 20.9 0.965 0.50 1.00GT25 25.0 0.650 0.50 0.50GT25R 24.7 0.500 0.50 0.50GT3O 29.8 0.965 0.50 0.50GT1OS 10.5 0.965 0.50 0.50GTO4N 3.9 0.965 0.50 0.50GT1ON 10.0 0.965 0.50 0.50GT18N 17.3 0.965 0.50 0.50GSO4 3.9 0.970 0.47 0.50GS1O 10.0 0.970 0.47 0.50GS17 17.0 0.970 0.47 0.50GMO4 3.9 0.980 0.44 0.50GM1O 10.0 0.980 0.44 0.50GM17 17.0 0.980 0.44 0.50GMO4C 3.9 0.965 0.47 0.50GMO4CR 3.9 0.965 0.47 0.50GMJOC 10.0 0.965 0.47 0.50GM1OCR 10.0 0.965 0.47 0.50GM18C 18.0 0.965 0.47 0.50GM18CR 18.0 0.965 0.47 0.50GM1OS 10.0 0.965 0.47 0.50GMO4N 3.9 0.965 0.47 0.50GM1ON 10.0 0.965 0.47 0.5093Chapter 6. Test ResultsTable 6.2: Summary of displacement-controlled tests on the geomembrane and aluminumsheetsTest code Applied Initial Width Rate ofnormal embedment (m) displacement, rstress, a length, L (mm/mm)(kPa) (m)ARO4 3.9 0.985 0.50 0.50ARO4R 3.9 0.945 0.50 0.50ARO8 8.0 0.948 0.50 0.50AR12 12.0 0.960 0.50 0.50AR12R 12.0 0.910 0.50 0.50MSO4 3.9 0.950 0.50 0.50MSO4R 3.9 0.950 0.50 0.50MSO8 8.0 0.950 0.50 0.50MSO8R 8.0 0.955 0.50 0.50MSO8S 7.5 0.950 0.50 0.50MS12 11.8 0.950 0.50 0.50MTO4 3.9 0.950 0.50 0.50MTO8 8.0 0.950 0.50 0.50MTO8S 8.0 0.956 0.49 0.50MTO8RR 8.0 0.965 0.50 0.50MT12 13.0 0.950 0.50 0.506.2.2 Influence of Rate of DisplacementThree tests were performed on Tensar grid specimens at rd=O.25, 0.50, and 1.00mm/mm. A normal stress of approximately 20 kPa was applied to all specimens, i.e., 19.8,19.9 and 20.9 kPa respectively. A similar response to loading is observed, especially at smallto moderate displacements, suggesting that the mobilized pullout resistance of the grid isessentially independent of the rate of displacement at these relatively slow rates ofdisplacement (see Figure 6.5). All of the tests subsequently reported were performed at astandard rate of 0.5 mm/mm.6.2.3 Aluminum Test SpecimensDisplacement of the clamped end (do) and embedded end (de) of the specimens, andmeasured pullout resistance are used to describe the response to loading. The relationshipbetween d and de for the rough aluminum sheet at different applied normal stresses is shown94Chapter 6. Test Resultsin Figure 6.6. All tests show a value d equal to de: the response is attributed to theinextensible behaviour of the specimens. An important aspect of this inextensible behaviour isthe development of a constant relative displacement between the soil and the test specimenalong its embedded length, and therefore mobilization of a uniform shear stress with length.6.2.3.1 Rough Aluminum SheetThe variation of pullout resistance for the rough aluminum sheet, with a= 4 to 12kPa, is shown in Figure 6.7. Mobilized resistance increases with the applied normal stress. Apeak value of resistance develops, and is followed by a strain softening behaviour. Three testsat a4 kPa gave a similar response at large displacement: one test (ARO4) was inadvertentlydisturbed during clamping of the specimen and is inconsistent at small displacement only. Astaged test was performed with a=8 kPa, unloading loop, and a=12 kPa. The 12 kPa stagetest exhibits a resistance similar to that of the corresponding AR12 test: the difference inpullout resistance for each test at large displacement is attributed to a shorter initialembedment length of the staged test. A unified interpretation of the data is presented inChapter 7, where the pullout resistance is normalized with respect to the resisting area andnormal stress.6.2.4 Geosynthetic Test SpecimensThe behaviour of the geogrids and geomembranes is described in general terms withreference to measured displacements d and de, prior to a separate description of themeasurements of load and strain. Results for the Tensar grid with a=4 to 30 kPa, see Figure6.8, show an initial displacement of the clamped end without any displacement of the95Chapter 6. Test Resultsembedded end. The response is dependent on applied normal stress. At a=4 kPa, de>0when d>5 mm, and d>10 mm at a=17 kPa. A non-linear relationship between d and defollows, and leads to a linear relationship for tests at a=4, 10 and 17 kPa. The response ofthe test at a30 kPa is very different: displacement of the embedded end was not observeduntil d>20 mm, and thereafter dc>de throughout the test. A non-linear response, in which theembedded end displaces significantly less than the clamped end, is attributed to a markedlyextensible behaviour of the test specimen.A similar relationship between d and de is observed for the Stratagrid, see Figure 6.9,which shows an inextensible behaviour after 5 mm with increasing displacement at a4 kPaand greater non-linearity at a=17 kPa. Again, the displacement of the clamped end that isnecessary to mobilize an initial displacement at the embedded end is observed to increase withthe applied normal stress. The general relationship is also true for tests on the Miragrid, seeFigure 6.10The characteristic response of the geosynthetic specimens is further illustrated inFigure 6.11, in which results for both the smooth and textured geomembrane with a=4 to 12kPa are presented. It is apparent that the smooth geomembrane (MS) exhibits a behaviourthat is essentially inextensible at all values of normal stress after 4 mm. The response of thetextured geomembrane (MT) at a4 kPa is similar to the smooth geomembrane, but not ata=12 kPa where it is distinctly non-linear at small displacement and tends toward a linearbehaviour at large displacement. A transition behaviour is observed in the test at a8 kPa.96Chapter 6. Test ResultsIt is clear from these test results that the response of the geosynthetic test specimenmay be characterized as inextensible or extensible. The behaviour is dependent on appliednormal stress. Pullout failure at constant strain must be associated with d = de, and aninextensible response. Details of the load and strain measurements for each geosynthetic testare presented below.6.2.4.1 GeogridThe detailed response of a geogrid to DC pullout testing is described frommeasurements of pullout resistance and mobilized strain with displacement of the clampedend. In this section the response of three geogrids (GT, GM and GS, see Table 6.1) ispresented at different values of normal stress.6.2.4.1.1 PuiJout ResistancePullout resistance is seen to increase with displacement d for the GT test specimens ata=4 to 30 kPa, see Figure 6.12. The characteristic response exhibits three zones: an initiallinear relationship, a non-linear transition and a limiting resistance at large displacement. Theslope of the linear zone is seen to increase with the magnitude of applied normal stress. Theextent of the non-linear transition zone is also dependent on the applied normal stress. InGTO4 test the non-linear transition zone occurs rapidly over a small range of displacementwhereas the GT tests at 17 kPa illustrate the zone clearly. Tests with a=4 to 17 kPa attain aconstant limiting value of pullout resistance at a value of displacement d that also increaseswith applied normal stress, being 6 mm for a=4 kPa and 30 mm for o17 kPa. Two testswere performed at a=17 kPa to examine the repeatability of the testing routine. The97Chapter 6. Test Resultsresponse of tests GT 17 and GT 1 7R are very similar and suggest an excellent repeatability (seeFigure 6.12).In contrast to the response at a=4 kPa, that at a=3 0 kPa shows a continued increaseof pullout resistance with displacement of the clamped end. The non-linear transition zonepredominates and no limiting value of resistance is attained. On continuation of the test, thespecimen may fail in tension if the load per unit width exceeds the ultimate tensile strength ofthe specimen material, which is reported as 86 kN/m from wide width testing (see Table 4.1).In practice this places an upper limit to the applied normal stress for a given dimension of thetest specimen if tensile failure of the specimen is to be avoided.The pullout resistance of the GM geogrids, in the range a=4 to 17 kPa, illustrates aslightly different initial response and a maximum value which again is dependent on stresslevel, see Figure 6.13. Displacement d required to attain the maximum value increases withthe applied stress, as in the case of the GT tests. Although the response at large displacementfor o=4 kPa and 10 kPa shows a nearly constant pullout resistance, the response for l7kPa is different in that there is a decrease as the displacement increases. After completion ofthe test, the sand was carefully removed to expose the specimen, and the displacement patternof the transverse elements recorded. It showed that the deformed shape was parabolic innature with a maximum displacement at the edges, see Figure 6.14. The behaviour could bedue to yielding of the junctions: visual inspection of the specimen after the test revealed thatthe junctions were damaged.To further examine the influence of grid orientation on measured pullout resistance,some tests were performed on the GM test specimens with the orientation changed to give the98Chapter 6. Test Resultsdirection of pullout in line with the cross-machine direction (weak) of the grid. The pulloutresistance illustrates clearly the significance of the orientation, see Figure 6.15. In thisorientation the transverse elements are stronger and the longitudinal elements weaker,therefore, the response is less stiff in the initial phase of the test when compared to that of thetests in machine direction (see Figure 6.13). The GM 1 OC and GM1 7C test specimens wereobserved to fail in tension at large displacement of the clamped end. Tests performed onspecimens without bearing elements (GMO4CN and GM1OCN) suggest that the pulloutresistance mobilized by the friction component is 65 to 70% of the total pullout resistance.The pullout resistance of the GS specimens exhibits a very similar response to GMspecimens, see Figure 6.16. Although the initial response at all stress levels is similar, thevalue of limiting resistance is observed to be dependent on normal stress. At a=17 kPa theresponse at large displacement exhibits a slight strain softening behaviour which is similar tothe GM1 7 test. This behaviour is attributed to the surface characteristics of the grids.6.2.4.1.2 Rib StrainStrain gauges were mounted on the longitudinal ribs of a geogrid test specimen (seeFigure 4.7). The variation of strain (Er) with displacement d for each geogrid at 10 kPa ispresented in Figures 6.17, 6.18, and 6.19. The strain gauge location is reported as thedistance (x) from the front wall of the apparatus (see Figure 3.10) normalized with respect tothe initial embedment length (La) of the specimen: values are shown in the legend, and anegative value is associated with a gauge mounted outside the pullout box on the specimenbetween the clamp and the front wall.99Chapter 6. Test ResultsA general trend is observed, wherein the strain response exhibits three distinct phasesas the displacement d0 increases. They are illustrated schematically in Figure 6.21. It is notedthat the rate of strain at any gauge location can be deduced, knowing the strain (Er),displacement (do), and rate of displacement for the test (rd). The behaviour at smalldisplacement is characterised by a rate of strain which is essentially linear. This initial rate ofstrain decreases with distance from the clamped end of the specimen. The initial linearbehaviour is followed by a second phase in which a transition occurs to the third phase inwhich variations in strain are typically small. Little or no variation in strain indicates that thespecimen is failing in pullout at nearly constant strain. The magnitude of this constant straindecreases with distance from the clamped end. Therefore the distribution of strain along thelength of the specimen is non-uniform, and different, at various stages of the test.Consider the GT1O test, see Figure 6.17, in which the initial linear response atlocations SG-1 to SG-3 shows a similar strain rate. The non-linear response is clearlyexhibited at all strain gauge locations. The curves tend toward a constant limiting value at alllocations except SG-3 and SG-5, where a small increment is observed at SG-3, and amoderate decrement at SG-5. A maximum strain is maintained constant throughout the test atother locations.The response of the GS specimen is similar to that of the equivalent GT test in bothshape and magnitude of the curves, see Figure 6.18. It should be noted the relative positionsof the gauges (XILe1) are comparable, but not identical, due to the different size of theapertures in type of each grid. Again there is evidence of a small variation of strain at largedisplacements. The strain response of the GM specimen at a=lO and 17 kPa is shown in100Chapter 6. Test ResultsFigures 6.19 and 6.20. A typical linear response at small displacements is observed in bothtests, where the linear strain rate again decreases with distance from the front wall of theapparatus.A greater rate of strain occurs in the test at a=17 kPa than at a=10 kPa. A differentbehaviour is also observed in the non-linear transition behaviour of the test: the response ata=l7 kPa is marked by a much stronger non-linear transition. There is also evidence fromSG-5, at this higher stress, of zero strain during early displacement (and straining) of the frontof the specimen. At larger displacement d a constant limit strain is mobilized in both thetests.The variation of the rate of displacement along the specimen during pullout testing isaddressed by the tests at rd=O.25, 0.50 and 1.00 mm/mm on the GT grid at stress a20 kPa,see Figure 6.22. Strain measured on the longitudinal ribs at SG-1 (x!Lep =0.073) and SG-5(0.744) are presented for these tests. The results indicate that the strain rate at SG-1 isessentially independent of rate of pullout displacement, although a somewhat greater limitingstrain is mobilized at rd=1 .00 mm/mm. In contrast the strain rate at SG-5 appears to bedependent on the rate of pullout.6.2.4.2 GeomembranesThe pullout resistance of the smooth and textured geomembrane are contrasted.Strain data are presented for the smooth geomembrane only, because of difficultiesencountered in mounting the gauges on the textured geomembrane due to its surfacecharacteristics.101Chapter 6. Test Results6.2.4.2.1 Pullout ResistanceThe pullout resistance of the smooth geomembrane at 4 to 12 kPa exhibits a stiffresponse, with small displacements in the range 1 to 4 mm sufficient to mobilize a markedpeak value of pullout resistance, see Figure 6.23. Nevertheless, the displacement to reach thepeak value increases with normal stress, as in the case for the geogrids. The post-peakresponse is typical of a strain softening behaviour and a nearly constant pullout resistance ismobilized at large displacement. The magnitude of peak pullout resistance increases withnormal stress, but the values are very low in comparison to those for the grid specimens.Again, the two tests performed at a=4 kPa illustrate the repeatability of the testingprocedure, see Figure 6.23.The pullout resistance of the textured geomembrane is shown in Figure 6.24. Theresponse of textured geomembrane is very different to that of smooth geomembrane. Asignificantly greater value of limiting pullout resistance is mobilized at similar normal stresseswhen compared to the smooth geomembrane, and there is no evidence of a strain softeningbehaviour. Comparison shows the limiting values exceed those obtained for the grids atcomparable normal stresses. The displacement necessary to mobilise the limiting pulloutresistance also increases with the increase in applied normal stress, from d =6 mm with a4kPa to d =35 mm for a=12 kPa.6.2.4.2.2 Local StrainStrains mobilized in the smooth geomembrane at a=4 to 12 kPa are shown in Figures6.25 to 6,27. The results indicate the magnitude of strain increases with increasing normalstress, and decreases with distance from the front wall of the apparatus. The strain102Chapter 6. Test Resultsmagnitudes are very small and fluctuate, particularly those at a=4 kPa, a response which isattributed to small strain redistribution as a consequence of incremental displacement inpullout. Comparing the curves with the schematic response illustrated in Figure 6.21, a rapidtransition is observed at all stress levels from a linear to non-linear behaviour. This isattributed to the distinct peak resistance mobilized in pullout. Deviations at largedisplacements are attributed to the relatively small magnitudes of strain (less than 0.4 %), andare considered uniform for all practical purposes.6.3 Load-Controlled TestsCyclic pullout tests were performed on both geosynthetic and aluminum testspecimens. Each test specimen was pulled at a constant rate of loading (CRL) to a targetedratio of the CRD pullout resistance (apm), where a< 1, after which cyclic loading wasimposed, see Figure 5.2. The cyclic loading phase is characterised by a variable rate ofloading (V.RL). Several series of cyclic loading, with an amplitude of loading (APm) that wasincreased with each series, were applied until the test specimen failed in pullout. Pulloutfailure of the specimen is defined as continued displacement with little or no increase inmobilized resistance. The number of cycles N=10 and frequency f of each series was keptconstant.A summary of all load-controlled pullout tests is given in Table 6.3. Variablesexamined in the program of testing are geometry of the specimen, normal stress andfrequency. Most tests were performed at f=0.01 Hz and a<2O kPa. Comparisons of pulloutresponse in the displacement-controlled (DC) tests and load-controlled (LC) tests are made103Test code Applied Test Test Frequency ofnormal specimen specimen cyclicstress, a length, Lei width (m) loading, f(kPa) (m) (Hz)GTO4 3.9 0.965 0.50 0.01GT1O 10.0 0.965 0.50 0.01GT1O 10.0 0.965 0.50 0.10GT17 17.0 0.965 0.50 0.01GSO4 3.9 0.970 0.47 0.01GS1O 10.0 0.970 0.47 0.01GS17 17.0 0.970 0.47 0.01GMO4 3.9 0.965 0.44 0.01GM1O 10.0 0.950 0.44 0.01GM17 17.0 0.980 0.44 0.01GMO4C 3.9 0.965 0.44 0.01GM1OC 10.0 0.965 0.44 0.01GM1OC 10.0 0.965 0.47 0.10GM18C 18.0 0.965 0.44 0.01ARO8 8.0 0.965 0.50 0.01MSO8 8.0 0.950 0.50 0.01MS12 11.8 0.965 0.50 0.01MTO8 8.0 0.960 0.50 0.01MTO8 8.0 0.960 0.50 0.10MT12 13.0 0.955 0.49 0.016.3.1 Aluminum Test Specimen6.3.1.1 Pullout ResistanceOne cyclic pullout test was performed on the rough aluminum sheet at a =8 kPa anda frequency of 0.01 Hz, for an embedment length identical to the equivalent displacement-controlled (DC) test (ARO8). Initially the specimen was pulled at r1=0.25 kN/m/min to atargeted value corresponding to 60% (a=0.6) of the pullout resistance in the DC test. In totalthe specimen was subjected to eight series of cyclic loading until it failed in pullout: theamplitude of loading was increased from one series to the next series, leading to imposedratios of a=0.625 for the first series and 0.65, 0.70, 0.80, 0.85, 0,90, 0.995 and 1.09Chapter 6. Test Resultsbased on measurements of tensile force, strain, and displacement of the clamped end andembedded end of the test specimen.Table 6.3: Summary of load-controlled pullout tests104Chapter 6. Test Resultsthereafter. The complete response to cyclic loading is shown in Figure 6.28 and the earlyresponse shown in further detail in Figure 6.29.The maximum pullout resistance in each series of loading forms an envelope. Theenvelope is parallel to, and coincident with corresponding DC curve up to the peak resistance.Thereafter it remains parallel to, but greater than, the DC test. At lower amplitudes of cyclicloading the response is relatively stiff, with little or no measured displacement of the clampedend taking place during the ten load/unload cycles. When the load amplitude is high, such thatthe total load per unit width exceeds that mobilized in the DC test, a rapid accumulation ofdisplacement takes place at the clamped end. After a few cycles of loading there is anaccumulation of excessive displacement that results in the specimen being pulled out rapidly.Visual observations at that instant confirm that pullout was indeed very quick.6.3.1.1.1 Displacement of the Embedded EndThe relationship between displacements d and d0 is shown in Figure 6.30. Data areshown at equal time intervals of 2 secs and therefore the distribution indicates that most of thedisplacement was accumulated in the final few cycles of loading. The data lie on a line givenby dc=de, confirming the inextensible behaviour of the specimen.6.3.2 Geosynthetic Test SpecimensCyclic pullout test results for the geogrids and geomembranes are presented in thissection.105Chapter 6. Test Results6.3.2.1 Geogrids6.3.2.1.1 Pullout ResistanceThe variation in pullout resistance of the Tensar grid at a4, 10 and 17 kPa is shownin Figure 6.31 for both the DC tests and the LC tests at a frequency of 0.01 Hz. In the DCtests, the geogrid exhibits an increase in pullout resistance with displacement of the clampedend to a limiting value at large displacement. The initial, nearly linear relationship mobilizedin a LC test is very similar to that of the corresponding DC test. An envelope describing thepeak values of pullout resistance mobilized by cyclic loading illustrates the same smoothtransition to a limiting value at large displacement. The limiting value tends to be greater inthe load-controlled tests.The incremental displacement that occurs with each cycle of load is seen to varysignificantly with the amplitude, and therefore relative magnitude, of loading, being small atthe lower amplitudes and larger at the higher amplitudes. The limiting value of pulloutresistance increases with increasing normal stress in all tests, together with the displacement atwhich it is achieved. The shape of the curves leads to a nearly constant magnitude of pulloutresistance under cyclic and monotonic loading, at large displacement.The cyclic pullout resistance of the Miragrid, see Figure 6.32 and the Stratagrid, seeFigure 6.33, is also compared with the corresponding DC test. At lower normal stresses,o=4 and 10 kPa, the envelope of maximum cyclic pullout resistance coincides with thedisplacement-controlled pullout resistance. In contrast at a=17 kPa the envelope to thecyclic pullout resistance of the Miragrid and Stratagrid (see Figure 6.34) is different: it liesbelow the corresponding DC test for the Miragrid but above for the Stratagrid. Nevertheless,106Chapter 6. Test Resultsthe envelope remains parallel to the corresponding DC test. The results indicate themobilisation of pullout resistance of a geogrid in cyclic loading is dependent on the appliednormal stress and stiflIiess of the grid. Comparison of the DC and LC results for each gridsuggests the stiffer Tensar geogrid (see Table 4.1) tends to mobilize a higher pulloutresistance in cyclic loading.6.3.2.1.2 Influence of Loading FrequencyTests were performed on the Tensar grid (GT) to examine the influence of loadingfrequency. The response at a 10 kPa and 0.1 Hz is shown in Figure 6.35. The response tothe common initial constant rate of loading in both tests (0.25 kN/m/min), see Figures 6.31and 6.35, is very similar in each case, and is considered indicative of the reproducibility of thetests. Thereafter the same generalized response to cyclic loading is evident from the curves,which exhibit a common envelope to the peak values of pullout resistance. The incrementaldisplacements of each test specimen during cyclic loading vary a little: a slightly greaterpullout displacement occurred during the series of load cycles up to a mobilized pulloutresistance of 11 kN/m in the test at a lower frequency. The difference in behaviour isattributed to more displacement taking place between each series of cycles as the imposedload was increased at the lower frequency. However, for practical purposes the response istaken to be independent of loading frequency.6.3.2.1.3 Rib StrainThe strain mobilized in each of the three types of geogrid during cyclic loading ata=10 kPa and f=0.01 Hz is shown in Figures 6.36, 6.37 and 6.38. A comparison of theenvelope to the cyclic strain, and the strain mobilized in the corresponding DC tests (Figures107Chapter 6. Test Results6.17, 6.18 and 6.19), shows a similar trend and shape. In each case the strain rate decreaseswith the distance from the clamped end, and the magnitude of strain at the front is greaterthan that at the embedded end. The variation of strain with each load cycle is evident atgauge locations SG-1 and SG-2, which are near the clamped end: these changes are not seenat the gauge locations near the embedded end even when the load amplitude is sufficient tocause pullout failure.At values of similar normal stress the Tensar geogrid mobilizes a maximum strain atrelatively larger pullout displacements when compared to the strain response of the Miragrid(Figure 6.37) and Stratagrid (Figure 6.38). This difference in behaviour is attributed to thedominating mechanism in effect during pullout which is the relative contribution of frictionand bearing resistance. Nevertheless, there is a tendency toward achieving a nearly constantstrain at all strain gauge locations during pullout itself.Again, a similar general response is observed in the geogrid tests at a,=1 7 kPa, seeFigures 6.39, 6.40 and 6.41. The magnitude of strain at all locations is greater than thatrecorded in the LC tests at a=1O kPa. The strain magnitude in the Tensar geogrid at theSG-1 location (outside the box) is higher than that at SG-2 (Figure 6.36) which is attributedto the difference between the unconfined and confined load-extension behaviour of thespecimen. This effect is significant for the Miragrid at higher normal stress, see Figures 6.37and 6.40, and the Stratagrid, see Figures 6.38 and 6.41. A similar comparison for the Tensargrid is not possible because the gauge at location SG-2 was inoperable during the GT17 test.An important characteristic of the variation of strain with pullout displacement isobserved at gauge locations closer to the embedded end of the specimen. The magnitude of108Chapter 6. Test Resultsstrain increase and decrease in response to cyclic loading is seen to be smaller: gauge locationsSG-4 and SG-5 in all tests show an unload/reload loop that is essentially horizontal. Theresponse is attributed to a “locking-in” of these small strains. In some cases, see for examplelocation SG-4, in test GS 17 (Figure 6.41) the behaviour changes as the test progresses and apullout failure develops.6.3.2.1.4 Displacement of the Embedded EndThe relationship between displacement of the embedded end and the clamped end ofthe Tensar grid at a = 4, 10 and 17 kPa is shown in Figure 6.42. At the lower normal stress,the behaviour is essentially inextensible, but at 17 kPa the response is markedly non-linear atsmall displacement and tends toward a linear behaviour as pullout occurs. The data wereacquired at constant time intervals. The magnitude of incremental displacements is very smallduring the initial phase of the test, but accumulates rapidly during the final stage when theload amplitude is sufficiently high to cause the specimen to pull out of the box. This generalbehaviour is also observed with the Miragrid, see Figure 6.43 and with the Stratagrid, seeFigure 6.44.6.3.2.2 Geomembranes6.3.2.2.1 Pullout ResistanceThe response of the smooth geomembrane at a = 8 kPa in the load-controlled pullouttest at f0.01 Hz is shown in Figure 6.45. An envelope to the peak values of pulloutresistance under cyclic loading shows an abrupt transition to a limiting value of nearly 3.2kN/m, and pullout failure occurs immediately. The failure is characterized by a brittlebehaviour that is attributed to the strain-softening nature of the interface evident in the109Chapter 6. Test Resultscorresponding DC test. Development of a significantly greater limiting value of pulloutresistance in the load-controlled test is a result of the control system which, in seeking toachieve a peak demand load in the last cycle, pulled the specimen out of the soil in 8.3 secs ata mean rate of displacement that was approximately 360 mmlmin.A similar response is observed at a=l2 kPa: the pullout resistance beyond the peakvalue in the DC test again exhibits an instantaneous pullout. An envelope to the cyclic loadingdefines the pullout resistance in the DC test. The abrupt transition from a stable to unstablebehaviour occurs at 4.3 kN/m which is the peak resistance value in the DC test.The pullout resistance of the textured geomembrane at a=8 and 12 lcPa and f0.01Hz is shown in Figure 6.46. For clarity only half of the unload/reload loops is shown for theLC test at 12 kPa. The nearly instantaneous pullout failure of the smooth geomembranecontrasts markedly with the more ductile behaviour observed for the textured geomembrane.The same response is observed in the DC test and LC test during the constant rate of loading(CRL) phase prior to load cycling. The characteristic response to cyclic loading is generallysimilar for both tests. Again, a very similar response is seen in the CRL phase of the test ato,8 kPa and f”O. 1 Hz, see Figure 6.47. A frequency dependent response is observed in theincremental displacements during cyclic loading which is similar to that exhibited by theTensar grid, with the test at a lower frequency experiencing greater displacement at acomparable cyclic pullout resistance.For the test at a=8 kPa and f=0. 01 Hz, the envelope of pullout resistance is similar tothat in the DC test. In contrast, the other two tests on the textured geomembrane exhibit anenvelope to the cyclic pullout resistance curve that is greater than the corresponding DC test.110Chapter 6. Test ResultsHowever, the trend is toward similar values of pullout resistance at large displacement, seeFigure 6.46.6.3.2.2.2 Local StrainStrain mobilized in the smooth geomembrane during the load-controlled test at G=8and 12 kPa shows a decreasing strain magnitude with distance from the front wall, see Figures6.48 and 6.49. At the instant of pullout, a uniform strain is mobilized at all gauge locations.Again, a characteristic horizontal strain loop is observed at SG-3, SG-4 and SG-5, anexception occurs at SG-4 in Figure 6.48, which is attributed to an improper electricalconnection.6.3.2.2.3 Displacement of the Embedded EndThe relationship between d and de for the smooth geomembrane at o=8 and 12 kPais shown in Figure 6.50. For d < 5 mm, the displacement of the embedded end is zero.Thereafter a typical inextensible response is observed. The textured geomembrane, at a8kPa and f=0.01 and 0.1 Hz, exhibits a similar response which is independent of frequency, seeFigure 6.51, and in agreement with the general behaviour of the specimen observed in thedisplacement-controlled tests, see Figure 6.11.111Chapter 6. Test ResultsFigure 6.1: Reference code for tests on the geogridsC - Cross-machine directionN - No bearing elementsR - RepeatedS - Arbonte front wallA - AluminumM - MembraneFigure 6.2: Reference code for tests on the geomembranes and aluminum sheetsGeometry Manufacturer Applied normal Test characteristicsG - Grid M - Mirafi stresskPaS - StrataT - TensarMaterial/Geometry Surface Applied normal Test characteristicsR - Rough stress R - RepeatedS - Smooth kPa S - Arborite front wallT - Textured112Chapter 6. Test Results15GTIOoooooooooo100Front Bound3y:-• Arboritesurfaca0 -— 11 111111111 I 111111 Fl I III iiI IlFf0 10 20 30 40 50 60 70 80 90 100Displacement of darrped end, d (rrni)Figure 6.3: Pullout resistance of the Tensar grid with an aluminum or arborite surface on thefront wall15 -________________________________________-MTO8• j Front boundary.• AxborftesurfaceQ PJLarinumsurface1111111111111111111111111111 F 11111111Ff II 11111110 10 20 30 40 50 60 70 80 90 100Displacement of darrçed end, dc (rrrn)Figure 6.4: Pullout resistance of the smooth and textured geomembranes with an aluminum orarborite surface on the front wall113Chapter 6. Test Results30-i--125-20-15-• 10—5—Displacement of darrped end, d (m)Figure 6.5: Influence of displacement rate on mobilized pullout resistance for the Tensar grid.t)II90_::80_Z70_Z60:5O4030:10 —Figure 6.6: Relationship between d and d for the aluminum rough sheet114Q GT2O, 0.25 rrnVninD GT2O, 0.50 rrm’rrinA GT2O,1.O0rrm’nin0 I 1111111 liii, 111111 I’ 1111111110 10 20 30 40 50 60 70 80 90 100100QARO4DR08ARI2R,0/00liii II I II I II I III I II II 11111 II10 20 30 40 50 60 70 80 90 100Displacement of clarrped end, dc (nTn)Chapter 6. Test Results25_______________- QRO420 iE.6RO4RR0 R1212R15 —10Zi_2 -0— I I II I II I I liii IlIllIllIll III I0 10 20 30 40 50 60 70 80 90 100Displacement of damped end, dc (m)Figure 6.7: Pullout resistance of the aluminum rough sheet at a4 to 12 kPa100_____E 9°Ht Gr17I°50 — 040 O0J3020100 r liii 11111 I lii II I I I0 10 20 30 40 50 60 70 80 90 100Displacement of damped end, d0 (ITrfl)Figure 6.8: Relationship between d and d. for the Tensar grid at a.4 to 30 kPa115Chapter 6. Test Results1002 : GS1OGS1770-60-i 40—_1— 0I 000030 ODD000020 00000010 rOD0 I III I I ii I 1111111110 10 20 30 40 50 60 70 80 90 100Dspacenient of darrped end, dc (rmi)Figure 6.9: Relationship between d and d. for the Stratagrid at a4 to 17 kPa100—‘ so—LJGMI02 : i2 GMI760—40—— 00020— DOCu- 00 10 20 30 40 50 60 70 80 90 100Displacement of danped end, d0 (m)Figure 6.10: Relationship between d and d. for the Miragrid at OB=10 and 17 kPa116Chapter 6. Test Results100 —-QMSO4MS0880— MS1270:•flO860— A MT1250-s_- 4*020AA10 :0— ir1fli’i iii 1111J1 H I1H I I 111110 10 20 30 40 50 60 70 80 90 100Displacement of dairped end, dc (rmi)Figure 6.11: Relationship between d and d. for the smooth and textured geomembrane at a=4to 12 kPa40—rio_ji1IilII’•’ z2 GT1730E A GT17R-• GI0ci) — .‘0— .C - .15A10 ØuffEEE1JJJXELJXD 0 j 0occcoDooccoQzcccocococcococcoo0 I I I Iii III II I I II III II I0 10 20 30 40 50 60 70 80 90 100Displacement of darrped end, dc (rmi)Figure 6.12: Pullout resistance of the Tensar grid at a—4 to 30 kPa1170 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d (mm)Figure 6.13: Pullout resistance of the Miragrid at o4 to 17 kPaEmbedded endFigure 6.14: A photograph illustrating the displacement pattern of transverse elements for theMiragridChapter 6. Test Results25 —20z -.15—100 --5—0oD GMIOGMI7Clamped end118Chapter 6. Test Results25—i--1j20—15—. =10—==5—0-Figure 6.15: Pullout resistance of the Miragrid when tested in the cross-machine direction ata=4 to 17 kPa25—20—____1=15—=0— I I liii I I 111111 II0 10 20 30 40 50 60 70 80 90 100Displacement of dalTped end, d0 (rmi)Figure 6.16: Pullout resistance of the Stratagrid at a4 to 17 kPaQGMO4CD GMIOCGMI7C• GM4CN• GMIOCNII I II I I I I I I0 10 20 30 40 50 60 70 80 90 100Displacement of darrped end, dc (m)rofl GS1OGS17119Chapter 6. Test Results1.0 —_____________________________ _________L =0.965 mSG xlL0 I, -0.0910.8 2, 0.073oooo°0 7 3, 0.240DDDDODC 4,0.549_0.6 —5,0.912c)•1‘ 0.4III liii III II I liii 11111111 I II liii III0 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d (mm)Figure 6.17: Mobilization of strain with d for the Tensar grid at =1O kPa1.0 —Lei = 0.970 m—SG XILe1—Q 1, -0.0460.8 —U 2, 0.106L 3, 0.3384, 0.5700.6_ ___7 5, 0.802C1..1-io 0.4c0.2-0.0— III III II I II I II III liii liii liii I II0 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d (mm)Figure 6.18: Mobilization of strain with d for the Stratagrid at a,,10 kPa120Chapter 6. Test Results1.0___________H L0.980mQ 1.0.0430.8—i 00 [1 2,0.2621-1°0 30447K) 4.0.635.-00.6 jo 7 5.0.821cf’0.4.0002— lIIIIIIIIIIIIIlIHlHII0.00 10 20 30 40 50 60 70 80 90 100Displacement of darrped end, d (mm)Figure 6.19: Mobilization of strain with d for the Miragrid at a10 kPa2.25 —__________L = 0.98Dm2.00— Q 1,0.043175 0• 2,0.262— C 3,0.447— 0150 — ° ) 4.0.635• 0— 7 5,0.821— 01.25 °•( 0.750.50liii I I I I I I0.250.000 10 20 30 40 50 60 70 80 90 100DspIacement of darrped end, d (mm)Figure 6.20: Mobilization of strain with d for the Miragrid at o=17 kPa121Chapter 6. Test ResultsConstant/LimitingNon-linear I strainStrain, (%)L2Displacement (mm)Figure 6.21: Characteristic variation of strain with displacement d2.00 —_________________________1.75_________I 5C) sc-i (niWflin), XfL.ejQ 0.25,0.0731.25 • 0.25,0.744E 0.50.0.073.9 1.00 • 0.50,0.7441.00,0.0730.75 SG-5 A 1.00,0.744—I I I I I I I I0 10 20 30 40 50 60 70 80 90 100Displacement of the damped end, d (m)Figure 6.22: Variation of strain with rate of pullout for the Tensar grid at a=2O kPa122Chapter 6. Test Results5—________QMSO4-• MSG4R4— LJMS08L0— III III III IIj III I I 11111 Iiio io 20 30 40 50 60 70 80 90 100Displacement of danped end, d (m)Figure 6.23: Pullout resistance of the smooth geomembrane at a4 to 12 kPa:10C C C Cif50—II ll II I I I II I II I1II I0 10 20 30 40 50 60 70 80 90 100Displacement of darrped end, d (nvi)Figure 6.24: Pullout resistance of the textured geomembrane at a.—4 to 12 kPa123Chapter 6. Test Results1.0SGmo 1.0A70.8 20255!) 417 0.776e...- 0.6—j0.4—III I II liii I I II liii I0 10 20 30 40 50 60 70 80 90 100Displacement of darrped end, d0 (m)Figure 6.25: Mobilization of strain with dfor the smooth geomembrane at a.4 kPa1.0 —______________________________________SG MSO8L=95mQ 1G70.8 D ZQZ5G 40O3V 5.0.7760.6—0.4—0.0—I I I I I I I I lij liii I IIIj 111111110 10 20 30 40 50 60 70 80 90 100Displacement of darrped end, d (rmi)Figure 6.26: Mobilization of strain with d for the smooth geomembrane at O8 kPa124Chapter 6. Test Results1.0 - -MSI2L_=Omo i7i0.8 Q ZO5o 41W3— V 776— 0.6—0.0 Ii I I I I I I I I I 11111 I I I I I I I I I I I I0 10 20 30 40 50 60 70 80 90 100DspIacement of danced end, d (nlT)Figure 6.27: Mobilization of strain with d for the smooth geomembrane at a=12 kPa15 —___________ARO8“‘. DCLC1;1105—0— III II I liii III liii II II II0 10 20 30 40 50 60 70 80 90 100Displacement of darred end, d (nir)Figure 6.28: Pullout resistance of the rough aluminum sheet at a—8 kPa and f=O.O1 Hz125Chapter 6. Test Results15 — —Figure 6.29:III/II)F‘__________‘I(Iii 1* IIIi i ii j*iiIII, Ii Ii iiIiitII IIiiit II ii11 I0 1 2 3 4 5 6 7 8 9Displacement of dairped end, d6 (m)Detailed response at small displacement, from Figure 6.28100 10 20 30 40 50 60 70 80 90Displacement of darrped end, d (rmi)100Figure 6.30: Relationship between d and d, for the rough aluminum sheet in the LC tests ata1=8 kPa and f=0.01 Hz.11.010 —5—0ARO8DCLCI I III I I 111111111 III 1111111 I II II1009080706050403020100- ARO8LJ/126II— — ‘—— , I’,-, JiJL l7kPa-i iv*”r “-‘IIIII I II, I I IIIIjt -“ -.II__________________—, I II‘Ill’,I I Ii’fiI,I4Chapfry 6. Test Results2015lOkPa10GTf=0.01 I-DC5- LC4kPa0II I II I I III I I 1111111111 I I I I0 10 20 30 40 50 60 70 80 90 100Displacement of damped end, d (mm)Figure 6.31: Pullout resistance of the Tensar grid in the DC and LC tests at a4 to 17 kPa andf=O.O1 Hz25—_GMf=O.O1 Hz20,%T-7kPa-. - - -1’r” ‘ — —154 //?t’*VI!wq I1Oka---°tIf1$-ØIIjI0_I III III IlilIlill j II I0 10 20 30 40 50 60 70 80 90 100Displacement of damped end, d (mm)Figure 6.32: Pullout resistance of the Miragrid in the DC and LC tests at o,4 to 17 kPa andf0.O1 Hz127Chapter 6. Test Results15_____________GSf0.O1 Hz- DC-10 — - LCCColOkPa5I?4kPa0— 1111111111 I I 1111111 II 1111 I I III0 10 20 30 40 50 60 70 80 90 100Displacement of clarrped end, d (rrwn)FIgure 6.33: Pullout resistance of the Stratagrid in the DC and LC tests at a1O kPa andfrO.O1 Hz25—_____________20,._x”1510GSI7f=0.01 FDCLZ.LC0—0 10 20 30 40 50Displacement of damped end, d (rmi)Figure 6.34: Pullout resistance of the Stratagrid in the DC and LC tests at a=17 kPa andf=O.O1 Hz128Chapter 6. Test Results20--GTf=O. 1 Hz-__DC15 —LC—r11,,If.9 i II/Afu10Displacement of damped end, d (rmi)Figure 6.35: Pullout resistance of the Tensar grid in the DC and LC tests at a.10 kPa andf0.1 Hz1.50—______________= GT1O- f0.01 Hz1.25 L-0.965mxJL1.00—SG-1,-O.0830.75 /4Tff—;:0.50 SG-4, 0.576S5,744.I ii I I I II I II II I0 10 20 30 40 50Displacerrent of clamped end, d (rrrn)Figure 6.36: Mobilization of strain for the Tensar grid in the LC tests at a1O kPa and fO.OlHz129Chapter 6. Test Results1.50______- GM1Of0.01 Hz1.25 - Lcj=0.980m- 1.00—XfLei0.75 SG-10.043SG-2, 0.2620 5 10 15 20 25 30 35 40 45 50Displacement of clamped end, d (mm)Figure 6.37: Mobilization of strain for the Miragrid in the LC test at a=1O kPa and f0.O1 Hz1.50—_GSIO-Z L=0.97Orr- 1.00—0.75 x/LSG-1,-0.0460.50_0.338p. / SG-4, 0.5700102030401150Displacement of danped end, d0 (mm)Figure 6.38: Mobilization of strain for the Stratagrid in the LC tests at a,=1O kPa andf=O.O1 Hz130Chapter 6. Test Results1.50—_____3r17- f0.OlHz1.25 Lei= 0.965 m SGI, -0.083100= S3, 0.240/ J SG-4, 0.576w0.75o.so SG-5, 0.7440.250.00_ IIIIIIIIIIIIIIII 1111Displacement of darrped end, d (m)Figure 6.39: Mobilization of strain for the Tensar grid in the LC tests at a17 kPa and f=O.O1Hz1.50—ISG-1 o.n4v GMI7A7 I f0.OlHz1.25 0.980m- 1.00 4fP SG-2, 0.262—Al’ -SG-3, 0.447::%IIIIIIIUIIIIDisplacement of damped end, d (rmi)Figure 6.40: Mobilization of strain for the Miragrid in the LC tests at a17 kPa and f0.01 Hz131Chapter 6. Test Results1.50—_________________GS17— f0.01 Hz1.25 L-0.98Om- 1.000.75 — /1’-/—0.50 SG-4, 0.570Displacement of clamped end, d (rrrn)Figure 6.41: Mobilization of strain for the Stratagrid in the LC tests at a17 kPa and f=0.0lHz100—I°—80--o 70—60-30—011111111111 I I I I I I j I I I I I I I I I I0 10 20 30 40 50 60 70 80 90 100Displacement of damped end, d (rrrn)Figure 6.42: Relationship between d and d. for the Tensar grid in the LC tests at a 4, 10and 17 kPaX1LeSi046SG-3, 0.338GTf=0.01 Hzp O4kPaD lOkPaA l7kPa132Chapter 6. Test Results100GMf0.OlHz) 80—I O4kPa-D I /_C 70—El lOkPa /60-H40-30—- 0 I I I I I I I I I I 1111111 I I I I I I I0 10 20 30 40 50 60 70 80 90 100Displacement of damped end, d (n-ni)Figure 6.43: Relationship between d6 andd1for the Miragrid in the LC tests at a 4 kPa and10 kPa100—GS90—8o: p O4kPa-g 70— El lOkPa. l7kPaI__ __________I liii III [I III III 1111 III 111111 I0 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d (nTn)Figure 6.44: Relationship between d and d. for the Stratagrid in the LC tests at a =4, 10 andl7kPa133Chapter 6. Test Results5—4 —jl,d-akParn 3 —-..---:.‘.‘ 8kPa-‘— 2— 4, *-o- MSf=O.O1 Hz1—DCLC0— ii ii I I ii ii I I jill ii I0 1 2 3 4 5 6 7 8 9 10Displacement of damped end, d (mm)Figure 6.45: Pullout resistance of the smooth geomembrane in the DC and LC tests25 —_________________________________________(4 — ——- - -- l2kPa20IL10 77’-—--—8kPa-Ir0— 1111111 I I liii lIIlj III0 10 20 30 40 50 60 70 80 90 100Displacement of darrped end, d (mm)Figure 6.46: Pullout resistance of the textured geomembrane in the DC and LC test at a=8 kPaand f=O.O1 liz134Chapter 6. Test Results25-rrf=0.lHzDCLC15——-- 8kPa—.-I1. iS.. I . — -—10——D— I 1Ip 1 iia..— ,I it5—•i i0 iii ii I ii ii liii II liiio 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d, (mm)Figure 6.47: Pullout resistance of the textured geomembrane in the DC and LC tests ata=8 kPa and f=O.1 Hz0.5_____________________________________________- MS0811 f0.01 Hz0.4L0.965m0.3SG-1,0.086I0 1 2 3 4 5 6 7 8 9 10Displacement of darrped end, d (mm)Figure 6.48: Mobilization of strain for the smooth geomembrane in the LC test at a8 kPa135Chapter 6. Test Results0.5 —_______________________- MS12 1- f0.OlRzL0.965m0.4—SG-1, 0.0860.3 — SG-2, 0.2510.2-0.1 / S5, 0.7640.0_JI I I I I I I I I I0 5 10 15 25Displacement of damped end, d (rrrn)Figure 6.49: Mobilization of strain d for the smooth geomembrane in the LC test at a12 kPa100—______90 f=0.01 Hzp MSO880—70ZIIIIIIIIjIIIII I I I 11111111 I I I I I I0 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d (mm)Figure 6.50: Relationship between d and d. for the smooth geomembrane in the LC tests ata=8 and 12 kPa136Chapter 6. Test Results100—IH0 -c 70—60-50—ci) -15 40—0 MTO8L,0.O1HzD MT12L, 0.01 HzL. MTO8L, 0.10 HzI’’’ 111111 1111111 111111111 II II liii 1111o io 20 30 40 50 60 70 80 90Displacement of clarrped end, d0 (rrrn)100Figure 6.51: ReJationship between d and d for the textured geomembrane in the LC tests ata=8 and 12 kPa0DpDD137CHAPTER 7ANALYSIS OF TEST RESULTS7.1 IntroductionIn this chapter the test results are analyzed and an interpretation made to obtain soilgeosynthetic interaction factors for engineering design practice. The influence of the frontboundary on the measured pullout resistance is discussed, and its implication for theinterpretation of the results is outlined. A generalized method is proposed to interpret pullouttest data that considers the extensibility of the test specimen. Several methods of interpretingmonotonic pullout tests to obtain the interaction factors are reviewed, and are shown to be aspecial case of the proposed generalized method. Further, the rationale for choosing onemethod over the other is discussed with reference to test results for both grids andmembranes.The interaction factor from displacement-controlled tests is compared with resultspublished by other researchers for both laboratory pullout tests and from instrumented fieldstructures. Finally, the interaction factor in cyclic pullout loading is assessed with respect tothe loading regime and characteristics of the specimen.7.2 Displacement-Controlled Pullout TestsThe displacement-controlled pullout test results are interpreted to obtain an interactionfactor for use in the design of reinforced soil structures and anchorage details for wastecontainment facilities. The interaction factor for design F*cc or fbtanp, see section 2.6.2, isdefined as the ratio between the mobilized shear stress at the interface and the effectivenormal stress acting on that interface (‘na), where F*a = fbtanØ = in/a. In determining this138Chapter 7. Analysis of Test Resultsinteraction factor from pullout testing, it is necessary to know the distribution of shear stressalong the embedded length of the test specimen at any displacement d.The interpretation of a pullout test results is simple when the shear stress does notvary along the embedded length of the specimen. The distribution of shear stress isestablished from displacements at the clamped and embedded ends of the specimen, togetherwith measurements of strain along the specimen. Since pullout resistance is influenced by thecharacteristics of the front wall of the apparatus, the following section presents data on theinfluence of the front wall on the test results.7.2.1 Influence of the Front BoundaryTotal pressure transducers (TPT) mounted on the front wall of the pullout apparatus,see Figure 3.9, record the distribution of lateral stress on the front wall. Measurements atlocations TPT- 1 and TPT-6 are used to determine a lateral earth pressure coefficient for thesoil sample after application of the surcharge pressure to the sand sample but before clampingthe specimen and application of pullout load. The relationship between lateral and normalstress at transducer locations TPT-1 and TPT-6 is shown for some tests in Figure 7.1. A bestfit line for the data through the origin is also shown, for which the deduced lateral earthpressure coefficient is 0.415. Scatter in the data is attributed to the sensitivity of thetransducers to the relatively low values of lateral stress at this stage in a test. Using Jaky’ sexpression for K0, the angle of friction for the sand for the relatively dense, undisturbed sandis computed to be 35.8°. For a soil deposit that is formed by layering, the lateral stresscoefficient is found to vary between 0.4 to 0.5 (Lambe, 1979). Thus, the observed lateral139Chapter 7. Analysis of Test Resultsearth pressure coefficient is in agreement with the expected values implying that the front wallbehaves as a rigid boundary.Mobilization of pullout resistance during testing induces additional lateral stresses onthe front wall of the apparatus. The incremental lateral stress (Aah) at any displacement dueto pullout is the difference between the the current stress and that after surcharge loading.Values are reported with respect to a non-dimensional depth ratio, which is the distance of theTPT location (y) from the centre line of the slot normalized by the half height of the soilspecimen (h), where h=30 cm. For locations above the slot the ratio y/h is positive, see Figure3.12. All transducer locations are symmetrical about the slot except for TPT-6 which isslightly closer than TPT- 1.The lateral pressure at maximum or peak pullout resistance is selected for use ininterpretation of results: the peak pullout resistance for those tests with strain softeningbehaviour, and the maximum resistance is for tests with a uniform resistance at largedisplacement. Note these values of lateral stress are not necessarily the maximum for the test:see for example Figure 7.2, where the maximum lateral stress at location TPT-3 is higher (70kPa) than that measured at the mobilization of maximum pullout resistance (55 kPa). It isapparent that the magnitude of lateral stress is higher at locations TPT-3 and TPT-4, whichare close to the slot on the front boundary. The values of lateral stress, and deducedcoefficient of lateral earth pressure, confirm our understanding that the vertical stress actingon the test specimen can increase in the vicinity of the front slot. At locations TPT-1 andTPT-6 which are fhrthest away from the slot, the magnitude of lateral stress is significantlylower.140Chapter 7. Analysis of Test ResultsResults for tests performed on the MS and the GT specimens at similar surchargepressures are shown in Figure 7.3. A general trend is observed where the incremental lateralstress decreases at locations away from the slot: the distribution is asymetric, with higherstresses above the slot than below it. This type of response is attributed to the differentboundary conditions at the top and bottom boundary of the apparatus. Similar observationshave been reported by Palmeira (1987), and Kharchafi and Dysli (1993). Further, themagnitude of lateral stress is significantly greater for the Tensar grid specimen than thesmooth membrane.The incremental lateral stress of Figure 7.3 is normalized with respect to the averageshear stress mobilized on the test specimen and is illustrated in Figure 7.4. From thenormalized behaviour the relationship appears to be unique with the stress ratio beingindependent of the type of specimen. Using this approach, the data for the other specimensare plotted at various normal stresses, see Figures 7.5 to 7.10.The curves show the stress ratio tends to an unique relationship. Thus, for the frontwall to exert a minimal influence on the measured pullout resistance the mobilized shear stressand hence normal stress used in tests should be relatively low.7.2.2 Mobilization of Pullout ResistanceA unified description of the mobilization process in the displacement-controlled (DC)tests is illustrated first with reference to the GT 10 test results. The relationship between thedisplacement of clamped (do) and embedded (de) ends is shown in Figure 7.11. It isdistinguished by three zones. In zone I (d = 0 to 5 mm) there is no significant displacementof the embedded end, indicating the imposed displacement at the clamped end is not141Chapter 7. Analysis of Test Resultstransferred along the entire length of the specimen, resulting in a non-uniform sheardisplacement. The response in zone II (d = 5 to 26 mm) shows the embedded endexperiences some movement that increases with the displacement d. The behaviour in zonesI and II is typical of an extensible element. In contrast, the relationship in zone III is linearand inclined at 450, indicating dedc and therefore increments of displacement are equal alongthe embedded length of the specimen.To complement the above interpretation, the strain measurements at variousdisplacements d are used to develop profiles of strain. The profiles are shown over theembedded length for the measured strains only: it is recognized that the strain at theembedded end is zero for all test specimens. Results for the Tensar grid at a=1O kPa areshown in Figure 7.12. At d=1 mm, the strain profile indicates zero strain at a normalizeddistance of 0.60 from the front wall of the apparatus. As the test continues, the point of thezero strain moves progressively toward the embedded end, and the slope of the profile isobserved to increase. Beyond d0 = 30 mm the strain profile appears to be unique and linear.This displacement corresponds to the onset of zone III in Figure 7.11, where d = de and thetest specimen behaves as an inextensible inclusion. Therefore, the condition of the testspecimen during pullout at constant uniform strain is associated with a strain profile that islinear.This concept of progressive strain mobilization is further illustrated by analysis ofresults for the Tensar grid test at a=20 and 30 kPa. Notwithstanding the absence of a zoneIII response in the GT3O test, see Figure 7.13, the strain profiles (Figure 7.14) show theposition of zero strain again moving toward the embedded end although less conspicuously142Chapter 7. Analysis of Test Resultsthan seen in the GT1O test. The strain profile is non-linear, with the slope of the profile beinggreatest near the front wall and decreasing rapidly toward the embedded end. The slope ofthe profile increases rapidly with displacement d. A similar response is observed in the GT2Otest, see Figure 7.15.Results for the Stratagrid and Miragrid (Figures 7.16 to 7.20) confirm the generalnature of the behaviour: inspection of the strain profiles for GT 10 and GS 10, and for 0T20,GS 17 and GM1 7, also reveal a characteristic nature in the magnitudes of strain and imply aresponse that is not overly dominated by differences in type or structure of the three grids.The relationship between d and de for the MSO8 test depicts a different behaviour,see Figure 7.21. The zones I and II are indistinct, and the relationship beyond d = 3 mm istypical of zone ifi. This fact is confirmed by considering the strain profiles of the test, seeFigure 7.22. The position of zero strain on the specimen moves towards the embedded endfor d < 2 mm. As the test continues further, the strain profile is defined by a unique lineforming an upper bound to the measured strain. The observed scatter of data points for d> 5mm is attributed to fluctuations in measurements at these small strain magnitudes.In summary all tests illustrate a progressive mobilization of strain and describe arelationship between displacement of the clamped end, and relative displacement along thetest specimen, that is non-linear. Interaction between the soil and test specimen is expressedin a non-dimensional form by normalizing the mobilized shear stress with respect to theapplied normal stress. The following sections present and comment on various methodologiesfor determining interaction factors by experimental as well as theoretical methods.143Chapter 7. Analysis of Test Results7.2.3 Experimental Interaction FactorsTo detennine the interaction factor experimentally, the most important parameter tobe assessed is the mobilized shear stress at the soil-geosynthetic interface. Analysis of theresults in the previous section has clearly demonstrated the variable tensile strain along theembedded length of the specimen. The response to pullout is one of progressive strain, with abehaviour that is either extensible or inextensible being dependent on the applied normalstress. This behaviour implies mobilization of a non-uniform shear stress along the embeddedlength of the specimen. Hence the shear stress distribution depends on the type of thespecimen, its stiffliess, and the magnitude of applied normal stress.The mobilized shear stress and its variation along the length of the test specimen maybe evaluated from the measurements of the pullout load at the clamped end if strainmeasurements are made along the length of the specimen. While interpreting the pullout testresults, it is important that the part of the specimen contributing to the resistance be clearlydelineated. Several researchers have addressed this aspect in different ways: the methods inuse may be broadly classified into two categories, namely the average resistance and themobilizing process methods,7.2.3.1 Average Resistance MethodIn this method the mobilized shear stress is assumed to be an average stress actingover a mobilized area of the test specimen. Depending on the definition of resisting area,several variations are used in practice: total area, effective area, and maximum slope methods.A schematic illustration in Figure 7.23 describes the definition of the resisting area. They areexplained in following sections.144Chapter 7. Analysis of Test Results7.2.3.1.1 Total AreaIn this method, the average shear stress is calculated using the total initial embeddedarea of the specimen. The “area method” of Bonckewicz et al. (1986) and the “total areamethod” of Ochiai Ct al. (1992) are identical. An expression for average shear stress is givenby:Pt = (7.1)av 2LeiVVrwhere:P is the pullout resistance of the specimen,tav is the average shear stress on the soil-specimen interface,Lei is the initial embedded length of the specimen, andWr is the width of the specimenThus, a measurement of pullout load is adequate to compute the average shear stress. Thismethod would give a reasonable value when the specimen is pulled out with no significantelongation, as in the case of zone III (Figure 7.21). However, marked extension will lead tothe resisting area being less than the initial, total embedded area, and an underestimation ofthe interaction factor. This method uses the total embedded length of the test specimen andhence is unsuitable for tests with relatively extensible specimens.145Chapter 7. Analysis of Test ResultsAn improvement to the total area method arises if displacement of the embedded endis measured, allowing the actual embedded length (Lea) to be calculated throughout the test,where:Lea=(Lejde) (7.2)Replace Lej by Lea in equation 7.1 to compute a revised shear stress.7.2.3.1,2 Effective AreaTo consider only that part of the specimen resisting the pullout load, Bonczkiewicz etal., (1986) introduced the corrected area method in which mobilized length was determined bymeasurement of displacement along the specimen. Data are plotted in terms of measuredpullout force and mobilized length. The mobilized length of the specimen is determined byassuming that movement at a gauge location indicates initiation of pullout at that point.A more recent variation is the effective area of Ochiai et al., (1992) used when thedistribution of pullout force along the embedded length of the specimen is known. Themobilized average shear stress in this method is given byT -T= max x (73)av 2WLXwhere:Tmax is the pullout force measured at the clamped end of the specimen,T is the pullout force measured or estimated at a section x on the specimenwhere the slope of the tensile force distribution changes direction (decreases), and146Chapter 7. Analysis of Test ResultsL is the distance from the front wall to the section x.The distribution of pullout force along the embedded length is obtained frommeasurements of displacement or strain. The constrained modulus of a specimen is requiredto facilitate the transformation. The point where the slope changes sign on the tensile forcedistribution curve is noted to obtain the effective distance (Lu) from the front wall of the box(Figure 7.23). This method ignores the resistance mobilized along the partial length of thespecimen near the embedded end.7.2.3.1.3 Maximum SlopeIn this method the maximum slope of the pullout force profile is determined and thisgives a maximum shear stress at the soil-specimen interface. This method will always give anupper bound to the interaction factor, Ochiai et al., (1992). The solution does not representthe actual interaction in any aspect, but will give an estimate of the possible maximum shearstress. When the strain or tensile force distribution is linear between the clamped end and theembedded end, the maximum slope method will predict an interaction factor that is identicalto that calculated from the effective area method and the total area method.7.2.3.1.4 Mobilizing Process MethodOchiai et al., (1992) proposed a method to interpret pullout tests on geogrids only byassuming that the pullout resistance is transferred at the grid junctions in a concentratedmanner. The shear stress acting on the specimen between consecutive junctions is obtained bydividing the difference in magnitude of pullout force per unit width by the spacing.147Chapter 7. Analysis of Test ResultsSimilarly, a method proposed by Juran et al., (1991) recognizes that the nodaldisplacement comprises two components. The first component is due to tensile strain of theelement and the second due to relative movement or shear displacement of the node itself.The difference between consecutive nodal displacements is converted to shear strain for eachelement. Again using a confined modulus for the test specimen, the tensile force is computedat all nodes. From a consideration of static equilibrium, an equation for the distribution ofshear stress along the specimen is then determined, and hence the interaction factor obtained.7.2.3.2 Generalized MethodFrom the discussion in the previous section, it is evident that a method to evaluate theshear stress, and hence the interaction factor, at any point on the interface should account forthe following:• mobilized embedded length;• the variation of pullout resistance along the mobilized embedded length; and• decreasing embedment length, Le, of the specimen with increasing displacement,d.Based on experimental observations of load and strain with pullout displacement, ageneralized method is proposed below which is applicable to various test specimens, andunifies the effective area and mobilizing process methods. A curve fitting technique is appliedto define the tensile force distribution along the specimen length. The generalized method isdescribed in following steps:STEP 1: Discretizing the test specimen148Chapter 7. Analysis of Test ResultsThe test specimen is divided into a series of elements such that the strain gaugelocation is at the centre of each element. The boundary between elements is defined as anode. A schematic illustration of nodes and elements for grids and membranes is shown inFigure 7.24.STEP 2: Relating measured local strain to element strainThe strain gauges record rib strain on a geogrid and local strain on the geomembranespecimen. The measured local strain is related to the global strain of the element byeg =ke11 (7.4)where:is global strain of the element i,k is a constant, andeis the local strain in the element i.Instron tensile tests (in-isolation) were performed in which the global strain wasmeasured by mounting an LVDT between two consecutive nodes, and the local strain wasmeasured with the strain gauge: the constant for the GT test specimen (Tensar UX- 1500) wasfound to be k = 1.82. Similar in-isolation tests on a stiffer Tensar UX- 1600 specimens havebeen reported by Bathurst (1991) where the value of the constant was determined to be 1.25.STEP 3: Relating measured local strain to the tensile forceThe tensile force, T, in the specimen is related to the measured rib or local strain C atthe first embedded strain gauge by a polynomial expression of the formT = a + b1e1 +c1 + d1e +e1 (7.5)149Chapter 7. Analysis of Test Resultswhere:a1, b1, c1 , d1 e1 are polynomial coefficients.STEP 4: Calculation of the actual embedment length, LeaThe position of the strain gauge changes with respect to the front wall of the box asthe test progresses. At any instant, the position is calculated from the average displacement ofeach element using the measured local strains as follows:The displacement of ith node is given by:d1 = d1_ — S8g1 (7.6)where:d and d11 are the displacements of the ith node and (i-i )th node respectively,S is the spacing between ith and (i-1)th node or length of the element, andis the global strain of ith element given by equation 7.4.The average displacement of the element i, dai , bounded by nodes i and i-i is given byequation 7.7(d.+d. )dai 2The distance between the new position of the ith gauge and the front wall, x, is givenby equation 7.8x = x01— dai (7.8)where:xc, is the initial distance of the ith gauge from the front wall of the apparatus.150Chapter 7. Analysis of Test ResultsThe actual embedded length of the test specimen, L, is determined byL =Lei’dai (7.9)where d1 is the summation of the average displacement of all elements.STEP 5: Fitting a polynomialEach strain gauge distance (xi) is normalized with respect to the initial embedmentlength of the test specimen (Lej). The deduced tensile force at each strain gauge location fromstep 3 is plotted with respect to the normalized distance of strain gauge locations from thefront wall of the apparatus. A polynomial is fitted through the deduced data points. Thedistribution of tensile force along the specimen with distance from the front wall of theapparatus is expressed as(7.10)where:a2, b2, C2, d .. . . are polynomial coefficients andm is the normalized distance of the strain gauge from the front wall of the apparatus.STEP 6: Evaluation of shear stress at any point on the interfaceThe shear stress at any point on the interface is given by the slope of the pulloutresistance profile. The pullout resistance profile is divided into n number of smaller segmentsand the shear stress for each segment is given byT-T.=Ch1(7.11)151Chapter 7. Analysis of Test Resultswhere:T• and T+, are the tensile forces at the ith and the (1+1) interval respectively,C is the perimeter of the test specimen, C=2 for sheets and grids,h, is the discretized interval of the polynomial which is Ixi+rxil.The shear stress distribution is obtained by substituting appropriate values in the aboveequations. Simpson’s rule is used to find the area under the shear stress distribution curve,which is divided by the actual embedded length to determine the average shear stress.STEP 7: Determination of interaction factorThe shear stress in each element from step 6 is normalized with respect to the appliedstress (an), to establish the variation of interaction factor along the length of the specimen.An average interaction factor is obtained by normalising the average shear stress with respectto the applied normal stress.The above steps are incorporated in a data reduction program that is illustrated inFigure 7.25.7.2.3.3 Application of the Generalized MethodThe generalized method for interpreting pullout tests is illustrated by considering testson all three geogrids and the smooth geomembrane. The method is not applied to thetextured membrane because there were no strain measurements taken on these specimens.Application of the method is described with respect to (i) displacement of the embedded end,(ii) pullout resistance, (iii) shear stress and (iv) interaction factors.152Chapter 7. Analysis of Test Results7.2.3.3.1 Displacement of the Embedded EndSince each specimen was instrumented with only five strain gauges, values of strain inelements without gauges were assigned by interpolation of the laboratory measurements. Thiswas necessary to calculate the nodal displacement of the last node (node 7 for a GT grid and0.965 m embedment length) and compare it with the measured displacement of the embeddedend. Measured and back-calculated displacements of the embedded end of the GT specimenat a=l0 kPa are shown in Figure 7.26. The calculated displacement of the embedded end,based on rib strain, compares very well with the measured displacement using an LVDTattached to a tell-tale on the embedded end.From these observations, it may be concluded that the generalized approach is capableof backcalculating the displacement of the embedded end when good strain measurements areavailable at all locations, and may be used in the absence of measured displacements of theembedded end.7.2.3.3.2 Tensile ForceThe variation of tensile force per unit width measured at the clamped end withmeasured rib strain at the first location inside the pullout box, for the Tensar grid, in DC testsat various normal stresses is shown in Figure 7.27. Included in the plot are data from inisolation Instron tests (Ii, 12 and 13) which exhibit a linear relationship in the given range ofstrain. Instron tests were performed in accordance with ASTM D4595, except for theimposed strain rate. The data from gauge location SG-1 (XILe0.073) in the pullout tests atdisplacement rates of 0.25, 0.50 and 1.0 mni/min all lie in a narrow band indicating that therelationship is essentially rate independent for the range of testing. The agreement confirms153Chapter 7. Analysis of Test Resultsthat confinement has little influence on the general force-strain response of the Tensar grid atthese relatively low magnitudes of normal stress. In accordance with step 3 of the generalizedmethod, polynomial coefficients were obtained for each test by relating the strain measured atthe first embedded gauge to the measured tensile force. These coefficients were used todescribe the variation of tensile force along the length of the specimen.Similarly, the relationship between tensile force per unit width at the clamped end andstrain measured at gauge location SG-2 (XILei:0. 106) for the Stratagrici at a=10 and 17 kPais shown in Figure 7.28. A stiffer response is observed in the displacement-controlled teststhan the load-controlled tests at similar normal stress. The strain softening behaviour at largepullout displacements is clearly evident. The tensile force versus strain relationship for theMiragrid also exhibits a strain softening behaviour at large pullout displacements, see Figure7.29. Measured local strain at gauge location SG-1 (XILeO.043) on the smoothgeomembrane is plotted with respect to measured tensile force in tests at a=4, 8 and 12 kPa,see Figure 7.30. An excellent relationship between force and strain is observed. Again,polynomial coefficients were obtained for each test by relating the measured force at theclamped end with the strain at first gauge location, and the resulting equation used todetermine the variation of tensile force along the length of the specimen.The deduced profile of tensile force/unit width for the Tensar grid, at various d fora=10 kPa, is presented in Figure 7.31. Initially, at d=1 and 2 mm, the profile is non-linearand the mobilized normalized length of the specimen is 0.65 and 0.70 respectively. As thedisplacement increases further, the profiles of pullout resistance tend to become linear andsimultaneously the slope of the profile increases. The entire length of the specimen is154Chapter 7. Analysis of Test Resultsobserved to have mobilized a resistance to pullout beyond d 5 mm. The pullout resistanceprofile for the GT2O test (Figure 7.32) exhibits a response which is similar to the GT 10 test.Again, at d >5 mm resistance is mobilized over the entire length of the specimen. In contrast,the GT3O test specimen exhibits a profile where mobilization of the entire length occurs atd>15 mm (Figure 7.33).7.2.3.3.3 Shear StressThe shear stress distribution obtained from the profile of tensile force in the GT 10 testspecimen is shown in Figure 7.34. The shape of the shear stress distribution is found to bevery sensitive to the shape of the tensile force profile. Therefore an accurate measurement ofstrain along the specimen is necessary for determining a reasonable distribution of shear stress.A maximum shear stress is mobilized near the front wall of the apparatus and the magnitudeof stress decreases with distance from the front wall. As pullout displacement increases, theslope of the shear stress profile tends toward a uniform value at large pullout displacement.This general trend is clearly illustrated by the shear stress profile for the GT2O test, see Figure7.35. The shear stress varies at all values of pullout displacement except after 50 mmdisplacement when the shear stress distribution becomes uniform over the entire embeddedlength.Contrary to the shear stress distribution shown in Figure 7.35, a different shape ofdistribution is obtained for the GT3O test, see Figure 7.36. The profile of tensile force in thistest was found to be best defined by a polynomial of degree 3. The shape of thecorresponding shear stress distribution is therefore non-linear, again with a maximum shearstress near the front wall, and rapidly decreasing values away from it. For d < 5 mm, the155Chapter 7. Analysis of Test Resultsshear stress is observed to approach a zero or an insignificant value at a normalized distanceof 0.5 to 0.7. This clearly demonstrates that the shear stress distribution is non-linear, andthat only part of the specimen mobilized resistance to pullout. Although the point of zeroshear stress shifts toward the embedded end as the displacement d increases, the shape of thedistribution appears to remain non-linear.The distribution of shear stress along the embedded length of the Stratagrid at a10kPa is shown in Figure 7.37. The magnitude of shear stress increases with pulloutdisplacement and attains a peak at d=10 mm. The post peak response shows that the shearstress decreases with increasing pullout displacement. The influence of an inextensible and anextensible behaviour on the distribution of shear stress is clearly illustrated by shear stressprofiles for the Miragrid at a= 17 kPa, see Figure 7.38. At d =2 and 5 mm, the shear stressis mobilized over a normalized length of 0.55 and 0.85 respectively. Beyond 10 mm ofdisplacement, the shear stress is mobilized over the total embedded length of the specimenalthough it is non-linear. A maximum shear stress is observed near the front wall at smalldisplacements (d < 10 mm) but decreases with further displacement. The shear stress profileat d =30 and 50 mm is uniform and is indicative of an inextensible behaviour in the testspecimen.The shear stress distribution for the smooth geomembrane at a=8 kPa is shown inFigure 7.39. A non-uniform profile of shear stress is observed at pullout displacements lessthan 2 mm, which corresponds with zones I and II illustrated in Figure 7.21. The inextensiblebehaviour beyond a pullout displacement of 3 mm manifests itself as a uniform shear stressprofile, and is essentially constant as pullout failure occurs.156Chapter 7. Analysis of Test ResultsFrom this discussion of shear stress, it follows that the proffle of mobilized shear stressdepends on whether the specimen behaves as an extensible or an inextensible inclusion. Shearstress has been deduced from values of force per unit width calculated from the measuredstrains. A consistent trend emerges where the variation of strain along the specimen is nonlinear at small displacements, tending toward linear at large displacements. Therefore theshear stress distribution is non-linear at small displacements, being a maximum near the frontwall and decreasing to a minimum value toward the embedded end. At large displacements auniform shear stress is mobilized over the length of the specimen. If the specimen behaves asan extensible inclusion, an appropriate data analysis procedure is necessary to establish theshear stress distribution: the proposed generalized method has been shown to account forsuch extensibility.7.2.3.3.4 Interaction FactorsThe interaction factor in pullout, at any displacement d, is obtained by normalising thedistribution of shear stress with respect to the applied normal stress,.Applied normalstress is maintained constant throughout the experiment, and hence the interaction factorvaries along the embedded length of the test specimen in a manner similar to that of the shearstress. An average shear stress may be evaluated by considering the area under the shearstress profile. The area under the shear stress profile is determined using Simpson’s 1/3rdrule, and divided by the mobilized length to obtain an average shear stress. The average shearstress so computed yields an average interaction factor at a particular pullout displacementand accounts for non-linear pullout resistance.157Chapter 7. Analysis of Test ResultsThe versatility of the generalized method is illustrated in Figure 7.40 where interactionfactors determined using the corrected total area method (Bonczkiewicz, 1986) and proposedgeneralized methods are compared. The corrected area method gives a lower value ofinteraction factor than the generalized method. This is attributed to the extensibility of thetest specimen.The variation of interaction factor with pullout displacement for the Tensar grid ata=4 to 30 kPa, from the generalized method is shown in Figure 7.41. The computed factorsat small displacement are very similar in magnitude for all tests at d<5 mm. This responsegives an important insight to the mobilization of the pullout resistance: irrespective of theapplied normal stress on an extensible inclusion, it is possible to obtain an unique interactionfactor if an appropriate method is used for analysis of the test data.Results for the Stratagrid and Miragrid at a=10 and 17 kPa are shown in Figure 7.42.The general trend is similar to the Tensar grid where the values obtained by the totalcorrected area method are of lower magnitude. Although there is some scatter in the valuesobtained from the generalized method, again the interaction factors obtained are higher thanthe total corrected area method.The generalized method is applied to the smooth geomembrane tests at a=8 and 12kPa, and the variation of interaction factors is shown in Figure 7.43. For the MSO8 test, theinteraction factor by both methods is similar because of a behaviour in pullout that wasessentially inextensible, see Figure 7.21. However at 12 kPa the test specimen has a welldefined displacement response which exhibits some extensibility, and an interaction factor158Chapter 7. Analysis of Test Resultsfrom the generalized method is in good agreement with that at a=8 kPa. Again theinteraction factor given by the generalized method is seen to be independent of applied normalstress.7.2.3.3.4.1 Peak and Limiting Interaction FactorsThe relationship between average shear stress and normal stress at maximum andlimiting pullout resistance helps to establish an interaction factor for design purposes. Resultsfor the geogrids are reported together with data from tests on the rough aluminum sheet.Since the rough surface of the aluminum is obtained by glueing sand to the surface of thesheet, the interface represents a sand-sand interface in the pullout test: a best fit line throughthe data points defines a peak (Ø=40.5°) and a large displacement angle of friction(p=34. 50) for the sand in a condition of plane strain, see Figure 7.44. Other tests on thesand in a small direct shear box at normal stresses between 4 and 10 kPa, see section 4.2.1,gave a deduced plane strain angle of friction at large shear displacements in the range 350 to32° This compares very well with the pullout test data. Further, the angle of friction indirect shear (Ød) and the constant volume angle of friction () are related to a plane strainfriction angle (Ø) by the expression (Rowe, 1969):tan øds = COSØc, tan (7.12)The above expression is valid for the measured values of Øds=310, Ø29°, and %3450The maximum and limiting value of shear stress for the Tensar grid (GT) are identical.The angle of interface friction between the Tensar grid and sand is defined by a line which liesbetween 0.8tan Ø to 0.9tan In contrast to this response, the Miragrid (GM) and the159Chapter 7. Analysis of Test ResultsStratagrid (GS) exhibit a noticeable peak value of shear stress at all normal stress levels. Themaximum value of interface friction angle for these two grids is similar to the limiting angle offriction of the rough aluminum sheet, being in the range 1.Otan Ø to O.9tan Ø. It wouldappear that the Miragrid and Stratagrid are slightly more efficient than the Tensar grid at verylow normal stresses.To further study the influence of grid orientation, results from tests performed on theMiragrid in the cross-machine direction are considered, see Figure 7.45. A slightly higherinterface friction is obtained at lower stresses for the cross-machine direction, however, theamount of displacement required to mobilize it is about 3 to 4 times that required in themachine direction (see Figure 6.15). At higher stresses a limiting interface friction of similarmagnitude is observed. This behaviour is attributed to the similar S/B ratio in both themachine and cross-machine directions of the grid.The peak and the limiting interface shear strength of the smooth and texturedgeomembrane are presented and compared with that of the rough aluminum sheet in Figure7.46. Both the peak and limiting shear strength for the textured geomembrane are identical atall stress levels and correspond to a value between the peak and limiting shear strengthobtained from rough aluminum sheet. It is believed the textured surface of the geomembranetransfers the shear surface into the soil mass above and below the specimen, thus resulting inshear between sand particles rather than at the specimen surface. The angle of interfacefriction for the textured geomembrane and sand is between the peak and limit values for thesand. Mobilization of a constant, maximum shearing resistance to the end of the test is160Chapter 7. Analysis of Test Resultsattributed to dilation of sand at the interface as a result of the uneven surface characteristics ofthe geomembrane and progressive strain of the specimen.In contrast to the textured geomembrane, the smooth geomembrane exhibits both apeak and limiting interface strength. A peak interface friction angle of 12° and a value at largedisplacement of 80 are obtained. The low interface friction angle realized in the pullout isdue to the rounded to subrounded shape of the soil particles and the very low normal stresses.7.2.4 Comparison of Interaction Factors With and Without Bearing ElementsSome tests were performed on the Tensar grid and Miragrid specimens with bearingelements removed to assess the contribution of bearing to the pullout resistance. In Figure7.47 the interaction factors for the grids with and without transverse bearing elements arecompared at different normal stresses. The limit interface strength for specimens withoutthese bearing elements is lower, and is found to vary between 65% and 75% of the strength ofthe specimens with bearing elements.The friction angle for the sand-smooth FIPPE geomembrane interface from pullouttesting is found to be 12° at peak and 8° at large displacement. Consider the Tensar grid: itexhibits a similar smooth ITDPE surface and has a solid area of 57.3%. The frictioncomponent should account for the measured resistance of the specimen without transversebearing elements, but this is not the case. The discrepancy is attributed to some component ofbearing present due to the ribbed profile of the nodes of the Tensar grid, even with thetransverse bearing elements removed.161Chapter 7. Analysis of Test Results7.2.5 Comparison of Theoretical and Experimental Interaction FactorsTheoretical interaction factors are calculated based on the geometry of the specimenand the soil properties. Two methods are available for computing theoretical interactionfactors (IJSFHWA, 1990, and Jewell et al., 1984). Both give an identical expression when thedegree of interference, DI (equation 2.11) is zero. Relating equations 2.7 and 2.14, gives* cxbBc5bF z=fbtanØ=czStan+——— (7.13)2 SaThe geometric characteristics of each geosynthetic test specimen and thecorresponding interface friction angle for the materials are tabulated in Table 7.1. Values oftan for the material are reported from the direct shear box tests. The interface friction angleof the Stratagrid and Miragrid is assumed to be that of the textured sheet in direct shearbecause of their surface texture.The USFHWA design manual recommends that in the absence of test data a value ofapproximately 20 be assumed for the non-dimensional stress ratio abIa based on availablepullout test results at that time. Deduced values of F*cc are tabulated in Table 7.2 along withthe components due to friction and bearing.The friction component of the interaction is maximum for the Stratagrid (73%) andminimum for the Tensar grid (3 6%). Farrag et al. (1993) report results on Conwed G-9027geogrid without bearing elements and conclude that the predominant resistance is due tofriction (up to 75% of total resistance). In contrast, the surface of the Tensar grid leads to arelatively small component derived from interface friction. The Miragrid exhibits a nearly162Chapter 7. Analysis of Test Resultsequal component of friction and bearing: the higher component of bearing in the Miragridcompared to the Stratagrid is attributed to the smaller S/B ratio.Table 7.1: Geometric and interface friction characteristics of the test specimensMaterial Cx8 Cti, B S S/B tan 6(mm) (mm)TensarUX-1500 0.573 0.520 4.32 162 37.5 0.22Stratagrid 700 0.534 0.615 1.45 75.7 52.2 0.60Miragrid 15T 0.453 0.780 1.10 32 29.1 0.60Novex Smooth 1 - - -- 0.22HDPE sheetGundle Textured 1 - - -- 0 60sheetTable 7.2: Theoretical interaction factor for the grid specimens, IJSFIIWA guidanceMaterial Friction Bearing F*x= fb tan 0(cx. tan 8) (20 B a,I2S)TensarUX-1500 0.127 0.226 0.353Stratagrid 700 0.320 0.118 0.438Miragrid 15T 0.272 0.268 0.540163Chapter 7. Analysis of Test ResultsIn the method of Jewell et al. (1984) it is suggested that stress ratio a1Ja be measureddirectly in pullout tests. Experimentally the interaction factor is found to vary along thelength of the embedded specimen with the displacement of the clamped end. The extent ofinteraction is dependent on relative shear displacement between the specimen and the soil. Ithas been shown that the normalized relationship of shear stress is unique for a specimen andindependent of applied normal stress, see Figure 7.44. At large displacements themobilization of shear stress corresponds to a limiting shear strength of the interface.Using the experimentally observed interaction factor at large displacement, a value forthe stress ratio is back-calculated for three geogrids and is tabulated in Table 7.3. For a soilfriction angle of 310 in direct shear, the upper bound solution to the bearing capacity of a deepburied anchor gives a value of 20 (equation 2.6) and the lower bound a value of 6 (equation2.5), see Figure 2.8. The tabulated values for the geogrids are slightly higher than thetheoretical upper bound but are in reasonably good agreement.Results from tests on the Tensar grid specimen without bearing elements suggests ahigher friction component: this discrepancy is attributed to the geometric characteristics whichimpart additional bearing due to the profile of the nodes in the vertical direction. Consideringan additional bearing component from a 3 mm thick node (node thickness - ribthickness=3mm), the stress ratio is computed to be 40. This is in the general expected range.7.2.6 Comparison of Geogrid Interaction Factors with Other Laboratory and FieldDataInteraction factors from the present study are compared with laboratory pullout tests reportedby Palmeira (1987) and Farrag et al., (1993), and with the performance of a field structure164Chapter 7. Analysis of Test Resultsdescribed by Fannin and Hermann, (1990) . Similar geogrids were used in the other twolaboratory studies, a Netlon SR2 and Tensar SR2 respectively. Tensar TJX- 1200 is a directequivalent of Tensar SR2. The reinforcement used in the field structure was Tensar SR55.The geogrid characteristics are given in Table 7.4: the notations used in Table 7.4 areillustrated in Figure 7.48. Soil properties used in the laboratory tests and the field structureare tabulated in Table 7.5.Table 7.3: Stress ratio Ob/On from pullout tests on the geogridsMaterial Friction Limiting interaction F=(aj,/cy)(cc tan ) factor (see Figure 7.44)TensarUX-1500 0.127 0.588 40Stratagrid 700 0.320 0.599 47Miragrid 1ST 0.272 0.644 27The pullout test results of Palmeira (1987) on the Netlon SR2 geogrid performed ata=25 kPa are converted to interaction factors using expression 7.13 and the reportedconstant volume friction angle of 350 for the Leighton Buzzard sand. Interaction factors forthe Tensar grid from Farrag et al. (1993) and Palmeira (1987) are compared with the resultsfrom the present study, see Figure 7.49. The corrected total area method is used to calculatethe interaction factors because appropriate strain measurements are unavailable. There is anexcellent agreement between the curves given the variation in apparatus and test procedures,see Table 2.1. A detailed initial response is shown in Figure 7.50.165Chapter 7. Analysis of Test ResultsTable 7.4: Typical properties of the geogrid specimensGeogrid Wide Width Strip Dimension (nun)Tensile, ASTM l 12 13 14D4595-86, Ultimatestrength (kN/m)TensarSR55 NA 156 16 6.7 2.6Netlon SR2/Tensar SR2 78 111 16.5 5.5 4.4TensarUX-1500 86 165 16 6.7 4.3* dimensions are shown in Figure 7.48.NA - Not availableTable 7.5: Properties of soil used in the laboratory studies and field structureUnit Particle ParticleResearcher Soil D50 C weight range shape Dr (%)(mm) (kN/m3) (mm)Palmeira (1987) Leighton 0.6 toBuzzard 1.180.80 1.3 17 angular 87Sand 14/25Farrag et al., (1993) Uniform 0.26 — 16.5 0.1 toblasting 1.18sandFannin and Uniform- 0.02 to subHermann, (1990) medium 10 rounded0.28 2.5 17coarse sandPresent study Uniform 0.82 1.5 17.8 0.6 to rounded >85Silica sand 1.18The response of the Stratagrid is compared with the results for Conwed 0-9027reported by Farrag Ct al. (1993), see Figure 7.51, which is a similar grid. Although the initialresponse is softer for the Conwed geogrid, this is to be expected at higher normal stress, and166Chapter 7. Analysis of Test Resultsthe interaction factors at large displacement are observed to be comparable. The deducedstrain profile from nodal displacements, see Figure 7.52, shows a similarity in shape with theobserved strain profiles in the present study shown in Figure 7.18. The larger magnitude ofstrain is attributed to the greater normal stress (48.2 kPa) and the different location of strainmeasurement. At pullout displacements between 4 and 10 mm, shear stress is mobilized overthe part of the embedded length of the specimen. On continuation of the test, the strainprofile is observed to become linear at a pullout displacement of 26 mm.Field observations of a sloped wall have been used to establish interaction factorsmobilized by the grid reinforcement under “in-service” conditions (Fannin et al., 1994). Thesevalues are compared with the laboratory pullout test results. The characteristics of the fieldstructure are illustrated in Figure 7.53. The 4.8 m high, slope (2V: 1H) reinforced soil wallcomprises two sections, each 10 m long and incorporating a different arrangement of geogridreinforcement. The reinforcement attaches to lightweight modular facing units that are 0.6 mhigh. Primary reinforcement was a Tensar SR55, and intermediate reinforcement was abiaxially-oriented polymer grid. Instrumentation was used to measure force and strain in thereinforcement, soil strain, and temperature, and earth pressure. The structure has been subjectto self-weight, a cycle of surcharge loading using water tanks, and finally a permanentsurcharge loading of 49.2 kPa since October of 1987. Performance data, Fannin andHermann (1990), show the measured forces in the reinforcement are in good agreement withpredicted values of the coefficient of active earth pressure.Global strain (Eg) is deduced from the separation of pairs of Bison inductance coilsthat were fixed to the geogrid at the nodal junctions, see Figure 7,48, by a nylon screw that167Chapter 7. Analysis of Test Resultsfitted through a central hole in the coil and a similar one drilled in the grid. Measurementswere taken at three locations (A, B and C) on instrumented strips (Figure 7.54). A profile ofmobilized strain in layer No. 7 of the structure located 1.2 m below the crest, see Figure 7.53,is illustrated in Figure 7.55 for each of the two sections. The mean value is that for allmeasurements taken during the 28 days of self-weight loading, and that for all measurementstaken during the first 720 days of permanent surcharge loading. Largest strains are observedat the front face of the slope, decreasing non-linearly to zero at the embedded end. A nearlyconstant value of strain is observed at any point during self-weight loading.Force in the reinforcement was measured using vibrating wire load cells connecteddirectly to the geogrid at a distance 0.86 m from the face of the structure. The mean value offorce in layer No. 7 during self-weight loading was 1.6 kN/m in section ‘J’ and 1.8 kN/m insection ‘N’; during the designated period of permanent surcharge loading the values were 2.4kN/m and 3.0 kN/m respectively. The vertical effective stress at this location is estimated tobe 20 kPa during self-weight loading, and 70 kPa after permanent surcharge loading.The mean value of interaction factor is determined knowing the embedded length, 1,behind the point where load was measured at A, see Figure 7,54. Values of 0.02 and 0.03represent section ‘J’ and ‘N’ respectively during self-weight loading, and 0.01 and 0.02 duringthe designated period of permanent surcharge loading. These values of interaction factors atworking conditions correspond to a very small displacement in the pullout test (less than 1mm), see Figure 7.50. The mean global strain mobilized under self-weight loading (20 kPa),was 0.52% in section ‘N’, and 0.33% in section ‘J’ (Fannin and Hermann, 1990): the168Chapter 7. Analysis of Test Resultscorresponding rib strain measured in the pullout test was 0.2 (global strain 0.36%), see Figure6.22.In summary, displacement-controlled pullout tests on extensible inclusions should beanalysed using appropriate interpretation methods to obtain interaction factors. A comparisonof the results from the present study with those studies that used other pullout equipmentshows good agreement. An excellent agreement is demonstrated between laboratory and fieldbehaviour at small strain.7.3 Load-Controlled Pullout TestsA series of pullout tests were performed to study the effect of cyclic loading onmobilized interaction factors. The nature of the cyclic loading and control system aredescribed in Chapter 5. The test results are discussed in the following sections with referenceto displacement of the clamped (&) and embedded (de) ends, and strain measurements onspecimens with gauges mounted on them. A unified method of interpretation is developed forthe imposed cyclic loading.Cyclic pullout tests were performed by loading the specimens monotonically at aconstant rate of loading of 0.25 kN/ni/min, to an initial targeted value (Po) between 60 and80% of the corresponding DC pullout resistance, and a series of load cycles then imposed (seeFigure 5.2). The demand signal for cyclic loading was a sinusoidal wave form of constantfrequency f= 0.1 or 0.01 Hz: each series comprised ten cycles, and the single amplitude (APm)was increased between each series. A load ratio (LR) is defined in the load-controlled testswith respect to the maximum pullout resistance in a displacement-controlled test (Pm), by169Chapter 7. Analysis of Test Results(7.14)PmThe load ratio increases with each series of load cycles. Each test was continued to adisplacement greater than 60 mm or to failure by pullout.7.3.1 Incremental Displacement ResponseThe cyclic pullout response is described by considering the incremental displacementsof the clamped (Ada) and embedded (Me) ends of the specimen. Incremental displacementsare calculated relative to the displacement at the beginning of each series of cyclic loading.Incremental displacement of the clamped end is plotted below with respect to the number ofcycles in a series, and the corresponding incremental displacement of the embedded end.The response of the GT1O specimen at f=0.01 Hz, is found to be dependent on thevalue of load ratio, see Figure 7.56. At LRO.93 and 0.97, a small M is observed during thefirst few cycles but during subsequent cycles it remains constant and no further displacementtakes place. It represents a stable behaviour. An increase in the LR leads to largerincremental displacements: at LR=1 .04 the magnitude of Ad increases significantly during thefirst 6 cycles. However very little displacement accumulates during next 4 cycles, and theresulting shape of the curve is concave-upwards. On increasing the LR further to 1.16 theincremental displacement in less than 1 cycle was of such a magnitude that the specimenexperienced an instantaneous pullout, see also Figure 6.31. It represents an unstablebehaviour that was approached as the LR was increased. The relationship betweenincremental displacements shows that at lower load ratios the incremental displacements aresmall, but when LR> 1, the incremental displacements of both ends increase.170Chapter 7. Analysis of Test ResultsThe response observed in the GT 10 test at 1’=O. 1 Hz is very similar to that observed atf’=O.Ol Hz, see Figure 7.57. Again, when the LR=1.19, Ad0 increases with number of cyclesand the shape of the relationship changes from a concave-upwards to a straight line, Thiscorresponds to an unstable behaviour and is indicative of a pullout failure due to anaccumulation of excessive incremental displacement.The cyclic pullout response of the Stratagrid at a=10 kPa (GS1O) shows a verydifferent behaviour, see Figure 7.58. Magnitudes of incremental displacement are smallduring most of the test. Although the response shows a stable behaviour during first fewcycles of the final loading series at LR= 1.01, there is a very abrupt change from a stable tounstable behaviour in the 4th cycle. At this stage of the test a rapid pullout of the testspecimen was observed. An inextensible pullout behaviour is associated with this response, asindicated by the incremental displacements Ad0 and Ade.A response similar to that of the GS 10 test is observed for the Miragrid at a 17 kPa,where again an abrupt change in behaviour occurs from a stable to an unstable response atLR=0.90, see Figure 7.59. The associated Ad0 versus Ade relationship shows zerodisplacement at the embedded end for first two cycles followed by an equal magnitude ofdisplacements in the third cycle.The response of the smooth and textured geomembranes at a=8 kPa are shown inFigures 7.60 and 7.61. The response of the smooth geomembrane (MSO8) at LR < 1illustrates a stable behaviour but a rapid pullout failure occurs when the ratio exceeds 1.Although the textured membrane (MTO8) exhibits a stable behaviour during first cycle when171Chapter 7. Analysis of Test ResultsLR >1 the rate of accumulation of displacement increases rapidly thereafter toward a pulloutfailure.All of the remaining cyclic pullout test data are plotted in a similar manner andreported in Appendix-B. From these results a general behaviour in cyclic pullout is observed.There appears to be a threshold load ratio beyond which the response moves from a stable tounstable behaviour with respect to pullout. The threshold ratio is around 1 for all types ofspecimens except for the GT specimens where a ratio greater than 1.1 was observed (seeFigures 7.56 and 7.57).Based on the results, a conceptual model is proposed in Figure 7.62 for the modes ofbehaviour observed in cyclic pullout testing. Curves ‘Ca’ and ‘ob’ represent a stable behaviour(Figure 7.56), curve ‘oc’ a transition, and curves ‘od’, ‘oe’ and ‘of’ an unstable behaviour(Figure 7.61). Curve ‘od’ represents a catastrophic failure because the behaviour changesabruptly from being stable to unstable (Figure 7.58). The relationship between Ad and Lde isnot unique for curves similar to ‘oa’, and the admissible range is bounded by oa1 and Ca2.However, the relationship is unique and lies along of1 if pullout failure occurs without flirthertensile strain of the test specimen.7.3.2 Strain ResponseIn this section the response to cyclic loading is described with reference to strainmeasurements. Based on the strain measurements in the displacement-controlled tests, it hasbeen shown that tensile force varies along the embedded length of the specimen. Therefore,172Chapter 7. Analysis of Test Resultsthe mobilization of strain during cyclic loading is also valuable to gaining an understanding ofthe distribution of incremental loads along the specimen length.Mobilization of rib strain, for the GT1O test at f0.01 Hz, with number of cycles ineach loading series is shown in Figure 7.63. As before, the strain gauge location is given interms of the normalized distance (XILej). As the load ratio increases, a marked increase instrain is recorded at all locations in the first cycle of loading. Mobilized strains at locationsSG- 1 to SG-3 indicate that the strain magnitude increases with the number of cycles. The rateof increase in strain decreases with the distance from the front wall, being greatest at locationSG- 1. At locations SG-4 and SG-5 the mobilized strain is observed to be essentially constantwith number of cycles at a given load ratio.The effect of cyclic loading on the strain profile for the same test is further illustratedin Figure 7.64. The strain profile at LR=0.89 represents the beginning of the cyclic loading.The increase of load ratio to 0.93 only increases strain at locations SG-2 and SG-3, and nochange occurs at other locations. Therefore only a part of the specimen near the front wallmobilizes resistance to the relatively small applied cyclic load. As the LR was increased to0.97 a nearly constant incremental strain was measured at all gauge locations. This type ofbehaviour was also observed when the LR was increased to 1.04.The mobilization of strain (Figure 7.65) and the strain profile (Figure 7.66) withincreasing load ratio and number of cycles for the GT 17 test specimen are also observed to beof similar shape to the GT 10 test specimen, though the magnitudes are greater. However astrain increase is measured for increased load ratios at all locations, irrespective of thedistance from the front wall.173Chapter 7. Analysis of Test ResultsThe mobilization of strain with number of cycles and load ratio for the Miragrid at a,,=10 kPa is illustrated in Figure 7.67. The slope of the relationship indicates that the strainaccumulates evenly between loading series and consecutive cycles. At LR > 0.8, strainaccumulation has essentially ceased and the specimen tends toward a unique strain profile, seeFigure 7.68. This behaviour is very similar to that in the DC tests. At a1,= 17 kPa a strainincrease is measured at locations near the front wall for smaller load ratios, and the embeddedend experiences a smaller strain increase, see Figure 7.69. In contrast, the strain profilerelationship tends to a highly non-linear shape, see Figure 7.70.The same general response is also observed in the Stratagrid tests under cyclic loading,see Figures 7.71 and 7.73. In these tests the LR was increased in smaller intervals, and is seento better define the mobilization of strain in a test specimen. The strain profiles at a=10 kPa,see Figure 7.72, indicate a fairly uniform increase of strain at all locations to a limitingenvelope. In contrast, a markedly different response is observed at a=17 kPa where a similaruniform strain increase occurs up to LR=0.89, and on further increase of the LR the responseshows a significant strain increase at locations closer to the front wall, see Figure 7.74.7.3.3 Interaction Factors for Cyclic LoadingA cyclic interaction factor may be determined by the generalized method for a testspecimen with strain measurements. A comparison of the variation of interaction factor withdisplacement determined by the generalized method and the corrected total area method, forthe GT 10 test specimen illustrates an important aspect of the cyclic pullout response, seeFigure 7.75. The corrected total area method uses the pullout load applied to the specimento determine an interaction factor. Consequently, when the magnitude of the load decreases174Chapter 7. Analysis of Test Resultsduring unloading, a lower interaction factor is predicted. In the proposed generalizedapproach, the variation of pullout resistance along the embedded length of the specimen isdetermined from strain measurements. From the strain profile it was observed that even whenthe magnitude of cyclic loading was less than the mean load level, there was on occasion nostrain reduction at some gauge locations inside the pullout apparatus. Therefore, theinteraction factor determined by the generalized approach is larger than that computed by thecorrected total area method. The unloading part of the cyclic loading sequence affects only apart of the specimen near the front wall, while most of the embedded portion remains loaded.A consequence of this phenomenon is that the test specimen experiences a ‘locked in’ stressdue to cyclic loading.7.4 Comparison of Interaction Factors from DC and LC TestsThe variation of interaction factor with pullout displacement in DC and LC tests iscompared. For purposes of comparative analysis, the corrected total area method is used toobtain the interaction factors. While the generalized method is recognized as a more rigorousapproach, the corrected total area method is selected for the comparisons in this sectionbecause not all DC and LC tests had a complete and adequate record of strain measurements.It should be noted that at low stresses and large displacement, when behaviour ispredominantly inextensible, both methods give comparable results. Although a majorlimitation of the corrected total area method is that the interaction factor corresponding to theunloading phase of the cyclic test is not correct, since an envelope to the cyclic response is ofprime interest, the use of the corrected area method for comparison purposes is not a175Chapter 7. Analysis of Test Resultslimitation. Note, also that the ratio of interaction factor in the LC test to that in the DC test isindependent of the method applied when a similar method is used.Cyclic interaction factors for the Tensar grid are compared with those from monotonicdisplacement-controlled tests at a=4 to 17 kPa (Figures 7.76 to 7.79). Also shown is thevalue recommended by USFHWA design manual for designing structures to resist dynamicloads, which is 80% of the interaction factor from a displacement-controlled test. For clarityonly half of the unload/reload loops are shown. Although an envelope to the cyclic interactionfactor is slightly higher than the corresponding DC test for small displacements in the test ato,.=4 kPa, the large displacement values are very similar, see Figure 7.76. In contrast, forother tests on the Tensar grid a higher cyclic interaction factor is obtained, see Figures 7.77,7.78, and 7.79. The envelope to cyclic interaction factors at f=0. 1 Hz (Figure 7.78) is similarto that observed for f=0.01 Hz (Figure 7.77), and is indicative of frequency independentbehaviour for the range used in testing.The comparison of cyclic interaction factors for the Ivliragrid at a4 to 17 kPa isshown in Figures 7.80 to 7.82. Results indicate a response which is dependent on themagnitude of normal stress. At lower stresses, an envelope to the cyclic interaction factor isvery similar to the monotonic DC test (Figures 7.80 and 7.81). A very different behaviour isobserved at a=17 kPa, where an envelope to the cyclic interaction factor indicates a lowervalue. The Stratagrid response at a4 and 10 kPa is very similar to the IVliragricl response,see Figures 7.83 and 7.84. In contrast, at a=17 kPa a higher interaction factor is mobilized incyclic loading, see Figure 7.85.176Chapter 7. Analysis of Test ResultsAn envelope to the cyclic interaction factors for the smooth geomembrane at a=8 kPaand 12 kPa coincides with the corresponding monotonic DC tests, see Figures 7.86 and 7.87.In both the tests a rapid pullout occurred during first cycle of the loading series when theinteraction factor just exceeded the monotonic DC interaction factor.An envelope to the cyclic interaction factors is seen to coincide with the correspondingDC interaction factors observed for the textured geomembrane at a=8 kPa and f0.01 Hz,see Figure 7.88. Although a test performed at a higher frequency (f=0. 1 Hz) shows the samegeneral response; the interaction factor is greater in magnitude, see Figure 7.89. At a1=12kPa, the factor mobilized in cyclic loading tends to a value similar to that mobilized inmonotonic DC test at large displacements, see Figure 7.90. Again the cyclic pulloutinteraction factor (tla) is seen to meet or exceed that from the constant rate of displacementtest.In summary, the response of extensible specimens in cyclic pullout tests shows that theincremental loads are resisted by part of the embedded specimen closer to the front wall of theapparatus. As the loading regime approaches the limiting interaction factor from thedisplacement-controlled test, resistance to pullout is mobilized by the entire embedded lengthof the specimen. The limiting interaction factor in cyclic loading is found to be dependent onthe specimen type but independent of the applied normal stress and the frequency in the rangeof frequency tested. Most of the results showed an interaction factor in cyclic loading to beequal to or higher than that of the interaction from the correspondng displacement-controlledloading.177ITJMeasuredlateralpressura,ah(kPa)Pulloutresistance(kNlm)--MC)C.).CITUI0101-0(IT001001OO101OO1O010ChMeasuredlateralpressure(kPa)IC., 0 a a II000cicj.--,‘3L’30010(110010 C,’0 -h 01 •1Chapter 7. Analysis of Test Results1.0_________y_________________—1.0- I j I15 30 45 60Incremental lateral stress, (kPa)Figure 7.3: Incremental lateral stress on the front wail for the smooth geomembrane andTensar grid at similar normal stress.-0.8I110 ‘ 15avFigure 7.4: Variation of normalized lateral stress ratio with depth ratio for the smoothgeomembrane and Tensar grid at similar normal stress179Chapter 7. Analysis of Test Results1.0-QGTO40.8 - Gr1OGT170.6 -0.4 -0.2 -* 0.0-0.2-08_1.0:‘ I10 15&h /tavFigure 7.5: Variation of normalized lateral stress ratio with depth ratio for the Tensar grid ata=4 to 30 kPa1.0_________QGSO4I0.8-f LGS1O0.6____GS170.4 -0.2 -0.0-0.2 --0.4-I I 110 I I I I 15-0.6-0.8-1.0-/ cvFigure 7.6: Variation of normalized lateral stress ratio with depth ratio for the Stratagrid ata=4 to 17 kPa180Chapter 7. Analysis of Test Results1.0-_________- Q GMO40.8-0.6 GMI 70.4 -0.2 -0.0--0.2-0.82_i.o— I I I I I I I I I I0 5 10 15h 1-t/ GVFigure 7.7: Variation of normalized lateral stress ratio with depth ratio for the Miragridtested in the machine direction at o=4 to 17 kPa1.0-_ __0 GMO4C—1.0— I I I I I I I I0 5 10 15h/ avFigure 7.8: Variation of normalized lateral stress ratio with depth ratio for the Miragridtested in the cross-machine direction at a=4 to 17 kPa181Chapter 7. Analysis of Test Results1.0-_________• REo10.8-0.6- A v1S120.4 -0.2 -0.0-0.4-0.8-I I I I I I I I I I I Iu 10 15&h/tovFigure 7.9: Variation of normalized lateral stress ratio with depth ratio for the smoothgeomembrane at a=4 to 12 kPa1.0-•M1IM1.OI1III 1111&h/tcjvFigure 7.10: Variation of normalized lateral stress ratio with depth ratio for the texturedgeomembrane ata11—4 to 12 kPa182Chapter 7. Analysis of Test Results100—GTIO90-a) 80—70—ci) : I60-I InextensibleI behaviour I: Extensible50_40 behaviour Zone: Ill20..ioEZo11eE:J0-0 10 20 30 40 50 60 70 80 90 100Displacement of danced end, d (m)Figure 7.11: Relationship between d and d. for the Tensar grid in the DC test ata=1O kPa1.00—____GTIOL= 0.965 md(nm)0.75— Q 1L 510Cdc: 050 • 150.25 —0.00 —_________________________________ _ ____ __I I I ui0.00 0.25 0.50 0.75 1.00Normalised distance from the front wall, x/LFigure 7.12: Strain profile for the Tensar grid in the DC test at a=1O kPa183Chapter 7. Analysis of Test Results100— GT3O90E -‘ 80—C 70—II) 60—a) -.0 50—Eci) -._ 40—0 —4-’ -30—ci) -Ea)o20Zonein 10 Zoneo0 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d (mm)Figure 7.13: Relationship between d and de for the Tensar grid in the DC test at a=3O kPa2.00 —___________GT3O= Lei=O.965m1.75 —1.50 0 1-L121.25— A 5= <C> i1.00 • 15=d0(mm)4- • 30Co -.0 0.75— A 500.500.25 —=iiirI•iiiiiii0.00 —________________________________0.00 0.25 0.50 0.75 1.00Normalized distance from the front wall, X/LeiFigure 7.14: Strain profile for the Tensar grid in the DC test at a3O kPa184Chapter 7. Analysis of Test Results2.00 —___________GT2O= Lei=0.965m1.75d(mm)Not1.50A[] 201.25 A 5• 151.0010•30AA 50U,0.50.0 0.750.250.00 —0.00 0.25 0.50 0.75 1.00Normalized distance from the front wall, X/LeiFigure 7.15: Strain profile for the Tensar grid in the DC test at a=2O kPa and rd=O.5Omm/mm100—- GSIOE -90E -80HVC 70—(I) : Extensible IV : Ia. 60 behaviour0 - I•Oa) - V Inextensible.0E(1)- I behaviour._40— Jo : I /4-. - I ZoneC 30—a)- I III ‘E :20—C.)= .7U, 10 Zone.j,O :jll0 II I I I0 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d (mm)Figure 7.16: Relationship between d and de for the Stratagrid in the DC test at a=1O kPa185Chapter 7. Analysis of Test Results1.00 —__________GSI 0L= 0.970 md (mm)0.75 0 iL12510C.. 151.4-0.50U,-o A 500.250.00 —________________________________ ____ _0.00 0.25 0.50 0.75 1.00Normalized distance from the front wall, )C/LeiFigure 7.17: Strain profile for the Stratagrid in the DC test at a=1O kPa1.25GSI 7L =0.970med(mm)1.000210- 0.7515C•304-,•5°U, 0.500.250.00—__________ ___0.00 0.25 0.50 0.75 1.00Normalized distance from the front wall, x/LFigure 7.18: Strain profile for the Stratagnd in the DC test at o17 kPa186Chapter 7. Analysis of Test Results100 —______- GMI7E -90 —E -80—070— InextensibleVbehaviourV 60—- IVVV- I.50— IE : IU)- Zone140— ExtensibleIIIo= behaviour30—U) —E =U)o 20—10-I0— ‘‘‘H0 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d (mm)Figure 7.19: Relationship between d and de for the Miragrid in the DC test at o=17 kPa2.25 —_____________________________________GMI72.00 Lej = 0.980 md0 (mm)1.75Q21.50 LI 5101.25 15C-• 30‘•- 1.004-,•50U)_ _.0i 0.75I,II!II0.500.250.00 —_______ ______ID,0.00 0.25 0.50 0.75 1.00Normalized distance from the front wall, )(fLeiFigure 7.20: Strain profile for the Miragnd in the DC test at a=17 kPa187Chapter 7. Analysis of Test Results100 —______- IMSO8EEw• 80—70—a)-a 60—a)50—Ea)‘i— 400C(1) 30 Zone IE and20 Zone II0Cl) 10•i:50—”III liii liii liii liii liii liii I II liii III0 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d (mm)Figure 7.21: Relationship between d afld de for the smooth geomembrane in the DC test ato=8 kPa0.5 —MSO8Lei=O.965md(mm)0.4o 0.5LiiA 20.3C•104-.•30U)0.20__________0-J0.10.0 —__________________________________ ___0.00 0.25 0.50 0.75 1.00Normalized distance from the front wall, X/LeiFigure 7.22: Strain profile for the smooth geomembrane in the DC test at kPa188Chapter 7. Analysis of Test ResultsDeducedMaximum slope5/5’E5.— NI—Effective area N‘ Total areaI ‘S\NFrort wall LX Entedded endLeaorLDistance from the front wall of the apparatusFigure 7.23: A schematic illustration of the interpretation of data by various resisting areamethods (modified after Ochiai et aL, 1992)189Chapter 7. Analysis of Test ResultsApparatus front wallElement No.1 2 3 4 5 60 i 2 3 4 5 0 7Node NodeLVOTFigure 7.24: Schematic ifiustration of nodes and elements for a) smooth geomembrane, b)Tensar grid and c) Stratagrid and MiragndLoad cellClampa)Apparatus front wallElement No.ActuatorLVDTNodeApparatus front watElement No.b)c)Load ceUC!amp-I-LVDTU 3 4 5 6Node Node190Chapter 7. Analysis of Test ResultsFLOW CHART OF THE GENERALIZED METHOD[/ Determine normalised/ distance,’q Print i, shear stress,interaction factorFigure 7,25: Flow chart of the generalized method for interpretation of a pullout test[ Start/ Read Strain /Compute tensile force in thespecimen, T, and the change inposition of strain gauge, xDiscretize the polynomial relationshipbetween T andi and determine the slope.Shear Stress =‘t=(slope)/2Interaction factor=(t/cy)Compute total shear stress using Simpson’srule/ andCall the subroutine to fita polynomial, andobtain coefficients ofpolynomial LEND D191Chapter 7. Analysis of Test Results100-:________ _I GTIOmeasured I___9°: -- calculated‘1) 80—7O-a)4Z• 30-/////20—//0—0 10 20 30 40 50 60 70 80 90 100Displacement of darrped end, d0 (mm)Figure 7.26: Comparison of measured and calculated displacements of the embedded end ofthe Tensar grid in the DC test at a=1O kPa25 —CO20- 15— AA •+___________A (Th I.te1_1AI.test2!A( I.test3A• GT1oSAG120, 0.25 nm’irinA GT2O, 0.50 nm’ninG120, 1.00 rrm’ninF2-+- GTIOoj0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00Rib strain, (%)Figure 7.27: Relationship between strain and tensile force per unit width for the Tensar grid192Chapter 7. Analysis of Test Results--cII20151050—0 GSIO, DC1_z GSIO,LC-• GSI7,DCGSI7,LC0.0I I I I I I I0.5 1.0Rib strain, Cr (%)I I1.5 aoFigure 7.28: Relationship between tensile force at the clamped end and the measured strain atlocation SG-2 (xILO.lO6) for the Stratagrid2520—::5 —I0 GMIO,DCGMI7,DC• GMIO,LC• GMI7,LC0.0 0.5 1.0 1.5 2.0 a5Rib strain, (%)Figure 7.29: Relationship between tensile force at the clamped end and the measured strain atlocation SG-1 (xILO.O43) for the Miragrid193Chapter 7. Analysis of Test Results5—0 MSO4MSO8E A MS12,_00.0 0.1 0.2 0.3 0.4 0.5Local strain, (%)Figure 7.30: Relationship between tensile force at the clamped end and the measured strain atlocation SG4 (XILeiO.074) for the smooth geomembrane in the DC tests30 —_______________________________________________GTIOLe10.965 m25 — d(mm)Qiz L1220—0.00 0.25 0.50 0.75 1 .00Normalized distance from the front wall, X/LeFigure 7.31: Profile of deduced tensile force/width and the generated polynomial fit for theTensar grid at a=10 kPa194Chapter 7. Analysis of Test Results30 —__________________________________________GT2O- Lei=0.965m25 d(mm)Q iZ — N 220— \AN- \NN L5N io150.00 0.25 0.50 0.75 1.00Normalized distance from the front wall, x/LFigure 7.32: Profile of deduced tensile force/width and the generated polynomial fit for theTensar grid at OH=2 kPa and rd=O.S mmlmin30—_____ _____ __________- GT3O- A Lei=0.965m25 d (mm)01z-0 2. 20— . A L 510A•150— I I liii I I0.00 0.25 0.50 0.75 1.00Normalized distance from the front wall, x/LFigure 7.33: Profile of deduced tensile force/width and the generated polynomial fit forTensar grid at a=3O kPa195Chapter 7. Analysis of Test Results10—9—8—_7—U) -a..U)InG) 54-U)-U) 4—ci)-U) 3_2—0—U)0-U)U)U)I4-,U)U)ci)-CCl)-.ju-— 15GTIO50d0 = 1 mmI I I I I I I I I I I I I I I I0.00 0.25 0.50 0.75 1.00Normalized distance from the front wall, X/LeiFigure 7.34: Shear stress variation along the embedded length of the Tensar grid at a1OkPa25— GT2O20—15— d=50mm0— I II I II0.00 0.25 0.50 0.75 1.00Normalized distance from the front wall, X/LeiFigure 7.35: Shear stress variation along the embedded length of the Tensar grid at oR=20kPa196U)U)00.00 0.25 0.50 0.75 1.00Normalized distance from the front wall, X/LeiFigure 7.36: Shear stress variation along the embedded length of the Tensar grid at a=3OkPa10 —9—8—7-Eft.U)-U)-U)-w 4—ci)-Cl)2—0Chapter 7. Analysis of Test Results252015 —10GT3Od= 15mm10d0 = 1 mGSIO1015305d0 = 1 nmI I I I I I I I I I I I0.00 0.25 0.50 0.75 1.00Normalized distance from the front wall, XILe1Figure 7.37: Shear stress variation along the embedded length of the Stratagrid at o,,=1O kPa1970 I I I r—i I I I I j I I I0.00 0.25 0.50 0.75 1.00Normalized distance from the front wall, X/LeFigure 7.38: Shear stress variation along the embedded length of the Miragrid at a=17 kPa3—0MSO810N N 1530d = 50 mrd0 = 1 mI I I I I I I I I I I I I I I0.00 0.25 0.50 0.75 1.00Normalized distance from the front wall, x/LejFigure 7.39: Shear stress variation along the embedded length of the smooth geomembrane ata=8 kPaChapter 7. Analysis of Test Results25 —_______GM170U)U)2015105305o2 mmCu0U,U,‘I)4-.U,CU-c(I)2—1—198Chapter 7. Analysis of Test Results0.6 —_______________________- L GT2O, 0.25 mm/mm, CM•GT2O, 0.25 mm/mm, GM0 5 Z GT2O, 0.50 mm/rn in, CM- A GT2O, 0.50 mm/mm, GM- Q GT2O, 1.00 mm/rn in, CM • •A • GT2O, 1.00 mm/mm, GM.- GT3O, 0.50 mm/mm, CM- .- • GT3O, 0.50 mm/mm, GM- •1 otb 0.3 — • o- • •A- IA 0A•AD 0- 4AQ0.2 ..Au 0- AD-00-Ol- D CM - Corrected area methodGM - Generalized method0.0 —0 1 2 3 4 5 6 7 8 9 10Displacement of clamped end, dc (mm)Figure 7.40: Interaction factors for the Tensar grid: corrected total area method andgeneralized method0.6 —0.5—000.=D-00.4 0 0Do- 1J- u9O-t/c 0.3 — •. Q GTO40.2 j GTI 0- K GT2O, 0.25 mm/mm0.1 —A GT2O, 0.50 mm/mm- • GT2O,1.Oommlmin-•0.0— I I I I I I I I I I0 5 10 15Displacement of clamped end, dc (mm)Figure 7.41: Interaction factors for the Tensar grid: generalized method199Chapter 7. Analysis of Test Results0.60—- --——————-—--—-----—CM - Corrected area rrthodGM - Generaltzed thod AH0.50_1I-H Ioio —I—. 0•000C.t/aO.30—i • 0-J •°°1 Gs1o,cM- • 0<— •• GS1O,GM-•( 08 0 GS17.cMI0.20• • 0<>• GSI7,GM• 0 A GM1O. cM0.10 —•A GM1O,GMGvi17M—• GM17,GM0.00—0 1 2 3 4 5Displacement of damped end, dc (nih)Figure 7.42: Interaction factor for the Stratagrid and Miragrid: corrected total area methodand generalized method0.25H—1 •—0.20 —•- ..0- •0•0.15— •- 11001tb : 0 MS0 cM0.10 .-• m • MSO8, GMMS12,CMHo—— a MS12GMJ— 0__005CM - Corrected area method_D GM - Generalized method0.000 1 2 3 4 5Displacement of damped end, d0 (rrrn)Figure 7.43: Interaction factor for smooth geomembrane using the corrected area andgeneralized method200Chapter 7. Analysis of Test Results-!o- GlTwiit m=ta%25- GNeak /-- • GMinit20Gspeak- A GSlirrft 1 m+15— )<15—III I liii0 10 20 30Nom,aI stress, a,. (kPa)Figure 7.44: Relationship between average shear stress and normal stress for the grids andrough aluminum sheet20—,-if Q a4,eak- • Gvlinit-i E GMCPeak flFtfl4ps /• GMCI1nIt_15—- + ARpeak-xAiint + m--H 0.8m-(I) 5__,-i0 ‘0 5 10 15 20Normal stress, a (kPa)Figure 7.45: Influence of grid orientation on pullout behaviour of the Miragrid201Chapter 7. Analysis of Test ResultsP0 MSpeakMSIinitA MTpeakKD rvmimftH- ARpeakLX ARlinit/+x20—1I5Hio/—45—42°40°34012°8°00111lI II II15 20Applied normal stress, a (kPa)Figure 7.46: Relationship between average shear stress and normal stress for thegeomembranes and rough alumimun sheet30—-42°25— /400- EIGMC- • GMCN20—-b ARpeak)< ARhiiit 30°15_Z 0025°+x 05I I I I0 5 10 15 20 25 30Applied normal stress, a (kPa)Figure 7.47: Relationship between average shear stress and normal stress for the Tensar gridand Miragrid with and without bearing elements202Chapter 7. Analysis of Test ResultsStrain gauge, e1Figure 7.48: Details of the geognd specimen (after Fannin et al. , 1994)0.7 —0.6t/a 0.5 —0.40.30.20.1 _:0.0 _:Figure 7.49: Comparison of Tensar grid interaction factors from laboratory pullout tests13Inductance coils, ç1.0—0.90.8 —$ Netion/Tensar SR-2 and UX-1 500ci1 Q Presentstudy,lOkPa[] Present study, 25 kPaI • Pahira(1987),25kPa• Farragetal.,(1993),482kPaI I I0 10 20 30 40 50 60 70 80 90 100Displacement of darrped end, d (nTn)203Chapter 7. Analysis of Test Results0.6 —______0.5— 0000LuO ••-04ZuI •t/a 0.3—rP°-0.2NetlonlTensar SR-2 and UX-1 500— Q Present study, 10 kPa0.1— o [] Present study, 25 kPa— • Palmeira (1987), 25 kPa— o • Farrag et al., (1993), 48.2 kPa0.______1I III II I I II0 5 10 15Displacement of clamped end, d, (mm)Figure 7.50: Comparison of interaction factors from Figure 7.49 for small displacement1.0 —_ _________________________________0.9 —0.8 —0.7 —00.6‘na 0.5 —00::0.4 — 0:-00.3 —_____ _____Conwed G-9027 I Stratagrid 700:j0.2—: • Present study, 4 kPa0.1 0 Present sttdy, 10 kPaLI Farragetal.,(1993),4S2kPa0.0—_0 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d (mm)Figure 7.51: Comparison of interaction factor for Conwed G9027/Stratagrid 700204Chapter 7. Analysis of Test ResultsCond 9027d (m)Q 1016AI’ll0.25 0.50 0.75Distance from the darrped end (m)Figure 7.52: Strain profile deduced from the reported nodal displacements of Conwed grid ata=48.2 kPa from Farrag et al. (1993)I’ 3.Om—/8I.Zm ZV/ //7I.Zm 0 6I.2m0.6m50.6thLayer no.Figure 7.53: Reinforcement in the field structure (after Fannin et al., 1994)I1510 —5—00.00 1.00Section ‘JIntermediate reinforcement4i 5747/ r- Primary reinforcementSechon NPrimary/‘ r.inforcem— 0.60. 6r’0.6”0.6m0.6.-v’0 .6 m0.6rn0.6m205Chapter 7. Analysis of Test ResultsLocationGeognd layerFigure 7.54: A schematic diagram showing strain gauge locations (after Faunin, 1990)Section ‘J’Section ‘N’0.52.2mPermanent surcharge loading(ar’. 70lcN/m2)—.— Self-weight loading(a —20 kNIm2)max+ mean- (mmFigure 7.55: Strain in layer No. 7 of the field structure (after Fannin and Hermann, 1990)A B‘4//an1.00.500 0.86 1.64 2.421.000 0.86 1.33 1.79206Chapter 7. Analysis of Test Results15— GTIO,O.OlHzz1o___i5• 0.93— A 0.97-.--1.04- p 1.1660110 201IIncremental displacement ofdamped end, Idc (rmi)Figure 7.56: Relationship between Ad and Ad for the Tensar grid at a,,10 kPa andf=O.Olllz207Chapter 7. Analysis of Test Results15— GTIO,O.lHzZIOi5o—L. 102O-___LR• 0.89A 0.9240— • 0.99-4- 1.06cG)50 01.1960—0 10 20 30 40 50 60Incremental displacement ofdamped end, A dc (nTfl)Figure 7.57: Relationship between Ad and Ade for the Tensar grid at a=1O kPa and f=O.lRz208Chapter 7. Analysis of Test Results15LR GSIO, 0.01Hz—— 0.76A 0.81z10 • 0.86• 0.91- p 0.96>.. IL 1.01O—H10 —O’ 2c 40—_G) -60—70—80—90—100z.L0 1020 3040 50 60 708090100Incremental displacement ofdamped end, bidc (flu)Figure 7.58: Relationship between Ad and Ade for the Stratagnd at o,=1O kPa and f0.OlHz209Chapter 7. Analysis of Test Results15—GM17, O.O1I-tz1Oi5Ip— LR0.7520 A 0.8060708090100 — I I I I0 1020 3040 50 60 70 80 90100Incremental displacement ofclamped end, z\ dc (mm)Figure 7.59: Relationship between Ad and Ade for the Miragrid at o=17 kPa and f=O.OlJlz210Chapter 7. Analysis of Test Results15Z 10 ——10 LRII- • 0.66. 20 A 0.7530 • 0.84p0.97550 A 1.0260g70bEC0)90100 — I I0 10 20 30 40 50 60 70 80 90 100,Incremental displacement ofdamped end, &l (m)Figure 7.60: Relationship between Ad and Ad. for the smooth geomembrane at a8 kPa andf=O.OlRz211Chapter 7. Analysis of Test Results15MTO8, 0.01HzZ 10 —Cl)10 LRa,5o0 10 20 30 40 50 60Incremental displacement ofclamped end, Adc (mm)Figure 7.61: Relationship between Ad and Ade for the textured geomembrane at a8 kPaand f0.Olflz212Chapter 7. Analysis of Test ResultsNLdeFigure 7.62: A conceptual model for the modes of behaviour observed in cyclic pullout testing213Chapter 7. Analysis of Test Results1.00 — 1.161.o0. 9cycPD0OOODu0.750.50GT1 0Ld=0.965m—SG, xIL...........0.25 0 1 -0.082..........— LI 2, 0.0723, 0.240D’ 4, 0.576• 5, 0.7440.00 —_____________________________0 5 10 15 20 25 30 35 40 45 50Number of cycles, NFigure 7.63: Mobilization of rib strain with number of cycles and increasing load ratio for theTensar grid at a=1O kPa and f0.O1 liz1.00—i GTI 0f=O.O1 HzLR0.75D 0.930.97K> 1.040.250.890.50•1.164-’U,-o0.00 —__ __ _ _ _ __ __ __ __ __ __ __ __ __I I I I I I I I I I I I I I I0.00 0.25 0.50 0.75 1.00Normalized distance from the front wall, X/LeFigure 7.64: Strain profile with loading ratio at the end of the loading series for the Tensargrid ata1=1O kPa and f=O.O1 Hz214Chapter 7. Analysis of Test Results1.50 —__________GT17L, 0.965 mSG, xIL1.25 — o 1-0.082QQ0000000000000000002, 0.2403, 0.4081.00 —• 4, 0.744AAA40AA0.750.50..1.08— •.••••••••0.251.010.970.00 —_______________________________ ___ _liii liii I liii liii I I liii II I0 5 10 15 20 25 30 35 40Number of cycles, NFigure 7.65: Mobilization of rib strain with number of cycles and increasing load ratio for theTensar grid at a=17 kPa and f=O.O1 liz1.00_- f=O.O1 Hz- LR— 0 0.890.75 ——1.01- \GTI70.50A 1.08w-4-,U) -0.250.00 —_______________________________ ___ __I I I I I I I I I I I I0.00 0.25 0.50 0.75 1.00Normalized distance from the front wall, XILeFigure 7.66: Strain profile with loading ratio at the end of the loading series for the Tensargrid at a=17 kPa and f=O.O1 liz215Chapter 7. Analysis of Test Results1.25- GMIO— L0.965m— SG, xlL— Q 1, 0.0431.00 ——2, 0.072- 3, 0.240 0.84 0.890.75LRL0.25 —0.00— I I I I I I I I I I I I I I I I I I0 10 20 30 40 50 60 70 80Number of cycles, NFigure 7.67: Mobilization of rib strain with number of cycles and increasing load ratio for theMiragrid at a=1O kPa and f=O.O1 liz1.00 —___________GMIOLe10.980mLR0.75 Q 0.620.660.00— I I III II I0.00 0.25 0.50 0.75 1.00Normalized distance from the front wall, X/LeiFigure 7.68: Strain profile with loading ratio at the end of the loading series for the Miragridat a=1O k.Pa and f=O.O1 liz216Chapter 7. Analysis of Test Results1.50 —________— GM17— L1 = 0.965 m— SG, xIL11.25 0 1,0.043 02,0.2620000- 3,0.447000000i.oo — ‘ 4,0.635 00000000— • 5,0.821 0.90ci 0000000000.750.85(I)- LR 0.80QQDD-o.so 0.75- mm AAAA-- AAAAAAAA0.25 —•........•••••••••••••0.00 —___ __________________________________I I I I I I I I I I I I0 10 20 30 40Number of cycles, NFigure 7.69: Mobilization of rib strain with number of cycles and increasing load ratio for theMiragrid at a=17 kPa and f=O.O1 Hz1.25 —___ _GMI7Le10.980m-A LR1.00— 0 0.75- U0.800.850.75 —0.90--- AI° 0.50—--A-0.25 —0.00 —_ ___ _________0.00 0.25 0.50 0.75 1.00Normalized distance from the front wall, x/LejFigure 7.70: Strain profile with loading ratio at the end of the loading series for the Miragridat a=17 kPa and 1=0.01 Hz217Chapter 7. Analysis of Test Results1.00 —_________-OSlO—LeiO.97m-SO, XILei—0 1,0.0460.75—E 2, 0.10630.338-4,0.5700.50 • :o::LiwiIlJ:Th0.250.00 I II II II I I60N umber of cycles, NFigure 7.71: Mobilization of rib strain with number of cycles and increasing load ratio for theStratagrid at 011=10 kPa and f=0.01 liz1.00 —__________________________-GSIO-LRQ 0.710.75 — 0.76—A 0.810e. - <C> 0.860.50—:0.25—1.010.00 I I I I0.00 0.25 0.50 0.75 1.00Normalized distance from the front wall, XILe1Figure 7.72: Strain profile with loading ratio at the end of the loading series for the Stratagridat 0,,10 kPa and f0.01 Hz218Chapter 7. Analysis of Test Results2.00 —___________= GSI7—LejO.97m1.75 — SG, X/Lei: 1,0.046 i.o1.50 D 2, 0.106— 3, 0.3380 -1.25= • 5,0.8020890951.00--(0 -D 0.75—0.50 —0.25 —0.00— liii II liii I 111111111 I II liii III liii III liii0 10 20 30 40 50 60 70 80 90 100 110 120Number of cycles, NFigure 7.73: Mobilization of rib strain with number of cycles and increasing load ratio for theStratagrid at o=17 kPa and f=O.O1 liz1.25 —_______GSI 7LRo 0.661.00 LI 0.710.75o 0.80• 0.840.75•0.89• 0.954-,(0 0.50 )< 0.97_D+ 1.00* 1.02\A 0.93* 1.040.250.00 —_________ _______________________ ___I I I I I I I I I I0.00 0.25 0.50 0.75 1.00Normalized distance from the front wall, X/LeiFigure 7.74: Strain profile with loading ratio at the end of the loading series for the Stratagridat a=17 kPa and f=O.O1 Hz219Chapter 7. Analysis of Test Results1.0—ri--———I GTIO0.9 — —— Coffeded area0.8 Generalized0.7 —-0.6 -0.50.4 —0.30.2:/0.1 _:0.011111111111 11111111 111111 I I I I I I I I I I I I I I I I0 10 20 30 40 50 60 70 80 90 100Displacement of danped end, dc (rmi)Figure 7.75: Cyclic pullout interactiti factor from the generalized and corrected total areamethods for the Tensar grid at a,=1O kPa and f=O.O1 Hz1.00.9 —0.8 —0.7—0.4_.1.1b1r+10.3— : f0.01 HZLC- DC0.1 —— IJSFHWA0.0II liji liii lilt I I I liii 11111 ii0 10 20 30 40 50 60 70 80 90 100Displacement of clamped_. end, d (mm)Figure 7.76: Comparison of interaction factors in the LC and DC tests for the Tensar grid ata=4 kPa and f=O.O1 Hz220Chapter 7. Analysis of Test Results1.0 —0.9 —0.8 —0.7 —0.6—‘‘ th.USFHWA0.0I I I I I I 1111111 11111 I 11111 III TI I liii I I 111111 I I I I0 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d0 (mm)Figure 7.77: Comparison of interaction factors in LC and DC tests for the Tensar grid ata=1O kPa and f=O.O1 Hz1.0 —_________________________________________0.9—0.8—0.7 —.i ._i:.‘:;: iI: I . I/‘EfT1O—- USFI-IWA0.0Displacement of damped end, d (mm)Figure 7.78: Comparison of interaction factors in the LC and DC tests for the Tensar grid ata=1O kPa and f=O.1 Hz221I I Ijib:I 1111111 t11 I 111111 I I 11111 I] III II liii If0 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d0 (mm)Figure 7.79: Comparison of interaction factors in the LC and DC tests for the Tensar grid atG17 kPa and f=0.01 Hz1.0 —__________________________________________0.9—-0.6 —Ø7Z0.6 —t/a 0.5 —0.4 —0.3 —0.2 —0.1 —0.0 I I I I I I I I I I I0 5 10 15 20Displacement of clamped end, d (mm)Figure 7.80: Comparison of interaction factors in the LC and DC tests for the Miragrid ata1=4 kPa and f=0.01 HzChapter 7. Analysis of Test Results1.00.90.80.70.60.50.40.30.20.10.0GTI 7f=0.01 HzLCDC— USFHWA• ‘•.•.q• - S •% ..1/1’ GMO4ILCDC— USFHWA222Chapter 7. Analysis of Test Results0.9 —0.8 —0.7 —0.6—0.5 —0.4 —0.3 —0.2 —0.1 —11111 III 1111111 I j111 liii I I 1111111 111111111111 111111 liii liii lilt j I lIllIllil liii liii0 5 10 15 20 25 30 35 40 45 50Displacement of clamped end, d (mm)Figure 7.82: Comparis áÜd DC1ets for be Miragridata=17 kPa and frO.O1 Hz2231.0—‘IiiI GMIOf=O.01 Hz0.0LCDC— USFHWA0 5 10 15 20 25 30 35 40 45 50Displacement of clamped end, d (mm)Figure 7.81: Comparison of interaction factors in the LC and DC tests for the Miragrid ata1=1O kPa and f0.01 Hz1.0 —0.9—:0.8 —0.7 —0.6 —0.5—:0.4—:0.3—0.2 —0.1—:0.0.di- 1 -_- — -GMI7IsI’ LCI’ DC—- USFHWAChapter 7. Analysis of Test Results1.0 — —0.9——, USFHWA0.0 —z I I I I I I I I I I I I I I I0 5 10 15 20 25Displacement of damped end, d (mm)Figure 7.83: Comparison of interaction factors in the LC and DC tests for the Stratagrid ata,=4 kPa and f=O.O1 Hi1.0—0.9 —— USFHWA0.0 I I I I I I I I I I I 111111 I 11111 1111111 I (I I I I I I I I0 5 10 15 20 25 30 35 40 45 50Displacement of clamped end, d (mm)Figure 7.84: Comparison of interaction factors in the LC and DC tests for the Stratagrid atu=1O kPa and f=O.O1 Hz2241.00.9—:0.8 —0.7—:0.6 —0.5 —0.40.3 —0.2—z0.1I I I 111111111111111 j I I liii I III I I I 11111111 I0 5 10 15 20 25 30 35 40 45Displacement of clamped end, d0 (mm)50Figure 7.85: Comparison of interaction factors in the LC and DC tests for the Stratagrid ata.=17 kPa and f=O.O1 Hz‘c/a0250.200.15—:0.100.05—0.00 II IllijI 1111 IIII iii liii I I II II 1110 1 2 3 4 5 6 7 8 9Displacement of damped end, d (mm)10Figure 7.86: Comparison of interaction factors in the LC and DC tests for the smoothgeomembrane at a=8 kPa and fO.O1 liz225Chapter 7. Analysis of Test Results-LCI0.0GSI7f=0.01 HzDC— (JSFHWAMSO8f=0.01 HzLCDC—- USFHWAChapter 7. Analysis of Test ResultsI -—1’1’ MSI211 f=0.01 HzLC_____DC—- USFHWAI IfIR— - —II1Figure 7.88: Comparison of interaction factors in the LC and DC tests for the texturedgeomembrane at a,=8 kPa and f=O.O1 Hz226tb0.250.200.150.100.050.0011111 I I 1111111111111111111 I 11111 I 1111111110 1 2 3 4 5 6 7 8 9 10Displacement of damped end, d (mm)Figure 7.87: Comparison of interaction factors in the LC andgeomembrane at a=12 kPa and f=O.O1 HzDC tests for the smooth1.00.9 —0.8 —0.7 —0.6 —t/a 0.5 —0.4 —0.3 —0.2 —0.1 —0.0 —MTO8f0.01 HzLCDC—- USFHWAII liii IIIjiIIi1iIlI1l IIIIIIIIIII II0 10 20 30 40 50 60 70 80 90Displacement of damped end, d (mm)100Chapter 7. Analysis of Test Results1.0 ——- USFHWA0.0 IIiIIIIIIIHIIIIIHIIIIIIIIIIIII1IIHIIIHHIIIII0 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d (mm)Figure 7.89: Comparison of interaction factors in the LC and DC tests for the texturedgeomembrane at aR=8 kPa and f=O.1 Hz0.9 —0.8 — ....0.7 —— :0.6—. 41 Ii0.5— ii— I0.4—0.3 MT12f=0.01 Hz0.2— LC0.1 - DC—- USFHWA0.0 — -0 10 20 30 40 50 60 70 80 90 100Displacement of damped end, d (mm)Figure 7.90: Comparison of interaction factors in the LC and DC tests for the texturedgeomembrane at a=12 kPa and f=0.01 Hz227CHAPTER 8SUMMARY AND CONCLUSIONS8.1 SummaryThe emphasis of this thesis was placed on the pullout testing of geosynthetic testspecimens in monotonic and cyclic pullout modes. The intent is to better understand theinterpretation of pullout test data for viscoelastic materials, and to evaluate currentapproaches used to characterize soil-geosynthetic interaction factors for design of anchoragedetails.Specifically the objectives of the thesis were as follows:• Design and commission a large pullout test apparatus, and associated controls toperform pullout tests under displacement-control and load-control;• Develop a routine for cyclic loading of test specimens, taking into account thecurrent method for monotonic loading in pullout tests;• Comprehensively describe the development of pullout resistance frominstrumentation on the test specimen and on the test apparatus;• Establish a method of interpretation for the response of the test specimen based onmeasurements of pullout load, and strain along the embedded length, that accountsfor the extensible behaviour of geosynthetic test specimens;• Compare and contrast behaviour of grid and sheet specimens;• Contrast the results of this work with the limited experimental database forlaboratory testing;• Assess experimental and theoretical interaction factors for geosynthetics;228Chapter 8. Summary and Conclusions• Compare the behaviour in pullout testing with that for “in-service” conditions; and• Contrast values of interaction factor for static and dynamic loading, within thecontext of the current approach used in design for selection of an interactionfactor.A program of experimental research was undertaken to meet these objectives. Asummary of the findings is presented below that addresses the apparatus and instrumentation,the test procedure and the interpretation of the tests. In concluding, the implications fordesign practice are discussed and some recommendations are made for the direction of fhturestudies.8.2 On the Pullout Test8.2.1 Apparatus and InstrumentationA large pullout apparatus was designed and fabricated to accommodate a sand sampleof length 130 cm, width 64 cm, and height 60 cm. Pullout tests were performed on testspecimens 0.5 m wide.Important features of the apparatus and instrumentation scheme are summarizedbelow:• The pullout apparatus has rigid boundaries, with exception of the top where astress controlled boundary is used to apply normal stress to the sand sample. Thefront wall incorporates a slot, through which the test specimen is pulled.• A sophisticated electro-hydraulic servo-controlled system was developed forcontrolling either displacement or load imposed on the pullout test specimen.229Chapter 8. Summary and Conclusions• Instrumentation was used to measure normal stress, pullout force, displacementand strain along the length of the test specimen; and lateral stress on the front wallof the apparatus.• A vertical array of pressure transducers on the centerline of the front wall revealeda distribution of lateral stress (Aah) that was asymmetric about the slot. Anormalised stress ratio (AGh/’tav) is developed that is independent of specimen typeand normal stress.• A procedure for strain gauging the polymeric test specimens was adapted fromBathurst (1990): a two part epoxy coating was used on the Stratagrid andMiragrid to allow mounting of gauges on a plane surface.• The consistency of sample preparation and test routine is evident from thereproducibility of results of tests that were repeated.8.2.2 Materials and Test Procedure• An air-pluviation technique was used to place the uniformly-graded, medium sandsamples to relative density between 85 to 90%.• Pullout tests were performed on geosynthetic test specimens, and the resultscompared with the response of a rigid, Ihily rough sheet, The geosynthetic testspecimens comprised three types of geogrids, a smooth geomembrane and atextured geomembrane.230Chapter 8. Summary and Conclusions• Tests were performed in one of two modes. Displacement-controlled (DC) testswere performed at a constant rate of displacement (rd). Typically DC tests wereperformed at rd=O.5 mm/mm. No significant variation in pullout resistance wasobserved for 0,25< rd <1.0 mm/mm, Load-controlled tests were performed at aconstant rate of loading to a targeted value between 60 and 80% of the resistancemeasured in the corresponding DC test. Thereafter a sinusoidal variation of loadwas applied as a loading series comprising 10 cycles of constant amplitude andconstant frequency. The amplitude of loading was increased with each series ofloading.8.2.3 Test Results and Interpretation• Independent measurements of pullout force, and strain along the length of thegeosynthetic test specimen, reveal a response that is characterized by a varyingextent of progressive strain. It is important to the interpretation of a pullout testresults that a distinction be made between an extensible and inextensible behaviourof the test specimen. It has been shown that the extensible and inextensiblebehaviour of a geosynthetic specimen is dependent on the magnitude of normalstress. This has implications for use of a particular method of interpretation todeduce a value of interaction factor,• Progressive mobilization of pullout is described with respect to displacementscharacterized by three zones (d>0, deO; d >0, d de; d >0, d =de).231Chapter 8. Summary and Conclusions• A review of the present state of practice for interpretation of pullout test data hasindicated the total area method is applicable to an inextensible response only.Although the effective area method is better it fails to address the non-lineardistribution of tensile force that may develop in the test specimen. However, bothmethods give a similar value when the tensile force distribution is linear, which isthe case at large pullout displacement. The mobilizing process method (Ochiai etal., 1992; Juran et al., 1991) accounts for a non-linear distribution of tensile forcealong the specimen during pullout. A generalized method is proposed, that unifiesaspects of the mobilizing process method and effective area method, and is testedagainst the laboratory data.• Geogrids are seen to develop a relationship between pullout resistance anddisplacement that is very similar in shape to that for the textured geomembrane,but not the smooth geomembrane, with no distinct peak value of pulloutresistance. The relationship between average shear stress and normal stress showsall three geogrids to be less efficient than the equivalent fully rough sheet.• Good agreement is observed when the variation of interaction factor withdisplacement for the Tensar grid and Stratagrid is compared with results publishedby Palmeira (1987) and Farrag et al. (1993). The comparison suggests theconfiguration of the apparatus does not influence significantly the measuredpullout resistance at relatively low values of nonnal stresses. Further, therelationship between interaction factor and angle of friction is seen to comparewell with upper bound values reported for various studies on grid specimens.232Chapter 8. Summary and ConclusionsA conceptual model is proposed that links a load ratio to stable and unstable behaviourin cyclic pullout, and identifies a threshold load ratio above which an unstable behaviourresults.8.3 Implications for Selection of a Pullout Interaction Factor in Design• Values of interaction factor for the three geogrids deduced from pullout testingwere compared with theoretical values. In all cases values of the stress ratio(a1,/) inferred by the laboratory pullout data exceed the default value of aiJa=20 recommended by USFHWA for use in the absence of specific test data. Itwould appear the USFHWA approach is conservative but not overly so.• Comparison of the laboratory data with field data from an instrumented slopedreinforced soil wall indicate mobilized values of interaction factor in the fieldstructure which correspond to a value mobilized in the pullout test at very smalldisplacements, d < 1 mm. This value at small displacement is associated withvery small strains, less than 0.5%, which lie within acceptable limits of existingcodes of practice incorporating permissible strains.• In design of a structure to resist dynamic loads the USFHWA approach(Christopher et al., 1990) recommends the interaction factor be taken as 80% ofthat used for static design. Results of the cyclic pullout tests performed in thisstudy would suggest the interaction factor is higher than or equal to theinteraction factor from corresponding displacement-controlled tests. This implies233Chapter 8. Summary and Conclusionsthat using a reduced value of interaction factor for dynamic loads is inappropriate,in that it does not properly describe the mobilized response.• A seismic event is associated with both horizontal and vertical accelerations.Vertical acceleration leads to the normal stress at the interface increasing anddecreasing in a cyclic manner during the event, which may adversely influence thebehaviour of a reinforced soil structure. The effect of a decrease in normal stressand simultaneous increase in horizontal thrust is to promote a pullout type offailure. Therefore, in design it would be more appropriate to use a reducednormal stress to account for the variation of imposed loading during the seismicevent.8.4 Recommendations for Future StudiesSpecifications are being developed for the pullout test apparatus and astandardized test method which will govern tests performed at a constant rate ofdisplacement. The following issues pertain to this ongoing development, and to theinterpretation of pullout test data.• To further evaluate the influence of a rigid front wall on measured pulloutresistance, tests should be performed with a stress-controlled boundary on thefront wall of the apparatus.• Direct measurement of the normal stress acting at the soil-specimen interface,using pressure cells embedded in the soil sample, is desirable to assess anyinfluence of boundary friction.234Chapter 8. Summary and Conclusions• The mechanism of pullout resistance involved in grids will vary with particle size.Use of different soils to study the influence of particle size and soil gradation, andinterlocking within the grids, is important to describe the behaviour of soils usedin construction.• Direct measurement of load at sections along the test specimen using profile-typeload cells will define more accurately the shape of the tensile force distribution. Inconjunction with the load measurement, measurement of strain will providespecific values for confined stress-strain properties of extensible test specimens.• In cyclic loading, the selection of loading rate is important to obtain a comparableresponse in initial phase of load-controlled test. Test specimens should be loadedmonotonically to a desired level before applying any series of cyclic loads, and theamplitude of loading should be selected to narrowly bound the pullout resistanceestablished from displacement-controlled test.235BIBLIOGRAPHYAl-Ashou, M. 0., and Hanna, T. H. (1990), “Deterioration of Reinforced Earth Elements undercyclic loading,” Performance of reinforced soil structures: Proceedings of theInternational Reinforced Soil Conference, edited by A. MeGown, K. Yeo and K. Z.Andrawes, pp. 303-307, published by the British Geotechnical Society, 1990.ASTM D4253-93. Standard Test Methods for Maximum Index Density and Unit Weight ofSoils Using a Vibratory Table. 1993 Annual book ofASTM Standards. Vol. 04.08, pp.661-673.ASTM D4254-91. Standard Test Method for Minimum Index Density and Unit Weight of Soilsand Calculation of Relative Density. 1993 Annual book ofASTM Standards. Vol. 04.08,pp. 674-681.ASTM D5321-92. Standard Test Method for Determining the Coefficient of Soil andGeosynthetic or Geosynthetic and Geosynthetic Friction by the Direct Shear Method.1993 Annual bookofASTM Standards. Vol. 04.08, pp. 1380-1384.Bathurst, R. J. (1990), “Instrumentation of Geogrid Reinforced Soil Walls,” PrivateCommunication.Bathurst, R. J. (1991), “Case Study of a Monitored Propped Panel Wall,” Proceedings of theInternatinal Symposium on Geosynthetic Reinforced Soil Retaining Walls, held atDenver, Colorado, 8-9 August 1991, edited by J. T. H. Wu, published by A. A. Balkema,Rotterdam, 1992.Bathurst, R. J., and Simac, M. R. (1993), “Two Computer Programs for the Design and Analysisof Geosynthetic-Reinforced Soil-Retaining Walls,” Geotextiles and Geomembranes,Elsevier, Vol. 12, pp. 381-396.Bauer, G. B., Halim A. 0. A., and Shang, Q. (1991), “Large Scale Pullout Tests: Assesment ofProcedure and Results,” Proceedings of the Geosynthetics ‘91, Atlanta, Georgia,Industrial Fabrics Association International, February 1991, Vol. 2, pp. 6 15-627.Bergado, D. T., Bukkanasuta, A., and Balasubramaniam, A. S. (1987), “Laboratory Pull OutTests Using Bamboo and Polymer Geogrids Including a Case Study,” Geotextiles andGeomembranes, Elsevier, Vol. 5, No. 3, pp.153-89.Bergado, D. T., Lo, K. H., Chai, J. C., Shivashankar, R., Alfaro, M. C., and Anderson, L. R.(1992), “Pullout Tests Using Steel Grid Reinforcements with Low-quality Backfill,”Journal of GeotechnicalEngineering, ASCE, Vol. 118, No. 7, pp. 1047-1063.236BibliographyBolton, M. D. (1990), “Reinforced Soil: Laboratory Testing and Modelling,” Performance ofReinforced Soil Structures: Proceedings of the International Reinforced SoilConference, edited by A. McGown, K. Yeo and K. Z. Andrawes, pp. 287-298, publishedby the British Geotechnical Society, 1990.Bolton, M. D. (1986), “The Strength and Dilatancy of Sands,” Geotechnique, Vol. 36, No.1, pp.65-78Bonaparte, R., Schmertmann, G. R., and Williams, N. D. (1986), “Seismic Design of SlopesReinforced with Geogrids and Geotextiles,” Proceedings of the 3 InternationalConference on Geotextiles, Vienna, Austria, International Geotextile Society, Vol. 1, pp.273-278.Bonaparte, R., Holtz, R. D., and Giroud, J. P. (1987), “Soil Reinforcement Design UsingGeotextiles and Geogrids,” Geotextile Testing and the Design Engineer, ASTM STP952, ed. J. E. Fluet, Jr. American Society for Testing and Materials, Philadelphia, PA,, pp.69-116.Bonczkiewicz, C., Christopher, B. R., and Atmazidis, D. K. (1986), “Evaluation of Soil-Reinforcement Interaction by Large-Scale Pull-out Tests,” Transportation ResearchRecord 1188, Washington, D.C., pp. 1-18.Bonczkiewicz, C., Christopher, B. R., and Simac M. (1991), “Load Distribution in GeogridsWith Low Junction Efficiency,” Proceedings of the Geosynthetics ‘91, Atlanta, Georgia,Industrial Fabrics Association International, February 1991, Vol. 2, pp. 643-652.Brown I. E. W., and Rochester, T. A., (1979), “Reinforced Earth - Technical Guidance Providedby the Department of Transport, England,” Proceedings of the Internatinal Conferenceon Soil Reinforcement, Paris, Vol. 2, pp. 423-430.C.G.S., (1992). Canadian Foundation Engineering Manual. Third edition, CanadianGeotechnical Society, Technical Committee on Foundations. BiTech Publishers Ltd,Richmond, B.C., 5l2p.Chalaturnyk, R. J., Scott, J. D., Chan, D. H. K., and Richards, E. A. (1990). “Stresses andDeformations in a Reinforced Soil Slope.” Canadian Geotechnical Journal, Vol. 27, pp.224-234.Chan, D. H., Yi, C. T., and Scott, J. D. (1993), “An Interpretation of the Pull-out Test,Proceedings of the ‘93 Geosynthetics Conference, Vancouver, Canada, Industrial FabricsAssociation International, April 93, Vol. 2, pp. 593-604.237BibliographyChang, J. C., Hannon, J. B., and Forsyth, R. A. (1977), “Pull-out Resistance and Interaction ofEarthwork Reinforcement and Soil,” Transportation Research Record 640, Washington,D.C., pp. 1-7.Christopher, B. R., Gill, S. A., Giroud, J. P., Juran, I., Mitchell, J. K., Schlosser, F. andDunnicliff, J., (1990), “Design and Construction Guidelines for Reinforced SoilStructures - Volume I,” and “Summary of Research - Volume II,” Report No. FHWARD-89-043, Federal Highway Administration, U.S Department of Transportation.Claybourn, A. F., and Wu, J. T. H. (1993), “Geosynthetic-Reinforced Soil Wall Design,”Geotextiles and Geomembranes, Elsevier, Vol. 12, 707-724.Collin, J. 0., Chouery-Curtis, V. E., and Berg, R. R. (1992), “Field observations of reinforcedsoil structures under seismic loading.” Proceedings of the International GeotechnicalSymposium on Earth Reinforcement Practice, edited by Ochiai, Hayashi & Otani,Balkema, Rotterdam, pp. 223-228.Costalonga M. A. R. (1988), “Geogrid Pull-out Tests in Clay,” The University ofAlberta, thesissubmitted in partialfulfillmentfor the degree ofM Sc.Cowell, M. J., and Sprague, C. J. (1993), “Comparison of Pull-out Performance of Geogrids andGeotextiles, “ Proceedings of the Geosynthetics ‘93, Vancouver, Canada, IndustrialFabrics Association International, April 93, Vol. 2, pp. 579-59 1.Deutsch Jr. W. L. (1993), “Strain Compatibility Considerations and Tensioning Analysis forGeosynthetic Lining Systems,” Proceedings of the Geosynthetics ‘93, Vancouver,Canada, Industrial Fabrics Association International, April 93, Vol 2, 703-7 18.Eigenbrod, K. D., and Locker, J. G. (1987), “Determination of Friction Values for the Design ofSide Slopes Lined or Protected With Geosynthetics,” Canadian Geotechnical Journal,Vol. 24, pp. 509-5 19.Eigenbrod, K. D., Burak, J. P., and Locker, J. G. (1990), “Differential Shear Movements at SoilGeotextile Interfaces,” Canadian Geotechnical Journal, Vol. 27, pp.520-6.Fannin, R. J., and Hermann, S. (1990), “Performance data for a Sloped Reinforced Soil Wall,”Canadian Geotechnical Journal, Vol. 27, pp. 676-686.Fannin, R. J. (1990), “Geosynthetics for Containment of Special Waste,” Proceedings of the 5thAnnual Symposium: Geotechnical Aspects of Contaminated sites, Vancouver, TheVancouver Geotechnical Society, May 25th 1990.238BibliographyFannin, R. J., and Raju, D. M. (1991), “Pullout Resistance of Geosynthetics,” Proceedings 44thCanadian Geotechnical Conference, Calgary, Vol. 2, October, 1991.Fannin, R. J., and Raju, D. M. (1993), “Large Scale Pull-Out Test Results on Geosynthetics,”Proceedings of the Geosynthetics ‘93, Vancouver, Industrial Fabrics AssociationInternational, March 1993, Vol. 2, PP. 633-643.Fannin, R. J., and Raju, D. M. (1993), “On the Pullout Resistance of Geosynthetics,” CanadianGeotechnical Journal, Vol. 30, June 1993.Fannin, R. J., Hermann, S., Vaslestad, J., and Raju, D. M. (1994), “Coefficients of InterfaceBond in Reinforced Soil Structures.” Proceedings of the 13th International Conferenceon Soil Mechanics and Foundation Engineering, New Delhi, India.Farrag, K. H., Acar, Y. A., and Juran, I. (1993), “Pullout Testing of Geogrids,” Geotextiles andGeomembranes, Elsevier, Vol. 12, pp. 132-158.Hanna, T. H., Sivapalan, E. and Senturk, A. (1978), “The Behaviour of Dead Anchors Subjectedto Repeated and Alternating loads,” Ground Engineering, Vol. 11, No. 3, pp. 28-34.Hanna, T. H., and Touhamia, M., (1991), “Comparative Behaviour of Metal and Tensar GeogridStrips Under Static and Repeated Loading, “ Proceedings of the Geosynthetics ‘91,Atlanta, Georgia, Industrial Fabrics Association International, February 1991, Vol. 2, pp.575-585.Handel, E., Schweiger, H. F., and Yeo, K. C. (1990), “A Simple Thin-layer Element to ModelSoil-Geotextile Interaction, “Performance of reinforced soil structures: Proceedings ofthe International Reinforced Soil Conference, edited by Alan McGown, Khen Yeo andK. Z. Andrawes, Pp. 317-321, published by the British Geotechnical Society, 1990.Hryciw, R. D. and Irsyam, M. (1993), “Behaviour of Sand Particles Around Rigid RibbedInclusions During Shear,” Soils andFoundations, Vol. 33, No. 3, pp. 1-13.Jewell, R. A., Milligan, G. W. E., Sarsby, R. W. and Dubois, D. D. (1984), “Interaction BetweenSoil and Geogrids,” Proceedingsfrom the Symposium on Polymer Grid reinforcement incivil engineering, pp. 18-30, London, England, Thomas Telford.Jewell, R. A. (1985), “Material Properties for the Design of Geotextile Reinforced Slopes,”Geotextiles and Geomembranes, Elsevier,Vol. 4, No. 2, pp. 83-109.Jewell, R. A., and Wroth, C. P. (1987), “Direct Shear Tests on Reinforced Sand,” Geotechnique,Vol. 37, No.1, PP. 53-68.239BibliographyJewell, R. A., and Greenwood, J. H. (1988), “Long Term Strength and Safety in Steep SoilSlopes Reinforced by Polymer Materials,” Geotextiles and Geomembranes, Elsevier, Vol.7, No. 1, pp. 81-118.Jewel!, R. A. (1990), “Reinforcement Bond Capacity,” Technical note, Geotechnique, Vol. 40,No.3, 5 13-518.Johnston, R. S. (1985), “Pullout Testing of Tensar Geogrids,” University of Cahfornia at Davis,Calfornia, thesis submitted in partialfulfillment ofMS degree.Juran, I., and Chen, C. L. (1987), “Soil-geotextile Pullout Interaction Properties: Testing andInterpretation,” Transportation Research Record 1188, Washington, D.C., pp. 37-47.Juran, I., Knochenmus, G., Acar, Y. B., and Arman, A. (1988), “Pull-out Response ofGeotextiles and Geogrids (Synthesis of Available Experimental Data),” Proceedings ofthe Symposium on Geosynthetics for Soil Improvement, Tennessee, May 1988; (editedby R. D. Holtz.), ASCE, pp. 92-111.Juran, I., Ider, H. M. and Farrag, K. H. (1990), “Strain Compatibility Analysis for GeosyntheticsReinforced Soil Walls,” Journal of Geotechnical Engineering, ASCE, Vol. 116, No. 2,pp. 3 12-329.Juran, I., Farrag, K. H., and Richmond, L. (1991), “Short and Long Term Performance ofPolymeric Geogrids,” Proceedings of the Geosynthetics ‘91, Industrial FabricsAssociation International, Atlanta, Georgia, February 1991, Vol. 2, pp. 587-599.Kharchafi, M. and Dysli, M. (1993), “Study of Soil-Geotextile Interaction by an X-Ray Method,”Geotextiles and Geomembranes, Elsevier, Vol. 12, pp. 3 07-325.Koerner, R. M., Hsuan, Y., and Lord Jr., A. E. (1993), “Remaining Technical Barriers toObtaining General Acceptance of Geosynthetics,” Geotextiles and Geomembranes,Elsevier, Vol. 12, pp. 1-52.Kutara, K., Aoyama, N., Yasunaga, H., and Kato, T. (1988), “Long-term Pull-out Tests ofPolymer grids in Sand,” International Geotechnical Symposium on Theory and PracticeofEarth Reinforcement, Fukoka, Japan, 5-7 October, Balkema, Rotterdam, pp. 117-122.Lentz, R. W., and Pyatt, J. N. (1987), “Pull-out Resistance of Geogrids in Sand,”Transportation Research Record 1188, Washington, D.C., pp. 48-55.240BibliographyLeschchinsky, D., and Perry, E. B. (1987), “A Design Procedure for Geotextile-Reinforcedwalls,” Proceedings of the Geosynthetics ‘87, New Orleans, Industrial FabricsAssociation International, Vol. 1, PP. 95-107.Martin, J. P., Koerner, R. M., and Whitty, J. E. (1984), “Experimental Friction Evaluation ofSlippage Between Geomembranes, Geotextiles and Soils,” International Conference onGeomembranes, Denver, U.S.A. pp. 19 1-196.McGown, A., Andrawes, K. Z., and Al Hasani, M. M. (1978), “Effect of Inclusion Properties onthe Behaviour of Sands,” Geotechnique, Vol. 28, No. 3, pp. 327-346,McGown, A., Andrawes, K. Z., Yeo, K. C., and Dubois, D. (1984) “The Load-Strain-Timebehaviour of Tensar Geogrids,” Proceedings from the Symposium on Polymer Gridreinforcement in civil engineering, London, England, Thomas Telford.McGown, A., Yeo, K. C., and Yogarajah, I. (1990). “Identification of a Dynamic InterlockMechanism,” Performance ofreinforced soil structures: Proceedings of the InternationalReinforced Soil Conference, edited by A. McGown, K. Yeo and K. Z. Andrawes,published by the British Geotechnical Society, 1990.McGown, A., Yogarajah, I., and Yeo, K. C. (1992), “The instrumentation and measurementperformance of synthetic polymers in reinforced soil structures,” Proceedings of theInternational Geotechnical Symposium on Earth Reinforcement Practice, edited byOchiai, Hayashi and Otani, Balkema, Rotterdam, pp. 115-120.Milligan, G. W. E., and Palmeira, E. P. (1987), “Prediction of Bond between Soil andReinforcement,” Prediction and Performance in Geotechnical Engineering, Calgary,June 1987, pp. 147-153.Mitchell R. A., and Mitchell J. K. (1992), “Stability Analysis of Waste Landfills,” Proc. ASCESpecialty Conference on Stability and Performance of Slopes and Embankments-II,Geotechnical Special Publication, No.31, edited by R. B. Seed and R. W. Boulanger, pp.1152-1187.Murray, R. T., and Bolden, J. B. (1979), “Reinforced Earth Wall Constructed with CohesiveFill,” Proceedings of the 31d1 International Conference on Geotextiles, Vienna,International Geotextile Society, Vol. 3, pp. 70 1-706.Murray, R. T., Carder, D. R., and Krawczyk, J. V. (1980), “Pullout Tests on ReinforcementEmbedded in Uniformly Graded Sand Subject to Vibration,” Proceedings of the 7th1European Conference on Soil Mechanics and Foundation Enginerring, Brighton, Vol.3,pp. 115-120.241BibliographyNegussey, D., Wijewickreme, W. K. D., and Vaid, Y. P., (1989), “Geomembrane InterfaceFriction,” Canadian Geotechnical Journal, Vol. 26, PP. 165-169.Nimmesgern, M., and Bush, D. (1991), “The Effect of Repeated Traffic Loading onGeosynthetic Reinforcement Anchorage Resistance,” Proceedings of the Geosynthetics‘91, Atlanta, Georgia, Industrial Fabrics Association International, Vol. 2, pp. 665-672.Ochiai, H., Hayashi, S., Otani, J., Umezaki, T., and Ogisako, E. (1988), “Evaluation of Pull-OutResistance of Geogrid Reinforced Soils,” Proceedings of the International GeotechnicalSymposium on Theory and Practice of Earth Reinforcement, Kyushu, Balkema,Rotterdam, pp. 577-582.Ochiai, H., Hayashi, S., Otani, J., and Hirai, T. (1992), “Evaluation of pull-out resistance ofgeogrid reinforced soils, “Proceedings of the International Geotechnical Symposium onEarth Reinforcement Practice, edited by Ochiai, Hayashi and Otani, Balkema,Rotterdam, pp. 141-146.O’Rourke, T. D., Druschel, S. J., and Netravali, A. N. (1990), “Shear Strength Characteristics ofSand-Polymer Interfaces,” Journal of Geotechnical Engineering, ASCE, Vol. 116, No.3, pp. 45 1-469.Palmeira, E. M. (1987), “The Study of Soil-Reinforcement Interaction by means of Large ScaleLaboratory Tests,” University of Oxford, thesis submitted in partial fulfillment for thePh.D. degree,Palmeira, E. M., and Milligan, G. W. E. (1989), “Scale and Other Factors Affecting the ResultsofPull-out Tests of Grids Buried in Sand,” Geotechnique, Vol. 39, No. 3, pp. 511-524.Raju, D. M. (1991), “Large Scale Pullout Testing of Geosynthetics,” The University of BritishColumbia, thesis submitted in partialfulfilment ofrequirementsfor MA. Sc degree.Richardson, G. N., and Lee, K. L. (1975), “Seismic Design of Reinforced Earth Walls,” Journalof Geotechnical Engineering, ASCE, Vol. 101, No. GT2, pp. 167-187.Richardson, G. N., Feger, D., Fong, A., and Lee, K. (1977), “Seismic Testing of ReinforcedEarth Walls,” Journal of Geotechnical Engineering Division, ASCE, Vol. 103, GT1 1,pp. 1-17.Richards Jr. R., and Elms, D. G. (1979), “Seismic Behaviour of Gravity Retaining Walls,”Journal of Geotechnical Engineering, ASCE, Vol. 105, No.4, pp. 449-464.242BibliographyRichards Jr. R., and Elms, D. G. (1992), “Seisimic Passive Resistance of Tied-back Walls.”Journal of Geotechnical Engineering, ASCE Vol.118. No. 7, pp. 996-1011.Rinne, N. (1989), “Evaluation of Interface Friction Between Cohesionless Soil and CommonConstruction Materials,” The University ofBritish Columbia, thesis submitted in partialfulfilment ofrequirementsfor MA.Sc degree.Schlosser, F., (1978), “History, Current and Future Developments of Reinforced Earth,”Proceedings of the Symposium on Soil Reinforcing and Stabilising Techniques, N. S.W.Institute of Technology, pp. 5-28.Schmertmann, G. R., Chourey-curtis, V. E., Johnson, R. D., and Bonaparte, R. (1987), “Designcharts for geogrid-reinforced soil slopes,” Proceedings of the Geosynthetics ‘87, NewOrleans, Industrial Fabrics Association International, Vol. 1, pp. 108-120.Schneider, H. R., and Holtz, R. D. (1986), “Design of Slopes Reinforced with Geotextiles andGeogrids,” Geotextiles and Geomembranes, Elsevier, Vol. 4, pp. 29-51.Seed, R. B., Ivlitchell, J. K., and Seed, H. B. (1990), “Kettleman Hills Waste Landfill SlopeFailure. II: Stability Analyses,” Journal of Geotechnical Engineering, ASCE, Vol. 116,No.4, pp. 686-693.Segrestin, P., and Bastick, M. (1988), “Seismic design of Reinforced Earth retaining walls-Thecontribution of finite element analysis,” Proceedings of the International GeotechnicalSymposium on Theory and Practice of Earth Reinforcement, Kyushu, Balkema,Rotterdam, pp. 577-582.Sluimer, G., and Risseeuw, P. (1982), “A Strain Gauge Technique for Measuring Deformationsin Geotextiles,” Proceedings of the 2nd International Conference on Geotextiles, LasVegas, U. S.A, International Geotextile Society, Vol. 3, pp. 835-838.Sommers and Wolfe, (1984), “Earthquake Induced Responses of Model Retaining Walls,”Proceedings of the World Conference on Earthquake Engineering, San Francisco,Vol. 3, pp. 5 17-524.Srinivasa Murthy, B. R., Sridharan, A., and Bindumadhava. (1993), “Evaluation of InterfacialFrictional Resistance,” Geotextiles and Geomembranes, Elsevier, Vol. 12, pp. 235-253.Sweeney, B. P., and Clough, G. W. (1990), “Design of a Large Calibration Chamber,”Geotechnical Testing Journal, ASTM, Vol. 13, No.1, pp. 36-44.243BibliographySwinianski, J., and Sawicki, A. (1991), “A Model of Soil-Pile Interaction Owing to CyclicLoading.” Canadian Geotechnical Journal, Vol. 28, PP. 11-19.Takasumi, D. L., Green, K. R., and Holtz, R. D. (1991), “Soil-Geosynthetic Interface StrengthCharacteristics: A Review of State-of-the Art Testing Procedures,” Proceedings of theGeosynthetics ‘9], Atlanta, Georgia, Industrial Fabrics Association International,February 1991, Vol. 1, pp. 87-100.Turner, J. P., and Kulhawy, F. H. (1990), “Drained Uplift Capacity of Drilled Shafts UnderRepeated Axial Loading,” Journal of the Geotechnical Engineering, ASCE, Vol. 116,No. 3, pp. 470-491.Udwari, J., and Kittridge, J. (1986), “Designing of Double Lined Impoundments-LessonsLearned,” Proceedings of the 31 International Conference on Geotextiles, Vienna,Austria, International Geotextile Society, Vol. 3, pp. 929-934.UK Department of Transport (1988), “Performance of A Reinforced Earth Bridge Abutment AtStirling,” Transport And Road Research Laboratory, Research Report No. 128.U. S. EPA Report No. 530-SW-85-014, 1985. Minimum technology guidance on double linersystems for landfills and surface impoundments-design, construction and installation.Washington, DC.Vaid, Y. P., and Negussey, D. (1988), “Preparation of Reconstituted Sand Specimens,”Advanced Triaxial Testing of Soil and Rock, ASTM STP 977, American Society forTesting and Materials, Philadelphia, pp. 405-417.Vesic, A. S., Banks, D. C., and Woodward, J. M. (1965), “An Experimental Study of DynamicBearing Capacity of Footings on Sand,” Proceedings of the 6thi International Conferenceon Soil Mechanics and Foundation Engineering, Vol. 1, Pp.209-4.White, D. M., and Holtz, R. D. (1992), “Seismic Analysis of Reinforced Slopes- A Review.”International geotechnical symposium on Earth Reinforcement Practice, edited byOchiai, Hayashi & Otani, Balkema, Rotterdam, PP. 311-316.Weiler, W. A., and Kuihawy, F. H. (1982), “Factors Affecting Stress Cell Measurements in Soil,”Journal of the Geotechnical Engineering Division, ASCE, Vol. 108, No. GT12. pp.1529-1548.Wilson-Fabmy, R, F., and Koerner, R. M. (1993), “Finite Element Modelling of Soil-GeogridInteraction with Application to the Behaviour of Geogrids in a Pullout LoadingCondition,” Geotextiles and Geomembranes, Elsevier, Vol. 12, pp. 479-501.244BibliographyWilson-Fahmy, R. F., and Koerner, R. M., and Sansone, L. J. (1994), “Experimental Behaviourof Polymeric Geogrids in Pullout,” Journal of the Geotechnical Engineering Division,ASCE, Vol. 120, No. 4, pp. 66 1-667.Yasuda, S., Nagase, H., and Marui, H. (1992), “Cyclic Pull-out Tests of Geogrids in Soils.”International Geotechnical Symposium on Earth Reinforcement Practice, edited byOchiai, Hayashi & Otani, Balkema, Rotterdam, pp. 185-190.Yegian, M. K., and Lahiaf, A. M. (1991), “Discussion on Kettleman Hills Waste Landfill SlopeFailure. I: Liner-System Properties,” Journal of Geotechnical Engineering, ASCE, Vol.117, pp. 643-645.Yegian, M. K., and Lahlaf, A. M. (1992), “Dynamic interface shear strength properties ofgeomembranes and geotextiles.” Journal of Geotechnical Engineering, ASCE, Vol.118,No.(5), pp. 760-779.Yogarajah, I., Yeo K. C. (1994), “Finite Element Modelling of Pull-Out Tests with Load andStrain Measurements,” Geotextiles and Geomembranes, Elsevier, Vol. 13, pp. 43-54.Yogendrakumar, M., Bathurst, R. J., and Finn, W. D. L. (1992), “Dynamic Response Analysis ofReinforced-Soil Retaining Wall.” Journal of Geotechnical Engineering, ASCE, Vol.118,No.2, pp. 1158-1167.245APPENDIX ATECHNIQUE OF STRAIN GAUGING PLASTICSA.1 IntroductionThe development of a strain gauging technique for plastics requires that considerationbe given to the mechanical, thermal and chemical properties of these polymeric materials.With regard to mechanical properties, plastics have a relatively low modulus of elasticity incomparison to metals. Consequently there is potential for large strain magnitudes, whichplaces a demand on the capacity for elongation of a strain gauge, the adhesive, and the wiringprocedures. In addition, any tendency of the strain gauge to impart an effect of localreinforcement to the test specimen must be recognized. With regard to thermal properties,polymeric materials have thermal coefficients approximately 5-10 times greater than those ofmetals and concrete. The thermal conductivity of plastics influences both the selection ofgauge size and excitation voltage to achieve an acceptable power dissipation per unit of gridarea; it also increases the difficulty of maintaining an active and dummy strain gauge at thesame temperature in a variable thermal environment. With regard to chemical properties, caremust be taken to avoid any reaction between the geosynthetic test specimen and thosechemicals used as cleaning solvents, adhesives, and protective coatings for the gauges.Consideration of these factors is important to the selection of a high-elongation straingauge for measuring relatively large strains, a suitable surface preparation technique for thetest specimen, compatible solvents and cleaning agents, and an adhesive to achieve a goodbond within an acceptable curing time.246Appendix AA.2 Characteristics of the Strain GaugeThe strain gauge selected for the program of laboratory testing is type EP-08-250BF-350 Option E, manufactured by the Micro-Measurements Division of Measurements GroupInc. It is selected for the following reasons:• the EP series gauges are made of a special annealed constantan foil with a toughhigh elongation polymide backing that offers high elongation capacity;• the geometry of the gauge, defined by the gauge pattern designation 250BF andreported in Table A- 1.1, fits well on the ribs of the geogrid test specimens;• a high resistance gauge minimizes heat dissipation, for which the 350 ohm isselected;• encapsulation of the gauge, the option E, protects the gauge circuit from damage byabrasion with the backfill sand.Table A-1.1: Dimensions of the strain gaugeGauge length Overall length Grid width Overall width Matrix size(mm) (mm) (mm) (mm) (mm)(LxW)6.35 9.53 3.18 3.18 13.2 x 5.6A.3 Strain Gauging ProcedureA.3.1 Chemicals for Surface PreparationA 1-1-1 Trichioro-ethylene solvent is used to degrease the surface of the test specimenbecause of its inertness to polyethylene. The degreaser prevents embedment of contaminantsin the surface of the geosynthetic specimen. A No. 400 grit paper is used to roughen the247Appendix Asurface for bonding. It is an important factor in getting a good bond between the polyamidebacking of the strain gauge and the polyethylene material. The surface is then neutralized witha mild ammonia solution, which leaves it with a slightly alkaline pH. Gauge installation isperformed within a few minutes of completing the surface conditioning.A.3.2 Adhesive Selection and PreparationM-Bond AE 10/15 adhesive was selected to obtain a high elongation capability. ResinAE (10 gram unit) with Curing Agent 10 will cure in 6 hours giving approximately 6%elongation capabilities. By extending the curing time from 24 to 48 hours at 24° C, a higherelongation capability of 10% may be obtained.A.3.3 Geosynthetic Surface PreparationSupplies required: 1-1-1 Trichioro-ethylene degreaser, No. 400 grit sand paper,gauze sponge, compressed air, cotton swab, and M-Prep neutralizer 5.Steps involved in surface preparation are:1. Trim the geosynthetic test specimen to the required dimensions. Secure it on cleanflat surface and mark the gauge locations. Precise alignment of the gauge with thedirection of loading is important for meaningful data. (For the Stratagrid andMiragrid specimens, an additional step was used to obtain a flat surface: the straingauge location was coated with two part 5 minute epoxy).2. Spray the gauge location with 1-1-1 Trichioro-ethylene degreaser and wipe cleanusing a gauze sponge.248Appendix A3. Use No. 400 grit sand paper to roughen up the surface, sanding first at a 450 angleto the direction of testing and then at right angles to get a pattern of cross hatches.Approximately 4 minutes of sanding is required.4. Using compressed air, clean the gauge location to remove any small particles.5. Neutralize the surface by wiping the location with M-Prep Neutralizer 5, a mildammonia solution, which leaves it with an alkaline pH.6. The gauge should be applied within 2 or 3 minutes of completing the surfacepreparation.A.3.4 Gauge PreparationSupplies required: Plexiglas frame (rectangular hollow), 1-1-1 Trichloro-ethylenedegreaser, tweezers, eraser, MGJ-2 tape, and strain gauges.Steps involved in the preparation are:1. Clean the plexiglas frame with the 1-1-1 Trichioro-ethylene degreaser, wiping witha gauze sponge.2. Take a small length of MJG-2 tape and tape it down on the plexiglas frame causingthe tape to be exposed at the hollow portion.3. Remove the strain gauge from its package, ensuring it is held on the edge usingtweezers.249Appendix A4. Place the gauge on to the exposed tape, aligning it parallel with the edge of thetape. Low air pressure from the compressed air supply is used to affix it firmly.5. The gauge is now ready for transfer to the geosynthetic test specimen.A.3.5 Application of the GaugeSupplies required: AE 10/15 adhesive kit, gauze sponge, TFE- 1 sheet, silicone pad,aluminum block, and MJG-2 tape.Steps involved in the adhesive preparation are:1. To prepare the adhesive mix, fill one of the calibrated droppers with Curing Agent10 exactly to the number 10 and dispense the contents into the jar of Resin AE.Immediately cap the bottle of Curing Agent to avoid moisture absorption.2. Thoroughly mix for 5 minutes using plastic stirring rods.3. The pot life or working time after mixing is 15 to 20 minutes. Perform applicationof the gauge within the working time.4. Discard the dropper, stirring rod and the adhesive mix after the gauge application.Steps involved in gauge application are:1. Lift the tape off the plexiglas frame along with the gauge and attach it to thegeosynthetic at the desired gauge location, aligning the gauge in the testingdirection. The tape on the side of the terminal should not be pressed firmly, but theopposite side should be.250Appendix A2. Peel back the tape from the terminal side at an acute angle so that the tape lifts offwith the gauge. Pull back the tape 3 mm further than the edge of the gauge.3. Apply two drops of prepared adhesive (M Bond AR 10) to the geosynthetic testspecimen at the gauge location and quickly lower the gauge to make contact.4. Using the gauze sponge, apply a uniform pressure to the gauge.5. Overlay the gauge with TFE-1 film, a silicone pad, and an aluminum block, andapply pressure using a dead weight to obtain a clamping pressure in the range 35to 135 kPa,6. Maintain the clamping pressure for 15 to 20 hours to obtain a reasonable elongationcapability.7. Carefully peel off the tape from the terminal side, pulling back at an angle of morethan 150°.8. The gauge is ready for soldering.A.3.6 Gauge SolderingSupplies required: Rosin solvent, 3-strand wires, and soldering accessoriesThe steps involved are:1. Cut the 3-strand wire into desired lengths, and pass it through the stiff plastictubing that is used to protect the wire from damage by the sand grains.2. Solder the ends of the wires and trim to leave 2mm exposed.251Appendix A3. Tape down the stiff tubing to the geosynthetic test specimen forming a loop ofexcess wire adjacent to the gauge.4. Brush the gauge surface with rosin solvent to remove dust particles.5. Using flux and solder, and taking care not to apply excess heat that will damage thetest specimen, quickly place solder on the tabs of the gauge.6. Solder the prepared wires to the solder on the gauge tabs.7. Check the resistance of the gauge and its connection using an ohm-meter.8. Clean the surface with rosin solvent to remove flux.9. The gauge assembly is now ready for protecting.A.3.7 Gauge ProtectionSupplies required: Cellophane tape, M-coat A, TEE-i and MJG-2tape.The steps involved are:i. Coat the gauge assembly with M-coat A, a polyurethane coating, placing threecoats at an interval of 30 minutes.2. Coat the exposed wires between the gauge and protective tubing as well.3, Cover the gauge assembly with TFE- 1 film, a Teflon film, and tape it down firmlyusing cellophane tape or MJG-2 tape.252Appendix AA.3.8 Analysis of Strain DataCorrections which are to be applied to the measured data are: transverse sensitivity;thermal output; gauge factor variation with temperature; Wheatstone bridge non-linearity; andgauge factor variation with strains. Considering all these factors, the measured percentagestrain in a full bridge circuit is related to the change in electrical output recorded, by thefollowing expression:F 4E*100 1%6=I I (Ad)[F + —2 *E(F + e)Jwhere:E0 is the output of the bridge in mV,E is the input to the bridge in mV, =5 000 mV,F is the gauge factor supplied by the manufacturer.253APPENDIX BRaw Data of Pullout Resistance and StrainIn this appendix, the data of pullout resistance and measured strain with pulloutdisplacement for some monotonic displacement-controlled tests are presented.15—_________1.0 —__________________________________________GTO4LmSO, xlL- 0.8 ———— 1-0.072- :—e- 2,0.08210 —: —9— 3, 0.410- 0.6 ——‘0’-— 4 0.576-: —V--5.0.744--- 0.4—o 5—’__0.2i-— 11111 ii I Ilii II 11111 11111 11111 0.0 — ill liii lii 11111 liii I II 1111111 liii0 102030405060708090100 0 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d (mm) Displacement of clamped end, d (mm)Figure B.1: Mobilization of pullout resistance and strain with pullout displacement for theTensar grid at a4 kPa15—____1.0—___ ___ ___ ___ ___ ___ __- GT1O GT1OL,4.965m- SG,xI1.Izt I0— 1111111111 III tIll 11111 liii 111111111 11111 liii 0.0 — lii liii jIll 11111 1111111 liii 111111111 I0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d0 (mm) Displacement of clamped end, d (mm)Figure B.2: Mobilization of pullout resistance and strain with pullout displacement for theTensar grid at GR=1O kPa254Appendix B15— GT1OS L.965m030 40 50 60 708090100Displacement of clamped end, d (mm) Displacement of clamped end, d (mm)Figure B.3: Mobilization of pullout resistance and strain with pullout displacement for theTensar grid ata1=1O kPa: smooth arborite front boundary15- GTO4N1 0GTO4N___________L,=a.965 m-- SG,xJL- 0.8— •—€— i,o.osE - : —s—. 2,0.24010 — ‘—a--— 3,0.410- 0.6 — —a-— 4,0.576-_Z5,744! 0.4—- 0.20—1111H H 00—_______________________________________0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d (mm) Displacement of clamped end, d0 (mm)Figure B.4: Mobilisation of pullout resistance and strain with pullout displacement for theTensar grid without bearing elements at a4 kPa255Appendix B15_________1.0 —_____________________________________________GT1ON I GTION I___ ___I L=0.965 m II SG,xil., I0.8— —e— 1,0.082—H— 2,0.2401—.—--— 3,0.4101—‘G—— 4,0.576 I—— 5,0.744(00.4 —-o.9 5—-50.2 —0— 0.0II I11111111II liii 11111111111 111 111111 I II 1111111111111111 1111111 I I 11111 1111111111110 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d (mm) Displacement of clamped end, d (mm)Figure B.5: Mobilisation of pullout resistance and strain with pullout displacement for theTensar grid without bearing elements at 011=10 kPaIS— 1.4 —_____________________________________________GT17N - I GTI7N I- I L,=0.965 m I0 1,0.0821.0 I—a— 2,0.2401I —k-— 3,0.410110-0.8I—G—— 4,0.57604C)C—v— 5,0.744CO (5Cl) 0612 SGXII..9.2 —— 0.0 —- 11111111111111111111111111111 II 11111111111 liii1111111111 111111111111111! 1111111111111 111111 II0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d (mm) Displacement of clamped end, d (mm)Figure B.6: Mobilisation of pullout resistance and strain with pullout displacement for theTensar grid without bearing elements at o=17 kPa256Appendix B30—____________1.4 —___________—— 01200025GT20D025 : L,,=0.965m- SG,xIL- 1.2 ——e--— 1,0.06220 — —.•-— 3,0.410—e—— 4,0.576080 5,0.744•1 / —s--- 2,0.24015E 25 10•1(Uc) 06.010 0.4—0H 0.2 —011111111111 III 11111111111 I 11111111111 II liii00 III 1W II 11111111111 1111111 I 11111111111 III0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d0 (mm) Displacement of clamped end, d (mm)Figure B.7: Mobilisation of pullout resistance and strain with pullout displacement for theTensar grid without bearing elements at a=2O kPa and rd=O.25 mm/mm30— 2.0___ _I GT2ODO5OI GT2ODO5O : L,0.gOSmI 1.8 — SO, xJL25 —1.6——e—— 1,0.082—6— 2,0.2401.4—20 —k—— 3,0.410—.—-- 4 057612 —CC15 — 1.0 _:0.6 -0.810a0.45 -0.2-0— 1111UH 000 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d (mm) Displacement of clamped end, d (mm)Figure B.8: Mobilisation of pullout resistance and strain with pullout displacement for theTensar grid without bearing elements at a=2O kPa and rd=O.SO mm/mm257Appendix B30 —______________________________________________________________- 2.0 —_ _ __ _ __ _18— LO.965m-- SG,Xll.e25 —1.6— —0— Qn9—— 2,0.2401.4—20——k—— 3,0.4101.2——0—— 4,0.576a -C) -I GT2ODIOC) EC -(9_c15 —‘a -0_0.8 —.2 10 —.50.2rIppIII1IIIJl rIIJI Hn0.4-5—0.0 _:_ _ __ ___ __ _— I 11111111111111 III 11111111111 I 1111111111 liii0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d (mm) Displacement of clamped end, d (mm)Figure B.9: Mobilisation of pullout resistance and strain with pullout displacement for theTensar grid without bearing elements at a=2O kPa and rd=l.OO mm/mm25 — 2.0 —GSI 7 I L1 = 0.97Gm I_1.8— I SC XJIejI 020 — 1.6 —2.OiOI12:3.O33I4.057815.02a 15 —C)- 03C‘a0.8—10 —00.2.2-.5. 1.0 -E:5— 0.0 III liii 1111 1W IHI 11WI I I I I0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100Displacement of clamped end, d (mm) Displacement of clamped end, d (mm)Figure B.1O: Mobilisation of pullout resistance and strain with pullout displacement for theStratagrid without bearing elements at a=17 kPaThe displacement response of cyclic pullout tests which are not shown in the mainbody of the thesis are presented below.258Appendix BFigure B.11: Relationship between Ad and Ade for Tensar grid ata11=4 and 17 kPa25915cn 10(U0‘Saz50‘5— 10.SQF 30(U(U(U 40Los(U.0C 0) 5060— GTO4,0.OlHz— LR——•— 0.66:: —A—- 0.60—:4:: —_-0.74——•---0.79——e— 0.85———zes-— 1.02r15us 100‘S0z50‘5— 102030t os(U V(U 40LwosbE& w60— GT17,0.OlHz!‘\LR-— 4r 1.01— —•---1.08‘ I I I ‘ I I0 10 20 30 40 50Incremental displacement ofclamped end, Adc (mm)60 0I I I I ‘ I I I10 20 30 40 50Incremental displacement ofclamped end, Adc (mm)60Appendix B10 —a)() ——0 —Z10 —U)C) ——0 —ZFigure B.12: Relationship between Ad. and Ad for Stratagnd at a=4 and 17 kPa15 15LR GS17, 0.01Hz—•— 0.66—A—- 0.75—•—0.84—•——0.93—0—— 0.975—A--— 1.02—E—— 1.04GSO4, 0.01 HzLR-•- 0.66I--0.75 II 0.84 II-•- 0.93 I--0.975‘5—.EU)(0’10. -.iQ. U)(U.U)0EwU) .00—10 —20 —30 —40 —50 —60 —70 —80 —90 —100 —010(1) 20U)30D )D 40. U)U) a50CU)— 6070*11111111 I’l’ I ‘I0 10 20 30 40 50 60 70 80 90 100Incremental displacement ofclamped end, A dc (mm)0 10 20 30 40 50 60 70Incremental displacement ofclamped end, A dc (mm)260

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