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UBC Theses and Dissertations

The development of a fibreglass cable bolt Mah, G. Peter 1994

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THE DEVELOPMENT OF A FIBREGLASS CABLE BOLTByG. Peter MahB. A. Sc., The University of British Columbia, 1990A THESIS SUBMITTED IN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFMASTER OF APPLIED SCIENCEinTHE FACULTY OF GRADUATE STUDIES(Mining and Mineral Process Engineering)(Rock Mechanics)We accept this. thesis as conformingto the required standardTHE UNIVERSITY OF BRITIS OLUMBIAMarch, 1994© G. Peter Mah, 1994in 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 arid 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 4 A/va tIN4 LThe University of British ColumbiaVancouver, CanadaDate/t41/////42.DE6 (2188)ABSTRACTThe development ofafibreglass cable bolt (FCB) as an alternative to steel cable boltshas been presented. The primary objective of the investigation was to develop a working FCBprototype that was cuttable and easily installed in hard rock mines. The FCB was required tobe cuttable by a continuous road-header without adverse affects to equipment, personnel orprocessing circuits. POLYSTAL, an advanced composite with a circularprofile, has been usedto develop the workingprototype. The methods of investigation, included: over seventy-five(75) laboratory and in situ pull-tests, five (5) preliminary laboratory shear tests, two (2) trial insitu installations and three (3) preliminaryflotation tests. Conclusions have been drawnregarding the selection ofa cuttable material, failure modes and mechanisms, axial and shearload/displacement behaviours, immediate andpotential applications, design guidelines, mineralprocessing effects, installation costs andfuture research directions. In general, it has beenproven that the FCB exists as a viable alternative to steelfor cable bolt reinforcement.However, the FCB does not currently exist as an optimized, or only, composite supportalternative to steel. These aspects remain outstanding to thefurther development ofcompositesfor use as cable bolt reinforcement. Control of the composite manufacturing process is crucialto achieve a more economicalproduct in thefuture.11TABLE OF CONTENTSABSTRACT iiTABLE OF CONTENTS iiiLIST OF FIGURES viiLIST OF TABLES ixLIST OF PHOTOPLATES xiACKNOWLEDGEMENTS xii1. INTRODUCTION 11.1 Continuous Hard Rock Methods and Equipment 11.2 Existing Support Measures 31.2.1 Underground Hard Rock Mining Support Methods 31.2.2 Underground Soft Rock Support Methods 51.3 Objectives and Scope 71.4 Areas of Investigation 82. SELECTION OF A CUTTABLE REII%iFORCING MATERIAL 92.1 Introduction 92.1.1 Polymer Matrix Classification 112.1.2 Composite Classification 142.1.3 Fibre Reinforcement Classification 162.1.4 FibreType 182.1.5 Range of Composites 212.1.6 Volume Fraction 222.1.8 Composite Surface Treatment 222.1.9 Composite Market Classifications 222.2 Selection Criteria 242.3 Manufacturing Techniques 322.3,1 Filament Winding 341112.3.2 Braiding.352.3.3 Pultrusion 372.3.4 Patented 402.4 Composite Tradename Comparisons 403. POLYSTAL SPECIFICATIONS AND PROPERTIES 423.1 Introduction 423.2 Specifications 433.3 Properties ofPolystal 443.4 Costs 484. FAILURE MODES AND BOND STRENGTH MECHANISMS 494.1 Introduction 494.2 Driving Forces 504.3 Pull-Test Resistance Mechanisms 514.4 FCB Failure Mode Categories 545. UBC LABORATORY PULL-TEST PROGRAM 565.1 Introduction 565.2 Objectives 595.3 Apparatus 595.4 Sample Preparation 605.5 Test Procedures 635.6 Design Experiments 645.6.2 Terminology 645.6.2 Two Level Fractional Factorial Design Basics 655.6.3 Fractional Factorial Design I (FFD-I) Results 675.7 Embedment Length Relationships 755.7.1 Introduction 755.7.2 Codes and Variables 75iv5.7.3 Pull-Test Curves.775.7.3 Critical Embedment Length Curve 795.8 Premature Tendon Failure (PTF) 805.9 Summary of Critical Embedment Length Determinations 826. USBM LABORATORY PULL-TEST PROGRAM 836.1 Introduction 836.2 Objectives 846,3 Pull-Test Apparatus and Sample 846.4 Sample Preparation 856.5 Test Procedure 876.6WickEffect 876.7 Codes and Variables 886.8 Unconflned Compressive Strength of Grout 896.9 Results and Analysis 907. iN SITU PULL-TESTS 957.1 Introduction and Objectives 957.2 Pull-Test Apparatus and Sample Preparation 957.3 Results and Analysis 968. TRIAL INSTALLATIONS 1008.1 Introduction 1008.2 Winston Lake Mine (Noranda) 7 m FCB’s 1018.2.1 Background 1018.2.2 Historical Instability, Stability Analysis and Design 1018.2.2 Installation Procedure and Acceptance 1078.2.3 Conclusions 1118.3 Detour Lake Mine (Placer Dome) 13 m FCB’s 1118.3.1 Introduction 111V8.3.2 Past Failure Background .1138.3.3 FCB Design 1168.3.4 Installation Procedure and Acceptance 1168.3.5 Evaluation of Ground Stabilisation 1188.3.6 MiningTliroughFCB’s 1188.3.7 Mucking Benefits 1208.3.8 Mineral Processing Effects 1208.3,9 Cost Effectiveness 1208.3.10 Continuous Mining Environment 1219.0 FLOATATION TESTS 1239.1 Introduction 1239.2 Test Procedure 1249.2.1 Test I 1249.2.3 Test II 1249.2.4 Test III 1259.3 Results 1259.4 Conclusions 12710. SHEAR TESTS 12811. DESIGN 12912. POTENTIAL APPLICATIONS 13113. FUTURE RESEARCH DIRECTIONS 13114. CONCLUSIONS 132References 138APPENDIX A - CALCULATION OF EFFECTS FOR FFD-I 142APPENDIX B - PULL-TEST CURVES FOR FFD-I 147APPENDIX C. PULL-TEST CURVES FOR SERiES ll-IV. CRITICALEMBEDMENT LENGTH DETERMINATIONS 153viLIST OF FIGURES1. Continuous CAPMini.22. A Typical Road-Header.23. Examples of Conventional and Birdcaged Steel Cable Bolts 34. Comparison of [0] and [±45] Composites 165. Creep Comparisons 296. Filament Winding Process 357. Braiding Method 378. Pultrusion 389. Stress-Strain Curves for POLYSTAL and Steel 4610. Elastic Beam Recovery 4711. Cost Breakdown for the FCB in 1991 Dollars 4812. Surface Area vs Tendon Diameter 5213. Free-Body Diagram ofLacing 5414. UBC Pull-Test Apparatus and Sample 6015. Resin Stage 6216. Plot of Residuals vs Predicted Pull-out 6917. FCB Configurations - FFD-I 7218. Normal Scores vs Estimated Effect Values - FFD-I 7419. Average Pull-Test Curve for Series A 7720. Critical Embedment Lengths for FCB’s 8021. USBM Pull-Test Apparatus and Sample 8522. A Typical Load/Displacement Curve for Uncoated POLYSTAL 9123. Load/Displacment Curves for Series FG18 9224. Load/Displacement Curves for Series FG12 9325, Comparison of Average Load/Displacement Curves for FCB’s and SCB’s 9426. Queen’s Pull-Test Apparatus 96vuList of Figures (continued)27. In Situ Pull-Test Curves forate.9828. In Situ Pull-Test Curves for Limestone 9929. In Situ Pull-Test Curves for Shale 10030. Typical Sill Development Prior to Wedge Failures at Winston Lake 10231. Typical Longhole Stoping with HW Pillar Removed at Winston Lake 10332. Stereonet Representation ofWinston Lake Joint Sets in Ore, Gabbro and Chert 10433. General Representation ofPotential Wedge Failures at Winston Lake 11034. Modified Stability Graph for Historically Caved Backs 10635. Schematic Cross-Section of the FCB’s at Winston Lake 10736. Uphole Installation Procedure at Winston Lake- Pump Toe to Collar 10837. Schematic Plan of the FCB Program - 300 M5#15, Detour Lake Mine 11238. Schematic of Typical Detour Fall of Ground 11439. Uphole FCB Installation at Detour Lake - Pump Collar to Toe 11740. DustJFibre Collection Using Positive Air Circulation Method for Continuous Mining..12241, Percent Copper Recovered in the Concentrate vs Percent ofPOLYSTAL to Feed 13042. Percent Recovery of Copper vs Percent POLYSTAL to feed 127viiiLIST OF TABLES1. Cable Bolt Practice 62. A Relative Guide for Thermoset Resin Selection 143. Compositional Ranges forE, S, C - Glass 194. Mechanical Property Comparison for Various Fibres 205. A Typical Sample of Composite Options 216. Composite Market Classifications 237. General Guide to Fibre Corrosion Resistance 278. The Potential of Various Composite Mfg. Processes for the Production of Cable and/orRock Bolts 339. Unidirectional Composite Comparisons 4110. POLYSTAL Composite and Constituent Material Properties 4311. Typical POLYSTAL - Construction Profile Specifications 4412, Typical Mechanical Properties for Rebar, Steel Strand and POLYSTAL 4513. Summaiy of Observed FCB Failure Modes 5514. Summary of Ultimate Pull-out Loads for Test Series A 5815. Factor Levels - FFD-I 6716. Matrix of Coded Levels, Responses, Estimated Responses and Residual Errors-FFD-I..7017. Alias Structure, FFD-I 7118. Estimated Effects and Normal Scores 7319. Series A & Series TI-TV Design Parameters and Ultimate Load 7620. Series A & Series Il-TV Failure Mode 7821. Summary of Critical Embedment Length Determinations - Series A & Series 11-TV 8322. Wick Effect - Conventional SCB’s 8823. USBM Pull-Test Samples 8824. Unconfined Compressive Strength of Grout (7 day cure) 8925. In Situ Pull-Test Results at Queen’s 97ixList of Tables (continued)26. Installed Cost Comparison for the FCB’s and SCB’s at Detour 12127. Masses and Assays for Concentrates and Tails 12528. Recovery and Grade for Typical Newmont Ore 12729. Preliminary Shear Test Results 12930. Selection ofFCB for Design-Portland Type 30 Cement, 0.35 w:c Ratio, 54 mm hole 130xLIST OF PHOTOPLATES1. Appearance of Tendon Failure 562a. Series FG12 Sample Preparation 862b. Series FGIS Sample Preparation 863. Taping 25 mm Grout Tube to Anchor-end ofFCB 1094. Looking For a Drill Hole to Insert the FCB 1095. Insertion and Wedging of the FCB 1106. Hand-Scoop Test for 0.35 w:c Ratio (Portland Type 10) 1107. Laced FCB After Blasting at Detour 1198. Shear Test Apparatus and Test Sample 128xiACKNOWLEDGEMENTSThe author wishes to thank the management and staffofHDRK Limited, Noranda ResearchCentre, Winston Lake Mine, Detour Lake Mine, U.S. Bureau ofMines, University ofBritishColumbia, Queen’s University and Con-Tech Systems for their sponsorship in this project.Special thanks to Doug Mime ofthe Noranda Research Centre for his, guidance, input, ideas andsupport; all were much appreciated. Appreciation to George Stewart ofWmston Lake Mine,Faramarz Kord ofFalconbridge, Jacques Nantel and Dr. Yves Potvin ofNoranda for theirpractical advice during progress meetings. Credit to CANMET and Brennan Lang for the trialinstallations at Detour Lake Mine, Placer Dome. Special thanks to John Goris ofthe U.S. BureauofMines for his vast knowledge regarding steel cable bolts and experience with test procedures.Acknowledgement to Dr. Will Bawden, Randy Reichart and Dr. Andrew Hyett for the in situtests performed at Queen’s University during my absence. Thanks to Horst Aschenbroich andCon-Tech Systems for supplying the POLYSTAL and related product information. Finally,gratitude to the staff ofthe University ofBritish Columbia’s Mining and Mineral Process andMetals and Materials Engineering Departments: Frank Schmidiger, Pius Lo, Dr. AnooshPoursartip, Andy Mular and especially Dr. Rimas Pakalnis whose continuous enthusiasm andexperience proved invaluable throughout this research.1. INTRODUCTION1 .1 Continuous Hard Rock Methods and EquipmentIn mining, continuous excavating machines have traditionally been restricted to soft rockconditions found predominantly in coal, salt and potash. Continuous excavator technologyadvances have expanded potential mining applications to hard rock. The increase in shapecontrol and decrease in wail damage of a continuously mined excavation can significantly reducesupport requirements over conventional drill and blast methods (Mcllwain, 1988). Research hasbeen conducted to develop a continuous hard rock mining method with positive results (Smith etal, 1992). Earlier attempts at developing continuous hard rock mining methods were alsodeemed successfhl. For example, American Borate adapted two road-headers to the cut and fillstoping of a borate ore deposit where rock strengths varied from 48 MPa to 138 MPa (Sparks,1980). To quote, “...we at American Borate are satisfied with the result ofthis ratherunorthodox mining system (Sparks, 1980).” The mining cycle consisted ofthree cycles:breasting, filling and an overhand pass (Figure 1). The road-headers evaluated were the: SuperRoc-Miner 330 and Dosco TB 600. A typical boom-type miner, or road-header, is illustrated inFigure 2 (Schenck, 1982). Both road-headers exhibited excellent selectivity and ability to cuthigh compressive strength rock at reasonable production rates and costs.1-—.110 O 0 0 I0 C) r m m Cl) - z C.C-)C) r m Cli 0 m I 1 0 -o (I) Cl)Not only have there been significant advancements in single and double-pass continuous hardrock methods and equipment, there have also been successful developments in ground support.One of the most promising break-throughs was the development of a ‘cuttable” support system.Glass fibre reinforced plastic (polyester resin) rock bolts manufactured by WEIDMANN ofSwitzerland were marketed in 1987 and successfully used in numerous civil and mining projectsthroughout the UK and West Germany. One such project was a double-pass highway tunnel(Meechan, 1989). An initial twin-tube pilot tunnel was driven with a full-face tunnelling machineand supported with 2 m WEIDMANN bolts. The pilot tunnel was subsequently enlarged to therequired profile with a roadheader. The WEIDMANN bolts were mined without problems ordamage to the cutter head. Further advantages of the WEIDMANN bolt included: improvedsafety since steel bolts did not have to be cut, improved cycle times (cutting steel bolts was verytime consuming), and reduced damage or interruptions to the mucking system.The support requirements for a multiple-pass continuous mining method demand new,innovative developments. Some of the support techniques currently used in hard and soft rockmining conditions have been used as a basis for the development of the FCB.1.2 Existing Support Measures1.2J Underground Hard Rock Mining Support MethodsOne of the oldest methods of support in hard rock mining consists of leaving ore behind aspillars to support the back and walls. Economic demands have led to the development of lessexpensive support techniques which can be categorised as: external and internal. Externalsupport prevents movement and failure of the exposed rock mass surface and may take the formof: steel sets, wood cribs, shotcrete or backfill. Internal support consists primarily of rock boltsand cable bolts that limit movement and maintain the cohesion or arching capacity of theexcavation walls from within the rock mass. Rock bolts resist load by relying on three mainanchoring systems: frictional, mechanical or grouted. The term cable bolt is reserved for “long”3cement grouted support reinforced with high strength steel wire. Steel cable bolts (SCB’s) utilizethree mechanisms of resistance: adhesion, friction and mechanical interlock (Fuller et a!, 1975).A number of steel wire configurations are used: plain (wires separated by spacer), strand, rope(strands twisted around a fibre core), and birdcaged. The most common cable bolt reinforcementused in Canadian hard rock mines is the 16 mm (5/8”) prestressing or high tensile strength strandwhich consists of six steel wires wrapped around one king wire. This strand can be inconventional, birdcaged or nutcase form (Figure 3).Figure 3. Examples of Conventional, Nutcase and Birdcaged SCB’s (Bawden et al, 1992)__—4The Australian method of separating the seven wires of a conventional strand and thenrecombining them in such a way as to form a series ofnodes and antinodes from the memory ofthe plastically deformed steel wires (approximately 178 mm periods) is called “birdcaging” (Goris1990). Birdcaging effectively increases the surfkce area ofwire exposed to the grout andchanges the mechanisms ofresistance. As a result, birdcaged SCB’s demonstrate greater pull-outloads than conventional SCB’s. This technology has been extended towards the development ofa “laced” FCB prototype. In underground mines, cable bolt lengths typically vary from 3 to 20 mand are usually passive.Grouted steel cable bolts were introduced to the Canadian mining industry during the 1960’s.Geco Mine, Noranda was the first underground mine to use tensioned cable bolts and documentthe results (Bray, 1967). It was discovered during these early installations that pre-tensioningwas not required and, in some instances, adversely affected performance. SCB have been used tosupport pillars, drawpoints, hanging/foot walls and ore. SCB’s have also allowed the transitionfrom cut and fill mining to more economical open stoping methods. A summary ofvarious cablebolt practices and their design parameters is found in Table 1 (Pakalnis 1989). The followingdescriptives have been abbreviated in Table 1: breather tube (BT) and grout tube (GT).1.2.2 Underground Soft Rock Support MethodsUnderground soft rock support methods are basically identical to hard rock internal supportsystems with the exception of low modulus wooden or bamboo grouted dowels. Hydraulic jacksare used primarily as external support for areas where a mechanical excavator passes. Shoteretehas also been used in soft rock applications. The development ofthe FCB was based on hardrock internal support techniques and has the potential to transcend the barrier between hard andsoft rock internal support applications.5Table 1. Cable Bolt Practice (Pakalnis et al, 1989)MINE METHOD BOLT PATTERN HOLE SIZELENGTH (m x m) (mm)(m)Brunswick Mining & cut & fill 17.7 1.8 x 1.8 57Smelting #12 4.9 m liftsFalconbridge, Strathcona cut & fill 17 1.8 x 1.8 543 m_liftsINCO, Thompson cut & fill 6.1,12.2 1.2 x 1.2 542.4 x 2.4Con Mine, Yellowknife cut & fill 10-23 2.2 x 2.4 573 m_liftsNew Broken Hill, Australia cut & fill 20 2 x 2 572.4 m_liftsHomestake, South Dakota open stope 15 3 x 3 57cut&fill 18.3 1.8x1.8 64Placer Dome Cambell open stope 15 2,4 x 2.4 51cut& fill 15 2.4x2.4 51Outokumpu Oy, Finland open stope 15-50 3 x 3 41HlWsupport lOx 10 64Mount Isa, Australia open stope 12 2 x 2 57-7011/W supportWestmin H-W mine cut & fill 15 2 x 1.5 516Table 1. (continued)M[NE PORTLAND STRAN]) STRAND OTHERCEMENT SIZE UTSTYPE/W:C (mm) (tonne)Brunswick Mining and Type 30 2 x 16 53 6 mm BTSmelting #12 0.4Falconbridge, Strathcona Type 10 1 x 16 27 6 mm BT0.4 12.5mmGTINCO Thompson Type 10 1-2 x 16 27 or 54 9,5 mm BT0.4 12.5 mm BTCon Mine, Yellowknife Type 10 2 x 16 58 6 mm BT0.33New Broken Hill, Australia Type 30 2 x 16 53 3 mm BT0.51Homestake, South Dakota Type 10 1 x 16 29 buttons0.5TypelO 2x16 58 12.5mmBT0.5 buttonsPlacer Dome Campbell Type 10 1 x 16 29 --0.4TypelO 1x16 29 --0.4Outokumpu Oy, Finland Type 10 2 x 15 50 --0.5,0.4TypelO 1x15 25 --0.5,0.3Mount Isa Mines, Australia Type 10 2 x 15 50 --0.5Westmin H-W Mine Type 10 2 x 15 50 --0.31 3 Objectives and ScopeHard Rock Mining Research Limited (HDRK) and the University of British Columbia (UBC)have conducted a research program to produce a cuttable, regional support system as part of alarger venture in developing a hard rock continuous mining method. The cuttable supportproject directed, by Doug Milne of the Noranda Research Centre and members ofHDRK, was7divided into two areas of study:A literature search into cuttable support alternatives conducted at McGill University underthe direction ofDr. Fern Hassani.The development of a cuttable cable bolt prototype as an alternative to steel. This portionof the program was conducted at the University ofBritish Columbia, Vancouver under thedirection ofDr. Rimas Pakalnis and was initiated to gain practical experience withcomposite materials as cable bolts. As a result, a FCB prototype was developed andtested in the laboratory prior to in situ trials.It was decided to focus this research on developing regional, internal ‘stope’ support sincecuttable, local internal support already existed such as fibreglass rock bolts (e.g. WELDMANNrock bolts), shotcrete and injection grouts.SCB’s are most frequently and economically used in conventional mining environments andthis work looks at a replacement to steel. Two cable bolt applications in conventional drill andblast operations were used as test-sites to compare FCB’s to SCB’s. Continuous mining test-sitesand control of the composite manufacturing method were not available for this study.1 4 Areas of InvestigationThe following areas were investigated:• raw material selection• composite types• costs• manufacturing methods• pull-test behaviour (laboratory and in situ)8• shear resistance (laboratory)• bond strength mechanisms• failure modes• trial installations• design• mineral processing effects• potential applications• fhture research directionsEach of these areas have been explored to varying degrees in the development of an FCB.Two investigative environments were studied: laboratory and in situ. The research combinedexisting grouted reinforcement technology and applied it to a cuttable material. A brief literaturesearch was conducted to determine the most suitable reinforcement. Next, laboratory and in situpull-tests and laboratory shear tests were conducted on the FCB. The pull-tests proved the FCBsupplied similar pull-out resistances to steel. As a result, enough confidence was generated toattempt trial installations and assess the FCB over time on a larger scale. Finally, the effect ofthe FCB on mineral processing circuits was assessed with a number preliminary floatation tests.2. SELECTION OF A CUTTABLE REINFORCING MATERIAL2.1 IntroductionEven though polymer composites with high fibre content possess equivalent to improvedmechanical and physical properties as compared to steel, little mining research has been initiatedin this area. Perhaps in the past, the relative high cost of composites and their low demand fromindustry has deterred interest. As problems associated with conventional SCB’s such as theirpoor corrosive resistance (Kaiser et al, 1990), low bond strength and high density have been9documented, an increasing need for alternate materials and configurations has become apparent.Recent developments in the manufacturing and application of “advanced” composites hasresulted in reduced costs and improved properties. Fibreglass and aramid fibre reinforcedpolymer composites have found use in many civil applications such as rock anchors or concretereinforcement (Preis, 1986). Some of the main advantages of advanced composite reinforcementrelative to steel are:• Easily taylorable mechanical and physical properties.• Easily taylorable shapes and surface profiles.• Low density (high strength to weight ratios).• Corrosion resistance.• Directional control of properties through fibre orientation.The selection of which composite to use was not straight forward since most compositesavailable on the market have not been developed for the mining industry. To truly evaluate thepotential for composites in the mining industry, one must have control of the manufacturingprocess. As already mentioned, this was not available at the time of this study so alternatesources of composite materials were sought.There were other factors that affected the selection of a composite for this study such asavailability. The availability of advanced composites in Canada is limited. The majority of thehigher strength, advanced tendons are manufactured in Europe, the United States and Japan.Thus, a fair portion of current advanced composite material costs in Canada can be attributed toimport and freight charges. Advanced composites also tend to be developed for low volume,specialty markets and as a result are higher priced. Less advanced composites, termed “lowtech” for the purposes of this investigation, are readily available in Canadian and world markets,but generally lack quality control measures to ensure their properties. This has precluded theirrecommendation for evaluation at this stage, but it does not mean that acceptable quality control10methods and support capacities cannot be developed for them. In fact, low-tech composites aregenerally available at a fraction of the cost of advanced composites with moderate mechanicalproperties. This investigation has concentrated on the evaluation of advanced composites toimprove safety during trial installations.2.1.1 Polymer Matrix ClassificationA composite material can be defined as a macroscopic combination of two or more distinctmaterials with recognizable interfaces (Reinhart et al, 1988). Structurally speaking, the definitionof composites can be restricted to include only those materials that contain a reinforcementmedium protected and supported by a binder material called the matrix. The matrix materialtransfers load to the reinforcement through interfacial shear. Composite mechanical propertiesdepend on the matrix, fibre and interfacial properties.Many structural composite matrix materials exist such as metal or ceramic, but not all arecurrently applicable to mining. This section is restricted to those which are easily cut, low cost,versatile, low to medium temperature resistant and low density, namely polymers. The polymermatrix in a composite has five distinct functions:• maintain shape• hold fibres together• introduce load to the fibres through interfacial shear• protect the fibres from the environment• provide support for fibres in compressionAll polymers consist of carbon chains with repetitive combinations of either H, 0, Cl, F, S orN. They are divided into 3 categories:11• Elastomers• Thermoplastics• ThermosetsElastomers are either natural or synthetic linear polymers that exhibit large elastic strain.Typical tensile strengths range between 2.1 MPa and 28 MPa while elongation to failure can beas high as 2000 %. Their low tensile strength and extremely high elongation to failure suggestpoor suitability for mine support.Thermoplastic polymers are formed and reformed at elevated temperatures without changingthe structure or properties ofthe polymer. They have separate carbon chains without chemicalbonding between them. They are reformable (can be recycled) by applying temperature andpressure. Thermoplastics offer the advantages ofhigh performance and the absence ofreactionkinetic problems experienced with thennosets. The cure cycle involves continuous thermoforming through progressive heating, compaction and cooling. A decrease in processing time ascompared to thermoset resins is often observed. Other advantages include:• improved toughness-• greater impact strength• unlimited shelf-life ofprepreg• faster processing cycleA disadvantage of a thermoplastic system is its’ high resin cost ranging from $10/kg to$100/kg, Resin cost becomes particularly important to price sensitive applications. For example,since the material cost ofpultrusion generally accounts for the majority ofthe overall fabricationcosts, thermoplastic resins are less attractive for the pultrusion of a competitive mining supportalternative to steel ifless expensive, adequate performance thermosets are available.Thermosetting resins are typically formed in two stages:12• Stage I -long, linear carbon chain formation• Stage II -chain cross-linking to produce rigid 3-D networksOriginal and cross-linked chains often involve either addition or condensation polymerisation.Thermosets cannot be reprocessed (recycled) after cross-linking. To initiate cross-linking, anexothermic process, a two part resin mixing system and/or temperature/pressure addition areused. The advantages ofthermoset matrices are:• good performance• low cost ($1/kg to $40/kg)• controlled processing• environmental stabilityThe disadvantages ofthermosets when compared to thermoplastics include:• low impact strength and toughness• limited shelflife• cure process is exothermic therefore the heat added must be balanced with the heat given offto prevent burning ofthe partThe resin industry has been dominated by thennosets in the past because oftheir low materialcosts, large range ofproperties and simple processing characteristics. They account forapproximately 92% of advanced composite matrices (Poursartip, 1990). Polyester resins are oneofthe least expensive thermosetting resins, but are restricted to low temperature uses.Generally, as temperature stability goes up, resin and resin curing costs increase. A generalguide to thermoset selection is outlined in Table 2.13Table 2. A Relative Guide for Thermoset Resin SelectionsTHERMOSET RESiN TEMPERATURE COSTpolyester low lowepoxy medium mediumbismaleimide high highpolyimide2.1.2 Composite ClassificationReinforced polymers can be divided into three categories:• discontinuous fibre (chopped fibres)• continuous fibre (fibre length comparable to composite length)• laminates (layered composites, two dimensions>> third)In terms of rock support, continuous fibre reinforced composites are recommended since theypossess the potential mechanical properties and adaptability for mining. Intuitively, the bondlength and therefore strength between fibre and matrix for discontinuous, or short fibre,composites is lower than continuous composites. As a result, the overall axial load carryingcapacity and stiffness of discontinuous composites is reduced. They tend to fail by matrix shearrather than fibre breakage. The fibre surface area is often too low to develop a sufficient bond totake advantage of peak fibre strengths. Fibre orientation is also more difficult. Conversely,continuous fibre composites have high mechanical properties.In addition to lower mechanical properties, short fibre composites are not recommended forrock support since the tendon diameter required to provide adequate support would increasedrilling costs which typically comprise 65% of the overall support cost. Conversely, it isconceivable that drill hole size and cost may be reduced by using smaller diameter higher strength14composites provided the surface area and profile characteristics of the tendon remain adequatefor a desired critical bond strength. This is one consideration for optimization.Laminates are a combination of single layers, lamina, consisting of a fibre orientation scheme.A unidirectional composite belonging to the continuous or laminate reinforcement family is coded[0]. An infinite possibility of fibre orientations exist, but four major categories are commonlyused for discussion:• Unidirectional All fibres lie in one direction (e.g. [0], [90]).• Bidirectional The fibres lie at 900 to each other. For example, this can be achieved usingwoven fabric or unidirectional layers (e.g. [0/90], [±45], [±60]).• Multidirectional - The fibres have more than two orientations. Each layer has unidirectionalcharacteristics (e.g. [0/901+451-45/90/0]= [Oi90/45])• Random - Fibres are randomly distributed in one plane.15The most likely orientations to succeed in mining are the unidirectional and bidirectionalformats (Figure 4).2.1.3Figure 4. Comparison of [0] and [±45] CompositesFibre Reinforcement ClassificationThis classification refers to continuous and laminate reinforcement prior to compositemanufacturing. The terms and reinforcement forms are in many ways analogous to the textileindustry. Both continuous rovings and roving fabrics are applicable to the manufacture of a.:...::: cL.zDuLayer 1 +45 V//ILayer 2 .4590 etc.degreesDbUnidirectional Composite [0JFabrication Technique- PuitruslonMining Application . Tension = Dominant DrivingForce(a)Bi.directionai Composite (+45]Fabrication Technique. Not fuiiy developedBest Fibre Orientation Combination tar ShearResistance(b)16FCB. Fibres are manufactured into mono-filaments which are gathered together to form thefollowing continuous reinforcements:• Strands - Normally an untwisted bundle or assemble of continuous filaments used as a basicunit for yarns or tows.• Yarns - An assemblage of twisted natural or synthetic filaments, fibre, or strands to form acontinuous length that is suitable for use in weaving or interweaving into textile materials.• Tows- An untwisted bundle of continuous filaments. A tow designated 140K has 140,000filaments.• Rovings - A number of strands yarns or tows collected into a parallel bundle with little or not4st.Strands are usually combined to form unidirectional fibre yarns (twisted bundles) or tows(untwisted bundles) which are then combined to form rovings. In the past, fibre manufacturershave supplied standard 6-12 km fibre tow creels weighing approximately 1 kg. As the demandfor higher capacities rose to compete with industries such as steel, desired creel sizes rose to 40km or larger to alleviate start-up losses.Woven rovings also show potential for mining. Fibre producers are capable of supplyingwoven fabrics in a number of forms applicable to mining:• weaves• braids• knits• PrepregAll of these formats have potential for ground support. Continuous rovings are the mostsuitable format for unidirectional tendons manufactured by pultrusion-like processes. In17principle, rovings, weaves, braids and knits can be used to achieve various fibre orientations witheither pultrusion, filament winding or braiding. For example, weaves, braids and knits are wellsuited for high capacity pultruded [±45] products since they tend to maintain fibre orientationunder tension. To achieve a [±45] composite with longitudinal rovings, more time consumingand expensive methods such as filament winding or braiding are required.Prepreg, which can be used in a number of composite manufacturing processes, is anacronym for “fibre PRE-imPREGnated with resin.” The impregnating resin can be a thermosetor thermoplastic. A thermoset cures at a defined rate and has a limited shelf-life. Athermoplastic requires heat and pressure to initiate cure and has an unlimited shelf-life. Theprepreg fabrication process eliminates wet-out, alignment and preforming problems associatedwith wet resin techniques. Problems associated with using prepreg include: increased cost,preheating, compaction and debulking ofB-staged (partially cured) resin.2.1.4 Fibre TypeAs previously mentioned, from a continuous mining perspective, steel cable bolting is not apractical solution and the necessity of a cuttable support system is obvious. The fibreglass rockbolt is an alternative that has been tested without adverse affects to continuous mining machines(Meechan, 1989) and has proven local support capacity. They therefore represent provencomposite technology as an alternative to steel. Five types of glass fibre are commonly used tomanufacture rods:• E-glass - electrical grade glass, least expensive.• S-glass - stronger stiffer.• R-glass - Civil engineering version of S-glass used for structural applications.• C-glass used where chemical resistance is required, especially in acidic environments.• Cemfil- resistant to the alkali in Portland cement.18Versatility and economy are two advantages of glass that are beneficial to future miningproduct developments. Poor corrosion resistance, poor handling resistance and moderatemechanical properties are their disadvantages as compared to other fibres. C-glass couldreinforce a polymer matrix of similar chemical resistance to produce a rock or cable bolt forhighly aggressive chemical environments. Cemfil might be another alternative for suchenvironments where a drill hole could be filled with fibre to provide reinforcement and Portlandcement Type 20 or 50 (sulphate resistant cement). The chemical composition for glass fibresvaries between manufacturer and for this reason ranges for E, S, C-glass are presented in Table3. However, these variations do not cause significant fluctuations in the mechanical or physicalproperties within a given glass type.Table 3. Compositional Ranges for E, S, C-glass(Reinhart et al,1988)OXIDE E-GLASS RANGE S-GLASS RANGE C-GLASS RANGE(%) (%) (%)Silicon 52-56 65 64-68Aluminum 12-16 25 3-5Boric 5-10-- 4-6Sodium and 0-2-- 7-10PotassiumMagnesium 0-5 10 2-4Calcium 16-25- 1 1-15Barium-- -- 0-1Zinc------Titanium 0-1.5----Zirconium------Iron 0-0.8-- 0-0.8Iron (not oxide) 0-1—--Other fibres with potential as ground support members include aramid and carbon. Aramidfibres are recommended for tensile applications only. Aramid fibres tend to form defects called“kink bands” under high strain compressive and flexural loads rendering the reinforcementineffective (Phillips, 1989). A comparison of the mechanical properties for various fibres190CD-4=Dp. e IIC, CD CD CD CD CD 0 CD CD CD CD C) CD 0- CD 0- 0 C) 0O.ODaII:J111-;0j2Clrr,ci00———J-00c0:o00co00%0w‘t’(‘a‘D 00—0.,$0o—0•0o0çj.J(‘a00010000000000—00.a00000000000000000000—S————00ç—0000i-00)—0E0t.3J00Q000000(Ja(‘a00—IS.)0()..•L’)t’3.I’.)——0t.)0—,•••:000(‘aCD(‘I—(2I0A—I0— —.000III——I°00Lii00 000 -,2.1.5 Range of CompositesA summary of the important factors affecting continuous fibre reinforced compositeproperties are fibre type, volume fraction (Vf) of fibres, fibre orientation, and matrix type. Atypical range of raw material combinations are listed in Table 5. A wide range of profile shapesare available. From a bond capacity perspective, circular profiles offer the largest bond surfacearea and a uniformly distributed interfacial shear. Circular profile, tendon, rod, and strand havebeen used interchangeably.Table 5. A Typical Sample of Composite OptionsFIBRE TYPE ORIENTATION MATRIX BEST MATCH FORA1’4D Vf ADHESIONpolyesterGlass UD (50-70%) vinylester glass/polyest.Aramid BD (30-55%) epoxy glass/epoxyCarbon Random(15-35%) polyimide aramid/epoxyPolyethylene bismaleimide carbon/epoxyphenolicDiscussions regarding fibre type have been restricted to glass, aramid and carbon since thesethree dominate the composites industry and have the greatest potential for mining applications.The mechanical properties of the fibre are important during selection of a composite for anapplication since the majority of the load is carried by the fibre. For example, a unidirectionalglass/polyester composite with approximately 70% fibre by volume will typically transfer 98.5%of its ultimate load carrying capacity to the fibres. The physical properties of the fibre are lessimportant than the physical properties of the matrix since the matrix (resin) acts as a protector.This is generally true except for cases where stress has cracked the matrix exposing the fibre tothe environment. To prevent stress corrosion and matrix cracking, the ultimate strain of the fibreand matrix must be matched.212.1.6 Volume FractionThe volume fraction of fibres in a composite is dependent on the fibre orientation, diameterand shape, and the manufacturing process. Unidirectional composites have high fibre contentswhile random composites have low contents. Considering the range of mechanical propertiespossible through fibre directionality, composites have the potential for developing groundsupport products with various combinations of tensile, shear and flexural strengths. Therelationships between ultimate tensile strength or modulus and fibre orientation are not linear.2.1.8 Composite Surface TreatmentComposite surface treatments act as protection against mechanical damage, impact,corrosion, abrasion and weathering. Surface treatments increase the service life and applicationrange of a composite. They can be altered to give a desired surface roughness or can be selectedto reduce die abrasion and drag in manufacturing processes such as pultrusion. Three types ofresin rich veils are common:• polyethylene• nylon (polyamide)• polypropyleneAdditives and reinforcement can be added to the veil to achieve desired properties such asflame retardancy and increased strength or frictional characteristics.2.1.9 Composite Market ClassificationsReinforced polymer composites have been classified according to their technology (Table 6):22TabPe 6. Composite Market ClassificationsCOMPOSITE RESiN REINFORCEMENT FIBRE QCCLASSIFICATION CONTENTreinforced thermoset discontinuous very low lowplastics particulatelow-tech thermoset continuous moderate moderatelaminateadvanced both continuous high high(high-tech) laminatethermoplastic thermoplastic continuous high highlaminateNote:QC = Quality ControlReinforced plastics have been rejected because of their low mechanical properties whilethermoplastics were rejected because of their extremely high cost. Low-tech and advancedcomposites exhibit excellent mining potential. Very few advanced polymer composites exist intendon form. The majority of the market is flooded with lower fibre content rods which aremanufactured with limited quality control measures or technical input. It must be stressed againthat quality control is vital to ensure proper safety standardsfor composite manufacturing andtheir use in ground control. Attempts to use low-tech compositesfor ground support arediscouraged unless acceptable verfication of the composite properties has been made. Thisdoes not rule out the possibility that relatively inexpensive existing quality control measurescould promote confidence in low-tech composite properties. Documentation on quality controland testing is abundant (Phillips, 1989). It is unlikely low-tech composites would be able todevelop tensile strengths greater than two-thirds of advanced composites without significantimprovements to manufacturing. This could be overcome by increasing the number of low-techrods used for cable bolt reinforcement provided drilling costs remained competitive. Emphasishas been placed on the application of advanced composites for cable bolt reinforcement and will23be referred to as composites for the remainder of this investigation.22 Selection CriteriaThe manufacturing processes currently used to produce composites are far from optimisedand property data is limited. For these reasons, a more flexible approach to material selection hasbeen presented. As mentioned, glass, aramid and carbon fibres are the most common plasticreinforcement. Since the majority of an applied load is carried by the fibres, they have thegreatest influence on the mechanical properties and behaviour of a composite. Physicalproperties such as the maximum working temperature and corrosion resistance in unstressedsituations are primarily determined by the matrix composition. An understanding of theconstituent material properties and their joint influence on the overall composite properties isessential to selection. Constituent material properties are most valuable when considering thedesign and manufacture of composites. The benefits and limitations of each composite andconstituent material are presented as they relate to mining. Certain properties have been omittedaccording to their relevance. It must be emphasised that composite material properties are vastlydifferent than constituent material properties. The reader is advised to be careflul in this respectand to ensure that similar test conditions exist between comparisons.The composite selected to replace steel as a reinforcing agent for cable bolts in continuous ordrill and blast mining operations must be comparable in overall cost, performance and handling.The ideal support requirements for mining are:1. Low flexural stiffhess to facilitate coiling (< 2 m diameter)2. Rigid enough to insert in hole3. Low density to promote handling4. High corrosion resistance5. High bond strength to grout246. Low creep of grout bond under static load7. Low creep of reinforcement.8. Safe handling (body contact and respiratory)9. Flame retardant10. Low coefficient of thermal expansion to prevent shrinkage or expansion of reinforcementwith respect to grout and stability at low temperatures.11. Electrically non-conductive12. High vibrational and dynamic resistance (rock burst or blast induced) and fatigue.13. High toughness14. High shear strength15. Mineral processing “friendly”In terms of the installation, quality control and handling of cable bolts, a relatively lowflexural stffiiess and density are preferred to uncoil and insert the cable in the hole.Unidirectional composites are easier to uncoil than SCB’s. The flexural stiffness of composites isa function of the matrix modulus, fibre modulus and fibre orientation. Lower modulus resins andfibres result in a more flexible tendon. Resins can be selected improve composite flexibility.Fibre orientations off-axis tend to supply bending and torsional rigidity. SCB’s store more energywhen coiled and as a result are more dangerous to uncoil and maintain a clean cableunderground. Grease and dirt are known to decrease the pull-out load by as much as 50%(Goris, 1990). Composites are easier to handle due to their low density which is approximatelyone quarter that of steel.High corrosion resistance is desired for long-term or aggressive environment cable boltapplications. A composite must therefore be resistant to a number of environments such as thealkaline conditions created by the Portland cement, acids generated by oxidation of sulphideminerals in the presence of water or humidity. Composite corrosion can also include solventdissolution, moisture absorbtion or chemical attack.25The rate at which chemical corrosion occurs for composites is dependent upon factors suchas the matrix type, fibre type, the corrosive solution, temperature, oxygen content in atmosphereor water, area of exposed surface, time, etc. The chemical resistance of a composite reliesheavily upon the matrix resistance to chemicals and cracking.A general ordering of the increasing corrosional resistance for various selected resins is asfollows:• orthophthalic polyester (least resistant)• isophthalic polyester• vinylester• biphenol• epoxy (most resistant)However, there are exceptions to the above ordering. The resin manufacturer’s advice shouldbe sought when determining corrosion resistances of a matrix.Under stressed conditions, the ability for the matrix to resist cracking is vital. Since one ofthe ftrnctions of the matrix is to protect the relatively sensitive fibres from harmfiul environmentsit is important to match the ultimate strain characteristics of the fibre and matrix. As aconsequence, the matrix becomes the limiting factor for chemical resistance under low strains.Polymer matrices have different chemical resistances as do fibres and should be chosen accordingto the service environment. Invariably, matrix cracking occurs as the applied stress approachesthe ultimate strength of the composite. In such cases, the chemical resistance of the fibrebecomes important to the overall corrosion resistance of the composite. Table 7 is a relativecomparison of typical fibre corrosion resistances.26Table 7. General Guide to Fibre Corrosion Resistance(Phillips, 1989)FIBRE BASES ACIDS WATER OTHERTYPE SOLVENTSSTRONG WEAK STRONG WEAKCarbon H H — H H HTechnora H H H H H HKevlar49 L G L 0 -- --E-glass VL L VL L G --Note:H= high0= goodL= lowVL = very lowE-glass is highly resistant to most chemicals, but it is susceptible to acids and alkalis at lowconcentrations. Corrosion resistant fibres such ECR-glass and R-glass are available.Aramid fibres can be categorised into two main groups according to their chemical resistance:• Low resistance (e.g. Keviar 49) - high modulus• High resistance (e.g. Technora) - low modulusKeviar 49 is sensitive to strong acids and bases and is resistant to most other solvents andchemicals (Pigliacampi, 1988). Technora, manufactured by Teijin of Japan, exhibits high strengthretention in both acids and alkalis (Phillips, 1989). Carbon fibres are not affected by moisture,atmosphere, solvents, bases and weak acids at room temperature (Diefendoi-f 1988).Composites comprised of fibres with low corrosion resistances can be protected by a surfacecoating. In conclusion, ECR-glass, Technora and carbon fibres are highly resistant to chemicalcorrosion.The most common cable bolt failure occurs at the cable/grout interface. In these instances,the pull-out bond strength of a cable bolt can be thought of as the sum of adhesion and frictional27resistance between tendon and grout (Jeremic et al, 1983). Adhesion is a fi.inction of thechemical attraction between the tendon and grout. The friction is determined by the tendonsurface profile, tendon configuration and confinement. It increases with normal stress. LacedFCB’s have an adhesive resistance, but more significant forms of frictional resistance andmechanical interlock contribute to their overall resistance.In general, the higher the bond strength, the lower the creep of that bond strength understatic load conditions. The bond strength of a conventional SCB is less than ideal. Nevertheless,SCB’s are used extensively in mining where high bond strengths are not required. BirdcagedSCB’s have excellent bond strength characteristics, but are not widely used in North America(Vancouver, 1991). Perhaps in the past the drill hole size necessary for the installation ofbirdcaged SCB’s, higher material cost or the lack of familiarity with birdcaged SCB’s hasdiscouraged their use. Current trends have revealed that birdcaged SCB’s are gaining acceptancein Canadian underground mines (Vancouver, 1991). Ground control engineers are realising theimportance of a high bond strength to the effectiveness of cable bolts, in blocky ground. Underlong-term static loading (62 months) prestressed cable anchors will experience a loss in load of8.2% (Benmokrane eta!, 1991). Load losses of up to 10% have been tolerated for anchorsprestressed to 75% oftheir rupture limit load (Littlejohn and Bruce, 1979).Composites creep rates and characteristics vary with the orientation of the fibres with respectto a load and temperature. When subjected to a tensile load in the direction of the fibres,composites exhibit linear elastic creep rates. Figure 5 compares creep data for variouscomposites and steel under these conditions. In general, carbon composites possess the greatestcreep resistance. Their creep rates are slightly less than low relaxation steel. E-glass compositeshave the next lowest creep rates followed by standard steel and the distant, aramid compositefamily.2812 [a E-gfassl10 — Kevlar49v carbon ;—•o standard steel• low-relaxation steel8 Eglass2Figure 5. Creep Comparisons Under the Same Loading Conditions (Phillips, 1989)For a composite with an off-axis static load, the matrix properties become more significant tocreep. This results in a reduction in the creep resistance and elastic recovery ofthe composite.This is due to the fact that polymers creep visco-elastically, which means they exhibit both alinear elastic and non-linear viscous response to external forces. Furthermore, as temperatureincreases so does the amount and rate of creep in composites. Thus, the heat deflectiontemperature (HDT) is an effective measure ofthe creep resistance of a polymer or composite. Ahigh HDT indicates high creep resistance. Typical HDTs for polyester resins range from 80-x=‘40.1time (h)1 10 100 100029140°C. In general, epoxies and thermoplastics have greater HDT’s.A coating is recommended for a composite intended for cable bolting. The coating enhancesthe bond strength, safer handling, abrasion resistance and toughness.Generally, fibre reinforced polymers have low coefficients of thermal expansion similar toPortland cement. In Canada, mining service temperatures typically range between -60°C and40°C depending on the geographic location. The mechanical properties of composites degradeas temperature increases. Large decreases occur as the temperature approaches the glasstransition temperature, Tg, of the matrix or fibre. The temperatures associated with mining liewell below the Tg for virtually all fibres and polymer matrices of interest. Low temperatureresins tend to degrade at much lower temperatures than fibres in the order of 300°C and, hence,are the limiting component for elevated temperature applications. During low temperatureservice, composite stifihess and strength are unaffected or slightly enhanced (Phillips, 1989).Glass and aramid fibres are electrical insulators. Carbon fibres on the other hand willconduct electricity. To quote from R. J. Diefendorf(Reinhart et al, 1988), “Carbon fibreconductivity varies with precursor type and heat treatment temperature and is 1/50 or less that ofcopper for commercial 230 GPa fibres.”In general, composites have a higher vibrational damping capacity when compared to steeland are more likely to withstand rockburst or blast induced vibrations. The tendency for seismicshock to propagate through steel cables can reduce the strength of the grout bond for peakparticle velocities greater than 500 mm/sec (Stillborg 1984). Phillips (1989) quotes, “Metals andceramics have particularly low internal losses and hence have poor damping characteristics.Polymer composites, on the other hand, and particularly CFRP (carbon fibre reinforced plastics)and ARP (aramid fibre reinforced plastics), have very good damping performance, which can beused to reduce vibration resonance.”Composites do not exhibit a definitefatigue limit at two million cycles. Fatigue is defined asthe gradual deterioration of a material through cyclical loading. In general, low moduluscomposite reinforcement causes excess matrix cracking under cyclical loads. This results in early30fatigue. The applied stress can be tension-tension, compression-compression or tension-compression. Such loading conditions can be induced to support systems by blasts, rockburstsor gradual changes in the mining induced stress field. The fatigue resistance of a composite is afbnction ofthe matrix as well as the fibre orientation, content and type. For example,unidirectional carbon fibre composites loaded in the direction ofthe fibres exhibit excellentfatigue resistance. The matrix plays a more dominant role in [±45] composites stressedtransverse to the fibre direction. This results in reduced fatigue resistances. Fatigue resistancealso decreases with decreasing fibre content. A general ordering offatigue resistances forunidirectional composites under longitudinal load cycles can be snnlniRlised as follows:• Carbon• Araniid• GlassCarbon fibre composites show a two to four fold increase in fatigue strength over steeL Theratio, after cycling, of tensile strength to short-term ultimate tensile strength for carbon fibrereinforced epoxy composite after tension cycles is in the range of 53-58%. This applies to[0], [±45], [90] and quasi-isotropic configurations and compares fhvourably with 2024 T3aluminum at 28% and 4130 steel at 44% (Phillips, 1989). Glass composites have greater fiexuralfatigue resistance than aramids for large numbers of cycles and have lower fatigue strengths thansteel Carbon fibre composites maintain their superiority over other composites for all fibreorientations and are relatively insensitive to fatigue when unidirectional, longitudinally loads areconsidered.Note that the potential disadvantages of SCB’s have been their failure to meet ideal supportrequirements (1),(3),(4),(l1) and (12) as outlined in Section 2.2.The potential disadvantages ofthe FCB are the ideal support requirements (8), (14) and (15).Filament winding and pultrusion are continuous composite fabrication techniques capable of31various off-axis fibre orientations which increase the shear strength of a tendon. Pultrusion iswell suited for both cable and rock bolts. When compared to filament winding, pultrusion isusually favoured due to its’ simplicity and production rate. The drawback with pultrusion islower shear strengths. Pultruded composite shear strength can be improved by using braided,woven or knitted rovings as opposed to standard roving feeds, but these composites will neverachieve shear strengths as great as those with equivalent cross-sectional areas produced fromfilament winding.Filament winding has slightly slower production rates than pultrusion, but improved fibreorientation, and thus, high shear strengths are possible with this technique. The drawback whenincreasing shear strength is sacrificed tensile strength. Larger cross-sectional areas to achieve adesired tensile strength and lower tendon flexibilities are the result of increasing shear strength.The effects of the fibres on the working environment and processing circuits were brieflyexplored. Results on these aspects are documented in Section 8.0 and 90.2.3 Manufacturing TechniquesA number of composite manufacturing techniques were briefly studied to evaluate theirversatility, commercial potential, advantages and disadvantages. Four continuous fabricationtechniques have potential for the commercial production of cable bolts:• Filament Winding• Braiding• Pultrusion (e.g. CELTITE, POLYGLAS, etc.)• Patented Methods (e.g. POLYSTAL and ARAPREE)Each method has been briefly presented. It was found continuous production methods werebasically limited by the maximum length of roving available on a spool and the mechanics of the32equipment to handle these lengths. In general, the roving feed size and their number of spoolscan be selected to best suit the production requirements in order to achieve a virtually“continuous” production of tendons. In each method, production ideally continues until thespools of rovings are used, at which time the system must be shut-down and new spools loaded.The manufacturing potential of each process was ranked according to the driving forcesdescribed in Section 4 (Table 8).Table 8. The Potential of Various Composite Manufacturing Processes for the Productionof Cable and/or Rock BoltsMANUFACTURING BOLT TYPE MOST FAVOURED RELATIVEMETHOD DRW1NG FORCE PRODUCTIONCASEb PATh RANKiNGFilament Winding RBa,CB (2) slowPatented RB,CB (1) mediumPultrusion RB,CB (1) fastNotes:a anchor device requires development (resin, cement, mechanical, etc.).b all fabrication methods have potential to manufacture tendons for applications with Case (1),(2) & (3) driving forces, but each is most suited to a particular Case.RB Represents rock bolt.CB Representscable bolt.Each method can potentially manufacture cable bolts or rock bolts. Filament winding is mostsuited to manufacture reliable composites for shear applications, however, the pultrusion andpatented methods also have potential in this respect. Control of a manufacturing method wouldbe necessary to evaluate these options.Braiding is a fibre format manufacturing method, but it can be combined with resinimpregnating stages to manufacture composites. Braided composites are used extensively in thefishing, skiing and golfing industries.Although each method was characterised by different capabilities and production potentials,33all have similar production concerns as summarized below:• Most efficient if operated on a 24 hour basis.• A significant investment is required to stock raw materials and equipment.• The raw materials represent the majority of the production costs.• Raw material availability can determine plant location.• Fibres are supplied on standard creel sizes limiting the continuous process.• The manufacturer usually has limited technical support and often draws on the knowledge ofthe raw material supplier.• Continuous consistent resin supply is required.• Manufacturers are unfamiliar with advanced composite problems such as void content,compaction, degree of cure and fibre volume determinations.• Start-ups should be minimized.2.3.1 Filament WindingFilament winding involves a continuous feed of fibre bundles (tows,rovings or yarns) througha resin bath onto a rotating mandrel (Figure 6). It is most suited for complex shapes requiringmulti-fibre directions. The component is partially or filly cured before removal. The process iscyclical and less suited for long component manufacturing. Advantages include precise fibreorientations and excellent fibre content control. The major disadvantage of filament winding isits’ slow production rate. This fabrication method has potential for short shear resistant boltconstruction, but its relatively high cycle time is a severe hindrance. One way of improving theproduction rate has been to combine filament winding or braiding with pultrusion technology. Inthis manner, acceptable production rates and mechanical properties can be achieved.34Figure 6. Filament Winding Process (Poursartip, 1990)2.3.2 BraidingBraiding is a continuous process capable ofbiaxial, triaxial and multiaxial fibre orientations(Figure 7). Fibre bundle spools are rotated on a track to form two dimensional tapes or threedimensional tubes. Resin impregnation can occur during the manufacture or service of the braid.Braiding has excellent potential for the manufacture of high shear strength rock or cable bolts.New Port Composites Inc., Fountain Valley, California supplies glass, aramid and carbon fibrebraided composite tubes varying in diameter from 1 cm to 15 cm. Braided tubes have the35potential to act both as the grout tube and the reinforcement in a cable bolt. If braided tubeswere used for this purpose, the bond surface area would be reduced to that of the tube’s outerdiameter. Adhesion between the tube’s inner diameter and the grout would not contribute to thebond strength of the cable bolt as a whole. Assuming an outer diameter of 40 mm, the bondsurface area for a unit length of tube would be equal to 126n2. Since bond surface area is acrucial factor to achieve high pull-out loads, this system has not recommended on its’ own.Alternatively on a microscopic level, it has been well established by the fibre reinforcedcomposites industry that reducing fibre diameter to less than approximately 20 micronssubstantially increases their mechanical properties (Poursartip, 1990). This technology can bedirectly applied on a macroscopic level to the development of a fibre reinforced composite cablebolt using braids. For example, many 1 cm diameter braids would have a high bond surface area,and as a result would have higher pull-out load, than one large tube of equivalent mechanicalproperties (cross-sectional area). Combinations using braided and UD composites also havepotential for cable bolting.36Figure 7. Braiding Method (Poursartip, 1990)2.3.3 PultrusionPultrusion is a continuous fabrication technique most suited for shapes with constant crosssectional areas (Figure 8). The advantages ofpultrusion are: low capital start-up costs, lowcycle times and simplicity of operation. It is the most well suited fabrication technique forcommercially produced rock or cable bolts. Off-axis fibre orientation can be achieved bypultruding braids, weaves or knits. A complete list of the benefits associated with pultrusion arelisted below:. can use thermoset or thermoplastic1—Track plate2—Spool carrier3—Braiding yarn4—Braiding point and former5—Take-off roll with change gears6—Delivery can37• low capital cost• low direct labour costs• decreased quality control costs• low tooling cost• longer tool life• easily automated• high continuous output compared to other fabrication processes• limited operator influence on properties• lack of secondary finish required• multiple die capacityFigure 8. Pultrusion (Poursartip, 1990)Mat creels5grfacing material (Nexus)—I I. /[ IGuideResin impregnatorSurfacing materialRoving creelsCut-off sawtForming and curing diePull blocks38The curing of fibres under tension is a disadvantage of this method. This can result in lowerstrain capacities and fibre relaxation causing debonding.The following product size ranges are possible:• thickness 2 to 76 mm• width 2tol000mm• length variousTwo major constraints are imposed on pultrusion are the: (1) rate of reaction kinetics for theresin and (2) process mechanics. Constraint (1) dominates thick cross-sectional shapes whileconstraint (2) dominates thinner shapes. In general, thicker thermoset shapes are subjected todifferential stresses during cure resulting in internal exothermic cracking. To solve this problemclose control of the resin properties affecting quality and the addition of radio frequency (RF)preheating is required. Typical large cross section production rates range from 0.6-1.2 rn/mm.Improvements to the reaction kinetics and mechanical workability of resins have led toproduction rates as high as 4.6 rn/mm (e.g. RF preheat treatment of solid glass/polyester 12.7mm diameter rod, Sumerak et al, 1985). To achieve such rates, the effects of the processparameters are often correlated to form empirical relationships used to automate production.Obstacles for capacity growth include low data-bases for advanced composite materials andlimited numbers of processors. Pultrusion has excellent potential for continuous, low costproduction of rock or cable bolts for tension dominated driving force applications. It also haspotential to manufacture bolts with moderate shear strengths.392.3.4 PatentedTwo advanced round bar composites: POLYSTAL and ARAPREE are manufactured underpatented processing methods and as a result these methods have not been presented. Theadvantages of these methods are clearly indicated by their products’ superior properties over lessadvanced composites.2.4 Composite Tradename ComparisonsTable 9 compares various composites by process, market classification, constituent materialsand cost per metre. The composites listed are either glass or aramid fibre reinforced epoxies orpolyesters. Other low-tech composites are available on the market, but before using them forcable bolting further product developments such as: manufacturing quality control, fibre content,corrosion resistance, void content control, and bond surface would be necessary. For thesereasons it was decided that slightly more expensive advanced composites such as POLYSTAL(construction profile) and ARAPREE should be considered for the development of a cable boltprototype.AR.APREE is a Twaron (AKZO tradename for aramid) fibre reinforced epoxy and isconsidered an advanced composite. Three companies supply aramid fibres worldwide, AKZO ofthe Netherlands, E. I. du Pont de Nemours & Co. of the United States and Teijin Company ofJapan. POLYSTAL is a glass fibre reinforced unsaturated polyester advanced compositemanufactured in Germany and distributed in Canada.40Table 9. Unidirectional Composite Comparisons (Khan et al, 1991)TRADENAME MMJUFACTURING MARKET FI]3RE RESIN COSTPROCESS CLASS ($/m)1ARAPREE 100 patented advanced Twaron epoxy 1.33(aramid)ARAPREE 200 “ advanced “ “ 2.56ARAPREE 400 “ advanced H 5•44POLYGLAS pultrusion low-tech Glass unsat’d 1.17polyesterCELTITE pultrusion low-tech Glass unsat’d n/a2polyesterEXTRENE pultrusion low-tech Glass polyester 2.39vinyl esterPOLYSTAL patented advanced Glass unsatd 2.56(construction polyesterprofile)Notes:1= approximate cost per metre of one 7-8 mm diameter rod2= 8 mm rods not standard size, but can be manufacturedPOLYSTAL and ARAPREE manufacturing processes are both capable of various resin-fibre combinations. Both are imports, but POLYSTAL is commercially sold in Canada whereasARAPREE is not. Currently, ARAPREE and POLYSTAL have a number of different profilesavailable, but only ARAPREE 200 and POLYSTAL (Construction Profile) have suitable coilingflexibility for transportation underground. Likely the largest disadvantages of araniid reinforcedcomposites are their expensive raw materials, low availability, relatively lower performance underflexural/shear loading, and relatively high creep rates (Phillips, 1989). Some of the advantagesof aramid fibres over glass include impact and chemical resistance. POLYSTAL was chosenbased on its’ high availability, moderate cost and suitable mechanical properties. However,fi.irther investigation into the potential for ARAPR.EE and other composites as a cable bolt arewarranted.413. POLYSTAL SPECIFICATiONS AND PROPERTIES3.1 IntroductionThis section outlines the properties ofPOLYSTAL and its’ behaviour as a prestressing strandas determined by BAYER. Research by BAYER to develop a continuous, moderate strengthand moderate modulus composite for prestressing a road bridge spanning 50 metres began in1978. The research evaluated glass fibre with polyester and epoxy resins. The bridge wascompleted on July of 1986 in Duesseldorf Germany and since then five other bridges have beenreinforced with POLYSTAL (Preis, 1986).To compete with prestressing steel, Bayer had to developed a cost effective, corrosion andabrasion resistant, high performance glass fibre and polyester resin composite. E-glass andunsaturated polyester resin were considered as the most economical constituent materials byBAYER.POLYSTAL tendons are made by a continuous “pultrusion-like” process and have a UD fibreorientation parallel to the tendon axis. This results in anisotropic mechanical properties, orsimply, properties that vary with the angle between the applied load and the fibres. When viewedin cross-section, a uniform distribution of end-on fibres can be seen. POLYSTAL is availablewith an optional polyamide coating which protects against corrosion and mechanical damage.Coated and uncoated POLYSTAL have potential for long-term (> 1 year) and short-term (< 1year) excavations respectively. Various diameters and profiles are available.The majority of the test work presented in this thesis evaluated coated tendon behaviour.Four, 7.5 mm diameter strands, each with a modulus of 1520 MPa, were used to give an ultimateload carrying capacity approximately equivalent to that of steel cables. This allowed for moredirect pull-test comparisons between the two.423.2 SpecificationsThe general properties for POLYSTAL (Construction Profile) and its’ constituent materialsare listed in Table 10.Table 10. POLYSTAL Composite and Constituent Material Properties (Preis, 1986)PROPERTY I DIMENSION I VALUEPOLYSTAL Rod (construction profile)Glass fibre content % by weight 80 ± 2.5coefficient of thermal exp. change in length per °C 6.6 * 10-6water absorption in 24 hrs @20 °C, % 0.1axial tensile strength MPa 1,600transverse compressive MPa 140strengthshear strength MPa 45modulus of elasticity MPa 52,000failure strain % 3Poisson’s ratio- 0.28density g/cm3 2.1Glass_Fibreaxial tensile strength MPa 2,300modulus of elasticity MPa 74,000failure strain % 3Polyester Resinaxial tensile strength MPa 75modulus of elasticity MPa 300failure strain % 4The Construction Profile POLYSTAL has been developed specifically for chemicallyaggressive environments and was selected for this evaluation. Table 11 lists the potentialdiameters which can be manufactured and corresponding mass per unit length, maximum length,tensile force at 0.5% elongation and breaking force.43Table 11. Typical POLYSTAL - Construction Profile Specifications(Con-Tech Systems, 1991)Type Diameter Mass per unit Maximum Tensile Force Breaking Forcelength Length at 0.5%[mm] [glm] [km] elongation [N][N________P10 1.00 1,6 15 200 1,100P12 1.22 2.3 15 290 1,630P14 1.40 3.0 15 380 2,500P16 1.56 3.7 16 480 3,200P17 1.70 4.4 16 570 3,700P20 1.95 5.9 16 750 5,000P21 2.10 6.8 16 860 5,700P24 2.40 8.6 16 1,100 7,600P26 2.57 10.2 16 1,300 8,900P28 2.75 11.5 16 1,460 10,300P29 2.90 12.4 14 1,470 10,500P30 3.08 14.8 16 1,820 13,000P33 3.30 17.8 16 2,100 14,900P35 3.45 18.8 16 2,340 16,900P36 3.60 20.5 16 2,510 17,100P40 4.05 26.3 13.5 2,850 20,000P45 4.50 33.0 13.5 3,696 22,440P50 5.00 42.0 13.5 4,704 28,560P62 6.20 60.8 13.0 6,400 45,000P70 7.00 75.4 10.0 9,072 55,080P77 7,75 96.0 10.0 10,000 70,000P115 11.50 225.0 3.0-- 155,000P160 16.00 444.0 4-6m- 296,0003.3 Properties of PolystalA comparison of mechanical properties for reinforcing and prestressing steel to POLYSTALis listed in Table 12. Composites have various grades of strength available depending on theirvolume fraction and fibre type. For fhture reference, the reader should be careflul not to confusecomposite properties with fibre properties and ensure equal dimensioned test specimens are usedto compare mechanical properties. Initially, the low modulus of composites was considered a44disadvantage to cable bolt performance, but the extensive test work presented in this thesis hasproven the overall modulus of a cable bolt system is primarily dependent on bond strength.However, in view ofthe fact that POLYSTAL does not have a yield strength, the bond strengthmust be low enough to allow for residual ffictional strength to develop. Residual strength iscritical when maintaining mining operations in cable bolted areas.Table 12. Typical Mechanical Properties for Rebar, Steel Strand and POLYSTAL(Preis, 1986)Property Reinforcing Prestressing POLYSTAL E-glass UnstaturatedSteel Steel (68% Glass- Fibre PolyesterBST 420 S ST 1470/1670 fibres) ResinUltimate Tensile 500 1670 1520 2300 75Strength (MPa)Yield Strength 420 1470— -- --(MPa)______________________Strain, c (%) 10 6 3.3 3.0 4.0Elastic Modulus 210 210 51 74 0.3(GPa)Density (g/cm3) 7.85 7.85 2.0 ----One ofthe decisive properties for the selection of a rock support member is tensile strength.Polystal compares favourably with prestressing steel in terms oftensile strength, however, thereare considerable differences in their stress-strain behaviours. A typical POLYSTAL stress-straincurve as compared to steel is illustrated in Figure 9. The tengile strength ofPOLYSTAL isnearly equivalent to that ofprestressing steel Steel typically has a stiffer linear elastic behaviourthan POLYSTAL. Steel exhibits plastic deformation to failure whereas POLYSTAL iscompletely elastic to failure. The absence ofyield strength in composites must be consideredduring design since no warning offailure is realised. The elongation atfailure for POLYSTALis approximately one half that of steel, but its’ elastic elongation and recovery is as much as 3times greater than steel. This is illustrated by Figure 10 which is an example of identical loadingand unloading oftwo prestressed concrete beams, one reinforced with POLYSTAL and the otherwith prestressing steeLFatigue tests on POLYSTAL reinforced beams have proven its’ superior elastic recovery45over steel in concrete reinforcing applications. This benefit would also be realised in the FCB.POLYSTAL’s elastic modulus is about one fourth that of prestressing steel which wasconsidered a disadvantage prior to the laboratory pull-tests, but it was discovered thatreinforcement modulus was less important to the overall modulus of the FCB than bond strength.POLYSTAL’s spec/Ic weight is also one quarter that of steel and could potentially save oninstallation, handling and freight charges.:::___- 1470,1670 —13Z 1520 N/mm2 —I E =51000N/mmEu= 3,3%- 420T-Figure 9, Stress Strain Curves for Polystal and Steel (Preis, 1986)Tensile stress (N/mm2)2000180016001400-1200-10008006004002000024 6 8 10 12 14 16Elongation E (%)46f..oadFigure 10. Elastic Beam Recovery (Preis, 1986)Creep is a function of time, fibre content and temperature. POLYSTAL alone will creep 2-3% of the initial elastic elongation over a period of 60 years. Creep of the bond strength betweenPOLYSTAL and Portland cement is vital to FCB design. It is expected that laced, polyamidecoated FCB’s will creep less than conventional SCB due to their higher bond strength. On theother hand, creep could be beneficial to support where yielding is required.Ptastc deformation ofprestressirç steel473.4 CostsThe current cost (F.O.B. Vancouver) of a laced FCB, where the POLYSTAL is importedfrom Germany in small quantities and the secondary lacing fabrication is completed by hand,would be approximately $10-li per metre (Figure 11). This cost could be reduced significantlyif commercial quantities were manufactured in Canada. Import and overseas freight chargeswhich account for 16% ofthe overall cost would be eliminated.Figure 11. Cost Breakdown for the FCB in 1991 Dollars - FOB Vancouver, Canada(Con-Tech, 1991)Currently, the total cost of constituent materials (glass fibre and resin) in Canada are in theorder of $5 CAN per kilogram. Large-scale production costs are more difficult to estimate thanraw material costs. Consultations with the manufacturer ofPOLYSTAL, BAYER, have revealedthe potential cost of a FCB could be equivalent to the cost of a conventional SCB. ConventionalPOLYSTAL FOB Germany67.8%Con-tech mart-up16.8%Based on total FCB cost per metre = $10.33 (1991)• ..saIestax6.1%48and birdcaged SCB’s cost $2.15 and $3.00 to $3.25 per metre respectively. Considering theimproved bond strength and other unique properties such as corrosion resistance and light weightofFCB’s, a reduction in the overall support cost as compared to SCB’s could also be realised.As a result, raw material costs were investigated further.An exercise was completed to analyse the raw material cost of POLYSTAL versus its’ sellingprice of $2. 56 per metre. The approximate cost for the polyester resin used in POLYSTALconstruction profiles is $3.00/kg. The cost ofE-glass fibre is approximately $2/kg. The mass ofa 7.5 mm diameter uncoated POLYSTAL rod with a glass content of 80% by weight asmeasured in the laboratory was approximately 75 grams. On a raw material basis then, it costsapproximately $0.21 per metre of 7.5 mm diameter, uncoated POLYSTAL. The thermoplasticcoating would cost in the order of $0.18 per metre. Therefore, the raw material cost ofPOLYSTAL per metre has been estimated as $0.39 per metre. This amounts to a staggering640% margin over the raw material cost (excluding all other manufacturing, production andmarketing costs). From this analysis, it is obvious there is great potential for the development ofan economically competitive FCB.4. FAILURE MODES AND BOND STRENGTH MECHANISMS4.1 IntroductionUnderstanding common cable bolt failure modes under pull-out loads is essential to properlyinstalled and designed systems. SCB failure mode theory has been applied to develop the FCB.Laboratory and in situ pull-tests were conducted to evaluate the FCB.As with most materials under load, the FCB will exhibit time dependent behaviour, Thestrength of a FCB can be determined by short-term or long-term tests and, depending on theapplication, either may be necessary for design. This investigation concentrates on evaluating theshort-term strength of the FCB. For example, the laboratory pull-tests conducted at UBC49determined short-term strength values since the cure times were low and the strain rate relativelyhigh (15 mm/mm). Such tests are directly applicable to the design of stopes where support isonly required for a few months to a year. An example of a long-term test might cover a period ofa number of years, and usually reveals such properties as creep, corrosion and fatigue resistance.Creep can be of particular interest in permanent hangingwall installations and is defined here asthe gradual deformation under static load below the ultimate short-term capacity of the support.Although this investigation has quantified short-term FCB capacities; a qualitative assessment ofthe long-term capacity has been conducted using trial installations (Section 8). Other failuremodes considered important to the strength of a FCB, but not investigated were stress corrosionand notch sensitivity. POLYSTAL’s protective coating has been developed to resist these failuremodes. The coating also helps to reduce inter laminar failure between fibre and resin. Thecoating was observed to delaminate from the tendon under high pull-out loads where the inter-tendon angle was extreme.4.2 Driving ForcesTypically, underground excavations are dominated by: Case (1) tension, Case (2) shear andCase 3) dynamic driving forces. It is possible that at any one time during the history of a mine’slife, a cable bolt system could experience a combination of driving forces. In Canadian hardrockmining, the most common failure mode occurs along the grout/tendon interface (Vancouver,1991). The developments presented in this thesis have concentrated on bond strengthimprovements to the FCB.To improve the bond strength of the FCB, various configurations were tested. Eachconfiguration was carefully selected to exploit three main resistance mechanisms which affectbond strength: surface asperities, tendon configuration and surface area. The selection of nodespacing, spacer diameter and turns per metre were crucial to the prevention of premature tendonfailure or surface coating delamination.50For Case (2) driving forces, a [±45] bidirectional tendon has been recommended forevaluation. Some preliminary laboratory shear tests have been conducted at the University ofBritish Columbia to ascertain the potential of the FCB.Case (3) driving forces are often observed during blasts, stress relief or rockbursts. Ingeneral, the performance of cable bolts under these conditions is less understood. Theapplication of the FCB in Case (2) and (3) driving force applications require further evaluationand trial installations.4.3 Pull-Test Resistance MechanismsThe following five mechanisms were varied to improve the bond strength of the FCB underpull-test conditions:• surface area(S.A.)• surface roughness (Sr)• adhesive bond (A.B.)• tendon geometry ()• number of turns per metre (T)The unlaced configuration utiised the first three mechanisms. The laced FCB provided pullout resistance by utilising all five mechanisms. An explanation for each mechanism has beenlisted below:S.A,: An exercise was completed where a total cross-sectional area of 176.71 mm2 waskept constant (four unit lengths of 7.5 mm diameter POLYSTAL tendons) while tendondiameter and number (n) were varied and related to surface area (Figure 12). It wasfound for circular profiles, surface area increases exponentially as tendon diameter51decreases and “n” increases. Since bond strength is directly related to surface area, itfollows that bond strength should increase exponentially as tendon diameter decreasesand “n” decreases. The majority of the effort to develop composites for miningshould concentrate on taking advantage of this factor.800_600—.--2E Diameter (mm) n 8. A. (mmE—____1.0 225 706.864.0 14 175.93Lii 5.0 9 141.37400 -- 7.5 4 94.268.66 3 81.62LU 10.61 2 66.6615.0 1 47.12TENDON DIAMETER (mm)Figure 12. Surface Area vs Tendon DiameterS: Bond strength increases as the tendon roughness, or microscopic interlock, increases(coating thicknesses varied between 0.5 and 1.0 mm for POLYSTAL, therefore ultimate52tendon diameters varied between 8.0 and 9.5 mm). Uncoated POLYSTAL has a smoothsurface profile except for a single layer of helically wrapped fibres which adds to its’overall mechanical interlock with the grout.• A.B.: The adhesion between the cement and the polyamide coating can be divided intofour components: microscopic mechanical interlock, adsorption theory, electrostatictheory and chemical bonding. According to the manufacture, BAYER, the polyamidecoating was selected to improve the cement adhesion.• The inter-tendon angle, 4, has been defined as the angle in degrees at the antinodebetween any two tendons directly opposite one another. The introduction of the inter-tendon angle reduces interfacial shear and improves the mechanical interlock betweentendon and grout. Figure 13 is a free-body diagram that illustrates the effect of lacing onthe bond strength of the FCB. It is believed straight tendon configurations tended to havehigher interfacial shear forces between the tendon and grout and lower normal forcesacting on the tendon. This might explain the lower bond strengths experienced withstraight tendon configurations. However, by introducing an inter-tendon angle it wasfound premature tendon failure occurred at the critical bond length. Therefore, acompromise between ultimate capacity and premature tendon failure was sought.53Figure 13. Free-Body Diagram of LacingT The most favourable laced FCB possessed approximately 1 turn per metre for tendonsseparated 11 mm at the node and a node spacing of 127 mm. Practically, as the spacerdiameter increased, so did the number of turns per metre.4.4 FCB Failure Mode CategoriesDuring the evaluation of the FCB, a number of failure modes were observed and categorisedaccording to the driving force and environment (Table 13).Normal Force Acting onTendon CreatingImproved FrictionalResistance andMechanical InterlockReducedInterfacialShear BetweenTendon andGroutResulting ResistantForce, RRFPoint AApplied Force54Table 13. Summary of Observed FCB Failure ModesMODE CLASS DRIVING FORCE ENVIRONMENT OBSERVATIONS_____________TESTEDI pull-test laboratory pipe/groutII pull-test laboratory tendon/groutin_situIII pull-test laboratory tendonin situIV shear at 900 laboratory tendonMode I was observed for the laboratory pull-tests and w:c ratios of 0.65 (using PortlandType 30), Goris (1990) states to prevent such failures with Portland Type 1111, water cementratios of less than or equal to 0.45 must be used.Mode II was most common for laced FCB’s with embedment lengths less than 432 mm andfor unlaced FCB’s with embedments less than or equal to 914.4 mm.Mode Ill, tendon failure, was most common where the critical embedment was reached orexceeded. Tendon failure can vary from single tendon failures with residual strength to failure ofall tendons and no residual strength. An example of complete tendon failure can be seen inPhoto Plate 1. The failure of the tendon appeared to initiate at the collar of the pipe andpropagate towards the resin chuck. For the most part, Mode III was characterised bycatastrophic fibre breakage and inter-facial shear between fibre and resin.55Photo Plate 1. Appearance of Tendon FailurePreliminary laboratory tests for failure Mode IV have been completed and require furtherstudy. Laboratory shear tests were completed to evaluate a shear load applied 900 to the axis ofa FCB (Section 10).5. UBC LABORATORY PULL-TEST PROGRAM5.1 IntroductionHaving selected a composite for reinforcement, a prototype for testing was developed. ThisI56was accomplished using four 7,5 millimetre diameter POLYSTAL tendons which gave a totalcombined ultimate tensile strength of 27.3 tonnes and allowed for more direct comparisonsbetween FCB’s and SCB’s. As a result, preliminary pull-tests were conducted to ascertain thepotential ofPOLYSTAL for cable bolting. It was found that the FCB could effectively resistpull-test loads in excess of 20 tonnes verifjing the selection ofPOLYSTAL as a potentialproduct for mine support. This was proven with test Series A and later verified at the UnitedStates Bureau ofMines, Spokane with test Series FG18-7 to 11. Series A consisted of 6 lacedsamples with the following design parameters:• Four 7.5 mm diameter POLYSTAL tendons.• 203 mm (8 inch) node spacing.• w:cratioof0.35.• Portland Type 30 cement.• 58 mm (2.3 inch) diameter Schedule 80 pipe.• Displacement rate of 15 mm per minute.Series A was the first successful test over 20 tonnes and indicated an effective FCB could bedeveloped with POLYSTAL. Once this series was completed, plans were established to optimisethe configuration with available POLYSTAL materials. Table 14 summarises the ultimate pullout load for Test Series A.57Table 14. Summary of Ultimate Pull-out Loads for Test Series ATEST NUMBER ULTIMATE PULL-OUTLOAD, TONNES1 20.322 20.653 20.114 19.615 20.716 20.58AVERAGE 20.33During the preliminary testing stages, it was also discovered, as a rule ofthumb, theembedment length should be at least two times the node spacing before a significant bondstrength increase over straight FCB’s configurations could be achieved. Under these conditions,the tendon failure mode predominated which indicated a relationship between critical embedmentlength and tendon configuration.The laboratory tests performed evaluated the effect ofthe following design parameters on theultimate pull-out load of a FCB:• Embedment length• Water: cement ratio• Cure time• Confinement• Node spacingThe most significant factors as determined using fractional factorial design experiments andwith high early strength cement were: embedment length, water:cement ratio and nodespacing/location. It was observed that higher pull-out loads corresponded with samples wherethe antinode was located at the simulated joint plane. It was also recognized that increasing the58surface area (e.g. increase the number of tendons while decreasing the tendon diameter) androughness (e.g. presence of a silicon grit coating) would greatly enhance the bond strength.Goris, 1990, has determined that silicon coatings increase conventional SCB bond strength by30%. These changes were beyond the scope of the investigation. Control of tendon fabricationwas not available to vary the FCB profile diameter and roughness for optimal bond strength.Although the factors affecting the pull-out characteristics for SCB’s are well documented,such data did not exist for FCB’s. Having proven the axial potential ofPOLYSTAL for cablebolting, one of the next goals of the pull-tests at UBC was to determine the most significant bondstrength mechanisms for the FCB.5.2 ObjectivesThe objectives of the UBC pull-test program have been summarised below:1. Develop a prototype and acceptable test procedure for pull-testing.2. Determine significant parameters using design experimentation to guide flirther testing.3. Determine critical embedment length curves for laced and unlaced polyamide coatedPOLYSTAL grouted in Portland Type 30 cement with a w:c ratio of 0.35 and 7 day curetime (Failure Mode III).4. Evaluate premature tendon failure.5.3 ApparatusThe pull-test apparatus consisted of a shaft-mounted load cell, 30 tonne ram and strand chuckhousing. The ram was driven by an electric motor (not shown) while the feed was controlled bya needle valve. An average displacement rate of approximately 15 mni/min was maintained. The50 tonne load cell (± 1.0 kg) and LVDT (linear voltage difference transducer, ± 0.01 mm) were59connected to separate digital readouts. The test samples were inserted strand chuck first, lockingscrew tightened and the slack taken up by the threaded shaft so that the embedded portion of thesample rested against the apparatus frame (Figure 14).5.4 Sample PreparationAll pull-test samples were cured at room temperature and humidity. Grout/pipe slippage wasobserved for all samples with a 0.65 w:c ratio and 77 mm pipe diameter (FFD-I runs 5,8,13 andFigure 14. UBC Pull-Test Apparatus and Sample6016). Two spot welds were placed on the inside of the pipe to prevent grout/pipe slippage. Therest of the UBC test samples did not exhibit grout/pipe slippage. All samples exhibited micro-shrinkage cracks which were considered detrimental to the pull-out resistance. Goris states thatwater to Portland Type I/Il cement ratios less than or equal to 0.40 are required to preventsignificant amounts of shrinkage in “fully cured” (28 days) samples. UBC samples with water toPortland Type 30 cement ratios greater than 0.45 did not have grout/pipe slip after 7 days ofcuring. This was likely due to the use of the high early strength cement. It was also visuallyobserved during hand mixing that the cement grout consistency was difficult to maintain below a0,35 w:c ratio for Portland Type 30 cement. The pull-test samples were cut open longitudinallyto observe the grout consistency and failure mode.In order to achieve as consistent results as possible, strict sample preparation steps werefollowed:Sample preparation:Stage A. Resin Stage (Fi2ure 15)1. Cut tendons to desired length.2. Peel polyamide coating off to a length of 96 mm.3. Force a 7 mm i.d. vinyl tube centralizer over peeled end.4. Cut cross-hatch in peeled end of the POLYSTAL to a depth of 20 mm.5. Insert aluminum, or similar type, wedge.6. Combine tendons, four at a time, into desired configuration using PVC spacers.7. Resin peeled ends into strand chuck using G2 unsaturated polyester resin (2A: 1B, IndustrialFormulators Vancouver, B. C.) ensuring the lock nut is between lacing and strand chuck.8. Allow to cure overnight prior to Stage B.61Strand chuckAluminum wedgeVinyl tube centralizer 7mm l.D.Split ends @ 9004 polystal tendons with polyamidecoating peeled off4 polystal tendons with polymidecoating (7.5mm )Locking nut for strand chuck1. Cut pipe to desired embedment length plus 50 mm.2. Wash pipe with. soap and water, rinse and dry.mmmmFigure 15. Resin StageStage B. Grouting Stage623. Hand mix cement at the desired w:c ratio.4. Place pipe in stand, centre over plastic covered hole.5. Fill pipe with cement to approximately 100 mm from top.6, Insert bolt into grouted column and push through plastic covered hole.7. Visually align sample.8. Use clay to plug the hole from beneath.9. Top off or remove excess cement from column.10. Place wet rag on top of cement.5.5 Test ProceduresOn the average, six samples could be tested per day. This resulted in an average cure timedifference between the first and last sample of approximately 9 hours. The test procedures wereas follows:1. Clean resin chuck and pipe surfaces thoroughly.2. Insert sample into test apparatus and tighten lock nut.3. Arrange LVDT telescopic arm with respect to ram stroke.4. Apply initial load of approximately 451 N (or 46 kg mass).5. Attach dial gauge at tail end of sample.6. Record initial load and displacement.7. Turn hydraulic pump on and tap the needle valve lightly to open and adjust so that thedisplacement rate was approximately 15 mm/mm.8. Record load at 1 mm intervals.9. Run test for 20-30 minutes unless tendon failure occurs.10. Remove sample and clean machine,635.6 Design ExperimentsDesign experiments are of significant value for (1) exploratory work where the individual andjoint influence of several variables must be determined quickly and (2) experimental programs toobtain empirical models over a range of operating or testing conditions. As a rule, the designresults should not be extended beyond the test conditions or range of factor levels unlesssignificant calibration data is available (Mular, 1989).Design experimentation was used as a tool to assist in determining the effect and significanceof design parameters in the development of the FCB. The design experimentation resultsprovided research direction and streamlined test-work.5.6.2 TerminologyBefore continuing, the following terminology has been explained:• Afactor refers to a controllable, test variable which can be set at predetermined values foreach test. Factors are generally quantitative.• A level is the value at which a factor is set for a particular run. High and low level factors arecoded with positive (+) and negative (-) signs respectively. Centre point levels are coded bya zero (0).• Runs are experimental tests where the factors are set at design levels.• A response is a numerical test result, such as pull-out load or displacement. The responsesare used to determine the “effect” of each factor on the response.• An effect is defined as the overall average change in response produced by an increase from alow to a high level of that factor.• A mean effect is the average of all responses.• A main effect is the difference between the average response of all runs carried out at the64higher level of the factor and that of all the runs at the lower level.• An interaction effect between two factors xi and X2 is the average difference between theeffect of an increase in level ofx1 at the higher level ofx2 and the effect of an increase inlevel ofxi at the lower level ofx.• Resolution. A design of resolution R is one in which no q-factor effect is confounded withany other effect containing less than R- q factors.• Confounded. In a fractional factorial design, where not all the required runs are tested, theestimated effect, Lijk can represent more than one effect of the complete factorial design, ‘ijk’It is then said that the estimated effects of a fractional factorial design are confounded.• An alias structure is a list of estimated effects and their confounded partners. The additionsigns in the alias structure represent the confounded partners, not the actual addition of effectvalues, The alias structure is used as a guide for determining an effect from its confoundedpartners.Hence, a factorial design varies the level of a number of factors and completes a run for eachvariation. The selection of an appropriate alias structure must be guided by the objective of theexperiment. In this case, the main effects were sought with the lowest number of acceptableruns. It is sometimes necessary to replicate a design to improve confidence.Once all runs of a design are complete, the main and interaction effects of all factors aredetermined. In other words, the statistical significance of each factor is found and assessed.From this process, a predictive equation is generated using the least squares method.5.6.2 Two Level Fractional Factorial Design BasicsThis design procedure is one of the simplest and leads to an estimated linear relationshipbetween responses and factors. Usually under the range tested, a linear equation sufficientlyapproximates the true response:65where the j’5 are the estimated response, ai’s are the constant coefficients determined by the leastsquares fit method, Xj’S are the factors, n equals the number of experimental factors to beassessed and ej’s are the residual error associated with each estimated response. All the possiblecombinations of high and low levels of the chosen factors are tested in a complete factorialdesign. Clearly, in order to test all the possible combinations of factor levels for FFD-I, 2=128runs were necessary. It was decided a fraction of the complete factorial design, FFD-I, would becompleted. As a result, the number of significant factors was reduced to three and more timewas spent evaluating their effect on the pull-out of the FCB.The rules for FFD’s and factorial designs are basically the same. We denote the number ofruns in a two level FFD as, 2np, where “n” is the total number of factors and hPpU represents thenumber of half-fractions of a complete factorial design desired. For example, a FFDcompletes three half-fractions, or one-eighth, of the total number of the possible outcomes of acomplete, 2 factorial design. The primary reason for selecting the FFD of RJV was that foras few as 20-24 runs, the main effects were not confounded with one another and therefore couldbe estimated with a fair degree of confidence. Since the two-factor effects were confounded forFFD-I, certain ambiguities arose when deciding which estimated two-factor effect wasrepresented within the alias structure. Three factor interaction effects were assumed negligible.This simplified the statistical analysis and was considered the most likely approach to successfiullyconclude the main effects using a limited number of runs. A summary of the steps taken toconstruct the FFD-I were as follows:1, Select a high, low and centre point level for each factor.2. Determine total number of economical runs = 2flP + (centre point runs).3. Code variables using x = + (for hi) or - (for low).664. Construct design matrix of coded levels using 2”P rows, in standard order where + and -signs are alternated along x column using the 2i rule.5. Construct matrix of effects in coded units.6. Calculate effects.7. Perform tests of significance on each effect.8. Eliminate insignificant effects.9. Calculate coefficients for significant effects.10. Obtain predictive equation in coded units.11. Obtain predictive equation in real units.12. Check the fit of the linear predictive equation.5.6.3 Fractional Factorial Design I (FFD4) ResultsThe levels of each factor were determined from operating ranges of steel cable supports andcan be found in Table 15.Table 15. Factors Levels - FFD-IFACTOR LOW LEVEL CENTRE HIGH LEVEL RANGEPOINTV1 (mm.) 5 10 15 10mix timeV2(mm) 152 305 457 305emb._lengthV3 (mm) 48 58 77 29pipe diam.V4 (days) 2 6 10 8cure timeV5 0.35 0.5 0.65 0.3w:c_ratioV6(mm) 20 23 26 6spacer_diamV7(mm) 0 305 610 610node_spacing67The variables, Xj, were coded by inserting the values of Table 15 into the following equation:= Va — centrept0.5*rangewhere V1 equalled the actual low or high value of a factor. This resulted in Xj’S being coded aseither + 1 or -1 respectively.All factor levels for the centre point runs were coded as 0. Runs 17 to 23 were also referredto as Series I. The seven factors, coded Xilto7, are defined below:• xi Mix time - the hand-mixing time in minutes from the moment the water was added to thefirst pouring of a sample.• X2 Embedment length - distance in millimetres from one end of the grout column to theother.• X3 Pipe diameter - the inner pipe diameter in millimetres of a Schedule 80 steel pipe.• X4 Cure time - the number of days the cement was allowed to cure.• X5 w:c ratio - the dimensionless ratio of the weight of water to the weight of cement.• X6 Spacer diameter - the inner diameter of a PVC spacer that determines the inter-tendonangle, 4.• X7 Node spacing - the distance in millimetres between any two successive nodes orantinodes.There were a total of 23 total runs, 7 of which were externally tested centre point runs usedto determine the error variance, Se2 = 0.846.The matrix of coded levels, measured responses, rest from the predictive equation andassociated residual errors for FFD I are found in Table 16. The predictive equation developed68by FFD-I reasonably approximated actual test results. Each residual error value was plottedversus its associated predicted response in order to check the adequacy of the fitted model(Figure 16). From this figure, two general trends were apparent:• The predictive equation over-estimated pull-out loads less than 5 tonnes or greater than 15tonnes.• The predictive equation under-estimated pull-out loads between 5 and 15 tonnes.Residual Error6ouffler a4• ouffler?2-a0•a•aa-4outHer-6 I I0 5 10 15 20Estimated Pull-out LoadFigure 16 Plot of Residuals vs Predicted Pull-out69Table 16. Matrix of Coded Levels, Responses, Estimated Responses and Residual ErrorsFFD-IRun mix emb pipe cure w:c spacer node ‘measured ‘estimate eNo. xl X X3 X4 X5 X7 tonnes tonnes tonnes1 - - - - - 6.80 7.75 -0.452 + - - - + - + 3.74 3.99 -0.253 - + - - + + + 8.54 10.39 -1.854 + + - - - + - 20.12 18.87 1.255 - - + - + + - 5.04 1.74 3.306 + - + - - + + 9.84 10.42 -0.587 - + + - - - + 16.71 16.99 -0.288 + + + - + - - 10.55 12.66 -2.119 - - - + - + + 7.30 5.16 2.1410 + - - + + + - 5.04 7.00 -1.9611 - + - + + - - 15.40 13.40 2.002 + + - + - - + 21.64 16.08 5.563 - - + + + - + 5.50 4.74 0.764 + - + + - - - 5.53 -1.8915 - + + + - + - 9.08 13.82 -4.746 + + + + + + + 15.92 15.66 0.2617 0 0 0 0 0 0 0 10.50 10.42 0.0818 0 0 0 0 0 0 0 12.76 2.3419 0 0 0 0 0 0 0 11.21 0.7920 0 0 0 0 0 0 0 10.42 10.42 021 0 0 0 0 0 0 0 10.14 10.42 -0.2822 0 0 0 0 0 0 0 10.23 10.42 -0.1923 0 0 0 0 0 0 0 11.23 10.42 0.81For this particular FFD there were p=3 principle generators which were calculated bymultiplying x by itself to yield xx = I = xlx2x3xs, X6 by itself to yield x6x = I =x2346,and X7 by itself to yieldx7= I =x1247.The principle generators were multiplied by eachother two and three at a time to yield a complete defining relation:I = XX2X3X5 =X2346= XjXX4X7 = X3X457= X1X4X5X6 =X13X67= X2X5X6X770From the complete defining relation, the alias structure was constructed by multiplying thefactor(s) involved in the effect times each term of the defining relation noting any factor timesitself equals one (Table 17). For example, L1 was calculated by multiplying x1 by each term inthe complete defining relation to give:L1 = ii +1235 + 1247+1456 + 1367 + 112346 + 113457+112567Since by definition, a FFD assumes all third and fourth order effects negligible, L1simply estimates I. In a similar manner, the remaining alias structure was calculated. Acomplete factorial design has n=7 main effects, n(n-1)/2!=21 two factor effects, n(n-1)(n-2)/3!three factor effects and so on. For FFD-I, seven main effects, seven two factor effects and onlyone three factor effect could be estimated. Judgement was used to interpret which confoundedtwo factor effect, ij was estimated by LJ. The mean, main and three factor effects were straightforward representations. Figure 17 illustrates the configurations tested.Table 17. Alias Structure, FFD-I1L2=1 IL3=1 I=14 F + (higher order effects assumed negligible)L5=1 IL6=1 IL7 =1712=1+35471L23 = 123 +146 + 1i5 I=+657L45 =145 +116 +137 F + (higher order effects)6=+127 IL67 = 167 + 113 + 125 I1=+243 -‘L123 = 1123 + 15 + (higher order effects)71Runs 2,8,9,13 (L • 152 mm) Runs 1,5,10,14 (L • 152 mm) Center Point RunsRuns 3,7,12,18(L • 457 mm) Runs 4,8,11,15 (L 457 mm) L • NS • 305 mmLaced FCB (NS 610 mm) Straight FCB (spacer used) Laced FOBFigure 17. FCB Configurations FFD-IThe centre point runs were external (completed separate from) to FFD-I and as a result werenot included in the calculation of the mean, main, two-factor and three factor effects. Thestandard equations used to calculate the effects are contained in Appendix A. A summary of theestimated effects, their ranks and normal scores is listed in Table 18.(a) (b) (c)CASE A CASE B CASE CPIPE GROUT72Table 18. Estimated Effects and Normal ScoresEffect Effect Rank, i pi = (1 -0.5)/rn Normal ScoresMagnitudeLj -3.14 1.5 0.07 -1.48L12 -3.41 1.5 0.07 -1.48L2 -2.99 3 0.17 -0.96L’4 -2.04 4 0.23 -0,74L3 -1.30 5 0.30 -0.53L67 -0.87 6 0.37 -0.40L6 -0.63 7 0.43 -0.18L4 -0.12 8 0.50 0L56 0.46 9 0.57 0.18L17 1.02 10 0.63 0.33L7 1.45 11 0.70 0,53Lj 2.25 12 0.77 0.74L12 2.37 13 0.83 0.96L4j 2.99 14 0.90 1.28L2 8.65 15 0.97 1.89Note:m = total number of estimated effects excluding L0Zj : P(Z z) = P = (zj) for probabilities 0.50 OR= 4(-zj) for probabilities < 0.50if effect magnitudes were tied, an average rank was assignedFigure 18 plots the normal scores versus the value of each estimated effect in order todetermine significant effects. From this graph, three significant main effects were found: mixtime (L1), embedment length (L2), w:c ratio (L5) and one significant two-factor interactioneffect between cure time and w:c ratio, L45. The coefficients for the predictive equation weredetermined from the significant effects and the coded units were transformed back to real units togive the following relationship:rest = 12.7 + 0,226*V1+ 0.0284*V - 26.4*V5+ 2.5*V4*V - 1.25*V5 (toflfleS)where V1 was mix time in minutes, V2 was embedment length in millimetres, V4 was cure time73in days and V5 was w:c ratio.2 a • I I 1L2:1.5 .1 tS.d—1.5 L5—2-4 -2 0 2 4 6 8 10VALUE OF ESTIMATED EFFECTSFigure 18. Normal Scores vs Estimated Effect Values - FFD-IA summary of the conclusions drawn from FFD-I is listed below:• An increase in embedment length from 152 mm to 457 mm increased pull-out loadsignificantly. However, critical embedment lengths were not determined.• A decrease in water cement ratio from 0.65 to 0.35 increased pull-out load significantly.• A cure time increase from 2 to 10 days did not significantly increase pull-out load forPortland Type ifi cement (high early strength).• An increase in pipe diameter from 48 mm to 77 mm did not significantly increase pull-out74load. This corresponds to tests with conventional steel cables (Mime 1988-90).• An increase in node spacing above 305 mm did not significantly increase pull-out load.• An increase in mix time increases pull-out load.• The effects of node spacing and spacer diameter required fhrther investigation.• The effects of increasing or decreasing the factors tested in FFD-I are similar to steel cablebolts (Goris, 1990).The pull-test curves for FFD-I are contained in Appendix B. For all runs, the FCB slippedwith respect to the grout.5.7 Embedment Length Relationships5.7.1 IntroductionCritical embedment length has been defined as the embedment length of a pull-test samplerequired to cause tendon failure. Comparisons of laced POLYSTAL, straight POLYSTAL,conventional steel strand and birdcaged steel strand have been made. The critical embedmentlength is particularly important to cable bolt designs in highly fractured ground.5.7.2 Codes and VariablesThe ultimate pull-out loads resulting in tendon failure of Series A, Series II to TV and thoseconducted by Peterson, 1991 were combined to form the critical embedment length relationshipspresented here (Table 19). All samples were tested under the following conditions:(1) Cement was hand-mixed for 15 minutes.(2) Grouted in a 58 mm pipe diameter.(3) Cured 7 days at a 0.35 w:c ratio.75CD CD‘T1T1T1MT1coo0000-II-0CD 1-Q CDCDCDC12CDCD. CDCD1-l)l200zoII00-pI CD 0- 0 CD 0 0- C.) 0 CDViViViViVit’)l’3t\)00000cL’)t%)t)t)ViViViViVi0 0- 0 CD p Vi I. I.-.‘J.........ViViViViViViViViViViVi00000-.-‘-L)t.)0000000000()t’)‘3I’.)L)L)i’.)-‘-‘13000000t)L)L.)ViViViViVi._).-.....0 %— c tljCI2’-oI)4OOOOOQOCT1Vi.00 C)_<0-CD0CDCD0—.00C)CDCD-.2. CDCD 1.IJ—JVi0L)CJ0000‘Jt)IppoVi-O00-’t’t’)t’3L)tt))00L0000ViL.)OOViJi—Vi0Vio00CDrA minimum embedment length to node spacing ratio of 2:1 was necessary to result intendon failure. Critical embedment lengths ranged from 432 mm to 508 mm for laced FCB’s.For comparison, the average ultimate pull-out load of Series FG1 8 was 7% higher than for SeriesA despite the differences in cement type.5.7.3 Pull-Test CurvesSix pull-tests were completed in Series A (Figure 19). The samples had 203 mm nodespacings and 457 mm embedment lengths. One (1) to three (3) tendon failures were observed inall the samples. The approximate stifThess of the average Series A pull-test curve was 1 tonneper millimetre of displacement.Approximate stiffness = 1 tonne/nim1-3 tendons failed. IFigure 19. Average Pull-Test Curve for Series A252015CC0a. 10500 5 10 15 20 25 30 35 40 45 50Displacement (mm)77Pull-test curves for Series II to IV are contained in Appendix C. A summary of theresults from the critical embedment length investigation are listed in Table 20.Table 20. Series A & Series 1I-IV Failure ModeSERIES EL NS EL:NS Average Normalised Failure(mm) (mm) RATIO Ultimate Load Mode(tonnes) (tonnes/m)A-coated 457 203 2.25 20.33 44.49 tendonII- uncoated 457 203 2.25 10.10 22.10 slipifia-coated 508 254 2.00 21.05 41.44 tendonfIb-coated 914 254 3.60 19.70 21.55 tendonWa-coated 305 127 2.4 19.34 63.41 slipIVb -coated 432 127 3.4 22.72 52.60 tendonNote:EL = embedment length.NS = node spacing.EL:NS = embedment length to node spacing ratio.Normalised Load = average ultimate load divided by embedment length, EL.The uncoated test Series II was dominated by the “slip-stick” failure mode as observedduring the pull-test on sample FG18W-6 at the United States Bureau ofMines, Spokane. TheSeries II sample were cut open longitudinally to investigate this failure mode. It was observed a“skin” containing the helically wrapped fibres had delaminated from the tendon and remainedbonded to the cement. As compared to coated tendons, uncoated tendons tend to have lowerultimate strengths and normalised loads.Coated tendon failure occurred at tested embedment lengths between 432 mm and 914mm. Ultimate loads were greater than 19 tonnes for all the series where tendon failure occurred.78Normalised load, defined as the average ultimate load divided by the embedment length rangedfrom 21.55 tonnes to 52.60 tonnes. Series IVb had the greatest bond strength at tendon failure.5.7.3 Critical Embedment Length CurveFigure 20 illustrates the critical laboratory embedment lengths for various FCBconfigurations. Ultimate pull-out loads and critical embedment lengths for the FCBconfigurations tested ranged from 20 to 23 tonnes and 432 to 914 mm respectively. Forcomparison purposes, SCB’s grouted with Portland Type I/il cement and cured for 28 days at aw:c ratio of 0.45 have a critical embedment length and ultimate pull-out load of 1067 mm and26.4 tonnes respectively (Goris, 1990). A clear trend towards higher pull-out loads at lowerembedment lengths was apparent as the node spacing is decreased.Lower ultimate loads were associated with larger node spacings, larger spacer diameters andunlaced tendon configurations. By increasing the spacer diameter (node diameter), it has beensuggested that the transverse shear component introduced to the tendon is increased. In suchcases, with the addition of the differential tendon displacement effects, premature tendon failureson the average ranged from 75% to 84% of the ultimate theoretical tensile strength ofPOLYSTAL. The optimal critical embedment length achieved was 432 mm (Series IVb). Thisconfiguration achieved the highest bond strength as determined by this investigation whileminimising premature tendon failure. For comparison, conventional SCB at an embedmentlength of432 mm have an ultimate pull-out load of 10 tonnes (Goris, 1990). Despite thedifferences in test parameters for the above comparisons, it is clear FCB’s exhibit dramaticimprovements in bond strength over conventional SCB’s. The critical embedment length forunlaced FCB’s is 914 mm at 21 tonnes.79C•10-0•0CCC—a 2.9C0.aC0zIE‘0V.0ELUCC.)1000900800700600500400’300200’10000.e.ec110.aVI20.63 tonnes23 tonnes20.33 tonnes0 100 200 300 400Node Spacing, mm500 600 700Figure 20. Critical Embedment Lengths for FCB’s5.8 Premature Tendon Failure (PTF)PTF has been defined as the abrupt failure of one or more members of the reinforcementconfiguration during a pull-test prior to developing the total combined UTS (in this case fourPOLYSTAL rods) and is a measure of the detrimental effect caused by lacing a UD composite.This phenomena is more predominant in POLYSTAL reinforced cable bolts than those reinforcedwith steel. For a tendon under ideal unconfined tensile loading conditions, the ultimate tensilestress a POLYSTAL tendon can achieve is 1520 MPa. A pull-test introduces confinement,transverse shear and less than ideal anchoring conditions otherwise not associated with idealtensile tests. As a result, the ultimate theoretical tensile strength ofPOLYSTAL is rarely reachedin mining. A tendon configuration was required to minimise this effect which was assumed to be80associated with the introduction ofnon-tensile forces and differential tendon displacement. Therod configuration for Series IVb limited premature tendon failure to 84% of the combinedultimate tensile strength. The introduction of shear, torsion and bending force components to thedriving force increases the likelihood of premature tendon failure. In most of the samples tested,the tendency for one or more of the grouted POLYSTAL rods to displace differentially withrespect to one another was unavoidable. This caused tendon overload and eventually failurebefore the combined UTS was reached. Differential tendon displacement was promoted by twosources:(1) Non-uniform bond between cement and POLYSTAL.(2) Differential loading at the collar of a pull-test sample where exposed POLYSTAL meetscement grouted POLYSTAL.Uneven bond distribution between the four POLYSTAL rods was likely the most significantfactor contributing to premature tendon failure. The addition of differential loading at the collaraggravated the situation. It was observed that tendon failure originated at the collar of the pipe orbottom of the resin chuck and propagated throughout the remainder of the exposed tendon. Thefailed tendon resembled a “broom-like” structure (Photo Plate 1). The following is an excerptfrom Mah eta!, 1991:“PTF was more prominent in the UBC test results where the tendonfailure mode occurred.First andforemost, one tendon often displaced with respect to the grout more than theothers causing tendon overload leading to prematurefailure. Second, the dfference indisplacement between thefree portion of the tendon and the groutedportion caused stresspeaks. This coincided with stffer grouts as a result of lower water:cement ratios and highercure times introducing larger transverse shearforces into the tendon and less groutcrushing It is suspected that this phenomenon contributed to premature tendonfailure81before the ultimate theoretical tensile strength of27.3 tonnes was reached. Thefree tendonin the UBC test apparatus promoted differential displacement. Premature tendonfailurewas much lesspronounced in the USBM and Queen’s results since the samples werefullygrouted minimizing the amount offree tendon to less than 10 mm.”The study has shown Series IVb was the best compromise between high bond strength andgreatest utilisation ofultimate tensile strength of the 7,5 mm diameter POLYSTAL tendons.However, this does not represent a fi.illy optimised, high bond strength FCB configuration.Future research should concentrate on increasing the number of tendons (surface area) in anunlaced fashion to reduce transverse loads.5.9 Summary of Critical Embedment Length DeterminationsTable 21 summarises the relationship between pull-out load, inter-tendon angle, criticalembedment length, normalised pull-out load, inside diameter of spacer, embedment length tonode spacing ratio, stiiThess and premature tendon failure (PTF). By reducing the inter-tendonangle and node spacing at the same time, it was possible to increase the pull-out load andpercentage of combined ultimate tensile strength used. The optimal configuration tested wasSeries IVb which had an average ultimate load of 23 tonnes at a critical embedment length of 432mm. Generally, a minimum embedment length to node spacing ratio of 2.0 is required to achievetendon failure. Further research supporting these results has been conducted by Peterson, 1991.82Table 21. Summary of Critical Embedment Length DeterminationsNODE 127 mm Straight* 254 mm 203 mmSPACING (5 inches) (10 inches) (8 inches)Series IVb Series ifia Series APull-out Load, 23 21 20.63 20.33tonnesInter-Tendon Angle 990 -- 10.4° 13°Critical Embedment 432 914 508 457Length (mm)Normalised Load 53 23 41 46tonnes/metreSpaceri,d. 11 20 20 20(mm)Approximate Stiffness 1.53 0.88 1.20 1.00at failure (tonnes/mm)Embedment length to 3.4 -- 2.0 2.25node spacing ratio.% of Combined 84% 77% 77% 74.5%UTS (PTh)Note:UTS = ultimate tensile strength of POLYSTAL 1520 MPa (Preis, 1986)PTF = premature tendon failure.* Peterson, 19916. USBM LABORATORY PULL-TEST PROGRAM6.1 IntroductionThe United States Bureau of mines (USBM), Spokane Washington, is presently conductingresearch to determine the properties and design guidelines for the installation of SCB’s. Theproject leader, John M. Goris, has assisted in the development of the FCB.An initial consultation took place with Goris in October, 1989 and plans for a FCB pull-testprogram at the USBM were established. The samples were prepared by Goris and Mah in lateJune, 1990. Subsequent testing and data reduction was completed one week later. The sample83preparation and testing of the FCBs were identical to the methods used by Goris for previoustests on SCBs. This allowed for more direct comparisons.6.2 ObjectivesThe objectives of the laboratory tests completed at the U. S. Bureau ofMines were:1. Compare laced FCBs to “standard” USBM birdcaged and conventional SCB’s.2. Test one laced uncoated FCB.3. Test one straight coated FCB.4. Compare Series A and FOl 8 results despite different cement types.Objective (1) and (4) have allowed definite conclusions. Objectives (2) and (3) were limitedto one sample each and completed for comparison purposes only.6.3 Pull-Test Apparatus and SampleThe pull-test apparatus shown in the schematic Figure 21 (Goris 1990, Fuller and Cox 1975)consisted of two, 58 mm i.d. Schedule 80 pipes separated by a rubber washer. The bottom pipe,or test column, was embedded either 305 mm or 457 mm (depending on the test) in PortlandType I/il cement. The upper pipe consisted of a 914 mm grout column and acted as an anchor.An additional 102 mm of tendon was left extended from the bottom pipe ungrouted to ensureconstant embedment length once the tendons fully mobilized with respect to the grout. Twopotentiometers were attached to either side of the pipe and an LVDT was stationed at the headof the machine. The upper head, coupling and anchor pipe moved away from the bottom bearingplate during a test.84Figure 21. USBM Pull-Test Apparatus and Sample (Goris, 1990)6.4 Sample PreparationFirst, the laced or straight POLYSTAL configurations were placed in the anchor pipe andcentred with a donut shaped No. 11.5 rubber stopper (Photo Plate 2 (a) and (b)). The anchorpipe was filled with continuously mixed Portland Type Jill cement. A 3 mm thick petroleumcoated rubber washer was placed on top of the anchor pipe. This helped seal the pipe. Next, thetest column was placed on top of the washer covered anchor pipe and held firmly in place by asleeve clamp. The test column was then grouted and the POLYSTAL centred with either tape ora screw cap.ANCHOR914.4 mmTESTLENGThEMBEDMENTO5 to 457 mm85Photo Plate 2 (a). Series FG12 Sample PreparationPhoto Plate 2 (b). Series FG18 Sample Preparation866.5 Test ProcedureThe samples were selected at random and threaded onto a 1.8 million Newton hydraulic stiffpull-test machine. The displacement rate of the upper plate with respect to the stationary lowerplate was set at 15 mm/mm. Axial loads and displacements were recorded by a load cell andlinear variable differential transformer (LVDT) respectively. Two potentiometers were attachedto the pipes and served as a backup to the LVDT; the displacement readings agreed. A thirdpotentiometer was attached to the free tendon of the test column tail end and indicated whentotal mobilisation with respect to the cement grout occurred in the test column. Grout/pipeslippage was not detected. Pipe rotation was monitored visually by etching reference lines on thepipes and bearing plates. No rotation was detected. Progressive debonding occurred in bothpipes, but by design, the test column reached peak pull-out load and displacement first due to itsshorter embedment length. The displacement of the tendon with respect to the grout wasassumed equal for the anchor length and test column. Hence, the displacement was calculated bydividing the total measured displacement by two.Longitudinal strain tests were performed near the pipe/coupling interface at 27 tonnes byGoris prior to the pull-test program and indicated the pipes were not overstrained. Actual strainswere less than the theoretical limits of the steel.6.6 Wick EffectEleven samples were grouted and very little bleeding or sedimentation took place. Thisverified the absence of the “wick effect” which has been known to cause the grouted columnlength to decrease by approximately 8% for SCB’s (Table 22). Over a 20 metre conventionalSCB this equates to 1.6 m. The samples were cured in place for 24 hours and then moved to ahumidity controlled room for the remaining six days at 21°C and 100% humidity. The FCB,epoxy covered conventional SCB and birdcaged SCB eliminate potential failures associated with87the wick effect.Table 22. Wick Effect - Conventional SCB’s(Goris, 1990)w:c 0.30 0.35 0.40 0.45decrease in grout 15.85 32.51 63.32 95.83column length1Note:1 values represent the decrease of a 1 m grout column in mm.6.7 Codes and VariablesTable 23 is a list codes, strand types, configurations, embedment lengths and w:c ratios forthe USBM test samples.Table 23. USBM Pull-Test SamplesSample Number Polyanide Coating Node Spacing (mm) w:c RatioFG12-1 yes 178 0.45FGI2-2 yes 178 0.45FG12-3 yes 178 0.45F012-4 yes 178 0.45FG12S-5 yes straight 0,45FG18W-6 no 203 0.35FG18-7 yes 203 0.35FGI8-8 yes 203 0.35F018-9 yes 203 0.35FG18-10 yes 203 0.35FG18-11 yes 203 0.35Note for Sample numbers in Table 23:FG = Fibreglass12= 305 mm (12 inch) embedment length18 = 457 mm (18 inch) embedment length-1 = Sample number 1 of 11S = Straight strands (not laced)W = Uncoated fibreglass strands88“Standard” SCB samples previously tested by (loris and used for comparison purposes in thisinvestigation consisted of single 15.88 mm (5/8”) conventional or birdoaged SCB grouted with a0.45 w:c ratio in Portland Type 1111 cement ((loris, 1990).6.8 Unconfined Compressive Strength of GroutTen compression samples were poured into ASTM standard 2 cubic inch brass molds andcured for seven days under identical conditions as the pull-test samples at 21° C and 100%humidity (Table 24).Table 24. Unconfined Compressive Strength of Grout(7 Day Cure)Sample Number w:c = 0.45 (MPa) w:c = 0.351 32.75 43.972 33.80 39.923 29.65 39.014 32,50 40.465 33.44 42.06Average 32.42 40.98The average unconfined compressive strengths for the FCB tests (7 day cure) with waterto cement ratios of 0.45 and 0.35 were 32.42 MPa and 40.98 MPa respectively. For comparison,tests conducted previously by Goris, 1990 on SCB with water to cement ratios of 0.45 and 0,35revealed average 28 day cure unconfined compressive strengths to be 50 MPa and 56 MParespectively. Therefore, the cement strengths for the FCB pull-tests using 0.45 and 0.35 water tocement ratios were 65% and 73% of the 28 day cure SCB pull-test cement strengths. Despitelower cement strengths, it has been shown the FCB has comparable pull-out strengths to steel.8969 Results and AnalysisFigure 22 illustrates the typical behaviour of an uncoated laced fibreglass cable bolt with twonodes spaced 203 mm apart. The curve displays some unique, and particularly adverse,characteristics for uncoated POLYSTAL. The initial stiffness, defined as load per unitdisplacement, of the uncoated system closely follows coated behaviour, but at approximately 9tonnes there was an abrupt reduction in stiffness followed by what has been termed the“slip/stick” failure mode. This failure mode was characterized by three stages which weredominated by different failure mechanisms as compared to the polyamide coated FCB’s:• Stage 1 was dominated by a progressive adhesion failure between the tendon and grout.• Stage 2 was dominated by what appeared to be resin/fibre interfacial shearing where a “skin”ofPOLYSTAL, consisting of a layer of helically wrapped fibre and perhaps few layers ofunidirectional fibre, remained bonded to the grout. Alkali corrosion of the POLYSTAL wassuspected to contribute the reduced stiffness in this area. Hence, the polyamide coating notonly enhances surface roughness, but it also reduces corrosion and distributes load to thetendon. In fact, some of polyamide’s virtues include toughness, ductility and abrasionresistance. A large displacement of 300 mm was accommodated before rapid unloading.• Stage 3 was dominated by a “slip-stick” failure mode between the cement and POLYSTAL.At this point, the tendon was completely mobilized.90Stage 3Figure 22. A Typical Load/Displacement Curve for Uncoated POLYSTALThe slip/stick behaviour was also observed in tests performed at the University ofBritishColumbia (Series II), but the reduction in stiffness was not. More test work is required todetermine the extent to which the slip/stick failure mode reduces the support capacity ofuncoated POLYSTAL in FCB’s. In general, it is recommended surface treatments be used to aidin the load-transfer between grout and a fibre reinforced composite. Uncoated tendons have thepotential for yielding support applications.Figure 23 shows the load/displacement curves for samples FG18-7 to FG18-1 1. Eachsample was dominated by the tendon failure mode where at least one tendon failed before alladhesion was lost. This resulted in high precision of the results since the tendons themselves wereconsidered to have consistent properties. An average peak load of approximately 21.75 tonnesor 78% of the theoretical strength was reached. Under the same laboratory load conditions andStage 218.0016.0014.0012.00aa10.0008.000-J6. 1100.00 200.00 300.00 400.00 500.00Displacement (mm)600.0091embedment lengths, conventional SCB’s exhibited grout/tendon bond failure at 14 tonnes (Goris,1990). This translates to a 50% increase in bond strength for series FG18 over conventionalSCB’s. These results were very similar to the Series A results at the University ofBritishColumbia.Figure 23. Load/Displacement Curves for Series FG18From a practical view point, the FOl 8 series has some drawbacks. Although its’ bondstrength was approximately 50% greater than conventional SCB’s, it had virtually no residualstrength. The average displacement at the ultimate pull-out load was 15 mm (1/2 inch). As aresult, the FG18 series is more suited to non-yielding applications.Figure 24 illustrates the load/displacement curves for samples FG12-1 to FG12-4 and2520150CC000-J 1050FG1B-7— FG18-8FG18-9— FG1B-10FG18-110 10 20 30 40 50Displacement (mm)6092failure mode. This was likely due to the nature of the failure mode and the high water:cementratios. The plot of FG12S-5, an unlaced tendon configuration, has similar load/displacementcharacteristics as laced tendons FG12-1 to FG12-4.fJ SlraightTendonI - ñhWaUoii-• .. -Ior stenglhFigure 24. LoadfDisplacement Curves for Series FG12Figure 25 is a comparison of average load displacement curves for laced FCB’s andconventional and birdcaged SCB’s. Both the FCB and SCB samples were grouted in PortlandType I/Il cement with a w:c ratio of 0.45. The major differences were: (1) the fibreglasssamples were cured for 7 days while steel samples were cured for 28 days and (2) POLYSTAL’selastic modulus was one quarter that of steel. The 7 day FCB had the same stiffness as thestandard conventional SCB samples, but a pull-out load equivalent to the standard birdcaged161412108Averae Ullima Load =i4lonnes FG12-1,2,,4)6420Legend- --• FGS-5F G 12-AVE— FG12-1— FG12-2— -— FG12-3FG12-4Insiae Spacer Diameler =20mma ,-. .. 0)CD 0)I.- 0)Displacemenl mm93samples. This evidence implies that reinforcement modulus is less important than bond strengthto the overall grouted reinforcement stiffness. The FCB pull-out load was greater thanconventional SCB’s by a factor of two and closely followed birdcaged SCB’s at one-quarter thecure time.In general, the FCB is a unique combination of “elastic” yielding capacity such as thatsupplied by conventional SCB’s and high ultimate pull-out resistance like birdcaged SCB’s.Figure 25. Comparison of Average LoadfDisplacement Curves for FCB’s and SCB’s2520115CC0I-1o500 10 20 30 40 50Displacement (mm)60947. IN SITU PULL-TESTS7.1 Introduction and ObjectivesThe two primary objectives of this section were to estimate reasonable in situ bond strengthsprior to the planned trial installations and to establish potential problem sources outside thelaboratory for the FCB. The factors deemed most significant aside from those established by thelaboratory pull-tests were: rock mass quality, confinement and quality control. Althoughquantification of the effects of these factors is highly desired, the number of pull-tests feasibleprecluded any such results. It is recommended that prior to designing any cable bolt system thatthe effect of the above factors on the capacity of that system be investigated through in situtesting.7.2 Pull-Test Apparatus and Sample PreparationThe test samples were prepared by the author while actual grouting and testing wasperformed by Dr. Andrew Hyett and Randy Reichart both of Queen’s University under thedirection ofDr. William Bawden. The pull-test apparatus was designed by Hyett and Reichart fortheir conventional steel cable testing program at Queen’s Figure 26. A hand operated hydraulicjack connected to a ram supplied the axial driving force to dislodge the grouted cables. A loadcell and LVDT measured the pull-out load and displacement respectively. An average pull rate of15 mm/mm was maintained. Each sample contained 100 mm of debonded tendon to ensurecontinuous embedment length once complete cable mobilization was reached. The FCB’s weregrouted in Portland Type 10 cement at a water to cement ratio of 0.40 and cured for 28 days.95Figure 26. Queen’s Pull-Test Apparatus7.3 Results and AnalysisFourteen tests were attempted in order to estimate reasonable bond strengths under variousnode spacings and rock units. Three samples were unsuccessful. Since tendon failure did notoccur in any of the test samples, a critical embedment length relationship was not derived. Thedesign parameters and resulting ultimate loads have been listed in Table 25. A large variation inultimate pull-out load was observed. The normalised bond strength (tonnes/metre) varied from96___—Dywidag nutHollow piston hydraulic jack________L,__—Steel plateCementbaseThreaded dywidag barI76 mm hole.Threaded coupling welded to dywidagPre-cast cylinder with grouted cable26.3 mm o.d, schedule 80___________Plywooddisk to set accurate depthof cable embedmentTesting length of cable - groutedIn the fieldroughly 45 to 60 tonnes per metre.Table 25. In Situ Pull-Test Results at Queen’sSample Embedment Spacer Node Embedment Normalised UltimateNumber (mm) Diameter Spacing Length to Node Bond Strength Load(mm) (nun) Spacing Ratio (tonnes/metre) (tonnes)QG1O-5 254 11 127 2.00 -- --QG12-8 305 20 203 2.25 55.74 17.0QG15-5 381 11 127 3.00 48.82 18.6QG16-8 406 20 203 2.00 44.83 18.2QG2O-10 508 20 254 2.00 >49.21 >25.0QS1O-5 254 11 127 2.00 49.22 12.5QS12-8 305 20 203 2.25 44.59 13.6QS15-5 381 11 127 3.00 44.62 17.0QS16-8 406 20 203 2.00 44.83 18.2QS2O-10 508 20 254 2.00 -- -QL12-8 305 20 203 2.25 59.67 18.2QL15-5 381 11 127 3.00 44.62 17.0QL16-8 406 20 203 2.00 -- --QL2O-10 508 20 254 2.00 47.24 >24.0Key to Sample Number 0G15-5:Q = Queen’sG = Granite (L = Limestone, S = Shale)15 = 15 inch embedment length-5 = 5 inch node spacingTaking a conservative estimate of the normalised bond strength of 45 tonnes per metre anddividing it into 75% of the ultimate tensile strength (to account for premature tendon failure) ofthe tendons resulted in an estimated ultimate pull-out load of 21 tonnes at a critical embedmentlength of 470 mm. Therefore, accounting for premature tendon failure, the estimated critical insitu embedment length for granite, shale or limestone was approximately 470 mm.For comparison, FCB’s in general developed ultimate pull-out loads 40% greater thanconventional SCB’s under equivalent test conditions at Queen’s (Hyett, 1990-9 1).The ultimate in situ loads were considerably lower than Series II to IV which were conductedin the laboratory at the University ofBritish Columbia. It is believed the higher w:c ratio of 0.4.97Portland Type 10 cement and larger drill hole diameter of 76.2 mm (3 inch) contributed to thelower in situ results.Displacements at ultimate pull-out load ranged from 20 to 30 mm. The pull-test curves canare shown in Figures 27 to 29. For granite, varying the embedment length from 305 to 406 mmand the node spacing from 127 to 203 mm did not significantly affect the pull-out load. For theseembedments and node spacings, slippage of the cable through the grout occurred resulting inreasonable residual strengths. Test QG2O-10 reached 25 tonnes before the apparatus failed.Results from the limestone tests were similar to granite. However, for shale, a significantdecrease in ultimate pull-out load was observed for embedment lengths below 381 mm.302520Cl,a,C0‘0o 15-JID0-j-JD00 20 40 60 80 100DISPLACEMENT (mm)120 140 160Figure 27. In Situ Pull-Test Curves for Granite98— 7 Apparatus Pipe Failure0)a,04-’.15-- —--_-.-// Bond FailureI— io- / .__... . .._______QL2O-1OD 5 -. —-----—. —--.--.-.— 0112-8/0115-50 I0 20 40 60 80 100 120 140 160DISPLACEMENT (mm)Figure 28. In Situ Pull-Test Curves for Limestone9920Figure 29. In Situ Pull-Test Curves for Shale8. TRIAL INSTALLATIONS8.1 IntroductiOnEnough confidence in the ultimate capacity and displacement was generated by the laboratoryand in situ pull-tests to attempt the trial installations. The FCB’s were installed first at WinstonLake Mine. No two cables were installed adjacent to one another. Conventional SCB’s wereinstalled around the FCB’s. Once it was established that no failures had occurred overapproximately 6 months an installation of FCB’s was planned to stabilise an unstable section of0,a)Cg15010-JID0_I 5-JDa-0 20 40 60 80 100 120 140 160DISPLACEMENT (mm)100the main ore zone at Detour Lake Mine. For this trial, the FCB’s were installed on a larger scalewithout the aid of SCB’s. Both installations were very successfiul and much has been learnedabout the potential hazards in the design of a FCB system.8.2 Winston Lake Mine (Noranda) 7 m FCBs8.2J BackgroundFive, seven metre uncoated POLYSTAL reinforced FCB’s were used for back support 510#3 open stope to assess the ease of installation, effectiveness and acceptability of the FCB’s. Theorebody consisted of a massive sphalerite deposit dipping at 40 to 60 degrees to the east. Thefootwall and hangingwall consisted of a gabbro unit with a highly chloritized ore contact. Azone of banded chert-rhyolite-tuff is often present between the ore and the hangingwall gabbroranging in thickness from 0 to 5 metres. In the wider ore zones the chert disappears and in thethinner ones, it reaches its’ maximum. The orebody itself ranges from 5 to 17 metres inthickness. Joint spacing in all units was greater than a metre; hence, the massive rock mass didnot require cable bolts of high bond strengths.The mine uses a modified avoca-longhole method. Overcuts and undercuts were separatedby twenty (20) metres. Instability in the stope back had been experienced. Conventional SCB’s,which have lower bond strengths than laced FCB’s and birdcaged SCB’s, have been usedeffectively to rectifj such problems.8.2.2 Historical Instability, Stability Analysis and DesignStructurally controlled instability was observed in stope backs where spans exceeded 10metres. As a result, overcuts were driven 10 metres wide and a hangingwall pillar left (Figure30). The hangingwall pillar was later mined with longholes. Upon removal of the hangingwall101pillar over strike lengths of 60 metres or greater, wedge failures frequently occurred in theovercut back/hangingwall contact (Figure 31).Figure 30. Typical Sill Development Prior to Wedge Failures at Winston Lake(Mime, 1989)102The wedge failures occurred along Joint Set A, a weak hangingwalllchert contact and Joint SetC, a cross-bedding set parallel to the ore strike. In some failures, the strike length of the wedgewas limited by Joint Set B. Figures 32 to 33 illustrate the typical joint sets and potential wedgefailures observed at the Winston Lake mine.Figure 31. Typical Longhole Stoping with 11W Pillar Removed Prior to Wedge Failures atWinston Lake (Mime, 1989)103J.S.J.S.J.S.J.S.J.S.JS.J.S,J.S.JOS.JOINTS IN CHERTJ.S. A 346/49 NE >15% PEAKJS. B - 068/83 SE 6% PEAKJ.S. C — 162/59 SW >15% PEAK485 OBSERVATIONSFigure 32. Stereonet Representation of Winston Lake Joint Sets in Ore, Gabbro andChert (Mime, 1989)104w ESJOINTS IN OREA- NOT PRESENTB— 075/87S 15%PEAKC — 169/43W 3% PEAK- 025/89SE 5% PEAK986 OBSERVATIONSJOINTS IN GABBROA — 333/57NE 15% PEAKB — 105/67 SW 6% PEAKC- 160/45 Sw 4% PEAKG— 203/56NW 6% PEAK— 316/04 NE 7.5% PEAK897 OBSERVATIONS---* O V-V::-V - VVVVV VwP:ESN/1E::N\WI/IAn empirical cable bolt support design (Potvin and Milne, 1992) was used to analyse stabilityof the stope backs. The stability number, N, for the stope backs in ore was estimated to be 1.4.Typical hydraulic radius calculations ranged from 4 to 5 metres for the overcut prior to longholeand greater than 5 metres upon removal of the longhole stope. As a result, cable bolts wererecommended for future mining in the area (Figure 34). To ensure stability, a conservativepattern with a 2 x 2 metre spacing was generally used. Pull-tests were conducted onFigure 33. General Representation of Potential Wedge Failures at Winston Lake (Milne,1989).105C)DP’0C)0‘‘_*)0Cn!’<CD—.CD0-—CDp4-tOoCDCDCDq..OQflaDCDCD—049c4CD0CD-CDCDrCDCD-t—-CD-E:t,r%0CD-.0—,.0_-0-C)—-0o CD Og‘aD--tECDCD•aD .0aD00CD—0CDU’0Cfl.q9CDCa0aD +-0 aDS.MODIFIEDSTABILITYNUMBER(N’)p-&000C0 01 0 01 0I I2 m Co I 0 0 IDue to the large ore width in the test area, a footwall and hangingwall drift had been drivenwith a pillar between (Figure 35). Five, seven metre FCB were installed with the SCB in thefootwall drift. The FCB’s were installed in the summer of 1990 and the area remained stable forover a year until September, 1991. At the end of August, 1991, mining below in the 530 #3stope undercut the unsupported pillar between the hangingwall and footwall drifts. The resultingfailure consisted of 3900 tonnes. The failure was attributed to the unsupported ground exposedby the mining below and did not reflect the performance of the FCBs.Figure 35. Schematic Cross-section of the FCB’s at Winston Lake (Section 10315 Nlooking north)8.2.2 Installation Procedure and AcceptanceThe FCB installation method was analogous to the one used at the mine-site for conventionalSCB’s. The quality control at Winston Lake mine was excellent. All five cables were wedged inthe hole in 20 minutes, A 25 mm o.d. grout PVC tube ran the full length of the hole. Grouting107commenced from top down using the Minepro pump developed by Inco and took 30 minutes.The grout tube remained in the hole. A water to cement ratio of 0.35 (Portland Type 10) wasbatch mixed in 30 minutes before pumping. The two metres ofFCB closest to the stope facewere laced with a node spacing of 127 mm which acted as a “plate.” Lacing the remainder of thecable was unnecessary since the critical embedment length for straight tendons was less than theanchor length of 1.5 metres (Figure 36 and Photo Plates 3 to 6).Figure 36. Uphole Installation Procedure at Winston Lake Pump Toe to Collar Ensurepumping is continued until a consistent grout is present at collar to remove air entrainedin hole.108Photo Plate 3. Taping 25 mm Grout Tube to Anchor-end of FCBPhoto Plate 4. Looking For a Drill Hole to Insert the FCB109Photo Plate 5. Insertion and Wedging of the FCBPhoto Plate 6. Hand-Scoop Test for 0.35 w:c Ratio (Portland Type 10)1108.2.3 ConclusionsAn increase in installation rate was not observed. This was likely due to the relatively shortlength and few numbers of the FCB’s as compared to those installed at Detour. Acceptance washigh as the operators involved praised the light weight of the FCB’s. The support effectivenesswas more difficult to assess due to the surrounding conventional SCB’s. A failure did not occurfor over one year after installation, however, once the unsupported pillar section was undercut, a3900 tonne fall of ground was reported. The failure was attributed to the unsupported groundbelow the FCB’s.8.3 Detour Lake Mine (Placer Dome) 13 m FCB’s8.3.1 IntroductionDetour Lake is a mechanised cut and fill gold mine where four metre lifts are taken permining cycle. During February, 1991, nineteen laced, polyanude coated FCB’s were installed aspre-reinforcement for Detou?s 300 M5 stope where production was delayed due to breastfailures (Figure 37). The FCB’s were laced and shipped to Detour where installation wassupervised by mine personnel.111Figure 37. Schematic of the FCB Program 300 M5 #15, Detour Lake MineTwo successive lifts, sixteen and seventeen, were taken after the FCB’s were installed.Approximately 4-5 m ofFCB remained as permanent sill pillar support. The FCB’s wereeffective in preventing breast failures,Each laced FCB consisted of four 7.5 mm (9 mm with coating) POLYSTAL tendons with127 mm node spacings. The spacers had a 7 mm inner-diameter. The angle betweenPOLYSTAL tendons was equal to 6.76°. This particular configuration had not been tested priorto its use and concern was expressed regarding grout penetration. However, similarconfigurations had been tested at the University ofBritish Columbia and Queen’s with excellentresults. The 0.4 w:c ratio was chosen to help facilitate grout penetration at the node.FW300 M5 #15 Stope0.4HW#5 Attack Drift1128.3.2 Past Failure BackgroundGround stability problems decreased productivity in the 300 M5 stope. During lift #13,approximately 24 tonnes of loose came down from the back as the result of two previouslyknown intersecting joint sets:• Striking 16002200, dipping 5°-15°, critical joint spacing = 457-610 mm.• Striking N-S, dipping 80°-90°, critical joint spacing = average is 3-4 m up to 10 m.The fall ofground occurred several hours after blasting near the face during mucking andprior to rock bolting. As a result, a potential hazard to personnel and equipment was createdlimiting production from the 300 M5 stope. The fall of ground broke to the last line of 1.8 mlong mechanical rock bolts which were installed on a 1.2 m x 1.2 m pattern during the previousbreast (Figure 38). The joint sets were observed to extend into the bolt area. It was believedthe failure initiated along these joint planes and the resultant bending moment caused the ore tobreak along the last row ofbolts.113Figure 38. Schematic of Typical Detour Fall of GroundThere were no falls of ground from the back during lift #14 despite the presence of the sametwo joint sets observed during lift #13 were present. However, “popping” and “cracking”, whichreportedly preceded the previous fall of ground, was heard by the miners. The stope was shutdown and the back was extensively bolted with 2.4 m and 3.6 m long mechanical and superswellex bolts respectively. The mining rate was further slowed as the breast face collapsed ontothe fill.steep jt setItypical fall of groundflatjt setmuck pile brow114On January 14, 1991 a 36 tonne fall of ground occurred during lift #15. The failure modewas analogous to the lift #13 failure. The following is an excerpt from the monthly groundcontrol report (Detour, 1991):300 MS Stope. Lift #15RIvIR 68% (10% deductedfor bad structure)SPAN 7-21 m (failure occur in wider area ofstope)SUPPORT 1.8 m mechanical bolts, spot bolting with Super Swellex (for previous breast)CONDITION Unstable“The stope is currently advancing east and west. The stope span is a maximum 21 metres.A blasting inducedfall ofground (FOG) occurred in this stope on January 14, 1991. TheFOG occurred in the back and came down shortly after the blast before the next shiftarrived in the stope. The FOG occurred as several large blocks approximately 0.4 m thickpeeled along a nearly horizontalfointfrom the breastface to a steeply dippingjoint 4metres back. The FOG occurred in unboltedground only. It was estimated to contain 36tonnes. Upon inspection ofthe area, theflatjoint was observed to be open 2-5 cm, but theground was being held by the rock bolts. There was no deformation of the rock bolt platesso anchor slippage is the probable cause of the slip opening up. An area approximately 7 mx 5.5 m x 0.4 m was blasted downfrom the back where this openjoint was believed toextend. The ground was re-supportedwith 1.8 m long mechanical bolts. Due to thefrequency ofgroundfalls which occur at the breastface before the ground has been boltedin this stope, a pre-support program will be implemented in this stope. Pre-supporting isnecessary in this area due to the combination ofaflat dippingjoint set and continuous N-Sverticaljoints which are notfound in other stopes at DLM.”A reinforcement with a higher bond strength was necessary due to the low critical jointspacing at Detour. The laboratory and in situ tests performed on the FCB’s have suggested the115critical bond strength of laced FCB’s was approximately 40-50% greater than conventional SCB’sand equivalent to birdcaged SCB’s. Modelling and historical records revealed the back to be in arelaxed state (Detour, 1991). In view of the modelling results and the combination of near-vertical and near-horizontal joint sets, tensile driving forces were dominant. This represented anideal application for the FCB.8.3.3 FCB DesignNineteen (19), thirteen (13) metre FCB’s were installed between the centre line and footwall(west side) of the 300 M5 #15 stope to pre-reinforce the back for lifts #16 and #17. The 44.45mm (1-3/4”) up-holes were drilled vertically and staggered on a 2.5 metre pattern. The designwas based on traditional conventional SCB spacings - -a conservative approach (Potvin et al,1992). The support capacity of each FCB was taken as 75% of Series IVb or 17 tonnes.Considering a 2.5 m x 2.5 m x 0.4 m block of ore with S.G. equal to 3.0, a conservative safetyfactor of approximately 2.3 was reached based on “dead weight” (17 tonnes ÷ 7.5 tonnes). Inview the successfiul FCB program and the potentially large critical joint spacing of the verticaljoints, an increase in drill hole spacing could have likely been accommodated. This would havegreatly reduced the drilling and subsequently the overall installed cost of the FCB’s.8.3.4 Installation Procedure and AcceptanceThe stope was filled to within 2 metres of the back. The FCB’s arrived to the stope as 1.2metre individual coils; this aided handling and was common practice for SCB installation atDetour. Uncoiling of the FCB’s was much easier and safer than conventional SCB’s. A 6.35 mm(1/4”) i.d. (9.5 mm o.d.) breather tube was taped to one end of the FCB and then the entire unitpushed up the hole. A 0.25 metre length of 19 mm (3/4”) o.d. grout tube was forced into thehole (Figure 39). It was discovered that this entire procedure could be accomplished by one116person whereas conventional SCB’s generally required a two men crew. The installationproductivity of the FCB’s showed a 250% increase over conventional SCB’s. Acceptance washigh due to their low weight and ease of handling.19 metresPortland Type 30Cement - w:c ratioQfone person installationprocedureFigure 39. Uphole FCB Installation at Detour Lake - Pump Collar to Toe - MinimalFracturing at CollarThe holes were grouted from the collar up with Portland Type 30 cement at a 0.40water:cement ratio. The end of the breather tube was inserted into a pail of water where theabsence of air bubbles and the expulsion of grout from the tube indicated a “fully grouted” holeand breather tube. The grout tube was then cut and crimped. The cement was allowed to curefor one month before mining continued,6.35 mm(1/4”)breather tubeflat joint setlaced with 127 mmnode spacing and 7mm i.d. spacern wedgesfabrene & resin1178.3.5 Evaluation of Ground StabilisationThe rock mass rating and discontinuities of the 16th lift were equivalent to the 15th. To date,the FCB’s have successfully stabilised the previously experienced ground problems in the 300 M5stope. Falls of ground were eliminated resulting in improved mining rates.8.3.6 Mining Through FCB’sFCB’s react differently to blasting than conventional SCB’s. First, no “grapes” were observedhanging from the FCB’s. Grapes are common at Detour for mined areas supported by SCB’s.This eliminated the dangerous task of cutting cables and improved the cycle time over SCB prereinforced stopes. Second, the length ofFCB projecting from the hole after blasting varied froma few centimetres to 3 metres. Third, the POLYSTAL either remained intact or “broomed” toform large, continuous bundles of resin and fibre. Small fibres were not observed. It issuspected they either settled or were removed by the ventilation system. It is not clear whether amask would be required on a larger scale. The potential respiratory health risk requires furtherevaluation. It would appear at this time that a limited amount of air-borne fibre was generated byblasting and that this phenomena increases as the distance between a FCB and blastholedecreases. It has also been postulated that the length ofFCB projecting and the ability for grapesto remain attached to the bolt are a function of the distance from the bolt to the blast hole and theshear force exerted on the POLYSTAL due to block rotation. The relatively low shear strengthofPOLYSTAL as compared to steel promotes effective blasting. Photo Plate 7 is a typicalexample of a FCB after it was mined through at Detour.118Photo Plate 7. Laced FCB After Blasting at DetourThe presence of grout within the nodes was discontinuous for some of the blasted bolts. Itwas unclear whether the blast or grouting procedure caused this. The former was the most likelyexplanation since observations of the FCB in the hole between lifts revealed the antinodes werecompletely filled. Similar laboratory configurations with w:c ratios lower than 0.4 were cut openlongitudinally and verified completely filled antinodes. In practice, pumping should continue untila consistent grout is observed through the breather tube and all air is removed from the hole.This is a difficult task to judge when grouting from the collar to the toe. For a given w:c ratio,an analysis of the grout flow characteristics and pressure head variation over the entire length ofa grout column would be valuable to determine minimum annulus sizes for completely filled FCBnodes and their boreholes. At this stage, it appears an angle of 6.76° between POLYSTAL119tendons is sufficient to allow a Portland Type 30 grout with a w:c ratio of 0.4 to completely fillthe node.8.3.7 Mucking BenefitsAt Detour, it is often necessary to attach SCB’s to an LI-ID and pull them from the muck pileto permit mucking. This reduced productivity and represented an annoyance to the muckingcrew. Muck piles that were previously supported with FCB’s were easier to muck. The FCB’sbroke more easily than SCB’s as the LHD crowded the muck pile. SCB’s remaining in the muckpile often required cutting.8.3.8 Mineral Processing EffectsPrior to mining through the bolted section, the mill operators were asked to record anyunexplained changes to the mill circuit, There was concern that POLYSTAL or its’ fibres wouldblind the mill screens, but this was not observed. No recovery or grade problems were observed.No other problems were reported. It is suspected ifFCB’s were used on a larger scale they mighthave a noticeable impact on the mineral processing circuit. If such a study were performed, themajority of the intact and broomed POLYSTAL could be removed from the conveyor belts orscreen decks by a mill operator prior to secondary and tertiary crushing.8.3.9 Cost EffectivenessTable 26 compares the installed costs for laced FCB’s and conventional SCB’s excludingoverhead. The laced FCB’s were not commercially available at the time of installation. TheFCB’s were manually laced and flown from Vancouver to Detour. These costs have beenincluded in the analysis. Lower labour installation costs have been realised. One and twopersons were used for the overall installed cost calculations of the FCB and SCB systems120respectively. Wages per person for the cable bolt crew averaged $20/hr excluding overhead.Polyamide coated POLYSTAL was used.Table 26. Installed Cost Comparison for the FCB’s and SCB’s at DetourCOMPONENT DETAIL CONVENVL SCB LACED FCB($ CDN) ($ CDN)Drilling 13m@$1O.78/m 140.14 140.14Strand/POLYSTAL’ 13 m 24.88 134.72FOB DetourCable Insertion SCB 1 x $40/hr 40,00 8.00FCB_0.4_x_$20/hrGrouting SCB 0.5 x $40/hr 20.00 10.00FCB_0.5_x_$20/hrMaterials2 -- 34.14 34.14TOTAL 259.16 327.00Note:1 Does not include lacing materials and labour or freight from Vancouver to Detour forPOLYSTAL2 Includes cement, breather tube & grout tubeThe overall installed cost of the FCB system was 20 percent higher than the conventionalSCB system. The FCB material cost included a 13% import tariff and a freight charge of$0.22/kg from Germany to Vancouver.8.3.10 Continuous Mining EnvironmentThe procedure for controlling air-borne glass fibres would be different for continuous miningmethods as compared to drill and blast methods. Continuous miners would tend to generate finerglass fibres. The generation of fine dust and glass fibre is inevitable in a continuous miningoperation, but a proper dust collection system such as the “positive air-circulation system” wouldcontrol the air quality at the face (Figure 40). The balance between fresh air supplied to the faceand suction from the dust collector results in a “dust curtain” which remains within 1 metre of the121face. Experience has shown that typically 1.5 to 2 m3/s of fresh air is required per 0.093 m2 ofcross-sectional area. For best results, the fresh air duct should be located at approximately 33%of the back height.4—t 1225OCFU_________________,75ocFu• ) -‘ I ftOW DWOER 28000CFM_____‘‘IDUST ‘— F.5 •) I ROTO.VENT5 / Z.FrtETTm3- —Figure 40 Dust/Fibre Collection Using Positive Air Circulation Method for ContinuousMining (Schenk, 1982)Cutting size is known to increase in naturally fractured rock (Schenck, 1982). This wouldreduce the amount of air-borne glass fibre.Degradation of intact POLYSTAL was not observed. Polyamide coated POLYSTAL has ahigh abrasion resistance. Intact coated POLYSTAL was ground in a laboratory ball mill for 45minutes with no visible degradation.1229.0 FLOATATION TESTS9.1 IntroductionThree mining environments have been considered during the development of the FCB: open,cut and fill and continuous stoping. Each method will dictates the degree to which POLYSTALwould enter the mill circuit differently.First, after completing the trial installations at Winston Lake Mine where open stope hangingwall support was used, no adverse affects to the mill was observed.Second, after completing the trial installations at Detour Lake Mine, it was concluded, fordrill and blast CAP operations, the likelihood of large quantities ofPOLYSTAL entering themineral processing circuit would be low. IfPOLYSTAL should enter the mill circuit, it is likelythe majority of the POLYSTAL would be removed by screens during crushing and grinding.However, blinding of screens may pose some operational problems.Third, it is proposed that the feed size and amounts ofPOLYSTAL to the mill would besmaller for continuous CAP mining than conventional CAF. This would potentially aggravatescreen blinding and, hence, more removal measures would be necessary in the mill circuit. As aresult, any mining method where the support must be mined with the ore requires the removalmeasures such as screen cleaning and conveyor belt picking. Further developments in removal ofcomposite materials from the mill circuit are necessary.This section evaluates the impact POLYSTAL would have on the floatation of a coppersulphide ore (Newmont samples, 1991) and suggests potential removal measures for the bulkfloatation stage, assuming relatively large amounts ofPOLYSTAL entered with the feed andpassed the screen removal measures.1239.2 Test ProcedureRoughly 4000 grams ofNewmont ore was riffled into 4 approximately equal sized samplesfrom which three were selected at random for the experiments. Ten (1% by weight of totalsample) and thirty grams (3% by weight of total) ofPOLYSTAL, without the coating, wasadded to Test samples II and ifi respectively. The POLYSTAL was cut into approximately 50nmi long pieces and resembled the broom-like, post-failure consistency of resin and fibre asdiscussed in the laboratory pull-tests. Test I was not doped with POLYSTAL and acted as areference point. Each sample was then individually ground at 60% solids by weight for 15minutes. Visual inspection revealed the glass fibres were reduced to less than 5 mm. Theamount of resin coating the glass fibres did not appear to affect their size reduction. Next, eachsample was passed through a simulated bulk floatation stage.9.2.1 Test ITest I was emptied into a flotation cell and conditioned with 0.15 g potassium amy! xanthate(KAX) for 10 minutes. The impeller speed was kept at 900 rpm. Compressed air flow was set at10 litres per minute. Ten drops ofDOW FROTH 1012 (1% concentration) were added in orderto achieve a stable froth. The ph was adjusted to 8.0. The froth was skimmed for approximately3 minutes upon which time 10 more drops of frother were added and the air flow was increasedto 20 litres per minute. At these setting, the froth was skimmed for an additional 7 minutesgiving a total floatation time of 10 minutes.92.3 Test IITest II was emptied into a flotation cell, the impeller set at 900 rpm and the compressed airturned on to observe the behaviour of the glass fibres. A small greyish mass of fibre appeared tofloat without the aid of reagents. Flotation procedure was identical to Test I. Large amounts of124fibre could be seen in the concentrate.9.2.4 Test ifiTest ifi was emptied into a flotation cell under the same conditions as Test II andimmediately a large greyish mass appeared on the surface of the pulp. The KAX was added andthis appeared to suppress the fibres to a small extent. Large amounts of fibre could be seen in theconcentrate.9.3 ResultsAlthough the composition of glass fibres was predominantly silica (60% by weight), they actextremely hydrophobic due to their long, slender shape. As mentioned, large amounts of fibrewere observed floating in Tests II and ifi.The concentrate and tails of each test were assayed for copper (Cu), total iron (Fe) and silica(Si02)(Table 27). The percentage of silica in the concentrate dramatically increased in Tests IIand ifi.Table 27. Masses and Assays for Concentrates and TailsTEST MASS Copper Iron Silicag % % %I-concentrate 121.80 11.80 24.40 18.22I-tails 871.80 0.18 4.80 44.70II -concentrate 134.10 9.05 22.30 20.7211-tails 839.10 0.17 4.60 45.12ifi-concentrate 161.20 7.90 18.90 25.98ifi-tails 862.10 0.19 4.70 46.16The percentage of copper recovered in the concentrate versus the percentage of POLYSTALin the feed was plotted to illustrate the effect of high concentrations of POLYSTAL (Figure 41).125To put the test results into perspective, if a 10 m x 10 m x 10 m cut and fill stope were supportedwith FCB’s on a 2 m by 2 metre pattern, the tonnage of POLYSTAL mined with the ore wouldbe equal to 0.08 tonnes ofPOLYSTAL (5 cables/ring * 5 rings * 10 rn/cable * 4 strands * 80g/m). For an ore with S.G. equal to 3.0 and assuming all the POLYSTAL reached the floatationstage, the percentage by weight ofPOLYSTAL to the mill feed would be 0.0027% or less thanone-thousandth (1000th) of that in Test II.. According to the laboratory tests completed, thiswould result in a reduction in copper recovery of less than 0.0 1%.:.z:.:.::z.::::Figure 41. Percent Copper Recovered in the Concentrate vs Percent of POLYSTAL toFeed (by weight)The addition of extremely large amounts ofPOLYSTAL did adversely affect the bulkfloatation of the Newmont ore (Table 28). A slight decrease in recovery and grade wasa,4-4-Ca,0C006C004200 0.5 1 1.5 2 2.5 3% POLYSTAL (uncoated) to Feed126observed (Figure 42).Table 28. Recovery and Grade for Typical Newmont OreCONCENTRATE % POLYSTAL RECOVERY, % FEED GRADE, %I 0 90.15 1.6II 1 89.50 1.4ifi 3 88.60 1.490.290D 89.80Mo 89.6>.i::88.888.6 I I I I0 0.5 1 1.5 2 2.5 3% POLYSTAL (uncoated) to FeedFigure 42. Percent of Copper Recovered vs Percent of POLYSTAL to Feed (by weight)9.4 ConclusionsIn general, it is expected that the glass fibres would pose problems to screening. Removal ofthe glass fibres should be accomplished prior to floatation stages. According to these results,127POLYSTAL would have little effect on the bulk floatation of a copper suiphide ore. The effectof resin was not investigated.10. SHEAR TESTSPhoto Plate 8 shows the shear-test apparatus used to evaluate the FCB. The apparatusconsisted of a load cell, dial gauge, hydraulic press and metal box to hold the sample. Thesamples consisted of three segments of pipe with a single FCB grouted over the entire column.The middle segment was loaded vertically at 90° to the FCB axis while the two outer segmentswere clamped to the metal frame to restrict vertical and horizontal movement of the two end-pipes.Photo Plate 8. Shear Test Apparatus and Test Sample128Table 29 summarises the shear-test results of four laced FCB’s with a 127 mm node spacing(inter-tendon angle of 9.9°) and grouted in a water to cement (Portland Type 30) ratio of 0.35.Table 29. Preliminary Shear Test ResultsSAMPLE NUMBER CURE TIME, DAYS VERTICAL SHEARLOAD1,(TONNES)1 7 7.852 29 5.593 47 6.034 120 5.91Note:1 The vertical shear load per end-pipe was equal to one half the total applied driving force.The average shear strength of a filly cured FCB was approximately 6.34 tonnes for a drivingforce oriented 90° to the FCB axis. No residual strength existed. Cure times greater than 29days did not significantly affect shear strength.11. DESIGNAs with most ground support design procedures, the engineer must evaluate stress, structure(wedge formation) and rockmass characteristics of an excavation. Once the potential failuremode and expected movements have been determined, the proper cable bolt, pattern and lengthcan selected.The Modified Mathew’s Method, an empirical design approach developed by Potvin andMilne, 1992 was used successfi.illy to design the FCB installations at Detour and Winston Lakemines. For discrete wedge failures, a stereonet analysis should be conducted to determineadequate cable lengths. For highly fractured and/or stress induced failures, FCB’s should extendbeyond historical failure heights and have a low critical embedment length.Selection of the proper FCB is critical to the design and subsequent extraction of ore. Two129basic FCB’s have been developed and field tested: (1) yielding and (2) high bond strength (Table30).Table 30. Selection of FCB for Design - Portland Type 30 Cement, 0.35 w:c Ratio, 54 mmholeTYPE APPLICATION ULTIMATE ESTIMATED CRITICALCAPACITY PEAK ELASTIC EMBEDMENT(tonnes) RECOVERY LENGTH(mm) (mm)Straight* massive 21 22 914yieldingLaced** blocky 23 16 432high bondstrengthNote:* Four POLYSTAL tendons separated by 20 mm i.d. spacer (results for this enclosed inPeterson, 1991).** Four POLYSTAL tendons separated by an 11 mm i.d. spacer and node spacings of 127 mm.The FCB’s developed in Table 30 do not possess residual strengths above the criticalembedment lengths as estimated by laboratory pull-testing. Therefore, to account for this, theoperating strengths of the FCB’s were taken as 75% of the ultimate laboratory pull-out load. Thereduction in operating load was effective in the trial installations at Detour and Winston Lakemines.Composites have other characteristics that are different from conventional materials.Composites have properties which are dependent on the position and angle of the applied loadwith respect to the reinforcing fibres. Composites themselves have no yield strength or straincapacity. These differences must be considered when designing safe, ground support systems.For large scale testing, particularly in entry type methods such as cut and fill, in situ pull-testsare recommended to verify ultimate pull-out loads, allowable displacements and critical130embedment lengths.As with SCB installation, cement quality is of primary importance to the effectiveness of aFCB. Water to cement ratios less than 0.35 or greater than 0.45 are not recommended for theFCB.12. POTENTIAL APPLICATIONSThe FCB exists as a viable alternative to steel cable bolt support in Canadian hardrock mines.Other potential applications which deserve further evaluation include:• Open stoping support.• Cut and fill back and overhang support.• Back support in sill pillar recovery operations.• Reinforcement for pillars and drawpoints.• Highly corrosive environments.• Soft rock support.• Support of ore where SCB mucking tangles are experienced.• Burst prone ground.13. FUTURE RESEARCH DIRECTIONSThe potential for fibre reinforced polymer composites in ground support applications hasbeen proven. The FCB exists as a viable alternative to SCB’s in a number of applications such ascut and fill and open stoping. But, the FCB is far from optimized. Likely the major stumblingblocks hampering industry use and acceptance of the FCB is its’ high cost and unproven shearstrength. Future research should concentrate on the following:131• Locate a lower cost Canadian manufacturer willing to develop mining products.• Develop higher bond strengths, ultimate capacities and residual strengths.• Evaluate composite surface coatings and tendon diameter effects.• Quantify the shear strength with respect to orientation of applied load.• Investigate the long-term support capacity.• Quantify design guidelines• Complete a market analysis.• Determine manufacturing constraints.• Assess other existing advanced and low-tech composites in the same manner,• Application development.14. CONCLUSIONSThe results in this thesis have been based on over fifty (50) laboratory pull-tests, fourteen(14) in situ pull-tests, four (4) laboratory shear tests, three (3) laboratory floatation tests and two(2) trial installations. The evaluation of potential composite materials and subsequentdevelopment of a working prototype has been accomplished.The fibreglass cable bolt (FCB) exists as a viable alternative to steel cable bolts. The bondstrength of the FCB was greater than conventional and equivalent to birdcaged SCB’s. The FCBconfiguration with the greatest bond strength consisted of four, 7.5 mm diameter POLYSTALrods laced with an internal angle between tendons of 9.9° and 127 mm node spacing. Foryielding support requirements, the straight FCB configuration has been recommended where four7.5mm diameter POLYSTAL rods are separated by a spacer. The overall installed cost of theFCB was a competitive 20% higher than conventional SCB’s.Continuously, fibre reinforced polymer composites have been recommended and categorised132according to the following fibre orientations: unidirectional (UD), bidirectional (BD) andmultidirectional all ofwhich have potential for cable bolt reinforcement. All testing in thisinvestigation has been conducted on a member of the UD composite family. The UD compositefamily has been divided into two fi.irther sub-categories according to quality control andmechanical properties: advanced and low technology. Advanced composites, usually reinforcedwith carbon, aramid or glass fibre, are manufactured with stringent quality control measures toensure high material properties and near “flawless” end-products. A high degree of qualitycontrol was considered vital to the selection of a cuttable reinforcement and the safety of aninstallation.Low technology composites are available for as low as $1/rn, but with lower mechanicalproperties (ranging from 500 MPa to 1000 MPa) and decreased quality control. They also tendto have poorly developed bond surfaces and/or corrosion resistances. It has been emphasisedthat low technology composites appear attractive as ground support based on their low cost, butrequire more stringent quality control measures in their manufacturing processes. Today, themost economical advanced UD composites available on the market in sufficient quantities toconduct laboratory tests are reinforced with glass (POLYSTAL, construction profile) or aramid(ARAPREE 200) fibre. POLYSTAL is commercially available in Canada (Con-Tech, 1991).POLYSTAL has a thermoplastic, glass filled, resin rich veil which is resistant to corrosion,abrasion and pull-out. ARAPREE possesses a silicon-grit enhanced surface roughness. Thelargest disadvantage of aramid reinforcements, as compared to glass or carbon, is the formationof”kink bands,” or buckling of the fibre under compressive loads (Pigliacampi, 1988). Theformation of “kink bands” limits their application to high strain compressive or flexural loadrequirements. Aramid and glass fibre costs range from $ 10-100 and $1-S per kilogramrespectively. Carbon fibre composites have superior properties to most materials and appear tobe the best reinforcement selection for dynamically loaded support systems, but are currently tooexpensive for mining ($ 10-1000/kg). The current downward trend of aramid and carbon fibrecost is expected to continue and will likely improve their feasibility in various applications (U.S.133Department of the Interior • Bureau ofMines, 1990). Of the candidates considered,POLYSTAL was chosen for this investigation based on its’ unique combination of high strength,corrosion resistance, low cost, versatility, flexibility and availability as compared to otheradvanced composites. If manufactured in Canada, the FCB has the potential to be costcompetitive with current prestressing steel prices. POLYSTAL’s low density equates to easierhandling and better acceptability throughout the involved work force as compared to steel cablebolts. Uncoated POLYSTAL has the potential for temporary support (<1 year), but it&performance is questionable and requires flirther investigation. Polyamide coated POLYSTALhas been recommended for virtually any tension dominated support application where limitedshear forces are present. The coated POLYSTAL had a higher bond strength to cement thanuncoated POLYSTAL.Laboratory tests at the University ofBritish Columbia and the United States Bureau ofMineshave revealed that axially loaded laced FCB’s demonstrated bond strengths 40-55% greater thanconventional SCB’s. The maximum pull-out load obtained was 23 tonnes at a critical embedmentlength, defined as the embedment length required for tendon failure, of 432 mm and a nodespacing of 127 mm. This configuration caused premature tendon failure at 84% of the combinedultimate tensile strength for four POLYSTAL tendons. Under similar load conditions and testparameters, conventional SCB’s developed an ultimate pull-out load of 13 tonnes at anembedment length of432 mm. Unlaced FCB’s had a critical embedment length of approximately914 mm at 22 tonnes. Unlaced bolts had a lower stiffness and bond strength than laced bolts.The load/displacement curve for the FCB was a compromise between conventional andbirdcaged steel cable bolts. The “elastic” portion of the pull-out curve closely followedconventional cable bolts, but the ultimate load was equivalent to birdcaged steel cable bolts.However, it has been shown that by increasing bond strength of a cable bolt, tendon failureoccurred at lower embedment lengths and residual strength was sacrificed.The fractional factorial design completed at the University ofBritish Columbia evaluated thefollowing factors: mix time, embedment length, w:c ratio, cure time, pipe diameter, spacer134diameter and node spacing. Under the operating levels and conditions of the design, three factorswere found most significant: hand-mix time, embedment length and water cement ratio. Thefollowing conclusions were made:• An increase in embedment length from 152 mm to 457 mm increased pull-out loadsignificantly. However, critical embedment lengths were not determined.• A decrease in water cement ratio from 0.65 to 0.35 increased pull-out load significantly.• A cure time increase from 2 to 10 days did not significantly increase pull-out load forPortland Type Ill cement (high early strength).• An increase in pipe diameter from 48 mm to 77 mm did not significantly increase pull-outload. This corresponds to tests with conventional steel cables (Mime 1988-90).• An increase in node spacing above 305 mm did not significantly increase pull-out load.• An increase in mix time increases pull-out load.• The effects of node spacing and spacer diameter required further investigation.• The effects of increasing or decreasing the factors tested in FFD-I are similar to steel cablebolts (Goris, 1990).In situ pull-tests conducted at Queen’s University revealed the FCB’s had a higher bondstrength than conventional steel cable bolts, Ultimate pull-out loads were typically 40% greaterthan those obtained for conventional SCB’s.Trial installations at Winston Lake and Detour Lake mines have been completed to assess theinstallation, blasting, mucking and mineral processing ofFCB’s in open stoping and mechanisedcut and fill mining. At the mechanised cut and fill operation at Detour, continual breast failureswere experienced. Conventional SCB’s did not develop the required bond strength to stabilisethe breast. As a solution, nineteen, thirteen metre laced FCB’s were installed to pre-reinforcedthe ore. The FCB’s successfully stabilised the back and breast where previous conventional SCBsupport failed. The installation rate was increased by 250% and acceptance was high. Blasting135did not degrade the FCB’s between lifts. The low shear strength of the FCB resulted in theelimination of cable “tangles” during the mucking cycle. No adverse health or mineral processingeffects were observed. Blasted FCB’s either remained in tendon form or “broomed” dependingon their location with respect to the blast hole. An installed cost analysis was completed for theDetour Lake trial installation and the FCB cost was 20% greater than the conventional SCB. Aone man crew with hydraulic fill placed 2 metres from the back was adequate for efficientinstallation.At Winston, five, seven metre FCB’s reinforced with uncoated POLYSTAL were used toassist SCB’s as back and hanging wall support. A hybrid configuration was used where thetendons were unlaced and separated by a spacer except the last 2 metres closest to collar whichwere laced with a 127 mm node spacing and an inter-tendon angle of 9•90, No increase ininstallation rate was observed as at Detour. This was likely due to the short length and smallnumber ofFCB’s installed as compared to Detour. Acceptance was high. No failures occurreduntil an unsupported area was undercut. However, the failure did not reflect the performance ofthe FCB’s as the fall of ground was initiated by the unsupported ground.It has been determined that the use ofPOLYSTAL would cause minimal problems to the millscreening processes where the FCB’s would be mined with ore such as in drill and blast orcontinuous mines.To assess the effects of POLYSTAL on the latter portions of mineral recovery, bulk flotationtests were conducted on a typical copper suiphide ore (Newmont mine) doped with KAX,Dowfroth and POLYSTAL were completed. It was found that if the POLYSTAL was in afibrous failed form, it ground easily in a laboratory ball mill and floated immediately when placedin an aerated flotation cell. Hence, removal of the ground POLYSTAL could be accomplishedduring floatation if necessary. Grade and recovery decreased slightly as the weight percent ofPOLYSTAL increased. However, standard cable bolt patterns would not result in significantreductions in grade or recovery.Immediate applications for the FCB have been established where the back is in a relaxed state136or near-relaxed state and a shear force of not greater than 5 tonnes is exerted 900 to the bolt axis.Such conditions commonly exist in Canadian cut and fill and open stoping operations. Thefeasibility of the FCB improves as the demand for its’ advantages over steel such as high bondstrength, efficient installation and corrosion resistance increase. Other potential applicationsinclude continuous excavations, rockburst protection, pillar reinforcement and prestressedanchors. The application environment and service life can range from short-term to long-term.Preliminary laboratory shear tests have been conducted and revealed the FCB’s to have alimited shear resistance of five (5) tonnes for a filly cured sample (at least 28 days) with a loadapplied 900 to the bolt axis. The limitations of the FCB in shear as they relate to the rock masscharacteristics, driving forces, confinement, normal force and grout remain to be determined.Conventional SCB design procedures have been used successfiully. However, the selection ofto proper FCB is critical to design. Operating strengths for the FCB’s are taken as 75% of theirultimate laboratory or in situ pull-tests. Water to cement ratios less than 0.35 or greater than0.45 are not recommended.Finally, flirther research to develop a composite particularly suited for cable bolt support hasbeen justified. The technology exists to develop a composite which meets the requirements ofthe aggressive cable bolt environment. However, it is highly recommended that futureinvestigations be conducted in conjunction with both a composite manufacturer and the miningindustry in order to develop practical, economical composite tendons for cable bolting.137ReferencesASKELAND, D.R., The Science and Engineering ofMaterials, Second Edition, PWS-KENTPublishing Company, (ISBN 0-534-91657-0), 1989.BARTON, N., BAKHTAR, K., Bolt design based on shear strength, Proceedings of theInternational Symposium on Rock Bolting, Abisko, pp. 368-376, 1983.BAWDEN, W.F., Hyett, A.J., Cortolezzis, D., Towards a Methodology for PerformanceAssessment in Cable Bolt Design, Rock Support in Mining and Underground Construction.Kaiser & McCreath, Balkema, Rotterdam, 1992.BENMOKRANE, B., BALLIVY, G., Five Year Monitoring ofLoad Losses on PrestressedCement Grouted Rock Anchors, Universite cle Sherbrooke, 1991.BOX, HUNTER, HUNTER, Statistics for Experimental Design, pp. 374-417, 1978.BRAY, R.C.E., Control ofground movement at the Geco Mine, Proceedings of the 4th rockmechanics symposium, Department of energy, mines and resources, Ottawa, pp. 3 5-66, 1967.BRAWNER, C.O., HAUGEN, M., Pre-Reinforcement to Improve Underground Stability, 112thA1ME Annual Meeting, Altanta, Georgia, March 1983.CON-TECH Systems, private communication, 1991.DETOUR, “Fibreglass Cable Bolt Program,” an internal report, B. Lang, 1991.DIEFENDORF, R. J., Carbon/Graphite Fibers, ASM Handbook of Composites, p.49, 1988.FARAH, A., AREF, K., Design Considerations ofFully Grouted Cable Bolts, paper # 151, C1MAGM in Montreal, 1986.FLIN, R.A., TROJAN, P.K., Engineering Materials and Their Applications, Third Edition, byHoughton Muffin Company, (ISBN 0-395-35660-1), 1986.FULLER, P.O., CADBY, G.W., Design of Cement Grouted Cable Dowels for Development of aStable Arch in a Stope Back, Commonwealth Scientific and Industrial Research OrganizationDivision of Applied Geomechanics, November, 1977.FULLER, P.G., COX, R.H.T., Mechanics of load transfer from steel tendons to cement basedgrout, Fifth Australasian Conference on the mechanics of structures and materials, Melbourne,pp. 189-203, 1975.FULLER, P.O., COX, R.H.T., Rock Reinforcement Design Based on Control of JointDisplacement - A New Concept, Proceedings of the 3rd Australasian Tunnelling Conference,138Sydney, 1978.FULLER, P.G., Cable Support in Mining, Proceedings of the International Symposium on RockBolting, Sweden, 1983.FULLER, P.G., WEST, D., DIGHT, P.M., Laboratory Puiltesting of Short Grouted Cablebolts,Mining Research Associates, Melbourne, Sydney, 1988.FULLER, P.O., WEST, D., DIGHT, P.M., MRA Cable Support Design For UndergroundOpenings in Metalliferous Mines, Mining Research Associates, Melbourne, Sydney, 1989.FULLER, P.O., BARRETT, J.R., MILLER, D.R., Influence of Cable Support in Assessing OpenStope Viability, Barrett Fuller and Partners, Melbourne, Australia.GORIS, 3M, Laboratory Evaluation of Cable Bolt Supports (In two parts) - 1, Evaluation ofsupports using conventional cables, U. S. Bureau ofMines, Spokane, Washington, 1990.HUNT, R.E,B., ASKEW, I.E., Installation and Design Guidelines for Cable Dowel GroundSupport at ZC/NBHC, AusiMivI Broken Hill Branch, Underground Operators’ Conference, Oct.,1977.HYETT, A., Private communication, 1990-91.JASTRZEBSKI, Z.D., The Nature and Properties ofEngineering Materials, Third Edition, byJohn Wiley & Sons mc, (ISBN 0-471-81841-0), 1987.JEREMIC, M.L., DELAIRE, G.J.P., Failure mechanics of cable bolt systems, CIM Bulletin, Vol.76, No. 856, pp. 66-71, 1983.JOHNSON & LEONE, Statistics and Experimental Design in Engineering and Physical Sciences,Volume II, 1968.KHAN, 0, Hassani, F., Continuous Hardrock Support Systems, Draft copy of Masters Thesis,McGill University, Montreal, January, 1991.KAISER, P.K., MALONEY, S.M., and SINGH, S.P., Feasibility of long-term ground controlwith stainless steel friction rock bolts, CIM Bulletin, Vol. 83, No. 940, pp. 5 5-59, 1990.KAISER, P.K., MALONEY, S.M., SINGH, S.P., A New Perspective on Cable Bolt Design,93rd CIM AGM, Vancouver, 1991.LAPPALA1NEN, P., PULKKTNEN, I., KUPARINEN, I., Use of Steel Strands in Cable Boltingand Rock Bolting, Proceedings of the International Sym. on Rock Bolting, Abisko, 1983.LITTLEJOHN, G.S., BRUCE, A., Rock Anchors - State of the Art, Ground Engineering, 1976.139LITTLEJONN. G.S., BRUCE, A., Long-term Performance ofHigh Capacity Rock Anchors atDovonport, Ground Engineering, 1979.LONDE, P., BONAZZI, D., Reinforced Rock, Proceedings 3rd International CongressionalSociety ofRock Mechanics, Volume 2, Denver, 1974.LORIG, L.J., A Simple Representation ofFully Bonded Passive Rock Reinforcement For HardRocks, CSIRO Division of Geomechanics, Melbourne, Victoria, Australia, 1985.MAH, G.P., PAKALNIS, R., MILNE, D., The Development of a Fibreglass Cable Bolt, CIMAGM, Vancouver, 1991.MARGOLIS, J.M,, Fabrication Techniques, Advanced Thermoset Composites, Chapter 2, pp.47-64, 1986.MARTIN, D., North America’s Longest Railway Tunnel Drives Hard Through CanadianRockies, Tunnel and Tunnelling, September, 1985.MCILWAIN, A.I.B., Review of the Mobile Miner at Isa Minte, The AusIMM North WestQueensland Branch, Underground Operators Conference, June, 1988.MEECHAN, B., Rock bolts, Tunnels and tunnelling, pp. 45-46, November, 1989.MILLER, D.R., Design of cable reinforcement patterns to resist shear failure in open stope walls,Stability in Underground Mining II, Chapter 20, pp. 346-362, 1983.MILNE, D., et al, Winston Lake Rock Mechanics Program and Ground Conditions, internalreport, Centre De Technologie Noranda, Montreal, Quebec, July, 1989.MULAR, A., Course Notes from Systems Analysis, UBC, 1989.PAKALNIS, R., Cable Support Practice in Open Stope Mining, Canmet Project No. 4-9147-1,March, 1989.PETERSON, D., Development of a Fibreglass Cable Bolt, Undergraduate Thesis, University ofBritish Columbia, Vancouver, British Columbia, April, 1991.PHILLIPS, L. N., Design with Advanced Composite Materials, The Design Council, London,1989.PIGLL&CAMPI, J.J., Organic Fibers, ASM Handbook of Composites, p.55, 1988.POLLACK, H.W., Materials Science and Metallurgy, Fourth Edition, by Prentice-Hall Inc.,(ISBN 0-8359-4287-2), 1988.140POTWN, Y., Empirical Open Stope Design in Canada, PhD Thesis, University of BritishColumbia, Vancouver, Canada, 1988.POTVTN, Y., and MELNE, D., Empirical Cable Bolt Support Design, Rock Support in Miningand Underground Construction. Kaiser & McCreath, Balkema, Rotterdam, 1992.POURSARTIP, A.P., Private Communication and UBC Courses, 1990.PREIS, L., BELL, T.A., Fibreglass tendons for post tensioning concrete bridges, Available fromthe Mobay Corporation, a Bayer USA Inc. Company, 1986.REINHART, T.J., CLEMENTS, L.L., Introduction to composites, ASM Handbook ofComposites, pp. 27-34, 1988.SCHENCK, G,H.K., Boom-Type Miners and Roadheaders, Underground Mining MethodsHandbook. Society fo Mining Engineering, Editor W.A. Hustrulid, pp. 1160-1168, 1982.SCHMUCK, C.H., Cablebolting at Homestake, Intermountain Minerals Conference, Vail,Colorado, July, 1979.SCHOENBERG, T., Boron and silicon carbide fibres, ASM Handbook of Composites, pp. 58-59, 1988.SMITH, H.A., et al, NDRK/EIMCO TM6O Project - Roadheader Technology for Hard Rock,94th Annual CIM AGM, Montreal, 1992.SPARKS, G.B., Application ofHard Rock Continuous Miners to Cut-and-Fill Slot Stoping,Mining Congress, 1980.STHEEMAN, W.H., A practical Solution to Cable Bolting Problems at the Tsumeb Mine, CIMBulletin, Feb., 1982.STILLBORG, B., Experimental investigation of steel cables for rock reinforcement in hard rock,Lulea University of Technology, Division of Rock Mechanics, Doctoral Thesis 1984:33D, 1984.SUMERAK, J.E., MARTiN, J., Pultruded Products - New Capability on the Horizon, AdvancedComposites Conference Proceedings, American Society for Metals, pp. 133-3 8, 1985.U.S. Departement of the Interior • Bureau ofMines, The New Materials Society, Challenges andOpportunities, Volumes I and II, 1990.VANCOUVER, Informal cable bolt discussion - minutes of meeting available from Dr. RimasPakalnis, University ofBritish Columbia, Rm. 517d, 6350 Stores Road, Vancouver, B.C. V6T1W5 Canada, 1991.141‘ii z C x C, r C, C LMain Effects:xoiyiLo=lo=2Xoi16Li = ii=16X2iyiL2=12= 1616L3=13= 1614316X4zyai=1L4=14= 162 //i=1 /16X5y1=1L5=15=Xi2 /=I ///16Xy’i=1L6=16= 162 /X6i /1=1/216XiZIi=1L7=17= 162 /LXii /1=1/2144Two-Factor Interaction Effects:XnX2y1L12=112+135+147= 1616XXyL23=123+146+liz= 161=1(xi2xi3),,,//”XI3Xi4))iL=l+l26+l5l 161=1(X13X14),//”16x’4xisyiL45 = 145 + 116 + 137= 161=1(Xi4Xi5,,,,//145XXyiL56=156+114+127= 161=1(Xi5Xi6),,,,/”16XXiy1L67=167+113+125= 16LiXiyiL17=117+124+136= 161=1(XiiXii),,,,,i/’Three-Factor Interaction Effect:16XaIXiXi3iL123=15= 16146APPENDIX B - PULL-TEST CURVES FOR FFD-I14720.0015.00 -C04-.— . .. run 13 10.00- run2I— ————run 3—I, I ‘so i run4IlJ f ta’I,‘ : ......... run 5D 5.00-li •••Ii : •.0000.00 10.00 20.00 30.00 40.00TENDON/GROUT DISPLACEMENT (mm)148Cl)CC00—IID0-J-JDTENDON/GROUT DISPLACEMENT (mm)15.0010. 10.00•._._run 6run 7————-run 8run 9run 1020.00 30.00149(I)CC001I0-JRUN 11RUN 12I II IRUN 13RUN 1420151050RUN 15RUN 16_________..—___...I_IImI..I.10 20 30 40 50TENDON/GROUT DISPLACEMENT (mm)150FRACTIONAL FACTORIAL DESIGNCenter Point Runs - Series I141312U)11——•lu,._ 4%.....I9 aifo 76 f5 F—.—.—•—Runl7-.1 4— Runl8D 3————— Run 19a2 Run2O100.00 4.00 8.00 12.00 16.00 20.00 30.002.00 6.00 10.00 14.00 18.00 25.00 35.00TENDON/GROUT DISPLACEMENT (mm)151FRACTIONAL FACTORIAL DESIGNCenter Point Runs - Series I1211 —4 ,— — — — — — — — — —(I) IU 4%C -Co7-6- iI— 5Do-I3- Run2l2 -————. Run 221- -Run230 0.00 4.00 8.00 12.00 16.00 20.00 30.00200 6.00 10.00 14.00 18.00 25.00 35.00TENDON/GROUT DISPLACEMENT (mm)152APPENDIX C. PULL-TEST CURVES FOR SERIES II-IV. CRITICAL EMBEDMENTLENGTH DETERMINATIONS15312.00PEAK LOADNO TENDON/ FAILURE10.00-1 RAPID SLIPPING& UNLOADINGI8.00-I- ////O 6.00--J II- /D / —SeriesIl-14.00- /______Series112-J /D /0.. embedded 457.20 mm (1½ feet)2.00 - node spacIng 203.2 mm (8 inches)no polyamid coating.0.000.00 4.00 8.00 12.00 16.00TENDON/GROUT DISPLACEMENT (mm)15425.00PEAK LOAD3 TENDONS_.. 20.00-FAILED—CCo \-I—15.00-NO TENDON FAILURE——o—-J— 1 TENDON FAILED10.00.————Seriesifla-101 // Series lila- 2D /__a. 5.00 - / Series lila -3// embedded 508.0 mm (20 inches)/ node spacing 254.0 mm (10 inches)0.000.00 5.00 10.00 15.00 20.00TENDON/GROUT DISPLACEMENT (mm)15525.00PEAK LOAD20.001 TENDONo FAILED15.00-1 TENDON/ FAILED0—-jID 10.00-o — —iTENDONFAILED-J I-I____D Series fib - 1Series IlIb-2500- Series IlIb -3embedded 914.4 mm (36 inches)node spacing 254.0 mm (10 inches)0.000.00 5.00 10.00 15.00 20.00 25.00 30.00TENDON/GROUT DISPLACEMENT (mm)15625.00‘ 20.00 - PEAKLOAD1’o 11/15.00-/0-j / NO TENDON FAILURE10.00-oI-ID——.—.—.-SeriesIVa-15.00 - —————- Series IVa 2Series IVa - 3embedded 304.8 mm (12 inches)node spacing 127 mm (5 inches)0.00 I I I0.00 10.00 20.00 30.00 40.00TENDON/GROUT DISPLACEMENT (mm)15725.00PEAK LOAD20.00 - 3 TENDONSFAILED —4,——15.00- 1o 2TENDONS/‘ FAILED10.00- // I,o /-J-J // Series lVb - 25.00- / Series IVb -3embedded 431.8 mm (17 inches)node spacing 127 mm (5 inches).10.000.00 5.00 10.00 15.00 20.00TENDON/GROUT DISPLACEMENT (mm)158


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