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An evaluation of the full displacement pressuremeter O’Neill, Bruce Ernest 1985

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AN EVALUATION OF THE FULL DISPLACEMENT PRESSUREMETER by BRUCE O'NEILL BASC, The U n i v e r s i t y of B r i t i s h Columbia, 1982 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF CIVIL ENGINEERING We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA J u l y , 1985 © Bruce O ' N e i l l , 1985 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r a n a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l m a k e i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s m a y b e g r a n t e d b y t h e h e a d o f m y d e p a r t m e n t o r b y h i s o r h e r r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t b e a l l o w e d w i t h o u t m y w r i t t e n p e r m i s s i o n . D e p a r t m e n t o f CIVIL ENGINEERING T h e U n i v e r s i t y o f B r i t i s h C o l u m b i a 1 9 5 6 M a i n M a l l V a n c o u v e r , C a n a d a V 6 T 1 Y 3 D a t e JUNE 20, 1985 D E - 6 C3/81-) ABSTRACT The s e l f - b o r i n g pressuremeter which i s inser ted in to the ground without d is turb ing the surrounding s o i l has two drawbacks. S k i l l e d operators are needed to i n s e r t the probe in to the ground without d i s turb ing the s o i l , and the s e l f - b o r i n g process requires a j e t t i n g act ion or a ro ta t ing cu t te r and d r i l l i n g mud. One method of s imp l i f y ing the pressuremeter i n s t a l l a t i o n procedure i s to i n s t a l l the probe in a f u l l displacement manner. A s o l i d t i p i s placed oh the end of the probe and then the pressuremeter i s pushed into the ground in the same manner as a cone penetrometer. This research project was performed to examine the s u i t a b i l i t y of using the f u l l displacement pressuremeter f o r determining shear modulus, i n s i t u horizontal s t r e s s e s , and undrained shear s t rength . The var iab les examined were; the type of pressuremeter, whether the pressuremeter was run in a s t ress or a s t r a i n c o n t r o l l e d manner, the s i ze of the t i p pushed in f ront of the pressuremeter, and whether time was allowed for the dynamic pore pressures to d i s s i p a t e . Tests were conducted in sand, s i l t , and c l a y . When the shear moduli measured with the f u l l displacement pressuremeter were adjusted to account f o r the d i f fe rences i n s t r a i n l e v e l , and mean e f f e c t i v e s t ress they compared very well with the dynamic shear moduli measured with the seismic cone. The attempts to determine the i n s i t u hor izontal s t ress by examining the l i f t o f f pressure were unsuccessfu l . The undrained shear strengths of c lay determined using cav i ty expansion theory compared very well with undrained shear strengths determined using the f i e l d vane. i i TABLE OF CONTENTS Page Abst rac t H L i s t of F igures v Acknowledgement v i i i Chapter 1. Introduct ion 1 1.1 History of the Pressuremeter 1 1.2 Thes is Out l ine 3 Chapter 2. Parameter In te rpre ta t ion 4 2.1 Parameters determined with the pressuremeter 4 2.2 Shear Modulus 5 2.3 Undrained Shear Strength 9 2.4 Ins i tu Hor izontal S t ress 15 Chapter 3. Equipment and Test Procedures 17 3.1 Introduct ion 17 3.2 Roctest Pencel 17 3.2.1 Desc r ip t ion of the Pencel Probe 18 3.2.2 Test Procedure and Data Acqu is t ion 22 3 .2 .2 .1 St ress C o n t r o l l e d Tes t 22 3 .2 .2 .2 C a l i b r a t i o n s fo r the S t ress C o n t r o l l e d Tes t 28 3 .2 .2 .3 S t r a i n C o n t r o l l e d Tes t 35 3 .2 .2 .4 C a l i b r a t i o n s f o r the S t r a i n C o n t r o l l e d Tes t 38 3.3 Hughes Pressuremeter 40 3.3.1 Desc r ip t ion of the Hughes Pressuremeter 40 3.3.2 Test Procedure and Data A c q u i s i t i o n 42 3.3 .2 .1 St ress C o n t r o l l e d T e s t 43 3 .3 .2 .2 C a l i b r a t i o n s fo r the S t ress C o n t r o l l e d Tes t 43 3 .3 .2 .3 S t r a i n C o n t r o l l e d T e s t 47 3 .3 .2 .4 C a l i b r a t i o n s f o r the S t r a i n C o n t r o l l e d Tes t 54 i l l Page Chapter 4. F i e l d Program 55 4.1 Introduct ion 55 4.2 Langley 57 4.2 .1 S i t e Desc r ip t i on 57 4 .2 .2 Results 57 4 .2 .2 .1 Shear Modulus 60 4 .2 .2 .2 Hor izontal S t ress 67 4 .2 .2 .3 Undrained Shear Strength 71 4.3 Boundary Road 76 4.3.1 S i t e Desc r ip t i on 78 4 .3 .2 Results 78 4 .3 .2 .1 Shear Modulus 82 4 .3 .2 .2 Hor izontal S t ress 86 4.4 McDonalds Farm 89 4.4 .1 S i t e D e s c r i p t i o n 89 4 .4 .2 Results 92 4 .4 .2 .1 Shear Modulus 95 4 .4 .2 .2 Horizontal S t ress 99 Chapter 5. Conclusions 106 5.1 Summary 106 5.2 Shear Modulus 106 5.3 Ins i tu Horizontal S t ress 107 5.4 Undrained Shear Strength 108 5.5 Recommendations f o r Fur ther Research 108 References 109 i v LIST OF FIGURES F igure No. Ti t i e Page 2.1 Summary of S t ress Paths And Pressure Expansion Curves as a Function of Pressuremeter I n s t a l l a t i o n 7 2.2 Shear Modulus Attenuat ion Curves 10 2.3 Determining Undrained Shear Strength from the Pressuremeter Curve 12 2.4 Determining Undrained Shear Strength from the Pressure vs Log Volumetr ic S t r a i n P l o t 14 3.1 Pencel Probe 19 3.2 Modif ied Menard G-Am Control Box 23 3.3 Pence l : Curves determined with var ious i n i t i a l volumes 26 3.4 Pence l : Type of curve generated by a s t ress c o n t r o l l e d t e s t 27 3.5 Pencel Membrane C a l i b r a t i o n : E f f e c t of c y c l i n g 30 3.6 Pencel Membrane C a l i b r a t i o n : E f f e c t of vary ing the time increment 31 3.7 Pencel Membrane C a l i b r a t i o n : E f f e c t of vary ing the s i z e of the pressure increment 33 3.8 S t r a i n Control Device 37 3.9 Pencel Membrane C a l i b r a t i o n : E f f e c t of vary ing the s t r a i n rate 39 3.10 Hughes Pressuremeter ( HPM ) 41 3.11 HPM Control Box 44 3.12 HPM Membrane C a l i b r a t i o n Curve 46 3.13 HPM: Comparison of pressure reading a t the surface and a t the probe 49 3.14 HPM: Comparison of vo lumetr ic s t r a i n and c i r cumferen t i a l s t r a i n measurements 51 v F igure No. Ti t i e Page 3.15 HPM: Comparison of curves generated with volumetr ic s t r a i n and those generated with c i r cumferen t i a l s t r a i n 53 4.1 S i t e Locat ion Map 56 4.2 Langley cone p r o f i l e 58 4.3 Ins i tu t e s t s conducted a t Langley 59 4.4 Pence l : Typica l Curves at Langley 61 4.5 Comparison of Pencel curves with HPM curves : Langley 62 4.6 P r o f i l e of Shear Modulus at Langley: Pencel 63 4.7 P r o f i l e of Shear Modulus at Langley: HPM 65 4.8 P r o f i l e of Measured Hor izonta l E f f e c t i v e S t r e s s At Langley: Pencel 68 4.9 P r o f i l e of Measured Hor izonta l E f f e c t i v e S t r e s s At Langley: HPM 70 4.10 P r o f i l e of Undrained Shear Strength Determined from the Pencel Curves 72 4.11 P r o f i l e of Undrained Shear Strength Determined from the HPM Curves 74 4.12 P r o f i l e of Undrained Shear Strength Determined from the P - Log S t r a i n P l o t : Pencel 75 4.13 P r o f i l e of Undrained Shear Strength Determined from the P - Log S t r a i n P l o t : HPM 77 4.14 Boundary Road Cone P r o f i l e 79 4.15 Ins i tu Tests conducted a t Boundary Road 80 4.16 Pence l : Typica l Curves a t Boundary Road 81 4.17 Comparison of Pencel Curves with HPM Curves: Boundary Road 83 vi F igure No. Ti t i e Page 4.18 P r o f i l e of Shear Modulus at Boundary Road Pencel and HPM 85 4.19 P r o f i l e of Measured Hor izontal E f f e c t i v e S t ress At Boundary Road: Pencel 87 4.20 P r o f i l e of Measured Hor izontal E f f e c t i v e S t ress At Boundary Road: HPM 88 4.21 McDonalds Farm cone p r o f i l e 90 4.22 Ins i tu t e s t conducted at McDonalds Farm 91 4.23 Pence l : Typ ica l Curves at McDonalds Farm 93 4.24 Comparison of Pencel curves and HPM curves : McDonal ds Farm 94 4.25 P r o f i l e of Normalized Shear Modulus at McDonalds Farm: Pencel 96 4.26 P r o f i l e of Normalized Shear Modulus at McDonalds Farm: Stress C o n t r o l l e d HPM 97 4.27 P r o f i l e of Normalized Shear Modulus at McDonalds Farm: S t r a i n C o n t r o l l e d HPM 98 4.28 P r o f i l e of Measured Hor izonta l E f f e c t i v e S t r e s s At McDonalds Farm: S t r a i n C o n t r o l l e d Pencel 101 4.29 P r o f i l e of Measured Hor izonta l E f f e c t i v e S t r e s s At McDonalds Farm: S t ress C o n t r o l l e d Pencel 102 4.30 P r o f i l e of Measured Hor izonta l E f f e c t i v e S t r e s s At McDonalds Farm: S t ress C o n t r o l l e d HPM 103 4.31 P r o f i l e of Measured Hor izonta l E f f e c t i v e S t r e s s At McDonalds Farm: S t r a i n C o n t r o l l e d HPM 104 v i i ACKNOWLEDGEMENT I would l i k e to thank my a d v i s o r s , Dr. P.K. Robertson, and Dr . R.G. Campanella, my co l leagues and the C i v i l Engineer ing techn ica l s t a f f f o r t h e i r ass i s tance with t h i s research p r o j e c t . The f i n a n c i a l support of the Natural Sciences and Engineer ing Research Counci l o f Canada i s a lso g r a t e f u l l y acknowledged. This presentat ion i s dedicated to my wife Sue, my fami l y , and a l l my f r i e n d s who provided u n s t i n t i n g support when I needed i t most. v i i i Chapter 1. Introduct ion 1.1 History of the Pressuremeter The s e l f - b o r i n g pressuremeter was developed in the ear ly 1970's as a method of i n s e r t i n g the pressuremeter i n to the ground without d i s turb ing the surrounding s o i l . Th is presented two major advantages over the t r a d i t i o n a l Menard-type pressuremeter; the tes ts were conducted on undisturbed s o i l s , and the a n a l y s i s could be c a r r i e d out using fundamental p r i n c i p l e s developed with cav i ty expansion theory. The s e l f - b o r i n g pressuremeter has two drawbacks; s k i l l e d • operators are needed to i n s e r t the probe in to the ground without d i s turb ing the s o i l , and the s e l f - b o r i n g process requires a j e t t i n g act ion or a ro ta t ing c u t t e r and d r i l l i n g mud. The complicated i n s t a l l a t i o n procedure i s of p a r t i c u l a r s i g n i f i c a n c e i f the t e s t i s to be conducted at cons iderable depth o f f shore . Reid et a l , 1982 developed an open-ended push-in pressuremeter ( PIP ) as one a l t e r n a t i v e to overcome the i n s t a l l a t i o n problems assoc ia ted with the s e l f - b o r i n g pressuremeter. The PIP was designed to be pushed a short distance in to the ground with s o i l passing through the c u t t i n g shoe and in to the hollow core of the instrument. The disturbance can be minimized somewhat with an appropriate c u t t i n g shoe design but the instrument i s a th ick walled tube and some disturbance i s 1 i n e v i t a b l e . One advantage of t h i s design i s that the probe i s withdrawn a f t e r each t e s t and the sample obtained i n the core of the instrument can be examined. The corresponding disadvantage i s that the instrument must be withdrawn a f t e r each t e s t to al low the s o i l i n the core to be removed. The F u l l Displacement Pressuremeter ( FDPM ) i s a fu r the r step in the process of s i m p l i f y i n g the i n s t a l l a t i o n procedure. A s o l i d t i p i s placed on the end of the probe and the FDPM i s then pushed in to the ground i n the same manner as a cone penetrometer. The s o i l around the probe i s f u l l y d i s t u r b e d . However research by Robertson, 1982 with the s e l f - b o r i n g pressuremeter ( SBPM ) showed that the moduli der ived from unload-re load cyc les were i n s e n s i t i v e to s o i l d i s turbance . This has important imp l i ca t ions i f the major parameter that i s to be der ived from the pressuremeter t e s t i s the s o i l s t i f f n e s s . The FDPM cou ld be combined with an e l e c t r o n i c p i e z o m e t e r - f r i c t i o n cone to form a cone pressuremeter. The cone cou ld provide a continuous log of the s o i l . The penetrat ion could be stopped a t regular i n t e r v a l s or in layers of s p e c i f i c i n t e r e s t and pressuremeter t e s t s cou ld be conducted. The add i t ion of good s t i f f n e s s measurements from the pressuremeter would al low bet te r c o r r e l a t i o n s to be developed f o r obta in ing s o i l parameters from the cone penetrat ion t e s t . T h i s research p ro jec t cont inues previous work conducted with the FDPM i n sand by Hughes and Robertson, 1984. 2 1.2 Thes is Out l ine Chapter 2 l i s t s the s o i l parameters that can be est imated with the pressuremeter. The methods of d e r i v i n g these parameters are d iscussed i n d e t a i l . Chapter 3 descr ibes the equipment used in t h i s research p r o j e c t . The t e s t procedures and the methods of data acqu is t ion are exp la ined . Considerable a t ten t ion i s given to the c a l i b r a t i o n s that are requ i red . Chapter 4 presents the r e s u l t s of the t e s t s at the three research s i t e s . The pressuremeter curves are examined, the shear moduli are compared with r e s u l t s from the UBC seismic cone, the undrained shear strength i s compared with r e s u l t s from the f i e l d vane, and the measured hor izonta l s t r e s s i s compared to the v e r t i c a l e f f e c t i v e s t r e s s . Chapter 5 presents the conc lus ions that were drawn from t h i s research and presents recommendations f o r fu r the r research . 3 Chapter 2 Parameter Interpretat ion 2.1 Parameters determined with the pressuremeter There i s a long l i s t of s o i l parameters that can be measured with the pressuremeter. They inc lude the undrained shear s t rength , the angle of in terna l f r i c t i o n , the shear modulus, the i n s i t u hor izontal s t r e s s , and the hor izonta l c o e f f i c i e n t of conso l i da t i on . The s t ress s t r a i n curve can a lso be der ived , and attempts have been made to use pressuremeter data to inves t iga te the s u s c e p t i b i l i t y of a s o i l to l i q u e f a c t i o n . Pressuremeter curves can a lso be modif ied to give pressure-displacement curves for use i n a beam spring ana lys is of l a t e r a l l y loaded p i l e s . This paper w i l l be conf ined to determination of the shear modulus (G), the undrained shear strength (Su), and the i n s i t u hor izontal s t r e s s . Research with the f u l l displacement pressuremeter has a lso been d i rected at the design of l a t e r a l l y loaded p i l e s . The development of pressure-displacement curves from the pressuremeter curves and the comparison of p red i c t i ons with actual p i l e tes t r e s u l t s i s presented in Robertson et a l , 1985a. Hughes and Robertson , 1984 showed that the angle of in terna l f r i c t i o n could not be determined from the f u l l displacement pressuremeter using ana lys i s developed for the s e l f — b o r i n g 4 pressuremeter. This does not however preclude the development of an empir i ca l c o r r e l a t i o n . Since the eventual goal i s to p a i r the f u l l displacement pressuremeter with a cone penetrometer where good c o r r e l a t i o n s f o r the angle of i n te rna l f r i c t i o n have a lready been developed i t does not appear to be necessary to fo l low that l i n e of research at t h i s t ime. 2.2 Shear Modulus Throughout the h i s t o r y of the pressuremeter a v a r i e t y of deformation moduli have been determined. When the Menard pressuremeter t e s t i s being i n t e r p r e t e d a modulus corresponding to the slope of the approximately l i n e a r por t ion of the pressuremeter curve i s measured. With the s e l f - b o r i n g pressuremeter a range of secant moduli are sometimes measured at s t r a i n s corresponding to p o s i t i o n s such as 0.5 of the l i m i t pressure or 0.5 of the peak s t r e s s . For these moduli to be used i n des ign, i t i s necessary to determine whether they are appropr iate to the s o i l model being used. Small s t r a i n cav i ty expansion theory says that i f the s o i l i s unloaded and then re loaded, the slope of the r e s u l t i n g l i n e on a pressure versus c i r cumferen t i a l s t r a i n p l o t would be twice the e l a s t i c shear modulus, i e . 2G. The shear modulus i s a parameter tha t has been well researched and can be used d i r e c t l y i n des ign . In t h e i r 1984 paper, F u l l Displacement Pressuremeter Test ing 5 i n Sand, Hughes and Robertson showed that the method of i n s t a l l i n g the pressuremeter into the ground should not s i g n i f i c a n t l y a l t e r the slope of the unioad-reload cyc le (see F igure 2 . 1 ) . Th is i s based on the assumption that s o i l that i s unloaded beneath a y i e l d surface w i l l behave e l a s t i c a l l y . Wroth, 1982 shows that there are l i m i t s on the s i z e of the uni oad-reload loop wi th in which the s o i l can be expected to be remain e l a s t i c . For a c l a y , the maximum al lowable s i ze of the s t ress cyc le i s 2 Su and, f o r a drained cohesionless s o i l , the maximum s ize of the s t ress c y c l e i s : 2 s i n J2 f , 1 + sin/5 0 i s the angle of in terna l f r i c t i o n o i s the e f f e c t i v e radia l s t ress Janbu, 1963 es tab l i shed that shear modulus i s proport ional to the mean e f f e c t i v e s t ress ra i sed to the nth power, where n i s t y p i c a l l y 0.5 f o r cohes ionless s o i l s . Th is means that as the mean e f f e c t i v e s t ress increases so does the measured shear modulus. G = Kg * Pa * ( <r£ / Pa f where: Kg = shear modulus number 67K = mean e f f e c t i v e s t ress Pa = reference s t ress A pressuremeter tes t run in a c l a y i s genera l ly considered to be undrained. If that i s the case, the to ta l s t ress i s increas ing 6 (a) Pre-Bored Pressuremeter Test (Me'nard) Strain, € 6 (b) Self-Boring Pressuremeter Test Strain, €g ( c) Full - displacement Pressuremeter Test Strain, € Q Stress Path during Installation Stress Path during Pressure-Expansion Test Summary of Stress Paths and Pressure Expansion Curves as a Function of Pressuremeter I n s t a l l a t i o n ( A f t e r Hughes and Robertson, 1984 ) dur ing the t e s t , but the e f f e c t i v e s t r e s s i s remaining approximately constant . Shear moduli measured a t var ious times during a pressuremeter t e s t ( PMT ) i n c lay should there fore be e q u a l . In r e a l i t y there are very high pore pressure grad ients generated during a pressuremeter t e s t in c lay and some drainage almost c e r t a i n l y occurs . T h i s r e s u l t s in the e f f e c t i v e s t r e s s r i s i n g during the t e s t , causing the shear moduli measured at l a t e r stages of the t e s t to be h igher than those measured a t the i n i t i a l stages (see sect ion 4 . 2 . 2 . 1 ) . During a PMT i n f ree dra in ing mater ia l the mean e f f e c t i v e s t r e s s r i s e s constant ly and t h i s must be accounted f o r i f measurements of G at var ious times during the PMT are to be compared. Robertson, 1982 showed that the mean e f f e c t i v e s t ress around a s e l f bor ing pressuremeter in sand cou ld be est imated as a func t ion of the e f f e c t i v e rad ia l s t r e s s . The s t resses around a f u l l displacement pressuremeter in sand are much more d i f f i c u l t to est imate because of the res idual s t resses caused by i n s e r t i o n of the probe. As a comprehensive understanding of the s t resses around the f u l l displacement probe was l a c k i n g , i t was decided to use the same approximate approach developed f o r the s e l f - b o r i n g pressuremeter where the mean e f f e c t i v e s t r e s s i s taken to be 0.5 times the e f f e c t i v e rad ia l s t r e s s . In order to compare the shear moduli from PMT's in sand a base or standard mean e f f e c t i v e s t r e s s must be e s t a b l i s h e d . The values of shear modulus are a l so to be compared to those obtained 8 from the UBC seismic cone so 1t was decided to normalize a l l the moduli to the i n s i t u mean e f f e c t i v e s t r e s s which 1s approximately the s t ress at which seismic cone t e s t s are conducted. A f u l l d e s c r i p t i o n of the UBC seismic cone and the technique of downhole seismic t es t ing i s presented in Robertson et a l , A p r i l 85. The un load-re load loops are not t r u l y e l a s t i c even wi th in the range descr ibed by Wroth, 1982. They e x h i b i t some h y s t e r e s i s and the shear modulus attenuates with inc reas ing shear s t r a i n . F igure 2.2 presents t yp i ca l shear modulus a t tenuat ion curves f o r sand and f o r c l a y . The shear modulus decreases with i n c r e a s i n g shear s t r a i n or , in the case of PMT, the un load-re load loop s i z e . Therefore the loop s i ze was standardized as much as p o s s i b l e i n order to decrease the number of v a r i a b l e s . 2cm and 5cnr loops 3 predominated the t e s t s with the Pencel probe. /.5"cm loops predominated the t e s t s with the Hughes pressuremeter. 2.3 Undrained Shear Strength { Su ) There are two approaches to determining undrained shear strength from pressuremeter t e s t s . Undrained s t rength can be i n t e r p r e t e d in an empir ica l manner or by c a v i t y expansion theory employed in conjunct ion with a s o i l model. It was the ob jec t of t h i s research p r o j e c t to examine the p o s s i b i l i t y of us ing present c a v i t y expansion theory methods to determine the undrained shear s t r e n g t h . Gibson and Anderson, 1961 modeled c lay as an e l a s t i c / 9 c o CO o OJ x: to "5 co _ 3 • D X ) o o to Dynamic Strains Static Strains c a> u \_ Q. I g II a V) _ 3 3 TJ O v_ O 0 ) x: to I .0 0.8 0.6 0.4 0.2 Range of va (After Seec lues for Sand — i and Idris, I97C 10 - 4 I0""3 10"' 10 Shear Strain, y % >-2 - i ( a ) OI 6.2 CX3 04 (X5 (X6 07 0.8 SHEAR STRAIN T ,% ( b ) Figure 2.2 Shear Modulus Attenuation Curves 10 p e r f e c t l y p l a s t i c mater ia l and der ived a method f o r determining Su . Several other more recent analyses were publ ished in 1972 which are not r e s t r i c t e d to t h i s s t r e s s s t r a i n model of the s o i l . Wroth, 1982 s ta tes that from experience gained with the Cambridge pressuremeter the extra s o p h i s t i c a t i o n of the 1972 analyses are not required and tha t f o r design purposes the Gibson and Anderson a n a l y s i s i s adequate f o r most c l a y s . The Gibson and Anderson approach was used i n t h i s research p r o j e c t . There are two methods of determining the Su that come out of the Gibson and Anderson a n a l y s i s . Both methods were employed during t h i s p ro jec t to see i f e i t h e r or both would work with the f u l l displacement pressuremeter. The f i r s t method of determining the undrained shear strength uses the pressuremeter curve d i r e c t l y . The Gibson and Anderson a n a l y s i s leads to the equat ion: ( PI - Po ) Su= — 1 + In ( G / Su ) As i s demonstrated i n F igure 2 .3 , the l i m i t pressure , P I , and the l i f t o f f pressure , Po, are determined d i r e c t l y from the pressuremeter curve . Su can be determined from an i n i t i a l est imate of the s t i f f n e s s r a t i o , G / Su, and then an i t e r a t i v e process i s f o l l owed . The problem i s then whether to use the dynamic shear modulus ( Gmax ) , a value of G corresponding to the s t r a i n l eve l a t f a i l u r e , o r some other value f o r G. During the a n a l y s i s i n t h i s paper, i t was decided to use a value of In ( G / Su ) = 6 . 5 . I f 11 Figure 2.3 Determining Undrained Shear Strength from the Pressure Expansion Curve 12 f o r example, Gmax was used to c a l c u l a t e the s t i f f n e s s r a t i o at a depth of 8m at Langley, the s t i f f n e s s r a t i o would be: In (Gmax / Su) = In (150 / 0.25) = 6 . 4 ~ 6 . 5 Gmax in the above example was determined with the seismic cone and Su was determined with the f i e l d vane. I t can be seen that t h i s method of c a l c u l a t i n g Su depends heav i ly on the value of Po, and P I . Because of the logar i thm func t ion the value of the s t i f f n e s s r a t i o i s l e s s important. The second method of determining undrained shear strength us ing the Gibson and Anderson a n a l y s i s i s demonstrated in F igure 2 .4 . App l ied pressure i s p lo t ted versus the logar i thm of vo lumetr ic s t r a i n . Th is should be a l i n e a r r e l a t i o n s h i p once f a i l u r e has been reached and i f natural logarithms are used, the slope of the l i n e i s equal to Su. The prime advantage of t h i s approach i s that no estimate of the s t i f f n e s s r a t i o i s r e q u i r e d , nor do Po or PI need to be measured. PI can sometimes be a problem to measure i f the t e s t i s not c a r r i e d to a high enough s t r a i n l e v e l . These analyses are based on the assumption that the c l ay i s undrained during the pressuremeter t e s t . As was already mentioned i n sec t ion 2.2 high pore pressure grad ients are created during the t e s t and some drainage does occur . Th is w i l l cause the c l ay to conso l i da te and thus the undrained shear s t rength inc reases . Th i s i s one of the reasons why undrained shear strengths determined from the PMT are genera l ly h igher than those determined by other conventional t e s t s ( see Wroth, 1984). Some of the other reasons 13 1 1 1 — I — 1 — I s lope 3-W < 03 UJ or in ui cc a. 1-Converting to natural logarithms Su = Slope / 2.303 10 T T T T T—i—r T 100 VOLUMETRIC STRAIN < X ) LANGLEY* 3BMM TIP STRAIN CONTROLLED DEPTH 6M Figure 2.4 Determining Undrained Shear Strength from the Pressure vs Log Volumetric.Strain P l o t 14 are; s t r a i n rate e f f e c t s ( PMT's are usua l l y run much f a s t e r than other conventional t e s t s and many cohesive s o i l s have s t r a i n rate dependent shear s t r e n g t h s ) , and the f a c t that a pressuremeter expansion i s a c t u a l l y somewhere between a c y l i n d r i c a l and a spher i ca l c a v i t y expansion, not a t r u l y c y l i n d r i c a l expansion as assumed in the a n a l y s i s . The undrained shear strengths der ived from the pressuremeter were compared to undrained shear strengths obtained with the N i l con f i e l d vane. A d e s c r i p t i o n of the N i l c o n f i e l d vane i s g iven in G r e i g , 1985. 2.4 Ins i tu Hor izontal S t r e s s The pressuremeter presents the p o s s i b i l i t y of measuring the i n s i t u hor izonta l s t r e s s , a parameter required f o r de ta i l ed computer a n a l y s i s . The s e l f - b o r i n g pressuremeter which i s supposed to be i n s t a l l e d without d i s t u r b i n g the s o i l i s the ideal tool f o r measuring the i n s i t u hor izonta l s t r e s s . However, when the probe i s s e l f - b o r e d i n t o the ground there i s s t i l l a small amount of d i s turbance . In sand t h i s small d isturbance can lead to s i g n i f i c a n t e r rors i n measuring the i n s i t u hor izonta l s t r e s s . When the probe i s i n s t a l l e d i n a f u l l displacement manner the s o i l i s f u l l y d i s tu rbed , Hughes and Robertson , 1984 examined the s t r e s s path fo l lowed by the s o i l near a f u l l displacement probe. They suggest that although the s o i l i s subjected to very high s t resses during the i n s e r t a t i o n of the probe, the l a t e r a l s t resses then 15 re lax and return to somewhere near the i n i t i a l l a t e r a l s t r e s s . Lacasse and Lunne, 1982 po in t out some of the d i f f i c u l t i e s in determining the l i f t o f f pressure from s e l f - b o r i n g pressuremeter t e s t s . The s implest method i s to v i s u a l l y determine the po int on the pressure versus c i r cumferent ia l s t r a i n p l o t where the membrane f i r s t begins to move. An allowance fo r the compliance of the system must be made and there i s cons iderab le room f o r judgment. Lacasse and Lunne have shown tha t t h i s method usua l l y y i e l d s s l i g h t l y lower estimates of the i n s i t u hor izonta l s t r e s s than the best est imates pred ic ted by methods other than the pressuremeter. V isua l i nspec t ion was considered to be a s u f f i c i e n t l y accurate est imate of the l i f t o f f pressure during t h i s p r o j e c t . One of the problems encountered when examining measurements of. i n s i t u hor izonta l s t r e s s i s what should they be compared t o . The l i f t o f f pressure represents the to ta l hor izonta l s t r e s s ac t ing around the probe. The l i f t o f f pressure minus the e q u i l i b r i u m pore pressure ( Uo ) represents the e f f e c t i v e hor izonta l p ressure . I f the measured e f f e c t i v e hor izonta l pressure i s p lo t ted together with the v e r t i c a l e f f e c t i v e s t r e s s the measured value of Ko can be observed d i r e c t l y . 16 Chapter 3 Equipment & Test Procedures 3.1 Introduct ion The two most common methods of i n s e r t i n g the pressuremeter i n to the ground are to s e l f - b o r e i t or to place the probe i n a pre-bored ho le . There i s , however, an a l t e r n a t i v e method and that i s to i n s t a l l the probe in a f u l l displacement manner. The pressuremeter i s f i t t e d with a s o l i d cone t i p and then pushed i n t o the ground i n the same manner as a cone penetrometer. Th is chapter examines the equipment used in t h i s study during the f u l l displacement pressuremeter t e s t s , the procedures needed to prepare the equipment, the type of data obtained and how i t i s obta ined. The procedures used to run the t e s t s and how d i f f e r e n t procedures and equipment a f f e c t the data w i l l be examined and d i scussed . Two types of pressuremeter probes were used during the course of t h i s research program. They were: a) the Roctest Pencel and b) the Hughes Pressuremeter. The pressuremeters were i n s t a l l e d using the UBC Ins i tu Test ing veh i c l e which i s descr ibed i n d e t a i l i n Campanella and Robertson, 1981. 3.2 Roctest Pencel The Pencel probe has a de f la ted diameter of 32mm. The main advantages of t h i s small pressuremeter are that the pushing force requi red to i n s t a l l the probe i s reduced and tha t the probe can be 17 placed behind an e l e c t r o n i c cone penetrometer. However a standard 10 sq.cm. e l e c t r o n i c cone has a diameter o f 36mm. Thus the Pencel probe i s smal ler than a standard e l e c t r o n i c 10 s q . cm. cone. An important aspect of t h i s research p ro jec t was to evaluate the e f f e c t of varying the diameter of the s o l i d t i p in f ront of the probe. The a l t e r n a t i v e to a 10 sq . cm. t i p i s a 32mm diameter t i p , which i s the same diameter as the probe. The use of a 36mm t i p i s s i m i l a r to the s i t u a t i o n where the probe i s p lace i n a pre-bored hole and the s o i l i s allowed to re lax . 3.2.1 Descr ipt ion of the Pencel Probe The Pencel probe d i f f e r s from previous Roctest pressuremeters, such as the Menard G-Am probe, in that i t has only one c e l l rather than three . The mono c e l l approach i s the one that has been adopted with s e l f - b o r i n g pressuremeters. The Pencel pressuremeter un i t shown in F igure 3.1 cons is ted of four components; the probe and f i t t i n g s , a membrane, the f l e x i b l e tubing and a contro l u n i t . The core of the probe was a 22mm diameter hollow steel c y l i n d e r with threads on e i t h e r end. Extending from e i t h e r end of the probe was a short piece of steel tub ing. The f l e x i b l e tubing from the contro l box attaches to one piece of steel tubing and the other piece of steel tub ing, which i s normally sealed, can be opened to a i d in the saturat ion process. Each piece of steel tubing was connected to a small passageway in the wall of the probe that ran to a point j u s t past 18 TO CONTROL UNIT FLUID INLET CORE LOCK NUT TAPERED METAL RING RUBBER MEMBRANE COVERED BY STAINLESS STEEL STRIPS Figure 3.1 Pencel Probe 19 the re ta in ing l i p . The two re ta in ing l i p s were centered on the probe and were 390mm apart . The membrane was sealed aga inst these re ta in ing l i p s by tapered metal r ings which were held in place by lock nuts. The membrane was a 2.5mm th ick rubber sheath with s ixteen 13mm wide s t a i n l e s s steel s t r i p s glued to the ou ts ide . The metal s t r i p s extended to within 25mm of the end of the 410mm long membrane and were only glued along one edge so that they did not p r o h i b i t the membrane from expanding. The ends of the metal s t r i p s were held underneath the tapered metal r ings which caused increased end c o n s t r a i n t s . Increasing the end c o n s t r a i n t decreased the a b i l i t y of the probe to expand as a r i g h t c y l i n d e r , an assumption made in the i n t e r p r e t a t i o n of the data . This i s d iscussed more f u l l y in sec t ion 3 . 3 . 2 . 3 . The 20m length of f l e x i b l e tubing used during t h i s study had an outs ide diameter o f 6.35mm and an ins ide diameter o f 2.0mm. The tubing was found to have a very small compliance f o r the range of pressures used i n t h i s study ( 0 to 20kpa). For the purposes of t h i s research pro jec t i t was decided not to purchase the contro l u n i t suppl ied by Roctest but rather to develop control un i t s that would be v e r s a t i l e enough to handle future research needs. The contro l u n i t s used are d iscussed in the fo l lowing subsect ions. 20 There was a problem encountered assembling the Pencel probe. When the tapered r ings were put in place to seal the membrane against the re ta in ing l i p , the membrane a lso sealed the f l u i d i n l e t . To overcome t h i s problem a groove was cut in the core of the probe that allowed the f l u i d to flow f a r t h e r along the probe before i t entered the area behind the membrane. New probes suppl ied by the manufacturer have t h i s mod i f i ca t ion already incorporated. The Pencel has been designed so that i t can be combined with an e l e c t r o n i c cone penetrometer. The ins ide diameter of the Pencel probe i s such that a shie lded 14 conductor cable such as used with the UBC e l e c t r o n i c cones can be passed through the probe but the probe i s not large enough to allow the s l i g h t l y l a r g e r connectors at the end of the cable to pass through. Th is necess i ta tes the cone cable being rewired each time the Pencel probe i s to be strung onto the cab le . The adapter that i s required between the probe and the cone penetrometer, however, does not have s u f f i c i e n t c learance ins ide to accept the c a b l e . The steel tubing used during the saturat ion must f i t i ns ide t h i s adapter and when i t does there i s i n s u f f i c i e n t room to thread the cone cab le . Th is cou ld be overcome i f the method of sea l ing the passageway was a l t e r e d . Instead of sea l ing the passageway by at tach ing a piece of steel tubing and then sea l ing the piece of tubing with a nut, a small screw could be threaded d i r e c t l y i n to the core of the probe to seal the passageway. The method of attaching the membrane to the probe appears to 21 l i m i t the type of s o i l i n which the t e s t can be performed. I t was found that whenever the CPT qc value exceeded about 150 b a r , the membrane was torn o f f the probe during pene t ra t i on . Th is severe ly l i m i t e d the depth to which the probe cou ld be i n s t a l l e d . The f a i l u r e of the membrane appears to o r i g i n a t e from the high f r i c t i o n force p u l l i n g the membrane out from between the lower tapered r i n g and the r e t a i n i n g l i p . Th is appeared to be a s e l f perpetuat ing problem s ince once a membrane had been pu l l ed from between the r e t a i n i n g l i p and the tapered r i n g , the tapered r i n g would become s l i g h t l y enlarged and would not ho ld the next membrane as t i g h t l y , there fo re the next membrane p u l l e d out more e a s i l y . 3.2.2 Test Procedure and Data A c q u i s i t i o n 3 .2 .2 .1 S t ress Cont ro l l ed Tes t The pressuremeter t e s t has t r a d i t i o n a l l y been c a r r i e d out in a s t r e s s c o n t r o l l e d manner. That i s , a c e r t a i n pressure i s app l ied and, a f t e r a s p e c i f i e d time i n t e r v a l , the corresponding s t r a i n i s recorded. The contro l u n i t from a Menard G-Am pressuremeter, shown i n F igure 3 .2 , was used to perform the s t r e s s c o n t r o l l e d t e s t . The Pencel probe has a much smal ler volume than the G-Am probe so i t was necessary to read the volume more accurate ly over a smal ler range. Therefore a s o l i d brass c y l i n d e r was inser ted in to the water r e s e r v o i r to decrease the c ross sect iona l a r e a . The scale was then r e c a l i b r a t e d to r e f l e c t the new 22 © ^ ® graduated c y l i n d e r L_ f=\ from gas b o t t l e U to orobe 1 fROCTESTl SS to probe Figure 3.2 Modified Menard G-Am Control Box 23 volume / length r e l a t i o n s h i p . Th is allowed a more accurate determinat ion of the volume and s t i l l maintained adequate volume range f o r the P e n c e l . The pressure and s t r a i n readings were recorded manually dur ing t h i s t e s t . The s t r a i n readings were recorded as changes in volume in the f l u i d r e s e r v o i r . In order to compare these t e s t s with those done with the Hughes pressuremeter the changes i n volume were converted to c i r cumferent ia l s t r a i n . T h i s was done using the asssumption that the membrane expands as a r i g h t c y l i n d e r . The v a l i d i t y of t h i s assumption i s d iscussed i n sec t ion 3 . 3 . 2 . 3 . One of the prime problems with analyz ing s t r e s s c o n t r o l l e d t e s t s i s attempting to understand the drainage c o n d i t i o n s . During the i n i t i a l por t ion of the t e s t the s o i l around the probe may be s t ra ined slowly enough that the s o i l i s f u l l y d ra ined . As the s o i l approaches f a i l u r e , the s t r a i n rate great ly increases and the s o i l may become undrained. In the middle of the t e s t the drainage cond i t ions are even more complex. One of the problems with using the Pencel probe i n a s t r e s s c o n t r o l l e d manner i s determining which value should be used f o r the i n i t i a l volume 1n the c a l c u l a t i o n s . A f t e r performing a pressure expansion t e s t , the membrane 1s allowed to c o l l a p s e back to the c losed p o s i t i o n . The membrane cannot be drawn back to any s p e c i f i c p o s i t i o n unless a vacuum source 1s attached to the contro l box. Th is leads to the quest ion of whether the I n i t i a l 24 volume should be taken as the volume at the s t a r t of each t e s t or should i t be taken as the t o t a l l y c o l l a p s e d volume so tha t i t can be cons i s ten t from t e s t to t e s t . I f the l a t t e r i s the case then most of the t e s t s w i l l s t a r t with some i n i t i a l c i r c u m f e r e n t i a l s t r a i n , s ince the membrane tends to remain s l i g h t l y i n f l a t e d even a f t e r the probe has been pushed to the next t e s t depth. The e f f e c t o f choosing d i f f e r e n t i n i t i a l volumes on the pressuremeter curves i s shown in F igure 3 . 3 . An add i t iona l curve i s shown f o r the s i t u a t i o n where the i n i t i a l volume was choosen to be the s i z e of the opening created by the 36mm t i p . For ease i n comparing with other t e s t s i t was decided to use the volume at the s t a r t of each t e s t as the i n i t i a l volume, thus the i n i t i a l c i r c u m f e r e n t i a l s t r a i n was zero at the s t a r t of each t e s t , as i t was with the other types of t e s t s . When the s t r e s s c o n t r o l l e d t e s t was i n i t i a l l y descr ibed i t was stated that the pressure increment was appl ied and then a f t e r a s p e c i f i e d time i n t e r v a l the volume reading was recorded. I f the volume reading was recorded cont inuous ly a curve such as shown in F igure 3.4 would be d e l i n e a t e d . As shown i n F igure 3.4 the pressure reading taken at the sur face increases immediately but time i s requ i red f o r the f l u i d to flow in to the probe. In the s t r e s s c o n t r o l l e d t e s t there i s no c o r r e c t i o n made f o r the head l o s s in the tubing there fo re s u f f i c i e n t time must be al lowed f o r the pressure in the probe and a t the surface to e q u a l i z e . Th is i s d iscussed f u r t h e r in the fo l l ow ing s e c t i o n . 2 5 -15 0 15 30 CIRCUMFERENTIAL STRAIN C X ) LANGLEY. 3BMM TIP STRESS CDNTROLLED DEPTH 8M LEGEND Ro - 32MM Ro - INITIAL R Ro - 36MM Figure 3.3 Pencel: Curves determined with various i n i t i a l volumes 26 CIRCUMFERENTIAL STRAIN < X > LEGEND CONTINUOUS READINGS 30 SECOND READINGS Figure 3.4 Pencel: Type of curve generated by a stress c o n t r o l l e d t e s t 27 3 .2 .2 .2 C a l i b r a t i o n s f o r the S t ress Cont ro l l ed Tes t Data readings from the Pencel probe must be adjusted to account f o r the system compl iance, the membrane s t i f f n e s s and the hydros ta t i c pressure caused by the f l u i d in the f l e x i b l e tub ing . Before the adjustments can be made two c a l i b r a t i o n s must be performed; a system compliance c a l i b r a t i o n and a membrane cal i b r a t i o n . The system compliance i s a measure of how much the cont ro l u n i t and the tubing expand under pressure . The system compliance of the Pencel probe was r e l a t i v e l y low and was approximately cons tant . The system compliance does not depend on whether the t e s t was run in a s t r e s s or s t r a i n c o n t r o l l e d manner. When the system compliance i s known, the volume i n j e c t e d in to the probe can be c a l c u l a t e d . Vpr = Vsur - Vcom where: Vpr = actual volume i n j e c t e d in to the probe Vsur = volume change recorded at the surface Vcom = volume a t t r i b u t e d to system compliance Vcom = P * System Compliance P = Pressure app l ied to the system The pressure measured a t the surface must be adjusted in two ways to r e f l e c t the pressure exerted by the probe on the s o i l . The hydros ta t i c head of water above the probe in the f l e x i b l e tubing must be added to the pressure measured at the surface and the 28 r e s i s t a n c e of the membrane to expansion must be subtracted from the measured pressure . The adjustment f o r the hydros ta t i c head i s s t r a i g h t forward and i s a procedure that has always been required with the Menard type pressuremeter. The membrane s t i f f n e s s was d i f f i c u l t to determine as i t depended on several f a c t o r s . The f i r s t f a c t o r tha t must be considered before c a l i b r a t i n g the membrane i s that i t softens with use. Th is was e s p e c i a l l y not iceab le when the membrane was new. It was recommended by the manufacturer that the membrane be i n f l a t e d i n a i r to maximum volume and then de f la ted to zero volume a tota l of f i v e t imes. Th is should be considered a minimum whereas twenty i n f l a t i o n / d e f l a t i o n cyc les would appear to be a be t te r recommendation. The e f f e c t tha t softening has on the membrane c a l i b r a t i o n i s shown in F igure 3 . 5 . A f t e r i n f l a t i n g and d e f l a t i n g the membrane a number of times the probe no longer returns to the same i n i t i a l volume a t zero pressure . The membrane can however, be de f l a ted back to the i n i t i a l volume but f o r t h i s to occur an external pressure i s requ i red . Th i s pressure i s small but i s important when t r y i n g to c a l c u l a t e the l i f t o f f pressure . In order to measure t h i s part of the membrane c a l i b r a t i o n curve , a vacuum source was app l ied to the contro l box. Under constant pressure the membrane creeps . There fore , as shown in F igure 3 . 6 , the membrane c a l i b r a t i o n curve i s dependent on the time between pressure increments. F igure 3 . 7 shows that the 29 cn cc < CO UJ CC D cn cn LU CC Q. 1 1 r 40 60 80 CHANGE IN VOLUME C CC ) PENCEL MEMBRANE 100 120 LEGEND • NO PRE-CYCLING • AFTER 10 CYCLES - AFTER 20 CYCLES Figure 3.5 Pencel Membrane C a l i b r a t i o n : E f f e c t of c y c l i n g 3 0 LEGEND • 30S INTERVAL 60S INTERVAL 180S INTERVAL BOOS INTERVAL Figure 3.6 Pencel Membrane C a l i b r a t i o n : E f f e c t of varying the time increment 31 s i z e of the pressure Increment a l s o a f f e c t s the membrane c a l i b r a t i o n curve . The quest ion then a r i s e s as to which pressure and time i n t e r v a l s should be used f o r the c a l i b r a t i o n . One p o s s i b l e approach would be to use the same pressure and time i n t e r v a l s that are used during the t e s t s . Take, f o r example, a t y p i c a l t e s t performed in medium dense sand. One bar pressure increments were appl ied every 30 seconds u n t i l a l i m i t pressure of 11 bars was reached. An un load-re load loop was a l so performed. The to ta l time of the expansion part of the t e s t was 10 minutes. I f the c a l i b r a t i o n curve was generated i n the same way only two data po in ts would be obtained s ince three bars would genera l ly exceed the l i m i t pressure fo r a membrane expanded in a i r . The tota l time required to i n f l a t e the probe would have been l e s s than one and a h a l f minutes. Since i t has been e s t a b l i s h e d t h a t the membrane e x h i b i t s time dependent c reep , us ing a curve tha t was generated qu i ck ly by the above approach does not appear to be c o r r e c t . Another approach would be to increase the time i n t e r v a l between pressure increments during the c a l i b r a t i o n so tha t the to ta l time to run the c a l i b r a t i o n approximates the to ta l time to run the t e s t i n the f i e l d . A l t e r n a t i v e l y , the to ta l time f o r expansion during the t e s t cou ld be dup l i ca ted by using the same time i n t e r v a l s but smal le r pressure increments during the c a l i b r a t i o n . A c lose look a t what i s happening when a pressure increment i s app l ied to the probe during a PMT shows that the pressure increment i s not c a r r i e d e n t i r e l y by the membrane nor i s the por t ion that 1s c a r r i e d by the membrane c o n s i s t e n t . The pressure increment 1s c a r r i e d mostly by the s o i l with the po r t i on c a r r i e d by the 32 LEGEND 1 BAR INCREM 0. 5 BAR INCREM Figure 3.7 Pencel Membrane C a l i b r a t i o n : E f f e c t of varying the size of the pressure increment 33 membrane dependent on the amount of s t r a i n corresponding to the increment. The quest ion s t i l l remains as to what pressure and time increment should be used. For the purposes of t h i s research program i t was des i red not to have to generate a separate c a l i b r a t i o n curve f o r each t e s t of d i f f e r e n t dura t ion . There fore , the pressure increment was standardized at 0.5bar and a time increment of 30 seconds was used fo r both the t e s t and the c a l i b r a t i o n . Th is was a small enough pressure increment to al low the c a l i b r a t i o n curve to be def ined and corresponded to the pressure increment used during t e s t s in c l a y , s i l t , and loose sand. The manufacturer 's recommendation fo r the Menard G-Am probe, which was a l so designed to be performed in a s t r e s s c o n t r o l l e d manner, i s to use standardized 0.25 bar increments app l ied at 60 second time i n t e r v a l s f o r both the t e s t and the c a l i b r a t i o n . I t was very d i f f i c u l t to determine the c o r r e c t membrane s t i f f n e s s c o r r e c t i o n fo r the unloading part of the pressuremeter curve . The membrane s t i f f n e s s during unloading was a func t ion of the maximum volume to which the probe had been expanded. The i n i t i a l por t ion of the unloading curve was very steep and small d i f f e r e n c e s i n the volume reading corresponded to large d i f f e r e n c e s in the pressure c o r r e c t i o n . Th is was e s p e c i a l l y important when unload-re load loops were being analyzed. A membrane c a l i b r a t i o n curve that inc luded a unload-re load loop s t a r t i n g at the same volume as the loop being analyzed was r e q u i r e d . Since the t e s t was performed in a s t r e s s c o n t r o l l e d manner i t was very 34 d i f f i c u l t to match the volumes at the s t a r t of the un load-re load l o o p s . A fami ly of c a l i b r a t i o n curves was therefore requ i red . Th is was l e s s of a problem with the s t r a i n c o n t r o l l e d t e s t . In a s t r a i n c o n t r o l l e d t e s t , the volume was c o n t r o l l e d so the unloading during the t e s t and dur ing the c a l i b r a t i o n cou ld be c a r r i e d out at s p e c i f i e d volumes. The other two components that required c a l i b r a t i n g were the graduated c y l i n d e r and the pressure guages. The c y l i n d e r was c a l i b r a t e d using standard laboratory techniques and the pressure gauge was c a l i b r a t e d with a dead weight pressure t e s t e r . 3 .2 .2 .3 S t r a i n C o n t r o l l e d Test The s t r a i n c o n t r o l l e d t e s t d i f f e r e d from the s t r e s s c o n t r o l l e d t e s t in that the volume of f l u i d i n j e c t e d i n t o the tubing was c o n t r o l l e d rather than the pressure . Th is allowed the t e s t to be performed at a constant ra te of s t r a i n rather than at the va r i ab le rates caused by pressure increments. There are many reasons fo r wanting to run the pressuremeter t e s t in a s t r a i n c o n t r o l l e d manner. The f a c t that the s t r a i n rate can be he ld constant f o r the durat ion of the t e s t and var ied from t e s t to t e s t i s important 1n deal ing with s o i l s that are known to have rate dependent p r o p e r t i e s . Equa l l y as important with the Pencel probe was the f a c t that membrane c a l i b r a t i o n s performed in a s t r a i n c o n t r o l l e d manner are dependent on fewer va r i ab les and 35 are more repeatab le . Th is 1s d iscussed i n de ta i l In the fo l l owing s e c t i o n . The s t r a i n contro l u n i t was developed and b u i l t at UBC to accommodate the needs of t h i s research program as well as the expected needs of fu ture programs. The u n i t which i s shown in F igure 3.8 i s s imple, v e r s a t i l e , and easy to use. The main components are a screw jack which i s attached to a p i s ton i n s i d e of a brass c y l i n d e r . Attached to the u n i t i s a f i l l e r c y l i n d e r , a LVDT to measure displacement, and a pressure t ransducer . The screw jack i s turned by a hand crank but there are f a c i l i t i e s f o r an e l e c t r i c motor to be used i n s t e a d . The use of the LVDT and the pressure transducer al lowed the measurement of pressures and volumes more accurate ly than was poss ib le with the s t r e s s c o n t r o l l e d t e s t equipment. The data was recorded by connecting the LVDT and the pressure t ransducer to an XYY chart recorder . One advantage of the s t r a i n contro l device was that i t was p o s s i b l e to apply a vacuum to the probe so that the membrane cou ld be drawn back to the same s t a r t i n g volume a f t e r each t e s t . Th i s was a great a id i n s tandard iz ing the t e s t and may have a l so reduced membrane damage because the probe was not being pushed to the next depth in a p a r t i a l l y expanded s t a t e , a common occurrence dur ing the s t r e s s c o n t r o l l e d t e s t . 36 I I i the pressure transducer i s Located behind • f i l l e r cylinder LVDT. screw jack brass pressure c y l i n d e r' the piston i s attached to the screw jack and i s located within the pressure c y l i n d e r Figure 3.8 St r a i n Control Device 3.2.2 .4 C a l i b r a t i o n s f o r the S t r a i n Cont ro l l ed Tes t When the pressuremeter t e s t was performed in a s t r a i n c o n t r o l l e d manner a unique r e l a t i o n s h i p between membrane c a l i b r a t i o n pressure and volume was es tab l i shed f o r any given s t r a i n r a t e , as shown i n F igure 3 . 9 . The major d i f f e rence between the c a l i b r a t i o n curve f o r the s t r a i n c o n t r o l l e d t e s t and the c a l i b r a t i o n curve f o r the s t r e s s c o n t r o l l e d t e s t was that the s t r a i n c o n t r o l l e d curve inc luded a component tha t corresponded to the head l o s s in the t u b i n g . The reason d i f f e r e n t s t r a i n rates produced d i f f e r e n t c a l i b r a t i o n curves ( F igure 3.9 ) was because the head l o s s var ied with the rate of f low of f l u i d in the tub ing . There may be some d i f f e rence in the membrane s t i f f n e s s due to s t r a i n rate but t h i s was not examined thoroughly . The s t r e s s c o n t r o l l e d c a l i b r a t i o n curve d id not have a head l o s s component because there was genera l l y an adequate time lapse between the time the pressure increment was app l ied and the time tha t the volume was recorded during which the pressures throughout the system e q u a l i z e d . F igure 3.9 a l s o shows that observat ion of the pressure drop when the i n f l a t i o n was stopped al lowed the head l o s s component of the c a l i b r a t i o n to be i d e n t i f i e d . However, i t was not necessary to i d e n t i f y t h i s component because the head l o s s during the t e s t was the same as the head l o s s during the c a l i b r a t i o n provided the s t r a i n rates were the same. 38 LEGEND • 5 SEC / REV — 2.5 SEC / REV Figure 3.9 Pence! Membrane C a l i b r a t i o n : E f f e c t of varying the s t r a i n r a t e 39 C a l i b r a t i n g the LVDT was simply a matter of record ing the volume of l i q u i d expe l led from the c y l i n d e r corresponding to a vo l tage increment. The pressure transducer was c a l i b r a t e d with the same dead weight pressure t e s t e r used to c a l i b r a t e the pressure gauge i n the Menard G-Am contro l box. 3.3 Hughes Pressuremeter The Hughes pressuremeter i s of i n t e r e s t because i t al lows d i r e c t comparison between pressuremeter t e s t s where the probe was i n s e r t e d by a s e l f - b o r i n g ac t ion with those inser ted i n a f u l l displacement manner. The only d i f f e r e n c e s between se l f -bored t e s t s with t h i s instrument and f u l l displacement t e s t s i s the manner of i n s t a l l a t i o n . With the Pencel probe the diameter, membrane type, and method of data c o l l e c t i o n are a l l d i f f e r e n t from those employed using the s e l f - b o r i n g pressuremeter. 3.3.1 Desc r ip t i on of Hughes Pressuremeter The Hughes pressuremeter ( HPM ) i s patterned a f t e r the one developed by Hughes and Wroth at Cambridge in the e a r l y 1970's. Th is p a r t i c u l a r model has been constructed with a s l i g h t l y smal ler diameter of 76mm so that i t can be lowered through a smal ler d r i l l c a s i n g , a concern on commercial p r o j e c t s . The probe which i s shown i n F igure 3.10 i s genera l ly i n f l a t e d with pressur i zed n i t rogen gas which i s c o n t r o l l e d by a pressure 40 Signal Wires to Surface N Pressure Hose• Cas ing Support' Air (Pressurized) E lec t r i ca l Signal Conditioners Pressure T ransducer -Pore Pressure Cell-Displacement Transducers-Flexible Membrane — ( Aft e r Hughes and Robertson, 1984 ) Sol id Cone Tip Figure 3.10 Hughes Pressuremeter ( HPM ) 41 r e g u l a t o r at the s u r f a c e . The expansion of the membrane 1s measured by s t r a i n gauges attached to three arms at the center of the membrane. These arms measure rad ia l displacement which 1s e a s i l y converted to c i r cumferen t i a l s t r a i n . Th is 1s 1n con t ras t to the Pencel probe where changes in volume are measured and then converted to volumetr ic s t r a i n . The e l e c t r o n i c a l l y monitored s t r a i n arms are more s e n s i t i v e and can detect smal le r movements than the Pencel measuring system. The pressure 1s measured by a t o t a l pressure c e l l i n s i d e the probe. The membrane on the HPM i s cons iderab ly more f l e x i b l e than the membrane used on the Pencel probe. One important in f luence of the f l e x i b l e membrane i s the smal le r membrane s t i f f n e s s c o r r e c t i o n s . The p r o t e c t i v e s t a i n l e s s stee l sheath i s not attached to the membrane but i s attached d i r e c t l y to the probe in such a way that i t i s f ree to s l i d e at one end. The expandable p o r t i o n of the membrane i s 456mm long with a r e s u l t i n g 1/d r a t i o of 6 . Th i s i s s l i g h t l y smal ler than the 1/d r a t i o of 7.5 f o r the Pencel probe. 3 .3 .2 Test Procedures and Data Acqu is t lon The HPM t e s t ( HPMT ) was performed i n two d i f f e r e n t formats. Tes t s were performed i n the s t r e s s c o n t r o l l e d format because tha t was how the l o c a l l y a v a i l a b l e s e l f - b o r i n g t e s t s were performed and the ob jec t was to compare the s e l f bor ing r e s u l t s to the f u l l displacement r e s u l t s as d i r e c t l y as p o s s i b l e . The HPMT was a l s o performed in a s t r a i n c o n t r o l l e d format f o r the same reasons as were l i s t e d i n sec t ion 3 . 2 . 2 . 3 . 3 .3 .2 .1 S t ress C o n t r o l l e d Tes t The contro l box shown i n F igure 3.11 was normally used f o r performing the HPMT when se l f -bored i n t o the ground and was a l s o used when the HPM was i n s t a l l e d in a fu l l -d i sp lacement manner. No mod i f i ca t i ons were necessary . The contro l box requ i red an e l e c t r i c a l power supply because i t was used to power the s t r a i n gauges and transducers i n the probe. A pressur i zed n i t rogen b o t t l e was attached to the contro l box. The contro l box inc luded a pressure regu lator and a flow contro l valve which regulated the supply of gas to the probe. The s igna l s from the probe were rece ived and ampl i f i ed i n the contro l box, and cou ld be read with a d i g i t a l vo l tmeter . The s i g n a l s cou ld a lso be recorded on a chart r eco rder . The f a c t that gas rather than a l i q u i d was being used to i n f l a t e t h i s probe meant that the pressure app l ied a t the surface was approximately the same pressure that was measured i n the probe. There was no hydros ta t i c pressure head. There was a small head l o s s in the tubing but i t was n e g l i g i b l e , e s p e c i a l l y at the shal low t e s t depths s tud ied i n t h i s research p ro jec t ( i e . < 20m). 3 .3 .2 .2 C a l i b r a t i o n s f o r the S t ress Cont ro l l ed Tes t There are four components that must be c a l i b r a t e d f o r t h i s t e s t ; the membrane, the to ta l pressure c e l l , the s t r a i n arms, and the system compl iance. 4 3 REGULATOR Figure 3.11 HPM Control Box The HPM membrane was much s o f t e r than the Pencel membrane. The membrane c a l i b r a t i o n which i s shown in F igure 3.12 was considered to be a constant . An i n i t i a l pressure of approximately 0.35 bar was required to cause the membrane to s t a r t i n f l a t i n g and i t continued to i n f l a t e to the maximum al lowable volume at t h i s p ressure . The s t r a i n arms were d i f f i c u l t to c a l i b r a t e i n d i v i d u a l l y once the membrane had been i n s t a l l e d . P r i o r to the membrane being i n s t a l l e d a voltage reading was recorded when the arms were f u l l y compressed and the amount of expansion corresponding to subsequent vol tage readings was measured d i r e c t l y . Th i s y i e l d e d d i f f e r e n t c a l i b r a t i o n f ac to rs f o r each s t r a i n arm. Once the membrane had been i n s t a l l e d i t was d i f f i c u l t to determine how much an ind iv idua l arm had expanded. However, the e l e c t r i c a l cable connect ing the probe to the surface was subject to a l o t of abuse and of ten needed to be r e p a i r e d . Whenever the e l e c t r i c a l cable was repa i red the c a l i b r a t i o n changed. Since the membranes are expensive ($66 each) i t was des i rab le not to have to remove and rep lace them every time a s t r a i n arm c a l i b r a t i o n was requ i red . The s t r a i n arms cou ld be c a l i b r a t e d with the membrane on by i n f l a t i n g the probe ins ide a steel c y l i n d e r of known diameter and making the assumption tha t a l l three arms expanded the same amount. The to ta l pressure c e l l was e a s i l y c a l i b r a t e d i n the same manner as the pressure t ransducer in the s t r a i n contro l dev i ce . 45 LEGEND STRAIN CONTROLLED STRESS CONTROLLED Figure 3.12 HPM Membrane C a l i b r a t i o n Curve The system compliance was measured and found to be very low and was genera l ly taken to be i n s i g n i f i c a n t w i th in the pressure range used during t h i s study ( i e . < 20 bar ) . 3 .3 .2 .3 S t r a i n C o n t r o l l e d Tes t The main problem encountered using the HPM in a s t r a i n c o n t r o l l e d manner was the s i z e of the head l o s s through the t u b i n g . Due to i t s l a r g e r s i z e , the volume of f l u i d required to expand the HPM to a given c i r cumferen t i a l s t r a i n was much greater than that required f o r the Pencel probe. Therefore , i f the s t r a i n rate was to be the same as was used during the Pencel t e s t s , more f l u i d must flow through the tubing r e s u l t i n g in even greater head l osses than with the Pencel probe. As i t was des ired to run the s t r a i n c o n t r o l l e d t e s t with the same contro l u n i t used with the Pencel probe, a non-compressible f l u i d was requ i red . The presence of e l e c t r o n i c s in the instrument meant tha t the f l u i d used must be non-conducting, un l ike the Pencel probe where water was used. The f l u i d o r i g i n a l l y chosen was a l i g h t hydrau l i c o i l . However, t h i s proved to be too v iscous and the head losses with the 20m of tubing were such that the f l u i d tha t was i n jec ted in to the probe cou ld not be drawn back i n t o the r e s e r v o i r even under a f u l l vacuum. The f l u i d tha t eventua l ly proved to work was WD-40, a commercial ly ava i l ab le mixture of l i g h t o i l and so l ven t . The only major drawback to the use of t h i s f l u i d was the tendency f o r the membrane to s t re tch cons iderab ly when the WD-40 was l e f t s i t t i n g i n the probe. Th is problem was 47 easy to contro l s ince the ends of the membrane could be undamped and the f l u i d drained from the probe when i t was not i n use. The ends of the membrane were reclamped without damaging the membrane. The s t r a i n contro l device used with the Pencel probe was used fo r the HPM s t r a i n c o n t r o l l e d t e s t in conjunct ion with the contro l box normally used with the HPM. The s t r a i n contro l device al lowed the rate at which f l u i d was in jec ted in to the probe to be contro l l e d . There were two b ig advantages to having both contro l systems operat ing on one probe. The f i r s t was the opportunity to compare the to ta l pressure in the probe to the pressure measured at the s u r f a c e . Th i s allowed an opportunity to d i r e c t l y measure the head l o s s in the tubing and to observe that pressure f l u c t u a t i o n s at the surface were not present in the probe ( see F igure 3.13 ) . The second advantage to having the two contro l systems was the opportunity to examine the d i f f e r e n c e between the volumetr ic s t r a i n c a l c u l a t e d from measuring the amount of f l u i d i n j e c t e d in to the probe with the c i r cumferen t i a l s t r a i n measured by the s t r a i n arms at the center of the membrane. The r e s u l t s of the comparison are shown i n F igure 3.14. The volumetr ic s t r a i n i s the change in volume d iv ided by the o r i g i n a l volume. The o r i g i n a l volume was c a l c u l a t e d us ing the o r i g i n a l diameter of the probe. The c i r cumferen t i a l s t r a i n i s the change in radius measured by the 48 0 2 4 6 8 10 CIRCUMFERENTIAL STRAIN < X > Figure 3.13 HPM: Comparison of pressure reading at the surface and at the probe 4 9 s t r a i n arms d iv ided by the o r i g i n a l rad ius of the probe. I f the assumption 1s made that the probes expand 1n the form of a r i g h t c y l i n d e r the volumetr ic s t r a i n should be approximately twice the rad ia l s t r a i n . Suyama e t a l , 1983 used X-ray radiography 1n model experiments and showed that pressuremeters employing the mono-cell design expand very c lose to a r i g h t c y l i n d e r when expanded i n sand. The exact formula r e l a t i n g the two types of s t r a i n 1s shown on F igure 3 .14. The f a c t that the membrane i s constra ined at each end means that i t can never expand as a t rue r i g h t c y l i n d e r but as the 1/d r a t i o increases the e f f e c t of the end c o n s t r a i n t d imin i shes . The HPM has a s o f t e r more f l e x i b l e membrane, and l e s s end c o n s t r a i n t because the p ro tec t i ve stee l sheath i s not clamped a t both ends as i t i s with the Pencel probe. However, the HPM has a smal ler 1/d r a t i o ( 6.0 vs 7.5 ) than the Pencel probe. The f i n a l r e s u l t i s that the HPM probably expanded in a shape c l o s e r to a r i g h t c y l i n d e r than did the Pencel probe. The purpose of previous pressuremeters having a t r i - c e l l design rather than the mono-cell design was to reduce the e f f e c t of the end c o n s t r a i n t . The r e s u l t s shown i n F igure 3.14 i n d i c a t e that the s t r a i n measured by the arms at the center of the probe was always greater than the s t r a i n c a l c u l a t e d from the volume measurements. T h i s i s to be expected because of the end c o n s t r a i n t . The r e s u l t s a l so show t h a t the volumetr ic s t r a i n agrees much more c l o s e l y with the c i r cumferen t i a l s t r a i n i n s t i f f e r m a t e r i a l . To understand t h i s i t 1s he lp fu l to cons ider the expansion of the probe i n a i r . In t h i s 50 < or i— in u Ul 2: _i o > CIRCUMFERENTIAL STRAIN LEGEND • THEORETICAL SAND SILT SILT CLAY CLAY Figure 3.14 HPM: Comparison of volumetric s t r a i n and cir c u m f e r e n t i a l s t r a i n measurements 51 case the expanded probe i s shaped somewhat l i k e a f o o t b a l l . When the probe i s expanded i n a s t i f f mater ia l the amount of c o n s t r a i n t i n the center of the probe i s going to be proport iona l to the amount of expansion. Therefore when the center of the probe begins to expand more than the ends of the probe i t meets more res i s tance and the membrane expands along the path of l e a s t r e s i s t a n c e which i s c l o s e r to the ends. The s t i f f e r the mater ia l the l e s s s i g n i f i c a n t the end r e s t r a i n t s become. F igure 3.15 i l l u s t r a t e s the e f f e c t of c a l c u l a t i n g the s t r a i n in d i f f e r e n t ways on the var ious pressure expansion curves . One curve i s shown with s t r a i n c a l c u l a t e d from the i n j e c t e d volume and the other from measured s t r a i n at the center of the probe. If the Pencel probe expands l e s s l i k e a r i g h t c y l i n d e r than the HPM than the r a t i o of s t r a i n at the center of the membrane to the average s t r a i n c a l c u l a t e d from the volume increase would be h igher than i t i s with the HPM. The quest ion that a r i s e s i s that i f the membrane i s not expanding as a r i g h t c y l i n d e r then what i s the c o r r e c t c i r c u m f e r e n t i a l s t r a i n . Should the measured s t r a i n at the center of the membrane be used or the one c a l c u l a t e d from the volumetr ic increase which represents some sor t of an average over the e n t i r e length of the membrane. 52 CIRCUMFERENTIAL STRAIN C X ) 0 2 4 6 8 10 12 < 0 4 8 12 16 20 24 VOLUMETRIC STRAIN < X > LEGEND — VOLUMETRIC STRAIN CIRCUMFERENTIAL STRAIN Figure 3.15 HPM: Comparison of curves generated with volumetric s t r a i n and those generated with c i r c u m f e r e n t i a l s t r a i n 53 3.3 .2 .4 C a l i b r a t i o n s f o r the S t r a i n C o n t r o l l e d Test The c a l i b r a t i o n s were b a s i c a l l y the same as those fo r the s t ress c o n t r o l l e d t e s t . The major exception was the membrane c a l i b r a t i o n . When the t e s t i s s t r a i n c o n t r o l l e d i t became apparent that the membrane c a l i b r a t i o n shown i n F igure 3.12 was a near ly l i n e a r r e l a t i o n between pressure and s t r a i n as was to be expected from a l i n e a r e l a s t i c m a t e r i a l . Note t h i s i s in contrast to the behaviour observed in the s t ress c o n t r o l l e d t e s t . In the s t ress c o n t r o l l e d t e s t the membrane behaved l i k e a ba l loon in that i t took a c e r t a i n i n i t i a l pressure to begin the i n f l a t i o n and very l i t t l e extra pressure to continue the i n f l a t i o n . 54 Chapter 4 F i e l d Program 4.1 Introduct ion F i e l d t e s t s with the f u l l displacement pressuremeter were conducted at three research s i t e s in the lower Fraser River V a l l e y . One s i t e cons i s ted p r i m a r i l y of sand, another p r i m a r i l y of organic s i l t , and the t h i r d p r i m a r i l y of c l a y . These s i t e s were chosen because they r e f l e c t e d the three s o i l types and because of the other i n s i t u t e s t s which had been or were being conducted t h e r e . The f i r s t s i t e was in Langley, j u s t o f f the Trans Canada Highway. The s o i l c o n s i s t s of normally conso l ida ted c lay with a l a y e r of over conso l idated mater ia l at the su r face . The second s i t e was at Boundary Road on Lulu Is land i n the F raser R iver . The s o i l p r o f i l e c o n s i s t s of organic s i l t over dense sand with a l a y e r o f peat near the s u r f a c e . The t h i r d s i t e was at McDonalds Farm on Sea Is land i n the F raser R iver d e l t a . The McDonalds Farm s i t e has been well documented i n many UBC research p u b l i c a t i o n s . The s o i l p r o f i l e at McDonalds Farm c o n s i s t s of 13m of sand of vary ing dens i ty o v e r l y i n g s i l t and c l a y . 55 1. Langley 2. Boundary Road 3. McDonalds Farm Figure 4.1 S i t e Location Map 4.2 Langley Langley was chosen as a research s i t e because the s o i l p r o f i l e conta ins a f a i r l y uniform c l ay l ayer at a r e a d i l y a c c e s s i b l e depth. Th is s i t e was a l so one of the l o c a t i o n s used in a research program i n v o l v i n g determinat ion of the undrained shear strength from the f i e l d vane and the cone penetrometer. As a r e s u l t of the other research program, several cone p r o f i l e s were a l ready a v a i l a b le at t h i s s i t e as well as several N i l con f i e l d vane p r o f i l e s . 4 .2 .1 S i t e D e s c r i p t i o n The s i t e i s l oca ted on the approach to the 232nd St reet overpass, j u s t o f f the Trans-Canada Highway in Langley, B.C. The p i e z o m e t e r - f r i c t i o n cone p r o f i l e shown i n F igure 4.2 g ives a good i n d i c a t i o n of the s o i l s t r a t i g r a p h y . The upper 6m c o n s i s t s of two d i s t i n c t l ayers of overconso l idated c l a y , with a very s t i f f l ayer l oca ted at 2.75m. Below 6m i s a uniform l a y e r of normally conso l ida ted c l a y . Interbedded s i l t l ayers begin at 14m and cont inue below that depth. The water table i s between 3 and 4 meters below the s u r f a c e . 4 .2 .2 Results The table shown i n F igure 4.3 l i s t s a l l the i n s i t u t e s t s that were conducted a t Langley and used i n t h i s research program. 57 U B C I M S I T U T E S T I N G S i t a L o c a t i o n ! LANGLEY CPT Data • 0CT02 1884 Poga Not 1 / 1 On S l t a Loci UPPER SITE Cona Uaadi CB FPSG 6UBC C o m a n t f i CB€ 8EARJNC FRICTION RATIO PORE PRESSURE INTERPRETED Oapth I n e r m n t i . 025 m M O M Oapth . I S . 82 m Figure 4.2 Langley cone p r o f i l e 58 TESTS CONDUCTED AT THE LANGLEY TEST SITE Test Designator Instrument Test Date Comments Depths at which PMTs were conducted Lanrl Pencel Probe 06/09/84 Stress controlled 32mm ti p 2.75,6,8,10,11.5,15 Lanr2 Pencel Probe 06/09/84 Stress controlled 36mm ti p 2.75,6,8,10,11.5,15 Lanr3 Pencel Probe 16/11/84 Stra i n controlled 36mm ti p 3,6,7,8,9,10,11 Lanr4 Pencel Probe 16/11/84 S t r a i n controlled 32mm ti p 3,6,8,9,10 LI HPM 18/07/84 Stress controlled 3,6,8,10,12 L2 HPM 19/07/84 Stress controlled 3,6,8,10,12 L3 HPM 20/01/85 Strain controlled 0.5,1,1.5,2.75,5,6 CPT #1 Seismic cone 02/10/84 Nilcon F i e l d Vane P r o f i l e Figure 4.3 Ins i t u tests conducted at Langley Typica l curves from each of the var ious types of t e s t s obtained using the Pencel 'probe at a depth of 6m are shown in F igure 4 .4 . Examining F igure 4.4 severa l s i m i l a r i t i e s are seen; the curves tended toward the same l i m i t pressure , and the c l o s i n g pressure was almost i d e n t i c a l with a l l four t e s t s . The l i f t o f f pressures var ied cons iderab ly and t h i s w i l l be d iscussed in sec t i on 4 . 2 . 2 . 2 . The s t r a i n c o n t r o l l e d t e s t y i e l d e d a very e r r a t i c pressuremeter curve , which was a func t ion of the hand cranking of the s t r a i n contro l dev ice . T h i s i s d iscussed f u r t h e r i n s e c t i o n 4 . 3 . 2 . F igure 4.5 compares the Pencel t e s t s conducted with the 32mm diameter t i p to the s t r e s s c o n t r o l l e d HPMT. Again the pressuremeter curves a l l tended towards the same l i m i t pressure . Note that a l l three of the t e s t s had the same c l o s i n g pressure . 4 .2 .2 .1 Shear Moduli F igure 4.6 i s a p r o f i l e of the shear modulus determined at the Langley s i t e with the Pencel probe. The r e s u l t s shown are those obtained during the s t r a i n c o n t r o l l e d t e s t s . It was not p o s s i b l e to determine shear moduli from unload-re load loops performed with the s t r e s s c o n t r o l l e d Pencel at any of the s i t e s . There were two reasons fo r t h i s . 1) The c a l i b r a t i o n c o r r e c t i o n s were a very s i g n i f i c a n t f a c t o r in the c a l c u l a t i o n and the c o r r e c t i o n s were a funct ion of so many va r i ab les that the appropr iate c o r r e c t i o n s were very d i f f i c u l t to determine. 2) The 60 i 1 1 r 0 5 10 15 20 25 CIRCUMFERENTIAL STRAIN C X > LANGLEY DEPTH 6M LEGEND • 32MM TIP STRESS 36MM TIP STRESS 3BMM TIP STRAIN 32MM TIP STRAIN Figure 4.4 Pencel: T y p i c a l Curves at Langley 61 C O or < CO or tn co ui or a. 32mm t i p s t r a i n ~1 1 1 5 10 15 CIRCUMFERENTIAL STRAIN C X > LANGLEY DEPTH 6M —V 20 25 LEGEND 32MM TIP STRESS 32MM TIP STRAIN HPM STRESS CONT Figure 4.5 Comparison of Pencel curves with HPM curves: Langley 62 2-• Gmax 457 bar 4-a. ui Q 6-8- • • 4Hd • 10- 4* • 12- 1 r— 100 200 SHEAR MODULUS C BARS ) LANGLEY 300 LEGEND 32MM TIP STRAIN 36MM TIP STRAIN GMAX C SEISMIC > Figure 4.6 P r o f i l e of Shear Modulus at Langley: Pencel 63 cont ro l u n i t used f o r the s t r e s s c o n t r o l l e d t e s t s was not capable of accurate ly r e g i s t e r i n g the small volume changes invo lved with un load-re load loops . F igure 4.6 a l so shows the dynamic shear modulus ( Gmax ) determined with the UBC seismic cone using the downhole seismic technique. The seismic cone obtains Gmax values from the average shear wave v e l o c i t y over a lm depth i n t e r v a l . The shear modulus measured by the Pencel probe i s at a shear s t r a i n l eve l of approximately 1%. The shear modulus measured with the seismic cone i s at very small s t r a i n l e v e l s . Shear modulus at tenuat ion curves f o r c l ay such as those shown in F igure 2.2 suggest that the shear modulus at 1% s t r a i n should be 10 to 40% of Gmax depending on the p l a s t i c i t y index of the c l a y . The unload-re load moduli values measured by the Pencel probe are between 25 and 50% of Gmax measured with the seismic cone. There seems to be no d i s c e r n i b l e d i f f e r e n c e between the un load-re load moduli measured when the probe was i nse r ted with the 32mm t i p and when the probe was i n s e r t e d with the 36mm overs i zed t i p . Note that the r a t i o between the measured un load-re load moduli and Gmax appears to remain constant even in the very s t i f f l a y e r where Gmax was 467 bar . Thin d iscont inuous sand l ayers were apparent on some of the cone p r o f i l e s . The occurrence of such a l a y e r would exp la in the high un load- re load G values recorded with the Pencel probe a t 11.5m. The un load-re load shear moduli measured with the HPM at Langley are presented i n F igure 4 . 7 . With the HPM, the unload-re load shear moduli were between 15 and 50% of those measured with 64 OL HI a 2-6-8-10-12-• m n d B f l ) (BDIZD an DO 1 1— 100 200 SHEAR MODULUS < BARS ) LANGLEY — i 300 LEGEND • STRESS CONTROLLED TEST o STRESS CONTROLLED TEST STRAIN CONTROLLED TEST Figure 4.7 P r o f i l e of Shear Modulus at Langley: HPM 6 5 the seismic cone. The s o i l i s assumed to be undrained during an un load-re load loop performed while the probe 1s 1n c l a y . I f t h i s 1s the case , the mean e f f e c t i v e s t r e s s in the s o i l w i l l remain constant and there fore the shear modulus should be constant regard less of when during the t e s t the un load-re load loops are conducted. In p r a c t i c e , very high pore pressure grad ients are created during a pressuremeter t e s t and some drainage w i l l be o c c u r r i n g . As a r e s u l t of dra inage, the mean e f f e c t i v e s t r e s s increases and the measured unload-re load shear modulus at l a t e r stages in the t e s t w i l l be somewhat h igher than those in the i n i t i a l s tages . The shear modulus number, Kg, w i l l be constant but t h i s cannot be c a l c u l a t e d unless the drainage cond i t ions are known and the mean e f f e c t i v e s t ress can be est imated. The un load-re load shear modulus measured with the HPM i s approximately 65% of that measured with the Pencel probe. The Pencel has a much smal ler diameter and the excess pore pressures would tend to d i s s i p a t e much f a s t e r than with the HPM. If t h i s 1s the case then the shear moduli measured with the Pencel would be expected to be h igher because of the h igher mean e f f e c t i v e s t r e s s . The shear moduli measured with the HPM were however, subjected to l e s s attenuat ion because the unload re load loops were smal ler than those performed with the Pencel probe. There 1s i n s u f f i c i e n t data to draw any conc lus ions about the 66 d i f f e r e n c e s between un load-re load shear moduli measured with s t r e s s and s t r a i n c o n t r o l l e d t e s t s with the HPM. 4 .2 .2 .2 Horizontal S t ress The l i f t o f f pressure measured by a fu l1-d isp lacement pressuremeter inser ted in c lay can be expected to be between the to ta l pore pressure ( the hydros ta t i c + the dynamic pore pressure ) and the i n s i t u hor izonta l to ta l s t r e s s . The l i f t o f f pressure measured w i l l depend on the time al lowed f o r drainage between the stop in penetrat ion and the s t a r t of the pressure expansion t e s t . The measured hor izonta l e f f e c t i v e s t r e s s can there fo re be expected to be between the dynamic pore pressure and the i n s i t u hor izonta l e f f e c t i v e s t r e s s . Immediately a f t e r i n s e r t i o n , the l i f t o f f pressure cou ld be expected to be dominated by the to ta l pore pressure . Th is i s complicated somewhat when the s o i l i s unsaturated, as i s the case with the overconso l idated l a y e r above a depth of 3m. A f t e r a l l the pore pressures have d i s s i p a t e d , the l i f t o f f pressure cou ld be expected to be a measure of the hor izonta l to ta l s t r e s s . The s o i l , however, has undergone some c o n s o l i d a t i o n during the d i s s i p a t i o n of the excess pore p ressures . There fore , i t can be expected that the measured hor i zonta l s t resses w i l l be somewhat higher than the i n s i t u hor i zonta l s t r e s s e s . F igure 4.8 shows a p r o f i l e of the measured hor izonta l e f f e c t i v e s t r e s s . Most of these t e s t s were quick t e s t s ; i e . where a pressure expansion t e s t was performed immediately a f t e r the stop 6 7 1 1 1 1 1 1 1 0 1 2 3 4 5 6 LIFTOFF PRESSURE MINUS Uo < BARS 5 LANGLEY LEGEND X 32MM TIP STRESS • 36MM TIP STRESS A 36MM TIP STRAIN O 32MM TIP STRAIN - VERT EFF STRESS Figure 4.8 P r o f i l e of Measured H o r i z o n t a l E f f e c t i v e Stress At Langley: Pencel 68 i n penetrat ion and the pore pressures were not given an opportunity to d i s s i p a t e . The except ions to t h i s are the t e s t r e s u l t s shown shaded i n F igure 4.8 where the pore pressures were al lowed to d i s s i p a t e up to an est imated 90%. The r e s u l t s of the 36mm t i p s t r a i n c o n t r o l l e d t e s t s appear to show that the opportunity f o r the pore pressures to d i s s i p a t e had l i t t l e i n f luence on the measured l i f t o f f p ressure . The s t r a i n c o n t r o l l e d t e s t with the 32mm t i p that was al lowed time f o r an estimated 90% pore pressure d i s s i p a t i o n shows a s l i g h t l y lower hor izonta l e f f e c t i v e s t ress than the other t e s t s performed during tha t sounding but the measured hor i zonta l e f f e c t i v e s t r e s s 1s s t i l l very much higher than the v e r t i c a l e f f e c t i v e s t r e s s . The t e s t s performed using the 36mm t i p recorded lower hor i zonta l s t resses than t e s t s using the 32mm t i p . Th is i s to be expected because the 36mm t i p produces a c a v i t y l a r g e r than the probe and the s o i l can re lax i n towards the probe. It i s not obvious why the s t r e s s c o n t r o l l e d t e s t s recorded c o n s i s t e n t l y lower hor izonta l s t resses than the s t r a i n c o n t r o l l e d t e s t s . The hor izonta l e f f e c t i v e s t r e s s e s recorded by the HPM and presented in F igure 4.9 fo l l ow the same pat tern as those recorded by the Pence l . The measured hor i zonta l e f f e c t i v e s t resses are a l l g r e a t e r than the v e r t i c a l e f f e c t i v e s t r e s s and seem to increase p r o p o r t i o n a l l y to the v e r t i c a l e f f e c t i v e s t r e s s . I t 1s In te res t ing to note the h igher hor izonta l s t r e s s e s measured i n the overconso l idated l a y e r above a depth of 6m. The r e s u l t s from the 69 LEGEND • STRESS CONTROL A STRESS CONTROL O STRAIN CONTROL VERT EFF STRESS Figure 4.9 P r o f i l e of Measured Horizontal E f f e c t i v e Stress At Langley: HPM 70 d i s s i p a t i o n t e s t s show no p a r t i c u l a r t rends . Some of the d i s s i p a t e d r e s u l t s are h igher than the r e s u l t s from the quick t e s t s and others lower as would be expected. The r e s u l t s from two o f the s t r a i n arms are shown f o r each of the HPMT's. They show tha t the arms were in good agreement. The few depths where only one data point i s shown are where the l i f t o f f pressures measured from the two arms were i d e n t i c a l . 4 .2 .2 .3 Undrained Shear Strength F igure 4.10 presents the values of the undrained shear s t rength determined from the d i f f e r e n c e between the l i m i t pressure and the l i f t o f f pressure which were taken from the pressure versus c i r cumferen t i a l s t r a i n p l o t s of the Pencel probe r e s u l t s . Two t rends are apparent: 1) the 32mm t i p y i e l d s s l i g h t l y lower Su values than the 36mm t i p and 2) the s t r a i n c o n t r o l l e d t e s t s y i e l d s l i g h t l y lower r e s u l t s than the s t r e s s c o n t r o l l e d t e s t s . The l i m i t pressures recorded by the var ious types of t e s t s a l l tended towards the same pressure but the 32mm t i p and the s t r a i n c o n t r o l l e d t e s t s c o n s i s t e n t l y y i e l d e d h igher l i f t o f f p ressures . The d i f f e r e n c e between the l i m i t and l i f t o f f pressures i s the re fo re smal ler dur ing those t e s t s . The c a l c u l a t e d undrained shear strength i s consequently sma l l e r . The c a l c u l a t e d undrained shear s t rengths are almost a l l lower than the r e s u l t s obtained from the f i e l d vane. Th is 1s in con t ras t to r e s u l t s reported by Wroth, 1984 where the determinat ion of undrained shear s t rength using the s e l f - b o r i n g pressuremeter was 71 CL UJ a i r .75 1 UNDRAINED SHEAR STRENGTH LANGLEY 1.25 < BARS > 1.5 1.75 LEGEND X 32MM TIP STRESS • 36MM TIP STRESS A 36MM TIP STRAIN 0 32MM TIP STRAIN FIELD VANE Figure 4.10 P r o f i l e of Undrained Shear Strength Determined from the Pencel Curves 72 genera l l y approximately 50% h igher than those measured with the f i e l d vane. However,this would depend somewhat on the value chosen f o r the s t i f f n e s s r a t i o , G / Su. A value of In (G / Su) = 6.5 was chosen fo r t h i s study. If a value of In (G / Su) = 5.0 was used e x c e l l e n t agreement would have been obtained between the Pencel der ived Su and the f i e l d vane va lues . F igure 4.11 shows the values of Su der ived from the HPM curves . They fo l low the same trend as the f i e l d vane p r o f i l e . In the overconsol idated l a y e r the r e s u l t s are lower than the f i e l d vane r e s u l t s but in the normally conso l ida ted s o i l the HPMT r e s u l t s are approximately 10 to 20% h igher than the f i e l d vane r e s u l t s . Thus the HPM i s i n d i c a t i n g h igher undrained shear s trengths than the Pencel probe. The second method of de r i v ing the undrained shear s t rength , where the pressure i s p lo t ted aga ins t the logar i thm of the volumetr ic s t r a i n , e l iminates the need to est imate G / Su. Th is method i s based on the assumption t h a t the material 1s e l a s t i c / p e r f e c t l y p l a s t i c . The values of Su der ived from the Pencel probe us ing the second method are shown 1n F igure 4.12. They are very s i m i l a r to the r e s u l t s obtained us ing the prev ious method. Th is would tend to conf i rm the estimate of the s t i f f n e s s r a t i o used in the prev ious c a l c u l a t i o n . There 1s, however, a much greater degree of s c a t t e r 1n t h i s second set of r e s u l t s . The r e s u l t s from the 36mm t i p 73 Q. LU a T .5 .75 1 UNDRAINED SHEAR STRENGTH LANGLEY 1.25 BARS > 1.5 1.75 LEGEND D STRESS CONTROL A STRESS CONTROL O STRAIN CONTROL FIELD VANE Figure 4.11 P r o f i l e of Undrained Shear Strength Determined from the HPM Curves 74 LEGEND X 32MM TIP STRESS D 36MM TIP STRESS A 36MM TIP STRAIN O 32MM TIP STRAIN — FIELD VANE Figure 4.12 P r o f i l e of Undrained Shear Strength Determined from the Pressure vs Log Volumetric S t r a i n P l o t : Pencel 75 s t r a i n c o n t r o l l e d t e s t s are c o n s i s t e n t l y about twice as high as any of the other r e s u l t s and no explanat ion has been found f o r t h i s . There does not seem to be a cons i s ten t trend 1n the r e s u l t s o f the s t r e s s or s t r a i n c o n t r o l l e d t e s t . The undrained shear strengths c a l c u l a t e d from the HPM using the second method are shown in F igure 4 .13 . They are very s i m i l a r to the Su values c a l c u l a t e d using the f i r s t method. One except ion i s at ten meters. The higher value of measured undrained shear s t rength at t h i s p a r t i c u l a r depth i s l i k e l y due to the presence of a d iscont inuous sand l e n s e . 4.3 Boundary Road T e s t P i l e S i t e The t e s t program was conducted a t a s i t e on the corner of Boundary and Dike Road i n New Westminister , B.C. Th is l o c a t i o n was the s i t e of a B.C. M i n i s t r y of Highways p i l e load t e s t . The p i l e was loaded both a x i a l l y and l a t e r a l l y . D e t a i l s of the p i l e t e s t program and the i n s i t u t e s t i n g program used to p red i c t the p i l e ' s r e a c t i o n i s given by Robertson e t a l , 1985a. The i r paper a l so compares the p r e d i c t i o n of ax ia l load capac i ty using the cone penetrometer, and the p r e d i c t i o n of l a t e r a l displacement us ing the fu l1-d isp lacement pressuremeter data to the measured r e s u l t s from the p i l e load t e s t . At t h i s s i t e , the s o i l parameters dea l t with in t h i s paper are the shear moduli and the hor i zonta l s t r e s s e s . i 76 3E 0. LU Q i 1 r .5 .75 1 UNDRAINED SHEAR STRENGTH C LANGLEY 1.25 BARS > 1.5 1.75 LEGEND • STRESS CONTROL A STRESS CONTROL O STRAIN CONTROL • FIELD VANE Figure 4.13 P r o f i l e of Undrained Shear Strength Determined from the Pressure vs Log Volumetric S t r a i n P l o t : HPM 77 4.3 .1 S i t e D e s c r i p t i o n The s i t e 1s covered with approximately 3m of rubble f i l l . In order to prevent damage to the probes, a 3m deep trench was dug, and b a c k f i l l e d with loose sand at the l oca t i ons of the i n s i t u t e s t s , and a t the l o c a t i o n of the t e s t p i l e . F igure 4.14 shows a p i e z o m e t e r - f r i c t i o n cone p r o f i l e of the s i t e a t Boundary Road. The cone p r o f i l e shows 3m of loose sand o v e r l y i n g 2m of peat and 10m of organic s i l t . Under ly ing the organic s i l t i s a dense l a y e r of sand extending to a depth of about 30m. A l i s t of a l l the var ious i n s i t u t e s t s conducted a t the Boundary Road P i l e Load Test s i t e and used as part of t h i s research program are l i s t e d i n the table in F igure 4 .15 . 4 .3 .2 Resul ts F igure 4.16 shows t y p i c a l curves from the Pencel t e s t s . The s t r a i n contro l t e s t data appears very e r r a t i c . Th is i s a funct ion o f the method used to run the t e s t s . The s t r a i n contro l device was run with a hand crank. V a r i a t i o n s i n the speed of cranking caused v a r i a t i o n s i n the head l o s s through the f l e x i b l e t u b i n g . The head l o s s in the tubing at the normal expansion rate i s approximately 0.4 bar , which i s greater than any of the f l u c t u a t i o n s In the cu rve . As the exact rate of i n f l a t i o n i s not recorded, the head l o s s c o r r e c t i o n can only be based on the average rate of i n f l a t i o n . 78 U B C I rsi s I T U S T I N G S i t e L o c o t l o n i BOUNDARY ROAD CPT Data t JUNE 06 19B4 P090 Noi 1/4 On S i to Loci PILE LOAD TEST Cona Ucadi UBC6 STD TIP Commentti 3m Pra-bor«c in L 0) -P Ql E 0. LU Q CONE BEARING Ot (bar) FRJCTJON RATIO Rf (X) 0 10 PORE PRESSURE U (a. of later] -P SO 10 15-ZD INTERPRETED PROFILE loose sand b a c k f i l l peat s o f t organic s i l t y c lay medium dense sand Dapth Increment i . OZS m Max Depth i 78.B25 m Figure 4.14 Boundary Road cone p r o f i l e TESTS CONDUCTED AT THE BOUNDARY ROAD TEST SITE Test Designator Instrument Test Date Comments Depths at which PMTs were conducted UBC #1 UBC #2 UBC #3 UBC #4 UBC #5 UBC #6 UBC #7 UBC #8 Seismic cone Seismic cone HPM Pencel Probe Pencel Probe HPM Pencel Probe HPM Ax i a l P i l e Load Test Axia l P i l e Load Test A x i a l P i l e Load Test L a t e r a l P i l e Load Test 05/07/84 12/07/84 10/08/84 06/08/84 05/08/84 18/08/84 30/10/84 22/01/85 Stress controlled Stress controlled 36mm t i p Stress controlled 32mm t i p Stress controlled S t r a i n controlled 32mm t i p St r a i n controlled P i l e Driven to 67m P i l e Driven to 78m P i l e Driven to 94m P i l e Driven to 94m 5,7,9,11,13,3 5,7,9,11,13,15 5,7,8,9,10,11,12,13,14, 3,5,7,9,11,13 3.5,5,7,9,11,13,15 1,2,3,5.5,7,9,10,11 Figure 4.15 Insitu Tests conducted at Boundary Road cn or < CD OH LO CO Ul a: a. 3-2-1-36mm t i p stress c o n t r o l l e d 32mm t i p s t r a i n c o n t r o l l e d ~1 1 1 r-5 10 15 20 CIRCUMFERENTIAL STRAIN C X > BOUNDARY ROAD DEPTH 7M 25 LEGEND 32MM TIP STRESS 36MM TIP STRESS 32MM TIP STRAIN Figure 4.16 Pencel: T y p i c a l Curves at Boundary Road 81 Four important fac to rs can be observed from Figure 4.16: 1) The l i m i t pressure of the var ious t e s t s seem to be approximately equal ; 2) The s t r a i n c o n t r o l l e d t e s t has a higher l i f t o f f pressure than the s t r e s s c o n t r o l l e d t e s t s ; 3) There does not seem to be a s i g n i f i c a n t d i f f e rence in shape between curves using the 36mm t i p t e s t s and curves using the 32mm t i p . 4) The c l o s i n g pressure from a l l three tes t s was the same. No s t ra in cont ro l l ed t e s t s were performed with the 36mm t i p . Figure 4.17 compares a t y p i c a l curve from the s t ress con t ro l l ed HPMT with t y p i c a l curves from the Pencel t e s t s with the 32mm t i p . The HPM ind i ca tes a l i f t o f f pressure in the same range as the s t ress c o n t r o l l e d Pencel t e s t but the l i m i t pressure was much higher . The r e s u l t s from the s t r a i n c o n t r o l l e d HPMT are not shown because there were equipment problems and the r e s u l t s were not considered representa t ive . 4 .3.2.1 Shear Modulus The s i t e i n v e s t i g a t i o n included a sounding with the UBC seismic cone. The dynamic shear modulus measured from the seismic cone was the standard to which the shear moduli measurements from the pressuremeter were compared. The seismic cone measures shear wave ve loc i t y and thus the shear modulus at the i n s i t u mean e f f e c t i v e s t r e s s . In the c l a y at Langley, i t was assumed that the s o i l was undrained during the PMT so that the mean e f f e c t i v e s t ress stayed constant . In the peat and 82 LEGEND 32MM TIP STRESS 32MM TIP STRAIN HPM STRESS CONT Figure 4.17 Comparison of Pencel Curves with HPM Curves: At Boundary Road 83 organic s i l t deposi t at Boundary Road the drainage cond i t ions are l e s s c e r t a i n . Some drainage may be occur r ing during the t e s t and the mean e f f e c t i v e s t r e s s may be r i s i n g . However as the pore pressures are not known during the t e s t , no attempt has been made to est imate the mean e f f e c t i v e s t r e s s , or what e f f e c t the v a r i a t i o n s have on the shear modulus measurements. F igure 4.18 compares the shear moduli measurements from the Pencel probe, the HPM, and the UBC seismic cone. The Pencel measurements f a l l w i th in a range of 20 to 50% of the measurements from the UBC seismic cone. The measurements are r e l a t i v e l y c o n s i s t e n t and do not seem to vary over a large range. At a given depth, the l a r g e r values of shear modulus were genera l ly measured from unload-re load loops performed at l a t e r stages in the t e s t . Th i s i s to be expected from the above d i s cuss ion on drainage. . The HPM r e s u l t s genera l ly show l e s s s c a t t e r than those from the Pencel at any i n d i v i d u a l depth. The exception to t h i s i s at lm and a t 10m. Near the surface the sand was f ree d ra in ing and the mean e f f e c t i v e s t r e s s increased dramat i ca l l y with consequent increases in the shear modulus as the t e s t progresses . From 9 to 11m occasional sandy s i l t l ayers were i d e n t i f i e d i n the adjacent cone penetrat ion soundings. Wherever one of these l ayers occurred , the s o i l was allowed to dra in with a r e s u l t i n g increase in shear modulus as the t e s t progressed. These layers were s t i f f e r than the surrounding s o i l , a r e s u l t which was r e f l e c t e d in higher shear modulus values measured by the pressuremeter. Thin s t i f f l ayers d id not show up in the seismic cone p r o f i l e of shear modulus 84 4-Q_ Ul a 12' 16-n i II II i D O • • •***• u r n • rrrw» • • • -T-50 100 150 SHEAR MODULUS C BARS BOUNDARY ROAD 200 250 LEGEND HPM STRAIN CONT PENCEL 32MM TIP GMAX C SEISMIC > Figure 4.18 P r o f i l e of Shear Modulus at Boundary Road; Pencel and HPM 85 because the shear wave v e l o c i t y used to c a l c u l a t e the shear modulus was averaged over a 2m i n t e r v a l . 4 .3 .2 .2 Horizontal S t resses The hor izonta l e f f e c t i v e s t resses measured with the Pencel are presented i n F igure 4 . 1 9 . They show three s i g n i f i c a n t t rends . F i r s t , the values a l l increase at approximately the same rate with depth. Th is rate i s s i m i l a r to the rate of increase of the v e r t i c a l e f f e c t i v e s t r e s s . Second, the 36mm t i p s t r e s s c o n t r o l l e d t e s t recorded the lowest hor izonta l s t r e s s e s . The 36mm t i p i s expected to i n d i c a t e the lowest hor izonta l s t resses because i t forms an overs ized ho le , and the s o i l can re lax up against the probe. The t h i r d trend i s cons i s ten t with that observed from the t e s t s at Langley, namely that the s t r a i n c o n t r o l l e d t e s t i nd i ca tes h igher hor izonta l s t resses than the s t r e s s c o n t r o l l e d t e s t . F igure 4.20 shows the hor izonta l s t resses measured from the s t r e s s c o n t r o l l e d HPMT's. The data i s shown i n p a i r s i n d i c a t i n g readings taken from two separate s t r a i n arms. The f a c t that the two arms responded s i m i l a r l y i n d i c a t e s a good t e s t . The one set of t e s t r e s u l t s at 9m that i nd i ca ted a much higher hor izonta l s t r e s s was i n a th in d iscont inuous sand l a y e r , where much h igher s t rengths were a lso noted. 86 1 1 1 —1 1 1 1 0 1 2 3 4 ( 5 6 LIFTOFF PRESSURE MINUS Uo C BARS 5 BOUNDARY ROAD LEGEND • 3BMM TIP STRESS A 32MM TIP STRESS O 32MM TIP STRAIN • VERT EFF STRESS Figure 4.19 P r o f i l e of Measured Horizontal E f f e c t i v e Stress At Boundary Road: Pencel 87 x 1 1 1 1 1 1 1 D 1 2 3 4 5 6 LIFTOFF PRESSURE MINUS Uo < BARS > BOUNDARY ROAD LEGEND • STRESS CONT #1 A STRESS CONT #2 - VERT EFF STRESS Figure 4.20 P r o f i l e of Measured Horizontal E f f e c t i v e Stress At Boundary Road: HPM 88 4.4 McDonalds Farm McDonalds Farm has been a research s i t e f o r the UBC i n s i t u t e s t i n g group since 1979. Many d i f f e r e n t types of t e s t s have been performed at t h i s s i t e , and the s o i l p r o f i l e and proper t i es are wel l known. Th is was the s i t e of some of the doctoral research , documented in Robertson, 1982 d i r e c t l y comparing the r e s u l t s of s e l f - b o r i n g and f u l l displacement pressuremeter t e s t s . These r e s u l t s are presented f o r comparison with the r e s u l t s obtained from t h i s research p r o j e c t . The main d i f f e rence between McDonalds Farm and the other two research s i t e s i s the drainage c o n d i t i o n s . The pressuremeter t e s t s at McDonalds Farm were performed in the l a y e r of c lean sand where the permeabi l i ty was high enough tha t the sand remained drained at a l l times during the t e s t s . 4 .4 .1 S i t e D e s c r i p t i o n The research s i t e at McDonalds Farm i s comprised of 2m of s i l t o v e r l y i n g 11m of c lean sand. Between 13 and 15m there i s a t r a n s i t i o n zone of s i l t y sand, and below 15m, the s o i l c o n s i s t s of a s o f t c layey s i l t . F igure 4.21 shows a t yp i ca l CPT p r o f i l e . The tab le presented i n F igure 4.22 shows the i n s i t u t e s t s tha t were performed at McDonalds Farm and analyzed i n t h i s study. 89 UBC IM S I T U T TING S i t e L o c o t l o n i MCDONALDS FARM CPT Ooto i 0CT23 18B4 Poga Not 1 / 2 On S l t o Loci CENTER OF PMTS Conn Uaadi 15 SO. CM. SEIS Comnantti CONE BEARING Ot (bar) 10-200 Qt max = 400 bar FRICTION RATIO Rf CO 0 S PORE PRESSURE U (a. of aotar) 0 100 10-INTERPRETED PROFILE 10-IS-EC-soft clay and s i l t coarse sand loose to dense with layers of f i n e sand f i n e sand some s i l t s o f t clayey s i l t Dapth Incramant i . 025 n Max Dapth i 31. 973 m Figure 4.21 McDonalds Farm cone p r o f i l e 90 TESTS CONDUCTED AT MCDONALDS FARM H" TO C H rt) 3 co H-rr C r f (D [A rr cn O O 3 a. c o r f (B a. 3 o O o 3 IB f— CL cn **1 D> >i 3 T e s t D e s i g n a t o r Instrument T e s t Date SBPM #1 SBPM #2 PPMT #1 PPMT #2 PPMT #3 PPMT #4 PPMT #5 PPMT #6 PPMT #7 PPMT #8 PPMT #9 PPMT #10 M2 M3 MA CPT HPM HPM HPM HPM 03/12/80 11/02/81 OA/12/81 20/01/82 Pe n c e l Probe 05/06/8A P e n c e l Probe HPM Pe n c e l Probe P e n c e l Probe P e n c e l Probe P e n c e l Probe Pencel Probe HPM HPM HPM Sei s m i c cone 06/06/8A ^18/06/84 09/10/8A 16/10/84 23/10/84 23/10/84 23/10/84 14/01/85 25/01/85 25/01/85 31/01/85 Comments S t r e s s c o n t r o l l e d * S t r e s s c o n t r o l l e d * S t r e s s c o n t r o l l e d S t r e s s c o n t r o l l e d Depths a t which PMTs were conducted 3,3.8,4.6,5.3,6.3 A.9,6.2,7,8.5,9.3,11,11.7,12.8 2.7,3.8,4.6 2.75,3.8,4.6,5.5,6.7,7.6 S t r e s s c o n t r o l l e d 36mm t i p 0.5,1.5,3.5,7.5,11.5, 13.5,16.5,18.5 S t r e s s c o n t r o l l e d 32mm t i p 3.5,5.5,7.5,13.5,14.5 S t r e s s c o n t r o l l e d 4,5,6,7,8 S t r a i n c o n t r o l l e d 32mm t i p 3,5,7,9 S t r a i n c o n t r o l l e d 36mm t i p 3,5,7,9,11 Pushed w h i l e p a r t i a l l y i n f l a t e d 3,5 S t r a i n c o n t r o l l e d 36mm t i p S t r a i n c o n t r o l l e d 32mm t i p 3,5,7,9 S t r a i n c o n t r o l l e d 0.5,1,1.5,3,7 S t r a i n c o n t r o l l e d 0.5,1,3,5,7 S t r a i n c o n t r o l l e d 1,3,5,7 * The pressuremeter was s e l f - b o r e d i n t o the ground 4.4 .2 Results Typ ica l pressuremeter curves obtained with the Pencel probe at McDonalds Farm are shown i n F igure 4 .23 . The h igher l i f t o f f pressure from the 32mm t i p s t r a i n c o n t r o l l e d r e s u l t s was c o n s i s t e n t with the r e s u l t s from Langley and Boundary Road. I t was i n t e r e s t i n g to note that the other three t e s t s a l l had s i m i l a r l i f t o f f p ressures , and that a l l four types of t e s t s had s i m i l a r c l o s i n g pressures . The c l o s i n g pressure i s a measure of the e q u i l i b r i u m pore pressure fo r pressuremeter t e s t s in sand. Note tha t with sands there i s no t h e o r e t i c a l l i m i t pressure so the f a c t that the curves d id not appear to converge i s not s u p r i s i n g . The t r a d i t i o n a l Menard type of pressuremeter i s p laced in a pre-bored hole and e x h i b i t s an S shape curve upon i n f l a t i o n . Only in a very few of the t e s t s with the overs i zed t i p ( 36mm t ip ) was t h i s ever v i s i b l e with the Pencel probe. The curves shown i n F igure 4.23 were t y p i c a l of the curves obta ined. F igure 4.24 compares the Pencel t e s t s conducted wi th the 32mm t i p to the s t r e s s c o n t r o l l e d HPMT. The l i f t o f f pressure obtained from the s t r e s s c o n t r o l l e d HPMT was comparable with the l i f t o f f pressure obtained from the s t r e s s c o n t r o l l e d Pencel t e s t . The c l o s i n g pressures were s i m i l a r f o r the two types of t e s t s where c l o s i n g pressure was measured. 9 2 I I I 1 1 1 0 5 10 15 20 25 CIRCUMFERENTIAL STRAIN C X > MCDONALDS FARM DEPTH LEGEND • 3BMM TIP STRESS 32MM TIP STRESS 36MM TIP STRAIN 32MM TIP STRAIN Figure 4.23 Pencel: T y p i c a l Curves at McDonalds Farm 93 LEGEND • 32MM TIP STRESS 32MM TIP STRAIN HPM STRESS CONT Figure 4.24 Comparison of Pencel curves and HPM curves: At McDonalds Farm 94 4 .4 .2 .1 Shear Modulus Shear modulus i s dependent on the mean e f f e c t i v e s t r e s s . The c l e a n sand a t McDonalds Farm i s f u l l y drained so there i s no excess pore pressure generated during the t e s t s and the mean e f f e c t i v e s t r e s s increases with rad ia l s t r e s s . In order to compare the measured shear modulus with the shear modulus obtained from the seismic cone, or to compare values obtained at d i f f e r e n t times dur ing the PMT the shear modulus must f i r s t be normalized to the i n s i t u mean e f f e c t i v e s t r e s s as was d iscussed in sec t ion 2 .2 . A shear modulus p r o f i l e obtained with the s t r a i n c o n t r o l l e d Pencel probe i s shown i n F igure 4 .25 . The moduli measured with the Pencel were approximately 10 to 20% of Gmax measured with the UBC se ismic cone. The r e s u l t s d id not seem to d i f f e r s i g n i f i c a n t l y whether the 32mm t i p or the overs i zed t i p was used. These moduli were obtained from 5cm unload re load loops . Th is represents about 2-2.5% s t r a i n . Th is was wi th in the bounds set by Wroth, 1984 where the sand w i l l behave e l a s t i c a l l y . Although Seed and I d r i s s ' shear modulus at tenuat ion curves presented i n F igure 2.2 do not extend to t h i s shear s t r a i n leve l they would i n d i c a t e that the measured shear modulus at 2% s t r a i n would be expected to be l e s s than 10% of Gmax. The Pencel shear moduli r e s u l t s obtained with 5cm 3 loops at McDonalds Farm appear to be more cons i s tent than the shear moduli a r e s u l t s obtained with 2cm loops at Langley. The c a l i b r a t i o n c o r r e c t i o n s are qu i te large compared to the sca le of an unload 95 0. LU a T 200 :- 400 600 eoo 1000 1200 noo SHEAR MODULUS NORMALIZED TO INSITU STRESS C BARS ) MCDONALDS FARM LEGEND D 32MM TIP 36MM TIP - GMAX < SEISMIC > Figure 4.25 P r o f i l e of Normalized Shear Modulus At McDonalds Farm: Pencel 96 0 . LU Q 200 400 600 600 1000 1200 1400 SHEAR MODULUS NORMALIZED TO INSITU STRESS C BARS > MCDONALDS FARM LEGEND * SBPMT D FDPMT - GMAX C SEISMIC 5 Figure 4.26 P r o f i l e of Normalized Shear Modulus At McDonalds Farm: Stress Controlled HPM 97 0. Ul a 2-4-6-8-10-12-OD E E X LTJDD x a o n • • x x » x Txsaaaa T T T — I 200 400 600 800 1000 1200 1400 SHEAR MODULUS NORMALIZED TO INSITU STRESS ( BARS ) MCDONALDS FARM D X LEGEND STRAIN CONT #1 STRAIN CONT #2 GMAX C SEISMIC > Figure 4.27 P r o f i l e of Normalized Shear Modulus At McDonalds Farm: S t r a i n Controlled HPM 98 re load l o o p , and d id not increase l i n e a r l y with the s i z e of the l o o p . The l a r g e r un load-re load loops have a p r o p o r t i o n a l l y smal ler c a l i b r a t i o n c o r r e c t i o n and appear to y i e l d e d more cons i s tent r e s u l t s . Shear moduli measured with the HPM are shown i n F igure 4 . 2 6 . Two types of t e s t s are shown on F igure 4 . 2 6 . The s e l f - b o r i n g pressuremeter r e s u l t s are p lo t ted aga inst the r e s u l t s from the three s t ress c o n t r o l l e d f u l l displacement pressuremeter t e s t s . The s e l f - b o r i n g t e s t s were a l so run in a s t r e s s c o n t r o l l e d manner. The moduli measured with the s t r e s s c o n t r o l l e d HPM f a l l w i th in the range of 20 to 50% of Gmax measured with the UBC se ismic cone. It was expected that the r e s u l t s would be higher than the r e s u l t s from the Pencel probe because the un load-re load loops represent a smal le r s t r a i n with the HPM than with the Pence l . Therefore there i s l e s s shear modulus at tenuat ion with the HPM. The normalized shear modulus measured with the s t r a i n c o n t r o l l e d HPM i s presented i n F igure 4 . 2 7 . There i s a l i t t l e more s c a t t e r than with the s t r e s s c o n t r o l l e d t e s t but the trend of the r e s u l t s i s almost the same. 4 . 4 . 2 . 2 Horizontal S t resses The hor i zonta l e f f e c t i v e s t resses recorded by the s t r a i n c o n t r o l l e d Pencel probe are shown i n F igure 4 . 28 and those recorded by the s t r e s s c o n t r o l l e d Pencel probe i n F igure 4 . 2 9 . 99 With both types of t e s t s , those recorded with the 32mm t i p have h igher l i f t o f f pressures than those with the 36mm t i p . With the s t r a i n c o n t r o l l e d t e s t s the l i f t o f f pressures with the 32mm t i p are much h igher . Comparison between the two f igures i n d i c a t e that the l i f t o f f pressures from the s t r a i n c o n t r o l l e d t e s t are much h igher than those from the s t r e s s c o n t r o l l e d t e s t . No explanat ion i s r e a d i l y apparent f o r t h i s observa t ion . The hor izonta l s t r e s s i s genera l ly assumed to be a parameter tha t the s e l f - b o r i n g pressuremeter i s capable of measuring. Th is i s however l e s s app l i cab le i n sands where small i n i t i a l d is turbances can lead to l a rge e r ro rs in determining the hor i zonta l s t r e s s e s . F igure 4.30 presents the l i f t o f f pressures measured by the s e l f - b o r i n g pressuremeter. A lso shown i n F igure 4.30 are the l i f t o f f pressures measured with the s t r e s s c o n t r o l l e d f u l l displacement pressuremeter. There i s a c t u a l l y l e s s s c a t t e r among the f u l l displacement r e s u l t s than there i s with the s e l f -bor ing r e s u l t s . Note that several t e s t s recorded l i f t o f f pressures l e s s than the e q u i l i b r i u m pore pressure and the re fo re recorded negat ive hor izonta l e f f e c t i v e s t r e s s e s . The l i f t o f f pressures recorded with the s t r a i n c o n t r o l l e d f u l l displacement HPM are shown i n F igure 4 .31 . The most s i g n i f i c a n t d i f f e r e n c e when compared to the s t r e s s c o n t r o l l e d t e s t s i s the lack of po ints above the v e r t i c a l e f f e c t i v e s t r e s s l i n e . Even more o f ten than with the s t r e s s c o n t r o l l e d t e s t s , l i f t o f f pressures were recorded that were l e s s than the e q u i l i b r i u m pore pressure . 100 X r-0-LU Q i 1 2 3 LIFTOFF PRESSURE MINUS Uo MCDONALDS FARM C BARS > LEGEND D 32MM TIP STRAIN X 36MM TIP STRAIN - VERT EFF STRESS Figure A.28 P r o f i l e of Measured Horizontal E f f e c t i v e Stress At McDonalds Farm: S t r a i n Controlled Pencel 101 Figure 4.29 P r o f i l e of Measured Hori z o n t a l E f f e c t i v e Stress At McDonalds Farm: Stress Controlled Pencel 102 3: I . LIFTOFF PRESSURE MINUS Uo C BARS ) MCDONALDS FARM LEGEND • FDPMT X SBPMT - VERT EFF STRESS Figure 4.30 P r o f i l e of Measured Horizontal E f f e c t i v e Stress At McDonalds Farm: Stress Controlled HPM 103 0 1 2 3 4 5 LIFTOFF PRESSURE MINUS Uo C BARS ) MCDONALDS FARM LEGEND D FDPMT STRAIN VERT EFF STRESS Figure 4.31 P r o f i l e of Measured Horizontal E f f e c t i v e Stress At McDonalds Farm: S t r a i n Controlled HPM 104 N o t e t h a t t h e P e n c e l s t r a i n c o n t r o l l e d t e s t s r e c o r d e d h o r i z o n t a l s t r e s s e s t h a t w e r e much h i g h e r t h a n t h o s e r e c o r d e d b y t h e s t r e s s c o n t r o l l e d t e s t . W h e r e a s t h e s t r a i n c o n t r o l l e d H P M T ' s r e c o r d e d h o r i z o n t a l s t r e s s e s t h a t w e r e l o w e r t h a n t h e o n e s r e c o r d e d by t h e s t r e s s c o n t r o l l e d t e s t s . 105 Chapter 5 Conclusions 5.1 Summary This research study was performed with the i n t e n t i o n of examining the s u i t a b i l i t y of using the f u l l displacement pressuremeter (FDPM) fo r determining shear modulus, i n s i t u hor izonta l s t r e s s e s , and undrained shear s t rength . The var iab les examined were; the type of pressuremeter, whether the pressuremeter was run in a s t r e s s or a s t r a i n c o n t r o l l e d manner, the s i z e of the t i p pushed i n f ront of the pressuremeter, and whether time was allowed fo r the dynamic pore pressures to d i s s i p a t e . Tests were conducted i n sand, s i l t , and c l a y . 5.2 Shear Modulus The shear modulus measured with the FDPM compared very well with the dynamic shear modulus measured with the seismic cone. Adjustments were made to account f o r the d i f f e r e n c e s in s t r a i n l e v e l , and mean e f f e c t i v e s t r e s s . The s i ze of the t i p in f ront of the instrument d id not a f f e c t the r e s u l t s . As was expected there was no d i f f e rence between shear moduli c a l c u l a t e d from s t r e s s c o n t r o l l e d t e s t s with the HPM and s t r a i n c o n t r o l l e d t e s t s with the HPM. The shear modulus measurements from t e s t s where the HPM were i n s t a l l e d in a s e l f - b o r i n g manner were very s i m i l a r from the measurements from t e s t s where the probe was i n s t a l l e d i n a f u l l displacement manner. The shear modulus measurements from the 106 s t r a i n c o n t r o l l e d Pencel probe were very s i m i l a r to the HPM measurements. However, the membrane s t i f f n e s s c o r r e c t i o n assoc ia ted with the Pencel t e s t s was a very s i g n i f i c a n t f a c t o r in s o f t s o i l s . The membrane c a l i b r a t i o n was dependent on so many v a r i a b l e s in a s t r e s s c o n t r o l l e d t e s t that i t was not poss ib le to determine the c o r r e c t i o n with any degree of c e r t a i n t y . As a r e s u l t i t was not poss ib le to determine shear modulus from any of the s t r e s s c o n t r o l l e d Pencel t e s t s . 5 . 3 Ins i tu Hor izontal S t ress In genera l , the attempts to determine the i n s i t u hor izonta l s t r e s s by examining the l i f t o f f pressure were t o t a l l y u n s u c c e s s f u l . There does not appear to be any p o s s i b i l i t y of improving t h i s technique to the po int where i t would be a useful method of a n a l y s i s . The l i f t o f f pressure was lower when an overs ized t i p was p laced i n f ront of the FDPM. Th is was to be expected as the s o i l was al lowed to re lax i n t o the c a v i t y surrounding the probe. A l so the l i f t o f f pressure was cons iderab ly higher when the t e s t s were run in a s t r a i n c o n t r o l l e d manner as opposed to a s t r e s s c o n t r o l l e d manner. The l i f t o f f pressures were so v a r i a b l e that i t was d i f f i c u l t to determine i f the l i f t o f f pressure showed any of the expected decrease when the dynamic pore pressures were given an opportunity to d i s s i p a t e before the pressure expansion t e s t was run . The general t rend of the l i f t o f f pressures was to Increase 107 with depth but they d id not appear to hold any other r e l a t i o n s h i p with the i n s i t u hor izonta l s t r e s s e s . 5.4 Undrained Shear Strength The undrained shear strengths of c l a y determined us ing cav i t y expansion theory compared very well with undrained shear strengths determined using the f i e l d vane. The undrained shear strength c a l c u l a t i o n i s dependent on the l i f t o f f pressure and the r e s u l t s r e f l e c t e d the observat ions that were made about the l i f t o f f p ressure . The t e s t s where the h ighest l i f t o f f pressures were measured ( i e . the s t r a i n c o n t r o l l e d t e s t s and the t e s t s with the smal ler t i p ) , were a lso the t e s t s where the lowest undrained shear strengths were c a l c u l a t e d . The HPM r e s u l t s were genera l ly about 25% higher than those from the Pencel probe. 5.5 Recommendations f o r Further Research The FDPM appears to be a p r a c t i c a l way of measuring the shear moduli of many types of s o i l and the undrained shear strength of c l a y . Further research should be conducted with the FDPM with those goals i n mind. The determinat ion of i n s i t u hor izonta l s t resses with the FDPM was not p o s s i b l e and the r e s u l t s do not appear promising enough to warrant f u r t h e r research . Some s p e c i f i c areas of research are suggested below: 1) Fur ther research should be conducted in to the d i f f e r e n c e s between the curves that are produced when the pressuremeter i s run 108 s t r e s s c o n t r o l l e d and when f t 1s run s t r a i n c o n t r o l l e d . Th is study i n d i c a t e d tha t there were some d i f f e rence but there was i n s u f f i c i e n t data a v a i l a b l e to draw any c o n c l u s i o n s . 2) Pressuremeters should be equipped with pore pressure measurement c a p a b i l i t y . Th is would be e s p e c i a l l y useful when t r y i n g to determine the mean e f f e c t i v e s t r e s s at which the shear modulus i s being measured. 3) The s t r a i n contro l device should be fitted with a motor d r i v e . Th is would e l im inate the head l o s s v a r i a t i o n s due to i n c o n s i s t e n t hand c r a n k i n g . A motor would make i t easy to completely standardize the s t r a i n rate and the s i z e of the s t r e s s c y c l e used in determining shear modul i . 109 REFERENCES Brown, P . T . , Masters of App l ied Science T h e s i s , 1985, Un ivers i t y of B r i t i s h Columbia. Campanella, R.G. and Robertson, P .K. , 1981, "Appl ied Cone Research", Symposium on Cone Penetrat ion Test ing and Exper ience, Geotechnical Engineer ing D i v i s i o n , ASCE, Oct . 1981, pg 343 -362. Faugeras, J . C . , Gourves, R., Meunier P . , Nagura M.,Matsubara, L . , Sugawara, N. , 1983, " On the Var ious Factors A f f e c t i n g Pressuremeter Test Resu l t s" , Proceedings of the Internat iona l Symposium on Ins i tu T e s t i n g , P a r i s , Volume 2, pg 275 - 281. G ibson, R .E . , and Anderson, W.F. , 1961, " I n - s i t u Measurement of So i l with the Pressuremeter". C i v i l Eng. and P u b l i c Works Review, V o l . 56, No. 658, May 1961, pg 615 - 618. G r e i g , J im, Masters of App l ied Science T h e s i s , 1985, Un ivers i t y o f B r i t i s h Columbia. Hughes, J .M.O. and Robertson, P .K . , 1984, "Fu l l -D isp lacement Pressuremeter Tes t ing i n Sand", Un ivers i t y of B .C . , C i v i l Engineer ing D e p t . , So i l Mechanics Ser ies No. 78 Janbu, N . , 1963, "So i l C o m p r e s s i b i l i t y as Determined by Oedometer and T r i a x i a l T e s t " , Proceedings of the European Conference on So i l Mechanics and Foundation Eng ineer ing , Wiesbadden, V o l . 1, pg 1 9 - 2 5 . Lacasse , S. and Lunne, T . , 1982, " Ins i tu Hor izontal S t ress from Pressuremeter Tes t" , Proceedings of the Internat iona l Symposium on the Pressuremeter and I t s Marine A p p l i c a t i o n s , P a r i s , pg 187 - 208. Massarsch, K.R. and Drnev ich , V . P . , "Deformation proper t ies of normally conso l idated c l a y s " , Design Parameters i n Geotechnical Eng ineer ing , BGS, London, 1979, V o l . 2, pg 251 - 255. Re id , W.M., S t . John, H.D., F y f f e , S. and Rigden, W . J . , 1982, "The Push-in Pressuremeter", Proceedings of the Symposium;; on the Pressuremeter and I t s Marine A p p l i c a t i o n s , P a r i s . Robertson, P .K . , 1982, " I n - s i t u Tes t ing of So i l With Emphasis on i t s A p p l i c a t i o n to L i q u e f a c t i o n Assessment", Phd Thes i s , U n i v e r s i t y of B r i t i s h Columbia. Robertson, P .K. , Campanella, R .G . , Brown, P . T . , G r o f f , I . , Hughes, J . M . O . , 1985a, "Design of A x i a l l y and L a t e r a l l y Loaded P i l e s Using I n - S i t u T e s t s : A Case H i s t o r y " , Submitted to the Canadian Geotechnical J o u r n a l , A p r i l 1985. 110 Robertson, P .K . , Campanella, R .G . , G i l l e s p i e , D .G . , R i ce , A, 1985, "Seismic CPT to Measure Ins i tu Shear Wave V e l o c i t y " , ASCE Spr ing Convention, Denver, A p r i l 1985. Seed, H.B. and I d r i s s , I . B . , 1970. "So i l Moduli and Damping Factors f o r Dynamics Response A n a l y s i s " , Report No. EERC 70-10, U n i v e r s i t y of C a l i f o r n i a , Berkeley, Dec. Suyama, K., Ohya, S . , Imai, T . , Matsubara, M., Nakayama, E, 1983, "Ground Behaviour During Pressuremeter Test ing" Proceedings of the Internat ional Symposium on In S i tu T e s t i n g , P a r i s , Volume 2, pg 397 - 402. Wroth, C P . , 1982, " B r i t i s h Experience wwith the S e l f - B o r i n g Pressuremeter", Proceedings of the Symposium on The Pressuremeter and I ts Marine A p p l i c a t i o n s , P a r i s , pg 143 - 164. Wroth, C P . , 1984, Rankine Lec ture , Imperial C o l l e g e , London,. QUEL Report No. 1541/84, Sm 051/84. I l l 

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