UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

The piezometer cone penetration test Gillespie, Donald G. 1981

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1982_A7 G55.pdf [ 5.17MB ]
Metadata
JSON: 831-1.0062481.json
JSON-LD: 831-1.0062481-ld.json
RDF/XML (Pretty): 831-1.0062481-rdf.xml
RDF/JSON: 831-1.0062481-rdf.json
Turtle: 831-1.0062481-turtle.txt
N-Triples: 831-1.0062481-rdf-ntriples.txt
Original Record: 831-1.0062481-source.json
Full Text
831-1.0062481-fulltext.txt
Citation
831-1.0062481.ris

Full Text

THE PIEZOMETER CONE PENETRATION TEST by DONALD G. GILLESPIE BASc, The U n i v e r s i t y of B r i t i s h Columbia, 1979 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n 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 r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA December, 1981 © Donald G. G i l l e s p i e , 1981 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y a v a i l a b l e for reference and study. I further agree that permission for extensive copying of t h i s thesis for s c h o l a r l y purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or pu b l i c a t i o n of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of c i v ^ gn^ ingg^ iA^  The University of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 i i A b s t r a c t Deep q u a s i - s t a t i c cone p e n e t r a t i o n t e s t s i n s a t u r a t e d s o i l s can develop l a r g e excess pore p r e s s u r e s . The l e v e l and sig n of t;he excess pore p r e s s u r e s depend on the volume change c h a r a c t e r i s t i c s , t h e s t r e n g t h and the p e r m e a b i l i t y of the s o i l . The recent a d d i t i o n of pore pressure measurements during cone p e n e t r a t i o n t e s t i n g adds a new dimension to the i n t e r p r e t a t i o n f o r g e o t e c h n i c a l parameters. T h i s r e p o r t shows how the pore pressure measurements enhance the s t r a t i g r a p h i c l o g g i n g a b i l i t i e s of the cone p e n e t r a t i o n t e s t . C a l i b r a t i o n s performed on the cone penetrometer are used to show the importance of c o r r e c t i n g bearing and f r i c t i o n measurements f o r pore pressure e f f e c t s . As w e l l as pore pressure e f f e c t s the importance of procedure and equipment i s d i s c u s s e d . The use of pore pressure d i s s i p a t i o n s recorded while p e n e t r a t i o n i s h a l t e d i s i l l u s t r a t e d . T h e o r e t i c a l s o l u t i o n s f o r pore pressure decay r a t e s are i l l u s t r a t e d and r e s u l t s p r e d i c t i n g the c o e f f i c i e n t of c o n s o l i d a t i o n are compared to l a b o r a t o r y measured v a l u e s . The c o e f f i c i e n t of c o n s o l i d a t i o n p r e d i c t e d from decay r a t e s i s shown to compare w e l l with l a b o r a t o r y measured valu e s f o r the s o i l i n the o v e r c o n s o l i d a t e d s t a t e . III Contents A b s t r a c t ii L i s t of Tables v L i s t of F i g u r e s vi Acknowledgement Vii Chapter 1. I n t r o d u c t i o n 1 1.1 H i s t o r i c a l Development of the Piezometer Cone Test 1 1.2 Report O r g a n i z a t i o n 2 Chapter 2. Equipment and Procedure 4 2.1 I n t r o d u c t i o n 4 2.2 The Probe and Recording U n i t s 4 2.3 D r i v i n g U n i t 7 2.4 Test Procedure 7 2.4.1 C a l i b r a t i o n 9 2.4.2 S a t u r a t i o n of the Porous Element 11 2.4.3 Cone P e n e t r a t i o n Test Procedure 12 2.4.4 Data Reduction 13 Chapter 3. Dynamic Pore Pressures and S t r a t i g r a p h i c Logging 16 3.1 I n t r o d u c t i o n .16 3.2 Pore Pressures Generated d u r i n g Cone P e n e t r a t i o n T e s t i n g 16 3.3 Dynamic Pore Pressure R a t i o 17 3.4 S t r a t i g r a p h i c Logging 21 3.4.1 CPT Example 1 F i g u r e 5 21 3.4.2 CPT Example 2 F i g u r e 6 24 3.4.3 CPT Example 3 F i g u r e 7 26 3.4.4 CPT Example 4 F i g u r e 8 28 3.5 S t a t i c Pore Pressures 30 3.6 C o n c l u s i o n s 31 Chapter 4. A n a l y t i c a l E x p r e s s i o n s f o r Dynamic Pore Pressure 33 4.1 I n t r o d u c t i o n 33 4.2 A n a l y t i c a l E x p r e s s i o n s 34 4.2.1 Comparison Between Models 36 Chapter 5. F i e l d O bservations of Dynamic Pore Pressure ....45 5.1 I n t r o d u c t i o n 45 5.2 F i e l d T e s t s Conducted 45 5.3 E f f e c t of P e n e t r a t i o n Speed 46 5.3.1 F i e l d Evidence 49 5.4 L o c a t i o n of the Porous Element 52 5.5 E f f e c t of S a t u r a t i o n 56 5.6 E f f e c t of Pore Pressure D i s s i p a t i o n 59 5.7 H y d r o f r a c t u r e : F i e l d Evidence 60 IV 5.7.1 R a d i a l E f f e c t i v e S t r e s s e s d u r i n g Cone P e n e t r a t i o n T e s t i n g 62 5.7.2 Pore Pressure Response and H y d r o f r a c t u r e ...67 Chapter 6. C o n s o l i d a t i o n C h a r a c t e r i s t i c s from Pore Pressure D i s s i p a t i o n a f t e r Piezometer Cone P e n e t r a t i o n 69 6.1 I n t r o d u c t i o n 69 6.2 C o n s o l i d a t i o n Process a f t e r P e n e t r a t i o n 70 6.3 S o l u t i o n s P o s s i b l e f o r O b t a i n i n g C o n s o l i d a t i o n C h a r a c t e r i s t i c s 73 6.4 Data Reduction 79 6.5 Comparison of E x i s i t i n g S o l u t i o n 79 6.6 Laboratory T e s t s Performed 81 6.6.1 T e s t i n g Procedure 82 6.6.2 R e s u l t s : Burnaby S i t e 82 6.6.3 R e s u l t s : Mcdonald S i t e 86 6.7 F i t of E x i s t i n g S o l u t i o n s 92 6.8 Comparison between P r e d i c t e d and Laboratory Measured Values 100 6.9 S e l e c t i o n of S o i l S t i f f n e s s R a t i o 102 6.10 Procedure Used During D i s s i p a t i o n T e s t s 103 6.11 C o n c l u s i o n 106 Chapter 7. E s t i m a t i n g S o i l P e r m e a b i l i t y from Cone P e n e t r a t i o n Test Data 108 7.1. I n t r o d u c t i o n 108 7.2 Laboratory T e s t s to Obtain C o m p r e s s i b i l i t y 110 7.3 F i e l d Loading 111 7.4 Estimates of C o m p r e s s i b i l i t y from Bearing Values ...111 7.5 Laboratory Index Te s t s to Obtain C o m p r e s s i b i l i t y ...113 7.6 I n s i t u T e s t s to Obtain S o i l C o m p r e s s i b i l i t y 113 Chapter 8. Con c l u s i o n s 114 8.1 C o n c l u s i o n s 114 8.2 Recommendations f o r F u r t h e r Research 117 References 119 Appendix A Complete CPT Logs Macdonald S i t e 122 Appendix B Table of Time F a c t o r s f o r D i s s i p a t i o n A n a l y s e s . . . 136 V L i s t of Tables Table I Input Parameters Used to Compare Dynamic Pore Pressure Models 37 Table II P u b l i s h e d R e s u l t s Showing the E f f e c t of P e n e t r a t i o n Rate on Bearing and Dynamic Pore Pressure 50 Table III Summary of E x i s t i n g S o l u t i o n s f o r Pore Pressure D i s s i p a t i o n 76 Table IV Comparison between Laboratory Data and C a l c u l a t e d C o e f f i c i e n t of C o n s o l i d a t i o n : McDonald S i t e 20.5 m 94 Table V Comparison between Laboratory Data and C a l c u l a t e d C o e f f i c i e n t of C o n s o l i d a t i o n : Mcdonald S i t e 25.5 m 95 Table VI Comparison between Laboratory Data and C a l c u l a t e d C o e f f i c i e n t of C o n s o l i d a t i o n : Burnaby S i t e 15.5 m 96 Table VII A n i s o t r o p i c P e r m e a b i l i t y of c l a y s 109 Table VIII E s t i m a t i n g the C o n s o l i d a t i o n of Clay from cu/p 112 VI L i s t of F i g u r e s F i g u r e T i t l e 1 5-Channel E l e c t r i c B e a r i n g - F r i c t i o n Piezometer Cone Penetrometer 5 2 T i p s Extensions Used 8 3 R e s u l t s of Piezometer F r i c t i o n Cone C a l i b r a t i o n ...10 4 S o i l P r o f i l e f o r Research S i t e at Mcdonalds Farm . . 1 8 5 CPT Example 1 22 6 CPT Example 2 25 7 Complete CPT Log and D e t a i l of Dynamic Pore Pressure 27 8 Before and A f t e r Compaction CPT Example 4 29 9 Example of Piezometer, F r i c t i o n Cone Log through T a i l i n g s Deposit 32 10 Comparison between A n a l y t i c a l S o l u t i o n s and Measured Dynamic Pore Pressures 41 11 Excess Pore Pressure D i s t r i b u t i o n around I n s t a l l e d P i l e s 44 12 Rate E f f e c t s , Clayey S i l t 48 13 P e n e t r a t i o n Rate E f f e c t s i n Clayey S i l t Deposit ...51 14 Pore Pressure D i s t r i b u t i o n along Shaft d u r i n g Cone P e n e t r a t i o n T e s t i n g 54 15 I n f l u e n c e of S a t u r a t i o n on Pore Pressure Response .58 16 E f f e c t of Pore Pressure D i s s i p a t i o n s d u r i n g CPT i n Clayey S i l t 61 17 Pore Pressure and F r i c t i o n D i s t r i b u t i o n along Shaft d u r i n g CPT 64 18 Estimated R a d i a l S t r e s s e s and Dynamic Pore Pressure 66 19 Excess Pore Pressure D i s t r i b u t i o n around a C y l i n d r i c a l C a v i t y with Time 72 20 I n f l u e n c e of Porous Stone L o c a t i o n 74 21 Time F a c t o r s f o r P r e d i c t i n g the C o e f f i c i e n t of C o n s o l i d a t i o n 77 22 Pore Pressure D i s s i p a t i o n s at Mcdonald and Burnaby S i t e s 80 23 C o m p r e s s i b i l i t y of Burnaby Clay 83 24 C o e f f i c i e n t of C o n s o l i d a t i o n : Burnaby Clay 84 25 P e r m e a b i l i t y of Burnaby Clay 85 26 C o m p r e s s i b i l i t y of Richmond Clayey S i l t 87 27 C o e f f i c i e n t of Consolidation:Richmond Clayey S i l t .88 28 P e r m e a b i l i t y of Richmond Clayey S i l t 89 29 E f f e c t of Remolding on the C o m p r e s s i b i l i t y of Richmond Clayey S i l t 90 30 E f f e c t of Remolding on the C o e f f i c i e n t of C o n s o l i d a t i o n : Richmond Clayey S i l t 91 31 F i t of T h e o r e t i c a l Curves to F i e l d Data: Mcdonald S i t e 20.5 m 97 32 F i t of T h e o r e t i c a l Curves to F i e l d Data: Mcdonald S i t e 25.5 m 98 33 F i t of T h e o r e t i c a l Curves to F i e l d Data: Burnaby S i t e 15.5 m 99 34 S e l e c t i o n of S o i l S t i f f n e s s R a t i o 104 VII Acknowledgements I would l i k e to express my s i n c e r e a p p r e c i a t i o n and g r a t i t u d e to Dr.Campanella fo r suggesting the study and p r o v i d i n g both l o g i s t i c a l support and guidance throughout. Much of the work was undertaken with Mr.P.K.Robertson who p r o v i d e d many suggestions and hours of f i e l d work. Thanks a l s o go to M r . B i l l B e r z i n s e s p e c i a l l y f o r w r i t i n g the computer g r a p h i c s r o u t i n e s . L a s t l y , s p e c i a l thanks go to my wife Brenda f o r her support and h e l p with p r e s e n t a t i o n . F i n a n c i a l support was p r o v i d e d by the Department of Energy Mines and Resources,Canada. Chapter 1 I n t r o d u c t i o n 1.1 H i s t o r i c a l Development of the Piezometer Cone Test The s t a t i c cone p e n e t r a t i o n t e s t has become the premier l o g g i n g t o o l f o r i n s i t u i n v e s t i g a t i o n s of s o i l d e p o s i t s . I t s main advantages over the standard p e n e t r a t i o n t e s t are the r a p i d i t y of the t e s t , i t s high r e p e a t a b i l i t y , and the continuous nature of the p r o f i l e s o b t a i n e d . Recent r e s e a r c h on the s t a t i c cone p e n e t r a t i o n t e s t has focussed on the measurement and i n t e r p r e t a t i o n of pore water p r e s s u r e s at and around the probe. Knowledge of pore water pr e s s u r e i s fundamental to any e f f e c t i v e s t r e s s i n t e r p r e t a t i o n of the measured parameters. In a d d i t i o n , i t has been r e a l i z e d that the measurement of pore water pressure p r o v i d e s an a d d i t i o n a l parameter to d e s c r i b e the s o i l b ehavior. The proceedings of the European Symposium on P e n e t r a t i o n T e s t i n g , ESOPT I, i n c l u d e d works by Janbu and Senneset 1974 and by Schmertmann 1974. Janbu and Senneset proposed an e f f e c t i v e s t r e s s i n t e r p r e t a t i o n of the s t a t i c cone p e n e t r a t i o n t e s t , but concluded that t h e i r knowledge of the d i s t r i b u t i o n of pore water p r e s s u r e s around the cone was inadequate. Schmertmann in t r o d u c e d the e f f e c t s of p e n e t r a t i o n pore pressure on cone r e s i s t a n c e . He d i s c u s s e d some of the parameters that e f f e c t the measured pore pressure and showed how the l e v e l of pore pressure would change the p e n e t r a t i o n r e s i s t a n c e measured. 2 At another conference, the ASCE S p e c i a l t y Conference on I n s i t u Measurement of S o i l P r o p e r t i e s , two very s i g n i f i c a n t papers i l l u s t r a t e d the use of the piezometer cone. Torstensson 1975 d e s c r i b e d how continuous i n f o r m a t i o n on the s o i l p r o p e r t i e s c o u l d be obtained from only the dynamic pore pressure r e c o r d . Wissa et a l . 1975 showed how the piezometer cone c o u l d be used to o b t a i n e q u i l i b r i u m pore p r e s s u r e s , as w e l l as c o n s o l i d a t i o n c h a r a c t e r i s t i c s from the pore pressure decay r a t e . U n t i l r e c e n t l y , a l l piezometer cones were e i t h e r made f o r the s o l e purpose of measuring pore p r e s s u r e s or were mo d i f i e d v e r s i o n s of the Fugro e l e c t r i c f r i c t i o n cone, i n which the pore p r e s s u r e measuring system was s u b s t i t u t e d f o r the f r i c t i o n s l e e v e . More recent cones such as the one used i n t h i s i n v e s t i g a t i o n i n c l u d e both the pore pressure measurement c a p a b i l i t y , as w e l l as bearing and f r i c t i o n measurements. T h i s paper shows how the a d d i t i o n of the pore p r e s s u r e measuring system can enhance the cone p e n e t r a t i o n t e s t . 1.2 Report O r g a n i z a t i o n A great v a r i e t y of i n f o r m a t i o n can be obtained from d i f f e r e n t a spects of the cone p e n e t r a t i o n t e s t ; the data can be used i n e i t h e r a q u a n t i t a t i v e or a q u a l i t a t i v e manner, depending on the r e s u l t s r e q u i r e d . T h i s r e p o r t i s d i v i d e d i n t o seven f o l l o w i n g c h a p t e r s , each of which o u t l i n e s some aspect of the t e s t . Chapter 2 d e s c r i b e s the equipment and procedure used dur i n g the i n v e s t i g a t i o n . A d d i t i o n a l d e s c r i p t i o n of s p e c i f i c d e t a i l s of the t e s t i s i n c l u d e d i n other chapters, where a p p r o p r i a t e . Chapter 3 i l l u s t r a t e s some examples of dynamic pore pressure records and shows how they can be used i n a q u a l i t a t i v e manner to enhance the s t r a t i g r a p h i c l o g g i n g c a p a b i l i t y of the cone p e n e t r a t i o n t e s t . Chapter 4 i n v e s t i g a t e s t h e o r e t i c a l s o l u t i o n s f o r the development of pore p r e s s u r e d u r i n g steady p e n e t r a t i o n and compares them to measured v a l u e s . Chapter 5 d e s c r i b e s the e f f e c t s of equipment and procedure v a r i a t i o n on the r e s u l t s obtained and c o n s i d e r s the p o s s i b i l i t y of h y d r o f r a c t u r e during cone p e n e t r a t i o n . Chapter 6 compares r e s u l t s obtained from c o n s o l i d a t i o n t e s t s to c o n s o l i d a t i o n c h a r a c t e r i s t i c s obtained from the rate of excess pore pressure d i s s i p a t i o n . Chapter 7 o f f e r s some recommendations on the s e l e c t i o n of c o m p r e s s i b i l i t y c h a r a c t e r i s t i c s t h a t , when combined with the c o e f f i c i e n t of c o n s o l i d a t i o n , can be used to c a l c u l a t e a p e r m e a b i l i t y v a l u e . Chapter 8 i n c l u d e s some a d d i t i o n a l c o n c l u s i o n s and recommendations f o r f u r t h e r r e s e a r c h . 4 Chapter 2 Equipment and Procedure 2.1 I n t r o d u c t i o n The purpose of t h i s paper i s not to d e s c r i b e the d e t a i l s of the r e s e a r c h and development that have gone i n t o the equipment necessary f o r the research undertaken, but rather to d e s c r i b e and i n t e r p r e t the r e s u l t s o b t a i n e d . Some d e s c r i p t i o n of the equipment and procedure i s , however, n e c e s s i t a t e d by the tremendous range in equipment and procedure used, a l l of which are termed piezometer cone l o g g i n g . T h i s chapter g i v e s a short d e s c r i p t i o n of the probe, the d r i v i n g u n i t , and the r e c o r d i n g d e v i c e s . I t then b r i e f l y d e s c r i b e s the procedures used i n c a l i b r a t i o n , set up, f i e l d t e s t i n g , and data r e d u c t i o n . A more complete d i s c u s s i o n of d e t a i l s , e s p e c i a l l y concerning the equipment, i s p r o v i d e d by Campanella and Robertson 1981. The importance of some of the procedures o u t l i n e d i n t h i s Chapter are f u r t h e r d i s c u s s e d in Chapters 5 and 6. 2.2 The Probe and Recording U n i t s The piezometer f r i c t i o n probe used i s i l l u s t r a t e d i n F i g u r e 1. The cone has a 60 apex angle, with a 10 cm p r o j e c t e d base area. The porous f i l t e r element s i t s immediately behind the cone and i s connected h y d r a u l i c a l l y to the pressure transducer f o r measuring the pore p r e s s u r e . The pressure transducer used i s a h e r m e t i c a l l y s e a l e d , a l l welded, f l u s h diaphragm, a b s o l u t e pressure type. F r i c t i o n i s measured on a f r i c t i o n s l e e v e having FIG. I 5- CHANNEL E L E C T R I C B E A R I N G - FRICTION -P I E Z O M E T E R C O N E P E N E T R O M E T E R wires -t her mister-stroin gages for cone^ bearing load cell porous polythylene-\i.< swoge fitting to lock lOconductor electric coble wires spliced to cable inside tube •wires -slope sensor -QUAD ring •stroin gouges for friction load cell - f r ic t ion sleeve (150cm areo) - 0 - rings pressure transducer -QUAD r ing small cavity 6 0 ° c o n e , 35.6mm 0.D. 6 an area of 150 cm 2. The c a p a c i t y of the t i p load c e l l used was 6 tons (about 540 b a r ) , and the c a p a c i t y of the pressure transducer was 150 p s i (10 b a r ) . Although i t was not necessary to do so, the pressure transducer was designed to be e a s i l y r e p l a c e d i n the f i e l d f o r one of a d i f f e r e n t c a p a c i t y . S i g n a l s from the load c e l l s and pressure transducer were sent to the s u r f a c e through a 10 conductor c a b l e . The use of common e x c i t a t i o n p ermitted the simultaneous measurement of the channels recorded (while only using 8 conductor c a b l e s ) . A 15 v o l t r e g u l a t e d power supply was used to provide a f i x e d 10 v o l t e x c i t a t i o n . Balance r e s i s t o r s were used to o b t a i n zero output at the r e f e r e n c e s e t t i n g f o r each transducer i n order to change range on the c h a r t recorder without an o f f s e t v o l t a g e . S c a l i n g r e s i s t o r s were used to d i r e c t l y p l o t i n t o e n g i n e e r i n g u n i t s on the c h a r t r e c o r d e r s . Two c h a r t r e c o r d e r s were used i n the i n v e s t i g a t i o n . One, a three channel r e c o r d e r d r i v e n by a pulse d r i v e - d i g i t a l s h a f t encoder, was a u t o m a t i c a l l y a c t i v a t e d during p e n e t r a t i o n to re c o r d b e a r i n g , f r i c t i o n , and dynamic pore p r e s s u r e s with depth. The other recorder was run on a time b a s i s to r e c o r d pore pressure response d u r i n g rod breaks and pore pressure d i s s i p a t i o n t e s t s . To d i f f e r e n t i a t e between the p a r t of the r e c o r d that was recorded d u r i n g p e n e t r a t i o n from the p a r t that was recorded d u r i n g rod breaks, each metre of p e n e t r a t i o n was manually i n d i c a t e d on the r e c o r d . To i n v e s t i g a t e the d i s t r i b u t i o n of pore p r e s s u r e s (and 7 f r i c t i o n ) up the cone s h a f t , s u c c e s s i v e l y longer t i p extensions were used to r e p l a c e the standard cone t i p . A d d i t i o n of the longer cone t i p s e f f e c t i v e l y moved both the porous element and the f r i c t i o n s leeve up the cone. The length and arrangement of the cone extensions used i s shown i n F i g u r e 2. R e s u l t s of t e s t i n g conducted with the longer t i p s i s presented i n Chapters 5 and 6. 2.3 D r i v i n g u n i t A complete d e s c r i p t i o n of the i n s i t u t e s t i n g v e h i c l e , i t s c a p a c i t y , and h y d r a u l i c c o n t r o l s i s given by Campanella and Robertson 1981. 2.4 Test Procedure During the i n v e s t i g a t i o n , i t was found necessary to pay c o n s i d e r a b l e a t t e n t i o n to c e r t a i n d e t a i l s i n the t e s t i n g procedure. In p a r t , t h i s was n e c e s s i t a t e d by the extreme range i n the parameters measured. For example, the t i p loa d c e l l had to measure bearing v a l u e s from 5 to 500 bars. Although not necessary f o r each f i e l d t e s t , the complete procedure r e q u i r e d can be broken i n t o four s t e p s : c a l i b r a t i o n ; s a t u r a t i o n of the pore pressure measuring system; f i e l d t e s t i n g ; and data r e d u c t i o n . Each of these steps i s d e s c r i b e d here because of the s e n s i t i v i t y of the r e s u l t s obtained to t h e i r proper completion. 8 S T A N D A R D D 10' CM 15" E X T E N S I O N S to P O R E P R E S S U R E •* E L E M E N T P R O B E F O R C E S T I P S L E E V E S T A N D A R D 10' 15' T A + S A , T A + S A + S B TA + S A + S B + S , * B sD FIGURE 2 TIP E X T E N S I O N S U S E D 9 2.4.1 C a l i b r a t i o n C a l i b r a t i o n of each of the load c e l l s and the pressure transducer was p e r i o d i c a l l y undertaken to ensure the accuracy of r e s u l t s . To t r y to reproduce as many f i e l d c o n d i t i o n s as p o s s i b l e , a l l c a l i b r a t i o n s were done i n the i n s i t u t e s t i n g v e h i c l e . During c a l i b r a t i o n , a l l v o l t a g e s were measured on both the c h a r t r e c o r d e r s and a 6 d i g i t multimeter using a 1 m i c r o v o l t r e s o l u t i o n . One of the most important f i e l d c o n d i t i o n s necessary to d u p l i c a t e was the use of the 10 channel conductor c a b l e intended f o r use i n the f i e l d . The b e a r i n g and f r i c t i o n l o a d c e l l s were c a l i b r a t e d a g a i n s t a r e f e r e n c e l o a d c e l l u s i n g a 7 ton c a l i b r a t i o n jack i n s t a l l e d i n the t e s t i n g v e h i c l e . L i n e a r i t y and s t a b i l i t y were found to be e x c e l l e n t . The pressure transducer was c a l i b r a t e d using a dead weight pressure t e s t e r connected h y d r a u l i c a l l y to the pressure t r a n s d u c e r . During c a l i b r a t i o n of each load c e l l , c r o s s - t a l k onto the other channels was recorded and found to be i n s i g n i f i c a n t . During e a r l y stages of the i n v e s t i g a t i o n , i t was found that the t i p recorded only about 71% of any water pressure around i t . As w i l l be d i s c u s s e d i n Chapters 3, 4, and 5, cone p e n e t r a t i o n t e s t i n g i n cohesive s o i l s generates high pore p r e s s u r e s . Since the t i p i s a t o t a l s t r e s s c e l l , i t should r e c o r d both the s o i l and water pressure a c t i n g upon i t . In f a c t , only 71% of the water pressure was recorded. The e x p l a n a t i o n of t h i s problem, from which a l l piezometer cones are thought to s u f f e r , can be 10 8 0 0 r CHAMBER PRESSURE (kPa) CHAMBER PRESSURE (kPa) FIGURE 3 RESULTS OF PIEZOMETER FRICTION CONE CALIBRATION. II seen i n F i g u r e 3. Some of the pore pressure i n the porous element r e a c t s a g a i n s t the f r i c t i o n s leeve and not through the bearing l o a d c e l l . F i g u r e 3 shows t h i s e f f e c t , recorded d u r i n g c a l i b r a t i o n of the load c e l l i n a pressure chamber. S i m i l a r h y d r o s t a t i c pressure c o r r e c t i o n s were found to be necessary to c o r r e c t f o r h y d r o s t a t i c p r e s s u r e s a c t i n g on unequal end areas of the f r i c t i o n s l e e v e . T h i s c a l i b r a t i o n , again performed with the cone i n a pressure chamber, i s shown i n F i g u r e 3. S l i g h t n o n l i n e a r i t y i n t h i s c a l i b r a t i o n i s due to c o m p r e s s i b i l i t y of the 0 and quad r i n g s . These c a l i b r a t i o n f a c t o r s are f u r t h e r d i s c u s s e d i n S e c t i o n 2.4.4. 2.4.2 S a t u r a t i o n of the Porous Element Proper s a t u r a t i o n of the pore water pressure measuring system was found to be extremely important f o r proper i n t e r p r e t a t i o n of t e s t r e s u l t s and w i l l be f u r t h e r d i s c u s s e d i n Chapter 5. G l y c e r i n e was found to be most e f f e c t i v e f o r s a t u r a t i o n . The c a v i t y between the pressure transducer and the porous element was s a t u r a t e d with g l y c e r i n e using a hypodermic tube when the cone was i n v e r t e d with the t i p arid f i l t e r removed. When no f u r t h e r a i r bubbles were seen emerging from the connecting c a v i t i e s , a s a t u r a t e d porous f i l t e r was put i n t o p l a c e and the hypodermic entrance was c l o s e d with a screw, as shown i n F i g u r e 1. Porous p o l y e t h y l e n e and polypropylene f i l t e r s were used 12 throughout the i n v e s t i g a t i o n . S a t u r a t i o n and c l e a n i n g of the elements was achieved by s o n i c a l l y v i b r a t i n g the porous elements while submerged i n g l y c e r i n e . 2.4.3 Cone P e n e t r a t i o n Test Procedure F o l l o w i n g a short warm up p e r i o d and s a t u r a t i o n of the pore p r e s s u r e measuring system, the cone was atta c h e d to the f i r s t rod, and the e x c i t a t i o n v o l t a g e s and zeros were a d j u s t e d with the cone hanging i n a v e r t i c a l d i r e c t i o n . When v e r t i c a l alignment was ensured, p e n e t r a t i o n was s t a r t e d . Unless otherwise d i s c u s s e d , the p e n e t r a t i o n r a t e used was 2 cm/sec. At one metre i n t e r v a l s , the pushing u n i t was r a i s e d and an a d d i t i o n a l rod at t a c h e d . T h i s delay u s u a l l y took approximately one minute, d u r i n g which time, pore p r e s s u r e s were recorded. At p e r i o d i c i n t e r v a l s , p e n e t r a t i o n was h a l t e d , and pore pressure d i s s i p a t i o n s were recorded with time. During t h i s p e r i o d , no load was p l a c e d on the rods by the pushing head. At the completion of the t e s t h o l e , the rods were withdrawn, and, with the cone hanging i n the v e r t i c a l p o s i t i o n , the zero l o a d readings were recorded by each channel. Zero d r i f t s were found to be completely the r e s u l t of temperature v a r i a t i o n between the l a b o r a t o r y , where c a l i b r a t i o n was performed, and the f i e l d . The zero used f o r i n t e r p r e t a t i o n of the r e s u l t s obtained was the zero recorded at the t e s t completion, while the cone was s t i l l at the ground temperature. Measurement of ground temperatures and p o s s i b l e temperature c o r r e c t i o n s i s given i n Campanella and Robertson 1981, who d e s c r i b e a 5 channel cone*that i n c l u d e s a t h e r m i s t e r . 13 2.4.4 Data Reduction The continuous records of bearing f r i c t i o n and pore pressure r e q u i r e c o n s i d e r a b l e h a n d l i n g and r e d u c t i o n , i n c l u d i n g c a l c u l a t i o n s of the f r i c t i o n r a t i o , the pore pressure r a t i o , and the d i f f e r e n t i a l pore pressure r a t i o . To f a c i l i t a t e the c a l c u l a t i o n s r e q u i r e d , the s t r i p c h a r t records were d i g i t i z e d on a g r a p h i c s t a b l e t . During the d i g i t i z i n g process, s u f f i c i e n t data p o i n t s were used to f u l l y d e s c r i b e the f i e l d r e c o r d s ; i n a d d i t i o n , a l l unwanted data were e l i m i n a t e d . These unwanted data were caused by l o a d i n g and unloading at rod breaks. Each of the c a l c u l a t i o n s and c o r r e c t i o n s performed i s d e s c r i b e d here. F r i c t i o n c o r r e c t i o n Before c a l c u l a i n g the f r i c t i o n r a t i o , the f r i c t i o n values were c o r r e c t e d f o r the pore pressure a c t i n g on the exposed d i f f e r e n t i a l end areas of the f r i c t i o n s l e e v e . The equation used was: F C C o r r e c t e d = F C Measured + 0.01 1U C o n s i s t e n t u n i t s The pore pressure c o r r e c t i o n f a c t o r , 0.011, was a r r i v e d at by a p p l y i n g a h y d r o s t a t i c pressure to the cone and measuring i t s e f f e c t on the f r i c t i o n s l e e v e , as d e s c r i b e d i n S e c t i o n 2.4.1. One assumption inherent i n t h i s equation i s that the pore pr e s s u r e , measured j u s t behind the t i p , i s r e p r e s e n t a t i v e of the pore pressure at the top of the f r i c t i o n s l e e v e . T h i s important 14 assumption i s f u r t h e r d i s c u s s e d i n Chapter 5, i n which the d i s t r i b u t i o n of pore p r e s s u r e s up the cone i s i n v e s t i g a t e d . Bearing C o r r e c t i o n The cone p e n e t r a t i o n t i p i s a t o t a l s t r e s s c e l l ; as such, i t should r e c o r d both pore pressure and e a r t h pressure r e a c t i n g a g a i n s t i t . As mentioned i n S e c t i o n 2.4.1, the cone used was found to r e c o r d approximately 71% of the water pressure a c t i n g around i t . The proper way, t h e r e f o r e , to account f o r t h i s i s to add to the bearing reading that p o r t i o n of the water pressure that i s not recorded, i . e . : Q cCorrected = Q c Measured + 0.29U C o n s i s t e n t u n i t s T h i s t i p c o r r e c t i o n i s s u b s t a n t i a l when t e s t i n g i n s o f t c l a y e y s o i l s , which have high dynamic pore p r e s s u r e s and low bearing v a l u e s . The importance of t h i s t i p c o r r e c t i o n i s f u r t h e r d i s c u s s e d i n Chapter 5. I t should, however, be noted that the c o r r e c t i o n f a c t o r used, 0.29, was a r r i v e d at by c a l i b r a t i n g the f r i c t i o n piezometer cone C6FPS-2UBC; other cones, a l l of which s u f f e r from t h i s problem, may have d i f f e r e n t c o r r e c t i o n f a c t o r s . I t i s , i n f a c t , the v a r i a t i o n i n c o r r e c t i o n f a c t o r s that n e c e s s i t a t e s proper b e aring and f r i c t i o n c o r r e c t i o n s . D i f f e r e n t i a l Pore Pressure D i f f e r e n t i a l pore pressure i s i n t r o d u c e d by Campanella et a l . 1981 as being a more fundamental parameter than the dynamic pore p r e s s u r e . T h i s d i f f e r e n t i a l pore pressure i s c a l c u l a t e d by: U Differential = U Measured ~ U S t a r i c S t a t i c pore pr e s s u r e s were i n t e r p o l a t e d between measured e q u i l i b r i u m v a l u e s . F r i c t i o n R a t i o F r i c t i o n r a t i o s were c a l c u l a t e d using an o f f s e t depth of 10 cm between simultaneous ( c o r r e c t e d ) bearing and f r i c t i o n v a l u e s . F r i c t i o n r a t i o s were p l o t t e d at the depth of the o f f s e t f r i c t i o n r e a d i n g and c a l c u l a t e d using a l i n e a r l y i n t e r p o l a t e d value f o r the b e a r i n g . Pore Pressure R a t i o Pore pressure and d i f f e r e n t i a l pore pressure r a t i o s were c a l c u l a t e d and p l o t t e d at the depth of the pore pressure reading using i n t e r p o l a t e d v a l u e s between the nearest d i g i t i z e d bearing v a l u e s . Chapter 3 Dynamic Pore Pressures and S t r a t i g r a p h i c Logging 16 3.1 I n t r o d u c t i o n The n e c e s s i t y f o r monitoring dynamic pore p r e s s u r e s to c o r r e c t the measured bearing and f r i c t i o n values was shown in Chapter 2. In a d d i t i o n to c o r r e c t i n g the bearing and f r i c t i o n v a l u e s , the dynamic pore pressure l o g and d i s s i p a t i o n records can enhance the s t r a t i g r a p h i c l o g g i n g a b i l i t i e s of the cone p e n e t r a t i o n t e s t . The use of b e a r i n g and f r i c t i o n measurements fo r s t r a t i g r a p h i c l o g g i n g i s thoroughly e x p l a i n e d by Schmertmann 1978 and o t h e r s ; t h i s chapter d i s c u s s e s only the ways i n which the a d d i t i o n of pore pressure measurements can be u s e f u l . The g e n e r a t i o n of pore p r e s s u r e s i s d i s c u s s e d , and the dynamic pore pr e s s u r e r a t i o i n t r o d u c e d . For i l l u s t r a t i o n purposes, s p e c i f i c examples are drawn upon and e x p l a i n e d . 3.2 Pore Pressures Generated During Cone P e n e t r a t i o n T e s t i n g Pore p r e s s u r e s generated d u r i n g cone p e n e t r a t i o n t e s t i n g depen.d upon the m a t e r i a l t e s t e d and the procedure used. Experience has shown that cone p e n e t r a t i o n t e s t i n g i n c l e a n sands i s e s s e n t i a l l y a d r a i n e d t e s t . In c o n t r a s t , cone p e n e t r a t i o n t e s t i n g i n c l a y s o i l s i s a f u l l y undrained t e s t . The degree of pore p r e s s u r e d i s s i p a t i o n d u r i n g t e s t i n g i n i ntermediate s o i l s i s f u r t h e r d i s c u s s e d i n Chapter 5. The magnitude and s i g n (greater or l e s s than the e q u i l i b r i u m pore pressure) i s a f u n c t i o n of the t e s t procedure, p r e e x i s t i n g 1 7 s t r e s s l e v e l , and the m a t e r i a l t e s t e d . Cone p e n e t r a t i o n t e s t i n g i n dense sands with s u f f i c i e n t f i n e s content ( p a r t i a l l y d r a i n e d ) o f t e n r e s u l t s i n the g e n e r a t i o n of negative pore p r e s s u r e s , whereas cone p e n e t r a t i o n t e s t i n g i n loose sands o f t e n r e s u l t s i n g e n e r a t i o n of p o s i t i v e pore p r e s s u r e s . As s o i l s become more p l a s t i c , p o s i t i v e pore p r e s s u r e s are generated; the magnitude of the pore pressure i s d i s c u s s e d i n Chapter 4. Pore pressures can a l s o be expressed as a r a t i o of the b e a r ing value (which should a l s o i n c l u d e the water p r e s s u r e a c t i n g on the t i p ) ; t h i s t o p i c i s o u t l i n e d i n the next s e c t i o n . The CPT logs from the Mcdonald s i t e are shown i n F i g u r e 4. The s i t e i s c h a r a c t e r i z e d by s i l t o v e r l y i n g c l e a n sands to 13 metres. Below 13 metres, the sands grade i n t o s i l t y sands with low bearing v a l u e s . Below 15 metres, a s o f t c l a y e y s i l t d e p o s i t can e a s i l y be i d e n t i f i e d by the bearing and pore pressure response, as w e l l as by the f r i c t i o n r a t i o . Very s l i g h t l y n egative pore pr e s s u r e s ,recored behind the t i p , c a n be seen i n the f i n e s i l t y sand from 13 to 15 metres. Although the sand above has much hig h b e a r i n g v a l u e s , i t i s f r e e d r a i n i n g and no negative pore pr e s s u r e s are observed. Even though the two sand d e p o s i t s , t h e r e f o r e , have s i m i l a r f r i c t i o n r a t i o s , an i n d i c a t i o n of t h e i r g r a d a t i o n a l c h a r a c t e r i s t i c s can be o b t a i n e d . The s o f t c l a y e y s i l t d e p o s i t s below 15 metres generate l a r g e p o s i t i v e pore p r e s s u r e s and can e a s i l y be d i s t i n g u i s h e d . 3.3 Dynamic Pore Pressure R a t i o An example showing l a r g e pore p r e s s u r e s generated d u r i n g FIG. 4S0IL PROFILE FOR RESEARCH SITE AT McDONALDS FARM, SEA ISLAND. 19 cone p e n e t r a t i o n t e s t s have been shown. For most c l a y e y s o i l s , the undrained shearing r e s u l t s i n l a r g e pore pr e s s u r e s and accompanying decrease i n the e f f e c t i v e s t r e s s l e v e l . The pore p r e s s u r e s generated r e s u l t from a combination of two f a c t o r s : The l a r g e shear induced pore p r e s s u r e ; and the compressive s t r e s s induced pore p r e s s u r e . B a l i g h et a l . 1980 introduced the pore pressure r a t i o U/QC as a means of no n d i m e n s i o n a l i z i n g the pore pressure generated. I t was proposed t h a t , when p e n e t r a t i n g s o f t c l a y e y s o i l s , the shear induced pore pressures would be p o s i t i v e , whereas the shear induced pore pressures generated d u r i n g cone p e n e t r a t i o n t e s t i n g i n o v e r c o n s o l i d a t e d s o i l s would be small or even n e g a t i v e . T h i s does not imply that the t o t a l pore pressure generated need n e c e s s a r i l y be negative because of the pore p r e s s u r e s generated by the compressive s t r e s s e s . As w i l l be shown i n Chapter 4, the magnitude of the t o t a l pore pr e s s u r e s generated i n c l a y e y s o i l s i s , to a degree, a f u n c t i o n of the undrained shear s t r e n g t h . By e x p r e s s i n g the' pore p r e s s u r e as a r a t i o of the be a r i n g , which i s a l s o a f u n c t i o n of the undrained shear s t r e n g t h , i t was hoped that the e f f e c t s of shear induced pore pressure and, t h e r e f o r e , s t r e s s h i s t o r y c o u l d be emphasized. Thus, i t was hypothesized that o v e r c o n s o l i d a t e d s o i l s t h a t generate small p o s i t i v e or negative pore p r e s s u r e s when sheared and have high bearing v a l u e s should have a low pore pressure r a t i o U/QC, whereas s o f t s o i l s should have a pore pressure r a t i o approaching 1.0. Since the bearing value i s a combination of s o i l r e s i s t a n c e and water p r e s s u r e a c t i n g on the t i p , the upper l i m i t of the 2 0 pore pressure r a t i o i s 1.0. In s p i t e of t h i s , pore pressure r a t i o s g r e a t e r than 1.0 are commonly r e p o r t e d . A l i s t of pore pressure r a t i o s i s shown with measured o v e r c o n s o l i d a t i o n r a t i o s : OCR U/QC B a l i g h et a l . 1980 6 0.6 60° T i p 4 1.0 2 1.2 B a l i g h et a l . 1980 6 0.15 18° T i p 4 0.4 2 0.75 Lacasse et a l . 1981 2.5 0.5 1 . 5 - 1 . 1 5 0.6 1.2 0.7 Roy et a l . 1980 2 . 2 - 2 . 5 0.56 T h i s I n v e s t i g a t i o n 1.0 0.8 - 1.0 The d i f f e r e n t i a l pore pressure r a t i o — t h e r a t i o of that pore pressure i n excess of the h y d r o s t a t i c value to the bearing v a l u e — w a s introduced by Campanella et a l . 1981 as being a more fundamental parameter. Cone p e n e t r a t i o n t e s t i n g i n granula r m a t e r i a l s may a l s o generate e i t h e r p o s i t i v e or negative pore p r e s s u r e s . In sands, 21 the b e a r i n g value i s u s u a l l y so l a r g e and the induced pore pressure so low that the r a t i o ( e i t h e r p o s i t i v e or negative) i s u s u a l l y very s m a l l . Mixed s o i l s may, however, r e s u l t i n l a r g e r pore p r e s s u r e r a t i o s , which c o u l d have a value s i m i l a r to that of an o v e r c o n s o l i d a t e d c l a y . D i f f e r e n t i a t i o n between an o v e r c o n s o l i d a t e d c l a y s o i l and a s i l t y s o i l may not be p o s s i b l e i f o nly the dynamic pore p r e s s u r e and b e a r i n g values are a v a i l a b l e . D i f f e r e n t i a t i o n between such s o i l s i s , however, p o s s i b l e with the a i d of f r i c t i o n measurements and the f r i c t i o n r a t i o . P o s s i b l e a d d i t i o n a l means of d i f f e r e n t i a t i n g such s o i l s u s i ng pore pressure decay r a t e s i s d e s c r i b e d i n Chapter 6. 3.4 S t r a t i g r a p h i c Logging S p e c i f i c examples of the u s e f u l n e s s of simultaneous measurements of dynamic pore p r e s s u r e s , r e c o r d e d behind the t i p , as w e l l as f r i c t i o n and b e a r i n g v a l u e s , are presented i n t h i s s e c t i o n . 3.4.1 CPT Example 1 F i g u r e 5 The complete cone l o g o b t a i n e d from a s i t e of the F r a s e r R i v e r d e l t a i s shown i n F i g u r e 5. The interbedded sands and s i l t s were d e p o s i t e d s i n c e the l a s t g l a c i a l p e r i o d . The s t r a t i g r a p h i c v a r i a t i o n shown r e s u l t s , i n p a r t , from v a r i a t i o n i n the l o c a t i o n of the r i v e r channel w i t h i n the prograding d e l t a . The m a t e r i a l types i n t e r p r e t e d from the cone logs are shown i n F i g u r e 5. Within each u n i t shown, the g r e a t e s t d e t a i l can be seen from the pore pressure l o g . For example, w i t h i n the P O R E F R I C T I O N B C A P . I N O F R I C T I O N P R E S S U C RE9STANCE R E S I S T A N C E R A T I O U(bor) FC(bar) QCtbor) RFl%) Q 2 5 0 2 0 250 0 5 O F F R r. S O I L R A T I O P R O F I L E MJ/QC 0 030 TTTT PIEZOMETER FRICTION CONE LOGGING IN STRATIFIED SOILS / / / (ANNACIS ISLAND SITE) KJ-LJ SAND SILT SILTY SAND F I G U R E 5 CPT E X A M P L E I 23 s i l t l e n s e s , the bearing and f r i c t i o n v a l u e s , which r e f l e c t the p r o p e r t i e s of a l a r g e r zone of s o i l , are n e a r l y constant, whereas the pore pressure l o g r e v e a l s small sandier p a r t i n g s w i t h i n each s i l t l e n s . The m a t e r i a l c l a s s i f i c a t i o n shown i n F i g u r e 5 i n c l u d e s the d i s t i n c t i o n between sand, s i l t , and s i l t y sand d e p o s i t s . Although the sand and s i l t d e p o s i t s are e a s i l y d i s t i n g u i s h e d using only the bearing and f r i c t i o n measurements, the s i l t y sand l a y e r s can o n l y be d i s t i n g u i s h e d from the s i l t l a y e r s by the pore p r e s s u r e measurements. The bearing and f r i c t i o n r a t i o f o r the two m a t e r i a l s are s i m i l a r ; each has a value of approximately 20 bar and 3.0 r e s p e c t i v e l y . I f only the f r i c t i o n and b e a r i n g measurements are a v a i l a b l e , each would be c l a s s i f i e d as a s i l t . I n s p e c t i o n of the dynamic pore pressure l o g s , however, r e v e a l s a d i s t i n c t l y d i f f e r e n t behavior of the two m a t e r i a l s . Compared to the s i l t , the s i l t y sand has a much lower dynamic pore p r e s s u r e . The v a r i a t i o n i n dynamic pore p r e s s u r e can occur because e i t h e r the s i l t y sand i s l e s s compressible or i s a more f r e e l y d r a i n i n g m a t e r i a l . Since the m a t e r i a l s have e q u i v a l e n t b e a r i n g v a l u e s , i t appears t h a t p e n e t r a t i o n of the s i l t y sand r e s u l t s i n a lower dynamic pore pressure because of p a r t i a l drainage of the dynamic pore p r e s s u r e s . A more complete i n d i c a t i o n of the g r a d a t i o n a l c h a r a c t e r i s t i c s can thus be o b t a i n e d from the pore pressure response. An a l t e r n a t e means of i d e n t i f y i n g the three s o i l types can be o b t a i n e d from the time to reach d i s s i p a t i o n of 50% of the excess pore p r e s s u r e , t 5 0 , such as those marked at t h e i r 24 a p p r o p r i a t e depths i n F i g u r e 5. For a given probe, the time f o r d i s s i p a t i o n of 50% of the excess pore p r e s s u r e i s a f u n c t i o n of the c o n s o l i d a t i o n c h a r a c t e r i s t i c s of the s o i l , and c l e a r l y d i s t i n g u i s h e s the three s o i l types. The l o c a t i o n of the pore p r e s s u r e d i s s i p a t i o n s shown i n F i g u r e 5 a l s o h i g h l i g h t s the n e c e s s i t y of i n s p e c t i n g the complete cone lo g s when i n t e r p r e t i n g d i s s i p a t i o n t e s t r e s u l t s . D i s s i p a t i o n s conducted w i t h i n the s i l t l e n s e s , but near sand boundaries, are a f f e c t e d by the g r e a t l y reduced drainage path l e n g t h . The time to reach t ^ 0 i s a u s e f u l parameter f o r d i s t i n g u i s h i n g s t r a t i g r a p h i c types. For many s o i l types such as those shown i n F i g u r e 5, the time to reach 50% d i s s i p a t i o n of excess pore pressure i s o f t e n achieved d u r i n g rod breaks, with very l i t t l e standby time. S i m i l a r r e s u l t s can be obtained u s i n g a s m a l l e r degree of d i s s i p a t i o n i n l e s s permeable s o i l s . 3.4.2 CPT Example 2 F i g u r e 6 A g e n e r a l i z e d s o i l p r o f i l e f o r t h i s s i t e would i n d i c a t e that the s i t e c o u l d be broken i n t o two b a s i c u n i t s : a sand d e p o s i t o v e r l y i n g s i l t , with interbedded sand l e n s e s . The sand l e n s e s are e a s i l y d i s t i n g u i s h e d by t h e i r h i g h b e a r i n g , low f r i c t i o n r a t i o , and low d i f f e r e n t i a l pore p r e s s u r e r a t i o . The s i l t has b e a r i n g v a l u e s ranging from 20 to 30 bar, i n c r e a s i n g with depth, and i s e a s i l y d i s t i n g u i s h e d by i t s h i g h dynamic pore pr e s s u r e r a t i o . In c o n t r a s t to the s i l t d e p o s i t s , a very low bea r i n g value m a t e r i a l can be seen between 28.5 and 30.0 metres. The b e a r i n g and f r i c t i o n r a t i o s alone i n d i c a t e t h at the m a t e r i a l PORE PRESSURE f l l C T I N RES1STRMCE BCRRING RESISTANCE FR1CTIOM RATIO BIFFEfiENTIflL P .P . B IBRRI Ft IBflRI DC IBRR) RF=FC/QC ('/) RRIIO &U/QC I 25 II 2 I 250 0 5 0 .80 F IGURE 6 C P T E X A M P L E 2 26 i s a s o f t c l a y s o i l ; examination of the pore pressure record, however, shows that no pore p r e s s u r e was generated d u r i n g p e n e t r a t i o n . Two very d i s t i n c t types of m a t e r i a l do not generate excess pore p r e s s u r e s when sheared: those that are so f r e e d r a i n i n g that the pore p r e s s u r e s immediately d i s s i p a t e ; and those t h a t are of a p a r t i c u l a r s t i f f n e s s such that n e i t h e r p o s i t i v e nor negative pore pre s s u r e s r e s u l t . Since m a t e r i a l with a much higher bearing v a l u e — t h e s i l t l e n s e s between 45 and 70 m e t r e s — r e s u l t s i n very l a r g e pore p r e s s u r e s , i t appears that the m a t e r i a l between 28.5 and 30.0 metres i s a f r e e d r a i n i n g , but very s o f t , m a t e r i a l . The b e a r i n g value i s too low and the f r i c t i o n r a t i o too high f o r the m a t e r i a l to be a sand. I t would appear, t h e r e f o r e , that the m a t e r i a l i s a f r e e d r a i n i n g organic d e p o s i t such as f i b r o u s peat. 3.4.3 CPT Example 3 F i g u r e 7 Pore pressure r e c o r d s , e s p e c i a l l y d i s s i p a t i o n s , are s e n s i t i v e to both the m a t e r i a l that the piezometer element l i e s w i t h i n and the m a t e r i a l surrounding the cone. To i l l u s t r a t e some of the e f f e c t s of s o i l s t r a t i g r a p h y on the pore pressure response, F i g u r e 7 shows a p o r t i o n of the dynamic pore pressure r e c o r d . As i n d i c a t e d i n F i g u r e 7, the r e c o r d i n c l u d e s both the dynamic pore pressure r e c o r d with depth, as w e l l as the d i s s i p a t i o n r e c ords o b t a i n e d d u r i n g rod breaks. D i s s i p a t i o n s conducted at 73.6 and 75.6 metres are of the type g e n e r a l l y recorded i n a c l a y e y d e p o s i t . D i s s i p a t i o n s of the type recorded at 74.6 metres, however, have a l s o been shown i n the l i t e r a t u r e . PDBE PRESSURE fRIMN RES1STRNCE "ERRING RESISTHCE FlltUII RATIO IIFFEfiEMIRL P.P. RF=F£/OC ID RRIIO U/IC D 52 18 U (bars) 72.6 73.6 73.6 E 74.6 x k UJ 74.6 Q 75.6 75.6 766 LEGEND DATA RECORDED DURING PENETRATION 0.5 m DATA RECORDED DURING DISSIPATION T DETAIL OF DISSIPATION LOCATION FIGURE 7- COMPLETE CPT LOG AND DETAIL OF DYNAMIC PORE PRESSURE RECORD 28 Many e x p l a n a t i o n s e x i s t f o r the apparent i n c r e a s e i n pore p r e s s u r e b e f o r e the u l t i m a t e decay of excess pore p r e s s u r e . In t h i s case, however, examination of the complete depth r e c o r d i n g s r e v e a l s that the piezometer element at 74.6 metres was w i t h i n a sand l e n s . As shown i n F i g u r e 7, pore p r e s s u r e s generated i n the s i l t l e n s , both above and immediately below the cone, r e s u l t e d i n a delayed pore pressure r i s e i n the sand lens a f t e r p e n e t r a t i o n was h a l t e d . Subsequent r a p i d d i s s i p a t i o n of pore p r e s s u r e was c o n t r o l l e d , i n p a r t , by the higher p e r m e a b i l i t y of the sand l e n s . Other d i s s i p a t i o n s of t h i s type are o f t e n seen i n l a y e r e d s o i l s ; c a r e f u l examination of the complete r e c o r d s , both with depth and with time, can f u r t h e r e x p l a i n such phenomena. 3.4.4 CPT Example 4 F i g u r e 8 F i g u r e 8 shows the b e a r i n g and pore pressure l o g s obtained before and a f t e r compaction i n adjacent h o l e s . The m a t e r i a l was h y d r a u l i c a l l y p l a c e d . I t has been s t a t e d that when she a r i n g s o i l s of s u f f i c i e n t l y low p e r m e a b i l i t y , dynamic pore p r e s s u r e s r e s u l t , the l e v e l of which depends on the volume change c h a r a c t e r i s t i c s of the s o i l . F i g u r e 8 i l l u s t r a t e s the change i n both magnitude and s i g n of the dynamic pore pressure that accompanies an i n c r e a s e i n compactiveness of the s o i l . Before compaction, l a r g e p o s i t i v e pore p r e s s u r e s are generated i n the s o f t s i l t between 2.5 and 7.5 metres; a f t e r compaction, the dynamic pore p r e s s u r e s become n e g a t i v e . Although the magnitude and s i g n of the dynamic pore pressure has only been used to date 62 30 i n a q u a l i t a t i v e manner, i t may prove to be a u s e f u l parameter to d e s c r i b e the p r o p e r t i e s of p a r t i a l l y d r a i n e d or undrained m a t e r i a l s . The s i g n of the dynamic pore p r e s s u r e probably depends on the l o c a t i o n of the measuring element. As s t a t e d i n Campanella et a l . 1981, the l o c a t i o n of the porous element used i n t h i s i n v e s t i g a t i o n probably encourages the measurement of negative pore p r e s s u r e s i n a l l but very loose s o i l s . F u r t h e r i n v e s t i g a t i o n of the e f f e c t of l o c a t i o n of the porous element i s ongoing. 3.5 S t a t i c Pore Pressures Piezometer cone l o g g i n g can be stopped at any depth and the e q u i l i b r i u m ground water c o n d i t i o n s measured. Although the cone generates dynamic pore p r e s s u r e s d u r i n g p e n e t r a t i o n , c a r e f u l m o n i t o r i n g of the decay of excess pore pressure with time can ensure that f u l l e q u i l i b r i u m has been achieved. In t h i s manner, cone p e n e t r a t i o n t e s t i n g can be a c o s t e f f e c t i v e means of o b t a i n i n g e q u i l i b r i u m ground water c o n d i t i o n s . As w i l l be shown in Chapter 6, the time to achieve any degree of d i s s i p a t i o n i s a f u n c t i o n of the c o n s o l i d a t i o n c h a r a c t e r i s t i c s of the s o i l and the r a d i u s of the probe squared. The f a c t that the time to reach e q u i l i b r i u m c o n d i t i o n s i n c r e a s e with the r a d i u s of the probe squared i s one of the reasons why e a r l y piezometer probes, which only measured pore p r e s s u r e s , were of very small r a d i u s . An example of the use of the piezometer cone f o r o b t a i n i n g 31 e q u i l i b r i u m ground water c o n d i t i o n s can be shown from Campanella and Robertson 1981. E q u i l i b r i u m ground water pre s s u r e s are shown with depth i n F i g u r e 9. Knowledge of the e q u i l i b r i u m pore p r e s s u r e s i s u s e f u l f o r flow net, seepage, and s t a b i l i t y a n a l y s i s , as w e l l as p r o p e r l y e v a l u a t i n g the cone bearing data. For example, present methods f o r e v a l u a t i n g bearing values f o r r e l a t i v e d e n s i t y or f r i c t i o n angle of sands r e q u i r e s an estimate of the i n s i t u e f f e c t i v e s t r e s s l e v e l . I f , i n t h i s example, h y d r o s t a t i c c o n d i t i o n s had been estimated, the l e v e l of e f f e c t i v e s t r e s s would be g r e a t l y underestimated and r e l a t i v e d e n s i t y d e t e r m i n a t i o n s from b e a r i n g v a l u e s overestimated. 3.6 C o n c l u s i o n s Examples showing how the dynamic pore p r e s s u r e and dynamic pore p r e s s u r e r a t i o change with both volume change c h a r a c t e r i s t i c s as w e l l as p e r m e a b i l i t y have been shown Although p e n e t r a t i o n of very d i f f e r e n t m a t e r i a l s may r e s u l t i n s i m i l a r dynamic pore p r e s s u r e by c a r e f u l l y i n s p e c t i n g the b e a r i n g and f r i c t i o n measurements as w e l l as the dynamic pore p r e s s u r e the m a t e r i a l type can be d i s t i n g u i s h e d . The e f f e c t of p e r m e a b i l i t y on the dynamic pore pressure w i l l be f u r t h e r d i s c u s s e d i n Chapter6. FIG. 9 E X A M P L E OF P I E Z O M E T E R , FRICTION C O N E L O G T H R O U G H T A I L I N G S D E P O S I T . 01 33 Chapter 4 A n a l y t i c a l E x p r e s s i o n s f o r Dynamic Pore Pressure 4.1 I n t r o d u c t i o n During cone p e n e t r a t i o n t e s t i n g , pore pr e s s u r e s have only been measured at one l o c a t i o n . The l o c a t i o n chosen during t h i s i n v e s t i g a t i o n was d i r e c t l y behind the t i p . In a d d i t i o n , pore p r e s s u r e s were a l s o measured up the s h a f t . Other r e s e a r c h e r s , Roy et a l . 1980 and B a l i g h et a l . 1980, have measured pore p r e s s u r e s at the t i p of the cone penetrometer. Alignment problems precl u d e the p o s s i b i l i t y of a c t u a l l y measuring pore p r e s s u r e s around the cone d u r i n g cone p e n e t r a t i o n t e s t i n g . P r e v i o u s experience i n measurement of pore p r e s s u r e s around d r i v e n p i l e s can, however,, be drawn upon to compare pore p r e s s u r e s with r a d i a l d i s t a n c e from the cone to those measured at the cone s u r f a c e . T h i s chapter compares a n a l y t i c a l e x p r e s s i o n s f o r the magnitude and d i s t r i b u t i o n of pore pr e s s u r e s with f i e l d o b s e r v a t i o n s of dynamic pore p r e s s u r e s around d r i v e n p i l e s . In a d d i t i o n , a n a l y t i c a l e x p r e s s i o n s f o r the magnitude of the pore pressure generated are compared with values measured d u r i n g cone p e n e t r a t i o n t e s t i n g at the Mcdonald s i t e . A knowledge of the magnitude and d i s t r i b u t i o n of pore p r e s s u r e s i s important f o r s e v e r a l reasons, i n c l u d i n g : 1) The d i s t r i b u t i o n of dynamic pore pr e s s u r e s r e p r e s e n t s the i n i t i a l c o n d i t i o n s f o r pore p r e s s u r e d i s s i p a t i o n a n a l y s i s used to c a l c u l a t e c o n s o l i d a t i o n 34 c h a r a c t e r i s t i c s . 2) P e n e t r a t i o n t e s t i n g i n f l u e n c e s a l a r g e zone of s o i l ; the d i s t r i b u t i o n of pore pr e s s u r e s i s fundamental to any e f f e c t i v e s t r e s s i n t e r p r e t a t i o n of bearing and f r i c t i o n measurements. 3) If a n a l y t i c a l e x p r e s s i o n s f o r the generated pore pressure that r e l y on fundamental s o i l p r o p e r t i e s compare w e l l with measured pore p r e s s u r e s generated -at the s u r f a c e of the cone, then dynamic pore pressure measurement may prove u s e f u l i n e v a l u a t i n g s o i l parameters. 4.2 A n a l y t i c a l E x p r e s s i o n s The t h e o r e t i c a l p r e d i c t i o n of the pore pressure d i s t r i b u t i o n induced d u r i n g steady cone p e n e t r a t i o n t e s t i n g i n s a t u r a t e d c l a y e y s o i l s i s the s u b j e c t of c o n s i d e r a b l e a t t e n t i o n because of i t s relevance to many problems, i n c l u d i n g p i l e i n s t a l l a t i o n and the i n t e r p r e t a t i o n of i n s i t u t e s t s , which i n c l u d e the piezometer cone and the pressuremeter t e s t s . Pore pr e s s u r e d i s t r i b u t i o n around the cone penetrometer i s complicated by: 1) complex boundary c o n d i t i o n s around the cone; 2) complex s t r e s s paths f o l l o w e d by the s o i l , e s p e c i a l l y near the cone; 3) very l a r g e s t r a i n s ; and 4) complexity of s o i l b ehavior. 3 5 In order to s i m p l i f y the problem, s e v e r a l assumptions must be made re g a r d i n g both the s o i l behavior and geometry. Experience gained by mon i t o r i n g of pore pr e s s u r e s induced by d r i v e n p i l e s has l e d to the r e l a t i v e l y widely accepted idea t h a t the complex geometry of cone i n s t a l l a t i o n can be modelled by e i t h e r expansion of a c y l i n d r i c a l or s p h e r i c a l c a v i t y . Past experience seems to i n d i c a t e t h at pore p r e s s u r e s generated a t the t i p can best be estimated by expansions of a s p h e r i c a l c a v i t y , whereas pore p r e s s u r e s up the sleeve or s h a f t can best be modelled by expansion of a c y l i n d r i c a l c a v i t y (Roy et a l . 1980 and V e s i c 1972). In a d d i t i o n to s i m p l i f i c a t i o n of the geometry, d i f f e r e n t s o i l models can be used t o d e s c r i b e the s o i l b e h avior. T h i s s e c t i o n summarizes a n a l y t i c a l e x p r e s s i o n s f o r pore pressure magnitude and d i s t r i b u t i o n . Chapter3 showed examples of very low dynamic pore p r e s s u r e r e c o r e d when p e n e t r a t i n g c e r t i a n c l a y e y s o i l s . Negative dynamic pore pr e s s u r e s were observed when p e n e t r a t i n g a compacted s i l t y s o i l . Other r e s e a r c h e r s have shown how the dynamic pore p r e s s u r e , e s p e c i a l l y when expressed as the dynamic pore pressure r a t i o , d e c r e a s e s with i n c r e a s i n g o v e r c o n s o l i d a t i o n r a t i o f o r a c l a y s o i l . Some of the a n a l y t i c a l e x p r e s s i o n s i l l u s t r a t e d i n t h i s Chapter apply only to normally c o n s o l i d a t e d s o i l s . Others attempt to account f o r the volume change c h a r a c t e r i s t i c s of the s o i l , t h e d i f f e r e n c e between the ex p r e s s i o n s should be noted. 4.2 .1 Comparison between Models A r i g o r o u s comparison between models i s dependent upon the s e l e c t i o n of input parameters. Recognizing that no s i n g l e t e s t procedure can r e s u l t i n a r e f e r e n c e parameter, Table I summarizes the s e l e c t i o n of input parameters and the p r e d i c t e d l e v e l of excess pore pressure f o r each of the models o u t l i n e d . The r e s u l t s are shown f o r the s i l t at 20 metres depth. Comparison between models and measured pore p r e s s u r e s at the Mcdonald s i t e i s d i s c u s s e d f u r t h e r . Parameters Used cu undrained shear s t r e n g t h I r r i g i d i t y index = E / 3 c u E e l a s t i c modulus - undrained U pore pressure r r a d i a l s t r e s s p average s t r e s s A^ Skempton's pore pressure parameter k at r e s t e a r t h pressure r a t i o Geometric Terms Plastic Zone Elastic Zone 3 7 MODEL Parameters Used (bar) cu I r Af 0' p' c s U c y l Usph P'nc 1. E l a s t i c p l a s t i c 0.55 167 2.81 3.75 2. E l a s t i c p l a s t i c 0.55 167 0.4 3.26 4.20 with volume hardening 3. Semi e m p i r i c a l 0.55 167 1.0 3.45 4.49 Torstensson 1977 4. Semi e m p i r i c a l 0.55 32° 1.94 Hagerty and Garlanger 1972 5. Semi e m p i r i c a l U/p 2.33 Roy et a l ^ 1979 =0.75 M a t e r i a l Tested Clayey S i l t QC = 8.2 bar rj v ' =2.0 bar PI = 1.5% .% sand 10 Uo = 2.0 bar LL = 38% % s i l t 70 Wn = 35% % c l a y 20 -cu = QC/NC = 8.2/15 =0.55 bar la - I r = Estimated from C o r r e l a t i o n s et a l . 1977 -Af = Estimated from c o r r e l a t i o n s Whitman 1969 -0' = Estimated from c o r r e l a t i o n s Whitman 1969 p n c = Estimated from c o r r e l a t i o n s E s r i g and K i r b y 1978 > vane - 5 - - 6 bar between cu and I r from Ladd between OCR and Af, Lambe and between PI and 0 ', Lambe and between p^.5 /p' n c a n a " C c ' T a b l e I Input P a r a m e t e r s Used to Compare D y n a m i c Pore P r e s s u r e M o d e l s 38 Method 1 E l a s t i c p e r f e c t l y p l a s t i c s o i l V e s i c 1972; Randolph and Wroth 1979; Torstensson 1977 C y l i n d r i c a l c a v i t y A err = cut 1 + In I r ) (1 ) a U = 2cu • In R/r (2) R/r = ( I r ) 1 ' 2 (3) S p h e r i c a l c a v i t y A^rr = 4/3CU(1 + In I r ) (4) A U = 4cu l n ( R / r ) (5) R/r = I r 1 / 3 (6) Method 2 E l a s t i c p l a s t i c s o i l with volume hardening s o i l s with OCR < 2.0 S c h o f i e l d and Wroth 1968; Roscoe and Burland 1968 A U s (p'j - p ' f ) + A p (7) M = q/p = 6 s i n 0 ' / ( 3 - sin0) (8) q = / 3 cu (9) A p = from egns 2 + 4 (10) C y l i n d r i c a l c a v i t y : a f t e r E s r i g and K i r b y 1978 A U = (p'j - p'f ) + Ap (11) A U = ( p ' n c - p; s) + 2cu In I r ' / 2 (12) JfcLnc ~ J2.cs A U = p'nc P'nc + 2cu In I r l / a (13) P'nc 3 9 S p h e r i c a l c a v i t y : a f t e r E s r i g and K i r b y 1978 A U = (p'j - p'f ) + AP (14) A U = (p'nc - Pes > + 4cu In I r 1 / 3 (15) JP_hc ~ p 'eg A U = phe £'nc + 4 c u In I r •/ 3 (16) P'nc Method 3 Semi e m p i r i c a l Torstensson 1977;Massarch 1978 A u = 1 /3 ( A cr, + A cr2+ A cjj) + a f [ ( A a, - A a 3 ) 2 + ( A cr 2- A fj 3)2 + ( a C T | - A f j 2 ) 2 ] " f c (17) a f = 1/ 2(3A f - 1) (18) C y l i n d r i c a l c a v i t y A U = c u [ l n I r + 0.577(3A f - 1)3 (19) S p h e r i c a l c a v i t y A U = cu[4/31n I r + 0.667(3A f - 1)] (20) Method 4 Semi e m p i r i c a l Hagerty and Garlanger 1972 C y l i n d r i c a l c a v i t y A U = pj> [ 1 - ( s i n 0 ' / s i n 0 ' ) • Cu/p",) ] (21 ) Method 5 Semi e m p i r i c a l Roy et a l . 1979 4 0 C y l i n d r i c a l c a v i t y A U = (1 - k ) crv'o + Uu/p)ma'p (22) C a l c u l a t e d values f o r the d i f f e r e n t i a l pore p r e s s u r e , ^ M e a s u r e d ~ u S t a f i c > a r e shown f o r the c l a y e y s i l t at the Mcdonald s i t e i n Table I. As can be seen i n the a n a l y t i c a l e x p r e s s i o n s f o r the dynamic pore p r e s s u r e , the models are not s e n s i t i v e to the s e l e c t i o n of a r i g i d i t y index ( s t i f f n e s s r a t i o ) ; they are, however s e n s i t i v e to the s e l e c t i o n of an Undrained shear s t r e n g t h . The undrained shear s t r e n g t h used was c a l c u l a t e d from the measured bearing v a l u e . The e f f e c t of i n c r e a s e d r i g i d i t y index i s mainly to extend the zone of s o i l i n f l u e n c e d by the c a v i t y expansion. F u r t h e r d i s c u s s i o n of the importance of the r i g i d i t y index w i l l be i n c l u d e d i n Chapter 6. A n a l y t i c a l estimates of the dynamic pore pressure can be compared to the f i e l d measured values shown i n F i g u r e 10 . For the purposes of i l l u s t r a t i o n , only the s o l u t i o n s obtained using the e l a s t i c p l a s t i c model are shown i n F i g u r e 10 . The s p h e r i c a l c a v i t y expansion s o l u t i o n compares fa v o u r a b l y with the pore p r e s s u r e s measured immediately behind the cone t i p . The s o l u t i o n f o r the c y l i n d r i c a l expansion compares w e l l with pore p r e s s u r e s measured 25 cm ( 7 . 1 d ) behind the cone t i p . An a b s o l u t e comparison between the r e s u l t s obtained with each model i s complicated by the s e l e c t i o n of input parameters, e s p e c i a l l y the undrained shear s t r e n g t h . The e l a s t i c p e r f e c t l y p l a s t i c model p r e d i c t s v a l u e s very c l o s e to the f i e l d measured 4 1 U (bar) 0 5 10 • • • » 1 • • « » in i_ E a. a LEGEND Hydrostatic pressure conditions Dynamic pore pressure measured with piezometer element immediately behind tip Spherical solution* for dynamic pore pressure Dynamic pore pressure measured with piezometer element 25 cm behind tip Cylindrical solution* for dynamic pore pressure Analytical solutions shown after Torstensson 1977. Assumption for input data derailed in Table I . FIGURE 1 0 COMPARISON BETWEEN ANALYTICAL SOLUTIONS AND MEASURED DYNAMIC PORE PRESSURES. 42 v a l u e s . The e l a s t i c p l a s t i c model with volume hardening p r e d i c t s s l i g h t l y high l i m i t and pore p r e s s u r e s . The semi e m p i r i c a l method o u t l i n e d by Massarch 1978, and Torstensson 1977 i n c l u d e s Skempton's A f pore pressure parameter. The i n c o r p o r a t i o n of an Af v a l u e , which v a r i e s with past l o a d i n g h i s t o r y , i n t o the e x p r e s s i o n f o r dynamic pore pressures i s c o n s i s t e n t with the b e l i e f t h a t the dynamic pore pressure r a t i o U/QC i s a good i n d i c a t o r of the l o a d i n g h i s t o r y of the s o i l . The semi e m p i r i c a l method proposed by Roy et a l . 1979 r e q u i r e s an estimate f o r U/p, best obtained from 'an undrained t r i a x i a l t e s t . As i n the case of models by V e s i c 1972, Massarch 1978, and Torstensson 1977, which i n c o r p o r a t e an Af value, the model by Roy et a l . 1979 attempts to i n c o r p o r a t e the e f f e c t of p r e v i o u s l o a d i n g h i s t o r y . The semi e m p i r i c a l method proposed by Hagerty and Garlanger 1972 tends to u n d e r p r e d i c t the dynamic pore p r e s s u r e s . Use of e i t h e r of the f i r s t three models o u t l i n e d appears to c o n f i r m that the pore p r e s s u r e s at the t i p can best be modelled by s p h e r i c a l c a v i t y expansion, whereas those measured some d i s t a n c e behind the t i p can best be modelled by c y l i n d r i c a l c a v i t y expansion. The d i s t r i b u t i o n of pore pr e s s u r e s p r e d i c t e d by the models can be compared to pore pr e s s u r e s measured during the i n s t a l l a t i o n of p i l e s . F i g u r e 11 shows the d i s t r i b u t i o n of pore p r e s s u r e around d r i v e n p i l e s . Each of the case h i s t o r i e s s e l e c t e d confirms the d i s t r i b u t i o n of pore p r e s s u r e p r e d i c t e d by 43 the a n a l y t i c a l e xpression (egns 2, 5). The excess pore pre s s u r e s shown in F i g u r e 11 a l l appear to decrease with the l o g a r i t h m of the r a d i u s . As p r e v i o u s l y s t a t e d , a knowledge of the i n i t i a l d i s t r i b u t i o n of excess pore p r e s s u r e s i s fundamental to the proper i n t e r p r e t a t i o n of pore pressure decay r a t e s . UJ >-cr -r O * a- UJ cr UJ 10 u ui UJ 0-Ul >-O 4 o- UJ cr Ul i/l O UJ X cr ui &• 2-5n 20 15H to 5H REFERENCE Lo and Stermac 1965 DEPTH (m)1 0-7 cu(bar) 2-25 o c r 1 DIAMETER (m) .09 0 1 20-1 1-5' \0 < a- UJ cr ^ Ul io U UJ x cr Ul 0. Ul >• a u u> § </> w Ul i/i U Ul x a Ul 0. \ \ • \ REFERENCE Koizumi and Ito 1967 DEPTH(m) 5 cu(bar) 3-35 o c r 25 DIAMETER (m) .3 0 25-, 20 15H \0 •5H REFERENCE Ismael and Klym 1979 DEPTH(m) 5 8 cu (bar) 13 OCT — DIAMETER H pile 12x12' 0 25-20-t 15-1 TO 0 REFERENCE ROY et ol 1979 DEPTH(m)6 cu (bar) 2 OCT 23 DIAMETER (m) .22 5 T 10 20 NORMALIZED RADIUS 50 r/R 100 Figure H Excess Pore Pressure Distribution Around Installed Piles: Case Histories 45 Chapter 5 F i e l d Observations of Dynamic Pore Pressure 5.1 I n t r o d u c t i o n T h e o r e t i c a l estimates of the magnitude of the pore pressure generated both at the s u r f a c e of the cone penetrometer and with r a d i a l d i s t a n c e from the cone have been presented i n Chapter 4. In a d d i t i o n , measured values of pore pressure generated d u r i n g f i e l d t e s t s have been compared to the t h e o r e t i c a l l y o b t a i n a b l e v a l u e s . T h i s chapter summarizes r e s u l t s of f i e l d t e s t i n g conducted by both the UBC i n s i t u r e s e a r c h team and o t h e r s , showing the importance of both t e s t i n g procedure and equipment. By changing both the speed of p e n e t r a t i o n and the l o c a t i o n of the porous element, measurements of the dynamic pore pressure at the cone t i p and up the s h a f t were obt a i n e d . Estimates of the r a d i a l e f f e c t i v e s t r e s s were made by u s i n g r e s u l t s of the f r i c t i o n s l e e v e and pore p r e s s u r e measurements. By using the c a l c u l a t e d l e v e l s of r a d i a l e f f e c t i v e s t r e s s and other f i e l d evidence, the p o s s i b i l i t y of h y d r o f r a c t u r e i s d i s c u s s e d . 5.2 F i e l d T e s t s Conducted F i e l d t e s t s were conducted at the Mcdonald s i t e to e v a l u a t e the e f f e c t s of t e s t i n g procedure and equipment. The t e s t s were conducted i n h o l e s spaced 1-2 metres a p a r t . The complete cone log s showing p e n e t r a t i o n r a t e and cone geometry used are i n c l u d e d i n Appendix A. 4 6 During cone p e n e t r a t i o n sounding pore pre s s u r e s are measured at one l o c a t i o n on the cone. C o n s i d e r a b l e debate s t i l l e x i s t s over the optimum l o c a t i o n of the porous f i l t e r (Roy et a l . 1980). A study was conducted i n which s u c c e s s i v e l y longer t i p e x tensions r e p l a c e d the standard cone t i p . T h i s e f f e c t i v e l y moved both the porous element and the f r i c t i o n s l e e v e f u r t h e r up the s h a f t . In a d d i t i o n to v a r y i n g the l o c a t i o n of the porous element, cone p e n e t r a t i o n r a t e s were v a r i e d . In order to optimize the f i e l d t e s t i n g time, most of the comparative data was c o l l e c t e d at a depth of 20.0 metres. T h i s procedure was n e c e s s i t a t e d by the extremely slow p e n e t r a t i o n r a t e used (as low as 0.027 cm/sec). Examples from other s i t e s have a l s o been drawn upon when the.y i l l u s t r a t e s p e c i a l f e a t u r e s . 5.3 E f f e c t of P e n e t r a t i o n Speed P e n e t r a t i o n r a t e a f f e c t s the cone p e n e t r a t i o n process by i n f l u e n c i n g the r a t e of s t r a i n i n g i n the s o i l around the cone. During t h i s study, the r a t e of p e n e t r a t i o n was v a r i e d between 5 cm/sec and 0.027 cm/sec and the r e s u l t a n t t i p , f r i c t i o n , and pore pressure measured si m u l t a n e o u s l y . The pore pressure measurements were found necessary to understand the r e s u l t a n t changes i n both the be a r i n g and f r i c t i o n measurements. The r a t e of p e n e t r a t i o n has been widely accepted at 2 cm/sec; i n s p i t e of t h i s , the e f f e c t of p e n e t r a t i o n r a t e i s important f o r s e v e r a l reasons: 4 7 1) At a p e n e t r a t i o n r a t e of 2 cm/sec, cone p e n e t r a t i o n t e s t i n g can be e i t h e r t o t a l l y undrained, d r a i n e d , or p a r t i a l l y d r a i n e d depending on the s o i l t e s t e d . 2) Use of l a r g e r or smal l e r cone t i p s at the standard r a t e of 2 cm/sec r e s u l t s i n a v a r i a t i o n i n s t r a i n r a t e . 3) Use of cone data f o r p r e d i c t i o n of p i l e performance i n v o l v e s r a t e changes over many ord e r s of magnitude. During cone p e n e t r a t i o n t e s t i n g at 2 cm/sec, experience has shown that some s o i l s ( c l e a n , medium-coarse sands) behave i n a completely d r a i n e d manner. Others such as c l a y e y s o i l s behave i n an e s s e n t i a l l y undrained manner. Mixed s o i l s having g r a i n s i z e d i s t r i b u t i o n midway between these two extremes have p e r m e a b i l i t i e s such that the measured pore p r e s s u r e s are i n f l u e n c e d by both the t i p p e n e t r a t i o n and simultaneous c o n s o l i d a t i o n . An example of each of these s o i l s i s provided at the Mcdonald s i t e . F i g u r e 12 shows r e s u l t s of one t e s t performed at the standard r a t e of 2 cm/sec and others performed at f a s t e r and slower r a t e s . S i l t d e p o s i t s between 0 and 3.0 metres behave e s s e n t i a l l y undrained. Sand d e p o s i t s between 3 and 13 metres behave i n a completely d r a i n e d manner, even at p e n e t r a t i o n r a t e s up to 5 cm/sec. Between 13 and 15 metres, a le n s of f i n e s i l t y sand generates pore p r e s s u r e s , the magnitude of which depends on the r a t e of p e n e t r a t i o n . The c l a y e y s i l t below 15 metres behaves i n an undrained manner when t e s t e d at r a t e s f a s t e r then 0.2 cm/sec (Campanella et a l . 1981). Only at p e n e t r a t i o n r a t e s l e s s than 0.2 cm/sec does p a r t i a l 4 8 UD BAR QC BAR U D / Q C 10 10 20 30 100 I 200 Penetration speed 5 cm/sec Penetration speed 2 cm/sec Penetration speed .04 cm/sec Penetration speed .027 Penetration speed 2 cm/sec Penetration speeds shown .0 _ i _ .5 _L_ 1.0 STANDARD CONE C6FPS-2UBC FIGURE 12 RATE EFFECTS, CLAYEY SILT. RICHMOND, BC 49 c o n s o l i d a t i o n i n f l u e n c e the measures v a l u e s . E x t e n s i v e t e s t i n g of t h i s d e p o s i t i s d i s c u s s e d next. 5.3.1 F i e l d Evidence The e f f e c t of p e n e t r a t i o n r a t e on t i p p e n e t r a t i o n r e s i s t a n c e and pore pressure measurements has been d i s c u s s e d by p r e v i o u s r e s e a r c h e r s . For p e n e t r a t i o n t e s t i n g i n c l a y s o i l s , p u b l i s h e d r e s u l t s showing the e f f e c t of v a r y i n g r a t e are summarized i n Table I I . In each of the cases shown in Table I I , the pore p r e s s u r e s generated w e r e - p o s i t i v e and the m a t e r i a l of low p e r m e a b i l i t y . In s p i t e of t h i s , l i t t l e agreement can be seen. The e x p l a n a t i o n f o r the apparent d i s c r e p a n c y can only be seen i f pore pressure measurements are a v a i l a b l e . I f , when the p e n e t r a t i o n r a t e i s reduced, the t e s t i s s t i l l e s s e n t i a l l y an undrained t e s t , then i t can be expected that a decrease in s t r a i n r a t e c o u l d r e s u l t i n a decrease i n apparent end bearing v a l u e . T h i s c o n c l u s i o n can only be e s t a b l i s h e d i f o b s e r v a t i o n s of the dynamic pore pressure show no decrease i n the pore pressure with decreased r a t e of p e n e t r a t i o n . An example of t h i s i s shown i n F i g u r e 13, which shows l i t t l e change i n bearing or dynamic pore p r e s s u r e between r a t e s of 0.2 cm/sec and 2 cm/sec. I f , however, a decreased r a t e of p e n e t r a t i o n r e s u l t s i n p a r t i a l c o n s o l i d a t i o n and, t h e r e f o r e , lower dynamic pore p r e s s u r e s , then an i n c r e a s e i n b e a r i n g v a l u e s can be expected. 5 0 Reference M a t e r i a l Type Re s u l t of Decreased Rate of P e n e t r a t i o n Roy et a l . 1980 s o f t s i l t y c l a y St-Alban s i t e - b e a ring decreases to a minimum, then i n c r e a s e s -dynamic pore pressure decreases Schmertman 1978 c l a y e y sand k = 10" 5 cm/sec OCR = 2 - b e a r i n g i n c r e a s e s B a l i g h et a l 1978. Janbu and Senneset 1 974 Boston blue c l a y moraine c l a y low p e r m e a b i l i t y - b e a r i n g decreases - b e a r i n g decreases -dynamic pore pressure i n c r e a s e s Casson 1978 s o f t c l a y - b e aring decreases T a b l e n : P u b l i s h e d R e s u l t s Showing the E f f e c t of P e n e t r a t i o n Rate on Bearing and Dynamic Pore P r e s s u r e . 0.4 0.3 0.2 0.1 0 v ' i i i n 11 I u i | | | I I I 11 0.01 0.1 I 10 10 8 6 4 2 Bearing corrected for temperature and water pressure effects I i i i i i 111 i i i i i i II I i l i l l 0.01 0.1 I 10 1 o i — Effective bearing °-c " O - c e " " T O T A L I I I I 1 1 1 1 1 . 1 1 I—I I I 11111 0.01 0.1 I 10 10 8 - 6 - i < S 4 t- [ y_ Equilibrium pore pressure i i i i i i 11 I i 1 1 1 i i i i i i 11 0.01 0.1 I 10 Penetration rate, cm/sec. All measurements at 20m depth FIG.I 3 PENETRATION RATE EFFECTS IN CLAYEY SILT DEPOSIT (McDonalds farm,Sea Island). 52 T h i s i s probably the case when t e s t i n g s o i l s of p e r m e a b i l i t y midway between that of a t o t a l l y undrained c l a y d e p o s i t and a t o t a l l y d r a i n e d sand d e p o s i t . R e s u l t s of measurements taken at 20 metres depth at the Mcdonald s i t e , shown i n F i g u r e 13, i l l u s t r a t e t h i s phenomenon. As p e n e t r a t i o n speed i s decreased below about 0.2 cm/sec, the pore pressure d u r i n g p e n e t r a t i o n decreases. Corresponding i n c r e a s e s i n bearing and f r i c t i o n are shown i n F i g u r e 13. The i n c r e a s e i s e s p e c i a l l y n o t i c e a b l e f o r the f r i c t i o n ; with i t s l o c a t i o n up from the t i p , a d d i t i o n a l time permits g r e a t e r c o n s o l i d a t i o n . The i n c r e a s e i s l e s s n o t i c e a b l e f o r the b e a r i n g , i n p a r t because the bearing i s a measure of both s o i l r e s i s t a n c e and pore water p r e s s u r e . Thus, as the water p r e s s u r e decreases, the bearing tends to decrease, but t h i s i s o f f s e t by the i n c r e a s e i n e f f e c t i v e s t r e s s i n the s o i l , which i n c r e a s e s the b e a r i n g . To i l l u s t r a t e t h i s behavior, the e f f e c t i v e b e a r i n g i s a l s o shown i n F i g u r e 13; the e f f e c t i v e b e a r i n g i s d e f i n e d as the c o r r e c t e d measured bearing l e s s the t o t a l water p r e s s u r e . A much l a r g e r i n c r e a s e i n s o i l r e s i s t a n c e i s e v i d e n t . In s o i l s with pore pressure r a t i o s c l o s e to u n i t y , v a r i a t i o n s i n p e n e t r a t i o n r a t e may r e s u l t i n such sm a l l changes i n the measured b e a r i n g value that they cannot be d e t e c t e d by the b e a r i n g measurement alone . Only simultaneous measurement of pore water pressure and b e a r i n g permits t h i s s e p a r a r t i o n of s o i l and water p r e s s u r e s . 5.4 L o c a t i o n of the Porous Element O p t i m i z i n g the dynamic response of the pore pressure probe 5 3 has been the sub j e c t of s e v e r a l recent papers, i n c l u d i n g Roy et  a l . 1980 and B a l i g h et a l . 1978. P u b l i s h e d r e s u l t s i n d i c a t e that maximum response should be ob t a i n e d when the porous element i s l o c a t e d the the t i p . The l o c a t i o n used f o r t h i s study, however, immediately behind the time has been found (Campanella et a l . 1981; Roy et a l . 1980) to r e c o r d dynamic pore p r e s s u r e s very c l o s e to maximum i n s o f t s o i l s . The area behind the t i p i s a l s o b e t t e r p r o t e c t e d f o r p e n e t r a t i o n through dense a b r a s i v e sands or impact onto bou l d e r s , c o n c r e t i o n s , wood, dense t i l l s , or bedrock. Recognizing that peak performance may be ob t a i n e d when the porous element i s l o c a t e d at the t i p , the porous element l o c a t e d behind the t i p appears to o f f e r a reasonable compromise. I t does appear, however, that l o c a t i o n of the porous element behind the t i p may r e s u l t i n a more d i l a t e n t dynamic pore pressure response (Campanella et a l . 1981). The f i e l d t e s t i n g conducted i l l u s t r a t e s the v a r i a t i o n i n pore p r e s s u r e s up the cone. F i g u r e 14 i n c l u d e s the pore pressure d i s t r i b u t i o n up the cone f o r t e s t s conducted at the standard r a t e of 2 cm/sec at the Mcdonald s i t e . As d i s c u s s e d i n Chapter 4, pore pressure development at the t i p and up the sl e e v e can probably best be modelled by s p h e r i c a l and c y l i n d r i c a l c a v i t y expansions. The r e d u c t i o n i n pore p r e s s u r e s up the cone can be due to two separate reasons: 54 150 40 E u Q_ I— O or u_ ui o 1 30 20 10 PENETRATION RATES 2.00 cm/sec 0.20 cm/sec 0.04 cm/sec RICHMOND CLAYEY SILT DEPTH 20 M 2 3 4 5 PORE PRESSURE (BAR) FIGURE 14 PORE PRESSURE DISTRIBUTION ALONG SHAFT DURING CONE PENETRATION TESTING. VARIABLE PENETRATION RATE. 55 1) changes i n t o t a l s t r e s s , s p h e r i c a l vs c y l i n d r i c a l c a v i t y expansions; or 2) pore pressure d i s s i p a t i o n . For the c l a y e y s i l t t e s t e d , at the standard r a t e of p e n e t r a t i o n , v i r t u a l l y no pore pressure d i s s i p a t i o n can take p l a c e and the decrease i n pore pressure up the s h a f t represents the t r a n s i t i o n from s p h e r i c a l to c y l i n d r i c a l c a v i t y expansion. At slower r a t e s of p e n e t r a t i o n , however, p a r t i a l pore pressure d i s s i p a t i o n was recorded. V a r i a t i o n i n the measured pore pressure f o r t e s t s conducted at d i f f e r e n t p e n e t r a t i o n speeds and with d i f f e r e n t cone t i p s i s shown i n F i g u r e 14. Since the cone geometry i s repeated at d i f f e r e n t p e n e t r a t i o n speeds, the d i f f e r e n c e i n measured pore pr e s s u r e between the t e s t s conducted at d i f f e r e n t r a t e s r e p r e s e n t s a measure of the pore pressure d i s s i p a t i o n . T h i s s u b j e c t i s d i s c u s s e d f u r t h e r i n Chapter 6. R e s u l t s showing the pore pressure d i s t r i b u t i o n up the cone from the t i p at the standard r a t e of p e n e t r a t i o n (Figure 14) r e v e a l an important c o n c l u s i o n r e g a r d i n g the pore water pressure c o r r e c t i o n a p p l i e d to the f r i c t i o n s l e e v e . As e x p l a i n e d i n S e c t i o n 2.3.4, the c o r r e c t i o n a p p l i e d to the f r i c t i o n s leeve reading was n e c e s s i t a t e d by unequal end area of the f r i c t i o n s l e e v e . As e x p l a i n e d i n S e c t i o n 2.3.4, an assumption inherent i n the c o r r e c t i o n i s that the pore pressure used i n the c o r r e c t i o n , measured at the f r o n t of the f r i c t i o n s l e e v e , i s the 5 6 same as the pore pressure at the back of the f r i c t i o n s l e e v e . I n s p e c t i o n of F i g u r e 14 shows that t h i s assumption i s approximate and may need r e v i s i o n . T e s t i n g s o i l s that have g r e a t e r p e r m e a b i l i t y and r e s u l t i n g l a r g e r pore pressure decay between the f r o n t and back of the f r i c t i o n s l e e v e may be g r e a t l y hampered by t h i s problem. An experimental procedure s i m i l a r to the one d e s c r i b e d above but conducted i n such a s o i l may prove u s e f u l . I t must s t i l l be remembered, however, than at unequal d i s t r i b u t i o n of pore p r e s s u r e s up the cone would r e s u l t i n a net l o a d on the f r i c t i o n s leeve having equal end a r e a s . T h i s load may prove f a i r l y l a r g e c o n s i d e r i n g F i g u r e 14, which shows pr e s s u r e s of 6.0 bar on the bottom and only 5.3 bar on the top of the f r i c t i o n s l e e v e . Only the design of cones having minimal and equal end areas prevent t h i s problem. 5.5 E f f e c t of S a t u r a t i o n D e t a i l s of the s a t u r a t i o n procedure used i n t h i s study are i n c l u d e d i n Chapter 1. The design d e t a i l s are d i s c u s s e d i n Campanella and Robertson 1981 and i n Campanella et a l . 1981. Experience has shown that i n order to measure proper dynamic and s t a t i c v a l u e s , complete s a t u r a t i o n must be maintained. As d i s c u s s e d i n Campanella et a l . 1981, g l y c e r i n has been found to work admirably; i t s v i s c o s i t y permits easy s a t u r a t i o n , a l l o w i n g i n v e r s i o n of the cone without the n e c e s s i t y of e n c a p s u l a t i n g the cone i n d e a i r e d water. In a d d i t i o n , g l y c e r i n maintains s a t u r a t i o n when t e s t i n g above the water t a b l e . As d i s c u s s e d i n Campanella et a l . 1981, the design used i n t h i s study was found 5 7 e f f e c t i v e even a f t e r being pushed f o r over 40 metres through unsaturated f i n e sands before encountering the water t a b l e . C o n f i r m a t i o n of the readings below the water t a b l e were obtained from a nearby standpipe piezometer. Response of the dynamic pore p r e s s u r e s appears to be s i g n i f i c a n t l y a f f e c t e d by entrapped a i r w i t h i n the sensing element. T h i s i s p a r t i c u l a r l y t r u e f o r s o f t low p e r m e a b i l i t y s o i l s . An i l l u s t r a t i o n of t h i s e f f e c t i s shown from Campanella et a l . 1981 i n F i g u r e 15. An e a r l i e r model piezometer cone that has a l a r g e sensing element c a v i t y t hat c o u l d not s a t i s f a c t o r i l y be s a t u r a t e d showed that when pushing was stopped d u r i n g p e n e t r a t i o n through a s o f t c l a y , the measured pore pressure continued to r i s e f o r a s h o r t p e r i o d , f o l l o w e d by the expected decrease due to pore p r e s s u r e d i s s i p a t i o n . When us i n g the more r e c e n t l y designed piezometer cone i n the same d e p o s i t , however, the continued i n c r e a s e i n measured pore pressure was not observed f o l l o w i n g a stop i n p e n e t r a t i o n . I t was concluded that the c o n t i n u e d i n c r e a s e i n measured pore p r e s s u r e observed i n the e a r l i e r model was due to time e f f e c t s due to water flow caused by some entrapped a i r w i t h i n the element. I t should a l s o be noted t h a t the dynamic pore pressure measured with the unsaturated piezometer i s s i g n i f i c a n t l y l e s s than the pore pressure measured by the s a t u r a t e d piezometer. S i m i l a r r e s u l t s are shown by B a t t a g l i o et a l . 1981, who found that with c a r e f u l s a t u r a t i o n procedure, they c o u l d minimize response d e l a y s . BURNABY SITE -VERY SOFT SILTY CLAY q c « 4kPa , k =IO"7cm/sec a) PIEZOMETER E L E M E N T Time (minutes) 90 r 80 h Penetrotion stopped ot 17.7m b) S A T U R A T E D PIEZOMETER E L E M E N T 70 60 Penetrotion from 16.7m to 17.7m Equilibrium pore pressure 20m 50 1 1 I 2 3 Time (minutes) FIG. 1 5 INFLUENCE OF SATURATION ON PORE PRESSURE RESPONSE OF PIEZOMETER CONE. 5 9 E a r l y piezometer cone r e s u l t s p u b l i s h e d by Janbu and Senneset 1974 and by Schmertmann 1974 i n d i c a t e l a r g e i n c r e a s e s in pore pressure before the s t a r t of pore pressure decay s i m i l a r to r e s u l t s shown i n F i g u r e 15. E x p l a n a t i o n s f o r t h i s response i n c l u d e : 1) Mandel Cryer e f f e c t , proposed by Tumay et a l . 1981; and 2) a zone of pore p r e s s u r e s adjacent to the cone that have sm a l l e r magnitude than pore p r e s s u r e s at some d i s t a n c e from the t i p . Only with c a r e f u l s a t u r a t i o n can i t be ensured that t h i s kind of response i s not the r e s u l t of poor s a t u r a t i o n procedure. 5.6 E f f e c t of Pore Pressure D i s s i p a t i o n During normal cone p e n e t r a t i o n l o g g i n g p a r t i a l or complete pore p r e s s u r e , d i s s i p a t i o n may take p l a c e at rod changes to e v a l u a t e c o n s o l i d a t i o n c h a r a c t e r i s t i c s , or to e v a l u a t e e q u i l i b r i u m pore p r e s s u r e v a l u e s . Upon the resumption of p e n e t r a t i o n , some displacement i s necessary i n order to generate e q u i l i b r i u m dynamic pore p r e s s u r e s . During t h i s i n t e r v a l , the measured b e a r i n g and f r i c t i o n parameters are a f u n c t i o n of the surrounding pore p r e s s u r e s , which may be e i t h e r higher or lower than the steady s t a t e p e n e t r a t i o n pore p r e s s u r e s . Care must be taken i n order to account f o r t h i s e f f e c t , e s p e c i a l l y i n s o f t s o i l s , which generate l a r g e pore p r e s s u r e s . An example of t h i s 6 0 e f f e c t i s shown in F i g u r e 16. Rod changes conducted on metre i n t e r v a l s and a d i s s i p a t i o n conducted at 20.0 metres r e s u l t i n p a r t i a l pore pressure d i s s i p a t i o n . On the resumption of p e n e t r a t i o n , some displacement i s recorded before pore p r e s s u r e s b u i l d to t h e i r steady p e n e t r a t i o n l e v e l s . T h i s does not appear to be the r e s u l t of a response l a g of the measuring system, as evidenced by the i n c r e a s e d f r i c t i o n and b e a r i n g v a l u e s . The i n c r e a s e i n f r i c t i o n i s due to the i n c r e a s e d s t r e s s e s caused by pore pressure d i s s i p a t i o n , as d i s c u s s e d i n S e c t i o n 5.3.1. In a d d i t i o n , g r e a t e r displacement i s necessary i n order to a t t a i n p r e v i o u s f r i c t i o n l e v e l s , because of the l o c a t i o n of the f r i c t i o n s l e e v e , which must f i r s t pass through s o i l having a l r e a d y undergone p a r t i a l c o n s o l i d a t i o n . The e f f e c t of p a r t i a l pore p r e s s u r e d i s s i p a t i o n s , as shown in F i g u r e 16, was recorded while p e n e t r a t i n g through r e l a t i v e l y impermeable (k = 10 7 cm/sec) c l a y e y s i l t . The e f f e c t of d i s s i p a t i o n s at rod breaks may be more pronounced when t e s t i n g s o i l s of higher p e r m e a b i l i t y . In some s o i l s , i t may even be the case that i t takes the e n t i r e next metre to f u l l y recover the dynamic pore p r e s s u r e s . 5.7 H y d r o f r a c t u r e : F i e l d Evidence The p o s s i b i l i t y of h y d r o f r a c t u r e must be addressed when a s s e s s i n g e i t h e r the magnitude of dynamic pore pre s s u r e s generated dur i n g cone p e n e t r a t i o n t e s t i n g , or the use of pore pressure d i s s i p a t i o n s f o r the p r e d i c t i o n of c o n s o l i d a t i o n c h a r a c t e r i s t i c s . Two types of f i e l d evidence suggest that 61 PORE PRESSURE FRICTION RESISTANCE BEARING RESISTANCE . U (BAR) FC (BAR) QC (BAR) 0 10 0 0.5 0 5 1 0 —»DEPTH OF DISSIPATIONS FIGURE 1 6 EFFECT OF PORE PRESSURE DISSIPATIONS DURING CONE PENETRATION TESTING IN CLAYEY SILT. RICHMOND, B.C. 6 2 h y d r o f r a c t u r e d i d not occur i n the s o i l s t e s t e d d u r i n g t h i s study. An estimate of the r a d i a l e f f e c t i v e s t r e s s c a l c u l a t e d from f r i c t i o n s leeve v a l u e s and pore pressure measurements suggests t h a t the r a d i a l e f f e c t i v e s t r e s s i s p o s i t i v e . A d d i t i o n a l evidence i s p r o v i d e d by the measurement of pore pressure decay and comparing measured valu e s to the expected response that would r e s u l t from h y d r o f r a c t u r e . 5.7.1 R a d i a l E f f e c t i v e S t r e s s e s During Cone P e n e t r a t i o n T e s t i n g An e f f e c t i v e s t r e s s approach to cone p e n e t r a t i o n t e s t i n g remains a h i g h l y d e s i r e d g o a l . Present t h e o r i e s of cone p e n e t r a t i o n t e s t i n g have r e s t r i c t e d themselves to t o t a l s t r e s s approaches f o r s e v e r a l reasons, i n c l u d i n g : 1) inadequate t h e o r e t i c a l a n a l y s i s f o r the h i g h l y complex d i s t r i b u t i o n of s t r e s s e s and pore p r e s s u r e s around the cone; and 2) p r e v i o u s i n a b i l i t y to measure pore p r e s s u r e . Although an e f f e c t i v e s t r e s s i n t e r p r e t a t i o n of bearing and f r i c t i o n measurements i s beyond the scope of t h i s paper, the a d d i t i o n of the pore pressure element does permit an estimate of the r a d i a l e f f e c t i v e s t r e s s e s . The cone p e n e t r a t i o n t e s t i n g conducted at the Mcdonald s i t e , Richmond B.C., i n c l u d e d v a r i a t i o n i n both p e n e t r a t i o n speed and i n the l o c a t i o n of the porous element and f r i c t i o n 63 s l e e v e . V a r i a t i o n i n pore pressures due to p a r t i a l c o n s o l i d a t i o n has al r e a d y been d i s c u s s e d . For the m a t e r i a l t e s t e d , c l a y e y s i l t , p e n e t r a t i o n r a t e s slower than about 0.2 cm/sec r e s u l t i n p a r t i a l c o n s o l i d a t i o n . An e f f e c t i v e s t r e s s approach remains h i g h l y d e s i r a b l e i n m a t e r i a l t h a t , when t e s t e d at standard p e n e t r a t i o n r a t e s , behave i n a p a r t i a l l y d r a i n e d manner. The v a r i a t i o n i n pore p r e s s u r e s and f r i c t i o n with d i f f e r e n t t i p e x t e n s i o n s and p e n e t r a t i o n speeds i s show p l o t t e d in Fi g u r e 17. Since the l o c a t i o n of the f r i c t i o n s l e e v e does not correspond to the exact l o c a t i o n of the porous element, some judgement must be made to estimate the pore pre s s u r e s c o r r e s p o n d i n g to the c e n t r e of f r i c t i o n s l e e v e . Some judgement i s a l s o necessary to e x t r a p o l a t e measured pore pressures i n order to o b t a i n an estimate of the pore pressure at the ce n t r e of the f r i c t i o n s leeve behind the 38.0 cm t i p e x t e n s i o n . If an estimate i s made of the e f f e c t i v e angle of f r i c t i o n between the s o i l and the s t e e l f r i c t i o n s l e e v e , then the e f f e c t i v e r a d i a l s t r e s s can be c a l c u l a t e d from: o r ' = FC/tan h ' where S' = M0' M = c o e f f i c i e n t to account f o r the s u r f a c e roughness of the s t e e l f r i c t i o n s l e e v e 0' = angle of f r i c t i o n of the s o i l T h i s assumes that t h e . m a t e r i a l can be modelled with a cohesion 64 PENETRATION RATES 2.00 cm/sec 0.20 cm/sec 0.04 cm/sec p 0.1 0,2 0-3 0 4 0.5 0-6 0-7 j I 1 1 1 1 1 1 FRICTION (BAR) 7 PORE PRESSURE (BAR) FIGURE 17 PORE PRESSURE AND FRICTION DISTRIBUTION ALONG SHAFT DURING CONE PENETRATION TESTING. VARIABLE PENETRATION RATE. i n t e r c e p t of zero; i n a d d i t i o n , the estimate of the value f o r the angle of f r i c t i o n between the s o i l and the f r i c t i o n sleeve i s c o m p l i cated by not knowing e i t h e r the e f f e c t i v e angle of f r i c t i o n of the s o i l or the i n t e r a c t i o n between the f r i c t i o n s l e e v e and the s o i l . An estimate of the f r i c t i o n angle should probably account f o r the l a r g e s t r a i n s a s s o c i a t e d with cone p e n e t r a t i o n t e s t i n g . Schmertmann 1978 estimates the undrained shear s t r e n g t h from the f r i c t i o n s l e e v e midway between CU peak and CU r e s i d u a l . An e f f e c t i v e s t r e s s i n t e r p r e t a t i o n should account f o r a s i m i l a r r e d u c t i o n i n 0 ' . For the purposes of i l l u s t r a t i o n , an angle of f r i c t i o n 8' between the s o i l and the s t e e l f r i c t i o n sleeve has been assumed to be 10 degrees. Using t h i s v a l u e , the e f f e c t i v e r a d i a l s t r e s s has been c a l c u l a t e d and i s shown i n F i g u r e 18. S t r e s s e s may vary with l o c a t i o n up the s h a f t due to the complex t r a n s i t i o n from s p h e r i c a l to c y l i n d r i c a l c a v i t y expansion. For each l o c a t i o n of the f r i c t i o n s l e e v e , however, the l e v e l to t o t a l s t r e s s should be independent of the p e n e t r a t i o n speed, s i n c e the p a r t i a l d i s s i p a t i o n of pore p r e s s u r e s should r e s u l t i n i n c r e a s e d f r i c t i o n s l e e v e readings. An i n d i c a t i o n of the v a l i d i t y of the estimate of the angle of f r i c t i o n between the p o l i s h e d s t e e l and the s o i l can be made by comparing the c a l c u l a t e d t o t a l s t r e s s at each l o c a t i o n up the s h a f t . The c a l c u l a t e d t o t a l s t r e s s e s shown i n F i g u r e 18 correspond reasonably w e l l , c o n s i d e r i n g the p o s s i b l e v a r i a t i o n r e s u l t i n g from n a t u r a l s o i l v a r i a b i l i t y . Although the c a l c u l a t e d v a l u e s of e f f e c t i v e r a d i a l s t r e s s 66 PENETRATION RATES 2.00 cm/sec 0.20 cm/sec 0.04 cm/sec Or PORE PRESSURE 0> 7 PORE PRESSURE AND STRESS (BAR) FIGURE 18 ESTIMATED RADIAL STRESSES AND DYNAMIC PORE PRESSURE. VARIABLE PENETRATION RATE. <rr'= F c / t a n M tf' M 0 • I 0 ° 67 are p o s i t i v e , they are s t i l l much smal l e r than the e f f e c t i v e s t r e s s l e v e l s before p e n e t r a t i o n . In a d d i t i o n , the r a d i a l s t r e s s probably corresponds to the maximum p r i n c i p a l s t r e s s d i r e c t i o n . An estimate of the v e r t i c a l or c i r c u m f e r e n t i a l e f f e c t i v e s t r e s s e s are not, however, p o s s i b l e from the f r i c t i o n s l e e v e r e a d i n g s . 5.7.2 Pore Pressure Response and H y d r o f r a c t u r e The h y d r a u l i c f r a c t u r i n g technique has been used i n both s o i l and rock to eva l u a t e the l e v e l of s t r e s s along the minimum p r i n c i p a l s t r e s s plane . During t h i s technique, i n c r e a s i n g water pressure i s a p p l i e d to an i s o l a t e d s e c t i o n of a borehole u n t i l f r a c t u r e occurs and the r a t e of in f l o w i n c r e a s e s d r a m a t i c a l l y . The a p p l i e d pressure i s then g r a d u a l l y reduced, and when the r a t e of water i n f l o w drops s i g n i f i c a n t l y , the c l o s u r e p r e s s u r e i s recorded. The c l o s u r e pressure i s used to estimate the minor p r i n c i p a l s t r e s s ( M i t c h e l l et a l 1978). I f , when h y d r a u l i c f r a c t u r e occurs i n s o i l s d u r i n g cone p e n e t r a t i o n t e s t i n g , i t may be expected, by analogy with the h y d r a u l i c f r a c t u r e technique, that the r a t e of pore pressure decay should be r a p i d u n t i l any r e s u l t i n g f r a c t u r e c l o s e s . No occurrence of t h i s phenomenon was recorded d u r i n g f i e l d i n v e s t i g a t i o n . A d d i t i o n a l evidence that h y d r a u l i c f r a c t u r e does not occur i s p r o v i d e d by comparing r e s u l t s of a n a l y s i s f o r the p r e d i c t i o n of c o n s o l i d a t i o n c h a r a c t e r i s t i c s from pore pressure d i s s i p a t i o n s . Although not shown here, pore pressure d i s s i p a t i o n r a t e s observed i n adjacent holes that were conducted 6 8 with d i f f e r e n t p e n e t r a t i o n speeds and r e s u l t i n g d i f f e r e n t i n i t i a l pore p r e s s u r e s p r e d i c t e d s i m i l a r c o n s o l i d a t i o n c h a r a c t e r i s t i c s . I f h y d r a u l i c f r a c t u r e was to have occurred, i t should only have happened i n the probe hole that generated the g r e a t e s t dynamic pore p r e s s u r e (no higher value c o u l d be a c h i e v e d ) ; the r e s u l t i n g pore pressure d i s s i p a t i o n r a t e s should have been d i f f e r e n t , with one c o n t r o l l e d by the f r a c t u r e s , the other by the c o n s o l i d a t i o n c h a r a c t e r i s t i c s of the s o i l . 69 Chapter 6 C o n s o l i d a t i o n C h a r a c t e r i s t i c s from Pore Pressure D i s s i p a t i o n a f t e r Piezometer Cone P e n e t r a t i o n 6.1 I n t r o d u c t i o n During cone p e n e t r a t i o n t e s t i n g in cohesive s o i l s , high excess p o s i t i v e pore p r e s s u r e s have been observed around the cone. The magnitude and d i s t r i b u t i o n of these pore p r e s s u r e s was d i s c u s s e d in Chapter 4; the use of pore pressures i n s t r a t i g r a p h i c l o g g i n g was d i s c u s s e d i n Chapter 3. The development of p o s i t i v e pore p r e s s u r e reduces the e f f e c t i v e s t r e s s and has long been known to ease the i n s t a l l a t i o n of p i l e s through c l a y s o i l s . D i s s i p a t i o n of excess pore p r e s s u r e s has, i n a few i n s t a n c e s , been documented and compared to the i n c r e a s e in load c a r r y i n g c a p a c i t y of p i l e s (Hagerty and Garlanger 1972). The parameter governing the c o n s o l i d a t i o n process around e i t h e r a cone penetrometer or a d r i v e n p i l e i s the c o e f f i c i e n t of c o n s o l i d a t i o n . T h i s chapter i l l u s t r a t e s the dependency of the r a t e of pore pressure d i s s i p a t i o n on the c o e f f i c i e n t of c o n s o l i d a t i o n and attempts to make use of t h i s f a c t by using pore pressure d i s s i p a t i o n records from two d i f f e r e n t s i t e s to o b t a i n c o n s o l i d a t i o n c h a r a c t e r i s t i c s f o r the s o i l s . Laboratory t e s t s conducted on samples obtained from the s i t e s w i l l be used f o r comparison. D e t a i l s concerning the l a b o r a t o r y t e s t procedure are o u t l i n e d i n S e c t i o n 6.6. A d d i t i o n a l d i s c u s s i o n of the 7 0 procedure used d u r i n g d i s s i p a t i o n s i s i n c l u d e d i n S e c t i o n 6.9. 6.2 C o n s o l i d a t i o n Process a f t e r P e n e t r a t i o n Before attempting to use the r e s u l t s of a v a i l a b l e t h e o r i e s of excess pore pressure d i s s i p a t i o n , i t i s important to understand the process that takes p l a c e when p e n e t r a t i o n i s stopped. P e n e t r a t i o n t e s t i n g induces l a r g e s t r a i n s on the s o i l i n the immediate area of the cone, i n d u c i n g some degree of remolding of the s o i l ; the exact nature of the remolding depends on the s o i l type and l o c a t i o n r e l a t i v e to the cone. An estimate of the degree of remolding that takes p l a c e around the cone was made by Schmertmann 1978, who estimates the undrained shear s t r e n g t h obtained from f r i c t i o n s l eeve readings t o be midway between the undrained shear s t r e n g t h and the remolded shear s t r e n g t h . As w e l l as p a r t i a l l y remolding the s o i l , the massive c a v i t y expansion produced by the cone generates l a r g e pore pressures i n cohesive s o i l s . These h i g h pore pressure reduce the l e v e l of e f f e c t i v e s t r e s s i n the s o i l surrounding the cone. An estimate of the e f f e c t i v e r a d i a l s t r e s s was made i n Chapter 5. The estimate was made by assuming the m a t e r i a l behaved as a granula r m a t e r i a l with an angle of f r i c t i o n between the s o i l and the f r i c t i o n s l eeve of 10 degrees. By b a c k c a l c u l a t i n g what e f f e c t i v e r a d i a l s t r e s s e s would be necessary to obt a i n the measured f r i c t i o n s l e e v e readings, the l e v e l of r a d i a l s t r e s s e s 7 1 was shown to be approximately 1/4 of the o r i g i n a l v e r t i c a l e f f e c t i v e str,ess; at the same time, the measured pore pressures were approximately 3 times the o r i g i n a l v e r t i c a l e f f e c t i v e s t r e s s . Upon a r r e s t of p e n e t r a t i o n , these pore p r e s s u r e s d i s s i p a t e , and the e f f e c t i v e s t r e s s around the cone i n c r e a s e s . T h i s i m p l i e s that the c o n s o l i d a t i o n process occurs with the s o i l i n an o v e r c o n s o l i d a t e d s t a t e , at l e a s t during e a r l y stages of d i s s i p a t i o n . The changes i n excess pore p r e s s u r e that take p l a c e a f t e r d r i v i n g are shown i n F i g u r e 19 i n a nondimensionalized form using the a n a l y t i c a l s o l u t i o n of Randolph and Wroth 1979. D i s s i p a t i o n of the excess pore pressure must occur away from the cone, s i n c e the cone i t s e l f i s a r i g i d , impermeable boundary. I t i s g e n e r a l l y accepted that f o r the porous stone l o c a t e d some d i s t a n c e above the t i p , say 10 x r a d i u s , only r a d i a l drainage can take p l a c e . These are the c o n d i t i o n s that take p l a c e around the pressuremeter (at l e a s t those with s u f f i c i e n t l y l a r g e l e n g t h / diameter r a t i o s ) and f o r the s h a f t p o r t i o n of d r i v e n p i l e s . With the usual l o c a t i o n of the porous element, at or near the t i p , some debate e x i s t s over the i n f l u e n c e of p o s s i b l e v e r t i c a l d rainage. B a l i g h and Levadoux 1980 conducted s e n s i t i v i t y a n a l y s i s u sing t h i s two-dimensional f i n i t e element a n a l y s i s and concluded t h a t , f o r an i s o t r o p i c s o i l , d i s s i p a t i o n i s only s l i g h t l y f a s t e r around a s p h e r i c a l c a v i t y than a c y l i n d r i c a l c a v i t y . As with so many a s p e c t s of i n t e r p r e t a t i o n of i n s i t u t e s t r e s u l t s , the r e l a t i v e importance 72 F i g u r e 19. E x c e s s P o r e P r e s s u r e D i s t r i b u t i o n A round a C y l i n d r i c a l C a v i t y w i t h T i m e . A d a p t e d f r o m R a n d o l p h and W r o t h , 1979 . 7 3 of v e r t i c a l drainage i s probably dependent on the r e l a t i v e v e r t i c a l and h o r i z o n t a l c o n s o l i d a t i o n c h a r a c t e r i s t c s . Torstensson 1977 o f f e r s s o l u t i o n s to both c y l i n d r i c a l and s p h e r i c a l d i s s i p a t i o n s , but i t i s not c l e a r which a n a l y s i s i s most a p p r o p r i a t e . In an attempt to gain some i n s i g h t i n t o the importance of the v e r t i c a l component of c o n s o l i d a t i o n , a s e r i e s of f i e l d t e s t s was conducted at the Mcdonald s i t e . By conducting d i s s i p a t i o n s at the same depth in holes spaced 1 - 2 metres a p a r t , but with d i f f e r e n t cone t i p s that e f f e c t i v e l y moved the porous f i l t e r element up the s h a f t from the t i p , the importance of the v e r t i c a l component can be shown. A short d e s c r i p t i o n of the cone and e x t e n s i o n t i p s i s i n c l u d e d i n Chapter 2. F i g u r e 20 shows the d i s s i p a t i o n of excess pore pr e s s u r e s f o r three of the cone t i p s used. The r a t e of d i s s i p a t i o n of excess pore p r e s s u r e s f o r the standard cone i s only s l i g h t l y g r e a t e r than fo r the cone with e i t h e r a 12.5 or 25 cm long t i p e x t e n t i o n . I t can be concluded t h a t , at l e a s t f o r the s o i l t e s t e d , h o r i z o n t a l drainage dominates the c o n s o l i d a t i o n process, and, t h e r e f o r e , i t i s the c o e f f i c i e n t of c o n s o l i d a t i o n i n the h o r i z o n t a l d i r e c t i o n that the r e c o r d r e f l e c t s . Only i n the u n l i k e l y case where the v e r t i c a l p e r m e a b i l i t y i s g r e a t e r than the h o r i z o n t a l p e r m e a b i l i t y would the v e r t i c a l component become very important. 6.3 S o l u t i o n s A v a i l a b l e f o r O b t a i n i n g C o n s o l i d a t i o n C h a r a c t e r i s t i c s S e v e r a l s o l u t i o n s are a v a i l a b l e f o r a n a l y s i s of d i s s i p a t i o n TIME (minutes) F I G U R E 2 0 INFLUENCE OF POROUS STONE LOCATION ON PORE P R E S S U R E DISSIPATION 7 5 r e c o r d s . These s o l u t i o n s are shown i n Table I I I , which h i g h l i g h t s the major d i f f e r e n c e s between the s o l u t i o n s . In order to compare r e s u l t s of the d i f f e r e n t s o l u t i o n s , they have a l l been nondimensionalized i n the same manner and shown i n F i g u r e 21. F i g u r e 21 shows the decay of excess pore pressure, u, p l o t t e d a g a i n s t a nondimensional time f a c t o r , T = c t / r 2 . Use of the time f a c t o r , T, a l l o w s a quick c a l c u l a t i o n f o r the c o e f f i c i e n t of c o n s o l i d a t i o n , c. Examination of F i g u r e 21 r e v e a l s important p o i n t s . The s o l u t i o n by B a l i g h and Levadoux 1980 and the c y l i n d r i c a l s o l u t i o n by Torstensson 1977 y i e l d e s s e n t i a l l y the same r e s u l t . The s o l u t i o n by Randolph and Wroth 1979 i s not shown because of i t s s i m i l a r i t y to t h a t of Torstensson 1977. The s o l u t i o n by Randolph and Wroth and the c y l i n d r i c a l s o l u t i o n by T o r s t e n s s o n were s o l v e d a f t e r making the same assumption regarding the i n i t i a l pore pressure d i s t r i b u t i o n . The c o n s o l i d a t i o n a n a l y s i s , however, was t r e a t e d s l i g h t l y d i f f e r e n t l y . Randolph and Wroth used an a n a l y t i c a l s o l u t i o n , whereas Torstensson used a f i n i t e d i f f e r e n c e approach. The s o l u t i o n by B a l i g h and Levadoux was s o l v e d i n q u i t e a d i f f e r e n t manner. Although B a l i g h and Levadoux used a s l i g h t v a r i a t i o n to the l o g normal d i s t r i b u t i o n of excess pore p r e s s u r e , they concluded that there was l i t t l e d i f f e r e n c e i n the p r e d i c t e d time f a c t o r , T. The major d i f f e r e n c e between B a l i g h and Levadoux's s o l u t i o n and the other s o l u t i o n s i s that B a l i g h and Levadoux conducted a two-dimensional a n a l y s i s and, thus, in a d d i t i o n to r a d i a l drainage, i n c l u d e d a v e r t i c a l component. As Table i l l Summary of Existing Solutions for Pore Pressure Dissipations Author Cavity Type Material Model Ini t i a l Pore Pressure Distribution Proposed Applications Remarks Baligh & Levadoux 1980 combined radial and spherical non-linear Boston Blue clay from F.E. studies using strain path method consoli dati on characteristics shows very small influence of spherical component of dissipation Randolph & Wroth 1979 cylindrical elastic-plastic Au. = 2 cu lnl—1 i r R t, -.1/2 - = (G/cuJ o consoli dati on around piles pressuremeter analysis analytical solution Soderberg 1962 cylindrical elastic-plastic u r. r l U i = r consolidation around piles Torstensson 1977 cylindrical elastic-plastic Au, = 2 cu Inf—1 i r O consolidation characteristics proposes average Torstensson 1977 spherical elastic-plastic Au. = 4 cu Inf—1 1 v r ' — = 1G/cu 1 / r v ' 0 consolidation characteristics vertical drains of two results c a coefficient of consolidation t a time r » radius of cavity ' I I I I I i • I I I I I I I • • I I i | | | | 111 • 1 • i » » n l 01 .1 1 10 100 T « c t / r 2 FIGURE 2 1 TIME FACTORS FOR PREDICTING THE COEFFICIENT OF CONSOLIDATION 78 p r e v i o u s l y s t a t e d , a d d i t i o n of t h i s r a d i a l component does not seem to have changed the time f a c t o r , T, a p p r e c i a b l y . In c o n t r a s t , Torstensson 1977 shows remarkably d i f f e r e n t s o l u t i o n s f o r the s p h e r i c a l and c y l i n d r i c a l s o l u t i o n s . The time f a c t o r , T, at any d i f f e r e n t l e v e l of d i s s i p a t i o n i s about 5 times g r e a t e r f o r the c y l i n d r i c a l s o l u t i o n . A p a r t i a l e x p l a n a t i o n f o r the apparent discrepancy i n the r e l a t i v e importance of i n c l u d i n g some component of v e r t i c a l drainage a r i s e s because, as w e l l as u s i n g a d i f f e r e n t geometric p a t t e r n fo r d i s s i p a t i o n , Torstensson determines the i n i t i a l excess pore pressure d i s t r i b u t i o n i n a d i f f e r e n t manner. For the s p h e r i c a l case, he uses a s p h e r i c a l c a v i t y expansion, whereas f o r the c y l i n d r i c a l case, he uses a c y l i n d r i c a l expansion. The two cases r e s u l t i n a much d i f f e r e n t d i s t r i b u t i o n of i n i t i a l excess pore p r e s s u r e s . The c y l i n d r i c a l s o l u t i o n r e s u l t s i n a much la r g e r . z o n e of i n c r e a s e d pore p r e s s u r e s (see equations i n Table I I I ) . Soderberg 1962 uses a d i s t r i b u t i o n of excess pore pressure that decays with the i n v e r s e of the r a d i u s . The s o l u t i o n s by Randolph and Wroth and by Torstensson r e q u i r e an estimate of the s o i l s t i f f n e s s r a t i o . The reason f o r t h i s i s that a s t i f f s o i l w i l l extend a zone of i n f l u e n c e much l a r g e r than a s o f t s o i l . The r e s u l t of a l a r g e r zone of i n f l u e n c e i s to decrease the rate of decay of excess pore p r e s s u r e s at the cone. 79 6.4 Data Reduction F i e l d records of pore pressure d i s s i p a t i o n , recorded as a f u n c t i o n of time, need to be c o r r e c t e d by s u b t r a c t i n g the ambient s t a t i c pore pressure from the measured excess v a l u e s . The excess pore p r e s s u r e s are nondimensionalized by d i v i d i n g by the i n i t i a l excess pore pres s u r e , then p l o t t e d a g a i n s t time. Data f o r the two s i t e s i n v e s t i g a t e d i n t h i s paper are shown in F i g u r e 22. In t h i s manner, the c o e f f i c i e n t of c o n s o l i d a t i o n can be c a l c u l a t e d at any d i s s i p a t i o n l e v e l by using the measured time and t h e o r e t i c a l value of the time f a c t o r , T. Thus, f o r any of the f i v e e x i s t i n g s o l u t i o n : c = T r 2 / t where t = time T = time f a c t o r r = r a d i u s of probe c = c o e f f i c i e n t of c o n s o l i d a t i o n 6.5 Comparison of E x i s t i n g S o l u t i o n s For any t h e o r e t i c a l s o l u t i o n of pore pressure d i s s i p a t i o n to be regarded as u s e f u l , i t must s a t i s f y s e v e r a l c r i t e r i a : 1) be r e p e a t a b l e ; 2) p r e d i c t the same c o e f f i c i e n t of c o n s o l i d a t i o n at a l l l e v e l s of c o n s o l i d a t i o n ; and 3) compare w e l l to r e f e r e n c e v a l u e s . 1 .9 .8 .7 % -6 \ 5 .5 < " A |3 .3 .2 .1 .01 BURNABY SITE 15.5 m — soft silty clay McDONALD SITE 25.5 m-clayey silt McDONALD SITE 20 5 m clayey si l t J I I I I III I 1 ' * * i i 1 1 1 i i i i i i 1 1 1 • 1 J-ULL .1 1 TIME (minutes) 10 100 F I G U R E 2 2 P O R E P R E S S U R E DISSIPATIONS AT M c D O N A L D AND B U R N A B Y S I T E S CD O 8 1 Repeated t e s t s done at the same depth i n adjacent holes c o n f i r m the r e p e a t a b i l i t y of the t e s t . 6.6 Laboratory T e s t s Performed Comparison between c o n s o l i d a t i o n parameters p r e d i c t e d from pore pressure d i s s i p a t i o n to those obtained from constant rate of s t r a i n c o n s o l i d a t i o n t e s t s i s i n c l u d e d i n t h i s chapter for the Burnaby c l a y s i t e and the Mcdonald s i t e . Two stages of sampling were undertaken f o r the Mcdonald s i t e . P r e l i m i n a r y sampling was performed with a 54 mm Swedish STI f i x e d p i s t o n sampler. At a subsequent date, l a r g e r 3.5 inch diameter Shelby tube samples were obtained. C o n s o l i d a t i o n t e s t s were performed as f o l l o w s : Sample Depth Sample Diameter Test Performed 25.5 m 50 mm v e r t i c a l compression remolded t e s t 20.5 m 76.2 mm v e r t i c a l compression h o r i z o n t a l compression Use of the l a r g e r diameter samples permitted v e r t i c a l trimming of the sample to o b t a i n h o r i z o n t a l c o n s o l i d a t i o n c h a r a c t e r i s t i c s . A l l samples were 2.54 cm t h i c k . Sampling was done at the Burnaby s i t e u s ing the 54 mm Swedish f i x e d p i s t o n sampler o n l y . C o n s o l i d a t i o n t e s t s were performed on a sample obtained from a depth of 15.5 m. An 82 undi s t u r b e d v e r t i c a l compression t e s t was performed; use of the smaller 50 mm diameter sample d i d not permit t e s t s f o r the h o r i z o n t a l compression c h a r a c t e r i s t i c s . 6.6.1 T e s t i n g Procedure Constant r a t e of s t r a i n c o n s o l i d a t i o n t e s t s were performed using the standard technique ( d e s c r i b e d by Wissa et a l 1971). Load and pore pressure were c o n t i n u o u s l y measured; p e r i o d i c measurements of displacement confirmed the r a t e of displacement. A f t e r some t r i a l , displacement r a t e s r e s u l t i n g i n 5-10% excess pore pressure found were: Richmond c l a y e y s i l t : 0.0030 cm/min Burnaby c l a y : 0.00061 cm/min 6.6.2 R e s u l t s : Burnaby S i t e R e s u l t s of c o n s o l i d a t i o n t e s t s f o r the h i g h l y compressible c l a y from the Burnaby s i t e are shown i n F i g u r e s 23, 24, and 25. As p r e v i o u s l y s t a t e d , the small diameter of the samples (50 mm) per m i t t e d t e s t s f o r v e r t i c a l c o n s o l i d a t i o n c h a r a c t e r i s t i c s o n l y . The extreme c o m p r e s s i b i l i t y of the sample can be seen i n F i g u r e 23. From F i g u r e 23, the p r e c o n s o l i d a t i o n pressure was estimated at 35 kPa. Although some evidence of high pore p r e s s u r e s was observed at the s i t e , the e x p l a n a t i o n f o r the seemingly low p r e c o n s o l i d a t i o n pressure f o r a sample c o l l e c t e d at 15.5 metres i s that the o v e r l y i n g sediments c o n s i s t of 2 . 2 1 — i — i — r — F T i i i 1 1 1—| 1 1 M 2 . 1 o' v o = 35 k Pa SAMPLE DEPTH 15.5 m 2 . 0 UNDISTURBED SAMPLE VERTICAL COMPRESSION 1-< cr 1.8 -Q §1.7 1.6 1.5 1 A -• i i 1 i J l J _ l I t i l l 1 _L_L_ 10 t o o VERTICAL EFFECTIVE STRESS ( kPa) FIG. 2 3 COMPRESSIBILITY OF BURNABY CLAY CRSC TEST 1 0 0 0 CD 0 . 8 8 o i 1—| i i i i | 1 1 1—| i i i i SAMPLE DEPTH 15.5 m UNDISTURBED SAMPLE VERTICAL COMPRESSION ' 1 • » i » » J I 1 I I I 1 0 1 0 0 EFFECTIVE STRESS (kPa) FIG. 2 4 COEFFICIENT OF CONSOLIDATION: BURNABY CLAY. CRSC TEST. 1 0 0 0 s FIG. 2 5 PERMEABILITY OF BURNABY CLAY CRSC TEST 86 f i b r o u s peat, amorphous peat, and very s o f t c l a y , whose water contents vary from 800 to 200 pe r c e n t . The v a r i a t i o n i n the c o e f f i c i e n t of c o n s o l i d a t i o n i s shown in F i g u r e 24. In the normally c o n s o l i d a t e d r e g i o n , l i t t l e change occurs i n the c o e f f i c i e n t of c o n s o l i d a t i o n . At high s t r e s s l e v e l s , near the p r e c o n s o l i d a t i o n p r e s s u r e , the c o e f f i c i e n t of c o n s o l i d a t i o n decreases to a value s l i g h t l y l e s s than 0.1 cm 2/min and remains n e a r l y c o n s t a n t . The s i g n i f i c a n c e of t h i s behavior i s that two d i s t i n c t r e g i o n s , the o v e r c o n s o l i d a t e d and the normally c o n s o l i d a t e d p o r t i o n s , can each be c h a r a c t e r i z e d by a s i n g l e value f o r the c o e f f i c i e n t of c o n s o l i d a t i o n . The decrease i n the c o e f f i c i e n t of c o n s o l i d a t i o n at or near the p r e c o n s o l i d a t i o n p r e s s u r e i s due to the decrease in p e r m e a b i l i t y and the change i n c o m p r e s s i b i l i t y , shown i n F i g u r e 23. Examination of the sample r e v e a l e d no evidence of h o r i z o n t a l l a y e r i n g , i n d i c a t i n g that h o r i z o n t a l and v e r t i c a l c o n s o l i d a t i o n parameters may be n e a r l y equal. 6.6.3 R e s u l t s : Mcdonald S i t e R e s u l t s of t e s t i n g conducted on the c l a y e y s i l t from the Mcdonald s i t e are shown i n F i g u r e s 26 to 30. As i n the case of the Burnaby c l a y , the behavior of the Mcdonald c l a y e y s i l t i s to a l a r g e degree determined by i t s past l o a d i n g h i s t o r y . The c o e f f i c i e n t of c o n s o l i d a t i o n i n both the h o r i z o n t a l and v e r t i c a l d i r e c t i o n are shown i n F i g u r e 27. The two curves are n e a r l y EFFECTIVE STRESS (kPa) FIG. 2 6 COMPRESSIBILITY OF RICHMOND CLAYEY SILT CRSC TESTS 00 FIG. 2 7 COEFFICIENT OF CONSOLIDATION^ RICHMOND CLAYEY SILT. CRSC TESTS 03 00 1—I I I I I I 1 1—I—I I I I I SAMPLE DEPTH 20.5 m PERMEABILITY (cm/sec) F IG. 2 8 PERMEABILITY OF RICHMOND CLAYEY SILT. CRSC TESTS. CD CD I i i r i i i i i.o i -< & 0.91 o > 0.8 0.7 10 REMOLDED SAMPLE —I 1 1—| I I I F SAMPLE DEPTH 25.5 m -I 1 I I I I I a v o= 200 kPa UNDISTURBED SAMPLE VERTICAL COMPRESSION J I I I I I 100 EFFECTIVE STRESS (kPa) 1000 FIG. 2 9 EFFECT OF REMOLDING ON T H E COMPRESSIBILITY OF RICHMOND CLAYEY SILT. CRSC T E S T S . (0 O 1 1 r | ? f M | 1 - i r 7 i i r T - SAMPLE DEPTH 25.5 m -UNDISTURBED SAMPLE -- VERTICAL COMPRESSION -- -_ -REMOLDED — 1 L_ 1 1 1 1 1 1 1 - l I 1 1 1 1 1 JL. 10 100 1000 EFFECTIVE STRESS (kPa) FIG. 3 0 E F F E C T OF REMOLDING ON THE COEFFICIENT OF CONSOLIDATION 5 RICHMOND CLAYEY SILT. CRSC TESTS 92 i d e n t i c a l . Both the h o r i z o n t a l and t h e , v e r t i c a l c o e f f i c i e n t s of c o n s o l i d a t i o n can be c h a r a c t e r i z e d by two reasonably d i s t i n c t r e g i o n s ; i n t h e i r o v e r c o n s o l i d a t e d s t a t e , d u r i n g p r e l i m i n a r y stages of l o a d i n g , they vary between 2.0 and 5.0 cm 2/min, then decrease at a s t r e s s l e v e l near t h e i r p r e c o n s o l i d a t i o n pressure to a s i n g l e e q u i l i b r i u m value l e s s than 1.0 cm 2/min. The change i n the c o e f f i c i e n t of c o n s o l i d a t i o n i s due to changes in both the c o e f f i c i e n t of c o m p r e s s i b i l i t y and the c o e f f i c i e n t of p e r m e a b i l i t y . V a r i a t i o n i n the c o m p r e s s i b i l i t y i s shown i n F i g u r e 26; the p r e c o n s o l i d a t i o n p ressure i s l e s s evident in the case of h o r i z o n t a l l o a d i n g , perhaps due to gr e a t e r sample d i s t u r b a n c e while trimming the sample. The e f f e c t of complete remolding was i n v e s t i g a t e d because of i t s p o s s i b l e e f f e c t d u r i n g cone p e n e t r a t i o n t e s t i n g . R e s u l t s are shown i n F i g u r e s 29 and .30. In comparison to the und i s t u r b e d sample, the remolded sample i s much more compressible i n e a r l y stages of l o a d i n g , causing a decrease i n the measured c o e f f i c i e n t of c o n s o l i d a t i o n . R e s u l t s of the t e s t i n g conducted f o r the Mcdonald c l a y e y s i l t i n d i c a t e two d i s t i n c t v a l u e s f o r the c o e f f i c i e n t of c o n s o l i d a t i o n : one f o r i t s behavior at s t r e s s e s l e s s than i t s p r e c o n s o l i d a t i o n p r e s s u r e ; the other f o r i t s behavior at s t r e s s e s g r e a t e r than the p r e c o n s o l i d a t i o n p r e s s u r e . 6.7 F i t of E x i s t i n g S o l u t i o n s For the d i s s i p a t i o n curves shown i n F i g u r e 22, p r e d i c t e d 93 values of the c o e f f i c i e n t of c o n s o l i d a t i o n have been compared i n Tables IV, V, and VI. To compare the f i t of the d i f f e r e n t s o l u t i o n s to the f i e l d data, F i g u r e s 31, 32, and 33 compare Torstensson's 1977 s p h e r i c a l and c y l i n d r i c a l s o l u t i o n s to the f i e l d d i s s i p a t i o n curves. Torstensson's c y l i n d r i c a l s o l u t i o n i s shown because of i t s s i m i l a r i t y to the s o l u t i o n s by B a l i g h and Levadoux 1980 and by Randolph and Wroth 1979. To p l o t the d i s s i p a t i o n curves on the same s c a l e as the t h e o r e t i c a l s o l u t i o n s , time f a c t o r s , T, have been c a l c u l a t e d using the l a b o r a t o r y measured values f o r c. The l a b o r a t o r y values have been s e l e c t e d only as a means of comparing the shapes of the d i s s i p a t i o n c u r v e s . F i g u r e 31 compares the shape of the a n a l y t i c a l s o l u t i o n s with the data from the Mcdonald s i t e at 20.5 metres. The f i e l d data compares reasonably w e l l with e i t h e r the s p h e r i c a l or the c y l i n d r i c a l s o l u t i o n . The p r e d i c t e d c o e f f i c i e n t of c o n s o l i d a t i o n i s , t h e r e f o r e , n e a r l y independent of the degree of d i s s i p a t i o n . F i g u r e 32 compares the a n a l y t i c a l s o l u t i o n s with the data c o l l e c t e d from the Mcdonald s i t e at a depth of 25.5 metres. The f i e l d curves show a more r a p i d r a t e of d i s s i p a t i o n at e a r l y stages than e i t h e r the s p h e r i c a l or c y l i n d r i c a l s o l u t i o n s . Use of the t h e o r e t i c a l s o l u t i o n s i s , t h e r e f o r e , complicated by the n e c e s s i t y of d e c i d i n g which l e v e l of d i s s i p a t i o n i s best used to p r e d i c t the a c t u a l c o e f f i c i e n t of c o n s o l i d a t i o n . Probable causes f o r departure of the f i e l d data from the 94 Table IV : Comparison between Laboratory Data and C a l c u l a t e d C o e f f i c i e n t of C o n s o l i d a t i o n : Mcdonald s i t e 20.5 m Laboratory Test R e s u l t s -CRSC Test c v - o v e r c o n s o l i d a t e d r e g i o n 3.50 cm 2/min c v -normally c o n s o l i d a t e d r e g i o n 1.10 cm 2/min c n - o v e r c o n s o l i d a t e d r e g i o n 4.50 cm 2/min c n -normally c o n s o l i d a t e d r e g i o n 0.75 cm 2/min P r e d i c t e d Values f o r C o e f f i c i e n t  of C o n s o l i d a t i o n (cm z/min) Method B a l i g h and Levadoux 1980 Torstensson 1977 S p h e r i c a l (E/cu = 500) S p h e r i c a l (E/cu = 200) C y l i n d r i c a l (E/cu = 500) C y l i n d r i c a l (E/cu = 200) Percent D i s s i p a t i o n 20 40 50 60 80 2.32 2.00 2.29 2.60 3.55 0.57 0.49 0.52 0.51 0.43 0.35 0.31 0.30 0.31 0.40 1 .78 2.26 2.72 3.34 3.12 0.95 1.12 1 .47 1 .53 1 .34 95 Table V : Comparison between Laboratory data and C a l c u l a t e d C o e f f i c i e n t of C o n s o l i d a t i o n : Mcdonald S i t e 25.5 m Laboratory R e s u l t s -CRSC Tes t s Undisturbed Sample: c v - o v e r c o n s o l i d a t e d region c v -normally c o n s o l i d a t e d region Remolded Sample: c -1.0 cm 2/min 6.00 cm 2/min 0.75 cm 2/min P r e d i c t e d Values f o r C o e f f i c i e n t of C o n s o l i d a t i o n (cm 2/min) Method B a l i g h and Levadoux 1980 Torstensson 1977 S p h e r i c a l (E/cu = 500) S p h e r i c a l (E/cu = 200) C y l i n d r i c a l (E/cu = 500) C y l i n d r i c a l (E/cu = 200) Percent D i s s i p a t i o n 20 40 50 60 80 1.17 2.14 2.73 3.31 5.67 0.29 0.52 0.61 0.64 0.69 0.18 0.31 0.36 0.39 0.40 0.90 2.42 3.42 4.26 4.98 0.48 1 .20 1 .75 1 .95 2.14 TableVI : Comparison between Laboratory Data and C a l c u l a t e d C o e f f i c i e n t of C o n s o l i d a t i o n : Burnaby S i t e 15.5 m Laboratory R e s u l t s -CRSC T e s t s c v - o v e r c o n s o l i d a t e d region 0.60 cm 2/min c v -normally c o n s o l i d a t e d region 0.08 cm 2/min P r e d i c t e d Values f o r C o e f f i c i e n t  of C o n s o l i d a t i o n (cm z/min) Percent D i s s i p a t i o n 20 40 50 Method B a l i g h and Levadoux 1980 Torstensson 1977 S p h e r i c a l (E/cu = 500) S p h e r i c a l (E/cu = 200) C y l i n d r i c a l (E/cu = 500) C y l i n d r i c a l (E/cu = 200) 0.23 0.27 0.27 0.056 0.065 0.060 0.035 0.039 0.035 0.18 0.30 0.32 0.095 0.15 0.17 T = c t / r 2 FIGURE 3 1 FIT OF THEORETICAL C U R V E S TO FIELD D A T A : McDONALD SITE 2 0 - 5 m to - 4 1 T = c t / r 2 F IGURE 3 2 FIT OF T H E O R E T I C A L CURVES TO F IELD DATA- McDONALD S ITE 25.5 m CD 1 .9 .8 .7 !- 6 I -5 - A .3 .2 .1 01 MEASURED CURVE c = 6.0 MEASURED CURVE c = 0.08 TORSTENSSON 1977 SPHERICAL SOLUTION TORSTENSSON 1977 CYLINDRICAL SOLUTION M M ' 1 i i i i i i i i I _ L i t i i i i i .1 10 1 100 T = c t / r 2 F I G U R E 3 3 FIT OF T H E O R E T I C A L C U R V E S TO F I E L D D A T A - B U R N A B Y S I T E 15 .5m CD CD 1 0 0 t h e o r e t i c a l s o l u t i o n s i n c l u d e : 1) i n a p p r o p r i a t e c o n s o l i d a t i o n a n a l y s i s , p o s s i b l y due to an i n c o r r e c t assumption of the i n i t i a l excess pore p r e s s u r e ; and 2) s i g n i f i c a n t m a t e r i a l nonhomogeneities near the cone. F i g u r e 33 compares the t h e o r e t i c a l s o l u t i o n s to the f i e l d data from the Burnaby s i t e . '.The f i e l d data f i t s e i t h e r of the t h e o r e t i c a l s o l u t i o n s w e l l . The p r e d i c t e d c o e f f i c i e n t of c o n s o l i d a t i o n i s , t h e r e f o r e , n e a r l y independent of the degree of d i s s i p a t i o n . 6.8 Comparison between P r e d i c t e d and Laboratory Measured Values Constant r a t e of s t r a i n c o n s o l i d a t i o n t e s t s performed on samples obtained at the two s i t e s can be used to o b t a i n r e f e r e n c e c o n s o l i d a t i o n parameters. For the Burnaby s i t e , u n d i s t u r b e d samples were used . to measure only the v e r t i c a l c o e f f i c i e n t of c o n s o l i d a t i o n . An absence of v i s i b l e l a y e r i n g i n the sample t e s t e d , however, i n d i c a t e d that the r a t i o of the v e r t i c a l to h o r i z o n t a l c o e f f i c i e n t of c o n s o l i d a t i o n should be c l o s e to 1.0. For the Mcdonald s i t e , c o n s o l i d a t i o n t e s t s were performed i n both the h o r i z o n t a l and v e r t i c a l d i r e c t i o n s f o r the sample c o l l e c t e d at 20.5 metres; r e s u l t s were s i m i l a r . In a d d i t i o n , v e r t i c a l and remolded c o n s o l i d a t i o n t e s t s were conducted i n samples c o l l e c t e d from 25.5 metres. The 101 c o n s o l i d a t i o n t e s t r e s u l t s are considered here as reference v a l u e s . A comparison between the l a b o r a t o r y v a l u e s and the p r e d i c t e d c o e f f i c i e n t of c o n s o l i d a t i o n i s best done at one degree of d i s s i p a t i o n . At the e a r l y stages of d i s s i p a t i o n , c o n s o l i d a t i o n d e f i n i t e l y takes p l a c e along the r e c o n s o l i d a t i o n curve in e f f e c t i v e s t r e s s space. A f t e r more d i s s i p a t i o n has occurred, some u n c e r t a i n t y about the t o t a l s t r e s s space confuses the e f f e c t i v e s t r e s s l e v e l and, t h e r e f o r e , which parameter c , normally c o n s o l i d a t e d , or c , o v e r c o n s o l i d a t e d , i s more a p p r o p r i a t e . Torstensson 1977 recommends c a l c u l a t i n g the c o e f f i c i e n t of c o n s o l i d a t i o n at 50% l e v e l of d i s s i p a t i o n . Using only the 50% l e v e l of d i s s i p a t i o n , T ables IV, V, and VI can be used to compare the d i f f e r e n t methods. For the Mcdonald s i t e at 20.5 metres, the s o l u t i o n s by B a l i g h and Levadoux 1980 and the c y l i n d r i c a l s o l u t i o n by Torstensson 1977 each p r e d i c t s a c o e f f i c i e n t of c o n s o l i d a t i o n measured in the o v e r c o n s o l i d a t e d s t a t e . For t e s t i n g conducted .at the Mcdonald s i t e at 25.5 metres, the c o e f f i c i e n t of c o n s o l i d a t i o n at the 50% l e v e l of d i s s i p a t i o n p r e d i c t e d by the s o l u t i o n s of B a l i g h and Levadoux and the c y l i n d r i c a l s o l u t i o n of Torstensson each compare reasonably w e l l with the l a b o r a t o r y value measured i n the o v e r c o n s o l i d a t e d s t a t e . S i m i l a r r e s u l t s are obtained from the Burnaby s i t e , where the s o l u t i o n s by B a l i g h and Levadoux and by Torstensson again 102 compare reasonably w e l l with the l a b o r a t o r y value measured i n the o v e r c o n s o l i d a t e d s t a t e . C o n s i d e r i n g the e f f e c t of p a r t i a l remolding, which i s to reduce the c o e f f i c i e n t of c o n s o l i d a t i o n , the f i e l d r e s u l t s obtained compare reasonably w e l l with l a b o r a t o r y measured values of the h o r i z o n t a l c o e f f i c i e n t of c o n s o l i d a t i o n i n the o v e r c o n s o l i d a t e d state.. 6.9 S e l e c t i o n of S o i l S t i f f n e s s R a t i o The pore pressure d i s s i p a t i o n s o l u t i o n s proposed by Torstensson 1977 and Randolph and Wroth 1979 r e l y on an assumption of the i n i t i a l d i s t r i b u t i o n of excess pore pressure . As was shown i n Chapter 4 (eqns.1-6) the i n i t i a l excess pore pressure was assumed to decrease l i n e a r l y with the l o g a r i t h m of the r a d i u s . In a d d i t i o n , t h e s i z e of the zone of i n c r e a s e d pore pressure was shown to i n c r e a s e with the square root of the s o i l s t i f f n e s s r a t i o from c y l i n d r i c a l c a v i t y expansion theory and with the cube root of the s o i l s t i f f n e s s r a t i o f r o n s p h e r i c a l c a v i t y expansion theory . The s o i l s t i f f n e s s can be expressed as e i t h e r , the undrained e l a s t i c modulas E or the undrained shear modulas G, to the undrained shear s t r e n g t h . The e l a s t i c modulas and the shear modulas can be r e l a t e d by: G=E/2(1+u) where u =0.5 f o r undrained l o a d i n g of s a t u r a t e d c l a y I n c r e a s i n g the s o i l s t i f f n e s s has the e f f e c t of extending the zone of excess pore pressure and s u b s i q u e n t l y reducing the pore p r e s s u r e g r a d i e n t f o r any given excess pore pressure at the c a v i t y f a c e . Use of e i t h e r the s o l u t i o n by Torstensson 1977 or 103 Randolph and Wroth 1979 thus r e q u i r e s an estimate of the s o i l , s t i f f n e s s r a t i o . S e l e c t i o n of an exact s t i f f n e s s r a t i o i s complicated by the v a r i a t i o n i n modulas with s t r a i n l e v e l . F i g u r e 34 shows the v a r i a t i o n i n s t i f f n e s s r a t i o f o r s e v e r a l d i f f e r e n t s o i l s . I t can a l s o be seen i n Fi g u r e 34 how s t i f f n e s s v a r i e s with s t r e s s l e v e l . With the complex v a r i a t i o n i n s t r a i n s around the cone i t seems reasonable to s e l e c t a s t i f f n e s s r a t i o at intermediate s t r e s s l e v e l s . Although some doubt surrounds the s e l e c t i o n of an a p p r o p r i a t e s t i f f n e s s r a t i o the s o l u t i o n s are not s e n s i t i v e to the s o i l s t i f f n e s s used. Appendix B i n c l u d e s the time f a c t o r s , T , used to c a l c u l a t e the c o e f f i c i e n t of c o n s o l i d a t i o n . For example the time f a c t o r at the 50% l e v e l of d i s s i p a t i o n i n Torstensson's c y l i n d r i c a l s o l u t i o n v a r i e s from T=1.37 to T=4.29 as E/cu v a r i e s from 100 to 500. 6.10 Procedure Used During D i s s i p a t i o n T e s t s There i s very l i t t l e a v a i l a b l e l i t e r a t u r e d e s c r i b i n g the procedures used duri n g d i s s i p a t i o n t e s t s . B a t t a g l i o et a l . 1981 and others report that they found i t necessary to clamp the rods at the ground s u r f a c e d u r i n g d i s s i p a t i o n t e s t s . They found that i f the rods were not clamped that a drop i n the measured pore pressure would r e s u l t when loa d was r e l e a s e d from the t i p . V a r i a t i o n s i n the amount of loa d a p p l i e d to the top end of the rods were made durin g the i n v e s t i g a t i o n at the Mcdonald s i t e . No d i f f e r e n c e i n decay response was noted when e i t h e r removing the l o a d e n t i r e l y or m a i n t a i n i n g a loa d only s l i g h t l y l e s s than 104 2000 c ^ 2 0 0 No, DESCRIPTION cu/p' Portsmouth CL C l o y PI = 15 -20 st-IO L L = 35 I _ Boston C L Cloy 2 L L = 4I Pl=22 3 Bongkok CH Cloy LL=65PI=4I 4 Maine CH OH Clay LL=65PI=38 AGS CH Cloy LL=7I Pl = 4 0 J 5 •20 •27 29 •26 •24 Atchafalaya 6 CH Clay LL=95 Pl = 75 j Taylor River P e a t w =50 0 % CKo U simple shear tests all soils normally consol i da ted 0-2 0-4 0-6 0-8 APPLIED SHEAR STRESS RATIO T h / c u Figure 3 5 Selection of Soi l Stiffness Rat io Adapted from Ladd et al 1977 105 that r e q u i r e d to resume p e n e t r a t i o n . Part of the ex p l a n a t i o n f o r the i n s e n s i t i v i t y of procedure v a r i a t i o n probably l a y s i n the d i s t r i b u t i o n of s t r e s s e s and s t r a i n s along the rods, e s p e c i a l l y those between the f r i c t i o n reducer and the cone t i p . Even when the pushing head i s f u l l y withdrawn from the rods, some loa d i s maintained on the t i p by the f r i c t i o n m o b i l i z e d along the s h a f t between the f r i c t i o n reducer and the t i p . T h i s t i p l o a d was measured d u r i n g s e v e r a l d i s s i p a t i o n s . In f a c t , the decay of the t i p load d i r e c t l y p a r a l l e l e d the decay of excess pore pressure recorded by the piezometer u n i t . T h i s i s not s u r p r i s i n g , c o n s i d e r i n g that the t i p i s a t o t a l s t r e s s c e l l . The amount of load maintained on the t i p when p e n e t r a t i o n i s h a l t e d probably depends on many f a c t o r s i n c l u d i n g v e r t i c a l i t y of the h o l e , squeeze of the s o i l above the f r i c t i o n reducer onto the rods, and the l o c a t i o n and s i z e of the f r i c t i o n reducer used. The apparent c o n t r a d i c t i o n i n the importance i n mai n t a i n i n g l o a d on the rod s t r i n g found i n t h i s i n v e s t i g a t i o n and that r e p o r t e d by B a t t a g l i o et a l . 1981 may be the r e s u l t of v a r i a t i o n i n the l o c a t i o n of the piezometer element. B a t t a g l i o et a l . 1981 employed a cone with the piezometer element l o c a t e d on the 60° face of the cone; when loa d was r e l e a s e d , the pore p r e s s u r e dropped immediately because of the v a r i a t i o n i n t o t a l s t r e s s at the cone. In other words, the pore pressure had to be in d i r e c t e q u i l i b r i u m with the bearing m o b i l i z e d . The piezometer element used i n t h i s i n v e s t i g a t i o n was l o c a t e d immediately behind the cone t i p i n the zone of f a i l e d s o i l . 106 V a r i a t i o n s i n the t o t a l s t r e s s at the t i p do not seem to have any e f f e c t on the response recorded up the s h a f t . 6.11 C o n c l u s i o n The two c y l i n d r i c a l s o l u t i o n s f o r pore pressure d i s s i p a t i o n around the cone by Randolph and Wroth and by Torstensson, and the two-dimensional s o l u t i o n by B a l i g h and Levadoux, provide a reasonable ^ p r e d i c t i o n of the h o r i z o n t a l c o e f f i c i e n t of c o n s o l i d a t i o n i n the o v e r c o n s o l i d a t e d s t a t e . Torstensson's s p h e r i c a l s o l u t i o n u n d e r p r e d i c t s the c o e f f i c i e n t of c o n s o l i d a t i o n ; t h i s i s probably due to the assumption of the i n i t i a l pore pressure d i s t r i b u t i o n a r r i v e d at d u r i n g s p h e r i c a l c a v i t y expansion. The s o l u t i o n s by Randolph and Wroth and by Torstensson that r e q u i r e a s t i f f n e s s r a t i o are not s e n s i t i v e to the s t i f f n e s s r a t i o chosen. For a f o u r - f o l d i n c r e a s e i n s t i f f n e s s r a t i o , the p r e d i c t e d c o e f f i c i e n t of c o n s o l i d a t i o n changes by a f a c t o r of about 2. The s o l u t i o n by Soderberg should be d i s c o u n t e d , as i t showed the poorest f i t to the f i e l d d a t a. Provided that e q u i l i b r i u m pore p r e s s u r e s are not r e q u i r e d , i t i s not necessary, f o r the purpose of o b t a i n i n g c o n s o l i d a t i o n c h a r a c t e r i s t i c s , to wait past the 50% l e v e l of d i s s i p a t i o n . The i n t e r p r e t a t i o n of r e s u l t s r e q u i r e s some judgement i n the event that d i f f e r e n t c o e f f i c i e n t s of c o n s o l i d a t i o n are 107 p r e d i c t e d at d i f f e r e n t stages of d i s s i p a t i o n . C o n s i d e r i n g the v a r i a b i l i t y of l a b o r a t o r y r e s u l t s and s o i l nonhomogeneity, t h i s d i f f i c u l t y may be of small consequence. A t a b l e of time f a c t o r , T, from e x i s t i n g s o l u t i o n s i s i n c l u d e d i n Appendix B. Some recommendations of p o s s i b l e methods fo r o b t a i n i n g s o i l p e r m e a b i l i t y are d i s c u s s e d in Chapter 7. I 08 Chapter 7 E s t i m a t i n g S o i l P e r m e a b i l i t y from Cone P e n e t r a t i o n Test Data 7.1 I n t r o d u c t i o n T h i s paper has addressed the p o s s i b i l i t y of o b t a i n i n g an estimate of the c o e f f i c i e n t of c o n s o l i d a t i o n from the pore pressure decay a f t e r p e n e t r a t i o n i s h a l t e d . As d i s c u s s e d i n Chapter 1, there i s o f t e n a need to o b t a i n a r e l i a b l e estimate of s o i l p e r m e a b i l i t y . Provided that an estimate of s o i l c o m p r e s s i b i l i t y can be obtained, an estimate of p e r m e a b i l i t y can be obtained from: k v = c vm v tfw (1 ) k h = C h m h t f w (2) R e s u l t s of l i m i t e d past experience suggests that s o i l c o m p r e s s i b i l i t y can u s u a l l y be regarded as i s o t r o p i c : mv = mn ( M i t c h e l l et a l 1978; Ladd et al.1977). If i t i s assumed that s o i l c o m p r e s s i b i l i t y i s i s o t r o p i c , i . e . mv=mn, then: C V = C h X jCy (3) kh An estimate of the r a t i o k v / k h can be obtained from Table V I I , a f t e r B a l i g h and Levadoux 1980. In a d d i t i o n , evidence of the 109 Anisotropic Permeability of Clays Nature of Clay ^ h ^ v 1. No evidence of layering 1.2 ± 0.2 2 . S l i g h t layering, e . g . , sedimentary clays with 2 to 5 occasional s i l t dustings to random lenses 3. Varved clays i n north- 10 ± 5 eastern U.S. T a b l e V I I A n i s o t r o p i c P e r m e a b i l i t y of C l a y s a f t e r : B a l i g h and Levadoux 1980 no h e t e r o g e n e i t y can be obtained from examination of the bearing f r i c t i o n and dynamic pore pressure l o g s . Methods that can be used to estimate s o i l c o m p r e s s i b i l i t y i n c l u d e : 1) Laboratory T e s t i n g ; 2) F i e l d Loading Test R e s u l t s ; 3) C o r r e l a t i o n s between QC and mv; 4) C o r r e l a t i o n s between Index T e s t s and mv,Cc 5) Other I n s i t u T e s t s . P r o v i d e d that an estimate of mv i s obtained, then estimates of h o r i z o n t a l and v e r t i c a l p e r m e a b i l i t y can be obtained from equations 1, 2, and 3. 7.2 Laboratory T e s t s to Obtain C o m p r e s s i b i l i t y S ince the purpose of t h i s paper i s to t r y to extend the use of the cone p e n e t r a t i o n t e s t , a d i s c u s s i o n of l a b o r a t o r y t e s t i n g i s unwarranted. Employment of a l i m i t e d number of l a b o r a t o r y t e s t s , however, combined with a l a r g e number of pore pressure d i s s i p a t i o n s , may be a very u s e f u l technique. C o n s o l i d a t i o n t e s t s performed on samples s e l e c t e d near d i s s i p a t i o n t e s t l o c a t i o n s would provide c o n f i r m a t i o n of the p r e d i c t e d c o e f f i c i e n t of c o n s o l i d a t i o n from d i s s i p a t i o n t e s t s r e s u l t s , as w e l l as an estimate of s o i l c o m p r e s s i b i l i t y f o r the s i t e . D i s s i p a t i o n t e s t r e s u l t s c o u l d then be used to extend r e s u l t s of ILL the c o n s o l i d a t i o n t e s t s . 7.3 F i e l d Loading B a c k c a l c u l a t e d v a l u e s from the performance of f i l l s and s t r u c t u r e s may permit the best estimate of an average value of s o i l c o m p r e s s i b i l i t y . 7.4 Estimates of C o m p r e s s i b i l i t y from Bearing Values Although no a n a l y t i c a l s o l u t i o n can be used to r e l a t e b e a r i n g to c o m p r e s s i b i l i t y , an estimate of deformation c h a r a c t e r i s t i c s of a s o i l can be obtained from QC; i t must, however, be recognized that QC i s an u l t i m a t e " s t r e n g t h " parameter that depends upon s o i l deformation, s t r e n g t h and c o m p r e s s i b i l i t y c h a r a c t e r i s t i c s . In a d d i t i o n , as has a l r e a d y been d i s c u s s e d , the p r e d i c t i o n of d r a i n e d parameters from an undrained t e s t i s not a p p e a l i n g . Any r e l a t i o n , t h e r e f o r e , that g i v e s a deformation c h a r a c t e r i s t i c from QC w i l l be p u r e l y e m p i r i c a l and c a r r y a c e r t a i n degree of i m p r e c i s i o n . The most commonly used r e l a t i o n between bearing and c o m p r e s s i b i l i t y i s : mv = J_ aQC where a = 7 - 10 f o r c l a y e y s o i l s a = 2 - 3.5 f o r sand Values f o r a as a f u n c t i o n of s o i l type have been compiled by 112 M i t c h e l l et a l 1978. An a l t e r n a t e procedure to o b t a i n c o m p r e s s i b i l i t y from cone p e n e t r a t i o n t e s t s given by Bri a u d 1980 i s : 1) estimate cu from QC; 2) estimate p 0 ' ; 3) r e f e r to r e l a t i o n s between cu/po' and c o m p r e s s i b i l i t y . One such r e l a t i o n i s shown below. c /p* u' p ov approx. OCR V * 1 + e o ) 0 - 0.1 0.1 - 0.25 0.26 - 0.50 0.51 - 1.00 1 - 4 over 4 less than 1 1 1 to 1.5 (assume 1) 3 6 greater than 6 greater than 0.4 (still consolidating) 0.4 0.3 0.15 0.10 0.05 TABLE VIII - Estimating the consolidation of clay from T - T * -pov F R O M B R I A U D 1 9 8 0 1 1 3 The r e l a t i o n between cu/po' and OCR was suggested as a method of c a l c u l a t i n g OCR from QC by Schmertmann 1974. Since t h i s method i n v o l v e s three separate c o r r e l a t i o n s , o b t a i n i n g cu from QC, OCR from cu/po', and Cc from OCR, i t l a c k s the appeal of simply c o r r e l a t i n g mv and QC. 7.5 Laboratory Index T e s t s to Obtain C o m p r e s s i b i l i t y Laboratory Index t e s t s have been used r o u t i n e l y i n the past to o b t a i n s o i l c o m p r e s s i b i l i t y . Although s o i l sampling i s n e c e s s i t a t e d , commonly used c o r r e l a t i o n s are i n c l u d e d here from B a l i g h and Levadoux 1980 f o r completeness: Cc = 0.009 (Wl% - 10%) T e r z a g h i and Peck 1967 Cc = 0.54 ( e 0 - 0.35) N i s h i d a 1958 Cc = 0.01 to 0.15 (Wn%) MPMR 1958 Cc = 0.6 ( e 0 - 1) ( K e 0 < 6 ) Kapp 1966 Cc = 0.013 PI Atkinson and Bransby 1978 7.6 I n s i t u T e s t s to Obtain S o i l C o m p r e s s i b i l i t y An a c c u r a t e e v a l u a t i o n of s o i l c o m p r e s s i b i l i t y can best be obtained by i n s i t u t e s t s , i n c l u d i n g screw p l a t e , p l a t e load, pressuremeter, and d i l a t o m e t e r t e s t s . An e v a l u a t i o n of these t e s t s i s i n c l u d e d i n M i t c h e l l et a l 1978 and B r i a u d 1980 and w i l l not be d i s c u s s e d here. As i n the case of l a b o r a t o r y t e s t i n g , the use of pore pressure d i s s i p a t i o n t e s t s may be enhanced, i f necessary, with other t e s t s that are more e x a c t i n g f o r e v a l u a t i n g s o i l c o m p r e s s i b i l i t y . 114 Chapter 8 C o n c l u s i o n s Some c o n c l u s i o n s have been presented w i t h i n the previous c h a p t e r s ; the c o n c l u s i o n s presented i n t h i s chapter e i t h e r r e i t e r a t e the most important c o n c l u s i o n s or t r y to t i e the d i f f e r e n t chapters t o g ether. 8.1 C o n c l u s i o n s 1) Much of t h i s r e p ort has c e n t r e d around the n e c e s s i t y f o r c a r e f u l c a l i b r a t i o n , s a t u r a t i o n , and proper data r e d u c t i o n . Although t h i s may seem to c o n t r a d i c t the b e l i e f that the cone p e n e t r a t i o n t e s t i s a simple, h i g h l y repeatable t e s t , i t has. been found that with c a r e , anomalous data c o u l d be c o r r e c t e d and meaningful r e s u l t s obtained. C o r r e c t i o n s and procedures found to be most s i g n i f i c a n t i n c l u d e : A) pore pressure e f f e c t s of unequal end areas of the f r i c t i o n s l e e v e ; B) pore pressure e f f e c t s on bearing measurements; C) e f f e c t s of s a t u r a t i o n ; and D) e f f e c t s > of r a t e . C o r r e c t i o n s found to be of secondary s i g n i f i c a n c e i n c l u d e : A) e f f e c t s of d i s s i p a t i o n s ; and B) unequal pore pressure d i s t r i b u t i o n up the s l e e v e , and subsequent net pore pressure c o r r e c t i o n to the 115 f r i c t i o n r e a dings. The a d d i t i o n of the dynamic pore pressure has been found to be a u s e f u l parameter to a s s i s t s t r a t a g r a p h i c l o g g i n g f o r two reasons: A) i t shows the g r e a t e s t d e t a i l ; and B) a knowledge of the p e r m e a b i l i t y can be obtained. The dynamic pore pressure and pore p r e s s u r e r a t i o has been shown to depend on both the p e r m e a b i l i t y and the volume change c h a r a c t e r i s t i c s of the s o i l . The infuuence of p e r m e a b i l i t y was shown by v a r y i n g p e n e t r a t i o n r a t e . The i n f l u e n c e of volume change c h a r a c t e r i s t i c s was shown i n an example that showed the change i n dynamic pore pressure that accompanied compaction. Because of the dependancy of the dynamic pore pressure on both of these s o i l parameters c o n s i d e r a b l e care must be used i n i n t e r p r e t i n g dynamic pore pressure logs.Use of simultaneous bearing , f r i c t i o n and pore pressure measurements reduces p o s s i b l e ambiguity i n i n t e r p r e t a t i o n s . The piezometer cone can be used to o b t a i n s t a t i c pore pressure v a l u e s . T h i s i n f o r m a t i o n , although e a s i l y o b tained, appears to be underemployed. A n a l y t i c a l e x p r e s s i o n s f o r the pore pressure generated d u r i n g s p h e r i c a l c a v i t y expansion compare w e l l with v a l u e s measured at the t i p , whereas val u e s measured up the sleeve compare w e l l with c y l i n d r i c a l c a v i t y expansion theory. The e f f e c t of r a t e on the bearing measurements has been 116 shown. To i l l u s t r a t e t h i s e f f e c t , the e f f e c t i v e b e a r i n g concept was i n t r o d u c e d . The e f f e c t of rate on f r i c t i o n s l e e v e readings was found to be more s i g n i f i c a n t because of the g r e a t e r time f o r c o n s o l i d a t i o n . 7) Estimates of the r a d i a l e f f e c t i v e and t o t a l s t r e s s were made from f r i c t i o n and pore pressure measurements obtained from v a r i a b l e p e n e t r a t i o n r a t e s and t i p e x t e n s i o n s . The s t r e s s d i s t r i b u t i o n up the s h a f t has important i m p l i c a t i o n s regarding the use of f r i c t i o n s l eeve readings f o r p r e d i c t i o n of p i l e s k i n f r i c t i o n c a p a c i t y . 8) The pore pressure d i s s i p a t i o n s o l u t i o n s used p r e d i c t e d c o e f f i c i e n t s of c o n s o l i d a t i o n that compared w e l l with l a b o r a t o r y measured values of the h o r i z o n t a l c o e f f i c i e n t of c o n s o l i d a t i o n in the o v e r c o n s o l i d a t e d s t a t e . 9) C o n s i d e r a b l e r e s e a r c h undertaken by others has shown that pore pressure measurements on the t i p face r e s u l t i n the hi g h e s t measured v a l u e s . Previous work has been done only i n c l a y e y s o i l s . For s e v e r a l reasons, the l o c a t i o n of the porous stone used i n t h i s study has been found to be an a c c e p t a b l e compromise that a l s o has the f o l l o w i n g advantages: A) The stone i s p r o t e c t e d both from wear and impact damage. B) The l o c a t i o n used r e s u l t s i n d i s s i p a t i o n s that compare to those measured f u r t h e r up the s h a f t and 117 to c y l i n d r i c a l d i s s i p a t i o n t h e o r i e s . C) The d i s s i p a t i o n s conducted do not appear to be s e n s i t i v e to procedure used. D) The l o c a t i o n used corresponds e x a c t l y to the pore pressure r e q u i r e d f o r c o r r e c t i n g the b e a r i n g value fo r pore pressure e f f e c t s . 8.2 Recommendations f o r Further Research C e r t a i n t o p i c s f o r f u r t h e r r e s e a r c h became apparent during t h i s i n v e s t i g a t i o n . These t o p i c s i n c l u d e : 1) One of the primary uses of the cone p e n e t r a t i o n t e s t i s to o b t a i n undrained shear s t r e n g t h . Undrained shear s t r e n g t h i s c a l c u l a t e d u sing c o r r e l a t i o n f a c t o r s Nc or Nk, which were obtained both t h e o r e t i c a l l y and e x p e r i m e n t a l l y . C o n s i d e r a b l e s c a t t e r i n a the a p p r o p r i a t e Nc f a c t o r has been obtained from comparing f i e l d vane to cone bearing r e s u l t s . I t has been suggested i n t h i s r e p o r t that p r e v i o u s p u b l i s h e d bearing values have s u f f e r e d (to v a r y i n g degrees) from pore pressure e f f e c t s . I t may be that much of the s c a t t e r i s Nc v a l u e s i s caused by i n c o r r e c t and i n c o n s i s t e n t b e a r i n g v a l u e s . In f u t u r e , bearing values should be c o r r e c t e d ; t h i s may r e s u l t i n b e t t e r agreement between t h e o r e t i c a l l y and e x p e r i m e n t a l l y obtained Nc v a l u e s . 2) Good c o r r e l a t i o n s were found between c o n s o l i d a t i o n c h a r a c t e r i s t i c s obtained from f i e l d d i s s i p a t i o n records 1 1 8 and r e f e r e n c e v a l u e s . F u r t h e r comparisons should be made when p o s s i b l e . In a d d i t i o n , simple c o r r e l a t i o n s between p e r m e a b i l i t y , the c o e f f i c i e n t of c o n s o l i d a t i o n , and the time f o r d i s s i p a t i o n of 50% of the excess pore •pressure should be e s t a b l i s h e d . 3) The pore pressure r a t i o and the excess pore pressure r a t i o show promise i n p r e d i c t i n g p r evious l o a d i n g h i s t o r y of c l a y s o i l s ; f u r t h e r work i n t h i s f i e l d i s warranted. 4) I t has been suggested t h a t the l o c a t i o n of the porous stone used i n t h i s i n v e s t i g a t i o n o f f e r s c o n s i d e r a b l e advantages. Other r e s e a r c h e r s p r e f e r to l o c a t e the porous element on the cone f a c e . Comparison between r e s u l t s obtained with each cone has only been done f o r c l a y s o i l s . L i t t l e d i f f e r e n c e i s seen i n the r e s u l t s o b t a i n e d . Future comparisons should be made i n s i l t and sand d e p o s i t s . 119 References B a l i g h , M.M. And Levadoux, J.N., 1980. "Pore Pressure D i s s i p a t i o n A f t e r Cone P e n e t r a t i o n " , Research Report R80-11, Department of C i v i l E n g i n e e r i n g , Massachusetss I n s t i t u t e of Technology, Cambridge, Mass. B a l i g h , M.M., V i v a t r a t , V., and Ladd, C.C., 1978. " E x p l o r a t i o n and E v a l u a t i o n of E n g i n e e r i n g P r o p e r t i e s f o r Foundation Design of Of f s h o r e S t r u c t u r e s " , Research Report R78-40, Department of C i v i l E n g i n e e r i n g , Massachusetts I n s t i t u t e of Technology, Cambridge, Mass. B a l i g h , M.M., V i v i t r a t , V., and Ladd, C.C. 1980. "Cone P e n e t r a t i o n i n S o i l P r o f i l i n g " , ASCE, J o u r n a l of  G e o t e c h n i c a l E n g i n e e r i n g D i v i s i o n , GT 4, A p r i l , p 447. B a t a g l i o , M., Jamiolkowski, M., L a n c e l l o t t a , R., Maniscalco, R., 1981. "Piezometer Probe Test i n Cohesive D e p o s i t s " , ASCE, St . L o u i s Convention, Session 35, Cone P e n e t r a t i o n T e s t i n g  and Experience, pp 264 - 302. Br i a u d , J . , 1980. "In S i t u T e s t s t o Measure S o i l Strength and S o i l D e f o r m a b i l i t y f o r O f f s h o r e E n g i n e e r i n g " , Texas A & M Research Foundation, I n t e r n a l Report. Casson,M.,1978 "Les E s s a i s In S i t u en Mechanique des S o l s " E d i t i o n s E y r o l l e s , P a r i s , p 98 V o l 1. Campanella, R.G. And Robertson, P.K., 1981. "A p p l i e d Cone Research", ASCE, S t . L o u i s Convention, Session 35, Cone  P e n e t r a t i o n T e s t i n g and Experience, pp 343 - 362. Campanella,R.G.,Robertson,P.K.and G i l l e s p i e , D . , 1 9 8 1 . " I n - S i t u T e s t i n g In Sa t u r a t e d S i I t , ( D r a i n e d or Undrained?)" Proceedings,34 t h . Canadian G e o t e c h n i c a l Conference Fredericton,Canada. E s r i g , M.I. And K i r b y , R.C., 1978. " S o i l C a p a c i t y f o r Supporting Deep Foundation Members i n C l a y " , State of the ,Art Paper, Proceedings, ASTM Symposium on Behavior of Deep Foundations, Boston, Mass. Hagerty, D.J. And Garlanger, J.E., 1972. " C o n s o l i d a t i o n E f f e c t s Around Driven P i l e s " , ASCE S p e c i a l t y Conference Performance of E a r t h and Earth-Supported S t r u c t u r e s , Purdue U n i v e r s i t y , L a f a y e t t e , Indiana, V o l 1, Part 2, pp 1207 1 222. Ismael, N.F. And Klym, J.W., 1979. "Pore-Water Pressure Induced by P i l e D r i v i n g " , J o u r n a l of the G e o t e c h n i c a l  D i v i s i o n , ASCE, V o l 105, pp 1349 -1354. Janbu, N. And Senneset, K., 1974. " E f f e c t i v e Sress I n t e r p r e t a t i o n of In S i t u S t a t i c P e n e t r a t i o n T e s t s " , 120 Proceedings, European Symposium on P e n e t r a t i o n T e s t i n g , Stockholm, Sweden, V o l 2.2, pp 181 - 193. Koizumi, Y. And I t o , K., 1967. " F i e l d T e s t s with Regard to P i l e D r i v i n g and Bearing C a p a c i t y of P i l e d Foundations", S o i l s and Foundations, Japan, V o l 7, No 3, pp 30 - 53. Lacasse, S., Jamiolkowski, M., L a n c e l l o t t a , R., and Lunne, T., 1981. "In S i t u S t r e s s - S t r a i n C h a r a c t e r i s t i c s of Two Norwegian Marine C l a y s " , Unpublished Manuscript. Ladd,C.C.,Foot,R.,Ishihara,K.,Schlosser,F.,and Poulos,H.G.,1977 "Stress-Deformation and Strength C h a r a c t e r i s t i c s Proceedings , N i n t h I n t e r n a t i o n a l Conference on S o i l Mechanics and Foundation E n g i n e e r i n g ,Tokoyo,Japan,Vol.ll,pp 421-494. . Lambe, T.W. And Whitman, R.V., 1979. S o i l Mechanics, Wiley P u b l i s h e r s , New York, 553 pp. Lo, K.Y. And Stermac, A.G., 1965. "Induced Pore Pressures During P i l e D r i v i n g O p erations", Proceedings, 6th I n t e r n a t i o n a l Conference on S o i l Mechanics and Foundations E n g i n e e r i n g , Montreal, Canada, V o l 2, pp 285 - 289. Massarsch, K.R., 1978. "New Aspects of S o i l F r a c t u r i n g i n C l a y " , J o u r n a l of G e o t e c h n i c a l E n g i n e e r i n g D i v i s i o n , ASCE, GT 8, pp 1109 -1123. Mitchell,J.K.,Guzikowski,F.and Villet,W.C.B.,1978. "The Measurement of S o i l P r o p e r t i e s I n - S i t u " , I n t e r n a l Report U n i v e r s i t y of C a l i f o r n i a Berkeley C a l i f o r n i a . Randolph, M.F. And Wroth, C P . , 1979. "An A n a l y t i c a l S o l u t i o n f o r the C o n s o l i d a t i o n Around a Driven P i l e " , I n t e r n a t i o n a l  J o u r n a l f o r Numerical and A n a l y t i c a l Methods in  Geomechanics, V o l 3, pp 217 - 229. Roscoe, K.H. And Burland, J.B., 1968. "On the G e n e r a l i s e d Behavior of Wet C l a y " , E n g i n e e r i n g P l a s t i c i t y , E d i t o r s J . Heyman and F.A. L e c k i e , Cambridge U n i v e r s i t y Press, England, pp 535 - 609. Roy,M.,Blanchet,R.,Tavenas,F.A.and LaRochelle,P.,1979. "Behavior of a S e n s i t i v e Clay During P i l e D r i v i n g " , Procedings 32nd Canadian G e o t e c h n i c a l Conference,Quebec,Canada. Roy, M., Tremblay, M., Tavenas, F. "Induced Pore Pressures i n S e n s i t i v e Clay", Proceedings, Conference, Calgary, Canada. And La R o c h e l l e , P., 1980. S t a t i c P e n e t r a t i o n T e s t s i n 33rd Canadian G e o t e c h n i c a l Schmertmann, J.H., 1974. " P e n e t r a t i o n Pore Pressure E f f e c t s on Q u a s i - S t a t i c Cone Bearing, q c " r Proceedings, European 121 Symposium on P e n e t r a t i o n T e s t i n g , Stockholm, Sweden, V o l 2.2, pp 345 - 351. S c h o f i e l d , A.N. And Wroth, C P . , 1968. C r i t i c a l State S o i l  Mechanics, McGraw H i l l , New York,430 pp. Soderberg, L.O., 1962. " C o n s o l i d a t i o n Theory A p p l i e d to Foundation P i l e Time E f f e c t s " , Geotechnique, V o l 12, pp 217 - 232. Torstensson, B.A., 1975. "Pore Pressure Sounding Instrument", Proceedings, ASCE S p e c i a l t y Conference on In S i t u Measurement, R a l e i g h , N.C., V o l I I , pp 48 - 54. Torstensson, B.A., 1977. "The Pore pressure Probe", Nordiske  Geotekniske Mote, Oslo, Norway, Paper No 34.1 - 34.15. Tumay, M.T., Boggess, R.L., and Acar, Y., 1981. "Subsurface I n v e s t i g a t i o n s with Piezo-Cone Penetrometer", ASCE, S t . L o u i s Convention, S e s s i o n 35, Cone P e n e t r a t i o n T e s t i n g and  Exper ience, pp 3 2 5 - 3 4 2 . Vesic,A.S.,1972."Expansion of C a v i t i e s i n I n f i n i t e S o i l Mass", J o u r n a l of the S o i l Mechanics and Foundation D i v i s i o n , A S C E , 98(SM3) pp 265-290. Wissa,A.E.Z.,Christian,J.T.,Davis,E.H.,and Heiberg,S.,1971. " C o n s o l i d a t i o n at Constant Rate of S t r a i n " , J o u r n a l of the  S o i l Mechanics and Foundation D i v i s i o n , A S C E , 97(SM8) pp 1393-1412. Wissa, A.E.Z., M a r t i n , R.T., and Garlanger, J.E., 1975. "The Piezometer Probe", Proceedings, ASCE S p e c i a l t y Conference on In S i t u Measurement of S o i l P r o p e r t i e s , R a l e i g h , N.C., Vo l I, pp 536 - 545. 122 Appendix A Complete CPT Logs Mcdonald S i t e 1 2 3 0 UD BAR 10 5 0 J i i_ QC BAR 10 20 30 UD/QC 200 . 0 . 5 1.0 _j i i PENETRATION SPEED 2 cm/sec PENETRATION SPEED .04 cm/sec PENETRATION SPEED .027 cm/sec DENOTES E Q U I L I B R I U M PORE 1 PRESSURE PH3 STANDARD CONE C6FPS-2UBC 124 « •» DENOTES C Q U I L I O n i U M P O R E 1 P R E S S U R E PH4 STANDARD CONE C6FPS-2UBC WITH 5 IN. TIP EXTENSION 1 2 5 PH 5 STANDARD CONE C6FPS-2UBC 1 2 6 0 UD B A R 10 5 0 J L L QC BAR 0 1 0 2 0 3 0 1 0 0 i ± U D / Q C 2 0 0 . 0 . 5 1.0 PENETRATION S P E E D 2 c m / s e c i " D E N O T E S E Q U I L I B R I U M POR E P R E 5 5 PH6 STANDARD CONE C6FPS-2UBC WITH 10 IN. TIP EXTENSION 1 2 8 UD B A R 10 5 0 _! I !_ QC B A R I 0 20 30 P H 8 U D / Q C 2 0 0 . 0 . 5 ! ' I— l o O PENETRATION S P E E D 2 c m / s e c .2 c m / s e c .0 4 c m / s e c i D E N O T E S E Q U I L I B R I U M P O R E P R E S S U R E STANDARD CONE C6FPS-2UBC WITH 15 IN. TIP EXTENSION 129 UD BAR QC BAR UD/QC PH10 STANDARD CONE C6FPS-2UBC PH3 STANDARD CONE C6FPS-2UBC 131 FS BAR QC BAR RF 7. STANDARD CONE C6FPS-2UBC WITH 5 IN. TIP EXTENSION 1 3 2 FS BflR i n 1 • 0 0 i i QC BflR 0. 0 50 100 150 200 RF '/. PENETRATION S P E E D 2 c m / s e c i d . 2CL i . 3 d PH6 STANDARD CONE C6FPS-2UBC WITH 10 IN. TIP EXTENSION 1 3 3 PH 7 STANDARD CONE C6FPS-2UBC WITH 10 IN. TIP EXTENSION 134 FS BAR QC BAR RF "/. P H 8 STANDARD CONE C6FPS-2UBC WITH 15 IN. TIP EXTENSION 135 FS BRR QC BAR RF 7. P H 1 0 STANDARD CONE C6FPS-2UBC Appendix B Time F a c t o r s f o r D i s s i p a t i o n Analy I 3 7 Values of Time F a c t o r T f o r V a r i o u s Percent D i s s i p a t i o n s Method 20 Percent 40 D i s s i p a t i o n 50 60 80 B a l i g h and Levadoux 1980 0 .44 1 .89 3.62 6.47 26 .85 Torstensson 1977 S p h e r i c a l (E/cu = 500) 0 . 1 1 0.46 0.81 1 .26 3 .28 S p h e r i c a l (E/cu = 400) 0 .10 0.40 0.68 1.12 2 .85 S p h e r i c a l (E/cu = 300) 0 .085 0.35 0.61 0.98 2 .36 S p h e r i c a l (E/cu = 200) 0 .66 0.28 0.47 0.77 1 .91 s p h e r i c a l (E/cu = 1 00) 0 .057 0.20 0.32 0.50 1 .16 Torstensson 1977 C y l i n d r i c a l (E/cu = 500) 0 .34 2.14 4.29 8.33 23 .60 C y l i n d r i c a l (E/cu = 400) 0 .30 1 .75 3.57 6.79 21 .00 C y l i n d r i c a l (E/cu = 300) 0 .24 1 .38 2.81 5.37 16 .29 C y l i n d r i c a l (E/cu = 200) 0 .18 1 .06 2.32 3.82 10 . 1 3 C y l i n d r i c a l (E/cu = 1 00) 0 . 1 4 0.83 1 .37 2.49 5 .03 Note: T i s the Time F a c t o r d e f i n e d as T = c h t / r 2 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0062481/manifest

Comment

Related Items