Use of the deep penetration test in sensitive clays/ Utilisation de l'essai de penetration en profondeur dans les argiles sensibles

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Use of the deep penetration test in sensitive clays/ Utilisation de l'essai

de penetration en profondeur dans les argiles sensibles

Ladanyi, B.

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U S E

OF

T H E D E E P P E N E T R A T I O N J E S T

IN

S E N S I T I V E C L A Y S

4 3

U T I L I S A T I O N

D E

L'ESSAI

D E

PENTETRATION EN PROFONDEUR ~;

:

D A N S LES ARGILES SENSIBLES

B . LADANYI, Ph.D., D e p t . o f M i n i n g E n g i n e e r i n g Ecole p o l y t e c h n i q u e , M o n t r e o l W . J . EDEN, Soil M e c h a n i c s S e c t i o n , Division o f B u i l d i n g R e s e a r c h

N o t i o n o I R e s e a r c h C o u n c i l o f C o n o d o , O t t o w o

SYNOPSIS T h e deep penetration t e s t w a s subjected t o t r i a l s i n both t h e field and laboratory a s a possible method o f &ermining t h e undrained shear strength. _{I t i s shown that i n s e n s i t i v e c b y s the bearing capacity} f a c t o r Nc i s c o n s i d e r a b l y l e s s than 9. T h e t r i a l s showed that the deep penetration test i s a promising method o f m e a s u r i n g undrained strengthias it i s not a f f e c t e d b y disturbance and yields a continuous record o f undrain- ed s t r e n g t h s .

INTRODUCTION

O f t h e s e v e r a l d i f f e r e n t m e t h o d s proposed f o r d e t e r - m i n i n g t h e undrained s t r e n g t h o f saturated c l a y s i n situ

,

t h e vane t e s t h a s probably b e e n t h e one m o s t c o m m o n l y u s e d . T h e vane t e s t m e a s u r e s d i r e c t l y t h e u l t i m a t e undrained shear strength o f c l a y on p r e d e t e r m i n e d f a i l u r e planes under conditions s i m i l a r t o t h o s e i n a d i r e c t shear t e s t . Its m a i n advantage i s i t s s i m p l i c i t y i n both p e r f o r m a n c e and i n t e r p r e t a t i o n . T h e vane t e s t i s considered t o f u r n i s h r e l i a b l e r e s u l t s i n s o f t c l a y s , provided t h e actual m o d e o f f a i l u r e c o r r e s p o n d s t o that a s s u m e d in i t s interpretation.

A disadvantage o f t h e vane t e s t i s that it can give only a discontinuous picture o f undrained shear s t r e n g t h v a r i a t i o n in a v e r t i c a l soil profile. Another disadvantage i s that t h e t e s t r e q u i r e s introduction o f t h e vane apparatus i n t o t h e soil b e f o r e t h e shear t e s t i s p e r f o r m e d . Although t h i s m a y b e o f l i t t l e consequence in m o s t t y p e s o f c l a y s , it i s thought t o produce a c e r t a i n amount o f disturbance i n s e n s i t i v e c l a y s , particularly i n t h o s e o f a b r i t t l e t y p e ( C r a w f o r d and Eden, 1965; Eden, 1966). Another t y p e o f t e s t that can b e used f o r t h e s a m e purpose i s t h e q u a s i - s t a t i c deep penetration t e s t . I f t h e t e s t i s p e r f o r m e d b y a s e l f -recording, f i x e d - point t y p e o f p e n e t r o m e t e r , a s was done in t h i s study, continuous i n f o r m a t i o n on undrained strength o f c l a y i s obtained, and n o objection can be r a i s e d concerning t h e e f f e c t o f c l a y disturbance prior t o t h e t e s t . T h e t e s t cannot f u r n i s h d i r e c t l y , h o w e v e r , t h e value o f t h e undrained shear strength (6,) o f t h e c l a y , but t h e l a t t e r h a s t o b e calculated f r o m t h e m e a s u r e d t i p r e s i s t a n c e ( q p ) using t h e bearing capac i t y f o r m u l a

w h e r e po i s t h e total overburden pressure at t h e l e v e l o f t h e point and Nc i s t h e bearing capacity factor. It i s obvious, t h e r e f o r e , that a correct evaluation o f penetrometer t e s t r e s u l t s i n saturated clays will depend on h o w i n g t h e numerical value o f t h e factor Nc.

On t h e b a s i s o f t h e o r y and model studies, t h e value Nc = 9 h a s been proposed ( M e y e r h o f , 1951;

Skempton, 1951) and v e r i f i e d in the field (Meyerhof and Murdock, 1953). Nc values a s low a s 5 and a s high a s 25 have also b e e n reported in the literature ( S o w e r s , 1961; W a r d , Marsland and S a m u e l s , 19651 It can b e s e e n that t h e value o f t h e bearing capacity factor & f o r deep penetration o f saturated clays i s far f r o m being a constant. I t appears t o b e i n f l u - enced b y a number o f f a c t o r s such as: ( 1 ) Over-all s t r e s s - s t r a i n behaviour o f t h e clay i n undrained shear; ( 2 ) r a t e o f penetration; and ( 3 ) shape o f pene- t r o m e t e r point. No s y s t e m a t i c investigation o f t h e Nc value h a s b e e n m a d e t o date, however, that would cover all t h e s e e f f e c t s and include d i f f e r e n t t y p e s o f natural undisturbed clays.

In

particular, t h e r e i s v e r y l i t t l e i n f o r m a t i o n available on t h e value o f Nc t o b e used i n evaluating deep penetra- t i o n t e s t s i n sensitive c l a y s such a s t h o s e encou- tered i n E a s t e r n Canada and Scandinavia. A recent theoretical study (Ladanyi, 1967) shows that i n such c l a y s Nc values as low a s 5 can b e expected. T h e m a i n purpose o f t h e present i q v e s t i - gation was t o d e t e r m i n e experimentally the values o f t h e factor Nc i n typical sensitive clays, a s found

-

in t h e Ottawa a r e a , and t o compare t h e s e values

with theoretical predictions.

qp = P o

+

e U N c

...

( 1 ) For t h i s purpose, t w o s e r i e s o f penetration t e s t s w e r e carried out:

L A D A N Y I on

d

EDEN a ) omall-scale l a b o r a t o r y t e n t s c a r r i e d out

with a specially deaigned s e l f - r e c o r d i n g penetrom

-

e t e r of 1. 55 c m d i a m e t e r ;

b) field t e s t s with a c o m m e r c i a l s e l f - r e c o r d i n g cone penetrometer of 3. 57 c m diameter.

Laboratory penetration t e s t s w e r e p e r f o r m e d on undisturbed specimens of sensitive clays f r o m two different locations. Field penetration t e s t s w e r e c a r r i e d out at the s a m e two locations in the Ottawa a r e a .

LABORATORY PENETRATION TESTS Apparatus and P r o c e d u r e

A s m a l l cylindrical probe with a f l a t p r e s s u r e - s e n - sitive t r a n s d u c e r installed in t h e b a s e waa used ( F i g u r e 1)

.

F o r c e t r a n s d u c e r R o l l e r b e a r i n g s E 0 CI 0 Fig. 1 Experimental A r r a n g e m e n t F o r L a b o r a t o r y P e n e t r a t i o n T e s t s . When mounted in a t r i a x i a l p r e s s , t h e a s s e m b l y permitted s e p a r a t e m e a s u r e m e n t and continuous r e - cording of both the p r e s s u r e a t t h e b a s e of the probe and the t o t a l force during penetration.

Undinturbed specimens of clay, obtained in a 5 -in. Onterberg piston aampler, w e r e placed in a 26-cm- long split s t e e l cylinder. Liquid wax was poured into the remaining space between t h e specimen and cylinder t o provide uniform l a t e r a l support.

The r a t e of penetration was 0. 356 cm/min in a l l t h e tents. Another s e r i e s of t e s t s was conducted to otudy t h e effect of r a t e of penetration with the s a m e p r o b e mounted in a u n i v e r s a l t e s t i n g machine where penetration r a t e s up t o 12.7 cm/min could be attained.

T e a t Resulta

C l a y s p e c i m e n s f r o m two different locations, a t t h e National R e s e a r c h L a b o r a t o r i e a and C l o u c e a t e r Naval Station ( C r a w f o r d and Eden, 1965), w e r e u s e d F i g u r e s 2 and 3 show t y p i c a l r e s u l t s of p e n e t r a t i o n t e s t s f r o m e a c h site. T h e c l a y a t the NRC s i t e had a s e n s i t i v i t y ranging f r o m 10 t o 35, w a t e r c o n t e n t s f r o m 72 t o 8 4 p e r cent and a field vane ength f r o m 0. 5 t o 0 . 7 kg/sq c m , i n c r e a s i n g n i t h depth. T h e G l o u c e s t e r c l a y had a s2nsitivity oi about 30 t o a 5 m depth, a water content f r o m 50 t u 70 and a field vane s t r e n g t h of 0. 25 kg/sq c m . Depth 1 0 . 8 0 ~ - 0 2 4 6 =E u 8 z 0 ; 10 4 a I- Y

5

12 CL 1 4 1 6 18 S K I N F R I C T I O N L. KG Fig. 2 L a b o r a t o r y P e n e t r a t i o n T e s t : NRC C l a y

In F i g u r e s 2 and 3 the variations with depth of penetration of the following two q ~ a n t i t i e s h a v e been plotted: (1) point r e s i s t a n c e a s r e c o r d e d by t h e p r e s s u r e t r a n s d u c e r a t t h e b a s e of t h e p r o b e , and (2) skin friction which i s equal to t h e d i f f e r e n c e

w h e r e

L

_{i s the s k i friction in kg, Qtot denotea the} t o t a l penetration f o r c e r e c o r d e d by t h e f o r c e t r a n s

-

d u c e r , and A = L885 s q c m i s the b a s e a r e a of the

probe. P

Analysis of T e s t R e s u l t s

Experimental evidence shows that f o r a f r i c t i o n l e e s p l a s t i c m a t e r i a l the punch h a s t o p e n e t r a t e t o a

D E E P P E N E T R A T I O N TEST

depth of a t l e a s t 4 d i a d e t e r s b e f o r e t h e effect of t h e f r e e s u r f a c e disappearb and a t r u e deep f a i l u r e phenomenon i s attained (Meyerhof, 1951). F o r t h i s r e a s o n , only t h e portion of t h e r e s u l t s below t h e depth m a r k e d by 4d in F i g u r e s 2 and 3 h a s been used in t h e following a n a l y s i s and comparison. T h e e f f e d of t h e bottom s u r f a c e of t h e s p e c i m e n was m a d e negligible by stopping p e n e t r a t i o n a t a distance of m o r e than 3 p r o b e d i a m e t e r s f r o m t h e bottom s u r - face.

S K I N F R I C T I O N L, K G

Fig. 3 L a b o r a t o r y P e n e t r a t i o n T e s t , Gloucester Clay.

The a v e r a g e r e s u l t f r o m a number of field vane t e s t s p e r f o r m e d c l o s e t o t h e s a m e location was used for comparison. In F i g u r e s 2 and 3 .the a v e r a g e s U line h a s been plotted and c o m p a r e d with t h e p a r a l l e l a v e r a g e qp-line f r o m l a b o r a t o r y p e n e t r a t i o n t e s t s , which i s shown a s a dashed line. A s t h e overburden p r e s s u r e was ~ r a c t i c a l l y z e r o in t h e laboratory testa, the e x p e r i m e n t a l a v e r a g e Nc values could be deter

-

mined f r o m t h e formula:

Nc = %/aU

. .

.

. .

. .

. . .

.

. .

.

.

.

.

.

( 3 ) T h e Nc v a l u e s s o obtained in a l l t h e t e s t s p e r f o r m e d on t h e NRC c l a y w e r e found t o v a r y f r o m 5.71 to 8.00, with a n over -all a v e r a g e f r o m t h e s i x t e s t s of Nc = 7. 23. On t h e other hand, Nc values obtained from t h r e e t e s t s on t h e Gloucester clay, a l l f r o m t h e s a m e level, did not differ much f r o m t h e value Nc = 6.85 shown in F i g u r e 3.

Some additional specimens from the s a m e level w e r e used f o r investigating t h e effect of the r a t e of pene- t r a t i o n on t h e m e a s u r e d point resistance. The teete w e r e p e r f o r m e d in a universal testing machine p e r

-

mitting controlled penetration r a t e s of up to 12.7 c m / min to be attained. It was found that for t h i s clay a tenfold i n c r e a s e i n penetration r a t e resulted in an i n c r e a s e of abbut 7. 5 p e r cent in tip resistance. FIELD PENETRATION TESTS

Apparatus and P r o c e d u r e

T h e B o r r o s penetrometer used 'in the field t e s t s i s a s e l f - r e c o r d i n g cone penetrometer with a loading potential up t o 4 tons a t t h e point. The varying load during penetration i s sensed by e l e c t r i c a l r e s i s t a n c e s t r a i n gauges mounted in a sealed piece behind t h e point, and t h i s i s continuously r e c o r d e d on a con-

stant speed chart. T o t a l r e s i s t a n c e a t t h e top of t h e r o d s i s not r e c o r d e d ty t h i s penetrometer. Figure

I

I

Location of

-+-I-

, s t r a l n gauges

:ri

w

Fig. 4a The Point of " B o r r o s l ' P e n e t r o m e t e r . Although a hand-operated jack i s provided for push- ing t h e penetrometer into t h e soil, t h e t e s t s were c a r r i e d out using a hydraulic d r i l l rig. T h i s allowed t h e drilling of a borehole through t h e d r i e d upper c r u s t and t h e pushing of the penetrometer into the s o i l a t a reasonably constant r a t e by m e a n s of the hydraulically-operated drillhead. Average r a t e of penetration was about 20 cm/min, with a variation of about f 5 cmlrnin. During the t e s t s , a constant r a t e of penetratlon was maintained for t h e full s t r o k e of the d r i l l head ( n e a r l y 2 cm).

T e s t R e s u l t s

The r e s u l t s of field penetration t e s t s a r e shown in F i g u r e s 4b and 4c. In t h e s e , Qtot, plotted against depth, r e p r e s e n t s t h e a v e r a g e load m kilograms r e g i s t e r e d by the s t r a i n gauges a t the point within s u c c e s s i v e 20 -c m intervals. As the r e s u l t s obtained

L A D A N Y I

o n d

E D E N

f o r e a c h location w e r e f a i r l y c o n s i s t e n t , only t h e A = 5 . 6 sq c m ; A' = 50 s q c m ;

a =

0.45;

B

= 0.10; a v e r a g e of Q v a l u e s m e a s u r e d a t a given l e v e l in a& 1.015 5 p 5 1.

oh.

F r o m t h e s e ,

a

a n d B v a l u e s

ot

a l l t e s t s p e r f o r m e d a t a p a r t i c u l a r location w e r e correspond t o t h e d a t a f r o m l a b o r a t o r y p e n e t r a t i o n u s e d in t h e following evaluation of t h e r e s u l t s . t e s t s and p h a s been evaluated by a n a p p r o x i m a t e

a n a l y s i s taking i n t o account a v e r a g e s h e a r s t r a i n s Q T O T A L ~ K C

100 125 produced i n t h e p l a s t i c region s u r r o u n d i n g t h e point

0 25 50 7 5 d u r i n g p e n e t r a t i o n . Q T O T A L . K C 0 O 25 5 0 7 5 1 0 0

I

I

-

T e s t C - 4 2

-

_---

T e s t G-5 4

-

6

-

I

z

8 - - C 4 LT I-

2

1 0 - 0 Y 0

E

1 2 - 0 Y 0 14

-

Fig. 4b T o t a l P o i n t R e s i s t a n c e , Q R e c o r d e d i n T h r e e F i e l d P e n e t r a t i o n a t NRG Site. 16

-

Evaluation of T e s t R e s u l t s 18

-

Owing t o t h e p a r t i c u l a r s h a p e of t h e point of the

B o r r o s p e n e t r o m e t e r and b e c a u s e t h e s t r a i n gauges

a r e located a t a c e r t a i n d i s t a n c e above t h e cone, i t 20

1

I

i s c o n s i d e r e d t h a t t h e r e c o r d e d value of Q c o n - 125

-

9

-

-

-

-

-

-

-

tot

t a i n s not only t h e point r e s i s t a n c e but a l s o s o m e Fig. 4c T o t a l P o i n t R e s i s t a n c e , Q R e c o r d e d i n r e s i s t a n c e due t o l a t e r a l s h e a r along the p a r t of t h e Two F i e l d P e n e t r a t i o n T e k ? ~ ' A t ~ l o u c e s t e r point between t h e cone and t h e s t r a i n gauges. T h e Site.

corresponding value of undrained s h e a r s t r e n g t h w a s

t h e r e f o r e , calculated f r o m the e x p r e s s i o n : Substituting t h e above v a l u e s i n Eq. 4, dividing by 5 o t

-

Ap Po

_...

A p = 10 s q c m , a n d e x p r e s s i n g s u , Qtot a n d p i n

s _u = ( 4) t s q m yields:

(A N~ t A L a t A L B ) ~

P %ot

-

Po

...

i n which A , A and A; ( F i g u r e 4(a)) a r e the a r e a s 8 = (5)

of t h e b a s z o f t k e cone, t h e c o l l a r , and t h e s u r f a c e u (Nc t 0. 7 5 2 ) ~ between t h e c o l l a r and t h e location of s t r a i n gauges,

r e s p e c t i v e l y ;

a

and

B

a r e reduction coefficients for T h e o r e t i c a l P r e d i c t i o n of Nc value

s u taking into account the remoulding and imperfect By extending t h e t h e o r y of expansion of a s p h e r i c a l contact, and P i s a s t r a i n r a t e f a c t o r t o enable c o r n - c a v i t y i n a n infinite m e d i u m t o a n e l a s t i c - p l a s t i c

-

p a r i s o n of 8 _{values obtained in t h e p e n e t r a t i o n t e s t s}

u f r i c t i o n l e s s m a t e r i a l c h a r a c t e r i z e d by a d r o p of with t h o s e m e a s u r e d in s o m e other types of t e s t s s t r e n g t h a f t e r f a i l u r e , Ladanyi (1967) h a s s h o w n p e r f o r m e d a t a different s t r a i n r a t e . _{t h a t , f o r a t y p i c a l s e n s i t i v e clay, a n a p p r o x i m a t e}

Nc value can b e calculated f r o m t h e e x p r e s s i o n F o r the p u r p o s e of evaluating t h e p r e s e n t t e s t r e - _{following Eq. (6). T h e v a l u e s of sU, s n E s a n d E,} a u l t ~ . t h e n u m e r i c a l values of v a r i o u s m a g n i t u d e s i n _{i n t h i s equation c o r r e s p o n d t o a s i m p l i f i e d s t r e s s -}

4.

4 have been taken a s follows: A _{= 10 sq ,-,,;}

D E E P P E N E T R A T I O N T E S T

undrained cOmPresSion t e s t ( F i g u r e 5). T h e value of r a t i o

E

/sU would probably be nearer to the i n t h e r e m o u l d e d adhesion between t h e cone s u r -

f a c e and t h e clay. &own above, Eq. 8 h a s been chosen f o r t h e _of

6 _{v a l u e s shown}

_in

_{Figures 6a and 6b.}

In

_{f i g u r e s h e s values w e r e obtained by a 110}

'a 4 'r 55 m m f i e l d vane? T h e r a n g e of s e n s i t i v i t y a t

NC

=-

8 +-3

-

8 d i f f e r e n t depths is a l s o indicated in the f i g u r e s . T h e

u u _{v a l u e s shown h a v e b e e n obtained by using a v e r a g e}

qot

values f r o m t h e penetration t e s t s shown in F i g - u r e a 4b and 4c, respectively. 5,. K G I C M ~ 2 S u 4 E s '

-

el^

E,

25,

b^

Slrnpllfled

$

A v g 5, from 3 fleld

...

-zC

penetration tests 0 CIP E l r & I Fig. 5 S i m p l i f i e d S t r e s s - S t r a i n Behaviour of A S e n s i t i v e C l a y in Undrained C o m p r e s s i o n T e s t A s s u m e d in Nc Calculation.

It h a s been shown (Ladanyi, 1967) t h a t f o r a t y p i c a l Leda c l a y f r o m t h e NRC s i t e with a s e n s i t i v i t y of about 16 t h e following n u m e r i c a l v a l u e s could b e t a k e n f o r d i f f e r e n t r a t i o s i n Equation 6:

250 s ( E /s ) r 5 0 0 ; (E / s r ) = 16; ( 8 / S ) = 0.45,

(sa/sU)

='o.

35. ~ c c o r J m ~ t o ~ ~ u a t i z n 6: f o r t h e a b o v e r a n g e of E /sU r a t i o t h e value of Nc should then b e s i t u a t e d b z t w e e n 5 . 8 5 S N c s 6.73.

F o r c o m p a r i s o n , it should b e n o t e d that f o r t h e s a m e r a n g e of E /s r a t i o , t h e s a m e a n a l y s i s would give, f o r an inse%si#ve clay,

8. 22 r Nc 9.15. Fig. 6a C o m p a r i s o n of s Values F r o m Field Vane

And ~ e n e t r o m e t 2 r T e s t s At NRC Site. It i s evident, t h e r e f o r e , t h a t Nc value depends con-

s i d e r a b l y o n t h e p o s t - p e a k behaviour of t h e clay. _{F i g u r e 6a shows t h a t a t t h e NRC s i t e su values f r o m} A r e c e n t i n v e s t i g a t i o n ( L a d a n y i e t al, 1968) shows _{t e s t s follow approximately t h e s a m e} t h a t t h e d r o p in s t r e n g t h i m m e d i a t e l y a f t e r t h e p e a k _{t r e n d a s t h o s e f r o m field vane t e s t s . T h e y a r e gen-} i e m u c h m o r e p r o n o u n c e d in s e n s i t i v e c l a y s t h a n i n e r a l l y lower than t h e a v e r a g e f r o m field vane t e s t s o r d i n a r y c l a y s . It follows, t h e r e f o r e , t h a t Nc value i n absolute value. It i s probable that, owing t o t h e should g e n e r a l l y b e e x p e c t e d t o d e c r e a s e with i n - _{b r i t t l e and jointed c h a r a c t e r of t h e p a r t i c u l a r clay,} c r e a s i n g s e n s i t i v i t y of clay. t h e a c t u a l Nc value is lower than that u s e d in t h e

evaluation. It was found that with Nc = 5. 50 t h e

R e s u l t s of Evaluation a g r e e m e n t would b e m o r e s a t i s f a c t o r y , e s p e c i a l l y T a k i n g 5.85 s N 5 6 . 7 3 , and 1.015 s p s 1.040, Eq. below t h e 12 m l e v e l w h e r e a highly s e n s i t i v e c l a y

5 yields: i s found.

f o r

Es/su = 250:

.

(Q

-

86

.

. . .

.

. .

.

.

.

.

(7) c o m p a r i s o n of s v a l u e s obtained a t theG10uceater u tot _{site, ( F i g u r e 6b), shows a s i m i l a r i n c r e a s e in sU} u

f o r with depth f o r t h e two types of test.

Es/sU = 500: 6 = (Qtot - p o )/7.60

. . .

. .

.

.

.

.

( 8 ) 6 values calculated f r o m Nc = 6 - 7 3 s e e m to b e a

u

liFtle t o o high. A b e t t e r a g r e e m e n t could h a v e been B e c a u s e it w a s thought t h a t f o r t h e c l a y in s i t u t h e

L A D A N Y I a n d E D E N obtained if N h a d been t a k e n t o e q u a l about 7. 50.

Fig. 6b C o m p a r i s o n of s V a l u e s F r o m F i e l d Vane And ~ e n e t r o m e t g r T e s t s a t G l o u c e s t e r Site. CONCLUSIONS On t h e b a s i s of t h i s investigation, t h e following conclusions a r e suggested: 1. F o r t h e p e n e t r a t i o n r a t e s u s e d in t h e t e s t s , s e n s i t i v e c l a y s behave d u r i n g deep punching a s o r d i - n a r y clays: f a i l u r e o c c u r s without any s i g n of even- t u a l liquefaction owing t o high l o c a l remoulding. 2. B e a r i n g c a p a c i t y v a l u e s t h a t a r e valid for d e e p p e n e t r a t i o n i n undrained s h e a r a r e lower in s e n s i - t i v e c l a y s t h a n i n o r d i n a r y c l a y s . Instead of a value Nc 4 9 commonly found i n o r d i n a r y c l a y s , t h e Nc

f o r s e n s i t i v e c l a y s v a r i e s f r o m about 5. 50 t o 8. 00, with the lower v a l u e s o c c u r r i n g a t high s e n s i t i v i t i e s . Actual Nc v a l u e s found in t h i s s t u d y by using, f o r c o m p a r i s o n , t h e b e s t f i e l d vane r e s u l t s a r e 5.70 < Nc < 8.00 in l a b o r a t o r y penetration t e s t s and 5. 50 _{< Nc < 7. 50 i n field penetration t e s t s . The} t h e o r y gives Nc = 6.73 f o r St ~ 1 6 . A s Nc is found t o v a r y with c l a y s e n s i t i v i t y , m o r e r e c o r d s f r o m field and l a b o r a t o r y p e n e t r a t i o n t e s t s will b e needed t o r e l a t e i t s value m o r e c l o s e l y with s e n s i t i v i t y . 3. R e s i s t a n c e t o p e n e t r a t i o n i n c r e a s e s w i t h in- c r e a s i n g r a t e of p e n e t r a t i o n . T h e i n c r e a s e i n point r e s i s t a n c e found i n l a b o r a t o r y s m a l l - s c a l e t e s t s w a s 7. 5 p e r c e n t f o r a tenfold i n c r e a s e in p e n e t r a t i o n r a t e ; t h i s follows t h e t r e n d n o r m a l l y found in t h e u n d r a i n e d c o m p r e s s i o n t e s t . It i s c o n c l u d e d t h a t t h e effect of t h e r a t e of p e n e t r a t i o n s h o u l d b e t a k e n i n t o .

.

account when c o m p a r i n g r e s u l t s of d e e p p e n e t r a t i o n t e s t s with r e s u l t s of o t h e r t y p e s of f i e l d a n d l a b o r a - t o r y t e s t s f o r u n d r a i n e d s t r e n g t h d e t e r m i n a t i o n s . ACKNOWLEDGEMENTS T h e a u t h o r s w i s h t o e x p r e s s t h e i r g r a t i t u d e t o t h e i r c o l l e a g u e s a t t h e S o i l M e c h a n i c s S e c t i o n who h a v e f a c i l i t a t e d t h e f i e l d a n d l a b o r a t o r y i n v e s t i g a t i o n s d e s c r i b e d i n t h i s p a p e r which is p u b l i s h e d with t h e a p p r o v a l of t h e D i r e c t o r of t h e D i v i s i o n of Building R e s e a r c h , National R e s e a r c h C o u n c i l of Canada. R E F E R E N C E S C r a w f o r d , C. B. and W. J. Eden, 1965, A c o m p a r i - s o n of l a b o r a t o r y r e s u l t s with i n - s i t u p r o p e r

-

t i e s of L e d a c l a y , P r o c . , 6th I n t e r n a t . Conf. Soil M e c h s . a n d Found. E n g . , M o n t r e a l . Vol. 1, p. 31-35. Eden, W. J . , 1966, An e v a l u a t i o n of t h e f i e l d v a n e t e s t i n s e n s i t i v e c l a y , A m e r . Soc. T e s t i n g M a t s . , S T P No. 399, p. 8-17.

Ladanyi, B.

,

1967, Deep punching of s e n s i t i v e c l a y s , P r o c . , 3 r d P a n a m . Conf. S o i l M e c h s . Found. Eng., C a r a c a s , Vol. 1 , p. 533-546. Ladanyi, B. et a l , 1968, P o s t - p e a k b e h a v i o u r of

s e n s i t i v e c l a y s i n u n d r a i n e d s h e a r , Can. Geotech. J . , Vol. V, No. 2, p. 59-68.

Meyerhof, G. G. , 1951, T h e u l t i m a t e b e a r i n g c a p a c

-

i t y of foundations, Ggotechnique, Vol. 2, p. 301-332. M e y e r h o f , G. G. a n d L. J. M u r d o c h . 1953, An i n v e s t i g a t i o n of t h e b e a r i n g c a p a c i t y of s o m e b o r e d a n d d r i v e n p i l e s i n London c l a y , GBotechnique, Vol. 3, p. 267-282. Skempton, A. W .

,

1951, T h e b e a r i n g c a p a c i t y of c l a y s , P r o c . , Build. R e s . C o n g . , London, p. 180-189. S o w e r s , G. F. , 1961, D i s c u s s i o n , S e s s i o n 3B, P r o c . , 5th Internat. Conf. S o i l M e c h s . Found. Eng., P a r i s , Vol. 111, p. 261 -263.

Ward, W. H., e t a l , 1965, P r o p e r t i e s of London c l a y a t A s h f o r d C o m m o n s h a f t , GCotechnique, Vol. 15, p. 321-344.