Laboratory studies of the adfreeze bond between small- scale model piles and frozen sand

(1)

READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE. https://nrc-publications.canada.ca/eng/copyright

Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.

Questions? Contact the NRC Publications Archive team at

PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.

NRC Publications Archive

Archives des publications du CNRC

This publication could be one of several versions: author’s original, accepted manuscript or the publisher’s version. / La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version acceptée du manuscrit ou la version de l’éditeur.

Access and use of this website and the material on it are subject to the Terms and Conditions set forth at

Laboratory studies of the adfreeze bond between small- scale model

piles and frozen sand

Parameswaran, V. R.

https://publications-cnrc.canada.ca/fra/droits

L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site

LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.

NRC Publications Record / Notice d'Archives des publications de CNRC:

https://nrc-publications.canada.ca/eng/view/object/?id=006d8b89-af3a-45b3-9c30-d45b6557a4db

https://publications-cnrc.canada.ca/fra/voir/objet/?id=006d8b89-af3a-45b3-9c30-d45b6557a4db

(2)

,t

- I

2

1

4

9

.Q

\3

2. I

_$

National Research

Conseil national

Council Canada

de recherches Canada

LABORATORY STUDIES OF

THE ADFREEZE BOND BETWEEN SMALLSCALE

MODEL PILES A N D FROZEN SAND

':

+LYZED

by

V.R

Parameswaran

0

Reprinted,

with

permission, f b m

Vol.

1,

Proceedings 3rd International Conference

on Permafrost

held

in Edmonton, Alberta, 10

13 July 1978

p.

714 720

DBR Paper No.

813 Divirtoa of

Building

R e r e d

(3)

LABORATORY STUDIES OF THE ADFREEZE BOND BETWEEN SMALL-SCALE MODEL PILES AND FROZEN SAND

V.R. Parameswaran, D i v i s i o n of B u i l d i n g R e s e a r c h , N a t i o n a l R e s e a r c h C o u n c i l of Canada, Ottawa, O n t a r i o , KIA OR6

The a d f r e e z e s t r e n g t h developed d u r i n g f r e e z i n g of c y l i n d r i c a l p i l e s t o f i n e Ottawa sand mixed w i t h 1 4 % by w e i g h t of w a t e r was measured under c o n s t a n t r a t e s of

I n a c r e e p p i l e d i s p l a c e m e n t on a n I n s t r o n t e s t i n g machine and under c o n s t a n t l o a d

equipment]. Four t y p e s of p i l e were s t u d i e d : n a t u r a l B.C. f i r , c o n c r e t e , s t e e l c o a t e d w i t h a r e d o x i d e p r i m e r , and c r e o s o t e d B.C. f i r . C o n s t a n t r a t e t e s t s showed t h a t a d f r e e z e s t r e n g t h i n c r e a s e d w i t h i n c r e a s i n g l o a d i n g r a t e . P r e l i m i n a r y d a t a from t h e c o n s t a n t l o a d c r e e p t e s t s i n d i c a t e t h a t t h e l o a d dependence of t h e s t e a d y - s t a t e c r e e p r a t e f o r p i l e s i n f r o z e n sand a g r e e s w i t h t h e d i s p l a c e m e n t r a t e depen- d e n c e of t h e a d f r e e z e s t r e n g t h s d e t e r m i n e d by e x t r a p o l a t i o n of t h e r e s u l t s of t h e c o n s t a n t r a t e t e s t s . I n g e n e r a l , maximum a d f r e e z e s t r e n g t h developed w i t h n a t u r a l B.C. f i r , and t h e minimum w i t h c r e o s o t e d B.C. f i r . V.R. Parameswaran, D i v i s i o n d e s r e c h e r c h e s e n b z t i m e n t , C o n s e i l n a t i o n a l d e r e c h e r c h e s du Canada, Ottawa, O n t a r i o KIA OR6

L t a d h 6 r e n c e due a u g e l d e p i e u x c y l i n d r i q u e s 5 du s a b l e f i n d ' 0 t t a w a c o n t e n a n t 14% d ' e a u , a u p o i d s , a 6t.G mesur6e s o u s d6placement d e s p i e u x

h

v i t e s s e c o n s t a n t e , d a n s une machine d ' e s s a i I n s t r o n , e t s o u s c h a r g e c o n s t a n t e (dans un a p p a r e i l Provo- q u a n t l a r e p t a t i o n ) . Q u a t r e t y p e s d e p i e u x o n t 6 t 6 6 t u d i 6 s : en s a p i n d e Colombie non t r a i t s , e n b g t o n , en a c i e r r e c o u v e r t d ' u n p r i m a i r e a u minium d e plomb e t en s a p i n d e Colombie c r 6 o s o t 6 . Les e s s a i s 2 v i t e s s e c o n s t a n t e o n t montr6 que lVadh.Grence due

a u g e l augmente a v e c l e t a u x d e m i s e en c h a r g e . Les r E s u l t a t s p r 6 l i m i n a i r e s d e s e s s a i s d e r e p t a t i o n b c h a r g e c o n s t a n t e i n d i q u e n t que l e r a p p o r t e n t r e l a c h a r g e e t l a r e p t a t i o n

h

v i t e s s e c o n s t a n t e d e s p i e u x d a n s l e s a b l e g e l 6 c o r r e s p o n d a u r a p p o r t e n t r e l e t a u x d e d t 5 ~ l a c e m e n t e t l a f o r c e d e lfadh.Grence due a u g e l e x t r a p o l 6 d e s r g s u l t a t s d e s e s s a i s h t a u x c o n s t a n t . Dans l ' e n s e m b l e , l q a d h 6 r e n c e maximale s e mani- f e s t a i t a v e c l e s a p i n d e Colombie non t r a i t 6 e t l ' a d h 6 r e n c e minimale, a v e c l e s a p i n d e Colombie cr.Gosot6. CuJIa C M e p 3 a H P i R Q P i J I l 4 H A p M ~ e C K P i X C B a f i C M e J l K 0 3 e p H H C T M M n e C K O M , C M e u a H w

c

1 4 Bet.% BO-,

a 3 ~ e p ~ n a c b

npx

n o c T o R H H H x C K O P O C T R X c M e u e - H U R C B a R H a U C n b J T a T e J 7 b H O R M a l L l M H e MHCTPOH W n p H IIOCTORHHOR H a I ' P Y 3 K e

/ ~ a

M a u u H e n n R u c n u T a H w R H a n o n s y s e c ~ b / . H a y s a n a c b s e T H p e T u n a csah: C O C H O B a R ; ~ ~ T O H H ~ R ; C T a J I b H a R , I l O K p b I T a R C Y p W K O M ; W C O C H O B a R , I I p O n u T a H - H a R K p e 0 3 0 T O M . ~ T MW C l T H T a H H R l l O K a 3 a J l W , s T O C M n a C M e p 3 a H H R B O 3 P a C T a e T

c

y s e n w s e H w e M

c ~ o p o c ~ w

H a r p y x e H w x . n p e n s a p u ~ e n b ~ M e n a H H b l e u c n M T a H n f i H a l T O J I 3 y s e C T b

npu

n O C T O R H H 0 R H a r p y 3 K e y K a 3 M B a E O T H a T O , s T 0 3 a B H C W M O C T b C T a 6 u J I b ~ o f i C K O P O C T M n O J I 3 y W 3 C T H O T H a r p Y 3 K W A J l R C B ~ R B M e P 3 J I O M n e C K e C O r J I a C Y e T C R C 3 a B H C U M O C T b I O M e m y C K O P O C T b I O C M e u e H U R I4 CUJ-IOR c M e p 3 a H n R r O n P e A e J I R e M O f i n y T e M 3 K C T p a I I O J I R Q b i X - i p e 3 y J I b T a T O B H C ~ T H T ~ H H ~ ~ . O T M ~ ~ ~ H O , YT.0 M a K C H M a J I b H a R

cwna c ~ e p 3 a ~ w ~

p a 3 ~ u s a e ~ c ~

npu

u c n o n b s o s a H H P i ~ e o 6 p a 6 0 ~ a H - HblX C O C H O B H X C ~ a f i ,

a

M H H H M a J l b H a R

-

n p H H C n O J l b 3 0 B a H H H C O C H O B H X

csafi,

I I p O n H T a H H H X K p e 0 3 0 T O M .

(4)

LABORATORY STUDIES OF THE ADFREEZE BOND BETWEEN SMALL-SCALE MODEL PILES

AND

FROZEN SAND

V.R. Parameswaran

Division of Building Research, National Research Council of Canada Ottawa, Ontario, KIA OR6

T~ is the adfreeze strength at the pile-

soil interface, INTRODUCTION

Af is the pile-soil interfacial area in Pile foundations incorporating an air space the permafrost zone,

between the structure and the ground surface are

-rd

is the frictional drag stress between used extensively in permafrost areas to transfer _{the pile and the unfrozen soil (if} the structure loads through the unstable active _{present) over the permafrost zone,} layer to the more stable permafrost. Various

types of piles, including timber, steel pipes and

Ad is the pile-soil interfacial area in H-sections, and precast concrete piles, may be this zone,

used. Wood piles are the most common, however, L is the structural load, because they are available locally in many parts

of the permafrost regions. Cast-in-place concrete

T~ is the stress due to frost heave in the

piles have been used occasionally in special cases., active layer in the ground As a rule of thumb, a minimum depth of embedment

Ah is the pile-soil interfacial area in the

in permafrost of

3

metres or three times the _{active zone,} maximum depth of the active layer during the

design life of the structure (whichever is larger) U is the uplift load due to wind is recommended for piles in permafrost regions.

Bv knowing the distribution of the allowable

A

pile foundation must resist uplift forces due to frost heave in the active layer and loads due to wind and the weight of the structure. Pile foundations in frozen ground transfer superimposed loads by two mechanisms: end bearing, and shear along the pile (adfreezing). The total bearing capacity of a pile is therefore the sum of the calculated contributions of the two mechanisms. Empirical formulae for these calculations have already been proposed by several workers in the Soviet Union (Vyalov and Porkhaev, 1969), based on their experience in building in the North.

The end bearing capacity of a pile can be obtained from the value of the compressive strengths of the soil determined under confined and unconfin- ed conditions. The shearing resistance developed at the pife-soil interface has two components: that due to adhesion of ice to the pile; and that due to soil grain friction at the pile-soil interface. The supporting capacity for a pile erabedded in permafrost results primarily from the shearing resistance at the pile surface. In general, for a pile supporting a structure in permafrost the following condition should be met:

where P is the end-bearing capacity for the pile, as determined from the compressive strength of the soil under the pile, the cross-

sectional area of the bottom end of the pile, and a suitable factor of safety,

-

adfreeze strength, T ~ , along the length of the pile, the depth of embedment in permafrost required to carry the applied load L can be calculated. Thus it is imperative that T~ be determined accurately to permit reliable design of foundations for structures in permafrost regions.

Although measurements of the adfreeze strength between piles and frozen ground have been taken since 1930 (mainly in the Soviet Union),

sufficient information is not yet available to make it possible to design for different foundation materials such as concrete, wood, and steel in various soils. The early tests were done by freezing a pile into the ground, then pushing it through or pulling it out of the completely frozen ground at a relatively fast rate and measuring the force required. The results of early work in the Soviet Union from short-term tests have been given by Tsytovich and Sumgin (1959), Tsytovich (1975) and Vyalov (1965). Crory (1966), Crory and Reed (1965) and Sanger (1969) have reported the results of pile load tests in the permafrost regions of North America for adfreeze strength, pile settlement under loads and heave of piles due to freeze-back of the active layer. Some of the tests were short term, and others were carried out ovCr periods of several weeks.

There has been no systematic laboratory measurement of the adfreeze strength between piles and soils. Recently, Laba (1974) measured the

(5)

c a l l e d i t ) b e t w e e n f r o z e n s a n d and c o n c r e t e u n d e r l a b o r a t o r y c o n d i t i o n s by p u s h i n g f r o z e n s a n d from a n i n n e r c y l i n d r i c a l c a v i t y i n a c o n c r e t e b l o c k a t a r a t e o f 1 . 2 mm p e r m i n u t e . These r e s u l t s i n d i c a t e , i n g e n e r a l , t h a t " f r o s t g r i p " d e c r e a s e d r a p i d l y w i t h i n c r e a s i n g p o r o s i t y , t h a t i t i n c r e a s e d w i t h i n c r e a s i n g i c e c o n t e n t i n t h e s a n d and t h a t " f r o s t g r i p " i n c r e a s e d w i t h d e c r e a s i n g t e m p e r a t u r e . L a b o r a t o r y s t u d i e s h a v e b e e n i n i t i a t e d o n t h e i n f l u e n c e o f v a r i a b l e s s u c h a s l o a d i n g r a t e , t y p e o f p i l e and p i l e s u r f a c e , t e m p e r a t u r e , m o i s t u r e , e t c . , on t h e a d f r e e z e s t r e n g t h and b e a r i n g c a p a c i t y o f p i l e s i n f r o z e n s o i l s . Some p r e l i m i n a r y r e s u l t s of measurement of t h e a d f r e e z e s t r e n g t h d e v e l o p e d a t t h e i n t e r f a c e between model p i l e s and f r o z e n s a n d - i c e m i x t u r e s a r e p r e s e n t e d i n t h i s p a p e r .

EXPERIMENTAL METHOD

Measurement o f A d f r e e z e S t r e n g t h u n d e r C o n s t a n t R a t e s of Displacemen!

The a p p a r a t u s used f o r t h e e x p e r i m e n t s i s i l l u s t r a t e d i n F i g . I . The model p i l e (A) was 76.2 mm i n d i a ~ . e t e r and 304.8 mm l o n g . Ottawa f i n e s a n d (ASTM S p e c i f i c a t i o n C-109, p a s s i n g S i e v e No. 3 0 and r e t a i n e d on S i e v e No. 1 0 0 ) mixed w i t h 14% by w e i g h t of w a t e r was p l a c e d and compacted a r o u n d t h e p i l e i n f i v e l a y e r s , e a c h 3 8 . 1 mm t h i c k , t o a n optimum d e n s i t y o f a b o u t 1 , 7 0 0 kg m-3, a s d e t e r m i n e d by a s t a n d a r d P r o c t o r t e s t . Box (B) was o f 25.4 mm t h i c k P l e x i g l a s p l a t e s , and t h e p l u g (C) and t h e b a s e (D) w e r e aluminum. The box c o n t a i n i n g b o t h p i l e and s a n d was p l a c e d i n a c o l d room ( m a i n t a i n e d a t -6Oc f 0.2"C) f o r f o u r d a y s t o e n s u r e c o m p l e t e f r e e z i n g of t h e s a n d . A thermo- c o u p l e (T) p l a c e d i n t h e m i d d l e of t h e sand w a s used t o d e t e r m i n e t e m p e r a t u r e

.

A f t e r c o m p l e t e f r e e z i n g t h e p l u g (C) was removed and t h e p i l e pushed o u t by a ram a t t a c h e d t o t h e c r o s s - h e a d of a f l o o r model I n s t r o n t e s t i n g machine (25000 kg c a p a c i t y ) i n s t a l l e d i n t h e c o l d room. Each t e s t was c a r r i e d o u t a t a c o n s t a n t r a t e of c r o s s - h e a d movement. D i s p l a c e m e n t of t h e p i l e was t a k e n t o b e e q u a l t o t h e d i s p l a c e m e n t o f t h e c r o s s - h e a d l e s s t h e d e f l e c t i o n o f t h e p l a t e (D), measured by a d i a l gauge o r a DCDT p o s i t i o n e d u n d e r t h e p l a t e n e a r t h e p i l e . Four t y p e s o f c y l i n d r i c a l p i l e s w e r e s t u d i e d : N a t u r a l B.C. f i r w i t h a smooth s u r f a c e f i n i s h . C o n c r e t e p i l e s w i t h a smooth s u r f a c e f i n i s h . T h e s e w e r e c a s t i n t h e l a b o r a t o r y from a commercial d r y mix, S a k r e t e , t o which w a t e r was added i n t h e recommended p r o p o r t i o n . A f t e r c a s t i n g i n P l e x i g l a s t u b e s h a v i n g a n i n t e r n a l d i a m e t e r of 76.2 mm and w a l l t h i c k n e s s of 1 2 . 7 mm, t h e c o n c r e t e mix was v i b r a t e d u s i n g a n e l e c t r i c v i b r a t o r t o e l i m i n a t e a s much o c c l u d e d a i r a s p o s s i b l e . The f i n i s h e d and c u r e d c o n c r e t e ' c y l i n d e r s had a d e n s i t y of 2250 kg m-3. S t e e l p i l e s made from m i l d s t e e l t u b e s h a v i n g o u t s i d e d i a m e t e r o f 76.2 mm and w a l l t h i c k n e s s o f 6 . 3 5 mm c l o s e d a t t h e b o t t o m end w i t h a welded s t e e l p l u g and a t t h e t o p by a r u b b e r s t o p p e r . T h e s e p i l e s w e r e p a i n t e d w i t h a r e d o x i d e p r i m e r t o p r e v e n t r u s t i n g i n t h e wet s a n d . C r e o s o t e d B.C. f i r . B.C. f i r p i l e s , machined t o a smooth s u r f a c e f i n i s h , were c r e o s o t e d i n a h i g h p r e s s u r e a u t o c l a v e i n t h e E a s t e r n F o r e s t P r o d u c t s L a b o r a t o r y , Department o f Environment, Ottawa. F o l l o w i n g c r e o s o t i n g , t h e wood was found t o h a v e a b s o r b e d , o n a n a v e r a g e , 9 6 . 3 kg m-3, i . e . e a c h p i l e would h a v e a b o u t 0.136 kg o f c r e o s o t e . R e s u l t s o f C o n s t a n t R a t e T e s t s When a p i l e was l o a d e d a t a c o n s t a n t r a t e , t h e l o a d - d i s p l a c e m e n t c u r v e was v e r y s i m i l a r t o t h e s t r e s s - s t r a i n c u r v e f o r a f r o z e n s o i l i n uncon- f i n e d c o m p r e s s i o n , a s shown i n F i g . 2 f o r a n u n t r e a t e d B.C. f i r p i l e . The l o a d r e a c h e d a p e a k , t h e n dropped q u i c k l y , i n d i c a t i n g t h a t t h e bond

between t h e wooden p i l e and s a n d had broken. A

s i m i l a r c u r v e was o b t a i n e d f o r c o n c r e t e p i l e s . F o r a p a i n t e d steel p i l e , t h e l o a d r e a c h e d a maximum, t h e n dropped a b r u p t l y , i n d i c a t i n g a c l e a n s h e a r o f t h e p i l e from t h e s o i l . I n F i g . 2 t h e l o a d d e c r e a s e s l e s s a b r u p t l y , i n d i c a t i n g t h a t t h e r e i s s t i l l some a d h e s i o n a t t h e i n t e r f a c e . A d f r e e z e s t r e n g t h was c a l c u l a t e d by d i v i d i n g t h e maximum l o a d a t t h e p e a k of t h e c u r v e by t h e s u r f a c e a r e a o f c o n t a c t between t h e p i l e and t h e s o i l . The I n s t r o n c r o s s - h e a d s p e e d s w e r e v a r i e d

between 0.0005 and 0 . 1 mm min-l. At t h e s l o w e s t

r a t e i t t o o k a b o u t 50 h o u r s t o r e a c h a p e a k , and a t t h e f a s t e s t r a t e o n l y a b o u t 30 m i n u t e s . D i s p l a c e m e n t a t peak l o a d was a b o u t 0 . 5 t o 1.5 mm, d e p e n d i n g upon t h e t y p e o f p i l e and t h e r a t e o f l o a d i n g . V a l u e s o f a d f r e e z e s t r e n g t h o b t a i n e d f o r t h e v a r i o u s p i l e s a t d i f f e r e n t r a t e s o f l o a d i n g a r e shown i n T a b l e I . F i g u r e 3 g i v e s a d f r e e z e s t r e n g t h s p l o t t e d a s a f u n c t i o n of l o a d i n g r a t e on a l o g - l o g s c a l e f o r t h e f o u r k i n d s of p i l e s . A d f r e e z e s t r e n g t h , T ~ v a r i e s w i t h r a t e of p i l e , d i s p l a c e m e n t

L,

a c c o r d i n g t o : The v a l u e s o f m and n , o b t a i n e d by 1 i ~ i e a r r e g r e s s i o n a n a l y s i s , a r e a s f o l l o w s : - B.C. f i r C o n c t e t e 0.2161 4 . 6 3 P a i n t e d s t e e l 0.1661 6.02 C r e o s o t e d B.C. f i r 0.1862 5 . 3 7

The maximum a d f r e e z e s t r e n g t h was f o r u n t r e a t e d B.C. f i r and minimum f o r c r e o s o t e d B.C. f i r and p a i n t e d s t e e l p i l e s . The a d f r e e z e s t r e n g t h v a l u e s o b t a i n e d f o r c o n c r e t e p i l e s w e r e l a r g e r t h a n t h o s e f o r . c r e o s o t e d B.C. f i r and p a i n t e d s t e e l , b u t c o n s i d e r a b l y lower t h a n t h o s e f o r u n t r e a t e d B.C. f i r . Constant-Load T e s t s I n a c t u a l p r a c t i c e , a p i l e f o u n d a t i o n s u p p o r t i n g

(6)

a structure is subjected to constant loads rather

than constant rates of load application. Creep is

the process of deformation under such conditions,

occurring at the interface between the pile and the

soil. To simulate these conditions in model

studies, a constant-load creep apparatus was built

for which the Plexiglas box with pile shown in Fig.

1 could be used.

Figure 4 is a schematic diagram of the creep

frame with the pile inside the sand box. Weights

were placed on the loading pan (B).

This load was

magnified by a factor of 4 at pile A due to the

ratio a n

(C).

The load on the pile was measured

by means of a BLH load cell (D) having a capacity of

4550 kg. The BLH load cell was calibrated on the

Instron load cell which was, in turn, calibrated

by a proving ring.

Two DCDT's, one positioned under the pile and the

other under the plate supporting the block of

frozen sand, monitored deflections due to the load.

Net pile displacement was taken to be equal to the

difference between the two deflections.

Results of Constant-Load Creep Tests

Figure 5 shows a typical net displacement-time

curve obtained for a painted steel pile. The load

on the pile was 1130.57 kg, corresponding to a

stress of 2.43 ?Pa on the pile head and 0.243

MPa

along the pile soil interface. This curve

resembles a classical creep curve, with a primary

region (A) where the creep rat? decreased to a

steady value, a short secondarg region (B) of about

8 hours, for which the steady-state creep rate was

1.04 x

nun

min-l, and a tertiary region (C)

where the creep rate accelerated until failure of

the pile occurred after about 34 hours.

The results of preliminary tests are shown in Fig.

6. The straight lines 1 to 4 are extrapolations

to the lower-rate regions of the adfreeze strengths

vs loading rate lines shown in Fig. 3; the plotted

points indicate the rates of motion of the piles

in the steady-state creep region under constant load

(region B in Fig. 5).

In Fig. 6, line 5 for creep

of painted steel has about the same slope as line

3, the adfreeze strength vs loading rate. For

concrete and creosoted B.C. fir, the data obtained

from the constant-load creep experiments are in

reasonable agreement with the results of the

adfreeze strength tests under constant rates of

loading, extrapolated to the lower strain rate

regions.

DISCUSSION

AND CONCLUSION

1

Data available in the literature on the adfreeze

strength of piles in ftozen soil are meagre, and

most laboratory tests to determine adfreeze

strength have been done at fast rates (Tsytovich

1975, Laba 1974, Rooney 1976).

The preliminary

results now presented indicate that adfreeze

strength decreases with decreasing rate of loading.

Preliminary data from creep tests indicate that

the load dependence of the steady-state creep rate

for piles in frozen sand appear to agree with the

displacement rate dependence of the adfreeze

strength determined by extrapolation of the results

of the constant rate tests. Long-term creep tests

give more realistic values for the long-term

adfreeze strengths and hence for the bearing

capacities for piles. The results obtained from

rapid tests cannot be used to calculate the long-

term bearing capacity of piles in frozen soil

unless a large factor of safety is used.

Few tests have been carried out to date and

further work must be done to determine the

behaviour of piles in various soils at different

temperatures and to obtain reliable data for design

of foundations in frozen soil. Work is in

progress in the cold rooms of the Division of

Building Research, National Research Council of

Canada, on the behaviour of steel H-section piles

in frozen sand, group piles (groups of 4 and 6)

in frozen sand and piles in frozen natural soils

under conditions of constant rates of load

application and constant loads.

ACKNOWLEDGEMENT

The author sincerely thanks G. Mould, Technical

Officer, DBRINRC for his help in designing the

equipment and carrying out the tests. This paper

is a contribution from the Division of Building

Research, National Research Council of Canada,

and is published with the approval of the

Director of the Division.

REFERENCES

Crory, F.E., 1966. Pile Foundations in

Permafrost. PERMAFROST. Proc., First

International Conference on Permafrost,

Lafayette, Indiana, National Academy of

Sciences, Washington, p. 467-476.

Crory, F.E. and Reed, R.E., 1965. Measurement

of Frost Heaving Forces on Piles. U.S. Army

Cold Regions Research and Engineering Laboratory,

Hanover, N.H., Technical Report No. 145,

p.

31. Laba, J.T., 1974. Adfreezing of Sands to Concrete.

U.S., National Research Council, Transportation

Research Board, Record No. 497, p. 31-39.

Rooney, J.W., 1976. Driven H-pile Foundations in

Frozen Sands and Gravel. Presented, Second

International Symposium on Cold Regions

Engineering, University of Alaska, Fairbanks.

Sanger, F.J., 1969. Foundations of Structures in

Cold Regions. U.S. Army Cold Regions Research

and Engineering Laboratory, Hanover, N.H., Cold

Regions Science and Engineering Monograph 111-C4.

Tsytovich, N.A., and M.I. Sumgin, 1959.

[Principles of Mechanics of Frozen Grounds],

U.S. Army Corps of Engineers, SIPRE Translation

No. 19, (now U.S. Army CRREL).

Tsytovich, N.A., 1975. THE MECHANICS OF FROZEN

GROUND. McGraw-Hill, New York, p. 426.

Vyalov, S.S., 1965. Rheological Properties and

Bearing Capacity of Frozen Soils. U.S. Army

Cold Regions Research and Engineering Laboratory,

Hanover, New Hampshire, Translation No. 74.

(7)

718

Vyalov, S.S. and Porkhaev, G.V., 1969. Handbook R e s e a r c h Council o f Canada, T e c h n i c a l T r a n s l a t i o n

f o r Design of Bases a n d F o u n d a t i o n s of B u i l d i n g s TT-1865, Ottawa, 19 76.

and 0 t h e r S t r u c t u r e s on P e r m a f r o s t . N a t i o n a l

TABLE I

/ VARIATION OF ADFREEZE STRENGTH WITH RATE OF LOADING

Cross-Hefd Adf r e e z e S t r e n g t h ( T ~ ) , MPa

Speed

(II)

P a i n t e d C r e o s o t e d -1 mm min B .C. F i r C o n c r e t e S t e e 1 B.C. F i r 0.0005 1.140 0.525 0.497 0 . 4 0 3 0 . 0 0 1 1.175 0.553 0.496 0.487 1.29 0.002 1 . 1 1 3 0.671 0.648 0.690 1.247 0.505 0 -005 1 . 6 1 0 . 7 3 3 0.677 0.720 0 . 0 1 1 . 5 6 0.866 0.679 0.813 0.940 0.02 1.936 1 . 1 6 0 . 9 7 3 0.920 0.05 2.231 1.293 1.026 0.875 0.10 ' 2.42 1 . 6 1 1 1.146 1.220 F i g u r e 1 Schema t i c Diagram o f t h e E x p e r i m e n t a l Set-Up t o Measure t h e Adf r e e z e S t r e n g t h Under C o n s t a n t R a t e of Cross-Head Moti.on A P i l c , 3" Dia

B P l e x i g l a s Box

C P l u g

D Base P l a t e

E Upper Compression Member from I n s t r o n Load C e l l

T Thermocouple

(8)

F i g u r e 2 Load-Dis t a n c e Curve f o r an U n t r e a t e d B.C. F i r P i l e i n F r o z e n Sand

(T

= ~ O C , Cross- Head Speed = 0 . 1 d m i n ) 10 I 1 1 1 1 1 1 1 1 I I 1 1 I 1 I l l - 1 I I I I I l I J - _{B C F I R} -

-

_{C O N C R E T E}

-

_-

-

P A I N T E D S T E E L 0 C R E O S O T E D B C F I R

-

F i g u r e 3 V a r i a t i o n o f A d f r e e z e S t r e n g t h w i t h R a t e of Loading 0 I I I 1 1 1 1 1 1 I I I I 1 I ~ r f I I 1 1 1 1 1 l o ' 2 1 0 - I C R O S S - H E A D S P E E D , r n m l m i n F i g u r e 4

Schematic Diagram of t h e Set-Up t o S t u d y t h e Creep o f P i l e s i n F r o z e n Sand Under C o n s t a n t Load (A

-

P i l e , B

-

Loading Pan, C

-

R a t i o A r m ( 1 : 4 ) , D

-

BLH Load C e l l , E - F r o z e n Sand)

(9)

F i g u r e 5

Creep Curve f o r a P a i n t e d S t e e l P i l e i n Frozen Sand

(T

= 6.Z°C, Loaded = 1130.57 kg)

720

0.6 0 . 5 - c ; 0 . 4 - Z u

5

> o I '0 . 3 - u 1

-

0.2 0. O.' I I I I I I

-

C R E E P R A T E =

r

1 . 0 4 x rnrnlrnin

-

i-

i

I d I I

7 -

-

A

I/

-

_;

_y

_i

-

/

I

!

I 1

-

./

I - 0 _n I I 1 I I I 5 10 15 20 25 30 35 TIME, h 1 0 . 0

-

I 1 1 1 1 1 1 1 1 I 1 1 1 1 1 1 1 1 I 1 1 1 1 1 1 1 -8 . 0 6 . 0 4.0 u

-

B . C . F I R -

-

----

m C O N C R E T E - 0 P A l N l E D S T E E L

-

---

0 C R E O S O I E D B . C . F I R -

-

F i g u r e 6 V 4 .d V a r i a t i o n o f A d f r e e z e S t r e n g t h (Under 2 - 2 . 0 -

-

C o n s t a n t Load) w i t h Creep Rate i n t h e -

-

S teady-S t a t e Creep Region 0

Y, 1.0

-

O R - w

-

=

0 . 6 - w

-

L . 9u, 0. 1 I I 1 1 1 1 1 1 1 I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 ' ~ lo-4 l o - 3 S T E A D Y - S T A T E C R E E P R A T E . m m l m i n I