Publisher’s version / Version de l'éditeur:
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.
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.
Proceedings of the 4th International Symposium on Ground Freezing, 2, pp.
201-206, 1985
READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.
https://nrc-publications.canada.ca/eng/copyright
NRC Publications Archive Record / Notice des Archives des publications du CNRC :
https://nrc-publications.canada.ca/eng/view/object/?id=cec24c67-7834-4235-935a-ce1c94588e2c
https://publications-cnrc.canada.ca/fra/voir/objet/?id=cec24c67-7834-4235-935a-ce1c94588e2c
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
Cyclic creep of frozen soils
Ser
m
N21d
~
PL"-m
National
Researdh
Corrsdl national
10013371+
c.
2
CoundlC.mda
dencharchgCMda
Division of
Division des
Building Research
recherches en Mtiment
Cyclic Creep of Frozen Soils
by V.R. Parameswaran
ANALYZED
Reprinted from
Proceedings of the Fourth International Symposium on
Ground Freezing
Sapporo, Japan. August 5-7,1985
iVolume 2, p. 201
-206
(DBR Paper No. 1337)
Price $1.50
NRCC 25199
L'auteur a Ctudie le fluage cyclique des sable saturC et
argiles geles en superposant des charges alternantes sur une
charge de compression statique moyenne posee sur les
echantillons. Le chargement cyclique a accru consid6rablement
la vitesse de fluage de ces matsriaux, ce qui pourrait
s'expliquer par l'augmentation de la teneur d'eau non gel6e
resultant de llCnergie thermique transitoire produite par
cyclage dcanique.
Ona observe que l'increment de dCforrnation
par cycle augmentait proportionnellement
3
l'accroissement de
la deformation du sable ge16, tandis qu'il diminuait dans Zes
argiles gelCes, montrant une tendancc
3
La resistance
progressive
3
la d6formation.
Fourth International Symposium on Ground Freezing/Sapporo/5-7 August 1985
Cyclic creep of frozen soils
V .
R.
PARAMESWARANDivision
ofBuilding Research, National Research Council of Canada, Ottawa, Canada,
A b s t r a c t
C y c l i c c r e e p behaviour of f r o z e n s a t u r a t e d sand and f r o z e n c l a y s was s t u d i e d by superimposing a l t e r n a t i n g s t r e s s e s over a mean s t a t i c compressive s t r e s s on t h e samples. C y c l i c l o a d i n g i n c r e a s e d t h e c r e e p r a t e of t h e s e
m a t e r i a l s c o n s i d e r a b l y , which could be due t o t h e i n c r e a s e i n unfrozen water c o n t e n t g e n e r a t e d by t h e t r a n s i e n t thermal energy produced by mechanical c y c l i n g . The s t r a i n increment p e r c y c l e was found t o i n c r e a s e w i t h i n c r e a s i n g s t r a i n i n f r o z e n s a n d , whereas i t d e c r e a s e d i n f r o z e n c l a y s , showing a tendency f o r s t r a i n hardening. I n t r o d u c t i o n Creep o r time-dependent i n e l a s t i c deformation of f r o z e n s o i l m a t e r i a l s h a s been s t u d i e d t o some e x t e n t a s a f u n c t i o n of t e m p e r a t u r e and s t r e s s , and a t t e m p t s have been made by s e v e r a l a u t h o r s t o f i t t h e e x p e r i m e n t a l c r e e p d a t a t o c l a s s i c a l c r e e p e q u a t i o n s developed from t h e observed behaviour of many v i s c o e l a s t i c m a t e r i a l s , i n p a r t i c u l a r m e t a l s and a l l o y s . For d e s i g n i n g f o u n d a t i o n s i n f r o z e n ground, t h e b e a r i n g c a p a c i t y of t h e f r o z e n s o i l h a s t o be known, which depends on t h e c r e e p c h a r a c t e r i s t i c s of t h e f r o z e n s o i l . I n g e n e r a l , t h e long-term c r e e p s t r e n g t h of t h e s o i l under c o n s t a n t s t r e s s i s used f o r d e s i g n . I n p r a c t i c e , however, f o u n d a t i o n s a r e i n v a r i a b l y s u b j e c t e d t o v a r i o u s k i n d s of dynamic s t r e s s e s from i n t r i n s i c and e x t r a n e o u s s o u r c e s , i n a d d i t i o n t o s t a t i c s t r e s s e s due t o s t r u c t u r a l l o a d s . Rapid changes i n mechanical s t r e s s e s could a l s o c a u s e thermal changes i n t h e s o i l , a l t e r i n g i t s c r e e p behaviour.
It h a s been shown t h a t s m a l l dynamic s t r e s s e s do indeed i n c r e a s e t h e
displacement r a t e of a p i l e f o u n d a t i o n i n f r o z e n s o i l (Parameswaran, 1982; 1984), but t o d a t e , t h e e f f e c t s due t o dynamic s t r e s s e s a r e taken c a r e of by u s i n g an i g n o r a n c e f a c t o r ( a s a f e t y f a c t o r ) i n t h e d e s i g n . Knowledge of t h e dynamic mechanical p r o p e r t i e s of f r o z e n s o i l s i s s p a r s e , except f o r some i n f o r m a t i o n on t h e dynamic moduli ( K a p l a r , 1969; S t e v e n s , 1975; Vinson, 1 9 7 8 ( a ) ; ( b ) ; ( c ) ) . Due t o t h e l a c k of such knowledge and
u n c e r t a i n t i e s i n t h i s a r e a , d e s i g n of f o u n d a t i o n s h a s t o be e x t r e m e l y c o n s e r v a t i v e . A b e t t e r u n d e r s t a n d i n g of t h e deformation behaviour of f r o z e n s o i l m a t e r i a l s under dynamic l o a d i n g o r combined l o a d i n g , and t h e u s e of s u c h i n £ ormation i n l i f e p r e d i c t i o n a n a l y s i s , w i l l r e s u l t n o t o n l y i n l e s s c o n s e r v a t i v e d e s i g n r u l e s , b u t a l s o i n t h e enhanced r e l i a b i l i t y of a s t r u c t u r e . This w i l l l e a d t o a r e d u c t i o n i n t h e f a c t o r of s a f e t y , t h e r e b y r e d u c i n g t h e c o s t of hardware, a s p i l e m a t e r i a l s can be more e f f e c t i v e l y used. The c h a l l e n g e s , t h e r e f o r e , a r e i n t h e dynamic c r e e p a r e a where t h e r e i s a need t o develop
c o n s t i t u t i v e e q u a t i o n s t o d e p i c t t h e behaviour of f r o z e n s o i l s and a l s o t h e need t o g e n e r a t e more e x p e r i m e n t a l d a t a on v a r i o u s f r o z e n s o i l s . This paper i s a s m a l l s t e p i n t h i s d i r e c t i o n and d i s c u s s e s r e c e n t r e s u l t s o b t a i n e d from c y c l i c c r e e p t e s t s on some f r o z e n s o i l s .
Experimental Procedure
M a t e r i a l s and Sample P r e p a r a t i o n : C y l i n d r i c a l samples were made from t h r e e d i f f e r e n t m a t e r i a l s : Ottawa sand (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. 30 and r e t a i n e d on s i e v e No. 100, and having a g r a i n diameter of 0.2 t o 0.6 m), a n a t u r a l c l a y from I n u v i k , N.W.T. and a s i l t y c l a y from Thompson, Manitoba.
C y l i n d r i c a l samples of f r o z e n sand were prepared i n s p l i t p l e x i g l a s molds. The sand was compacted i n l a y e r s , a t an optimum m o i s t u r e c o n t e n t of 14%. The mold was then connected t o a vacuum pump t o remove e n t r a p p e d a i r . A f t e r e v a c u a t i o n t h e sand was s a t u r a t e d w i t h d e a e r a t e d d i s t i l l e d w a t e r . The specimens were then f r o z e n u n i a x i a l l y i n t h e mold k e p t i n s i d e an i n s u l a t e d box w i t h t h e t o p end exposed t o t h e c o l d room a i r , maintained a t -lO°C. The water e x p e l l e d d u r i n g f r e e z i n g was removed from t h e bottom through a c a p i l l a r y t u b e c o n t a i n i n g a h e a t e r wire. A f t e r f r e e z i n g , t h e ends of t h e
c y l i n d r i c a l sample were trimmed and f a c e d on a l a t h e i n s i d e t h e c o l d room. The f i n i s h e d t e s t specimens c o n t a i n e d about 20% m o i s t u r e and had a b u l k d e n s i t y of about 2040 kgm-3. C y l i n d r i c a l samples of t h e n a t u r a l c l a y s from permafrost a r e a s ( I n u v i k , N.W.T. and Thompson, Manitoba) were prepared by mixing t h e d r i e d s o i l w i t h water (50% by weight of d r y s o i l ) and packing t h e r e s u l t i n g s l u r r y i n t o t h e c y l i n d r i c a l c a v i t i e s of a s t y r o f oam block t h a t was l i n e d w i t h p o l y e t h y l e n e s h e e t s . The samples were allowed t o f r e e z e u n i d i r e c t i o n a l l y by exposing t h e open end t o t h e a i r i n s i d e t h e c o l d room. A f t e r complete f r e e z i n g t h e c y l i n d r i c a l samples were removed from t h e styrofoam block and t h e i r ends trimmed and f a c e d on a l a t h e . The i c e l e n s e s i n t h e f r o z e n s o i l samples were d i s t r i b u t e d u n i f o r m l y , but o r i e n t e d randomly. The average m o i s t u r e c o n t e n t i n t h e samples was about 45%.
The f i n i s h e d t e s t specimens had d i a m e t e r s of 50.8 mm ( 2 i n ) and 76.2 mm ( 3 i n ) , and l e n g t h t o diameter (LID) r a t i o s s l i g h t l y g r e a t e r t h a n 2.
Equipment and T e s t Method: A diagram of t h e e x p e r i m e n t a l set-up t o s t u d y t h e c r e e p of f r o z e n s o i l samples i s shown i n Fig. 1. A c y l i n d r i c a l t e s t specimen (A), wrapped i n a c e l l o p h a n e j a c k e t w i t h a thermocouple (T) a t t a c h e d t o i t , was mounted on a p e d e s t a l ( B ) , and t h e l e v e r arm (D) was a d j u s t e d h o r i z o n t a l l y w i t h t h e l o a d c e l l (C) above t h e specimen. A
h y d r a u l i c j a c k ( J ) was used t o r a i s e and lower t h e l e v e r arm (D). The combined
Fig. 1 Apparatus t a s t u d y c r e e p of f r o z e n s o i l s .
weight of t h e beam (D), t h e shaker (E),
and t h e l o a d i n g p l a t f o r m (P) provided t h e s t a t i c l o a d on t h e specimen. Weights were p l a c e d on t h e p l a t f o r m (P) t o i n c r e a s e t h e s t a t i c l o a d i n some t e s t s . Dynamic l o a d was a p p l i e d on t h e f r o z e n s o i l sample by
an e l e c t r o d y n a m i c shaker (E). Larger c y c l i c l o a d s were a p p l i e d by an e l e c t r o h y d r a u l i c shaker (H) (shown i n Fig. 2). The f r e q u e n c y and amplitude of t h e dynamic l o a d was c o n t r o l l e d by f e e d i n g a s u i t a b l e s i n u s o i d a l wave form s i g n a l t o t h e shaker from a wave g e n e r a t o r and a m p l i f i e r . Dynamic l o a d s w i t h f r e q u e n c i e s of 10 Hz and 15 Hz, and peak-to-peak amplitudes of up t o 10% of t h e s t a t i c l o a d , were used.
The s t a t i c and dynamic components of t h e l o a d a p p l i e d on t h e specimen were monitored c o n t i n u o u s l y from t h e o u t p u t of t h e l o a d c e l l (C) on a c h a r t r e c o r d e r . The dynamic l o a d was a l s o monitored a c c u r a t e l y u s i n g an o s c i l l o s c o p e having a camera attachment. The deformation of t h e sample ( a x i a l compression), measured by a l i n e a r v a r i a b l e d i f f e r e n t i a l t r a n s d u c e r (LVDT) ' L ' , was a l s o recorded on t h e c h a r t r e c o r d e r . A l l t h e d a t a from each t e s t , such a s t h e t e m p e r a t u r e of t h e sample, room a i r t e m p e r a t u r e n e a r t h e specimen, t h e s t a t i c l o a d on t h e sample, and a x i a l d e f o r m a t i o n , were a l s o logged a t r e g u l a r i n t e r v a l s ( 1 t o 2 h o u r s ) through an a u t o m a t i c d a t a a c q u i s i t i o n system u s i n g a desk t o p computer, and t h e s t r e s s , s t r a i n , and s t r a i n r a t e of t h e sample were
c a l c u l a t e d f o r e v e r y r e a d i n g . T e s t s were c a r r i e d o u t a t -2.5OC and -lO°C, t h e
t e m p e r a t u r e of t h e sample b e i n g monitored by s m a l l thermocouples (T) a t t a c h e d t o t h e sample. P r i o r t o s t a r t i n g a t e s t , t h e t e m p e r a t u r e of t h e sample was allowed t o come t o e q u i l i b r i u m w i t h t h e room temperature.
F i g u r e 2 shows t h e e x p e r i m e n t a l s e t u p i n s i d e t h e c o l d room and Fig. 3 shows a close-up view of t h e specimen and LVDT.
R e s u l t s and D i s c u s s i o n s
F i g u r e 4 shows t y p i c a l c r e e p curves d e p i c t i n g t h e v a r i a t i o n of a x i a l s t r a i n w i t h time f o r f r o z e n samples of Thompson
Fig. 2 I n s i d e t h e c o l d room: (H) i s t h e e l e c t r o h y d r a u l i c s h a k e r .
Fig. 3 Close-up of t e s t specimen and LVDT.
c l a y , I n u v i k c l a y and s a t u r a t e d sand. The r e g i o n s w i t h and w i t h o u t t h e superimposed a l t e r n a t i n g l o a d a r e shown by t h e dashed and f u l l l i n e s . The e f f e c t of a l t e r n a t i n g l o a d i n i n c r e a s i n g t h e c r e e p r a t e i s obvious i n t h e s e f i g u r e s , a s shown by t h e i n c r e a s e i n s l o p e of t h e c r e e p curves i n t h e s e r e g i o n s . The increments i n c r e e p s t r a i n and s t r a i n r a t e a r e p a r t i c u l a r l y marked i n F i g u r e 4 ( c ) f o r t h e f r o z e n sand sample s u b j e c t e d t o a much l a r g e r s t r e s s than t h e o t h e r two samples. F i g u r e 5 shows t h e c o r r e s p o n d i n g c r e e p r a t e c u r v e s f o r t h e s e samples. The v a l u e s of t h e c r e e p r a t e s w i t h and w i t h o u t a l t e r n a t i n g s t r e s s , t h e increments i n c r e e p s t r a i n per c y c l e of l o a d , s t r a i n a t t h e beginning of c y c l i n g and t h e s t r e s s on t h e s e samples a r e given i n Table 1. The s t r a i n
increment per c y c l e ( A E / A N ) d e c r e a s e s w i t h i n c r e a s i n g s t r a i n f o r t h e Thompson c l a y samples, whereas i t i n c r e a s e s w i t h i n c r e a s i n g s t r a i n f o r t h e f r o z e n sand. This s u g g e s t s t h a t c y c l i c s t r e s s i n g c a u s e s s t r a i n h a r d e n i n g i n f r o z e n c l a y , whereas i n f r o z e n s a n d , i t c a u s e s s o f t e n i n g w i t h i n c r e a s i n g s t r a i n . For I n u v i k c l a y , which was of much f i n e r g r a i n s i z e than Thompson c l a y , t h e r e was n o t much v a r i a t i o n i n t h e v a l u e of (&€/AN) w i t h s t r a i n ( E ) . C o n s o l i d a t i o n o c c u r r i n g under c y c l i c s t r e s s could c o n t r i b u t e t o s t r a i n h a r d e n i n g of t h e c l a y samples, w h i l e t h e s o f t e n i n g observed i n t h e f r o z e n sand samples could p a r t l y be due t o d i l a t i o n .
A l l t h e t e s t s r e p o r t e d h e r e were c a r r i e d o u t i n a c o l d room a t a t e m p e r a t u r e of -2.5'C f 0.5OC. A few t e s t s were a l s o done a t - l O ° C , but a t t h i s lower t e m p e r a t u r e t h e r e was h a r d l y any i n c r e a s e i n c r e e p r a t e due t o c y c l i c l o a d i n g . I f t h e peak-to-peak a m p l i t u d e of t h e a l t e r n a t i n g l o a d could be i n c r e a s e d , t h e r e i s a p o s s i b i l i t y t h a t one could o b s e r v e t h e i n f l u e n c e of c y c l i c l o a d i n g a t t h e lower t e m p e r a t u r e too. To s t u d y t h e e f f e c t of changing t h e frequency of l o a d i n g , some t e s t s were a l s o done a t 15 Hz, and i n some t e s t s , a l t e r n a t i n g s t r e s s e s of both 10 Hz and 15 Hz were superimposed i n t e r m i t t e n t l y . The e f f e c t of t h e a l t e r n a t i n g s t r e s s was much l e s s pronounced a t t h e h i g h e r f r e q u e n c i e s than t h a t a t 10 Hz. This could be due t o t h e l i m i t a t i o n of t h e machine and p r e s e n t s e t u p , where t h e s t r e s s amplitude d e c r e a s e s a s f r e q u e n c y of l o a d i n g i s i n c r e a s e d . P l a s t i c deformation of f r o z e n s o i l s i s mainly due t o t h e v i s c o u s f l o w o c c u r r i n g i n t h e i c e phase. At any t e m p e r a t u r e , unfrozen water i s always p r e s e n t i n t h e s o i l a t t h e i n t e r p a r t i c l e
" 0 50 100 150 200 250 300 350 400 450 TIME, h TIME, h ( b ) 9 I I I I I I 8 - 7
-
s 6 -/I
2- 5 --
2
4 - C,
3 --
/',
2-
,'//
I
- 1-
0 I I I 1 I I 0 50 100 150 200 250 300 350 TIME, h 0 50 100 150 200 250 300 350 600 450 TIME, h TIME, h ( b ) TIME, h Fig. 4 V a r i a t i o n of a x i a l s t r a i n w i t h time.( a ) Thompson c l a y (Temperature: -2.5OC; m o i s t u r e : 45%)
( b ) Inuvik c l a y (Temperature: -2.5OC; m o i s t u r e : 45%)
( c ) s a t u r a t e d sand (Temperature: -2.5OC; m o i s t u r e : 20%)
Fig. 5 V a r i a t i o n of s t r a i n r a t e w i t h time.
( a ) Thompson c l a y (Temperature: -2.S°C;
moisture: 45%)
(b) Inuvik c l a y (Temperature: -2.5OC; m o i s t u r e : 45%)
( c ) s a t u r a t e d sand (Temperature: -2.5OC;
TABLE 1: Dynamic Creep Data from Three R e p r e s e n t a t i v e Samples
Mean Peak-to-peak S t r a i n S t r a i n a t S t a t i c a l t e r n a t i n g Creep S t r a i n Rates Increment s t a r t of T e s t S t r e s s s t r e s s per c c l e
J
c y c l i n g No. M a t e r i a l om(MPa) ua(MPa) Without (Shaker) With ( s - ~ ) (10- ) ( % )10 Thompson 0.534 0.032 3.21x10-~ 5.31x10-~ 2 . l O x l 0 - ~ 1.27 Clay (-6%) 3.31 " 5.19 " 1.88 " 2.04 3.26 " 4.94 " 1.68 " 2.77 2.88 " 3.91 " 1.03 " 3.67 2.26 " 3.18 " 0.92 " 4.20 1.94 " 2.44 " 0.50 " 4.64 15 I n u v i k 0.833 0.013 8 . 1 0 x 1 0 - ~ ~ 2.20x10-~ 9 . 2 3 ~ 1 0 - l 1 0.73 Clay (-2%) 13.9 " 1.95 " 5.62 " 0.79 0 2.32 " 2.32 " 0.82 30 Ottawa 2.237 0.224 1.48x10-~ 8 . 6 6 ~ 1 0 - ~ 7.18x10-~ 1.90 Sand (-10%) 1.39 " 10.70 " 9.27 " 2.48 2.84 " 14.9 " 12.06 " 3.50 32 Ottawa 2.609 0.330 6.19x10-~ 10.3 x 1 0 - ~ 4.10x10-~ 5.91 Sand (12.6%) 2.47 " 9.94 " 7.47 " 7.84 2.83 " 7.57 " 47.8 " 8.77 j u n c t i o n ; t h e amount i s h i g h e r , t h e c l o s e r a s s o c i a t e d w i t h t h e g e n e r a t i o n and t h e t e m p e r a t u r e i s t o O°C and t h e f i n e r accumulation of p o i n t d e f e c t s ( v a c a n c i e s ) t h e g r a i n s i z e of t h e s o i l . This unfrozen and v o i d s . During c y c l i n g more p o i n t water d e c r e a s e s t h e i n t e r p a r t i c l e f r i c t i o n d e f e c t s a r e formed than under s t a t i c s t r e s s , d e c r e a s e s t h e v i s c o s i t y of t h e s t r e s s and t h e s e could cause a c c e l e r a t i o n s o i l , and p r o v i d e s p a t h s f o r d i f f u s i v e of c r e e p deformation. These v a c a n c i e s and f l o w i n t h e s o i l . The unfrozen water can v o i d s a r e n u c l e a t e d a t g r a i n boundaries o r a l s o m i g r a t e a l o n g t h e p a r t i c l e i n t e r f a c e s g r a i n - p a r t i c l e i n t e r f a c e s due t o s t r e s s from r e g i o n s of h i g h s t r e s s t o t h o s e of c o n c e n t r a t i o n s and e l a s t i c accommodation. low s t r e s s and d e c r e a s e t h e s t r e n g t h of The f a i l u r e p a t t e r n under h i g h t e m p e r a t u r e t h e s o i l . I n p u t of mechanical energy, a s c y c l i c l o a d i n g was a l s o found t o be i n c y c l i c l o a d i n g , could i n c r e a s e t h e d i f f e r e n t from c l a s s i c a l c r e e p o r f a t i g u e thermal energy i n t h e s o i l by a h y s t e r e t i c f a i l u r e s i n t h a t c r a c k s f r e q u e n t l y f o l l o w e f f e c t and cause an i n c r e a s e i n t h e amount g r a i n boundaries and p a r t i c l e - g r a i n of unfrozen water c o n t e n t . I n f r o z e n i n t e r f a c e s . It i s p o s s i b l e t h a t i n f r o z e n s o i l s it i s probably t h i s mechanism t h a t s o i l s v o i d s could be g e n e r a t e d a t t h e a c c e l e r a t e s c r e e p d u r i n g c y c l i c l o a d i n g ,
above t h e t h r e s h o l d s t r e s s . In t h e p r e s e n t experiments t h e r e was a l s o
e v i d e n c e of an i n c r e a s e i n t e m p e r a t u r e of
,
- 2 . 0 I I It h e sample d u r i n g c y c l i n g , a s shown i n F i g u r e 6 f o r a sand sample. The dashed p o r t i o n s of t h e lower curve d e n o t e t h e p e r i o d s of c y c l i c s t r e s s i n g , and t h e corresponding t e m p e r a t u r e s , measured by a
thermocouple embedded i n t h e middle of t h e */-x--
I t e s t specimen, a r e shown i n t h e upper
.
Z-
:
---
curve. In t h i s t e s t t h e c y c l i c s t r e s s wasP
a p p l i e d by a heavy e l e c t r o - h y d r a u l i c
E
6 shaker w i t h a peak-to-peak l o a d c a p a c i t y",
5of 1360 kg. The t e m p e r a t u r e of t h e t e s t
o
5 0 100 150 specimen was found t o i n c r e a s e by almost TIME, hone degree d u r i n g c y c l i n g .
I n many m a t e r i a l s such a s m e t a l s and Fig. 6 E f f e c t of c y c l i c s t r e s s on ceramics, c r e e p a t h i g h t e m p e r a t u r e i s t e m p e r a t u r e of f r o z e n sand.
i n t e r p a r t i c l e j u n c t i o n s and c r a c k s could be propagated a l o n g t h e i n t e r p h a s e boundary r e g i o n s where unfrozen water
could be p r e s e n t . In unfrozen s o i l m a t e r i a l s , t h e c y c l i c c r e e p e f f e c t i s more complicated due t o t h e i n f l u e n c e of w a t e r , b u t c y c l i c c r e e p h a s been found t o d e c r e a s e w i t h i n c r e a s i n g l o a d c y c l e and m o i s t u r e c o n t e n t due t o c o n s o l i d a t i o n (Holubek, 1969; 1970).
The i n p u t of thermal energy caused by mechanical c y c l i n g and t h e amount of unfrozen water produced can be roughly
c a l c u l a t e d . The e l e c t r o d y n a m i c s h a k e r h a s
a f o r c e r a t i n g of 133 N w i t h a maximum
s t r o k e c a p a b i l i t y of 159 m (6.25 i n ) peak
t o peak. I f we u s e t h e rms v a l u e of peak
f o r c e and 50% of s t r o k e a s t h e o p e r a t i n g l e v e l , t h e mechanical energy i n p u t per
c y c l e i s 0.707 x 133 x (15.912) x
lo5
dyne-cm, which i s approximately e q u a l t o
7.5 j o u l e s p e r c y c l e o r 1.786 c a l o r i e s .
T h i s could cause m e l t i n g of 1.786180 =
2.23 x g of i c e producing about
0.024 cm3 of water. I f t h i s water is
assumed t o be d i s t r i b u t e d uniformly around t h e s o i l g r a i n s i n a t e s t specimen, i t can be c a l c u l a t e d , u s i n g t h e s p e c i f i c g r a v i t y of sand and t h e m o i s t u r e c o n t e n t of t h e sample, t h a t a l a y e r of water of t h i c k n e s s e q u a l t o 100 A0 (10 N.m) w i l l be formed. Not a l l t h e mechanical energy w i l l be converted t o thermal e n e r g y , and even i f only a f r a c t i o n i s converted t o h e a t t h a t w i l l cause m e l t i n g of i c e , s u f f i c i e n t unfrozen water w i l l be formed i n s e v e r a l hundred c y c l e s t o cause a c c e l e r a t e d v i s c o u s c r e e p of t h e f r o z e n s o i l samples. Conclusions
Creep r a t e of f r o z e n s a t u r a t e d sand and c l a y s under compressive l o a d i n g was i n c r e a s e d c o n s i d e r a b l y by superimposed a l t e r n a t i n g s t r e s s e s of amplitude up t o
10% of t h e mean s t a t i c s t r e s s . T h i s could
be a t t r i b u t e d t o t h e i n c r e a s e i n t h e amount of unfrozen water caused by t r a n s i e n t thermal energy produced by
mechanical c y c l i n g of t h e m a t e r i a l . Such i n c r e a s e s i n c r e e p r a t e s caused by c y c l i c l o a d i n g could reduce t h e b e a r i n g c a p a c i t y of f o u n d a t i o n s i n f r o z e n s o i l s , and could n e c e s s i t a t e an i n c r e a s e i n t h e v a l u e of t h e s a f e t y f a c t o r t o be used i n t h e d e s i g n of f o u n d a t i o n s i n p e r m a f r o s t a r e a s . Acknowledgements
S i n c e r e t h a n k s a r e due t o Colin Hubbs and Harold Dahl f o r making t h e t e s t
specimens and c a r r y i n g o u t t h e t e s t s , t o Douglas B r i g h t f o r h i s h e l p i n a c c e s s i n g t h e d a t a through a d a t a l o g g e r and a d e s k t o p computer, and t o Dr. Lorne Gold f o r h i s comments.
This paper i s a c o n t r i b u t i o n from t h e D i v i s i o n of B u i l d i n g Research, N a t i o n a l Research Council of Canada.
References
Holubec, I., 1969. C y c l i c c r e e p of
g r a n u l a r m a t e r i a l s . Department of
Highways O n t a r i o , Report No. RR 147, 46 p.
Holubec, I. and K.H. Wilson, 1970. A
c y c l i c c r e e p s t u d y of pavement
m a t e r i a l s . Department of Highways
O n t a r i o , Report No. RR 163, 26 p.
Kaplar, C.W., 1969. Laboratory
d e t e r m i n a t i o n of dynamic moduli of
f r o z e n s o i l s and i c e . U.S. Army Cold
Regions Research and Engineering L a b o r a t o r y , Research Report 163, 48 p.
Parameswaran, V.R., 1982. Displacement of
p i l e s under dynamic l o a d s i n f r o z e n
s o i l s . The Roger J.E. Brown Memorial
Volume, Proceedings of Fourth Canadian P e r m a f r o s t Conference, Calgary, 1981, N a t i o n a l Research Council of Canada, Ottawa, pp. 555-559.
Parameswaran, V.R., 1984. E f f e c t of
dynamic l o a d s on p i l e s i n f r o z e n
s o i l s . Proceedings of Third
I n t e r n a t i o n a l S p e c i a l t y Conference, Cold Regions E n g i n e e r i n g , Vol. I , pp. 41-52.
S t e v e n s , H.W., 1975. The r e s p o n s e of
f r o z e n s o i l s t o v i b r a t o r y l o a d s .
U.S. Army CRREL, T e c h n i c a l
Report 265, 103 p.
Vinson, T.S., 1978(a). Dynamic p r o p e r t i e s
of f r o z e n s o i l s under s i m u l a t e d e a r t h q u a k e l o a d i n g c o n d i t i o n s . Proceedings of Third I n t e r n a t i o n a l Conference on P e r m a f r o s t , Vol. I , pp. 743-749. Vinson, T.S., T. Chaichanavong, R.L. Chajkowski, 1978(b). Behaviour of f r o z e n c l a y under c y c l i c a x i a l
l o a d i n g . J. Geotech. Eng. Div.,
ASCE, Vol. 104, No. GTF, pp. 779-800.
Vinson, T.S., T. Chaichanavong, 1978(c).
Dynamic behaviour of i c e under c y c l i c
a x i a l l o a d i n g . J . Geotech. Eng.
Div., ASCE, Vol. 104, No. GTF, pp. 801-814.
T h i s paper. w h i l e being d i s t r i b u t e d i n r e p r i n t form by t h e 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 , remains t h e c o p y r i g h t of t h e o r i g i n a l p u b l i s h e r . It s h o u l d n o t be reproduced i n whole o r i n p a r t w i t h o u t t h e p e r m i s s i o n of t h e p u b l i s h e r . A l i s t of a l l p u b l i c a t i o n s a v a i l a b l e from t h e D i v i s i o n may be o b t a i n e d by w r i t i n g t o t h e P u b l i c a t i o n s S e c t i o n . 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 C a n a d a . O t t a v a , O n t a r i o . K I A OR6. Ce document e s t d i s t r i b u s s o u s forme d e t i r 6 - % p a r t par l a D i v i s i o n d e s r e c h e r c h e s e n batiment. Les d r o i t s d e r e p r o d u c t i o n s o n t t o u t e f o i s l a p r o p r i Q t 6 d e 1 'Q d i t e u r o r i g i n a l . Ce document n e p e u t S t r e r e p r o d u i t en t o t a l i t s ou en p a r t i e s a n s l e consentement de l l € d i t e u r . Une l i s t e d e s p u b l i c a t i o n s d e l a D i v i s i o n p e u t O t r e o b t e n u e en S c r i v a n t l a S e c t i o n d e s p u b l i c a t i o n s . D i v i s i o n d e s r e c h e r c h e s e n b l 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 Canada. Ottawa, O n t a r i o , K I A 0R6.
