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Proceedings of an international Symposium on Frost Action in Soils, 1, pp.
92-101, 1977
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The dependence of frost heaving on load application - preliminary
results
Penner, Edward; Ueda, Takao
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THE DEPENDENCE OF FROST HEAVING ON LOAD
APPLICATION!= Preliminary Results
by Edward pnner and Takao Ueda
Reprinted from
VoL 1, Proceedings of an International Symposium on Frost Action in Soils
held at the University of Lulea, Sweden February
1977,
p. 92-
101DBR Paper No.
738
Division of Building Research
L466
7
SO MMAIRE
Le gonflement dii au g e l e t l ' a u g m e n t a t i o n d e l a t e n e u r e n eau puis s a diminution ont CtC m e s u r g s
k
p a r t i r de q u a t r e Cchantillons de s o l sk
d e s s u r -p r e s s i o n s a l l a n t de 0 . 5
>
4 ~ ~ / c m ~ . L e modeo p 6 r a t o i r e p r C v o y a i t d e modifier g r a d u e l l e m e n t l a
t e m p b r a t u r e
k
une extrCmitC de llCchantillon, q u iCtait
>
une t e m p C r a t u r e u n i f o r m e au dCpart, d a n sl e but de p r o d u i r e un g e l unidirectionnel dans l a cellule d ' e s s a i c o n f u e & cet effet. L e s s o l s 6taient de t e x t u r e moyenne e t avaient CtC prClevCs s u r l e
t r a c k d e l a f u t u r e r o u t e Mackenzie, T. N . - 0 . . Les
rCactions aux conditions de p r e s s i o n e t de g e l s e sont avCrCes s e m b l a b l e s pour tous l e s Cchantillons.
F a i t
k
n o t e r , l e t a u de gonflement e s t d e m e u r Cconstant pour chaque e s s a i . A p r e s s i o n 6 l e v 6 e ,
l l e a u 6 t a i t chassCe de llCchantillon m a i s , d a n s tous l e s c a s o b s e r v e s , une rCabsorption s u r v e n a i t d'es que l e taux de pCn6tration du g e l diminuait.
Taken from Vol. 1, Proc. of International Symposium on Frost Action in Soils, held at U. of Lulea in February 1977. WE DEPENDENCE OF FROST HEAVING ON LOAD APPLICATION - -
PRELIMINARY RESULTS
4
N
yzEb
~
~
Edward Penner, Head, Geotechnical S e c t i o n , Division o f B u i l d i n g Research, National Research Council o f Canada, Ottawa Takao Ueda, Guest worker from Takenaka Technical Research
Laboratory, Tokyo
SUMMARY
Heave and m o i s t u r e i n t a k e and e x p u l s i o n were measured i n f o u r s o i l samples a t d i f f e r e n t overburden p r e s s u r e s from 0 . 5 t o 4 kg/cm2. A s t e p change i n temperature, a requirement o f t h e procedure, was imposed a t one end o f t h e sample, which was o r i g i n a l l y a t a uniform temperature, t o induce u n i d i r e c t i o n a l f r e e z i n g i n a s p e c i a l l y - d e s i g n e d t e s t c e l l . S o i l s were medium i n t e x t u r e and had been o b t a i n e d a l o n g t h e proposed Mackenzie Highway, N . W . T. The response t o p r e s s u r e and f r e e z i n g condi- t i o n s imposed were s i m i l a r f o r a l l s o i l s . Of p a r t i c u l a r n o t e was t h e constancy i n t h e heave r a t e throughout each t e s t . A t h i g h p r e s s u r e s , water was e x p e l l e d from t h e sample i n i t i a l l y , b u t i n a l l c a s e s t h i s was followed by water i n t a k e a f t e r t h e r a t e o f f r o s t p e n e t r a t i o n had decreased.
INTRODUCTION
The main causes o f f r o s t heaving i n s o i l s had been i d e n t i f i e d w e l l b e f o r e t h e e a r l y s t u d i e s o f Beskow, Tabor and Casagrande. I t was understood even t h e n t h a t , d u r i n g f r o s t p e n e t r a t i o n , f r o s t heaving i n a f r o s t - s u s c e p t i b l e s o i l could b e a t t r i b u t e d t o t h e volume change o f i n s i t u p o r e w a t e r and t o t h e i c e s e g r e g a t i o n p r o c e s s when w a t e r flows t o t h e f r e e z i n g p l a n e from o u t s i d e s o u r c e s . S c i e n t i s t s and e n g i n e e r s agreed then, a s they do now, t h a t t h e more s e r i o u s cause o f heave i s t h e i c e s e g r e g a t i o n p r o c e s s . S i m i l a r l y , t h e s h a r p r e d u c t i o n i n t h e heave r a t e r e p o r t e d by Beskow (1935) r e s u l t i n g from s u r c h a r g i n g t h e s o i l has never been c o n t e s t e d . Opposing views, however, a r e now h e l d by s c i e n t i s t s and e n g i n e e r s about t h e e x a c t mechanism t h a t i s o p e r a t i v e i n t h e r e d u c t i o n o f f r o s t heave a s i n c r e a s i n g s t r e s s e s a r e a p p l i e d t o an open s o i l system i n which t h e r e i s a p e n e t r a t i n g f r o s t l i n e .
One school o f thought i s t h a t a t a p a r t i c u l a r s t r e s s , which can b e found e x p e r i m e n t a l l y , t h e f r e e z i n g o f i n s i t u w a t e r and i t s a t t e n d a n t expansion w i l l proceed w h i l e t h e heave a t t r i b u t e d t o t h e f r e e z i n g o f migratory water from o u t s i d e s o u r c e s , e . g . , water t a b l e o r from un- f r o z e n l a y e r s , w i l l be stopped. From t h i s concept t h e term "shut-off'' p r e s s u r e was i n t r o d u c e d i n t o s o i l mechanics l i t e r a t u r e by Arvidson and Morgenstern (1974). which was d e f i n e d by McRoberts and Nixon (1975) a s t h e " e f f e c t i v e s t r e s s a t t h e f r o s t f r o n t which w i l l cause n e i t h e r flow of water i n t o o r away from t h e f r e e z i n g f r o n t . "
A second school o f thought ( t o which t h e a u t h o r s s u b s c r i b e ) i s t h a t i t i s n o t p o s s i b l e t o c o n t r o l independently t h e two p r o c e s s e s o f f r o s t heaving by l o a d i n g t h e s o i l .
The experiment on which t h e opposing views a r e p r e d i c a t e d can be d e s c r i b e d a s f o l l o w s . A f r o s t - s u s c e p t i b l e s o i l sample o f f i n i t e l e n g t h i s w a t e r s a t u r a t e d and t h e n thermally c o n d i t i o n e d a t a tempera- t u r e n e a r 0°C. The sample i s f r o z e n u n i d i r e c t i o n a l l y by applying a
s u f f i c i e n t l y l a r g e s t e p change i n temperature (below O°C) a t one end o f t h e sample t o m a i n t a i n f r e e z i n g c o n d i t i o n s . Free a c c e s s t o w a t e r i s maintained a t t h e end o f t h e sample o p p o s i t e t o t h e c o l d end where f r e e z i n g was i n i t i a t e d . I t i s b e l i e v e d t h a t t h e s e c o n d i t i o n s a r e f u l - f i l l e d by t h e t e s t c e l l and experimental technique d e s c r i b e d i n t h i s paper.
EXPERIMENTAL
The t e s t c e l l (Fig. 1) used i n t h e s e experiments was borrowed from Northern Engineering S e r v i c e s , Calgary, A l t a . M o d i f i c a t i o n s made by t h e a u t h o r s were:
(a) A s e p a r a t e p r e s s u r e chamber was mounted on t h e t o p end of t h e c e l l t o apply l o a d s t o t h e sample.
(b) A s p i r a l grooved metal backing p l a t e was i n s t a l l e d behind t h e porous p l a t e t o f a c i l i t a t e a i r bubble removal from t h e w a t e r supply system a f t e r t h e sample was c o n s o l i d a t e d . ( c ) A rubber 0 r i n g was p l a c e d i n a machined groove around t h e
porous p l a t e t o completely c o n f i n e t h e w a t e r - s a t u r a t e d sample w i t h i n t h e h o l d e r . The c y l i n d e r was l i n e d with t e f l o n , thus making p i s t o n movement r e l a t i v e l y f r e e from f r i c t i o n .
The t e s t c e l l was designed t o h o l d a sample 4 i n . long and 4 i n . i n diam. (10.2 cm). The t e s t s were conducted i n s i d e a temperature chamber where t h e a i r temperature could be c o n t r o l l e d w i t h i n f0.05"C. Thermocouples p l a c e d i n shallow grooves around t h e i n s i d e w a l l s of t h e sample h o l d e r s o as t o b e i n c o n t a c t w i t h t h e o u t s i d e o f t h e sample were used t o monitor temperatures, determine temperature g r a d i e n t s and l o c a t e t h e 0°C p o s i t i o n w i t h i n t h e sample.
Loading o f t h e sample f o r t h e c o n s o l i d a t i o n phase and c o n f i n i n g t h e sample d u r i n g t h e t e s t was achieved by a i r p r e s s u r i z i n g t h e chamber mounted on top o f t h e f r e e z i n g c e l l . A p r e c i s i o n r e g u l a t o r was used t o c o n t r o l t h e chamber p r e s s u r e .
Measurements were c a r r i e d o u t on f o u r d i f f e r e n t s o i l s , o b t a i n e d l a t e i n May 1973 from d i f f e r e n t l o c a t i o n s along t h e alignment f o r t h e proposed Mackenzie Highway: Sample 2 was taken a t Mile 951.5 n e a r t h e town o f Inuvik, N I n ; sample 4 was taken 2 miles s o u t h e a s t o f Mackenzie Mountain Lodge, Norman Wells, NWT; combined sample ( r e f e r r e d t o a s No. 5 and No. 6) was taken a t t h e T r a i n i n g S t a t i o n , Lake o f Two Mountains, NWT. (Mile 410.7); and sample 9 was t a k e n a t Mile 314.3, n e a r F o r t Simpson, NWT. The p h y s i c a l p r o p e r t i e s o f t h e s o i l s a r e given i n Table I .
Aqueous s l u r r i e s were p r e p a r e d a t moisture c o n t e n t s j u s t above t h e l i q u i d l i m i t . In o r d e r t h a t t h e s t r e s s h i s t o r y would be s i m i l a r , t h e same c o n s o l i d a t i o n p r e s s u r e was used f o r a l l specimens from one s o i l . A f t e r t h e secondary s t a g e o f c o n s o l i d a t i o n was reached t h e p r e s s u r e was reduced t o t h e v a l u e a t which f r e e z i n g was t o be c a r r i e d o u t . Freezing o f t h e o v e r - c o n s o l i d a t e d specimen was s t a r t e d when t h e s t r e s s c o n d i t i o n had e q u i l i b r a t e d w i t h t h e a p p l i e d l o a d and i t s temperature was i n e q u i l i b r i u m with t h a t o f t h e c o n t r o l l e d chamber.
A methanol/water s o l u t i o n a t a temperature o f about -10°C was i r c u l a t e d through t h e c o l d - s i d e h e a t exchanger o f t h e c e l l t o induce
TABLE 1 - PHYSICAL PROPERTY OF SOILS
S o i l % Clay S i z e % S i l t % Sand % Gravel
No. < 0.002 m 0.002-0.06 0 . 0 6 - 2 . 0 > 2.0
/
wL' % Wp' % I % P, P I S T O N 9 0 0 R 1 9 P U t S S U R X INLET--- / U L A W f M G G U I D E 0 - R l & G S H A F I SEAL -6EdAlNG C t l l D c ~ V O L Y I I R E I Y h M E " I N ~ U I ~ T I ~ H l O A O P I J I V N f N O C A P T U P E i A R l N G P L A T E O I F F U S E R P l A I E P O R O U S O I S K !NO C h P B O T T O M " P O t Y U R t T H n N t * I N S U L n T l n N E L E X I C L A S S T U B E S T H E R U O i O l r P L [ I CADS 9 0 n O M E M 0 C A P H F 4 T I X C H A S C E R C U P H [ 4 1 E X C H A Y F E P BOTTOM V L 4 T E S I Y R O F O A M BbSL I N S U L 4 T I O A -- - L ~ h ~ l ~ ~ ~ ~ ~ l ~ ~ ~ ~ ? * . C I R C U l R T I 3 I 1:IRFS Fig. 1 F r o s t heave r e s t c e l l9 5
c r y s t a l l i z a t i o n i n the s o i l . 'Ihe i n i t i a t i o n 05 c r y s t a l l i z a t i o n was
i n d i c a t e d by a sudden temperature rise i n the sample next t o the heat
exchanger. This u s u a l l y o c c u r r e d a t around - 2 " ~ . A p r e s e l e c t e d s t o p
temperature w a s then applied t o the sample from a second methanol/water
c i r c u l a t a r tank through a s e r i e s o f i n t e r c o n n e c r i n g s h u t - o f f valves.
Freezing was a l l o w e d t o proceed without changing t h e temperatures of
the chamber o r t h e c o l d - s i d e h e a t exchanger u n t i l t h e experiment w a s
completed. ?he temperature d i s t r i b u t i o n i n t h e s o i l , water movement
eitlter i n t o o r o u t o f the s ~ i J , and amaunt o f heaving (if any] were
recorded with a Hewlett Packard 2010 I1 data a c q u i s i t i o n system.
The e x t e n t o f moisture flow and heave a t each s t r e s s l e v e l were
determined on s e p a r a t e specimens. Normally f o u r s e p a r a t e f r e e z i n g
runs were r e q u i r e d t o e s t a b l i s h t h e s t r e s s / h e a v e r a t e behaviour f o r any p a r t i c u l a r s o i l o v e r t h e r e q u i r e d range. The t e s t c o n d i t i o n s a r e given i n Table 1 1 .
RESULTS
Examples o f t y p i c a l f r e e z i n g r e s u l t s a r e shown i n F i g s . 2 and 3
f o r S o i l No. 2 . 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 was 5 kg/cm2; t h e con-
f i n i n g p r e s s u r e s d u r i n g f r e e z i n g were 1 and 4 kg/cm2 r e s p e c t i v e l y . The r e s u l t s i n d i c a t e t h a t t h e r a t e o f t o t a l heave :7 was e s s e n t i a l l y c o n s t a n t throughout t h e r u n f o r any p a r t i c u l a r p r e s s u r e l e v e l . Figure 3 shows
t h a t , even under a high c o n f i n i n g p r e s s u r e ( 4 kg/ cm2), w a t e r movement r e v e r s e d from e x p u l s i o n t o i n t a k e a f t e r about 1000 min. from t h e s t a r t o f t h e r u n . The t r e n d 0 2 0 0 0 3 0 0 0 4 0 0 0 observed i n t h e t e s t d a t a E L A P S E D T I M E , m i n p r e s e n t e d i n t h i s p a p e r o b t a i n e d f o r a l l t h e s o i l s s t u d i e d .
Fig. 2 F r o s t p e n e t r a t i o n and heave r a t e
measurements a t 1 kg/cm2 f o r S o i l No. 2 Figures 4 t o 7 show t h e
r e l a t i o n s h i p between con-
i i f i n i n g p r e s s u r e , t h e r a t e o f t o t a l heave and heave r a t e by w a t e r i n t a k e f o r t h e 4 s o i l s . The t o t a l heave r a t e u s u a l l y became c o n s t a n t s h o r t l y a f t e r t h e experiment was s t a r t e d ; where e x p u l s i o n o c c u r r e d t h e heave r a t e by w a t e r i n t a k e was o b t a i n e d a f t e r t h e w a t e r
I : flow had r e v e r s e d from
0 1 0 0 0 2 0 0 0 1 0 0 0 4000 e x p u l s i o n t o inflow. t l n v s t o T I M E m l n
Fig. 3 F r o s t p e n e t r a t i o n and heave r a t e The " s h u t - o f f " p r e s -
S o i l P r e c o n s o l . P r e s s u r e Temp. o f Temp. o f I n i t i a l I n i t i a l Void T o t a l Heave R a t e
No. P r e s s u r e Chamber Cold S i d e h t . m.c. R a t i o Heave R a t e by W a t e r I n t a k e
kg/cm2 kg/cm 2 O C OC cm mm/ min mm/ m i n 2 5 0 . 5 + 2 . 4 0
-
1 . 6 0 1 0 . 8 7 1 6 . 1 0 . 4 1 9 2 7 . 8 x lo-' 2 0 . 5 x lo-' 2 5 1 . 0 - 1 . 4 5 1 0 . 6 6 1 6 . 9 0 . 4 6 2 2 4 . 1 x 10:; 2 0 . 0 x 10:' 2 5 3 . 0 t v - 1 . 3 5 1 0 . 6 4 1 6 . 3 0 . 4 4 1 7 . 0 x 1 0 5 . 0 x 10'
2 5 4 . O-
1 . 4 5 1 0 . 5 7 1 6 . 3 0 . 4 3 5 3 . 4 5 x 10:' 3 . 0 8 x 10:' 2 1 5 5 . 9 - 1 . 5 5 1 0 . 8 7 1 6 . 2 0 . 4 3 4 1 . 7 6 x 1 0 4 1 . 2 5 x 1 0 4 4 4 0 . 5 + 1 . 9 0 - 1 . 7 5 9 . 8 6 1 9 . 2 0 . 5 2 7 38 x 3 3 lo-'' 4 4 0 . 5 !I - 0 . 9 5 1 0 . 6 3 1 9 . 7 0 . 5 4 1 29 x 10:' 24 x 10:: 4 4 1 . 5-
1 . 7 5 9 . 4 0 20.0 0 . 5 4 8 1 8 x 10 14 x 1 0 4 4 1 . 5 - 0 . 9 0 9 . 9 0 1 9 . 4 0 . 5 3 1 1 5 x 10:' 1 1 . 5 x 10:' 4 4 2 . 5 I - 1 . 8 0 9 . 7 6 1 9 . 5 0 . 5 3 4 8 . 5 x 1 0'
6 . 0 xlo-'
4 4 3 . 5 P i-
1 . 7 5 9 . 8 8 1 8 . 8 0 . 5 1 5 4 . 5 ~ 1 0 : : 2 . 5 x l O - : 4 4 3 . 5 I, - 0 . 8 5 9 . 0 0 1 9 . 0 0 . 5 2 0 2 X 10 1 . 7 5 x 10 5 & 6 5 1 . 0 + 2 . 3 5 - 0 . 8 5 9 . 7 3 1 8 . 4 0 . 5 1 6 1 6 . 8 x 10:"4.4 x 10:' 5 E 6 5 2 . 0,
-
0 . 8 5 9 . 9 7 1 8 . 3 0 . 4 9 6 8 . 2 x 10 7.4 x 10'
5 6 6 5 4 . 0, ,
- 0 . 8 5 9 . 6 4 1 8 . 2 0 . 5 0 1 4 . 3 x l 0 I 4 3 . 6 x 10:: 5 6 6 5 5 . 0 - 0 . 9 0 9 . 4 3 1 8 . 0 0 . 4 8 1 1 . 6 3 x 10'
1 . 5 7 x 1 0 - 3-
3 9 4 0 . 5 + 1 . 9 0-
1 . 8 0 9 . 8 2 2 3 . 7 0 . 6 5 4 5 . 2 5 x 4 . 9 x 9 4 1 . 5 - 1 . 8 5 1 0 . 1 5 23.2 0 . 6 5 3 3 . 7 5 x 3 . 2 5 x 9 4 2 . 5 I ? - 1 . 7 5 1 0 . 0 7 2 4 . 1 0 . 6 6 2 2 . 6 5 ~ 1 0 - ~ Z . ~ O X ~ O - ~ 9 4 3 . 5 I,-
1 . 7 0 9 . 9 6 2 3 . 9 0 . 6 5 6 1 . 5 x 10 1 . 3 x 10F i g . 4 F r o s t h e a v e r a t e , t o t a l h e a v e a n d h e a v e by w a t e r i n t a k e f o r S o i l No. 2 F i g . 5 F r o s t h e a v e r a t e , t o t a l h e a v e and h e a v e by w a t e r i n t a k e f o r S o i l No. 4 F i g . 6 F r o s t h e a v e r a t e , t o t a l h e a v e a n d h e a v e by w a t e r i n t a k e f o r S o i l No. 5 o
E
6 combined 0 Fn!55LAuc, "8,8rm7 P 0 5-3 I k g l r m 2 F i g . 7 F r o s t h e a v e r a t e , t o t a l h e a v e a n d h e a v e by w a t e r i n t a k e f o r S o i l N O . 9any o f t h e s o i l s s t u d i e d , a l t h o u g h t h e heave r a t c s a t t h e h i g h e s t p r e s s u r e s werc n e a r z e r o . S o i l No. 2, t h e m a t e r i a l w i t h t h e l e a s t f i n c s , was t o o c o a r s e - g r a i n e d t o d e t e r m i n e meaningful A t t e r b e r g l i m i t s , which i n d i c a t e s t h a t r e l a t i v e l y h i g h c o n f i n i n g s t r e s s e s a r e r e q u i r e d t o s t o p h e a v i n g even i n r a t h e r c o a r s e m a t e r i a l s . An i n t e r e s t i n g f e a t u r e o f t h e h e a v i n g e x p e r i m c n t s i s t h a t i t i s p o s s i b l e t o p r c d i c t t h e t i m e , t o , when r e v e r s a l o f w a t c r flow w i l l o c c u r and t h e t i m c , t l , a t which t h e t o t a l w a t e r e x p e l l e d i s e q u a l t o t h e t o t a l w a t e r i n t a k e , i . e . , where t h e t o t a l w a t e r flow c u r v e c r o s s e s t h e zero l i n e ( F i g . 8 ) . The p r e d i c t a b i l i t y o f to and tl i s p r e d i c a t e d on a c o n s t a n t heave r a t e which c o n t i n u e s l o n g a f t e r t h e S t e f a n r e l a t i o n s h i p
x = a f i
where X = d e p t h o f f r o s t p e n e t r a t i o n , mm t = t i m e , n ~ i n . 1 a = c o n s t a n t , mm/minino l o n g e r shows l i n e a r i t y when p l o t t i n g X vs a s shown i n F i g s . 2 and 3 .
The t o t a l h e a v e , hl., can h e d i v i d e d i n t o two components: heave due t o i n s i t u p o r e w a t e r e x p a n s i o n , hi, and t h a t a s s o c i a t e d with w a t e r i n t a k e , hL, hence
hi = hT - h i , ( i n mm) (2)
I f i t i s assumed t h a t t h e r e l a t i o n s h i p between f r o s t p e n e t r a t i o n and time i s s u f f i c i e n t l y l i n e a r f o r Eq. (1) t o a p p l y and t h a t t h e t o t a l heave r a t e a l i s e q u a l t o a c o n s t a n t , Eq. (2) becomes
where a 2 = 0 . 0 9 nq = (hT - 11 ) / X , t h e i n s i t u heave p e r u n i t
II
f r o s t p e n e t r a t i o n , n = ~ o r o s i t y , = f r c c z i n g e f f i c i e n c y e x p r e s s e d a s a f r a c t i o n a =2,
(111111/rnin) 1 Differentiating Eq. ( 3 ) w i t h r c s p c c t t o timc g i v c s t h c r a t c c q u a t i o nr---
-
1
F i g . 8 Vie p o s i t i o n s o f to and t l w i t 1 1 r e s p e c t t o t i m eL e t t i n g h i , t h e heave due t o water i n t a k e , equal 0 and s o l v i n g f o r time i n E q . (3) gives ( s e e a l s o Fig. 8 ) :
tl can be p r e d i c t e d from t h e v a l u e s o f a l , a 2 and a e s t a b l i s h e d very
e a r l y i n t h e experiment.
d h i
.
S i m i l a r l y , l e t t i n g - d t I n E q . ( 4 ) equal 0 and s o l v i n g f o r t g i v e s
t o , t h e minimum i n w a t e r e x p u l s i o n c u r v e . This too can be p r e d i c t e d w i t h accuracy.
Table 111 gives comparisons between p r e d i c t e d and observed values o f t l . to and h i f o r times given f o r s o i l No. 2, using Eqs. ( 5 ) , (6) and
(3) r e s p e c t i v e l y .
An assessment o f t h e s e r i e s o f 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 paper l e d t o t h e f o l l o w i n g o b s e r v a t i o n s .
1 . When t h e r e i s a p o s i t i v e t o t a l heave
rate
i n a f r e e z i n g r u n ,although w a t e r may b e e x p e l l e d from t h e sample i n i t i a l l y , t h e w a t e r flow must r e v e r s e from e x p u l s i o n t o i n t a k e provided t h e
experiment i s n o t t e r m i n a t e d t o o e a r l y . I t follows t h e r e f o r e ,
because t h e t o t a l heave r a t e s have been shown t o b e c o n s t a n t under t h e experimental c o n d i t i o n s d e s c r i b e d t h a t o n l y when t h e
totaZ heave r a t e i s zero w i l l t h e e x p u l s i o n o f water n o t be followed by water i n t a k e . These o b s e r v a t i o n s a r e c o n s i s t e n t w i t h t h e second school o f thought d e s c r i b e d a t t h e beginning o f t h i s p a p e r .
2 . I f t h e f r e e z i n g p l a n e p e n e t r a t e s through t o t h e bottom o f t h e
sample and heaving occurs d u r i n g p e n e t r a t i o n , t h e r e i s t h e p o s s i b i l i t y t h a t t h e e x p u l s i o n o f w a t e r observed i s temporary. I t would b e i n c o r r e c t t o assume t h a t t h e "shut-off" p r e s s u r e had been exceeded.
3 . The c o l d - s i d e t e m p e r a t u r e imposed on t h e sample has a
s i g n i f i c a n t i n f l u e n c e on t h e c o n s t a n t heave r a t e observed a t
low p r e s s u r e s . A t high p r e s s u r e s , when heave r a t e s a r e low,
t h e c o n f i n i n g p r e s s u r e has an o v e r r i d i n g i n f l u e n c e on heave
r a t e (Fig. 5 ) .
4 . The r e s u l t s i n F i g . 9 c h a r a c t e r i z e t h e change i n r a t e o f
heave due t o water i n t a k e from o u t s i d e t h e sample i n an open
system, p e r u n i t depth o f f r o s t p e n e t r a t i o n . Near t h e begin-
n i n g , when t h e r a t e o f f r o s t p e n e t r a t i o n i s f a s t (: 0 . 1 mm/
min) t h e w a t e r i n f l u x i s low; n e a r t h e end when t h e f r o s t
p e n e t r a t i o n i s an o r d e r of magnitude slower (1 0.01 mm/min),
TABLE 1 1 1 - COMPARISON O F CALCULATED VALUES AND OBSERVED VALUES BASED ON E Q . ( 3 ) FOR S O I L NO. 2
NOTES: (1) When h ~ i s n e g a t i v e , water i s e x p e l l e d .
When hQ i s p o s i t i v e , water i s taken i n .
2
( 2 ) when h i s a minimum, t ; (3) when hQ = 0, then t
9 . F i g . 9 F r o s t heave p e r u n i t depth o f f r o s t p e n e t r a t i o n r a t i o as a f u n c t i o n o f f r o s t pene- t r a t i o n r a t e
ACKNOWLEDGEMENTS
Appreciation i s expressed t o Northern Engineering S e r v i c e s f o r t h e use o f t h e i r f r o s t heave c e l l and f o r allowing m o d i f i c a t i o n s t o b e made. This p a p e r 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 o f B u i l d i n g Research, National Research Council o f Canada and i s p u b l i s h e d w i t h t h e approval o f the D i r e c t o r o f t h e D i v i s i o n .
REFERENCES
Arvidson, W . D . and N . R . Morgenstern (1974)
.
Water flow induced by s o i l f r e e z i n g . P r o c . , 27th Can. Geotech. Conf., Edmonton, A l t a . , p . 137-143.Beskow, G . (1935). S o i l f r e e z i n g and f r o s t heaving. Swedish Geol. Soc., S e r . C., 26th Year, Book No. 3, T r a n s l a t i o n by
J.O. O s t e r b e r g (194 7).
McRoberts, E .C . and J .F. Nixon (1975). Some g e o t e c h n i c a l o b s e r v a t i o n s on t h e r o l e o f surcharge i n s o i l f r e e z i n g . P r o c . , Conf. on S o i l Water Problems i n Cold Regions, Calgary 1975, p . 42-57.