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Acoustic and mechanical properties of frozen sand
N21a
no.
1338
National Research
Conseil national
C .
2
Council Canada
de recherches Canada
BLBG
Division of
Division des
Building Research
recherches en bitirnent
Acoustic and Mechanical
Properties
of
Frozen Sand
by T.H.W. Baker and
P.J. Kurfurst
ANALYZED
Reprinted from
Proceedings of the Fourth International Symposium on
Ground Freezing
Sapporo, Japan. August 5 -
7, 1985
Volume 1, p. 227
-
234
(DBR Paper No. 1338)
Price $2.50
NRCC 25200
I1 existe une d6pendance entre d'une part la vitesse de propagation des ondes longitudinales 3 -10 et -3,2OC et la resistance 3 la compression sans Btreinte laterale, et, d'autre part, la densit6 seche d16chantillons de sable satur6 d'eau douce et gel6 dans la gamme de densit6s 1 550
-
1780
kg/m3. La vitesse de propagation des ondes transversales est indgpendante de la densit6 sPche aux deux temp6ratures mentionn6es. La propagation des ondes sonores et la r6sistanceB la compression sans 6treinte lat6rale ne varient pas avec la densit6 sSche lorsqu'on ajoute du sel 3 l'eau interstitielle avant le gel. L'accroissement de la salinit6 reduit grandement la vitesse de propagation des ondes sonores et la resistance. Cette r6duction est particulierement sensible lorsque la salinit6 se situe entre 0 et
5
ppt. On a compare les constantes 6lastiques ultrasoniques B la densit6 seche etB
la salinit6.I1
faudrait effectuer des essais de mesure de la densit6 sPche et de la salinit6 lors des 6tudes techniques portant sur la cong6lation du sol et sur la construction dans les sols gel&, et utiliser des mesures acoustiques pour d6terminer les constantes 6lastiques des sols gel& employees dans la mod6lisation num6rique.Fourth International Symposium on Ground Freezing /Sapporo /5-7 August 1985
Acoustic and mechanical properties of frozen sand
T.H.W.BAKER
National Research Council Canada, Ottawa
P.J.KURFURST
Geological Survey o f Canada, Ottawa
ABSTRACT: Compressional wave velocities at -10.0 and -3.2OC and the unconfined
compressive strength show a dependency on the dry density of frozen freshwater sand
specimens in the density range 1550 to 1780 kg/m3. Shear wave velocities are
independent of dry density at both temperature levels. Acoustic wave velocities and
unconfined compressive strength are independent of dry density when salt is added to the
pore water prior to freezing. Increasing the salinity greatly reduces acoustic wave
velocities and strength. These reductions are most pronounced when the salinity is
between 0 and
5ppt. Ultrasonic elastic constants were compared with dry density and
salinity. Dry density and salinity tests should be included in engineering site
investigations related to artificial ground freezing and frozen ground construction and
acoustic measurements should be used to determine the elastic constants of frozen soils
used in numerical modelling.
'
1 INTRODUCTION
I
Acoustic wave propagation and mechanical
strength tests are important laboratory
techniques for engineering investigations
of soils and rocks. This paper compares
results of such tests on frozen sand and
describes the effects of specimen dry
density and salinity on the measurement
of unconfined compressive strength. shear
and compressional wave velocities and the
calculation of Young's modulus, Poisson's
ratio, shear modulus and bulk modulus.
These properties are used in finite
element analyses and other numerical
modelling techniques employed in the
design of artificially frozen soil
structures and geological engineering
investigations in frozen ground.
2 TESTING PROCEDURES
AND EQUIPMENT
Sample preparation followed the methods
described by Baker and Konrad (1985).
Three sets of samples were prepared at
various dry densities ranging from 1550
to 1780 kg/m3 and were saturated with
de-aired, distilled water. These samples
are referred to in this paper as
freshwater samples. Two more sets of
samples were prepared, one at a density
of 1550 kg/m3 (low density samples) and
the other at a density of 1780 kg/m3
(high density samples).
These samples
were saturated with sea salt solutions
ranging from 0.5 to 40 ppt. All samples
were frozen unidirectionally in a cold
room at -lO.O°C and then were prepared by
machining and end facing on a bandsaw and
lathe. Some specimens heaved during the
freezing process and were discarded. The
final specimens were cylinders approx.
76
mmin diameter and 150
mmin height.
All machined frozen specimens were
stored at -lO.O°C, but were transferred
to -3.2OC for about 24 hours for acoustic
velocity testing. The specimens were
then returned to -lO.O°C prior to the
mechanical tests. Temperature
measurements indicated that frozen
specimens required about 12 hours to
adjust to these temperature changes.
Specimens with pore water salinities
greater than 10 ppt crumbled when warmed
to -3.2OC and replacement specimens were
made at 20 and 30 ppt for the mechanical
strength testing.
2.1
Acoustic Tests
The acoustic wave propagation
measurements were made on one set of
f r e s h w a t e r specimens and on a l l of t h e s a l i n e w a t e r specimens. These measure- ments were made a t -10.0 and -3.2"C u s i n g a n OYO 5217-A, Sonic-viewer. D e t a i l s of t h e measuring t e c h n i q u e and equipment have been d e s c r i b e d e l s e w h e r e by King, (1970) and K u r f u r s t and King (1972).
The c o m p r e s s i o n a l (V ) and s h e a r wave P (V ) v e l o c i t i e s were c a l c u l a t e d a s f of lows : where V = p u l s e p r o p a g a t i o n v e l o c i t y ( m / s ) , L = p u l s e t r a v e l d i s t a n c e (m), T = e f f e c t i v e p u l s e - t r a v e l t i m e ( 6 ) . U l t r a s o n i c e l a s t i c c o n s t a n t s (E, p , G, K) were c a l c u l a t e d u s i n g f o r m u l a s recommended by t h e American S o c i e t y f o r T e s t i n g and M a t e r i a l s , S t a n d a r d D2845-83 (ASTM, 1984):
where E = Young's modulus of e l a s t i c i t y ( P a ) ,
p = d e n s i t y (kg/m3);
where = P o i s s o n ' s r a t i o ;
where G = s h e a r modulus ( o r modulus of r i g i d i t y ) ( P a ) ; where K = b u l k modulus ( P a ) . 2.2 Mechanical S t r e n g t h T e s t s Unconfined c o m p r e s s i o n t e s t s were performed o n one s e t of f r e s h w a t e r specimens and o n a l l s a l i n e w a t e r specimens a t -lO.O°C, u s i n g a s c r e w - d r i v e n t e s t i n g machine ( I n s t r o n Model 1927, 250 kN l o a d c a p a c i t y frame). T e s t i n g p r o c e d u r e s c l o s e l y f o l l o w e d t h e g u i d e l i n e s proposed by t h e I n t e r n a t i o n a l Working Group on T e s t i n g Methods f o r F r o z e n S o i l s (Baker e t a 1 1985). The t e s t s were performed a t a nominal s t r a i n r a t e of 1.67 x s-l (1% min-I). The d e t a i l s of equipment u s e d a r e d e s c r i b e d i n Baker e t a 1 (1981). A second s e t of f r e s h w a t e r t e s t specimens was t e s t e d u s i n g a c l o s e d - l o o p , s e r v o - h y d r a u l i c t e s t i n g machine (MTS Model 810.15, 1.0 MN l o a d c a p a c i t y frame and a 250 IcN c a p a c i t y a c t u a t o r ) . The s t r a i n r a t e was c o n t r o l l e d d u r i n g t h e t e s t a t 1.67 x 10-4 s-1 ( 1 % min-1) u s i n g a c o n t r o l gauge mounted on t h e t e s t specimens. The t h i r d s e t of f r e s h w a t e r t e s t specimens was t e s t e d i n t h e c l o s e d - l o o p , s e r v o - h y d r a u l i c t e s t i n g machine t o d e t e r m i n e t h e e l a s t i c modulus d u r i n g r a p i d u n l o a d i n g . The specimens were l o a d e d i n compression, a t a c o n s t a n t s t r a i n r a t e of 1.67 x s - I , up t o a s t r e s s of 4 MPa and t h e n r a p i d l y (0.3 t o 0.4 s ) unloaded. The rebound of e a c h specimen was r e c o r d e d and t h e i n i t i a l r a p i d (0.15 s ) d i s p l a c e m e n t was u s e d t o c a l c u l a t e t h e u n l o a d i n g modulus (EU). When t h e d i s p l a c e m e n t s t o p p e d , t h e specimen was a g a i n s u b j e c t e d t o l o a d s of 5 and 6 MPa and unloaded a t e a c h s t r e s s l e v e l . I n t h i s way, t h r e e d e t e r m i n a t i o n s of t h e e l a s t i c u n l o a d i n g modulus were made on e a c h specimen. 3 TEST RESULTS 3.1 A c o u s t i c T e s t s The r e s u l t s of t h e a c o u s t i c wave p r o p a g a t i o n t e s t s on t h e f r e s h w a t e r specimens a r e shown i n F i g u r e s 1 t o 3. An i n c r e a s e i n t e m p e r a t u r e from -10.0 t o -3.2"C r e s u l t e d i n a s m a l l i n c r e a s e i n c o m p r e s s i o n a l wave v e l o c i t y ; however t h e changes i n t h e s h e a r wave v e l o c i t y were w i t h i n t h e e r r o r of t h e t e s t method. The change i n c o m p r e s s i o n a l v e l o c i t y may b e due t o t h e v e r y s m a l l changes i n u n f r o z e n w a t e r c o n t e n t between t h e s e two t e m p e r a t u r e s o r t o o t h e r c h a r a c t e r i s t i c s of t h e i c e m a t r i x .
When t h e d r y d e n s i t y was i n c r e a s e d from 1550 t o 1780 kg/m3, t h e a c o u s t i c wave v e l o c i t i e s and e l a s t i c c o n s t a n t s
i n c r e a s e d w i t h i n c r e a s i n g d r y d e n s i t y o f sand. The s h e a r wave v e l o c i t y i s
r e l a t i v e l y i n d e p e n d e n t of d r y d e n s i t y o v e r t h e d e n s i t y and t e m p e r a t u r e r a n g e s measured. The c o m p r e s s i o n a l wave
v e l o c i t y i s more dependent on d r y d e n s i t y a t -lO.O°C t h a n a t -3.2"C. An anomaly i n t h e a c o u s t i c d a t a e x i s t s a t a d e n s i t y of a b o u t 1630 kg/m3. T h i s was a t t r i b u t e d t o i c e l e n s e s i n t h e specimen.
FRESHWATER SAMPLES Bulk Modulus 24 t- 1- -3.2O C FRESHWATER SAMPLES -+ T = -3.2' C
-
T = -10.0.C E 7 3 1600 1800 DRY DENSITY, kg/m3 Fig. 1. E f e c t of changing d r y d e n s i t y on a c o u s t i c v e l o c i t i e s s f 16W 1 BOO DRY DENSITY, kg/m3 Fig. 3. E f f e c t of changing d r y d e n s i t y on s h e a r and bulk moduliThe r e s u l t s of t h e a c o u s t i c wave m P p r o p a g a t i o n t e s t s on t h e s a l i n e w a t e r o specimens a r e p r e s e n t e d i n F i g u r e s 4 ln
2
30.:!;":
t o 8. Specimens w i t h s a l i n i t i e s g r e a t e r t h a n 10 p p t a t -3.2OC crumbled under t h eo minimum l o a d s r e q u i r e d t o s e c u r e t h e
cn
25 a c o u s t i c t r a n s d u c e r s . Some measurements
were made on specimens w i t h 20 ppt
e
s a l i n i t y a t -3.Z°C; t h e s e measurements have been p l o t t e d , b u t t h e i r v a l i d i t y i s q u e s t i o n a b l e . I n c r e a s i n g t h e t e m p e r a t u r e from -10.0"9aa""
t o -3.Z°C r e s u l t e d i n a moderate d e c r e a s e2
0L3-+
i n compressional wave v e l o c i t i e s a t s a l i n i t i e s up t o 5.0 ppt and a v e r y l a r g e=
0.2- d e c r e a s e a t h i g h e r s a l i n i t i e s . Shear lni FRESHWATER SAMPLES wave v e l o c i t i e s showed a v e r y l a r g e
8
-t T = -3.2' c d e c r e a s e between -10.0 and -3.2OC w i t hur
*
T = - 1 0 . O ° Cg
0.1-
i n c r e a s i n g s a l i n i t y o v e r t h e e n t i r e r a n g e s t u d i e d . The t e m p e r a t u r e e f f e c t on b o t h v e l o c i t i e s was more pronounced a t t h e0
-
h i g h e r s a l i n i t i e s , corresponding t o t h e1600 1800 l a r g e r amounts of u n f r o z e n w a t e r p r e s e n t DRY DENSITY, kg/m3 i n t h e s o i l .
Changes i n t h e unfrozen w a t e r c o n t e n t Fig. 2. E f f e c t of changing d r y d e n s i t y o c c u r r i n g i n s a l i n e s a n d s when t h e on P o i s s o n ' s r a t i o and Young's modulus t e m p e r a t u r e changed from -10.0 t o -3.2OC
SALINE WATER SAMPLES
t T= -3.2'C. low denmy T: -3.2- C. hlgh demlty +T= -10.0' C . low demlty
4 T. -lO.oO C , high d.n*ny
law4 a , , , , A
1.0 3.0 5.0
*
20.0 40.0SALINITY, p p t
SALINE WATER SAMPLES
4 T = -3.2' C. low density 4 T = -3.P C, hlgh denslty A T =-10.0' C. low denslty ----bT= -10.0' C, high density 20.0 10.0 SALINITY, p p t
Fig.
4.
E f f e c t of changing s a l i n i t y on Fig. 6. E f f e c t of changing s a l i n i t y on compressional wave v e l o c i t y Young's modulusSALINE WA'mER SAMPLES
4 T = -3.2' C. low densny 4 T = -3.Z9 C, hlgh denmy - T I
-
-10.0' C . low denslty T = -10.0' C . hlgh denslty F i g . 5. E f f e c t of changing s a l i n i t y on shear wave v e l o c i t ySALINE WATER SAMPLES + T = -3.Z0 C, low denslty + T = -3.P C, hlgh dsnrlty ---C T = -10.0' C, low denslty + T s -1O.P C, hlgh density SALINITY, p p t Fig. 7 . E f f e c t of changing s a l i n i t y on Poisson's r a t i o
40
i
SALINE WATER SAMPLESShear Moduhls B u K y o d u l l .
1- -3.1. C. low d-My --c- T- -3.2- C, low denmy
T = -3.2' C. h!+h denam,
-
T = -3.2. C. hlph d a l l y-
1. -lO.Oo C. low denblly t T 3 -lO.OD C, low denstty\
-bT = -IO.Oo C, hlgh d-"-
T = -fO.OD C. high d-y1 1.0 3.0 5.0
*
aoa 40.0 SALINITY, ppt measurements. There is a n e x p o n e n t i a l r e l a t i o n s h i p between t h e r a t i o of u n f r o z e n w a t e r c o n t e n t and s a l i n i t y t h a t i s n o t r e f l e c t e d i n t h e r a t i o of a c o u s t i c v e l o c i t y measurements below 5 p p t , b u t d o e s a p p e a r t o be s i m i l a r t o changes o c c u r r i n g between 5 and 10 ppt. The e f f e c t of i n c r e a s i n g s a l i n i t y on t h e a c o u s t i c v e l o c i t i e s and e l a s t i c c o n s t a n t s i s shown i n F i g u r e s 4 t o 8. Compressional and s h e a r v e l o c i t i e s and Young's s h e a r and b u l k moduli a l l e x h i b i t d r a m a t i c d e c r e a s e s a t s a l i n i t i e s up t o 5 p p t and, f o r t h e most p a r t , l e v e l o f f a t h i g h e r s a l i n i t i e s . P o i s s o n ' s r a t i o was a p p r o x i m a t e l y c o n s t a n t f o r a l l s a l i n i t y l e v e l s . Changes of l e s s t h a n 10% a r e p r o b a b l y n o t s i g n i f i c a n t .The p h y s i c a l mechanisms which a f f e c t t h e s e measurements a r e n o t f u l l y under- s t o o d . However, i t a p p e a r s t h a t t h e bond s t r e n g t h between t h e i c e m a t r i x and t h e sand p a r t i c l e s becomes g r e a t l y reduced a t s a l i n i t i e s g r e a t e r t h a n 5 p p t .
Fig. 8; E f f e c t of changing s a l i n i t y on
s h e a r and b u l k moduli 3.2 Mechanical S t r e n g t h
were c a l c u l a t e d ; t h e c a l c u l a t i o n s were based on t h e f r e e z i n g p o i n t d e p r e s s i o n , due t o s a l t i n t h e p o r e w a t e r , and t h e s p e c i f i c s u r f a c e a r e a of t h e sand
,
p a r t i c l e s . R e s u l t s of t h e s e c a l c u l a t i o n s , which must be c o n s i d e r e d approximate because o f t h e n a t u r e of t h e c o n d i t i o n , a r e p r e s e n t e d i n T a b l e 1. The r a t i o of t h e u n f r o z e n w a t e r c o n t e n t s between -10.0 and -3.2"C i s compared w i t h t h e r a t i o of a c o u s t i c wave v e l o c i t y T a b l e 1. E f f e c t of changes i n t h e r a t i o of u n f r o z e n c o n t e n t (WU) a t -10.0 and -3.2OC on t h e a c o u s t i c wave v e l o c i t i e s P o r e Water R a t i o of v a l u e s S a l i n i t y a t -10.0:-3.2OC 0.5 1: 400 1:1.14 1:1.32 2.0 1: 600 1:1.05 1:1.39 5 .O 1: 700 1:1.07 1:1.36 10.0 1: 1,000 1:1.34 1:1.84 20.0 1: 6,000-
-
30.0 1:50,000-
-
40.0 Not f r o z e n-
-
a t -3.Z°C R e s u l t s of t h e unconfined compression t e s t s a r e p r e s e n t e d i n F i g u r e s 9 and 10. A t a s t r a i n r a t e of 1.67 x loW4 s-l and a t e m p e r a t u r e of -lO.O°C, t h e unconfined compressive s t r e n g t h of f r e s h w a t e r s a n d specimens i n c r e a s e s o n l y s l i g h t l y w i t h i n c r e a s e i n d r y d e n s i t y up t o -1630 kg/m3. A t h i g h e r d e n s i t i e s , t h e i n c r e a s e i n unconfined compressive s t r e n g t h i s s i g n i f i c a n t l y g r e a t e r . T h i s t r a n s i t i o n i s more d r a m a t i c i n t h e s t r a i n d a t a , a s t h e s t r a i n i s about c o n s t a n t a t low d e n s i t i e s b u t i n c r e a s e s s h a r p l y a t a d e n s i t y of -1650 kg/m3. T h i s t r a n s i t i o n r e p r e s e n t s a change i n t h e mode of f a i l u r e from a lower y i e l d t y p e , u s u a l l y a s s o c i a t e d w i t h f r a c t u r e s i n t h e i c e m a t r i x , t o a n upper y i e l d t y p e of f a i l u r e a s s o c i a t e d w i t h t h e f r i c t i o n a l r e s i s t a n c e of t h e s o i l p a r t i c l e s t r u c t u r e ( S a y l e s and Carbee 1980).Three e l a s t i c moduli were d e t e r m i n e d u s i n g t h e r e s u l t s of t h e mechanical l o a d i n g and u n l o a d i n g t e s t s : 1. t h e s e c a n t modulus (E ) d e t e r m i n e d from t h e i n i t L a 1 s l o p e of t k e s t r e s s - s t r a i n c u r v e ( J e s s b e r g e r and E b e l 1981); 2. t h e d e f o r m a t i o n modulus (E50) d e t e r m i n e d from t h e t a n g e n t t o t h e s t r e s s - s t r a i n c u r v e a t 50% of t h e lower y i e l d s t r e s s ( J a p a n Gas A s s o c i a t i o n 1979); and 3. t h e u n l o a d i n g modulus (EU) d e t e r m i n e d from t h e i n i t i a l s l o p e of t h e s t r e s s - s t r a i n c u r v e when t h e specimen h a s
20 I I 0
0 0
1 5 -
* .
.
.
0 0-
l . m l10
-
-
NOMINAL STRAIN RATE. 1.67 l o 4 ,-I (1% ,in-')
5 - TEMPERANRE. -lODC 7
STRAIN RATE
I
t
m 0 INCRM-G TEST0 CONSTANT W R I N G TEST SOLID SYMBOL INDICATES LOWER
YIELD FAILURE OPEN SYMBOL INDICATES UPPER
YIELD FAILURE 500 1600 1700 1800 DRY DENSITY, kglm3 F i g . 9. E f f e c t of changing d r y d e n s i t y on u n c o n f i n e d c o m p r e s s i v e s t r e n g t h and f a i l u r e s t r a i n , , , ( ( ( , ( ( . ( , , , , , , , , , , , ,
FROZEN OTTAWA FINE SAND
TEMPERATURE -LOmC S T R A I N R A T E 1 6 7 x 1.' F i g . 10. E f f e c t of changing s a l i n i t y and d r y d e n s i t y on u n c o n f i n e d compressive s t r e n g t h been i m m e d i a t e l y unloaded a f t e r a s m a l l l o a d i s a p p l i e d ( S i n h a 1982).
The moduli from t h e m e c h a n i c a l t e s t s on t h e f r o z e n f r e s h w a t e r specimens a r e p r e s e n t e d i n T a b l e 2. The v a l u e s of t h e u n l o a d i n g modulus r e p r e s e n t t h e a v e r a g e of t h r e e v a l u e s o b t a i n e d f o r e a c h specimen. Although t h e r e i s n o t a c o n s i s t e n t t r e n d w i t h i n c r e a s i n g d e n s i t y , t h e most d e n s e specimen had t h e h i g h e s t modulus. The v a l u e s of Ei and ES0 a r e comparable t o o t h e r p u b l i s h e d d a t a f o r sandy s o i l s a t - 1 0 ° C (Parameswaran 1980; T a b l e 2. E l a s t i c moduli from m e c h a n i c a l and a c o u s t i c t e s t s Dry D e n s i t y kg /m3 1580 1600 1630 1660 1690 1780 Mechanical T e s t s E i
GPa E50 GPa a;:
14 14 28 18 9 2
7
5 6 30 3 6 13 33 19 1 G 26 30 30 45 A c o u s t i c T e s t s E GPaJapan Gas A s s o c i a t i o n 1979). The low v a l u e s measured a t a d e n s i t y of 1630 kg/m3 may b e r e l a t e d t o t h e p r e s e n c e of i c e l e n s e s i n t h e specimen. The u n l o a d i n g modulus E was t h e h i g h e s t of t h e moduli. S i n c e Y t was d e t e r m i n e d i n 0.15 s , i t i s c o n s i d e r e d t o be t h e most r e p r e s e n t a t i v e of t h e e l a s t i c b e h a v i o u r of t h e specimens. The change i n
u n l o a d i n g moduli was n o t c o n s i s t e n t w i t h i n c r e a s i n g d e n s i t y , b u t was w i t h i n t h e same r a n g e of v a l u e s a s d e t e r m i n e d from t h e a c o u s t i c t e s t s ( F i g u r e 2). The e f f e c t of s a l i n i t y on t h e u n c o n f i n e d compressive s t r e n g t h a t -lO.O°C i s shown i n F i g u r e 10. A s m a l l i n c r e a s e of s a l i n i t y from 0 t o 0.5 p p t g r e a t l y r e d u c e s t h e c o m p r e s s i v e s t r e n g t h . The r e d u c t i o n of s t r e n g t h w i t h i n c r e a s e d s a l i n i t y i s most s i g n i f i c a n t up t o 5 p p t , w i t h more g r a d u a l d e c r e a s e s o c c u r r i n g w i t h h i g h e r s a l i n i t i e s . Changes i n d r y d e n s i t y of t h e specimens had v e r y l i t t l e e f f e c t on t h e i r s t r e n g t h . The mode of f a i l u r e was c o n s i s t e n t l y a l o w e r y i e l d t y p e of f a i l u r e a t a n a x i a l s t r a i n of l e s s t h a n lX, i n d i c a t i n g t h a t t h e i c e m a t r i x was r e s p o n s i b l e f o r t h e o b s e r v e d b e h a v i o u r . S a l t i n t h e specimens i n c r e a s e d t h e u n f r o z e n w a t e r c o n t e n t and weakened t h e c o n t r i b u t i o n of t h e i c e m a t r i x t o t h e c o m p r e s s i v e s t r e n g t h . The f r i c t i o n a l component of s t r e n g t h d i d not a f f e c t t h e b e h a v i o u r of any of t h e f r o z e n s a l i n e specimens a t a s a l i n i t y of 0.5 p p t . 4 CONCLUSIONS The r e s u l t s of t h e a c o u s t i c t e s t s of f r o z e n f r e s h w a t e r specimens show t h a t t h e c o m p r e s s i o n a l wave v e l o c i t y and t h e e l a s t i c c o n s t a n t s i n c r e a s e d i r e c t l y w i t h i n c r e a s i n g d e n s i t y a t b o t h -10.0 and -3.2"C. However, t h e s h e a r wave v e l o c i t y
i s r e l a t i v e l y i n d e p e n d e n t of d r y d e n s i t y o v e r t h e d e n s i t y and t e m p e r a t u r e r a n g e s measured. The r e s u l t s of t h e a c o u s t i c t e s t s on f r o z e n s a l i n e specimens show t h a t t h e a c o u s t i c measurements a r e i n d e p e n d e n t o f d r y d e n s i t y . However, b o t h t h e a c o u s t i c wave v e l o c i t i e s and e l a s t i c c o n s t a n t s d e c r e a s e d i r e c t l y w i t h i n c r e a s e d t e m p e r a t u r e , e s p e c i a l l y a t s a l i n i t i e s between 0.5 and 5 ppt. These changes a r e a s s o c i a t e d w i t h t h e i n f l u e n c e of t h e i c e m a t r i x and t h e bond s t r e n g t h between t h e i c e and s a n d s t r u c t u r e s . The r e s u l t s of t h e mechanical s t r e n g t h t e s t s i n d i c a t e t h a t t h e u n c o n f i n e d compressive s t r e n g t h of f r o z e n f r e s h w a t e r specimens i n c r e a s e s w i t h i n c r e a s e d d r y d e n s i t y , w i t h t h e r a t e of i n c r e a s e g r e a t e r a t t h e h i g h e r d e n s i t y r a n g e ; t h e s t r a i n d a t a show a s i m i l a r t r a n s i t i o n . T h i s t r a n s i t i o n i n d i c a t e s a change i n f a i l u r e mode from a lower y i e l d t y p e of f a i l u r e , a s s o c i a t e d w i t h f r a c t u r e s i n t h e i c e m a t r i x , t o a n upper y i e l d t y p e of f a i l u r e a s s o c i a t e d w i t h t h e f r i c t i o n a l r e s i s t a n c e of s o i l p a r t i c l e s t r u c t u r e .
The l o a d i n g and u n l o a d i n g moduli d e t e r m i n e d i n t h i s s t u d y a r e s i m i l a r i n v a l u e t o t h o s e documented i n t h e l i t e r a t u r e . The u n l o a d i n g modulus h a s t h e h i g h e s t v a l u e and a g r e e s w e l l w i t h
,.
t h e Young's modulus d e t e r m i n e d from t h e' a c o u s t i c t e s t s . b The u n c o n f i n e d c o m p r e s s i v e s t r e n g t h at -lO.O°C d e c r e a s e s d i r e c t l y w i t h i n c r e a s e d p o r e w a t e r s a l i n i t y . A l a r g e r e d u c t i o n i n s t r e n g t h o c c u r s from a s a l i n i t y of 0 t o 5 p p t , and d e c r e a s e s more g r a d u a l l y o v e r t h e r a n g e from 5 t o 30 ppt. The u n c o n f i n e d c o m p r e s s i v e s t r e n g t h of s a l i n e f r o z e n s a n d s i s i n d e p e n d e n t of t h e d r y d e n s i t y . Measurement of a c o u s t i c wave v e l o c i t y i s a n i n e x p e n s i v e , n o n d e s t r u c t i v e method f o r o b t a i n i n g e l a s t i c c o n s t a n t s ,
e s p e c i a l l y t h e Young's modulus. These v a l u e s a r e o f t e n u s e d i n t i n e dependent c o n s t i t u t i v e e q u a t i o n s f o r n u m e r i c a l m o d e l l i n g . 5 RECOMMENDATIONS D e n s i t y , s a l i n i t y and a c o u s t i c measurements s h o u l d be performed on a l l s o i l samples o b t a i n e d from e n g i n e e r i n g s i t e i n v e s t i g a t i o n s r e l a t e d t o t h e u s e of a r t i f i c i a l l y f r o z e n ground a s a l o a d b e a r i n g s t r u c t u r e . S i m i l a r measurements s h o u l d be made on samples o b t a i n e d d u r i n g i n v e s t i g a t i o n s f o r f o u n d a t i o n s o r o t h e r l o a d e n g i n e e r i n g s t r u c t u r e s t o be s u p p o r t e d by n a t u r a l l y f r o z e n s o i l s . A c o u s t i c wave v e l o c i t y measurements a r e e a s i e r t o p e r f o r m t h a n m e c h a n i c a l t e s t s f o r t h e d e t e r m i n a t i o n of r e a l i s t i c v a l u e s of t h e e l a s t i c moduli of f r o z e n s o i l s . A d d i t i o n a l t e s t s s h o u l d b e performed t o v e r i f y i f t h i s i s a l s o t h e c a s e f o r f i n e - g r a i n e d s o i l s a t v a r i o u s s a l i n i t i e s . ACKNOWLEDGEMENTS
The a u t h o r s wish t o acknowledge t h e a s s i s t a n c e of J.G. B i s s o n , J.-F. Morel and A. Krol i n p e r f o r m i n g t h e l a b o r a t o r y t e s t s . T h i s p a p e r i s a j o i n t c o n t r i b u t i o n o f 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 , 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, and of t h e T e r r a i n S c i e n c e s D i v i s i o n , G e o l o g i c a l Survey of Canada and i s
p u b l i s h e d w i t h t h e a p p r o v a l of t h e D i r e c t o r s of b o t h D i v i s i o n s . REFERENCES American S o c i e t y f o r T e s t i n g and M a t e r i a l s , 1984, S t a n d a r d t e s t method f o r l a b o r a t o r y d e t e r m i n a t i o n of p u l s e v e l o c i t i e s and u l t r a s o n i c e l a s t i c c o n s t a n t s of rock. i n Annual book of s t a n d a r d s , V. 0 4 . 0 8 , x o . D2845-83, P h i l a d e l p h i a . Baker, T.H.W. e t a l . , 1985, G u i d e l i n e s f o r c l a s s i f i c a t i o n and l a b o r a t o r y t e s t i n g of a r t i f i c i a l l y f r o z e n ground: Report of t h e I n t e r n a t i o n a l Working Group on T e s t i n g Methods f o r F r o z e n S o i l . & P r o c e e d i n g s of t h e T h i r d I n t e r n a t i o n a l Symposium on Ground F r e e z i n g , v. 2 , Hanover, N.H. Baker, T.H.W., J o n e s , S.J. and
Parameswaran, V.R., 1981, Confined and u n c o n f i n e d c o m p r e s s i o n t e s t s on f r o z e n s a n d s . & P r o c e e d i n g s of t h e F o u r t h Canadian P e r m a f r o s t Conference (The Roger J.E. Brown memorial volume): Ottawa, N a t i o n a l R e s e a r c h C o u n c i l o f Canada.
Baker, T.H.W. and Konrad, J.-M., 1985, E f f e c t of sample p r e s e r v a t i o n o n t h e s t r e n g t h of f r o z e n sand.
&
P r o c e e d i n g s of t h e F o u r t h I n t e r n a t i o n a l Symposium on Ground F r e e z i n g , Sapporo: I n s t i t u t e of Low Temperature S c i e n c e , Hokkaido U n i v e r s i t y . J a p a n Gas A s s o c i a t i o n , 1979, Recommended p r a c t i c e f o r l i q u i f i e d n a t u r a l g a s i n g r o u n d s t o r a g e . J a p a n Gas A s s o c i a t i o n Committee on L i q u i f i e d N a t u r a l Gas S t o r a g e , Tokyo. J e s s b e r g e r , H.L. and E b e l , W., 1981, Proposed method f o r r e f e r e n c e t e s t s on
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King, M.S., 1970, S t a t i c and dynamic moduli of r o c k s u n d e r p r e s s u r e . i n Somerton, W.H., ed., Rock ~ e c h a n i z , Theory and P r a c t i c e : New York, N.Y.,
American I n s t i t u t e of Mechanical E n g i n e e r i n g . K u r f u r s t , P.J. and King, M.S., 1972, S t a t i c and dynamic e l a s t i c p r o p e r t i e s of two s a n d s t o n e s and p e r m a f r o s t t e m p e r a t u r e s . & T r a n s a c t i o n s American S o c i e t y of Mechanical E n g i n e e r i n g , v. 253, New York, N.Y.
Parameswaran, V.R., 1980, Deformation b e h a v i o u r and s t r e n g t h of f r o z e n s a n d : Canadian G e o t e c h n i c a l J o u r n a l , v. 17, p. 74-88. S a y l e s , F.H. and Carbee, D.L., 1980, S t r e n g t h of f r o z e n s i l t a s a f u n c t i o n of i c e c o n t e n t and d r y u n i t w e i g h t . i n P r o c e e d i n g s of t h e Second ~ n t e r n a t i o n x Symposium on Ground F r e e z i n g ,
Trondheim: The Norwegian I n s t i t u t e o f Technology, Trondheim. Sinha. N.K., 1982, Delayed e l a s t i c s t r a i n c r i t e r i o n f o r f i r s t c r a c k s i n i c e . P r o c e e d i n g s of t h e Symposium on Deformation and F a i l u r e of G r a n u l a r M a t e r i a l s , D e l f t : I n t e r n a t i o n a l Union of T h e o r e t i c a l and Applied Mechanics, D e l f t .
T h i s p a p e r , w h i l e b e i n g 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 . I t s h o u l d n o t be r e p r o d u c e d 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 w a . O n t a r i o . KIA 0R6. Ce document e s t d i s t r i b u 6 s o u s forme d e t i r 6 - 3 - p a r t p a r 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 b a t i m e n t . 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 6 t 6 d e 1 1 6 d i t e u r o r i g i n a l . Ce d o c u m e n t n e p e u t C t r e r e p r o d u i t en t o t a l i t 6 ou e n p a r t i e s a n s l e c o n s e n t e m e n t d e 1 1 6 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 S t r e o b t e n u e en 6 c r i v a n t .3 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 a 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 . KIA OR6.
