Field measurements of the shear strength of columnar- grained sea ice

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Field measurements of the shear strength of columnar- grained sea ice

Frederking, R. M. W.; Timco, G. W.

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Field Measurements of the Shear Strength

of Columnar-Grained Sea Ice

by R. Frederking and G.W. Timco

Appeared in

Proceedings of IAHR Ice Symposium 1986

Iowa City, Igwa, 18-22 August 1986

Vol. I, p. 279-292

(IRC Paper No. 1424)

Reprinted with permission

Price $3.00

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Les a u t e u r s ont u t i l i s g avec succ&s l a d t h o d e du chargement

asymgtrique en q u q t r e p o i n t s pour mesurer l a r ' e s i s t a n c e au

c i s a i l l e m e n t de l a g l a c e de

mer 3 g r a i n s p r i s m a t i q u e s .

Les

mesures o n t

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r g a l i s g e s e n mai 1984 l o r s d e s e s s a i s e f f e c t u g s

p a r l e n a v i r e de r e c h e r c h e .brise-glace

" P o l a r s t e r n " au l a r g e

d e l a c a t e du Labrador.

A

c e t t e o c c a s i o n , on a 'etudi6 l e s

e f f e t s du volume de saumure, de l a t e n e u r e n a i r , de l a

tempgrature de l a g l a c e a i n s i que de l a s t r u c t u r e g r a n u l a i r e

s u r l a r g s i s t a n c e au c i s a i l l e m e n t .

Les v a l e u r s de r g s i s t a n c e

au c i s a i l l e m e n t

se

s i t u a i e n t e n t r e

550 e t 900 kPa, s e l o n l a

p o r o s i t g t o t a l e e t l ' o r i e n t a t i o n d e s g r a i n s e n f o n c t i o n de l a

d i r e c t i o n de chargement.

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IAHR Ice Symposium 1986

Iowa

City,

Iowa

FIELD MEASUREMENTS OF THE SHEAR STRENGTH OF COLUMNAR-GRAlNED SEA ICE

R.

Frederking National Research Senior Research Officer Council of Canada

G.W.

Timco National Research

Associate Research Officer Council of Canada

Ottawa

Ontario, Canada

Ottawa

Ontario, Canada

Abstract

The asymmetric four-point loading method was used successfully to measure the shear strength of columnar-grained sea ice. The tests were performed during the icebreaking trials of the

R.V.

"Polarstern" off the Labrador coast in May 1984. Brine volume, air content, ice temperature, and grain-structure effects on shear strength were investigated.

Shear-strength values were between 550 kPa and 900 kPa, depending on total porosity and grain orientation with respect to the loading direction.

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Introduction

The determination of ice forces on structures has traditionally considered the ice in the interaction zone to be under a uniaxial or multiaxial compressive stress condition. It is quite possible, however, that

significant parts of the interaction zone are subjected to biaxial stress conditions involving tensile in addition to compressive stresses. This condition is commonly known as shear. Therefore information on shear strength is necessary in analytical predictions of ice loads where this type of failure behaviour is occurring. Shear-strength data are also useful in determining the failure envelope of ice under multiaxial stress conditions.

The shear strength of ice has been a difficult property to measure in an unambiguous fashion. The techniques commonly used, direct shear, punching4 or torsion, create stress fields that cannot be quantified simply.

Normally it is assumed that a uniform shear stress is generated on a plane of failure, but in many instances indeterminate normal stresses are also generated on the plane of failure. For example, Butkovich (1956) using th8 double shear technique obtained values in the range 1000 to 2500 kPa, whereas Paige and Lee (1967) and Dykins (1971), using a direct shear

technique, obtained values in the ranges 500 to 1200 kPa and 100 to 250 kPg respectively. In all three cases results were for first-year sea ice of similar salinity and temperature. This large disparity in results brings into question the validity of the test methods used in the past.

The asymmetric four-point loading method has been proposed as a means of

performing improved shear tests (Iosipescu, 1967). This method was applied

to an investigation of essentially granular-structured first-year ice from the Beaufort Sea and consistent results were obtained (Frederking and

Timco, 1984). This paper will present results of tests on columnar-grained

and frazil ice using this new method. The influence of temperature, salinity, density, and grain orientation on shear strength will be presented, together with an assessment of the test method.

Background

In May, 1984 the Research Vessel (R.V.) "Polarstern" carried out

icebreaking trials off the coast of Labrador between Nain and Saglek. The

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I n s t i t u t e of Bremerhaven, F e d e r a l Republic of Germany, and i s used t o c a r r y o u t r e s u p p l y m i s s i o n s t o t h e A n t a r c t i c and v a r i o u s r e s e a r c h voyages. It h a s a n i c e b r e a k i n g c a p a b i l i t y and i s equipped w i t h e x t e n s i v e onboard s c i e n t i f i c f a c i l i t i e s , i n c l u d i n g c o l d rooms. These f a c i l i t i e s p r o v i d e d a n o p p o r t u n i t y t o p r e p a r e specimens immediately a f t e r sampling and t o t e s t them w i t h a minimum change of i c e p r o p e r t i e s . The s h e a r t e s t s r e p o r t e d h e r e were p a r t of a l a r g e program of i c e - r e l a t e d i n v e s t i g a t i o n s ( F r e d e r k i n g and Laframboise, 1985).

The i c e i n v e s t i g a t e d i n t h i s s t u d y was r e c o v e r e d a t t h r e e d i f f e r e n t l o c a t i o n s i n t h e v i c i n i t y of 58' 12'N

-

62O 34'W ( s e e Fig. 1). These l o c a t i o n s were s e l e c t e d t o r e p r e s e n t t h r e e t y p i c a l t y p e s of l e v e l

f i r s t - y e a r s e a i c e encountered i n t h e t r i a l s . A t s i t e 1 t h e i c e c o v e r had p r i m a r i l y a f r a z i l s t r u c t u r e w i t h a g e n e r a l l y random o r i e n t a t i o n of t h e g r a i n s . Water d e p t h a t t h i s l o c a t i o n was about 150 m. S i t e 2 was a t t h e e n t r a n c e t o Hebron F i o r d o v e r a s i l l w i t h w a t e r d e p t h of a b o u t 90 m. The t o t a l i c e t h i c k n e s s was 1.16 m, w i t h t h e t o p p a r t of t h e i c e a l a y e r e d m i x t u r e of f r a z i l and g r a n u l a r s n o w l c e w h i l e t h e lower 0.4 m of t h e i c e cover was columnar-grained w i t h random o r i e n t a t i o n of t h e c-axes i n t h e h o r i z o n t a l plane. Average g r a i n d i a m e t e r was about 5 mm. S i t e 3 was w e l l w i t h i n Hebron F i o r d a t a l o c a t i o n where t h e water d e p t h was about 220 m.

The i c e a t t h i s l o c a t i o n was a g a i n columnar w i t h some tendency f o r a p r e f e r r e d c-axis o r i e n t a t i o n a l o n g t h e l o n g a x i s of t h e f i o r d . I c e t h i c k n e s s was about 1 m. A t t h e time of t h e t r i a l s a i r t e m p e r a t u r e s were above f r e e z i n g and t h e i c e cover was beginning t o show s i g n s of

d e t e r i o r a t i o n , i.e., t h e r e were meltwater ponds on t h e s u r f a c e and l a r g e b r i n e d r a i n a g e c h a n n e l s i n t h e i c e cover.

Specimen P r e p a r a t i o n

Large samples were o b t a i n e d by chain-sawing completely t h r o u g h t h e i c e c o v e r t o o b t a i n b l o c k s 1 x 1.5 m, which were l i f t e d on board u s i n g one of t h e v e s s e l ' s cranes. The block was immediately c u t up i n t o s m a l l p i e c e s , l a b e l l e d , and t r a n s p o r t e d t o t h e c o l d rooms. I n a d d i t i o n t o i t s u s e i n t h i s s t u d y , t h e i c e was used i n p a r a l l e l s t u d i e s of t h e f a i l u r e envelope of i c e (Timco and F r e d e r k i n g , 1986) and f r i c t i o n ( T a t i n c l a u x and Murdey,

1985). S t o r a g e and p r e p a r a t i o n t e m p e r a t u r e was -15OC. Specimens were c u t t o rough dimensions w i t h a band saw and t h e n p l a n e d on a power p l a n e r t o f i n a l nominal dimensions of 350 rnm l e n g t h , 50 mm w i d t h , and 100 mm depth.

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Specimens having three different orientations were prepared in order to

produce pure shear on a vertical, horizontal, or 45' diagonal surface in

the ice cover. The specimen orientations are shown schematically in

Fig. 3. Depending on the orientation of the 45' diagonal specimen either

tensile or compressive stress could be generated in a direction parallel to the original growth direction. Before measurement, weighing, and testing,

specimens were conditioned at the test temperature (-Z°C or -12'C) for at

least 18 hours.

Test Method

The asymmetrical four-point bending method was used in performing the sheal: tests. Load is applied at four points on a beam so that a region of high shear stress and low bending stress is generated at the mid-section of the beam. The geometry of load application and resulting shear forces and

bending moments are illustrated in Fig. 2. The shear-stress distribution

at the centre plane, x = 0, is parabolic with a maximum value at the

centre of

where P is total applied load, b is specimen thickness, h is specimen

depth, and a relates to the loading geometry. The specimen geometry

proposed by Iosipescu,

(1967)

included notches in the top and bottom

surfaces of the beam at the mid-plane, x = 0. This procedure has the

effect of reducing the cross-sectional area subjected to the shear stress and of producing a nearly uniform shear-stress distribution, provided that

the notch depths are

20 -

25% of the specimen height. For the notched

beam, shear stress is given by

where P, a, and b are as defined for equation (1) and h is the net height

0 of the beam across the notches.

A test apparatus has been built along the lines indicated in Fig. 2. The

distance of the ball, 1, is 150 mm from the centre line,

x =

0. Two sets

of notches are provided in each plate at 15 and 30 mm distance (a = 0.1 and

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4 &

5 1 J O H N ' S

Figure 1. Maps showing l o c a t i o n s of ice-sampling s i t e s , Hebron Fiord, Labrador U P P E R P L A T E 5 PEC I M E N L O ~ E R 1 P L A T E + Y - a - P - a P

_-

'

S H E A R F O R C E D I A G R A M 1 - O B E N D I N G M O M E N T D I A G R A M

Figure 2. Asymmetric four-point loading apparatus and shear f o r c e and bending moment diagrams (from Frederking and Timco, 1984)

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P i s a p p l i e d , i s f r e e t o r o t a t e about t h e l o a d - a p p l i c a t i o n p o i n t . Loading was c a r r i e d o u t u s i n g a 50-kN c a p a c i t y S o i l t e s t CT-405 compression t e s t e r , which h a s a screw d r i v e a c t u a t o r . A l l t e s t i n g was done a t a nominal a c t u a t o r r a t e of 2 x 10-2 mm s-l.

T e s t R e s u l t s ( a ) F r a z i l i c e

The i c e f o r t h e s e t e s t s was recovered from s i t e 1. An i n i t i a l series of 14 t e s t s was c a r r i e d o u t on specimens of f r a z i l i c e a t a t e m p e r a t u r e of -1z0C. The purpose of t h i s s e r i e s was t o examine t h e e f f e c t of s p a c i n g of t h e l o a d i n g b a r s and n o t c h e s on t h e s t r e n g t h r e s u l t s . The l o a d i n g c o n d i t i o n was v e r t i c a l s h e a r (Fig. 3a). R e s u l t s of t h e s e t e s t s a r e summarized i n Table 1. The i c e was r e l a t i v e l y uniform and homogeneous i n s t r u c t u r e , w i t h a n a v e r a g e s a l i n i t y of 1.2 f 0.4'/,, and d e n s i t y of 830 f 40 kg/m3. I n a l l c a s e s f a i l u r e was u l t i m a t e l y by r u p t u r e of t h e specimen, but i n s e v e r a l c a s e s f a i l u r e was preceded by s i g n i f i c a n t i n d e n t a t i o n of t h e specimen by t h e i n n e r l o a d i n g b a r s . For t h e c a s e of c l o s e s p a c i n g of t h e i n n e r b a r s ( a = 0.1), a s i n g l e f r a c t u r e always r a n between t h e b a r s , whereas f o r t h e c a s e of wider s p a c i n g , ( a = 0.2), t h e r e tended t o be two f r a c t u r e s running between t h e b a r s o r d i r e c t l y t o t h e p o i n t of maximum t e n s i l e s t r e s s

( p o i n t f i n Fig. 2). The f r a c t u r e s f o r t h e notched specimens r a n from each n o t c h t o t h e o p p o s i t e l o a d i n g bar. The notched specimen g i v e s more

r e l i a b l e r e s u l t s because of t h e uniform s h e a r - s t r e s s d i s t r i b u t i o n , but i t

r e q u i r e s much more e f f o r t i n specimen p r e p a r a t i o n . The p l a i n beam w i t h c l o s e s p a c i n g of t h e b a r s ( a = 0.1) produced s h e a r - s t r e n g t h r e s u l t s almost i d e n t i c a l t o t h e notched specimen. T h e r e f o r e t h e c l o s e s p a c i n g p o s i t i o n ( a = 0.1) was adopted f o r subsequent t e s t i n g .

(b) Unaligned columnar-grained i c e

A second t e s t s e r i e s was performed on columnar-grained i c e o b t a i n e d from t h e lower 0.4 m of t h e i c e c o v e r a t s i t e 2. Temperature and g r a i n - o r i e n t a t i o n e f f e c t s were i n v e s t i g a t e d , and s a l i n i t y , d e n s i t y , and l o a d i n g time were determined f o r each t e s t . Two t e s t t e m p e r a t u r e s , -2'C and -12OC, were used f o r each of t h e f o u r l o a d i n g c o n d i t i o n s shown i n Fig. 3.

T y p i c a l l y s i x t e s t s were conducted f o r e a c h c o n d i t i o n . S a l i n i t i e s of a melted sample of t h e specimen were determined with a c o n d u c t i v i t y b r i d g e .

D e n s i t i e s were c a l c u l a t e d from measured mass and dimensions of t h e specimens. Because t h e specimens were prisms and planed t o a smooth

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f i n i s h , d e n s i t i e s could be determined t o an accuracy of f 5 kg/m3. S a l i n i t i e s and d e n s i t i e s were 1.7 f 0.3O/,, and 830 f 25 kg/m3, and 1.9 f 0.2°/00 and 850 f 15 kg/m3 a t -2OC and -lZ°C r e s p e c t i v e l y . These v a l u e s a g r e e w e l l w i t h r e s u l t s from o t h e r specimens of t h e same i c e (Timco and Frederking, 1986).

Load-time p l o t s of t h e t e s t r e s u l t s a r e p r e s e n t e d i n Figs. 4 t o 7. Within a t e s t s e r i e s , specimen dimensions were r e l a t i v e l y uniform

-

a v e r a g e specimen h e i g h t and width a r e i n d i c a t e d on each p l o t . A l l t e s t s were conducted a t t h e same nominal l o a d i n g r a t e , but i t can be s e e n t h a t t h e a c t u a l l o a d i n g r a t e s v a r i e d from t e s t t o t e s t . Also shown on t h e p l o t i s i n f o r m a t i o n on t h e f a i l u r e mode. For t h e t e s t s a t -2OC t h e observed load-time curve resembled t y p i c a l d u c t i l e behaviour, and i n some c a s e s t h e specimen d i d n o t r u p t u r e but reached an upper y i e l d load combined with i n d e n t a t i o n of t h e i n n e r l o a d i n g b a r s i n t o t h e specimen ( s e e Fig. 5). Tne load-time c u r v e s a r e very non-linear. I n a l l c a s e s f o r t e s t s a t -1Z0C f a i l u r e of t h e specimen o c c u r r e d a b r u p t l y w i t h an i n s t a n t a n e o u s d e c r e a s e of load. The load-time c u r v e s tended t o be r e l a t i v e l y l i n e a r t o f a i l u r e .

Also shown on Figs. 4

-

7 a r e s k e t c h e s of t y p i c a l f r a c t u r e p a t t e r n s . I n c a s e s of a b r u p t f a i l u r e one o r two f r a c t u r e p l a n e s extended between t h e two l o a d i n g bars. No c o n s i s t e n t p a t t e r n of f r a c t u r e w i t h r e s p e c t t o t h e t y p e of s h e a r l o a d i n g o r t e s t t e m p e r a t u r e could be d i s c e r n e d . The a c t u a l f r a c t u r e s u r f a c e was g l a s s y i n appearance b u t non-planar. Over a d i s t a n c e of 10 t o 20 mm, s u r f a c e v a r i a t i o n s had an amplitude of about 1 mm and a wave l e n g t h of 3

-

5 mm. Over t h e t o t a l d e p t h of t h e specimen t h e f a i l u r e s u r f a c e was e i t h e r smoothly curved o r i r r e g u l a r , w i t h a v a r i a t i o n of 5 t o 10 mm.

The r e s u l t s of each i n d i v i d u a l t e s t s e r i e s were examined i n t e r m s of l o a d i n g r a t e ( s h e a r s t r e n g t h d i v i d e d by time t o f a i l u r e ) , d e n s i t y , and s a l i n i t y , b u t no s i g n i f i c a n t c o r r e l a t i o n s were observed. A l l of t h e r e s u l t s a r e summarized i n Table 2 i n terms of t e m p e r a t u r e and t e s t type.

Cox and Weeks (1983) have developed s i m p l e e x p r e s s i o n s f o r d e t e r m i n i n g t h e t o t a l p o r o s i t y of t h e i c e from a knowledge of t e m p e r a t u r e , s a l i n i t y , and bulk d e n s i t y of t h e i c e . Table 3 summarizes t h e b r i n e volume, a i r volume, and t o t a l p o r o s i t y of t h e i c e a t t h e two t e s t t e m p e r a t u r e s of -2OC and

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GROWTH DIRECTION

(b) HORIZONTAL SHEAR

( c ) 45" D IAGONAL-TENS ILE SHEAR

( d l 45" DIAGONAL-COMPRESS IVE SHEAR _PRINCIPAL STRESSES

Figure 3. Specimen orientation with respect to growth direction and corresponding pure shear priikcipal stresses with respect to grain structure

S P E C I M E N CROSS-SECTION SPECIMEN CROSS-SECTION

99 x 48 mm 102 x 50 mm

1 0 0 0 5 0 1 0 0 15 0

T I M E , s

Figure 4. Load-time curves for shear of columnar-grained sea ice at - Z 0 C

(a) vertical shear

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SPECIMEN CROSS-SECTION SPECIMEN CROSS-SECTION

87 x 46 mm

" 0 100 0 50 100 1 5 0 T I M E , s

Figure 5. Load-time curves for shear of columnar-grained sea ice at -2'C

(a) 45' diagonal-tensile shear (b) 45' diagonal-compressive shear

S PECl MEN CROSS-SECTION SPECIMEN CROSS-SECTION

5 0 100 5 0 100 150 T I M E , 5

Figure 6. Load-time curves for shear of columnar-grained sea ice at -12OC

(a) vertical shear (b) horizontal shear

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-12OC. It is noteworthy that the air volume is three to ten times the brine volume of this ice.

Discussion

The first aspect of these tests to be examined was the influence of

temperature on the shear strength.

A

consistent pattern of lower shear

strength at higher temperatures occurs for all loading conditions except in the case of vertical shear. The influence of temperature and salinity of sea ice on mechanical properties is usually discussed in terms of brine volume. For the ice tested here this may not be a true reflection of the state of the ice cover. Considerable deterioration of the ice cover had occurred, as indicated by the low densities and the large brine drainage channels visible in the ice and by the elevated air porosity and low

salinities of the specimens (see Table

3).

Earlier work by Timco and

Frederking (1986) showed that, in the case of compressive strength of saline ice, total air porosity has a stronger correlation to strength than brine volume. Therefore the results of these tests are plotted versus total porosity in Fig. 8.

The other major aspect of these tests is the influence on shear strength of specimen orientation with respect to the applied stress. At -12OC the horizontal shear strength was greater than the vertical shear strength.

Such a difference in strength would be expected, since the orientation of the grain boundaries of the columnar-grains provides planes of weakness in the case of the vertical shear specimens. The diagonal shear specimens have a substantially higher strength than either the vertical or horizontal shear specimens. It is also interesting to note that for the diagonal shear it makes no difference whether an equivalent tensile or compresive stress is generated across the grain boundaries. This fact, together with the failure plane running between the two loading points, suggests that in the loading condition generated in the test, failure of the ice is

controlled by the shear strength rather than by the tensile strength. At

a

temperature of -2OC there is little difference in the shear strength, as determined from various specimen orientations. The vertical shear strength at -2OC is greater than the shear strength at other orientations and even

greater than the value at -lZ°C. There is no immediate explanation for

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SPECIMEN CROSS-SECTION SPECIMEN CROSS-SECTION

0 5 0 100 0 5 0 1 0 0 1 5 0

T I M E ,

s

Figure 7. Load-time curves for shear of columnar-grained sea ice at -12'C

(a) 45' diagonal-tensile shear

(b) 45' diagonal-compressive shear T O T A L P O R O S I T Y , v T .

Oleo

i 800 VERTICAL SHEAR HORIZONTAL SHEAR I c A DIAGONAL-TENSILE SHEAR A DIAGONAL-COMPRESSIVE SHEAR W CL: C

0 _{VERTICAL SHEAR (PAIGE AND LEE,} 1967)

LO _{4 0 0}

1

_{VERTICAL AND HORIZONTAL SHEAR IDYKINS, 19711} a:

( T O T A L P O R O S I T Y . ~ ~ 1 ' ' ~

Figure 8. Shear strength for various specimens orientations as a function

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The s t a n d a r d d e v i a t i o n from t h e means of t h e v a r i o u s t e s t s e r i e s a r e r e l a t i v e l y small, r a n g i n g from 3% t o 23%, w i t h a n a v e r a g e of 13% (Table 2). T h i s v a r i a b i l i t y i s much s m a l l e r t h a n t h a t i n p r e v i o u s l y r e p o r t e d

s h e a r - s t r e n g t h d a t a .

Comparison of t h e r e s u l t s f o r columnar i c e from t h e l i t e r a t u r e and t h i s s t u d y (Fig. 8 ) show a s t r o n g i n v e r s e r e l a t i o n between t o t a l p o r o s i t y and s h e a r s t r e n g t h . Previous work (Weeks and Assur, 1967; Timco and

F r e d e r k i n g , 1986) h a s shown i c e s t r e n g t h t o be l i n e a r l y r e l a t e d t o t h e s q u a r e r o o t of t h e b r i n e volume o r t o t a l p o r o s i t y . A l i n e a r r e g r e s s i o n a n a l y s i s performed on t h e v e r t i c a l s h e a r - s t r e n g t h d a t a of t h i s s t u d y and Paige and Lee's (1967) r e s u l t e d i n t h e f o l l o w i n g e x p r e s s i o n

where v i s t o t a l p o r o s i t y i n p a r t s p e r thousand ( c o r r e l a t i o n c o e f f i c i e n t t

r 2 = 0.81). More d a t a a r e r e q u i r e d b e f o r e s i m i l a r e x p r e s s i o n s c a n be developed f o r s h e a r s t r e n g t h under o t h e r l o a d i n g o r i e n t a t i o n s .

Conclusions

1. Shear-strength v a l u e s ranged s y s t e m a t i c a l l y from 550 t o 900 kPa f o r columnar-grained s e a i c e under t h e c o n d i t i o n s of t h i s t e s t program. 2. The asymmetric f o u r - p o i n t l o a d i n g method produces more c o n s i s t e n t and

r e l i a b l e r e s u l t s t h a n o t h e r s h e a r - t e s t methods.

3. The t o t a l p o r o s i t y t h a t combines t h e e f f e c t s of b r i n e volume and a i r c o n t e n t a s w e l l a s t e m p e r a t u r e i s a s a t i s f a c t o r y b a s i s f o r e v a l u a t i n g t h e i n f l u e n c e of t h e s e f a c t o r s on s h e a r s t r e n g t h . 4 . A t -2OC g r a i n - s t r u c t u r e o r i e n t a t i o n w i t h r e s p e c t t o l o a d i n g d i r e c t i o n had no s i g n i f i c a n t e f f e c t on s h e a r s t r e n g t h , whereas a t - 1 z 0 C g r a i n - s t r u c t u r e o r i e n t a t i o n was a c o n t r i b u t i n g f a c t o r . 5. F a i l u r e of t h e i c e was c o n t r o l l e d by s h e a r r a t h e r t h a n t e n s i o n i n t h e s e t e s t s . Acknowledgements

The a u t h o r s wish t o thank Joachim Schwarz f o r t h e o p p o r t u n i t y of

p a r t i c i p a t i n g i n t h e Labrador i c e b r e a k i n g t r i a l s of t h e R.V. " P o l a r s t e r n " . The t e c h n i c a l a s s i s t a n c e of Guenther Hackbarth, Hamburgische

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Schiffbau-Versuchsanstalt, i n c a r r y i n g o u t t h e t e s t program i s g r e a t f u l l y

acknowledged. The i c e b r e a k i n g t r i a l s were funded by t h e German M i n i s t r y

f o r Research and Technology. The R.V. " P o l a r s t e r n " was made a v a i l a b l e by

t h e Alfred-Wegner-Institute f o r P o l a r Research.

References

Butkovich, T.K. 1956. S t r e n g t h of s e a i c e . Snow, I c e and Permafrost

Research E s t a b l i s h m e n t , Kesearch Keyort KK-20. W i l l a m e t t e , I l l i n o i s ,

15 p.

Cox, G.F.N. and Weeks, W.F. 1983. Equations f o r d e t e r m i n i n g t h e gas and

b r i n e volumes i n s e a i c e samples. J o u r n a l of Glaciology, Vol. 29

( 1 0 2 ) , p. 306-316.

Dykins, J.E. 1971. I c e e n g i n e e r i n g

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m a t e r i a l p r o p e r t i e s of s a l i n e i c e f o r

a l i m i t e d range of c o n d i t o n s . Naval C i v i l Engineering L a b o r a t o r y ,

T e c h n i c a l Report R720, P o r t Hueneme, C a l i f o r n i a , 96 p.

Frederking, K.M.W. and Timco, G.W. 1984. Measurement of s h e a r s t r e n g t h of

granular/discontinuous-columnar s e a i c e . Cold Regions S c i e n c e and Technology, Vol. 9, p. 215-220.

Frederking, R.M.W. and Laframboise, J . E . (ed.) 1985. P o l a r s t e r n t r i a l s o f f

t h e Labrador c o a s t , ,Yay 1984

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Report from t h e Canadian team.

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m e t a l s . J o u r n a l of M a t e r i a l s , Vol. 2 ( 3 ) , p. 537-566.

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Table i

R e s u l t s of s h e a r t e s t s on f r a z i l s e a i c e a t -12OC

Average s h e a r Standard

s t r e n g t h d e v i a t i o n No. of

Bar s p a c i n g (kPa) (kpa) T e s t s

a = 0.1 620

a = 0.2 790

notch 6 30

Table 2

R e s u l t s of s h e a r t e s t s on columnar-grained s e a i c e a t -2'C and -12OC

Average s h e a r Standard

s t r e n g t h d e v i a t i o n No. of

Test t y p e (kPa) (kPa) T e s t s

V e r t i c a l H o r i z o n t a l Diagonal

-

Tension Diagonal

-

Compression V e r t i c a l H o r i z o n t a l Diagonal

-

Tension Diagonal

-

Compression Temperature -2'C Temperature -12OC Table 3

Brine volume, a i r volume, and t o t a l p o r o s i t y of columnar-grained i c e specimens