the adfreeze strength of sandy and clayey soils during the breakway - shusherina

8/12/2019 The Adfreeze Strength of Sandy and Clayey Soils During the Breakway - Shusherina

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by E.p. Sh us her inaA A ZharovM I ZbolotskayaA D P e r e l 'm i t e r a n dT.S. Momotova

THE ADFREEZE STRENGTH OF SANDY AND CLAYEY SOILS DURING THE BREAKAWAYMost of t h e d a t a a v a i l a b l e o n t h e a d f r e e z e s t r e n g t h o f s o i l s h av e be eno b t ai n e d d u r i n g t h e d i s pl a ce m en t of f r o z e n s o i l a c r o s s t h e a d f r e e z i n g

i n t e r f a c e b et we en t h e s o i l a nd t h e ( c o n s t r u c t i o n ) m a t e r i a l . To so l v e someof t h e p ro bl em s e n co u nt e re d i n e n g i n e e r i n g p r a c t i c e (e .g . t r a n sp o r t of s o i l sd u r in g t h e w i n t e r, d i s t u r b a n c e of f r o z e n s o i l s f o r c o n s t r u c t i o n o r mi ni ngp u rp o se s , e v a l u a t i o n of t h e r e s i s t a n c e of p i p e l i n e s t o f r o s t h ea vi ng , e t c . )we must , however, know the ad f r eeze s t r e ng th cha ra c t e r i s t i c s of s o i l s andi c e w i t h m a t e r i a l s , n o t o n l y d u r i n g t h e i r d i sp l ac e me n t, b u t a l s o d u r i n gt h e i r s e p a ra t i on a Stud ies pe rformed under th es e cond i t ion s and~ . c { 'r eviewed i n [ l ] a r e , owever, f ew and f r agmentary .

I n t h i s p ap e r we c o n s i d e r t h e r e s u l t s f ro m e x p e ri m e n ta l s t u d i e s onadf r e e z e s t r e n g t h , a of sandy and c l ayey s o i l s wi t h a meta l, undercon di t ion s of breaka ySover th e temperaure range of 0 t o -lOC. Theset e s t s were ca r r i e d ou t i n th e Department o f Pe rmaf rost S tud ies a t t he MoscowS t a t e Un ive rs i ty i n 1978-1979. The s tu d ie s were accompanied byi n v e s t i g a t i o n s of t h e t e n s i l e s t r e n g t h a of f r o ze n s o i l s , s i n c e t h emagnitude a Ps determined not only by t he s t r e ng th of th e bond betweent h e f r o z e n g PY a nd t h e m a t e r i a l , b u t a l s o by t h e r e s i s t a n c e of t h e c o n t a c tl a ye r of t he f roze n so i l . The compos i t ion and s t r uc tu re of t he specimens ,t h e p a t t e r n of t h e i r d i s i n t e g r a t i o n , a nd t h e r ou gh ne ss of t h e s u r f a c e of t h e( c o n s t r u c t i o n ) m a t e r i a l were a l s o e v a lu a t ed .

The d a t a on a .c and a were ana lysed on th e ba s i s o f po s t u l a t es o fPphysicoc hemical meghagics of di sp er se systems.Ch ar ac te r i s t i c s of th e spec imens , exper imen ta l cond i t ion s and methods .The t e s t s we re c a r r i e d o u t a t -0.5, -2 -5 and -10'C wi th two typ es of s o i l s

w d l y d i s t r i b u t e d i n t h e n o r t h of W e ste rn S i b e r i a , nam ely, a n a l l u v i a l sa nd1 2QIT and a technoge nic c l ay loam t Q I V The samples were taken from thesu r f ace hor i zons (0.03-0.35mm). Ch ar ac te r i s t i c s of t hes e s o i l s a r e g iven i n[ I ] . The clay loam s s i l t y and t h e s an d s medium-grained. The s o i l s a r en o t s a l i n e an d c o n t a i n l a r g e q u a n t i t i e s of p l a n t r em ai ns . M o n tm o ri ll o ni t es th e dominant component of th e c l ay f r a c t i o n i n th e loam. The da ta on th eunf rozen wa te r c on ten t WH (de te rmined by ca lo r i me t r i c method a t t h e

Fundamentproekt under th e su per vis ion of B oroz inet s) , and on th e t ime of t sl a t e r a l r e l ax a t io n T [de te rmined wi th th e use of th e nuc lea r -magne t i cresonan ce tec hniq ue MR) by Golovanova under t h e su pe rv is io n of Anany an]a r e g i v e n f o r t h e c l a y loam an d s an d i n F i g u r e 1.

The samples were p repared us ing d i s tu r bed s o i l s , and co r ruga ted meta lw i th o ut p l a t i n g ( s t e e l ) . The roughness of th e meta l s ur fa ce waschar ac te r i zed by the magn itude of th e average a r t i hm et i c dev ia t io n of th e


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p r o f i l e Ra = 3.7-10.3 pm. The i n i t i a l c h a r a c t e r i s t i c s of t h e s o i l s pe cim enswere: porosi ty-n3 and t h e degree of s a t u ra t i o n wi t h moisture-G3. Thecor respond ing va lu es of moi s tu re con te n t W3 and den s i t y y3, t h a t were usedd i r e c t l y i n t h e p r e p a ra t i o n of t h e s pe ci me ns , w er e c a l c u l a t e d o n t h e b a s i so f t h e s e c h a r a c t e r i s t i c s , a c co rd i ng t o t h e f or mu la s p ro vi de d i n [ I ] .Sele cted valu es of n3 , G and y3 a nd d e s c r i p t i o n of t h e p r e p a r a t i o n o ft h e sp ec im e ns a r e g i v e n 711

The t e n s i l e s t r e n g t h of th e f ro zen s o i l spec imens and th e b reakawaya d f re e z e s t r e n g t h betw een t h e s o i l and t h e m a t e r i a l s were de te rmined wi tht h e h e l p o f a s p e c i a l a p p a r a t u s c o n s t r u c t e d a t t h e D ep art me nt of P e r m af r os tS tu d ie s o f t h e Moscow S t a t e Un iv er s i t y and desc r ibed i n [A]. The t e s t s werer e p e a t e d t h r e e t i m e s w i t h a r a p i d (3-5 t o 10-20s.) uni form load ing t of a i l u r e t o d e te r mi n e i n s ta n t an e o u s s t r en g h .

A f t e r t h e t e s t s t h e s u r f a c e s o f t h e m e ta l and of t h e f r o z e n s o i l we reo bs er ve d, t h e d i f f e r e n t i a l m oi s t ur e c o n t e n t of t h e s o i l was d et er mi ne d, andi t s micr o fab r i c ( a t -So and - l O C w a s s tu d ie d by th e method o f r e p l i cac a s t i n g [ 2 ] fro m t h e s u r f a c e of f a i l u r e of t h e f r o z e n s o i l and f ro m t h es h e a r su r f a c e p e rp e nd i cu l ar t o f i t .

R e su l t s of t h e te s t s A l l t h e spec imens exh i b i t ed a mass ive c ryogen ics o i l s t ru c t u r e . No i c e fo rmat ion was obse rved wi th t h e naked eye i n any ofth e specimens in t en ded f o r de te rmina t ion s o f a a t t h e i n t er f ac eP.C#.b etw ee n t h e f r o z e n s o i l a nd t h e m e t a l. On t h e o t e r a nd r e d i s t r i b u t i o n ofm ois tu re i n t h e s o i l as a r e s u l t o f f r e ez in g was obse rved i n many of th es espe ci me ns and v a r i e d i n c h a r a c t e r [ I ] .

The m i c r o f a b r ic of t h e f r o z e n s o i l specimens w a s a na ly se d a f t e r t h ed e te r mi n at io n of t h e i r t e n s i l e s t r e n g t h a and b reakaway ad f r eeze s t r eng tht o t h e m e ta l, a .c . and t h i s p ro ve d t o ge dependen t on th e k ind o f th et e s t s as w e l l a; ok t h e t y p e of t h e s o i l .

A f t e r t h e d e t e r m i n a t i o n of a t h e f rozen sand spec imens had a b as a lc r yo g en i c m i c r o s t r u ct u r e w i t h i n d f v i d u a l s o i l p a r t i c l e s s e p a r a t e d by i c e .The d i s t r i b u t i o n o f t h e i c e and s o i l s k e l e t o n p a r t i c l e s w a s usua l ly un i fo rm.Th i s t y p e o f m i c r o s t r u c t u r e was o b ser v ed a t b o t h t e m p e r a t u r e s (-5O and- lO C a t t h e f a i l u r e s ur fa ce , a s w e l l as a t t h e v e r t i c a l s h ea r s ur fa ce . I nsome c a se s i c e pr ed om in at ed a t t h e r u p t u r e su r f a c e . A s i m i l a r m i c ro f a br i cwas obse rved i n th e sand specimens a f t e r th e de te rmina t ion of a ItP.CP*was noted t h a t t h e i c e con tent of th e breakaway su r f ac e was somewhatg r e a t e r .

A f t e r t h e d e t e r m i n a t i o n of u a t -SC t h e fr oz en cl a y loam specimensPhad a p o r p h y r i t i c c r y o ge n i c m i c r o s t r u c tu r e b o th a t t h e f a i l u r e s u r f a c e anda t t h e v e r t i c a l s h e a r s u r fa c e . D is se mi na te d m i cr o sc o pi c s p h e r i c a l i s o m e t r ici c e p a r t i c l e s m e a su ri ng 0.2 t o 0 .05 mm w ere un i fo r ml y d i s t r i b u t e d i n t h es o i l . I s o l a t e d a r e a s w i t h a b a s a l m i c ro t e xt u r e, i n w hich s o i l a g gr e ga t eswere se p a r a t e d by i c e , were a l s o o bs er ve d. S i n g l e i n t e r l a y e r s ofs e g g r e g a t e d i c e were d e t e c t e d i n t h e p e r i p h er y o f t h e spe ci me ns . S o i la g g r e g a t e s were i so m e t r i c , e l o n g a t e d o r i r r e g u l a r l y sh p ae d, a nd m ea su re d0.3 0.4; 0.4 0.2; 0.8 0.2; o r 0.1 0.1 mm. The aggregates measur ingless than 0.1 mm were l e s s compac t and had uneven s inuous ou t l in es , bu t th el a r g e r a g g r e g a t e s ha d c l e a r l y d e f i n e d c o n t o u r s a nd f a i r l y e ve n b o un d ar ie s .A t -lOC t h e c l a y l oam sp ec im en s e x h b i t i e d a b a sa l m i c r o s t r u c t u r e a t t h e


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breakaway su r f ace . So i l aggrega tes o f t he same s i z e and con f ig ura t io n werecompact a n d h ad b e t t e r d e f i n e d o u t l i n e s . A re as w i t h p o r p h y r i t i c o r b a s a lc r y og e n ic m i c r o s t r u c t u r e s w ere d i s t r i b u t e d more un i f or m l y o v e r t h e v e r t i c a ls h e a r s u r f a c e .

The mi cro fab r ic of th e f ro zen c l ay loam specimens on the breakaway andv e r t i c a l s h e a r s u r f a c e s d i s p la y e d u ni fo rm ly d i s t r i b u t e d a r e a s w i t hp o r p h y r i t i c o r b a s al m ic r o st r u ct u re s . Small i s o l a t e d i n t e r l a y e r s ofs e g r e g a t e d i c e we re o b se rv e d i n t h e z on e of c o n t a c t of t h e s o i l w i t h t h em et al . S o i l a g g re g a te s v a r i e d i n c o n f i g u r a ti o n i s o m e t r i c , e lo n g a te d o ri r r e gu la r l y shaped) and s i z e 0.4 t o 0.1 mm) and had c l e a r ly de f inedo u t l i n e s a nd f a i r l y e ve n bo un da ri es . A t - lO C th e breakaway s ur fa ce of th ec l a y l oam sp ec im en s was r i c h e r i n i c e an d e x h i b i t e d a b a sa l m i c r o s t r u c t u r e .I n i so l a t e d i n s t a n c e a l mo s t c o n ti n u o us i c e f i l m s w ere o bser ve d. The s o i laggrega te s were more compac t and had be t t e r de f ine d ou t l i ne s t han a t -5OC,i .e . t h e d i f f e r e n t i a t i o n of i c e and s o i l w a s more pronounced. The s i z e andsha pe of th e aggr ega tes remained, however , unchanged.

The p a t t e r n of i c e d i s t r i b u t i o n i n t h e s o i l v ar ie d a t t h e v e r t i c a ls u r f a c e . I n t h e c o n t a c t a r e a betw een t h e s o i l a nd t h e m e t a l a 1-1.5cen t imet r e - th i ck hor i zon wi th a l aye red c ryogen ic mic r os t ru c tu re wasn o t ic e d . I c e i n t e r l a y e r s up t o 0.2 mm i n t h i c k n e s s a nd u p t o 1.7 i nl e n g t h , w i t h o u t an y s o i l p a r t i c l e s we re ob se rv ed . The m i dd l e p o r t i o n of t h es pe ci me ns h ad a p o r p h y r i t i c m i c ro s t ru c t u re . I c e i n s e t s h ad a s p h e r i c a lisometric shape and measured 0.3-0.1 mm I s o l a t e d t h i n v e i n s of s e g r eg a t edi c e m e asur in g l e s s t h a n 0.1 mm i n t h i ck n e ss w ere a l s o s ee n. P o r p h y r i t i c I c ew a s d i s t r i b u t e d u ni fo rm ly .

The m ac ro sc op ic d e sc r i p t i o n o f t h e m e t a l a nd f r o z e n s o i l su r f a c e i nd i s t u r b e d spe ci me ns shows t h a t t h e spe ci me ns d i s i n t e g r a t e d u r i n g t h ese p a r a t i o n of t h e f r o z e n s o i l fr om t h e m e ta l i n a v a r i e t y o f ways d ep en di ngp r i ma r i ly on t h e i r m o is t ur e c o n te n t t a b l e ) [ l ] .

A f t e r t h e d e te r mi n at i on of t h e t e n s i l e s t r e n g t h t h e f a i l u r e s u r f a c e oft h e f ro z en s o i l s s always uneven.

The d a ta on th e magni tudes u and uP of f r o z e n s o i l s a r e a na l ys e don the b as is of fundamental propositionsP ?b~hysicohemical echanics ofd i s pe r se sys t ems and o f modern no t ion s o f th e s t r e ng th o f f roz en andunf rozen snady and c l ayey s o i l s [3-51. According to thes e th e main f a c t o r sd e te rm i ni n g t h e m ec ha ni ca l s t r e n g t h o f f r o z e n s o i l s a r e 1 ) t h e s t r e n g t h oft h e i r s t r u c t u r a l bonds , i . e. t h e f o r c e s of i n t e r a c t i o n of t h e s t r u c t u r a le le me nt s of f r o z e n s o i l s p a r t i c l e s of t h e s o i l s k e l e t o n , i c e c r y s t a l s andt h e i r a g g r e g at e s ), 2 t h e s t r e n g t h of t h e c r y s t a l l a t t i c e , and 3) t h ep r e se n c e o f d e f e c t s .

The s t r e n g t h of t h e s t r u c t u r a l b onds d e v e lo p in g a t t h e c o n t a c t s o fd i f f e r e n t s t r u c t u r a l el em en ts a t t h e p o i n t s where t he y a r e c l o s e s t t o onea n o t h e r ) s determined by th e number pe r u n i t volume) and ch ar ac te r ar eaa nd s t r e n g t h ) o f t h e s e c o n t a c t s . F ro ze n s o i l s h av e a t l e a s t t h e f o l lo w i n gc o n t a c t s : betw een t h e p a r t i c l e s of t h e s o i l s k e l e t o n and t h e i c e c r y s t a l s .When t h e s o i l a d f r e e z e s t o t h e m e t a l , c o n t a c t s a r e f orm ed be tw ee n t h e i c ea nd t h e m e ta l a s w e l l as between t h e s o l s k e l e t o n p a r t i c l e s a nd t h e m et al .A l l t h e s e c o n t a c t s may b e e s t a b l i s h e d d i r e c t l y p o i n t o r p ha s e c o n t a c t s


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accord ing t o Reb inder ) o r th rough a f i l m of u n f ro z e n w a t e r ( c o a g u l a t i o nc o n t a c t s ) [SI

The s t r e n g t h of t h e c o n t a c t s b et we en t h e c r y s t a l s of i c e a nd t h es t r e n g t h of i t s c r y s t a l l a t t i c e d et er mi ne t h e s t r e n g t h of t h e i c e i nc l u si o n sembedded i n t h e f r o z e n s o i l ( po re i c e o r t h e i c e fo rm in g t h e s t r u c t u r a l i c ef ramework). The s t r u c tu r a l bonds formed by th e pres ence of i c e in cl us io nsand by t h e i r c o n t a c t s w i t h t h e s o i l s k e le t o n p a r t i c l e s , h av e bee n s e t a p a r ta s a sp e c i a l "ic e-c em ent " t y p e o f s t r u c t u r a l b ond s.

The most i n t e r e s t i n g r e su l t s o f t h e me ch an ic al t e s t s p er fo rm ed w i t hf r o z e n s o i l s pe ci me ns ( s e e t h e t a b l e a n d t h e d r aw in g) a r e t h e d a t a on t h es t r e n g t h c h a r a c t e r i s t i c s ap and a a s f u n c t i o n s of t e m p er a t ur e ,PCmois tu re con ten t and degree of d i sp e r ion .

Comparison of a and a shows tha t , a l l t h e o t he r c on d it io n s ( s o i lP=Cl+.t y p e , t e m p er a t ur e , m oi s u r e c o n t e n t an d d e n s i t y ) b e i ng e q u a l , t h e t e n s i l es t r e n g t h of f r o ze n s o i l s i s u su a l l y much g r e a t e r t h a n t h e i r a d f r e e z es t r e n g t h t o t h e m e t a l d u r i n g t h e breakaw ay ( a a p . ~ p . Given thec h a r a c t e r of d i s i n t e g r a t i o n o f t h e s pe ci me ns , 't hi s shows t h a t t h e s t r u c t u r a lbonds a t t h e f a i l u r e s u r f ac e of t h e f r oz e n s o i l a r e s t ro n g er t h a n a t i t sa d f r e e z e su r f a c e t o t h e m e t a l , w he re t h e se b onds a r e de t er m in e d by t h es t r e n g t h of t h e i c e - m e t a l and s o i l s k e l e t o n p a r t i c l e s - m e t a l c o n t a c t s .

The d a t a o b ta i n ed show t h a t t h e t e n s i l e s t r e n g t h of f r o z e n e a r t hm a t e r i a l s a nd t h e i r a d f re e z e s t r e n g t h t o t h e m e ta l v ar y w i th d i s p e r s i on ,t empera tu re and mois tu re con ten t .

The e f f e c t o f t he degree o f d i spe r s ion . A t a temperature of -0.5, -3o r - 5 - B f c l a y loam, b u t a t 8 = -lOCth e s t r e ng th g f sand d rops-be low th a t o f loam. The c u r v e s d e p i c t i n g a a s afunc t ion o f 8 in tersect around -gC. Th i s d ep en de nc e of t h e t e n s i l e Ps t r e n g t h of f r o z e n s o i l s on t h e d e gr ee of t h e i r d i s p e r s i o n o v er t h etempera tu re r ange examined , a s we l l a s a t lower temperature va lue s (-10 t o-60C [ 7 ] , c an b e e x p l ai n e d i n t er ms o f t h e d i s t i n c t i v e n a t u r e of s t r e n g t hof s a nd an d cl a y ey so i l s .

I n f r o z e n s a nd t h e v a l u e s o f a are determine d mainly by t he ice-cementcohes ion (ICC) w i t h t h e i n t e r p a r t i c l e bonds o f t h e s o i l s k e l e to n p l a yi n g am in or r o l e . The f a c t t h a t t h e v a l u e of a i n s an d i s l a r g e r th an t h a t i nPcl ay loam a t -0 .5 , 2 and -5' may be due p ri m a ri ly t o i t s g r e a t e r I C C due t ot h e i c e i n c l u s i o n s a nd be c au se o f t h e b on ds b etw een t h e i c e a nd s o i lsk e l e t o n p a r t i c l e s . The d i f f e r e n c e i n t h e amount o f u nf r o ze n w a t e r a t t h eabove temperatures WH = 0.0 15-0.02 i n sa nd and WH = 0.13-0.18 i n loam)a c co u nt s f o r t h e g r e a t e r s t r e n g t h of t h e i c e -s k e l et o n bonds i n sa nd. T h i s ,combined wi t h th e development of th e bas al type of ice-cement i n sand,c au se s t h e f a i l u r e of t h e i c e in c l us i o ns i n i t n t h e o t h e r h an d i n loam,w here t h e s t r e n g t h of t h e i c e - so i l sk e l e t o n bonds i s s m a l l e r , b a s a l a s w e l las p o r p h y r i t i c ice -ce me nt e x i s t , and t h e r o l e of i c e i n c l u s i o n s a nd of I C Ci n d ev el op in g t h e t e n s i l e s t r e n g t h i s g e n e r a l l y l e s s i m po r ta n t, i n s p i t e oft h e f a c t t h a t l oam ha s a g r e a t e r i c e c o n t e n t t h a n s an d ( s e e t h e d ra wi ng ).The f a i l u r e su r f a c e may d e v e lo p i n f r o z e n l oam o v e r t h e w ea ke st l o c ia v oi d in g t h e i c e i n c l u s i o n s . The c o n t a c t s betw een t h e p a r t i c l e s o f t h e s o i lsk e le ton may be among such a r ea s , a s a r e de fec t ( c r ac ks o r vo ids ) andi c e - so i l sk e l e t o n c o n t a c t s . W ith d e c r e a se of t e m p er a t ur e t h e s t r e n g t h of


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t h e bonds b etw een t h e p a r t i c l e s o f t h e s o i l s k e l e t o n i n c r e a s e s ( a s d oe s i t sICC). The p a r t i c l e s move c l os e r t o one ano ther as a r e s u l t of d e f o r m a ti o n sd ev el op in g i n t h e f r o z e n s o i l d ue t o t e m p e ra t u re - r el a t e d c o n t r a c t i o n , asw e l l a s d u e t o t h e d e c r e as e i n t h e m o i st u r e c o n te n t o n ac co un t o f u n fr o ze nwater and i t s i n c r e a s i n g v i s c o s i t y ( s e e d a t a o n T2 i n t h e d ra wi ng ). Thes t r u c t u r a l i n t e r p a r t i c l e bonds i n t h e s o i l s ke l e to n of c l a y l oam f o r 8 above-9OC do no t , however , compensate f o r t h e f a c t t h a t i t s I C C i s lower thanth a t o f sand , even though th e I C C of loam a l s o i n c r e a s e s w i t h d e c re a s e i ntemperature . s t h e t empera tu re d rops below -gC, th e s t r e ng th of th ei n t e r p a r t i c l e bonds of t h e s k e l e t o n a nd p a r t l y i t s I C C c o n t in u e t o i n c r e a s ei n loam, which accoun t s f o r i t s g r e a t e r t e n s i l e s t r e n gt h r e l a t i v e t o t h a t ofsand.

I t sh o u ld be no t ed t h a t a c c o r d i n g t o t h e d a t a of o t h e r a u t h o r s ( e .g .[ 6 ] , w i t hi n t h e ra ng e of 0 t o - 1 0 ' ~ c l a y s o i l s ha ve a g r e a t e r s t r e n g t h t h ansand. Th is may b e d ue t o t h e s p e c i f i c n a t u r e o f t h e s a nd spe ci me ns s t u d i e dby t h e e s p e c i a l i s t s , p a r t i c u l a r l y t o t h e f a c t t h a t t h e i r d eg re e ofs a t u r a t i o n was l ow er t h a n i n o u r t e s t s .

Comparison of sand and loam wi th rega rd t o t h e i r breakaway ad f re ez es t r e n g t h t o t h e m e ta l s hows a c l e a r c u t d ep en de nc e o f t h e m ag ni tu de ao n d i sp e r s i o n . T h i s i s c o n t r a r y t o o b se r v a t i o n s f ro m some of t h e e a r I i % *t e s t s t h a t w e re c a r r i e d o u t a t t h e same t em p e r a tu r e s un d er c o n d i t i o n s ofs h e a r a cr o s s t h e s u r f a c e of t h e m et al , an d, t o a s i g n i f i c a n t e x t e n t i t maybe due t o t h e a bs en ce of a v i s i b l e f i l m of i c e a t t h e f r o z e n s o i l - m e t a li n t e r f a c e i n o u r t e s t s . Sand h a s a much g r e a t e r a t ha n loam a t a l l t h et e mp e ra t ur e s i n t h e r a n g e -0.5 t o - lOC. ~o r e o v e r S ) '%i d i f f e r e n c e be twe enthem i n c r e a s e s w i t h d e c r e a se i n t e m pe r at u re .

The e f f e c t o f d i sp e r s ion on th e magni tude o f a .c i n f r o z e n s o i l s mayb e e x p l ai n e d fr om t h e f a i l u r e p a t t e n o f t h e i r s p e c i & n k m a l o n g t h e f r o z e ns o i l - m e t a l c o n t a c t and w i t h i n t h e f r o z en s o i l ) , by t h e c o r r e l a t i o n of t h er e s p ec t i ve t e n s i l e s t r e n g t h s a o f t h e f r o z e n s o i l s s t u d i e d ( s an d a nd l oa m ),Pa nd f ro m t h e s t r e n g t h of t h e i r a d f r e e z e bond w i t h t h e m e t a l. A s was showne a r l i e r , s an d h as a g r e a t e r a than loam (up t o 8 -gC). Presumably t h ePbond between fro ze n sand and metal i s a l s o s t r o n g e r t h a n t h a t betwee n f r o z e nloam and metal . Thi s i s due ma in ly t o t h e g r e a t e r i c e c o n t e n t i n t h e loamspe ci me ns a nd t o t h e i r p r o p o r t i o n a l l y s t r o n g e r i ce -m et al bond ( a c c o r d i n g t ot h e d a t a of r a p id d e t e rm i n a ti o n s o f t h e a d f r e e z e s t r e n g t h i n s h e a r , i t i s= c f o r f ro z en s o i l s and f o r i c e [ I ] , w i t h z ~ C L r asueYiC:; t o t h e s m a l l e r s t r e n g t F p ~ f * s t r u c t u r a l onds bet% grth e loams k e l e t o n p a r t i c l e s a nd m et al . I t shou ld be kep t i n mind th a t t he loamspe ci me ns h a d a n i n c r e a se d i c e c o n t e n t i n t h e c o n t a c t l a y e r , a s shown by t h et o t a l moi s tu re con ten t and mic ro fab r i c . Due t o t h i s the magn itude o f a i nt h e co n t a ct l a y e r of f r oz e n s o i l i s f u r t h e r re du ce d f o r loam , a nd t h e Ps t r e n g t h of t h e f r o z e n s o i l - m e t a l c o n t a c t i s a l s o s m al l er t h an t h a t f o rsand, which accounts f o r th e aforement ioned a .cp. c o r r e l a t i o n f o r s a n d a ndloam pe r s i s t i ng no t on ly t o -gC, bu t even be fow th a t t empera tu re .

The e f f e c t of temperature . A s 8 drops f rom -0.5 t o - lO C t h e t e n s i l es t r e n g t h a, of f r o z e n s o i l s a nd t h e i r ad r e e z e s t r e n g t h w i t h t h e m e ta l.cp. i n c f e a se a p p r e c i a b l y ( s e e t h e dr aw in g a nd t h e t a b l e ) . The na tu re o ft g a t dependence i s d i f f e r e n t , h ow ev er, f o r s a n d a nd loa m a nd f o r a and

Thi s i s c l e a r l y i l l u s t r a t e d by t h e eq u a t io n s d e s c r i b i n g up andP oc p* a s f u n c t i o n s o f t e m p er a t u re 8 or loam: Pap cp.


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For sand:

Eq ua t io n s ( I ) , ( 2 ) and ( 4 ) d e s c r i b e t h e d ep en de nc e o v e r t h e e n t i r etem pe rat ure ran ge examined (-0.5 t o -lOC); e q u a t i o n (3 ) i s g iv en f o r t h e-0.5 t o -5 C in t e rv a l of 8 va lues , and equa t ion (3 ) f o r the 5 t o - lO Ci n t e r v a l . 8 i s t h e a b s o l u t e v a lu e .

Wi th in the -5 t o - lO C range the dependence of a on 8 i s c l o se t ol i n e a r f o r loam , b u t n o n - li n e a r f o r s a nd : t h e v a l u e 8f a i n c r e a s e s w i t hd e c r e a s e i n 8 b u t t h e r t e of inc rea se dec reases . [ see fh e d rawing ande q u a t i o n s ( I ) , ( 3 ) a nd ( 3 ) . ] W it hi n t h e 0.5 t o -2OC i n t e r v a l t h e t e n s i l es t r e ng th o f sand ( a inc rea se s much more r ap id ly than t h a t of loam; as 8d r op f ro m -2 t o -5 08 , t h e r a t e of t h e i n c r e a se of a v a l u e s i s rough ly thesame i n sand and loam. Wi th in th e -5 t o - lOC i n t e g v a l t h e a values ofloam con t inue t o i nc rea se a s t empera tu re d rops wi th t he same pa te o fi n c r e a s e s t h igh er t empera tu res , whereas i n sand a r e m a i n s p r a c t i c a l l yc o n s t a n t P

Comparison of t h e a -8 curves ob ta in ed f o r sand and loam wi t h s imi la rPc ur ve s f o r i c e [ ] shows t h a t t h e dependence of a on 8 g e n e r a l l y m a n i f e s t si t s e l f much more s t r o n g l y i n f r o z e n s o i l s , a s i s E l s o t h e c a s e a t l ow er 8v al ue s [ 7 ] . T hi s p ro ve s t h a t i n a d d it i o n t o t h e s t r e n g t h of i c e , t h e r e a r eo t h er f a c t o r s r e s p on s ib l e f o r t h e f a c t t h a t a of f r o ze n s o i l s i s a f u n c t i o nPof 8, i nc lud ing , a s i s w e l l known, phase t ra n s i t io n s of water . Thed i f f e r e n e s i n t h e s h a pe of a -8 c u r v es f o r sa n d a nd loam r e f l e c t t h ePd i f f e r e n c e s i n t h e mechanism o f t em pe ra tu re -d ep en de nt v a r i a t i o n s i n a oft h e s e s o i l s . P

A s was ment ioned ear l ier , a f o r s a n d i s determined mainly f rom thePmagnitude of I CC . The h i g h r a t e of i n c r e a se of t h e a v a l u e s w i t h d e c r e a sei n tem pe rat ure from -0.5 t o -2OC i s r e l a t e d t o t h e i n gr e as e i n I C C caused byt h e h a rd en in g of i c e a s w e l l t o t h e i n c r e a s i n g s t r e n g t h of s t r u c t u r a l bondsbetween t h e i c e an d t h e s o i l s k e l et o n p a r t i c l e s a s a r e s u l t o f t h ei n c r e a s i n g a r e a a nd s t r e n g t h of t h e i r c o n t a c t s . The l ow er r a t e o f i n c r e a seof a i n f roz en sand wi th a drop i n temperature f rom -2 t o -5 C may ber e l a t e d t o t h e l o w er in g of i t s I CC . The f a c t t h a t a of sand remainsp r a c t i c a l l y c o n s t a n t w i t h a d r op i n 8 fr om -5 t o -10 C a nd f u r t h e r d e c re a seof I C C c an pr ob ab ly a l s o be a t t r i b u t e d t o t h e i n c r e a s i n g r o l e o f d e f e c t s i nfrozen sand on account of i t s i nc re as in g s t i f f n e s s ( r i g i d i t y ) t h a t l e ad s t oa l a r g e r s t r e s s c o nc e nt ra t io n s.

For loam the v alu e of a i s co n t r o l l ed no t on ly by I C C b u t a l s o by t h ePs t r e n g t h of i n t e r p a r t i c l e bonds of t h e s o i l s k e l e t o n , w hich i n c r e a s e s w i t hdecreas e i n t empera tu re . The less r a p i d i n c r e a s e of a i n l oam o v e r t h eP


8/11

-0.5 t o -2OC i n t e r v a l r e l a t i v e t o t h a t of sand may be due t o i t s muchg r e a t e r c o n t e n t o f u n f ro z e n w at e r. The unf rozen wa te r impedes t o a ce r t a inex te n t th e work of th e i c e i n c l u s i o n s ( a s was me nt io ned e a r l i e r , t h e f a i l u r es u r f a c e c a n s k i r t a ro un d t h e s e i n c l u s i o n s ) and r e du c es t h e s t r e n g t h o fi n t e r p a r t i c l e bo nd s of t h e s o i l sk e l e t o n a nd o f t h e sk e l e t o n - i c e bonds. Thef a c t t h a t t h e t e n s i l e s t r e n g t h ( a i n c re a e s i n loam o v er t h e i n t e r v a l of -2Pt o -lOC, a s r a p i d l y a s a t h i g h e r v a l u es , i n s p i t e o f t h e n e g li g i bl y s m a l land d e c l i n i n g p ha se t r a n s i t i o n s of w a t e r and i n c r e a s i n g s t r e n g t h of i c e , i sl a r g e l y d ue t o t h e a ) i n c r e a s i n g s t r e n g t h of t h e b onds b etween t h e p a r t i c l e sof t h e s o i l sk e l e t o n on a cc o u n t o f t h e f i l m of u n f ro z e n w a t e r b e i n g f o r c e do u t of t h e i n t e r p a r t i c l e c o n t a c t s by t h e d e ve l op i ng t he r ma l s t resses , and b)t h e i n c r e a s i n g v i s c o s i t y of u n f r o z e n w a t e r ( s e e t h e d ra w in g) .

I n t h e s o i l s s t u d i e d t h e d ep en de nc e of t h e a d f r e e z e s t r e n g t h t o t h emeta l a on temperature 8 i s non- linea r : a s th e t empera tu re d rops f rom-0.5 toP1fbs~, a i n c r e a s e s l ess r apd i ly . [See th e d rawing ande q u a t i o n s 2 ) an 'fgf.] I n conformi ty wi th th e cha rac te r o f f a i l u r e( d i s i n t e g r a t i o n ) o f t h e spe ci me ns , t h e sha p e of t h e c ur v e s o b t a i n e d f o r t h edependence of a .cpq on c a n b e e x p l a i n e d by t h e s t r e n g h t of t h e f r o z e ns o i l ( i n t h e c o g t a c t l a y e r ) a nd by i t s c o n t a c t w i t h t h e m e ta l .

W it h d e c r e a se i n t e m pe r a tu r e o v er t h e -0.5 t o - lO C r a n g e t h e v a l u e s o fa i n c r e a s e i n loam less r a p i d l y t h a n t h o se o f a which may dueP*CP* Pp r i m a r i l y b e t o t h e f a c t t h a t t h e s t r e n g t h of t h e f r o z e n l oa m -m et al bondi n c r e a s e s l e s s r a p i d l y t h a n a Moreover, i t sh o u ld b e k e p t i n mind t h a tt h e m o is t u re c o n t e n t of c l a y foam i n t h e c o n t a c t a r e a i n c r e a s e s , a s wasm entioned e a r l i e r , r e l a t i v e t o i t s i n i t i a l c o n di ti on p r i o r t o f r ee zi ng .Th i s c i r cumstance r educes th e in t e n s i ty of th e t empera ture -dependen ti n c r e a s e i n t h e t e n s i l e s t r e n g t h of t h e c o n t a ct l a y e r and i n t h e s t r e n g t h oft h e f r o z e n l o a n r m e t a l bond, a nd l ow e r s a c c o r d i n g l y t h e o v e r a l l o f o rloam. P*CP-

I n s an d a l e s s i n t e n s i v e i n c r e a s e o f a r e l a t i v e t o t h a t o f a h a sPbeen obse rved on ly i n th e in t e rv a l of -0.5 ? G ~ E ~ ~ cnd c an be a t t r i b u t e d t ot h e same f a c t o r s a s i n t h e c a se of loam. W ith f u r t h e r t e m p e r a tu r edepress ion f rom -2 t o -lOC apeCp. f sand inc res es more r a p i d l y than i t su w hich a p p e ar s t o be t o t h e n a t u r e o f t h e r e l a t i o n sh i p b e tw ee n a and 8P'i n t h a t s o i l , a s w s d i s c u s s e d e a r l i e r . P

The e f f e c t of t h e m oi s t ur e c o nt e n t on t h e t e n s i l e s t r e n g t h of f r o z e ns o i l s a a nd on t h e i r a d f r e e z e s t r e n g t h w i t h t h e m e ta l aP i s d i f f e r e n ti n s an d a nd loam, r e sp e c t i v e l y ( s e e t h e t a b l e a n d t h e d r%&).

I n s a nd a n i n c r e a se i n t h e m o i s t u re c o n t e n t w i t h i n t h e r a n g e exam inedinduces a s u b s t a n t i a l i n c r e a s e of a and aP p .cp. w hich p r a c t i c a l l y f o l l ow st h e l i n e a r la w, and t h e de pe nd en ce s of t h e two s t r e n g t h c h a r a c t e r i s t i c s of Wa r e s i m i l a r ( t h e a nd a P n C p .W c ur ve s a r e p a r a l l e l ) . An inc rea se i n Wof sand from 0.12 t o 0.16 w a s accompanied by a de cr ea se of i t s poros i ty andby an inc re as e of i t s degr ee of sa tu ra t i on from 0 .5 t o 0.8. W i t h f u r t h e ri n c r e a se o f W ( t o 0.20) t h e d e g re e of s a t u r a t i o n r em ai ne d p r a c t i c a l l yu nc ha ng ed , b u t t h e p o r o s i t y i n c r e a se ( s e e t h e d r aw in g) . The i n c r e a s e i n aof sand wi th inc r eas ing W c an t h e r e f o r e be e x p la i n ed by t h e i n t e n s i f i c a t i o xof th e i ce -cemen t cohes ion (ICC) on account of th e inc r ea se i n th e u n i t a r e aof t h e i c e - s o il s k e l e t o n c o n t a c t s ( i n t h e i n i t i a l i n t e r v a l of m oi st ur e andi c e c o n t e n t s ) . The i n c r e a se o f a w i t h t h e r i s e of W may be r e l a t e dP*clr


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p r i m a r i l y t o t h e i n c r e a s e of a Moreover, t must be kep t i n mind th a tw i t h i n c r e a s i n g W t h e f a i l u r e s u r f a c e becomes l e s s e v e n an d i n c r e as e s i na r e a i n f r o z e n s o i l s . F ur th er mo re , w i t h t h e r i se of W p a r t i c u la r l y i n t he0.12-0.16 i n t e r v a l of W3 t h e s t r en g t h of t h e b ond s be tw een t h e f r o zen s o i land t h e m e t a l i n c r ea se s on acco u nt of t h e i n c r e a s i n g i ce - me t al co n t ac ta rea .

I n c r e a s e s i n t h e m o is t u re c o n t e n t W) of th e loam specimens wereaccom pn aied by chang es i n p o r o s i t y and sa t u r a t i o n s i m i l a r t o t h o se o b se r vedf o r sand (s ee the drawing). However, th e na tu re of th e dependence of a onPW was d i f f e r e n t i n loam fr om t h a t r e co r ded f o r s an d: a i n c r e a s e d w i t h W a tPf i r s t , b u t de cr ea se d w i t h f u r t h e r i n cr e a se i n W. The inc re as e of up can beex p l a i n ed p r i m a r i l y by t h e i n c r ea s i n g s t r en g t h of t h e i c e - so i l sk e l e t o nbonds and of t h e bonds b et ween t h e p a r t i c l e s o f t h e s o i l sk e l e t o n , and t h edecrease of a by t h e d ec r ea s i n g s t r en g t h of t h e s e s t r u c t u r a l bonds. Withi n c r e a s i n g mo ys tu re co n t en t t h e ad f r eeze s t r en g t h of t h e loam t o t h e m e t a l( U r i s e s s moo th ly w i t h a p r o gr e s s iv e l y g r e a t e r i n t e n s i t y . I n o t h erwo dgpbe does no t obs erve a peak va lu e f o r a .c a s o bs er ve d i n t h e c a s eof a T h i s i s due t o t h e f a c t t h a t i n loam p l e ss i m po r ta n t i n t h edeveyopment of up .cp. t h a n i n s an d.

I n c on cl us io n l e t u s compare t h e r e s u l t s of o u r t e s t s w i t h e a r l i e rf i n d i n g s . A ccor di ng t o t h e d a t a of S ad o v sk i i [ 8 ] a t a t em p er a t ur e o f-5.5OC a = 0.76 MPa, o u r v a l u e i s 1.01 MPa. The d is c re pa n c ie s ca n beex p l a i n e8 * & 'd i f f e r en t t e ch n i q u es employed i n t h e t e s t s , p r i m a r i l y by t h ed i f f e r en c e s i n t h e r a t e s a t w hi ch t h e s am pl es we re l o ad ed ( i n o u r t e s t s t h et im e t o f a i l u r e was 3 t o 20 s., w he re as i n S a d o vs k i i' s t e s t s i t a p pe a rs t ohave been se ve ra l minutes) . t i s eq u a l l y p o s s i b l e t h a t t h e sp ec i m en ss t u d i e d by S a do v sk i i w ere d i f f e r e n t f ro m t h o s e d i s c u s s e d i n t h e p r e s e n tpaper.


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BIBLIOGRAPHY1 Shusherina E.P., Zharov A.A., Nikolaev A.A. et al. Prochnost'smerzaniya gruntov pri otryve (Adfreeze strength of soils during the

breakaway). -In: Merzlotnye issledovaniya (Permafrost studies).Moscow, Izd-vo MGU, 1980, issue 19, pp. 178-195.2. ~hestkova .N., ~abolotska~a.I., Rogov V.V. Kriogennoe stroeniemerzlykh porod (Cryogenic Structure of Frozen Soils). Moscow, Izd-voMGU, 1980, 137 p.3. Vyalov S.S. Reologicheskie svoistva i nesushchaya sposobnost' merzlykhgruntov (Rheological Properties and Bearing Capacity of Frozen Soils).Moscow. izd-vo AN SSSR. 1959. 188 p.r 'ko;a I .M. struktu;nye i - ef o atsionnye osobennosti osadochnykhporod razlichnoi stepeni uplotneniya i litifikatsii (Structural andDeformation Characteristics of Sedimentary Rocks of Different DegreesConsolidation and Lithification). Moscow, Nauka, 1965, 128 p.

Rebinder P.A. Fiziko-khimicheskaya mekhanika dispersnykh struktur(Physicochemical mechanics of disperse structures). -In:Fiziko-khimicheskaya mekhanika dispersnykh struktur (PhysicochemicalMechanics of Disperse Structures). Moscow, Nauka, 1966, pp. 3-17.6. Pekarskaya N . K . Vyalov S.S., Rovinskii M.I. et al. Issledovaniyaparametrov prochnosti merzlykh gruntov, operdelyayushchikh protsess ikhrazrusheniya zemleroinymi mashinami (Studies on strength parameters offrozen soils controlling the process of their disturbance byearth-moving equipment). -In: Tr. IV soveshch. -seminars po obmenuopytom stroitel'stva v surovykh klimaticheskikh usloviyakh (Proceedingsof the IV Conference for Exchange of Experience Pertaining toConstruction under Harsh Climatic Conditions). Vorkuta, Kn. izd-vo,

1966 v. 8 pp. 1-17.7. Shusherina E.p. Soprotivlenie merzlykh porod i l'da razryvu v oblastinizkikh temperatur /do -60c/ (Resistance of frozen soils to rupture inthe region of low temperatures /to -60C/). -In: Merzlotnyeissledovaniya (Permafrost Studies). Moscow, Izd-vo MHU, 1974, issue 14,pp. 179-190.8. Sadovskii A.V. Prochnost' smerzaniya gruntov s materialom fundarnenta(Adfreeze strength of soils to the material of the foundation). -In:I1 Mezhdunar. konf. po merzlotovedeniyu (I1 International PermafrostConference). Koklady i soobshcheniya (Papers and Communications).Yakutsk, Kn izd-vo, 1973, issue 7, pp. 210-214.


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Figure 1 Tensile strength, a of frozen soils and their adfreeze strengthto the metal a 'during the breakaway. a-a 1,2) and a(3,4) as functPc %'of temperature : 1 and 3-gand, W3 o.PoP ~and 4-clay loam, W3= 0.49; b a (5,6) and spec (7,8) of frozensoils as functions of the moisture content W d -2.1C);c-Characteristics of the frozen soil specimets over thetemperature range investigated: 9 and lo-unfrozen water contentVH (in volume units relative to the frozen soil); 11 and 12-icecontent Vx (same units); 13 and 14-porosity n; 15 and 16degreeof saturation with moisture G; 17 and 18-time of lateralrelaxation of unfrozen water T 9, 11, 13, 15 and 17-sand (forcurves 1 and 3); 10, 13, 14, 1 and 18-clay loam (for curves 2and 4 ; d-characteristics of frozen soil specimens: 19 and20-VH; 21 and 22-4; 23 and 2411; 25 and 26-G; 19, 21, 23, 25 and27-sand (for curves 5 and 7); 20, 22, 24, 26 and 28-clay loam(for curves 6 and 8 .

the adfreeze strength of sandy and clayey soils during the breakway - shusherina

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