Principles of Geocryology (Permafrost Studies). Part II, Engineering Geocryology. Chapter II, Deformation of Structures Resulting from the Processes of Freezing and Thawing. p. 18-27

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Principles of Geocryology (Permafrost Studies). Part II, Engineering

Geocryology. Chapter II, Deformation of Structures Resulting from the

Processes of Freezing and Thawing. p. 18-27

Dement'ev, A. I.

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PREFACE

T h i s t r a n s l a t i o n i s t h e t h i r d from t h e Russian p e r m a f r o s t p u b l i c a t i o n " P r i n c i p l e s o f ~ e o c r y o l o g y " , P a r t I1 ( ~ n g i n e e r i n g Geocryoloq). The f i r s t t r a n s l a t i o n i n t h i s group was Chapter I e n t i t l e d , P r i n c i p l e Aspects of E n g i n e e r i n g Geocryology (perma- f r o s t ~ t u d i e s ) " by N . I . S a l t y k o v (TT-1215). The second was Chapter V I I

articular

Aspects of Mining i n Thick ~ e r m a f r o s t " by V.P. Bakakin (TT-1217).

T h i s t r a n s l a t i o n o f Chapter I1 by A . I. Dement lev d i s c u s s e s deformation of e n g i n e e r i n g s t r u c t u r e s founded on f r e e z i n g and thawing s o i l s under two headings. The f i r s t i s concerned w i t h s t r u c t u r a l deformation caused by s e a s o n a l f r e e z i n g and thawing o f t h e ground, and t h e second w i t h d e f o r m a t i o n caused by thawing o f permaf r o s t

.

The D i v i s i o n i s g r a t e f u l t o M r . V. Poppe, T r a n s l a t i o n s S e c t i o n , N a t i o n a l Research Council, f o r t r a n s l a t i n g t h i s c h a p t e r and t o D r . R.J.E. Brown of t h i s D i v i s i o n who checked t h e

t r a n s l a t i o n . Ottawa

November 1965

R.F. Legget D i r e c t o r

T i t l e :

NATIONAL RESEARCH COUNCIL OF CANADA

Technical T r a n s l a t i o n 1219

Deformation of s t r u c t u r e s r e s u l t i n g from t h e p r o c e s s e s of f r e e z i n g and thawing

(Deformatsii s o o r u z h e n i i , vyzyvaemye p r o t s e s s a m i promerzaniya i

p r o t a i v a n i y a )

Author: A. I. Dement 'ev

Reference : P r i n c i p l e s of geocryology (permafrost s t u d i e s ), P a r t 11, Engineering geocryology, Chapter 11. Academy of Sciences of t h e U.S.S.R. Moscow 1959. p.18-27

( ~ s n o v y g e o k r i o l o g i i (merzlotovedeniya), C h a s t f vtoraya,

Inzhenernaya geokriologiya, Qlava 11. Akademiya Nauk SSSR

.

Moskva 1959. 8.18-27)

DEFORMAT I O N OF STRUCTURES RESULTING FROM THE PROCESSES OF FREEZING AND THAIJING*

I n t r o d u c t i o n . I. Deformation of s t r u c t u r e s r e s u l t i n g from s e a s o n a l f r e e z i n g and thawing (group A ) . 2. Deformation of s t r u c t u r e s r e s u l t i n g from thawing of p e r m a f r o s t (group B ) .

3 . Conclusions.

I n t r o d u c t i o n

It was mentioned i n Chapter I t h a t t h e p r o c e s s e s o f f r e e z i n g and thawing r e s u l t i n g from phase t r a n s f o r m a t i o n s o f m o i s t u r e have a d e t r i m e n t a l e f f e c t on t h e s t r e n g t h and s t a b i l i t y of' s t r u c t u r e s . Because of t h i s , i t i s e s s e n t i a l t o c o n s i d e r t h e laws governing t h e s e p r o c e s s e s when e r e c t i n g and u s i n g v a r i o u s

structures.

A d i s r e g a r d f o r t h e s e laws r e s u l t s i n t h e deformation o f a s t r u c t u r e , u s u a l l y i n v o l v i n g b r e a k s i n i t s c o n t i n u i t y , 1 . e . i n t h e appearance and propa- g a t i o n of c r a c k s l e a d i n g t o b r e a k s i n s t r u c t u r a l elements and sometimes t o t o t a l f a i l u r e .

The p r e s e n t c h a p t e r d e a l s o n l y w i t h deformation caused by t h e p r o c e s s e s of f r e e z i n g and thawing which t a k e s p l a c e i n t h e ground o r i n t h e masonry d u r i n g t h e f r e e z i n g o f w a t e r o r t h e m e l t i n g of i c e c o n t a i n e d i n them. S t r u c t u r a l deformation caused by o t h e r f a c t o r s , s u c h a s i n a d e q u a t e work methods, i n f e r i o r c o n s t r u c t i o n m a t e r i a l s , e r r o r s i n design, e t c . a r e n o t d i s c u s s e d h e r e .

When t h e ground f r e e z e s o r thaws, t h e s t r u c t u r e s a r e s u b j e c t e d t o h e a v i n g o r s e t t l e m e n t . Heaving r e s u l t s i n uneven u p l i f t of t h e s t r u c t u r e and d i s t u r b s i t s c o n t i n u i t y . If t h e s t r u c t u r e i s anchored i n t h e b e a r i n g medium b u t i t s weight i s unable t o w i t h s t a n d t h e d e v e l o p i n g f o r c e s , t h e n h e a v i n g may d e s t r o y t h e f o u n d a t i o n . On thawing, t h e b e a r i n g c a p a c i t y o f t h e b e a r i n g medium

d e c r e a s e s , t h e ground becomes weaker and begins t o s e t t l e . A s a r u l e , t h e s e t t l e m e n t does n o t o c c u r e v e n l y o v e r t h e e n t i r e a r e a occupied by t h e s t r u c - t u r e o r one of i t s s e c t i o n s . Due t o d i f f e r e n t i a l movement of t h e s t r u c t u r e , t h e i n t e r n a l s t r e s s e s i n i t a r e r e d i s t r i b u t e d , l e a d i n g t o t h e predominance of bending and s h e a r i n g f o r c e s which r e s u l t i n deformation of s t r u c t u r a l elements n o t adapted t o such mechanical changes. If t h e r a t e of displacement o f

*

31 _{Chapters I1 and X I and i n S e c t i o n s 1 , 4 , 6 and 7 of Chapter X I 1 c o n t r i b u t e d} by A . I . Dementlev, t h e e d i t o r s have changed t h e terminolo@;y o f t h e a u t h o r t o make i t a g r e e w i t h terminology used i n o t h e r c h a p t e r s .

masonry i s n e g l i g i b l e and amounts t o a few hundredths of a m i l l i m e t r e p e r day, t h e n t h e r h e o l o g i c a l p r o p e r t i e s and c r e e p o f t h e maoonry w i l l e n s u r e t h a t t h e c o n t i n u i t y o f t h e s t r u c t u r e and i t s 1-1gid j o i n t s w i l l remain i n t a c t . I n s p i t e o f t h i s , i n t e n s i v e ( i n a b s o l u t e v a l u e s ) d i f f e r e n t i a l s e t t l e m e n t may r e s u l t i n pronounced t i l t i n g of a s t r u c t u r e and i n t e r r u p t normal o p e r a t i o n s .

S t r u c t u r a l deformation r e s u l t i n g from f r e e z i n g o r thawing o f t h e ground and masonry o c c u r a t any g e o g r a p h i c a l p o i n t , where p o s i t i v e t e m p e r a t u r e s a 1 te r n a t e w i t h n e g a t i v e t e m p e r a t u r e s o f t h e ground. The l a r g e s t d e f o r m a t i o n s a r e observed i n t h e p e r m a f r o s t r e g i o n .

The p h y s i c a l n a t u r e o f t h e p r o c e s s e s o f ground f r e e z i n g and thawing i s d i s c u s s e d i n Chapter 111, s o t h a t h e r e t h e y a r e mentioned o n l y a s c a u s e s o f s t r u c t u r a l d e f o r m a t i o n . It should be mentioned t h a t t h e deforming e f f e c t o f t h e s e p r o c e s s e s depends on t h e i r o r i g i n and t h e form t h e y may t a k e .

Taking i n t o a c c o u n t a l l t h a t h a s been s a i d t h u s f a r and i n o r d e r t o make t h e p r e s e n t a t i o n more s y s t e m a t i c , we can s u g g e s t a c l a s s i f i c a t i o n o f t h e pro- c e s s e s r e s u l t i n g i n s t r u c t u r a l deformation, which s h a l l i n c l u d e t h e forms t h e s e p r o c e s s e s may t a k e and t h e i r outcome ( T a b l e 1 1 ) . The human a c t i v i t y which d e t e r m i n e s t o a c o n s i d e r a b l e e x t e n t t h e c o n d i t i o n s o f i n s t a l l a t i o n and o p e r a t i o n o f a s t r u c t u r e w i l l e i t h e r f a v o u r t h e o c c u r r e n c e o f p r o c e s s e s o f ground f r e e z i n g and thawing, o r w i l l p r e v e n t t h e i r development.

1. S t r u c t u r a l Deformation Caused by S e a s o n a l F r e e z i n g and Thawing o f t h e Ground

( ~ r o u p A, T a b l e 1 1 )

When d i s c u s s i n g deformation caused by s e a s o n a l f r e e z i n g and thawing o f t h e ground, i t i s e s s e n t i a l t o b e a r i n mind t h e c o n t i n u o u s i n t e r r e l a t i o n s h i p o f t h e two p r o c e s s e s which r e s u l t from t h e change i n s e a s o n s . The r e l a t i o n - s h i p between d e f o r m a t i o n caused by s e a s o n a l f r e e z i n g and s e a s o n a l thawing i s v e r y w e l l i l l u s t r a t e d by t h e e x a m p l e ' o f s o - c a l l e d " p u l s a t i n g " f o u n d a t i o n s , i n s t a l l e d c l o s e t o t h e ground s u r f a c e which a r e e i t h e r h e a v i n g o r s e t t l i n g . T h e r e f o r e , t h e b a s i c r u l e o f s t a b l e c o n s t r u c t i o n h a s always s t a t e d t h a t

changes i n t h e r m a l c o n d i t i o n s o f t h e b e a r i n g medium should be avoided a t a l l c o s t s . However, a l t h o u g h s t r u c t u r a l d e f o r m a t i o n caused by s e a s o n a l f r e e z i n g and thawing a r e i n t e r r e l a t e d , e a c h o f t h e s e p r o c e s s e s t a k e s p l a c e s e p a r a t e l y , a t d i f f e r e n t t i m e s o f t h e y e a r , and p o s s e s s e s i t s own c h a r a c t e r i s t i c s .

Deformation caused by f r e e z i n g ground m o i s t u r e . The f r e e z i n g o f m o i s t u r e i n t h e b e a r i n g medium and of m o i s t u r e p e r c o l a t i n g from t h e l a y e r s which a r e s t i l l u n f r o z e n l e a d t o ground h e a v i n g i n t h e form o f a n uneven volume expan- s i o n . Heaving i s t h e most common cause o f d e f o r m a t i o n o f v a r i o u s s t r u c t u r e s . Heaving ground a f f e c t s t h e b a s e and s i d e s of f o u n d a t i o n s , o r t h e e l e m e n t s of

underground s t r u c t u r e s l o c a t e d i n t h e zone of s e a s o n a l f r e e z i n g .

The heaving of ground under highways, r a i l r o a d s and a i r f i e l d s r e s u l t s i n c o n s i d e r a b l e u p l i f t o f f r o z e n ground In t h e w i n t e r and s e t t l e m e n t i n e a r l y summer. Heaving and s e t t l e m e n t , which 11.1 some c a s e s r e a c h 20 t o 30 cm, d i s - t u r b t h e normal o p e r a t i o n of s t r u c t u r e s and r e q u i r e a s y s t e m a t i c a p p l i c a t i o n o f p r e v e n t a t i v e measures, which h a s t o be done c o n t i n u o u s l y from y e a r t o y e a r . T h i s i s e s p e c i a l l y cumbersome i n t h e c a s e o f r a i l r o a d s .

Ground heaving r e s u l t s a l s o i n deformation of r e s i d e n t i a l and i n d u s t r i a l b u i l d i n g s , p i l e s and p o l e s , manhole c a s i n g s , e t c . There had been c a s e s of heaving f o r c e s c a u s i n g a complete s e p a r a t i o n of t h e upper p a r t of a manhole from t h e r e s t of t h e s t r c t u r e which remained anchored i n t h e f r o z e n ground. L i g h t s t r u c t u r e s , such a s f e n c e s , hanging r o o f s , porches, i n d i v i d u a l p o l e s , s m a l l b u i l d i n g s , e t c . , a r e t h e most f r e q u e n t v i c t i m s o f heaving. Depending on t h e d i r e c t i o n of h e a t flow, t h e r e may be v e r t i c a l , h o r i z o n t a l o r l a t e r a l

heaving. V e r t i c a l heaving i s t h e most common. H o r i z o n t a l h e a v i n g a f f e c t s s u p p o r t i n g w a l l s , t h e w a l l s o f underground r e s e r v o i r s , e t c .

A t t i m e s heaving r e a c h e s very l a r g e p r o p o r t i o n s which i s e s p e c i a l l y t r u e i n t h e c a s e of p e r e n n i a l , s o - c a l l e d r e s i d u a l heaving, when t h e heaving of some p a r t s of a s t r u c t u r e i n t h e w i n t e r i s n o t balanced completely by s e t t l e m e n t d u r i n g summer thawing of t h e ground. A s a r e s u l t , t h e sum t o t a l of heaving i n c r e a s e s from y e a r t o y e a r and r e a c h e s such p r o p o r t i o n s t h a t s i n g l e t e l e g r a p h p o l e s , bench marks, e t c . , a r e e v e n t u a l l y pushed o u t of t h e ground and f a l l .

A s a n example we reproduce a photograph o f a bench mark l o c a t e d w i t h i n

15

km

of Moscow which was pushed up 1.1 m i n a 1 4 y e a r p e r i o d . A t t h e time o f

i n s t a l l a t i o n , t h e t o p of t h e cement b l o c k was a t t h e ground s u r p a c e ( F i g . 1 ) .

The e f f e c t o f heaving on t h e f o u n d a t i o n s of s t o n e b u i l d i n g s i s u s u a l l y seen i n t h e form of c r a c k s i n t h e w a l l s , When t h e heaving o f t h e b e a r i n g medium Is uneven, t h e b u i l d i n g load is d i s t r i b u t e d o v e r t h i s ground i n t h e same uneven f a s h i o n , s o t h a t t h e g r e a t e s t load f a l l s on t h e p o r t i o n s of t h e ground which were pushed up most. T h i s r e s u l t s i n t h e development o f bending and s h e a r i n g f o r c e s i n t h e f o u n d a t i o n s and t h e w a l l s n o t accounted f o r i n t h e d e s i g n o f t h e b u i l d i n g . Depending on where t h e s e f o r c e s a r e developed, v a r i o u s t y p e s o f c r a c k s appear i n t h e w a l l s .

F r e q u e n t l y t h e f r e e z i n g and thawing of t h e ground and subsequent s t r u c t u r a l deformations o c c u r because o f wrong c o n s t r u c t i o n methods and ignorance of o p e r a t i o n a l r u l e s . In p r a c t i c e t h i s happens mainly i n t h e

absence of a n t i - h e a v i n g measures, o r when t h e f o u n d a t i o n s a r e l a i d a t s h a l l o w d e p t h s , t h e s i t e i s maintained i n c o r r e c t l y d u r i n g temporary work s t o p p a g e s , and t h e normal mode of o p e r a t i o n i s d i s t u r b e d .

Deformation caused by thawing of p o u n d s u b j e c t e d t o s e a s o n a l freeze-up. t h e n t h e ground s u b j e c t e d t o seasorla1 f r e e z i n g and heaving thaws, i t s e t t l e s and i t s b e a r i n g c a p a c i t y drops r e l a t i v e t o what i t was b e f o r e freeze-up.

Because of non-uniform physico-mechanical p r o p e r t i e s of t h e b e a r i n g

medium and t h e i r r e g u l a r f a s h i o n i n which i t f r e e z e s and thaws, s e t t l e m e n t i s n o t uniform e i t h e r and l e a d s t o s t r u c t u r a l deformation.

During; thawing of t h i s type of ground on highways, r a i l r a o d s and a i r - f i e l d s , t h e most harmful e f f e c t s a r e observed on heaved s e c t i o n s of t h e road- bed, where thawing i s accompanied by a s h a r p drop i n b e a r i n g c a p a c i t y of t h e ground. Deformation r e s u l t i n g from thawing of t h e ground under p i p e l i n e s and o t h e r communication l i n e s occurs l e s s f r e q u e n t l y .

A s a g e n e r a l conclusion we may s a y t h a t among t h e p r o c e s s e s t a k i n g p l a c e d u r i n g s e a s o n a l f r e e z i n g and thawing of t h e ground, of g r e a t e s t danger f o r t h e s a f e t y o f a s t r u c t u r e a r e heaving of f r e e z i n g ground under a l i g h t s t r u c t u r e and s e t t l e m e n t o f thawing ground under a heavy one.

Deformation caused by f r e e z i n g of moisture and i t s subsequent thawing i n t h e masonry. The f r e e z i n g of f r e e moisture i n t h e c a v i t i e s o f masonry may r e s u l t i n f a i l u r e of some s t r u c t u r a l elements. D e s t r u c t i o n i s most s e v e r e when t h e r e a r e f r e q u e n t a l t e r n a t i o n s between f r e e z i n g and thawing. The most commonly a f f e c t e d o b j e c t s a r e e x t e r n a l s t r u c t u r a l elements, such a s w a l l s of b u i l d i n g s and o t h e r e n g i n e e r i n g s t r u c t u r e s . Deformation of t h i s type i s n o t n e c e s s a r i l y due t o the presence of permafrost b u t may occur in a l l geographi- c a l r e g i o n s with low w i n t e r a i r temperatures.

Free moisture, t h e f r e e z i n g and subsequent thawing of which l e a d s t o f a i l u r e of t h e masonry, may e n t e r t h e l a t t e r i n d i f f e r e n t ways: (1) from t h e o u t s i d e , i n t h e form of atmospheric moisture, o r a s a r e s u l t of c a p i l l a r y r i s e of groundwater; ( 2 ) from t h e i n t e r i o r of t h e b u i l d i n g , a s a r e s u l t of condensation of steam which e n t e r s t h e masonry due t o d i f f e r e n c e s i n p r e s s u r e between t h e o u t s i d e and i n s i d e of t h e b u i l d i n g .

I n t h e f i r s t case, t h e moisture i n t h e c a v i t i e s f r e e z e s i n w i n t e r , which r e s u l t s i n p a r t i a l f a i l u r e of t h e masonry. Subsequent s a t u r a t i o n of damaged masonry i n c r e a s e s from y e a r t o y e a r and i n t h i s way damage may r e a c h consider- a b l e p r o p o r t i o n s . F a i l u r e of t h e w a l l s a s a r e s u l t of moisture e n t e r i n g t h e masonry from t h e o u t s i d e occurs only l o c a l l y and t i m e l y r e p a i r s would e l l m i - n a t e t h e dangers t o t h e s t r u c t u r e a s a whole. Local damages of t h e same type may be observed i n t h e s u p p o r t s and spans of s t o n e b r i d g e s and i n t h e e x t e r n a l masonry of o t h e r e n g i n e e r i n g s t r u c t u r e s .

In t h e case of moisture e n t e r i n g the masonry from t h e i n t e r i o r of a b u i l d i n g s , t h e f a i l u r e i s of a d i f f e r e n t type and occurs n o t i n t h e suri'ace l a y e r b u t w i t h i n t h e w a l l s themselves. This type of deformation i s much more

r a r e and o c c u r s a l m o s t e n t i r e l y i n r e g i o n s w i t h v e r y low w i n t e r t e m p e r a t u r e s .

In

t h i s c a s e t h e m o i s t u r e i s d i s p l a c e d i n t h e w i n t e r a s a r e s u l t of d i f f e r e n c e s i n t h e a i r t e m p e r a t u r e s o u t s i d e and i n s i d e t h e b u i l d i n g , which may r e a c h 60

-

8 0 ° C and l e a d t o a c o n s i d e r a b l e drop i n t h e buoyancy of steam. In t h e w i n t e r t h e buoyancy of steam i n t h e i n t e r i o r of' t h e b u i l d i n g i s much h i g h e r t h a n on t h e o u t s i d e , c a u s i n g t h e steam t o be d i s p l a c e d w i t h i n t h e w a l l towards t h e o u t e r , 1 . e . t h e c o l d e r , s u r f a c e . On d i s p l a c e m e n t w i t h i n t h e w a l l , t h e steam meets p r o g r e s s i v e l y c o l d e r l a y e r s of masonry which l e a d s t o c o n d e n s a t i o n . The h i g h e r t h e t e m p e r a t u r e and m o i s t u r e g r a d i e n t w i t h i n t h e masonry, t h e more

i n t e n s i v e t h e condensation of steam.

Condensation does n o t t a k e p l a c e throughout t h e e n t i r e t h i c k n e s s o f t h e w a l l b u t o n l y i n i t s middle p a r t and somewhat c l o s e r t o t h e o u t e r s u r f a c e . On f u r t h e r c o o l i n g of t h e w a l l , t h e m o i s t u r e i n t h e c a v i t i e s f r e e z e s and on

expanding d i s r u p t s t h e c o n t i n u i t y of t h e masonry and damages t h e l a t t e r . During t h e f o l l o w i n g w i n t e r , t h e i n c r e a s e d volume of c a v i t i e s i n t h e damaged s e c t i o n of t h e w a l l l e a d s t o a s t i l l g r e a t e r accumulation of m o i s t u r e , t h e f r e e z i n g o f which r e s u l t s i n s t i l l more damage.

In some c a s e s t h i s p r o c e s s may r e s u l t i n a l m o s t t o t a l f a i l u r e of a

b u i l d i n g . T h i s is e s p e c i a l l y t r u e i n t h e c a s e of b u i l d i n g s w i t h h i g h m o i s t u r e c o n t e n t and h i g h g e n e r a t i o n of steam, such a s p u b l i c b a t h s , l a u n d r i e s , d i s - i n f e c t i o n b a r r a c k s , d r i e r s , e t c . A s an example w e may c i t e t h e d e f o r m a t i o n o f a t w o - s t o r e y b r i c k b u i l d i n g which f o r

45

y e a r s s e r v e d a s a p u b l i c b a t h i n C h i t a . I n t e n s i v e c o n d e n s a t i o n of steam accompanied by t h e f r e e z i n g of mois- t u r e r e s u l t e d i n a complete s e p a r a t i o n of t h e brickwork i n t h e w a l l s , which was e s p e c i a l l y n o t i c e a b l e i n t h e window openings ( ~ i g . 2 ) .

The g i v e n example i n d i c a t e s t h a t t h e w a l l s of b u i l d i n g s w i t h a h i g h gener- a t i o n of steam must be designed by c o n s i d e r i n g t h e mode of t h e i r o p e r a t i o n , 1.e. t o make them impermeable t o steam. I n t h e w a l l s of b u i l d i n g s w i t h a

s l i g h t d r o p i n t e m p e r a t u r e and m o i s t u r e c o n t e n t , e

.

g . i n r e s i d e n t i a l b u i l d i n g s , o f f i c e b u i l d i n g s , e t c . , t h e above phenomena do n o t o c c u r .

E f f e c t of i c i n g s on s t r u c t u r e s . I c i n g s a r e t h e c a u s e of c e r t a i n deforma- t i o n i n e n g i n e e r i n g s t r u c t u r e s , r e s i d e n t i a l and o f f i c e b u i l d i n g s . They cause t h e g r e a t e s t damage on r o a d s , where i n p l a c e s t h e y may c r e a t e hazardous t r a f - f i c c o n d i t i o n s i n w i n t e r ( c h a p t e r V I I I ) . Enormous i c i n g s o c c u r i n h o l e s and d e p r e s s i o n s , t h e removal of which r e q u i r e s a g r e a t d e a l of time and expense.

I c i n g s a r e found n o t o n l y i n p e r m a f r o s t a r e a s b u t i n o t h e r a r e a s a s w e l l . It i s known t h a t s e r i o u s h a z a r d s a r e caused by i c i n g s on r o a d s i n c e r t a i n p a r t s o f T r a n s b a i k a l and t h e P r i m o r s k i i K r a i i n t h e S o v i e t F a r E a s t .

2 . S t r u c t u r a l Defor~natiori -- Caused by Thawing o f P e r m a f r o s t ( ~ r o u p B, T a b l e 111

The main cause o f much d e f o r m a t i o n i n v a r i o u s e n g i n e e r i n g s t r u c t u r e s e r e c t e d on p e r m a f r o s t i s t h e i r s e t t l e m e n t on thawing. F o r example, t h e w a l l s o f a locomotive d e p o t s e t t l e d

80

cm a s a r e s u l t o f thawing o f p e r m a f r o s t below i t s f o u n d a t i o n ( ~ i v e r o v s k i i and Morozov, 1941); a f t e r t h r e e y e a r s of u s e , t h e s e t t l e m e n t o f r a i l r o a d workshops i n C h i t a reached 50 cm ( ~ o g d a n o v ,

1912); t h e i n d u s t r i a l b u i l d i n g a t s t a t i o n Domna i n t h e C h i t a O b l a s t t became d e r e l i c t a f t e r o n l y two y e a r s of u s e ; t h e t h r e e - s t o r e y r e s i d e n t i a l b u i l d i n g s n e a r C h i t a ( ~ i g . 3 ) were i n a dangerous c o n d i t i o n 4 t o 7 y e a r s a f t e r comple- t i o n and t h e y had t o be abandoned ( ~ a l t y k o v , 1950), i n t h e same l o c a l i t y t h e s i d e s o f one b u i l d i n g s e t t l e d more t h a n 100 cm r e l a t i v e t o i t s c e n t r a l p a r t s and o n l y t h e p r e s e n c e o f s e t t l e m e n t j o i n t s saved t h e b u i l d i n g from t o t a l f a i l u r e . On one o f t h e s i t e s i n T r a n s b a i k a l , s e t t l e m e n t o f p e r m a f r o s t below a w a t e r tower reached 46 cm a f t e r o n l y

18

months o f o p e r a t i o n (Dementlev, 1952 )

.

D i f f e r e n t i a l s e t t l e m e n t o f t h e ground and i t s h i g h r a t e o f development a r e i m p o r t a n t f a c t o r s c a u s i n g s t r u c t u r a l d e f o r m a t i o n . The s e t t l e m e n t o f ground on thawing may n o t o n l y be c o n s i d e r a b l e b u t i n some c a s e s may t a k e p l a c e a t a v e r y r a p i d r a t e , r e a c h i n g 3

-

4 and even

6

mm p e r day. I n one o f t h e b o i l e r b u i l d i n g s i n T r a n s b a i k a l , t h e s e t t l e m e n t o f t h e ground below t h e b o i l e r s reached 3 0 cm in a p e r i o d o f o n l y f o u r months.

The b e s t method of p r o t e c t i n g t h e s t r u c t u r e s from s u c h d e f o r m a t i o n i s t o e l i m i n a t e a l l p o s s i b i l i t i e s of p e r m a f r o s t thawing below them. However, if

d e f o r m a t i o n h a s a l r e a d y s t a r t e d , t h e n i n some c a s e s t h e r e g u l a t i o n of ground thawing below t h e s t r u c t u r e and t h e c o n t r o l of ground s e t t l e m e n t may prove t o be an e f f e c t i v e measure. The r e g u l a t i o n of t h e thawing p r o c e s s may be

a c h i e v e d e i t h e r by r e d u c i n g t h e amount o f h e a t e n t e r i n g t h e ground, o r by i n c r e a s i n g t h e thawing r a t e o f some s e c t i o n s o f t h e b e a r i n g medium which a r e thawlng more s l o w l y t h a n t h e r e s t of t h e a r e a . A s a n example of t h i s t y p e o f c o n t r o l we may c i t e a c h a r a c t e r i s t i c c a s e t a k e n from p r a c t i c a l e x p e r i e n c e (Dement lev, 1944). A b o i l e r hovse and a n a d j o i n i n g w a t e r tower were b u i l t n e a r C h i t a i n 1941. Only two months a f t e r t h e s t a r t o f o p e r a t i o n s , s t r u c t u r a l deformation was d i s c o v e r e d i n t h e b o i l e r s and t h e b u i l d i n g i t s e l f , and a f t e r a n o t h e r month i t reached s u c h p r o p o r t i o n s t h a t t h e o p e r a t i o n o f t h e b o i l e r house had t o be s t o p p e d . A t t h e same time, i t was observed t h a t t h e w a t e r tower began t o l e a n v e r y n o t i c e a b l y a t a s t e a d i l y i n c r e a s i n g r a t e towards t h e b o i l e r house, which c o n t i n u e d t o s u f f e r d e f o r m a t i o n due t o t h e p r e s s u r e of t h e tower. By May 1941 t h e h o r i z o n t a l s h i f t o f t h e t o p o f t h e tower had reached 78 cm, t h e b o i l e r house was l e a n i n g b a d l y , p l a s t e r had f a l l e n o f f and

window panes were c r a c k e d . Some i d e a about t h e c o n d i t i o n o f t h e b u i l d i n g and t h e p o s i t i o n o f t h e p e r n l a f r o s t t a b l e below i t may be o b t a i n e d from F i g . 4 . To e q u a l i z e thawing of t h e ground, i t was decided t o thaw i t on t h e o t h e r s i d e o f t h e tower, where i t was s t i l l f r o z e n , and i n t h i s way c r e a t e c o n d i t i o n s

n e c e s s a r y f o r f r e e s e t t l e m e n t under t h e e n t i r e tower t o s t r a i g h t e n i t . T h i s r e s u l t e d i n t h e t e r m i n a t i o n o f f u r t h e r deformation o f t h e tower, and t h e l a t t e r g r a d u a l l y assumed i t s v e r t i c a l p o s i t i o n which i t h a s r e t a i n e d a l r e a d y f o r more t h a n 15 y e a r s of c o n t i n u o u s and normal o p e r a t i o n .

The e r r o r s committed because of i n a d e q u a t e c o n s t r u c t i o n methods and wrong u s e s o f b u i l d i n g s on p e r m a f r o s t g r e a t l y i n c r e a s e t h e danger o f deforma-

t i o n r e s u l t i n g from d i f f e r e n t i a l thawing o f f r o z e n h e t e r o g e n e o u s ground. Let u s c i t e an example o f t h i s t y p e of e r r o r which a l m o s t caused f a i l u r e of a b u i l d i n g ( ~ e l ' n i k o v , 1 9 5 0 ) . It waa decided t o i n s t a l l b o i l e r s f o r c e n t r a l h e a t i n g I n one o f t h e o l d two-storey b u i l d i n g s in Yakutsk. The p r o j e c t d i d n o t i n c l u d e any s p e c i a l measures t o r e t a i n t h e ground below t h e f o u n d a t i o n of t h e b o i l e r s i n a f r o z e n s t a t e . The i n t e n t i o n was t o b u i l d t h e b o i l e r house and t o i n s t a l l t h e equipment i n t h e s p r i n g and summer, and t o complete a l l work p r i o r t o . t h e s t a r t of t h e h e a t i n g s e a s o n . No a t t e n t i o n was p a i d t o t h e f a c t t h a t t h e p e r m a f r o s t 3elow t h e b o i l e r house would have thawed r a p i d l y r e s u l t i n g i n s e t t l e m e n t of t h e e n t i r e b u i l d i n g . The s i t u a t i o n was f u r t h e r complicated by t h e f a c t t h a t t h e f l o o r of t h e b o i l e r house was below t h e bottom o f t h e f o u n d a t i o n s o f t h e e x t e r n a l w a l l s , which would have caused t h e ground below t h e s e f o u n d a t i o n s t o be pushed o u t on thawing. However, t h e e r r o r was n o t i c e d and c o r r e c t e d i n t i m e . V e n t i l a t i o n was i n s t a l l e d below t h e b o i l e r s and t h e basement, s o t h a t i n t h e w i n t e r cold a i r reached t h e b o i l e r f o u n d a t i o n s through s p e c i a l c o n d u i t s and r e t a i n e d t h e b e a r i n g medium i n a f r o z e n s t a t e . Also, d u r i n g t h e o p e r a t i o n s , t h e f o u n d a t i o n s were p r o t e c t e d by t h e r m a l i n s u l a t i o n . The i n v e s t i g a t i o n s c a r r i e d o u t a f t e r t h e s t a r t of opera- t i o n o f t h e b o i l e r house have i n d i c a t e d t h a t t h e ground below t h e f o u n d a t i o n s of w a l l s and t h e b o i l e r s r e t a i n n e g a t i v e t e m p e r a t u r e s t h r o u g h o u t t h e y e a r .

3. Conclusions

1. One o f t h e most corrmon c a u s e s of d e f o r m a t i o n o f v a r i o u s s t r u c t u r e s a r e t h e p r o c e s s e s o f f r e e z i n g and thawing of t h e b e a r i n g medium, which may o c c u r anywhere on t h e e a r t h w i t h changes i n n e g a t i v e and p o s i t i v e t e m p e r a t u r e s . The magnitude of deformation a r i s i n g from t h e s e p r o c e s s e s may v a r y between n e g l i g i b l e s t r u c t u r a l changes o f no p r a c t i c a l importance and t o t a l f a i l u r e .

2 . The e x t e n t t o which t h e p r o c e s s e s o f f r e e z i n g and thawing o f t h e

ground a f f e c t a s t r u c t u r e and t h e magnitude of d e f o r m a t i o n caused by them vary i n r e l a t i o n t o t h e n a t u r a l environment. They become more pronounced under

c o n d i t i o n s of s e v e r e c l i m a t e and a r e a t t h e i r maximum i n permafrost a r e a s . I n t h e s e a r e a s t h e y a r e t h e main cause of s t r u c t u r a l deformation and sometimes t o t a l f a i l u r e of a s t r u c t u r e .

3.

S t r u c t u r a l deformation caused by t h e p r o c e s s e s of f r e e z i n g and thawing may a r i s e a l s o on f r e e z i n g of water contained i n t h e masonry and on m e l t i n g of i c e i n t h e l a t t e r .

4. The magnitude and n a t u r e of deformation caused by t h e s e p r o c e s s e s a r e o f t e n r e l a t e d t o man's i n d u s t r i a l a c t i v i t y , which may c r e a t e c o n d i t i o n s

e i t h e r f a v o u r i n g o r i n h i b i t i n g t h e i r development.

5.

S t r u c t u r a l deformation r e s u l t i n g from f r e e z i n g o r thawing may be e l i m i n a t e d only a f t e r a thorough and c o r r e c t e v a l u a t i o n of proceesee which have taken p l a c e and of t h e i r e f f e c t on t h e s t r u c t u r e . The a u c c e s e f u l elim-

i n a t i o n of t h i s deformation depends n o t only on t h e measures c a r r i e d o u t b u t a l s o on t h e i r timing. A s soon a s deformation appears, t h e measures designed t o e l i m i n a t e t h e i r causes should be c a r r i e d o u t without d e l a y .

6.

The most dangerous a f t e r - e f f e c t s o f u s i n g wrong work methods may occur d u r i n g c o n s t r u c t i o n and o p e r a t i o n of s t r u c t u r e s on permafrost.

7. It i s e s s e n t i a l t o c o n s i d e r t h e s p e c i a l p r o p e r t i e s of permafrost n o t only d u r i n g t h e c o n s t r u c t i o n s t a g e b u t a l s o on r e p a i r i n g o r r e d e s i g n i n g t h e s t r u c t u r e s , i f t h i s work might change t h e e s t a b l i s h e d c o n d i t i o n s i n t h e f r o z e n ground below t h e foundation. It i s q u i t e unacceptable t o c a r r y o u t work which may a f f e c t t h e p r i n c i p l e adopted t o e n s u r e t h e s t a b i l i t y of a s t r u c t u r e .

One of t h e l e a d i n g t a s k s of e n g i n e e r i n g geocryology i s t h e s e a r c h f o r d e s i g n s , a s w e l l a s methods of c o n s t r u c t i o n and maintenance of s t r u c t u r e s ,

which would e l i m i n a t e any l i k e l i h o o d of deformation by r e g u l a t i n g t h e p r o c e s s e s of f r e e z i n g and thawing i n an a p p r o p r i a t e way. Accordingly, t h e f o l l o w i n g c h a p t e r s c o n t a i n information on t h e e x i s t i n g methods of r a t i o n a l c o n s t r u c t i o n i n permafrost a r e a s , t h e u t i l i z a t i o n of which should p r o t e c t t h e s t r u c t u r e s from deformation d e s c r i b e d above and e n s u r e t h e i r s t a b i l i t y d u r i n g t h e e n t i r e o p e r a t i o n a l p e r i o d .

L i t e r a t u r e

Bogdanov, N.S. Permafrost and s t r u c t u r e s r e s t i n g on i t . SPb. 1912. Dementlev, A . I . E l i m i n a t i o n of d i f f e r e n t i a l s e t t l e m e n t of s t r u c t u r e s by

a r t i f i c i a l h e a t i n g . Vestnik Akademii Nauk SSSR, No.9, 1944,

Dementlev, A . I . Deformation of b u i l d i n g s due t o e f f e c t s of f r o s t and how t o e l i m i n a t e i t . Tr. i n - t a merzlotov. AN SSSR, Vol.11, 1952.

L i v e r o v s k i i , A.V. and Morozov, K.D. Construction i n permafrost r e g i o n s . S t r o i i z d a t Narkomstroye, 1941.

Meltnikov, P.I. Permafrost g e o l o g i c a l c o n d i t i o n s f o r c o n s t r u c t i o n c f c i v i l i a n and i n d u s t r i a l b u i l d i n g s i n C e n t r a l Yakutiya and use of experience gained i n c o n s t r u c t i o n work n e a r Yakutsk. Izd-vo AN SSSR, 1950.

Saltykov,

N.I.

Foundation of s t o n e b u i l d i n g s on f i r s t t e r r a c e s above t h e f l o o d p l a i n s of t h e Ingoda and t h e Chitinka R i v e r s . Tr. i n - t a merzlotov. AN _SSSR,

_{~ 0 1 . 8 ,}

_1950-a.

Saltykov, N . I . I n s t r u c t i o n f o r l a y i n g foundations in t h e s o u t h e r n a r e a s of t h e permafrost r e g i o n in t h e Z a b a i k a l t . Tr. i n - t a merzlotov. AN.SSSR,

4 s 6 a ' u s 0 a, 0 0 :z G L X acn LO fn G k C . d 0 v, O r : a 'd ad Q) cu 4 ' G F c V 7 i L l O T 7 U Q L l c Q a a 0 aJ G U ' 0 I G a L a , 1 G 0 m u d k 3 d N c, 3 d) ha, h O C 4 ,-I n c, m 0 k k m

E

a, a acn

a

%

'0 d C a cnk

F i g . 1

Bench mark pushed up 1 . 1 0

m

In

a

14-year period (photo by U.S. ~ s p e n s k i i )

F i g . 2

Masonry crakcing i n window opening8 In o u t e r w a l l s r e s u l t i n g from t h e f r e e z i n g o f steam

F i g .

3

R e s i d e n t i a l build l n g deformed by thawing o f

frozen ground below

i t s

foundation

(photo by

A.I.

Dementfev)

P i g .

4

Leaning o f a water tower and deformation o f a b o i l e r house r e s u l t i n g from the thawing

o f frozen ground :