Frost and foundations: elementary conditions for the planning and construction of foundations in areas with winter frost and permafrost

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Frost and foundations: elementary conditions for the planning and construction of foundations in areas with winter frost and permafrost

Nielsen Greenland Technical Organization; National Research Council of Canada. Division of Building Research

The problems of engineering construction in perma-

frost are of special concern to Canada which has nearly

one half of its land area underlain by permanently frozen

ground.

In

recognition of this, the Division of Building

Research has from its inception considered permafrost

studies as a vital part of its research.

Many of these studies have been concerned with

techniques of foundation construction which, although

varying in detail with local conditions, do depend for

their success on adherence to certain basic principles of

permafrost engineering. It is these principles that form

the subject of this report by the Greenland Technical

Organization.

The Division of Building Research is pleased to be

able to arrange for this translation from the Danish and

wishes to record its appreciation to Mr.

H.A.Q.

Nathan of

the Translations Section of the National Research Council

for his assistance In its preparation.

Ottawa

March 1962

R.F.

Legget

Title

:

NATIONAL RESEARCH COUNCIL OF CANADA

Technical Translation 1021

Frost and foundations. Elementary conditions for the

planning and construction of foundations in areas with

winter frost and permafrost

(~rost

og fundering. Elementaere forudsaetninger for

projektering og udfbrelse af fundamenter ti1 omr8der

med vinterfrost og permafrost

)

Authors

:

Nielsen and Rauschenberger

A N A L Y Z E D

Reference:

G.T.O.* Publikation Nr. 1, 1957. 20p.

Translator: H.A.G. Nathan, Translations Section, N.R.C. Library

TABLE OF CONTENTS

Page

A

.

Introduction

...

4

...

B

.

Winter frost and permafrost

5

...

.

I

Definition and depth

5

I1

.

Destructive action

...

6

General

...

6

...

6

Thawing

...

9

...

C

.

Preliminary investigations and fundamental rules

10

I

.

Preliminary investigations

...

10

...

Soil investigations

10

Surface investigations

...

13

I1

.

Fundamental rules

...

14

...

Winterfrost areas with no permafrost

14

Permafrost areas

...

15

...

.

D

Rules-

for the designing of pernmfrost foundations

18

I

.

General

...

18

I1

.

Permafrost foundations for smaller permanent

...

buildings

18

...

I11

.

Permafrost foundations for temporary buildings

19

Figures

...

20

FROST

AND

FOUNDATIONS

Elementary Conditions f o r t h e Planning and C o n s t r u c t i o n of Foundations i n Areas with Winter F r o s t and Permafrost

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

The combination of f r o s t and foundations has caused problems e v e r s i n c e i t e x i s t e d .

In r e g i o n s with o l d b u i l d i n g t r a d i t i o n s most of t h e s e problems have been g r a d u a l l y solved, l a r g e l y by e m p i r i c a l means.

However, m a t t e r s a r e d i f f e r e n t i n t h e a r c t i c r e g i o n s , where b u i l d i n g methods which had evolved under

a

c o n s i d e r a b l y milder c l i m a t e have been a p p l i e d .

In some c a s e s t h i s has worlced well, c h i e f l y because t h e founda- t i o n s were b u i l t on s o l i d rock whenever p o s s i b l e . In o t h e r c a s e s i t

has f a i l e d , p a r t i c u l a r l y i n a r e a s with permafrost, where t h e p e r e n n i a l l y f r o z e n s o i l p r e s e n t e d a s e r i e s of unknown problems.

The problems have come t o a head d u r i n g t h e p a s t

20

y e a r s with t h e tremendous expansion of b u i l d i n g a c t i v i t y i n t h e a r c t i c r e g i o n s .

In o r d e r t o s o l v e t h e s e problems r e s e a r c h was c a r r i e d o u t on a l a r g e s c a l e , e s p e c i a l l y i n Canada, Russia and t h e U.S.A. A s a

r e s u l t more l i t e r a t u r e d e a l i n g with both f r o s t problems i n g e n e r a l and permafrost problems In p a r t i c u l a r i s now a v a i l a b l e . The

p r e s e n t r e p o r t i s based on some of t h e s e f o r e i g n r e p o r t s , p a r t i c u - l a r l y on S . M u l l e r t s " ~ e r m a f r o s t " , and on

a

number of Danish

a r t i c l e s d e a l i n g with f r o s t problems.

F i n a l l y , t h e r e s u l t s of p r a c t i c a l experience obtained i n connection with t h e l a t e s t Danish b u i l d i n g a c t i v i t y i n Greenland

have a l s o been included.

-

-

I

The r e p o r t i s d i v i d e d i n t o t h r e e main s e c t i o n s , t h e f i r s t of which ( B ) g i v e s a g e n e r a l account of t h e n a t u r e of t h e f r o s t problems.

The second s e c t i o n

(.c),

which has been w r i t t e n e s p e c i a l l y f o r t h e b e n e f i t of t e c h n i c i a n s charged w i t h e x p l o r a t o r y work f o r l a r g e -

s c a l e b u i l d i n g p r o j e c t s , d e a l s w i t h p r e l i m i n a r y i n v e s t i g a t i o n s and l a y s dovm

a

_{nwnber of f u n d a r w n t a l r u l e s .}

The t h i r d s e c t i o n ( D ) rnay be r e a d independent of t h e second s e c t i o n . It c o n t a i n s some simple r u l e s f o r d e s i g n i n g f o u n d a t i o n s f o r teniporary o r s m a l l permanent b u i l d i n g s f o r whicn

i t

rrlay be impossible t o cai-ry o u t e x t e n s i v e p r e l i m i n a r y i n v e s t i g a t i o n s and p l a n n i n g i n each i n d i v i d u a l c a s e .

B. Winter F r o s t and Pel-mafrost

I. D e f i n i t i o n and Denth

S o i l s t r a t a ( o r bedrock), which f r e e z e i n w i n t e r and thaw i n sunmer, a r e g e n e r a l l y k n o w as a c t i v e l a y e r s . I n t h e f r o z e n s t a t e t h e y a r e r e f e r r e d t o as w i n t e r f r o s t i n t h e p r e s e n t r e p o r t .

S o i l s t r a t a ( o r bedrock) which have been f r o z e n permanently throughout many y e a r s a r e r e f e r r e d t o by t h e common t e r m p e r m a f r o s t .

_--

Unless t h e ground s u r f a c e i s covered w i t h snow o r i c e t h e y e a r

round, t h e r e i s always a n a c t i v e l a y e r between t h e p e r m a f r o s t and t h e ground s u r f a c e .

Winter f r o s t e x t e n d s o v e r a l l t h e r e g i o n s where t h e w i n t e r t e m p e r a t u r e i s below f r e e z i n g . The d e p t h of t h e w i n t e r f r o s t v a r i e s between 0 . 2 and 4.0 m, depending on t e m p e r a t u r e c o n d i t i o n s , v e g e t a t i o n c o v e r , n a t u r e of t h e s o i l , e t c .

Permafrost i s l i n k e d w i t h t h e a r c t i c r e g i o n s i n p a r t i c u l a r ( I ? . 1 ) . A y e a r l y average a i r t e m p e r a t u r e of l e s s t h a n o O C i s

e s s e n t i a l f o r t h e f o r m a t i o n and p r e s e r v a t i o n of p e r m a f r o s t .

Most e x i s t i n g p e r m a f r o s t formed from 2 t o 10,000 y e a r s ago, b u t because o f changes i n t h e c l i m a t e t h e p e r m a f r o s t a r e a s a r e c o n t i n u o u s l y i n c r e a s i n g and d e c r e a s i n g i n e x t e n t .

I n Greenland p e r m a f r o s t e x i s t s under t h e i c e - c a p . North o f approxinlately t h e 6 6 t h d e g r e e o f l a t i t u d e p e r r e f r o s t i s a l s o encountered i n t h e ' i c e - f r e e r e g i o n s . Even i n t h e more s o u t h e r l y l i t t o r a l r e g i o n s p a t c h e s of p e r m a f r o s t a r e found h e r e and t h e r e .

Pernlafrost a r e a s need n o t c o n s i s t of c o n t i n u o u s l a r g e s t r e t c h e s .

below o°C s m a l l p a t c h e s of perniafrost a r e found a l t e r n a t i n g w i t h a r e a s t h a t a r e f r e e of permafrost.

The depths of permafrost l a y e r s vary between approximately 1 metre a t t h e edges of t h e permafrost a r e a s and s e v e r a l hundred metres i n t h e c o l d e s t zones. A t c e r t a i n p o i n t s a l o n g t h e n o r t h e r n c o a s t of S i b e r i a thiclcnesses of permafrost up t o approximately 400 metres have been measured ( F i g . 2 ) .

D e s t r u c t i v e Action ( a ) General

It rriay be assumed t h a t t h e main f e a t u r e s of t h e problems

connected with w i n t e r f r o s t a r e g e n e r a l l y known. They a r c nlentloned h e r e merely f o r t h e sake of completeness and a l s o because problems of permafrost normally cannot be d e a l t with independently of t h o s e of w i n t e r f r o s t .

Winter f r o s t and permafrost have c e r t a i n problems i n comnlon. Some of t h e s e problems a r e s p e c i a l . However, corlmion t o a l l t h e problems i s t h e f a c t t h a t t h e y a r e due t o t h e moisture ( o r i c e ) c o n t e n t of t h e s o i l s t r a t a and t h a t t h e y a r i s e on t r a n s i t i o n from t h e f r o z e n t o t h e thawed s t a t e o r from t h e thawed t o t h e f r o z e n s t a t e .

Therefore it i s o n l y n a t u r a l t o d e s c r i b e t h e problems caused by f r e e z i n g s e p a r a t e l y from t h o s e due t o thawing.

( b ) F r e e z i n g

t h e n water f r e e z e s i t s volume i n c r e a s e s by approximately 10 p e r c e n t , and when s o i l l a y e r s c o n t a i n i n g moisture f r e e z e t h e e n t i r e

l a y e r correspondingly i n c r e a s e s i n volume u n l e s s t h e volume of voids i s s o g r e a t t h a t i t can hold t h e n o i s t u r e c o n t e n t i n t h e f r o z e n s t a t e .

For example, i f t h e s o i l l a y e r s a r e s a t u r a t e d with

a

moisture c o n t e n t of s a y 20 p e r c e n t of t h e t o t a l volunie, f r e e z i n g w i l l r e s u l t i n approximately a 2 p e r c e n t i n c r e a s e i n volume.

However, t h e i n c r e a s e i n volume of t h e s o i l l a y e r s , which norli~ally m a n i f e s t s i t s e l f i n heaving of t h e ground, i s o f t e n much

T h i s behaviour can b e s t be understood by stu&*,ring t h z condi- t i o n s o f i c e f o r m a t i o n . Idhen t h e f i r s t i c e c r y s t a l s form ( n o r m a l l y i n t h e s u r f a c e l a y e r ) t h e y tend t o a t t r a c t much of t h e s u r r o u n d i n g moisture and by means of t h e c r y s t a l l i z i n g f o r c e i n t r o d u c e

i t

i n t o t h e c r y s t a l l a t t i c e , and i f t h e c a p i l l a r y f o r c e s a r e s u f f i c i e n t l y g r e a t t h e moisture t h e y withdraw w i l l be r e p l a c e d by a b s o r p t i o n of moisture from any l o w e r - l y i n g water r e s e r v e s t h a t may be a v a i l a b l e . The f a c t t h a t t h e moisture i n t h e narrower c a p i l l a r y t u b e s f r e e z e s o n l y a t t e m p e r a t u r e s below oOC f u r t h e r prornotes t h e movement o f

water.

I n t h e absence of any o b s t r u c t i o n a q u a n t i t y o f water t h e n

s t e a d i l y flows t o t h e bottom of t h e c r y s t a l and t h e l a t t e r i n c r e a s e s i n t h i c k n e s s . Under "favourable" c o n d i t i o n s c l e a r l y - d e f i n e d i c e c o n c e n t r a t i o n s , s o - c a l l e d i c e l e n s e s , which may be up t o h a l f a metre i n t h i c k n e s s and s e v e r a l metres i n d i a m e t e r , a r e o b t a i n e d . The i n c r e a s e i n volume t a k e s p l a c e i n t h e d i r e c t i o n o f l e a s t r e s i s t - ance, which normally means upwards.

I n c o a r s e s o i l t y p e s ( s a n d and f i n e s a n d ) t h e c a p i l l a r y r i s e i s s o n e g l i g i b l e t h a t t h e c r y s t a l l i z a t i o n comes r a p i d l y t o a s t a n d s t i l l because of i n s u f f i c i e n t water supply. A c o r r e s p o n d i n g behaviour can be observed i n l a y e r s o f p e a t y s o i l s .

The c a p i l l a r y r i s e i n m e d i m - f i n e s o i l t y p e s ( c o a r s e

s i l t

and medium-coarse s i l t ) i s s o g r e a t t h a t t h e y can absorb moisture from a d e p t h of between 1 o r 2 metres. A t t h e same time t h e p e r m e a b i l i t y ( t o water) i s r e l a t i v e l y g r e a t , s o t h a t t h e c o n d i t i o n s f o r adequate flow t o t h e f r e e z i n g zone a r e f a v o u r a b l e . In f i n e s o i l t y p e s ( f i n e s i l t and c l a y ) t h e c a p i l l a r y r i s e i s v e r y g r e a t , b u t t h e p e r m e a b i l i t y i s s o s m a l l t h a t t h e c r y s t a l l i z a - t i o n i s o n l y s l i g h t b e f o r e t h e f r o s t i s f o r c e d dorm beneath t h e c r y s t a l and b l o c k s t h e movement o f m o i s t u r e .

A s i s e v i d e n t from what h a s been s a i d above, f r o s t heaving

i s

of t h e g r e a t e s t inlportance f o r s o i l l a y e r s c o n s i s t i n g of c o a r s e s i l t

and medium-coarse s i l t and where t h e s e s o i l l a y e r s c o n t a i n

a

g r e a t d e a l of moisture o r a r e simply water-bearing, s e v e r e f r o s t heavings of t h e ground

( 5

t o

50

cm) rnay be e x p e c t e d .

S i n c e t h e a d f r e e z i n g f o r c e of f r o z e n s o i l t o wood and c o n c r e t e i s g r e a t (approximately 2 t o 20 k g / c r 2 ) , f o u n d a t i o n s i n f r o s t -

s u s c e p t i b l e s o i l s a r e s u b j e c t t o corresponding heaving u n l e s s t h e y a r e h e a v i l y loaded o r u n l e s s s p e c i a l s t e p s a r e talcen t o anchor them.

When t h e a c t i v e l a y e r thaws i n s p r i n g t h e s o i l w i l l noimally s u b s i d e a s much a s i t heaved d u r i n g w i n t e r , whereas t h e f o u n d a t i o n s f r e q u e n t l y renlain more o r l e s s d i s p l a c e d ( F i g .

3 ) ,

one of t h e

r e a s o n s being t h a t when thawing begins t h e f o u n d a t i o n i s r e t a i n e d by t h e lowest p a r t of t h e a c t i v e l a y e r , which i s s t i l l f r o z e n . I n t h i s way t h e annual disp1acei:ients can a c c u n ~ u l a t e s o t h a t t h e founda- t i o n can l i t e r a l l y be l i f t e d up through t h e s o i l .

I c i n ~ i s a n o t h e r problem i n connection with t h e f r e e z i n g o f t h e a c t i v e l a y e r . It i s a g e n e r a l term f o r t h e formation of i c e masses tvhere water flows o u t a t t h e ground s u r f a c e d u r i n g t h e w i n t e r .

t h e n t h e ground s u r f a c e i s f r o z e n , moisture flows s t e a d i l y under t h e f r o z e n c r u s t , b u t i f t h e a c t i v e l a y e r i s u n d e r l a i n by

s o l i d rock o r perraafrost t h e water-bearing l a y e r i s g r a d u a l l y reduced a s t h e f r o s t p e n e t r a t e s deeper. Because of t h e more

r e s t r i c t e d space t h e w a t e r i s s u b j e c t e d t o p r e s s u r e which may become s o g r e a t t h a t t h e water f o r c e s i t s way t o t h e s u r f a c e ( F i g .

4 ) .

The c o n d i t i o n s f o r i c i n g a r e optinlum tvhere: ( 1 ) t h e a c t i v e l a y e r i s water b e a r i n g ,

( 2 ) t h e l i n e of p e r m a f r o s t o r r o c k i s c l o s e t o t h e ground s u r f a c e and

( 3 )

t h e a i r temperature i s low and t h e snow cover i n e a r l y

w i n t e r i s t h i n .

The snow cover, moreover, h a s a d e c i s i v e e f f e c t on t h e tirne when i c i n g f i r s t a p p e a r s . A t h i n snow cover rneans e a r l y i c i n g and a t h i c k one l a t e i c i n g .

Heated houses, t ~ i ~ e r e t h e h e a t from t h e house m a i n t a i n s a gap i n t h e f r o z e n c r u s t , c o n s t i t u t e a s p e c i a l i c i n g h a z a r d . The

I1

p r e s s u r e water" which i s o f t e n supercooled, t h e n s e e p s up through t h i s gap ( ~ i g .

5 ) .

I n Alaska and S i b e r i a t h e r e a r e inany i n s t a n c e s of houses becoming l i t e r a l l y f i l l e d with i c e .

( c ) Thawing

In t h e f r o z e n s t a t e s o i l c o n t a i n i n g i c e h a s c o n s i d e r a b l e b e a r - i n g power and cohesive energy. The i c e cements t h e i n d i v i d u a l

g r a i n s i n such a way t h a t t h e f r o z e n l a y e r s have almost t h e charac- t e r of sandstone.

However, when a s o i l l a y e r i s thawing t h e i c e c o n s t i t u t e s t h e weak member. If t h e i c e has assumed a g r e a t e r volume t h a n t h a t which corresponds t o t h e volume of v o i d s and t h e u n d e r l y i n g s o i l l a y e r c o n s i s t s of s o l i d m a t e r i a l , t h i s w i l l r e s u l t i n g r e a t e r o r s m a l l e r s e t t l e m e n t s of t h e t o p s o i l , and f o u n d a t i o n s may s u b s i d e with i t . I n o t h e r words, t h e s o i l l a y e r i n q u e s t i o n i s s e n s i t i v e t o thawing. In t h e c a s e of c o a r s e - g r a i n e d s o i l s s e t t l e m e n t s occur o n l y if t h e i c e i t s e l f m e l t s away, b u t i n t h e c a s e of f i n e - g r a i n e d s o i l s water and s o i l j o i n t l y forin a p l a s t i c mass, which i s d i s p l a c e d on account of t h e p r e s s u r e e x e r t e d by t h e f o u n d a t i o n .

( 1 ) In t h e c a s e of w i n t e r f r o s t t h e hazards from thawing a r e a d i r e c t r e s u l t of t h e t y p e of f r e e z i n g s o t h a t t h e c o n d i t i o n s f o r s e n s t i v i t y thawing a r e t h e same t h o s e s t a t e d above ( l a y e r s medium-fine s o i l s c o n t a i n i n g m o i s t u r e ) .

( 2 ) I n t h e c a s e of p e r m a f r o s t t h e p o s s i b l e s e n s i t i v i t y t o thawing cannot be p r e d i c t e d from t h e composition of t h e s o i l . The c o n d i t i o n s under which t h e l a y e r s i n q u e s t i o n f r e e z e a r e e s s e n t i a l l y d i f f e r e n t fro111 th o s e f o r w i n t e r f r o s t . If f r e e z i n g t a k e s p l a c e

g r a d u a l l y ( i . e . o v e r s e v e r a l years), l a r g e i c e c o n c e n t r a t i o n s may r e a d i l y be encountered i n both t h e f i n e s t g r a i n e d s o i l s ( s i l t s and

c l a y ) and t h e c o a r s e s t g r a i n e d g r a v e l . I c e c o n c e n t r a t i o n s may a l s o be assunled t o have formed where t h e p e r m a f r o s t l a y e r s have cracked r i g h t up t o t h e a c t i v e l a y e r , e . 3 . because of t e n p e r a t u r e changes. In e x p l o r a t o r y d i g g i n g o r b o r i n g t h e i c e c o n t e n t may be determined a f t e r m e l t i n g s o i l samples frorn t h e p e r ~ ~ l a f r o s t l a y e r s . F r e q u e n t l y t h e i c e c o n t e n t i s many tinies g r e a t e r t h a n t h e c o n t e n t of s o l i d

m a t e r i a l s . It i s c l e a r t h a t thawing of t h e s e p e r m a f r o s t l a y e r s w i l l r e s u l t i n l a r g e s e t t l e ~ l i e n t s and corresponding damage t o o v e r l y i n g rrm-made s t r u c t u r e s .

The danger of l a n d s l i d e s p r e s e n t s a n o t h e r problem i n c o n n e c t i o n with t h e thawing of f r o z e n s o i l . l a y e r s .

A s mentioned above, when a f r o z e n s o i l which c o n s i s t s of f i n e - g r a i n e d m a t e r i a l s mixed w i t h i c e thaws,

i t

t u r n s i n t o

a

p l a s t i c mass. On a s l o p e t h i s may produce s l i d i n g of t h e s o i l l a y e r s w i t h d i s a s t r o u s r e s u l t s .

These s l i d e s a r e p a r t i c u l a r l y p r e v a l e n t I n p e r m a f r o s t a r e a s because t h e a c t i v e l a y e r f r e q u e n t l y c o n t a i n s a g r e a t d e a l of mois- t u r e immediately above t h e permafrost l a y e r , s o t h a t a l u b r i c a t i n g l a y e r i s o b t a i n e d a t t h e p e r n ~ a f ~ o s t t a b l e .

It should a l s o be remembered t h a t thawing of t h e t o p l a y e r of p e r ~ n a f r o s t ( a s a r e s u l t o f e x c a v a t i o n s , h e a t t r a n s f e r from houses,

e t c

.

) may cause l a n d s l i d e s , r e g a r d l e s s o f t h e - f a c t t h a t t h e e x i s t i n g a c t i v e l a y e r c o n s i s t s o f d r y and s t a b l e m a t e r i a l .

C

.

Pre l i l n i n a r y I n v e s t i g a t i o n s and Fundamental Rules I. Pre l i r i ~ i n a r y In v e s t i g a t i o n s

A s i s e v i d e n t from t h e p r e c e d i n g s e c t i o n s , t h e damage r e s u l t i n g from f r o z e n s o i l l a r g e l y depends on t h e t h i c k n e s s of t h e a c t i v e

l a y e r , t h e conlposition of t h e v a r i o u s s o i l t y p e s and t h e s u p p l y of moisture. The s t u d y of t h e s e c o n d i t i o n s f a l l s n a t u r a l l y under t h e two headings of s o i l i n v e s t i g a t i o n s and s u r f a c e i n v e s t i g a t i o n s . ( a ) S o i l i n v e s t i g a t i o n s

The thiclcness of t h e a c t i v e l a y e r can be determined i n a r e

l a

t i v e l y simple way. ( 1 ) The s i m p l e s t way of d e t e r m i n i n g t h e t h i c k n e s s of t h e a c t i v e l a y e r i n a r e a s with w i n t e r f r o s t o n l y i s by e x p l o r a t o r y d i g g i n g ( b l a s t i n g ) a t t h e end of t h e w i n t e r a t t h e tirne of m a x i m u m p e n e t r a - t i o n of t h e s o i l by t h e f r o s t . I n g e n e r a l i t may be s a i d t h a t t h e f r o s t p e n e t r a t e s most d e e p l y i n t o t h e s o i l i n a r e a s where t h e w i n t e r s a r e long and c o l d . I n

a r e a s having t h e s e teniperature c o n d i t i o n s t h e f r o s t p e n e t r a t i o n i s g r e a t e s t i n coarse-grained and d r y s o i l l a y e r s having no v e g e t a t i o n cover. T h i s p e n e t r a t i o n i s o n l y s l i g h t i n f i n e - g r a i n e d , moist s o i l l a y e r s with a v e g e t a t i o n c o v e r .

( 2 ) I n a r e a s vrith p e r m a f r o s t t h e t h i c k n e s s of t h e a c t i v e l a y e r

i s determined by e x p l o r a t o r y d i g g i n g a t t h e end o f t h e swruner when thawing i s a t i t s rnaximurriJC. I n s t e a d of e x p l o r a t o r y d i g g i n g ,

e x p l o r a t o r y b o r i n g o r hand d r i l l i n g w i t h a round i r o n b a r , v h i c h may be d r i v e n I n vrith a hanlrner, may be c a r r i e d o u t .

BJl1e.n e x p l o r a t o r y b o r i n c ( o r d r i l l i n g ) i s c a r r i e d o u t i n a r e a s where t h e a c t i v e l a y e r c o n t a i n s rock, c a r e must be t a k e n n o t t o confuse l a r g e p i e c e s of r o c k w i t h t h e p e r m a f r o s t t a b l e . IIovrever, w i t h t h e t e s t d r i l l ( o r p r o b i n g r o d ) h e a v i l y loaded and d e p e ~ i d i n g on t h e t y p e of d r i l l , i t should be p o s s i b l e t o d r i v e doim some d i s t a n c e i n t o t h e p e r m a f r o s t u n t i l t h e p e r m a f r o s t a d h e r e s t o t h e d r i l l ( o r p r o b i n g r o d ) , malcing it d i f f i c u l t t o t u r n . I f a p i e c e of r o c k i s h i t , t h e d r i l l n o r r ~ l a l l y can be t u r n e d round f r e e l y , r e g a r d - l e s s of t h e load and when a blow i s s t r u c l : on a p r o b i n g rod r e s t i n g on a p i e c e of rock a d i s t i n c t m e t a l l i c sound i s h e a r d .

G e n e r a l l y i t may be s a i d t h a t thawing d e p t h s a r e g r e a t e r where t h e summer i s r e l a t i v e l y l o n g and v r a r m . I n a r e a s w i t h such tenlpera- t u r e c o n d i t i o n s thawin= i s g r e a t e s t i n c o a r s e - g r a i n e d and d r y s o i l l a y c r s having no v e g e t a t i o n cover and o n l y s l i g h t i n f i n e - g r a i n e d , moist s o i l l a y e r s vrith a v e g e t a t i o n c o v e r .

The composition of t h e d i f f e r e n t s o i l t y y e s i s determined by s i e v i n g a r e p r e s e n t a t i v e s e l e c t i o n of s a n p l e s . The s i e v e s e t used must i n c l u d e s i e v e s of 2 t o

0.075

mli mesh s i z e s .

I f l e s s t h a n 20 p e r c e n t of t h e sample p a s s e s through a 2 nlm s i e v e , t h e f r o s t s u s c e p t i b i l i t y nay be i g n o r e d . If illore t h a n 20 p e r c e n t p a s s e s through, a more d e t a i l e d s t u d y o f t h e f r a c t i o n s having a g r a i n s i z e t2 mm i s c a r r i e d o u t .

The f r o s t s u s c e p t i b i l i t y of t h e s o i l t ~ y p e rnay be determined by riieans o f t h e c u r v e s and n o t e s i n F i g .

6 .

A s can be s e e n from

*

F o r t h e sake of c o m ~ l e t e n e s s i t must be mentioned t h a t t h e method i s n o t 100 pcrceil'c r e l i a b l e , s i n c e a t t h e edves of p e r m a f r o s t x e a s p e r e n n i a l l y tha:rcd l a y c r s ( i n E u s s i a n ' t a l i k " = thawed s o i l ) n:ay be e n c o ~ u l t e r e d between t h e p e r m a f r o s t and t h e a c t i v e y e . ILo~~cver, t h i s c o n e i Lion i s n o r ~ ~ ~ a l l y ~ r i t h o u t p r a c t i c a l irr~portance

.

P i g .

6,

t h e p o r t i o n v ~ l ~ i c h p a s s e s through t h e s i e v e of 0.074, nun mesh s i z e i s of prime i n t e r e s t h e r e . However, t h i s p o r t i o n cannot be determined i n t h e c o n v e n t i o n a l tray by s h a k i n g t h e s i e v e s . I n s t e a d , r i n s i n g under running water i s n e c e s s a r y i n t h e f o l l o w i n g manner:

" ~ f t e r d r y i n g t h e s o i l sample, m a t e r i a l having g r a i n s i z e s

> 2 mm i s s o r t e d o u t . The reniainllng p o r t i o n of t h e sample i s weighed and p l a c e d on t h e 0.075 mnl s i e v e , where i t i s c a r e f u l l y r i n s e d f o r approximately f i v e minutes. By d r y i n g and weighing a g a i n t h e p e r - centage of t h e f r a c t i o n s < 2 rnrn which have d ( i . e . t h e g r a i n

d i a m e t e r ) < 0.075 mm i s determined.

If t h e p e r c e n t a g e i s s m a l l e r t h a n 5, t h e sample

i s of

a

t y p e of s o i l n o t f r o s t - s u s c e p t i b l e .

If t h e p e r c e n t a g e i s between 5 and

35,

i t s f r o s t s u s c e p t i b i l i t y must be deterrilined fro111 th e g r a i n curve f o r a l l t h e f r a c t i o n s € 2 mm

( c f . n o t e i n Fig.

6 ) .

If t h e p e r c e n t a g e i s g r e a t e r t h a n 35, t h e sa~tiple r e p r e s e n t s a t ~ y p e of s o i l which i s f r o s t - s u s c e p t i b l e under a l l c o n d i t i o n s . " If t h e above t e s t s i n d i c a t e a b o r d e r l i n e c a s e of f r o s t s u s c e p t i b i l i t y , t h e n t h e m a t e r i a l must e i t h e r be c o n s i d e r e d f r o s t - s u s c e p t i b l e ( t o be on t h e s a f e s i d e ) , o r t h e d e c i s i o n must be l e f t t o a s o i l mechanics s p e c i a l i s t .

The moisture c o n t e n t of t h e s o i l i s determined by e x p l o r a t o r y d i g g i n g o r b o r i n g , p r e f e r a b l y d i r e c t l y b e f o r e t h e f r o s t s e t s i n . The moisture c o n t e n t o f s o i l samples may be determined e i t h e r by d r y i n g o r from o b s e r v a t i o n of t h e anlount o f water r u n n i n g i n t o t h e borehole.

The e x c e s s o f i c e i n a f r o z e n s o i l sample and hence i t s

s e n s i t i v i t y t o thawing i s d e t e m i n e d by thawing;

i t i n

a graduated g l a s s v e s s e l . The f r e e water on t o p o f t h e s o i l m a t e r i a l p r o v i d e s

a c r i t e r i o n o f t h e s e t t l e m e n t t h a t may be expected when t h e s o i l l a y e r i n q u e s t i o n thaws.

To form an i d e a as t o whether a s o i l l a y e r w i l l flow o r s l i d e a f t e r thawing, sarnples of f r o z e n s o i l can be thawed and d r i e d on a h o t pan. If t h e s m p l e r u n s , t h e s o i l l a y e r i s s e n s i t i v e t o thaw-

o u t b e i n g n i x e d w i t h t h e s o i l m a t e r i a l , t h e s o i l l a y e r i n q u e s t i o n w i l l p r o b a b l y be s t a b l e .

I n s t u d y i n g t h e conlposition of p e r r ~ i a f r o s t o n l y t h e t o p l a y e r can be examined u n l e s s s p e c i a l d r i l l i n g equipment i s a v a i l a b l e . It

n u s t be remembered, moreover, t h a t no i n f o r r t a t i o n can be o b t a i n e d on t h e d e e p e r l a y e r s , n o r on t h e t h i c k n e s s of t h e p e r m a f r o s t . However, t h e s e d a t a a r e n o t v e r y i m p o r t a n t i n any c a s e as l o n g as

t h e p e r m a f r o s t i s thawed as l i t t l e as p o s s i b l e when a s u i t a b l e

f o u n d a t i o n i s chosen. A s mentioned above, i n t h e u n d i s t u r b e d s t a t e perrilaf r o s t i s e:ctremely s t a b l e and h a s g r e a t b e a r f n g c a p a c i t y .

( b ) S u r f a c e i n v e s t i g a t i o n s

A l l t h e above p r e l i l ~ l i l i a r y i n v e s t i g a t i o n s r e q u i r e p e n e t r a t i o n o f t h e growid s u r f a c e , b u t much v a l u a b l e d a t a may a l s o be o b t a i n e d f roni s u r f a c e o b s e r v a t i o n s and measurements

.

A v i g o r o u s v e g e t a t i o n i n d i c a t e s t h a t t h e m o i s t u r e c o n t e n t of t h e a c t i v e l a y e r i s h i g h and t h a t a c o r r e s p o n d i n g s u s c e p t i b i l i t y t o f r o s t a c t i o n e x i s t s i f t h e a c t i v e l a y e r c o n t a i n s c o a r s e and

medium-coarse s i l t .

Low

l y i n g g r a o s - t u f t e d and p a t c h y s t r e t c h e s o f p l a i n are c h a r a c t e r i s t i c i n t h i s r e s p e c t . In t y p i c a l per1,lafrost a r e a s a v i g o r o u s v e g e t a t i o n a l s o i n d i c a t e s a h i g h p e r m a f r o s t t a b l e . I f t h e v e g e t a t i o n i s c l e a r e d we can e x p e c t t h e p e r n i a f r o s t t a b l e t o be lolvered a p p r e c i a b l y . In t r a n s i t i o n a l a r e a s ( i . e . a r e a s w i t h s p o r a d i c p e r ~ n a f r o s t ) a moist l a y e r of v e g e t a t i o n o f t e n i n d i c a t e s t h e absence of p e r m a f r o s t a t t h e p a r t i c u l a r l o c a t i o n . ( s p o r a d i c p e r m a f r o s t i s f r e q u e n t l y r e s t r i c t e d t o r e l a t i v e l y d r y a r e a s c o n s i s t i n g of f i n e - g r a i n e d riiaterial )

.

In l o o s e s o i l l a y e r s which a r e n o t u n d e r l a i n by c o n t i n u o u s s o l i d r o c k i n o r d i r e c t l y underneath t h e a c t i v e l a y e r , t h e occur- r e n c e of i c i n g w i l l i n d i c a t e t h e p r e s e n c e of p e r ~ l a f r o s t . I f t h e i c i n g z p p e a r s i n e a r l y w i n t e r , tlie permafrost l e v e l i s h i g h , b u t if i t a p p e a r s o n l y towards t h e end of w i n t e r , t h e p e r m a f r o s t l e v e l w i l l norr!lally be lower.

A s nlentioi?ed above, f r o s t s u s c e p t i b i l i t y shol.~s i n t h e h e a v i n g of the ground i n w i n t e r . Such heaving i s f r e q u e n t l y heterogeneous

and t h u s r e s u l t i n a s e p a r a t i o n of m a t e r i a l , s i n c e t h e c o a r s e r o c k m a t e r i a l i s pushed froril t h e s p o t s tlhere t h e ground heaves most t o

s p o t s where i t heaves l e a s t . I n t h i s way r o c k m a t e r i a l c o l l e c t s

i n

c h a r a c t e r i s t i c polygons which a r e a c l e a r i n d i c a t i o n of f r o s t

s u s c e p t i b i l i t y .

An e x a c t i d e a of p o s s i b l e f r o s t h e a v i n g may be o b t a i n e d by l e v e l l i n g a f i e l d a t t h e end of summer and w i n t e r . The l e v e l l i n g must of course be r e f e r r e d t o a p o i n t rvllich i s d e f i n i t e l y n o t a f f e c t e d by f r o s t heaving. The h e a t of t h e sun h a s a v e r y g r e a t e f f e c t on t h e l e v e l of t h e p e r m a f r o s t . Sunny a r e a s ( s o u t h s l o p e s ) have t h e p e r m a f r o s t t a b l e a t r e l a t i v e l y g r e a t d e p t h b u t i n shaded a r e a s ( n o r t h s l o p e s ) t h e p e r m a f r o s t t a b l e i s h i g h . \ h e n b u i l d i n g s a r e e r e c t e d

a

c o r r e s p o n d i n g l o w e r i n g of t h e p e r m a f r o s t t a b l e nay be expected a l o n g t h e s o u t h faqade where t h e

s u n ' s r a y s a r e d e f l e c t e d t o t h e ground, b u t as a r u l e t h e perma- f r o s t t a b l e r i s e s a l o n g t h e shaded n o r t h faqade ( ~ i g .

7 ) .

In v~11at follovrs, c e r t a i n f u n d ~ ~ e n t a l r u l e s a r e g i v e n f o r d e s i g n i n g f o u i ~ d a t i o n s f o r b u i l d i n g s i n a r e a s w i t h w i n t e r f r o s t and p e r m a f r o s t . ( a ) l l i n t e r f r o s t a r e a s w i t h no p e r m a f r o s t I f t h e r.:intel- f r o s t i s n o t u n d e r l a i n b y p e r n ~ a f r o s t , problems a r e er-countered o n l y v~here th e a c t i v e l a y e r c o n s i s t s of m a t e r i a l s which c o n t a i n w a t e r and which a r e f r o s t - s u s c e p t i b l e .

The f o a q d a t i o n problems nay norr:,ally be s o l v e d by t a k i n g one of t h e follovring s t e p s .

(1) The a n c h o r i n g of t h e f o u n d a t i o n coupled w i t h t h e dead weight of t h e b u i l d i n g can c o u n t e r a c t t h e f r e e z i n g f o r c e s . I f t h e f o u n d a t i o n r e s t s on bedrock i t may be anchored w i t h b o l t s .

Anchoring i n l o o s e s o i l l a y e r s may be c a r r i e d o u t w i t h p i l e s o r r e i n f o r c e d p i e r s which 121ust be sunk below t h e ground t o

a t

l e a s t t h r e e t i n e s t h e thiclcness of t h e a c t i v e l a y e r .

( 2 ) The f r o s t s u s c e p t i b l i t y ]nay be e l i m i n a t e d by d r a i n i n g t h e a r e a and t h e n f i l l i n g i n i n m e d i a t e l y a d j a c e n t t o t h e f o u n d a t i o n s with c o a r s e i n a t e r i a l . Wherever p o s s i b l e a l a y e r of a s p h a l t e d f e l t p a p e r should be p l a c e d between t h e c o a r s e m a t e r i a l used as a f i l l and t h e a d j a c e n t s o i l l a y e r , which i s s u s c e p t i b l e t o f r e e z i n g , i n o r d e r t o p r e v e n t g r a d u a l encroachment by f i n e sand and s i l t ( ~ i g .

8).

( 3 ) By conducting s u f f i c i e n t h e a t from t h e b u i l d i n g t o t h e u n d e r l y i n g and a d j a c e n t s o i l l a y e r s t h e s e may be k e p t i n a s t a t e of p e r e n n i a l thaw ( P i g .

9).

I f t h c b u i l d i n g h a s rooms below ground,

i t must be rerrlenlbered t h a t t h e s e

w i l l f r e q u e n t l y be f l o o d e d u n l e s s t h e a r e a i s d r a i n e d .

Of c o u r s e ,

i t

niust f i r s t be determined whether t h e s o i l l a y e r s on v ~ h i c h th e f o u n d a t i o n s r e s t can w i t h s t a n d t h e p r e s s u r e from t h e f o u n d a t i o n s . T h i s i s a' p r e r e q u i s i t e f o r a l l t h e above methods. I c i n g rnay o c c u r i n t h e c a s e of l a y e r s o f l o o s e s o i l w i t h under- l y i n g bedrock i n o r d i r e c t l y below t h e a c t i v e l a y e r . F o r s t e p s t a k e n t o c o u n t e r a c t i c i n g t h e r e a d e r i s r e f e r r e d t o p o i n t

P

I n

t h e n e x t s e c t i o n . ( b ) Permafrost a r e a s I n p e r m a f r o s t a r e a s t h e problems a r e d i v i d e d i n t o t h r e e groups: ( a ) f r o s t s u s c e p t i b i l i t y i n t h e a c t i v e l a y e r ,

( B )

i c i n g , ( y ) thatring of pernlafrost l a y e r s . ( a ) P r o s t s u s c e p t i b l i t y i n t h e a c t i v e l a y e r . Analogous t o hat h a s bee11 s a i d above, t h e f r o s t s u s c e p t i b i l i t y may be c o n t r o l l e d by one of t h e f o l l o w i n g t h r e e ways:

( 1 ) By a n c h o r i n g t h e f o u n d a t i o n s i n t h e u n d e r l y i n g p e r m a f r o s t l a y e r . The d e p t h t o which t h e f o u n d a t i o n must be sunk i n t o t h e perrrlafrost dcpcnds on t h e shape o f t h e f o u n d a t i o n . Smooth p i l e s

should be sunk below t h e ground froin 2.5 t o

3

t i m e s t h e t h i c k n e s s of t h e a c t i v e l a y e r .

The p i l e s a r e d r i v e n a f t e r h o l e s have been thawed i n t h e perma- f r o s t w i t h

a

steam j e t . No l o a d should be a p p l i e d t o t h e p i l e s b e f o r e t h e y a r e conlplctely f r o z e n i n , i . e . n o t u n t i l

12

t o

3

months a f t e r d r i v i n ~ (Fig. 1 0 ) .

( 2 ) The f r o s t s u s c e p t i b i l i t y can be e l i m i n a t e d by d r a i n i n g t h e a r e a around t h e f o u n d a t i o n , p o s s i b l y suppleraented by f i l l i n g w i t h c o a r s e m a t e r i a l . I'herever p o s s i b l e ,

a

l a y e r of a s p h a l t e d f e l t

paper should be p l a c e d b e t m e n t h e f i l l and t h e a d j a c e n t s o i l l a y e r vrhich i s s u b j e c t t o f r o s t a c t i o n i n o r d e r t o p r e v e n t g r a d u a l

encroachrxent by f i n e sand and s i l t .

( 3 )

A t t h e boundary of perniafrost a r e a s , where t h e p e r m a f r o s t l a y e r may be very t h i n ( a p p r o x i m a t e l y 1 n i ) , t h e l a t t e r itlay be

thawed and t o g e t h e r w i t h t h e a c t i v e l a y e r (which i s f r o s t - s u s c e p t i - b l e ) may be k e p t i n a s t a t e of thaw wit11 h e a t from t h e b u i l d i n g

( I ? . 1 ) . The thawing rilust talce p l a c e b e f o r e t h e f o u n d a t i o n i s s t a r t e d and i t n u s t be c e r t a i n t h a t t h e thawed l a y e r i s s t a b l e w i t h r e s p e c t b o t h t o t h e p r e s s u r e from t h e f o u n d a t i o n and t h e danger of l a n d s l i d e s .

The above method must n o t be a p p l i e d under any c i r c u m s t a n c e s where t h e p e r m a f r o s t l a y e r i s of g r e a t e r t h i c k n e s s , s i n c e t h e thaw- i n g o b t a i n e d may be u n c o n t r o l l a b l e , w i t h i n c a l c u l a b l e conscquences f o r t h e s t a b i l i t y of t h e f o u n d a t i o n s .

( p ) I c i n g . I c i n g underneath b u i l d i n g s can normally be avoid- ed, i f c a r e Is t a k e n t o e n s u r e t h a t t h e u n d e r l y i n g s o i l l a y e r s f r e e z e a t t h e same time as t h e a d j a c e n t ground.

T h i s i s achieved by v e n t i l a t i n g v i g o r o u s l y w i t h f r e s h a i r underneath t h e house and by niaking s u r e , by e f f e c t i v e i n s u l a t i o n ,

t h a t no h e a t i s s u p p l i e d frorn t h e b u i l d i n g t o t h e u n d e r l y i n g s o i l l a y e r .

( y ) Thawing of t h e pcrnmafrost l a y e r s . Thawing o f t h e perma- f r o s t l a y e r s should be p r e v e n t e d as f a r as p o s s i b l e . By p r o p s r i n s u l a t i o n of t h e b u i l d i n g s ( e s p e c i a l l y t h e f l o o r s ) and by p e r m i t - t i n g adequate c i r c u l a t i o n of f r e s h a i r between t h e b u i l d i n g s and t h e ground ( c f .

P )

changes i n t h e p e r m a f r o s t l e v e l u s u a l l y w i l l n o t be g r e a t . Foundations on p i l e s should be p r e f e r a b l e t o continuous f o u n d a t i o n s , s i n c e t h e l a t t e r conduct a r e l a t i v e l y l a r g e amount of t h e h e a t from b o t h t h e b u i l d i n g and t h e sun down i n t o t h e s o i l .

F u r t h e r , as an a d d i t i o n a l s a f e t y measure, i t may even be

of g r a v e l between t h e o r i g i n a l ground s u r f a c e and t h e house (FIG. 1 2 ) .

F o r t h e e r e c t i o n of l a r g e r h i g h - c o s t b u i l d i n g s i t i s always n e c e s s a r y t o d e t e r m i n e f i r s t whether t h e t o p p e r m a f r o s t l a y e r h a s a

h i g h i c e c o n t e n t . I f s o , s p e c i a l measures must be talcen i n o r d e r t o d e t e r m i n e d whether t h e r e i s a d a n g e r of l o w e r i n g t h e l e v e l of t h e p e r m a f r o s t t a b l e a f t e r t h e e r e c t i o n o f t h e b u i l d i n g .

The f o u n d a t i o n ( p i l e s ) rnzy be d r i v e n s o f a r down i n t o t h e

perrilafrost ( c f . a, p o i n t 1 ) t h a t s l i g h t t h a v i n g v i i t l i e n s u i n g s e t t l e - riient of t h e o v e r l y i n s s o i l l a y e r s w i l l be u n i m p o r t a n t . I f s i n k i n g t h e f o u n d a t i o n s t o such a d e p t h i s t o be a v o i d e d , t h e l a y e r t h a t i s f r o s t - s u s c e p t i b l e may i n s t e a d be e x c a v a t e d t o t h e maximurn d e p t h o f t h e e x p e c t e d thawing 2nd r e p l a c e d by i c e - f r e e , c o a r s e m a t e r i a l ( ~ i g . 1 2 ) .

Iio~vever, t h e l a t t e r method i s v e r y cwnbersome and should be a p p l i e d o n l y i f e f f i c i e n t earth-worlcing machinery i s a v a i l a b l e and i f i t economizes on t h e tirrie r e q u i r e d f o r b u i l d i n g t h e f o u n d a t i o n s t h e m s e l v e s .

A s mentioned above, i t i s e s s e n t i a l f o r a l l p e r r n a f r o s t founda- t i o n work t h a t t h e p e r r n a f r o s t be d i s t u r b e d

as

l i t t l e as p o s s i b l e . T h i s a l s o r e f e r s t o t h e e x e c u t i o n of t h e erorl: i t s e l f . E x c a v a t i n g f o r f o u n d a t i o n s s h o u l d be c o n f i n e d t o t h e s ~ n a l l e s t a r e a p o s s i b l e ( p o i n t f o u n d a t i o n s ) . F u r t h e r , e x c a v a t i n g and back f i l l i n g s h o u l d be c a r r i e d o u t w i t h i n t h e s h o r t e s t p o s s i b l e tirne

.

It i s a l s o d e s i r a b l e , b u t r a r e l y p r a c t i c a b l e , f o r t h e founda- t i o n v~orlc t o be e x e c u t e d t h e y e a r b e f o r e t h e a c t u a l c o n s t r u c t i o n vrorlc i s c a r r i e d o u t i n o r d e r t o z i v e t h e per1:lafrost t a b l e t i m e t o becorne s t a b i l i z e d a f t e r i t s d i s t u r b a n c e by t h e f o u n d a t i o n work.

To t h e g r e a t e s t e x t e n t p o s s i b l e any rearrangenlent of t h e ground s h o u l d be c a r r i e d o u t by f i l l i n g . A s nlentioned above, i n t h i s way t h e p e r ~ l a f r o s t l e v e l m a y be r a i s e d , t h u s f u n l i s ' n i n g an a d d i t i o n a l niargir~ o f s a f e t y z g a i n s t t h a t ~ l n c o f t h e o r i g i n a l p e r n l a f r o s t l a y e r .

E x c a v a t i : ~ ~ , on t h e o t h e r hand, ~ ~ 1 1 1 - r e s u l t i n thawing of t h e p e r n a f r o s t l a y e r on a minor o r x a j o r s c a l e , wj-th i n c a l c u l a b l e conse- quences. The l o r r e r i n g of t h e p e r m a f r o s t l e v e l may e x t e n d o v e r a

l o n g time, s o t h a t s e t t l e m e n t of t h e ground, p o s s i b l y w i t h t h e b u i l d i n g s t h e r e o n , may occur many y e a r s a f t e r completion of t h e e x c a v a t i o n work.

The above c o n d i t i o n s should a l s o be t a k e n i n t o a c c o u n t i n t h e e x e c u t i o n of earthworlcs i n c o n j u n c t i o n w i t h t h e c o n s t r u c t i o n of roads, runways, s p o r t s grounds, e t c

.

D . Rules f o r t h e Designing of Permafrost Foundations

I. General

The d e s i g n of b u i l d i n g f o u n d a t i o n s f o r a r e a s with o n l y w i n t e r f r o s t i s s o w e l l knovm t h a t

i t

i s unnecessary t o go i n t o g r e a t e r d e t a i l h e r e .

Not so, however, w i t h r e s p e c t t o p e r m a f r o s t f o u n d a t i o n s , s i n c e o n l y r a r e l y have t h e s e been c o n s t r u c t e d a p p r o p r i a t e l y .

The scope of t h e p r e s e n t r e p o r t does n o t p e r m i t t h e d e t a i l e d d i s c u s s i o n of f o u n d a t i o n s f o r l a r g e , permanent b u i l d i n g s ; t h e l a y - o u t of such f o u n d a t i o n s , moreover, should always be l e f t t o

e n g i n e e r s with

a

more thorough knowledge o f p e r m a f r o s t .

However, t h e f o u n d a t i o n work f o r s m a l l e r , permanent houses and temporary b u i l d i n g s can r e a d i l y be c a r r i e d o u t without s p e c i a l

e x p e r t a s s i s t a n c e i f t h e f o l l o w i n g r u l e s a r e observed.

11. Permafrost Foundations f o r S m a l l e r Perillanent B u i l d i n g s

Permanent b u i l d i n g s a r e o n l y e r e c t e d i n a r e a s where t h e a c t i v e l a y e r i s n o t f r o s t - s u s c e p t i b l e , i . e . e i t h e r on s o l i d r o c k o r on coarse-grained, l o o s e s o i l l a y e r s .

On s o l i d rock t h e f o u n d a t i o n s can t a k e t h e form of t r a d i t i o n a l massed c o n c r e t e f o u n d a t i o n s s i n c e e f f e c t i v e f l o o r i n s u l a t i o n s ( a minimum of 10 cm m i n e r a l b a t t s ) a r e merely r e q u i r e d .

On l o o s e s o i l t y p e s t h e houses should be e r e c t e d on t i m b e r f o u n d a t i o n s c o n s i s t i n g of p o s t s and beams. blhere c o n d i t i o n s p e r m i t , i t may be e x p e d i e n t t o e r e c t a house on

a

mat of g r a v e l i n o r d e r t o o b t a i n t h e b e s t p o s s i b l e i n s u l a t i o n between t h e house and t h e

A c h a r a c t e r i s t i c t i m b e r f o u n d a t i o n i s shorm i n F i g .

13.

The beams which a r e b o l t e d t o t h e p o s t s have t h e upper edges a p p r o x i - mately 90 cm above t h e f i n i s h e d ground.

The p o s t s a r e p l a c e d a t i n t e r v a l s of 2

-

3

m and a r e d r i v e n dovm belovr t h e f i n i s h e d ground t o a d e p t h o f a t l e a s t 1 m. The bottoms of t h e p o s t s a r e provided with

a

c r o s s b a r which d i s t r i b u t e s t h e p r e s s u r e on t h e ground and a n c h o r s t h e b u i l d i n g .

The p l i n t h c o v e r i n g

i s

made of b e v e l l e d boards i n such a way as t o p e r m i t v e n t i l a t i o n b u t n o t t h e p e n e t r a t i o n o f t h e s u n ' s r a y s below t h e house. The f l o o r i s i n s u l a t e d w i t h 1 0 cm m i n e r a l - w o o l b a t t s .

111. Permafrost Foundations f o r Temporary B u i l d i n g s

Temporary b u i l d i n g s can be b u i l t

as

s t a t e d above i f t h e a c t i v e l a y e r i s n o t f r o s t - s u s c e p t i b l e .

I f t h e a c t i v e l a y e r i s f r o s t - s u s c e p t i b l e , t h e f o u n d a t i o n f o r

a

b u i l d i n g should b e s t be p l a c e d above t h e ground.

The b u i l d i n g w i l l t h e n be exposed t o t h e same h e a v i n g s and

s e t t l e m e n t s

as

t h o s e o f t h e a c t i v e l a y e r , b u t t h e d i s p l a c e m e n t s w i l l n o t accumulate from y e a r t o y e a r ( c f . F i g .

3 ) .

F r e e c i r c u l a t i o n o f a i r under t h e b u i l d i n g s i s e s s e n t i a l u n d e r

a l l

c o n d i t i o n s . I f t h e b u i l d i n g s a r e h e a t e d

an

e f f e c t i v e f l o o r i n s u l a t i o n i s r e q u i r e d

as

w e l l .

Fig. 1

The permafrost areas of the northern hemisphere

70' ' L e n a Rivrr

I

I

Amur River

I

F i g . 2

S e c t i o n through S i b e r l a from t h e A r c t i c Ocean t o t h e Sea of Jagan, showing t h e r e l a t i v e depth of t h e

permafrost and t h e a c t i v e l a y e r ( a c c o r d i n g t o S. W. l ~ ~ u l l e r : Permafrost )

A. Active l a y e r i n t h e thawed s t a t e ; f o u n d a t i o n a t t h e o r i g i n a l l e v e l

B. Active l a y e r i n t h e f r o z e n s t a t e ; f r o s t heaving o f a c t i v e l a y e r and f o u n d a t i o n

C. Active l a y e r once more i n t h e thawed s t a t e w i t h t h e same t h i c k n e s s a s i n t h e c a s e of A;

t h e f o u n d a t i o n h a s r e t a i n e d p a r t of t h e displacement

Ground w a t e r i s f r e e l y f l o w i n g i n t h e a c t i v e l a y e r The active L d y 8 r

is ~ o r n ~ l e i e l ~

C r o z e n here a n d

forms d b d r r r r r t o

The p r e s s u r e from t h e ground w a t e r r a i s e s t h e ground s u r f a c e

The p r e s s u r e from t h e ground vrater h a s f o r c e d a gap i n t h e f r o z e n s o i l c r u s t and i c i n g h a s formed

below t h e gap

The ground w a t e r , which i s under p r e s s u r e , s e e p s up through t h e f r o s t - f r e e s o i l

Fine _{Coarse sand} Medium

gravel Medium sand Fine sand Coarse silt silt

Fig.

6

The frost susceptibility is determined on the basis of samples <2 mm

1. All the soil types containing less than

58

with d (0.075, I. e. soil types in which the grain-size curve drops below point A are not frost-susceptible.

2. The other soil types are divided as follows:

a. Sediments are not frost-susceptible when less than 50$ is smaller than 0.125 mm and at the same time not more than

35%

is smaller than 0.075 mm, 1.e. when the grain-size curve lies below points B and C. Sediments, the grain-size curve of which lies above points B and C, are frost-susceptible.

b. Ungraded soil types are not frost-susceptible when the graln- size curve lies below curve D. Ungraded soil types, the grain-size curve of which lies above curve E, are frost- susceptible.

Foamed conc r e t e

-

-

r

+6

cm l a y e r r e i n f o r c e d conc l i g h t expanded crushed s t o n e c o a r s e g r a v e l f i l l r e t e c l a y aggregate F i g .

8

Foundation d e t a i l 1 : 20

Pig. 9

The s o i l embankments along t h e b u i l d L n g f s periphery, i n conjunction with h e a t t r a n s f e r from t h e b u i l d i n g ,

prevent t h e f r o s t from p e n e t r a t i n g i n t o t h e s o i l l a y e r s about t h e p i l e s which a r e f r o s t - s u s c e p t i b l e

D i r e c t l y Surnrner Winter ~ f t e r d r i v i n g S a f e l o a d : S a f e l o a d a

+

In o r d e r t o P x A P x A p r e v e n t heav- i n g , P

+

a > b A = a r e a o f p i l e p = maximum a l l o w a b l e p r e s s u r e on p e r n i a f r o s t a = a d f r e e z i n g f o r c e between p i l e and p e r m a f r o s t b = a d f r e e z i n g f o r c e between p l l e and w i n t e r f r o s t ( a c t i v e l a y e r ) F i g . 10 S t r e s s e s on t h e p i l e s anchored i n p e r m a f r o s t

Frost-free . - .

lower level of permafrost Fig. 11

The heat from the building keeps the underlying layer free from frost

Act fro

Fig. 12

Insulating mat of gravel between house and ground raises the permafrost level. The dot-and-dash

line gives the lower level for possible filling with ice-free, coarse-grained material