Principles of Geocryology (Permafrost Studies). Part II, Engineering Geocryology. Chapter I, Principle Aspects of Engineering Geocryology (Permafrost Studies), p. 5-17

Publisher’s version / Version de l'éditeur:

Technical Translation (National Research Council of Canada), 1965

READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.

https://nrc-publications.canada.ca/eng/copyright

Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.

Questions? Contact the NRC Publications Archive team at

PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.

NRC Publications Archive

Archives des publications du CNRC

For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien DOI ci-dessous.

https://doi.org/10.4224/20331463

Access and use of this website and the material on it are subject to the Terms and Conditions set forth at

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

Geocryology. Chapter I, Principle Aspects of Engineering Geocryology

(Permafrost Studies), p. 5-17

Saltykov, N. I.

https://publications-cnrc.canada.ca/fra/droits

L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.

NRC Publications Record / Notice d'Archives des publications de CNRC: https://nrc-publications.canada.ca/eng/view/object/?id=590adc6b-09e6-4c98-9bc0-69c46147c3b5 https://publications-cnrc.canada.ca/fra/voir/objet/?id=590adc6b-09e6-4c98-9bc0-69c46147c3b5

This translation is the first from the Russian permafrost publication "Principles of Cleocryology~, Part I1 (~ngineering ~ e o c r ~ o l o ~ ~ ~ , which follows the translation of Part I completed earlier this year. The National Research Council intends to issue the entire contents of Part I1 which consists of thirteen chapters.

This translation of Chapter

I

by N.I. Saltykov introduces engineering geocryology by outlining the principle aspect8 of this subject. It begins with a description of the physical and economic conditions in the North which are relevant to perma-. frost, and the place of engineering geocryology in this environ- ment. This is followed by a discussion of the mechanioal and

thermal aspects of engineering structures and their interaction with perennially frozen ground.

The Division of Building Research is grateful to Mr. V. Poppe, Translations Section, National Research Council, for translating this chapter and to

Dr.

R.J.E. Brown of this Divieion who checked the translation.

Ottawa R.F. Legget

Title :

NATIONAL RESEARCH C OUNC

IL

OF CANADA

Technical Translation 1215

Principle aspects of engineering geocryology (permafrost studies)

(0snov e polozheniya inzhenernoi geokriologii (merzlotove- d e n i y a 8

Author :

N

.

I

.

Sal tykov

Ref erenue : Principles of geooryology ( p e m a f rost studies), Part 11, Engineering geocryology, Chapter I. Academy of Sciendes of the U .S . S . R . _{Moscow 1959.} p .5-17

(0snovy geokriologii (merzlotovedeniya), Chast I vtoraya,

Inzhenernaya geokriologiya, Qlava

I.

Akademiya Nauk SSSR,

Moskva 1959. s .5-17)

PRINCIPLE ASPECTS OF ENGINEERING GEOCRYOLOGY ( PERTxlAFROST STUDIES )

1. Special conditions of economic activity in the North. Engineering geocryology and its place among allied disciplines. 2. The mechanical interaction between structures and frozen, freezing and thawing ground and nleans of controlling it.

3.

Thermal interaction between structures and the ground and engineering methods of controlling thermal processes in the ground. 4. Complex Interaction between structures and the ground and methods of ensuring norrnal operation of the former.

1. Special Conditions of Economic Activity in the North Engineering Geocryology and Its Place Among

Allied Disciplines

In

the North, as everywhere else on earth, the development of economic activity remains closely related to natural phenomena, is affected by them and in turn changes them to a very considerable extent. Natural phenomena which affect the economic development of the North are very varied and

specific. Permafrost, whose physico-mechanical and construction properties change with thawing as well as with changes in temperature below O°C, and processes which accompany the change in the aggregate state of the ground

-

swelling on freezing and settlement on thawing

-

create special problems in building and mining. Of great importance also are icing (naled) formation, melting of ground ice, regional variations in ground and air temperatures,

etc

.

These phenomena determine the nature of mechanical and thermal inter- action between the ground and the structures and create the conditions under. which work has to be performed.

To the engineer working under permafrost conditions the peculiarities of mechanical interaction between the structures and the ground are of prime

interest, namely: stability and bearing strength of the ground on swelling, magnitude and rate of swelling, magnitude, rate and nature of settlement of frozen ground on thawing, as well as the ease with which excavation work and mining may be carried out in the frozen ground.

These are the problems with which we shall begin the discussion of basic principles of engineering geocryology. At the same time we must not forget that the strength of frozen ground, in contrast to the strength of unfrozen ground, does not remain constant but, with all other conditions remaining

t h e same, w i l l depend on t h e temperature and d u r a t i o n of t h e l o a d . Therefore t h e s e two f a c t o r s should be considered i n a l l c a l c u l a t i o n s concerning t h e mechanical i n t e r a c t i o n between a s t r u c t u r e and t h e ground and i n o p e r a t i o n a l p l a n n i n g .

It i s a comparatively r a r e p r a c t i c e t o s u b j e c t t h e ground d e l i b e r a t e l y t o t h e e f f e c t s of h e a t ; t h i s i s done mainly f o r t h e r e g u l a t i o n of tempera- t u r e of c e r t a i n l i q u i d s and g a s e s i n p i p e s i n s t a l l e d i n f r o z e n ground (water mains, sewers, o i l p i p e l i n e s , e t c . ) . Much more o f t e n , thermal a c t i o n s e r v e s as a f a c t o r which determines t h e p r o p e r t i e s of t h e ground ( s t r e n g t h , c r e e p , e a s e of handling, p e r m e a b i l i t y ) and r e g u l a t e s t h e mechanical i n t e r a c t i o n between a s t r u c t u r e and t h e ground.

It w i l l not be a mistake t o assume t h a t t h e main d i f f e r e n c e between c o n s t r u c t i o n on permafrost and under normal c o n d i t i o n s i s t h a t i t i s I n v a r i - a b l y necessary t o c o n s i d e r and t o r e g u l a t e t h e thermal exchanges between t h e ground and t h e s t r u c t u r e a s w e l l a s t h e environment, and t o t a k e i n t o account t h e temperature of t h e ground. T h i s means t h a t an e n g i n e e r i s f o r c e d t o c o n s i d e r problems which r a r e l y e x i s t under normal c o n d i t i o n s .

I n e n g i n e e r i n g geocryology t h e i n v e s t i g a t i o n of thermal i n t e r a c t i o n i s a must. The thermal i n t e r a c t i o n between t h e ground and t h e s t r u c t u r e o f t e n assumes mechanical forms, and a s

a

r u l e t h i s change l e a d s t o deformation. A s a n example, we may t a k e t h e p r o c e s s e s o c c u r r i n g i n g r a d e s of r a i l r o a d s , highways and a i r f i e l d s . Here we f i n d two a l t e r n a t i n g p r o c e s s e s . The f i r s t c o n s i s t s i n c o o l i n g and f r e e z i n g of t h e ground, m i g r a t i o n of moisture, and heaving of t h e ground accompanied by

a

mechanical a c t i o n of t h e ground on t h e road s u r f a c e , which may be n o t o n l y u p l i f t e d but a l s o deformed. The second p r o c e s s c o n s i s t s i n thawing of t h e foundation s o i l s accompanied by s e t t l e m e n t which i s u s u a l l y d i f f e r e n t i a l and r e s u l t s i n a d d i t i o n a l deforma- t i o n of t h e road s u r f a c e . I n t h e course of economic development of

a

permafrost a r e a , t h e engineer o f t e n makes use of o t h e r forms of energy i n h i s t r e a t m e n t of t h e f r o z e n ground, such as chemical energy, e l e c t r i c a l energy, e t c . , but he u s u a l l y c o n v e r t s them i n t o thermal o r mechanical forms f i r s t .

Because of

a

p e c u l i a r n a t u r a l environment i n permafrost r e g i o n s , e n g i n e e r s make use of n o t only g e n e r a l l y accepted d e s i g n s and o p e r a t i o n a l methods when e r e c t i n g v a r i o u s s t r u c t u r e s ( i n d u s t r i a l , road, hydro, c i v i l i a n , e t c . ) and i n mining, but a l s o of methods q u i t e d i f f e r e n t t o t h o s e used under normal c o n d i t i o n s . Attempts t o i n t r o d u c e methods and d e s i g n s used success- f u l l y under normal c o n d i t i o n s i n t o permafrost r e g i o n s o f t e n produce inadequate, sometimes even c a t a s t r o p h i c r e s u l t s and almost i n v a r i a b l y l e a d t o unnecessary l o s s e s i n l a b o u r , m a t e r i a l and time.

I n c o n t r a s t t o g e n e r a l (fundamental) geocryology*, which i s based mainly on n a t u r a l phenomena t a k i n g p l a c e under c o n d i t i o n s n o t a f f e c t e d by human

a c t i v i t y , e n g i n e e r i n g geocryology c r e a t e s a r t i f i c i a l experimental c o n d i t i o n s whlch resemble t h e a c t u a l i n d u s t r i a l environment a s c l o s e l y a s p o s s i b l e . T h i s I s t h e reason f o r o t h e r d i f f e r e n c e s between t h e two s c i e n c e s : c e r t a i n p r o c e s s e s which form t h e o b j e c t of s t u d y i n g e n e r a l geocryology sometimes t a k e thousands of y e a r s t o complete and occur over enormous a r e a s ; t h e pro- c e s s e s s t u d i e d i n engineering geocryology and which a r e a f f e c t e d by human a c t i v i t y occur over a span of a few decades, sometimes over a p e r i o d of one o r two hundred y e a r s , and over r e l a t i v e l y small a r e a s . But I n s p i t e of t h e b r e v i t y of human i n f l u e n c e , man as a r u l e can e x e r t w i t h i n a c e r t a i n p e r i o d of time a s t r o n g e r thermal i n f l u e n c e on a u n i t of ground s u r f a c e t h a n t h a t produced by n a t u r a l f a c t o r s . A c h a r a c t e r i s t i c t a s k of e n g i n e e r i n g geocryology

i s t o d e r i v e a q u a n t i t a t i v e s o l u t i o n t o v a r i o u s problems.

On s o l v i n g problems i n engineering geocryology, a p a r t from g e n e r a l

geocryology which s u p p l i e s t h e engineer w i t h necessary i n f o r m a t i o n concerning g e n e r a l , r e g i o n a l and l o c a l mechanisms of formation of t h e s e a s o n a l and

p e r e n n i a l cryolithozone**, use i s made a l s o of many o t h e r s c i e n c e s ,and branches of knowledge. The most important of t h e s e a r e : thermal p h y s i c s , which h e l p s I n t h e s o l u t i o n of problems of h e a t exchange and c o n t r o l of

thermal c o n d i t i o n s i n t h e ground; p h y s i c s and mechanics of f r o z e n , f r e e z i n g and thawing ground which a s s i s t i n understanding t h e problems concerning t h e deformation and s t a t e of s t r e s s i n t h e ground and t h e s t r u c t u r e s ; g e n e r a l p h y s i c s , g e o l o g i c a l s c i e n c e s ( e n g i n e e r i n g geology, hydrogeology), s o i l mechanics, s o i l s c i e n c e , e t c .

Apart from t h e above s c i e n c e s , a g e o c r y o l o g i s t with a l e a n i n g towards engineering must be a complete master of t h e narrow t e c h n i c a l s u b j e c t t o whlch he a p p l i e s h i s knowledge of geocryology; without t h i s a l l h i s experl- ence may be q u i t e u s e l e s s .

*

Under g e n e r a l geocryology we understand a complex of i d e a s aoncerning t h e p r o c e s s e s of s e a s o n a l and p e r e n n i a l f r e e z i n g and thawing of s o i l and rock, t h e c h a r a c t e r i s t l c a o f t h e i r composition, s t r u c t u r e and s t a t e , t h e mech- anisms of t h e i r formation and geographical d i s t r i b u t i o n , as w e l l a s t h e development of o t h e r n a t u r a l cryogenic and postcryogenic p r o c e s s e s and formations (Baranov, 1956).

*+

Seasonal c r y o l l t h o z o n e i s a zone of ground s u b j e c t e d t o s e a s o n a l f r e e z i n g l y i n g on unfrozen ground. P e r e n n i a l c r y o l i t h o z o n e i s t h e f r o z e n zone i n t h e l i t h o s p h e r e where t h e ground Is s u b j e c t e d t o s e a s o n a l thawing, which e x i s t s continuously f o r many ( n o t l e s s than t h r e e ) y e a r s .

While n o t i n g t h e n e c e s s i t y of c o n s i d e r i n g t h e physico-mechanical pro- p e r t i e s of t h e ground, h e a t exchange and geocryological phenomena mainly d u r i n g t h e planning and e r e c t i o n of s t r u c t u r e s i n t h e permafrost r e g i o n , and t h e f a c t t h a t i t was t h e c o n s t r u c t i o n i n d u s t r y i n t h i s r e g i o n t h a t gave t h e main impetus t o t h e development of e n g i n e e r i n g geocryology, we must not exclude from t h e scope of this s c i e n c e problems concerning t h e thermal and mechanical i n t e r a c t i o n between t h e ground and t h e s t r u c t u r e s i n t h e r e g i o n s of s e a s o n a l f r e e z i n g of t h e ground.

From t h e p o i n t of view of a c o n s t r u c t i o n worker and a miner a t t e m p t i n g t o e v a l u a t e h e a t exchange phenomena and t h e p r o c e s s e s of ground f r e e z i n g and ground thawing dependent on t h e s e phenomena, t h e r e g i o n of s e a s o n a l f r e e z i n g d i f f e r s g r e a t l y from t h e permafrost r e g i o n . I n r e g i o n s where t h e r e i s no permafroat, i t i s p o s s i b l e t o bypass d i f f i c u l t i e s connected w i t h f r e e z i n g by l a y i n g f o u n d a t i o n s and p i p e l i n e s and by mining i n t h e unfrozen ground l y i n g below t h e l a y e r of s e a s o n a l f r e e z i n g . I n permafrost r e g i o n s , however, i t i s not p o s s i b l e t o bypass t h e s e phenomena and p r o c e s s e s . They must be s t u d i e d and understood, and a method must be found t o c o n t r o l them. Besides, i n t h e permafrost r e g i o n s , g e o c r y o l o g i c a l phenomena* a r e more i n t e n s i v e . F i n a l l y , we must not f o r g e t t h a t permafrost i s not n e c e s s a r i 1 y . a n e g a t i v e f a c t o r . For example, i t may s e r v e a s a sound support f o r a s t r u c t u r e o r a s a r e l i a b l e medium f o r l a y i n g a foundation, capable of s u p p o r t i n g a l i v e load o r r e s i s t i n g t h e heaving f o r c e s developed i n t h e l a y e r of s e a s o n a l f r e e z i n g . A l l t h e s e f a c t o r s n a t u r a l l y favoured t h e development of e n g i n e e r i n g geo- cryology f i r s t and foremost i n permafrost r e g i o n s . However, r e c e n t e x p e r i - ence h a s shown t h a t engineering geocryology may be of h e l p a l s o t o economic development under c o n d i t i o n s of s e a s o n a l f r e e z i n g .

Like any o t h e r s c i e n c e , e n g i n e e r i n g geocryology may be d i v i d e d i n t o t h e o r e t i c a l and a p p l i e d s e c t i o n s . T h e o r e t i c a l e n g i n e e r i n g geocryology

i n c l u d e s f i r s t of a l l t h e study of b a s i c mechanisms determining t h e physico- t e c h n i c a l and c o n s t r u c t i o n p r o p e r t i e s of f r o z e n ground and ground s u b j e c t e d t o s e a s o n a l f r e e z i n g and thawing, p r i m a r i l y i n r e l a t i o n t o t h e temperature and t h e d u r a t i o n of load a p p l i c a t i o n . The combination of t h e s e mechanisms which we s h a l l c a l l t h e physlco-mechanical b a s i s of engineering geocryology i s d i s c u s s e d i n Chapter 111: Basic mechanics of f r o z e n , f r e e z i n g and thawing s o i l s . The second group of p r o c e s s e s s t u d i e d i n t h e o r e t i c a l e n g i n e e r i n g geocryology c o n s i s t s i n thermal i n t e r a c t i o n s between t h e s t r u c t u r e s and t h e

*

Q e o c r y o l o g i c a l phenomena a r e s p e c i a l p h y s i c a l geographical phenomena which a r i s e on f r e e z i n g o r thawing, a s w e l l a s d u r i n g v a r i a t i o n s i n t h e n e g a t i v e temperature of t h e ground, water b a s i n s and water streams.

ground, investigated against the background of general heat exchange which forms the basis of thermotechnical estimates and methods of controlling the thermal conditions in the ground. This is discussed in Chapter IV: Thermo- physical principles of controlling .the interaction between structures and frozen soils.

Applied engineering geocryology is based on the mechanisms mentioned above and industrial experience. It concerns itself with the evaluation of conat.ruction projects, design of novel types of structures, operational and production methods and development of a general theory concerning measures which could be applied to overcome difficulties caused by geocryological factors. It include8 also methods of investigating construction sites and thorough evaluations of natural phenomena and processes characteristic of a given area in permafroet conditions.

2.

Mechanical Interaction Between Structures and Frozen, Freezing

and

Thawing Ground and Means

of Controlling it

The mechanical interaotion between structures and frozen, freezing and thawing ground consists in the transmission of forces first from the atruc- ture to the ground, and aecond from the ground to the structural elements. Both sides of this interaction in permafrost areas differ from those under normal condit ions.

Modern engineering geocryology haa established that the interaction between a

structure

and the supporting ground may assume different forms depending on the condition of the ground, 1.e. on whether it is frozen, freezing or thawing.

The ease of transmission of a force from a structure to the frozen ground is limited by the strength of the latter, which depends on marry fac- tors, first of all on the ground temperature and duration of load. The combination of these factors determines the amount of critical pressure on the frozen ground as well as the bearing capacity of piles driven into frozen ground and of other structural supports erected on a frozen bearing medium. Frozen ground which is subdected to a load for a long time is deformed by relatively low pressures. The duration of a load, which is of relatively small Importance as far as the stability of structures on unfrozen ground is concerned, becomes the decisive factor in determining the strength and

stability of structures on permafrost, especially at temperatures approaching

O 0 C .

The dependence of mechanical and building properties of frozen ground on the temperature, duration of load and other factors is discussed in great

d e t a i l i n Chapter 111. These f a c t o r s determine t h e c r i t i c a l v a l u e s of normal and t a n g e n t i a l s t r e s s e s i n t h e f r o z e n ground and c o n s t i t u t e t h e b a a i c d a t a which must be considered by a d e s i g n e r when determining t h e dimensions of such s t r u c t u r a l elements a s t h e s u p p o r t i n g p a r t of a foundation, t h e l e n g t h and d i a m e t e r of p i l e s , e t c .

The temperature and d u r a t i o n of load assume s t i l l g r e a t e r importance when f r o z e n ground and e s p e c i a l l y i c e aerve a s c o n s t r u c t i o n m a t e r i a l .

A t t h e p r e s e n t l e v e l of development of mechanics of f r o z e n ground and engineering geocryology, t h e r e a r e two methods of c o n t r o l l i n g t h e mechanical i n t e r a c t i o n between t h e s t r u c t u r e s and t h e f r o z e n ground. The f i r s t c o n s i s t s i n d e s i g n i n g a s t r u c t u r e and i n p a r t i c u l a r i n l i n k i n g t h e f o u n d a t i o n and

t h e upper s t r u c t u r e s w i t h t h e b e a r i n g medium i n such a way t h a t t h e s t r e s s e d s t a t e and c r e e p of f r o z e n ground, i c e and c o n s t r u c t i o n m a t e r i a l do not emerge beyond t h e s a f e t y l i m i t s ( t h e s t r u c t u r a l method). The second method c o n s i s t s of m a i n t a i n i n g an a r t i f i c i a l temperature of t h e b e a r i n g medium and i n

a p p r o p r i a t e c a s e s of c o n s t r u c t i o n m a t e r i a l as w e l l , which would ensure t h e s t a b i l i t y of t h e s t r u c t u r e ( t h e thermotechnical method). A s examples of s t r u c t u r a l c o n t r o l of t h e mechanical i n t e r a c t i o n s between t h e s t r u c t u r e and t h e f r o z e n ground we may mention t h e following: t h e i n c r e a s e i n t h e b e a r i n g s t r e n g t h of p i l e s d r i v e n i n t o f r o z e n ground by expanding t h e i r l a t e r a l s u r - f a c e s ( t h e double-T p i l e s of r e i n f o r c e d c o n c r e t e designed by K.E. Egerev), t h e i n s t a l l a t i o n of a pad of f r o z e n sand between t h e bottom of t h e foundation and t h e s u r f a c e of ground i c e , e t c . A s an example of thermotechnical c o n t r o l we may mention t h e c o o l i n g of t h e b e a r i n g medium by means of a v e n t i l a t e d basement. More o f t e n both methods ( t h e s t r u c t u r a l and t h e t h e r m o t e c h n i c a l ) a r e used simultaneously. I n some c a s e s t h e s t r e n g t h of t h e f r o z e n bond

between t h e foundation and t h e ground may be s u b s t a n t i a l l y v a r i e d by d e c r e a s - i n g o r i n c r e a s i n g t h e moisture c o n t e n t i n t h e ground.

The mechanical i n t e r a c t i o n between a s t r u c t u r e and t h e f r e e z i n g ground makes i t e e l f f e l t mainly i n t h e e f f e c t of t h e ground on t h e s t r u o t u r e d u r i n g heaving. On i n c r e a s i n g i t s volume, t h e ground may a f f e c t t h e s t r u c t u r e i n t h e normal o r t a n g e n t i a l d i r e c t i o n r e l a t i v e t o i t s s u r f a c e , cause l o c a l s t r e s s e s i n c o n e t r u c t i o n m a t e r i a l s and d i s p l a c e t h e s t r u c t u r e i n s p a c e .

Almost a l l t y p e s of s t r u c t u r e s l o c a t e d on t h e ground s u r f a c e o r i n t h e ground undergoing f r e e z i n g o r thawing, e . g . f o u n d a t i o n s , t h e s u r f a c e s of r o a d s and a i r f i e l d s , r a i l r o a d s , e a r t h dams, e t c . , a r e s u b j e c t e d t o t h e e f f e c t s of heaving.

S e v e r a l meaeures may be adopted i n o r d e r t o reduce t h e t a n g e n t i a l f o r c e s of heaving. They a r e : thermal d r y i n g ( t h e h e a t i n g of t h e c o n t a c t s u r f a c e between t h e foundation o r p i l e and t h e f r o z e n ground, i n s t a l l a t i o n of thermal

i n s u l a t i o n ) , s t r u c t u r a l ( p i l e s d r i v e n i n t o ground a t an a n g l e , i n c l i n e d l a t e r a l s u r f a c e s of f o u n d a t i o n , e t c . ) , chemical ( a d d i t i o n of hydrophobic s u b s t a n c e s t o t h e s o i l ) , and s o on. The earthworks c o n s i s t of well-drained s o i l and adequate d r a i n a g e i s provided f o r s u r f a c e and groundwater.

The e f f e c t of t h e s t r o n g e s t heaving f o r c e s normal t o t h e base of t h e f o u n d a t i o n a r e e l i m i n a t e d by l a y i n g t h e l a t t e r below t h e l a y e r of s e a s o n a l f r e e z i n g and thawing.

The heaving of f o u n d a t i o n s and p i l e s may be prevented by s u b j e c t i n g them t o g r e a t e r l o a d s and by s e c u r i n g ( a n c h o r i n g ) them i n t h e p e r m a f r o s t .

The mechanical i n t e r a c t i o n between a s t r u c t u r e and t h e thawing ground l a u s u a l l y accompanied by a d i s t u r b a n c e i n t h e s t a b l e c o n d i t i o n s which e x i s t e d p r i o r t o thawing. On thawing, t h e adhesion between s o i l p a r t i c l e s i s g r e a t l y reduced, t h e b e a r i n g s t r e n g t h of t h e ground i s reduced a l s o , and t h e ground i s s u b j e c t e d t o deformation due t o c o n s o l i d a t i o n and p l a s t i c d e f o r m a t i o n s . Under t h e s e c o n d i t i o n s a l l p o s s i b l e s t r u c t u r e s , such a s f o u n d a t i o n s , p i p e l i n e s , road and a i r f i e l d s u r f a c e s , e t c . , a r e s u b j e c t e d t o u s u a l l y d i f f e r e n t i a l s e t t l e m e n t accompanied by a r e d i s t r i b u t i o n of r e a c t i o n 0 i n t h e f o u n d a t i o n s o i l s and t h e c r e a t i o n of a d d i t i o n a l s t r e s s e s i n t h e

s t r u c t u r e s .

I n some i n s t a n c e s , a s f o r example i n mining, t h e i n c r e a s e i n p r e s s u r e from t h e thawed ground on s u p p o r t i n g s t r u c t u r e s i s uneven and asyrnrnetrical, t h e ground may cave i n , t h e underground workings may be invaded by ground- water, e t c . The most r a d i c a l and e f f e c t i v e measure which would ensure normal

o p e r a t i o n s of a s t r u c t u r e i s t h e e l i m i n a t i o n of t h e main cause of deformation, 1 . e . t h e p r e v e n t i o n of thawing by c o o l i n g t h e ground i n a n a p p r o p r i a t e way. I f t h i s i s not p o s s i b l e , t h e n t h e r e a r e two o t h e r ways of e n s u r i n g normal o p e r a t i o n of a s t r u c t u r e : by s t r u c t u r a l m o d i f i c a t i o n s which would e n a b l e a s t r u c t u r e t o a d a p t i t s e l f t o ground thawing d u r i n g t h e p e r i o d of o p e r a t i o n , and by thawing t h e ground p r i o r t o c o n s t r u c t i o n ( c h a p t e r V I ) .

The f o l l o w i n g g e n e r a l p o i n t s should be c o n s i d e r e d while s e a r c h i n g f o r methods of c o n t r o l l i n g t h e mechanical i n t e r a c t i o n between s t r u c t u r e s and t h e ground.

1. The e n g i n e e r i n g d e c i s i o n should be based on a thorough u n d e r s t a n d i n g of g e o c r y o l o g i c a l and o t h e r n a t u r a l p r o c e s s e s i n t h e rock o r s o i l s e r v i n g a s a medium of o r a s u p p o r t f o r t h e given s t r u c t u r e . The a d o p t i o n of t h i s d e c i s i o n should be preceded by a thorough engineering-geocryological

i n v e s t i g a t i o n of t h e c o n s t r u c t i o n s i t e .

2 . I f p o s s i b l e , t h e e n g i n e e r i n g d e c i s i o n should be d i r e c t e d towards t h e e l i m i n a t i o n o f f a c t o r s which complicate c o n s t r u c t i o n work. For example, i n

the presence of active icing, the first requirement would be to investigate the possibilities of damming and complete diversion of groundwater from the construction site.

3.

When investigating the possibilities of ensuring normal operation of structures erected in regions where special geocryological processes and phenomena occur, it is always necessary to consider the possibility of re-

locating the structure at a site more favourable from the point of view of engineering geocryology.

4. When designing structures on the basis of ultimate conditions, the latter may be defined in two ways:

(a) for structures designed in such a way as to retain the frozen state of the ground, one should consider the ultimate long-term stresses; (b) for structures erected on thawing or thawed ground, as well as for

structures erected on frozen ground or ice, one should consider the ultimate deformation.

5.

The natural conditions at the construction site should form the basis of not only the structural design but also of all plans concerning operation and production.

3.

Thermal Interaction Between Structures and the Ground and En~ineering Methods of Controlling Thermal

Processes in the Ground

Any variations in the temperature of the ground, including variations resulting in the freezing of ground moisture and melting of ground ice, are due to the variable nature of the heat exchange between the ground and the structures or the atmosphere (for example, as a result of changes in lnsula- tion, radiation, etc.), as well as to the introduction or elimination of

artificial sources or absorbers of heat. In order to predict any temperature changes, and consequently any changes in the mechanical properties of the ground, as well as to foresee various phenomena which may affect human activ- ity and structures, the engineer must know the nature and rate of the thermal interaction between the ground and the structures, the sources of heat, and the atmosphere.

If the consequences of thermal Interaction between the structures and the ground or of any engineering measures lead to radical changes in the condition and mechanical properties of the ground, then the engineer is faced with the task of controlling the heat-exchange processes.

Engineering geocryology regards thermal interaction between the struc- tures and the ground in a general sense by considering the fact that frozen, freezing or thawing ground may serve as a bearing medium for building

foundations, o r may accommodate p i p e l i n e s and c a b l e s , o r s e r v e a s conatruc- t i o n m a t e r i a l i n dams, road beds, e t c .

I n each case t h e temperature of t h e ground and t h e d e s i r e d conditions of h e a t exchange depend on t h e purpose of t h e s t r u c t u r e and t h e ground i t s e l f . For example, t h e s t a b i l i t y of a b u i l d i n g o f t e n r e q u i r e s t h e r e t e n t i o n of t h e f r o z e n s t a t e of i t s b e a r i n g medium, but f o r t h e normal o p e r a t i o n of water mains it i s e s s e n t i a l t h a t a l a y e r of surrounding ground, however small,

should remain unfrozen. A l t e r n a t i n g p o s i t i v e and n e g a t i v e temperatures a r e t h e g r e a t e s t danger t o t h e s t a b i l i t y of s l o p e s of embankments b u i l t of s i l t y s o i l , r e s u l t i n g i n e x c e s s i v e accumulations of i c e and subsequent s l o p e

f a i l u r e . The engineer i s o f t e n faced with requirements which c o n t r a d i c t each o t h e r . Such c o n t r a d i c t i o n s occur, f o r example, when water l i n e s a r e i n s t a l l e d i n a b u i l d i n g l o c a t e d on ground s a t u r a t e d w i t h i c e and c o n s t r u c t e d with a

view t o r e t a i n i n g t h e ground i n a f r o z e n c o n d i t i o n . I n such c a s e s , wrong c o n s t r u c t i o n methods may cause, and o f t e n have caused, damage t o t h e b u i l d i n g o r d i s t u r b t h e normal o p e r a t i o n of t h e water mains.

The c o n t r o l of t h e h e a t exchange between t h e ground and t h e s t r u c t u r e s o r t h e atmosphere by way of an expedient r e g u l a t i o n of t h i s g e ~ p h y ~ i c a l pro- c e s s i s one of t h e most important engineering t a s k s , s i n c e a c o r r e c t a o l u t i o n of t h i s problem makes it much e a s i e r t o r e g u l a t e t h e mechanical i n t e r a c t i o n s . The n e c e s s i t y of c o n t r o l l i n g t h e thermal i n t e r a c t i o n s between a s t r u c t u r e and f r o z e n , f r e e z i n g o r thawing ground demands a c l e a r understanding of t h e

mechanisns of t h e s e i n t e r a c . t i o n s and of methods of r e g u l a t i n g them by way of a p p r o p r i a t e s t r u c t u r e s and o p e r a t i n g techniques. Table I c o n t a i n s d a t a concerning a r t i f i c i a l v a r i a t i o n of ground temperature by a l t e r i n g t h e n a t u r e of t h e h e a t exchange between t h e ground and t h e atmosphere o r a s t r u c t u r e

( a f t e r P.F. ~ h v e t s o v ) .

T h i s scheme provides f o r t h e t h r e e most t y p i c a l c a s e s of d e l i b e r a t e v a r i a t i o n of ground temperature: ( a ) c o o l i n g of t h e ground when t h e tempera- t u r e d r o p s from p o s i t i v e t o negative; ( b ) c o o l i n g of t h e ground w i t h ternpera- t u r e s remaining negative; ( c ) warming of t h e ground w i t h temperatures r i s i n g from n e g a t i v e t o p o s i t i v e . For each c a s e t h e r e i s a b r i e f summary of methods of v a r y i n g t h e temperature, of phenomena and p r o c e s s e s t a k i n g p l a c e when t h e temperature of t h e ground changes, of t h e e f f e c t of t h e s e p r o c e s s e s on

s t r u c t u r e s and o t h e r a s p e c t s of human a c t i v i t y , and f i n a l l y of aims of a r t i f i c i a l v a r i a t i o n of ground temperature.

Among thermal phenomena s t u d i e d i n e n g i n e e r i n g geocryology, t h e r e a r e two b a s i c forms of h e a t exchange.

1. U n i d i r e c t i o n a l h e a t exchange which i n time may lead t o v i r t u a l l y steady s t a t e c o n d i t i o n s i n t h e ground.

2. Heat exchange which changes p e r i o d i c a l l y and i s c h a r a c t e r i z e d by

a

s t e a d y average temperature l e v e l , i . e . t h e average temperature remains s t a b l e w i t h i n t h e period of time corresponding t o a thermal c y c l e d u r i n g a l t e r n a - t i o n s of c o o l i n g and warming.

Both forms of h e a t exchange r e s u l t i n t h e c r e a t i o n of unsteady thermal c o n d i t i o n s i n t h e ground and r e p r e s e n t t h e most t y p i c a l proceeses s t u d i e d i n e n g i n e e r i n g geocryology.

The f i r s t form of h e a t exchange, when h e a t flows c o n s t a n t l y i n one d i r e c t i o n only, i s observed under heated b u i l d i n g s without any c o o l i n g i n s t a l l a t i o n s , around p i p e l i n e s i n s t a l l e d i n f r o z e n ground, under c o o l i n g i n s t a l l a t i o n s i n r e g i o n s of s e a s o n a l f r e e z i n g , e t c . The main f e a t u r e of t h i e type of h e a t exchange i s a prolonged and g r a d u a l l y slowing down displacement of t h e z e r o geoisotherm, which c o n t i n u e s u n t i l s t e a d y c o n d i t i o n s a r e a t t a i n e d

( t h e establishment of d e f i n i t e o u t l i n e s of

a

thaw b a s i n under a heated b u i l d i n g o r of a t a l i k around a p i p e , e t c . ) .

T h i s f a c t g i v e s r i s e t o an important r u l e of e n g i n e e r i n g geocryology, which s t a t e s t h a t i t i s impossible t o r e t a i n t h e f r o z e n s t a t e of t h e ground under a h e a t - e m i t t i n g b u i l d i n g by means of thermal i n s u l a t i o n only 'and w i t h - o u t p e r i o d i c c o o l i n g through v e n t i l a t i o n .

Let u s now d i s c u s s i n g r e a t e r d e t a i l t h e second form of h e a t exchange, which may be observed i n a p p r o p r i a t e c a s e s on t h e ground s u r f a c e and i n t h e l a y e r c l o s e t o t h e s u r f a c e .

I n t h e i n i t i a l s t a g e s of changes i n average temperature i n t h e given d i r e c t i o n , on t h e s u r f a c e where t h e h e a t exchange i s t a k i n g p l a c e e i t h e r d i r e c t l y between t h e ground and t h e atmosphere o r between t h e ground and t h e atmosphere v i a t h e b u i l d i n g , t h e h e a t exchange i n t h e l a y e r c l o s e t o t h e s u r f a c e must be asymmetrical*. If i t i s d e s i r e d t o reduce t h e average tem- p e r a t u r e , i t i a necessary t o reduce t h e inf'low of h e a t and t o i n c r e a s e i t s l o s s e s ; i f it i s d e s i r e d t o I n c r e a s e t h e average temperature, i t i s necessary t o i n c r e a s e t h e inflow of h e a t and t o reduce i t s l o s s e s . T h i s asymmetry of h e a t exchanges w i l l d i s a p p e a r w i t h time i f

a

r e l a t i v e e q u i l i b r i u m s e t s i n between t h e inflow of h e a t i n t o t h e ground from t h e o u t s i d e ( o r from a

s t r u c t u r e ) and t h e h e a t l o s s e s . The average temperature w i l l become s t a b l e and w i l l correspond t o t h e environmental c o n d i t i o n s . But any changes, how- ever small, i n o u t e r o r i n n e r ( t e c h n o l o g i c a l , g e o l o g i c a l , hydrogeological and

+ The term "symmetrical h e a t exchange" corresponds t o t h e r e l a t i v e e q u i l i b r i u m

between h e a t r e c e i v e d by t h e s o i l from o u t s i d e and h e a t l o s t by t h e s o i l t o t h e surrounding medium. The term "asymmetrical h e a t exchange" means t h e o p p o s i t e ( ~ h v e t s o v ,

1954).

geochemical) conditions of the heat exchange between the ground and the atmosphere or a structure will cause the asymmetry to reappear.

4. Complex Interaction Between Structures and the Ground and Methods of Ensuring Normal

Operations of the Former

When evaluating the consequences of variations in the average temperature of the heat exchange resulting from the erection of structures on a new site, we must always differentiate between the effect of these variations on the mechanical strength of clayey soils saturated or supersaturated with moisture and containing macrobodies of ice, and the effect on the strength of dry or slightly moist sandy soil and gravel. Therefore, the directions of and the intervals between the changes in the average annual temperature of the bearing medium depend not only on the natural physical geographical (for example, climatic) conditions of the heat exchange between the upper layer of the earth's crust and the atmosphere, but also on such qualitative factors as the grain size and petrographic composition, the moisture content and the ice content of the bearing medium.

Because of these considerations based on practical experience and the results of theoretical and experimental studies, the structural designers

take different views on the possible variations in the conditions of soil and rock serving a8 structural supports or as surrounding media.

This gave riae to a classification of engineering-geocry,ological deci- sions concerning methods of ensuring stability and normal operation of

structures. The classification is used both in the literature and in practice and is known as the classification "according to principles or methods of construction", which refers to the bearing medium and the foundations. The choice of a building site must be regarded as one of the most important decisions which determines the subsequent development of the proJect in all its aspects.

Below we give a brief summary of all mentioned methods of ensuring the stability and normal operation of a structure, or, which means the same thing, of construction methods and where to apply them. The summary refers mainly to foundation engineering.

Retention of the frozen state of the bearing medium is now widely practised In the construction of foundations in permafrost regions and is beginning to be used in the construction of dams and other hydrotechnical structures, as well as in mining and road construction. This method is used mainly in cases where the thawing of the ground results in a significant

d e t e r i o r a t i o n of i t s properties. P r a c t i c a l e x p e r i e n c e h a s i n d i c a t e d t h a t i n t h e p r e s e n c e of t h i s t y p e of ground, which could be r e t a i n e d i n a Frozen s t a t e , t h i s method i s by f a r t h e b e a t . Severe c l i m a t i c c o n d i t i o n s and low t e m p e r a t u r e s of a i r and p e r m a f r o s t make i t e a s i e r t o a p p l y t h i s method, b u t i t can be used a l s o i n r e l a t i v e l y m l l d c l i m a t i c c o n d i t i o n s .

A d a p t a t i o n of 3 t r u c t u r n l desj<yn t o d i f f e r e n t i a l s e t t l e m e n t of b e a r i n g medium on thaaving, i s used when i t i s d i f f i c u l t t o r e t a i n t h e ground i n a

f r o z e n s t a t e and i t i s expected t h a t t h e s e t t l e m e n t w i l l n o t be v e r y uneven. The m a r g i n a l c a s e of t h i s i s one where i t i s no l o n g e r n e c e s s a r y t o a d a p t s t r u c t u r a l d e s i g n t o ground s e t t l e m e n t , 1 . e . t h e c a s e where a s t r u c t u r e i s e r e c t e d on t h e ground which cannot be compressed and which d o e s n o t change i t s p r o p e r t i e s on thawing, f o r example on s o l i d r o c k , f i r m l y packed p e b b l e s , g r a v e l and s a n d .

P r e c o n s t r u c t i o n thawing of t h e ground and t h e improvement of i t s p r o p e r - t i e s a s r e g a r d s c o n s t r u c t i o n r e p r e s e n t s an a t t e m p t t o make t h e c o n d i t i o n s of c o n s t r u c t i o n work on p e r m s f r o s t e q u a l t o t h o s e under normal c i r c u m s t a n c e s by a r t i f i c i a l means. I n f o u n d a t i o n e n g i n e e r i n g , and t o a c e r t a i n e x t e n t i n t h e c o n s t r u c t i o n of dams, t h e a d o p t i o n of t h i s method means t h e e l i m i n a t i o n of t h e most dangerous f a c t o r i n t h e l i f e of a s t r u c t u r e : t h e d e c r e a s e i n t h e

e x t e n t and, what i s even more i m p o r t a n t , t h e r a t e of s e t t l e m e n t o f t h e s t r u c - t u r e d u r i n g thawing of t h e b e a r i n g medium. T h i s method may be used on

d i f f e r e n t t y p e s o f ground when it i s p o s s i b l e t o d i v e r t t h e e x c e s s w a t e r a f t e r thawing, and it can be o f s p e c i a l s i g n i f i c a n c e i n t h e c a s e of c o n s t r u c t i o n on t h e ground h i g h l y s a t u r a t e d w i t h i c e and s u b j e c t e d t o s t r o n g t h e r m a l s e t t l e - ment. A t p r e s e n t , t h i s method i s widely used i n p l a c e s where t h e b e a r i n g medium c o n s i s t s of sand o r g r a v e l . However, t h e t a s k of g e o c r y o l o g i s t s d o e s n o t end t h e r e and t h e e n g i n e e r i n g thought i s d i r e c t e d towards t h e u t i l i z a t i o n of t h i s method on c l a y e y and s i l t y s o i l s as w e l l , which a r e c h a r a c t e r i z e d by h i g h i c e c o n t e n t and t h e f a c t t h a t t h e y become much more compact on thawing. One of t h e most i m p o r t a n t a s p e c t s o f t h e method i n v o l v i n g p r e c o n s t r u c t i o n

thawing o f t h e ground i s t h e removal o f w a t e r from t h e thawed ground. However, i t h a s been e s t a b l i s h e d t h a t t h i s i s n o t always n e c e s s a r y , because l a r g e

volumes of c l a y e y and s i l t y s o i l s do n o t a p p e a r t o be s u p e r s a t u r a t e d w i t h w a t e r a f t e r thawing ( ~ h u k o v , 1957-a ( s i c ) ? s e e 1958-a).

The above method may be recommended f o r a r e a s w i t h patchy p e r m a f r o s t d i s t r i b u t i o n , b u t i t can be used a l s o under s e v e r e c l i n a t i c c o n d i t i o n s i f t h e s t r u c t u r a l and t h e r m a l c h a r a c t e r i s t i c s o f a b u i l d i n g i n v o l v e a t r a n s f e r of l a r g e q u a n t i t i e s o f h e a t i n t o t h e ground. An i m p o r t a n t c o n d i t i o n f o r t h e a p p l i c a b i l i t y of this method i s t h e e l i m i n a t i o n o f n a t u r a l f r e e z i n g of thawed ground once t h e s t r u c t u r e h a s been e r e c t e d .

The c h o i c e between t h e l a s t two tnethoda, a l l o t h e r c o n d i t l o n e being e q u a l , l a determined mainly by t h e c o m p r e s o i b i l i t y of f r o z e n ground on thaw- i n g . I f t h e compressibility 1s l a r g e , p r e f e r e n c e should be given t o t h e method i n v o l v i n g p r c c o n s t r u c t i o n thawing of t h e ground, i f i t i s s m a l l

-

t o t h e method i n v o l v i n g t h e a d a p t a t i o n of s t r u c t u r e d e s i g n t o d i f f e r e n t i a l s e t t l e m e n t of t h e b e a r i n g mediurn on thawing. I n some c a s e s a cornbination of both methods i s a l s o p o s s i b l e .

Apart from s p e c i a l measures of e n s u r i n g normal o p e r a t i o n of a s t r u c t u r e i n h e r e n t i n each of t h e above methods, t h e r e a r e a l s o g e n e r a l requirement8 which a p p l y t o c o n s t r u c t i o n i n permafrost r e g i o n s . We s h a l l name t h e most important of t h e s e :

( a ) Any method of e n s u r i n g t h e s t a b i l i t y of a s t r u c t u r e w i l l b r i n g p o s i - t i v e r e s u l t s o n l y i f t h e i d e a s whlch form t h e b a s i s of t h e method a r e c a r r i e d o u t i n t h e proper sequence and with utmost c a r e , and due c o n s i d e r a t i o n i s given t o environmental c o n d i t i o n s .

( b ) There should be an agreement between measures designed t o e n s u r e t h e s t a b i l i t y and s u i t a b i l i t y of a s t r u c t u r e d u r i n g a l l a t a g e s of c o n s t r u c t i o n

( p l a n n i n g s t a g e , a c t u a l c o n s t r u c t i o n work, and t h e o p e r a t i o n a l s t a g ' e ) . For example, i f i t h a s been decided t o ensure t h e s t a b i l i t y of a s t r u c t u r e by r e t a i n i n g 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 , t h e n t h i s d e c i s i o n should be t h e governing f a c t o r i n t h e s t r u c t u r a l d e s i g n , c o n s t r u c t i o n work and t h e o p e r a t i o n a l r u l e s .

( c ) There should be good agreement between t h e d e s i g n s of a d j a c e n t s t r u c t u r e s , which e x e r t t h e r m a l ' e f f e c t s on each o t h e r . For example, s p e c i a l a t t e n t i o n should be given t o t h e i n s t a l l a t i o n of underground sewers and t h e i r e n t r a n c e i n t o a b u i l d i n g b u i l t by t h e method i n v o l v i n g t h e r e t e n t i o n of 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 . Any shortcomings i n t h e d e s i g n of such i n s t a l l a t i o n a may l e a d t o a d i s t u r b a n c e of thermal c o n d i t i o n s , which i s d e t r i - mental no m a t t e r what c o n s t r u c t i o n method h a s been adopted. S t i l l more

harmful i s t h e leakage of water p i p e s l o c a t e d i n t h e v i c i n i t y of b u i l d i n g s . Contemporary e n g i n e e r i n g geocryology o f f e r s methods which enable t h e b u i l d e r s t o avoid dangerous defortnation 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 of t h e ground, and t h e s e deformations a r e g r a d u a l l y becoming a r a r e r phenomenon i n t h e e n g i n e e r i n g development of permafrost r e g i o n s . N e v e r t h e l e s s , as l o n g as deformation has not been e l i m i n a t e d com- p l e t e l y , i t i s a d v i s a b l e t h a t a l l d e s i g n e r s and b u i l d e r s become acquainted wl-th t h e most t y p i c a l of t h e s e deformations and l e a r n what c a u s e s them. T h i s

L i t e r a t u r e

Baranov, I.Ya. Purpose, p r e s e n t development and aims of g e n e r a l geocryology ( g e n e r a l permafrost s t u d i e s ) . Paper read a t t h e i n t e r d e p a r t a r n e n t a l meeting on permafrost s t u d i e s , 1956.

Baranov, I.Ya. Diagrammatic g e o c r y o l o g i c a l map of t h e U.S.S.R. Fondy i n - t a merzlotovedeniya, 1956.

Shvetsov, P.F. Basic p r i n c i p l e s of e n g i n e e r i n g methods of r e g u l a t i n g thermal and mechanical i n t e r a c t i o n of s o i l and rock on i n s t a l l i n g s t r u c t u r e s on them o r i n them. Manuscript. Fondy i n - t a merzlotov. AN SSSR, 1954. Zhukov, V.F. P r e - c o n s t r u c t i o n thawing of permafrost below t h e foundation

( a new method of c o n s t r u c t i o n ) . Izd-vo AN _{SSSR, 1958-a.}

Table I

The aims and methods of a r t i f i c i a l change of ground temperature, phenomena which occur d u r i n g such changes and t h e e f f e c t

of t h e s e phenomena on s t r u c t u r e s and o t h e r a s p e c t s of human a c t i v i t y

On c o o l i n g t h e ground when temperature drops from

p o s i t i v e t o n e g a t i v e

On c o o l i n g t h e

ground with On warming t h e ground w i t h temperature temperature r i s i n g from

remaining n e g a t i v e t o p o s i t i v e negat i v e

!

1. A i m s of a r t i f i c i a l temperature change R e t e n t i o n o f b e a r i n g media of s t r u c t u r e s i n a f r o z e n s t a t e and t h e i n c r e a s e i n t h e i r b e a r i n g s t r e n g t h . To make i t e a s i e r t o p r e v e n t water from e n t e r - i n g e x c a v a t i o n s and under- ground workings i n ground s a t u r a t e d w i t h water o r ground very permeable t o w a t e r . To make t h e hydrotechni- c a l e a r t h s t r u c t u r e s and t h e i r s u p p o r t s impermeable. The accumulation of moisture i n upper s o i l h o r i z o n s ( i n r e g i o n s where t h e moisture c o n t e n t of t h e s o l l a i s not a d e q u a t e ) . To improve b e a r i n g media c o n s i s t i n g of f r o z e n ground

.

To improve t h e w o r k a b i l i t y of t h e ground i n t h o s e

c a s e s where thawing does n o t r e s u l t i n t h e inflow of water making t h e opera- t i o n s d i f f i c u l t

.

P r e - c o n s t r u c t i o n thawing of t h e b e a r i n g medium as a method of ensuring t h e s t a b i l i t y of s t r u c t u r e s . P r o t e c t i o n of underground p i p e l i n e s i n o r d e r t o pre- vent t h e l i q u i d s and g a s e s i n t h e p i p e s from f r e e z i n g . A g r i c u l t u r a l development i n a r e a s w i t h excessive s o i l moisture content i n t h e s o u t h e r n f r i n g e of t h e permafrost r e g i o n . C _{ont inued}

-18- Table I

-

continued

On c o o l i n g t h e ground when temperature drops from

p o s i t i v e t o n e g a t i v e On c o o l i n g t h e ground w i t h temperature remaining n e g a t i v e On warming t h e ground w i t h temperature r i s i n g from n e g a t i v e t o p o s i t i v e

2. Methods and means of changing t h e temperature I n summer: by reducing t h e i n s o l a t i o n (by exposing t h e ground s u r f a c e t o and p r o t e c t i n g i t from l i g h t , c o n s t r u c t i o n of i n s u l a t i n g c o v e r ) ; c r e a t i o n of a r t i f i - c i a l and improvement of n a t u r a l e v a p o r a t i o n . I n w i n t e r : by i n c r e a s i n g r a d i a t i o n (removal of cover, d e c r e a s e i n t h i c k n e s s and i n c r e a s e i n d e n s i t y of snow c o v e r ) ; c r e a t i o n of c o l d a i r c i r c u l a t i o n over exposed ground s u r f a c e o r i n underground c o n d u i t s ; c i r c u l a t i o n of cooled b r i n e i n underground p i p e s . A t any time: c o n s t r u c - t i o n of thermal i n s u l a t i o n between t h e ground and h e a t e m i t t i n g s u r f a c e s of s t r u c - t u r e s ; c r e a t i o n of v e n t i l a - t i o n by means of a i r o r b r i n e between t h e ground and h e a t emit t i n g s u r f a c e s of s t r u c t u r e s which g i v e out l a r g e q u a n t i t i e s of h e a t

.

I n summer: by i n c r e a s i n g t h e i n s o l a t i o n (removal of v e g e t a t i o n cover, darkening of s u r f a c e ) ; by reducing t h e e v a p o r a t i o n ( d r y i n g , r i s e of h e a t t r a n s p a r e n t f i l m s )

.

I n w i n t e r : by reducing r a d i a t i o n fiy c r e a t i n g h e a t i n s u l a t i n g c o v e r s , i n c r e a s i n g t h e t h i c k n e s s of t h e snow c o v e r and making i t l e s s d e n s e )

.

A t any time: warming of f r o z e n ground by means of water, steam o r e l e c t r i c

c u r r e n t .

3 . Phenomena and p r o c e s s e s which occur with changes i n ground temperature

Heaving of ground w i t h e x c e s s i v e i c e s e g r e g a t i o n o r without i t ; formation of f r o s t mounds, ground ae t t l e m e n t l e a d i n g t o formation of f i s s u r e s , cementation of s o i l p a r t i - c l e s , rock fragments and f i s s u r e d rocks; i n c r e a s e i n s t r e n g t h o f ground (improved cohesion, g r e a t e r r e s i s t a n c e t o o u t s i d e f o r - c e s ) ; l o s s of p e r m e a b i l i t y t o f r e e rnoiature. F u r t h e r i m - provement i n s t r e n g t h of f r o z e n ground, r e d u c t i o n i n unfrozen water c o n t e n t of f r o z e n ground. Compact i o n of m i n e r a l 8011, reductio'n i n s t r e n g t h ( s h a r p d e c r e a s e i n cohesion); t h e ground becomes permeable t o f r e e m o i s t u r e . Thermo- k a r s t , s o l i f l u c t i o n , s o i l c r e e p .

-1g- T a b l e I

-

c o n t i n u e d On warming t h e ground w i t h t e m p e r a t u r e r i s i n g from n e g a t i v e t o p o s i t i v e On c o o l i n g t h e ground when t e m p e r a t u r e d r o p s from p o s i t i v e t o n e g a t i v e

4 . I n f l u e n c e of above phenomena on s t r u c t u r e s and o t h e r a s p e c t s of human a c t i v i t y On c o o l i n g t h e ground w i t h t e m p e r a t u r e remaining n e g a t i v e Uneven u p l i f t of b e a r i n g media and s t r u c t u r e s l e a d - i n g t o a d d i t i o n a l s t r e s s e s i n t h e l a t t e r , o f t e n r e s u l t i n g i n f a i l u r e ; i n c r e a s e i n s t r e n g t h and imperviousness of r o o f s and f l o o r s of underground workings, f l o o r s and w a l l s of e x c a v a t i o n s and t r e n - c h e s ; i n c r e a s e i n s t a b i l i t y and imperviousness of e a r t h w o r k s . I n c r e a s e d h e a t l o s s e s i n p i p e l i n e s , changes i n pro- p e r t i e s and s t a t e of l i q u i d s o r g a s e s i n t h e p i p e s , o c c a s i o n a l p i p e b r e a k . F u r t h e r i n - c r e a s e i n s t a - b i l i t y and imperviousness of w a l l s , r o o f s and f l o o r s of underground workings, o f w a l l s and f l o o r s of ex- c a v a t i o n s and t r e n c h e s ; f u r - t h e r i n c r e a s e i n t h e s t a b i l - i t y and imper- v i o u s n e s s of e a r t h w o r k s . D i f f e r e n t i a l s e t t l e m e n t of b e a r i n g medium l e a d i n g t o a d d i t i o n a l s t r e s s e s i n s t r u c t u r e s , i f t h e l a t t e r a r e n o t a d a p t e d t o changes i n ground c o n d i t i o n s ; f a i l u r e of w a l l s of e a r t h - w o r k s ; c o l l a p s e of under-

ground workings and i n c r e a s e d

1

i n f low of w a t e r underground; i n c r e a s e d s o i l - f o r m i n g pro- c e s s e s and improved condi- , t i o n s f o r a g r i c u l t u r e ( i n ' a r e a s w i t h e x c e s s m o i s t u r e ) .