Principles of Geocryology (Permafrost Studies). Part II, Engineering Geocryology. Chapter VII, Particular Aspects of Mining in Thick Permafrost. p. 219-230

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

Geocryology. Chapter VII, Particular Aspects of Mining in Thick

Permafrost. p. 219-230

Bakakin, V. P.

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PREFACE

T h i s t r a n s l a t i o n i s t h e second from t h e Russian p e r m a f r o s t p u b l i c a t i o n " P r i n c i p l e s o f [)eocryology", P a r t 11 ( ~ n g i n e e r i n g Geocryoloq\. The f i r s t t r a f i s l a t i a n i n t h i s group was Chapter I.

e n t i t l e d , ' P r i n c i p l e Aspec ts of E n g i r ~ e e r i n g Geocryology (Perma- f r o s t ~ t u d i e s ) ~ ' by N . I. S a l t y k o v (TT-1215).

T h i s t r a n s l a t i o n o f Chapter

VII

by V.P. Bakakin d e s c r i b e s b r i e f l y t h e mining i n d u s t r y i n t h e n o r t h e r n and n o r t h e a s t e r n r e g i o n s o f t h e U.S.S.R. Problems imposed by p e r m a f r o s t on t h e v a r i o u s t y p e s o f mining, i n c l u d i n g open c u t , underground and p l a c e r m i n h g a r e d i s c u s s e d . The c o s t s of mining i n p e r m a f r o s t a r e a s a r e compared w i t h c o s t s i n a r e a s where t h e r e i s no p e r m a f r o s t . The c h a p t e r concludes w i t h a number of recommendations f o r improved mining p r a c t i c e and r e d u c i n g c o s t s .

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

Ottawa R.F. Legget

T i t l e :

NATIONAL RESEARCH COUNC 11, OF CANADA

Technical T r a n s l a t i o n 1217 P a r t i c u l a r a s p e c t s of mining I n t h i c k p e r m a f r o s t ( 0 s o b e n n o s t i p r o i z v o d s t v a gornykh r a b o t v moshchnoi t o l s h c h e merzlykh porod ) Author : V.P. Bakakin Reference : P r i n c i p l e s o f geocryology ( p e r m a f r o s t s t u d i e s ), P a r t 11, E n g i n e e r i n g geocryology, Chapter V I I . Academy of S c i e n c e s of t h e U.S.S.R. Moscow 1959. p.21.9-230

(Osnovy g e o k r i o l o g l i ( m e r z l o t o v e d e n i y a ) , C h a s t f v t o r a y a , Inzhenernaya g e o k r i o l o g i y a , Glava V I I . Akademiya Nauk SSSR. Moskva 1959. s .219-230)

PARTICULAR ASPECTS OF M I N I N G

IN

T H I C K PERMAFROST

1. Mining i n d u s t r y i n n o r t h e r n and n o r t h e a s t e r n r e g i o n s o f t h e U.S.S.R. 2. B r i e f d e s c r i p t i o n of n a t u r a l environment of mining o p e r a t i o n s i n p e r m a f r o s t . 3 . E f f e c t of n a t u r a l environment on t h e e f f e c t i v e n e s s and c o s t of mining o p e r a t i o n s i n p e r m a f r o s t r e g i o n s . 4 . Recomniendations and c o n c l u s i o n .

1. Mining I n d u s t r y i n Northern and N o r t h e a s t e r n Regions o f t h e U.S.S.R.

In accordance w i t h d e c i s i o n s t a k e n a t t h e 2 0 t h and t h e 2 1 s t Congresses of t h e Communist P a r t y of t h e U.S.S.R. c o n c e r n i n g l a r g e i n c r e a s e s i n t h e

p r o d u c t i o n of c o a l , o i l and o t h e r m i n e r a l r e s o u r c e s , i t i s n e c e s s a r y t o improve f u r t h e r a l l methods of mining c o n s t r u c t i o n , t o i n c r e a s e t h e e f f e c t i v e n e s s of mining o p e r a t i o n s , and t o improve t h e t e c h n o l o g y of p r i m a r y t r e a t m e n t of m i n e r a l r e s o u r c e s . In t h e n o r t h e r n and n o r t h e a s t e r n r e g i o n s o f t h e U.S.S.R. t h e s e measures w i l l have t o be c a r r i e d o u t under v e r y d i f f i c u l t and. p e c u l i a r n a t u r a l c o n d i t i o n s .

The c o n s t r u c t i o n and o p e r a t i o n of mines, r e f i n e r i e s , m e t a l l u r g i c a l p l a n t s , b u i l d i n g s f o r o r e s t o r a g e and o t h e r s t r u c t u r e s i n t h e s e r e g i o n s is

I n v a r i a b l y much more expensive t h a n under normal c o n d i t i o n s and i s o f t e n v e r y

d i f f i c u l t * .

E v i d e n t l y t h e f u t u r e development of t h e mining I n d u s t r y i n t h e n o r t h e r n r e g i o n s o f t h e U.S.S.R. w i l l s t i l l be a f f e c t e d by t h e p e c u l i a r n a t u r a l

environment.

T h e r e f o r e t h e s y s t e m a t i z a t i o n of o u r knowledge and e x p e r i e n c e In t h e

, c o n s t r u c t i o n and o p e r a t i o n o f mines under t h e s e c o n d i t i o n s i n o r d e r t o i n c r e a s e t h e g e n e r a l e f f e c t i v e n e s s o f p r o d u c t i o n methods i s one o f t h e p r i m a r y t a s k s o f geocryology and mining s c i e n c e .

The most Important d e p o s i t s o f many e c o n o m i c a l l y i m p o r t a n t m i n e r a l r e s o u r c e s a r e c o n c e n t r a t e d i n t h e enormous p e r m a f r o s t r e g i o n . The known d e p o s i t s o f c o a l amount h e r e t o 6@, mica go$, g r a p h i t e 7@, f l u o r s p a r

6 6

o f a l l d e p o s i t s i n t h e c o u n t r y . There a r e i m p o r t a n t d e p o s i t s o f t i n and t u n g s t e n . Enormously r i c h o r e and p l a c e r d e p o s i t s o f gold make t h i s r e g i o n one o f t h e most i m p o r t a n t gold d e p o s i t o r i e s i n t h e world. The known d e p o s i t s o f f e r r o u s

*

Sometimes, a c c o r d i n g t o Gubkin (1946) and Kalabin ( 1 9 5 6 ) , t h e f r o z e n s t a t e o f t h e s u r r o u n d i n g ground i s a p o s i t i v e f a c t o r , a s i s t h e c a s e , f o r example, w i t h t h e c o s t of s u p p o r t i n g s t r u c t u r e s and p r o t e c t i o n a g a i n s t w a t e r .

m e t a l s a r e r i c h and v a r i e d . The development o f diamond d e p o s i t s h a s been s t a r t e d .

The m i n e r a l d e p o s i t s developed h e r e b e f o r e World War I1 were mined mainly i n t h e upper h o r i z o n s o f p e r m a f r o s t . In t h e m a j o r i t y of c a s e s t h e open c u t method was adopted, w h i l e i n underground o p e r a t i o n s o n l y upper h o r i z o n s were mined by means of i n c l i n e d d r i f t s and s h a l l o w v e r t i c a l s h a f t s . The open c u t method i s s t i l l w i d e l y used d u r i n g t h e warm s e a s o n s . The s e a s o n a l n a t u r e o f work i s due t o s e v e r e c l i m a t e and t h e n e c e s s i t y of p e n e t r a t i n g t h e f r o z e n Q u a t e r n a r y and o t h e r u n c o n s o l i d a t e d d e p o s i t s p r i o r t o mining, which i s more d i f f i c u l t and much more e x p e n s i v e i n w i n t e r . Only d u r i n g t h e l a s t t e n y e a r s , due t o t h e i n t r o d u c t i o n o f almost t o t a l mechanization o f t h e most d i f f i c u l t t a s k s i n t h e b e t t e r developed a r e a s , a n a t t e m p t h a s been made t o keep t h e open c u t mines i n c o n t i n u o u s o p e r a t i o n , w h i l e underground mining h a s been g r a d u a l l y t r a n s f e r r e d t o t h e d e e p e r l e v e l s . T h e r e f o r e , a l t h o u g h t h e development of

m i n e r a l r e s o u r c e s of t h e r e g i o n was s t a r t e d l o n g ago, a f a i r l y complete p i c - t u r e of t e c h n i c a l a s p e c t s of mining h a s become a p p a r e n t o n l y i n t h e l a s t few y e a r s .

2 . B r i e f D e s c r i p t i o n of N a t u r a l Environment of Mining O p e r a t i o n s i n P e r m a f r o s t

While mining d e p o s i t s s i t u a t e d in p e r m a f r o s t , i t i s n e c e s s a r y t o c o n s i d e r t h e f o l l o w i n g p o i n t s :

( 1 ) d i f f i c u l t i e s involved i n mining f r o z e n ground;

( 2 ) thawing o f f r o z e n ground on p a s s i n g warm a i r through t h e workings;

( 3 )

s p e c i f i c h y d r o g e o l o g i c a l c o n d i t i o n s , which v e r y o f t e n c o m p l i c a t e mining o p e r a t i o n s

.

Depending on t h e i r mechanical composition, m o i s t u r e c o n t e n t and tempera- t u r e , i t i s 1 0 t o 1 5 t i m e s more d i f f i c u l t t o mine f r o z e n s u r f a c e d e p o s i t s t h a n thawed ground. It i s most d i f f i c u l t t o mine d e p o s i t s c o n t a i n i n g a l a r g e

number o f b o u l d e r s , a s w e l l a s f r o z e n ground w i t h p e b b l e s and r o c k d e b r i s . Mining becomes e a s i e r w i t h an i n c r e a s e i n t h e c o n t e n t o f sand p a r t i c l e s . The mining o f f i n e sand i s t h e l e a s t d i f f i c u l t , b u t a d m i x t u r e s o f s i l t and c l a y p a r t i c l e s i n t h e sand and t h e p r e s e n c e o f sandy loam i n c r e a s e t h e d i f f i c u l t i e s by 3 5

-

40$ ( ~ i g . 6 0 ) .

The e a s e o f mining o p e r a t i o n s i s g r e a t l y a f f e c t e d by t h e d e g r e e of s a t u r a t i o n of t h e f r o z e n ground w i t h i c e . The g r e a t e s t d i f f i c u l t i e s a r e encountered w i t h s u r f a c e d e p o s i t s i n which t h e p o r e s a r e c o m p l e t e l y f i l l e d w i t h i c e . A f u r t h e r i n c r e a s e i n t h e i c e c o n t e n t makes t h e mining of f r o z e n ground e a s i e r ( F i g . 6 1 ) . The e a s e of mining i s e q u a l l y a f f e c t e d by t h e thermal c o n d i t i o n s i n t h e ground. For example, a c c o r d i n g t o A . N . Z e l e n i n ( 1 9 5 0 ) ~ t h e

r e s i s t a n c e of thawed c l a y e y loam w i t h a m o i s t u r e c o n t e n t o f a b o u t 2C@ t o c u t t i n g amounts t o

5

-

7 k@;/cm2. On l o w e r i n g t h e t e m p e r a t u r e t o -l°C, t h e f o r c e n e c e s s a r y t o c u t t h e same c l a y e y loam must be i n c r e a s e d t o

50,

and a t -25OC t o 150 kg/cm2. The drop i n t e m p e r a t u r e o f sandy loam w i t h a m o i s t u r e c o n t e n t o f a b o u t 14% from -4.6 t o -25OC makes it n e c e s s a r y t o i n c r e a s e t h e c u t t i n g f o r c e by more t h a n t h r e e t i m e s . Approximately t h e same r e l a t i o n s h i p e x i s t s between t h e r e s i s t a n c e t o c r u s h i n g and t h e t e m p e r a t u r e of c l a y e y loam, when i t i s p e n e t r a t e d by an i c e wedge ( ~ i g . 6 2 ) . Judging by t h e e x p e r i e n c e o f i n d u s t r i a l concerns, i n c r e a s e d consumption o f e x p l o s i v e s o c c u r s a l s o i n mining f r o z e n bedrock.

A complex r e l a t i o n s h i p e x i s t s between t h e s t a b i l i t y of f r o z e n rock, i t s

deformation c h a r a c t e r i s t i c s , t e m p e r a t u r e , i c e c o n t e n t , and d i s p e r s i o n o f t h e m i n e r a l b a s i s . T h i s r e l a t i o n s h i p was p a r t i a l l y e x p l a i n e d i n C h a p t e r 111.

A s f a r a s s t a b i l i t y i s concerned, t h e f o l l o w i n g s u b d i v i s i o n s may be made i n mines i n t h e p e r m a f r o s t r e g i o n :

( 1 ) Q u a t e r n a r y and o t h e r s u r f a c e d e p o s i t s cemented w i t h i c e ;

( 2 ) u n d e r l y i n g zone o f m e c h a n i c a l l y weathered bedrock cemented w i t h i c e ( u p p e r zone o f w e a t h e r i n g ) ;

( 3 ) zone o f t r a n s i t i o n i n t o h o r i z o n s s i t u a t e d below t h e p e r m a f r o s t , which a r e n o t v e r y s t a b l e m e c h a n i c a l l y and o f t e n leached t o a c o n s i d e r a b l e e x t e n t . T h i s lower zone o f w e a t h e r i n g i s c h a r a c t e r i s t i c o f t h e n a t u r a l environment of t h i s r e g i o n b u t a s y e t cannot be r e g a r d e d a s a p r o d u c e r .

A s f a r a s t h e e a s e o f mining i s concerned, t h e e n t i r e c r o s s - s e c t i o n o f f r o z e n rock may be subdivided i n t o r o c k s w i t h a d i s t i n c t l a y e r e d t e x t u r e and f i s s u r e d bedrock cemented w i t h i c e . The d e g r e e of c e m e n t a t i o n of rock w i t h i c e depends on i t s r e l a t i v e i c e c o n t e n t , s i z e o f i t s a c t i v e s u r f a c e , roughness o f m i n e r a l p a r t i c l e s , g e n e r a l p o r o s i t y , and t e m p e r a t u r e . The s t a b i l i t y and e a s e o f mining r o c k i n t h e above zones a r e determined mainly by t e m p e r a t u r e and i c e c o n t e n t , t h e t h e r m a l c o n d i t i o n b e i n g t h e most I m p o r t a n t f a c t o r . By v a r y i n g i t a r t i f i c i a l l y it i s p o s s i b l e t o change t h e s t a b i l i t y of f r o z e n r o c k and s o i l and t h e s p e c i f i c e n e r g y r e q u i r e d f o r t h e i r c r u s h i n g i n m i n i n g .

The s t a b i l i t y of f r o z e n r o c k i s g r e a t l y a f f e c t e d by thawing which i s

u s u a l l y due t o t h e p a s s i n g o f warm a i r through t h e underground workings. A

t h e r m a l s t r e a m i s i n v a r i a b l y e s t a b l i s h e d between t h e a i r p a e s i n g through t h e mine and t h e s u r r o u n d i n g r o c k , and t h i s l e a d s t o a g r a d u a l i n c r e a s e i n t h e t e m p e r a t u r e o f t h e f r o z e n r o c k and t o a d e c r e a s e i n i t s i c e c o n t e n t . On t h e o t h e r hand, n a t u r a l v e n t i l a t i o n i s o f t e n accompanied by t h e c o o l i n g of r o c k and i c i n g o f underground workings. The n a t u r e and i n t e n s i t y o f t h e h e a t exchange between t h e a i r and t h e w a l l s o f underground workings depend mainly

On comparing t h e main i n d i c a t o r s shown in t h e t a b l e s i t may be s e e n t h a t

t h e o p e r a t i n g e f f i c i e n c y i n mining hard ( f = 12-14) f r o z e n r o c k i s 35 t o 50$ lower t h a n Is t h e c a s e w i t h u n f r o z e n r o c k . T h i s may be e x p l a i n e d by a s i g n i f - i c a n t i n c r e a s e i n t h e amount o f l a b o u r r e q u i r e d f o r b r e a k i n g t h e o r e , f r e e z i n g o f t h e muck and o t h e r phenomena which make t h e mining o f d e p o s i t s i n f r o z e n ground more d i f f i c u l t

.

S t i l l more i m p o r t a n t i s t h e i n c r e a s e d mechanical s t r e n g t h of f r o z e n ground mlned by t h e open c u t method. Economically f e a s i b l e mining o f f r o z e n Q u a t e r n a r y and o t h e r l o o s e s u r f a c e d e p o s i t s i s n o t p o s s i b l e w i t h o u t p r e l i m i n - a r y t r e a t m e n t i n v o l v i n g l o o s e n i n g and thawing. T h i s r e q u i r e s s u c h an enormous amount o f l a b o u r , t h a t i t i s mainly t h i s o p e r a t i o n which d e t e r m i n e s t h e oper- a t i n g e f f i c i e n c y . T h i s e x p l a i n s why t e c h n i c a l i d e a s a r e c o n t i n u o u s l y d i r e c t e d toward r e d u c i n g t h e s t r e n g t h of t h e f r o z e n s u r f a c e d e p o s i t s on t h e one hand, and on t h e o t h e r toward e s t a b l i s h i n g a t h e o r e t i c a l b a s i s f o r t h e d e s i g n o f machines c a p a b l e of o p e r a t i n g i n f r o z e n s u r f a c e d e p o s i t s w i t h o u t any p r e l i m i n -

a r y t r e a t m e n t of t h e r o c k .

The e f f e c t o f t h e f r o z e n s t a t e of t h e ground on t h e o p e r a t i n g e f f i c i e n c y

i s w e l l i l l u s t r a t e d by t h e example of d r e d g i n g . T h i s widely used and one o f t h e most up-to-date methods of open c u t mining i s n e v e r t h e l e s s g r e a t l y a f f e c t e d by a v a r i a t i o n i n o p e r a t i n g c o n d i t i o n s .

The e f f i c i e n c y of 2 1 0 - l i t r e c a p a c i t y dredges o p e r a t i n g i n unfrozen a l l u v i a l d e p o s i t s amounts on t h e a v e r a g e t o about 1,200,000 m 3 o f r o c k p e r y e a r , w h i l e i n f r o z e n ground, a l l o t h e r c o n d i t i o n s b e i n g e q u a l , i t r e a c h e s o n l y 50,000

-

850,000 m3, 1 . e . a b o u t 50$. T h i s makes mining two t o two-and-a- h a l f t i m e s more e x p e n s i v e .

The f r o z e n s t a t e of t h e ground a l s o a f f e c t s o t h e r methods o f open c u t mining. A s f a r a s e f f i c i e n c y i s concerned, e x c a v a t i o n i n p e r m a f r o s t r e g i o n s i n v o l v i n g p r e l i m i n a r y l o o s e n i n g o f t h e ground i s a l m o s t e q u a l t o manual l a b o u r r e q u i r e d f o r mining t h e same ground i n t h e u n f r o z e n s t a t e , while t h e c o s t of p r e l i m i n a r y l o o s e n i n g a l o n e i s a l ~ o s t always h i g h e r t h a n t h e c o s t o f e x c a v a t -

i n g t h e same r o c k i n t h e u n f r o z e n s t a t e .

The e x c a v a t i o n and o t h e r mechanized methods of open c u t mining i n t h e s e r e g i o n s a r e more economical i f t h e y i n v o l v e thawing u n d i s t u r b e d f r o z e n ground. The e f f i c i e n c y o f p r e l i m i n a r y l o o s e n i n g and thawing may be compared by

examining T a b l e XLVII which shows t h e c o s t s o f t h e s e o p e r a t i o n s c a l c u l a t e d from a c t u a l examples. They i n d i c a t e t h a t thawing i s c h e a p e r t h a n loosening*.

*

According t o Kalabin ( 1 9 4 6 ) , t h e c o s t o f l o o s e n i n g 1 m3 of ground by

e x p l o s i v e s i n t h e S o v i e t N o r t h e a s t amounts t o 12 r u b l e s o r more, t h e c o s t of thawing by means o f steam j e t s i s 4.35 r u b l e s and by d r a i n a g e 1.45 r u b l e s .

-

E d i t o r .

The c o s t of p r e p a r i n g t h e ground f o r mining v a r i e s g r e a t l y , e s p e c i a l l y

i f t h i s i n v o l v e s p r e l i m i n a r y l o o s e n i n g by means of e x p l o s i v e s . The g e n e r a l r e l a t i o n between t h e c o s t o f mining, t h e t h i c k n e s s o f t h e p e r m a f r o s t l a y e r b e i n g mined and t h e method of p r e p a r i n g t h e ground i s shown g r a p h i c a l l y on F i g . 63, which i s based on a c t u a l d a t a from mechanized open c u t o p e r a t i o n s i n t h e S o v i e t N o r t h e a s t . I r r i g a t i o n w i t h warm w a t e r i s a l m o s t always much

c h e a p e r t h a n p r e l i m i n a r y l o o s e n i n g o r thawing a t d e p t h , b u t t h e l o n g time i t t a k e s t o c a r r y o u t t h i s o p e r a t i o n i s an I m p o r t a n t drawback.

The n e x t i m p o r t a n t f a c t o r a f f e c t i n g t h e o p e r a t i n g e f f i c i e n c y i n open c u t mining and o t h e r s u r f a c e o p e r a t i o n s is t h e s e v e r e c l i m a t e .

A t p r e s e n t , t h e immediate e f f e c t o f t h i s f a c t o r on t h e o p e r a t i n g

e f f i c i e n c y of man i s determined by a nominal i n d i c a t o r of s e v e r i t y o f weather comprising t h e e f f e c t of a i r t e m p e r a t u r e and wind. According t o S.V. Trofimov, t h e l o s s o f working time due t o s e v e r e weather, amounts i n n o r t h e r n r e g i o n s t o

335, which cannot be regarded a s an e x a g g e r a t i o n . The nominal i n d i c a t o r of s e v e r i t y of weather h a s a d i r e c t b e a r i n g o n l y on t h e o p e r a t i n g e f f i c i e n c y of man and does n o t a c c o u n t f o r many o t h e r e f f e c t s of s e v e r e c l i m a t e , such a s g r e a t e r d i f f i c u l t i e s i n o p e r a t i n g p r e s e n t - d a y mining machines, f r e e a i n g of v a r i o u s t r a n s p o r t a t i o n f a c i l i t i e s , more d i f f i c u l t w a t e r s u p p l y , e t c . Due t o low a i r t e m p e r a t u r e i n w i n t e r , i t i s n e c e s s a r y t o d r y compressed a i r by a r t i - f i c i a l means and t o p r o t e c t a i r l i n e s and v a r i o u s w a t e r l i n e s from f r e e z i n g . Muck, o r e and moist c o n c e n t r a t e s may f r e e z e on prolonged s t o r a g e on t h e

s u r f a c e , o r i n t h e mine, and d u r i n g t r a n s p o r t a t i o n . I n t h e m a j o r i t y o f c a s e s s t o r a g e in b i n s i s p o s s l b l e o n l y i f t h e l a t t e r a r e p r o p e r l y h e a t e d , o r a f t e r p r e l i m i n a r y d r y i n g o f o r e and c o n c e n t r a t e s . S p e c i a l measures have t o be adopted t o overcome d i f f i c u l t i e s a r i s i n g d u r i n g c o n s t r u c t i o n and o p e r a t i o n of r a i l r o a d s , h y d r o t e c h n i c a l s t r u c t u r e s , rams, head frames, h o i s t s , compressors, h e a t i n g i n s t a l l a t i o n s , e t c

.

A l l t h i s makes mlning o p e r a t i o n s more d i f f i c u l t and g r e a t l y i n c r e a s e s c o n s t r u c t i o n c o s t .

For example, t h e i n s t a l l a t i o n o f w a t e r l i n e s i n p e r m a f r o s t r e g i o n s i s two t o t h r e e t i m e s more e x p e n s i v e t h a n i s t h e c a s e under normal c o n d i t i o n s

( T a b l e x L V I I I )

.

The c o s t o f i n s t a l l i n g h e a t i n g networks on t h e s u r f a c e i n c r e a s e s i n a p p r o x i m a t e l y t h e same p r o p o r t i o n . The c o s t o f t h e i r i n s t a l l a t i o n d u r l n g c o n s t r u c t i o n o f r e f i n e r i e s w i t h d a i l y c a p a c i t i e s of 500 and 1000 t o n s i s

shown on Table XLIX.

A t p r e s e n t , t h e e r e c t i o n o f h y d r o t e c h n i c a l s t r u c t u r e s n e c e s s a r y f o r a mine and r e f l n e r y w i t h a d a i l y c a p a c i t y o f 1000 t o n s i s more t h a n t w i c e a s e x p e n s i v e i n p e r m a f r o s t a r e a s a s Is t h e c a s e o u t s i d e t h i s t e r r i t o r y ( w i t h o u t

t a k i n g i n t o c o n s i d e r a t i o n t h e c o s t of i n s t a l l a t i o n s f o r r e g u l a t i n g t h e o u t f l o w o f w a t e r ) .

In e v a l u a t i n g mining c o n d i t i o n s i n t h e p e r m a f r o s t r e g i o n many a u t h o r s assume t h a t t h e f r o z e n s t a t e of o r e and s p e c i f i c h y d r o g e o l o g i c a l c o n d i t i o n s a r e f a c t o r s which make b r e a k i n g and 3 l u s h i n g e a s i e r . T h i s p o i n t of view i s e x p l a i n e d l a r g e l y by t h e f a c t t h a t u n t i l r e c e n t l y mainly t h e upper o r e h o r i z o n s were mined i n t h e p e r m a f r o s t r e g i o n . In f a c t , i n t h e i n i t i a l p e r i o d o f opera- t i o n of s m a l l mines, a l l e n g i n e e r i n g s t r u c t u r e s remained s t a b l e and were d i s - t u r b e d o n l y by g r a d u a l and u r ~ a v o i d a b l e changes i n t h e r m a l c o n d i t i o n s i n t h e f r o z e n rock. A more o b j e c t i v e e v a l u a t i o n of n a t u r a l c o n d i t i o n s i n t h i s r e g i o n may be found i n t h e g e n e r a l sununaries o f i n d u s t r i a l e x p e r i e n c e i n l a r g e r mines, and e s p e c i a l l y i n i n s t a n c e s where underground workings r e a c h t h e o r e h o r i z o n s

l y i n g below t h e permafrnost. I n long-term o p e r a t i o n s , a g r a d u a l warming up of s u r r o u n d i n g r o c k i n t h e mines, which is due f i r s t o f a l l t o v e n t i l a t i o n w i t h h e a t e d a i r , sometimes makes i t moat d i f f i c u l t and e x p e n s i v e t o m a i n t a i n under- ground workings i n an o p e r a t i n g c o n d i t i o n . The a s s e r t i o n t h a t i n t h e perma- f r o s t r e g i o n h y d r o g e o l o g i c a l c o n d i t i o n s f a v o u r t h e mining o p e r a t i o n s i s n o t based on f a c t . A c o n s i d e r a b l e i n f l o w of w a t e r has been noted i n many mines i n t h e n o r t h e r n and t h e n o r t h e a s t e r n p a r t s o f t h e U.S.S.R. F o r e i g n l i t e r a t u r e c o n t a i n s r e f e r e n c e s t o t h e i n f l o w of w a t e r i n underground workings c u t t h r o u g h f r o z e n r o c k i n t h e mines o f Alaska and Canada. On comparing a l l t h i s informa- t i o n i t becomes obvious t h a t t h e e x i s t i n g i d e a s c o n c e r n i n g t h e e f f e c t o f hydro- g e o l o g i c a l c o n d i t i o n s on mining o p e r a t i o n s i n t h i s r e g i o n a r e n o t c o n s i s t e n t . It i s t r u e t h a t i n extreme n o r t h e r n r e g i o n s w i t h a thiclc l a y e r o f p e r m a f r o s t t h e f r o z e n s t a t e of t h e rock i s indeed a f a c t o r which makes i t somewhat e a s i e r t o s u p p o r t t h e underground workings and sometimes p r o t e c t s them from t h e i n - flow o f groundwater, i f mining does n o t s t r e t c h o v e r a l o n g p e r i o d o f time and I n v o l v e s s i n k i n g of s h a l l o w s h a f t s o n l y . However, t h e p e r m a f r o s t p r o t e c t s t h e underground workings from ground and s u r f a c e w a t e r o n l y t e m p o r a r i l y and n o t always a t t h a t .

A s t i m e s goes on and t h e mine becomes d e e p e r , t h e t h e r m a l c o n d i t i o n s o f t h e f r o z e n r o c k change and d e f o r m a t i o n o f t h e e n t i r e s u r f a c e l a y e r t a k e s p l a c e , which i s o f t e n accompanied by s u b s i d e n c e o r a c a v e - i n . I n many c a s e s t h e

c o l l a p s e d f r o z e n rock thaws t o a c o n s i d e r a b l e d e p t h and t h e c a v e - i n zone

becomes an enormous r e s e r v o i r f i l l e d w i t h underground w a t e r , which c o n t i n u o u s l y p e n e t r a t e s t h e workings lower down.

blhen t h e t e m p e r a t u r e o f t h e r o c k i s n e g a t i v e , t h e w a t e r e n t e r i n g t h e underground workings f r e e z e s , v ~ h i c h a l s o c o m p l i c a t e s m a t t e r s and, a s may be s e e n from Table XX, a c o n s i d e r a b l e amount o f l a b o u r i s r e q u i r e d t o c l e a r t h e workings and e s p e c i a l l y t h e t r a c k s from i c e .

The a s s e r t i o n t h a t n e g a t i v e r o c k t e m p e r a t u r e may g r e a t l y reduce d u s t f o r m a t i o n and p r e v e n t t h e e s c a p e of underground g a s i s most d o u b t f u l . The f a c t t h a t many mines I n t h e p e r m a f r o s t r e g i o n a r e now c o n s i d e r e d u n s a f e be- c a u s e o f d u s t and e s p e c i a l l y g a s s p e a k s f o r i t s e l f .

4. Recommendations and Conclusion

It may be s e e n from t h e p r e c e d i n g s e c t i o n s t h a t t h e n a t u r a l environment o f mining o p e r a t i o n s i n t h e n o r t h e r n and n o r t h e a s t e r n r e g i o n s o f t h e U.S.S.R.

i s n o t o n l y complex and v e r y v a r i e d , b u t i n t h e m a j o r i t y o f c a s e s a l s o

u n f a v o u r a b l e . We a r e n o t y e t i n a p o s i t i o n t o e v a l u a t e c o m p l e t e l y t h e e f f e c t o f t h e environment, e s p e c i a l l y i n t h e c a s e o f mining underground. Neverthe- l e s s , i t i s c l e a r t h a t w h i l e mining underground, i t i s a b s o l u t e l y i m p e r a t i v e t o m a i n t a i n t h e n a t u r a l t h e r m a l c o n d i t i o n s o f t h e f r o z e n r o c k by any f e a s i b l e means and a t t i m e s even lower t h e t e m p e r a t u r e of t h e r o c k in t h e upper h o r i - zon. T h i s measure h e l p s t o m a i n t a i n t h e s t a b i l i t y o f t h e f r o z e n r o c k in

underground workings, t o i n c r e a s e t h e s t r e n g t h of r o c k l e f t i n t h e r o o f and t h e p i l l a r s , and t o p r o t e c t them from s u r f a c e and underground w a t e r .

In o r d e r t o e l i m i n a t e o r a t l e a s t reduce t h e a f t e r - e f f e c t s o f thawing i n t h e mine, i t i s recommended t o a d o p t t h e most s i m p l e methods which would make i t p o s s i b l e t o r e t a i n t h e n a t u r a l t h e r m a l c o n d i t i o n o f t h e p e r m a f r o s t above t h e f i r s t o r e h o r i z o n . T h i s makes i t n e c e s s a r y :

( 1 ) t o r e t a i n t h e v e g e t a t i o n and s o i l c o v e r i n t h e mining a r e a ;

( 2 ) t o make c e r t a i n t h a t no s t r u c t u r e s a r e e r e c t e d i n t h e mining a r e a which could be i n s t a l l e d beyond t h e l i m i t s o f t h e mine;

( 3 ) t o remove t h e snow c o v e r from t h e zone o f a p o s s i b l e c a v e - i n w i t h t h e a r r i v a l o f v e r y c o l d weather; ( 4 ) i n t h e summer t o i n s u l a t e a l l workings l e a d i n g t o t h e s u r f a c e , e x c e p t t h o s e which a r e a b s o l u t e l y e s s e n t i a l ;

( 5 ) i n t h e w i n t e r t o i n c r e a s e t h e v e n t i l a t i o n o f t h e mine s e c t i o n

d e s t i n e d f o r c o o l i n g by means o f a d i r e c t i n f l o w o f a i r from t h e s u r f a c e ;

( 6 )

i f n e c e s s a r y , t o b u i l d up i c e r e s e r v e s i n t h e worked-out s e c t i o n s i n t h e w i n t e r by means o f i n c r e a s e d i n f l o w o f v e n t i l a t i o n a i r and t o i s o l a t e t h e s e s e c t i o n s from o t h e r mine workings, e t c .

I n open c u t o p e r a t i o n s , t h e most i m p o r t a n t f a c t o r i s t h e d e c r e a s e i n t h e amount o f e n e r g y r e q u i r e d f o r b r e a k i n g t h e ground. The b e s t and most economi- c a l methods o f r e d u c i n g t h e rock s t r e n g t h i s i r r i g a t i o n w i t h warm water, which makes i t p o s s i b l e t o c r e a t e f a v o u r a b l e mining c o n d i t i o n s f o r mechanized open c u t o p e r a t i o n s . A s f a r a s mining i n p e r m a f r o s t w i t h o u t p r e l i m i n a r y t r e a t m e n t o f r o c k i s concerned, i t may be concluded t h a t a t p r e s e n t t h i s t y p e o f

o p e r a t i o n i s p o s s i b l e o n l y w i t h s p e c i a l l y designed nnchines equipped w i t h powerful c u t t e r s .

A t p r e s e n t , t h e p r e v e n t i o n of d e e p s e a s o n a l f r e e z i n g of s u r f a c e d e p o s i t s , which g r e a t l y r e d u c e s t h e g e n e r a l e f f l c l e n c y o f e x c a v a t i o n machines, s h o r t e n s

t h e o p e r a t i o n a l p e r i o d and c o m ~ l i c a t e s a l l a s p e c t s of open c u t mining, i s achieved by means of i n s u l a t i n g covexls of v a r i o u s t y p e s . It should be noted t h a t t h e s e c o v e r s a r e e f f e c t i v e o n l y i f t h e y a r e i n s t a l l e d a t t h e end of t h e suinmer o r in t h e very e a r l y f a l l . Apart from a p r o t e c t i o n o f s u r f a c e l a y e r s from t h e c o l d , a l e s s economical thawing o f ground undergoing s e a s o n a l

f r e e z i n g i s a l s o w i d e l y used i n t h e e a r l y s p r i n g i n mechanized mining opera- t i o n s i n t h e r e g i o n ( C h a p t e r V ) .

I n open c u t o p e r a t i o n s , s p e c i a l a t t e n t i o n should be g i v e n t o t h e p r e p a r a - t i o n of t h e mining a r e a , 1 . e . d r a i n a g e of swanpy a r e a s , removal of i c i n g s , s o l l f l u c t i o n and s o i l c r e e p , e t c . The p r e v e n t i o n of t h e s e n a t u r a l phenomena i n p e r m a f r o s t a r e a s requires l a r g e s u n s of money.

Let u s a l s o mention t h e mixed method of mining, which I n v o l v e s open c u t o p e r a t i o n s a t f i r s t and underground mining o f lower h o r i z o n s l a t e r . T h i s method i s n o t always f e a s i b l e i n p e r m a f r o s t a r e a s because even d u r i n g t h e open

c u t s t a g e t h e thernml c o n d i t i o n of t h e f r o z e n ground i s g r e a t l y d i s t u r b e d o v e r a l a r g e a r e a .

On t r a n s f e r r i n g t h e o p e r a t i o n s underground, t h i s d i s t u r b a n c e i s i n t e n s i - f i e d s t i l l f u r t h e r because o f v e n t i l a t i o n , and t h e thawing p r o c e s s b e g i n s t o p e n e t r a t e s t i l l d e e p e r o r e h o r i z o n s . A s t h e t e m p e r a t u r e of f r o z e n ground i n t h e o r e zone i s i n c r e a s e d , a l l mining c o n d i t i o n s b e g i n t o change a l s o .

S p e c i a l a t t e n t i o n should be g i v e n t o t h e f i l t r a t i o n c a p a c i t y of Q u a t e r n a r y d e p o s i t s and u n d e r l y i n g f i s s u r e d bedrock, which reaMned impermeable w h i l e f r o z e n . T h i s v e r y i m p o r t a n t p r o p e r t y d i s a p p e a r s on thawing, s o t h a t t h e mine b e g i n s t o be f i l l e d w i t h s t e a d i l y i n c r e a s i n g volumes o f w a t e r , which e a s i l y e n t e r t h e underground workings t h r o u g h t h e thawed s u r f a c e d e p o s i t s and f r a c t u r e d bedrock ( F i g . 6 4 ) .

I n t h e worked-out s e c t i o n s i n t h e caved-in zone, which i n time w i l l

r e a c h t h e s u r f a c e , t h e r e a r e c r e a t e d a l l n e c e s s a r y c o n d i t i o n s f o r t h e accunlu- l a t i o n of s u r f a c e w a t e r and w a t e r from t h e l a y e r s above t h e p e r m a f r o s t , which w i l l f l o o d a l l o r e h o r i z o n s . Because of t h i s , i t i s n o t recommended t o

commence mining of l a r g e d e p o s i t s l y i n g e i t h e r p a r t i a l l y o r e n t i r e l y i n perma- f r o s t by t h e open c u t method, and i n underground mining t o l e a v e t h e worlced- o u t s e c t i o n s unf l l l e d .

The p e c u l i a r i t i e s of mining o p e r a t i o n s d e s c r i b e d above w i l l s e t t h e g e n e r a l t r e n d of f u t u r e i n v e s t i g a t i o n . Without a d e t a i l e d s t u d y of t h e s e p e c u l i a r i t i e s i t i s n o t p o s s i b l e t o form a c o r r e c t o p i n i o n on t h e e f f e c t of

r e g i o n a l environment on such lmportant mining problems a s t h e choice of t h e r i g h t methods of exposing and mining t h e d e p o s i t . It i s a l s o very important t o s t u d y i n d i v i d u a l mining o p e r a t i o n s , such a s d r i l l i n g and b l a s t i n g , methods of s u p p o r t i n g underground workingn i n permafrost, v e n t i l a t i o n , w a t e r d r a i n a g e , and compression equipment, a s well. an t o d e s i g n t h e most economical methods of p r e v e n t i n g t h e o r e , c o a l and rock from f r e e z i n g i n s t o r a g e dumps and b i n s . The g e n e r a l t r e n d of i n v e s t i g a t i o n s should be d i r e c t e d towards u n d e r s t a n d i n g how t o r e g u l a t e t h e thermal p r o c e s s e s , s i n c e o n l y a complete e v a l u a t i o n of t h e h e a t exchange t a k i n g p l a c e on t h e s u r f a c e and underground w i l l make i t p o s s i b l e t o form a s c i e n t i f i c b a s i s f o r t h e s o l u t i o n of e n g i n e e r i n g problems, concerning open c u t and underground mining, p r o t e c t i o n of s u r f a c e d e p o s i t s from deep

w i n t e r f r e e z i n g , p r e p a r a t i o n of mining a r e a s , and o t h e r lmportant a s p e c t s of mining.

References

Gubkln, N.V. Permafrost hydrogeology and t h e c o n s t r u c t i o n of mine s h a f t s i n t h e Okhotsko-Kolymkii K r a i . Kolyma, No.8, 1946.

Kalabin, A . I . Permafrost s t u d i e s i n t h e development of t h e n o r t h e a s t . Sb. D a l ' s t r o y a , Magadanakoe knizhnoe i z d a t e l ' s t v o , 1956.

Zelenin, A.N. P h y s i c a l a s p e c t s of t h e t h e o r y of c u t t i n g of s o i l s . Izd-vo

AN SSSR, 1950. Table XLV Operating e f f i c i e n c y of mines i n m3 p e r s h i f t i n t h e overhead system of mining Type Of work D r i l l e r Mine l a b o u r e r Drop i n e f f i c i e n c y , $ 37 45 I n t h e mine In perrna- f r o s t a r e a s 1.65 0.22 Outside perma- f r o s t a r e a s 2.60 0.40

Table XLVI

-

Operating e f f i c i e n c y of mines i n m 3 p e r s h i f t i n shrinkage mining Table XLVII Type Of D r i l l e r Mine l a b o u r e r Range i n c o s t of p r e p a r i n g ground by loosening and thawing a t depth, $

*

Due t o t h e i n c r e a s e i n c o s t of excavation and t r a n s p o r t a t i o n . Drop i n e f f i c i e n c y , $ 33 48 In t h e mine

Method of excavation and t r a n s p o r t a t i o n

Dragline with 1 . 9 1 m 3 bucket and dump c a r Mechanical s h o v e l with 1.91 m3bucket and dump

c a r

Mechanical shovel with 0.57 m3 bucket and t r u c k s

Table X L V I I I

Cost of one running metre of a water l i n e on i n s t a l l i n g s t e e l p i p e s a t a de t h of up t o 3 metres ( i n r u b l e s ? I n perma- f r o s t a r e a s 2.85 0.43 Outside perma- f r o s t a r e a s 4.24 0.83 I n c r e a s e in c o s t of p r e p a r i n g ground f o r mining by Loosening 40

-

300 50

-

400 25

-

210 Location of c o n s t r u c t i o n I n permafrost a r e a s Outside permafrost a r e a s Thawing a t depth 30

-

150 40

-

160 20

-

80*

Pipe diameter, mm 1000

-

900 1520

-

1140 745

-

640 600

-

500 745

-

625 358

-

286 450

-

350 530

-

430 255

-

206 200

-

150 300

-

260 105

Table XLIX Cost of i n s t a l l i n g h e a t i n g networks on t h e s u r f a c e d u r i n g c o n s t m c t i o n o f r e f i n e r i e s (thousand r u b l e s ) Table L Amount of l a b o u r r e q u i r e d t o c l e a r mine workings and t r a c k from i c e

( from d a t a s u p p l i e d by s p e c i a l Chief ~ d m i n i s t r a t i o n ) Increase i n c o s t ,

5

260 200 Opera t i n g c a p a c i t y of r e f i n e r y , 500 1000 Cost of h e a t i n g network Main i n d i c a t o r s 1. Length of t r a c k ( i n $ of l e n g t h o f t r a c k i n d r i f t NO. 1 )

...

2 . Labour r e q u i r e d t o c l e a r

and maintain workings ( i n man-days ) : ( a ) f o r 100 m of h o r i z o n t a l workings p e r y e a r

.

. .

.

.

( b ) I n $ of t o t a l amount o f l a b o u r r e q u i r e d f o r t h e s e c t i o n a s a whole

. .

. .

In perma- f r o s t a r e a s 123 0 1520 Outside perma- f r o s t a r e a s 470 780 S e c t i o n S h a f t No. 1

80

463 15.6 D r i f t No. 1 100 470 20 D r i f t No. 2 88 455 15

F i g . 60

The e f f e c t of mechanical composltlon o f f r o z e n f r i a b l e ground on t h e amount o f l a b o u r r e q u i r e d f o r mining i t n

-

sand c o n t e n t , $ b

-

amount o f r e q u i r e d l a b o u r , m i n / m 3 F i g . 61 The e f f e c t of m o i s t u r e c o n t e n t o f f r o z e n c l a y e y loam on t h e e a s e o f b r e a k i n g i t a t 3 = - 7 . 5 O C . Dimensions of wedge: n =

60

mrn, 1 = 60 mm, a = 30'; d

-

amount of energy r e q u i r e d f o r b r e a k i n g , ke/m3; v

-

amount of c l a y e y loam o f g i v e n m o i s t u r e c o n t e n t broken o f f w i t h wedge, cm3

F i g . 62

R e l a t i o n between amount of work s p e n t during p e n e t r a t i o n of wedge and temperature of

clayey loam with moisture c o n t e n t of

1.9

-

2C$ Dimensions of wedge: 1 =

60

mrn a =

30"

Thickness OF layer, m F i g . 63 R e l a t i o n between c o s t of mining f r o z e n ground and t h i c l m e s s of l a y e r s being

prepared f o r mining and method of p r e p a r a t i o n

1

-

i r r i g a t i o n with warm water; 2

-

loosening by b l a s t i n g i n b l a s t h o l e s ;

F i g .

64

Destruction o f natural rock t e x t u r e on f r e e z i n g and subsequent thawing o f