Electrical potentials developed during thawing of frozen ground

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Electrical potentials developed during thawing of frozen ground

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Electrical Potentials Developed

During Thawing of Frozen

Ground

by V.R. Parameswaran, G.H. Johnston and J.R. MacKay

ANALYZED

Reprinted from

Proceedings of the Fourth International Symposium

on Ground Freezing

Sapporo, Japan. August 5

-

7,

1985

Vol. 1, p. 9-16

(DBR Paper No. 1339)

Price $2.50

NRCC 25201

NRC

-

ClSTi

BLOC. RES.

L I B R A R Y

86-

01-

1

5 B I S L I O T H ~ Q U E

P-ch. Btim.

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Les a u t e u r s o n t mesure l e s p o t e n t i e l s k l e c t r i q u e s p r o d u i t s l o r s du d k g e l du m o l l i s o l d a n s un s i t e e x p e r i m e n t a l s i t u 6

a

I n u v i k , d a n s l e s T e r r i t o i r e s d u N o r d - O u e s t . On a i n s t a l l 6 v e r t i c a l e m e n t d e s s o n d e s c o n t e n a n t d e s e l e c t r o d e s d e c u i v r e d i s p o s k e s 3 i n t e r v a l l e s r k g u l i e r s d a n s un t e r t r e a r g i l e u x , d a n s un s o l r i c h e e n g l a c e

B

l a j o n c t i o n d e t r o i s t e r t r e s , a i n s i que d a n s d e s t u b e s d e c a r t o n e n d u i t s d e c i r e , l ' u n r e m p l i d e g r a v i e r s a b l e u x e t l ' a u t r e d ' a r g i l e r e c o n s t i t u k , e t p l a n t e s d a n s un t e r t r e a d j a c e n t . La t e n s i o n maximale mesurge d e p a r t e t d ' a u t r e d e l a l i m i t e d e l a zone d e d k g e l e t a i t de l ' o r d r e d e 500 mV dans l e s o l f i n e t d ' e n v i r o n 200 rnV d a n s l e s o l grassier. La d i f f e r e n c e d e c o u l e p e u t - d t r e du p l u s f o r t d e g r e d ' h u m i d i t e du s o l f i n .

(4)

Fourth International Symposium on Ground Freezing /Sapporo

/ 5-7

August

1985

Electrical potentials developed during thawing

of frozen ground

V.R.PARAMESWARAN & G.H.JOHNSTON

National Research Council of Canada, Ottawa

J.ROSS MACKAY

University of British Columbia, Vancouver, Canada

ABSTRACT: E l e c t r i c a l p o t e n t i a l s d e v e l o p e d d u r i n g thawing of t h e a c t i v e l a y e r i n f r o z e n

ground have been measured a t a t e s t s i t e i n I n u v i k , Northwest T e r r i t o r i e s . P r o b e s

c o n t a i n i n g c o p p e r e l e c t r o d e s s p a c e d a t r e g u l a r i n t e r v a l s were i n s t a l l e d v e r t i c a l l y i n a c l a y hummock, i n a n i c e - r i c h s o i l a t t h e j u n c t i o n of t h r e e hummocks, and i n a sandy g r a v e l and r e c o n s t i t u t e d c l a y i n wax-coated c a r d b o a r d t u b e s p l a c e d i n a n a d j a c e n t

huunnock. The maximum v o l t a g e measured a c r o s s t h e thaw boundary was of t h e o r d e r of

500 mV i n t h e f i n e - g r a i n e d s o i l and a b o u t 200 mV i n t h e c o a r s e - g r a i n e d s o i l . The

d i f f e r e n c e may be due t o t h e l a r g e r amounts of m o i s t u r e i n t h e f i n e - g r a i n e d s o i l .

1 INTRODUCTION

E l e c t r i c a l f r e e z i n g and thawing p o t e n t i a l s have been measured d u r i n g phase changes i n aqueous s y s t e m s s u c h a s p u r e w a t e r , d i l u t e s o l u t i o n s o f i o n i c s o l u t e s , and even m o i s t s o i l s and r o c k s . T h e s e p o t e n t i a l s between t h e f r o z e n and u n f r o z e n p a r t s of t h e s y s t e m c a n a r i s e

from two d i f f e r e n t c a u s e s : from

e l e c t r i c a l c u r r e n t s and p o t e n t i a l s s p e c i f i c a l l y r e l a t e d t o t h e p h a s e change o f w a t e r , and from p o t e n t i a l s a r i s i n g o u t of c h a r g e s e p a r a t i o n d u r i n g f r e e z i n g and i o n i n c o r p o r a t i o n , commonly known a s t h e Workman-Reynolds e f f e c t . I n s o i l s , t h e o b s e r v e d p o t e n t i a l s may w e l l be a c o m b i n a t i o n of b o t h e f f e c t s . I n a d d i t i o n t o p o l a r i z a t i o n o f w a t e r m o l e c u l e s and a l i g n m e n t of d i p o l e s due t o t h e p o t e n t i a l b a r r i e r a c r o s s t h e boundary between f r o z e n and u n f r o z e n z o n e s , c h a r g e s i n h e r e n t on t h e s u r f a c e s of m i n e r a l p a r t i c l e s c a n c o n t r i b u t e t o t h e development o f p o t e n t i a l s by exchange a b s o r p t i o n p r o c e s s e s i n s o i l s . F r e e z i n g p o t e n t i a l s have b e e n r e p o r t e d i n d i l u t e aqueous s o l u t i o n s of v a r i o u s s a l t s ( s e e , f o r example. Drost-Hansen, 1967; G r o s s , 1968; Cobb and G r o s s , 1969)

,

and i n p u r e w a t e r d u r i n g f r e e z i n g ( G i l l and A l f r e y , 1952; G i l l , 1953; Murphy,

i

1970; Korkina, 1975; and Parameswaran.

1982). I n a d d i t i o n . a r e v e r s e p o t e n t i a l h a s b e e n o b s e r v e d d u r i n g m e l t i n g of i c e ( G i l l and A l f r e y , 1952). a l t h o u g h i t s magnitude was s m a l l e r t h a n t h a t o b s e r v e d d u r i n g f r e e z i n g . R e p o r t s o f o b s e r v a t i o n s of e l e c t r i c a l f r e e z e l t h a w p o t e n t i a l s i n s o i l s and r o c k s , however, a r e meagre and i n c o n -

c l u s i v e . Whereas t h e f r e e z i n g p o t e n t i a l s o b s e r v e d i n p u r e w a t e r and d i l u t e s o l u t i o n s were of t h e o r d e r of a few v o l t s , t h e magnitude of t h e p o t e n t i a l s g e n e r a t e d i n f r e e z i n g s o i l s was u s u a l l y of t h e o r d e r of a few m i l l i v o l t s o n l y

(Parameswaran and Mackay, 1983). Very

few measurements o f e l e c t r i c a l f r e e z e l t h a w p o t e n t i a l s under n a t u r a l c o n d i t i o n s have b e e n r e p o r t e d . A s i d e from work by B o r o v i t s k i i ( 1 9 7 6 ) , t h e o n l y documented measurement o f f r e e z i n g p o t e n t i a l s under n a t u r a l c o n d i t i o n s i n t h e f i e l d i s t h a t of Parameswaran and Mackay (1983). who measured p o t e n t i a l s d e v e l o p e d on c o p p e r e l e c t r o d e s a t v a r i o u s d e p t h s i n t h e a c t i v e l a y e r a t I n u v i k , N.W.T. They a l s o u s e d t h i s t e c h n i q u e t o s t u d y f r e e z i n g p o t e n t i a l s d e v e l o p e d a s p e r m a f r o s t a g g r a d e d a t t h e bottom of a n a r t i f i c i a l l y d r a i n e d l a k e on R i c h a r d s I s l a n d i n t h e Mackenzie D e l t a . Both

B o r o v i t s k i i (1976) and Parameswaran and Mackay (1983) have a l s o o b s e r v e d p o t e n t i a l s g e n e r a t e d d u r i n g t h a w i n g of f r o z e n s o i l i n t h e a c t i v e l a y e r . As a c o n t i n u a t i o n of f i e l d s t u d i e s , p r o b e s were r e c e n t l y i n s t a l l e d i n d i f f e r e n t m a t e r i a l s i n t h e a c t i v e l a y e r a t a s i t e n e a r I n u v i k , N.W.T., t o s t u d y t h e n a t u r e and magnitude of t h e

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e l e c t r i c a l p o t e n t i a l s g e n e r a t e d d u r i n g f r e e z i n g and thawing of t h e ground u n d e r n a t u r a l c o n d i t i o n s . P r e l i m i n a r y r e s u l t s from t h e i n i t i a l measurements a r e p r e s e n t e d i n t h i s p a p e r .

2

FIELD INSTRUMENTATION F i v e p a i r s of e l e c t r o d e and thermocouple p r o b e s were i n s t a l l e d i n l a t e August

1983

i n a n a r e a of c o l l u v i u m where e a r t h hummocks a r e w e l l developed ( F i g u r e 1). The e l e c t r o d e and thermocouple p r o b e s were made of PVC t u b i n g ,

20.6

mm OD,

12.7

mm I D , e a c h

2.5

m l o n g and c l o s e d a t t h e bottom. Each probe c o n s i s t e d of

14

copper e l e c t r o d e s i n t h e form of c i r c u l a r bands,

20.6

mm i n d i a m e t e r and

12.7

m wide w i t h a w a l l t h i c k n e s s of 1 mm, i n s t a l l e d i n g r o o v e s s p a c e d

150

mm a p a r t a l o n g t h e PVC t u b e . C o a x i a l c a b l e s were s o l d e r e d t o t h e e l e c t r o d e s and t h e w i r e s were l e d t h r o u g h t h e c e n t r e of t h e t u b e and c o n n e c t e d t o t h e t e r m i n a l s of a r o t a r y s w i t c h . Each thermocouple probe had

14

c o p p e r - c o n s t a n t a n thermocouples i n s t a l l e d

150

mm a p a r t a t p o s i t i o n s c o r r e s p o n d i n g t o t h o s e of t h e e l e c t r o d e s . TOWN OF INWII( F i g .

1.

L o c a t i o n of t e s t s i t e n e a r I n u v i k , N.W.T

The thermocouple w i r e s

(24

gauge, w i t h an o u t e r g l a s s f i b r e s h e a t h ) were b r o u g h t up t h r o u g h t h e c e n t r e of t h e PVC t u b e and c o n n e c t e d t o a r o t a r y s w i t c h . A p r e c i s i o n v o l t m e t e r w i t h a n i c e b a t h r e f e r e n c e j u n c t i o n was u s e d t o measure ground t e m p e r a t u r e s . P a i r s of p r o b e s were i n s t a l l e d v e r t i c a l l y s i d e by s i d e t o a d e p t h of a b o u t 1.5 m ( t h e d e p t h of t h e f r o s t t a b l e ) a t f i v e d i f f e r e n t l o c a t i o n s ( F i g u r e

1).

Probes

1, 2

and

3

were i n s t a l l e d i n augured h o l e s about

25

mm i n d i a m e t e r , w i t h t h e bottom e l e c t r o d e s below t h e l a t e August f r o s t t a b l e . Probe

1 was i n t h e middle of a hummock about

2.5

m i n d i a m e t e r and probe

2

was between t h e c e n t r e and edge of t h e hummock. Probe

3

was i n a d e p r e s s i o n a t t h e j u n c t i o n of t h r e e hummocks; much i c e was e n c o u n t e r e d when d r i l l i n g h e r e . Probes

4

and

5

were i n s t a l l e d i n open-end, w a x - c o a t e d ' c a r d b o a r d t u b e s ,

300

m i n d i a m e t e r , a t t h e c e n t r e of a n a d j a c e n t hummock. One t u b e was f i l l e d w i t h t h e l o c a l c l a y and t h e o t h e r w i t h a sandy g r a v e l b r o u g h t from a nearby borrow p i t . The c e n t r e of t h e hummock was e x c a v a t e d by hand t o t h e f r o s t t a b l e and t h e wax-coated c a r d b o a r d t u b e s were i n s t a l l e d v e r t i c a l l y and t h e n b a c k f i l l e d .

An e l e c t r o d e probe and a thermocouple probe were p l a c e d s i d e by s i d e i n t h e middle of e a c h t u b e and t h e r e s p e c t i v e s o i l s p l a c e d i n t h e t u b e s and compacted by ramming w i t h a rod. The m a t e r i a l s were t h e n s a t u r a t e d w i t h w a t e r . As t h e t u b e s were open a t t h e bottom, much o f t h e w a t e r p r o b a b l y d r a i n e d away. The f i n e - g r a i n e d c l a y m a t e r i a l would r e t a i n some m o i s t u r e , b u t t h e g r a v e l would l o s e most of i t . F i g u r e s 2 and 3 i n d i c a t e t h e l o c a t i o n s of t h e p r o b e s and t h e p o s i t i o n s of t h e e l e c t r o d e s i n e a c h probe; F i g u r e

4

shows t h e s i t e f o l l o w i n g i n s t a l l a t i o n .

3

DISCUSSION OF RESULTS

I

Although t h e p r o b e s were i n s t a l l e d i n l a t e August

1983,

no r e a d i n g s were t a k e n d u r i n g t h e f r e e z i n g p e r i o d of

1983-84.

R e g u l a r bi-weekly r e a d i n g s were begun o n l y i n June

1984.

The p o t e n t i a l (DC v o l t a g e ) a t e a c h e l e c t r o d e w i t h r e s p e c t t o t h e bottom one (number

0)

was measured u s i n g a p r e c i s i o n v o l t m e t e r . Ground t e m p e r a t u r e s were a l s o measured a t t h e d e p t h s c o r r e s p o n d i n g t o e a c h e l e c t r o d e . T y p i c a l c u r v e s showing t h e v a r i a t i o n o f v o l t a g e and t e m p e r a t u r e w i t h d e p t h below t h e ground s u r f a c e a r e p l o t t e d i n

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T H A W E D A C T I V E L A Y E R F R O S T T A B L E . L A T E A U G 1983 D I M E N S I O N S . A P P R O X I M A T E I k 0 . 5 m+

F i g . 2. Schematic diagram showing p r o b e l o c a t i o n s 1, 2 and 3 i n a hummock

D I M E N S I O N S A P P R O X I M A T E s c a l e . k O . 5 m+

F i g . 3. Schematic d i a g r a m showing probe l o c a t i o n s 3 and 4 i n a hummock F i g u r e 5 ( a t o e ) f o r t h e f i v e p r o b e l o c a t i o n s , c o v e r i n g t h e thaw s e a s o n from J u n e t o September 1984. It may b e s e e n t h a t t h e r e is a n a b r u p t change i n t h e magnitude of t h e v o l t a g e a t t h e thawing f r o n t ( a s measured by t h e e l e c t r o d e s on t h e p r o b e ) . S i n c e i o n s p r e s e n t on t h e m i n e r a l s u r f a c e s , s o i l m o i s t u r e c o n t e n t , Fig. 4. S i t e a f t e r i n s t a l l a t i o n of p r o b e s and c o n c e n t r a t i o n of i o n s i n t h e s o i l w a t e r a r e unknown v a r i a b l e s , i t was i m p o s s i b l e t o p r e d i c t t h e s i g n of t h e change i n p o t e n t i a l w i t h c o n f i d e n c e . N e v e r t h e l e s s , i t i s s i g n i f i c a n t t h a t t h e r e i s a p o t e n t i a l induced i n t h e e l e c t r o d e l o c a t e d a t t h e thawing f r o n t and t h a t i t i s q u i t e e v i d e n t i n e a c h s o i l i n v e s t i g a t e d .

The thawing p o t e n t i a l may be t a k e n a s e q u a l t o t h e d i f f e r e n c e between t h e v a l u e s of t h e v o l t a g e s on e l e c t r o d e s i n t h e f r o z e n and u n f r o z e n p a r t s of t h e ground. F o r example, a t probe 1 i n t h e c e n t r e of t h e hummock t h e i n d u c e d v o l t a g e measured o n e l e c t r o d e No. 4 ( l o c a t e d i n f r o z e n ground a t a t e m p e r a t u r e of -0.5OC) was -62 mV, whereas t h a t on e l e c t r o d e No. 5 ( a t a t e m p e r a t u r e of -0.2OC) was +445 mV ( F i g u r e 5 ( a ) ) . Thus t h e p o t e n t i a l a c r o s s t h e thawing i n t e r f a c e a t t h i s l o c a t i o n c a n be c o n s i d e r e d t o b e 507 mV. (The t e m p e r a t u r e a t which f r e e z i n g i t h a w i n g of f i n e g r a i n e d s o i l s o c c u r s i s u s u a l l y l e s s t h a n O°C, s o t h a t t h e t e m p e r a t u r e i n d i c a t e d a t e l e c t r o d e No. 5, where thawing was supposed t o o c c u r a t t h e t i m e of measurement, was -0.2OC. T h e r e may a l s o b e a n e r r o r i n t h e t e m p e r a t u r e o b s e r v a t i o n s owing t o l i m i t a t i o n s i n t h e a c c u r a c y of f i e l d measurements.) F i g u r e 5 ( b ) shows t h a t a t p r o b e 2, i n t h e same hummock, t h e

p o t e n t i a l measured between t h e f r o z e n and thawed ground was 540 mV, t h i s b e i n g t h e d i f f e r e n c e i n t h e v o l t a g e induced on e l e c t r o d e s No. 2 and 3 a t d e p t h s where t e m p e r a t u r e s were -0.2 and +0.2"C, r e s p e c t i v e l y . The magnitude o f t h e s e

(7)

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4 5 6 7 8 1.---..-. a " " -1.0 -0.5 0 0.5 D E P T H B E L O W G R O U N D S U R F A C E , m Fig. 5(a-e). Variation of voltage induced on the electrodes at different depths below the ground surface and corresponding temperature for locations 1

to 5, June-September 1984

potentials in clay is similar to the freezing potentials reported earlier by Parameswaran and Mackay (1983).

At probe 3, where much ice was

encountered during drilling, the jump in potential across the boundary between the frozen and unfrozen zones was about

200 mV (Figure 5(c)). Figure 5(d) shows that the potential measured across the thaw front in the clay in the cardboard tube at probe

4

was about 280 mV. In the gravelly material in the tube at probe 5

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t h e p o t e n t i a l a c r o s s t h e thaw boundary was 180 mV ( F i g u r e 5 ( e ) ) . Values o f t h e maximum e l e c t r i c a l p o t e n t i a l s o b s e r v e d a t t h e thawing boundary i n m a t e r i a l s a t t h e f i v e d i f f e r e n t l o c a t i o n s a r e summarized a s f o l l o w s : P o t e n t i a l a c r o s s Thawing F r o n t Probe M a t e r i a l (mV) 1 N a t u r a l c l a y 500 a t c e n t r e of a hummock 2 N a t u r a l c l a y 540 i n hummock 3 I c e - r i c h s o i l 200 a t j u n c t i o n of t h r e e hummocks

4

_{Clayey s o i l i n} ₂₈₀ waxed c a r d b o a r d t u b e 5 Sandy g r a v e l i n 180 waxed c a r d b o a r d t u b e Under n a t u r a l c o n d i t i o n s t h e f i n e - g r a i n e d , c l a y e y s o i l i n t h e middle of t h e hummock d e v e l o p e d a much l a r g e r p o t e n t i a l between f r o z e n and u n f r o z e n zones t h a n d i d t h e i c e - r i c h s o i l a t t h e j u n c t i o n of t h e hummocks. I n t h e r e c o n s t i t u t e d c o n d i t i o n a l s o , t h e f i n e - g r a i n e d , c l a y e y m a t e r i a l showed a h i g h e r p o t e n t i a l t h a n d i d t h e c o a r s e - g r a i n e d m a t e r i a l . These d i f f e r e n c e s c a n p r o b a b l y be a t t r i b u t e d t o t h e l a r g e r amounts of m o i s t u r e p r e s e n t around s o i l p a r t i c l e s i n t h e f i n e - g r a i n e d

'

s o i l . It i s n o t c l e a r w h e t h e r t h e p o t e n t i a l s measured between f r o z e n and u n f r o z e n zones d u r i n g thawing of t h e ground a r e r e a l l y thawing p o t e n t i a l s , t h e r e v e r s e of t h e f r e e z i n g p o t e n t i a l r e p o r t e d by

s e v e r a l a u t h o r s . Although B o r o v i t s k i i

( 1 9 7 6 ) a s w e l l a s Parameswaran and Mackay ( 1 9 8 3 ) have r e p o r t e d p o t e n t i a l s d e v e l o p e d i n t h e f i e l d d u r i n g thawing of t h e a c t i v e l a y e r , t h e l a t t e r have s p e c u l a t e d t h a t s u c h p o t e n t i a l s may r e s u l t when m e l t w a t e r p e r c o l a t e s downward t o t h e s t i l l - f r o z e n l o w e r l e v e l s and f r e e z e s t h e r e , c a u s i n g t h e r e p o r t e d f r e e z i n g p o t e n t i a l . T h i s

I

p o s s i b i l i t y was b a s e d on t h e o b s e r v a t i o n t h a t d u r i n g t h e summer thaw p e r i o d w a t e r

I

may m i g r a t e f r o m t h e thawed p a r t of t h e

I

a c t i v e l a y e r i n t o t h e s t i l l - f r o z e n lower

1

l a y e r s o f t h e ground t o r e - f r e e z e and i n c r e a s e t h e i c e c o n t e n t t h e r e (Cheng, 1982; Mackay, 1983; Parmuzina, 1978; W r i g h t , 1981 and 1983). G i l l and A l f r e y (1952) o b s e r v e d t h a t i n p u r e w a t e r t h e thawing p o t e n t i a l i s of s m a l l e r magnitude t h a n t h e f r e e z i n g p o t e n t i a l . Workman and Reynolds (1950) d i s c o u n t e d any p o s s i b i l i t y of a t h a w i n g p o t e n t i a l i n d i l u t e s o l u t i o n s b e c a u s e of p r i o r n e u t r a l i z a t i o n of accumulated c h a r g e s i n t h e i c e , which behaves l i k e a s e m i c o n d u c t o r . I n t h e p r e s e n t measurements, t h e magnitude of t h e o b s e r v e d p o t e n t i a l s was t h e same a s t h a t of f r e e z i n g p o t e n t i a l s o b s e r v e d e a r l i e r (Parameswaran and Mackay, 1983) i n t h e same t y p e of c l a y e y s o i l a t a n e a r b y l o c a t i o n . The d i s p u t e a s t o whether t h e r e i s a t r u e thawing p o t e n t i a l , o r w h e t h e r t h e s o - c a l l e d thawing p o t e n t i a l i s due t o m e l t w a t e r p e r c o l a t i n g downward and f r e e z i n g i n t h e s t i l l - f r o z e n lower r e g i o n s c a n p e r h a p s b e s e t t l e d by c a r e f u l l a b o r a t o r y e x p e r i m e n t a t i o n . S u i t a b l e p r o b e s might be i n s t a l l e d i n a f r o z e n s o i l t h a t i s t h e n a l l o w e d t o thaw from t h e bottom upwards, s o t h a t m e l t w a t e r c a n n o t f l o w by g r a v i t y i n t o t h e u n f r o z e n zone. A s r e a d i n g s were n o t t a k e n d u r i n g t h e f r e e z i n g p e r i o d of 1983-84, t h e v a r i a t i o n i n e l e c t r i c a l f r e e z i n g p o t e n t i a l t h a t d e v e l o p e d w i t h t i m e o n e a c h e l e c t r o d e could n o t be p l o t t e d , a s was done e a r l i e r

(Parameswaran and Mackay, 1983). The few

r e a d i n g s o b t a i n e d do i n d i c a t e , however, t h e development of f r e e z i n g p o t e n t i a l s . F i g u r e 6 shows t h e v a r i a t i o n of t h e p o t e n t i a l i n t h e i c e - r i c h s o i l a t e a c h e l e c t r o d e , probe 3, a s measured w i t h r e s p e c t t o t h e bottom e l e c t r o d e l o c a t e d i n t h e f r o z e n ground 17 October 1984. A t t h e d e p t h c o r r e s p o n d i n g t o e l e c t r o d e No. 9 , where t h e t e m p e r a t u r e of t h e

ground was a b o u t -0.3OC, t h e r e i s a n

a b r u p t p o t e n t i a l d r o p . F i g u r e 7 shows

t h e v a r i a t i o n of e l e c t r i c a l p o t e n t i a l and t e m p e r a t u r e w i t h t i m e f o r e l e c t r o d e No. 6, probe 1 , i n c l a y e y s o i l a t t h e

c e n t r e of a hummock. Between 5 and

17 O c t o b e r , when t h e ground t e m p e r a t u r e a t t h i s e l e c t r o d e dropped from +O.l°C t o

-0.05"C, t h e p o t e n t i a l i n d u c e d on t h e e l e c t r o d e jumped from a b o u t 100 t o 555 mV, i n d i c a t i n g t h e development of a f r e e z i n g p o t e n t i a l of 455 mV. It i s hoped t h a t c u r r e n t r e a d i n g s t a k e n a t r e g u l a r i n t e r v a l s w i l l e s t a b l i s h a t r e n d i n t h e development of e l e c t r i c a l p o t e n t i a l s a t t h e f r e e z e - t h a w boundary a t a l l f i v e l o c a t i o n s .

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I

P R O B E N O . 3, 84ilOlli

I

E L E C T R O D E 1 2 3 4 5 6 7 8 9 I I I I L I I I

._fl_t&_

--.-

-

--_.__.___.___I

_',

T '*, -1.0 -0.5 0 D E P T H B E L O W G R O U N D S U R F A C E , m F i g . 6. V a r i a t i o n i n v o l t a g e and t e m p e r a t u r e w i t h d e p t h f o r i c e - r i c h s o i l a t p r o b e No. 3, October 1984 S E P T O C T N O V F i g . 7. V a r i a t i o n of e l e c t r i c a l p o t e n t i a l and t e m p e r a t u r e w i t h t i m e , e l e c t r o d e No. 6 , p r o b e No. 1 , i n a c l a y e y s o i l 4 CONCLUSIONS E l e c t r i c a l p o t e n t i a l s measured d u r i n g thawing of n a t u r a l s o i l s i n t h e a c t i v e l a y e r and i n r e c o n s t i t u t e d f i n e - and c o a r s e - g r a i n e d s o i l s (by means of e l e c t r o d e and thermocouple p r o b e s a t a f i e l d s i t e i n I n u v i k ) were of t h e o r d e r of 500 mV i n a c l a y e y s o i l i n a hummock and 200 mV i n a c o a r s e - g r a i n e d s o i l p l a c e d i n a t u b e i n t h e middle of a n o t h e r hummock. I t i s p o s s i b l e t h a t w i t h r e f i n e m e n t i n equipment and methods of

measurement t h e t e c h n i q u e c a n be used t o d e t e c t t h e boundary between f r o z e n and u n f r o z e n zones i n s o i l s . From t h e magnitude of measured p o t e n t i a l s i n s o i l s i t may a l s o be p o s s i b l e t o d e t e r m i n e t h e i r t y p e and m o i s t u r e c o n t e n t . ACKNOWLEDGEMENTS The a u t h o r s e x t e n d t h e i r s i n c e r e t h a n k s t o t h e f o l l o w i n g : C. Hubbs f o r f a b r i c a t i n g t h e e l e c t r o d e and thermocouple p r o b e s i n t h e l a b o r a t o r y a t DBRINRCC, S. I r w i n , K. Champion and A. Podrouzek (summer s t u d e n t s of J.R. Mackay), who h e l p e d t o i n s t a l l t h e p r o b e s a t I n u v i k i n August 1983; J.D. O s t r i c k and h i s team a t t h e I n u v i k S c i e n t i f i c Resource C e n t r e f o r p r o v i d i n g f i e l d f a c i l i t i e s , and i n p a r t i c u l a r M. Macrae and M. Bosch f o r t a k i n g r e a d i n g s a t r e g u l a r i n t e r v a l s ;

J . C . P l u n k e t t and W.G. Cooke of DBRINRCC f o r t h e i r h e l p i n t h e f i e l d and f o r t a k i n g o c c a s i o n a l r e a d i n g s . The f i e l d work of J.R. Mackay was s u p p o r t e d by t h e G e o l o g i c a l Survey of Canada, t h e P o l a r C o n t i n e n t a l S h e l f P r o j e c t , Canada, and t h e N a t u r a l S c i e n c e s and E n g i n e e r i n g R e s e a r c h C o u n c i l of Canada. T h i s paper i s a c o n t r i b u t i o n from t h e D i v i s i o n of B u i l d i n g R e s e a r c h , N a t i o n a l R e s e a r c h C o u n c i l of Canada, and i s p u b l i s h e d w i t h p e r m i s s i o n of t h e D i r e c t o r of t h e D i v i s i o n . REFERENCES B o r o v i t s k i i , V.R., 1976. The development of i n h e r e n t e l e c t r i c a l f i e l d s d u r i n g t h e f r e e z i n g of r o c k s i n t h e a c t i v e l a y e r and t h e i r r o l e i n t h e m i g r a t i o n of t r a c e e l e m e n t s , J. Geochem. E x p l o r a t i o n , Vol. 5 , pp. 65-70.

Cheng. G., 1982. The forming p r o c e s s of t h i c k l a y e r e d ground i c e , S c i e n t i a S i n i c a ( S e r i e s B), Vol. XXV, pp. 777-788.

Cobb, A.E. and G.W. G r o s s , 1969.

I n t e r f a c i a l e l e c t r i c a l e f f e c t s o b s e r v e d d u r i n g t h e f r e e z i n g of d i l u t e e l e c t r o l y t e s i n w a t e r , J. Electrochem. Soc., E l e c t r o c h e m i c a l S c i e n c e s , Vol. 116, pp. 796-804. Drost-Hansen, W., 1967. The w a t e r - i c e i n t e r f a c e a s s e e n from t h e l i q u i d s i d e , J. C o l l o i d and I n t e r f a c e S c i . , Vol. 25, pp. 131-160. G i l l , E.W.B. and G.F. A l f r e y , 1952. P r o d u c t i o n of e l e c t r i c a l c h a r g e s on w a t e r d r o p s , N a t u r e , Vol. 169, pp. 103-104

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G i l l , E.W.B., 1953. E l e c t r i f i c a t i o n by f r e e z i n g , B r i t . J. Appl. Phys., Suppl. 2, pp. 516-519. G r o s s , G.W., 1968. Some e f f e c t s of t r a c e i n o r g a n i c s on t h e i c e / w a t e r system, j.& Advances i n Chemistry, S e r i e s 73, pp. 27-97. K o r k i n a , R.I., 1975. E l e c t r i c a l p o t e n t i a l s i n f r e e z i n g s o l u t i o n s and t h e i r e f f e c t on m i g r a t i o n , U.S. Army, CRREL, D r a f t T r a n s l a t i o n 490, 15 p. Mackay, J.R. 1983. Downward w a t e r

movement i n t o f r o z e n ground. Western A r c t i c c o a s t , Canada, Can. J. E a r t h S c i . , Vol. 20, pp. 120-134.

Murphy, E.J., 1970. The g e n e r a t i o n of e l e c t r o m o t i v e f o r c e s d u r i n g t h e f r e e z i n g of w a t e r , J. C o l l o i d and I n t e r f a c e S c i . , Vol. 32, pp. 1-11. Parameswaran, V.R., 1982. E l e c t r i c a l f r e e z i n g p o t e n t i a l s i n w a t e r and s o i l s , P r e s e n t e d T h i r d I n t e r n a t i o n a l Symposium on Ground F r e e z i n g , Hanover, New Hampshire, 7 p.

Parameswaran, V.R. and J.R. Mackay, 1983. F i e l d measurements of e l e c t r i c a l f r e e z i n g p o t e n t i a l s i n p e r m a f r o s t a r e a s , P e r m a f r o s t

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P r o c e e d i n g s F o u r t h I n t e r n a t i o n a l C o n f e r e n c e , A l a s k a , N a t i o n a l Acad. P r e s s , Washington, D.C., pp. 962-967. Paramuzina, 0 . Yu., 1978. C r y o g e n i c t e x t u r e and some c h a r a c t e r i s t i c s of i c e f o r m a t i o n i n t h e a c t i v e l a y e r ( i n R u s s i a n ) , Problemy k r i o l i t o l o g i i , No. 7, pp. 141-164. ( T r a n s l a t e d i n P o l a r Geography and Geology.

July-September, 1980, pp. 131-152.) Wright, R.K., 1981. The w a t e r b a l a n c e o f a l i c h e n t u n d r a u n d e r l a i n by p e r m a f r o s t , McGill U n i v e r s i t y , S u b a r c t i c Research P a p e r No. 33, C l i m a t o l o g i c a l R e s e a r c h S e r i e s No. 1 1 , 110 p. Wright, R.K., 1983. R e l a t i o n s h i p s between r u n o f f g e n e r a t i o n and a c t i v e l a y e r development n e a r S c h e f f e r v i l l e , Quebec, P e r m a f r o s t

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P r o c e e d i n g s F o u r t h I n t e r n a t i o n a l C o n f e r e n c e , A l a s k a , N a t i o n a l Academy P r e s s , Washington, D.C., pp. 1412-1417.

Workman, E.J. and S.L. Reynolds, 1950. E l e c t r i c a l phenomena o c c u r r i n g d u r i n g t h e f r e e z i n g of d i l u t e aqueous s o l u t i o n s and t h e i r p o s s i b l e r e l a t i o n s h i p t o t h u n d e r s t o r m e l e c t r i c i t y , P h y s i c a l Review, Vol. 78, pp. 254-259.