Field measurements of electrical freezing potentials in permafrost areas

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FIELD MEASUREMENTS OF ELECTRICAL FREEZING POTENTIALS

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by V.R. Parameswaran and J.R. Mackay

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Permafrost: Fourth International Conference

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Reprinted from:

Permafrost: Fourth International Conference, Proceedings

ISBN

0-309-03435-3 National Academy Press Washington,

D.C.

1983 FIELD MEASUREMENTS OF ELECTRICAL

FREEZTNG POTENTIALS I N PERMAFROST AREAS V. R. parameswaranl and J. R. Mackay2

l ~ i v i s i o n of Building Research, National Research Council Canada, Ottawa, Ontario, Canada KIA OR6 2 ~ e p a r t m e n t of Geography, U n i v e r s i t y of B r i t i s h Columbia, Vancouver, B r i t i s h Columbia, Canada V6T 1W5

E l e c t r i c a l p o t e n t i a l s developed d u r i n g f r e e z i n g of n a t u r a l s o i l s have been measured i n two permafrost areas: one i n a s a t u r a t e d sand i n a d r a i n e d l a k e ( I l l i s a r v i k ) on Richards I s l a n d where permafrost was aggrading downward 5.65 m below ground; t h e o t h e r , i n a mud hummock i n t h e a c t i v e l a y e r a t Inuvik. Peak p o t e n t i a l s of up t o 1350 mV were measured on e l e c t r o d e s l o c a t e d on t h e advancing f r e e z i n g f r o n t a t I l l i s a r v i k . A t I n u v i k , maximum f r e e z i n g p o t e n t i a l s of up t o 700 mV were measured a s t h e a c t i v e l a y e r f r o z e i n winter. There was a l s o evidence of downward water m i g r a t i o n and f r e e z i n g a s t h e ground s t a r t e d t o thaw a t t h e s u r f a c e i n spring.

INTRODUCTION

The phenomenon of 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 of aqueous s o l u t i o n s and o t h e r systems such a s moist s o i l s has been known f o r some time, although t h e e x a c t mechanism of

development is not f u l l y understood. S e v e r a l p l a u s i b l e e x p l a n a t i o n s have been proposed f o r pure water and d i l u t e aqueous s o l u t i o n s , but no such theory has been suggested f o r s o i l s .

When water f r e e z e s on t h e s u r f a c e of a s o l i d , t h e d i p o l e f i e l d of t h e o r i e n t e d w a t e r molecules i n t h e i n i t i a l i c e l a y e r causes r o t a t i o n and

r e o r i e n t a t i o n of t h e molecules i n t h e l i q u i d a d j a c e n t t o t h e i c e . An e l e c t r i c a l double-layer of a few nanometers i s formed a t t h e i n t e r f a c e between t h e f r o z e n and unfrozen p a r t s . It behaves l i k e a semipermeable membrane, allowing one k i n d of charge t o pass through more r e a d i l y than t h e o t h e r , and c a u s e s s e l e c t i v e i n c o r p o r a t i o n of a n e x c e s s charge of one s i g n i n t h e f r o z e n p a r t and an e q u a l and o p p o s i t e charge i n t h e unfrozen p a r t . The p o t e n t i a l developed i n t h i s way i s commonly c a l l e d t h e

f r e e z i n g e l e c t r i c a l p o t e n t i a l . During f r e e z i n g , t h e r e is a tendency f o r water t o migrate t o t h e f r e e z i n g f r o n t , and t h u s s e v e r a l e l e c t r o k i n e t i c e f f e c t s (such a s e l e c t r o p h o r e s i s , electro-osmosis, streaming p o t e n t i a l , and sedimentation p o t e n t i a l ) may a l s o a r i s e a s a r e s u l t of t h e r e l a t i v e motion between w a t e r and s o l i d phase.

E a r l y measurements of f r e e z i n g p o t e n t i a l s were c a r r i e d o u t i n water and i n d i l u t e aqueous s o l u t i o n s c o n t a i n i n g d i f f e r e n t kinds of i o n s , f o r example, a l k a l i metals, ammonia, halogens, and hydroxyl i o n s

( f o r e a r l y r e f e r e n c e s , s e e Parameswaran 1982). The e a r l y i n v e s t i g a t i o n s showed t h a t t h e magnitude and s i g n of t h e f r e e z i n g p o t e n t i a l depend upon v a r i o u s f a c t o r s , i n c l u d i n g t h e t y p e of i o n i n s o l u t i o n , t y p e and d i s t a n c e between e l e c t r o d e s , c o n c e n t r a t i o n of e l e c t r o l y t e s o l u t i o n , and r a t e of cooling.

Reports on t h e o b s e r v a t i o n of f r e e z i n g p o t e n t i a l s i n s o i l s and r o c k s a r e meagre and

inconclusive. Jumikis (1958) measured p o t e n t i a l s of 40-120 mV d u r i n g f r e e z i n g of Dunellen s i l t y s o i l ( a g l a c i a l t i l l ) and suggested t h a t such p o t e n t i a l s could enhance moisture t r a n s p o r t i n t h e m a t e r i a l .

Korkina (1975) s t u d i e d t h e f r e e z i n g e l e c t r i c a l p o t e n t i a l s i n suspensions c o n t a i n i n g p a r t i c l e s of l e s s than a micron and s a t u r a t e d w i t h d i f f e r e n t k i n d s of i o n s such a s 17e3+, ~ a + + , ~ a + , and NH,++.

The magnitude and p o l a r i t y of t h e induced v o l t a g e depended on t h e d e n s i t y of t h e suspensions, t y p e of p a r t i c l e s , and type of ions. Under l a b o r a t o r y c o n d i t i o n s , B o r o v i t s k i i (1976) measured f r e e z i n g v o l t a g e s of 150-200 mV i n a r g i l l a c e o u s r o c k s , and Yarkin (1974, 1978) measured f r e e z i n g v o l t a g e s of up t o 325 mV i n powdered sand c o n t a i n i n g about 23% moisture and s m a l l e r f r e e z i n g v o l t a g e s i n o t h e r s o i l s . More r e c e n t l y , Hanley and Ramachandra Rao

(1980, 1981) s t u d i e d t h e e f f e c t s of v a r i o u s c a t i o n s on t h e g e n e r a t i o n of f r e e z i n g p o t e n t i a l s i n a b e n t o n i t e clay. The maximum p o t e n t i a l s were i n t h e range of 30-50 mV, and they concluded t h a t t h e development of f r e e z i n g p o t e n t i a l and m i g r a t i o n of moisture a r e c l o s e l y a s s o c i a t e d phenomena, e,;

i n f l u e n c i n g t h e o t h e r . Parameswaran (1!362) h a s .>so r e p o r t e d l a b o r a t o r y 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 w a t e r and s o i l s under v a r i o u s r a t e s of cooling. I c e - p o s i t i v e p o t e n t i a l s of 4-19 V developed i n pure w a t e r under r a p i d c o o l i n g ; and i n moist sands and s o i l s i c e - n e g a t i v e p o t e n t i a l s of

100-200 mV were measured. Under slow c o o l i n g a t -2.2OC r e c o n s t i t u t e d n a t u r a l s o i l s from permafrost a r e a s showed f r e e z i n g v o l t a g e s of 200-300 mV. The f r e e z i n g p o t e n t i a l s i n water could be due t o a combination of t h o s e r e l a t e d t o t h e phase change of water and those a r i s i n g out of charge s e p a r a t i o n and i o n i n c o r p o r a t i o n from t r a c e s of i m p u r i t i e s (known a s Workman-Reynolds e f f e c t ) . I n a d d i t i o n t o p o l a r i z a t i o n of w a t e r molecules and alignment of d i p o l e s a c r o s s t h e p o t e n t i a l b a r r i e r a t t h e f r e e z i n g boundary, charges i n h e r e n t l y p r e s e n t a t t h e s u r f a c e of mineral p a r t i c l e s i n s o i l s could a l s o c o n t r i b u t e t o t h e development of f r e e z i n g p o t e n t i a l s by exchange a b s o r p t i o n processes. The development of c o n t a c t e l e c t r i c a l p o t e n t i a l s during f r e e z i n g i s of c o n s i d e r a b l e importance i n many c o n s t r u c t i o n problems i n n o r t h e r n North America, t h e USSR, and Europe, where v a s t a r e a s a r e u n d e r l a i n by p e r e n n i a l l y and s e a s o n a l l y f r o z e n ground. Under t h e i n f l u e n c e of a n e l e c t r i c a l g r a d i e n t such a s t h a t caused by f r e e z i n g , w a t e r i s

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transported through frozen clay and s i l t towards t h e f r e e z i n g f r o n t where segregated i c e can form

(Verschinin e t a l . 1949, Hoekstra and Chamberlain 1963). Such movement of water under t h e influence of g e o e l e c t r i c f i e l d s i n t h e presence of a thermal gradient could a l s o cause electro-osmotic drainage of unfrozen and f r o z e n s o i l s (Nersesova and Tsytovich 1966). The a d d i t i o n a l heave caused by such processes could n e c e s s i t a t e s p e c i a l

construction techniques f o r p i p e l i n e s , foundations f o r buildings, and o t h e r s t r u c t u r e s i n ~ e r m a f r o s t areas. ~ e o e l e c t r i c f i e l d s generated near buried p i p e l i n e s could a l s o a f f e c t t h e i r cathodic protection.

FIELD STUDIES

Very few 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 under n a t u r a l conditions have been published. The only documented r e p o r t t o t h e authors' knowledge i s t h a t of B o r o v i t s k i i (1976), who measured t h e inherent e l e c t r i c a l f i e l d s developed i n t h e a c t i v e l a y e r between frozen and thawed p a r t s i n a permafrost region of t h e USSR. The measured values did not exceed 50 mV, although t h e value of the p o t e n t i a l varied with depth i n t h e ground. This he a t t r i b u t e d t o d i f f e r e n c e s i n q u a n t i t y and d i r e c t i o n of moisture movement. Mackay has a l s o c a r r i e d o u t measurements of t h e p o t e n t i a l s developed i n e l e c t r o d e s embedded t o d i f f e r e n t depths i n t h e a c t i v e l a y e r and i n perennially frozen ground i n t h r e e d i f f e r e n t a r e a s of t h e Northwest

T e r r i t o r i e s . When e l e c t r o d e s were placed i n t h e a c t i v e layer, he observed a p o t e n t i a l change a s t h e f r e e z i n g f r o n t passed the e l e c t r o d e s . Values of p o t e n t i a l s measured i n t h e f i e l d were of t h e same order of magnitude a s values measured i n t h e laboratory on n a t u r a l s o i l s (Parameswaran 1982). This s i m i l a r i t y of t h e f r e e z i n g p o t e n t i a l s measured i n t h e laboratory and i n t h e f i e l d prompted t h e author- t o i n s t a l l f i e l d e l e c t r o d e assemblies i n two

L r r o & a r e a s and t o measure f r e e z i n g p o t e n t i a l s

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an attempt t o understand t h e physical processes $ t h a t occur during f r e e z i n g of t h e ground. One

chosen a r e a was t h e middle of an a r t i f i c i a l l y &rained l a k e ( I l l i s a r v i k ) on Richards I s l a n d , N.W.T., where permafrost was aggrading from t h e top down (Mackay 1981). The o t h e r a r e a was a t Inuvik, N.W.T., where t h e a c t i v e l a y e r i n a mud hummock was monitored. This paper d e s c r i b e s t h e equipment and some of t h e r e s u l t s .

resin. The tubes were designed t o be joined with p l e x i g l a s couplings a s they were i n s t a l l e d .

Wires from t h e e l e c t r o d e s were connected t o a r o t a r y switch having 24 terminals (Figure l b ) . The bottom e l e c t r o d e was connected t o the common p o i n t (-); t h e o t h e r s were connected t o switch p o i n t s 1 t o 21. The c e n t r a l switch contact p o i n t was made t h e (+) terminal. The s h i e l d s from a l l t h e cables were connected t o t h e ground terminal, which was i n t u r n

connected t o a grounding s t e e l post a t t h e l a k e I s i t e .

Two thermistor cables were i n s t a l l e d near t h e

h

e l e c t r o d e s f o r temperature measurements. The f i r s t

cable had 12 thermistors (YSI 44033, c a l i b r a t e d t o

+O.Ol°C a t O°C), each i n s i d e a s o i l s a l i n i t y sensor

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(Soilmoisture No. 5100-A). These were embedded i n a

30 mm diam WC rod a t 500 mm i n t e r v a l s . The rod (with s a l i n i t y s e n s o r s ) was i n s t a l l e d i n a hole d r i l l e d by water-jet 0.4 m from t h e e l e c t r o d e assembly (Figure 2). A second temperature cable with 26 thermistors (YSI 44033) spaced 150 mm a p a r t was i n s t a l l e d

4

m from t h e e l e c t r o d e assembly.

Depth of permafrost was 5.65 m when t h e e l e c t r o d e s were i n s t a l l e d i n June 1981. The uppermost e l e c t r o d e (21) was a t a depth of 6.11 m and t h e bottom e l e c t r o d e (0) was 9.31 m below ground l e v e l (lake bottom). This placement ensured t h a t t h e O°C isotherm would soon reach t h e uppermost e l e c t r o d e . The m a t e r i a l i n which t h e e l e c t r o d e s were i n s t a l l e d was a s a t u r a t e d sand with mediuorto- f i n e g r a i n s i z e .

Inuvik S i t e

I

This s i t e i s about 3 b n o r t h of t h e town of Inuvik i n an a r e a of colluvium t h a t has developed a p a t t e r n of m d hummocks. The e l e c t r o d e probe consisted of a WC tubing (20.6 mm OD, 12.7 mm I D , 3 m long, closed a t one end) on which 12 copper e l e c t r o d e s i n t h e form of bands o r r i n g s (12.7 mm

wide and about 1 mm t h i c k ) were i n s t a l l e d i n s u i t a b l g grooves 150 mm a p a r t . Coaxial cables were soldered t o t h e e l e c t r o d e s and t h e wires were l e d out through a c e n t r a l hole and connected t o t h e terminals of a r o t a r y switch. The o u t e r s h i e l d s of t h e cables were grounded t o a s t e e l post a t t h e s i t e . A thermistor c a b l e with 13 thermistors (YSI-44033) was a l s o made. The e l e c t r o d e probe and t h e thermistor c a b l e (Figure 3) were i n s t a l l e d (by hand d r i l l i n g ) i n August 1981 i n t h e c e n t r e of a mud hummock about 2 m i n diameter.

I l l i s a r v i k Lake S i t e , Richards I s l a n d RESULTS AND DISCUSSIONS

I

An e l e c t r o d e probe c o n s i s t i n g of f i v e p l e x i g l a s

tubes, each 1.93 m long, 38 Imn OD and 25 mm I D , was i n s t a l l e d a t t h e s i t e , t h e middle of a drained lake, on 20 June 1981. Twenty-two 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 (12.5 mm wide) were i n s t a l l e d on the probe i n s u i t a b l e grooves 1 mm

deep. The bottom e l e c t r o d e (numbered zero) was 89 mm from the t i p of t h e plug c l o s i n g t h e f i r s t tube. A l l t h e o t h e r s , numbered 1 t o 21 from t h e bottom upwards, were s e t 150 mm a p a r t . A shielded c o a x i a l c a b l e (RG 174lU) was connected t o each e l e c t r o d e through a s l a n t e d hole i n t h e wall of t h e tube and t h e soldered j o i n t s were protected by epoxy

I l l i s a r v i k Lake S i t e , Richards I s l a n d

Owing t o t h e thermal disturbance of t h e ground caused by d r i l l i n g and t h e r e s u l t i n g freeze-back, t h e readings taken i n August 1981 a r e questionable and a r e not reported here. The I l l i s a r v i k s i t e i s

r e l a t i v e l y i n a c c e s s i b l e and frequent readings were impossible, s o t h a t t h e next readings were taken 23 March 1982, 8 June 1982, and 12 August 1982. The temperature and f r e e z i n g p o t e n t i a l p r o f i l e s f o r t h e s e d a t e s a r e p l o t t e d i n Figure 4(a-c). None of t h e t h r e e temperature p r o f i l e s shows any change i n g r a d i e n t i n c r o s s i n g O°C, from p o s i t i v e t o negative

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temperatures. I n F i g u r e 4 ( a ) t h e r e i s a g r a d u a l change i n t h e p r o f i l e at about -0.l0C; and i n F i g u r e 4(b, c ) a d e f i n i t e i n f l e c t i o n p o i n t a t -O.l°C. With l i t t l e doubt t h i s marks t h e f r e e z i n g p o i n t d e p r e s s i o n s o commonly observed i n s o i l s . The I l l i s a r v i k sediments c o n s i s t mainly of sand, and t h e f r e e z i n g p o i n t d e p r e s s i o n i s s l i g h t l y lower t h a n might be expected. Since t h e sub-permafrost pore w a t e r h a s a n i n c r e a s e d s a l i n i t y from i o n r e j e c t i o n d u r i n g permafrost aggradation, however, a f r e e z i n g p o i n t d e p r e s s i o n below t h a t of t h e o r i g i n a l sands i s

t o be expected. To i l l u s t r a t e , i n t h e summer of 1982 t h e s p e c i f i c conductance of t h e p o r e w a t e r j u s t below permafrost, a s measured w i t h t h e s o i l s a l i n i t y s e n s o r s , was about 300 pohm-l cm-l; s a l i n i t y had i n c r e a s e d a p p r e c i a b l y s i n c e t h e previous summer. Nearby measurements of heave of t h e ground s u r f a c e suggest t h a t most of t h e i c e formed d u r i n g t h e downward growth of permafrost was pore i c e and n o t s e g r e g a t e d i c e .

F i g u r e 4(a-c) s h m s p l o t s of peak p o t e n t i a l s and temperature g r a d i e n t s . On 23 March 1982 t h e r e was a very pronounced peak i n t h e p o t e n t i a l a t

1.08 V a t a depth j u s t 15 cm below t h e 0 deg isotherm. A s t h e temperature measurements were taken 0.4 m from t h e e l e c t r o d e s , t h e agreement seems good. By way of c o n t r a s t , on 8 June 1982 t h e peak p o t e n t i a l (about 1.35 V) occurred a t a ground temperature of -O.l°C, t h e peak c o i n c i d i n g c l o s e l y w i t h t h e i n f l e c t i o n p o i n t on t h e temperature curve. By 12 August 1982, however, t h e peak p o t e n t i a l was unchanged a t t h e same depth a s on 8 June 1982, although permafrost had aggraded 50 cm and t h e ground temperature had decreased t o about -0.4"C. I n summary, t h e r e s u l t s from t h e I l l i s a r v i k s i t e i n d i c a t e t h a t f r e e z i n g p o t e n t i a l s develop on e l e c t r o d e s l o c a t e d a t t h e f r e e z i n g f r o n t , b u t t h e s e r e s u l t s a r e by no means conclusive. I n u v i k S i t e The I n u v i k s i t e c o n t r a s t s w i t h t h e I l l i s a r v i k s i t e i n s o i l t y p e and t h e placement of t h e e l e c t r o d e s . Here t h e s o i l i s a s i l t y c l a y , w i t h p a r t i c l e s about 50 % f i n e r t h a n 0.002 mm and a s p e c i f i c s u r f a c e a r e a of about 120 m2/g. The amount of unfrozen p o r e w a t e r i n t h e c l a y , u s i n g t h e s p e c i f i c s u r f a c e a r e a method of Anderson and Tice (19721, i s e s t i m a t e d a t about 9 % a t -5°C and 7 % a t -lO°C. Voltage and temperature readings were t a k e n every two weeks by t h e s t a f f of t h e I n u v i k

S c i e n t i f i c Resource Centre. V a r i a t i o n s of v o l t a g e and temperature w i t h depth below s u r f a c e were much more p r e d i c t a b l e and s y s t e m a t i c t h a n t h o s e a t t h e I l l i s a r v i k Lake s i t e . Figure 5(a-e) shows t h e v a r i a t i o n s of v o l t a g e and temperature a t v a r i o u s depths a s t h e ground f r o z e and thawed i n t h e 1981- 1982 season. A t d e p t h s of 0.05 and 0.20 m,

r e s p e c t i v e l y , a f r e e z i n g p o t e n t i a l developed a s t h e temperature passed through O°C i n t h e month of October 1981 (Figure 5 ( a , b ) ) . The maximum f r e e z i n g p o t e n t i a l s developed were a s high a s 650 mV. A s t h e ground temperature a t t h e s e l o c a t i o n s dropped i n w i n t e r , t h e p o t e n t i a l dropped t o o and remained a t t h e lower l e v e l . I n s p r i n g (May 1982), a s t h e ground s t a r t e d t o thaw and t h e temperature r o s e above O0C, t h e p o t e n t i a l s a g a i n r o s e t o values of up t o 700 mV. The i n t e r p r e t a t i o n of t h i s p o t e n t i a l i s u n c e r t a i n , but t h e r e i s c o n s i d e r a b l e evidence t h a t

d u r i n g t h e summer thaw period water may m i g r a t e ftom t h e thawed 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 a c t i v e l a y e r t o 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 (Cheng 1982, Mackay, i n p r e s s ; Parmuzina 1978, Wright 1981). A minor f r e e z i n g p o t e n t i a l may t h u s develop d u r i n g t h e summer thaw period. T h i s behaviour of meltwater, p o s s i b l y p e r c o l a t i n g downwards and f r e e z i n g t o g e n e r a t e a f r e e z i n g p o t e n t i a l , was n o t observed a t t h e e l e c t r o d e s a t lower l e v e l s . For example, i n Figure 5 ( c ) t h e f r e e z i n g p o t e n t i a l on t h e e l e c t r o d e a t a d e p t h of 0.51 m below s u r f a c e l e v e l r o s e t o 700 mV a s t h e ground temperature passed through -O.l°C. With f u r t h e r d e c r e a s e i n ground temperature t h e f r e e z i n g p o t e n t i a l remained unchanged. A s l i g h t drop i n p o t e n t i a l was noted when t h e temperature passed through O°C i n June 1982 a s t h e ground thawed, but e s s e n t i a l l y t h e v o l t a g e was c o n s t a n t around 700 mV even when t h e ground

s t a r t e d t o f r e e z e a g a i n i n October 1982. The same type of behaviour was observed 0.96 m below ground l e v e l ( F i g u r e 5 ( d ) ).

Figure 5 ( a , b ) shows t h e development of

pronounced f r e e z i n g p o t e n t i a l s a t d e p t h s of 0.05 and 0.20 m, r e s p e c t i v e l y , i n t h e upper p a r t of t h e a c t i v e l a y e r where i c e l e n s i n g connnonly t a k e s place. I n a d d i t i o n , p o t e n t i a l s a t 0.51 and 0.96 m remained a t 600-700 mV d u r i n g t h e w i n t e r , a f t e r temperatures dropped below O°C. Measurements c a r r i e d o u t a t I n u v i k f o r many y e a r s have shown a prolonged and very g r a d u a l f r o s t heave i n t h e w i n t e r months l o n g a f t e r t h e temperature h a s dropped below 0°C (Mackay e t a l . 1979). This s u g g e s t s t h a t , i n w i n t e r , upward m i g r a t i o n of unfrozen w a t e r from t h e f r e e z i n g f r o n t i n t o t h e f r o z e n a c t i v e l a y e r could cause a minor f r e e z i n g p o t e n t i a l t o develop. At l e v e l s c l o s e t o t h e permafrost t a b l e , where ground temperature i s maintained a t o r below O°C, no f r e e z i n g p o t e n t i a l s developed on t h e e l e c t r o d e 1.42 m below grdund l e v e l

(Figure 5 ( e ) ) . F i g u r e 5(a-e) a l s o shows t h a t a s d e p t h i n c r e a s e s below ground l e v e l t h e minimum

temperature, a s expected, becomes higher. For example, a t 0.05 m t h e lowest ground temperature measured was -lO°C, whereas a t 0.96 and 1.42 m t h e lowest s o i l temperatures measured were -3.5 and -2.5"C, r e s p e c t i v e l y .

CONCLUSION

Freezing p o t e n t i a l s appear t o have developed on e l e c t r o d e s i n s t a l l e d i n s a t u r a t e d sand a t I l l i s a r v i k where t h e 0°C i s o t h e r m was t h a t of a n aggrading lower permafrost s u r f a c e , but t h e r e s u l t s a r e inconclusive. Peak p o t e n t i a l s of up t o 1350 mV were measured on e l e c t r o d e s l o c a t e d on t h e advancing f r e e z i n g f r o n t . A t I n u v i k , t h e e l e c t r o d e s were placed i n t h e a c t i v e l a y e r on top of permafrost, i n a s i l t y c l a y . The e l e c t r o d e s i n t h e upper p a r t of t h e a c t i v e l a y e r where l e n s i c e forms i n t h e freeze- back p e r i o d r e g i s t e r e d s u b s t a n t i a l i n c r e a s e s i n p o t e n t i a l a s t h e f r e e z i n g f r o n t passed t h e

e l e c t r o d e s . The maximum f r e e z i n g p o t e n t i a l measured h e r e was about 500 mV when t h e ground temperature was about -O.l°C. There was a l s o evidence of downward water m i g r a t i o n and f r e e z i n g , a s evidenced by a r i s e i n f r e e z i n g p o t e n t i a l a t l e v e l s below t h e s u r f a c e a s t h e ground thawed a t t h e s u r f a c e . These f i e l d measurements i n d i c a t e t h a t by s u i t a b l y modifying e l e c t r o d e probes and improving measuring

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techniques i t

i s

p o s s i b l e t o l o c a t e and study t h e advancing f r e e z i n g f r o n t and water migration a t d i f f e r e n t l e v e l s below t h e s u r f a c e a s ground f r e e z e s and thaws.

ACKNOWLEDGEMENTS

The a u t h o r s would l i k e t o express t h e i r s i n c e r e thanks t o t h e following: C. Hubbs, J.C. P l u n k e t t , and G.H. Johnston; t h e DBRINRCC Workshop s t a f f , and t h e s t a f f of t h e I n u v i k S c i e n t i f i c Resource Centre. F i e l d support f o r J.R. Mackay from t h e Geological Survey of Canada, t h e P o l a r C o n t i n e n t a l Shelf P r o j e c t (Department of Energy, Mines and Resources) and t h e N a t u r a l Sciences and Engineering Research Council is g r a t e f u l l y acknowledged. This 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 Building Research, National Research Council Canada, and i s published w i t h t h e approval of t h e D i r e c t o r of t h e Division.

REFERENCES

Anderson, D.M. and T i c e , A.R., 1972, P r e d i c t i n g unfrozen water c o n t e n t s i n f r o z e n s o i l s from s u r f a c e a r e a measurements: Highway Research Record No. 393, p. 12-18.

B o r o v i t s k i i , V.P., 1976, The development of inherent 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 rocks 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 migration of t r a c e elements: J o u r n a l of Geochemical Exploration, v. 5, p. 65-70. Cheng, C., 1982, The forming process of t h i c k

layered 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), v. 25, No. 7, p. 777-788.

Hanley, T. O'D. and Ramachandra Rao, S., 1980,

Freezing p o t e n t i a l s i n wet clays: I. Early r e s u l t s , and 11. S p e c i f i c systems: Cold Regions Science and Technology, v. 3, p. 163-

168, 169-175.

Hanley, T. O'D. and Ramachandra Rao, S., 1981, Freezing p o t e n t i a l s t u d i e s i n wet c l a y systems: Presented ASME (Heat T r a n s f e r D i v i s i o n ) , 16- 21 Nov. 1980, Chicago ( P r e p r i n t

No. 80-WAlHT-81, 5 p.

Hoekstra, P. and Chamberlain, E., 1963, Electro- osmosis i n f r o z e n s o i l s : Nature, v. 203, p. 1406.

Jumikis, A.R., 1958, So= concepts p e r t a i n i n g t o t h e f r e e z i n g s o i l systems: Highway Research Board, S p e c i a l Report 40, p. 178-190.

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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 e f f e c t on migration. U.S. Army, Cold Regions Research and

Engineering Laboratory, Draft T r a n s l a t i o n 490, 15 p.

Mackay, J.R., 1981, An experiment i n l a k e drainage, Richards I s l a n d , Northwest T e r r i t o r i e s ; Progress Report: Current Research, P a r t A , Geological Survey of Canada, Paper 18-lA,

p. 63-68.

Mackay, J.R., I n p r e s s , Downward water 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. Mackay, J.R., O s t r i c k , J., Lewis, C.P. and MacKay,

D.K., 1979, F r o s t heave a t ground temperatures below O°C, I n u v i k , Northwest T e r r i t o r i e s : Current Research, P a r t A, Geological Survey of Canada, Paper 79-lA, p. 403-405.

Nersesova, Z.A. and Tsytovich, N.A., 1966, Unfrozen

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Academy of Sciences, Washington, D.C., p. 230-

234.

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 water and s o i l s : Presented, Third I n t e r n a t i o n a l Symposium on Ground

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Pa-zina, 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 formation i n t h e a c t i v e l a y e r ] ( i n Russian) : P r o b l e w k r i o l i t o l o g i i , No. 7, p. 14 1-164. (Translated i n Polar Geography and Geology, July-September 1980, p. 131-152.)

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,

Deriagin, B.V., and V i r i l e n k o , N.V., 1949, The non-freezing water i n s o i l : U.S. Army, Cold Regions Research and Engineering Laboratory, T r a n s l a t i o n No. 30. Wright, R.K., 1981, The water balance of a l i c h e n

tundra u n d e r l a i n by permafrost: McGill University, McGill S u b a r c t i c Research Paper No. 33, Climatological Research S e r i e s No. 11, 110 p.

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f r e e z i n g s o i l s and ways of c o n t r o l l i n g them:

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Foundation and Underground S t r u c t u r e Research I n s t i t u t e , Moscow,

p. 59-81.

Yarkin, I.G., 1978, E f f e c t of n a t u r a l e l e c t r i c a l p o t e n t i a l s on water migration i n f r e e z i n g s o i l s : Permafrost

,

Proceedings of t h e Second I n t e r n a t i o n a l Conference, National Academy of

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FIGURE l ( a ) The I l l i s a r v i k electrode assembly. FIGURE l ( b ) Switching box. ROZM GROUND APPROXiMATE PM ITION OF WE FRFEZING FRONT AWAtKING DOWNWARDS. UNFRaZM GRWND

FIGURE 2 Schematic diagram showing the location of FIGURE 3 Schematic diagram showing the location of

electrodes and thermistors a f t e r i n s t a l l a t i o n , electrodes and thermistors a f t e r i n s t a l l a t i o n a t the

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1200

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8 JUNE 1982 1200

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, ,

,

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1000 23 MARCH 1982 l a 1 800

:

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ELECTRODE LOCATION 1981 1982 - 0 . 2 0 u' - 4 . 2

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FIGURE 4 Variation of voltage and temperature with FIGURE 5 Variation of voltage and temperature with

depth below ground surface a t the I l l i s a r v i k s i t e , time a t d i f f e r e n t depths below the surface, Inuvik ( a ) 9 months, (b) about 1 year, and ( c ) 14 months s i t e .