Application of time-domain reflectometry to determine the thickness of the frozen zone in soils

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Application of time-domain reflectometry to determine the thickness of

the frozen zone in soils

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APPLICATION OF TIME-DOMAIN REFLECTOMETRY TO DETERMINE THE THICKNESS OF THE FROZEN ZONE I N SOILS

by T.H.W. Baker and J.L. Davis

Presented at

Third International Symposium on Ground Freezing Hanover, New Hampshire, 21

-

24 June 1982, 8 p.

ANALYZED

1

Printed with permission

DBR Paper No. 1215

Division of Building Research

La r 6 f l e c t o d t r i e a s s o c i d e au temps e s t une t e c h n i q u e f a i s a n t i n t e r v e n i r d e s impulsions dlectromagn6tiques q u i a b t b u t i l i s 6 e pour mesurer l a c o n s t a n t e d i d l e c t r i q u e d e s s o l s 3 d e s frdquences v a r i a n t e n t r e 1 MHz e t 1 GHz. La c o n s t a n t e d i g l e c - t r i q u e de l ' e a u 6quivaut 3 30 f o i s c e l l e de l a g l a c e , ce q u i f a i t q u ' i l e s t p o s s i b l e de s i t u e r l e f r o n t de c o n g d l a t i o n dans l e s s o l s . Les r b s u l t a t s d ' e x p g r i e n c e s en l a b o r a t o i r e s o n t p r b s e n t b s a f i n d ' i l l u s t r e r l ' a p p l i c a t i o n de c e t t e t e c h n i q u e l a mesure de 1 1 6 p a i s s e u r de l a zone g e l e e de s o l s 3 granulo- m 6 t r i e g r o s s i S r + a+ f j - - -_L'melaceaent de l a

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APPLICATION OF TIME-DOMAIN REFLECTOMETRY TO DETERMINE THE THICKNESS OF THE FROZEN ZONE I N SOILS

T.H.W. Baker, D i v i s i o n of Building Research, N a t i o n a l Research Council of Canada, Ottawa, O n t a r i o ,

KIA

0R6, Canada J.L. Davis, EarthTech Research Ltd., Baltimore,

MD,

21227, U.S.A.

ABSTRACT

Time-domain r e f l e c t o m e t r y is an e l e c t r o m a g n e t i c p u l s e t e c h n i q u e t h a t h a s been used t o measure t h e d i e l e c t r i c c o n s t a n t of s o i l s a t f r e q u e n c i e s between 1 MHz and 1 GHz. The d i e l e c t r i c c o n s t a n t of w a t e r i s 30 t i m e s t h a t of i c e , making i t p o s s i b l e t o d e l i n e a t e t h e f r e e z i n g f r o n t i n s o i l s . R e s u l t s of l a b o r a t o r y experiments w i l l be p r e s e n t e d t o show t h e a p p l i c a t i o n of t h i s t e c h n i q u e t o determine t h e t h i c k n e s s of t h e f r o z e n zone i n c o a r s e g r a i n e d and f i n e g r a i n e d s o i l s . The l o c a t i o n of t h e f r e e z i n g boundary u s i n g t ime-domain r e f l e c t o m e t r y w i l l be compared w i t h temperature

measurements and i n t e r p r e t a t i o n s from X- ray photographs.

INTRODUCTION

During t h e c o n s t r u c t i o n and r e p a i r of s h a f t s and t u n n e l s , a r t i f i c i a l ground f r e e z i n g has been used t o supply

temporary s t r u c t u r a l s u p p o r t and t o c o n t r o l w a t e r i n f i l t r a t i o n . I n t h e s e p r o j e c t s i t i s n e c e s s a r y t o monitor t h e t h i c k n e s s of t h e f r o z e n l a y e r f o r s a f e t y and economic reasons. S e v e r a l t e c h n i q u e s have been used i n c l u d i n g temperature measurement, e l e c t r i c a l r e s i s t i v i t y , f r o s t - t u b e , u l t r a s o n i c , s e i s m i c and r a d a r methods. This paper d e s c r i b e s t h e u s e of a n o t h e r technique, time-domain r e f l e c t o m e t r y , t o l o c a t e t h e f r e e z i n g f r o n t and t o c a l c u l a t e t h e t h i c k n e s s of t h e f r o z e n zone. Time-domain r e f l e c t o m e t r y was f i r s t u s e d by Davis e t a l . (1976) t o measure t h e a p p a r e n t d i e l e c t r i c c o n s t a n t of s o i l s . They found t h a t t h e a p p a r e n t d i e l e c t r i c c o n s t a n t was s t r o n g l y dependent on v o l u m e t r i c w a t e r c o n t e n t and weakly dependent on s o i l t y p e , d e n s i t y , t e m p e r a t u r e (above O°C) and s o l u b l e s a l t c o n t e n t i n t h e frequency

range between 20 MHz and 1 GHz

.

Topp e t a l . (1980) proposed an e m p i r i c a l r e l a t i o n s h i p between t h e a p p a r e n t d i e l e c t r i c c o n s t a n t and t h e v o l u m e t r i c w a t e r c o n t e n t of s o i l s . S i m i l a r l y , P a t t e r s o n and Smith (1981) i n v e s t i g a t e d t h e r e l a t i o n s h i p between t h e a p p a r e n t d i e l e c t r i c c o n s t a n t of f r o z e n s o i l s and unfrozen w a t e r c o n t e n t u s i n g time-domain r e f l e c t o m e t r y . TIME-DOMAIN REFLECTOMETRY Time-domain r e f l e c t o m e t r y i s used t o determine t h e d i e l e c t r i c c o n s t a n t of t h e medium s u r r o u n d i n g a t r a n s m i s s i o n l i n e by measuring t h e p r o p a g a t i o n v e l o c i t y (V) of a n e l e c t r o m a g n e t i c wave t r a n s m i t t e d a l o n g t h e t r a n s m i s s i o n l i n e f o r a known

d i s t a n c e . For t h e complete range of s o i l s s t u d i e d by Topp e t a l . (1980) t h e e l e c t r i c l o s s was found t o b e s m a l l and d i d n o t a f f e c t t h e measured p r o p a g a t i o n v e l o c i t y . They e x p r e s s e d t h e p r o p a g a t i o n v e l o c i t y a s : where c = v e l o c i t y of l i g h t i n a vacuum (30 cmlns)

K

,

= a p p a r e n t d i e l e c t r i c c o n s t a n t of t h e medium. The p r o p a g a t i o n v e l o c i t y

(V)

a l o n g a

t r a n s m i s s i o n l i n e of known l e n g t h (L) i s given by: where t = t i m e of t r a v e l Combining e q u a t i o n s 1 and 2 y i e l d s a n e x p r e s s i o n f o r Ka i n terms of t h e t r a n s m i s s i o n l i n e l e n g t h (L) and t h e t r a v e l time ( t ) : The t r a v e l t i m e s of e l e c t r o m a g n e t i c waves t r a n s m i t t e d along a t r a n s m i s s i o n l i n e a r e measured u s i n g a time-domain r e f l e c t o m e t e r (TDR). T h i s i n s t r u m e n t i s widely used i n t h e e l e c t r o n i c s i n d u s t r y t o measure t h e r e f l e c t i o n c h a r a c t e r i s t i c s of t r a n s m i s s i o n l i n e s . A d e s c r i p t i o n of how t h e instrument o p e r a t e s i n r e l a t i o n t o t h e t r a n s m i s s i o n l i n e i s p r e s e n t e d i n Baker e t a l . (1982). The TDR o u t p u t c o n s i s t s of a waveform w i t h a time b a s e d i s p l a y e d on a cathode r a y t u b e (CRT) and photographed o r p l o t t e d on a n x-y

p l o t t e r . The shape and amplitude of t h e r e f l e c t e d wave, i n r e l a t i o n t o t h e outgoing wave, r e v e a l t h e n a t u r e and magnitude of t h e impedance mismatches and d i s c o n t i n u i t i e s a l o n g t h e t r a n s m i s s i o n l i n e .

The amplitude of t h e r e f l e c t e d waveform i s dependent upon t h e change i n impedance along t h e t r a n s m i s s i o n l i n e . The impedance i s dependent upon t h e l i n e and t h e e l e c t r i c a l p r o p e r t i e s of t h e g e o m e t r i c a l shape of t h e t r a n s m i s s i o n surrounding medium. For a balanced p a r a l l e l w i r e t r a n s m i s s i o n l i n e , t h e c h a r a c t e r i s t i c s impedance (Zo) i s g i v e n by: where K = d i e l e c t r i c c o n s t a n t of t h e surrounding medium S = s p a c i n g between t h e rods (cm) d = diameter of t h e r o d s (cm). I n t h e s e experiments, t h e p a r a l l e l w i r e t r a n s m i s s i o n l i n e i s t e r m i n a t e d i n an open c i r c u i t . The impedance a t an open c i r c u i t i s i n f i n i t e and t h e energy from impinging s i g n a l s i s t o t a l l y r e f l e c t e d . Events on t h e TDR waveform can be used t o c a l c u l a t e t h e d i e l e c t r i c c o n s t a n t of t h e medium, u s i n g e q u a t i o n 3, provided t h e p h y s i c a l d i s t a n c e between t h e d i s c o n t i n - u i t i e s i s known, o r t h e y c a n b e u s e d t o l o c a t e t h e d i s c o n t i n u i t y provided t h e d i e l e c t r i c c o n s t a n t of t h e medium i s known. The d i f f e r e n c e i n t h e d i e l e c t r i c c o n s t a n t of f r o z e n and unfrozen s o i l w i t h a h i g h w a t e r c o n t e n t c a u s e s a n impedance change a t t h e f r e e z i n g f r o n t producing a r e f l e c t i o n o n t h e TDR waveform. Using t h e t i m e base on t h e waveform i t i s p o s s i b l e t o measure t h e time f o r t h e wave t o t r a v e l through t h e f r o z e n zone ( t f ) and unfrozen zone (t,). I n making t h e c a l c u l a t i o n s t h e s e t r a v e l t i m e s a r e d i v i d e d i n h a l f because r e f l e c t e d waves a c t u a l l y t r a v e l t w i c e t h e d i s t a n c e along t h e transrmlssion l i n e . P r i o r measurement of t h e d i e l e c t r i c c o n s t a n t of t h e f r o z e n and/or u n f r o z e n m a t e r i a l c a n b e used t o l o c a t e t h e f r e e z i n g f r o n t r e l a t i v e t o t h e f r o z e n o r u n f r o z e n end of t h e t r a n s m i s s i o n l i n e u s i n g e q u a t i o n 3 w r i t t e n i n t h e f o l l o w i n g form: Being a b l e t o c a l c u l a t e t h e l o c a t i o n of t h e f r e e z i n g f r o n t , w i t h r e s p e c t t o b o t h ends of t h e t r a n s m i s s i o n l i n e , improves t h e accuracy of t h e t e c h n i q u e (Baker e t a l .

,

1982). I f t h e u n i f o r m i t y of t h e d i e l e c t r i c c o n s t a n t i s b e t t e r i n one zone t h a n t h e o t h e r , t h e n i t i s b e t t e r t o l o c a t e t h e f r e e z i n g f r o n t from one s i d e o n l y , a s i n t h e f i e l d measurements r e p o r t e d i n Baker e t a l . (1 982). LABORATORY EXPERIMENTS The s o i l s u s e d i n t h i s s t u d y were a graded s t a n d a r d q u a r t z sand from Ottawa, I l l i n o i s (ASTM Spec. C-log), and a l o c a l marine s i l t y c l a y . A l l samples were prepared from t h e i r d r y s t a t e and compacted i n t o waxed cardboard

c y l i n d r i c a l moulds (15.2 cm i n d i a m e t e r and 28 c m i n depth). Two s t e e l r o d s (0.2 cm i n d i a m e t e r , 3 c m s p a c i n g ) were i n s e r t e d i n t o d r i l l e d h o l e s t o a d e p t h of 25 cm. A s t r i n g of thermocouples was a l s o i n s e r t e d i n t o t h e s o i l w i t h s e n s o r s spaced a t 2 c m i n t e r v a l s . Two o t h e r t h e m o c o u p l e s were placed, one on t h e s u r f a c e of t h e s o i l and one on t h e bottom of t h e mould. The c y l i n d r i c a l sample mould was s e a t e d on a b a t t e r y h e a t e r , surrounded w i t h 10 cm of v e r m i c u l i t e i n s u l a t i o n and p l a c e d i n a c o l d room a t -5.5OC.

F i g u r e s 1 t o 3 show i n f o r m a t i o n on t h e r e l a t i o n s h i p between v o l u m e t r i c w a t e r c o n t e n t and t h e measured d i e l e c t r i c

c o n s t a n t f o r t h e s o i l s u s e d i n t h e s e experiments. D i e l e c t r i c c o n s t a n t measurements were made on t h e u n f r o z e n s o i l s a s soon a s t h e t r a n s m i s s i o n l i n e s were i n p l a c e . When t h e t r a n s m i s s i o n

l i n e s had become completely f r o z e n i n and t h e temperature had s t a b i l i z e d , t h e f r o z e n d i e l e c t r i c c o n s t a n t was measured.

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V O L U M E T R I C W A T E R C O N T E N T . % F i g u r e 1. Volumetric w a t e r c o n t e n t v e r s u s a p p a r e n t d i e l e c t r i c c o n s t a n t f o r Ottawa sand a t v a r i o u s ambient

t e m p e r a t u r e s

X-RAY NEASUREMENT S

I n t h e s i l t y c l a y experiments, i t

was f e l t n e c e s s a r y t o have a means of observing t h e f o r m a t i o n of i c e i n t h e sample d u r i n g f r e e z i n g . The r a d i o g r a p h i c equipment used by Penner and Goodrich

(1980) had proven u s e f u l i n l o c a t i n g s e g r e g a t e d i c e i n t h e i r l a b o r a t o r y f r o s t heaving experiments. The X-ray

photographs were t a k e n through t h e c y l i n d r i c a l sample on a 20 x 2 5 cm f i l m placed behind t h e sample mould. The exposure t i m e was a b o u t 7 t o 8 minutes a t a d i s t a n c e of 1.5 m and a s e t t i n g of 200 25 TOPP ET A 1 119801 MEAN + Z

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1 0 n 4 5 0 o 10 2 0 30 a o V O L U M E T R I C W A T E R C O N T E N T . % F i g u r e 2. Volumetric w a t e r c o n t e n t v e r s u s a p p a r e n t d i e l e c t r i c c o n s t a n t f o r s i l t y c l a y a t 22OC A N N A N A N D D A V I S ( 1 9 7 8 ) B A K E R A N D D A V I S ( T H I S P A P E R ) T E M P E R A T U R E . O C F i g u r e 3. Temperature e f f e c t on a p p a r e n t d i e l e c t r i c c o n s t a n t of s i l t y c l a y

Figure 4. TDR waveforms f o r t h e sand experiment s c a l e : v e r t i c a l 200 mpldiv; h o r i z o n t a l 2 n s / d i v

kV and 5 ma. A 1 cm2 l e a d t a r g e t was p l a c e d on t h e f r o n t of t h e mould t o a c t a s l o c a t i o n i n d i c a t o r on t h e r a d i o g r a p h and t o p r o v i d e i n f o r m a t i o n on t h e maximm d i s t o r t i o n . The l e a d t a r g e t and s t e e l r o d s showed up very c l e a r l y on t h e radiographs. I c e s t r i n g e r s o r v e i n s could be s e e n i n t h e f r o z e n zone and formed t h e c h a r a c t e r i s t i c r e t i c u l a t e p a t t e r n of f r o z e n c l a y . The lowest i c e s t r i n g e r o r l e n s o c c u r r i n g between t h e s t e e l rods and/or w i t h i n one rod s p a c i n g around t h e r o d s was used t o i n d i c a t e t h e depth of i c e i n t h e sample. This i s

r e f e r r e d t o i n t h i s paper a s t h e X-ray

measurement. SAND EXPERIMENT

Some TDR t r a c e s from t h e s a n d

experiment a r e shown i n F i g u r e 4. These t r a c e s were made from photographs of t h e TDR s c a n on t h e CRT. The t i m e i n h o u r s i s i n d i c a t e d i n t h e upper l e f t c o r n e r of e a c h t r a c e and i s r e l a t i v e t o t h e t i m e of t h e f i r s t i n d i c a t i o n of t h e f r e e z i n g f r o n t on t h e TDR t r a c e s . The f i r s t t r a c e a t -20 h o u r s shows t h e sample t o be

completely unfrozen. The sample was allowed t o f r e e z e from t h e t o p down and t h e l o c a t i o n of t h e f r e e z i n g f r o n t a s

S U R F A C E T E M P E R A T U R E 30 25 20 E u ; 1 5 C n w 10 T I M E , h

F i g u r e 5. Data from t h e sand experiment

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time progressed i s i n d i c a t e d i n Figure

4

by a n arrow. A t 218 hours, t h e sample was completely f r o z e n and had reached a n i s o t h e r m a l temperature of about -5.6OC. The d i e l e c t r i c c o n s t a n t of t h e f r o z e n sand was used t o l o c a t e t h e f r e e z i n g f r o n t from t h e f r o z e n s i d e .

F i g u r e 5 shows TDR measurements i n comparison w i t h t h e l o c a t i o n of t h e z e r o degree isotherm i n t e r p o l a t e d from t h e temperature measurements. V e r t i c a l l i n e s on t h e l o c a t i o n of t h e z e r o degree

i s o t h e r m i n d i c a t e e r r o r s a s s o c i a t e d w i t h shallow thermal g r a d i e n t s i n t h e v i c i n i t y of 0°C. I n t h e e a r l y s t a g e s of t h e experiment, t h e r e was almost an

i s o t h e r m a l c o n d i t i o n w i t h d e p t h a s t h e sample approached 0 O C . This c o n d i t i o n

remained f o r t h e f i r s t 30 hours b e f o r e t h e bottom temperature was i n c r e a s e d . I n F i g u r e 4, t h e TDR t r a c e a t 25 hours showed a d i s t i n c t r e f l e c t i o n which t h e a u t h o r s a t t r i b u t e d t o t h e f r e e z i n g f r o n t even though t h e temperature d a t a

i n d i c a t e d a n i s o t h e r m a l c o n d i t i o n a s d e s c r i b e d above. A s time progressed and t h e thermal g r a d i e n t i n c r e a s e d , t h e TDR measurements and t h e thermal measurements agreed more c l o s e l y . Between 120 and 150 hours a s l i g h t thaw-back of t h e f r o z e n l a y e r was i n d i c a t e d by b o t h t h e TDR and

--

temperature measurements.

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SILTY CLAY EXPERIMENT

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Some TDR t r a c e s from t h e s i l t y c l a y experiment a r e shown i n F i g u r e 6. The f i r s t t r a c e a t -25 hours shows t h e sample completely unfrozen a t 22OC. The sample was allowed t o f r e e z e from t h e t o p d a r n , s i m i l a r t o t h e sand experiment. The

f r e e z i n g f r o n t i s i n d i c a t e d on e a c h of t h e TDR t r a c e s i n F i g u r e 6 by a n arrow. R e f l e c t i o n s from t h e f r e e z i n g f r o n t a r e n o t a s d i s t i n c t a s t h o s e i n t h e sand experiment (Fig.

4).

A l l TDR t r a c e s were simultaneously produced on t h e x-y

p l o t t e r where t h e l a r g e r s c a l e made t h e r e f l e c t i o n s from t h e f r e e z i n g f r o n t much more d i s t i n c t t h a n shown i n F i g u r e 6. T r a v e l times i n t h e unfrozen zone were used t o l o c a t e t h e p o s i t i o n of t h e f r e e z i n g f r o n t from t h e unfrozen s i d e . A t 336 h o u r s (Fig. 8 ) , t h e sample had s t a b i l i z e d a t a n i s o t h e r m a l temperature of -5.7OC. For t h e t i m e s 240 h o u r s and 336 h o u r s , r e f l e c t i o n s a r e noted a t a l o c a t i o n s i m i l a r t o t h a t p r e v i o u s l y a t t r i b u t e d t o t h e f r e e z i n g f r o n t . The

temperature d a t a i n d i c a t e d t h a t t h e sample had been completely lowered w e l l below O°C and t h a t some i c e s h o u l d e x i s t

F i g u r e 6. TDR waveforms f o r t h e s i l t y c l a y experiment s c a l e : v e r t i c a l 200 mp/div; h o r i z o n t a l 2 n s l d i v along t h e e n t i r e l e n g t h of t h e sample. F i g u r e 7 p r e s e n t s d a t a from t h e s i l t y c l a y experiment. During t h e i n i t i a l f r e e z i n g s t a g e , t h e TDR measurements remained a t a s h a l l o w e r d e p t h t h a n t h e z e r o d e g r e e isotherm. I n t h e second h a l f of t h e experiment, t h e h i g h bottom t e m p e r a t u r e produced a thaw- back of t h e f r o z e n zone and t h e TDR

measurements and z e r o d e g r e e i s o t h e r m a r e c o i n c i d e n t . X-ray measurements were made d u r i n g t h e experiment and t h e y showed i c e s t r i n g e r s o c c u r r i n g about 1.5 t o 2 c m deeper t h a n t h e TDR measurements. A t 173 hours, t h e TDR measurements and t h e X-ray measurements c o i n c i d e . Three r a d i o g r a p h s

t a k e n a t 7.5, 79 and 173 h o u r s ,

r e s p e c t i v e l y , a r e p r e s e n t e d i n F i g u r e 8.

A t 7.5 h o u r s , t h e r e t i c u l a t e ice s t r u c t u r e i n d i c a t e s t h e e x t e n t of t h e f r o z e n zone down t o a d e p t h of about 12

cm. By 79 h o u r s , t h e f r o z e n zone e x t e n d s down t o about t h e same d e p t h a s t h e l e a d

t a r g e t . The i c e s t r i n g e r s a p p e a r t o have grown i n s i z e from t h e previous

photograph. A t 173 hours, t h e f r o z e n zone h a s thawed back t o between 10 and 1 1

cm i n d e p t h and a s e g r e g a t i o n of i c e ( i c e l e n s ) i s c l e a r l y v i s i b l e . It i s f e l t

t h a t t h e i c e l e n s was formed d u r i n g t h e c o o l i n g t r e n d i n i t i a t e d by t h e lowering of t h e bottom t e m p e r a t u r e a t 144 hours.

The growing i c e l e n s would account f o r t h e r e f l e c t i o n s on t h e TDR t r a c e s i n F i g u r e 6 a t 144 and 336 hours.

CONCLUSIONS

Time-domain r e f l e c t o m e t r y has been used t o d i s t i n g u i s h t h e f r e e z i n g f r o n t i n l a b o r a t o r y experiments i n v o l v i n g t h e u n i a x i a l f r e e z i n g of Ottawa sand and a s i l t y c l a y . Measurements of t h e a p p a r e n t d i e l e c t r i c c o n s t a n t s have been used t o c a l c u l a t e t h e t h i c k n e s s of t h e f r o z e n

zone. These measurements have been

compared w i t h t h e s t a n d a r d t e m p e r a t u r e method of l o c a t i n g t h e p o s i t i o n of t h e z e r o degree i s o t h e r m and showed e x c e l l e n t c o r r e l a t i o n s i n t h e sand experiment.

I n t h e s i l t y c l a y experiment, t h e t h r e e measurement techniques depended upon t h r e e d i f f e r e n t p r o p e r t i e s of w a t e r a s s o c i a t e d w i t h f r e e z i n g s o i l s . The t e c h n i q u e u s i n g time-domain r e f l e c t o m e t r y was dependent upon t h e change i n

e l e c t r i c a l p r o p e r t i e s of w a t e r when i t

changed from a l i q u i d t o s o l i d s t a t e . L o c a t i o n of t h e z e r o d e g r e e i s o t h e r m from

temperature measurements was not a

p r e c i s e i n d i c a t o r of t h e change of s t a t e of w a t e r i n f i n e - g r a i n e d s o i l s due t o a

f r e e z i n g p o i n t depression. The X-ray

technique provided a q u a l i t a t i v e

i n d i c a t i o n of t h e p r e s e n c e of s e g r e g a t e d i c e i n t h e f r o z e n s o i l . The u n c e r t a i n t y between t h e TDR and X-ray measurements

was i n t h e o r d e r of 2 cm. This

d i f f e r e n c e may be a t t r i b u t e d t o t h e r e s o l u t i o n of t h e TDR measurements o r t h e dependence on t h e volume and t h i c k n e s s of i c e r e q u i r e d t o produce r e f l e c t i o n s on t h e TDR t r a c e .

The TDR measurements a l o n e may n o t i n themselves p r o v i d e enough i n f o r m a t i o n t o t o t a l l y d e l i n e a t e t h e e x t e n t of t h e f r o z e n zone, but s h o u l d be used i n c o n j u n c t i o n w i t h o t h e r methods now being a p p l i e d .

REFERENCES

Annan, A.P. and J.L. Davis. 1978. High

frequency e l e c t r i c a l method f o r t h e

d e t e c t i o n of freeze-thaw i n t e r f a c e s .

Proc. T h i r d I n t . Permafrost Conf.,

Edmonton, A l b e r t a , Vol. 1, pp. 496-500.

Baker, T.H.W., J.L. Davis, H.N. Hayhoe

and G.C. Topp. 1982. Locating t h e f rozen/unfrozen i n t e r f ace i n s o i l s u s i n g

time-domain r e f l e c t o m e t r y . Can. Geot.

Jour. ( i n p r e s s ) .

Davis, J.L., G.C. Topp and A.P. Annan.

1976. Electromagnetic d e t e c t i o n of s o i l

w a t e r c o n t e n t . Proc. of Workshop on

Remote Seesing of S o i l Moisture and Ground Water, Toronto, 1 3 p.

P a t t e r s o n , D.E. and M.W. Smith. 1981.

The measurement of unfrozen w a t e r c o n t e n t by time-domain r e f l e c t o m e t r y :

r e s u l t s from l a b o r a t o r y tests. Can.

Geot. Jour., Vol. 18, No. 1, pp. 131- 144.

Penner, E. and L.E. Goodrich. 1981.

Location of s e g r e g a t e d i c e i n f r o s t -

s u s c e p t i b l e s o i l . Engineering Geology,

Vol. 18, pp. 231-244.

Topp, G.C., J.L. Davis and A.P. Annan.

1980. Electromagnetic d e t e r m i n a t i o n of

s o i l w a t e r content: measurements i n

c o a x i a l t r a n s m i s s i o n l i n e s . Water Resources Research, Vol. 16, No. 3, pp. 574-582.

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 Building Research,

N a t i o n a l Research Council of Canada, and i s published w i t h t h e permission of t h e D i r e c t o r of t h e Division.

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F i g u r e 7. Data from t h e s i l t y c l a y experiment

F i g u r e 8. Radiographs from t h e s i l t y c l a y experiment, ( a ) 7.5 hours ( b ) 79 hours ( c ) 1 7 3 hours

T h i s paper, w h i l e being d i s t r i b u t e d i n r e p r i n t form by t h e D i v i s i o n of B u i l d i n g Research, remains t h e c o p y r i g h t of t h e o r i g i n a l p u b l i s h e r . It should n o t be reproduced i n whole o r i n p a r t w i t h o u t t h e permission of t h e p u b l i s h e r . A l i s t of a l l p u b l i c a t i o n s a v a i l a b l e from t h e D i v i s i o n may be o b t a i n e d by w r i t i n g t o t h e P u b l i c a t i o n s S e c t i o n , 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, O t t a w a , O n t a r i o ,

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