11.3.
SPECIFIC HEATS AND UNFROZEN WATER CONTENT
O F FROZEN SOILS
P. J. Williams
I t was o b s e r v e d m a n y y e a r s ago that w a t e r in s o i l s did not
f r e e z e until the t e m p e r a t u r e w a s lowered appreciably below 0°C (1 1).
Subsequent e x p e r i m e n t s d e m o n s t r a t e d t h a t i n n a t u r a l s o i l s t h e r e is
no single f r e e z i n g point b u t t h a t the w a t e r f r e e z e s p r o g r e s s i v e l y a s
the t e m p e r a t u r e f a l l s (1, 3 ) . In fine-grained s o i l s one-third of the
w a t e r m a y r e m a i n unfrozen a t s e v e r a l d e g r e e s below 0 ° C (8, 9).
The s t r e s s e s s t i l l existing i n the s o i l - w a t e r s y s t e m a r e g e n e r a l l y
r e g a r d e d as the m o s t i m p o r t a n t c a u s e of t h i s phenomenon.
The changing p r o p o r t i o n s of f r o z e n and unfrozen w a t e r a r e
significant i n consideration of the s t r e n g t h and deformation of f r o z e n
ground (10, 15), and the f r e e z i n g and thawing of w a t e r i n s o i l a t temp e r a t u r e s below 0 ° C h a s i m p o r t a n t effects on i t s t h e r m a l p r o p e r t i e s .
S e v e r a l s o i l s have r e c e n t l y been studied by c a l o r i m e t r y a s p a r t of a n
investigation by the author of the unfrozen w a t e r content. The experim e n t a l o b s e r v a t i o n s and calculation of unfrozen w a t e r content f r o m
t h e m a r e b r i e f l y d e s c r i b e d and d i s c u s s e d i n t h i s paper. I t will b e
shown that the application of the r e s u l t s to field p r o b l e m s r e q u i r e s
consideration of the f a c t o r s influencing the 'freezing of w a t e r i n soil.
CALORIMETRIC INVESTIGATIONS
A c a l o r i m e t e r h a s been constructed which p e r m i t s m e a s u r e m e n t of the amount of h e a t added t o o r r e m o v e d f r o m a s o i l s a m p l e
t o r a i s e o r lower i t s t e m p e r a t u r e by a given amount. T h r e e thermocouples i n s e r t e d i n the s a m p l e m e a s u r e i t s t e m p e r a t u r e , which i s
continuously r e c o r d e d . T e m p e r a t u r e differences within the s a m p l e
a r e n o r m a l l y l e s s than l / l 0 " C .
During the w a r m i n g of a s a m p l e , a m e a s u r e d h e a t input i s
supplied e l e c t r i c a l l y by a c o i l wound around the holder containing the
s a m p l e (Fig. 1). I t i s n e c e s s a r y t h a t t h e r e 'be no significant exchange
of heat with the s o i l s a m p l e o t h e r than that a r i s i n g f r o m the heating
coil. T o achieve t h i s , the s a m p l e holder i s suspended inside a b r a s s
container maintained a t a t e m p e r a t u r e a l m o s t equal to that of the
s a m p l e holder. T h e r e i s t h u s no significant t e m p e r a t u r e gr.adient and
negligible exchange of h e a t between t h e m . The t e m p e r a t u r e of the
b r a s s container i s regulated by a h e a t e r i n the r e f r i g e r a t e d ethylene
glycol surrounding it. T h i s h e a t e r is controlled automatically by a
m e c h a n i s m which o p e r a t e s when a s m a l l t e m p e r a t u r e difference
o c c u r s between the b r a s s container and the s u r f a c e of.the s a m p l e
holder .
F r o m m e a s u r e d values of the t i m e taken f o r the t e m p e r a t u r e
of the s o i l to r i s e a given amount and r a t e of heat input to the s a m p l e ,
the quantity of h e a t supplied to c a u s e the t e m p e r a t u r e r i s e i s calcul a t e d . I n the thawing c u r v e s of F i g u r e s 2 to 4 inclusive, r e s u l t s of
t h i s type a r e shown, a s the specific h e a t of the s o i l (i.e. the amount
of h e a t i n c a l o r i e s r e q u i r e d to r a i s e the t e m p e r a t u r e of one g r a m of
s o i l b y 1 "C) f o r v a r i o u s negative t e m p e r a t u r e s .
T h e s p e c i f i c he.ats during f r e e z i n g a r e obtained i n a s i m i l a r
way ( F i g u r e s 2 to 4) except that the b r a s s container i s held a t a temp e r a t u r e l o w e r b y a constant amount than that of the s a m p l e holder.
T h e heating c o i l on the s a m p l e i s not o p e r a t e d . T h e r e i s then a s t e a d y
e x t r a c t i o n of h e a t f r o m the h o l d e r , the magnitude of which i s d e t e r mined by p r i o r calibration.
W e r e a l l the w a t e r t o f r e e z e a t O°C,one would expect t h a t
v a l u e s of the s p e c i f i c h e a t below 0 "C would be roughly constant and
of m u c h the s a m e magnitude a s those above 0°C. In f a c t , the latent
h e a t r e l e a s e d o r a b s o r b e d a s w a t e r i s p r o g r e s s i v e l y f r o z e n o r thawed
r e s u l t s i n s p e c i f i c h e a t s many t i m e s a s g r e a t . F o r a given s a m p l e ,
t h e s p e c i f i c h e a t s d e t e r m i n e d during cooling differ somewhat f r o m
t h o s e d e t e r m i n e d d u r i n g f r e e z i n g . Not only i s the value of s p e c i f i c
h e a t f o r a given t e m p e r a t u r e different i n the two c a s e s , but f o r one
s o i l type ( F i g u r e 4), t h e values obtained f o r t h e . c a s e of cooling
r e p e a t e d l y showed a n unexpected r i s e i n the region of -1. 1 "G.
Instrumental Accuracy
T h e a c c u r a c y of the c u r v e s shown i n F i g u r e s 2 to 4 inclusive,
depends s u b s t a n t i a l l y on the quality of the t e m p e r a t u r e m e a s u r i n g and
c o n t r o l equipment a s s o c i a t e d with the c a l o r i m e t e r . Calibration t e s t s
i n d i c a t e t h a t the s p e c i f i c heat v a l u e s r e p r e s e n t e d by the smoothed
g r a p h a r e c o r r e c t t o within a few p e r cent. The periodic fluctuations
of points a t l o w e r t e m p e r a t u r e s a r e probably due to e x p e r i m e n t a l
e r r o r . The conspicuous peak a t - 1 . 1 " C i n F i g u r e 4, e x c e e d s by m a n y
t i m e s t h e value t h a t would b e expected should the c u r v e i n fact b e
smooth, and it cannot b e r e g a r d e d a s a n e x p e r i m e n t a l e r r o r . On the
o t h e r hand, t h e v a r i a t i o n s on the thawing curve a t about - 0 . 5 "C
r e p r e s e n t deviations which, r e g a r d e d a s a percentage, a r e no g r e a t e r
t h a n those a p p e a r i n g f o r the lower specific h e a t s a t lower t e m p e r a t u r e s.
CALCULATION O F THE PROPORTION O F ICE
AND UNFROZEN WATER IN THE SOIL
T h e c a l o r i m e t e r r e s u l t s c a n be u s e d to calculate the i c e f o r m a t i o n taking place i n the s o i l . By deducting amounts c o r r e s p o n d i n g
to the specific h e a t of the m i n e r a l components, i c e and w a t e r p r e s e n t ,
f r o m the heat involved in a given t e m p e r a t u r e change, a value f o r the
heat involved i n f r e e z i n g o r thawing w a t e r during that t e m p e r a t u r e
change i s obtained. Assuming the latent h e a t of f r e e z i n g to have the
s a m e value a s that of f r e e w a t e r , a figure i s obtained f o r the amount
of ice f o r m e d o r m e l t e d . By a p r o c e s s of summation between the
t e m p e r a t u r e of initial f r e e z i n g , o r completed thawing, and t e m p e r a t u r e s below t h e m , c u r v e s of the type shown ( F i g u r e s 5 to 7) a r e
obtained.
The finer-grained s o i l s show higher unfrozen w a t e r contents.
F o r e a c h s o i l t h e r e i s a m a r k e d h y s t e r e s i s , such that the amount of
unfrozen w a t e r p r e s e n t a t a given negative t e m p e r a t u r e will depend
on whether the s o i l i s undergoing w a r m i n g o r cooling. F u r t h e r m o r e ,
during thawing the amount i s a l s o dependent on the lowest t e m p e r a t u r e r e a c h e d i n that freeze-thaw cycle ( F i g u r e 9).
Repeated t e s t s on the s a m e s a m p l e , and on different s a m p l e s
of the s a m e s o i l , give r e s u l t s within 3 . 5 % d r y weight f o r the unfrozen
m o i s t u r e content at - 4 ° C . Various r a t e s of cooling w e r e u s e d . The
t i m e taken f o r cooling f r o m -1" to -4°C w a s v a r i e d f r o m 4 h o u r s to
16 h o u r s , and a p p e a r e d to have no effect on the r e s u l t s ( F i g u r e 8).
The unfrozen m o i s t u r e content i s shown to be independent of the t o t a l
m o i s t u r e content ( ~ i ~ u 9),
r e so long of c o u r s e , a s i t i s g r e a t e r than
this.
PHYSICAL PROCESSES RESPONSIBLE FOR
THESE OBSERVATIONS
The physical p r o c e s s e s giving r i s e to t h e s e o b s e r v a t i o n s a r e
incompletely understood, and the c a l o r i m e t r i c r e s u l t s by t h e m s e l v e s
provide only l i m i t e d information. D i s c u s s i o n of the p r o c e s s e s i s
a p p r o p r i a t e b e c a u s e they a p p e a r likely to have considerable r e l e v a n c e
i n the p r a c t i c a l application of the c a l o r i m e t r i c r e s u l t s .
H v ~ o t h e s e sInvolving S t r e s s e s i n s o i l Water
When i c e and w a t e r e x i s t t o g e t h e r under a p r e s s u r e g r e a t e r
than a t m o s p h e r i c , the f r e e z i n g point i s lowered below 0 "C. Edlefson
and Anderson point out a l s o that if i c e a t a t m o s p h e r i c p r e s s u r e i s i n
contact with w a t e r a t a p r e s s u r e lower than a t m o s p h e r i c , t h i s too will
c a u s e a f r e e z i n g point d e p r e s s i o n ( 6 ) .
That the w a t e r i n u n s a t u r a t e d s o i l s i s not at a t m o s p h e r i c press u r e i s shown by the fact that w a t e r m o v e s into such s o i l s f r o m a
s o u r c e a t a t m o s p h e r i c p r e s s u r , e . T h i s s t a t e of s t r e s s , o r so-called
"suction", of the w a t e r of .soils i s g r e a t e r the lower the w a t e r content.
S e v e r a l a u t h o r s point out that, a s i c e f o r m s in a s o i l , the remaining
w a t e r will b e u n d e r a n i n c r e a s i n g l y different s t a t e of s t r e s s to that
of f r e e w a t e r a t a t m o s p h e r i c p r e s s u r e . Accordingly, to f r e e z e s u c h
w a t e r r e q u i r e s p r o g r e s s i v e l y lower t e m p e r a t u r e s .
Different t h e o r i e s have b e e n put f o r w a r d a s to the n a t u r e of
the s t r e s s e s i n s o i l w a t e r that might be responsible f o r the lowering
of the f r e e z i n g point. Winterkorn (16), Jung (9) and E d l e f s e n and
A n d e r s o n (6)) have proposed t h a t the adsorption f o r c e s of the s o i l
p a r t i c l e s a c t i n g o n the adjacent w a t e r molecules r e s u l t i n p r e s s u r e s
i n the s o i l w a t e r t h a t a r e higher than a t m o s p h e r i c . When t h e s e p r e s s u r e s e x i s t a t a n i c e / w a t e r i n t e r f a c e , t h e r e will be a lowering of the
f r e e z i n g point. A s t h e p a r t i c l e s u r f a c e i s approached, the p r e s s u r e
due t o t h e a d s o r p t i o n f o r c e s i n c r e a s e s , and the f r e e z i n g point b e c o m e s
lower.
I n . c o n t r a s t , o t h e r s (12) maintain that m o s t of the w a t e r i n uns a t u r a t e d s o i l s is b e c a u s e of c a p i l l a r y effects, under tension (suba t m o s p h e r i c p r e s s u r e , o r negative s t r e s s ) . T h i s a l s o c a n r e s u l t i n a
l o w e r e d f r e e z i n g point provided any i c e p r e s e n t i s under a t m o s p h e r i c
o r h i g h e r p r e s s u r e s (6) (this is a l s o i m p l i c i t i n the equation used by
Schofield (14), and C r o n e y and Coleman (4)).
I t is not known t o what extent different p r e s s u r e s c a n o c c u r i n
a d j a c e n t i c e and w a t e r p h a s e s i n a soil. Nor i s it a p p r o p r i a t e i n t h i s
p a p e r to d i s c u s s the r e l a t i v e i m p o r t a n c e i n the s o i l w a t e r of s t r e s s e s ,
g r e a t e r , o r l e s s , than a t m o s p h e r i c p r e s s u r e . E i t h e r of the situations
outlined above c a n provide a reasonable explanation of the "suction"
p r o p e r t i e s of s o i l s . B y using e x p e r i m e n t a l l y o b s e r v e d v a l u e s of s o i l
"suction" f o r p a r t i c u l a r m o i s t u r e contents, values of f r e e z i n g point
d e p r e s s i o n m a y b e calculated f o r t h e s e m o i s t u r e contents (6, 14).1
T h e s e f r e e z i n g point v a l u e s c a n then be c o m p a r e d with the t e m p e r a t u r e s found to give e q u a l contents of unfrozen w a t e r i n f r o z e n s o i l s :
Depending upon which of the two situations d i s c u s s e d i s accepted,
somewhat different v a l u e s a r e obtained f o r the f r e e z i n g point d e p r e s s i o n . With the l i m i t e d information a t p r e s e n t available, both a p p e a r
r e a s o n a b l e f o r c e r t a i n r a n g e s of m o i s t u r e content. Investigations a r e
a t p r e s e n t being c a r r i e d out t o d e t e r m i n e m o r e p r e c i s e l y t h i s r e l a t i o n
between suction c h a r a c t e r i s t i c s of s o i l s and the amount of unfrozen
w a t e r p r e s e n t a t v a r i o u s negative t e m p e r a t u r e s .
I n t h i s p a p e r a typographical e r r o r h a s apparently o c c u r r e d i n the
equation which should r e a d : -
H=(LJ) x t
(T d
w h e r e X = c m . of w a t e r ; T = a b s o l . t e m p .
L j = latent h e a t
t = f r e e z i n g point
of fusion;
depression.
F r o m the p r e s e n t e x p e r i m e n t a l observations, and the o b s e r vations and d i s c u s s i o n s of o t h e r s , i t can be .concluded that the s t r e s s e s
i n the s o i l i n the p0r.e w a t e r and solid p h a s e s have considerable
influence on the c o u r s e of f r e e z i n g .
D e p r e s s i o n of F r e e z i n g Point b y Dissolved Salts
Bouyoucos (2) and o t h e r s believed that the s o i l w a t e r contained
sufficient s a l t s such that, a s f r e e z i n g p r o g r e s s e d , the concentration
would r i s e sufficiently (because the s a l t s a r e substantially excluded
f r o m the i c e ) (to give lowered f r e e z i n g t e m p e r a t u r e s of the magnitude
o b s e r v e d . I n f a c t , a s pointed out by Edlefsen and Anderson, the s a l t
concentration i s f a r too low f o r t h i s to be s o i n m o s t s o i l s . The s o i l
solution e x t r a c t e d f r o m the L e d a clay a t about 30% m o i s t u r e content
w a s found to f r e e z e a t approximately -0. 1 "C. When a l l but 5% moist u r e content i s f r o z e n , the d e p r e s s i o n of the f r e e z i n g point on t h i s
account will b e approximately 0. 6 ° C .
Value Ascribled to the L a t e n t Heat of F r e e z i n g
I n calculating the amounts of unfrozen w a t e r , a value of
79. 68 ~ a l o r i e s / ~ r w
ma s adopted f o r the latent h e a t of f r e e z i n g . T h i s
i s not s t r i c t l y c o r r e c t f o r f r e e z i n g o c c u r r i n g below 0°C. F i g u r e s a r e
available f o r the latent heat a t f r e e z i n g below 0°C o c c u r r i n g a s the
r e s u l t of a p r e s s u r e applied equally t o both the i c e and w a t e r (5).
Were t h e s e f i g u r e s used, the calculated values of unfrozen m o i s t u r e
content a t , f o r example, -5 "C might differ by about 1/2% d r y weight
f r o m those shown. Values a r e not known f o r situations w h e r e the
p r e s s u r e s on the i c e and w a t e r p h a s e s might differ, but s u c h v a l u e s
a r e probably of s i m i l a r magnitude.
When w a t e r i s added to oven d r i e d s o i l s , m e a s u r a b l e quantit i e s of h e a t a r e l i b e r a t e d . T h i s "heat of wetting" r e s u l t s , a t l e a s t i n
p a r t , f r o m the adsorption of w a t e r on to s o i l p a r t i c l e s . Such s o i l
w a t e r , f r o m which h e a t h a s b e e n l o s t , might have a substantially
lowered latent h e a t of f r e e z i n g ( 7 , 13). The h e a t s of wetting have b e e n
d e t e r m i n e d ( F i g u r e 10) f o r the s o i l s shown i n F i g u r e 5. T h e t e m p e r a t u r e r i s e o c c u r r i n g when a weighed quantity of the s o i l w a s mixed
with a g r e a t e r quantity of w a t e r was o b s e r v e d . F o r s a m p l e s i n which
s o m e m o i s t u r e was a l r e a d y p r e s e n t , the h e a t l i b e r a t e d w a s much l e s s
r e Already a t quite low m o i s t u r e
than f o r oven d r i e d s o i l s ( ~ i ~ u 10).
contents, the addition of f u r t h e r w a t e r does not r e s u l t i n significant
heat of wetting. I t i s r e a s o n a b l e to a s s u m e that the w a t e r f r o m which
significant h e a t i s l o s t , b e c a u s e i t includes the m o s t s t r o n g l y adsorbed,
would only f r e e z e a t the lowest t e m p e r a t u r e s . When F i g u r e s 4 to 6
i n c l u s i v e a r e c o m p a r e d with F i g u r e 10, i t i s s e e n that the quantity of
w a t e r r e m a i n i n g unfrozen, even a t the lowest t e m p e r a t u r e s r e c o r d e d ,
.
p r o b a b l y i n c l u d e s a l l the w a t e r t h a t is a s s o c i a t e d w i t h the heat of wetting. The question of latent heat of s u c h w a t e r does not t h e r e f o r e a r i s e .
VALIDITY OF THE CALORIMETRIC RESULTS IN
FIELD PROBLEMS
The c a l o r i m e t r i c o b s e r v a t i o n s do not r e p r e s e n t exactly the
t h e r m a l p r o p e r t i e s of the s o i l u n d e r n a t u r a l conditions. E s p e c i a l l y
w h e r e t h e o v e r b u r d e n is thick, the s t r e s s e s within the s o i l will b e
d i f f e r e n t f r o m those i n the c a l o r i m e t e r s a m p l e . The s t r e s s e s i n both
i c e a n d ' w a t e r p h a s e s m a y give r i s e to corresponding differences i n
the p r o p o r t i o n s of f r e e z i n g and unfrozen w a t e r . The specific h e a t s
d u r i n g f r e e z i n g will often be a p p a r e n t l y i n c r e a s e d by m i g r a t i o n of
w a t e r and the a s s o c i a t e d i c e l e n s growth. F o r many p r a c t i c a l
p r o b l e m s , however, involving n e a r s u r f a c e conditions, and w h e r e i n
a n y c a s e the t e m p e r a t u r e and s o i l conditions a r e not v e r y p r e c i s e l y
defined, a useful qualitative evaluation m a y be obtained f r o m the
calorimetric observations.
GENERAL SUMMARY
The unfrozen w a t e r of f r o z e n s o i l s h a s been shown to b e a
significant and quite complex phenomenon. It is a p p r o p r i a t e to
s u m m a r i z e t h o s e a s p e c t s likely to be of g e n e r a l i m p o r t a n c e .
I n m o s t s o i l s the f r e e z i n g and thawing p r o c e s s e s a r e prog r e s s i v e with the l a t e n t heat of f r e e z i n g being involved through a wide
r a n g e of t e m p e r a t u r e . F o r the sub-zero t e m p e r a t u r e s o c c u r r i n g i n
m a n y field s i t u a t i o n s , a significant proportion of the s o i l w a t e r is
unfrozen. At a given negative t e m p e r a t u r e the amount of unfrozen
w a t e r p r e s e n t v a r i e s considerably with the type of soil, being g r e a t e r
with f i n e r - g r a i n e d s o i l s . I t a l s o depends on whether the s o i l i s
f r e e z i n g o r thawing, and i n the l a t t e r c a s e f u r t h e r depends o n the
l o w e s t t e m p e r a t u r e r e a c h e d during f r e e z i n g .
I n c e r t a i n field p r o b l e m s t h e application of the specific h e a t s
a n d unfrozen w a t e r contents d e t e r m i n e d by the c a l o r i m e t r i c o b s e r v a t i o n s r e q u i r e s c o n s i d e r a t i o n of the e f f e c t s of o v e r b u r d e n p r e s s u r e s
and m o i s t u r e supply.
REFERENCES
1. Bouyoucos, G. J. A New C l a s s i f i c a t i o n of the Soil M o i s t u r e . Soil
Science, Vol. 9, No. 1, 1921.
2.
Classification and M e a s u r e m e n t of the Different
F o r m s of Water i n the Soil .by m e a n s of the Dilatometer Method.
Mich. A g r i c . Coll. Ex;. St., T e c h . Bull. No. 3 6 , 1917. 48 p.
Bouyoucos, G. J. and M. M. McCool. F u r t h e r Studies on the
F r e e z i n g Point Lowering of Soils. Mich. A g r i c . Coll. Exp. St.,
Tech. Bull. No. 31, 1916. 5 1 p.
Croney, D., Coleman, J. D. and P a m e l a M. B r i d g e . The Suction
of Moisture Held i n Soil and Other P o r o u s M a t e r i a l s . Road
R e s e a r c h Technical P a p e r No. 24. Dept. of Scientific and Indust r i a l R e s e a r c h , Harmondsworth, Middlesex. 1952.
Dorsey, N. E . P r o p e r t i e s of O r d i n a r y Water-Substance. National
B u r e a u of Standards, Washington, D. C.
Edlefsen, N. E . and Alfred B .C. Anderson. Thermodynamics of
Soil Moisutre. J o u r n . of Agric. Science, Vol. 15, No. 2, 1943.
G r i m , R. E . Clay Mineralogy. McGraw-Hill. 1953. 384 p.
Institut Me rzlotovedeniia. M a t e r i a l y po laboratornym
issledovaniiam m e r z l y k h gruntov. Akademiia Nauk SSSR, Izd.
Moskva, i m . V.A. Obrucheva, Sbornik 1, 2, 3, 1953-57.
Jung, E . Weitere r B e i t r a g z u r a g g r e g i e r e n d e n Einwirkung d e s
F r o s t e s auf den Erdboden. Z e i t s c h r . f u r Pflanzenern. Dting. u.
Bodenk. A. Wiss. Teil, Bd. 1932. p. 1-20.
Lovell, C. W. T e m p e r a t u r e Effects on P h a s e Composition and
Strength of Partially-frozen Soil. Highway R e s e a r c h B o a r d ,
Bull. 168. 1957.
P e t i t , A . Untersuchungen tiber den Einfluss d e s F r o s t e s auf die
T e m p e r a t u r v e r h a l t n i s s e d e r Boden von v e r s c h i e b e n e r
physikalische Beschaffenheit. F o r s c h . Agrik. - Phys. LXXII.
1893.
P o r e P r e s s u r e and Suction i n Soils. C o d . organized by B r i t i s h
National Society of the International Society of Soil Mechanics
and Foundation Engineering a t the Institution of Civil E n g i n e e r s ,
London. 1960.
Rosenqvist, I. Th. Investigations i n the Clay-Electrolyte Water
System. Norwegian Geotechnical Institute, Oslo. Publ. No. 9,
1955. 125 p.
Schofield, R.K. T h e p F of the Water i n Soil. International Cong r e s s of Soil Science. T h i r d , Vo1. 2, 1935. pp. 37-48.
Discussion f r o m Vo1.3, 1935. pp. 182-186.
Vialov, S. S. C r e e p and Long-Term s t r e h g t h of F r o z e n Soils.
Dok. Akad. Nauk SSSR, Vol. 104, No. 6, 1955. pp. 850-853.
T r a n s l a t e d F e b r u a r y 1957, Defence R e s e a r c h B o a r d , Canada,
T 2 0 3 R , 4 p.
Winterkorn, H. F. The Condition of Water i n P o r o u s S y s t e m s .
Soil Science, Vo1.56, 1943.
Discussion
R. Yong asked, with r e f e r e n c e to the unfrozen m o i s t u r e cont e n t s of s a m p l e s with different.tota1 m o i s t u r e contents, whether the
density of s u c h s a m p l e s d i f f e r s initially, to which the author r e p l i e d
t h a t i t would differ initially. yon; enquired f u r t h e r what m e c h a n i s m s
w e r e c o n s i d e r e d r e s p o n s i b l e f o r the p r e s e n c e of unfrozen w a t e r .
T h e a u t h o r s t a t e d h i s belief that c a p i l l a r i t y i s r e s p o n s i b l e a t l e a s t
f o r t h e f i r s t 1 " - 2 "C below 0 "C. Yong's first question might be
a n s w e r e d b e t t e r by saying that although the initial density was changed
b y changing the i n i t i a l m o i s t u r e content, the question w a s whether the
magnitude of the change was significant. F u r t h e r m o r e , a s f r e e z i n g
p r o g r e s s e s , the unfrozen water content b e c o m e s lower and lower, and
i t i s t h i s ( d e c r e a s i n g ) quantity of w a t e r which d e t e r m i n e s the d e g r e e
of packing of the p a r t i c l e s .
A. E . C o r t e r e q u e s t e d i n f o r m a t i o n on the possibility of e x p r e s s i n g the r e s u l t s a s t i m e / t e m p e r a t u r e c u r v e s f o r the s o i l s . The author
r e p l i e d t h a t i n f a c t s u c h c u r v e s w e r e o b s e r v e d d i r e c t l y with the
c a l o r i m e t e r . They w e r e not v e r y meaningful, however, u n l e s s the s i z e
of the s a m p l e w a s t a k e n into account. C o r t e s a i d he w a s i n t e r e s t e d i n
m o r e d e t a i l s on supercooling. The author a n s w e r e d that t h i s was
shown c l e a r l y , the t e m p e r a t u r e falling slowly to somewhat below 0°C
a n d t h e n r i s i n g suddenly to just below 0°C. After that a much slower
cooling t a k e s place. Supercooling v a r i e d with s o i l type and with diff e r e n t s a m p l e s of the s a m e soil. Although h a r d l y s t a t i s t i c a l l y signifi-.
c a n t , it i s f e l t t h a t results. of the r e p e a t e d f r e e z i n g of the s a m e sample
showed l e s s v a r i a t i o n than that between f r e e z i n g s of different s a m p l e s
of the s a m e s o i l .
N. W. Radforth wanted f u r t h e r information a s to the "suction
p r o p e r t i e s of the w a t e r 1 ' which w e r e suggested a s the c a u s e of the
unfrozen w a t e r . The a u t h o r c l a r i f i e d the question by stating that i t
would b e m o r e p r e c i s e to s a y "suction p r o p e r t i e s of the soil" b e c a u s e
the w a t e r i s r e g a r d e d a s being l a r g e l y just o r d i n a r y w a t e r . The suct i o n p r o p e r t i e s w e r e t h o s e often r e f e r r e d to a s " m o i s t u r e potential1'
o r "pF" of the s o i l . Radforth then a s k e d i f the m o i s t u r e is distributed
evenly throughout t h e s a m p l e . The author replied that even i n those
t e s t s c a r r i e d out m o s t slowly, the u n f r o z e n m o i s t u r e content was
s i m i l a r to t h a t found i n the o t h e r t e s t s . T h e r e f o r e a s t a t e of equilibr i u m could be a s s u m e d to have been r e a c h e d i n the s a m p l e . A s f a r a s
the unfrozen w a t e r i s concerned, t h i s m e a n s the suction p r o p e r t i e s ,
o r p F , would b e uniform throughout (the w a t e r having no tendency to
m i g r a t e ) . B e c a u s e e a c h s a m p l e is quite uniform, i t c a n be a s s u m e d
t h a t the unfrozen m o i s t u r e content w a s uniformly distributed.
HEATER
GLYCOL
HEATING
COIL ON
SAMPLE
HOLDER
LUCITE TANK
7
VALVE T O
ALLOW
FLOW FROM
3ER
STIRRER
SAMPLE HOLDER (DURAL)
B R A S S CONTAINER
THE
CALORIMETER
FIGURE I
31
30
29
I
I
I
TEMPERATURE,
26
27
28
I
I
1
OF
25
24
23
22
I
I
I
I
TO 92.78
NIAGARA SILT
LEGEND:
-
-
II I
0
-I
-2
FREEZING RUN
THAWING RUN
UNFROZEN
-3
TEMPERATURE, O C
-4
-5
FIGURE 2
SPECIFIC HEAT O F NIAGARA SILT DURING
FREEZING AND THAWING.
TEMPERATURE, OF
1
31
30
29
28
27
26
25
24
23
22
I
I
I
I
I
I
I
I
I
I
1
I1
LEDA CLAY 100-7
LEGEND:
-
FREEZING RUN
THAWING RUN
UNFROZEN
TEMPERATURE,
OC
FIGURE 3
S P E C I F I C HEAT O F LEDA CLAY 100-7
DURI NG F R E E Z I N G AND THAW1 NG.
LEDA CLAY KNB
LEGEND:
-
FREEZING RUN
THAWING RUN
UNFROZEN
TEMPERATURE, 'C
FIGURE 4
SPECIFIC HEAT OF LEDA CLAY KNB DURING
FREEZING AND THAWING.
3032
30
l
l
28
l
l
TEMPERATURE, O F
26
24
22
l
l
l
l
l
l
l
20
l
I(
l
1
25
I-
x
s
>
20
a
NIAGARA SILT
0
a-"
i
W
Z
t
g
15
LEGEND:
-
W
a
3
I-
v,
FREEZING RUN
THAWING RUN
0
5
Z
W
g
I0
a
Z
LL
2
5
I
OL
-
1
'
-
-
-
TEMPERATURE,
-
t
OC
FIGURE 5
UNFROZEN WATER CONTENT O F NIAGARA SILT
DURING F R E E ZING AND THAWING
TEMPERATURE,
2
28
30
1
1
1
1
24
26
1
1
1
1
1
LEDA CLAY 100-7
OF
22
1
20
1
-
1
1
1
'
LEGEND:
- FREEZING RUN
-- THAWING
I
-1
I
-2
I
1
RUN
I
-5
TEMPERATURE, O C
-3
-4
I
I
-6
-7
FIGURE 6
UNFROZEN WATER CONTENT OF LEDA CLAY 100-7
DURING F R E E ZING AND THAWING.
TEMPERATURE, OF
30
28
26
22
24
LEGEND:
--
FREEZING RUN
o-
\
THAWING RUN
LEDA CLAY K N B
-2
-3
-4
TEMPERATURE "C
-
FIGURE 7
U N F R O Z E N WATER CONTENT O F L E D A CLAY KNB
DURING F R E E ZING AND THAWING.
'2
I
-1
TEMPERATURE, *OF
26
24
22
20
28
30
I
I
-2
-3
I
I
I
-5
-6
TEMPERATURE, "C
-4
18
I
I
-7
-8
FIGURE 8
T H E U N F R O Z E N WATER CONTENT O F L E D A CLAY
KNB A P P E A R S INDEPENDENT O F T H E R A T E S
O F F R E E ZING SHOWN.
""""j"
TEMPERATURE,
OF
LEGEND:
- FREEZING RUN
-- THAWING
RUN
c,
c,
25
"b -I
-
-
-
-b
TEMPERATURE,
-A -;
OC
FIGURE 9
UNFROZEN WATER CONTENTS O F SAMPLES O F
LEDA CLAY, O F 32 P E R CENT MOISTURE CONT E N T (CURVES C1, C2), AND 22 P E R CENT
MOISTURE CONTENT, (CURVES A1, AZ AND B1,
B2).
NIAGARA SILT
INITIAL MOISTURE CONTENT OF SOIL, % DRY WEIGHT
LEDA CLAY KNB
INITIAL MOISTURE CONTENT OF SOIL. % DRY WEIGHT
LEDA CLAY 100-7
INITIAL MOISTURE CONTENT OF SOIL, %
' DRY WEIGHT
FIGURE
10
HEAT O F WETTING OF SOIL SAMPLES O F VARIOUS
INITIAL MOISTURE CONTENTS. IT IS APPARENT
THAT THE ADDITION O F WATER AT MOISTURE
CONTENTS ABOVE ABOUT 4 P E R CENT DRY W T .
IS NOT ASSOCIATED WITH LIBERATION O F HEAT.