Effects of initial soil-water conditions on frost heaving characteristics

Engineering Geology, 13 (1979) 41--52

41

© Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

EFFECTS OF INITIAL SOIL-WATER CONDITIONS ON FROST HEAVING CHARACTERISTICS

S. KINOSITA

Institute of Low Temperature Science, Hokkaido University, Sapporo (Japan) (Received June 15, 1978)

ABSTRACT Kinosita, S., 1979. Effects of initial soil-water conditions on frost-heaving characteristics. Eng. Geol., 13: 41--52. Frost heavings have been observed on the soils in waterproof basins (four basins denoted by A, B, C and D) at the Tomakomai field site, Hokkaido, Japan. Basins A, B and C were filled with the same silty soil, and Basin D with four layers, namely, pebbles (0--5 cm below the surface), a mixture of pebbles and silty soil (5--20 cm), silty soil (20--60 cm) and sand (60--160 cm). In the winter of 1976--77 water levels in the basins were set at the levels of the ground surface in A, 40 cm below the surface in B, the bottom in C and 30 cm below the surface in D. Basin C had no free groundwater. The highest surface heave was 32 cm in A, 26 cm in B, 19 cm in C and 14 cm in D. A water supply from the free groundwater toward the freezing front extended over 220 cm through the silty soil, but was limited to 63 cm through the sand. The migration speeds of the soil water supplied from the unfrozen part were calculated for A, B and C from the measurements of their volumetric water-content profiles. INTRODUCTION

When a soil containing water freezes, the expansion observed is, in some cases, greater than the expansion resulting from the freezing of the water contained in the soft. In these cases, the water in the unfrozen part of the soil moves towards the freezing front, where it segregates in the form of ice lenses. This p h e n o m e n o n is called "frost heave" and this t y p e of soil is defined as frost-susceptible. It can show a fairly remarkable volume increase if a supply o f water is available, for example, when the level of a groundwater table is near the freezing front. Observations were c o n d u c t e d on the relations between the a m o u n t of frost heaving and the quantity of available water for test soils p u t in the w a t e r p r o o f basins in the Tomakomai field site. The quarLtities of the available water were changed in such a way that the initial levels of the free groundwater were set at various depths. The test soils used were silt (f~ost susceptible) and sand (non frost susceptible). Measurements were conducted of the migration speeds of soil water and the distance it traversed from the free groundwater table during frost heaving.

42 DESCRIPTION OF FIELD SITE

All the work was c o n d u c t e d in the field site prepared in the Tomakomai experimental forest of Hokkaido University [ 1 ]. The site is located 6 km northward from T o m a k o m a i Harbor which faces the Pacific Ocean, and 50 km southward from the center of Sapporo City. The area is situated at the b o t t o m of a small basin, which has a rather low temperature in clear weather. The daily mean air temperature drops to 0°C, starting mid-November, and rises above 0°C, starting late March, every year. The freezing index and daily mean air temperature in the winter of 1976--77 are shown in Fig.1. The total freezing index amounted to 750°C.day. The monthly mean air temperature was +1.6°C in November, --3.7°C in D e c e m b e r , - - 1 0 . 8 ° C in January, --7.4°C in February, --1.3°C in March and +4.1°C in April. The minimum air temperature in winter was -30.4°C, as recorded at 0710, February 2, 1977. In order that an exact quantity o f moved soil water be obtained, waterp r o o f basins were constructed [2]. The following four basins typify the basins used.

.~NOV I DEC 1 ,.ll:oC30,~ 20 lO 20

FEB JAN I0 20 3C I0 20

MAR . -A~PR I0 20 30 I0 20

AIR TEMP. DAILY MEAN

-5

- -

IUO"P~

200" FREEZING

INDEX day

700

Fig.1. Daily mean air temperature and freezing index in the winter of 1976--77. (Tomakomai field site, Hokkaido, Japan).

43

(1) Basin A: 5 × 5 m wide, 2.30 m deep, filled with silty soil. (2) Basin B: 3 X 3 m wide, 1.90 m deep, filled with silty soil. (3) Basin C: 5 X 5 m wide, 2.00 m deep, filled with silty soil. The silty soil is frost susceptible and consists of sand (particle size > 0.05 mm), silt (between 0.05 and 0.005 ram) and clay (< 0.005 mm) in percentages of 55, 24 and 21 respectively;the average specific surface is 54 m2/g [ 3 ] , the specific gravity is 2.54--2.58 and D60 (the upper limit of diameters o f soil particles that account for 60% of the total weight) is 0.08 mm. The plastic limit is 38% and liquid limit 46%. (4) Basin D: 3 X 3 m wide, 1.60 m deep, filled with pebbles (1--10 cm dia.) at depths of 0--5 cm, a mixture of pebbles and the same silty soil as in the other basins at depths of 5--20 cm, silty soil at depths of 20--60 cm and sand at depths o f 60--160 cm; the average specific surface of the sand is 1 m2/g, the specific gravity is 2.60--2.70, and D60 is 0.4 mm. Before the start of ground freezing, water levels in the basins were set at the levels of the ground surface in A, 40 cm below the ground surface in B, the b o t t o m in C and 30 cm below the ground surface in D. Basin C had no free groundwater. A soil-water m o v e m e n t t o o k place only inside a basin, independent of the outside. Once a water m o v e m e n t occurred in the basin, the level of the water table changed. The level was measured in the pipe placed close b y and connected to the basin. There was no supply o f water, either from outside the basin or from above, after the soil began to freeze. Whenever there was a snowfall the surface was cleaned so as to be always exposed to the air. The m a x i m u m height of snow cover amounted to a b o u t 40 cm every winter at places where the snow was n o t removed. INSTRUMENTATION

(1) Soil temperature. Strain-gauge-type thermometers were buried at depths o f 0, 5, 10, 20, 30, 40, 60, 8 0 , 1 0 0 and 130 cm below the surface and at the b o t t o m of the basin. At depths of 100 cm and above the thermometers were inserted into the side openings of a vinyl pipe (7.6 cm dia.) beforehand. Therefore, each interval of the thermometers did n o t change t h r o u g h o u t the winter, though they rose together with the heaving of the ground surface. The other thermometers, which were buried at 130 cm depth and at the b o t t o m , did not change their original positions, because the maximum frost penetration was less than 80 cm from the ground surface. (2) Frost penetration. The level of a frost line was easily determined b y a thin transparent pipe filled with a 0.01% methylene-blue d y e solution in winter; this remains blue in an unfrozen state and turns colorless in a frozen state. This probing pipe was sheathed from above down into another pipe with a little larger diameter e m b e d d e d vertically in the soil with its open t o p end protruding from the ground surface. The probing pipe can then be lifted from the larger pipe when necessary to determine the frozen and

44

colorless portion surrounded b y a frozen layer of soil. As a buffer to allow for an increase in volume of the solution in the pipe when frozen, a fine, empty, soft vinyl pipe was placed alongside within it [ 4 ] . (3) Heave a m o u n t o f surface. Levelling of the surface was conducted by the t o p of a steel rod which extended upright from the b o t t o m of the basin, as a fixed point. (4) Level o f water table. This level was measured by recording the level of a b u o y floating in the pipe placed close by and connected to the basin. RESULTS

Frost-heaving characteristics observed in Basins A, B, C and D are shown respectively in Figs.2--5. (1) Basin A (initial water level is the ground surface) in Fig.2. Ground freezing began around November 27. After then the ground surface continued to rise and reached a highest point of 32 cm on March 8. Both the freezing front and the level of the water table continued to sink. The level reached the b o t t o m o f the basin (230 cm below the initial ground surface) on January 15. By then the freezing front had reached a level of only 10 cm below the initial ground surface, while the ground surface heave totalled 24 cm. The heave ratio a m o u n t e d to a fairly large value of 240%. The heaving occurred b y the growths of ice lenses (see Fig.6) segregated in the freezing front. The water which was the origin of these ice lenses had been supplied from below. This result proves that free groundwater can rise more than 220 cm through silty soft. The heaving speed was a b o u t 5 m m / d a y from November 27 to January 15 b u t it decreased to 2.5--0 m m / d a y thereafter because the basin had no free groundwater and a soil-water movement t o o k place at the drying of the unfrozen soil below the freezing front. On March 8 the freezing front reached a deepest level of 28 cm below the initial ground surface; the total heave ratio ~amounted to 118%. The heave ratio was only 44% in the freezing period from January 15 to March 8. Melting began around March 9 in the ground surface. The frozen layer melted completely around May 2, when the water level returned to the original level. (2) Basin B (initial water level 40 cm below ground surface) in Fig.3. Beginning o f freezing November 25; maximum heave amount 26 cm (March 8); total heave ratio 55%; m a x i m u m frost penetration 51 cm (March 20); complete melting May 18. The water level reached the b o t t o m (190 cm below the initial ground surface) on January 5. By that time the freezing front had reached a level of 17 cm below the ground surface, while the heave a m o u n t o f the ground surface totalled 14 cm. The heave ratio was 120%. The heaving speed was a b o u t 3.5 m m / d a y from November 27 to January 5, and 3.0--0 m m ] d a y thereafter. The heaving process was slower than that in Basin A, while the frost penetrated deeper; complete melting delayed by 16 days compared with that of Basin A.

45

NOV 1 3,

DEC ~'0 2'0 3~

J,N I "0 ~0 36

30

FEB 1'0 2'0

mR I ,~ 2b 36

,~ '~Y 'b 26 3~ I0

I

10

MEL "w

I-- d

,

FRONT

~,~,

/lO ~ ~ I I"-.. I I~° \~TER I FR°N~ I--'''. I ~0 \T'~E I I ~------~-'----T I-~'

II

~ ,

L4o..--.-~ / ~ l-so ~

O' ~

II

'I' loo 200 W3oo4oo i ...... :

o'

{'BOTTOM 230~.

I I I I II

1' . ~qo . . .I I

~

27o 3Qo

. .

~

',b

('-WATER

4~,o

I XCE

l I

JAN.7

NOV.25

50 crn

o

50

II

cm

II

'

I

.......

FREEZING FRONT

IG

II

5O cm

I

--

I--I---FREEZING W I FRONT

Iw IG

ii

I I

SO

cm

II 100"

) 1.5 G g/cm3

W : WATERCONTENT

I

I

l 1.5 G g/cm3

,,,i..

G : DENSITY

lOi I

O0

o

~

l. . . . i : 5 g/crn3 G

1. . . . . 1.5 g/cm 3 G

Fig.2. Heave--time relationship of the ground surface, and depth--time relationships of the freezing front and the water table. Water content and density profile on November 25, January 7, March 8 and May 10. Basin A. Initial water table is the ground surface. (3) Basin C (no free groundwater) in Fig.4. Beginning of freezing November 25; m a x i m u m heave a m o u n t 19 cm (March 8); total heave ratio 36%; maximum frost penetration 55 cm (March 16); complete melting May 12. The heaving process was slower than in Basins A and B, while the frost penetrated deeper; complete melting delayed b y 10 days compared with that of Basin A. (4) Basin D (initial water level 30 cm below ground surface) in Fig.5. Beginning o f freezing November 25; m a x i m u m heave a m o u n t 14 cm (February 25); total heave ratio 24%; m a x i m u m frost penetration 58 cm (March 10); complete melting May 6.

46 NOV

, DEC,

,

JAN

FEB

l:

MAR

20

]

MAY

fo 2b 3~I 1'o ~ 3o1 1~

lb ~b

3O

APR

SURFACE

cm

I

MELIIN~'. FRONT " ,

lO[~*'="--*~*~.~_ I ~ ~130 ' ~ FREEZ~NT~

I

t6o I ~

1ooW oo 3oo ' ' ' ~ II II JAN.7

L~' ~ o I { B O T T ~ 19~ I w 1oo~cm JAN.SJ o~-4~ I I NOV'2s

IW IG II II I I -I I

5O cm

o

' ' '

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I

I

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so II WATER

cm I j IG

TABLE

I I I I 1

"'",

I

i

. . . . . . FREEZING FRONT

.......... ' l 1.5 2 G g/cm 3

50 cm

I I

II

I I I )

1,5 2 G g/cm3

lO0' W : WATER CONTENT

I

G : DENSITY

II lO0

,| . . . . .

l G

,,,J

1.5 2 g/cm 3

II T"Y.5 G g/cm3 I

Fig.3. Heave--time relationship of the ground surface, and depth--time relationships of the freezing front and the water table. Water content and density profile on N o v e m b e r 25, January 7, March 8 and M a y 10. Basin B. Initialwater table is 40 c m below the ground surface.

Four layers constituted Basin D; namely, pebbles, mixture of pebbles and silt,siltand sand. The frost line passed through the upper two layers for only a few days after freezing began because of their large thermal conductivities. W h e n the frost line reached the siltysoil,the rate of sinking became slower because of the latent heat caused by ice segregation in the siltysoil.Heaving of the ground surface took place and the water level began to subside. By January 29 the level reached a depth of 123 c m below the initialground

47 NOV

~(~._.~JAN

DEC 10

10

20

20

3

MAR

FEB 10

MAY "'1" 10

APR

20

GROUNDSURF,a~E %•-

MELTING

%%

#

I00

.60

200

o

w1,oo

I

°'ll, FRONT

I

50

cm

II

=

II

I I

100

r- .....

II

......

1

1.5 g/cm3

FREEZING

FRONT

II 5O

=

II I I

I

100

II

I I

1~.1

I

!

G W : WATERCONTENT

1.5 g/cm3 G

G : DENSITY

li ,11 I IG

II

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MAR.8

cm

I I II II

I

I

5O

50

IIG

O" I

lo

~1 I NOV.2S wl

MAY.10

I

i""i. s g/c~3 G

I I

I

-t"~. s G g/cm3

Fig.4. Heave--time relationship of the ground surface, and depth--time relationships of the freezing front and the water table. Water content and density profile on November 25, January 7, March 8 and May 10. Basin C. Initial water table is the bottom (no free groundwater).

surface inside the sand layer, 63 cm below the t o p of the sand layer, thereafter maintaining this level till melting began. This proves that the height of a water supply from free groundwater is limited to 63 cm through sand. On the other hand, it extends over 220 cm through silty soil. This phenomenon depends on the height o f capillary rise of water through the soil. The larger the size o f pore in the soft, the lower the height. The heaving rate was a b o u t 2 ram/day till January 29. Subsequently,

48 NOV

DEC

JAN

I

FEB

MAR

APR

__',,, SI .

~.~RONT

I

....

\ SI "40[~\ '~~ ' ~J

j "'-4

~FREEZING I ' ~ FRONT

~'./

:°oi\

]~. P : PEBBLES,

I

! S]

I

: SILT,

i

i

II

I

i

I

I

i

J

SA : SAND

Fig. 5. Heave--time relationship of the ground surface, and depth--time relationships of the freezing front and the water table. Basin D. Initial water table is 30 cm below the ground surface. it decreased to 0.7--0 m m / d a y and the freezing f r o n t cont i nued to subside, reaching a level 2 cm higher than an interface between silt and sand in late February. Analyses were m a de o f core samples taken by boring. ANALYSES OF CORE SAMPLES TAKEN BY BORING Core samplings were done for the soils in Basins A, B and C from the surface to a b o u t 100 cm on N o v e m b e r 25 (before freezing), January 7 and March 8 (during freezing), and May 10 (after melting), using a boring machine with high-speed rotating edge. Observations were made o f core samples 10 cm in di am e t e r t o exam i ne the layer structure. Using the sliced samples taken at intervals o f 5 cm, measurements were made o f density G, water c o n t e n t W and density o f soil particles G,. The value o f G o f a frozen

49

Fig.6. Ice lenses in frozen core samples. (a) 22--29 cm below the heaved ground surface in Basin A. (b) Large ice lenses in Basin A. (c) A frozen core sample in Basin C placed horizontally, the left end showing the upper part of the core.

sample was obtained by weighing it both in air and in kerosene; i.e., G = KMa/(Ma --Me), where K, Ma and Me are the density of kerosene and the weights of the sample in air and in kerosene respectively. The values of G and W obtained for the core samples are plotted in the lower parts o f Figs.2--4. The value of Gs was obtained as 2.48--2.54. The value o f W became larger during freezing than before freezing, while it became smaller in an unfrozen layer immediately below the freezing front. The increase o f W in the frozen layer corresponds to the content of ice lenses, i.e., the heave ratio o f the layer. Thus, the increasing order of W in Basins A, B and C. In Basin A, the value o f W in the uppermost layer extends to 40%. In the frozen layer o f each basin the upper part has a larger value o f W than the lower part. The volume ratios o f water Vw, soil particles Vs and air Va contained in the unfrozen soil of a unit volume are calculated b y the equations: Vw = WG/(1

+ W),

Vs=

G/Gs(1 + W),

V a = 1 -- Vw -- V,

The volume ratios o f ice Vi, soil particles V, and air V~ contained in the frozen soil o f a unit volume are calculated b y the equations: V i = 1.1WG/(1

+ W),

Vs = V/Vs(1

+ W),

V a = 1 -- Vi -- Vs

These values obtained in the core samples of Basins A, B and C and given in Table I.

A

60

30

41 34 increase

uppermost

40

60

40--

100

Va (%)

10

25

0

21 decrease

35---40 0 saturated

~ (%)

43 36 increase

60---65

whole

7--12

Vw (%)

~p~ (cm)

Basin Before freezing (Nov. 25)

TABLEI

0--10 10--30 30--

0--20 20--50

0--20 30--

unfrozen top apart

frozen

unfrozen top apart

frozen

unfrozen top apart

frozen

depth (cm)

35 33

Vs

Vw 43 50

20--25 30

70--80 60--65

36--39 40

V~

Vw 46 57

12--20 30

35--38 35--37

v~

8--10 20 25

Vs (%)

70--80 70

49 55--60

Vw

80--90 80 75

Vi (%)

22 17

Va

5 5

15--17 5

Va

3--9 0

13--17 4--10

v~

2--10 0 0

Va (%)

During freezing (Jan. 5--Mar. 8)

60

Vw (%)

40 saturated

Vs (%)

100

56

uppermost 42--50 increase

36

32--35

not completely melting

whole

depth (cm)

After melting (May 10)

8

15--24

0

Va (%)

O

Freezing period

Nov. 27--Dec. 10 Dec. l l - - D e ~ . 25 Dec. 26--Jan. 7 Jan. 8--Feb. 1 Feb. 2--Mar. 8

Nov. 25--Dec. 10 Dec. 11--Dec. 25 Dec. 26--Jan. 7 Jan. 8--Feb. 1 Feb. 2---Mar. 8

Nov. 25--Dec. 10 Dec. 11--Dec. 25 Dec. 26--Jan. 7 Jan. 8--Feb. 1 Feb. 2--Mar. 8

Layer

I II HI IV V

I II III IV V

I II III IV V

Basin

A

B

TABLE II

15 15 13 25 35

15 15 13 25 35

13 15 13 25 35

Days

14 9 12 19.5 17.5

13 9 12 20 19 9.0 6.0 7.5 11.6 10.3

8.4 6.9 8.8 12.9 11.2

7.9 9.2 6.8 10.4 9.2

(g/cm 2)

10 12 9 15 13

M 2

dD + dh

(cm)

dD

8 3.5 7 17.5 17

8 3 7 13 16

3 3.5 2.5 8 10

(cm)

3.4 1.5 3.0 7.5 7.3

3.4 1.4 3.2 6.0 7.4

1.9 1.7 1.2 3.9 4.9

(g/cm 2)

M I

6 5.5 5 2 0.5

6 5 7 3 6

7 8.5 6.5 7 3

(cm)

h

dh/dD

75 157 71 11 3

63 200 71 54 19

230 41 38 87 30

(%)

5.6 4.5 4.5 4.1 3.0

5.0 5.5 5.3 6.9 3.8

6.0 7.5 5.7 6.5 4.3

(g/cm 2)

M 2 -- M 1

0.37 0.30 0.34 0.16 0.086

0.33 0.37 0.41 0.28 0.11

0.46 0.50 0.44 0.26 0.12

(g/cm2/day)

v

r~

52 MIGRATION OF SOIL WATER FROM THE UNFROZEN PART TOWARDS THE FREEZING FRONT

Migration o f soil water during frost heaving is postulated as follows. The ground surface rises from level h to level h + dh, while the freezing front advances from level D to level D + dD; the layer dD in thickness expands to the thickness dD + dh when freezing takes place. The water volume M1 contained in this layer before freezing is VwdD, while the waterequivalent volume M2 after freezing is Vi(dD + dh)/Gi, where Gi is the density of ice. The increase of the water volume M2 -- M, is supplied from the unfrozen part [5]. These values in Basins A, B and C are given in Table II, for the five layers during the following freezing periods : the beginning of the freezing to December 10, December 11--25, December 26--January 7, January 8-February 1, February 2--March 8. The migration speed v was fastest in the early part of the winter and then became slower. It corresponded to the existence of dense ice lenses in the upper part of the frozen layer. For the same freezing period v was larger for the higher initial water level. CONCLUSION

Characteristics of frost heaving were observed for the soils filled in the w a t e r p r o o f basins which had different initial water levels. (1) The higher the initial water level, the larger the heave amount of the ground surface. (2) When the basins had no free groundwater a weak heaving t o o k place, caused b y drying of the unfrozen soil. (3) The migration speed o f soil water from the unfrozen layer was larger in the early part o f the winter; it corresponded to the existence of dense ice lenses in the upper part of the frozen layer. (4) The distance of a water supply from the free groundwater extended over 220 cm through silty soil, b u t was limited to 63 cm through sand. ACKNOWLEDGEMENTS

The author expresses his gratitude to the members of the frost heaving section of the Institute o f Low Temperature Science, Hokkaido University, for helping c o n d u c t the field researches. REFERENCES 1 Kinosita, S., 1975. Soil-water movement and heat flux in freezing ground. Proc. Conf. Soil-Water Problems in Cold Regions, 1975, Calgary, Canada. 2 Haas, W.M., 1962. Frost action theories compared with field observations. Highw. Res. Board, Bull. 331. 3 Horiguchi, K., 1975. Relations between the heave amount and the specificsurface area of powder materials. L o w Temp. Sci., 33. 4 Kinosita, S., Suzuki, Y., Horiguchi, K., Tanuma, K. and Aota, M., 1967. Frost heave in Monbetsu (1966--1967). L o w Temp. Sci., 25. 5 Kinosita, S., 1973. Water migration in the soilduring the frost heaving. Frost I Jord., 11.