ῐJ. Jpn. Soc. Soil Phys.
ῒῐ῏ΐ῔ῑ
No. 32, p. ++ῌ+3 ῍,**.῎Analysis of Ground Freezing Process by Unfrozen
Water Content Obtained from TDR Datain Hetao Irrigation District of China
Liping WANG* and Takeo AKAE*** Graduate School of Natural Science and Technology, Okayama University,-ῌ+ῌ+ Tsushima-naka, Okayama 1**ῌ2/-*, Japan** Faculty of Environmental Science and Technology, Okayama University,-ῌ+ῌ+ Tsushima-naka, Okayama 1**ῌ2/-*, Japan
Abstract
In this paper, the ground temperatures and the unfrozen water contents estimated from Time
Domain Reﬂectometry (TDR) measurements at experimental site A(cultivated land) and C(salinized land) , were applied to analyze the ground freezing in Hetao Irrigation District, Inner
Mongolia of China. Based on the di#erent transportation status of unfrozen water, the frozen soils
were divided into extensively frozen and partially frozen layer. In extensively frozen layer theunfrozen water content is kept as constant without remarkable changes, whereas below this layer,
the unfrozen water content changed abruptly, the layer is referred partially frozen layer. It isfound the isotherms of ῍+., and ῍,.+῎ are the boundary temperatures between extensively andpartially frozen layers at site A and C, respectively.

The estimated unfrozen water content

showed the partially frozen layers still existed in the depth of *.1*ῌ*.3* m at the end of April.
Key word : Unfrozen water content, Ground temperature, Extensively frozen layer, Partiallyfrozen layer+.

Introduction

Inner Mongolia Hetao Irrigation District is atypical arid, cold agricultural area in westernChina. Salt and alkali accumulation occurs
every year, especially going through a groundfreezing- thawing course. It is considered thatthe water transportation in freezing-thawing
ground is a signiﬁcant factor on the evolution
and transition of soil salinity and alkalinity.
Although in some theoretical approaches,mass and heat transfer mechanisms are focused on freezing soils as a successive process(Kinosita, +32, ; Chen, et al., +332), the ﬁeld
facts show there exists a transitional freezingzone between frozen and unfrozen layer inﬁnely dispersed media. It is considered thetransportation mechanisms of the dissolved

salts in soil solution are di#erent in the frozen,freezing and thawing stages. Therefore, to detect the soil freezing stages is essential for theanalysis of salinity in this region.
Some experiments have been done withfrozen soil in Hetao during +32-ῌ+321, it realized that the transportation of the unfrozen
water was a most e#ective factor for salinity
accumulation (Wang, et al., +33-). However,
because of the limitation of experimental techniques, to obtain unfrozen water content wasimpossible at that time.
To analyze soil freezing stage, moisturestatus, temperature range, advancement rate is
the purpose of this paper. The measured ground temperatures on experiment spots and theunfrozen water contents which were estimatedfrom TDR data are applied to the analysis.

῏

12,.

Materials and Methods

The experiment sites are located in the ﬁelds
which belong to Shaohaoqu Experiment Station, Hetao Irrigation District of Inner Mongolia. The mean annual air temperature here is0.-1.1, the wind average speed is ,./ms+, but it always gets stronger in spring andthe maximum rate is up to +3.0 ms+. It is coldand has a little snow in winter. Therefore only
single cropping is available round a year. Theground begins to freeze from the end of November and thaws in the head of May. The
lowest air temperature, which is about ,.during recent years, appears in January. Thecoldness sum is calculated as /.*03*ῌday.
The maximum soil frost depth changes in arange of +.**+.-* m.
In Hetao, according to the land utilizationand irrigation status, the lands are separated
into cultivated land with regular irrigation andwaste salinized land without irrigation. Forcomparison, site A and C were chosen from thecultivated land and salinized land as the investigation spots, respectively. The location isshown in Fig. +. The soil texture, particle density, speciﬁc surface area, dry bulk density,
EC+ : / and pH values were measured.
The soil volumetric water contents weremonitored by a portable TDR, type of TRIMEFM, P-Z, in each *.+* m layer from surface toFig. +32,**.

the depth of +.0* m once a week through a year
from +331. The measurements were obtainedby extending the probe along a polyvinyl chloride pipe which was buried into ground beforehand. It had been a di$cult object to measureliquid water in frozen soil till the TDR technique was ensured to be reliable in situ (Steinand Kane, +32- ; Patterson and Smith, +32. ;Spaans and Baker, +33/ ; Derby and Knighton,,**+). The authors combined Birchak model toestimate the liquid water content along the soillayers and improved its validity (Wang andAkae, ,**-).
Simultaneously, -. meters away from TDR
observation point, the ground temperatures
were surveyed by thermocouples in each *.+* mlayer till ,./* m.
In order to detect the total gravimetric watercontent, dry bulk density and salinity, the soil
sections were excavated artiﬁcially three times
through the freezing-thawing period (for example, initial freezing stage : Dec.++, +331 ; maximum freezing stage ; March -rd, +332 ; thawing
stage : April ,1, +332), the undisturbed soilsamples were taken and investigated in each*.+* m depth till +.0* m.
-.

Result and Discussion-. + The properties of the soils
Table + shows the fundamental properties ofthe soils at site A and C. The soils are classiﬁed

Sketch of the experiment sites.

῏῎ : Analysis of Ground Freezing Process by Unfrozen Water Content Obtained from TDR Data in Hetao Irrigation District of China

Table +13

The basic properties of soils at site A and C
EC+ : / (mS/cm)

SampleParticle size
distribution (ῌ)

Texture Particle Speciﬁcdensity surfacearea

Dry
bulk
densityin thawing period(g/cm-)(m,/g)(g/cm-)

top

pH in thawing period

*ῌ+*
cm

average
below+*ῌ,**
cm

top
*ῌ+*
cm

averagebelow+*ῌ,**
cm

Clay

Silt

Sand

CultivatedSite A,34-*

.-4/*

,14,*

Light
Clay

,400

,*41,+4.,*43-*403

143*

24**

Salinized
Site C-/4/*

.*4**

Clay
Loam,402+/4.2+4./143,4-3

24/*

24.*

Fig. ,,.4/*The soil temperature proﬁles during freezing-thawing period of +331ῌ+332 at site A and C.

into light clay and clay loam at site A and C,
respectively, which are the most common soil
textures in Hetao. The two sites show few
di#erences in physical properties except speciﬁc surface area because of the di#erent fraction of clay component. Moreover, the salinity
and alkalinity at site C are stronger than thoseat site A, especially in the surface layer.
-. , Ground temperature proﬁles
The ground temperatures during freezingthawing period in +331 to ,*** were collectedand analyzed. In Fig. , +331ῌ+332’s data areshown. All of the three years’ data demonstrated that from the end of January to thebeginning of February the surface ground temperature became the lowest. In the sameperiod, the soils froze up to the depth of *.3*ῌ
+.+* m. Then the soils began to thaw ﬁrstly
from the surface and then both of surface andbottom. The temperatures were found to bebelow *῍ in the depth of *.3*ῌ+.+* m till
middle of April. And the frozen soils thawed atthe beginning of May.

14Fig. -32

,**.

The liquid water content proﬁles in freezing processes of +331ῌ+332 at site A and C.

-. - Depression of freezing point
The presence of the solute always decreases
the freezing point of the solvent. The following equation is generally used to determine thefreezing point depression Tm of dilute solution (Kubo, et al., +321).
TmiKfm

ῌAssuming the equation is also ﬁt for soil water
solution and the main solute is NaCl in thispaper. Where, m (mol kg+) is the gravimetricmolar concentration of the solution ; i is van’t
Ho#’s coe$cient, i, when the main solute isNaCl ; Kf (Kῌkg mol+) is the molar cryoscopic
constant, Kf+.20 when the solvent is water.
According to Eq. (+), the freezing point depressions in site A and C are calculated to be between *.-* and -.*2 in surface layer of *
+* cm, between *.,1 and *.3- below thesurface layer, respectively.
-. . Liquid water proﬁles in freezing period
The proﬁles of liquid water contents in freezing period in +331+332 are shown in Fig. -.

Some di#erences between site A and C can beobserved. The reason is the original di#erenceof soil structure and initial water content condition. However, with the time, the tendency offreezing advancement took on similar witheach other. In the surface layers, the unfrozen
water content kept unchanged in range of *.*/
*.+ m- m-. These layers developed thicker
downward with time but the unfrozen watercontent did not change signiﬁcantly. Therefore, these layers are considered to be extensively frozen. Below these layers the unfrozen water content became increasing
dramatically up to *.-/*..* m- m- under subzero temperature condition. The thickness ofthe layer was about *.-*-*..* m. The big di#erence makes it necessary to decide a borderline
for the analysis and management.
The ground temperature, liquid water andthe water retention curve were plotted in Fig.
.. The points are all not on a single line but
dispersed to some extent. It is partly due to thedi#erent circumstances of the soil water andpartly due to the error in ground temperatureῐ῏ : Analysis of Ground Freezing Process by Unfrozen Water Content Obtained from TDR Data in Hetao Irrigation District of ChinaFig. .

15The soil water retention curves and the liquid water contents vs. soil temperatures at site A and C.

and water content measurements. The directlines are applied to approximate the development of liquid water content vs. ground temperature : Line ῌ represents the unfrozen
stage ; line ῍ : the freezing stage ; line ῎ : thefrozen stage. The intersection points of line ῍and ῎ at site A and C are (*.*1 m- m῍-, ῍+.,῎)and (*.*2 m- m῍-, ῍,.+῎). According to thewater retention curves, when the unfrozen
water content are *.*1 and *.*2 m- m῍-, the coincident pF values are greater than pF ..,. It isknown that if the pF value is larger than ..,,
the water will be kept in intensively boundstate around the surface of soil particles (Association of Soil Physics, Japan, +313), that means
the movement of the unfrozen water in theextensively frozen layers becomes extremely
di$cult and therefore can be actually neglected. As a result, the unfrozen water contentsof *.*1 m- m῍- and *.*2 m- m῍-, the groundtemperatures of ῍+., and ῍,.+῎ can be regarded as the boundary values between extensively frozen layers and partially frozenlayers. The di#erence of the boundary temperature between site A and C is mainly due to thedi#erence of salt concentration of the two soils.
It is noted that the liquid water contents
decreased at the depth where the temperature
were ῌ*.,/ and ῌ*.,῎ at site A and C, respectively. It is considered that the water in theunfrozen layers just below the freezing front
was strongly absorbed due to the suction
yielded at the freezing front. The same phenomena are also found in some experiments inlaboratory (Mizoguchi, et al., +320 ; Inoue, ,**,)and observations in situ (Stein and Kane, +32- ;Cary, +321). In fact, the line ῌ and ῍ shouldintersect theoretically on the depressed freezing points of ῍*.,1 and ῍*.3-῎ at site A and C,
respectively.
-. / Delimitation of freezing soils
Through the evidences in the liquid watercontent and ground temperature, it reveals
that ῍+.,῎ and ῍,.+῎ can be used as thediscrimination between frozen and freezing forthe site A and C. Here, following deﬁnitions areproposed :+. “extensively frozen layers” : In theselayers, the unfrozen water contents are smaller
than the amount of *.*1 or *.*2 m- m῍- and are

16Fig. /32,**.

The comparison of estimated liquid water content and measured total water content in +331
ῌ+332 at site A and C.

kept almost unchanged. The ground temperatures are lower than +., or ,.+ at site A orC, respectively. The transformation of water toice is so small that can be neglected.
,. “partially frozen layers” : In these layers,
the unfrozen water contents increase abruptly
from *.*1 or *.*2 to *.-/*.-0 m- m-. The
ground temperatures are within +.,*.,+
or ,.+*.0- for site A or C, respectively.
The transforming amount of liquid water to ice
is relatively large.
The liquid water contents estimated fromthe TDR data and the total water contents
measured gravimetrically from the soil samples are compared in Fig. /. In thawed soils
which are judged by ground temperature, theestimated liquid water contents are in good
agreement with those measured ones. Whenthe soil freezes, the estimated liquid water content represents the unfrozen water content.
There seems no reason why the estimated unfrozen water contents in frozen soil are notreliable.

Penetration rates of frozen and freezing layers
From the proﬁles of ground temperaturesand liquid water contents in Fig. , and -, thefreezing penetration rates were investigated.
The average rates of extensively partiallyfrozen layers were *.1, cm d+ and *.03 cm d+at site A and C, at the same time they were +.+1cm d+ and *.30 cm d+ of partially frozen
layers at site A and C, respectively. The frontsof extensively and partially frozen layers are
showed in Fig. 0.
-. 1 Liquid water proﬁles in thawing
periodThe soil started to thaw from the beginningof March. At site A and C, the layers thoseliquid water contents were lower than *.+mm- still existed in the depth of *.-**..* mand *.-**.0* m in the beginning of March(Fig. 1). Such layers disappeared in the end ofMarch. The layers those temperatures werebelow the depression of freezing points werepresent in depth of *.1**.3* m till the end ofApril. The average thawing rate was +..cmd+ in March and ,.20-./1 cm d+ in April,-. 0῍ῌ : Analysis of Ground Freezing Process by Unfrozen Water Content Obtained from TDR Data in Hetao Irrigation District of China

Fig. 017The advancement of extensively frozen layers and partially frozen layers in +331ῌ+332 atsite A and C.

Fig. 1The liquid water proﬁles in thawing period in +331ῌ+332 at site A and C.

18

which is estimated corresponding to theground temperature.
..

Conclusion

Through the analysis of ground temperatureand unfrozen water content, the soil freezing
stages and properties are revealed at site A andC in Hetao. The unfrozen water content of *.*1m- m- and *.*2 m- m-, isotherm of +., and,.+ can be applied to distinguish di#erent
freezing stages, that is helpful for the study ofsalts transportation in this region. The deﬁnitions of “extensively frozen layer” and “partially frozen layer” are proposed and their penetration rates are also evaluated. The thawing rate
was higher than freezing rate and it became
faster in April than in March.
Acknowledgement
The authors would like to express their gratitude to the sta# in Shaohaoqu Experimental
Station, Hetao Irrigation District, Inner Mongolia. This research has been partly supported by
the Core Research for Evolution Science andTechnology (CREST) program of Japan Science and Technology Corporation (JST).
References
Association of Soil Physics, Japan (+313) : Soil
Physics-soil engineering basis, Morikita Press,,,*ῌ,,/.
Cary, J.W. (+321) : A new method for calculating
frost heave including solute e#ects, Water
Resour. Res., ,- : +0,*ῌ+0,..
Chen, X.F., Mitsuno, T., Horino, H. and Maruyama,
T. (+332) : Numerical experiment method of thesoil freezing and thawing by coupled heat and32,**.

water transfer model : studies on the analysisof the freezing and thawing process of soils (I),
Journal of the Japanese Soc. of Soil Physics, 12: ,/ῌ-..
Derby, N.E. and Knighton, R.E. (,**+) : Field-scalepreferential transport of water and chloride
tracer by depression-focused rechange, J.
Environmental Quality, -* : +3.ῌ+33.
Inoue, M. (,**,) : A study on the measurements ofsoil water, solute and thermal conductivity infreezing and thawing courses, Master’s Dissertation, Okayama University Graduated School,+0ῌ,,.
Kinosita, S. (+32,) : Physics of frozen ground,Morikita Press, ,+-ῌ,,,.
Mizoguchi, M., Nakano, M. and Shirai, K. (+320) :Simultaneous change of water content, soluteand temperature layers in a partially frozen
unsaturated soil, Trans. JSIDRE, +,, : ++ῌ+1.
Patterson, D.E. and Smith, M.W. (+32.) : Liquidwater content in saline soils : results using
time-domain reﬂectometry, Can. Geotech. J., ,,: 3/ῌ+*+.
Spaans, E. J.A. and Baker, J.M. (+33/) : Examining
the use of time domain reﬂectometry for measuring liquid water content in frozen soil,Water Resour.Res., -+ : ,3+1ῌ,3,/.
Stein, J. and Kane, D.L. (+32-) : Monitoring theliquid water content of soil and snow using
time domain reﬂectometry, Water Resour.Res.,+3 : +/1-ῌ+/2..
Wang, L.P. and Akae, T. (,**-) : Estimation ofliquid water content by TDR measurements infrozen soils, Trans. of JSIDRE, ,,. : 23ῌ3/.
Wang, L.P., Chen, Y.X. and Zeng, G.F. (+33-) : Irrigation drainage and salinization control inNeimenggu Hetao Irrigation District, Chinese
Water Resource and Electric Power Press.
Kubo, R., Nagakura, S., Iguchi, H. and Ezawa, H.
(+321) : Handbook of Physics and Chemistry,Iwanami Press, +,3/.

 : Analysis of Ground Freezing Process by Unfrozen Water Content Obtained from TDR Data in Hetao Irrigation District of China19TDR *ῌ***
**   1**ῌ2/-*   -ῌ+ῌ+  1**ῌ2/-*   -ῌ+ῌ+

TDR  !"#$%&'()*+,-./ 0123456789:;( A <=( C 8>?:@ABCDEF8G/HIJ !K L@$BMNOPQR @ASTU VWX@ATY ' V%@ATY 87Z[\!K ](B^_`abcB Site A ' C 8>/H WX@ATUd\e\ *.*1 m- mf-,*.*2 m- mf- ghBL@$%&-ij klhmnCDo:B8p  %@ATUq[ *.-*r*..* m B

ST1L@$%&sd\e\ *.*1 m- mf-, *.*2 m- mf- QR *.-/ m- mf-, *.-0 m- mf- ntu8vwo:xy-z !K ()f+.,{ f,.+{ Ud\e\B^_`abcB VWX@ATY ' V%@ATY B
|8}~H/:'s !K
 ! " : L@$%& () WX@AT %@AT  : ,**-  +,  : ,**.  0- +. 