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On the functional dependence of the freezing point of soils on the
composition of water soluble salts in an interstitial solution
Author/Auteur: Ti tle/T itre:
Reference/Reference:
NATIONAL RESEARCH COUNCIL CANADA CONSEIL NATIONAL DE RECHERCHES CANADA
TECHNICAL TRANSLATION TRADUCTION TECHNIQUE
Yu.Ya. Velli and P.A. Grishin.
On the functional dependence of the freezing point of soi ls on the composition of water soluble salts in an interstitial solution.
Rheology of soils and engineering geocryology, 193-196, 1982.
Translator/Traductrice: H. Pidcock.
Canada Institute for Scientific and Technical Information
Institut canadien de l'information scientifique et technique
Ottawa, Canada KlA OS2
PREFACE
Many coastal communities in Arctic Canada are underlain by permafrost and are
si tuated wi thin a few hundred metres of the shores of the Arctic Ocean.
Depending on their geological origin and depositional history, the soils in
these communi ties may be high in pore water salt content. Saline pore water
may also be encountered in offshore permafrost.
It is often taken for granted in the design of engineering structures on
permafrost that mean annual subzero ground temperatures indicate the presence
of ice bonded soils, thus the widespread practice of designing pile
foundations based on the soil adfreeze strength. This paper indicates the
relationship of the salt concentration, salt type and moisture content on the freezing point (formation of ice) in soils.
The Division wishes to express its sincere thanks to Hazel Pidcock who
translated this paper under contract to the National Research Council Canada,
Canada Institute for Scientific and Technical Information and to Mr. T.H. W.
Baker, of this Division for checking the translation for technical accuracy.
OTTAWA C.B. Crawford,
Director,
ON THE FUNCTIONAL DEPENDENCE OF THE FREEZING POINT OF SOILS ON THE COMPOSITION OF WATER SOLUBLE SALTS IN AN INTERSTITIAL SOLUTION
by Velli, Yu.Ya., and Grishin, P.A.
The freezing point of soils is the boundary of change of physical state; the
transition from thawed to frozen state and is the beginning of the phase
transi tions of the interstitial solution. Quantitatively, the freezing point
is dependent on many factors including, in the case of saline soils, the
quantitative and qualitative composition of readily soluble salts and must,
therefore, be determined by experimental means. In this connection, the
determination of the fundamental factors influencing the temperature at the
freezing point of saline soils is of interest.
To this end, experiments were conducted with soils from the Arctic coast;
these were of differing granulometric composition (suglinoksl, supes2 and
sands) with differing mineralization and composition of the salts. The soils
were of marine origin. The rock forming minerals of the clayey fraction were
kaolinite - 40%, acid salt - 30%, montmorillonite - 25% and chlorite - 5%;
quartz sands.
Salts from soil extractions or from sea water identical in composition, and
also NaCl and CaC1
2 solutions were used for the artificial salination of the
soil samples.
1 - clayey silty loam 2 - sandy silty loam
The soil extractions and the sea water had the following salt composition (in
. 2+ 2+ + +
percentage equ LvaLent ) Ca 1.73; Mg - 9.56; (Na + K ) - 38.71;
4
-In the experiments, the moisture content of the samples corresponded to the
moisture content in natural bedding of analogous soils, i.e. for clayey soils the moisture content was that at the point of fluidity (liquid limit) and for
sands, it was that at the saturation stage. The salinity varied from 0.2 to
1%, or (expressed in terms of concentration of interstitial solution) from
0.006 to 0.055. The freezing points of the saline solutions used for the
mineraliztion of the experimental samples were determined at the same time. A
thermometric method was used to measure the freezing point of the soils and
solutions. The results obtained are shown in the table.
As the temperature falls below OOC in the SOil, three stages are observed
during cooling: supercooling - a sudden change in temperature; a phase of
comparatively constant temperature - the beginning of phase transitions; and a
gradual fall an alignment of the temperature of the soil with the
surrounding environment. The sudden change in temperature typifying the
supercooling stage of the interstitial solution can exceed the freezing point
by 1.5 2 times. However, this stage is not always observed in the
experiments, and depending on the size of the sudden temperature change has
di fferent impl ica tions; the factors influencing it have not yet been
successfully explained. A constancy of temperature with time was observed at
the beginning of phase transitions in all the experiments, within the limits
of accuracy of measurement; its duration depending on the type of soil, the
moisture content, the type and quantity of the dissolved salts and the
temperature of the cooling environment. The temperature at the beginning of
this process is taken as the freezing point.
For all types of soils having the same salinity, the freezing point falls as
the moisture content decreases. However, if the salinity is assessed using
the concentration of interstitial solution (in ppm) K
=
Z/(W + Z), where Z isthe soil salinity
%
by dry weight of soil, and W is the total moisture content(GOST 5180-75) % by dry weight of soil, then when salinity values are
identical, freezing points will be identical.
at freezing point T
f• p. is proportional
interstitial solution (figs. 1 and 2).
In this case, the temperature
5
-"P'mperc,h..re at- frc-e-z:..I()'j pCJ:"r( ) r -SDI.'1" :X"ls
ｲｲｾ［ＹｖＮｦｾＮＡ aon<:enf ...hO» ｬＶｊｦＢＧｦＧｬＱｉＭｵＮｾ cJＭＨｾｾＬｲＺ＾Ｇｪ pe.n/- "c ｃ＼ｬｮｾＮＬｲ iｾＧｬＢＧＬｾＩＧ &1,,'1£ of
mto· ｾ ｾ -fOl"".<dct
IPr
'Jt,rmida..% % ｃｃＱｾＺｨＧｌＢｬ "1t'rS/".hc,1 ｸｊｾｪＭＬＢｴｬ liI4,. (2) (3) 1 ｾｬＮｩｬｾ 30,0 0.2 ｾｾ
...
0.007 -0.5 -0.4 -0.4 30.6 0,2 0.006 -0.2 -0,3 -0.3 26.5 0.2 0.008 -0.3 -0.5 -0,4 27,6 0.2 NeCI 0.007 -0.5 -0.4 -0.4 26.7 0.2 CICI, 0,007 -0.2 -0.2 -0.2 20.0 0.5 ＮＵｬＧｴ＾ＮＮｾｾ 0,016 -1.0 -0.9 -0.9 30.6 0.5 0.016 -0.9 -0.9 -0.9 28.0 0,5 0.018 -1,0 -1.0 -1,0 27.5 0,5 NaCI 0.018 -1.2 -1.1 -1.1 26.2 0.5 CICI, 0.019 -0.6 -0.6 -0.6 30.0 1.0 Stet SQlI- 0.032 -1.8 -1.8 -1.8 30,6 1.0 0.032 -1.7 -1.8 -1,8 25.6 0.5 0.038 -2.1 -2.2 -2.1 27.0 0.5 NaCI 0,036 -2.3 -2.2 -2,2 26.6 D,S CaCI, 0.036 -1,0 -1.2 -1.2 Su.peS 21.0 0.2 .soc>.sc>/.. 0.009 -0.6 -0.5 -0,5 22.1 0.2 NaCI 0.009 -0.6 -0,6 -0.6 21.5 0.2 CeCI, 0.009 -0.3 -0.3 -0,3 21.6 0.5 SeQ.s-J" 0.023 -1.4 -1.3 -1,3 21.7 0.5 NaCI 0.022 -1.6 -1.4 -1,0 21.8 0.5 CaCI, 0.022 -0,7 -0.7 -0,7 20.9 1.0 ｾｓｴ＾ｉＢ 0.046 -2.6 -2.6 -2.6 21.1 1.0 CaCI, 0.045 -1.6 -1,5 -1.5 21.7 1.0 0,044 -1.3 -1,4 -1,4 ｾ 19A 0.2 ｾ ... 904t" 0.10 -0.5 -0,6 -0.6 17,2 0,2 0.012 -0.8 -0.7 -0,7 19.6 0,2 NaCI 0.01 -0,5 -0.6 -0.6 19.4 0.2 cscr, 0,01 -0.3 -0,3 -0.3 20.7 0.5.se....
S".Jr 0,024 -1.2 -1,4 -1.3 16,6 0.5 0.029 -1,6 -1.7 -1,6 19.5 0.5 NaCI 0.025 -1.4 -1.5 -1,6 19.5 0,5 CaCI, 0.025 -0.6 -0.2 -0.8 18.6 1,0 &a.,;aJI- 0,051 -2,4 -2,4 -2.7 17.2 1.0 0.055 -3.3 -3,1 -3.1Remaining (1) 0.01 0,02 o,OJ 0.01( Kｾ S • f 02 6j elf -2 -I 6 -• I 02 6] elf for CaCl
2 and NaCl solutions.
!lOI qot 0.03 0,01( Ki,S 0
o
-I - J ' - - - ' ｾ.,. ·c
'f' ' 'f,,.•,"C .f. -2 Tf.p.=
aK. loS. ois an empirical coefficient, which has values 57, 62 and 32.5 C
notation, as in Fig. 1.
indicate a good comparison. As can be seen from the tables, these
have a divergence not exceeding O.20C and only in one instance out of
3 -
experimental valuesAnalytically this dependence can be expressed by the formula
Comparison of experimental values and those calculated by formula (1) for
for sea salt, NaCl and CaC1
2 respectively.
where "a"
T
f.p , values
the 34 observations is the calculated temperature at freezing point lower than
the measured temperatures by O.50C. From the experimental results, it
follows that the analytical expression (1) is valid for each salt dissolved in
the interstitial water and for its solution. At the moisture contents of the
experiment, the type of soil (sug linok , supes and sand) has no influence on
Fig. 1. Freezing point of soils and sea salt solution dependent on the
concentration of interstitial solution.
1 - suglinok; 2 - supes; 3 - sand; 4 - sea salt solution
Fig. 2. Freezing point of soils and CaC1
2 (1) and NaCl (2) solutions at
different concentrations of interstitial solution.
its freezing point, if concentrations of interstitial solutions are
7
-When there are identical concentrations of interstitial solutions, it is the composition of the salts that influences the freezing point of the soil and the difference in the values T can turn out to be substantial (fig.
f.p.
2. ). For example, if the soil pores are filled with solutions of NaCl and CaC1
2, then in the first instance the freezing point is 1.9 times lower. For soils of marine origin, under these same conditions, the freezing point values were observed to be 1.1 times higher that in soils with an NaCl salinity, and 1.75 times lower than with CaC1
2 salinity.
Analysis of experimental data and their statistical treatment allowed the analytical relationship between the temperature at the freezing point of saline soils and the qualitative composition of water soluble salts to be established:
T
=
-3.6(K.
1m)f.p. l . S .
where
3.6
is the empirical coefficient,(2)
o
C; m is the concentration of the solution (in fractions of the unit), when there is one gram-molecule of salt in one kilogram of its solution. For sea salt, NaCl and CaC1
2, m is 0.064; 0.058 and 0.111 respectively.
The table depicts the calculated values at freezing point of soils in accordance with formula (2). By considering the accuracy of the measurement of the temperature +O.loC and some spread of experimental data, it is possible to conclude that the calculated values agree with the experimental data.
The established dependence allows the determination of the freezing point of the soil from the values of moisture content and from the qualitative composition of the water soluble salts and their quantitative content. Moreover, this dependence more or less allows the prediction of the bearing
capacity of saline permafrost from the value m, if the value of its freezing point and the concentrations of the interstitial solution are known. To do this, the knowledge that Na salts reduce the mechanical characteristics of frozen soil is used. Thus, if the value m, calculated by formula (2) approaches 0.058, then it can be anticipated that the bearing capacity of the saline soils will be small. Research into the mechanical properties of soils from marine deposits, for which m
=
0.064 substantiate this observation.8
-The research conducted allows the following conclusions:
1. The type of soil does not influence the freezing point when the moisture
content is equal to or exceeds the boundary of fluidity (liquid limit)
for clayey soils and water saturated sands having an identical degree of mineralization of water in the pores of the soil.
2. When there are equal concentrations of interstitial solution, only the
qualitative composition of the interstitial salts influences the freezing
point. Within the limits of the researched concentrations, the freezing
point of the soil is inversely proportional to the molecular weight of the soluble salts.
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