Permafrost

influence its temperature change process. The temperature increase and decrease process in the
layer of high ice content is relatively slow.
2) The factors of drilling methods
Drilling in different methods disturbs the frozen ground to varying degrees. In the process
of percussion boring, the circulation of slurry carries a great quantity of heat into the ground
and brings about great heat exchange with the frozen ground and causes the increase of the
frozen ground. For instance, after 2 months of the boring process the temperature of frozen
ground at the center of piles group increases about 0.5℃.
For the rotary drilling, the frozen ground temperature increase caused by the friction heat is too
small to be neglected comparing with the percussion boring.
3) The factors of volume and thermal physical properties of concrete
The bigger the concrete pile is, the greater thermal disturbance to the frozen soil
foundation will be. Especially for the piles group, the influence between the piles will lead to
superimposed effect, and causes the temperature of the frozen soil rising obviously.
The concrete mix proportion, the cement hydration heat and the concrete temperature
before pouring influence the temperature of frozen soil and the refreezing process of the
foundation greatly. The greater the cement hydration heat and the higher temperature of
concrete, the larger quantity heat will be carried into the ground and the more difficult for
foundation to refreeze.
The adfreezing force between large-diameter cast-in-situ pile and the frozen soil
dependents on the temperature of frozen soil around the pile. The regression analysis result of
pile load in-situ tests shows that the adfreezing force increases 0.08~0.1MPa while the
temperature of frozen soil around the pile decreasing 1℃ in the range from –0.3 to –2.5℃.
Strength Behavior and Unfrozen Water Content of Saline Fine-grained
Frozen Soils
Xi-zhong Yuan 1,2 , Yuan-lin Zhu 1 , Wei Ma 1
(1 State Key Laboratory of Frozen Soil Engineering, CAREERI, CAS, Lanzhou Gansu 730000)
(2 Key Laboratory for Special Area Highway Engineering of Ministry of Education, Chang’an University,
Xi’an 710064)
Abstract: The influence of soil type, initial water content, temperature, strain rate and salinity
on strength of three different fine-grained saline frozen soil under conditions of unconfined
constant strain rate tests is studied in this paper. The soils include silt, silty clay and clay which
were taken from the sites along the Qinghai-Xizhang railway in construction. The range of
initial water content is from 4% to 50%, and the salinity varies from 0 to 40 parts per thousand
(ppt). The range of temperature of strength test is from –2 to –10℃, and the range of strain rate
is from 1.1*10 -3 to 1.1*10 -6 s -1 .
The effects of temperature and salinity can be normalized through unfrozen water content
in frozen soil, so the measurement of unfrozen water content at different temperature
corresponding to the strength test condition were carried out using pulsed nuclear magnetic
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