Permafrost

which offers the referrence for further perfecting the anti-frozen and anti-seepage theories and
applied experience of EPS.
Key words: hydraulic structure, frost heaving, EPS, heat preservation foundation,
temperature field
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Study on the Thermal Regime of Frozen Ground after Construction of
Large-diameter Cast-in-place Piles in Permafrost Regions
Xi-zhong Yuan 1,2 , 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 results obtained from 2 typical sites of pile test alone Qinghai-Tibet Highway in
permafrost regions indicate that the thermal regime and the refreezing process of frozen soil
around the large-diameter cast-in-situ piles dependent on such factors as the engineering
geology characteristics of frozen ground, the construction methods, the heat carried by the
concrete and released during cement hydration period and the seasons of construction.
1) The factors of engineering geology characteristics of frozen ground
After the thermal disturbance of construction the low-temperature frozen ground can
gradually refreezes in the short construction period. The temperature of side surface of test piles
(diameter=1.2m, length=15m) in Kunlun Mountains pass test site (the mean annul ground
temperature=-2℃) drops to freezing temperature 15 days after concrete casting; then reduces to
-1~-2℃ 50 days after casting. But the high-temperature frozen ground of large-diameter piles
can’t refreeze in the limited construction period. The temperature of side surface of test piles
(diameter=1m, length=12.5m) in Beiluhe test site (the mean annul ground temperature=-0.8℃)
decreases to freeing temperature 90 days after concrete pouring, and remains around -0.1℃
even 270 days after concrete pouring.
The regression analysis result shows that the period (t) from concrete pouring to the
temperature of the pile side surface decreasing to freezing temperature is inverse proportion to
the initial temperature (θ) of the frozen soil around the piles.
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t = − − 2.
5,
(R 2 = 0.98)
θ
After dropping to freezing point the temperature decreasing rate of low-temperature frozen
ground slows down and this process can be express as followed according to regression analysis
result:
= −a
ln t + b
θ , (R 2 = 0.8~0.9)
where parameter a=0.6, and b=1.4~1.6.
The temperature of high-temperature frozen ground around the large-diameter piles
remains to freezing temperature and temperature dropping process ceases.
The thermal physical properties such as ice content and thermal conductivity of frozen ground