EXPERIMENTAL STUDY OF BEARING CHARACTERISTICS OF LARGE-DIAMETER CAST-IN-PLACE BORED PILE UNDER NON-REFREEZING CONDITION IN LOW-TEMPERATURE PERMAFROST GROUND
WANG Xu1，2，JIANG Daijun1，LIU Deren1，HE Fei1
(1. School of Civil Engineering，Lanzhou Jiaotong University，Lanzhou，Gansu 730070，China；2. Key Laboratory of Road，Bridge and Underground Engineering of Gansu Province，Lanzhou Jiaotong University，Lanzhou，Gansu 730070，China)
Abstract：For the large-diameter cast-in-place concrete bored piles in low-temperature permafrost ground，a large amount of heat produced by concrete hydration would result in thawing of permafrost soil around the pile，and thus the interface between the pile and the soil would not have enough freezing strength，making it impossible the pile to reach the designed bearing capacity at an early stage after the construction. Thus，the bearing and deformation features of the piles under a non-refreezing state were studied. A series of in-situ ground temperature tests and static loading tests were performed for the pile foundations of the Sonam Dargye Bridge located at the Qinghai-Tibet railway during its construction. The pile-soil-surface thermometer holes，pile-side thermometer holes(30 cm from the pile skin) and reference thermometer holes to measure the ground temperature undisturbed by construction，denoted by SB，SC，and JZ，respectively，were set up to obtain the corresponding temperatures. The temperature distributions for the pile-soil system at various ages were obtained when the piles were cast in summer and the initial concrete temperature was 11 ℃. The refreezing process of the pile-soil system as well as the distribution characteristics of the vertical bearing capacity，vertical deformation and skin friction(or freezing force) of the pile under various ground temperatures were analyzed. Test results show that 30 days after the construction of the pile，the temperature along the pile skin is negative(approximately －0.43 ℃–－1.26 ℃) except in the section 0–2 m below the ground surface；50 days after the construction of the pile，it becomes a bit lower(approximately－1.0 ℃–－1.85 ℃). Compared with the original undisturbed state，the pile-soil system is not fully refrozen. When a maximum vertical load of 7 600 kN is applied，the vertical pile-head displacement is 4.93 mm while the residual deformation after unloading is 1.01 mm. It shows that the pile has a high vertical bearing capacity and a small deformation under a non-fully refreezing condition with the pile age of 30 days.
铁道部第三勘测设计院. 冻土工程[M]. 北京：中国铁道出版社，2002：225-260.(Third Railway Survey and Design Institute. Frozen soil engineering[M]. Beijing：China Railway Publishing House，2002：225-260.(in Chinese))
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2013, Vol. 32 
