高纬度低海拔岛状多年冻土桩基回冻前后承载力的试验研究

冻土与普通的土体相比具有独特的工程性质。在冻土地区进行桩基础施工后，桩和周围土体在冻土地温及大气温度的作用下逐渐回冻，回冻过程中在冰的胶结作用下桩与周围土体联结成整体共同承受外荷载作用。为了研究回冻前后桩基的承载力变化及变形性质，在大兴安岭地区浇筑了2根15 m试验桩，试验桩中布设了温度监测系统，采集了桩基回冻过程中的温度数据。根据温度监测结果在桩基回冻前后进行了自平衡静载试验，研究了回冻前后桩基承载力、各土（岩）层的侧摩阻力及桩端阻力。研究结果表明，桩基回冻后冻土地温保持在-1.9 ℃桩基的承载力是回冻前承载力的1.42倍；端阻力是回冻前的1.49倍为964 kN，占桩基承载力的12.98%；各土（岩）层的侧摩阻力均有所增长，平均增长率为40.3%。研究结果可为类似冻土条件下的桩基设计及施工提供理论依据。

Experimental study of bearing capacity of island permafrost pile foundation before and after refreezing in low altitude and high latitude area

Compared with the common soils, frozen soils have unique engineering properties. After the pile foundation was constructed in regions with polygonal permafrost, the frozen soil and pile sustain the load as an integral due to the cementing effect between pile and surrounding frozen soil in the refreezing process. In order to obtain the properties of capacity and deformation before and after refreezing process, two 15 m testing piles were constructed in Daxinganling, China. Temperature monitoring system was adopted to record the temperature change in refreezing process. Based on the monitoring results, self-balanced static load test was conducted to determine the bearing capacity, tip and lateral friction within different stratus. The results show that the frozen soil was -1.9°C after refreezing. The capacity is 1.42 times of that before refreezing, and the tip friction is 1.49 times of that before freeing, which consisted about 12.98% of the total pile capacity. The average increment in pile lateral friction is 40.3%. This paper can serve as an evidence for the pile design and construction in permafrost areas.