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Modeling frost jacking behaviors of screw piles subjected to one-dimensional freezing condition(PDF)


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Modeling frost jacking behaviors of screw piles subjected to one-dimensional freezing condition
WANG Teng-fei LIU Jian-kun TAI Bo-wen HU Tian-fei YU Qian-mi WANG Li-yang
1. School of Civil Engineering, Beijing Jiaotong University, Beijing 100044, China; 2. Key Laboratory of Highway Construction & Maintenance Technology in Permafrost Region, Qinghai Research Institute of Transportation, Xining 810001, Qinghai, China
road engineering subgrade numerical analysis screw pile frost jacking cold region
Soil in active layer undergoes volume expansion during winter, and foundations will be ejected from the ground due to the frost-heaving force acting on them. Screw piles are usually applied to foundations of projects in cold regions to minimize such problems. FE model was established by using commercial software COMSOL Multiphysics, to simulate screw pile-soil system under one-dimensional freezing condition. Hydro-thermal calculation was sequentially coupled with stress analysis, i.e., within self-defined module, the ice-water phase change and resistance of ice were taken into consideration for Richard’s equation. A semi-empirical model was proposed to connect frost heave with volumetric ice content and temperature, and stress analysis was conducted by using data derived from previous hydro-thermal calculation. The stress and displacement were obtained on the basis of this. Due to geometric symmetry, the computational approach was performed under axisymmetric condition. Three kinds of screw piles, including small double-helix pile, large double-helix pile and multi-helix pile, were compared with a no-helix pile as a control. The results show that when freezing depth exceeds the full embedment length of pile after seven days’ freezing (boundary temperature -15 ℃), screw piles generally perform better in mitigating frost jacking than no-helix pile, and bottom helix bears more loads than the rest helices. Cooling energy transferred through pile shaft gives rise to freezing of soil adjacent to the pile. By comparisons among different piles, main geometric parameters are summarized, and it is found that screw pitch, blade width and number, position of top blade are crucial to frost jacking performance of screw pile. This work is a preliminary step towards optimized designing of screw piles in cold regions engineering applications.



Last Update: 2017-07-17