深层开挖条件下抗拔桩极限承载力分析

Analysis for ultimate uplift capacity of tension piles under deep excavation

抗拔桩极限承载力的确定对于工程设计有决定性作用,由于实际工程情况和现场试验条件的限制,深层开挖条件下的抗拔桩极限承载力实际上无法通过现场试桩得到,因而理论研究显得尤为重要。采用基于直接约束算法的桩土库仑摩擦模型,借助于弹塑性有限单元法对上海某工程的等截面和扩底抗拔桩单桩足尺试验进行对比分析,验证了所采用的理论计算分析方法的合理性,得到了上海软土地区抗拔桩有限元计算的相关参数。然后在此基础上,对比了等截面和扩底抗拔桩受力特性,通过在不同开挖宽度和埋置深度条件下抗拔桩极限承载力的对比分析和影响因素的探讨,最后得到了深层开挖条件下抗拔桩承载力变化的一般规律。

Determination of the ultimate uplift capacity for tension piles play a dominant role in engineering design. Unfortunately, due to the limitation of in-situ test conditions, it is almost impossible to obtain the ultimate uplift capacity of tension piles under deep excavation from field tests, and the theoretical study becomes the only feasible way to solve this problem. Adopting the Coulomb friction model for the pile-soil interface with direct constraints, two full-scale field tests on single uplift pile with uniform cross-section and enlarged head were simulated by employing the elastoplastic finite element method, and the simulated results were in good accordance with the field test data. Based on the above-mentioned analysis approach and calculation parameters, the difference between the uniform cross-section piles and the belled piles was examined and a comprehensive study focusing on the effects of excavation width and embedment depth was performed. Finally, suggestions for determining the ultimate uplift capacity of tension piles under deep excavation were given.