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托底抗拔桩是一种通过无黏结钢绞线将上拔荷载传至桩底,使桩身混凝土受压工作的一类新型抗拔桩。能合理解决桩身受拉开裂问题和基础筏板受桩顶托问题,其承载特性与普通抗拔桩存在差异。通过室内模型试验,对比分析了普通抗拔桩与托底抗拔桩在极限抗拔承载力、桩身轴力传递、桩侧摩阻力分布方面的差异及其原因。探讨了泊松效应对上述两种桩承载力的影响。基于普通抗拔桩承载力确定方法,引入桩相对柔度参数确定托底抗拔系数,提出了托底抗拔桩极限承载力的计算方法与关键参数得取值建议,并通过模型试验数据对该计算方法的合理性进行了验证。
Bottom upturning pile is a kind of new type uplift pile which transmits the uplifting load to the pile bottom through unbonded steel strands and makes the pile body concrete work under pressure. It can reasonably solve the problem of tension and tear of the pile body and the problem of the foundation raft supported by the pile. The bearing characteristics of the pile are different from that of ordinary pile. Through the indoor model test, the differences and their causes between the ultimate pull-out bearing capacity, the axial force transmission of pile and the distribution of pile friction are compared and analyzed. The effect of Poisson effect on the bearing capacity of the two piles is discussed. Based on the method of determining the bearing capacity of common pile, the relative coefficient of pile flexibility is introduced to determine the coefficient of bottom bracket pull-out resistance. The calculation method of the ultimate bearing capacity of bottom pile and the obtaining of key parameters are put forward. The rationality of this calculation method is verified.