托底抗拔桩承载特性的模型试验研究

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。

Model tests on shaft capacity properties of bottom uplift pile

The bottom uplift pile is a new type uplift pile for solving the problems of concrete cracks in pile shaft and the effect of interaction between strata and pile head. The unbonded steel strand with both ends anchored in the toe of concrete pile and slab of underground structure respectively is adopted to transmit the uplift load into pile bottom. There are some differences between tensile pile and bottom uplift pile in shaft capacity properties. The model pile tests are adopted to investigate the characteristics of the ultimate shaft capacity, shaft axial force and shaft friction of tensile pile and bottom uplift pile. The effects of Possion’s ratio are discussed for the above two types of piles. For the method calculating the shaft capacity of tensile pile, pile stiffness coefficient is used to determine the tension coefficient of bottom uplift pile. The method for shaft capacity is proposed and validated for bottom uplift pile.