刚性桩复合地基荷载传递规律模型试验

Physical model study on load transfer law of rigid pile composite foundation

针对刚性桩复合地基所受上覆荷载下难以定量计算桩土间荷载分配的问题,设计了缩尺模型箱试验,通过人工模拟桩端下卧层为砂土、桩身段加固区地基为黏性土的工况,进行桩、土承载特性和桩身荷载传递规律的研究。假设基底桩土相对位移下路堤内土柱间滑移面剪应力垂直分布,考虑桩顶上刺入路堤、桩端下刺入下卧层以及桩侧负、正摩阻力非线性分布,理论推导了路堤-桩-地基土整体在应力与位移协调下的相互作用过程及荷载分配方法。结果表明：刚性桩复合地基可有效减少地基沉降,桩身最大轴力位于距离桩顶1-2倍桩径深度处,最大负、正侧摩阻力随着荷载的增加而增加,且最大正摩阻力位置向桩身下部转移;基于侧摩阻力与附加应力成比例关系条件,桩端下卧层砂土为Winkler地基并赋以刚度系数的定义,推导出的桩土应力比与荷载分担与实测值接近,验证了计算方法的合理性。研究结论可作为现场实际工程应用借鉴。

It is difficult to determine the load sharing ratio between rigid pile and soil when a composite foundation un- derlain an embankment. In this study, a small scale physical tank was designed to simulate working conditions of a single rigid pile, in which sand was set as the sublayer and clay as the surrounding soil. The load transfer law was adequately analyzed by monitored earth pressures and pile axial stresses. Then assuming only vertical shearing stress at the filled basement, a computational physical model which considered the existence of negative and positive friction force was pres- ented. Further, this model could take into account the pile upward and down stick into the soil layers as well as the inter- action among embankment, pile and soil. Results indicated that rigid-pile composite foundation could efficiently reduce the total embankment settlement. The maximum axial force located at a depth of one or two times of the pile diameter. The maximum negative and positive frictions on the pile increased with the increasing embankment load, and the maxi- mum positive friction position moved downward. According to a proportional relationship between the additional stress and friction, a stiffness factor of the sublayer as Winkler foundation was defined. Calculated results of pile-soil stress ratio and load share were closed to measured results. This validated the rationality of the proposed method which could provide reference for practical engineering application.