刚性桩复合地基桩土应力比的时效分析及计算方法

为了研究考虑时效的刚性桩复合地基桩土应力比计算方法，首先对桩体承载力和桩间土排水固结理论进行分析，假设桩间土体为均质材料，且考虑土体沉降时忽略桩体的存在，考虑到刚性桩复合地基仅在竖向排水固结，采用太沙基一维固结理论，开展了对桩体应力和桩间土应力时效性的研究。选取单根桩和其四周加固区的土体作为一个计算单元体进行分析，基于荷载传递法，得到计算单元体各组成部分的沉降变形关系，从而推导出刚性桩复合地基中各个构成部位之间的变形关系表达式。之后将桩侧摩阻力分布曲线进行合理简化，得到桩体应力和土体应力随深度变化的表达式，再联合之前得到的变形协调方程，可解得桩顶部位桩体应力和桩间土应力，引入考虑时效性的桩土应力比修正系数，从而推得考虑时间效应后的桩土应力比计算式。最后在某工程中使用该方法对其进行了计算分析，得到不同地质条件下桩土应力比随时间变化的关系曲线。研究结果表明：刚性桩复合地基中桩土应力比具有较为显著的时效特性，在实际计算中不能忽视，桩土应力比时效特性表现为随时间的推移而增大，当桩间土地基压缩模量减小时桩土应力比增大，桩土应力比出现峰值时，刚性桩受力最不利，设计中应加以考虑，随后桩土应力比有所减小，最后趋于稳定。

Time Effect Analysis and Calculation Method of Pile-soil Stress Ratio of Rigid Pile Composite Foundation

In order to investigate the calculation method of pile-soil stress ratio in rigid pile composite foundation considering time effect, the pile bearing capacity and drainage consolidation of soil between piles were analyzed theoretically. The time effect of the pile stress and the soil stress was investigated by dint of Terzaghi's one-dimensional consolidation theory in which there were three assumptions. That is to say, the soil between piles was assumed to be homogeneous material. The piles were ignored considering soil settlement, and the vertical drainage consolidation existed only on rigid pile composite foundation. Subsequently, a single pile as well as the soil around it was selected as a calculation unit, and the deformation relations in each component of the calculation unit were obtained by the load transfer method. Based on this, the formulas of deformation relations in each component of rigid pile composite foundation were derived. By simplifying the distribution curve of pile side friction reasonably, the formulas of the pile stress and soil stress with depth were obtained, whilst the pile stress at the top of pile and soil stress were calculated combined with the deformation coordination equation. Meanwhile, the formulas of the pile-soil stress ratio considering time effect was derived by introducing a correction coefficient of the pile-soil stress ratio. The time history curves of pile-soil stress ratio under different geological conditions were obtained by the application of method in practical engineering. The researches show that there is the significant time effect of pile-soil stress ratio in the rigid pile composite foundation which can not be ignored in actual calculation, and the time effect of pile-soil stress ratio becomes more and more obvious over time. The pile-soil stress ratio increases when the compression modulus of soil between piles decreases. When pile-soil stress ratio reaches its maximum, the rigid pile is in the most disadvantageous state of stress which should be paid much attention during the design. Furthermore, the pile-soil stress ratio decreases and tends to be stable.