基于变固结系数的静压桩周土体力学特性研究

Study of mechanical properties of soil around jacked piles considering variable consolidation coefficient

以静压沉桩后桩周土体的应力状态为初始条件,根据桩周土体孔隙比、渗透系数和有效应力之间的相关性,在考虑固结系数随固结时间变化的条件下改进了轴对称条件下的太沙基固结控制方程。随后,采用分离变量法和离散化分析推导得出了桩周超孔隙水压力消散的半解析半数值解,并将解答与实测数据进行对比验证。在此基础上,采用空间滑动面理论改进的修正剑桥模型(SMP-MCC)定义土体三维不排水抗剪强度,研究了静压桩周土体强度、剪切模量随固结时间的变化规律。研究结果表明:由于解答考虑了固结系数随固结时间的变化,因而与实测结果吻合良好;土体压缩指数与渗透指数之比对土体固结系数和孔压消散速率影响较大;当土体压缩指数与渗透指数之比为1时,土体固结系数保持不变,解答退化为经典的太沙基轴对称固结方程;土体强度和剪切模量随固结时间的增长而逐步增加,固结完成后其值超越了土体原位强度和原位剪切模量。

Taking the stress state of soil around jacked pile as the initial condition, a Terzaghi＇s consolidation equation is modified under the axisymmetric conditions considering that the consolidation coefficient varies with time regarding the correlation between void ratio, permeability coefficient and effective stress. Subsequently, a semi-analytical and semi-numerical solution of excess pore water pressure dissipation is derived by using separation of variables and discrete analysis and compared and verified with the measured data. On this basis, the soil 3D undrained shear strength is defined by using SMP criterion-based Cam-clay model. The strength of soil around jacked piles and the variation of shear modulus with consolidation time are researched. The results show that the theoretic solution is well consistent with the measured data because of considering the change of the consolidation coefficient. And the ratio of the compressibility index and the permeability index has significant effects on the variations of consolidation coefficient and the consolidation rate. When the ratio equals to 1, the consolidation coefficient will be constant, the solution is degenerated into the conventional Terzaghi＇s axisymmetric consolidation equation. Also the soil strength and the shear modulus gradually increase along with the consolidation time. In the long-term stage of consolidation, their values exceed in-situ strength and in-situ shear modulus.