修正等应变假定下刚性桩复合地基固结特性分析

Analysis of consolidation properties of rigid pile composite foundation based on modified equal strain assumption

刚性桩复合地基固结特性是影响工程进度的重要因素。为研究外荷载作用下刚性桩复合地基固结特性,结合刚性桩和桩间土应力-应变特点对等应变假定进行修正。在此基础之上,考虑涂抹效应、桩间土和下卧层土体固结特性的影响,推导得到桩间土和下卧层土体固结微分方程。基于双层地基固结理论,考虑单级匀速施加荷载和附加应力沿深度变化等边界条件,推导得到其固结度解析解。最后,利用数值模拟方法对解析解进行验证,并对影响刚性桩复合地基固结特性的因素进行分析。结果表明:理论计算与数值模拟结果较为吻合;刚性桩复合地基固结速率受到贯入比影响较大,当贯入比较小时,与天然地基相比,其固结速率较小,贯入比较大且桩端阻力系数较小时,复合地基固结速率大于天然地基;随着贯入比、桩-土相对刚度和垫层-土体相对刚度的增大,复合地基整体固结速率加快;随着置换率的增大,复合地基整体固结速率降低。

The consolidation characteristics of rigid pile composite foundation is a key factor affecting the progress of the project.To study the consolidation properties of rigid pile composite foundation under external load,the equal strain assumption was modified based on stress-strain characteristics of rigid pile and its surrounding soil.Considering the smearing effect,the consolidation behavior of surrounding soil and underlying stratum,the governing equations for the average excess pore water pressure within the surrounding soil and the underlying soil were developed.According to the boundary conditions of a time-dependent loading and additional stress varied with time and depth,the analytic solutions of consolidation degree were derived based on the consolidation theory of double-layered ground.The proposed method was validated by numerical simulation method.The factors that affect consolidation properties were systematically analyzed.It shows that the analytical solutions have great agreement with the numerical simulation results.The average consolidation rate strongly depends on the penetration ratio of the rigid pile.The average consolidation rate is slower than that of natural ground when the ratio is small.The average consolidation rate of rigid pile composite foundation with a greater penetration ratio and a smaller pile end resistance coefficient is faster than that of natural ground.With the increase of pile penetration ratio,the ratio of the constrained modulus of the pile to that of the soil and the ratio of the constrained modulus of the cushion layer to that of the soil,the overall consolidation rate of the composite foundation is accelerated.With the increase of the replacement rate,the overall consolidation rate of the composite foundation decreases.