考虑土体非线性特性的散体材料桩复合地基沉降计算

Settlement calculation of composite foundation with granular material pile considering nonlinear compressibility of soil

散体材料桩具有良好的加固效果且造价相对较低,被广泛应用于工程中的软弱地基加固处理。散体材料桩复合地基的沉降计算是复合地基设计的重要内容之一,然而目前规范中采用的应力修正法和复合模量法均未能考虑土体的非线性压缩特性,即认为土体的压缩模量E_s为常数,然后应用分层总和法开展复合地基的沉降计算,由此导致计算的复合地基沉降量往往大于实测值。事实上,土体具有典型的非线性压缩特性,其压缩模量往往与作用于土体的应力密切相关。鉴于此,本文首先阐述了土体的非线性压缩特性,引入经典e-lgσ非线性关系,推导建立土体压缩模量E_(s)随不同深度处有效应力变化的规律,进而对规范中的应力修正法和复合模量法进行改进,并通过分层总和法完成复合地基的沉降计算,最终获得考虑土体非线性压缩特性的散体材料桩复合地基沉降计算公式。最后,应用不同沉降计算方法对室内模型试验和某实际工程展开分析,将改进后的沉降计算方法与规范方法及实测值开展对比分析,结果表明,本文提出的考虑土体非线性特性的复合地基沉降计算方法计算结果更接近于实际工程实测值。

Granular material pile is widely used in the reinforcement of soft foundation in engineering because of its good reinforcement effect and relatively low cost.The settlement calculation of composite foundation with granular material pile is one of the important contents of composite foundation design.However,both the stress correction method and composite modulus method adopted in the current code for foundation design fail to consider the nonlinear compression characteristics of soil.This implies that the compression modulus Es of soil is considered as a constant,and then the layered summation method is used to calculate the settlement of composite foundation,which leads to the calculated settlement of composite foundation is often greater than the measured value.In fact,soil has typical nonlinear compression characteristics,and its compression modulus is often closely related to the stress acting on the soil.In view of this,the nonlinear compression characteristics of soil are described,and the classical e-lgσ nonlinear relation is taken to deduce the law of soil compression modulus E_(s) changing with the effective stress at different depths.Furthermore,the stress correction method and composite modulus method adopted in the code are improved.Finally,a formula for calculating the settlement of composite foundation with granular material piles considering the nonlinear compression characteristics of soil is obtained by using the improved method.Besides,comparisons are made among results of the indoor model tests,actual engineering data and theoretical calculation values by different settlement calculation methods.The results show that the improved settlement calculation method used in this paper presents a better agreement with the measured values than that of the results from the code methods.