有效应力法和有效固结压力法在预压地基强度计算中的应用

Application of effective stress method and effective consolidation stress method for strength calculation in preloading ground

计算预压地基抗剪强度的现行规范公式是基于土体不等向固结过程推导而来的,理论上并不适用于含有等向固结过程的预压地基。为此,分析现有强度增长理论(有效应力法和有效固结压力法)的计算原理,基于有效固结压力法并结合不同类型预压土体的固结过程,推导了计算预压地基抗剪强度的新公式;从理论分析的角度讨论了规范公式和新公式应用于真空预压和联合预压时的计算结果,最后结合某联合预压地基处理工程检验了规范公式和新公式的适用性,并对比分析了计算强度与实测强度的差异。结果表明:有效固结压力法可以考虑土体在等向固结和不等向固结中强度增长的差异,规范公式理论上仅适用于堆载预压地基的强度计算;规范公式对真空预压和联合预压地基强度的理论计算值均小于所提出的新公式,两者相对误差的大小仅与土体内摩擦角φcu有关,且随φcu的增大而增大;在某联合预压地基处理工程中,新公式的强度预测值相较于规范公式与实测值更为接近,能更加准确地反映地基土强度增长规律。根据不同预压类型来选取相应的强度计算公式,这对于实际工程计算有一定的参考意义。

The standard formula for calculating the soil shear strength of the preloading ground under anisotropic consolidation is not applicable to isotropic consolidation process.In this paper,a new formula was proposed to calculate the soil shear strength of the preloading ground under isotropic consolidation process.This new formula was derived by analyzing the calculation principle of the two existing fundamental methods,which are effective stress method(ESM)and effective consolidation stress method(ECSM),respectively.Then the results that calculated by the new formula and the standard formula applied to vacuum preloading and vacuum combined surcharge preloading were theoretically discussed and compared.Finally,the applicability of the new formula and the standard formula were tested by the practical engineering,and the difference between the calculated strength and the measured strength were also analyzed.The results show that the ECSM can be applied to the preloading ground under both the isotropic consolidation and the anisotropic consolidation,while standard formula is only applicable to surcharge preloading ground theoretically.The values of soil shear strength of the vacuum preloading and vacuum combined surcharge preloading that calculated by the standard formula are smaller than those calculated by the new formula.The relative difference of the two calculation values only relates to the friction angleφcu and increases as the friction angle increases.In the vacuum combined surcharge preloading treatment project,the shear strength prediction values by the new formulas are closer to the measured values than those by the standard formulas.The result of this study can be potentially helpful for calculating different kinds of preloading grounds in practice.