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地下工程施工引起的土体扰动区可分为剧烈扰动区、扰动区、微扰动区和未扰动区。为全面反映土体在扰动下的应力路径和力学响应,必须考虑全应变范围的土体特性,尤其是小应变范围内的力学响应,因此对小应变硬化土本构模型关键参数(初始剪切模量和剪应变阀值)的确定方法进行介绍。开展上海典型软土的三轴固结排水剪切试验和固结试验研究,给出确定上海软土小应变硬化土模型(HSSmall)参数的方法,建议采用原位测试的方法确定土体的初始弹性模量。基于土单元数值模拟进行初始弹性模量和剪应变阀值的参数敏感性分析。随着初始弹性模量的增大,初始压缩曲线与卸载-再压缩曲线的斜率均增大。由于对应的回弹模量不变,初始弹性模量与回弹模量的差值增大,应变与偏应力试验曲线的回滞环宽度也随之增大。随着剪应变阀值的增大,初始压缩曲线和再压缩曲线的近似直线段增长,在同样剪应力情况下,土体的应变值减小,土体保持初始弹性模量刚度的区间增大。
Soil disturbance caused by underground construction can be divided into violent disturbance zone, disturbance zone, micro disturbance zone and undisturbed zone. In order to fully reflect the stress path and mechanical response of soil under perturbation, the soil characteristics in the whole strain range must be considered, especially the mechanical response in the small strain range. Therefore, the key parameters of the constitutive model of small strain hardening soil (initial shear Modulus and shear strain threshold) to determine the method are introduced. The triaxial consolidation drainage test and consolidation test of typical soft clay in Shanghai are carried out. The method of determining the HSSmall parameter of Shanghai soft soil is given, and the method of in situ testing is proposed to determine the initial Elastic Modulus. Parameter Sensitivity Analysis of Initial Elastic Modulus and Shear Strain Threshold Based on Soil Element Numerical Simulation. As the initial elastic modulus increases, the slope of both the initial compression curve and the unloading-recompression curve increases. Since the corresponding elastic modulus does not change, the difference between the initial elastic modulus and the elastic modulus increases, and the hysteresis loop width of the strain and deviatoric stress test curve also increases. With the increase of the shear strain threshold, the approximate straight line segment of the initial compression curve and the recompression curve increases. Under the same shear stress, the strain value of the soil decreases and the interval of the soil retaining the initial elastic modulus increases .