Geotechnical construction disturbs soil mass,destructs soil fabrics,reduces soil strength,and causes soil deformation,all of which can result in the deformation and destruction of adjacent buildings.According to the value of soil shear strain,the soil surrounding a construction site can be divided into:strongly disturbed zone,disturbed zone,micro-disturbed zone,and undisturbed zone.Therefore,a soil constitutive model needs to consider the small strain characteristics and disturbance characteristics of the soil.Methods for determining key parameters of a hardening soil model with small strain stiffness (HS-Small model),including initial shear modulus and threshold shear strain,have been presented and analyzed.Drained triaxial tests and oedometer tests were performed on typical soils in Shanghai,and the corresponding model parameters were determined.The in situ testing methods are recommended for determining the initial elastic modulus of soils.Sensitivity analysis of the HS-Small model parameters,including initial shear modulus and threshold shear strain,revealed that the initial slope of the compression curve and the unloading-recompression curve increased with the increase of the initial elastic modulus.With increasing threshold shear strain,both the approximate straight segments of the compression curve and the unloading-recompression curve lengthened.Under same shear stress conditions,the shear strain of the soil decreased,while the interval range of the initial elastic modulus of the soil constantly increased.%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(HS-Small)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.
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