黏性土固结不排水剪切的滑动损伤模型研究

A damage constitutive model for clay based on the analysis of sliding of skeleton grains

在工程荷载范围内,不计骨架颗粒的变形,骨架的变形实际是颗粒接触面变形的总和。当剪应力达到某个临界值时,黏性土骨架中有一部分颗粒接触面开始滑动,随着剪应力的增大,出现滑动的颗粒接触面的取向范围也会扩大。将这种颗粒接触面的滑动视为一种损伤。在损伤阶段,黏性土骨架中既有未滑动的接触面,也有已滑动的接触面,宏观剪切模量是这两种接触面的剪切模量的加权平均。在σ?τ平面中,根据应力圆与颗粒起始滑动包络线的相对位置,计算出已出现了滑动的颗粒接触面的取向范围,并定义该取向范围与其所能达到的最大值(由破坏时的应力圆计算)之比为骨架的损伤比。按损伤比进行加权平均得到骨架的整体剪切模量。模型中的参数完全可以根据常规三轴试验确定,模型的形式简单,可适用于复杂的应力路径。对试验结果的拟合表明,该模型能较好地反映黏性土在固结不排水条件下剪切变形的主要特征。

A hypothesis that the skeleton deformation of clay is only the deformation of the interfaces of grains, and the deformation characteristics including nonlinearity and plastic deformation are controlled by the sliding of interfaces of grains within skeleton, is presented. Such a sliding can occur whenever the shear stress on interfaces of grains reach a critical value, and the direction range of sliding increases with the shear stress. This paper view that the sliding of interfaces of grains is a sort of damage in the clay skeleton, and there are two sorts of interfaces within the clay skeleton, the one contacts perfectly, and the other one contacts imperfectly. On σ-τ plane, according to the relative distance from the stress circle to the initial sliding envelope line, the direction-range value of the sliding interfaces can be determined. The damage ratio is defined as the ratio of the previous direction-range values to its maximum value （determined by failure stress circle）. The overall shear modulus is the weighting average of the perfect contact shear modulus and sliding contact shear modulus. The proposed model simulates the shear deformation for saturated clay under consolidated undrained condition reasonably well. In addition, the mechanical properties of the model can be conveniently obtained through conventional triaxial compression test; and the model is capable for predicting deformation behavior under various conditions including varying hydrostatic stress and stress paths.