多孔介质岩土材料剪切带孔隙特征研究(1)——孔隙度局部化

ANALYSIS OF VOID CHARACTERISTICS IN SHEAR BAND OF POROUS MEDIA (1):LOCALIZED POROSITY

基于梯度塑性理论,分析了剪切局部化引起的剪切带内部孔隙度的不均匀性。以剪切带内部的微小单元体为研究对象,假设剪胀引起的局部塑性剪切应变与局部塑性体积应变成比例,比例系数为扩容角,得到了局部孔隙度的解析解。结果表明,剪胀后的孔隙度、孔隙比、孔隙度增量、孔隙比增量、孔隙度变化率及孔隙比变化率均具有局部化特征,在剪切带中部其值最大。在应变软化过程中,剪切带内部的孔隙度、孔隙比、孔隙度增量及孔隙比增量越来越不均匀。随着剪应力卸载率的增加,孔隙度变化率及孔隙比变化率越来越明显。内部长度越小,剪胀后剪切带内部孔隙比梯度越大。内部长度不影响剪切带内部最大孔隙比,而剪切降模量则影响剪切带内部最大孔隙比和孔隙比梯度。

Based on gradient-dependent plasticity, the non-homogeneous porosity and void ratio in shear band after initiation of shear localization is investigated. In order to deduce the analytical solution on local porosity, a typical micro-element body in shear band is analyzed with the assumption that the local plastic shear strain is proportional to local plastic volumetric strain. The analytical results show that porosity, void ratio, increment of porosity, increment of void ratio, rate of porosity and rate of void ratio are non-homogeneous in shear band. In the center of the shear band extremely large voids exist and in the boundary of the shear band the void ratio approaches to the initial void ratio. In the strain softening process, the maximum porosity in shear band increases gradually. Rate of porosity apparently increases with decrement of shear stress rate. Moreover, influences of shear softening modulus and internal length parameter of void ratio are investigated. Smaller internal length parameter leads to larger void ratio gradient, and the internal length parameter has no influence on maximum void ratio in shear band. However, void ratio gradient and maximum void ratio are dependent on shear softening modulus.