剪切带形成过程中的边界约束和加载速度效应

基于有限变形理论，研究了正常固结藤森黏土的边界约束效应和加载速度效应。用中井的子负荷面本构关系模型模拟土体的变形和强度特性，并对该模型采用高精度的欧拉向后应力积分算法。在土体表面不需要人为地假定任何形式缺陷的情况下，得到了两种形式的剪切带模式。在慢速加载条件下，端面约束较强的试样形成2条共轭型剪切带；端面约束较弱的试样，形成单一型剪切带。而在快速加载条件下，则没能形成明显可见的剪切带。通过研究剪切带及其附近土体单元的体积变形发现，即使是正常固结的黏土，在剪切带的局部化过程中也会出现一定程度的应变软化和体积膨胀现象，而靠近剪切带附近的单元则出现一定的卸载情况。同时指出，利用考虑柯西应力的转动张量影响的单元分叉条件，可以为土体的剪切带局部化分析提供大量有用的信息。

Effects of boundary condition and loading speed on shear band localization

The finite deformation theory is applied to investigate the effects of boundary condition and loading speed on shear band localization of normally consolidated Fujinomori clay. The Nakai's subloading tij model is used to simulate the soil behavior. In the model the high precision backward Euler integration algorithm is adopted. On this basis two types of shear band patterns under the condition of without man-made deficiency on soil surface are obtained. In case of slow loading, strong constrain condition on the top of soil sample leads to the emergence of a coupled shear band pattern and weak constraint condition will lead to a single band pattern. In case of rapid loading, no shear band is observed. It is also indicated that even in normally consolidated clay the deformation softening and volume expansion will exhibit to a certain extent in the process of shear band localization. In the vicinity of a shear band, the elements exhibit elastic unloading. Simultaneously, the element bifurcation considering the spin tensor of the Cauchy stress can provide a large amount of useful information about the shear band localization.