非饱和土耦合本构模型的三维化

非饱和土本构关系模型通常是建立在修正剑桥模型的基础上,并采用了广义的von Mises准则,以描述非饱和土在一般应力状态下的本构行为。该准则假设在π平面上屈服面是个圆形,高估了土体除三轴压缩以外的强度,在平面应变中也会错误估计中主应力比。空间滑动面破坏准则（SMP）考虑了第三应力不变量的影响,屈服面在π平面上为曲边三角形,可以较好地描述一般应力状态下土体的剪切屈服和破坏特性。采用变换应力方法,将SMP准则应用到最近建立的非饱和土耦合本构模型中使其合理的三维化,能够有效地将模型从轴对称应力状态扩展至一般应力状态。根据与试验结果对比表明,改进后的模型在不增加任何参数的情况下,能够较好地模拟非饱和土在三轴伸长等一般应力状态下的行为特性。

SMP-based representation of a constitutive model for unsaturated soils

The constitutive models for unsaturated soils are usually developed within the framework of the modified Cam-clay model, and with the generalized von Mises criterion, they are used to describe the constitutive behaviors of the unsaturated soils at general stress states. In using the generalized von Mises criterion, the yield surface is assumed to be a cycle in the plane. This assumption overestimates the strength of soils except that under the triaxial compression condition, yielding an incorrect estimation for the ratio of intermediate principal stress. The spatially mobilized plane (SMP) criterion takes into account the effect of the third stress invariant, and the shape of the resulted yield surface is a curved triangle in the plane, so that the resulted constitutive model is capable of describing very well the yielding and failure of soils. In this paper, a newly developed constitutive model for unsaturated soils, which is developed in the triaxial stress state, is generalized to the general stress space based on the SMP criterion. Comparisons between the model simulations and experimental results show that the new model can describe very well the behaviors of unsaturated soils without introducing any new parameters.