中文摘要：

应变软化是指应力-应变曲线中轴向应力随应变的增加而减小的现象，许多种类的岩土介质在工程扰动的作用下呈现应变软化的行为。在分析应变软化问题时，其应力-应变关系式中的切线刚度矩阵是非正定的，由此导致计算求解的困难。将岩体应变软化过程简化为一系列脆塑性过程，于是应变软化问题的求解归结为一系列脆塑性过程的分析。基于经典弹塑性力学理论，提出了应变软化过程模拟方法及其相应的有限元求解过程，编制了计算程序，研究了应变软化本构模型中不同强度弱化速率对圆形洞室围岩塑形区分布的影响，进一步分析了应变软化模型对应的隧道径向变形沿洞轴方向的分布特征，并与已有监测数据得到的分布规律进行了对比。初步的研究结果表明，应变软化模型得到的计算结果是比较合理的。

英文摘要：

In stress-strain curve, the process of decline of uniaxial stress at increasing strain is defined as strain-softening. Many types of geomaterials behave in strain-softening way in the case of disturbance of engineering activities. When the stress-strain relationship is described in mathematical formulation, the matrix of tangential elastic moduli is no longer positive-definite. Thereby difficulties arise in finding the solution to strain-softening problem. Strain-softening process is simplified into a series of brittle-plastic behavior;and solving brittle-plastic problem comes down to obtaining a series of brittle-plastic solutions. On the basis of classic plasticity theory, the method for analyzing strain-softening behaviour is proposed;and the corresponding solution process is implemented in finite element code. Furthermore, the influences of different strength-weakening modes on the distribution of plastic zone in the surrounding rock mass of a circular tunnel are studied. The longitudinal deformation profile （LDP） obtained by strain-softening constitutive model is also analyzed; and it is compared with the measurements in a tunnel. The preliminary numerical analyses indicate that the presented results look reasonable.