强度折减有限元法分析边坡失稳判据讨论

Discussion on analysis of slope instability criterion by strength reduction FEM

对同一算例边坡,分别采用有限元计算不收敛判据、等效塑性应变或塑性区贯通判据、及特征部位位移(或位移增量)与折减系数关系曲线发生突变判据来确定边坡的整体稳定安全系数,提出在对土体抗剪强度指标进行折减的同时,若同步调整其弹性模量和泊松比,就可以使上述几种失稳判据计算的安全系数基本相一致。将算例边坡在外接圆屈服准则下的安全系数转换成莫尔-库伦等面积圆屈服准则下的安全系数,并与Spencer极限平衡法的安全系数和滑动面相比较,证明了文章提出方法的正确性。最后分析了泊松比和弹性模量对上述3种失稳判据给出安全系数的影响。

An example slope is analyzed by using the elastoplastic finite element method （FEM） based on the shear strength reduction （SSR） technique and its overall safety factor is obtained by three yield criteria respectively, i. e., the criterion of non - convergence by FEM, the criterion of equivalent plastic strain or connectivity of plastic zone, and the criterion of abrupt change of the relationship between the displacement （or displacement increment） and the reduction coefficient at a certain characteristic location. It is founded out that the overall safety factor, based on the above three instability criteria, will be consistent with each other, if their Young＇s modulus and Poisson＇s ratio are adjusted simultaneously in the process of computing the safety factor with the SSR. And then, the safety factor calculated in the circumcircle yield criterion is transformed to that in Mohr - Coulomb equivalent area circle criterion, and compared to the safety factor of Spencer＇s limit equilibrium method and sliding plane. It is shown that the safety factor and the sliding plane of the SSR are fairly close to the results of the traditional Speneer＇s limit equilibrium method. So the applicability Of the method proposed in this paper is clearly exhibited. Finally, the influence of Young＇s modulus and Poisson＇s ratio on the overall safety factor computed on the above three instability criteria is also analyzed.