边坡稳定强度折减有限元分析中的若干问题讨论

强度折减有限元法在边坡稳定性分析中得到了广泛应用,但仍存在一些问题未能很好地解决。首先探讨了不同单元类型对边坡稳定安全系数计算精度的影响,指出采用三角形二阶单元,能够较好地模拟土坡的渐近破坏过程,且相对网格大小控制在0.1～0.15之间时能获得较精确的解;其次讨论了边坡失稳的4个判据问题,指出在合理网格大小区间内,有限元强度折减至土坡破坏时,先后出现塑性区贯通、等效塑性应变带贯通、位移陡增与数值计算不收敛等4种表征,以此分别作为边坡失稳判据,所得到的安全系数具有较好的一致性;最后讨论了边坡破坏时滑动面深浅、滑出点位置与坡体材料的黏聚力、内摩擦角及坡角间的关系,指出黏聚力越大、内摩擦角越小或坡度越小,滑动面越深,且滑出点越远离坡脚。

Discussion on several issues in slope stability analysis based on shear strength reduction finite element methods (SSR-FEM)

Some problems have not still been solved smoothly in slope stability analysis using shear strength reduction finite element method (SSR-FEM) until now. The effect of mesh shape, size and order on the factor of safety is systematically discussed at first; triangular second-order element is thought to be the optimal one, as it can be able to both simulate the failure process of slope and obtain the accurate solutions during the relative element size from 0.1－0.15. When a slope arrives at the critical failure state by SSR-FEM, the four failure criteria as plastic zone extension from the toe to the top of slope, equivalent plastic strain exceeding a certain value developed along the potential slip surface, uncontrollable increase in characteristic nodal displacement on slope surface; and the iteration non-convergence of nonlinear FEM numerical calculations can be found in turn. Calculation results show that the four evaluation criteria are highly consistent. Location of potential slip surface and out-slip point is associated with cohesion, internal friction angle and slope angle. The bigger cohesion, smaller friction angle or the lower slope angle can make slip surface deepen, and the out-slip point is far from the slope toe.