多层边坡破坏机制数值模拟研究

通过大量的多层边坡算例来分析FLAC3D强度折减法在不同强度、坡比和层厚的情况下所得安全系数与滑动面位置的变化规律,并与极限平衡法进行对比,探究强度折减法和极限平衡法所得结果产生差异的原因,揭示多层边坡的破坏机制。数值模拟计算结果表明:①对于上层土体强度较软的边坡,当上下层强度相差到一定程度,表现为上层破坏,强度折减法与极限平衡法的安全系数相对差值最大,达5%~7%;上层土体厚度h增加时,安全系数逐渐减小;上层土体位于地表以下时,滑动面通过坡趾,安全系数保持不变。②对于下层土体强度较软的边坡,当上下层强度相差到一定程度,强度折减法所得安全系数基本保持不变,但极限平衡法仍保持增长趋势,最大相对差值可达12%;上层土体厚度h增加时,安全系数也相应增大,h位于9~12 m,边坡表现为深层破坏;而h=12 m时,极限平衡法的滑动面却通过坡趾,但安全系数相差很小。当h的变化范围在3~5 m,两种方法的安全系数相对差值最大,达6%~10%。破坏区分布分析表明,边坡呈拉伸-剪切复合破坏,对于下层土体强度较软的边坡,复合破坏模式更显著,与单一剪切破坏模式相比,最大有10%左右的相对差值。

Numerical simulation of failure mechanism of multilayer slope

Through massive examples of multilayer slopes with different intensities, slopes and thicknesses of soil layer, the factors of safety and the locations of critical failure surfaces obtained by the strength reduction method and limit equilibrium method are compared. The differences between two methods are investigated. Failure mechanism of multilayer slopes is studied. The result of numerical simulation shows: ①If the shear strength of the lower layer is larger than the upper one, when difference in shear strength between two layers increases to a certain degree, soil in the upper breaks. Meanwhile, the relative difference of strength reduction method (SRM) and limit equilibrium method (LEM) is in maximum, about 5%-7%. When thickness of upper soil layer increases, the factor of safety gradually decreases; when the upper layer locates below surface, critical failure surface throughs the toe of slope; the factor of safety remains unchanged. ②If the shear strength of the upper layer is larger than the lower, when difference in shear strength between two layers increases to a certain degree, the factors of safety obtained by SRM tend to be stable. As to LEM, the factors of safety maintains increase, the relative difference of is 12% in maximum. When thickness of upper soil layer is increased, the factor of safety increases correspondingly. When thickness of upper soil layer is in the range of 9-12 m, failure mode is deep layer slide, while h=12 m, critical failure surface obtained by LEM just throughs the toe of slope; but with a very small difference in the factor of safety. When thickness of upper soil layer is in the range of 3-5 m, the relative difference of two method is in maximum, about 6%-10%. The distribution of failure zone indicates that multilayer slope is caused by tension and shear failure. As to the slope which the shear strength of the upper layer is larger, this composite failure mechanism is obvious. In comparison with single shear failure, the relative difference is about 10% in maximum.