基于边坡渐进破坏特征对传统极限平衡法几点假设的合理分析

边坡的渐进破坏特征一直以来是边坡计算仿真中的一个难点。实际边坡的破坏很少是一个整体达到极限状态，突然滑动的过程，往往是逐步发展由局部破坏到最终整体失稳，即临界状态小扰动导致的链式多米洛骨牌式失稳。利用颗粒流软件，设计了0.1 m粒径高10 m土坡的数值模型，粒间黏聚力为36 kPa，摩擦系数为0.36。初始模型在重力作用下不会发生破坏，通过单独折减粒间黏聚力到18 kPa使得边坡破坏，监测竖向颗粒组group的变化获取每20 000个时间步的边坡破坏形态，实现200 000个时间步内边坡的渐进破坏过程。边坡总是从局部开始破坏，坡体物质的运移造成次一级破坏，形成最终的近似弧形的滑动面，说明滑体不是整体下滑，不是刚体，不是整体达到极限状态；坡体内应力的变化也不是单调的，有涨有落，均区别于当前极限平衡法中有限条块的刚体假设；滑动面上同时达到极限状态假设，问题本身是静不定的，通过给出条间力的传递方式使之静定可解；整体分析不能考虑破坏的局部化和渐进特征。这说明边坡计算方法的未来在于能反映动力问题和材料破坏特征的离散元方法。

Analysis of reasonability of several assumptions used in typical limit equilibrium methods based on progressive failure feature of slope

Progressive failure feature of slope is difficult for numerical simulation of slope.Also practical slope failure process is rarely a whole and sudden slipping one,is often step by step one from local deformation to final and overall instability,which is a chain domino style failures triggered by small disturbance under critical condition.Here by particle flow code(PFC),a numerical slope with cohesion between particles being 36 kPa,friction coefficient between particles being 0.36,0.1m particle size and 10m height is designed,initial models damage will not occur under gravity condition.Slope failure is done by cohesion strength between particles reduced to half of initial one.Slope shapes of each 20 000 steps,total steps being 200 000,are obtained by monitoring change of vertical particle groups at horizontal intervals of 1m,which directly reveals progressive failure of slope.Found that failure is always beginning from local part,movement of slope body material results in secondary damage in slope,which forms final arc sliding surface.These account for sliding isn’t a whole declining of slope body,the body isn’t a rigid one.Stress conditions along slip surface don’t reach limit state at the same time.Change of stress in slope body isn’t a monotonous one,but a process with rises and falls.All these conclusions contradict assumptions in current limit equilibrium methods such as rigidity of finite slice,simultaneously reaching limit sate on slip surface,making statically indeterminate problem solved by force transfer mode between slices given,overall analytical method not presenting localization and progressive feature of failure,which hints future of slope computing method lies in discrete element methods can present dynamic practical problem and material real failure characteristics.