岩质边坡断续裂隙阶梯状滑移模式及稳定性计算

Step-path failure mode and stability calculation of jointed rock slopes

阶梯状滑移破坏是一类典型岩质边坡破坏失稳模式。在总结断续裂隙阶梯状滑移的岩质边坡地质结构特征的基础上,利用离散元二维颗粒流程序(PFC2D)模拟研究了边坡阶梯状滑移破裂模式及其演化过程。边坡岩桥可归纳为剪切贯通破坏、张拉贯通破坏及张–剪混合贯通破坏3类。通过岩石细观颗粒黏结力场、岩桥段应力及破裂贯通演化分析,揭示了重力作用下阶梯状滑移是从下而上岩桥逐个渐进性破裂贯通演化的过程,坡体后缘张裂纹发展贯通是下部坡体的牵拉作用造成;以缓倾角阶梯状平行裂隙边坡(岩桥倾角90°,裂隙倾角30°)为例,阶梯状滑移过程大致可分为坡体弹性稳定变形、下部岩桥贯通破坏、中上部岩桥贯通–后缘张裂、整体沿贯通面滑移共4个阶段,其中第3个阶段坡体微断裂数急剧增加,为滑裂带扩展至贯通的临界失稳状态。基于滑移模式及其演化过程的认识,建立了岩桥剪切贯通、张拉贯通和张–剪混合贯通三类阶梯状滑移边坡稳定性计算理论模型,推导了考虑岩桥强度和贯通率的边坡安全系数极限平衡计算公式。

Step-path failure is a kind of typical instability mode in rock slopes.Based on the summary of geological structural features of jointed rock slopes,the step-path failure mode and evolution process are studied by using the discrete element method,particle flow code in two dimensions(PFC2D).Three rock bridge failure modes in slopes can be summarized:tensile coalescence,shear coalescence and mixed tensile-shear coalescence.Through the evolution analysis of the rock mesoscopic particle bond force vector field,stress state of rock bridges and rock bridge failure,the progressive step-path failure process that rock bridge fractures one by one from the bottom up under the action of gravity is revealed,and the tensile crack development in the trailing edge of slope is due to the traction of lower part of slope.Take the slope with shallow dipping step-path parallel fissures for example(dip angle of rock bridge is 90°,and that of fissure is 30°),the step-path failure process can be distributed into four stages:elastic steady deformation of slope,failure of the lower rock bridges,failure of the upper rock bridges and development of tensile crack in the trailing edge of the slope,and the overall slipping of the slope along the failure surface.It is the critical state of instability at stage No.three that slip band sufficiently extends with micro-cracks expanding dramatically.Based on the understanding of failure modes and evolution process,three slope stability models for the step-path failure by shear coalescence,tensile coalescence and mixed tensile-shear coalescence of rock bridges are established,and the limit equilibrium formulae for the safety factor of slopes considering strength and coalescence coefficient of rock bridges are deduced.