频发微震下上覆软弱岩体边坡动力稳定及失稳模式

水库蓄水诱发的高频次微小地震对库岸边坡稳定性存在一定影响。采用振动台物理模型试验,结合UDEC离散元分析方法,以三峡库区杉树槽滑坡为原型,研究了频发微震作用下典型上覆软弱岩体边坡的累计损伤过程、动力响应特征及破坏模式。结果表明：在频发微震作用下,模型边坡自振频率不断降低,阻尼比不断升高,完整性降低;坡体加速度响应在初始阶段和微震阶段体现出“高程效应”和“趋表效应”,而在小震加载后,坡体动力响应与上述特征出现偏离;在反复微震下,坡体的破坏演化过程可概括为“次级节理发育→次级节理扩展→上部岩体破碎→后缘裂隙扩张→滑面贯通→边坡失稳破坏”阶段;离散元数值分析结果表明,上覆软弱岩体边坡在频发微震下的变形主要发生于岩层分界面以上,后缘裂隙以下的上部岩体,随着地震次数的增加,其永久位移不断增大,边坡稳定性系数不断降低,边坡破坏特征与振动台试验结果相吻合。

Dynamic stability and failure mode of slopes with overlying weak rock mass under frequent micro-seismic actions

The micro earthquakes with high frequency induced by reservoir filling may exert an influence on the stability of bank slopes. Based on Shanshucao landslide in the Three Gorge Reservoir area,the shaking table tests and the discrete element method (UDEC) are used to analyze the dynamic response, cumulative damage process and failure modes of a typical slope with overlying weak rock mass under frequent micro-seismic actions. The results are as follows: under the actions of frequent micro-seism, the natural frequency of vibration of the model slope reduced gradually, whereas its damping ratio continues to raise, which shows the decrease of rock integrity. During the initial stage and the micro-seismic action stage, the acceleration response of the slope is characterized by“elevation effect”and“aspect effect”, while the results begin to deviate as the small seism is louded. The failure evolution process of the model slope can be summarized as “development of the secondary joints→extension of the secondary joints→breaking of the upper rock mass→expansion of the rear crack→formation of the slip plane→failure of the slope”. The discrete element numerical results show that the deformation of the slope with overlying weak rock mass under frequent micro-seismic actions mainly occurs in the upper rock mass, which is above the rock interface and below the rear crack. With the increasing number of earthquakes, the permanent deformation of the slope continues to enlarge, and its stability coefficient decreases simultaneously, which is accordant with the results of the shaking table tests.