考虑岩体开挖卸荷动态变化水电站坝肩高边坡三维稳定性分析

金沙江一双曲拱坝最大坝高277 m,左岸坝肩开挖边坡高约300 m;右岸坝肩开挖边坡高约480 m,由于坝肩槽开挖所形成的边坡属于高陡边坡,其开挖后的稳定状况会极大影响大坝的正常运行。通过对坝址区地质资料的详细分析,建立坝肩边坡三维计算模型,并结合卸荷岩体力学理论,通过弹塑性有限元法研究坝肩边坡在开挖过程中的动态稳定性。研究结果表明：该高边坡在开挖过程中及开挖后,除开挖面附近局部区域不稳定外,整体并无失稳趋向;考虑岩体在开挖过程中的动态卸荷过程后,边坡岩体的位移和塑性区面积比不考虑时有所减小;岩体的破坏区随着开挖的进行不断变化,可根据每步开挖后岩体的破坏情况选择合理的加固措施及加固时间。

THREE-DIMENSIONAL STABILITY ANALYSIS OF DAM ABUTMENT HIGH SLOPE DYNAMIC BEHAVIORS CONSIDERING ROCK MASS UNLOADING

A double-curved arch dam is located in Jinshajiang River with a maximum height of 277 m.The excavation height of the left dam abutment is about 300 m,and the right is about 480 m.Because the excavated slopes are high and steep the stability of the slopes has great influence on dam operation and safety.After a detailed analysis of dam site geological data,the 3D elastoplastic finite element model of dam abutment slope is established.And according to the unloading rock mass mechanics theoryt,he degree and areas of unloading can be gained by contrasting the initial stress field with the field after excavation.Then the degree of rock mass quality deterioration after excavation can also be achieved.With the progress of excavation,the areas and degree of unloading change constantly.Thus in order to study the dynamic stability of the high slopes,the rock mass mechanical parameters are adjusted continually according to the changing areas and degree of unloading after each excavation step.The results show that except partial regions near excavation surface,the abutment slopes are stable during and after excavation processes.After taking the effects of dynamic unloading into consideration,the displacement and plastic zones of slope rock mass after excavation decrease;and the rock mass failure regions change with the course of excavation.According to the distribution of unloading regions and plastic zones after each excavation step,the optimized reinforcing measures can be reasonably selected.