韧性剪切带和蚀变岩体对边坡开挖稳定性的影响

Influence of ductile shear zone and altered rock mass on excavation stability of slope

野外现场地质调查结果显示,拟建的澜沧江班达水电站河谷右岸发育有数条倾向坡内的韧性剪切带和蚀变带,这使坝址区的地质条件更加复杂化。为探究水电站建设开挖过程中剪切带和蚀变带对边坡稳定性的影响,选取中坝址右岸边坡为研究对象,根据野外调查所得资料建立三维地质模型,并模拟边坡由三级开挖而导致的应力场变化过程和变形破坏过程。结果表明:韧性剪切带和蚀变带内的应力表现为应力松弛,而剪切带和蚀变带与周围正常岩体接触部位表现为应力集中;由开挖产生的应力释放主要在向坡内水平深度150 m范围内;天然状态下边坡稳定性较好,但二级开挖后,坡表最小主应力由压应力转为拉应力,且使塑性变形区贯通,坡体易从高高程的韧性剪切带和蚀变带出露部位剪出而整体失稳。

According to the field geological survey, there are several steep ductile shear zones and alteration zones that stretch into the right bank slopes of the river valley of Banda Hydropower Station on the Lancang River, which makes the geological conditions of the dam site more complicated. In order to study the influence of shear zone and alteration zone on slope stability during the construction and excavation of hydropower station, the right bank slope of the middle dam site is selected as the research object, and the 3 D geological model is established according to the data obtained from field investigation. The variation process of stress field and slope deformation and failure caused by three-stage excavation are simulated. The results show that: the stress in the ductile shear zone and the altered zone is released, while the stress in the contact part between the two zones and the surrounding rock mass is concentrated. The stress release caused by excavation is mainly within the horizontal depth of 150 m in the slope. The slope is stable in natural condition, but after the second stage excavation, the minimum principal stress of slope surface changes from compressive stress to tensile stress, making the plastic deformation zone penetrate. The slope body is likely to slip out from the outcrop parts of ductile shear zone and alteration zone at high elevation.