某水电站韧性剪切带的发育特征及边坡开挖变形响应研究

Study on the Development Characteristics of Ductile Shear Zone and Deformation Response of Slope Excavation in a Hydropower Station

拟建的澜沧江某水电站右岸岩质高边坡开挖近400 m,根据现场地质调查,边坡岩体为硬脆性的英安岩,卸荷强烈,且边坡内中小型断层发育。此外,右岸边坡还发育有2条陡倾坡内的韧性剪切带,剪切带内产生了糜棱化,这导致了右岸边坡的地质条件和岩体结构都非常复杂。为了探究此条件下岩质高边坡的开挖变形响应机制及规律,选取水电站右岸坝轴线边坡为研究对象,通过离散元程序UDEC来模拟边坡的开挖过程。研究结果表明:开挖导致韧性剪切带浅表层岩体产生较大变形,影响边坡稳定性;开挖引起的变形主要受倾坡外的卸荷裂隙及溢流面的控制,其地质-力学变形破坏模式以“滑移-拉裂”为主;边坡开挖后主要产生横向位移,其累计位移模式为向高高程传递、在后缘累积;边坡开挖与产生的变形能基本保持同步,最终受岩体弹性恢复滞后的影响,在接近开挖结束时剩余变形较小。

The high rock slope on the right bank of a hydropower station on Lancang river,which is to be built,is excavated for nearly 400 m.According to the on-site geological survey,the rock mass of the slope is hard and brittle dacite with strong unloading,and small and medium-sized faults developed in the slope.In addition,there are two ductile shear zones that dipping toward to the inside slope in the right bank slope,and mylonization occurs in the shear zone,which leads to the very complex geological conditions and rock mass structure of the right bank slope.In order to study the mechanism and rule of deformation response of high rock slope excavation under this condition,this paper selects the right-bank dam axis slope of hydropower station as the research object,and simulates the excavation process of the slope by the UDEC(universal distinct element code).The results show that:(1)The excavation results in large deformation of the shallow rock mass in the ductile shear zone,which affects the stability of the slope;(2)The deformation caused by excavation is mainly controlled by the unloading fissure and overflow surface that dipping toward to the outside slope,and the geological-mechanical deformation and failure mode is mainly slipping and fracturing;(3)The slope mainly occurs lateral displacement after excavation,and its cumulative displacement mode is transmission to high elevation and accumulation at the trailing edge;(4)The slope excavation and the resulting deformation energy are kept in sync,and finally affected by the elastic recovery lag of rock mass,and the residual deformation is small near the end of excavation.