黄土细沟流跌坑的形成与作用机理

Stability Analysis on Surrounding Rock Mass in Underground Caverns Based on Discrete Element Simulation and Microseismic Monitoring

跌坑是细沟侵蚀过程中形成的一种床面形态,其是床面形态和水流流动相互作用的结果。借鉴下切型阶梯-深潭理论采用6种坡度（2°、4°、6°、8°、10°、12°）,5种流量（8、16、24、32、40L/min）完全组合冲刷试验,系统研究了黄土坡面细沟流跌坑形态发育过程及动力特性。结果表明：跌坑平均深度随坡度的增加而增加,跌坑平均间距与跌坑平均深度的比值随坡度的增加而减小,表明跌坑随坡度的增加发育越加成熟,且流量对两者影响均较少;跌坑发育系数随坡度的增加而增大,其值介于1.01和1.14之间,与细沟阻力系数呈正势变化,表明随着跌坑发育越显著,水流阻力越大,能量耗散越剧烈。相同坡度下,跌坑消能率随流量的增加呈线性减小趋势;而消能率随坡度和跌坑发育系数的增加呈幂函数增加关系,消能率范围在87.28%~98.58%之间,研究结果表明跌坑的发育及作用机制对细沟流流动特性及侵蚀产沙具有重要作用。

Aiming at the stability problems of the surrounding rock mass in the underground caverns at the Houziyan hydropower station subject to excation, based on the discrete element theory, the numerical simulation of excavation of the underground powerhouse caverns was performed using PFC2D software. The influences of the controlling structural planes on surrounding rock mass deformation and failure were simulated, and the damage evolution law was reproduced. Moreover, a high-resolution microseismic monitoring system was adopted to real-time monitor and analyze the microseismic activity in deep underground caverns. Then the results of numerical simulation were compared with microseismic monitoring. The results showed that excavation damage zone of surrounding rock mass was closely related to faults, and the surrounding rock mass damaged regions obtained from numerical simulation was in good agreement with those revealed by microseismic monitoring. Therefore the approach of combining numerical simulation and microseismic monitoring was proven to be very promising for evaluating the excavation damage zones and predicting the potential instability of surrounding rock mass in the underground caverns subjected to excavation.