Research on Temperal-spatial Characteristics of Microseismic Activity in Hard Rock Tunnel at Baihetan Hydropower Station

摘要

The underground cavern group of Baihetan hydropower station is characteristic with complex geological condition, large buried depth and high stress, the local failures of surrounding rock mass which often occurred frequently during the construction process. To study the mechanisms of failures result from the unloading effect of excavation, in situ microseismic monitoring system was established on the No.1 construction branch tunnel of spillway tunnel located on the left bank of Baihetan Hydropower Station, the relation between microseismic activity, geological condition and failures of surrounding rock is studied. The results show that: 1) the region with abundant underground water was hard to gather stress and energy quickly in short time. 2) a low excavation rate weakened the risk of the failure of the surrounding rock of hard rock tunnel because of the unload effect of excavation. 3) the microseismic events were more active on north side of the tunnel and assembled on the north spandrel with opening structure plane.4) the risk of rockburst in the microseismic monitoring tunnel during the excavation is low. The research results provide reference for the optimization of the excavation and support and are meaningful for reducing the risk of the rock failures during the excavation.