Analysis Of Evolution Process And Seismic Early Warning Of Rockburst Induced By Excavation Unloading In Deep-Buried Tunnel

The deep-buried rock tunnel projects commonly encounter sudden and devastating rock burst disasters. According to incomplete statistics, only the deep tunnel projects of Jinping Ⅱ hydropower station occurred thousands of varying degrees rock bursts. Facing a large amount of microseismic monitoring data, as it is difficult to find the internal relation and evolution rule about microseismic and rock burst evolution process, there is no very successful case about rock burst prediction in China so far. So it is very essential to carry out rock burst prediction process and microseismic warning under the high in-situ stresses conditions of deep-buried tunnels. Based on rock damage mechanics theory, this paper reveals the excavation unloading rock burst evolution process by means of numerical simulation analysis and microseismic monitoring. Based on microseismic monitoring data analysis to explore the rock burst precursor law, and it has laid the theory and technology foundation for rock burst early warning, prevention and control.The various unloading stress paths and numerical models under rock medium conditions are established, and the numerical simulation of rock burst evolution process data simulation research is carried out. The main contents include:(1) use the sample uniaxial compression rupture process to simulate the pillar burst that occurs in the rock pillar between the adjacent tunnels or under the condition of the excavation in opposite directions of a same tunnel; (2) use the samples multiaxial-instantaneous unloading rupture process to simulate the rock burst that occurs due to the sudden unloading generated by the excavation under high in-situ stresses, and reveal the mechanism of rock burst induced by excavation unloading; (3) By the numerical simulation about rock burst of one step and multistep excavation in rock tunnels, and it shows that the energy and frequency released by microseismic events are closely related to construction methods, and the microseismic events develop from disorder to concentrate development and appears basic regulations of self-organization.In the mechanical mechanism, it is thought that the rock heterogeneity is the root of the existence of the rock burst precursor; the deformation localization is the internal cause of rock burst; while the interaction between the rock and the surrounding environment is the external cause. On this basis, the arrangement forms of the sensors and data collection working ways were proposed according to different geological and excavation conditions in Jinping II hydropower station. Based on the site monitoring data analysis of the drainage tunnel, quantify multi-factors of microseismic events, event location, event energy, energy release rate and event density contours, combine with the numerical simulation of the excavation process, develop the evolution process and rock burst early warning, and the reveal the early warning mechanism of pole-strength and strong rock burst. These research results set the theory foundation for rock burst disaster early warning, prevention and control, and provide the technical support for guiding the safe construction. Based on the analysis of the monitoring data in 1# water tunnel, it reveals that the construction plan of first pilot tunnel and then TBM bottom can reduce or control the rock burst. Through the 3D numerical simulation and the microseismic monitoring data analysis, the occurrence site of rock burst was severely affected by the adjacent tunnel under the circumstances of multiple adjacent working faces advancing at the same time in 3# and 4# water tunnels.