Study On The Mechanism And Microseismic Monitoring For Rockburst In Deep Tunnels

Rock burst, the failure phenomenon of brittle rock under high-stress, such as rock fragmentation, ejection and even earthquake, is caused by the sudden release of elastic deformation energy from excavation. The mechanism of the burst is relatively complex, and the study on it remains hypothesis and in a stage of experience. As a dynamic instability induced by multi-factor coupling, the formation mechanism of rock burst is complex and correlation theory is imperfect, so the practical application effect of rock burst predictive theory is non-ideal, and since now there is no mature theory and method.In recent years, an increasing number of rock burst issues stand out, rock burst not only destruct the production facilities and delay construction deadline, but also seriously threaten the workers'personal safe, which has become a major technical barrier in construction of deep underground in the future. Micro-seismic, as an effective way of monitoring three-dimensional rock mass fracture orientation and intensity, has developed rapidly. Micro-seismic monitoring technology is able to fix the time, location and magnitude of the focus(also called the three elements of space time and strength) through acoustic wave analysis, micro-seismic monitoring system with high sensitivity can obtain even precursor of rock fracture with smaller magnitude, so as to provide the possibility of rock burst prediction.Supported by the National Natural Foundation of China (2007CB209404) and National Natural Science Foundation of International Cooperation Project (50820125405), with the monitoring and early warning of rock burst in deep drainage tunnel construction of Jinping-2 hydroelectric power station, a new real-time micro-seismic monitoring system is established. Through the data analysis and conclusion of micro-seismic monitoring of rock burst, and numerical simulation with software RFPA, the influence of advanced tunnel to rock burst is studied. The rock burst size and number of the monitoring results and field research statistics is compared, the possibility of micro-seismic monitoring and forecasting of rock burst is explored, which provides some reference frame for the field construction organization.Through the analysis and conclusion of micro-seismic monitoring data, the conclusions are as following:1. Micro-seismic data monitored in the process of tunnel construction indicates that there are microfracture precursors in rock burst:the micro-seismic instruments is able to monitor rock burst damage of some tens of meters or even hectometers, and then the strong rock burst region can be fixed. In terms of time, the precursors appeared before rock burst, ranging from a few hours to a few days, depending largely upon the tunneling.2. The changing situation of amount and energy distribution in the process of TBM excavation is analyzed, rock burst judgments and early warning of the changing stress of rock mass before and after the tunnel face is carried out.3. Excavation of advanced tunnel caused excavation stress concentration at both ends of the hole, which effectively avoid the occurrence of intense rock burst in high stress tunnel section.