Studies On Preparation Causes Of Rockburst In Deep Tunnel Based On Microseismic Information

With the increasing demands in mineral resources, hydroelectric energy and transportation to adjust the rapid development of economic construction, the exploration of underground space needs continuously develops to the deeper. Consequently, the issue of rockburst under high stress environment induced by excavation unloading is becoming increasingly prominent. As a special engineering geological hazard, rockburst has became one of the cosmopolitan problems in underground engineering due to it not only destroys the project and influences the construction schedule but also damages equipments and threats physical security. Therefore, the research on causes of rockburst and taking some corresponding prevention measures to reduce and avoid the hazards of rockburst has becomes a key research topic from poles to poles which needs to be solved urgently with vital theoretical and practical significance in the safety construction of mineral, hydropower, transport and other deep underground engineerings.Based on the engineering background of severe rockburst proneness section in deep-buried tunnel of Jinping ? Hydropower Station and by the method of micro-seismic monitoring technique, this dissertation studies the spatial and temporal distribution and correlation of micro-seismic activity and rockburst in deep-buried tunnels. And then corresponding prevention measures are proposed after the in-depth analysis of the evolution process and causes of immediate rockburst and time delayed rockburst. In summary, specific studies are as follows:(1) The spatial and temporal distribution and correlation of both micro-seismic activity and rockburst in deep-buried tunnels were analyzed systematically. In terms of time domain, the correlation, under the excavation of drilling and blasting method and TBM respectively, among the micro-seismic events, rockburst and excavation, were explored; the evolution laws of micro-seismicity (cumulative apparent volume, energy index, Schmidt number and frequency of micro-seismic events) with time in the development process of rockburst were elaborated, which well revealed the temporal evolution of predictive signs of rockburst. When it comes to space, the distribution laws of both micro-seismicity and rockburst along along the tunnel during the excavation were studied, in which the spatial relationship among micro-seismicity, rockburst and excavation activities were discussed as well; the mechanism of rockburst development process was illustrated during deeply analyzing the law of spatial evolution of micro-seismicity information in the rockburst development process; after detecting significant characteristics of spatial aggregated distribution by analyzing the spatial distribution law and relationship of both the micro-seismic events and rockburst from the perspective of wide range throughout the project area, dominant factors which control the spatial aggregated distribution emphatically were focused to discussed.(2) The study of the evolution causes of immediate rockburst was conducted on both the factors of excavation and geological structure plane. Influences of the rate of excavation and blot supporting on microseismic activities during the development process of immediate rockburst were deeply analyzed respectively. The verdict that it was reasonable to use drilling and blasting method for deep-buried tunnel with severe rockburst proneness, was formed by analyzing the characteristics of micro-seismicity and the risks of rockburst on the condition of different excavation methods by the way of comparison. The control actions of geological structure plane on macro-failure morphology, spatial distribution, strength, frequency and evolution law of immediate rockburst were focused to researched. Simultaneous, the conclusion that the mechanism of rockburst development process would become more and more complex with the increasing number of noodles and groups of geological structure plane was summarized by investigating the effects of geological structure plane on immediate rockburst.(3) The dissertation systematically analyzes the temporal-spatial evolution characteristics of micro-seismicity in that rockburst development process. According to the significantly vital control role of blasting disturbance, resulting from the discussion of evolution causes of such rockburst, the mechanism of that sort of rockburst induced by blasting disturbance was deeply illustrated. In the process, the law of time delayed rockburst occurred in the blasting disturbance was the main focus. Meanwhile, this paper indicated that rupture form of rock was transformed to a certain extent under dynamic loading, which was summarized during the procedure of analyzing the influence of blasting disturbance on evolution mechanism of time delayed rockburst.(4) New method, utilizing information of micro-seismicity from the process of upper bench excavation in deep-buried tunnel to identify the scope of high rockburst risk, was presented. And the evolution causes and mechanism of both immediate rockburst and time delayed rockburst in the process of suffering secondary excavation were focused to researched and discussed.(5) Based on those studies above, the general idea of preventing and curing both immediate and time delayed rockburst during construction phases was established, and the corresponding countermeasures of prophylaxis and treatment were raised according to different levels of such two types of rockburst.