Research Of Mechanism And Controlling Technology Of Floor Burst In Coal Seam Roadway

Floor burst is one kind of the rock bursts, and it often seriously happens during the coal seam excavation and roadway driving in some coal mines. As the special burst position and no prevention measures are used, floor bursts have caused seriously damages. According to lots of research data and excavation and mining conditions of Yuejin Coal Mine, theory analysis, numerical simulation, similar simulation and industry practice are used to research the influence factors, the stress and physical and mechanical parameters preparatory process of floor burst during excavation, floor burst appearing laws under dynamic loads, floor burst hazard discriminatory, intensity weakening measures and support structures. The research results are applied to burst control practice in order to verify correctness of the theory.Through numerical simulation and similar simulation methods, the influence factors and preparatory process are researched. The results show that the conditions have great influence on floor burst, such as mining depth, roof condition and roadway drifting and layout ways.On the influence of the heave hard roof, the mining of working face will increase the stress of adjacent coal seam of working face. In high coal seam, roadway is cut along roof of the coal seam, so the floor is coal seam. After roadway is cut, there are areas of vertical stress rising and horizontal stress reducing in the floor, and this raises the burst hazard of floor failure. During the roadway is cutting, the plastic zone of floor is bigger than the two sides, and tensile failure zone distributes in the floor obviously, and this is the sally port of floor burst.Fourier transform is used to analyze the frequency spectrum characters of microseismic signals of rock bursts induced by dynamic disturbance , the results show that dynamic disturbance is necessary condition for rock bursts. The dynamic module of FLAC2D soft is used to analyze the rock burst appearing laws under dynamic loads. The results show that the stress and physical mechanical parameters have changed greatly under dynamic loads. In the dynamic loads process, horizontal stress ,vertical stress and stress difference increase in a small extent and decrease substantially, and the floor velocity and accelerate change rapidly soon after. At the same time, the plastic zone expands, and tensile failure zone appears obviously in the floor with the vertical displacement increases subsequently. After the process, horizontal concentrated stress disappears, and this is the floor burst process under dynamic loads.According to the theory analysis and characteristics of floor burst, a mechanical model is set up, and the dangerous coefficient of floor burst is also initially given. The research results show that the depth, the elastic modulus of rock, the thickness of soft rock in the floor, the horizontal tectonic stress, and the heave hard roof are seriously relevant to the floor burst. The dangerous coefficient of floor burst Kfb is also initially given to evaluate the floor burst hazard .As the dangerous coefficient of floor burst is more than or equal to 1, the floor failure will happen. Based on the critical thickness of floor failure and floor bursts data of Yuejin Coal Mine, floor burst hazard is classified into three categories: no floor burst dangerous, weak floor burst dangerous and strong floor burst dangerous.According to numerical simulation, the two sides intensity weakening can indirectly decrease the horizontal stress of floor. In practical application, the two sides blasting can weaken floor burst dangerous indirectly, and can induce floor burst directly. Based on the numerical simulation results and field application, the floor intensity weakening can remove the horizontal concentrated stress, and it is an effective method to weaken the floor burst dangerous.In order to solve the support technique of floor burst of coal seam roadway, theoretical analysis and numerical simulation is used to research the control function of closed compressible supporting structure made up of anchor net and"O"type shed on floor burst. The research results show that closed flexible supporting structure can not remove shock hazard entirely, however, it can reduce the rock burst extent. The results provide theoretical foundation for roadway support in the same coal mine conditions.According to the research results, the appropriate measures for floor burst prevention are applied in the lower gateway of 25110 coal face and 23130 coal face in Yuejin Coal Mine, and has gained good effect, and this proves the theory of mechanism and controlling technology of floor burst in coal seam roadway is correct.