Research On Rockburst Mechanism Induced By Fault Slip During Coal Mining Operation

The fault rockburst is a serious natural disaster in coal mine operation. At present, many fault rockburst have been recorded in practice. However, the studies of theory and experiment were deficient. Aiming at the insufficiencies, the research methods of similar material simulation experiment in laboratory, FLAC5.02D numerical simulation, theory analysis and engineering research have been carried out in this dissertation. The rules of risk of fault rockburst were researched during coal mining operation. A mechanics model is established of fault slip induced rockburst, and the criterion was discovered. The evolvement rules of micro-seismic(MS) signals were analyzed when working face advancing to the fault. The practices of prevention and cure about fault rockburst have been carried out in-situ, and optimized the parametes of relieving shot in roof.The effect of coal mining operation on fault rockburst is studied by using similar material simulation and FLAC5.02D numerical simulation. The results indicate that when the working face advances from the footwall to the fault itself, the slip displacement increases due to the decrease of normal stress and the increase of shear stress, the fault begins to activate, roof rock-mass is broken and with poor stability, the abutment pressure ahead of working face obviously increases. The underground pressure is low when the working face has passed the fault. However, when the working face advances from the hanging wall to the fault itself, it is difficult for the fault to activate due to the increase of normal stress, the roof rock-mass is ease to become balance structure. The slip displacement increases due to the decrease of normal stress and the increase of shear stress after the fault have passed the fault, the stability of roof becomes weak and the abutment pressure increases. The different MS such as coal mining operation, roof collapse, fault activation, are different frequency spectra.The FLAC5.02D software is used to study the effect of fault and roof on abutment pressure. The results indicate that the effect of roof strength on abutment pressure is obvious when the working face advances from the footwall to the fault itself, and the effect of fault dip angle on abutment pressure is obvious when the working face advances from the footwall to the fault itself. The risk of a fault rockburst is higher when the working face advances from the footwall to the fault itself than when the face advances from the hanging wall to the fault.The voussior beam theory was used to explain the effects of faults with different dip direction on roof balance structure and underground pressure. A mechanics model of Strike-Slip and Viscous-Elastic-Brittle is established in order to study the mechanism of fault slip induced rockburst. According to damage mechanism, the fault slip induced rockburst can be analyzed by the following two mechanics criterion. The first mechanism is fault slip dynamically induce rockburst when the fault with a high slip velocity, such as fault slip destabilization. The second mechanism is fault slip statically induce rockburst when the fault with a low slip velocity. In the first kind, more energy is violently released comparability. The velocity of fault slip is related to the velocity of working face advancing, the distance from working face to the fault, strength property of fault, normal stress of fault plane and the mining depth.A zoning monitoring method is applied to study the evolvement rules of MS signals when the working face advancing to the fault based on the Seismological Observation System. The results indicate that the fault begins to activate when the working face approach to the fault, MS signals is activity with the increase of total energy, maximum energy and frequency. The MS signals reach peak value when working face in fault zone. The MS signals quickly decrease when the working face far away from the fault.The researches of prevention and cure about fault rockburst have been carried out in the No.6303 working face of the Jining No.3 Coal Mine. The forecasting technique of mine geological structure was applied to forecast the fault. The strength of coal and rock mass can be weakened in risk range by using some active measures of rockburst such as unload with borehole, relieving shot in coal seam, relieving shot in roof. So, the danger of fault rockburst can be avoided or reduced.