Rock burst risk evaluation based on dynamic-static stress analysis in complex working face

In order to quantitatively evaluate the rockburst impact hazard level and the division of hazard area before the mining of complex working face,and based on the dynamic and static superposition principle of rockburst,the complex condition working face of Jining No.3 Coal Mine is taken as the engineering background,a rockburst assessment method based on dynamic and static stress analysis was proposed in this paper.Laboratory tests have shown that the critical stress of dynamic failure of coal was closely related to the uniaxial compressive strength.According to the uniaxial compressive strength of coal,the critical impact stress of Jining No.3 Coal Mine was determined to be 70MPa.The FLAC numerical software was used to study the distribution law of the original rock stress and the mining support pressure,and the static load stress distribution curve was obtained.The stress evolution law of the working face during the fault crossing was discussed.According to the distance of the fault from the working face,the influence of the supporting pressure near the fault under the mining activity was divided into 4 grades,that is,the plastic deformation zone (less than 10 m),the impact elastic zone(10～20 m),the stress superposition zone(20 to 50 m),and the original stress zone(more than 50 m).Based on theoretical analysis,the energy release law of hard roof breaking was calculated.When the breakage step distance of the main roof reaches 50 m,the release of energy canreach 105 J and the corresponding dynamic load stress is 10 MPa.Based on the static and dynamic stress level,the rockburst hazard eval-uation criteria are given and the impact risk is divided into 4 levels.No impact risk when the maximum superimposed stress of dynamic and static load is less than 50 MPa,weak impact risk at 50 MPa to 70 MPa ,medium impact risk at 70 MPa to 105 MPa ,and strong impact hazard when the stress is more than 105 MPa.The impact risk of the 123 working face was evaluated and divided,which was consistent with the results of the on-site microseismic monitoring and this provides support for the safe mining of the working face.