Stress-Seismicity Evolution Law And Rock Burst Control Of Thick And Hard Roof Working Face

More than half of the coal mines in China have hard roofs above the coal seams.Most of the hard roofs have the characteristics of thick and hard,with large collapse steps.Their first or square fracture is likely to strongly disturb the coal body enduring high stress and induce rock burst accidents.The five rock burst accidents in recent years show the commonality of"large mining depth and thick hard roof".Affected by the factors such as kilometer mining depth and thick and hard roof,the 23 mining district of Zhangshuanglou coal mine has a high probability of inducing rock burst.In order to achieve scientific and effective prevention and control of rock burst in the thick and hard roof working face in this mine,this thesis takes 23908 working face as the engineering background,adopting theoretical analysis,numerical simulation,field monitoring and engineering practice and other research methods to work out the results about the influencing factors of the rock burst hazard in the working face of thick hard roof,the first fracture distance and fracture mode of thick hard roof,the stress evolution law of surrounding rock during mining,the spatiotemporal intensity evolution law of seismicity,as well as the monitoring and prevention technology of rock burst in the working face.The research results are as follows:（1）The main influencing factors of rock burst in 23908 working face include buried depth of coal seam,thick and hard roof,fault structure and abutment pressure of adjacent goaf.The main inducing factors are high original rock stress and the strong dynamic load generated by the fracture of thick hard roof.（2）The mechanical model of deep beam of thick roof is established,and the thick and hard main roof fine sandstone is determined to be the inferior key strata by combining with the key stratum theory.Based on the characteristics and physical and mechanical parameters of overlying strata in 23908 working face,it is calculated that the first fracture distance of the whole thick and hard main roof fine sandstone is161.5m,and the fracture mode is tensile fracture.The whole and stratified fracture characteristics of thick roof are discussed.It is concluded that the fracture modes of thick roof with weak intercalary strata can be divided into stratified uncoordinated movement and stratified linkage movement.（3）Through numerical simulation using FLAC^3D software,it is found that the stress concentration area of the 23908 working face is located in the coal body in front of the working face,the coal body along the goaf side,and the remaining coal body in the staggered area outside the stop mining line;When the working face is in the square period,the static load of the surrounding rock is significantly higher than those in the non-square period,simultaneously combine the dynamic load generated by the roof square fracture,resulting in the highest rock burst risk.（4）The results of field microseismic monitoring show that the seismicity concentration area is consistent with the high stress area of numerical simulation.When mining reaches the first square period,the microseismic events show the"S"structure of plane and"F"structure of dip direction,causing frequent microseismicity along the goaf side.The microseismic energy and frequency of the working face are reduced by30.9%,24.5%and 49.4%,15.6%after first square and second square period respectively,and the linear increase of microseismic energy and frequency before goaf square and the period of"lack of seismicity"can be regarded as the precursor of the rock burst hazard.（5）The joint monitoring program of"stress field-vibration field"of rock burst hazard has been designed,and the roof management program of deep hole blasting,directional hydraulic fracturing and ultra-deep hole segmental fracturing was formulated.The significant effect of rock burst prevention and control has been verified through borehole peeping,fracturing monitoring holes,and microseismic activity.The research results of this thesis have a guiding effect on the rock burst hazard monitoring and prevention of thick hard roof working faces in Zhangshuanglou coal mine,which can provide a scientific basis for the rock burst hazard monitoring and prevention,roof management and mining layout design of successive working faces,and help the safe recovery of the rock burst hazard working face in the mine,and can provide a reference for the rock burst hazard monitoring and prevention of similar working faces.This thesis has 76 figures,17 tables and 130 references.