| Due to the special coal and rock occurrence and mining method,the breaking motion of overburden rock and the resulting surrounding rock static stress distribution and dynamic disturbance characteristics are quite different from those of gently inclined coal seams.Rockbursts frequently occur in steeply inclined coal seams(SICS),posing severe challenges to safe mining.To guide the prevention and control of rock burst in SICS,systematic research on the mechanism and early warning of rockburst has theoretical and practical value.Therefore,the thesis uses laboratory tests,field monitoring,numerical simulation,theoretical analysis,and engineering practice to study the rockburst mechanism and early warning in SICS under fully mechanized caving and filling mining.The rockburst damage characteristics and inducement factors in SICS under fully mechanized caving and filling mining were studied.All the rockbursts occurred in the pre-mining working face B3+6,in which the rockburst damage appeared mainly in the mining roadway,located 0～209 m in the front of the fully mechanized caving face,and the damage range of a single rockburst was 75～418 m.The destuctional form of roof and floor roadway showed asymmetry and directionality,in which the roof roadway was dominated by roof side shoulder angle subsidence,side heave and roof subsidence,while the floor roadway was dominated by floor heave at the south side of rock pillar and roadway side heave.The damage of SICS is more serious than that of eastern typical horizontal and gently inclined coal seams under the same mining method.Microseismic events,sources of rockburst,and high wave velocity areas were located in the suspended roof and rock pillar near the working face where the coal body was compressedpried.Fully mechanized mining induced subsidence of the filling body,and the suspended roof and rock pillar of the surface showed the potential of pulling to the goaf.The compressive and pried stress acted on the coal body is the basic static load that induces the rockburst.The tectonic stress,the dynamic disturbance caused by subsidence of the filling body and rupture of the suspended roof and rock pillar have important inducing effects on the rockburst.The distribution law of static stress in the mining of SICS was studied.The stress field of surrounding rock of coal seams presents asymmetric distribution characteristics,the peak value of strike horizontal stress of B3+6 coal seam is 20.7 m ahead of the working face,and the inclination distance is 39.3 m from the top of fully mechanized caving face,both of which are larger than that of B1+2 coal seam.Fully mechanized mining induced the migration of the roof and rock pillars to the mined-out area,exerting greater pressure and prying effect on the coal,the horizontal and vertical displacements of roof are 10 and 3.5 times of rock pillar respectively,and the subsidence phenomenon of coal body on the roof side is more obvious than the side of rock pillar.Except for the stress concentration of B3+6 coal seam is negatively related to the filling material density,the stress concentration of the coal seams are positively correlated with the mining depth,the filling material density,the lateral pressure coefficient and the coal seam inclination.The structure of the suspended roof and rock pillar of the SICS is relatively intact compared with other inclined coal seams.The equation of seismic displacement field was established,the function of the synchrosqueezing transform was deduced,and the action law of the dynamic load inducing the rockburst in SICS was studied.The type of medium affects the propagation of the seismic wave,presenting isotropic attenuation in same strata.The surrounding rock of the roadway is stressed by the seismic wave and finally decompressed and destroyed.The damage caused by the S wave is significantly greater than that of the P wave.Affected by the location of the seismic source,the damage caused by rockburst is obviously directional from north to south,and the roadway damage is asymmetric.The dynamic disturbance caused by the rock mass rupture plays an important role in inducing the rockburst in SICS.The physical and mechanical model of the strike and dip of the suspended structure was established,and the elastic deformation energy distribution function of the model was deduced.The research reveals the mechanism of rockburst under the condition of caving and filling mining of SICS.The filling length and the reaction force of the filling body affect the stability of the basic roof and interlayer rock pillar strike rock beam composite support structure and the regional stress field of the working face.The energy of surrounding rock is affected by the dip angle of coal seam,lateral pressure coefficient,supporting force coefficient and length of suspended structure,the elastic energy of compressed and pried area is the largest,the roof and rock pillar in the area have the ability to break and produce dynamic load.The suspended roof and rock pillar structure are the main sources of static load and dynamic load.The rockburst process model is obtained,the mechanism of rockburst is as follows:suspended roof compression and breakage-induced rockburst mechanism,rock pillar prying and breakage-induced rockburst mechanism and rockburst induced by coupling of compressive and prying action.Early warning index system of rockburst suitable for SICS was studied and constructed,and a multi-index integrated early warning model was established.The application results show that each index has obvious response characteristics to rockburst risk,the precursory characteristics of the temporal and spatial warning indicators of the SICS is different from that of the horizontal and gently inclined coal seams.The multi-index integrated early warning method can timely warn the rockburst risk,solve the problem of independent warning results of each system,and improve the accuracy of early warning.The research results provide theoretical and technical support for safe mining of coal seams with similar occurrence conditions.The thesis contains 125 figures,15 tables and 282 references. |
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