Controlled Reconstruction And Application Of Lateral Overburden Structure Of Fully Mechanized Caving Face With Large Burial Depth

The high-intensity mining of large-buried and deep coal seams has a wide range of disturbances,and the structure of the overburden has a significant impact on the stress environment of the surrounding rock of the roadway.Under certain conditions,the mining roadway has severe mining pressure,high gas concentration in the corners,and increased safety hazards,which bring serious challenges to the safe and efficient mining of mines.Therefore,the influence mechanism of overburden structure evolution on stress transfer in large-scale mining space is systematically studied.Through the controlled transformation of the lateral overlying rock structure of the stope,roof cutting and pressure relief reduce the stress of the surrounding rock of the roadway,and the caving block compaction and sealing control the gas concentration in the corner.It has important theoretical and practical significance to ensure the control of surrounding rock and gas control of roadways in large buried deep coal seam mines.Based on the fully mechanized caving mining conditions of Wangpo coal mine with large burial depth,high gas and thick seam,this thesis focuses on the controlled transformation and application of the lateral overburden structure of the fully mechanized caving face in Wangpo mine.Systematic research is carried out from the aspects of overburden stress transfer and control mechanism,stope stress evolution and gas migration law,controlled transformation of overburden structure and key application technologies.The main results are as follows:(1)The macroscopic characteristics of the Wangpo coal body with hard,welldeveloped fissures,thick roof,high strength and strong integrity were clarified.The stress-strain characteristics of coal and rock mass under different stress environments and stress paths were mastered,and the positive correlation between confining pressure and elastic modulus,and the negative correlation between Poisson’s ratio and Poisson’s ratio were quantitatively characterized.A constitutive model of linear strain softening of rock mass and nonlinear strain softening of coal mass under triaxial stress environment was established,and the secondary development of numerical simulation of the two types of constitutive models was carried out.The fitting formula of the minimum principal stress transfer path of coal and rock mass under three-dimensional stress state was obtained.(2)Revealed the evolution process of the lateral overburden structure of Wangpo Mine with large burial and deep roof fully mechanized caving mining,"basic top long cantilever beam in the initial stage-masonry beam with upper hard rock layer in the middle stage-double long cantilever roof with overburden compaction in the later stage".The evolution model of lateral support stress in stope was established,and the influence law of coal strength,buried depth and roof space shape on lateral stress distribution was clarified.The transfer path of the load from the upper hard rock stratum to the adjacent coal and rock mass in the later stage of mining was mastered,and the mechanical mechanism of the multi-purpose roadway adjacent to the large coal pillar in the high stress environment was clarified.(3)Revealed the stress transfer effect of the lateral overlying rock “large angle,high-level” topping on the “low-level unloading,high-level transfer” of the double-long cantilever structure.The gas driving and sealing effect of "caving driving,compacting and sealing" of rock blocks at the end of high gas environment.The stress transfer effect of different roof cutting parameters was clarified.After roof cutting,the minimum principal stress peak value of the coal seam roof was transferred from the multi-purpose roadway to the depth of the coal body,and the maximum stress peak value can be reduced by 25.01%;The "stress-fracture-permeability" model of coal and rock mass was established,and the distribution of stress and permeability in the stope and gas migration law before and after top cutting were mastered.After top-cutting,the gas plugging effect was obvious,and the gas concentration in the corner was reduced by42.28%.The controlled reconstruction scheme and parameters of the lateral overburden structure of the stope were determined.(4)Developed and implemented the controlled transformation technology of lateral overburden structure for directional hydraulic fracturing with small-aperture pregrooving on the roof.The surrounding rock control mechanics model of "three zones and two circles" of rectangular mining roadway was established.Established the control strategy of "high-strength support to effectively control the inelastic zone,multi-layer reinforcement of broken surrounding rock with composite grout" after the reconstruction of the multi-purpose roadway surrounding rock after pressure relief.Aiming at the characteristics of instantaneous increase in the periodic driving of corner gas,a key technology of corner gas dynamic regulation and enhanced drainage was proposed.Jointly constructed and formed a key technology process system for the controlled transformation and application of the lateral overburden structure of the fully mechanized caving face with large burial depth.The above research results have been applied in engineering in the 3312 transport roadway of Wangpo Coal Mine.The results showed that the stress of surrounding rock near the multi-purpose roadway was reduced by 25.6%,the strength was increased by10.9%-34.43%,the maximum deformation was reduced by about 80%,and the gas concentration in the corner was reduced by 15.28%.The optimization of the lateral overburden structure was realized,and the synergistic effect of ensuring the stability of the surrounding rock of the roadway and zero gas overrun was achieved.This paper has 172 Figures,32 Tables and 177 references.