Study On Strata Movement Mechanism Of Multi-seam Mining

Underground coal mining induces deformation,cracking,crushing and compaction of overlying rock mass.Especially in multi-seam mining,the movement mechanism of strata is more complex.A correct understanding of the movement mechanism of strata in multi-seam mining can provide theoretical support for the prevention and control of mining pressure and the prediction of surface subsidence.Predecessors have done a lot of work on the deformation and movement of rock mass induced by underground mining,and achieved rich results.However,in the multi-seam mining,the mechanism of the upper coal seam goaf on the lower coal seam mining,the compaction deformation characteristics of the broken rock in the caving zone,and the influence of the coal seam spacing and the overlapping shape of the working face on the mechanical behavior of the rock mass need to be further studied.In this paper,model test and numerical simulation are used to study this problem,and the main work and innovation achievements are as follows:(1)Large scale model test was used to study the fracture mechanism of rock mass between coal seams and the deformation activation mechanism of overlying goaf caused by multi seam mining.The fracture mechanics model of the rock mass between coal seams is mainly divided into the compression shear failure of the simply supported beam with a long first fracture step and the subsequent bending failure of the cantilever beam;the compression step of the upper coal seam mining cycle controls the fracture step of the rock mass between coal seams,and causes the fracture rock mass to be inverted trapezoidal occlusal structure;the gradual collapse of the trapezoidal structure will disturb the goaf of the upper coal seam and cause the overlying rock mass to continue to collapse The overburden is more broken,the fracture height increases,and the surface subsidence basin shifts to the stoppage line;(2)Small scale model test was used to study the compaction deformation characteristics of broken rock in caving zone.The mechanical mechanism of deformation was analyzed.In the early stage of deformation,the gap between particles is mainly reduced due to particle rotation and sliding,and the energy dissipation is mainly to overcome the friction,and the contact between particles is "point" and "point-surface" type;in the late stage of deformation,the particle edges and corners are broken and the volume is compressed,and the energy dissipation is mainly to break and compress the particles,and the contact is changed into "surface-surface" type,and the structure is tighter;The particle size and gradation control the speed of deformation and the strain of each stage;(3)The influence of coal seam spacing on the movement mechanism of strata was studied by introducing the compaction characteristics of caving zone into the numerical simulation.After the mining of each working face is completed,the broken rock is not fully compacted at the open cut and stop mining line,and the ground subsidence basin is fully compacted;the uncompacted area at the stop mining line is larger than that at the open cut,and the phenomenon of repeated mining is more obvious;when the coal seam spacing is small,the coal seam goaf will be connected,the mutual disturbance is violent,and the ground subsidence basin bottom will collapse With the increase of coal seam spacing,the mutual disturbance is weakened,and the surface subsidence basin is shifted towards the cut-out direction;(4)The numerical simulation method was used to study the movement mechanism of strata in the multi seam mining project of Yangquan No.2 coal mine,and the influence of working face overlapping shape on the mechanical behavior of rock mass was analyzed.When the overlapping shape is parallel,because the overlying rock has been damaged after the mining of the upper coal seam,the pulling effect between the rock masses is weakened,when the mining of the lower coal seam,the rock mass is mainly downward subsidence;when the overlapping shape is vertical or oblique,the mining of the lower coal seam will lead to the collapse of the residual coal and rock between the working faces of the upper coal seam,and induce the large-area displacement of the damaged rock mass;when there is no overlapping of the working faces,the mining effect is the subsidence boundary will be superimposed,and the development direction of rock fracture in the lower coal seam mining will be guided by the unloading of overlying damaged rock mass,and it will develop towards the direction of the old goaf.