Study On The Law Of Overburden And Surface Movement Deformation In The Paste Backfilling And Replacement Mining Of The Strip Pillar

For a long time,in the middle and eastern coal areas in China,strip mining method is often used to extract coal under villages,and more than billion tons of detention coal reserve has been created in the past decades.It has become the key of sustainable development for the middle and eastern coal mines how to exploit the remaining strips coal pillars safely.The use of backfilling mining on the basis of strip mining to recycle the remaining stripe coal pillars not only frees up a large amount of coal resources,but also reduces the backfilling cost and ultimately controls the settlement of the surface.However,stripe mining has undergone a mining effect on overburden and surface,and second mining will be produced after backfilling and replacement mining of the remaining strip coal pillar,so the law of overburden and second moving deformation of the surface and the long-term stability condition have become the key to the study of backfilling replacement mining.Based on mechanical derivation,theoretical analysis,physical simulation,numerical simulation and field measurement,this paper studies the law of second moving deformation of overburden and surface in backfilling and replacement mining,and the main research contents and conclusions are as follows,taking the 2300 district of Daizhuang coal mine as the research background.Main contents and conclusions are as follows:(1)Based on the bracket theory and elastic thin slab theory,this paper establishes the stability mechanics model of surrounding rock in backfilling replacement mining,deduces the expression of mechanical relationship between the support force of the backfilling body and the key rock parameters through theoretical derivation,and gives the formula criterion of whether the key rock layer is broken or not.(2)Through the simulation study of indoor similar materials,it can be seen that the original stable overburden structure began to move two times after the filling and replacement mining of the left strip coal column,resulting in the activation and collapse of the roof in the goaf of the strip,and the settlement of the roof of the filling face,and the final roof and filling body reached a new equilibrium state,The filling body and the coal pillar of the roadway form a stable common support body to support the overburden,and it is observed that when the model is stable after second mining effects,a key rock layer is found at 20cm from the roof of the coal seam,and the rock layer below the key rock formation is wavy,and the above rock formations are bent and sinking as a whole.,The sinking amount of the whole overburden increased after the residual strip filling and replacement mining,but the sinking amount gradually became smaller with the increase of the height.(3)Though the numerical simulation of FLAC3D.the theoretical derivation conclusion is supplemented and verified,the motion change of overburden and surface affccted by second mining is analyzed synthetically,and the stress of solid coal at the boundary of mining area after filling and replacement mining of residual strip is increased,and the internal stress of the filling body is in a three-way force state.A large stress concentration is produced at the coal pillar of the roadway,and it is greater than the stress of the boundary coal pillar,and after the instability and activation of the belt goaf,the height of the roof tensile failure increases,the shear failure depth on both sides increases,and the plastic zone range becomes larger,and with the increase of the strength of the filling body,the control effect on The results show that filling replacement mining has a good control effect on the sinking of the surface,and can protect the surface buildings from damage.The surface subsidence decreases with the increase of the strength of the backfilling body into a nonlinear descent relationship.(4)Through the analysis of the observation results of the surface movement in the backfilling and replacement face,it is concluded that the maximum sinking amount of the inclined line is 271mm and sinking coefficient is 0.09,the horizontal deformation value is 0.395mm/m,the curvature value 0.009mm/m and the tilt value 0.796mm/m,all of which are smaller than the level I failure range of the surface building.Guarantee the safety and stability of the surface buildings.