Study On The Law And Application Of Strata Movement In Solid Filling Mining Under The Condition Of Repeated Mining

Many areas in eastern China are faced with the problem of coal resource depletion,and the mine reserves are also decreasing,and most of the remaining reserves are located under buildings,water bodies and railways.At the same time,a large number of coal resources are occupied by various protection pillars,such as shaft protection pillars and industrial Plaza protection pillars,which restrict the rational development of coal resources.With the large-scale exploitation of coal resources,the proportion of "three lower" pressure coal in the recoverable coal reserves will be further increased,so how to mine "three lower" pressure coal is a problem that coal enterprises need to solve.In recent years,the comprehensive mechanized solid filling coal mining technology has become mature,which can reduce the movement and deformation of the overburden and the earth's surface,and at the same time,it can protect the environment and solve the problems encountered in the mining of "three down" coal pressure.Many mining areas in our country are using the solid filling mining technology to recover the coal resources under the buildings.With the mining of coal resources,there will be the problem of repeated mining with filling mining,and the current research on this problem is still blank.In order to predict the subsidence of the surface and the interior of the rock mass during the multi seam solid filling mining,the following research work has been carried out and some research results have been obtained:(1)Based on the analysis of the measured data of the surface movement observation station in the No.73 and No.29 working face of Nantun coal mine,the characteristics of the surface movement and the mechanism of the secondary deformation of the surface during the repeated mining with caving method are summarized.The influence of the old goaf on the surface subsidence of the new mining face when the caving method is repeated mining its essence is that the additional stress produced by the mining of the new working face disturbs the structure of the strata in the goaf,the cavities and pores in the overlying strata are compacted,resulting in the secondary subsidence,and finally spread to the surface.(2)By using the method of similar material model,the dynamic process of overlying strata movement and the development law of fracture field of overlying strata are studied.When the 3 upper coal seam is mined,only a certain height of fracture zone and bending zone are developed.There are a lot of gaps between the fracture zone and the overlying strata.At the same time,there are cracks between thestrata above the open cut hole in the goaf.When the multi coal seam is filled and mined,the surface movement and deformation value is abnormal mainly because the cracks in the overlying strata are compacted due to the first mining.(3)By means of numerical simulation,the law of the movement and deformation propagation of the surface and the interior of the rock mass is studied.On this basis,the propagation rules of the movement and deformation of the surface and the interior of the rock mass are studied,and the influence of the interval and the mining height on the surface movement and deformation value is also studied.When single seam filling mining,with the increase of overburden height,the maximum subsidence value shows a decreasing trend,the horizontal movement value shows a first decreasing and then increasing trend,and the deformation direction shows two opposite directions with the increase of height.In multi seam filling mining,with the increase of interval,the surface horizontal movement and surface subsidence caused by the mining of 3 upper coal seam and 3 lower coal seam decrease.The subsidence value of the roof corresponding to the 3 upper coal seam in the middle of the goaf is decreasing,while the subsidence value corresponding to the goaf boundary is increasing,the horizontal movement value corresponding to the roof of the upper coal seam is increasing,and the position where the maximum horizontal movement value appears is shifted to the outside of the goaf.The change trend of the corresponding horizontal movement value at the surface is opposite to that at the roof.When the layer spacing increases,the horizontal movement value at the surface tends to decrease,and the position where the maximum horizontal movement value appears shifts to the inner direction of the goaf.(4)According to the results of numerical model and similar material model,this paper summarizes the selection method of surface subsidence prediction parameters in single coal seam filling mining,and then summarizes the selection method of surface subsidence prediction parameters in multi coal seam filling mining.For the first mining subsidence prediction,each probability integral parameter can be selected by referring to the subsidence prediction parameter of caving method,while the subsidence coefficient and the main influence angle tangent change linearly in the interior of the rock mass during the prediction of the interior deformation of the rock mass,the horizontal movement coefficient is processed insections in the interior of the rock mass,and the inflexion offset distance and the mining influence propagation angle remain unchanged.When the surface subsidence is predicted under the condition of repeated mining,the selection of the surface subsidence coefficient is related to the layer spacing of the two coal seams.When the layer spacing of the two coal seams is less than the development height of the fracture zone caused by the mining of the three coal seams,the subsidence coefficient Q increases by 10%;when the layer spacing of the two coal seams is greater than the development height of the fracture zone caused by the mining of the three coal seams,the subsidence coefficient Q increases by 3%.The surface horizontal movement coefficient b refers to the first mining time.The inflexion offset is taken as 0,the tangent value of the main influence angle is reduced by 0.2,and the influence propagation angle of mining refers to the first mining.When the predicted parameters in the rock mass are selected,the subsidence coefficient is still considered as linear propagation,and the horizontal movement coefficient is processed in sections in the rock mass.The value is the same as that of single coal seam filling mining.The inflexion offset is taken as 0.The main influence tangent value is considered as linear propagation in the rock mass,and the influence propagation angle of mining is unchanged.There are 58 pictures,10 tables and 97 references in the paper.