The Overburden And Surface Movement Research Induced By Mmulti-steep-seam Mining

Underground mining of steeply inclined coal is likely to induce drastic deformation of the overburden above the goaf,which will cause deformation and damage to the surface above the mined area.In the previous studies,most of the analysis and research were from the perspective of single-layer mining conditions.However,there is still insufficient understanding of the model and mechanism of induced rock movement in steep-slope multilayer coal mining.It is urgent to study the evolution law of mechanical behaviors such as overburden and surface deformation induced by steeply inclined multi-layer coal miningBased on this,this paper,combined with the mechanical analysis method,the similar model test method and the discrete element numerical simulation method,studies the mode and mechanism of induced rock movement in multi-seam steeply inclined coal mining,and obtains the following results:(1)Through the physical model test and numerical simulation analysis of similar materials,the law of strata movement induced by steeply inclined multi seam mining is revealed.In the initial stage of multi-layer steep seam mining,the rock mass destruction is mainly caused by the small-scale collapse of the cut hole and the roof;after the roof of the goaf is suspended for a certain range,the rock mass in the direction of the roof of the coal seam is squeezed into the goaf.If the distance between the two coal seams is not large,under the action of the vertical pressure of the upper and lower rock masses and the transverse force of the broken rock masses that have been collapsed stably,the rock pillars between the goafs will have a secondary composite collapse similar to the domino effect.The collapse of overlying strata in goaf has certain lag in time scale.In addition,there will be narrow cavities in the overlying strata in goaf.The cavities propagate upward in inclined coal seam with nonlinear movement track.The size of the cavities generally decreases gradually,and the shape changes from separation layer to cracks.(2)In this paper,a zoning criterion of disturbed rock mass based on the coefficient of variation of rock mass displacement is proposed.Firstly,the disturbed rock mass in the steep coal goaf is divided into several small blocks,and then the boundary and range of the three zones are determined according to the variation coefficient of the rock mass displacement in each block.Finally,the zoning criterion of the disturbed rock mass overlying the steep coal goaf is established to realize the zoning of the disturbed rock mass in the steep coal goaf.(3)The characteristic curve of the surface residual settlement in the gob of multi-layer steep seam is generally in the form of "W",the surface residual deformation at the edge of the surface subsidence pit in the mining area is relatively large,while the residual deformation in the middle of the collapse pit is relatively small;the activation of the gob of multi-layer steep seam changes periodically,resulting in the subsidence speed characteristic of the surface residual settlement in the form of "wave".