Study On Strata Failure Mechanism And Surface Subsidence Theory In Steeply Inclined Coal Seam Mining

Study of strata failure mechanism and surface subsidence theory in steeplyinclined coal seam mining,is the important component of mining subsidence theory. For the coal seam dip angle is larger than 45°,the effect of forces along the plane of rock strata is bigger than the effect of forces perpendicular to the plane,so the strata failure mechanism and strata movement pattern are distinctly different from horizontally or gently inclined coal seam mining.In the past research,no matter what strata movement geometrically described or stress deformation mechanically described,no suitable theoretical models were put forward to study strata movement model for steeply- inclined coal seam mining.So compared to the study of strata movement of gently-inclined coal seam mining,the theoretical research of strata and surface movement in steeply-inclined coal seam mining is insufficient in the aspect of strata failure mechanism,strata movement pattern and surface subsidence prediction.Based on the geological and strata pressure-bring characteristic in steeply inclined coal seam mining,the mechanisms of rock strata and surface movement were theoretically studied intensively.An overburden movement model combined by strata bending deformation and slipping deformation was established for steeply-inclined coal seam mining.The paper used numerical simulation model of UDEC to study the influence of coal seam dip angle,mining height,level vertical height of goaf,and multi-seam mining sequence on the stress,deformation and strata movement.As an application example study,the paper also proposed a new mining design method for steeply-inclined coal multi-seam mining under buildings.The paper mainly carried through the following studies:(1) For the first time the effect of axial force was taken into account to study the strata deformation and failure in steeply-inclined coal seam mining,and the beam-pillar models were established.Because rock strata are simultaneity subjected to the transverse and axial forces,and that the axial force is bigger than the transverse force,so the axial force becomes mostly important factor to effect on the strata deformation and failure.Compared with the strata deflection value calculated by beam or lath models,the value calculated by beam-pillar models is bigger,and the location of the maximum deflection is partial to the upside of goaf.(2) The underlying strata deformation and failure in steeply-inclined coal seam mining were studied in this paper.For the larger dip angle,the axial force acting on the underlying strata becomes bigger,and then it is more possible that the underlying strata destroyed.By the beam-pillar model this paper studied the influence of mining depth,goaf size and strata thickness on the stability of underlying strata,which was of great importance to analyze the underlying strata destroy in steeply-inclined coal mining.(3) An overburden movement model combined by strata bending deformation and slipping deformation was firstly established for steeply-inclined coal seam mining, and a theoretical model of wedge-shaped failure region was put forward.In the extension of wedge-shaped failure region,the strata suffered tensile failure caused by bending deformation.And on top of the wedge-shaped failure region,the strata suffered shear failure caused by slipping deformation.The asymmetrical surface subsidence basin in steeply-inclined coal seam mining is generally caused by the existing of wedge-shaped failure region.(4) On the basis of the theoretical model of wedge-shaped failure region,a new surface movement prediction method by transforming of original mining space to slipping space was put forward to solve the calculation problem of asymmetrical basin caused by steeply-inclined coal seam mining.(5) In order to solve the problem of steeply-inclined coal seam mining under buildings,raise productive efficiency of coal mining enterprises,a new method of coal pillar arrangement with barrier pillars and goaf triangle pillars was presented to control surface subsidence.With barrier pillars to decrease the strata movement along the strike,and goaf triangle pillars to decrease the strata slipping along the dip, surface subsidence could be preferably controlled.