Shallow and extra-thick coal seam miningin the bottom layer paste filling overburden deformation control mechanism

SUN Xikui; FAN Jianguo; CHANG Qingliang

Abstract：Due to the unique characteristics of its roof structure and mining pressure manifestation,shallow buried coal seams have different rock control mechanisms.In response to the problem of subsidence control in shallow buried thick coal seam layered paste filling mining,the top layered filling material is used as a false roof during lower layered min-ing.Due to the dense structure and absence of joints and fissures in the filling material,exploring the overburden con-trol mechanism under the false roof conditions of shallow buried coal seam layered filling material is of great signifi-cance.This article adopts comprehensive research methods such as theoretical analysis,numerical simulation,and engi-neering measurement to construct a direct roof mechanics model for paste filling mining.The critical conditions for di-rect roof fracture instability are analyzed,and the core element for controlling shallow buried coal seam rock layers is proposed as the filling rate.The deformation control mechanism of overlying rock in shallow buried thick coal seam lay-ered paste filling mining is revealed,and a numerical calculation model for shallow buried thick coal seam layered paste filling mining is established.The deformation characteristics of overlying rock and surface movement under differ-ent filling rates are explored,and the stress characteristics and surface movement deformation of the filling body are measured.Research has shown that the ultimate span of the roof rock beam is 17.9 m,with a corresponding deflection of 0.54 m.The mining heights of the upper and lower layers are 4.65 m and 3.65 m respectively.The calculated filling rate of the upper layer is not less than 88％,and the overall filling rate is not less than 93％,which can ensure that the roof will not fracture or become unstable;As the filling rate increases,the stress concentration coefficient and deforma-tion of the overlying rock continuously decrease,the bearing capacity of the filling body gradually increases,and the surface movement deformation gradually decreases.When the overall filling rate of the upper and lower layers reaches 98％,the surface movement deformation can meet the requirements of building protection;After the upper layer filling mining,the stress on the filling body gradually increased and stabilized at around 2.3 MPa.The measured maximum subsidence of the surface was 57 mm,the maximum inclination value was 0.82 mm/m,and the maximum curvature value was 0.03 mm/m2.The surface movement and deformation were all within the range of the Level Ⅰ fortification in-dex,and the filling effect was good.