Analysis on the Influence of the Average Thickness of Sandstone in Overburden upon Mining Subsidence

摘要

The layered structure of overburden strata of coal measures is a remarkable geological characteristic of coal occurrence. The average thickness of sandstone is one of the key characteristics in the overburden layered structure, which can impact significantly the development of mining subsidence. Based on the geological characteristic of 2~(-2) coal seam and the representative drilling in the Yushen coal mining area and under conditions of the same depth and bedrock thickness (200m), 18 simplified models with different types of layered structure of overburden strata were constructed by taking the number of sandstone layers, their average thickness and the ratio of sand-shale as variables. On this basis, study was made on the influence rule of the sandstone average thickness upon the subsidence coefficient through the structural mechanics analysis and numerical simulation test. The results show that: first, based on analysis of structural mechanics, with the increase of the average thickness of sandstone, the maximum tensile stress and maximum deflection of overburden strata could decrease under the same load and elastic deformation so that the effect extent of same load on overburden strata can be decreased, and vice versa. Second, based on numerical simulation, the law that subsidence factor decreases while the average thickness of sandstone increases is discovered, and its change process includes two stages which are rapid decreased and tendency of stability. The fitted equation of the average thickness of sandstone and subsidence factor is established.