Research on surface subsidence laws and prediction models under repeated mining of multiple coal seams

With the gradual extension of global coal mining to the deep, the problem of surface subsidence caused by repeated mining of multiple coal seams has attracted much attention. In this paper, the methods of theoretical analysis, numerical simulation and field monitoring are used to study the settlement model and settlement law under the condition of repeated mining of multiple coal seams, and the engineering application is carried out. Through theoretical analysis, it is concluded that there is a linear relationship between the amount of broken expansion of overlying rock mass, the buried depth of coal seam, the thickness of coal seam and the maximum subsidence value of surface. The opening size of surface subsidence basin in multi-coal seam mining is still linear with the mining depth of coal seam. Based on the probability integral method, fully considering the factors such as rock mass expansion and separation caused by repeated mining of unequal thickness and multiple coal seams, the prediction model of surface subsidence caused by repeated mining of multiple coal seams is constructed, and the calculation method and calculation formula of surface subsidence coefficient caused by repeated mining of multiple coal seams are given. The law of overlying strata and surface subsidence caused by repeated mining of multiple coal seams is analyzed by numerical simulation. The results show that the trend of surface subsidence is similar to that of repeated mining (second-layer coal) in multi-coal seam mining area. The subsidence curve is symmetrically distributed in the early stage of mining and asymmetrically distributed in the later stage. The maximum value of surface subsidence is located on the side of open-off cut. The numerical simulation results are highly similar to the calculation results of ' prediction model of surface subsidence caused by repeated mining of multi-coal seam '. The surface subsidence prediction model constructed in this paper is used to predict the coal mine site. The prediction results are compared with the field measurement results. The maximum relative error value of the working face tendency is 5.7%, and the average relative error value is 2.9%. Along the strike of the working face, the maximum relative error value is 6.7%, and the average relative error value is 5%. The overall prediction error is small, which verifies the rationality of the prediction model of the surface subsidence law of multi-coal seam repeated mining.