Numerical Simulation and Analysis of Sand-Shale Ratio of Bedrock Impacting Mining Subsidence

Significant geological factor of coal occurrence is layered structure of coal measures overburden rock, and bedrock sand-shale ratio is a key element of coal measures overburden rock layered structure. On the background of geological occurrence conditions of 2-2 coal in Yushen coal mining area, the sandstone layer, sandstone average thickness and sand-shale ratio are taken as variables to build the 18 different types of layered structure models. On this basis, basic law of coal measures bedrock sand-shale ratios which is a key characteristic of layered structure impacting mining subsidence is mainly studied by using numerical simulation method. The results show that: firstly, in spite of any condition of sandstone layer coefficient subsidence coefficient always decrease with the increase of sand-shale ratios. However, the effect of sand-shale ratios on subsidence coefficient continuously decreased with the increasing of sandstone layer coefficient. Secondly, when the sandstone layer coefficient is less than 70%, the different sand-shale ratios have significant influence on the subsidence coefficient, and when the sandstone layer coefficient is more than 90%, subsidence coefficients corresponding to different sand-shale ratios show obvious convergence characteristics. The gap between each other is only 1%~2%. Thirdly, taking the subsidence coefficient corresponding to the sand-shale ratio is 6:4 as reference, the curves about the rate of decrease in subsidence coefficient is set up when the sand-shale ratio is 7:3 or 8:2, and the fitting equations are presented on the basis of Log3P1 mathematical model.