Top-coal drawing law of LTCC mining based on stochastic medium theory

The top-coal drawing has a significant impact on the recovery ratio and rock mixed ratio in longwall top-coal caving mining. Based on a model experiment conducted,firstly the offset formula of top-coal settlement curve extreme point was fitted with the consideration on the influence of shield beam,and then the boundary of top-coal and drawing body equation were built with stochastic medium theory. The results show that the shield beam and drawing opening have an important influence on the shape of boundary and drawing body of top-coal. The boundary of top-coal presents standard funnel plots in the places away from shield beam,and changes into convex curve gradually near shield beam, while in the places near drawing opening,the boundary of top-coal bends to shield beam. When the caving coal height is small,drawing body leans forward to top after shield beam and the shape is irregular,as well as the axial deviation angle is relatively big. With the increase of caving coal height,the shape of drawing body presents quasi-ellipsoid and its anterior inferior part is cut by shield beam,and the axial deviation angle reduces to 0,the coal at the top after shield beam is the major component of drawn top-coal.