Caving Thickness Effects on Stability of Coal-rock Pillar against Water on Steep Coal Seam Mining under Water

To study the failure law of coal-rock pillar against water while caving thickness vary in steep coal mining condition, we used numerical calculation and analog simulation methods to study caving thickness effects on roof collapsing characteristic and the stability of coal-rock pillar, based on the geohydrologic condition of LONGHU mine The result showed that: with caving thickness increase, the ratio of inbreak height to saving thickness decrease, while the ratio of fractured height to caving thickness raise, caving fore-behind angle basically stay the same; with caving thickness increase, stress concentration on main roof more obvious, rock mass downward fall features more obvious, coal-rock pillar against water easier fall. Research conclusion provide the basis for coal-rock pillar remaining, ensure mining safety in production under water.