Utilizing angular displacement to monitor failure of coal seam floor

At present, it is difficult to accurately forecast the water inrush from coal seam floor. For safety, it is necessary to monitor and predict water inrush. Rock angular displacement can be observed easily and can show whether the coal seam floor has bent and destroyed or not. The elastic-plastic analysis and numerical simulation indicate that, 1) when angular displacement of rock is greater than the critical value, water inrush shall take place; 2) the critical value of angular displacement is 2 (1 + μ)/E × τ0 by elastic-plastic analysis while the critical values of angular displacement in Buchun mine are 0.0019 radian for shale stone and 0.005 radian for fine sandstone, respectively, by numerical simulation. Based on these conclusions, we designed the early warning system of water inrush to obtain the laws of the damage depth of floor rock and angular displacement. The practice shows that using the method of rock angular displacement is very effective for monitoring and forecasting water inrush caused by coal seam floor failure.