Experimental study on disaster of water-sand inrush and roof cuttingin working face with thin bedrock roof

The coal seam thickness in one-time mining becomes larger, which leads to an increase in the height of the direct roof caving, and under the condition of thin bedrock,it is not easy to form a stable structure after the roof breaks.The breakage of the roof can easily lead to the occurrence of water inrush and sand burst disasters in the working face, which seriously affects the production of the working face.In order to reveal the mechanism of concurrent disasters caused by water inrush and sand burst and roof cutting under high-intensity mining conditions in thin bedrock and thick loose rock formations, similar simulation experiments were performed using the self-developed roof dynamic pressure and water and sand burst test platform, taking the No.31406 fully-mechanized mining face of Jinjie Coal Mine as the engineering background, the plane strain model was used in the test, and the geometric similarity ratio was selected as 100∶1.combined with auxiliary infrared imagers and ultrasonic detectors, which obtained the characteristics of energy accumulation and dissipation and the development of cracks when the roof was broken. The test results show that when the roof breaks in advance, vertical through cracks are generated in the same rock layer, and the bedding is prone to“displacement” cracks due to the different strength and thickness of the rock layers. When water bursts and sand breaks and roof cuts occur concurrently, obvious cracks are produced, and the working resistance of the support will increase significantly, causing water burst and sand burst accidents in the pressure frame and working surface; based on the basic principle of rolling friction, the rolling friction mechanics is established. The model reveals the mechanism of the block slipping and instability caused by the influx of water and sand into the fissure; the water-sand body enters the roof structure from the through cracks, and the original sliding friction is transformed into rolling friction, which significantly reduces the friction between the blocks and causes the roof to slipunstably.Combined with experiments and theoretical analysis, it is found that timely support frame removal,increased support setting force, and acceleration of the advancement of the working face can reduce the probability of occurrence of water-sand inrush and roof cutting disaster.