Prevention of water and mud inrush in longwall top coal cave mining under shallow buried thin bedrock

During longwall top coal caving mining of shallow buried thin bedrock and thick coal seams, penetrating fractures may form in the rock strata above the roof, causing an inrush of water and sand at the working face. The 507-working face of the Madiliang Coal Mine in Inner Mongolia, China, is a shallow buried thin bedrock and thick coal seam, mined by longwall top-coal caving mining. The field exploration results showed that the immediate roof consists of a layer of yellow mud within 400 m of the working face. The yellow mud has greater fluidity when encountering water and sits below a layer of yellow sandstone, which has a high risk of inrushing water and mud. Considering the roof lithology, longwall top coal caving mining characteristics, the fluidity of yellow mud, and the progressive failure of the coal seam, the particle flow code in two dimensions was used to establish the longwall top coal caving mining numerical model and analysed the movement characteristics of the top coal and yellow mud under different top coal thicknesses. Based on the results of field investigations and numerical calculations, a work-safe mining scheme was proposed, where the working face retains 4 m of top coal for mining. When the top coal thickness is less than 4 m, shearer cutting floor rock mining. A real-time mine pressure monitoring system was also established. The field application showed no incidents of water and mud inrush during the recovery period, which protects the working face.