Simulation test on mixed water and sand inrush disaster induced by mining under the thin bedrock

Coal seam mining under thin bedrock will make transmission fissure zone go through to the water-rich aquifer under the covering layer, which will cause water flooding and sand gushing in the working face. The test model of the mixed water and sand inrush transfer and inrush was designed and manufactured to simulate the startup, transfer and inrush process of the mixed water and sand inrush in the overburden fracture channel. The characteristics of the mixed water and sand inrush in the fracture channels were researched. The variation characteristics of water pressure in different positions of the fracture channel were revealed through analyzing “\/” type fracture form which is wide at the top and goes narrower down to the base, of various inclination angles under the water pressure of 0.06 MPa and 0.08 MPa. The results show that the water and sand inrush took place instantly in the mined area. Based on the characteristics of water pressure variations, changes in water pressure are divided into two phases: rising phase and lowering to stable phase. Under the other same conditions, when the fissure channel angle increases, the pore water pressure and its sudden drop will increase too, and the inrushing process will get more rapidly; the bigger the water pressure is, the pore water pressure increases more rapidly and violently. From this, the transfer characteristics and dynamic mechanism of the mixed water and sand inrush were explored.