THE TWO-PHASE FLOW OF WATER-SAND INRUSH UNDER SHALLOW COAL SEAM MINING:A COUPLED NUMERICAL STUDY

In order to study the flow performance of mixed water-sand two-phase flow of the overlying water bearing loose bed under the shallow coal seam mining, a coupled numerical method based on discrete element software PFC^3D and finite element software GID is used to simulate the whole processes of water-sand inrush in precast ideal fracture with different opening widths and dip angles in overlying rock strata. The analysis of the contact force of the fracture channel, flow velocity of water and the drag force between water and sand variation law along with time steps show that, the opening widths and dip angles of fracture change the flow patterns of water-sand flow inrush, and have great impact on the contact force of the fracture channel, flow velocity of water and the time of mixed water-sand flow. However, the drag force is mainly influenced by the dip angles of fissure channel. The fracture channel entrance is the most dangerous position, where has the largest contact force in the process of water-sand coupled flow. The final flow velocity of water and the time steps to stabilize the water velocity in the fissure are in linear correlation with the fracture angles and the fracture opening widths, respectively. The drag force is greater and water-sand inrush is more intense in dip side than underside of the fissure channel.