Numerical investigation on mechanism and fluid flow behavior of goaf water inrush: a case study of Dongyu coal mine

Goaf water inrush has become one of the most prominent issues threatening the safety production of coal mines. To better understand how this hazard develops, a mechanical model and a nonlinear flow model were used to study an inrush that occurred in Dongyu mine. Based on the dominant hydraulic characteristics of groundwater in the fractured rock and the variation of plastic zone during excavation, an equivalent water inrush channel (WIC) was established. By coupling Darcy flow, Brinkman flow, and turbulent flow, the nonlinear flow model reproduced the dynamic process of goaf water inrush. Results showed that the inrush was a result of the combined effect of excavation disturbance and hydraulic pressure of goaf water. With the digging of roadway, fractures in the floor communicated with fractures in the roof of goaf, promoting the generation of WIC. Under the action of hydraulic pressure, groundwater entered into the roadway from the caving goaf along WIC and the disaster occurred. Along the flow path, water pressure continued to decrease, while velocity showed an increasing trend, but both of them remained stable in the roadway. In addition, as a transition area of laminar in caving goaf and turbulent in roadway, the permeability of WIC had a significant impact on the evolution of water pressure and velocity along the flow path. The results provided references for understanding the evolution process of similar inrush hazards.