Water inrush mechanism in mines and nonlinear flow model for fractured rocks

The water inrush in mines may experience three processes including Darcy flow in a confined aquifer, non-Darcy flow in fractured zone in fault and Navier-Stokes' turbulent flow in tunnel. A water-inrush model, in which the Brinkman equation is thought to be suitable for describing the fluid flow in the fractured zone in fault, and also the Darcy equation and the Navier-Stokes s equation are receptively used to characterize the flow in confined aquifer and in tunnel, is proposed based on conservation of mass and pressure balance, in order to predict the hydraulic processes during the water inrush. This model is considered to be promising and practical for characterizing the whole fluid flow and water-inrush processes. Then, as a typical example, the water-inrush due to karstic collapse columns, which is considered to be a coupled processes that can be characterized with Darcy equation in confined aquifer, Brinkman equation in fractured zone and Navier-Stokes's equation in tunnel, is simulated when the above-proposed model is implemented into COMSOL Multiphysics. The complete fluid flow process in confined aquifer, fractured zone and tunnel are all numerically predicted. The numerical results indicate that, the karstic collapse column, being a fractured zone in rock mass, is the transition zone between linear Darcy flow in confined acquirer and water-inrush in tunnel, and its permeability is very sensitive to the water pressure and the flow velocity. The karstic collapse column or fractured zone is the channel that connects the confined aquifer and tunnel, and the recharge of confined aquifer is the main cause that leads to the high water pressure and the water inrush through the karstic collapse columns.