Dynamic Response of a Non-Darcian Seepage System in the Broken Coal of a Karst Collapse Pillar

Dynamic research methods were used to assess the stability of non-Darcian seepage and verify that parameter changes are an important cause of mine water inrush due to a karst collapse pillar (KCP). A KCP is an infiltration system that contains a large amount of partially cemented crushed coal and rocks, and can be very dangerous. We analysed the influence of parameter changes on the stability, the initial permeability, the equilibrium flow velocity, and the deviation factor β to study the non-Darcian seepage characteristics of this crushed coal media system. The permeability parameters of the internal structure of a KCP were used to characterize the evolution of a KCP water inrush accident. In the physical tests, the porosity of the framework was the factor that determined the seepage state of the porous medium and the initial permeability of the framework. For mines with a risk of KCP water inrush, the permeability parameters also have a safe range. Numerical calculations verified that the system’s equilibrium state was stable, and that it has two equilibrium flow rates v s2 (3.5 × 10 −4 m/s) and v s3 (5.5 × 10 −4 m/s); this interval will not cause a change in flow regime. Thus, the limiting value of the non-Darcian deviation factor β was defined given the experiment’s initial conditions: when it is less than − 1.5 × 10 11 kg/m 4 , the system is not in equilibrium, and the seepage system will lose stability.