Mechanical behavior of groundwater seepage in karst collapse pillars

Groundwater inrush has an impartible relationship with geological structures such as karst collapse pillars (KCPs), which are widely distributed in North China. In order to study the mechanism of groundwater inrush from coal seam floor, the variable mass dynamics and nonlinear dynamics were introduced. A mechanical model–plug model is established to describe the behavior of water seepage flow in coal-seam-floor containing KCP. The study shows that: (1) If the mass of the KCP keeps steady, the water seepage velocity in the KCP and the surrounding rocks will reach a constant value soon; (2) if the mass of the KCP and the surrounding rocks increases by grouting, etc, the seepage velocity in the KCP and the surrounding rocks will reach its minimum value gradually, and (3) if the mass of the KCP and the surrounding rocks decreases by scouring, the flow velocity in the KCP and the surrounding rocks shows a monotone increase, the water flow may change into pipe flow, especially when a large number of the mass of the KCP and the surrounding rocks enters into goaf road, which may lead to instable flow and cause groundwater inrush.