Seepage property of karst collapse pillar: experiments and engineering applications

The Karst collapse pillar (KCP) is a special geological structure, which is easy to form the fissure channels between the coal seam working face and the aquifer to cause the water inrush disasters. The KCP was sampled on site in this paper. The confined uniaxial compression test was carried out on the KCP to simulate its field consolidation, and seepage test on the KCP under different axial loads was conducted by using self-developed seepage test system. The KCP connecting to the underground Ordovician limestone aquifer in the sampling area was considered; the difference in the seepage properties between the KCP and the broken limestone was analyzed. The results show that the water-resisting capacity of the KCPs in 3# coal seam floor is 6.24–13.74 MPa, which is far greater than the water pressure of aquifer on 3# coal seam. The water-resisting capacity of the KCPs in 15# coal seam floor is in the range of 1.89–4.71 MPa, which is less than the water pressure of aquifer on 15# coal seam. The specific measures were conducted to prevent the water inrush during the mining process. Before exposing the X3 KCP, the roof drainage borehole drained the roof water to avoid the excessive water inflow in a short time. The grouting holes were arranged to reinforce the floor of sandstone aquifer. According to these treatment methods, the mining work safely passed through the X3 KCP, ensuring engineering safety and economic production. It is not recommended to directly expose the X3 KCP in the roadway or working face of 15# coal seam, and the floor of 15# coal seam should be grouted and reinforced in the future.