Seepage characteristics of collapse column fillings

With concealment and hysteresis, water-inrush from Karst collapse column has become an important security hazard of lower group coal mining in North China. Based on the MTS815.02 seepage test system, we analyzed the impact of consolidation pressure, initial moisture content and confining pressure on the permeability of fillings in order to study the seepage characteristics of collapse column fillings. The results show that: (1) The permeability of collapse column fillings is of the order of 10−16–10−15 magnitude and decreases with an increase in consolidation pressure and decrease in initial moisture content. (2) The essence of filling seepage law change is the change in porosity, and a power function relationship exists between the permeability ratio and porosity ratio. (3) With increasing confining pressure, the permeability of fillings decreases. However, under low confining pressure (1.2–4 MPa), the change of confining pressure has no obvious influence on the permeability.