Abstract: The floor water-inrush accident caused by karst collapse column is easy to break over the aquifer and coal seam. This kind of accident has become the serious danger of lower group coal mining in northern China. For the well-consolidated collapse column, the permeability of the fillings directly affects that of the overall collapse column, and the permeability of fillings constantly changes under the influence of mining. The study on seepage characteristic of collapse column fillings is conducted with MTS815.02 seepage test system in a complete stress-strain process and the variation of permeability under different strain states. Meanwhile the influence of initial moisture content and confining pressure on the fillings permeability is analyzed in this test. The results show that: 1) The representative stress-strain-seepage relationship of fillings is divided into pressure elastic segment, damage and creep stage, and the permeability presents the change rule of decrease-increase-decrease in complete stress-strain process; 2) The peak value of permeability decreases with the increasing confining pressure, and the ratio of the permeability in the complete stress-strain process has a exponential function relation with the confining pressure difference in complete stress-strain process; 3) The initial permeability and porosity of fillings decreases with the increase of initial moisture content, and the ratio of permeability and porosity have a power function relationship. The difference between peak and initial permeability decreases with the increasing initial moisture content in complete stress-strain process.

Key words: collapse column fillings, complete stress-strain process, permeability, initial moisture content, confining pressure effect