Influence of Stress and Water Pressure on the Permeability of Fissured Sandstone Under Hydromechanical Coupling
We investigated the permeability of fissured sandstone in the Lao Sangou coal mine to understand how to reduce water seepage through the mine roof and to provide a scientific basis for how the permeability changes. First, the physical and mechanical parameters of the sandstone samples were measured in laboratory tests. The discrete element method was used to establish a corresponding model, which was calibrated using uniaxial compression tests. Then, five calculation models were established and used to analyse the permeability of fissured sandstone at varied axial pressures, confining pressures, and water pressures under hydromechanical coupling. A further triaxial seepage experiment was carried out to test the permeability of the fissured sandstone samples. The results indicated that a horizontal hydraulic aperture was more sensitive to axial stress than a vertical hydraulic aperture, and that a vertical hydraulic aperture was more sensitive to confining stress than a horizontal hydraulic aperture, suggesting that confining stress affects permeability more than axial stress. Changes in permeability occur in three stages, i.e. slowly declining, sharply declining, and steady state, reacting to water pressure and stress. There is a cubic polynomial relationship between both the average flow rate and the average hydraulic aperture and stress, with R2 ≥ 0.95. After the permeability traverses the slowly declining stage, an exponential relationship exists between both the average flow rate and the average hydraulic aperture and stress, with R2 ≥ 0.97. A series of numerical calculation models were used to suggest a partition scheme, in which water pressure plays a leading role in zone I, the stress and water pressure work together in zone II, and stress plays a dominant role in zone III.
Keywords: Coal mining, Water seepage, Discrete element method, Triaxial seepage experiment