Study on the variation of the permeability coefficient of soil–rock mixtures in fault zones under different stress states

Abstract

As the first gold mine discovered at the sea in China and the only coastal gold mine currently mined there, Sanshandao Gold Mine faces unique challenges. The mine's safety is under continual threat from its faulted structure coupled with the overlying water. As the mining proceeds deeper, the risk of water inrush increases. The mine's maximum water yield reaches 15 000 m3/day, which is attributable to water channels present in fault zones. Predominantly composed of soil–rock mixtures (SRM), these fault zones' seepage characteristics significantly impact water inrush risk. Consequently, investigating the seepage characteristics of SRM is of paramount importance. However, the existing literature mostly concentrates on a single stress state. Therefore, this study examined the characteristics of the permeability coefficient under three distinct stress states: osmotic, osmotic–uniaxial, and osmotic–triaxial pressure. The SRM samples utilized in this study were extracted from in situ fault zones and then reshaped in the laboratory. In addition, the micromechanical properties of the SRM samples were analyzed using computed tomography scanning. The findings reveal that the permeability coefficient is the highest under osmotic pressure and lowest under osmotic–triaxial pressure. The sensitivity coefficient shows a higher value when the rock block percentage ranges between 30% and 40%, but it falls below 1.0 when this percentage exceeds 50% under no confining pressure. Notably, rock block percentages of 40% and 60% represent the two peak points of the sensitivity coefficient under osmotic–triaxial pressure. However, SRM samples with a 40% rock block percentage consistently show the lowest permeability coefficient under all stress states. This study establishes that a power function can model the relationship between the permeability coefficient and osmotic pressure, while its relationship with axial pressure can be described using an exponential function. These insights are invaluable for developing water inrush prevention and control strategies in mining environments.