This paper presents an experimental investigation on hydraulic conductivity of coarse and fine sands from a deep underground mine under high confining pressures using a static triaxial permeability test system. A series of experiments for hydraulic conductivity is performed under high confining pressures to investigate the correlation between the hydraulic conductivity and the confining pressure in the same hydraulic gradient

the relationship between the hydraulic conductivity and hydraulic gradient in the same confining pressure

the differences between hydraulic conductivities from the confining pressures by stepwise loading test and the direct loading test under the same hydraulic gradient. The results show that the hydraulic conductivity of the coarse sand and fine sands are all gradually decreased with the increasing confining pressure under the same hydraulic gradient. Under the same confining pressure

the hydraulic conductivity of the sand increases gradually with the increasing hydraulic gradient. It is also found that the hydraulic conductivity of the sand with stepwise loading is much higher than that with the direct loading under the same hydraulic gradient. The volume change and grain size compositions of the sand sample before and after the test are studied to find the reason why the hydraulic conductivity changes with the confining pressure. The results indicate that the volume of the sand sample decreases during the process of confining pressure increasing and permeation

which lead to the decreasing hydraulic conductivity. The grain size compositions of the sand samples before and after the permeability test show that some sand grains are crushed under high confining pressure

which increase the finer particles and decrease the porosity of the sample therefore decrease the hydraulic conductivity.