Experimental Study on Hydraulic Conductivity of Coarse Sandstone in Deformation and Failure Process

Abstract

Variation law of hydraulic conductivity of coarse sandstone in deformation and failure process under different confining pressure is studied in this paper. Firstly the new Triaxial Cell coupling test instrument researched by the University of Lille and the company of Top Industria in France is introduced in detail. This test instrument can be used to do permeability experiment of standard sample under triaxial compression condition. This test instrument can work in a range from normal temperature to 90 °C. The maximum of the axial stress is 300 MPa, the maximum of the confining pressure is 60 MPa and the maximum of the pore water pressure is 60 MPa. Then permeability experiments in deformation and failure process of coarse sandstone under different confining pressure are carried out in this new triaxial test instrument and the relationship between hydraulic conductivity and volume strain is studied by using the mass conservation equation of porous media and Kozeny-carman equation. It is shown that in a complete stress-strain process, the variation law of hydraulic conductivity is periodic similar with the curve of stress-strain. The hydraulic conductivity reduces slightly with the increase of deviatoric stress in the stage of micro-fracture compressing and elasticity. After coming to the elasto-plastic stage, along with the expansion of new fractures, hydraulic conductivity increases slowly at first and then suddenly reaches to the maximum after peak stress. At residual stage, the penetrated fracture which controls hydraulic conductivity of coarse sandstone is compressed because of the confining pressure, so hydraulic conductivity decreases. During the process of deformation and failure, hydraulic conductivity is more sensitive to the change of lateral strain. With the increase of confining pressure, the peak and residual value of hydraulic conductivity in deformation and failure process decreases and the curve of hydraulic conductivity-strain tends to be gentle. It is shown from comparison of the theoretical results and test results that relationship between hydraulic conductivity and volume strain getting from the mass conservation equation of porous media and Kozeny-carman equation has good applicability when pores dominate the flow channel. The triaxial test instrument has a good control stability in the test, simple operation and high accuracy. It is suitable for rock mechanics and permeability test in civil engineering and hydropower construction.