Triaxial test on physical and mechanical properties of sandstone for different diagenesis degree

The paper systematically analyzes the failure mechanism, the pore ratio, permeability and the mechanical property of sandstone under different confining pressure by using of triaxial test system. And the qualitative and quantitative relationship is established between the mechanical property of sandstone and confining pressure. It is shown that the pore ratio and permeability of sandstone are reduced with the increasing of confining pressures conforming to the rule of logarithmic function. The stiffness and strength of sandstone increase with increasing of its confining pressures presenting obvious compressive hardening. The descending gradient of residual strength after rock failure reduces when the confining pressure increases,but the residual strength was relatively improved. The failure mechanism was obviously different under different confining pressures. When confining pressure increases, the stress strain curve of sandstone with relatively weak diagensis transits from strain softening to approximate strain hardening. But the sandstone with relatively strong diagensis performs brittle tensile failure in uniaxial compressive test, and with increasing of confining pressure,the rock comes to shearing failure and its stress strain curve performs obviously brittle and strain softening properties.