EXPERIMENTAL STUDY OF MECHANICAL PROPERTY OF SANDSTONE UNDER PORE WATER PRESSURE AND CONFINING PRESSURE

Testing study is made on sandstone under two types of triaxial compression experiments with rock mechanic system MTS815.Based on the Mohr-Coulomb criterion,under the condition of non-pore water pressure and different confining pressures,the influence of confining pressure on the parameters such as peak failure strength σ 1max,axial strain e 1max,shear strength τ and normal stress σ is analyzed;under the condition of pore pressure and constant confining pressure,the influence of pore water pressure P on the parameters such as peak failure strength σ 1maxand the corresponding axial strain e 1max,effective peak intensity σ 1'm ax,effective confining pressure σ 3',effective shear strength τ'and effective normal stress σ' is analyzed.The following conclusions are drawn:(1) Under the condition of pore water pressure,with the increase of the effective confining pressure,the effective peak failure strength σ 1'max increases.Under the same confining pressure,however,with the increase of the pore water pressure,the effective peak failure strength σ 1' maxreduces.(2) Under either the condition of non-pore water pressure or pore water pressure,both unary quadratic equation and linear equation are fit for the stress-strain relationship;and the corresponding intensity curve is in good agreement with the Mohr-Coulomb criterion.(3) The effective shear strength reduction factor can well demonstrate the influence of the pore water pressure on the effective shear strength.