Analysis on the Triaxial Loading Mechanical Properties of Sandstone under High Stress and High Hydraulic Pressure

Abstract

The mechanical properties of deep rocks are highly sensitive to hydraulic pressures. The existing associated studies mainly focused on the mechanical properties of rocks under high stress, but few studies analyzed the collaborative influences of high stress and high hydraulic pressure on deep rocks. To analyze the special mechanical properties of deep rocks under high hydraulic pressure, sandstone samples were collected from a deep tunnel of the Yuanliangshan Line in Chongqing, China. All rock samples were saturated in vacuum conditions and then wrapped with oil in a specially made fluororubber cover. Then the confining pressure was loaded to 15, 25, 35, and 45 MPa at a loading rate of 1 MPa/min under hydrostatic pressure conditions. After reaching the preset confining pressure, the rock samples were resaturated in the experimental apparatus. The outlet pressure was maintained at a barometric pressure, while the inlet pressure was the preset hydraulic pressures of 1, 4, and 7 MPa, thus forming a one-way interstifial flow. A triaxial compression test was performed on the sandstone samples under high stress and high hydraulic pressure. Results demonstrate that under high stress, the compressive strength of sandstone decreases in the logarithmic function along with an increasing hydraulic pressure (p). A regression analysis was performed on the elasticity modulus of sandstone with an increasing confining pressure (σ3) and under different hydraulic pressures. Under different confining pressures, the elasticity modulus of sandstone decreases in logarithmic function along with an increasing hydraulic pressure. Meanwhile, under an increasing confining pressure, the sandstone samples shift from a brittle state to a ductile state. However, the brittleness of these samples is positively related with hydraulic pressure. The findings of this work provide references for analyzing the excavation-induced mechanical properties of deep rocks in tunnels under high hydraulic pressure.