Strength and energy exchange of deep sandstone under high hydraulic conditions

Abstract

To investigate the influence of confining pressure and pore water pressure on strength characteristics, energy storage state and energy release intensity at peak failure of deep sandstone, a series of triaxial compression tests under hydraulic coupling conditions are carried out. By analyzing the process of rock deformation and failure, the stress thresholds of the rock are obtained. The change trend of total energy density, elastic energy density and dissipated energy density of deep sandstone in the pre-peak stage is obtained by the graphical integration method. By comparing the dynamic energy storage level of rocks under different confining pressures, the influence of pore water pressure on the energy dissipation at stress thresholds of crack closure stress, crack initiation stress, crack damage stress and peak stress is analyzed. Based on the ratio of pre-peak total energy density to post-peak total energy density, the interaction mechanism of confining pressure and pore water pressure for the rock burst proneness of deep sandstone is studied. The experimental results show that the peak stress of sandstone increases with the increase of confining pressure, while the existence of pore water pressure can weaken the peak stress of sandstone. In the stress stage from crack closure stress to peak stress, the dynamic energy storage level of rock presents a trend of the inverse “check mark”. Meanwhile, the larger the confining pressure, the higher the energy storage level of rock. However, the pore water pressure increases the degree of energy dissipation of rock and reduces the energy storage capacity of rock, and the degree of dissipation is linear with pore water pressure. The increase of confining pressure aggravates the instability and failure of deep sandstone, while pore water pressure has the opposite effect. The research results will provide necessary data support for the stability analysis of rock mass excavation in sandstone stratum under high stress and high pore water pressure.