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.

摘要

为了研究围压和孔隙水压对深部砂岩强度特征、储能状态和峰值破坏时能量释放烈度的影响规 律, 开展一系列水力耦合条件下的三轴压缩试验。通过分析岩石变形破坏过程, 获得其应力阈值。利 用图形积分方法获得深部砂岩在峰前阶段总能量密度、弹性能量密度、耗散能量密度的变化趋势。对 比不同围压下岩石的动态储能水平, 分析孔隙水压对岩石闭合应力、起裂应力、损伤应力、峰值应力 等应力阈值处能量耗散的影响。基于峰前、后总能量密度的比值, 研究围压与孔隙水压对深部砂岩岩 爆倾向性的相互作用机理。实验结果表明, 砂岩峰值应力随着围压的增加而增加, 而孔隙水压的存在 可以削弱砂岩的峰值应力。在自闭合应力至峰值应力间的应力阶段, 岩石的动态储能水平呈现出反“对 勾”的演化趋势。同时随着围压的增加, 动态储能水平上升。然而, 孔隙水压增大岩石的能量耗散程 度, 降低岩石的储能能力, 耗散程度与孔隙水压呈线性关系。围压的增大加剧深部砂岩的失稳破坏现 象, 而孔隙水压具有相反作用。研究成果将为高应力、高孔隙水压下砂岩地层工程岩体开挖稳定性分 析提供有力的数据支撑。