The mechanical and hydraulic properties of rock mass play a crucial role in underground engineering. To study the effect of hydraulic pressure, confining pressure, and axial cyclic loading-unloading on variation of the deformation and permeability in fractured rock mass, the coupling triaxial experiment of sandstone was conducted. The concept of permeability recovery rate (PRR) and permeability enhancement reduction rate (PERR) was proposed to characterize the change in permeability. The results show that the permeability of fractured sandstone quadratically varies with the change of hydraulic pressure and confining stress. In detail, the permeability decreases with the decrease of hydraulic pressure and increases with the decrease of confining stress, respectively. Compared with the single-fracture permeability, the double-fracture permeability is more sensitive to the change of hydraulic pressure. Furthermore, the permeability of fractured sandstone is more dependent on the hydraulic pressure than the confining stress. With the performance of axial cyclic loading-unloading, the permeability spirals down, and both the axial and radial residual strains quadratically evolve. Following the first axial cyclic loading-unloading, an obvious deformation memory phenomenon characterized by a parallelogram shape in axial stress-strain curves was observed for the sandstone. The cumulative PRR of 85%-95% was maintained in double-fracture sandstone. On the contrary, a fluctuation of cumulative PRR characterized by “V shape” was observed for single-fracture sandstone. The enhancement effect of axial cyclic loading on the permeability was characterized by the decrease of PERR for double-fracture sandstone and increase of PERR with a greater gradient for single-fracture sandstone.

中文翻译：

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循环加卸载作用下裂隙砂岩流体力学耦合特性

岩体的力学和水力特性在地下工程中起着至关重要的作用。为研究水压、围压和轴向循环加卸载对裂隙岩体变形和渗透率变化的影响，进行了砂岩耦合三轴试验。提出了渗透率恢复率（PRR）和渗透率增强减少率（PERR）的概念来表征渗透率的变化。结果表明，裂缝砂岩的渗透率随水压和围压的变化呈二次方变化。具体来说，渗透率随着水压的降低而降低，随着围压的降低而增加。与单裂缝渗透率相比，双裂缝渗透率对水压变化更为敏感。此外，裂缝砂岩的渗透率更多地依赖于水压力而不是围压。随着轴向循环加卸载的进行，渗透率呈螺旋下降趋势，轴向残余应变和径向残余应变均呈二次方演化。在第一次轴向循环加卸载后，砂岩出现明显的变形记忆现象，其轴向应力-应变曲线呈平行四边形。双裂缝砂岩的累积PRR保持在85%-95%。相反，对于单裂缝砂岩，观察到了以“V形”为特征的累积PRR波动。