Creep behavior of rocks under coupled high stress and water pressure

Abstract

Understanding the time-dependent deformation and failure mechanisms of rock under coupled high stress and water pressure is essential for evaluating the long-term stability of deep rock engineering. This study employs a self-developed triaxial hydraulic loading system to investigate the seepage–creep behavior of sandstone, marble, and granite under different hydraulic boundary conditions. The results show that unpressurized seepage increases creep strain and reduces failure time, leading to tensile failure on the rock surface. Lateral pressurized seepage not only accelerates primary creep strain in dry rock samples but may also suppress secondary creep behavior. A notable finding is that as water pressure increases, the creep failure time presents a distinct U-shaped trend. Specifically, the shortest failure time is observed at 1 MPa when the axial stress exceeds the saturated uniaxial compressive strength (UCS). Compared with previous studies, the results indicate that pressurized seepage produces a dual strengthening effect under saturated conditions: pore water pressure partially offsets the axial stress, while lateral water pressure enhances creep resistance. Lithology is a dominant factor; high-porosity sandstone undergoes rapid degradation owing to weak cementation. However, creep failure still occurs once the cumulative microscopic damage induced by pore water pressure surpasses the strengthening effects. Notably, the unloading of water pressure can trigger an instantaneous increase in creep strain or even immediate failure, particularly in marble and granite. Overall, these findings provide important insight into developing a comprehensive understanding of both delayed and instantaneous water-induced failures in deep rock engineering.