Mechanical Responses of a Porous Red Sandstone to Quasi-Static Cyclic Loads Under Uniaxial Compression

Porous rocks exhibit mechanical behaviors characterized by high compressibility and stiffness enhancement under quasi-static cyclic loads. In this study, we investigated the mechanical responses of a porous red sandstone subjected to different cyclic loads and revealed the mesoscopic mechanisms for the evolution of stiffness and strength. Rock stiffness was enhanced by increasing stress and number of load cycles during pre-peak loading, and the normalized viscoelastic strain evolved uniformly during all the unloading phases. Void compaction and microfracturing caused irreversible structural changes and subsequent changes in the stiffness of the rock, and there was a positive linear relationship between the unloading secant modulus and axial irreversible strain. In addition, a new parameter, named the plastic strain increment ratio, was defined to describe the asynchronous development of the axial and lateral irreversible deformation induced by void compaction and microfracturing. These results can provide a better understanding of the mechanical properties of porous sandstone. Low-frequency cyclic loads cause stiffness enhancement on the porous red sandstone.Unloading recovery of viscoelastic strain follows a uniform exponential law regardless of loading conditions.The evolution of stiffness is linearly related to the accumulation of irreversible strains.The evolution of stiffness is caused by void compaction and microfracturing.