Influence of Intermediate Principal Stress on Mechanical and Failure Properties of Anisotropic Sandstone

Since an increasing number of rock engineering structures are constructed in the stratified rock mass, a comprehensive understanding of the mechanical properties of anisotropic rock is crucial for the stability evaluation of these structures. In this study, the combined influences of the dip angle of the bedding plane and intermediate principal stress on the strength and failure behavior of anisotropic rock are experimentally investigated. True triaxial compression tests on a sandstone possessing seven different bedding plane angles (i.e., 0°, 15°, 30°, 45°, 60°, 75°, and 90°) are conducted under six different intermediate principal stresses (i.e., 10 MPa, 60 MPa, 100 MPa, 130 MPa, 160 MPa, and 190 MPa). The effects of intermediate principal stress and bedding plane angle on the stress–strain curve, Young's modulus, strength, and failure mode of the rock are soundly examined and discussed. The results show that both intermediate principal stress and bedding plane angle have a large influence on the deformation properties of the rock. In addition, the peak strength exhibits a typical U-shaped variation with increasing bedding plane angle under low intermediate principal stress condition, and the U-shaped behavior gradually diminishes with the increase in intermediate principal stress. Multiple failure planes can be observed after the failure of the rock specimens, showing asymmetric V-shaped patterns. The failure angle of the tested rock is found to generally increase as the applied intermediate principal stress gradually increases. The results in the present study deepen our understanding of the strength and failure behavior of anisotropic rock under true triaxial loading conditions.