Mechanical characterization of sandstone with bedding under true triaxial conditions

In order to study the mechanical properties and anisotropic characteristics of bedded sandstone, mechanical tests were conducted under different bedding inclination angles and intermediate principal stresses. True triaxial compression tests were conducted on sandstone with seven different bedding plane angles (0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees, and 90 degrees) under three different intermediate principal stresses (10 MPa, 100 MPa, and 160 MPa). The effects of inclination angle of bedding plane on the deformation, strength and failure modes of sandstone were investigated. The results show that sandstone anisotropy gradually decreases and tends to be isotropic with the increase of intermediate principal stress. Under high intermediate principal stress, both Young's modulus and failure angle gradually increase with the increase of anisotropy angle. The peak strength is also influenced by the combined effects of bedding plane angle and intermediate principal stress. It exhibits a typical U-shaped variation with increasing bedding plane angle under low intermediate principal stress condition, and the U-shaped curve flattens with increasing intermediate principal stress. The results are significant for guiding the design and construction of deeply buried hard rock projects.