Experimental study of the effect of the inclination angle on mechanical characteristics and failure modes of layered sandstone

This study investigates the effect of the inclination angle on the strength, deformation and failure characteristics of layered sandstone specimens with inclination angles prepared for uniaxial compression tests. The deformation distribution was analysed using digital image processing. The results reveal that the stress–strain curves of layered sandstone can be classified into distinct stages: initial compression; elastic deformation; inelastic and crack expansion; and post-peak failure. Compressive strength is significantly influenced by the inclination angle, displaying a right-biased ‘U’ shape across various angles, with the lowest strength observed at 75°. A similar left-biased ‘U’ trend is noted for elastic modulus and longitudinal wave velocity as the inclination varies. Digital image processing highlights significant differences in surface deformation with varying angles, primarily influenced by the bedding structure. Deformation concentrates in the bedding zones, identifying potential crack initiation and expansion. The failure mode is notably affected by the bedding structure, progressing from splitting tensile failure to single incline plane shear failure through the bedding structure and matrix, shear failure along the bedding structure, and X-conjugated shear and tensile failure as the inclination angle increases. This paper discusses the mechanical properties and failure mechanisms of layered sandstone based on these parameters and failure modes.