Effects of bedding angle and specimen geometry on the failure of layered rocks

Layered rocks exhibit pronounced mechanical anisotropy, and their mechanical response depends on specimen geometry. This work investigates the effects of bedding angle and height-to-diameter ratio on the mechanical response, fracture morphology, and crack evolution of layered rocks. Experimental characterization combined uniaxial compression tests with three-dimensional fractography, while numerical simulations utilized two-dimensional discrete-element method. Specimens with bedding angles of 0°, 30°, 60°, and 90° were tested, and the resulting fracture surfaces were evaluated using fractal dimension, joint roughness coefficient, and statistical morphological descriptors. Numerical models incorporating random bedding distributions were developed for height-to-diameter ratios of 0.5, 1.0, 2.0, and 3.0. The results show that bedding orientation governs compressive strength, elastic modulus, failure mode, and fracture-surface morphology. Compressive strength exhibits a U-shaped dependence on bedding angle, while both compressive strength and elastic modulus generally decrease as the height-to-diameter ratio increases. Fracture surfaces formed at bedding angles of 0° and 30° are relatively rough and geometrically complex, whereas those formed at 60° and 90° are smoother because failure is increasingly controlled by bedding-parallel slip or separation. Increasing the height-to-diameter ratio reduces end-constraint effects, promotes shear-crack development and damage localization, and enhances the continuity of the principal failure zone. These findings clarify the coupled effects of bedding anisotropy and specimen geometry on the failure behavior of layered rocks and provide a basis for evaluating the stability of layered rock masses.