Mechanical behavior and failure characteristics of double-layer composite rock-like specimens with two coplanar joints under uniaxial loading

To study the combined action of joints and bedding plane on crack evolution of flawed layered rock masses, uniaxial compression tests and digital image correlation (DIC) tests were carried out on double-layer composite rock-like specimens with multi-inclination two coplanar joints under different bedding angles. Based on the experimental results, the existence of bedding plane and joints performs a significant effect on characteristics of stress-strain curves and strength parameters. The failure modes are divided into four different types. The existence of bedding plane inhibits the coalescence of cracks in rock bridge area, and the variation of bedding angle affects the crack propagation path and failure mode transition greatly. For specimens with bedding angle of 30° and 45°, the larger the joint angle, the less the influence of bedding plane on failure characteristics. Besides, a new tensile crack type which initiates from the bedding plane and is easier to propagate in the upper layer was observed.