Study on the influence of bedding plane on fracturing behavior of sandstone

The mechanical behavior of layered stone is much influenced by the weak bedding planes. To further explore how the layered structure influences the fracture characteristic of layered sandstone, a series of three-point-bending tests on sandstone specimens with different inclination angles was conducted and the anisotropy of fracture toughness and fracture pattern was discussed. Then a numerical model based on cohesive elements was proposed to simulate the fracture of semi-circular sandstone specimens under three-point-bending test and the effects of bedding strength on the fracturing behavior of semi-circular bending(SCB) specimens with different inclination angles were discussed by simulation with the proposed model. The results show that fracture toughness and fracture pattern are anisotropic under the influence of the inclination angle of the bedding and fracture toughness increases with the increase of bedding strength for a fixed inclination angle. In addition, the influence of joint strength on the fracture toughness is greater for lower inclination angles and the fracture patterns are not only influenced by joint strength, but also related to the inclination angle. Fracture patterns of theta = 0 degrees specimens are almost not influenced by the joint strength, and the specimens all split along the bedding plane with tensile failure; tensile or shearing failure along the bedding plane occurs on theta = 30 degrees specimens and the crack length along the bedding plane increases with the decrease of joint strength; when the joint strength is higher, tensile failure along the bedding plane occurs on theta = 45 degrees specimens and tensile failure crossing the bedding plane occurs on theta = 60 degrees-90 degrees specimens, while shearing failure along the bedding plane occurs on theta = 45 degrees-90 degrees specimens when the joint strength becomes lower. Furthermore, the maximum shearing length occurs on theta = 45 degrees specimens. In addition, the impacts on the crack initiation angle and crack propagation path caused by both bedding strength and inclination angle are discussed based on the numerical results. The findings in this paper may enrich the theory of fracture mechanics on layered rock.