(1. School of Energy Science and Engineering，Henan Polytechnic University，Jiaozuo，Henan 454000，China；
2. State Key Laboratory of Geomechanics and Geotechnical Engineering，Institute of Rock and Soil Mechanics，
Chinese Academy of Science，Wuhan，Hubei 430071，China)
Abstract：In order to deeply understand the fracture propagation mechanisms and bedding directivity effect of shale under tension，three-point bending and Brazilian tests were performed on Longmaxi shale specimens in various bedding orientations with respect to the loading direction to study the fracture propagation patterns and then to explore the fracture propagation mechanisms and bedding directivity effect under tension. For three-point bending condition，It is shown that weak bedding cracks and fracture path deflects in the case of a fracture propagating in the Arrester orientation，producing a complex fracture pattern with fracture branching and deflection，that fracture path usually deflects for a fracture propagating in Divider orientation，which is resulted from shear fracture across bedding planes，and that the fracture path is the bedding plane without deflection for the case of a fracture propagating along a bedding plane. For Brazilian condition，the bedding orientation has a great impact on the initiation point，initiation mechanism，propagation path and propagation mechanism of fractures. When the compressive load is loaded in the direction normal or oblique to the bedding，the fracture is usually initiated from the loading jaws with an arc-shaped fracture path and frequently accompanied by shear fractures across or along bedding planes，and the fracture pathway is determined by tensile and shear fractures which shift during propagation. Only in the Short-Transverse configuration，fracture starts from the disc centre and extends along the bedding plane without deflection. When a tensile fracture propagates along a bedding plane，it can be deviated away from the bedding plane due to the local stress. Complex fracture behaviours such as fracture branching，deflection and weak bedding cracking easily occurs while a tensile fracture propagates in a direction normal or oblique to the bedding. These complicated propagation behaviours are directly related to the stress condition and the relative orientation between the fracture and the bedding plane，and both the bedding and stress state play a dominant role in fracture propagation of shale under tension.
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2019, Vol. 38 
