Abstract: Brazilian tests are conducted on shales with different bedding angles, and a high speed camera and an acoustic emission (AE) system are used to investigate the effect of stratification on shale mechanical properties, crack propagation and AE characteristics. The results indicate that: (1) Brazilian split destruction process can be divided into three stages: compaction stage, elastic stage and destruction stage. (2) The anisotropic characteristics of tensile strength, splitting modulus and deformation at the stress peak point are highly distinct. The most obvious effect of stratification is found at the angle of 30°, whereas the smallest effect is found at the angle of 90°. (3) For samples with angles of 0° and 15°, the failure surfaces are normally along the direction of bedding plane. At the angle of 30°, the failure surface intersects bedding planes and coincides with the loading baseline surface. In contrast, fracture surfaces deviate from the loading baseline surface with varying degrees and turn out to be curved surface for samples with angles of 45°, 60°, 75° and 90°. (4) 30°and 45° are transformation angles of failure mechanisms. At 30°, tension failure occurs along bedding converts to cross-cut bedding plane failure along the loading baseline, while cross-cut bedding plane failure happens along the loading baseline converts to cross-cut bedding planes failure with varying degrees of shear slip at 45°. (5) AE activities and energy releases demonstrate obviously with increasing bedding angles caused by the bedding plane, which results in the anisotropy of failure mechanism. Moreover, there exists a good linear relationship between the peak value of AE energy rate and tensile strength, which indicates that the peak value of AE energy rate can reflect the variation of tensile strength well.

Key words: shale, Brazilian splitting, acoustic emission, anisotropy, crack propagation