Acoustic emission pattern of shale under uniaxial deformation

The brittle fracture mechanism of shale is an important issue to both borehole stability and hydraulic fracturing. A number of experimental studies on shale macroscopic mechanical properties have been carried out; however, the acoustic emission (AE) patterns of anisotropic shale are not fully understood. In this paper, a series of uniaxial compressive strength tests were conducted on cylindrical shale obtained by drilling at different orientations to the bedding plane. The anisotropic failure modes of shale samples have been monitored by real-time AE monitoring and stress–strain response, under ambient conditions and uniaxial stresses. The experimental results suggest that the pronounced bedding planes of shale have a significant influence on the mechanical properties and the AE responses. The AE counts and AE accumulative energy release curves clearly indicate the initiation and propagation of cracks during compression, and the ‘U’ shaped curves well reflect the anisotropic failure mechanism. The sounded...