Bedding Plane Angles and a Horizontal Prefabricated Flaw Affecting the Cracking Characteristics of Shale Specimens

Understanding the cracking characteristics of shale is significant for tunnel engineering and exploitation of oil and gas in shale. Unconfined compression tests were conducted on prismatic shale specimens with a horizontal prefabricated flaw. The angle between the bedding plane and the vertical compression direction changes from 0 degrees to 90 degrees at an interval of 30 degrees. A high-speed camera was used to capture the cracking behavior, and the moment tensor inversion method of acoustic emission waveform was adopted for the source location and evaluation of the microfailure mechanism. The cracks compete to initiate due to stress-state dynamic redistribution, which determines the cracking behavior. The different bedding plane angles and prefabricated flaws significantly influence the cracking characteristics of shale specimens in unconfined compression tests. Five cracking modes and four main failure mechanisms were observed. The bedding planes greatly reduce shear cracks when their direction approaches the loading direction. This study provides a further understanding of the failure modes and mechanisms of shale specimens, which provides some references for projects involving shale.