Role of bedding plane in the relationship between Mode-I fracture toughness and tensile strength of shale

• Published in: Bulletin of engineering geology and the environment Vol. 81; no. 2
• Main Authors: Shi, Xiaoshan, Zhao, Yixin, Danesh, Nima Noraei, Zhang, Xin, Tang, Tiewu
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.02.2022
• Subjects: Earth and Environmental Science; Earth Sciences; Foundations; Geoecology/Natural Processes; Geoengineering; Geotechnical Engineering & Applied Earth Sciences; Hydraulics; Nature Conservation; Original Paper; Anisotropy; Mode-I fracture toughness; Tensile strength; Bedding angles; Shale
• ISSN: 1435-9529; 1435-9537
• DOI: 10.1007/s10064-022-02572-8

Shale exhibits strong anisotropy due to the sedimentary environment and pre-existing micro-fractures. It is of great significance to characterize the bedding-plane-induced fracture toughness anisotropy in shale and its relationship with other physical and mechanical properties. Samples with different bedding angles (0°, 30°, 45°, 60°, and 90°), defined as the angle between loading axis and bedding plane, are prepared for cracked chevron notched Brazilian disc test and Brazilian disc test. The results indicate that both fracture toughness and tensile strength are positively correlated with the bedding angle. As the bedding angle rises, the elastic modulus and wave speed decrease nonlinearly. With the increase in bedding angle, Poisson’s ratio decreases first and then increases. It can be concluded that fracture toughness and mechanical properties of shale reveal the degree of anisotropy induced by bedding structure. In this study, the relationship between these parameters is discussed in detail. Also, an exponential function is proposed to improve the previously developed linear functions by researchers, defining the relationship between fracture toughness and the mechanical properties. In geological-engineering projects, the fracture toughness of shale under different loading directions can be determined from the proposed exponential function and these mechanical properties.