Influence of bedding plane orientation on strength and micro-cracking behavior of anisotropic sandstone: insights from DEM modelling

Bedding plane, as an important structural feature of rocks, significantly affects the mechanical behavior of anisotropic rock. A good understanding of how bedding plane orientation affects deformation and strength properties is therefore crucial for better evaluation of stability in geotechnical engineering. In this study, the PFC3D software is used to investigate the combined effects of intermediate principal stress and bedding plane orientations (i.e., inclination and strike) on the strength and deformation behavior, and the associated micro-cracking processes within anisotropic rock under true triaxial stress condition. The results reveal that the inclination angle (IA) of bedding plane is a key factor determining the brittle-ductile transition behavior in the stress-strain response. Conversely, the strike angle (SA) of bedding plane has a negligible influence on the deformation behavior of the model. The simulated peak strength shows a typical U-shaped variation with the increase of IA at low SA (i.e., ω < 45°). However, the U-shaped variation of model strength gradually diminishes with increasing intermediate principal stress when SA is higher than 60°. In addition, the peak strength of the model is found to gradually increase as SA increases. On the other hand, with the increase of IA, the failure pattern undergoes a transition from being parallel to the σ₂ direction to being parallel to the bedding plane and finally returns to being parallel to the σ₂ direction. The findings of this study provide an essential basis for understanding the mechanism of how bedding planes affect the mechanical behavior of rocks under true triaxial compression.