Understanding stress thresholds in anisotropic rocks is essential for predicting instability and designing safe underground structures. However, crack initiation and crack damage thresholds in layered sandstones remain insufficiently quantified due to the inherent complexity of bedding-induced anisotropy. In this study, layered sandstone specimens were investigated through a combined experimental–numerical approach to evaluate the influence of bedding orientation on threshold stresses and deformation behavior. Laboratory tests included uniaxial and triaxial compression and Brazilian tensile tests, while numerical simulations were conducted using a bonded-particle discrete element model under quasi-static, dry conditions. Lateral and volumetric strain responses were identified as the most robust indicators for determining stress thresholds, as they reduce subjectivity in threshold identification. Results show that bedding-related anisotropy exerts a strong control on crack initiation and damage evolution, with certain orientations leading to abrupt brittle failure, whereas others exhibit progressive deformation. Systematic variations in strain partitioning and deformation stages with bedding orientation further highlight pronounced anisotropic effects. By integrating experimental observations with numerical analyses, this study provides a consistent framework for quantifying crack initiation and damage processes in layered sandstones. The findings offer practical guidance for identifying bedding orientations prone to sudden failure that require conservative support measures, as well as orientations suitable for monitoring-based control strategies. These results improve the understanding of failure mechanisms in anisotropic rocks and contribute to more reliable spalling prediction in layered formations. • The normalized stress ratios define the elastic, stable, and unstable crack stages. • The 30° failure mechanism led to σ cd equaling σ p and a rapid transition to failure. • Deformation in compression and dilation is strongly affected by bedding orientation. • The corresponding experimental and numerical results in this study agree well with one another.
Noori et al. (Wed,) studied this question.