Mechanical behavior of shale considering spatial variability of matrix properties

Layered shale, with its pronounced anisotropy in deformation, strength, and failure patterns stemming from intrinsic layering and structural discontinuities, presents significant challenges for stability assessments in underground engineering. This study investigates the fracture failure modes of transversely isotropic layered shale using Brazilian splitting tests, employing a modeling approach that incorporates the random distribution characteristics of matrix mechanical parameters in layered rocks. Brazilian splitting tests on shale samples (θ = 0°–90°) were used to analyze tensile strength and failure modes. Acoustic emission (AE) and digital image correlation (DIC) techniques captured damage evolution, while a 3D random field model Simulated rock Heterogeneity. Results indicate that failure strength peaks at 60°, potentially due to the shear-tension coupling effect along bedding planes. Layer activation (LA) is the dominant failure mode for angles between 0° and 60°, while mixed failure occurs at 45° and 60°. Compared to conventional homogenized models, incorporating spatial variability via a random field approach allows for a more realistic representation of rock heterogeneity. This allows the numerical simulations to capture localized yielding and crack evolution patterns that would otherwise be overlooked in uniform-property models. The Yield Approach Index (YAI) effectively describes the evolution of yielding regions during loading, demonstrating that stress redistribution and crack propagation are influenced by the spatial variability of rock properties. Adjustments to random field parameters, rock matrix properties, and foliation parameters significantly influence failure strength and modes; foliation parameters exhibit a more pronounced effect at lower loading angles. This research offers valuable insights into the mechanical behavior of layered shale, thereby contributing to the stability assessment of underground engineering projects situated in anisotropic rock masses.