Fracture Mechanisms and 3D Surface Morphology of Bedding Sandstone Under Asymmetric Loading

Structural anisotropy has a significant impact on the fracturing of sedimentary rocks. However, many studies using asymmetric semicircular bending (ASCB) fail to examine the coupled effects of fracture modes, energy considerations, and three‐dimensional (3D) surface characteristics. This study investigates Mode I, Mode II, and mixed‐mode (I/II) fracturing in bedded sandstone at various orientations. The ASCB tests are integrated with high‐resolution laser scanning to reconstruct 3D fracture surfaces, thereby quantifying anisotropy through directional roughness and fractal dimensions. An energy‐based analysis is introduced to interpret fracture processes beyond peak‐load criteria. The findings demonstrate systematic transitions from matrix‐dominated cracking to bedding‐controlled ruptures that reveal instabilities induced by tensile‐shear interactions under mixed‐mode (I/II) loading. By explicitly linking fracture modes, bedding orientations, energy partitioning, and 3D morphology, this framework enhances conventional ASCB analyses. It provides a comprehensive mechanistic foundation for predicting fractures and assessing the stability of bedded rock masses in geotechnical engineering.