Failure characteristics of unloading red shale with different bedding angles based on the particle discrete element.

Understanding the unloading failure behavior of layered red shale is crucial for the stability of deep roadways and other underground structures. This study combines triaxial unloading experiments with discrete element method (DEM) simulations to reveal the mechanical, acoustic emission (AE), and meso-mechanical responses of red shale with different bedding orientations.Laboratory tests demonstrate that unloading reduces peak strength by 15-25% compared with conventional triaxial loading, and bedding angle critically controls the failure mode: 0° specimens exhibit shear-dominated failure, whereas 90° specimens tend to split in tension. The DEM model, calibrated with experimental results (error < 2%), reproduces stress-strain behavior and captures the brittle-ductile transition.AE analysis shows concentrated activity under low confining pressures and continuous ductile emissions under high pressures, reflecting the correlation between AE characteristics and crack evolution. Force-chain network and fabric anisotropy analysis reveal that unloading accelerates crack coalescence and structural reorganization, with fabric anisotropy increasing by more than 25-fold.This integrated framework (AE + DEM + fabric evolution) provides a robust basis for evaluating unloading-induced instability. The findings advance understanding of bedding-controlled failure in red shale and offer practical guidance for roadway support optimization and underground engineering safety, with potential extension to related fields such as shale gas development.