Meso-structure deterioration of redbeds soft rocks and its cross-scale disaster-causing mechanism

The complex water-induced deterioration of redbeds soft rocks poses a critical challenge in cross-scale disaster characterization, which is pivotal for mitigating geological hazards. Conventional experimental and numerical models mostly focus on a single scale, failing to capture the cross-scale evolution from meso-structural degradation to macro-hazard triggering, thus hindering disaster prevention and engineering safety. To address this gap, this study quantitatively bridges meso-scale deterioration mechanisms (pore evolution, mineralogical transformation, surface strain) with macro-scale disaster prediction. We conducted experiments on meso-structural deterioration under water action and explicitly linked the observations to a hydraulic-geotechnical coupling model based on Darcy’s law. Key findings reveal: (1) Porosity increased by 9.3% after 5 dry-wet cycles, with clay minerals (e.g., montmorillonite) decreasing by 47% due to dissolution and recrystallization. (2) The coupling model successfully predicted the transition from microcrack coalescence (0.016% strain threshold) to macroscopic shear failure, consistent with triaxial compression tests (peak strength reduction of 35% after 3 cycles). (3) Case studies of landslides in Zigui County showed that the model accurately simulated sliding displacements (91.3 m trailing edge vs. 373.1 m maximum) and accumulation patterns, validating the cross-scale mechanism linking mineral swelling, pore expansion, and slope instability. These results quantitatively bridge microstructural deterioration (e.g., Al/Mg leaching, quartz enrichment) with macro-disasters, providing a theoretical framework for predicting redbeds landslides and optimizing engineering interventions such as drainage systems and slope reinforcement.