Macro-micro changes of clayey loess subjected to wetting-drying cycles induced by extreme weather and the effect on geological hazard

Clayey loess is highly vulnerable to mechanical deterioration under repeated wetting-drying (WD) cycles driven by extreme weather events, which poses a substantial threat to slope stability and increases geological hazards.This study investigates the progressive deterioration of the mechanical performance of loess subjected to WD cycles. A combined mechanistic process of deterioration was proposed, integrating laboratory tests and image processing techniques to analyze microstructure changes, water retention behavior, and crack development. Results indicate that the surface crack ratio increased progressively with each cycle. The developing crack network compromised the structural integrity of the loess and accelerated its degradation. The increase in large pores (with entrance pore diameter > 32 μm) after WD cycles creates more void space, accommodating greater compression and collapse deformation. The shift toward more hydrophilic clay minerals contributes to the weakening of clay bonding strength upon inundation. The microstructural changes also modified the water retention behavior. Specifically, the reduction in small pores (8-2 μm) weakened the soil’s ability to maintain suction, particularly at pressures below 50 kPa. In contrast, the increase in micropores (< 2 μm) and clay particles (0.1 to 0.4 μm), along with the changes in clay minerals, enhanced suction generation capacity at pressures exceeding 100 kPa. Collectively, these micro- to macro-scale transformations degrade the mechanical behavior of clayey loess, thereby elevating landslide susceptibility. The findings underscore how climate-induced WD cycling can intensify loess slope instability, highlighting the need to incorporate such processes into landslide hazard assessments and climate adaptation strategies.