Influence of slope crest soil cracks on water dynamics and gully wall stability under varying rainfall patterns

Cracks at the slope crest of collapsing gully erosion areas significantly influence soil hydrological processes and mechanical properties; however, the response mechanism between crack development and gully wall destabilization under rainfall conditions remains unclear. In this study, typical collapsing gully walls with and without cracks in the red soil hilly region of China were selected as the research objects. The effects of short-duration rainstorms, long-duration light rainfall and crack conditions on soil hydrology and slope stability were quantitatively analysed. The results showed that the annual average soil moisture of soils with cracks in collapsing gully walls was significantly lower than that of soils without cracks. Under long-duration light rainfall, collapsing gully walls exhibited significantly higher increases and faster growth rates of soil moisture than under short-duration rainstorms. Across both rainfall scenarios, the soil with cracks in collapsing gully walls consistently showed greater increases and faster growth rates compared to that shown by soils without cracks. The safety factor was consistently lower for collapsing gully walls with cracks than for those without cracks and lower under short-duration rainstorms than under long-duration light rainfall. Compared with soils without cracks at the slope crest, the minimum safety factor of soils with cracks decreased by 29.4% and 39.0% under short-duration rainstorms and long-duration light rainfall, respectively. These results demonstrated that the presence of cracks increases cumulative soil moisture during rainfall events and significantly weakens the stability of collapsing gully walls, particularly under long-duration light rainfall.