[Objective] This study aimed to an investigation into the relationship between the dimensions of the concave cavity and the development of collapsed gullies and collapsed gully erosion in order to provide a scientific basis for the prevention of collapse and the engineering treatment of collapsed gullies.[Methods] The study focused on the collapse mound profile in Tongcheng County in Hubei Province. We calibrated the basic calculation parameters for each soil layer of the collapsed wall

through a series of indoor experiments and actual collapse conditions

introducing the "unit life and death method

" which modeled the evolution of the concave cavity

and applied analytical methods to the stability of the caved wall. Initially

2D finite (FE) numerical models of the collapsed wall-concave cavity were established

based on the ABAQUS software platform

which can be applied to quantitatively analyze the critical splash erosion pit depth value (D0) required for triggering the collapse of the wall under natural conditions. The sensitivity of the main factors that lead to the failure of the collapsed wall was evaluated by means of the orthogonal experimental design; furthermore

this article selected a series of depths of the concave cavity (less than D0). This study elucidated the quantitative relation between depths of concave cavity and the saturation threshold value that caused the collapse of the overlying red clay layer.[Results] The safety factor of the collapsed gully wall decreased linearly as the depth of the deep-cut hole increased. The water content of the red clay layer overlying the concave cavity was the most vital factor influencing collapse. In addition

the gradient of the collapsed wall had a significant impact on the stability of the collapsed wall. The relative depth of the concave cavity and the height of collapsed gully wall had little effect on the stability of the collapsed gully wall.[Conclusion] The possibility of collapse of gully walls depends largely on the size of the deep-cut hole and the moisture content of the soil above the concave cavity. Future research should apply this understanding to the prevention of collapse and to the engineering treatment of collapsed gullies.