Stability analysis of unsaturated soil slopes with cracks under rainfall infiltration conditions

Pre-existing (open) cracks at slope crests, especially tension cracks, are a significant factor in the transition from shallow to deep-seated landslides in unsaturated soil slopes induced by rainfall. This paper presents an analytical framework to assess the stability of unsaturated soil slopes for deep-seated rotational failure considering arbitrary crack depths and unsteady infiltration, and its effectiveness is verified by previous literature and finite element analysis. A closed-form formula is proposed for the maximum depth of cracks in unsaturated soils by the stability of the vertical crack boundary. A parametric study is performed to investigate the impact of some key parameters on the stability of unsaturated soil slopes with cracks. Dimensionless stability charts are developed, which can calculate the factor of safety for the slopes with cracksof any depth and can reflect that the potential slip surfaces through or without passing through the crack tip. In addition, given the existence of a critical crack depth and maximum crack depth, with a ratio ranging from 0.5 to 0.6 based on the stability charts, deep-seated rotational failure is more likely to occur than failure caused by a crack boundary.