Hydro-mechanical performance of granite residual soil slopes reinforced by combined biocementation-vegetation treatment under extreme rainfall

Rainfall-induced shallow failures of granite residual soil slopes are widespread in humid regions because these soils are highly susceptible to erosion, rainfall infiltration, and strength degradation. This study combined outdoor model experiments and numerical simulations to investigate the hydro-mechanical performance of granite residual soil slopes reinforced by biocementation and combined biocementation-vegetation treatment under extreme rainfall. Three slope systems, namely an unreinforced slope, a biocemented slope, and a combined biocementation-vegetation (CBV) reinforced slope, were comparatively evaluated. In this study, extreme rainfall refers to the selected model-scale rainfall condition of 200 mm/h for 2 h, which was adopted to simulate an unfavorable short-duration intense rainfall episode. The CBV-reinforced slope showed the strongest erosion resistance, with a cumulative soil loss of only 1.10 kg/m 2 , corresponding to reductions of 90.95 % and 60.1 % compared with the unreinforced and biocemented slopes, respectively. Although vegetation roots induced localized preferential infiltration near the shallow surface, the combined treatment delayed wetting-front migration and limited pore water pressure buildup in deeper soil. The calculated safety factor decreased from 1.976 to 1.923 after 2 h of rainfall and reached 1.773 in the idealized 24 h simulated rainfall extension. These results suggest that CBV treatment can improve the erosion resistance and hydro-mechanical performance of shallow granite residual soil slopes under the selected extreme rainfall condition.