Positive role of low-infiltration bare land patches in slope stability during extreme rainfall events

• Grass showed no enhancement in saturated hydraulic conductivity relative to bare land. • Soil pore-water pressure in grassland was more sensitive to extreme rainfall. • The slope stability was more sensitive to changes in vegetation coverage in the upper zone. • Concentrating bare land patches in the upper zone could improve slope stability. Vegetation exerts positive or negative hydrological effects on slope stability remains controversial due to environmental variability. The impacts of vegetation on slope stability through soil infiltration require further investigation under extreme rainfall. This study induced shallow landslides through artificial rainfall (270 mm total, 60 mm·h −1 intensity) to analyze soil infiltration and pore-water pressure dynamics in experimental plots with four grass coverage levels (0 %, 30 %–40 %, 70 %–80 %, >90 %), and the experiment was repeated twice at each coverage level. By combining properties of vegetation patch and bare land patch with landslide depth/location, slope stability was analyzed using numerical simulation. Results showed that grass did not increase vertical saturated soil hydraulic conductivity. However, the infiltration rates in bare land (BL) plots were lower than grassland plots due to rainfall-induced physical crust, and this maintained lower pore-water pressure (<1.0 kPa) in BL plots during rainfall. Soil pore-water pressure in grassland plots was more sensitive to rainfall, and its rapid increase in shallow soil was the key reason why landslides only occurred in grassland plots with > 90 % coverage. Numerical simulations indicated that increasing coverage (evenly distributed) from 0 % to 70 %, the safety factor decreased, reaching a minimum value of 0.876. Moreover, the slope stability was more sensitive to changes in vegetation coverage in the upper zone. Concentrating bare land patches in the upper zone could improve slope stability, making the safety factor greater than 1.0. These results prove the benefits of bare land patches in upper zone on slope stability under extreme rainfall.