Combined measure of geometry optimization and vegetation for expansive soil slopes

Expansive soil swells upon wetting and shrinks upon drying. During repeated drying-wetting cycles, expansive soil slope can show desiccation cracks on the slope surface to provide pathways for rainwater infiltration. Hence, the conventional method of cutting a slope with a gentle inclination becomes less effective for expansive soil slope, where the magnitude of rainfall infiltration outweighs the amount of surface runoff. The combination of steep slope and vegetation is proposed and evaluated in this investigation. A field test is conducted to understand the slope condition after artificial rainfalls. Controlled laboratory tests are also performed to compare the behaviour of bare and vegetated slopes for use to calibrate a numerical model. A numerical parametric study is then carried out to assess the influence of vegetation, rainfall precipitation, and soil properties. It is found that erosion occurs on the slope surface, which can be prevented by vegetation due to the interception effect. Larger leaf area and greater root depth can reduce the water content in the soil, contributing to the increase of shear strength. A steep slope is beneficial to reduce the rainfall infiltration and maximize the surface runoff.