Effects of mixed planting on stability of three-dimensional vegetated slope under extreme rainfall

To address the ecological restoration and slope stabilization needs, various plant species are utilized in soil bioengineering techniques. Existing studies consider only single-species due to lack of suitable modelling approach for hydro-mechanical reinforcements of individual species in a mixed-species condition. This study presents three-dimensional numerical analyses to investigate the hydrological response and stability of vegetated slopes under mixed planting conditions. A novel 3D numerical model is employed for simulating hydrological and mechanical reinforcements of different plant species, namely grass and shrub. Three series of numerical parametric studies are conducted: grass-only, shrub-only, and mixed grass-shrub planting conditions. The computed results illustrate that the factor of safety under mixed planting condition surpasses that of the shrub-only condition, primarily due to the amplified hydrological benefits. The interplay of plant spacing and mixed planting is also evident in 3D vegetated slopes. As plant spacing widens from 1 m to 3 m, the differences induced by mixed planting in retained suction following a 100-year extreme rainfall event significantly increase from 24 % to 75 %. The enhanced factor of safety resulting from the adoption of a mixed planting strategy escalates from 3 % to 16 %. Therefore, it is recommended that bioengineering designs for slope stabilization can incorporate mixed planting to reduce planting density.