Stability of unsaturated soil slopes covered with Melastoma malabathricum in Singapore

Past studies have shown that slopes covered with vegetation are less susceptible to rainfall-induced slope failures. This research was focused on the unsaturated properties of soil consisting of mangrove roots and their effects on the stability of an old alluvium soil slope during rainfall. Melastoma malabathricum was selected in this study since this mangrove is best suited for tropical climatic conditions. The results of laboratory tests indicated that the air-entry value and shear strength of soil with roots of M. malabathricum were higher than those of the soil without roots. The saturated permeability of the soil with roots was lower than that of the soil without roots. Numerical analyses indicated that the slope without M. malabathricum experienced significant decreases in the factor of safety during rainfall than the slope covered with M. malabathricum. M. malabathricum can thus be used as a vegetative cover for minimising rainwater infiltration in slope layers with a slope angle up to 35 degrees.