CHARACTERISTICS OF UNSATURATED SOIL SLOPE COVERED WITH CAPILLARY BARRIER SYSTEM AND DEEP-ROOTED GRASS UNDER DIFFERENT RAINFALL PATTERNS

Rainfall-induced slope failures commonly occur in residual soil slopes. Slope failures are triggered by the reduction in soil strength. This is attributed to the decrease in soil suction due to rainwater infiltration. Slope covers like capillary barrier system and vegetative cover are effective methods that can be used to prevent rainfall-induced slope failures. The capillary barrier system is able to limit the rainwater infiltration, and vegetation can contribute to the increase in soil strength. Vetiver grass is widely planted in tropical and subtropical areas of the world for soil and water conservation. This study investigates the characteristics of unsaturated soil slope covered with capillary barrier system and Vetiver grass in comparison with the original slope through numerical analyses and field measurements. The analyses were carried out under the advanced, normal, and delayed rainfall patterns. The results of the analyses indicated that the capillary barrier system played a more significant role than the Vetiver grass in maintaining slope stability, although both the capillary barrier system and Vetiver grass contributed to the slope stability. In addition, both numerical analyses and field measurements showed that under the delayed and normal rainfall patterns, when antecedent rainwater infiltration could increase the soil moisture, the capillary barrier system performed much better compared to Vetiver grass in maintaining soil matric suctions and slope stability