The effect of tree-induced suction on two-layered slope stability under rainfall infiltration

Abstract

Rainfall-induced landslide is a common problem in tropical region, such as Malaysia. In general, Malaysia is covered extensively with different weathering stage of earth materials, which create non-homogenous layered soil slope profile. The rainfall infiltration in layered slope is complex and it is found the slope stability to be depended on rainfall infiltration mechanisms into the slope. In contrast, vegetation roots help to dissipate the pore-water pressure and create sufficient matric suction in stabilizing the slope. This study focuses on the effect of tree-induced suction in slope stabilization by determining the rainfall infiltration mechanisms into the layered slope in response to rainfall infiltration. A field instrumentation work was carried out on a residual soil slope with and without present of mature Tree Acacia Magnium to monitor variation in developed matric suction on slope under different rainfall patterns. The suction distributions are simulated using numerical modeling by employing selected rainfall data in SEEP/W software. The rate of evaporation and rate of transpiration can be determined by manipulated the model to generate porewater distribution similar to those measured in the field for slope without and with present of tree respectively. Consequently, slope stability analysis is carried out to calculate factor of safety of the slope from the generated pore-water distribution in the modeling. In this study, it is found that the matric suction decreasing when subjected to rainfall but increasing during dry period. The tree helped to maintain the matric suction during rainfall and further to increase the matric suction during dry period. The average evapo-transpiration rate by numerical simulation is 4.64mm/day. The capillary barrier effect maintained negative pore-water pressure for bottom layer hence caused shallow landslide. Continuous rainfall infiltration lead to slope failure and the stability of slope can be increased by tree-induced suction about 59.4%.