Influence of vegetation in improving the stability of a hill slope in a tropical climate setting

This paper aims at investigating and highlighting the hydrological benefit of vegetation via root water uptake (RWU) in preventing or at the least delaying the rainfall-induced slope failures in Island of Guam. In particular, the results from field instrumentation and monitoring via moisture and suction sensors, laboratory and field testing for geotechnical and hydrological soil properties, and rainfall-induced numerical simulations of transient seepage coupled with slope stability analysis are presented. Two case studies, one with a 45 degrees and another with a 60 degrees slope were studied for three different case scenarios. Only one set of vegetation and root reinforcement data was idealized, and the results confirm that matric suction induced within shallow depth due to RWU helps in providing the buffer, which prevents slope failure during smaller precipitation events. However, this stabilization effect ceases after saturation during long duration precipitation. On the other hand, complimentary analysis considering mechanical root reinforcement effect showed that it is a dominating factor in improving factor of safety even after the slope gets saturated. In general, the native hill slopes with 45 degrees angle were stable, but the one with 60 degrees failed when a real case rainfall event with the climate-vegetation data was applied in this study.