Stability of Tropical Residual Soil Slope Reinforced by Live Pole: Experimental and Numerical Investigations

Abstract

The occurrence of numerous shallow slope failures in Malaysia has resulted in the slope stabilization using live poles as a cheaper and eco-friendly measure. Woody vegetations or live poles were used to reinforce the slope of residual tropical soil at three sites to improve stability of slopes as they provide an immediate shear strength enhancement and modify the saturated soil water regime (mechanical and hydrological effects). The branches of 11 trees/shrubs were tested for root and stem growth in containers under shade-house conditions and three species (Dillenia indica, Dillenia suffruticosa and Hibiscus tiliaceus) were shortlisted based on root growth, diameter and length of root, and survival rate for further evaluating their mechanical strength. Based on the results of the mechanical tests (bending, shear and tensile strength), two species (D. suffruticosa and H. tiliaceus) were finally selected for planting on the slopes. Laboratory tests were also carried out on these root and soil matrix for the determination of its shear strength parameters. The live poles from these two selected trees were planted on three slopes to be monitored for 12 months to observe their growth for the purpose of providing low-cost and environmentally suitable alternative to the conventional methods of slope stabilization. Finally, the stability analysis of the slopes was carried out using finite element software PLAXIS. It was observed that Dillenia suffruticosa and Hibiscus tiliaceus can be used to stabilize slopes against failure. The results obtained from PLAXIS showed that the factor of safety of the slopes increased significantly by the reinforcing effects of the live poles.