THE MECHANISM OF SOIL-BIOENGINEERING FOR SLOPE STABILITY DURING HEAVY RAINFALL ON UNSATURATED SOIL.

Abstract

Slope instability induced by rainfall is a serious geotechnical hazard all over the world. The characteristics of water flow, pore water pressure changes and shear strength of the soil are the main factors involved in slope failure mechanisms. This research begins with a study of the vegetation contribution on shear strength using vetiver as a vegetation specimen. Root observation and determination of root area ratios were carried out in the laboratory. To observe the shear strength, vetiver specimens at 4 and 6 months were tested using direct shear tests. This research also aims to illustrate the mechanism of soil bio-engineering for slope stability induced by rainfall using a rainfall simulator in a geotechnical centrifuge. A sloping rooted surface layer was simulated by polyester fibre in the centrifuge tests. The results indicate that a rise in the groundwater table due to rainwater infiltration was responsible for slope failure and failure near the toe propagated up-slope in a bare soil slope. The test results also reveal that roots can help to reduce the infiltration of rainwater into the ground, delay a rise in groundwater table and increase the shear strength of the soil. To confirm this, the transient and limit equilibrium analysis were conducted. The important parameters incorporated in transient analysis are volumetric of water content and hydraulic conductivity as well as apparent cohesion and friction angle of root-reinforced soils. The analysis result has shown agreement with the trends observed in the centrifuge tests.