Root Reinforcement of Soil with Australian Native Flora

Abstract

Landslides due to slope instability caused significant fatalities and economic losses globally. This thesis explores bio-engineering methods using vegetation for slope stabilisation and soil reinforcement, a cost-effective and ecologically friendly alternative to traditional concrete and steel methods. It specifically investigates the role of native Australian plant species in enhancing slope stability through root reinforcement. The research focuses on the impact of soil water content on root reinforcement, quantifies the tensile strength and elastic modulus of roots, and examines the behavior of roots in unsaturated soils. Experimental methods include laboratory and field pull-out tests on native vegetation, tensile tests on roots, and pull-out tests using a root analogue in unsaturated soil. A numerical model was developed to simulate individual root pull-out in unsaturated conditions, validated through experimental data. Results indicate that soil moisture significantly affects root-soil bundle pull-out strength, with higher soil water content reducing pull-out strength. For individual root analogue, the peak pull-out stress of the root analogue was interpreted using three unsaturated strength models. Among them, the effective stress model by Khalili and Khabbaz’s (1998) aligned most closely with the observed outcomes. The tensile strength of roots shows a negative correlation with both diameter and root moisture content, suggesting a double-power-law relationship. The study highlights the potential of Elaeocarpus reticulatus and Angophora costata for slope reinforcement, considering their root characteristics and ecological benefits. This research contributes to the field by providing data for more accurate root reinforcement models, emphasising the need to consider soil moisture and mechanical interactions between roots and soil in futuring study on root reinforcement of soil.