Slope stability thresholds for vegetated hillslopes: a composite model

Abstract

Location of the critical shear plane (CSP) plays a major role in determining landslide-initiation thresholds. Depth to the CSP increases as the soil shear strength increases. Tree roots provide a significant strength contribution to soil shear strength. Our objective is to understand how vegetation can be used to increase landslide-initiation thresholds by changing the location of the CSP. This will enable us to select and compare combinations of plant species and densities to suit any given situation to increase landslide-initiation thresholds and improve slope stability. The CSP location is estimated incorporating available root cross-sectional area – root depth data in the stability analysis in terms of energy. The energy approach has been developed to take into account the contribution of the roots to soil strength. Generalization of the original energy approach is required to enable its use outside our study areas. Once depth to the CSP is found, the time for the wetting front to reach it is found using a soil-water infiltration model. The composite model described may be used as a simple tool to choose the most appropriate plant density to maximize the stability of a given hillslope. A worked example of the model demonstrates how the approximate thresholds for different hillslopes with known plant densities under different climatic conditions are estimated.Key words: slope stability, safety factor, roots, energy, threshold.