Impact of Hydrological and Mechanical Correlations on the Reliability of Vegetated Slopes

Vegetation enhances the strength characteristics of soil by inducing suction in soil through root water uptake. This in turn affects the stability of a wide variety of geotechnical structures, including slopes. In order to properly assess the stability of vegetated slopes, it is essential to address the hydrological (suction, ψ, and volumetric water content, ψw) and mechanical (cohesion, c, and angle of internal friction, ψ) properties of vegetated soil. Both hydrological and mechanical parameters share negative correlations among each other, by virtue of which the stability of vegetated slopes is significantly affected. This study addresses the individual and combined effects of both ψ-ψw and c-ψ correlations on the reliability of vegetated slopes in a probabilistic framework. The aforementioned dependencies are incorporated utilizing copula theory, which establishes a unique relationship between the individual bivariate density functions and their respective marginal distributions. The bivariate data of the aforementioned hydrological and mechanical parameters are obtained from a field monitoring program conducted on a homogeneously compacted vegetated slope. To better comprehend the unsaturated behavior of vegetated slopes, the effect of ψ-ψw correlation on the soil water characteristic curve (SWCC) of vegetated soil is established. It is found that vegetation induces uncertainties in c-ψ parameters to a greater extent than does ψ-ψw correlation. The randomness induced by vegetation is found to be more in the saturation zone than in the desaturation zone. Moreover, the impact of mechanical correlations on slope stability is found to be more significant than that of hydrological correlation.