Climatic effects on pore-water pressure, deformation and stress mobilization of a vegetated volcanic soil slope in Hong Kong

Rainfall-induced landslide has been increasingly reported in the past 20 years due to increasing intense rainfall under the impact of global climate change. Previous research has investigated the hydrological behaviour of soil slopes extensively, including the responses of pore-water pressure, water content and groundwater table. Mechanical slope behaviour in relation to stress-deformation characteristics is rarely studied, especially for residual and volcanic soils that are typically found in the sub-tropical region of the world. In this keynote paper, some new findings from a comprehensive field monitoring work conducted in a volcanic soil slope in Hong Kong are summarised and reported. The field monitoring programme included two parts: Part I - in-situ measurements of soil hydraulic properties; and Part II - field monitoring of groundwater responses and slope movements due to climatic effects. In-situ measured stress-dependent soil-water retention curves (SDSWRCs) and permeability functions of unsaturated volcanic soils are used to interpret the slope hydrological responses through a three-dimensional anisotropic transient seepage analysis. Based on the improved understanding of the slope hydrology, some observed seasonal slope movements and the associated mobilisation of soil stress are explained under the framework of unsaturated soil mechanics.