Numerical modelling of the application of capillary barrier systems for prevention of rainfall-induced slope instability

The most common cause of slope instability is intense or sustained rainfall, which may induce reduction in soil suction, and thus, shear strength. Capillary barrier systems (CBSs) can be used to prevent rainwater infiltration into the underlying soil and thus, prevent slope instability. The application of CBSs for prevention of slope instability was studied by means of advanced 2D thermo-hydraulic finite element simulations and limit analyses. The roles of materials and thickness of the CBS, slope height and weather conditions were investigated. Climatic conditions of dry and warm (Cagliari, Italy) and wet and cool (London, UK) European areas were simulated. Sloping CBSs having the finer layer made of finer-grained materials, such as silty sand, were proven to be more effective in regions with warm and dry climates (with occasional intense rainfall events), because their key working mechanism is water storage, whereas sloping CBSs having the finer layer made of slightly coarser-grained materials, such as fine sand, are effective under a wider range of climatic conditions, because their key working mechanism is lateral water diversion. The effectiveness of CBSs was found to decrease with increasing slope height. However, two solutions were proven to be effective at widening the range of applicability of CBSs to higher slopes: multi-layered CBSs and multiple drains. All the CBSs analysed were proven to be effective at preventing rainfall-induced slope instability.