On the effectiveness of slope-stabilising piles for soils with distinct strain-softening behaviour

The stabilisation of slopes with rows of discrete vertical piles is a commonly adopted method for both cuttings and embankment slopes. The majority of existing design procedures consider the pile only as an additional force or moment acting on the critical slip surface of the unstabilised slope. Based on simplified models, existing design methodologies effectively ignore any interaction of the pile with the evolution of the failure mechanism, while they do not consider important aspects of soil behaviour for slope stability relating to a strain-softening response. This paper presents a numerical investigation that challenges the above-mentioned simplifications, demonstrating the importance of the soil/pile interaction. Two-dimensional plane-strain hydro-mechanically coupled finite-element analyses were performed to simulate the excavation of a slope, considering materials with both a strain-softening and non-softening response. The impact of pile position and time of pile construction on the stability of a cutting were parametrically examined, comparing and contrasting the findings for the different material types. The results suggest that an oversimplification during design regarding the soil/pile interaction could entirely miss the critical failure mechanism.