Design of slope-stabilizing piles: from Ultimate Limit State approaches to displacement based methods

Slope stabilizing piles are often considered an efficient solution for landslide risk mitigation. They are employed not only to prevent the slope collapse (therefore designed, in this case, by means of Ultimate Limit State analyses referred to the activation of localized failure mechanisms within the soil mass), but even to reduce the soil displacement rate in creeping mechanisms or under seismic actions (designed, in these cases, by employing diplacement-based design approaches). Rigorous design methods would require the numerical solution of a complex soil-structure interaction problem, taking into account the nonlinear behaviour of soil, structure and relative interfaces. These methods are rather well established for research purposes, but they are still too demanding (from both computational and economic viewpoints) to be considered a standard design tool for practical engineering applications. In the last decades, several alternative simplified design methods have been proposed (generally based on the classical solutions for piles under horizontal loads) but numerous aspects of the mechanical behaviour of these stabilizing systems have not been yet fully clarified in a well structured framework. Therefore, this paper is intended to guide the designer from the definition of the geometrical and structural properties of these systems toward a rational application of the design methods, by critically considering the structure performance. The proposed framework can even conceptually be extended to seismic applications.