Innovative performance-based design of slope stabilizing piles for a railway embankment

The paper presents a simplified displacement-based approach for the design of a slope stabilising system. On the top of the slope, a railway ballasted track induces repeated dynamic loads on the subgrade soil, that, in conjunction with other cyclic environmental loads (seasonal temperature and soil moisture variation) induce a progressive accumulation of soil displacements, despite the safety factors for the slope, if computed by means of traditional limit equilibrium methods, are all larger than one. The design procedure started then from the analysis of preliminary (pre-operam) monitoring data, in order to define the shape and amplitude of the soil displacement field, by interpreting them within a viscoplastic constitutive framework. This allowed to conveniently optimise the slope stabilising system (consisting in FRC piles connected to each other by means of a precast FRC beam and reinforced by pre-stressed ground anchors) with the aim of reducing the soil displacement rates below a prescribed threshold. The focus of the work, rather than presenting advanced constitutive or numerical simulations, is on the design approach, which allows the designer to get a reliable and safe design solution, even in lack of rich and sophisticated site characterisation, as it is often the case in real applications.