Piled foundations are largely employed as settlement reducers in the design of artificial embankments on soft soil strata. The commonly employed design methods are, however, based on simplified approaches not allowing the assessment of average and differential settlements at the top of the embankment. With this objective, the authors introduce a generalised constitutive relationship capable of accounting for irreversibilities stemming from both geometrical evolution and soil yielding. The model derives from the interpretation of the results of a campaign of three-dimensional elastic–plastic finite-difference numerical analyses describing the embankment construction process. Numerous simplifying assumptions (for instance smooth pile shaft, drained conditions) have been employed. Nevertheless, this does not compromise the theoretical value of the proposed approach. From a practical point of view, this model is a useful tool for geotechnical engineers to employ with a displacement-based design perspective.

In recent years, the employment of deep foundations as settlement reducers has become increasingly popular in the design of earth embankments over soft soil strata. To further improve the system response, geosynthetic layers are often positioned at the embankment base. Owing to the presence of both piles and geosynthetics, complex interaction mechanisms, transferring stresses towards the piles and reducing those on the soft foundation soil, take place. Although these mechanisms are governed by the relative stiffness of the various elements constituting this system (piles, foundation soil, embankment and georeinforcements), the approaches commonly adopted to design these “geostructures” do not explicitly take into consideration the stiffness of the single element as design parameters. Moreover, the effect of the stepwise embankment construction process is often disregarded. As a consequence, the settlements at the top of the embankment cannot quantitatively be estimated.

In this paper a new model for the evaluation of the settlements at the top of the embankment, considering both the deformability and the yielding of the soils, is presented. The model introduces both the geometry and the soil mechanical properties as constitutive parameters, and explicitly puts in relationship the embankment settlements to the embankment height (herein considered as a generalized loading variable), thus allowing the geotechnician to adopt a direct displacement-based design approach.

Anchored wire meshes, commonly adopted to stabilise potentially unstable slopes in granular soils, are composed of wire meshes, geosynthetics, anchorage bars/ties and spike steel plates. In many cases, this reinforcement system is employed as a “passive” reinforcement, i.e. it transfers loads to the unstable domain only when this develops irreversible displacements. During this displacement accumulation, complex interaction mechanisms between the deformable reinforcement system and the underlying material take place. To study these interaction mechanisms, a series of large displacement 3D FEM numerical analyses is performed. The mechanical behaviour of the material constituting the wire mesh and the soil is reproduced by means of elastic-perfectly plastic constitutive relationships. In particular, for the mesh a von Mises failure condition and an associated flow rule are employed, whereas for the soil a Mohr-Coulomb criterion and a non-associated flow rule. The constitutive parameters are calibrated on a series of experimental punching test results. The numerical results are reported by means of the characteristic curve, relating the penetration of the steel plate to the system reaction force. In order to stress the role of (i) both soil and wire mechanical behaviour and (ii) the spike plate dimensions in influencing the mechanical response of the whole system, the results of a parametric study are finally discussed.

In spite of the increasing diffusion of tunnel boring machines, conventional tunnelling is still preferred for economic reasons in case of short tunnels, unconventional cross sections or irregular tunnel trajectories. In conventional tunnelling, the mechanical response of the tunnel front is a main concern and, when tunnels are excavated in cohesive soils, this is dominated by the time factor, related to geometry, to the mean excavation rate and to the hydro-mechanical properties of the materials involved. This is particularly evident during excavation standstill: front displacements progressively increase with time and, in many cases, the system response under long-term conditions becomes unstable. In conventional tunnelling, a common technique employed to improve the system response (under both short- and long-term conditions) is the installation of fibreglass tubes within the advance core. In this paper, the mechanical response of both unreinforced and reinforced deep tunnel fronts in cohesive soils is experimentally analysed. In particular, the results of a series of 1 g small-scale tests, taking into account both the influence of the excavation rate (the unloading time) on the system response and the evolution with time of the tunnel face displacements, induced by a rapid reduction in the horizontal stress applied on the tunnel face, are reported.