Accurate evaluation of undrained shear strength of soils is crucial in geotechnical design and assessment. In the practice, undrained shear strength is obtained most frequently from CPT data, dividing the net cone tip resistance by a cone factor, 𝑁𝑁!". For organic soils, values between 8.6 and 15.3 are reported, depending on the stress history. The cone factor can be conditioned to the results of laboratory tests, although uncertainties remain on the variety of stress paths followed by the soil elements around the tip of the cone, compared to the ones tested in the laboratory. Non-uniqueness in the definition of the cone factor may lead to either unsafe or over-conservative choices, partly undermining both the reliability and the sustainability of the design. This contribution analyses numerically the inversion technique used to determine the undrained shear strength of organic clays, exploiting data from an extensive in situ and laboratory investigation. The adopted constitutive model was calibrated on the results of laboratory tests. Cone penetration tests were simulated performing coupled hydro-mechanical numerical analyses via G-PFEM, developed in the last decade at CIMNE-UPC. The role played by initial stress state and previous stress history upon stress distribution at failure, cone factor and sleeve friction is discussed. The numerical results suggest how the sleeve friction could be used to condition the cone factor depending on the over-consolidation ratio and demonstrate how combining the different available CPT readings with the aid of numerical results may reduce the uncertainty in the estimation of undrained shear strength.

Anchored wire meshes are commonly adopted to stabilize potentially unstable soil slopes. This reinforcement technique, employed either as an active or a passive anchoring system, is commonly designed according to ultimate limit state approaches. In this paper, an interaction model, useful for the design of anchored wire meshes, is proposed. The model is based on the results of a series of 3D large displacement finite element numerical analyses, in which the wire mesh mechanical behaviour is modelled as either an elastic or an elastic–plastic membrane. The model is inspired to standard load–displacement curves for shallow foundations, and the wire mesh presence is taken into account by suitably modifying the bearing capacity formula. The proposed model predictions are compared with experimental punching test results. The use of the model, only requiring the definition of geometry and soil–wire mesh mechanical properties, allows the pre-design of the reinforcement system without performing ad hoc finite element numerical analyses.

The increasing demand of sustainability of the construction of new structures and the necessity of verifying/retrofitting the existing ones require reliable design tools. To this aim, fundamental is gathering new insights in the mechanical response of foundations. As far as shallow foundations are concerned, one aspect commonly disregarded in the current engineering practice is the influence of the mechanical interaction among adjacent foundations. The authors approach this problem by performing a parametric finite element non-linear numerical study on a squared shallow foundation, loaded by a vertical centred load under fully drained conditions. The numerical results put in evidence that the interaction, for any spacing value, causes an initial increase in settlements, whereas the dependence of bearing capacity on spacing seems to be, according to the case, either beneficial or detrimental. For particular geometries and mechanical properties, the reduction in bearing capacity may reach about the 30%. These dependences are justified in the light of the findings at the local scale, i.e. discussing the spatial distributions of irreversible strain, displacement and stress fields as the applied load increases. Finally, the authors have proposed a simplified design approach to derive not only the bearing capacity, but also a preliminary prediction in terms of displacements accounting for the reciprocal foundation interaction.

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.