The Peer review has evaluated this group as Excellent
(A) Shallow foundations under cyclic loading. In a country like Italy, characterised by high seismic hazard and vast cultural heritage, the protection of historical monuments against the effects of seismic events is of great importance. The seismic safety of these structures is usually evaluated by disregarding soil-structure interaction, that can instead play an important role. The aim of this research consists in introducing simplified approaches for taking numerically into account soil-structure interaction in cyclic conditions. This goal is reached by interpreting the foundation system as a macro-element, whose mechanical response is described by an elastohypoplastic constitutive relationship. The implemented constitutive relationship, which has been validated on the experimental results obtained at Politecnico di Milano on small scale prototypes, is capable of simulating both the mechanical response of the system during each cycle and the ratcheting effect associated to a large amount of cycles. In this perspective, also cyclic finite element analyses were performed by implementing different types of elasto-plastic constitutive relationships for the unit volume of soil. These latter were used to calibrate the macro-element constitutive parameters. The same problem was also studied by considering some techniques finalised to reduce cyclic settlements, in particular geotextile reinforced foundations were studied. The effects of environmental loading on foundations, such as drying-wetting cycles, or degradation by chemical attack of the foundation soils have been studied too. It is also important to stress that some researchers of the group are among the best known experts at International level in geotechnical earthquake engineering and dynamic soil-structure interaction analyses. They are presently involved in different research projects, dealing with the seismic response of shallow foundations, of flexible retaining structures and underground structures such as buried pipelines and tunnels. (B) Pipes along unstable slopes and/or active faults. The analysis of the mechanical response of pipelines subject to soil mass movements is a crucial problem in the design and in the management of this particular type of lifelines. Temporal evolution of landslides, geometrical effects and soilpipe interaction analysis are the main aspects of the problem. For numerically simulate the response of the structure, usually the structure is discretised in linear finite elements and the interaction between pipelines and soil is described by means of lumped uncoupled elastoplastic springs. In order to better simulate the interaction between the soil and the pipe the coupling effects between loads and displacements must be investigated. The springs at each node of the pipe can be substituted by a “macroelement” capable of taking such coupling into account. The failure locus is piecewise linearised and the equations governing the macroelement behaviour are set in a form such that an elastoplastic linear complementarity problem can be formulated. The numerical code has been implemented in small and large displacements for simulating even Eulerian instabilities within small radius pipes whose axis is parallel to the slope. Once the numerical tool is conceived, the crucial point concerns the comparison of numerical results with monitored data. In this case, this was possible thanks to the data made available by Snam Retegas, the most important company in gas distribution in Italy. Moreover the group has acquired experience both in the creation of earthquake motion scenarios in terms of ground strains, suitable for application to design and/or vulnerability studies of buried pipelines and tunnels, and in the analysis of structural systems such as foundations or pipelines subject to fault-rupture effects. New simplified formulas for earthquake-induced ground strain evaluations have been proposed, together with new simplified approaches and criteria for the seismic assessment of buried structures subject to fault-ruptures 194 (C) Design of artificial tunnel for rockfall protection. This research topic is aimed at highlighting the complex process of impacts of rock boulders on artificial tunnels. This subject has been developed experimentally, theoretically and numerically. The approach followed consists in analysing separately the phase of impact of boulders on the soil layer, the propagation of the stress wave within the dissipative cushion and the dynamic response of the structure. Two real scale experimental test series were performed at the Aerospace Laboratory of Politecnico di Milano and on a real artificial tunnel thanks to the collaboration with Veneto Strade S.p.A., a regional company managing the highway network in the North East of Italy. As far as the numerical approach is concerned, the experimental results were simulated by using DEM, FEM and SEM codes.
Claudio di Prisco