The Peer review has evaluated this group as Average
The research activity, developed since 1975, mainly concerns: - Stability of slopes in static and dynamic conditions, of reinforced earth structures and of shallow and underground excavations. - Backanalysis of field measurements and parameter identification (deterministic and bayesian approaches). - Compatible and equilibrium finite element approaches. Spectral collocation method (in the 1990s this method, frequently used in fluid/gas dynamics, was extended to treat linear and nonlinear engineering problems). - Numerical analysis of seepage, grouting, artificial freezing, soil consolidation. - Experimental investigation on mechanical behaviour of natural and reinforced soil, weak rocks, etc The 2003-2006 activity was focused on three topics: A - EXPERIMENTAL AND NUMERICAL INVESTIGATION ON MECHANICAL BEHAVIOUR OF EARTH REINFORCED WITH GEOTEXTILES KEYWORDS: plane strain test, inclined reinforcement. B - EXPERIMENTAL INVESTIGATION ON BACKFILLING MATERIALS KEYWORDS: seismic and subartic regions, natural sand, lightweight aggregate. C - TUNNEL EXCAVATIONS, REHABILITATION PROCEDURES, EARTHQUAKE EFFECTS KEYWORDS: underground opening, surface displacements, rehabilitation, earthquake damage. Part A Assemblages of fibres were adopted in ancient times in the construction of earth works (Ziggurats) and the "reinforced earth" technique can be seen as the development of those early applications. Since geotextiles carry tensile stresses, their effectiveness is maximised if they are parallel to the major principal stress. This condition, fulfilled in triaxial tests on samples with horizontal reinforcements, leads to the highest values of shear resistance. This resistance, however, could be safely adopted in design only when reinforcements lie along tensile trajectories. Since this is not always possible (in practice reinforcements lie horizontally) the reinforced mass resistance is overestimated, for example at the sloping side of embankments. The experimental and numerical investigation concern an ongoing research initiated after completing the numerical study of an earth wall. The study showed that the available information on samples containing inclined reinforcements was not sufficient to properly model the behaviour of reinforced earth structures. Consequently a laboratory investigation was carried out on prismatic sand samples, showing the influence of reinforcement slope and spacing on the overall properties of the "composite" material. Subsequently, the experimental results were compared with those from finite element analyses based on “inhomogeneous” and “homogeneous” schemes. On these bases it is pointed out that the experimental investigation, motivated by a numerical study, and its numerical modelling represent two necessary and interlaced steps towards the understanding of the mechanical behaviour of reinforced sands and the stress analysis of actual engineering problems. 155 Part B The experimental investigation constitutes part of a research activity carried out at the Department of Mechanics on the behaviour of onshore pipelines subjected to large displacements in seismic and subartic regions. The influence of granular backfill (natural sand or manufactured lightweight aggregate) on buried lifelines suggests identifying proper laboratory procedures for its mechanical characterization. Certain condition to be considered in this process are that the backfill be placed and compacted in wet conditions; that the water content may increase during time and that low-stress levels be in general present, among others. Advantages and shortcomings of the geotechnical tests suitable for mechanical characterization of sand were critically evaluated, considering the low-stress level condition for loose and dense, partially saturated specimens. As to manufactured material having relatively large size grains, its characterisation was restricted to direct shear testing, using a large shearbox. For completeness the obtained resistance was compared with that measured using a small shearbox, since it could be proposed to use a conventional shearbox, with or without scaling the grain size distribution curve. Part C The finite element method (FEM) is frequently used in engineering practice for solving stress analysis problems whose characteristics (e.g. dimensions, mechanical behaviour, etc) are a priori chosen by the designer. This approach restricts the numerical model to the same role of standard hand-calculations or simplified methods for stress analysis. Alternatively the FEM can be used to develop a model of the geotechnical structure for predicting its response to various different conditions with the goal of obtaining a deeper understanding of its behaviour and possible improvements of the design, of the adopted constitutive laws and of their relevant parameters. The backanalysis of measurements performed in situ during time represented an example of the “flexible” use of numerical models in three case histories, concerning underpinning of a bridge pier, stabilization of a slope undergoing cyclic movement and prediction of surface heave caused by grouting (aimed at improving granular soil prior to shallow tunnel excavation). Presently, in cooperation with researchers from Turin and Pavia, information on earthquake damages to underground openings in rock are collected as preliminary step to the review of procedures currently employed in seismic analyses of underground openings and of their rehabilitation procfor the RBSMdures.