1,721,020 research outputs found
Un approccio integrato per la valutazione prestazionale della stabilità di una diga ad arco
No full textLa nota presenta un metodo per valutare le prestazioni sismiche di cunei in roccia alle spalle di una diga ad arco, secondo un approccio agli spostamenti di tipo Newmark opportunamente modificato per includere le forze trasmesse dalla diga e tutti i possibili cinematismi tridimensionali del cuneo all’interno della nicchia di distacco. Nell'ipotesi di blocco rigido e assenza di rotazioni, il metodo è in grado di tenere conto delle tre componenti dell'input sismico, il progressivo distacco del blocco dai piani di appoggio del giunto, l'eventuale recupero del contatto e anche il temporaneo distacco completo del blocco attraverso una fase di volo libero. Oltre alle azioni inerziali gravitazionali e sismiche, sono incluse nell’analisi le forze statiche e dinamiche esercitate al contatto diga-cuneo, comprese quelle relative all'interazione inerziale con l'invaso. Il metodo viene applicato per la verifica sismica della diga ad arco-gravità di Ridracoli (Italia), fondata su una formazione rocciosa fittamente stratificata di origine turbiditica. In particolare, la spalla destra viene verificata rispetto alla formazione di cunei adagiati su piani di strato con caratteristiche di resistenza particolarmente scadenti
The role of soil constitutive assumptions in the numerical assessment of tunnel performance under seismic conditions.
No full textAnalisi delle condizioni di stabilità della spalla destra della diga di Ridracoli alla luce degli sviluppi tecnici e normativi
No full textNel presente studio si analizza la stabilità della spalla destra della diga ad arco-gravità di Ridracoli nei confronti di possibili cinematismi lungo le discontinuità della roccia di fondazione. Prove di taglio in sito realizzate durante la costruzione della diga evidenziano la presenza di alcuni livelli marnosi laminati, con parametri di resistenza particolarmente scadenti, all’interno dell’ammasso roccioso fittamente stratificato.
Per consolidare l’ammasso, durante le fasi di scavo propedeutiche alla realizzazione della diga, furono posti in opera numerosi tiranti di ancoraggio. Le analisi sono svolte secondo il metodo all’equilibrio limite tridimensionale e delineano un possibile cinematismo di collasso fortemente condizionato dalla direzione di spinta della diga per effetto arco. L’azione sismica è stata considerata per mezzo di analisi pseudo-statiche, a partire da uno specifico studio sismotettonico
dell’area, che delinea un aumentato quadro di pericolosità sismica rispetto alla situazione progettuale
Remarks on axisymmetric modelling of deep tunnels in argillaceous formations. I: plastic clays
No full textThe paper analyses the response of argillaceous formations to the excavation of deep tunnels, focusing on the role of hydro-mechanical behavior. First, two different types of geologic formations are identified: plastic, soil-like, and stiff, rock-like, argillaceous formations. This paper is specifically concerned with deep tunnels in plastic clays. In particular, the influence of pore pressure changes on the stability of the excavation and on the loading of the support systems is investigated. The state of stress and deformation is analyzed in the short- and long-term, by applying analytical and numerical solutions to the idealized situation of an axisymmetric tunnel. General remarks on the influence of hydro-mechanical coupling, artificial boundary conditions and lining permeability are presented. Theoretical predictions are compared with measurements made in some tunnels excavated in the Boom clay formation at Mol (Belgium). The suggestions provided in the paper may contribute to refining practical design approaches, hence filling the gap between the application of advanced hydro-mechanical models and conventional uncoupled elasto-plastic models. In a companion paper, the behavior of rock-like materials is considered. In particular, the effect of scaly structure, typical of many deep argillaceous formations, and fissure opening around the tunnel walls is examined. Results of conventional and novel models, purposely formulated to analyze such situations, are compared
Progettazione e collaudo di sistema geotermico per lo sfruttamento delle acque di drenaggio presso la galleria di base del Brennero
No full textL’articolo illustra brevemente le fasi di progettazione, installazione e collaudo relative a uno scambiatore geotermico innovativo ideato per sfruttare il calore proveniente dalle acque di drenaggio e operare in gallerie realizzate con scavo meccanizzato. Il prototipo, che nasce dalla collaborazione tra BBT SE e l’Università di Bologna, trova la sua applicazione nel cunicolo esplorativo della Galleria di Base del Brennero
Remarks on axisymmetric modelling of deep tunnels in argillaceous formations. II: fissured argillites
No full textIn a companion paper, basic differences between the hydro-mechanical behaviour of plastic and stiff clay formations were highlighted and some issues, such as the influence of hydro-mechanical coupling and boundary conditions, were pointed out.
This paper focuses on the effect of the scaly structure, frequently caused by tectonic shearing, typical of many relatively old and deep-sited argillaceous formations. Different engineering models for the prediction of short- and long-term response to tunnel excavation are compared. The proposed approaches consider some typical features of the hydro-mechanical behaviour of the plastic annulus around the tunnel, focusing on the influence of fissure opening, which may cause loss of saturation, in the short-term, and a general increase in permeability in the long-term. The case of the Raticosa tunnel (Italy), excavated through tectonised argillites, is chosen as an example case to apply the proposed approaches and investigate the aforementioned issues. Laboratory test results and in situ measurements are also discussed. The interpretation of convergence measurements, with the help of empirical correlations and the results of hydro-mechanical analyses, highlights the relevance of time-dependent creep deformation, which could therefore be tentatively distinguished from deformation due to consolidation.
The potential of an ‘‘observational’’ approach in which early tunnel convergence measurements are used to predict the total final increment in convergence due to time-dependent deformation is also discussed
Influence of hydro-mechanical coupling on tunnel response in clays
No full textThe design of deep tunnels underneath the water-table in clayey soils should carefully take into account the influence of pore pressures and seepage forces on the stability of the excavation and on the loading conditions of the support systems. The paper focuses on the application of analytical solutions and numerical models for the analysis of stress and deformation around deep tunnels, in the short- and long-term, considering the idealized situation of axisymmetric conditions. General remarks on the influence of hydro-mechanical coupling, artificial boundary conditions and lining permeability are presented. Theoretical predictions are compared with measurements made in tunnels excavated in the Boom clay formation at Mol (Belgium)
Practical estimate of deformations and stress relief factors for deep tunnels supported by shotcrete
No full textEven though ground-support interaction in the vicinity of the tunnel face is a typical 3D problem,
tunnel support design is usually based on simplified plane strain models, which are strongly
dependent on the assumed degree of ground stress relief at the time of lining installation. The
paper focuses on tunnels supported by shotcrete close to the face, where the interaction between
the loading process and progressive hardening of the green shotcrete makes the problem timedependent.
A constitutive law characterized by the time-dependent stiffness and strength of the
shotcrete is employed herein. The results of an extensive parametric study based on 3D axisymmetric
models are presented in the form of non-dimensional design charts, which can provide
guidance to a preliminary evaluation of convergences and support loadings.
Moreover a strategy is proposed to enhance the capability of simplified design methods (2D
models, Convergence-Confinement Method). This consists in a ‘‘guided estimate’’ of stress relief
factors, which again is based on the results of 3D time-dependent analyses. Finally, by way of
example, the proposed method is applied to two well-documented case-histories.
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