Analisi numerica dell’efficacia dei muri sacrificali per la riduzione degli spostamenti indotti da scavi profondi

In questa nota si presentano i principali risultati di uno studio parametrico finalizzato al confronto dell’efficacia di diversi tipi di pareti sacrificali, cross-wall (CW) e buttress-wall (BW), nel ridurre il campo di spostamenti indotto da scavi profondi. Nelle analisi sono stati presi in considerazione diversi interassi e diverse geometrie di pareti sacrificali. Il profilo del terreno è costituito da un potente deposito di terreno argilloso sovrastato da uno strato di terreno a grana grossa, e può essere considerato tipico della zona centrale di Roma. Il comportamento del terreno è stato modellato con una legame costitutivo elastico-plastico incrudente. Sia il diaframma sia le pareti sacrificali sono state modellate con elementi solidi, così come gli elementi all’interfaccia terreno-parete e parete-parete. I risultati ottenuti dalle analisi numeriche consentono di mettere in relazione il valore di riduzione dello spostamento con i principali parametri geometrici dei muri sacrificali

The crossing of the historical centre of Roma by the new underground line C: a study of soil-structure interaction for historical buildings

This work deals with the soil structure-interaction problems posed by the construction of the third line of Roma underground (Line C), which, in its central stretch, crosses the historical centre of the city with significant interferences with the archaeological and monumental heritage. The paper describes the methodological approach developed to evaluate the effects of tunnelling on the existing monuments and historical buildings, starting from a careful geotechnical and structural characterisation and including the development of reliable geotechnical and structural models. Experts in several disciplines were committed to this multidisciplinary work, ranging from geologists to geotechnical and structural engineers, archaeologists, and professionals working in the field of conservation and restoration of works of art and monuments. The study of the interaction between the construction activities and the built environment was carried out following procedures of increasing level of complexity, from green field analyses, in which the stiffness of the existing buildings was neglected, to full soil-structure interaction analyses, performed in both two- and three-dimensional conditions, accounting for the stiffness of existing buildings and considering possible long-term effects. The paper illustrates the main aspects of this procedure, using the example case studies of the Basilica di Massenzio and of the building of the Amministrazione Doria Pamphili

Il processo di Building Risk Assessment condotto sulla chiesa di MarmorKirken (Cityringen Metro)

Nell´ambito dei lavori di costruzione della nuova metropolitana di Copenhagen Cityringen, la costruzione di una delle stazioni è stata prevista dinanzi la chiesa di Marmorkirken. Questa chiesa risulta la più importante dell’intera Danimarca, ed è una struttura eterogenea composta da massi granitici, blocchi e colonne di marmo e muratura. Il processo di Building Risk Assessment ha dovuto tenere conto delle pecurialità dei caratteri strutturali della Chiesa; è quindi stato necessario impostare una campagna di rilievi e indagini strutturali per definire le caratteristiche meccaniche dei materiali per impostare un modello ad elementi finiti in grado di valutare con migliore approssimazione gli effetti dello scavo di stazione sulla struttura. Le tempistiche dello scavo della stazione hanno consentito di attuare un confronto continuo tra le previsione numeriche e i dati di monitoraggio per ogni fase di scavo, permettendo di tarare il modello numerico e renderlo ancora più aderente al fenomeno fisico. La stazione è attualmente completata e gli spostamenti finali misurati sulla chiesa sono risultati allineati alle previsioni del modello. Nella nota si descrive l’intero processo di analisi seguito.For the expansion of the existing metro in Copenhagen (Cityringen project), the construction of one station has been envisaged in front of the church of Marmorkirken (out of the 18 new stations in total). This church is the most important of the whole of Denmark, and it’s an ancient heterogeneous structure composed of granite rocks, boulders, marble columns and masonry. The process of the Building Risk Assessment had to take into account the peculiarities of the structure. A cadastral research has been done in order to collect as much of Church’s data as possible, and a campaign of structural investigations has been performed in order to assess the mechanical properties of the building materials; these data have been used as input for the numerical model. For each phase of excavation of the station a continuous comparison has been performed between the numerical forecast and the monitoring data. The comparison allowed for the fine tuning of the numerical model and make it even more adherent to the physical model. The station is actually completed and the final displacements measured on the church have been perfectly aligned with the predictions of the numerical model. The note describes the whole process of analysis

Predicting tunnelling-induced displacements and associated damage to structures

The ability to predict with confidence tunnelling-induced displacements and the associated potential for damage to structures is of increasing importance to the viability of urban tunnelling in soft ground. To assess the response of a structure to tunnelling the three-dimensional nature of both the structure and the construction process should be taken into account in a soil-structure interaction analysis. The paper illustrates some of these issues, with reference to a recent study of the effects of the construction of the new C Line of Roma Underground, currently at the design stage, on several monumental buildings in the historical centre of the city. The interaction of the running tunnels with the monumental structures along the proposed route was evaluated with three-dimensional numerical analyses and the potential for damage was assessed

The role of ground motion characters on the dynamic performance of propped retaining structures.

The paper presents the main results of a number of numerical dynamic analyses of propped embedded retaining structures in the time domain. The numerical model entails the static condition of an excavation 4 m height in presence of a pair of retaining cantilever walls in a dry, coarse-grained soil. Afterwards, two structural elements (props) connecting the two opposite walls have been introduced. Four recorded strong-motion acceleration time histories, and four equivalent analytical wavelets, characterized by frequency content rather different have been applied to the bottom of the model. The analyses were carried out considering different maximum accelerations, by scaling the dynamic input. A nonlinear hysteretic soil model coupled with a Mohr-Coulomb strength rule has been adopted. The results of the analyses show the role played by a number of parameters that characterize the seismic signal and the effects of the seismic response on the increment of forces acting on structural elements

Dynamic analyses of propped retaining structures

The paper presents the main results of several numerical dynamic analyses of propped embedded retaining structures. The numerical model entails the static condition of an excavation 4m height in presence of a pair of retaining cantilever walls in a dry, coarse grained soil. Successively, two structural elements (props) connecting the opposite walls have been introduced. Two strong motion acceleration time histories, recorded during two Italian earthquakes, and two equivalent analytical waveforms have been applied to the bottom of the model. The results indicate a very complex response of the system, due to the effects of local seismic response and soil-structure interaction phenomena. Increments of forces acting on structural elements due to seismic actions are significant; however, yield bending moments of wall section are only reached for seismic events of high intensity. © 2014 Taylor & Francis Group, London

Predicting tunnelling-induced displacements and associated damage to structures

The ability to predict with confidence tunnelling-induced displacements and the associated potential for damage to structures is of increasing importance to the viability of urban tunnelling in soft ground. To assess the response of a structure to tunnelling the three-dimensional nature of both the structure and the construction process should be taken into account in a soil-structure interaction analysis. The paper illustrates some of these issues, with reference to a recent study of the effects of the construction of the new C Line of Roma Underground, currently at the design stage, on several monumental buildings in the historical centre of the city. The interaction of the running tunnels with the monumental structures along the proposed route was evaluated with three-dimensional numerical analyses and the potential for damage was assessed

A study of the interaction between the new C line of Roma underground and the Aurelian Wall

A study of the effects of the construction of the C Line of Roma Underground on the Aurelian Wall has been carried out as a research project sponsored by the municipality of Roma through STA S.p.A. This paper summarises the results of the study for a section where the two closed-shield (10m in diameter) running tunnels pass directly beneath the Wall, with a skew of about 45 degrees. At first, ground movements induced from construction of the tunnels, for different positions of the excavation face, were estimated in greenfield conditions using empirical methods. In a second stage, three dimensional finite difference analyses were carried out to simulate the interaction between the Wall and the construction of the tunnels. A distinctive feature of the research was the extended investigation aimed at an adequate definition of a model of the subsoil and of the geometry and quality of the foundations of the Wall

A study of the interaction between the new C line of Roma underground and the Aurelian Wall

A study of the effects of the construction of the C Line of Roma Underground on the Aurelian Wall has been carried out as a research project sponsored by the municipality of Roma through STA S.p.A. This paper summarises the results of the study for a section where the two closed-shield (10 m in diameter) running tunnels pass directly beneath the Wall, with a skew of about 45°. At first, ground movements induced from construction of the tunnels, for different positions of the excavation face, were estimated in greenfield conditions using empirical methods. In a second stage, three dimensional finite difference analyses were carried out to simulate the interaction between the Wall and the construction of the tunnels. A distinctive feature of the research was the extended investigation aimed at an adequate definition of a model of the subsoil and of the geometry and quality of the foundations of the Wall. © 2006 Taylor & Francis Group