I CEDIMENTI INDOTTI DALLO SCAVO DEL TUNNEL DELLA NUOVA LINEA B DELLA METRO DI RENNES: INTERPRETAZIONE DEI DATI DI MONITORAGGIO E ANALISI A RITROSO

The thesis aims to present and interpret measurements of tunnelling-induced settlements collected during the construction of the new line B of Rennes (France) underground, with particular focus on the portion included between the TBM introduction shaft and the Station Cleunay. The tunnel is being excavated in a highly fractured rock totally under the water table by an earth pressure balance (EPB) machine. The settlements measurements are back-analysed by means of the classical Gaussian empirical closed-form solutions, both in transverse and longitudinal directions, leading to an accurate description of their evolution and of the EPB tunnelling performance. Moreover, the influence of some excavation parameters (face support pressure, volume and pressure of the injected grout and advancement speed) on the evaluated volume loss is investigated. Finally, a numerical analysis (performed with the numerical code PLAXIS 2D AE) is performed in order to determine the settlements at steady state conditions and make a comparison with the ones obtained from the empirical back-analysis. Two methods, the so called M-stage and Contraction method, have been used to simulate the various phases of the excavation process.