Risks assessment and mitigation of an urban shield tunnel demolition and consequent excavation of a branch tunnel

Abstract

The Red Line of the Metropolitano de Lisboa runs between the Oriente station and the Alameda station. At the Oriente side, the line is being extended to the Lisboa Airport, while in the Alameda side, the line is being extended to the new S. Sebastião station, at the heart of Lisboa. For the construction of the Metro link between Alameda and São Sebastião Station, an EPB TBM was used. The construction started with a 22 m circular shaft at the Alameda side, where the TBM was assembled. The access shaft position was lateral to the alignment of the existing main Red Line alignment. A 110 m long NATM connection tunnel was necessary to connect the new branch from Alameda to São Sebastião to the existing one, at the Alameda II station end,...