EXTENDING LINE D OF THE LYONS METRO

This article describes the extension of Line D of the Lyons metro in France into the Vaise quarter of Lyons; the extension will also enable the construction of a multi-modal public transport interchange there. It was not feasible to use cut-and-cover for any part of the project. A method of tunnelling under buildings was sought, which would not require any subsequent urban renovation. Geotechnical surveys were conducted, to determine which type of tunnelling should be used in the various ground types found. Alluvium and clay, sometimes of an almost liquid consistency, were found, together with gravelly sand alluviums and aquifers, so that the geology was very difficult. The inconsistent ground could mean sizeable collapse. The varying position of the gneiss platform made the overall profile of the tunnel very delicate. It was decided to use a Herrenknecht Mixshield slurry shield and earth air pressure balance tunnelling machine. The two stations in the extension were built as open cut excavations, using the support of cast segments. The central part of the route, drilled by the tunnelling machine, included two 900m long parallel tubes with 5.3m internal diameter. There were many exploratory borings and trial sections, and computer monitoring was used. The tunnel segments were injection grouted.