In the Faido section of the Gotthard Base Tunnel (GBT), two open gripper tunnel boring machines (TBM) with a bored diameter of 9.4 m are each driving about 11 km of single-track tunnel. No extensive fault zones were expected in the entire section except for the Piora-Mulde. A special tunnel was driven to investigate the Piora-Mulde, from which investigation boreholes were drilled down to tunnel level. Because of the finding of sugar-grain dolomite, the tunnelling work was tendered by drilling and blasting as well as mechanically, but the tenders led to the award being based on TBM tunnelling.In the course of construction, a stretch some hundreds of metres long unexpectedly had to be bored through squeezing rock, where the temporary support was destroyed and the West TBM and backup almost became jammed. This article describes the experience from the mechanical tunnelling of the Faido section and then gives details about the intended support, the design of the TBM, the difficulties that arose and the experiences gained. ProjectContractually, the Faido section is combined with the Bodio section. After the two open TBMs had completed the Bodio section between 2002 and 2006, they were refurbished in the assembly cavern at the Faido multi-function railway station (MFS) for further tunnelling towards Sedrun. As had already been laid down in the construction contract for the Faido tunnel section, the intention was to increase the cutterhead diameter from the Bodio section of 8.8 m to 9.3 m. On account of the experience with TBM tunnelling in the Bodio section and the excavation of the MFS Faido, where very squeezing conditions were encountered in places, and the fact that hydraulically extendable overcutters did not work on the Bodio section, the decision was made to increase the bore diameter to 9.4 m. The geological conditions encountered at the TBM starting area were flatly bedded and relatively weak Lucomagno gneiss. The overburden at starting was 1,500 m and increasing to a maximum of 2,500 m. It was decided to use movable gauge cutters for an achievable bore diameter of 9.5 m. This was intended to create sufficient room for displacement and for support measures.The design of the cutter head draws on experience from the Raron-Ferden drive of the Loetschberg Base Tunnel. The cutterhead is flat and closed and fitted with
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.