Last Breakthrough in the Uetliberg Tunnel with Tunnel Bore Extender (TBE) Using Undercutting TechniqueOn 18th May, 2006 the Uetliberg tunnel construction crew celebrated the TBE's last breakthrough in the second tube to Chur. The tunnel bore extender (TBE), a technology developed and assembled by Wirth, had started in June 2005 enlarging the 5 m-diameter pilot tunnel to a diameter of between 14.1 and 14.4 m. After driving 1,845 m, the machine reached its goal. Visit www.wirth-europe.comThe Uetliberg tunnel forms part of Zurich's new outer ring road in Switzerland. It comprises two parallel tunnel tubes, Basel and Chur, each with a length of 4.4 km, to connect the Birmensdorf bypass (N20) in the west to the existing Zurich-Chur national motorway (A3) in the east. Click here and here. The pilot tunnel was not only for subsurface investigation. It also gave the possibility to evacuate the dust away from the working miners. The third function of the pilot tunnel was for bracing the cutterhead of the TBE.With the undercutting technique of the TBE, the cutting rollers worked against the rock's tensile strength, which is much lower than its compressive strength. This reduced the energy consumption for excavating the molasse rock (sandstone and marl) by 50%.Inner works, in particular at the tunnel crown and walls, are now under way as well as the installation of the roadway concreting and paving, drainage system, hydrant piping and electromechanical equipment. It is now expected that the Uetliberg tunnel will be opened for traffic at the end of 2008. Click here and ch/24. Visit www.westumfahrung.ch, www.uetlibergtunnel.ch, www.arge-uetli.ch, www.amberg.ch and www.rowa-ag.ch/images/PDFs/ref_Uetliberg_e.pdf 24/06.