On 18 May, the second tube of the Uetliberg Tunnel in Switzerland was completed using Wirth’s 14.4m diameter tunnel reamer. The reamer expanded a previously bored 5m diameter pilot tunnel and maintained 18m advances daily.
Wirth claims to have pioneered reaming technology in the 1970s. Since then it has been used for highspeed rail tunnels in Spain, inclined shafts for hydroelectric schemes in Korea and Japan and road tunnels in Switzerland and Italy. The singular claim for the Uetliberg application is that is marks the first time that Wirth has combined reaming with undercutting to break the rock in tension rather than in compression when it is much stronger. This is said to offer significant savings in energy costs although it is unclear whether the pilot bore energy figures are included in this claim. The performance per cutter is improved, yet with the approach requires less installed power than a standard fullface TBM cutting a similar section. Wirth said it is only 50% of the weight of such a fullface machine.
The Uetliberg tunnel features two parallel tubes 4.4km long that will form part of the new outer ringroad system for Zürich when commissioned. An initial 5m diameter pilot tunnel was bored for each using a Wirth hardrock TBM. The Tunnel Bore Extender (TBE) was then used to ream out the pilots to the final size. Wirth told T&TI the 14.4m diameter TBE is the world’s biggest hard rock tunnelling machine.
The first tube was completed in February last year, (T&TI, April ‘05, p10), following which the TBE was relocated to commence the second bore in June 2005. Wirth told T&TI that after initial adjustments, up to 18m daily drivages were achieved.
