Uetliberg Tunnel: heading methods and interior works

Abstract

The Uetliberg Tunnel in Switzerland is the key element of Zurich's west bypass project, which is of great national and international importance. The Uetliberg Tunnel Project comprises two parallel tunnel tubes, each 4.4 km long. The two tubes are connected every 300 m by a transverse walkway and every 900 m by a transverse roadway. The SOS niches are spaced 150 m apart. Portal stations with machinery rooms are located at both ends of the tunnel. In the event of traffic backups or fires, an underground ventilation facility can exhaust waste air from specific points through openings in the intermediate roof. Three traffic crossover links are provided for emergencies (accidents, fires, etc.) and maintenance work, one before each portal station and one near the ventilation facility underground. From west to east, the Uetliberg Tunnel passes under two parallel ranges of hills, Ettenberg and Uetliberg. A valley divides the Uetliberg Tunnel into two independent tunnel sections during construction (Eichholz Tunnel L 1/4 710 m and Uetliberg Tunnel L 1/4 3450 m). The tunnel has to be driven through two molasse and three soft ground sections. The molasse sections consist of flat layers of the upper fresh water molasse. The soft ground sections lie partly in the groundwater and comprise very heterogeneous moraine complexes. The standard cross-section of the Uetliberg molasse section is 14.20 m wide and 14.40 m high. The horseshoe cross-section of the other sections is 14.70 m wide and 12.70 m high. The tunnel will be finished with an all-around full seal, which will be drained (pressurelessly) in the Uetliberg molasse section and be built to maintain pressure in the other sections. The soft ground sections will be excavated with the core method of tunnel construction. The Eichholz molasse section will be excavated by blasting in three stages: crown, bench and base. In the Uetliberg molasse section the tunnel will be excavated first with a tunnel boring machine (TBM, diameter 5.00 m) for the pilot tunnel, followed later by a tunnel bore extender (TBE) employing undercutting. The TBE extends the pilot tunnel to the final cross-section of 14.20-14.40 m. The TBE started extending the pilot tunnel bore in April 2003. Its progress over the first 400 m showed that the undercutting principle works well. By May 2004 about 1500 m of tunnel bore will be extended by the machine, so the world's tunnel builders will hear more about the experience with the TBE at the ITA-AITES 2004. The Project costs are about CHF 1.12 billion. The Opening of the Uetliberg Tunnel is planned in 2008. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.