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Lungern Exploratory Tunnel

The towns of Giswil and Lungern were to be relieved of through traffic in conjunction with the upgrading of the A8 (Lucerne-lnterlaken). The Giswil Tunnel went into service at the end of 2004 but a geological exploration was first required for the Lungern Bypass. The Lungern exploratory tunnel driven by mining means is 3,770 m long. From the south, a soft ground zone was penetrated on the dip by drill+blast. The main drive from the north was executed mechanically on the rise. As both headings are located in the crown area of the main tunnel, the drill+blast support is the final one. The drill+blast drive was 244 m long and was located in Quinten Limestone and was driven by full excavation. A 73 m long soft ground section at the centre of the tunnel was secured by means of a pipe umbrella. The mechanised drive was originally planned to be 2,915 m long. However, it increased to some 3,530 m on account of geological difficulties. The tunnel is mainly located in lime and marl formations with an unpredicted earth slip being encountered in Palfris marl. The single pre-tensioned open TBM possesses an excavated diameter of 4.75 m and together with its 125 m long backup weighs 330 t. The excavated material was transported via a conveyor belt to a temporary dump in front of the portal. The TBM was designed in such a manner that all support operations could be executed parallel to the excavation. The peak rate of advance amounted to 45 m per day. The excavation was secured by GFK roof bolts and wet shotcrete with steel fibres while steel arches were installed in poor geological conditions. As from 1,000 tm the ground was no longer stable so that an advance roof heading had to safeguard the TBM drive. The TBM protected by the roof heading progressed with a gap of approx. 5 m to the face. This excavation was supported using steel arches, roof bolts and wet shotcrete. There was no longer any need for this approach as from 1,220 tm. This had consequences on the horizontal alignment of the tunnel. As from 1,000 tm, the tunnel curves with a radius of 500 m upslope. No curve needed to be driven between 1,220 and 1,400 m. As from 1,400 m, a counter-radius of 550 m was adopted towards the southern portal. The new axis of the exploration tunnel now runs parallel to the main tunnel. This part of the exploration tunnel is to be used subsequently as the southern safety tunnel.


  • Country: Switzerland
  • Region: Canton Obwalden
  • Tunnel utilization: Other
  • Type of utilization: Exploratory Tunnel
  • Client: Civil Engineering Department of the Canton Obwalden
  • Consulting Engineer: IUL Ingenieurgemeinschaft N8
  • Contractor: Batigroup AG, Bilfinger BergerAG, Frutiger AG, Carl Garovi AG
  • Main construction method: Trenchless
  • Type of excavation: Tunnel boring machine (TBM)
  • Lining: Shotcrete
  • No. of tubes: 1
  • Tunnel total length: 3,770 m, including 3,530 m driven byTBM
  • Cross-section: 17.26 m² corresponding to 4.75 m diameter
  • Contract Volume: € 27 million
  • Construction start/end: November 2000 to February 2002