As one of the last sections of the A9 Motorway through the Upper Rhone Valley, the by-pass around the city of Visp is currently under construction, comprising of two blast-and-drill tunnels of 2.7 km and 4.2 km respectively. The shorter tunnel is the more demanding one, as an existing old tunnel is to be incorporated into one of the two tubes while staying in use. This creates a delicate situation at the north portal in terms of construction sequence and slope stability. These factors are discussed in this paper.

1.1 Traffic situation in the upper Rhone valley

When completed in 2017, the Visp by-pass will link the Rhone Motorway A9 from Lake Geneva with the Simplon pass and alleviate the densely populated town of Visp from the commuting traffic to and from Brig (A9-VS). As the industrial area north of Visp makes it difficult to accommodate a 4-lane motorway, it was decided to place the by-pass south of the town in the mountains which mark the junction of the Saas valley with the Rhone valley (Fig. 1).

1.2 Altering an existing tunnel

The two tunnels, the 2.7 km long tunnel Visp to the west and the 4.2 km long Eyholz tunnel to the east, are linked by a bridge crossing Staldbach creek. Tunnel Visp is the shorter one, but has to integrate an existing single-tube tunnel via an underground junction, which will stay in use during construction as access/exit tunnel into the Saas valley and accommodate the tourist traffic toward the well-known skiing resorts Zermatt and Saas Fe. Apart from the caverns necessary for the underground junction and the connecting tube over-passing the new motorway, an unusual design problem is posed by enlarging the existing Vispertal tunnel to become the south tube of the motorway.

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