ABSTRACT:
The Susten Pass road in central Switzerland was constructed from 1938 to 1946 and follows the topographic feature caused by the northern boundary of the intrusive body, known as the Aar massif, in the central Alps. The road has since become a major tourist attraction, but the tunnels no longer fulfilled requirements for traffic space and safety. During winter the road was covered with ice from inflowing water, and the tunnel lining had deteriorated due to freeze-thaw effects. The true ground conditions did not reveal themselves prior to the reconstruction of the tunnels and caused various problems, once in the tunnel and near the portals. The shear zones were all of different character, but are related to the multiphase tectonic sequence of the zone during formation of the Alps.
1 GENERAL DESCRIPTION
1.1 Location
The Susten Pass is located in central Switzerland and runs parallel to the main structure of the Alps. It links Innertkirchen in the Bernese Oberland to Wassen on the Gotthard road which is the main northsouth link through the Alps (Fig. 1). The 36 km long road over the Susten Pass (elevation 2,224 m) was built from 1938 to 1946 and was initially considered a strategic road within the Swiss defence planning. After World War II the road became a major tourist attraction as it passes through an area of particular natural beauty (Zschokke 1997) and is part of practical and popular round trips over several Alpine passes. The 14 km long section, which is open to traffic all year round, begins at the western base of the Susten Pass road at Innertkirchen (elevation 622 m) and reaches the village of Gadmen with a population of a few hundred inhabitants at 1,200 m altitude.
