Grafenort – Engelberg Tunnel

Work was delayed by two years due to a particularly severe flood that started in August 2005; it had been recognised beforehand that water ingress was a particular threat, thus the project included the construction of a concrete inner vault.

Various risk assessments were performed and mitigation measures implemented due to some of the surrounding local geography being particularly vulnerable to floods, landslides, and avalanches.

The specific route selected for the tunnel featured gradients varying between 6% and 10.5% along a total length of 4,060 meters (2.5 miles), considerably superior to the old surface alignment that involved a much greater ascent.

[4][7] Multiple technical challenges were encountered during the construction phase;[8] these have been attributed with a significant rise in the project's cost, totalling 176.5 million CHF.

[10] During the fitting-out phase of the tunnel's construction, some relatively innovative techniques were employed to accelerate the rate of work, such as the staged installation of the overhead conductor rails, track, and signalling/communication equipment.