Herrenknecht engineers created a pionieering hightech piece of engineering for the Grauholz Tunnel. For the first time, a Herrenknecht tunnel boring machine was design for the conversion from slurry discharge to belt discharge. The unbeatable advantage: different geological formations on a tunnel route can be excavated with a single machine.

The S-50 was designed to operate in slurry mode with active and precise support of the tunnel face in soft ground with groundwater pressure as well as the excavation as an open hard-rock machine with belt discharge. In hard rock, the machine achieved performances up to 29 meters per day and in closed mode up to eleven meters per day. The conversion from one mode to the other could be realized within one day. Another novelty in Swiss tunnel construction was the use of single-shell lining segments.

The Grauholz Tunnel is part of the highspeed rail connection from Bern via Olten to Zurich and, thus, is like the Murgenthal Tunnel (Herrenknecht Single Shield TBM) a center piece of the "Bahn 2000" project with which the Swiss were making their rail network future-proof.