This project involved boring two parallel road tunnels under the busy Western Scheldt estuary in order to link the Dutch regions of Zuid-Beveland and Zeeuwsch-Vlaanderen. Considering the record depth of 65 meters below sea level at which the tunnel had to be constructed and the demanding, varying geological conditions the tunnelling machines had to drive through, this was a truly ambitious project.
The mechanical design of the Herrenknecht Mixshields S-137 and S-138 was ideally suited to cope with the geologically difficult properties of the highly plastic "Boom clay", which can clog tunnelling machines. An open spoke-type cutting wheel with rim, an active center cutter with its own flushing circuit, agitators and a roller crusher in front of the intake ensured that the excavated material was removed with maximum efficiency. The Mixshields proved itself well able to withstand pressures of up to 7.5 bar and completed their tunnelling work in February 2002, after operating successfully for a good two years.
