The first of two Herrenknecht mixed shield tunnel boring machines (TBMs) has completed what is claimed to be the world's deepest mechanically excavated tunnel, in the Netherlands.
The 11.34m diameter TBM descended to 65m below sea level and had to work in water pressure up to 6.5bar to bore one of two 6.6km long tunnels under the Westerschelde inlet in Zuid-Beveland in Zeeland in the north of the country. The second TBM, boring the east tunnel, was due reach its destination in mid to late February.
After completion in 2003 the tunnels will provide two layers of traffic in each direction. Main contractor for the project is a joint venture between Kombinatie Middleplaat and Westerschelde. Work began on the east tunnel in the summer of 1999 and on the west that autumn. Excavation of both tunnels started at the north bank in Zeewsch-Vlaanderen towards the south bank in Zuid-Beveland.