As an island state, Singapore obtains a significant portion of its water supply from state-of-the-art rainwater and used water treatment. Back in the 1990s, Singapore’s National Water Agency, PUB launched a massive project to strengthen the nation’s water security: when completed, the "Deep Tunnel Sewerage System", or DTSS for short.

With DTSS Phase 2, deep underground beneath the city-state some 50 kilometers of new tunnel tubes are being built for this purpose. They serve to feed the sewage from the south and west into the new Tuas Water Reclamation Plant. No elaborate pumping stations are needed because thanks to an appropriately planned gradient, the sewage in the tunnels flows to the destination by itself.

20 x Herrenknecht

Herrenknecht is the only supplier of mechanized tunnelling technology for the DTSS II project. The contractors ordered 18 Mixshields and an EPB Shield with diameters between 4.50 and 7.56 meters to bore the sewage collectors at a depth of 35 to 55 meters and line them with concrete segments. A Vertical Shaft Sinking Machine (VSM) from Herrenknecht is used for the safe and fast construction of shafts. Herrenknecht also supplied 12 separation plants for the Mixshield drives and provided comprehensive support services throughout the entire project. This included, for example, remote access to individual machines, enabling them to be monitored and controlled remotely.

In close cooperation with the customers, Herrenknecht engineers adapted the design of the TBMs to the expected complex geological conditions. The planned tunnel runs mainly through the Jurong Formation with limestone, sandstone and argillite. In Lot T-08 the machines have to cross about 3.5 kilometers under an estuary to build the section leading to the Tuas Water Reclamation Plant.