Singapore is the world leader in sustainable water and sewage management. Around 30% of drinking water requirements are covered by seawater desalination plants, around 40% is obtained by means of state-of-the-art rainwater and sewage treatment. Only a small proportion still needs to be imported from neighboring Malaysia. And the Public Utilities Board (PUB) continues to invest in the efficiency of the infrastructure for the collection and treatment of sewage.

With the Deep Tunnel Sewerage System (DTSS) Phase II, 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 with diameters of 10 to 12 meters and depths between 35 and 60 meters.

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.