THE SINGAPORE government is replacing its sewerage system by Deep Tunnel Sewerage System (DTSS) techniques as part of an upgrade of water infrastructure.
The scheme will be carried out in stages over two decades and provide two large deep tunnels across the island, plus two central water conditioning plants, a system of sewerage conduits into the Straits of Singapore.
About 80km of tunnels will be built up to 50m below surface level with diameters up to 6.5m. These sit beneath the existing water system to catch wastewater by gravity and avoid the expense of pump stations. Some 100km of smaller connecting lines will be included, with the first 60km due to finish in 2008.
Microtunnelling contractor L&M Geotechnic will carry out the work with a Wirth RVS 800 S bought for the job. The machine started on a 2.5km long section of the smaller lines dubbed 'Tuas Hockey Stick' in the south west of the island.
As site investigations revealed coarse-grained silt from the land reclamation, clay and friable sandstone, the head was designed for medium to hard soil and equipped with four cutters.
Torque is up to 415,000Nm.
The soil is very cohesive, consisting of a clay/limestone mixture tending to stick at the crusher cone and the cutting wheel. To avoid clogging, a flushing system directs jets of high pressure water to exposed areas.