The alignment will transfer water from the Semantan River in Pahang State to the Selangor/Kuala Lumpur region, travelling as far as 1,200 metres beneath the Titiwangsa mountain range. Excavation is scheduled to begin in late 2010 using three Robbins Main Beam tunnel boring machines (TBM).

The 5.2 metre diameter machines and continuous conveyor systems will be provided to the SNUI joint venture, a consortium led by Shimizu Corporation and Nishimatsu Construction of Japan, along with local companies IJM Corporation and UEM Builders Bhd. After shop assembly, the three machines are scheduled to begin boring between October and December 2010.

“Robbins’ experience in hard rock ground conditions, along with their willingness to work together and be a reliable partner with us, were the main factors in choosing the Main Beam machines,” said Project Manager Mr Kawata.

In addition to the machines, three continuous conveyor systems will be provided for muck removal. The fabric belt conveyors will extend the length of each tunnel section, and will be capable of transporting 400 metric tonnes of muck per hour. Each system will be driven using a 370 kW main drive plus a 370 kW booster drive.

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TBMs 1, 2, and 3 will be used to excavate sections of tunnel that will measure 11.6, 11.6, and 11.2 kilometres in length, respectively. The three machines will be assembled outside their particular adits, then ‘walked’ down a 12 per cent grade for launch from NATM-excavated starter tunnels. TBM 3 will be launched first from an intermediate adit, followed by TBM 1, which will bore in the same direction. TBM 2 will be launched last, boring in the opposite direction towards TBM 3. Conventional drill and blast headings will complete the remaining tunnel sections.

The back-loading cutterheads are the smallest ever designed using 19 inch disc cutters – a size that will allow for longer cutter life in hard rock. Geologic conditions are expected to consist of 200 MPa (29,000 psi) UCS granite, with moderate squeezing ground and fault zones. During excavation, ring beams and rock bolts will be used in addition to shotcrete, which can be applied from working platforms directly behind the cutterhead. If unstable ground is encountered, invert thrust systems can be used to avoid gripping against the tunnel walls.

Once complete in 2013, the tunnel will convey approximately 27.6 cubic metres of water per second (7,300 gallons per second) for use in domestic and industrial applications. Untreated water will be pumped from the Semantan River and will then flow using gravity from the intake structure to an outlet connecting the basin and a planned water treatment facility near Kuala Lumpur.