Desiree Willis, Technical Writer, The Robbins Company

Three Robbins main beam TBMs are heading to Malaysia to excavate the near 50km long Pahang-Selangor raw Water Tunnel, currently the country's largest infrastructure project.

Fig1. Location of raw water tunnel

Since the 1980s, Malaysia's capital city, Kuala Lumpur and its surrounding areas have experienced rapid economic growth. The area sources most of its water from a network of local rivers and is forecast to run short of supply in the near future. To address forecasted needs, the Ministry of Energy, Green Technology, and Water has commissioned construction of the 44.6km (27.7 mile) long Pahang-Selangor Raw Water Tunnel. The alignment will transfer water from the Semantan River in Pahang State to the Selangor/Kuala Lumpur region, traveling as far as 1,200m (3,900ft) beneath the Titiwangsa mountain range en-route. Excavation is scheduled to begin in late 2010.

The three 5.2m (17.2ft) diameter Robbins machines and their continuous conveyor muck-haulage systems will be provided to the SNUI JV - a consortium led by Shimizu Corporation and Nishimatsu Construction of Japan and including local companies IJM Corp and UEM Builders Bhd. After delivery and site assembly, the three machines are scheduled to begin boring between October and December 2010.

"The 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 Kawata for the SNUI JV.

The continuous conveyors delivered with each machine will be capable of transporting 400 metric tons (440 US tons) of muck per hour. Each system will be driven using a 370kW main drive plus a 370kW booster drive.

Fig2. Raw water tunnel scheme

Each TBM will excavate 11.6km, 11.6km, and 11.2km sections of the full tunnel system respectively. Each will be assembled outside their particular adits and 'walked' down a 12% grade for launch from NATM-excavated starter tunnels. TBM 3 will be launched first from an intermediate adit, followed by TBM 1 boring in the same direction (Fig 2). TBM 2 will be launched last, boring in the opposite direction and towards TBM 3. Conventional drill+blast headings will complete the remaining tunnel sections.

The 5.2m diameter back-loaded cutterheads are the smallest ever designed using 19in disc cutters - a disc size that will allow for longer cutter life in hard rock. The geology along the alignment is expected to be largely granite of up to 200MPa (29,000psi) UCS with moderate squeezing ground and fault zones. During excavation immediate support of ring beams, rock bolts and shotcrete will be applied from working platforms set directly behind the cutterhead. If unstable ground is encountered, invert thrust systems can be utilized to avoid gripping against the tunnel walls.

Once complete in 2013, the tunnel will convey approximately 27.6m³/sec of water (7,300 gal/sec) for use in domestic and industrial applications. Untreated water will be pumped from the Semantan River and flow via gravity from the intake structure to an outlet connecting basin and a planned water treatment facility near Kuala Lumpur.

References

Malaysian raw water tunnel awarded - TunnelTalk, May 2009

Ministry of Engergy, Green Technology and Water