The US$500m 6km Airport Line will carry MRT passengers from the city centre to Changi Airport in 30 mins. The tunnelled section features 1km of cut+cover and 3.5km of bored tunnels of 5.4m i.d. which feed into a new station at Changi Airport. Nishimatsu Construction Co. is undertaking the US$61.8m Contract 503 – the bored tunnel element. Work began in mid-1998; completion is scheduled for end 2001.
Two 6.2m o.d. Lovat EPBMs were specified and purchased by the LTA after a competitive tendering process and novated to the winning contractor. While not a cheap option, the LTA is confident that it is the correct one, and the highly automated, articulated machines, delivered in June and Aug ’99, are performing well. The contractor has decided to maintain the closed mode configuration throughout the drives and bore through good material with no face pressure. Unusual aspects include heavily armoured cutterheads and provision of chilled air to the face.
The TBMs were erected in the cut+cover tunnels leading from the Expo Station and started on a 2.2% decline on a curve. The drives for the west bound tube started in July 1999, for the east in September. As this was later than originally planned, seven days/week working is enforced. Eleven tonne Tomoe battery locos are used to transport the 5.4m i.d., 1.4m wide rings and remove spoil.
At the time of the visit, the west bound tube had advanced 900m, the east bound 280m. Ground was being conditioned to keep down torque and the operator praised the TACSS guidance system. The lead TBM was about 600m ahead, although this distance is permitted to close to a minimum of 15m. So far, the best advance rate is 77 rings/week or 9 rings/ shift (11 rings/ shift has since been achieved). However, the contractor was looking for 12 rings/shift to achieve targets. In addition to the main drive, the contract also calls for a total of 12 x 15m cross passages to be excavated concurrently with the TBM drive and lined with precast rings from Charcon.
In April 2000, the EPBMs will pass under Runway 1 with 16m cover. The best method of operation for this section will be determined in the 2.5km of drive before entering the airport enclosure. It is anticipated that full closed mode operation will be used for this highly sensitive final section.
Changi Airport Station – Contract 504 – is highly complex, mainly because of the difficulties of accomplishing such a scheme in an operating airport. The three main elements are: the crossover tunnels accommodated in a 170m cut+cover section; the 205m long x 24m wide x 25m deep station box; and the 140m overrun tunnels. All are being built by cut+ cover techniques using diaphragm walls. Ground is reclaimed sand fill and Old Alluvium – material which is highly unstable when wet and highly abrasive.
The new station, awarded to a Kumagai Sembawang JV, lies under the access road network which crosses the main service arteries of the busy airport. During construction of the crossover tunnels under the future Terminal 3, provision has been made for the foundations of the future structure. A cut+cover baggage tunnels is also being built under the running tunnels. The station box is being built as a top-down construction. The finished station will have three levels, including the baggage tunnel.
The 140m overrun tunnels under Terminal 2 are being built in cut+cover in preparation for a future link to a proposed Terminal 4. Detailed monitoring was performed to ensure minimum movement, including the use of a Leica real time monitoring system.
At the time of the visit, the project was behind schedule but was expected to catch up once top down station construction began and operations moved below the surface away from airport operations.
