Better-than-expected results for the first of two tunnel drives under Singapore airport have been achieved during the last month. Settlement was less than 2mm for the passage under Runway One, which is in continuous use for major international flights.
“It went exceptionally well. We had been anticipating anything between 2-5mm, so this was excellent,” said Michael Thomas, Singapore’s Land Transport Authority project manager for the airport tunnel.
The 3.5km long bore, and a parallel drive due to reach the runway point this month, are part of the Changi airport extension to the Singapore Mass Rapid Transit system. A 6km spur from the existing East-West line will connect the airport to the city centre.
A “Rolls-Royce” specification Lovat EPB machine negotiated the 280m under the 60m wide runway and a 130m wide taxiway alongside without incident. The 6.2m outside diameter TBM was passing through Old Alluvium, a material considered to be more like a weakly cemented rock than its name would suggest.
A sophisticated, on-board German Tacs guidance system and extensive above-ground monitoring combined to control ground movement for what had been the most critical part of the route. The tacs displays are 99% replicated above ground, allowing the LTA to monitor what is happening.
The $10M machine was on course to break through into the tunnel excavation at the end of June.
The LTA and contractor team had negotiated with Singapore’s airports authority for access to the restricted airside runway several times a day for surveying. Additionally, a robotic total station scanned surveying prisms set along the runway edge to alert on unforeseen movement.
Contractor Nishimatsu of Japan began work on the US$61.8M tunnel in July 1999 with the first of two drives dropping down 2.2% from an elevated track section at Singapore’s exhibition centre.
A second drive began that September with both passing under a main highway and along the airport perimeter before curving into an underground station between the two terminals.
