Together with its joint-venture partner, Kumagai Gumi Co. Ltd., Sembawang E&C was awarded with the design and construction of 5.1km long tunnel project that crosses the alignment of the then newly built twin tunnels of MRT North East Line (NEL). The invert level of the 5.8m internal diameter of NEL twin tunnels was only 2m clearance above the crown of T03 tunnel and therefore additional precautions had to be taken to prevent any potential movement to the existing NEL tunnels.
A 7.2m diameter Dual Mode Tunnel Boring Machine (TBM) was used to drive the tunnel from Braddell Road to Paya Lebar Road some 30 to 35m underground. Despite varying ground conditions along the tunnel drive – from dense sands and silts to loose sands and marine clay – the TBM managed to record a maximum progress of 535m in a month, 150m in a week and 31.5m in a day.
In this project, the T03 TBM had to pass through DTSS Advance Tunnel, a tunnel constructed to provide a barrier between the T03 tunnel and NEL tunnels. Instead of leaving the DTSS Advance Tunnel empty for the T03 TBM to pass through, we made a decision to backfill it then bored through on reviewed of many technical difficulties and risks.
Contract T03’s TBM could travel through the DTSS Advance Tunnel unaided, maintaining normal advance rates, and help the project to safe time and cost as compared to the tender method, without any adverse effect to the NEL twin tunnels.
Design and construction of 5.1km long by 6.5m internal diameter by 30m deep tunnel and 6 shafts.