As part of the works for Thomson-East Coast Line (TEL), LTA embarked on a pilot project to construct pedestrian underpasses with a Rectangular Tunnel Boring Machine (RTBM) at two sites at Havelock and Stevens stations to leverage on this method to increase productivity.
What is an RTBM?
The RTBM uses a mechanised shield tunnelling method used to construct underground pedestrian and vehicles crossings. It is a more effective method compared to conventional cut-and-cover method of constructing these crossings.
The RTBM features a rectangular shield box jacking technique which makes use of the principles of an Earth Pressure Balance Machine during excavation. The thrust cylinders in the box jack remains in the shaft, and push forward the entire box segment. New segments are installed within the shaft as the machine advances. As the RTBM advances and cuts through the soil, it turns the excavated material into a soil paste that is used as pliable, plastic support medium, to balance the pressure conditions at the tunnel face.
The Use of RTBM for TEL Projects
Compared to the conventional cut-and-cover methods used by LTA in our construction projects, the trenchless method with an RTBM brings about an estimated 30% increased productivity or reduction in manpower, seamless and better continuity of work, and higher quality and workmanship.
First RTBM drive at Havelock station
The RTBM was first launched at the site of Havelock station under Zion Road in May 2016 and completed its drive after six months in November 2016. As opposed to the use of conventional cut-and-cover method, the use of the RTBM resulted in a much shorter construction duration.
Second RTBM drive at Stevens station
After completing the pedestrian underpass at the site of Havelock station, the RTBM is currently being deployed at the site of Stevens station to construct an approximately 60m-long pedestrian underpass beneath Dunearn Road, a pair of Wayang Satu viaduct structures, and the Bukit Timah Canal.
With the RTBM, LTA will be able to complete the tunnelling of the pedestrian underpass in January 2018, and the underpass will be able to open to public in year 2020, ahead of the completion of the TEL Stevens station.
With the early opening, pedestrians – including students from Singapore Chinese Girls’ School and St Joseph’s Institution – will be able to cross Dunearn Road and Bukit Timah Road safely and seamlessly with the new underpass that connects between the Downtown Line Stevens station and these schools.