As part of the works for Singapore’s Thomson-East Coast Line (TEL), the Land Transport Authority (LTA) embarked on a pilot project to construct pedestrian underpasses with a rectangular tunnel boring machine (RTBM) at two sites - the Havelock and Stevens stations - in order to increase productivity.

The RTBM uses a mechanised shield tunnelling method to construct underground pedestrian and vehicles crossings. It is a more effective method compared to conventional cut-and-cover method of constructing these crossings, said LTA.

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.

According to LTA, compared to the conventional cut-and-cover methods used in its construction projects, the trenchless method with an RTBM brings about an estimated 30 percent increased productivity or reduction in manpower, seamless and better continuity of work, and higher quality and workmanship.

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, said LTA.

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 60-m-long pedestrian underpass beneath Dunearn Road, a pair of Wayang Satu viaduct structures, and the Bukit Timah Canal.

With the RTBM, LTA said it 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.

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