A Herrenknecht S-975 EPB Shield has been used by Tiong Seng Contractors (Pte) Ltd to bore two 1,000-m-long drainage tunnels in Singapore. The tunnel boring machine (TBM) has a shield diameter of 5,250 mm and torque of 2,739 kNm. The final TBM breakthrough occurred in December 2017.
The new tunnels expand the existing drainage system and will relieve the Singapore River in the long-term, especially during heavy rain, and thus reducing the risk of flooding in the country. The new twin tunnels complement the existing 5-km-long Stamford Canal.
Due to the inner-city location, the smallest possible diameter of 24 m was chosen for the round launch shaft. With such a limited space, the TBM was made to be as compact as possible. Its individual parts arrived just-in-time at the jobsite. Afterwards the machine was lowered carefully into the launch shaft, component by component, until it was ready for operation.
Upon completion of the first tunnel, the TBM was returned to its starting point in the launch shaft, where it then began excavation of the second tunnel tube. Featuring a 630-kW drive power, the Herrenknecht S-975 worked its way through complex ground conditions (highly weathered granite) and with small overburdens crossed under the busy inner city, surrounded by skyscrapers with shopping malls and apartments.
In 2010 and 2011, Singapore’s Orchard Road - which runs near the Stamford Canal - was repeatedly affected by major flooding because the existing drain could not accommodate the water masses during heavy rain and flash floods. In recent years, rains in Singapore have become heavier and floods more frequent, according to the National Water Agency. The expansion of the drainage system is designed to prevent this problem in future and relieve the Stamford Canal by up to 30%.
Additional challenges on the project were posed by the short distance between the two tunnels and a tight curve radius of 180 m in the course of the alignment. As such, precision and intricate work was required. With shield articulation cylinders, the curve drive was continuously adjusted so that deviations were always within the tolerance. In this way, a continuous advance with top performances of up to 18 m per day and 91 m per week could be achieved.