Tight squeeze for Singapore sewer drives 08 Nov 2018

Twin tunnels to accommodate two large drains have been excavated for the Stamford diversion water canal in Singapore for client PUB (Public Utility Board), Singapore national water agency and customer Tiong Seng Contractors.

A special challenge for the site crew was the 180m curve radius

Connecting to the existing 5km long Stamford Canal in the heart of Singapore, the new tunnels will expand the existing drainage system and relieve flooding of the city from the Singapore river during heavy rain.

A 5.2m Herrenknecht EPB shield encountered winding bottlenecks and an inner-city drive in one of the most densely populated cities in the world on the challenging 1,000km long twin tunnel project with breakthrough in September 2018.

Due to the inner-city location, the smallest possible diameter of 24m was chosen for the round launch shaft. Because of the limited space, the machine was designed to be as compact as possible.

The 5.2m Herrenknecht shield TBM with 630 kW power drive

Top performance of 91m/week was achieved

After delivery at the job site, the TBM was lowered component by component into the launch shaft until it was ready for its tunnel mission.

On completion of the first tunnel, the machine was returned to its starting point in the launch shaft, where it began excavation of the second tunnel tube. With a drive power of 630kw, the TBM worked its way through complex ground conditions of highly-weathered granite and with small overburdens crossed under the busy city. Additional challenges were posed by the short distance between the two tunnels and a tight curve radius of 180m in the course of the alignment.

Precision and intricate work were called for here: 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 18m/day and 91m/week was possible.

In 2010 and 2011, 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 have become heavier and floods in Singapore more frequent, according to the National Water Agency.

The expansion of the drainage system is designed to prevent this in future and relieve the Stamford Canal by up to 30%.