Designing underground tunnels for Singapore’s water treatment network

Designing the Deep Tunnel Sewerage System Phase 2 (DTSS2)

DTSS2 covers 98 km of deep tunnels in western Singapore, extending the existing network for Public Utilities Board (PUB), Singapore’s National Water Agency. We delivered tunnelling, geotechnical, and civil and structural engineering services for 10.1km of tunnels for Penta Ocean Construction Co.,Ltd and Koh Brothers Building & Civil Engineering Contractor Joint Venture (POKB JV) .  

We designed the tunnels and associated hydraulic structures which convey used water to the Tuas Water Reclamation Plant (TWRP). These structures include: 3km South Tunnel, 7.1km Industrial Tunnel, 16 shafts, six diversion chambers/drop shafts, three air jumpers, and 10 mined tunnels.

Hydraulics design

Our team improved the reference design by combining multiple shaft structures into a single shaft, enhancing buildability, reducing construction time and saving up to 40 per cent of space compared to the original reference design. We designed a vertical deaeration chamber, instead of the commonly used and more space-consuming horizontal design, to meet minimum distance requirements to existing gas transmission pipelines. We commissioned a design verification test, which confirmed that our design meets performance requirements.

Geotechnics and tunnel design

PUB requested the tunnels meet a service life of 100 years and their secondary lining to be made of microbiologically induced corrosion (MIC) resistant concrete. We designed a concrete mix to meet these requirements, consulting with a concrete specialist. We then commissioned accelerated biogenic sulfuric acid corrosion tests, which validated the corrosion-resistance performance of our concrete design mix.  

Civil and structural engineering

We refined the construction methodology in the original design of the hydraulic structures by reducing the number of construction materials to one: MIC-resistant concrete. This approach reduced the total thickness of the tunnel structure by approximately ten per cent, reducing materials, cost and construction time.

Moving treated water from Tuas Water Reclamation Plant to Jurong Island

At TWRP, water undergoes treatment at the Tuas NEWater Factory to transform it into NEWater, which is then transported to be used in factories and industrial estates on Jurong Island.

We provided Shanghai Tunnel Engineering Co (Singapore) Pte Ltd (STEC) with civil engineering and water engineering services for the tunnels which connect TWRP and the Tuas NEWater Factory to Jurong Island. We designed the 1.6km tunnel, two shafts, and provided mechanical and electrical engineering.

Geotechnics and tunnel design

Over 95 per cent of the tunnels are under the seabed and pass under gas transmission pipelines with a vertical clearance of six metres. We provided robust operating parameters for the tunnelling works to ensure safety and protection of the existing infrastructure above and below ground.