Photo: PUB, Singapore's National Water Agency

COWI wins Singapore super sewer design contract

17.05.18

In partnership with CPG Corporation, COWI has been awarded the design works for Contract T-09 of the Deep Tunnel Sewerage System (DTSS) Phase 2. The contract was awarded by Leighton Asia, who are contracted to Singapore’s National Water Agency, PUB.

The scope includes the design of a 7.9km-long section of sewer tunnel, with a 6m internal diameter, as well as shafts, hydraulic structures and other facilities associated with the sewerage conveyance system.

Focus on South East Asia

COWI has extensive recent experience in mega sewer projects through successful design & build partnerships with multinational contractors in Abu Dhabi, Doha and London.

The contract is the first win for COWI's newly established Singapore office. The multinational engineering group recently announced its best-ever financial results and signaled plans to expand its operations, with South East Asia a particular focus.

"This is a hugely significant contract for COWI" said Andy Sloan, Executive Director for COWI's tunneling business in the UK and SE Asia. "We are extremely pleased to be working with Leighton on this technically challenging project. The win sees us expanding from our base in Hong Kong into the Singapore market where we feel we can bring great value to contractors and clients alike'.

Unique challenges

Singapore is one of the most densely populated cities in the world, bringing major design challenges. The work site is highly constrained, with deep shafts required in challenging geology adjacent to major civil infrastructure.

Under this design contract, COWI and CPG will work closely with Leighton Asia to devise solutions to these challenges, including investigating options to combine temporary work shafts to minimise land take and designing ground improvement measures to reduce any impact on adjacent structures.

Investment in the future

Singapore is building the DTSS Phase 2 to meet its long-term needs for wastewater collection, treatment, reclamation and disposal. The deep tunnels in Phase 2 will connect to the existing deep tunnels in Phase 1 serving the eastern part of Singapore and the public sewer network to create one seamless integrated system. The whole of Singapore will be served by the DTSS when Phase 2 is complete by 2025.

The scheme uses deep tunnel sewers to convey wastewater by gravity to water reclamation plants, where it is purified into ultra-clean, high-grade reclaimed water - known as NEWater - or discharged to the sea through outfalls.

DTSS Phase 1, completed in 2008, saw the construction of a 48km-long deep sewer tunnel in the east and north of Singapore, and a new water reclamation plant at Changi. The tunnels slope downwards towards the plant to negate the need for pumping stations.

Phase 2 will include the construction of 40km of deep tunnel sewer stretching across the western part of Singapore, starting under Keppel Road at 35m below ground and following the Ayer Rajah Expressway (AYE) all the way to Tuas Road, where it will be 55m below ground. Contract T-09 incorporates a key central section of the tunnel in the Pandan Gardens area.

The Phase 2 tunnels will be lined with Microbiological-Influenced Corrosion (MIC) – Resistant Concrete and High Density Polyethylene (HDPE), which will protect against corrosion. Fibre optic cables will be embedded in between this concrete lining to enable remote monitoring of the tunnels' structural integrity.