Tunnelling works for the second phase of the Deep Tunnel Sewerage System (DTSS) has concluded, and the decades-long project will be completed in three years.
Tunnelling for DTSS Phase 2
Tunnelling works for the second phase started in 2019.
The tunnels, built between 35 and 55m below surface, are approximately the size of a single-track MRT tunnel.
Image by Kow Zi Shan.
Image by Kow Zi Shan.
The 98km-long network will channel wastewater from the western Singapore to the Tuas Water Reclamation Plant.
The plant will have an initial capacity of up to 650,000m3 of domestic wastewater per day and up to 150,000m3 of industrial wastewater per day.
This is equivalent to 320 Olympic-sized swimming pools of water.
Tunnelling works for Phase 2 were carried out by five different contractors, and took over 40 million man-hours, with over 5,000 workers contributing to the project at its peak.
What is DTSS and why do we need it?
DTSS is an extensive network of deep tunnel sewers that will collect used water from all over Singapore to centralised water reclamation plants (WRPs) which will be purified into NEWater.
It was first conceived in 1995 as a cost and land efficient solution for Singapore's used water management.
DTSS will free up 150 hectares of land used by water infrastructure, nearly twice the size of Singapore Botanic Gardens.
Less energy will also be required to pump water, as it will be conveyed by gravity to the three water reclamation plants at Tuas, Changi and Kranji.
Image from PUB.
Due to its complexity and scale, the construction of DTSS is being carried out in two phases.
The first phase, which serves the eastern side of Singapore, was completed in 2008.
Altogether, the DTSS network is 206km long, slightly longer than the length of Singapore's coastline.
The entire project costs around S$10 billion and is designed to last for 100 years.
A necessary investment
At the ceremony to mark this milestone on Aug. 21, Minister for Sustainability and the Environment Grace Fu said that the project is a "significant investment" but a "necessary one" to ensure Singapore's water supply stays resilient and sustainable.
"Today, our water demand is 440 million gallons per day, equivalent to 800 Olympic-sized swimming pools. This figure is projected to double by 2065."
While tunnel boring works are completed, the tunnel is not yet ready to receive used water.
Over the next year, PUB will be lining the tunnels with two layers of material to protect them from corrosion.
The Tuas Water Reclamation Plant will also be completed in 2026.
The plant will be located with the National Environment Agency's Integrated Waste Management Facility to form part of Singapore's first integrated used water and solid waste treatment facility, known as Tuas Nexus. It will be fully energy self-sufficient.
Ready in 2026
The original timeline given for the completion of the project was set at 2025.
The national water agency PUB cited the Covid-19 pandemic as the reason for pushing back the completion date by a year.
To combat the disruption in 2020, PUB built two dormitories for DTSS workers and also hosted workers in its offices to reduce their risk of catching Covid-19.
Compared to the first phase, Phase 2 also posed a greater challenge in the tunnelling process.
The tunnels cut through numerous rock types of different properties in the Jurong Formation such as sandstone, siltstone and limestone.
Such varied ground conditions required greater care during the operation of the tunnel boring machine.
Phase 2 also has several new features. There are air jumpers to control air flow, isolation gates that allow for flow diversion, fibre optic cables running throughout the length of the tunnel which remotely monitors the tunnel's structural integrity.
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Top images via Kow Zi Shan.