Phase 2 of deep tunnel sewer system designed to last 100 years

Liyana Othman Channel NewsAsia 20 Nov 17;

SINGAPORE: The second phase of the Deep Tunnel Sewerage System (DTSS) will incorporate innovative features in order for the infrastructure to last 100 years, national water agency PUB said on Monday (Nov 20).

The features include embedded fibre optic cables for remote monitoring; air jumpers to prevent odorous air from escaping into the surroundings; and additional linings to protect against corrosion from bacteria and other micro-organisms.

This was announced at a groundbreaking ceremony on Monday to commemorate the beginning of construction for DTSS Phase 2, which aims to create a network of 40km of deep tunnels and 60km of link sewers.

When completed in 2025, the 100km of tunnels and sewers - equivalent to the length of about 1,100 football fields - will extend the deep tunnel system to cover the western part of Singapore, including the downtown area and major upcoming developments such as Tengah Town and Jurong Lake District.

“The construction of the conveyance system for DTSS Phase 2 will pose a new set of exciting challenges for us, as we look forward to dig deep to navigate through a variety of ground conditions in the Jurong Formation as well as tunnel beneath existing underground infrastructure and even under the sea”, said the director of DTSS Phase 2 Yong Wei Hin, at the groundbreaking ceremony.

Environment and Water Resources Minister Masagos Zulkifli said planning for DTSS started in the 1990s "with a recognition that this is a costly but critical investment that we needed to make to strengthen our long term water security to benefit Singaporeans for generations to come”. DTSS Phase 2 is a S$6.5 billion project, with deep tunnels and link sewers alone costing about S$2.3 billion.

The DTSS Phase 2 conveyance system comprises the South Tunnel, which will transport domestic used water, the Industrial Tunnel for non-domestic used water and associated link sewers, which will largely run under the Ayer Rajah Expressway, as well as underwater.

The tunnels in phase two will connect to the existing ones in the first phase, which is currently serving eastern Singapore. When the entire project is completed in 2025, the whole island will be served by the DTSS.

The DTSS is the nation’s way of collecting and transporting used water from the whole of Singapore to three water reclamation plants - Changi, Kranji and soon, Tuas – for treatment.

The water is then treated and purified to become NEWater, or discharged into the sea.

INNOVATIVE FEATURES FOR A LONGER LIFESPAN

According to the plans, the deep tunnels will be lined with two layers to protect against corrosion, particularly from bacteria and other micro-organisms, as well as gaseous fumes in the harsh sewage environment. For underwater tunnels, there is an additional waterproof membrane to ensure water-tightness.

Fibre optic cables will also be embedded in the concrete lining so as to enable remote monitoring of the tunnels’ structural integrity without the need for physical inspection. PUB said this is especially important when there are construction works in the vicinity.

In the event a physical inspection or repairs are needed, gates will be lowered down vertical shafts to temporarily isolate that part of the tunnel. This makes it dry and safe for workers to carry out inspections. During this time, the incoming used water will be diverted to the link sewer network, before it rejoins the tunnel downstream.

DTSS phase 2 will include innovative features to ensure a 100-year design life.

The second phase of the DTSS will be the first project in Singapore to use air jumpers, whose aim is to push odorous air rising from the deep tunnel back down. The gas will then flow to Odour Control Facilities - which are located away from residential areas - treated, and then released. The air jumpers will also help cut down the number of OFCs.

Once DTSS phase 2 is completed, the existing water reclamation plants at Ulu Pandan and Jurong, as well as pumping stations, will be shut down. This will enable about 214 football fields of land to be freed up for development, PUB said.

“The DTSS is a more cost-effective and sustainable way of meeting Singapore’s used water needs and securing NEWater supply for the future, than simply renewing and expanding the existing conventional used water infrastructure”, added Mr Yong.

It’s also one way to deal with the challenges posed by climate change, like prolonged dry seasons and unpredictable weather patterns, said Mr Masagos.

“It is therefore critical to augment our water sources by reclaiming water so that it can be used again and again, in an endless cycle”, he said, adding that Phase 2 of DTSS will further boost Singapore’s NEWater supply.
Source: CNA/mz


Construction begins for S$6.5 billion, 100km superhighway for used water
SIAU MING EN Today Online 20 Nov 17;

SINGAPORE — Construction work began on Monday (Nov 20) on a 100km underground “superhighway” to transport used water to water reclamation plants, which when completed in 2025, allows 83ha of land to be freed up.

This second phase of the deep tunnel sewerage system (DTSS), estimated to cost S$6.5 billion, will serve the western part of Singapore, including the downtown area and upcoming major developments such as Tengah Town and Jurong Lake District.

It will run largely under the Ayer Rajah Expressway, starting from Keppel Road, crossing undersea at Tuas Bay, and end at the upcoming Tuas Water Reclamation Plant, where a new NEWater factory will be built.

The sloping deep tunnels of the DTSS convey used water from homes and industries by gravity to various water reclamation plants. The used water is then treated and purified into NEWater or discharged into the sea.

When completed, the deep tunnels in the second phase will be connected to those built in the earlier phase — completed in 2008 — to serve the eastern part of Singapore, and the public sewer network.

Speaking at a groundbreaking ceremony on Monday, held at the first tunneling shaft for this phase of the project in Penjuru Road, Minister for the Environment and Water Resources Masagos Zulkifli said Singapore’s NEWater supply will be boosted to up to 55 per cent of the water demand here, when the DTSS is fully up and running with the completion of the second phase.

Currently, NEWater meets 40 per cent of the Republic’s water demand.

Mr Masagos called the DTSS a “key strategic asset” in enhancing Singapore’s water security. Singapore has also experienced unpredictable weather patterns and can expect dry seasons to worsen with climate change.

“It is therefore critical to augment our water sources by reclaiming water so that we can use it again and again, in an endless cycle,” he added.

The existing water reclamation plants at Ulu Pandan and Jurong, and the intermediate pumping stations can also be progressively phased out, once the second phase is completed.

Combined with the land freed from phase one of the project, the DTSS will halve the amount of land taken up by used water infrastructure, from about 300ha in the 1990s to 150ha in the long term.

The total size of the land freed up for higher value development is equivalent to about 214 football fields.

In response to TODAY’s queries on redevelopments on land freed up by the first phase of the DTSS, a spokesperson of the Singapore Land Authority said the site formerly occupied by the Seletar Water Reclamation Plant has been turned into Seletar Aerospace Park.

Where Kim Chuan Water Reclamation Plant stood is being used for industrial development — Defu Industrial City — and for the development of Integrated Construction and Prefabrication Hubs, she said.

The parcel that Bedok Water Reclamation Plant sat on is zoned for industrial and utility uses, she added.

Director of DTSS Phase 2 Yong Wei Hin told reporters that tunneling over 100km of land in Jurong could be challenging, given the geology of the area. There are a lot of sedimentary rock and cavities, which are not ideal for tunneling, he noted.

Nineteen Tunnel Boring Machines will be used to dig at depths of between 35m and 55m below ground and under the sea, which is deeper than some of the underground MRT lines.

Advanced technologies will also be used in the operations and maintenance of the tunnels, said a spokesperson from national water agency PUB.

For instance, the deep tunnels will be lined to protect them against corrosion from bacteria and other micro-organisms. Sections undersea will also have an additional water-tight membrane. These features are expected to make the tunnels last 100 years.

Along the tunnel above ground, devices called air jumpers will be installed to push odorous air rising from the tunnel to odour control facilities downstream and away from residential areas.

Singapore’s water comes from four “national taps”. About half is imported from Johor, Malaysia under two bilateral agreements. The first one expired in 2011 and the second, signed in 1962, will lapse in 2061.

Singapore has had dry weather and Johor has also experienced water supply issues in recent years.

The rest come from NEWater, local catchment areas and desalination. By 2020, the Keppel Marina East Desalination Plant, the first large-scale desalination plant that can treat both seawater and freshwater, will begin operations. In that same year, a fifth desalination plant on Jurong Island will also open.


Work starts on $6.5b deep underground tunnels to transport used water, freeing up land above for redevelopment
Samantha Boh Straits Times 20 Nov 17;

SINGAPORE - Phase two of construction for a $10 billion underground sewage superhighway, one of the world’s largest, started on Monday (Nov 20).

The Deep Tunnel Sewerage System, which will be the conduit for all used water islandwide, will boost water recycling and free up space in land-scarce Singapore.

When completed in 2025, the sloping infrastructure of giant pipes will harness gravity to channel used water in the western parts of the island to a new water reclamation plant in Tuas.

Phase 2 of the project by water agency PUB, which costs $6.5 billion, will also free up an additional 83ha of land - about the size of 116 football fields - currently housing the Ulu Pandan and Jurong Water Reclamation Plants, about 70 pumping stations and many more sewage treatment plants.

Minister for the Environment and Water Resources Masagos Zulkifli marked the start of construction at a ground-breaking ceremony held in Penjuru Road in Jurong East.

He said: "We have experienced how unpredictable weather patterns can be, and we expect dry seasons to worsen with climate change. It is therefore critical to augment our water sources by reclaiming water, so it can be used again and again, in an endless cycle."

DTSS Phase 2 will boost Singapore’s Newater supply, he added.

DTSS will eventually channel all of the island’s used water to water reclamation plants in Changi, Kranji and Tuas, where it will be treated and purified to either produce Newater, or be discharged into the sea.

The tunnels, which sit under the Republic's railway network and above its electricity grid, slope downwards towards the three plants as they are dug at a gradient.

Phase 1, which cost $3.4 billion, was completed in 2008. It serves the eastern parts of Singapore, channelling used water to the Kranji and Changi Water Reclamation Plants.

DTSS Phase 2 will stretch 30km across the western part of Singapore, starting under Keppel Road, at 35m below ground, following the Ayer Rajah Expressway (AYE) all the way to Tuas Road, where it will be 55m below ground. It will also include a separate 10km tunnel in Tuas for industrial used water.

PUB has appointed five contractors to design and build the tunnels, including home-grown company Koh Brothers Eco Engineering.

The system will also comprise 60km of link sewers, which will convey used water from existing sewerage network to the DTSS.

The deep tunnels and link sewers alone will cost about $2.3 billion.

The 30cm thick tunnels in DTSS Phase 2 will be constructed with several safety features.

They will be lined with a special concrete and high density polyethylene (a type of plastic), which protect against corrosion, particularly from bacteria and other microorganisms, and the gaseous fumes from sewage. Sections under the sea will have an additional waterproof membrane layer.

Fibre optic cables will be embedded in the concrete lining, which will be used to monitor the structural integrity of the tunnels remotely, and detects things such as cracks.

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There will be 18 shafts, which will allow human access. Each will come with gates that can be lowered to isolate certain sections of the tunnels for repair works.

Air jumpers, essentially giant fans, within the tunnels will be used to direct sewage fumes to four odour control facilities.

With these features, the tunnels are expected to last 100 years.

Mr Yong Wei Hin, director of DTSS Phase 2 at PUB, said the construction "will pose a new set of exciting challenges for us".

"There are a lot of sedimentary rocks and cavities along the way, which is not ideal for tunneling," he added.