Rising to new heights with depth

The growth of megacities

Singapore's economy is booming – but the lack of resources presents the island nation with challenges. A new sewerage system and several water treatment plants present numerous solutions. One of many examples that show: The future is decided underground.

The future of Singapore begins in Tuas, at the south-western tip of the island. Between factory buildings, refineries and warehouses, Dirk Schrader puts on a hard hat and greets a group of engineers and technicians in green overalls. Herrenknecht’s General Manager Asia Pacific is standing with his men on the edge of a 60-meter-deep shaft. A blue cutting wheel shines at its base. A blue cutting wheel shines at its base.

End of 2019 began this tunnel boring machine to bore its way meter by meter beneath the city. "Our customers have an ambitious schedule, so we have to work with absolute reliability," says Schrader. Today he wants to discuss the next steps with his colleagues.

Super highway for sewage

68 hectares of building land on remote terrain: this is where city history will soon be written. The "Tuas Water Reclamation Plant", a huge used water treatment plant, is scheduled to go into operation in just a few years. It will be able to process up to 800,000 cubic meters of used water daily. Drinking water is chronically scarce in the island state - the plant is helping to solve an urgent problem.

It is part of a comprehensive system that is currently being installed under Singapore. The "Deep Tunnel Sewerage System", or DTSS for short, is a kind of underground "superhighway" for sewage: more than 200 kilometers of pipes and tunnels measuring up to six meters in diameter are being installed up to 60 meters below the city. The first 100 kilometers of sewerage as well as the Changi water treatment plants in the east were completed in 2008 already.

This first phase of construction, DTSS Phase 1, will be followed by another 100 kilometers to the south and west as well as the treatment plant in Tuas. DTSS Phase 2 is due for completion in 2025. Singapore is investing S$ 6.6 – this is a decisive step toward security of supply.


A model for the world

Lai Lynn Woo, Chief Engineer at Singapore's national water agency, has been involved with the megaproject for more than 20 years. “It will change our city and do so much good," says the geotechnical engineer. She took over project management for DTSS Phase 1. The large water treatment plants in particular are groundbreaking: "In the future, we will reuse up to 85 percent of our wastewater – for industry, but also for households."

As the system operates on a natural gradient and transports sewage to three central treatment plants, around 130 pumping stations in the city can be removed. "We are gaining about 150 hectares of land we can make good use of," explains Woo. A new garbage processing plant will transform waste from the city and from used water into energy. This electricity alone will cover the needs of 300,000 four-room apartments from 2027.

“Cities around the world are following what we are doing here”

Lai Lynn Woo, Chief Engineer at Singapore's national water agency

Solutions underground

For Singapore, the DTSS projects are milestones on the journey from a developing country to an urban laboratory of the future. After independence in 1965, the city-state was faced with problems such as poverty, unemployment and a lack of resources. With its development into a global trade hub it then made the leap to become an industrial nation – within a generation.

Rapid growth with a lack of space – this is a challenge that is decided underground. The metro went into operation in 1987, and today Singapore's route network measures almost 200 kilometers. It is one of the most modern and efficient in the world. Over the years, more and more infrastructure has moved below ground: roads and pedestrian paths, a pipe system for garbage disposal that is also underground, even oil and ammunition storage facilities.


Complex geology

In March 2019, the urban development agency presented the "Underground Master Plan": extensive studies and 3D plans for the most efficient use of underground potential. An exhibition by the agency reveals the vision of the future for the next 30 years: entire pedestrian zones and shopping malls, streets and metro stations, sewers, supply lines and storage facilities growing downward over many floors.

Singapore's highly complex geology, meanwhile, keeps contractors in suspense: below Tuas, for example, lies the "Jurong Formation". It consists of dolomite, limestone, mud, sand, schist and conglomerates, which are strongly folded due to tectonic plate movements. Along a tunnel alignment, and even in the cross section of a tunnel, a wide variety of soil types often alternate.

A seasoned tunnelling pro experienced with challenging underground missions is therefore responsible for the T-08 construction section in Tuas: Englishman David Helliwell worked as an engineer in mining for a long time and later oversaw tunnel projects in Egypt and Asia. He took over the project management in Singapore for the consortium of Penta Ocean and Koh Brothers.

"Working here is always a real challenge," says Helliwell. Existing metro tunnels, sewer lines or cable conduits make planning even more difficult. "But thanks to the latest tunnelling technology, we will be able to keep to our schedules this time too."

Safely on target

Although the main DTSS tubes are so deep down that the alignment is not critical, before tunnelling can begin the 19 Herrenknecht TBMs involved must be lowered down into the ground through deep shafts. In addition, 18 maintenance shafts are distributed across the city area. In addition, 18 maintenance shafts are distributed across the city area.

"The biggest problem here is the high water pressure," says Wang Yang, Project Director for the T-11 construction section being built by Chinese company Shanghai Tunnel Engineering (STEC). "The shafts must be absolutely watertight, and the groundwater in the area must not sink. "To handle the shaft sinking safely and within the designated time, STEC relies on a Herrenknecht Vertical Shaft Sinking Machine (VSM).

"This is the first time VSM technology has been used in the Asia-Pacific region," says Yang. "With a project like this, know-how is the decisive factor. And with Herrenknecht, we're guaranteed to be on the safe side.

Singapore Map

The DTSS consists of around 200 kilometers of new sewers, up to 60 meters deep underground. In Phase 1, between 1999 and 2008, 48 kilometers of main tunnel and 60 kilometers of link sewers were constructed in the eastern part of Singapore – large and smaller Herrenknecht TBMs were involved. In the second phase of the project (DTSS Phase 2), the contractors for all five construction lots are relying on Herrenknecht technology.

LOS T-07

Maschinentyp: 4x Mixschild

Los T-08

2x Mixschild, 2x AVN Maschine

Los T-09

3x Mixschild

Los T-10

2x Mixschild, 1x EPB Schild

Los T-11

5x AVN Maschine


Maschinentyp: 4x Mixschild

2x Mixschild, 2x AVN Maschine

3x Mixschild

2x Mixschild, 1x EPB Schild

5x AVN Maschine

Contract T-07

Four TBMs are excavating a total of 12 kilometers of tunnels. Odour Control Facilities (OCF) will be installed at the connections between the inlets and the main tunnel. They extract air from both the link sewers and tunnels and remove the odour before releasing into the surroundings.

Contract T-08

Four TBMs are boring a total of 10 kilometers of tunnels. Construction contract T-08 is comprised of a tunnel for industrial wastewater and two undersea tunnels. The tunnel, which is more to the west, is 6 meters in diameter and 2 kilometers long.

Contract T-09

Contract T-09 will be constructing 8 kilometers of 6 meters inner diameter tunnels. Three TBMs are used in this construction contract.

Contract T-10

Three TBMs are used for lot T-10, including the only Earth Pressure Balance Shield used for DTSS Phase 2. All other machines are Mixshield type TBMs. A total of 8 kilometers of tunnel will be excavated in this construction lot.

Contract T-11

This contract is the starting point of the new sewerage system and it is the shallowest. A total of 5 TBMs are used here. For this section Herrenknecht supplied the only shaft sinking system to be used for the project.

Customer Voices

Shinjiro Arimura, Project Director DTSS T-10, Nishimatsu Construction Co., Ltd.

„The TBM alignement crosses two existing metro lies and a cable tunnel a short distance apart.“

Paul Anthony, Project Manager, DTSS T-09, Leighton Contractors (Asia) Ltd.

„The weathered geology in Singapore, the change between soft and hard is a tough one.“

David Helliwell, Project Director, DTSS T-08, Penta Ocean Construction – Koh Brothers JV

„DTSS is by far the most challenging tunnel project I ever worked for.“

Wang Yang, Project Director, DTSS T-11, Shanghai Tunnel Engineering Co., Ltd.

„Herrenknecht´s know-how was the deciding factor. We are using a VSM in Asia for the first time.“

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