„The TBM alignement crosses two existing metro lies and a cable tunnel a short distance apart.“
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.
Today Singapore is a financial metropolis in Asia and one of the richest countries in the world. With almost 5.6 million inhabitants in an area the size of Hamburg, it is also extremely densely populated. By 2030 already, six million people could be living here As a comparison: in 1980 there were only 2.4 million.
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.
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.
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.
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."
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.
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.
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