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Auckland Ring Road Dives Underground

Aerial view rendering of the 4.8 km Waterview Connection
The 4.8 km long Waterview Connection will include dual 2.4 km long bored tunnels, which will descend to a depth of 45 m to avoid a volcanic rock layer. Aboveground highways will be built on either end of the tunneled roadways to connect them to existing highways. The Well-Connected Alliance

The Waterview Connection, the last link in a ring road around Auckland, New Zealand, has begun tunnel-boring operations that will reach depths of 45 m.

March 11, 2014—As the population of the island country of New Zealand has increased in the two centuries since European settlement, the metropolis of Auckland has also expanded into the largest urban area in the nation. Occupying a narrow isthmus between two harbors, the city has long been dependent upon a single north-south highway. With the completion of the 4.8 km long Waterview Connection in 2017, a ring road around the city will be ready for use. Following years of preparatory work, tunnel boring on dual 2.4 km long, three-lane roadways that will extend deep underneath a thick layer of volcanic rock has finally begun.

“The Waterview Connection is the largest and most complex [road] project ever undertaken in New Zealand,” said Tommy Parker, the Auckland highways manager for the NZ Transport Agency, who is overseeing the work on the behalf of the New Zealand government. Parker responded in writing to questions posed by Civil Engineering online. Despite its location on a relatively narrow band of land, Auckland is home to more than 30 percent of New Zealand’s population and is responsible for more than a third of its gross national product, he noted.

“[The ring road’s] completion in early 2017 will give the region the connected and cohesive strategic road transport system it needs to underpin economic growth and sustainable development,” Parker said. “It will also provide a direct motorway link between Auckland’s central business district and [its] international airport.” The project has been identified as a road of national significance and has been deemed by the national government as critical to the country’s future economic prosperity.

The $NZ1.4-billion (U.S. $1.16-billion) Waterview Connection will not only complete a 48 km western route around the city, thus offering improved travel times and reliability for residents, it will also reduce congestion and enhance network resilience, improving routes for light and heavy freight traveling between industrial areas and transportation hubs, according to Parker. 

As part of the new roadway segment, aboveground highways are being built to connect the tunneled sections with existing highways, State Highway 20 to the southwest of the city and State Highway 16 to the northwest. Sixteen cross-bore passages will allow egress points from one tunnel to the other in case of emergency.

“The Waterview Connection route runs under valued community green space, residential areas, and some major road and rail infrastructure,” Parker said. Environmental and social considerations were critical to the decision to tunnel, despite the added cost. “By tunneling approximately half of the 5 km route, the Transport Agency is able to preserve green space, reduce construction impacts, and avoid severance of residential areas,” he noted.

 Map of the so-called “Waterview Connection” will become part of a ring road around the city of Auckland, New Zealand 

Upon its completion in 2017, the so-called “Waterview Connection”
will become part of a ring road around the city of Auckland, New
The Well-Connected Alliance

“For the most part the tunnel route passes through sandstone of varying strength and degrees of weathering,” Parker said. “[However,] an old lava flow—Auckland is built on a volcanic field—overlaid the southern approach to the tunnels.” This hard, basalt rock layer was 14 m deep at the location where the tunnel would begin, at the southern connection point, so approximately 100,000 m3 of volcanic rock had to be removed before the boring could begin, he noted. The tunnels must descend to 45 m at their deepest point to avoid the remaining volcanic rock layer, according to the project’s website.

The tunneling is being completed with a 14.5 m diameter earth pressure balance (EPB) tunnel-boring machine (TBM). “This method best addressed the project’s geotechnical risks and uncertainties,” Parker explained, while still minimizing costs and risks to the program. “Criteria considered during this evaluation were safety, cost, program, risk/opportunity, construction sequence, and sustainability,” he explained. While the TBM can operate 24 hours a day with a crew of between 16 and 20 people, periodically the machine will be paused while other construction tasks are completed and equipment is moved into the tunnel.

“The EPB tunnel boring machine provides the best capability to handle the varying soil and rock conditions that will be encountered,” Parker said. The selected TBM can also cope with groundwater inflows and limits the risk of lowering the groundwater table, which would have been prohibited because of the environmental conditions at the project site, he noted.

The TBM works by injecting water into the soil to make a slurry that is easier to remove than dry earth. Once the spoil is scraped and removed along the tunnel via conveyer belt, “the [tunnel] lining is installed inside the tail skin of the tunnel-boring machine’s shield and grouted from the tail skin as the machine pushes forward,” Parker explains. “This means there is never an unprotected void that could be subject to settlement—the tunnel is fully constructed by the tunnel boring machine as it goes.”

The spoil is carried to a building outside the tunnel, where the water drains from the earth for 24 hours. At that point, the earth is then removed to a unused quarry, according to the project website.

The single-pass, precast-concrete segmental lining that is being installed as the tunnel-boring machine moves forward will create a tunnel with an internal diameter of 13.1 m. The panels are actually rings that are 2 m wide and 450 mm thick, comprising 9 interconnected segments and a smaller key segment, Parker said. In all, 2,414 of these rings will line the two bore holes.

An inverted U-shaped box culvert will be placed in the bottom of the tunnel to carry the necessary services required to operate the tunnels. The bottom of the tunnel will then be backfilled with aggregate to the level of the road. Ventilation and lighting will occupy an obvert at the top of the tunnel and will be connected to ventilation stations at the tunnel exits, Parker said.

A consortium was created to design, construct, and operate the new roadway. Dubbed the Well-Connected Alliance, it comprises Auckland-based Fletcher Construction; Hawthorn, Australia-based McConnell Dowell Constructors, Auckland-based Parsons Brinckerhoff NZ; Auckland-based Beca Infrastructure; Auckland-based Tonkin & Taylor; Tokyo-based construction company Obayashi Corporation; and the New Zealand Transport Agency. It is an alliance that is working extremely well together, Parker reports.

“The programming and sequencing of work on this project is an enormous task,” Parker said. “An extraordinary success was being ready to bore on the very day (October 31, 2013) that had been planned more than two years earlier. Meeting the target date required the completion of major tasks on the critical path, each with significant risks associated with it.” These tasks were delivered within days of their scheduled completion dates, he said, and included such major projects as the design, fabrication, and delivery of the TBM; the construction and completion of the precasting yard at which the tunnel rings and culvert segments would be fabricated; the preparation of the 27 ha clean fill site for the tunnel’s 800,000 m3 excavated soil; and the completion of the southern approach trench, which involved excavating a thick layer of volcanic rock.

The TBM has now excavated 500 m of the first tunnel, and will take a three-week break so that preliminary work for the tunnel’s culvert can be completed. When the machine reached 250 m last month, its probationary period—during which the team familiarized itself with its operation and its capabilities—was completed, and the machinery began operating at full capacity. An additional 1,900 m of tunneling remains in the machine’s first pass, which will create the tunnel’s southbound passage. At that point, the machine will be turned around, and return along the same route to create the project’s northbound passage.

The alliance has also partnered with Auckland-based Wilson Tunnelling, a precast concrete supplier, as well as Madrid, Spain-based Sociedad Ibérica de Construcciones Eléctricas, S.A. (SICE), a tunnel controls specialists, to manage the construction of the tunnel segments and its long-term maintenance and operation, according to the project website.

The tunnel boring is anticipated to be complete in late 2015 and the new ring road is scheduled to be open by 2017.



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