Tunnel to Wonderland: TBM Alice starts second drive
In mid-December, one of the world's largest tunnel boring machines started its second drive for the large-scale "Waterview Connection" project in Auckland, New Zealand. The first 2.4 km long tunnel was completed in September after only eleven months. In the heart of the metropolis, the Herrenknecht EPB Shield S-764 is creating the shell for a road tunnel that will link two of the main State Highways together. In March 2013, Herrenknecht delivered the TBM to the companies Fletcher Construction, McConnell Dowell and Obayashi.
The tunnel boring machine Alice has begun its second drive in New Zealand. Earlier, Alice – named after the main character of "Alice in Wonderland" – excavated the first 2.4 km long tunnel in just eleven months, with outstanding best performances of 126 meters per week and 452 meters per month. On September 29 at 1:45 p.m. local time the gigantic boring shield finally broke through the wall to the first target shaft in Waterview.
"This is a fantastic achievement. Our construction partners on the Well-Connected Alliance completed the breakthrough safely and ahead of schedule," Brett Gliddon, New Zealand Transport Agency's Highway Manager, said afterwards. "It is a huge engineering feat for New Zealand, one that is attracting worldwide attention. It demonstrates that with local and international experience and expertise, we can deliver infrastructure to equal the best in the world."
The "Waterview Connection" tunnel project is one of the largest infrastructure projects in New Zealand. It is the centerpiece of a total of six related construction projects. They are designed to close the glaring gap in Auckland's Western Ring Road. With three lanes each, the two tubes of the road tunnel will connect the two nationally significant motorways Highway 16 and Highway 20. The tunnel alignment runs below a densely populated residential area and several parks. The 2.4 km long link will become the longest road tunnel in New Zealand. During a visit in May 2014 Prime Minister John Key called the structure an amazing piece of engineering. "It is going to be a fantastic addition to the motorway network here in Auckland." The tunnel creates a time-saving connection between the Central Business District and the International Airport.
For this project, Herrenknecht delivered to the companies Fletcher Construction, McConnell Dowell and Obayashi – as part of the Well-Connected Alliance – a machine concept perfectly adapted to the geological and structural conditions. With a boring diameter of 14.46 meters, the EPB Shield S-764 is one of the world's largest tunnel boring machines of its kind. Its gigantic cutting wheel is driven by 24 electric motors with a total output of 8,400 kilowatts. It has relatively large openings for optimum removal of the excavated material and has been specifically designed for the expected geology. In the first section the TBM went through soils composed mainly of sandstone and siltstone. The cutting wheels’ central cutting tools could be changed from the rear area. The ripper tools for softer grounds were thus replaced with disc cutters for harder rock when needed.
In addition to the actual TBM with three back-ups, which creates the tunnel shell, Herrenknecht designed and delivered an autonomous, fourth back-up. This followed TBM Alice at a distance on the first section already. Its task is to lay a "tunnel within the tunnel". It creates a part of the tunnel invert that supply lines will later pass through. This method of operation fully independent of the TBM advance offers an important advantage: advance performances of the TBM and the lining of the invert do not limit each other and can be done in parallel to save time.
After the first breakthrough the TBM and the first back-up were turned by 180 degrees in a very tight space and moved to the starting position for the second drive. Because of the limited space, a temporary second back-up, also supplied by Herrenknecht, was docked onto the machine. In the initial phase it is responsible for the extension of the supply and disposal lines. With it, Alice is now boring an approximately 300 meter long "launch tunnel". After this first part of the second tube has been driven, the original configuration with the longer back-ups 2 and 3 will be re-docked to the TBM. Then Alice will get going at full speed.
The shell of the second tube is due to be completed in 2015. The opening to traffic is scheduled for the beginning of 2017.