Completing a motorway ring route around Auckland, the Waterview Connection, a New Zealand Transport Agency (NZTA) project, will complete the long-planned Western Ring Route (WRR), a 48 km north-south motorway alternative to State Highway 1.
The Waterview Connection will deliver five km of six-lane motorway through and beneath Auckland’s western suburbs, linking State Highways 16 and 20 to complete the city’s WRR by 2017. Half of this new motorway link will be tunnelled. By undergrounding so much of the motorway, the NZTA is able to deliver maximum regional and national benefits with minimum long-term footprint on the surrounding communities.
It is the largest and most complex road project ever undertaken in New Zealand, with a price tag of $NZ1.4 billion.
Construction alliance
The NZTA chose a competitive alliance procurement model as the most appropriate method to deliver a project of this complexity and significance. Under this model, the participants – including the client – work together following the principles of openness, transparency, equality and common objectives to promote innovative thinking and deliver outstanding results.
Following a competitive tender process, the NZTA appointed a combined local and international consortium known as the Well-Connected Alliance to manage the design, construction and initial maintenance and operation of the Waterview Connection. The alliance comprises Fletcher Construction, McConnell Dowell Constructors, Parsons Brinckerhoff NZ, Beca Infrastructure, Tonkin & Taylor, Obayashi Corporation and the NZTA. This alliance brings together the knowledge and strong, home-grown reputation of leading New Zealand engineering companies with the tunnelling expertise of its international partners.
The contract was awarded in September 2011 and construction began in January 2012. Completion is scheduled for early 2017, after which the alliance will operate and maintain the connection for ten years.
Project details
The Waterview Connection project involves the design, construction and commissioning of a six-lane, 4.8 km motorway joining State Highway 16 and State Highway 20. This nationally significant new infrastructure includes:
- Twin 2.4 km three-lane tunnels, one for northbound traffic and one for southbound traffic
- Building the motorway connections between the tunnels and the existing motorways.
Site considerations
The Waterview Connection route runs under valued community green space, residential areas and some major road and rail infrastructure. By tunnelling approximately half of the five km route, the NZTA is able to preserve green space, reduce construction impacts, and avoid severance of residential areas. Environmental and social considerations were therefore critical to the decision to tunnel.
Tunnelling aspect
The tunnels are being constructed by the Herrenknecht earth pressure balance (EPB) tunnel boring machine (TBM) No S-764, with a length of 87 m and a cutting diameter of 14.5 m. Named Alice, it is the tenth-largest diameter TBM ever produced worldwide and weighs in at 3,102 tonnes.
The machine was fabricated at Herrenknecht’s plant in China, factory tested, then disassembled and shipped to New Zealand. In Auckland it was reassembled in the southern approach trench to the tunnels.
Each tunnel comprises a single pass precast concrete segmental lining with an internal diameter of 13.1 m. The lining comprises 2 m wide rings, 450 mm thick – each with a conventional configuration of nine interconnected segments and a smaller key segment.
A major achievement for the project was being ready to bore on the exact day specified two years earlier in the tender phase for the project. This milestone required the completion of a large number of work streams, many of them major projects within themselves.
They included the:
- Procurement, design, fabrication, delivery and reassembly of the TBM
- Design, construction and commissioning of a pre-cast factory for manufacture of tunnel lining segments
- Excavation and construction of the southern tunnel approach
- Construction of the surface motorway between the southern approach
- trench and Southwestern Motorway to give direct motorway access for heavy construction vehicles
- Design and construction of infrastructure to support the tunnelling, including water treatment facilities and grouting plant
- Development of the project’s 27 hectare cleanfill site where all excavated material is being disposed of.
Challenges
The decision to construct the tunnels using a 14.5 m diameter EPB TBM was made following multi-criteria analysis which concluded that this method best addressed the project’s geotechnical risks and uncertainties while minimising cost and program risk. Criteria considered during this evaluation were safety, cost, program, risk/opportunity, construction sequence and environmental sustainability.
For the most part the tunnel route passes through sandstone of varying strength and degrees of weathering. The EPB TBM provides the best capability to handle the varying soil and rock conditions that will be encountered. It will also cope with groundwater inflows and limit the risk of lowering the groundwater table as required by the environmental conditions of the project’s consents.
The most significant challenge was excavation of hard basalt rock – the remains of an ancient lava flow that was up to 14 m thick – that lay directly beneath the surface on the southern approach to the tunnels. Its excavation required extensive blasting.
Tunnelling to date
After a probationary period of several weeks, during which the tunnelling team familiarised itself with the machine’s operation and systems, Alice is currently achieving her expected production of around 20 m (10 rings) of tunnel constructed per day. Her best day yet has been approximately 22 m.
The TBM is on target to break through at the northern end in late September or early October. Alice will then be turned around over approximately three months to begin her 2.4 km journey south, constructing the second tunnel as she goes.
Future outlook
Tunnelling is expected to be completed in October 2015 and the Waterview Connection will open in early 2017.
When it opens, the Waterview Connection will unlock Auckland’s potential to become a truly world class city, combatting regional congestion and creating a direct, time-saving link between the International Airport and CBD.
Tunnelling the connection
The Waterview Connection’s TBM has been specifically designed for the local geology by Herrenknecht. The TBM is the tenth-largest machine of its type in the world and the largest ever built for use in Australasia. The cutting head and shield are as high as a four-storey building.
The machine is the length of a rugby field. It comprises a 14.5 m diameter rotating cutting head attached to the front of a 12 m long shield, followed by three back-up cars, or gantries, that house all the equipment needed to run it, place the precast concrete rings that will line the tunnels and to remove the material extracted.
As it bores its way from Owairaka to Waterview and back, it will install 2,414 rings of reinforced concrete to form the tunnel lining. Each ring is 2 m wide and 50 cm thick and comprises ten pre-cast reinforced concrete segments. Nine of these segments each weigh approximately 10.5 tonnes. The tenth is a smaller “÷key’ ring that locks the ring together.
When theTBM has finished its job, it will have extracted around 800,000 cubic metres of spoil – enough earth to fill 320 Olympic sized pools.
Key project milestones
November 2011: Agreement signed
January 2012: Start of enabling works in the south
July 2012: Start of construction in the south
December 2012: Start of construction in the north
October 2013: Start of tunnelling, south to north
December 2014: Start of tunnelling, north to south
September 2015: Completion of tunnelling/start of commissioning
April 2017: Project completion