Shani Wallis, TunnelTalk

Twin EPBM tunnels of 14m diameter lie at the heart of the largest infrastructure project in New Zealand's history. Estimated at NZ$1.4 billion, the Waterview Connection highway construction project in Auckland is integral to completing the city's Western Ring Route. The project is one of seven Roads of National Significance, identified by the NZTA in 2009 as being vital to the country's economic prosperity. A completed ring route will reduce dependency on the Auckland Harbour Bridge Highway (SH1) for through traffic and provide a continuous highway link from the city centre to the international airport (Fig 1).

Fig 1. Highway connections for Auckland

On Friday 19 August, the project took a major step forward with the selection of the Well Connected group as the preferred partner to join the New Zealand Transport Agency (NZTA) in a modified Alliance partnership to design and build the new 4.8km of six-lane highway. Well Connected comprises contractors and engineers Fletcher Construction, McConnell Dowell, Obayashi Corporation, Beca, Parsons Brinckerhoff, and Tonkin & Taylor, with sub consultant SICE of Spain providing specialist M&Eand operational expertise for the tunnel.

In a conference call with senior project managers, TunnelTalk learned of the specific approach adopted for realizing New Zealand's most complex tunnelling and transportation infrastructure project to date. Sumi Eratne, Project Director in NZTA, is responsible for delivery of the project and is the owner's interface with the Alliance organization; Peter Spies is Project Manager for project procurement and NZTA's representative within the Alliance Governance Board, and Rob James the Specialist Tunnelling Advisor to NZTA, explained the background to the project, its Alliance procurement model and the technical challenges of the twin tube tunnel.

"Planning of the project goes back several years," explained Project Director Eratne. "Various options were studied and the final route beneath Waterview gives rise to the project's name."

Procurement strategy
As New Zealand's largest construction project, the Waterview Connection contract is some four times larger than its NZ$340 predecessor in dollar terms. the next largest project to have been undertaken. "To cope with the scale and complexities of the undertaking, we decided early on to adopt the Alliance method of procurement," said Project Manager Spies. "It is the fifth Alliance that the NZTA has engaged, and is the preferred procurement model for large, complex and risky projects where early collaborative engagement with designers and constructors is vital."

With the Alliance model all risks are shared and the non Owner participants in the Alliance are incentivised through the 'pain share – gain share' concept. "For Waterview we have used also the GBR concept to set limits for the geological risk to be carried by the non Owner participants," explained Spies, "After agreeing the geological risk limits with the non Owner participants, these have been incorporated in our procurement contract as an Alliance GBR (AGBR)."

2.5km of minimum 14m o.d. twin tube EPBM tunnelling is required

GBRs, explained Spies, are best applied to hard-money contracting but NZTA saw the value in the concept for dealing with unforeseen conditions. If the Alliance was to encounter a hard dyke intrusion that holds up TBM advance, for example, the hard cost consequences will be carried by the Owner with mechanisms in place to ensure no profiteering from the situation by the contracting companies. “With this clause in place, we were pleasantly surprised that the allocation to risk in the two Alliance proposals considered was low,” he said.

Another part of the modified Alliance is appointment of a Strategic Review Panel (SRP). Similar to a Disputes Review Board, but with the ability to make recommendations rather than rulings, the SRP will have three members - one nominated by the Client, to be filled by current NZTA Specialist Tunnel Advisor Rob James; another by the Contractor; and the third an independent chair.

The NZTA has also taken responsibility for providing principal arranged insurance for the project. Given the complexities of the project, a provisional sum was allowed in the tender for public liability, professional indemnity and contract works insurance and the NZTA and the non Owner participants are working with a broker in London to procure all-risks project-wide coverage.

Tunnel specifications and evaluations
The process of selecting a design-build Alliance partner began in early 2010 when three groups submitted expressions of interest. In November 2010 this was reduced to a shortlist of two, with the selection based on non-price attributes and experience of completing similar-sized contracts and tunnelling projects. The shortlisted groups were the Well Connected consortium of Fletcher Construction, McConnell Dowell, Obayashi, Beca and Parsons Brinkerhoff and a consortium of Leighton Constructors, Fulton Hogan, John Holland, Aecom and Sinclair Knight Merz. The third team had been a group led by Baulderstone with Bouygues and designers Opus and URS.

During the following seven months, a series of interactive meetings, totalling 400-500 hours with each group, examined all aspects of the project and the proposals.

"The process started with a reference design from which the groups presented technical and value engineering departures which were accepted if they complied with all necessary standards," explained Spies. "There were discussions for example on changing the spacing of cross passages through the tunnel and of elimination of a central ventilation station and shaft, as well as various alternatives for the highway connection interchange. All these were considered and either permitted or denied as part of each group's final proposal."

Local residents campaigned for the tunnel option

On June 22, the bidding process closed and on Friday 19 August the NZTA selected Well Connected as its preferred Alliance partner. It is expected a contract will be signed within the coming weeks when detailed design, beyond the 30-40% tender design, and procurement of the minimum 14m o.d. mega-sized EPBM can then begin.

Each tube accommodates three 3.5m-wide traffic lanes and a 0.2m shoulder either side. This requires a minimum i.d. clearance of 13m. The tunnel has a longitudinal ventilation system and high pressure water deluge fire-response system. Vehicles carrying dangerous good will be banned from the tunnel and directed to alternative surface routes.

"Through the procurement process the life-cycle costs of the tunnel were as important as the construction capital costs," said Eratne. "To keep this in focus, the Alliance partner is responsible for the first 10 years of the tunnel's operation and maintenance."

As part of the evaluation process NZTA bought the design development of each group for an estimated 50% of the costs, about NZ$8 million, to secure ownership of the technical details of each and incorporate the best of both into the final project. For the most part, both groups had a lot of similarities of approach, but there were some significant differences. One of these differences was in the treatment of the tunnel invert and road deck. One proposed a complete invert infill; the other a precast road deck that provides long term benefits by including access beneath the road to create a man-entry cable and service conduit. Consideration is being made to incorporate this together with a number of other whole-of-life value design features into the selected design.

Tunnel design
The tunnels dive to a maximum 45m below the urban area to pass beneath a cap of hard basalt, deposited by one of 48 now-extinct volcanoes in the region, and stay within the soft sedimentary bedrock of the Eat Coast Bays Formation. At the northern end, the parallel tubes pass through saturated silts of the Tauranga Group. Controlled excavation of these soft, non-cohesive soils require closed-face TBM excavation.

Within the project budget, the tunnel element accounts for some two-thirds of the NZ$1.4 billion total. The mega-EPBM for the project brings New Zealand into the international league of maga soft-ground TBM users. This follows the country's use of the world's second largest hard rock gripper TBM. The Robbins machine used to excavate the new tailrace for the Manapouri hydro scheme on South Island in the late 1990s was increased in size to excavate the 14.4m diameter water diversion tunnel at Niagara in Canada.

"At the start of the design process, contractors were tasked with coming up with their own solutions to drive the tunnels with options including slurry or EPBM technology or of tunnelling with NATM-type headings," explained NZTA Tunnel Advisor James. "But it soon became clear that the Tauranga Group deposits at the north end were unsuitable for open-face excavation. Both shortlisted groups proposed using closed-face TBM technology as well as extending the original length of the tunnels to stay in bored tunnel through the Tauranga Group materials and underneath a major arterial road carrying some 40,000 vehicles per day. Of the two TBM systems, both groups favoured EPBM."

EPBM excavation with appropriate conditioning agents will be applicable for the full 2.5km length of the tunnels. Both McConnell Dowell and Obayashi bring EPB experience to the Well Connected Alliance partnership. McConnell Dowell used EPBMs to complete 3km long drives for the Rosedale outfall and Hobson Bay transfer tunnel in Auckland. Both these projects are within 15km of the new highway tunnel. Obayashi has experience of mega-sized TBM operation. John Holland and Leighton in the other shortlisted group respectively had large diameter TBM experience on the current Brisbane Airport Link and completed CLEM 7 highway tunnel under the Brisbane River in Brisbane, Australia.

It is understood that in developing their proposals both shortlisted groups had meetings with the six top TBM manufacturers who have experience of building machines of more than 10m in diameter. As a significant investment for the project, the final supply decision will be presented to the board of the Alliance for approval and ratification.

Including the 2.5km long twin-tube underground alignment on the SH20 was the result of a successful campaign by residents of the fast-growing western suburbs to avoid surface alternatives through the area. The tunnel runs 85% under existing open space and roads with the remaining 15% impacting about 160 private properties. In New Zealand property is owned to the centre of the earth. NZTA will be purchasing sub-strata titles for the properties on the alignment.

Delivery of the EPBM is set for early 2013 to complete the northbound drive ahead of its southbound twin. The Waterview Connection project is scheduled to be complete in 2016.

References

Design-build responsibility at Rosedale - TunnelTalk, Feb 2009
Underwater works for Hobson Bay - TunnelTalk, Feb 2009
Tracking the world's mega TBMs - TunnelTalk, Jul 2011

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