Boring times ahead for Waterview Connection project

0

The head diameter of the 97 metre-long tunnel boring machine is 14.5m. The 12 metre-long shield will arrive in New Zealand in eight pieces, collectively weighing 2300 tonnes

The world’s 10th largest tunnelling machine is on its way to New Zealand from the Guangzhou, China factory of German manufacturer Herrenknecht.

The $54 million machine has been designed specifically to cope with ground conditions on the $1.4 billion Waterview Connection. PHIL WHYTE finds out about the biggest roading construction project in New Zealand’ history.

The Waterview Connection is part of the Western Ring Route road of national significance and will join Auckland’s Southwestern and Northwestern motorways to complete a 47 kilometre-long motorway alternative to SH1 and the Auckland Harbour Bridge.

Completion of the connection is expected to bring some relief to SH1 north of Manukau, and also for many major routes.

“There is also suppressed demand for travel, for instance between Manukau and West Auckland. An example of a motorway relieving suppressed demand is the fact that the completion of the Hobsonville link has eased travel between West Auckland and North Shore,” says the NZ Transport Agency’s state highways manager for Auckland and Northland, Tommy Parker.

The $220 million Waterview Connection, including the allied Southwestern motorway causeway upgrade, is being handled by a NZTA consortium of built by the Well Connected consortium, which includes NZTA and Fletcher Construction.

Many of the recent Auckland motorway construction contracts have been alliances.

“For reasons of risk management, NZTA prefers to have a balance of alliances and ‘hard money’ contracts,” says Mr Parker.

“The size of this project and the size of the tunnel boring machine (TBM) are both on a scale the likes of which we have never seen before in New Zealand.

“Since mid-2012 we have been preparing a trench that will not only form the southern tunnel approach, but provide the TBM’s launch pad,” Mr Parker says.

“This requires us to excavate to a depth of 30 metres initially, drilling and blasting through a 15 metre-thick layer of very hard volcanic rock.”

To construct two tunnels, each wide enough for three lanes of traffic, the TBM will pass beneath the rock and tunnel through softer, clay-like soil known as the East Coast Bay Formation. It is expected to take a year to complete the first tunnel, emerging beyond Great North Rd in Waterview, where work is already underway to prepare for its arrival and turnaround for the return journey.

“We have done a lot of testing and geotech modelling, and are expecting to be dealing largely with a sedimentary limestone composite. But we will be tunnelling below sea level, and there is the risk of the unknown,” says Mr Parker.

“We are using tunnelling best practice. As people know there are regular ventilation holes and the two tunnels will be linked so that one can be evacuated into the other if necessary.”

The tunnel boring machine (TBM) will start digging in October after arriving in Auckland in July and being reassembled.

The associated Southwestern motorway causeway upgrade is needed to cope with extra traffic generated by the Waterview connection from the Southwestern motorway and its twin 2.4km tunnels. The 61-year-old causeway will also be raised by 1.5m to cope with rising sea levels and widened from six to nine lanes, with priority space for buses and a cycling/walking path.

Mr Parker says that when completed in 2017, the project will help unlock Auckland’s potential for economic growth and will also have considerable benefits for its Northland and Waikato/Bay of Plenty neighbours. There will be no tolls to force traffic choices.

“Easing pressure on the city’s existing motorway network will have flow-on effects that will encourage business growth, tourism and jobs. For the first time there will be a direct motorway link between Auckland International Airport and the CBD. The network will become more resilient – two motorway links through Auckland reduce the risk of any disruption to traffic bringing the city to a standstill,” says Mr Parker.

“Tunnelling obviously allows us to do this, and a strong focus on urban design and landscaping – like the rehabilitation work we’ve already carried out around Oakley Creek – ensures that the effects of all above ground work are carefully mitigated,” says Mr Parker.

Share.