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More than just the clients were happy with Fulton Hogan’s performance on the East Taupo Arterial project. BY HUGH DE LACY.
But they weren’t the only ones delighted with the innovative design-and-build tender that the listed civil construction company entered for the 16 kilometre deviation round the lakeside holiday resort. The ETA essentially involved re-routing through-traffic round the eastern side of the township, from the Wairakei thermal centre at the intersection of State Highway 1 and State Highway 5 in the north, to Taupo Airport in the south. Inevitably affected were listed electricity generator Contact Energy, which operates the Wairakei geothermal power station, and the local iwi, guardians of the Waikato River that the deviation had to cross. The original specimen design issued to tenderers anticipated a series of three or four short bridges over Contact’s steam pipes and infrastructure, and the temporary shutdown of the scheme to allow a re-injection pipeline, called the Otupu Crossing, to be realigned under the new road. It also called for the Waikato to be crossed by an 83-metre clear-span bridge for which resource consent had been obtained to re-shape the banks to suit the span, and for piles to be sunk into the riverbank.
As well as saving Contact from major disruptions to its power generation and reducing the encumbrances on its future infrastructure layout, the Fulton Hogan innovation allowed the Taupo District Council to renegotiate the land purchase agreement to cover the footings only, plus a strata title for the air space, instead of having to buy the land for the embankment footprints. It also reduced the total cost of the scheme by about $2 million to $97.4 million, and brought the finish date forward from March 2011 to October of this year. For the bridge over the Waikato, Fulton Hogan’s alternative was a 100-metre span network arch bridge to clear the river banks altogether, thereby protecting the river’s mauri (lifeforce) and earning the unqualified approval of the local iwi. There are actually four bridges on the ETA, with the southernmost two being a 28-metre super-T span grade-separator over Taupo’s Centennial Drive, and a 20-metre double hollow-core grade-separator interchange over Broadlands Road.
While the Centennial Drive and Broadlands Road bridges were built on shallow foundations with no piles, the main span over the Waikato featured what may be the country’s biggest boxed piles: four of them with a diameter of 2.4 metres sunk 20 metres deep into the banks. This is only the second network arch bridge to be built in New Zealand, after the 85-metre single-lane Mangamahu Bridge built by Rotorua’s Concrete Structures last year over the Mangawhero River in the Whanganui backblocks (see Contractor, September 2009). The Waikato bridge’s 100-metre span is one of the longest in the country, and is served at either end by 25-metre, steel-ladder back-spans. The steelwork was fabricated by Tenix in its New Plymouth workshop and erected on site. It sports outriggers on either side – for cycle and pedestrian access on the western side, and for Contact’s steam pipes on the eastern. There’s also provision for a further steam pipe to be added on the eastern outrigger.
The bridge incidentally saw the successful employment of self-compacting concrete, supplied by the Taupo branch of Allied Concrete, on the arch structure. The underground Otupu Crossing for Contact’s re-injection line originally imposed a considerable constraint on the whole scheme because the shut-down of the pipe was scheduled for November of this year, and everything else pretty well revolved around it. Instead Fulton Hogan proposed a multi-arch culvert – similar to the one that Palmerston North company Stringfellows Civil Engineering Contractors used earlier this year to take State Highway 1 over the Main Trunk railway line at Ohingaiti, south of Taihape (see Contractor, March 2010) – to carry the pipe over the ETA. This not only allowed the project to be finished early, but also reduced the tender price. The original project design parameters reflected the gradual increase in the return period requirement that the NZ Transport Agency has been imposing on State Highway 1 structures over the past five or six years, raising the bar for a destructive seismic or flooding event from 1000 to 2500 years.
The whole project was run by the district council with the asset transferring to the NZTA at the end of the defects liability period. Taupo District Council has funded 23.4 percent of the project and the NZTA has met the balance. Opus International Consultants has been acting for the clients, with Sinclair Knight Merz performing the head designer’s role. The key designers comprised the Holmes Group, Boffa Miskell, Sigma Consultants, Marshal Day and Fulton Hogan, with Bloxham Burnett Olliver doing the peer review. The outcome is that, from October this year, the residents of Taupo will no longer have to endure the endless stream of trucks trundling down their main street on the long trek between Auckland and Wellington.
Contractor Vol.34 No.7 August 2010 |
Fulton Hogan’s slashing the projected timeline by five months, and carving a couple of million dollars off the estimated cost of the East Taupo Arterial (ETA) certainly impressed the client – the Taupo District Council.
Instead, Fulton Hogan, in its tender, proposed a 440-metre steel-ladder fly-over bridge at Contact’s steam-pipe farm to replace the multiple small bridges, incidentally obviating the need for a series of associated large embankment fills.
The specimen design had suggested the local roads go over the top of the deviation, but by turning that aspect of the plan upside down, Fulton Hogan was able to prevent disruption to a series of running and triathlon sports events that feature on Taupo’s annual programme.
Project manager Andrew McRae described the bridge to Contractor as, “an elegant, iconic and cost-effective solution” in the face of cultural and physical challenges.
This might prove reassuring to the people of Taupo who have lately been reminded by the national news media that the North Island’s biggest lake sits in the cone of an active volcano that is long overdue to blow.