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Huge cranes were used to lift piling rigs, diggers and other equipment in and out of the riverbed

Taramakau Bridge reaches the halfway stage

It’s a challenging job building a bridge over the West Coast’s fast-changing Taramakau River, but the team working on the new Taramakau Bridge are making good progress, with the project reaching the halfway stage a year into construction.

The Taramakau Bridge lies on State Highway 6 about 
15 km south of Greymouth. It’s an important link on the West Coast route, connecting Greymouth to Christchurch, via Arthur’s Pass, and to Hokitika and onwards to Haast and the Otago region.

The existing bridge is a one-lane combined road/rail bridge which was built during the early 1880s. Traffic congestion had become a major issue, with vehicles often having to queue to cross the 220 m long structure.

The installation of the super-tee beams to create the bridge deck was completed on 21 January

An initial investigation was completed in 2002 with a preferred option identified, but the project did not proceed. It was resurrected in 2014 after the government announced funding would be made available from the National Land Transport Fund to accelerate a package of regionally important state highway projects.
Jim Harland, southern regional director for the NZ Transport Agency, says the new bridge will add resilience to the region’s road network and the good progress on the project will be welcomed by many.
The new two-lane road bridge is 250 m long and is being built downstream of the existing bridge, with a realignment of a section of SH6. The old bridge will be used solely by the rail line, and a new overpass will be built to take road traffic over the rail line.
A shared path will also be provided on the new bridge, linking pedestrians and cyclists to the current facilities. The cycle links play an important part in the growing tourism opportunities developing on the West Coast, such as the Wilderness Trail.

Fluctuating river levels

Contractors Fulton Hogan have made good progress since the official sod turning in December 2016, marking the halfway stage in December last year, and are on track to complete the project by the end of this year.
Coping with the fluctuating river levels has been one of the major challenges – the river can change from flat and low to wild and high in the space of a few hours. To reduce the risk and to make work safer and quicker, the team have used precast beams, which meant they could plan when they would be in the riverbed, and plunge columns have created better accuracy and improved safety.
A 250 tonne crane has been used to lift piling rigs, diggers and other equipment into the riverbed when the water is low and lift it back out as the river rises during floods. In October last year, the team completed a ‘staging structure’ – a temporary bridge – which has been used as a base from which to build the new bridge.
A coffer dam has also been used, allowing a crew of up to four at a time to stay dry as they work on the new bridge pile and pier columns below water level. The 
6 m high structure is clamped onto the piles and a pump keeps the inside dry.

Super-tee beam installation

Transporting the massive concrete super-tee beams over Arthur’s Pass during the winter was another challenge for the team.
Fulton Hogan manufactured the beams at a factory in Christchurch. The beams make up the bridge spans, and each one measures 34.5 m long and weighs in at 
62 tonnes. There are 42 in total and each one had to be transported by truck to the worksite. The team started bringing them over in May, taking them one at a time through the narrow and steep Arthur’s Pass.

Transporting the massive concrete super-tee beams over the narrow and steep Arthur’s Pass during the winter was another challenge for the team

Each move was subject to weather, and the move would be postponed if there was snow or a forecast of snow. The team worked closely with the local road maintenance crews to make sure each eight-hour journey was a success, checking for slippery sections and grit so they could plan ahead.
The main truck was assisted by a six-wheel-drive Iveco Trakker tractor unit, ready to help pull the load up or support it down the steep sections. The last beam arrived onsite in late October.

Stitching the bridge deck together

The northern and southern abutments were completed in about six months and the team started work on the bridge deck in November. A lot of time has been spent on the ‘stitch’, the concrete and steel that connects each bridge beam together, and the pier headstocks and columns.
“We have had a good run with the warm weather,” says Matt Loach, Fulton Hogan’s project engineer. “We completed the piling and the precast plunge piers in December, and made a real push over early January, completing the accelerated bridge construction portion of the works by installing the sixth and final precast headstock.
“We installed four spans of super-tee beams, equating to 24 beams, over a four-day period, which saw the biggest visual progress on the project so far.”
The installation of the super-tee beams to create the bridge deck was completed on 21 January.

Seismic resilience

Work on the rail overpass is also going well; the team finished constructing the east and west mechanically stabilised earth walls and bridge abutments in nine months. The earth walls are made up of 750 concrete blocks, each one weighing 3.5 tonnes, which are reinforced with 65 km of ‘paraweb’ strapping to keep 
them in place, and overlaid with 20,000 cu m of earth fill. The strapping will aid in the seismic resilience of the structure during an earthquake.
“In mid-December we installed 47 double hollowcore beams at the rail overpass over a two-day period,” says Matt. “We have been continuing with the upper in-situ construction of this structure, precasting onsite the edge-deck panels that will enable the structure to be wide enough for the road and cycleway – there’s quite a skew between the road alignment and the railway.”
The rail overpass is due to be completed in early April, following installation of the precast panels, pouring the 200 mm thick concrete deck, installing the precast TL5 road barriers and sealing the deck with asphalt.
The team have also had a big push on the earthworks, bringing in approximately 10,000 cu m of bulk fill material and diverting the road onto part of the new alignment at the southern end of the project. “We have been continuing to bring in fill material to complete the southern approaches to the rail overpass. We have also been installing the topsoil and erosion protection over the project, of which we anticipate approximately 7000 cu m of topsoil will be required,” Matt adds.

The Taramakau River is renowned for whitebaiting – one of the conditions of the project’s resource consent is to ensure the riverbed and bank are restored to enable the whitebaiters to fish

In full swing

Over the coming months work will continue on constructing the bridge deck. Work on the concrete safety barriers and steel cyclist railing on the new bridge will also start once the deck is underway.
“We are going to be in full swing with construction of the road pavements over the next two months in order to have them constructed over the entire project and sealed within the sealing season,” Matt says. “Once the sealing is complete we will commence the installation of 1000 m of cycleway fencing and the installation of the wire rope barrier. During the late summer and autumn periods we will be placing some 22,000 native plants across the project.”
The entire project is expected to be complete by December at a projected cost of $25.8 million. Jim Harland says the bridge is part of their wider investment in the region. “This is a long-awaited project for the West Coast and will provide significant improvements for locals and tourists alike in terms of safety, travel times and journey experience. The new two-lane bridge means local business operators, freight vehicles and residents will no longer have to wait at each end on their daily commutes.”

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