The bridge over the Clarence River at Harwood has been labelled ‘by far the most iconic structure' of the Woolgoolga to Ballina upgrade by Pacific Complete’s Section Manager for the bridge, Simon Cross.

The $250 million, 1.5 km, four-lane bridge, which opened to traffic on 6 December 2019, is the longest and highest crossing of the 170 bridges in the Woolgoolga to Ballina section of the Pacific Highway upgrade.

Pacific Complete, a joint venture between Laing O’Rourke & WSP, are Transport for NSW’s primary delivery partner for the Woolgoolga to Ballina upgrade but the bridge was delivered under a subcontract to Pacifico, a joint venture between Acciona and Ferrovial, with engineering by Arup.

The new bridge sits just 20 metres from the existing steel truss liftspan bridge built in 1966 which is being retained for local traffic. 13 piers of the bridges 35 are in the river and were designed to align with the old bridge’s piers to reduce the impact on marine traffic and riverbed scour.

Gradually rising up to a maximum height of 30 m above the Clarence River, the deck allows for a shipping lane in the middle of the river. 

144 post-tensioned precast U girders support the bridge deck, each 44 m long and weighing 168 tonnes. They required the use of a 750-tonne crawler crane in super-lift configuration to erect including 48 which were lifted into place from flat top barges on the river with help from Brady Marine and Civil.

U girders were developed by the Arup-Aurecon Design Joint Venture as part of the Warrell Creek to Nambucca Heads section of the Pacific Highway upgrade and use 30% less concrete than Super T’s. They were used on major bridges in the project including the Nambucca River Bridge, Upper Warrell Creek Bridge and Warrell Creek Bridge.

The designers cite several other advantages of the U girders compared to its T-shaped counterpart including longer spans, greater stability / vertical orientation, and less total girders required (two for a typical two lane Pacific Highway twin bridge, instead of five Super T’s).

The girders were cast within a precast facility built on-site and used a two-stage post-tensioning process in order to control hogging (curving up in the centre as a result of strain). This involves stressing the strands once before the girder is removed from the moulds, two days after the concrete pour. And then again after the girder is removed from the moulds, before being lifted into place.

The piers consist of two slender cylindrical concrete columns up to 2.4 m in diameter with a rounded-edge headstocks and pile caps adding to the minimalist and sleek appearance of the bridge. 

Over 150 lineal metres of custom-made steel circular column formwork were designed and supplied for the piers whilst four 170 m2 table systems were used as formwork which included a combination of custom fabricated steel and proprietary formwork.

“Through many hours of design and coordination we were able to provide.. ..a simple and efficient system that was overall safe to use with the majority of issues resolved through meticulous planning.. ..before work began” says Matthew Caporella, National Manager – Engineering Operations at Acrow Formwork & Scaffolding.

Supporting the piers, 117 concrete-filled tubular steel piles were driven on land and in the river, with the deepest pile extending 67 metres. The use of driven steel tube piles meant soil displacement was minimised in the presence of high acid sulphate soils.

Careful consideration went into the selection of the expansion joints which were required to have a movement capacity of 800 mm for thermal expansion and contraction of the long deck and minimise traffic noise.

A modular expansion joint, Mageba Group’s TENSA®MODULAR system, fitted with noise-reducing features on both the topside and underside of the deck was chosen. It is the first time the system has been used in Australia.

Sinus plates on the driving surface span the bridge joint to minimise wheel impact and thereby reduce the resulting vibration and noise by up to 80%, according to Mageba Group.

Meanwhile, noise protection mats, called ROBO®MUTE, encapsulates the space directly beneath the joint to block the transmission of noise using “a mat of layered membranes, trapping noise and directing it towards the channel’s ends, where its intensity is reduced by noise-absorbing padding.”

The Woolgoolga to Ballina upgrade is expected to be completed later this year which will mark the completion of the 20-years-in-the-making Pacific Highway upgrade project from Hexham to the Queensland border.

Video footage courtesy of Simon Hughes Photography and Mediakoo.