Many attempts have been made to maintain the road in an open condition, none with long term success. During 2003 major cracks approaching one metre wide developed, and significant repairs became necessary. A maintenance resolution was not possible, and with the road considered an intolerable risk to public safety a long term answer had to be found. In August 2003 the Minister for Roads announced that Lawrence Hargrave Drive would be closed for two and a half years to enable a more permanent solution to be constructed.
In a first for the Roads and Traffic Authority of NSW, the Lawrence Hargrave Drive (LHD) Link Alliance was formed between RTA, Barclay Mowlem Construction Limited, Maunsell Australia and Coffey Geosciences. The Alliance method of delivery enabled the rapid and effective completion of a challenging amenity. Conventional methods would have taken considerably longer, adding to community dislocation and cost. The $49 million project was approved and the construction phase commenced in June 2004.
Construction was completed on a bridge structure, up to 70 metres east of the original alignment, in places, standing in the Pacific Ocean . The structure consists of a five span 450 metre long Balanced Cantilever Bridge (BCB) adjoining a seven span 203 metre long Incremental Launched Bridge (ILB), sharing a common pier. The Balanced Cantilever structure was chosen for the main southern structure as the 108 metre central spans enabled the foundations to fit on the few available areas and could still follow the road's necessary geometry.
The goal of this ambitious project was to provide a fully available road with a design life of 100 years. The bridges incorporate two traffic lanes of 3.5 metres to 3.8 metres, 2 metres x 1 metre wide shoulders and a 2.5 metre shared pathway on the eastern side. The entire bridge has a constant longitudinal gradient of 2.531 per cent, and a variable crossfall of up to 3 per cent.
With a budget of $50 million, durability and long term performance were not optional. This is the most aggressive environment that an RTA structure will endure. Ongoing maintenance was a consideration and needed to be minimised by careful detailing and quality construction. Chloride induced corrosion is the most serious cause of deterioration in reinforced concrete structures. Two key features - quality concrete and cathodic protection were integrated into the design/construction to maximise durability.
Good quality concrete was essential, requiring an optimum balance of durability and timely construction. Boral Country Concrete & Quarries erected an on-site concrete batch plant to supply the project with the mix refined to consist of Boral Shrinkage Limited cement and fly ash.