Lawrence Hargrave Drive is a spectacular section of coast road just north of Wollongong NSW. This road has had a long history of geotechnical instability between Clifton and Coalcliff, resulting in road closures, sometimes for months at a time. Initially constructed in the 1860's, this road was known as the Lower Coast Road until 1947, when it was renamed Lawrence Hargrave Drive , after the famous Aviator and the first Australian to fly at the nearby Stanwell Park.
Many attempts have been made to maintain the road in an open condition, none with long term success. During 2003 major cracks approaching 1m 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 recently completed on a bridge structure, up to 70m east of the original alignment, in places, standing in the Pacific Ocean . The structure consists of a 5 span 450m long Balanced Cantilever Bridge (BCB) adjoining a 7 span 203m long Incremental Launched Bridge (ILB), sharing a common pier. The Balanced Cantilever structure was chosen for the main southern structure as the 108m 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 2 traffic lanes of 3.5 to 3.8m, 2 x 1m wide shoulders and a 2.5m shared pathway on the eastern side. The entire bridge has a constant longitudinal gradient of 2.531%, and a variable crossfall of up to 3%.
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 Blue Circle Southern Cement Shrinkage Limited cement and fly ash. Approximately 5,000 tonnes of Shrinkage Limited cement and 1,000 tonnes of fly ash were consumed.
The use of Blue Circle Southern Cement Shrinkage Limited cement was crucial in achieving the required shrinkage tolerances and strengths. The specified performance was for a workable, high quality concrete, delivering ~25MPa for stressing in 24-36 hours, 50MPa at 28days, and 60MPa at 56 days.The maximum shrinkage allowance was 650 microstrain with the exception of the BCB superstructure, which was restricted to 600 microstrain - all measured at 56 days.
