Lansdowne Bridge
The Landsdowne Coopernook bridge was situated on the mid north coast of NSW and was made redundant due to the completion of the new Pacific highway upgrade. The project saw demolition methodologies not seen before and was of interest to several different authorities including Roads & Traffic Authority NSW (RTA) and NSW Fisheries. These demolition methods included the lowering of bridge’s 95 tonne counterweight to allow it to be dismantled and removed, underwater blasting of reinforced concrete pylons and the first use of the fish scare method and underwater air curtain.
Upon inspection of the bridge’s super structure and support systems, it was identified that the best method for the demolition of this structure was a combination of conventional demolition of the super structure and the use of explosive techniques on the pylons.
The above decision to combine these two methods was due to a number of challenging issues. Special consideration had to be considered to ensure the demolition process had no negative impact on the environment. The surrounding area was largely populated with mangroves and the river was classed as a marine park. This meant limiting access areas to, on the bridge, below the bridge (by way of barges) and one access track for a truck on the bank to allow debris to be retrieved from the barges. To protect the aquatic environment, rubble barges were positioned under the bridge’s footprint. Steel plates were placed across the rubble barges to ensure that no concrete from demolition process would enter the waterway.
Blasting of the bridge pylons to one metre below riverbed level also posed another issue of possible fish kill. Two methods were developed and tested by our blast technicians for this project which were called the “Fish Scare” and the “Air Curtain”. The use of these methods was to deploy marine inhabitants safely away from an immediate area prior to the initiation of a main explosive charge being used. These procedures worked extremely well with no marine species being kill or injured during the blasting works. These methods have now been adopted by the NSW Fisheries Department for use when performing blasting works in marine environments.
The successful completion of this project using these innovative techniques set a benchmark of how future bridges were to be demolished.
