Dorset: Christchurch Cofferdams

Christchurch WwTW involved the installation of approx 250nr steel sheet piles measuring 9m in length. Piles were installed through very dense sands, gravels and clays using our TM18/22 leader rig with Vibro hammer attachment. The piles were designed and installed by Dawson WAM to form 2 nr temporary works cofferdams. One for a rectangular aeration tank and the second was a 26m diameter circular cofferdam to facilitate the excavation and construction of a new final settlement tank. The works involved the extensive liaison with Wessex Water to complete the works within the restrictions of a confined, operational treatment works. Part of the works was completed adjacent to overhead power lines imposing height restrictions which required an alternative installation method using shorter pile sections installed and welded using an excavator mounted vibration hammer.