THE ENTRANCE SEAWALL, WYONG Shire
Before development of a seaside restaurant could proceed at The Entrance, Wyong Shire Council required that the deteriorated section of reinforced concrete piled seawall within the development be repaired and cathodically protected. It was also determined that the existing ground anchors were inadequate for the proposed loading, and a new set of anchors and a strengthened capping beam would be required for the 135m length affected. Council awarded a Design and Construct contract to Marine & Civil Maintenance in 2002.
The specification called for 9m long Platipus ground anchors. These were installed by driving them into the ground with a hydraulic ram mounted on a digger, and then stressing them to the required load against temporary walers fixed to the seawall piles. Because of ground loading restrictions, an innovative method was devised to spread the weight of the digger between the wall and the fill behind it.
After the anchoring was complete, the concrete capping beam was demolished and rebuilt, and the anchor loads were transferred to the new beam.
The cathodic protection (CP) system was designed for MCM by Dr Bruce Ackland. It consisted of four zones, of which one was the capping beam and comprised two ribbon anodes cast into the pour, and the other three were the piles and anchors in the ground. These were protected by a MMO/Ti/Cu anode ground-bed in a calcined coke backfill. The entire system was monitored by reference electrodes cast into the beam and piles, and a control and monitoring unit was installed at the nearby kiosk.
Final works carried out were the reinstatement of paving and a timber jetty.
The CP system was commissioned in 2003 and was maintained and monitored by MCM for two years, after which it was handed over to Council.