U. Kreher, I. Solomon, A. Vinnell – Aurecon Australia Pty Ltd
A 1.2km long 4.35m diameter crossharbour tunnel was constructed in 1996 for an iron ore conveyor. This used 5,154 reinforced concrete lining segments bolted together by mild steel bolts located within bolt pockets. Since early in its construction the tunnel experienced seawater leakage through segment seals and grout ports. Due to the water pressure, leakage of tunnels under a harbour is not uncommon and regular wash down and maintenance would be required. However, with a conveyor that operates continuously, it is only possible to undertake minimal maintenance. Over time saltwater ingress caused severe corrosion of the exposed mild steel bolt assemblies. This corrosion has led to surface cracking and spalling of the concrete (Figure 1). The salt encrustation from leaks had resulted in diffusion of chlorides into the concrete thereby initiating reinforcement corrosion. Concrete remediation and installation of an impressed current cathodic protection (ICCP) system was required in order to achieve the desired life of 50 years for this 15 year old asset.