Abstract
The steel shell immersed tube tunnel will be embedded under the complex environment of marine brackish/deposited sea mud/backfilled stone. Traditional design of sacrificial anode cathodic protection (SACP) had been challenged because of a high resistivity heterogeneous media. In this paper, aluminum anodes have been firstly evaluated so as to ensure an excellent electrochemical performance under the brine/backfilled stone media. The long-term capacity testing for twelve months were conducted. The result shows that the average capacity value of the Al-Zn-In-Si-Sn-Ti alloy anode was 2303 – 246A-h/kg and the close circuit potential was more negative than -0.95V. That indicates this type alloy anode owns an excellent activation with uniformed dissolving performance. Therefore a relatively higher driving voltage than common anodes could be available via the high resistivity testing media. To know the protection potential distribution of steel shell, the numerical calculation was investigated. The anodic and cathodic polarization behaviors were both measured as the boundary conditions. Moreover, the practical potential had been measured for the E01 tunnel immersed in the seawater. The fitted value of CBF was set as an input of BEM simulation so that it was able to obtain the overall potential distribution of the initial tunnel embedded in backfilled stone/brine media. The future effect of SACP of the practical tunnels embedded under the backfilled stone would be evaluated by the integration with modeling process and monitoring of cathodic protection.
