Port Works Design Manual : Part 2

39against corrosion for the design life of the structure. To account for the uncertainty ofcorrosion below the seabed, corrosion protection should be extended to a minimum depth of3 m below the seabed level. Below seabed, an allowance for corrosion loss of 0.05 mm peryear is considered reasonable on the outside face of the piles without corrosion protection.For temporary structures, with a design life not greater than 10 years, an allowance forcorrosion loss of 0.5 mm/year may be assumed on the outside face of the piles below the tidalzone where there is no corrosion protection. At and above the tidal zone, full corrosionprotection is strongly recommended, even for temporary structures.3.7.2 Reinforced Concrete PilesFor reinforced concrete bored piles, the concrete should follow the marine concretespecification as given in Chapter 6 of Part 1 of the Manual and should be cast under drycondition with adequate compaction and curing as far as possible. The steel casing forforming the bored pile may act as a sacrificial casing as an additional benefit to providecorrosion protection for the concrete. The sacrificial casing should not be included in thedesign of the piles.3.7.3 Corrosion MonitoringRegular inspection on the integrity of the protective coatings of the piles and the extent ofcorrosion of the sacrificial casing, as appropriate, is essential to ensure the structural safety ofthe piers during the design life. For each pile, a sufficient number of measurements shouldbe made at each level during each inspection, to ensure an overall assessment of the conditionof the piles. For cathodic protection system, the inspection, monitoring and maintenance ofthe piles should be undertaken by a suitably qualified expert.3.8 CatwalkThe catwalk connecting the shore and a piled deck jetty may be in the form of a concreteblockwork structure, a piled deck structure or a rubble mound structure, depending on the siteconditions, configuration of the pier and other project considerations. Guidance on thedesign of a piled deck structure and a blockwork structure are given in this chapter and thenext chapter, respectively. For a rubble mound structure, the structural design is similar tothat for a rubble mound breakwater, given in Part 4 of the Manual. For a blockwork orrubble mound catwalk, openings may be introduced at appropriate intervals to enhance the