Durability

It is important that the long term performance of the structure is considered both in the choice of structural form and in the design of construction details. Failure to do s may result in maintenance problems requiring costly repair. 

Section 4 of Eurocode 3 Part 5 covers the design for durability of steel piles. Two basic approaches exist for designing to counteract corrosion. The first of these is to accept that it occurs and include a sacrificial thickness in the calculation of required section thickness during design. The second is to include some measure to protect the pile in some way, with a coating (paint or galvanising) or encasement (concrete or grout protection), or cathodic protection. For steel basements, including a sacrificial thickness and painting are the most likely protection measures. 

Designing to include for a sacrificial thickness requires an estimate of section loss over the design life of the project. Piles with a design life of less than four years do not need to take account of corrosion, but for most basement design, it will need to be considered.

Corrosion rates depend on whether the pile is in contact with soil, air, fresh or salt water, and whether the soil is aggressive or not. Different zones of the pile will be under different conditions and so all relevant combinations and locations need to be considered relative to the moment demand on the sheet pile.

Loss of section due to corrosion is presented in the UK NA of Eurocode 3 Part 5 and lists the section loss per side of sheet pile as recommended for different conditions adjacent to the wall. Although the marine and freshwater conditions are more applicable to river and quay walls, there may be unusual situations where they are applicable to building retaining walls and hence they are included for completeness.

To complement EN1993-5 the Steel Piling Group has published P422 Durability of Steel Piling. This is an in depth guide providing industry with an overview of the corrosion process, it outlines the corrosion performance of steel piling in various environments, and reviews the protective measures that can be taken to increase the life of steel piles where necessary. The guide presents a worked example of steel sheet pile design to illustrate the approach to designing for durability. The guide is free of charge and can be obtained from the downloads page.

Manufacturers’ product data typically include charts which can be used to determine the revised elastic section modulus for the calculated total thickness loss for different section types.

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