AS 4678 “Earth Retaining Structures” is a Limit-State Standard

AS 4678 is modern limit-state design standard, that employs partial load (action) factors and partial resistance factors (rather than global factors of safety). This approach allows for greater flexibility and better understanding of the behaviour of retaining structures and their design for factored loads from supported structures.

When considering the relevant limit states (aka failure modes), an engineer must select appropriate load and resistance factors, including those that relate serviceability modes of failure. Appropriate factors must also be used when determining the soil/structure interaction.

With some exceptions, Australian retaining structures must comply with the structural reliability indices for ultimate structural failure, set out in the National Construction Code (NCC 2025). AS 4678 is Deemed-to-Satisfy with NCC 2025. Also required, but not quantified, is reliability under serviceability actions and responses.

I welcome ongoing discussion on the interaction of practical considerations, NCC, AS 4678 and previously used global factor of safety approaches to retaining wall design.