Design and construction of a multi-anchored retention system within Ashfield Shale

Excavation for a four-storey basement alongside a busy commuter railway line required both temporary and permanent support within the Ashfield Shale formation. Rail authority requirements were such that the new building had to remain independent from the retaining wall supporting the railway line. A multi-anchored wall was therefore adopted to permanently support the excavation.

The design of the permanently anchored retaining wall was carried out using allowable or ‘working’ stress methods based on the worst ‘credible ’ design wedge load, taking into account surcharge and earthquake loading. A probabilistic analysis was used to determine the worst ‘credible ’ design wedge load acting on the wall based on a review of geological data in the area. This paper briefly presents some of the considerations involved in the design of the permanent wall with emphasis on the methods used and experience gained during construction.