Characterisation of the effects of time on the shaft friction of displacement piles in sand

Abstract

This paper describes a new approach to represent the effects of time on the shaft friction of displacement piles in sand. The proposal is based on the findings from pile test programmes performed at a test bed site in Western Australia in addition to data from well-documented full-scale pile tests. The investigation reveals a significant influence of installation disturbance on the subsequent gain in capacity (set-up) of shaft friction. Set-up is viewed as a recovery process, rather than a capacity gain, following the disturbance induced by pile installation. Gains in capacity in the medium and longer term tend to vary with the logarithm of time, while capacity changes shortly after installation are seen to be relatively small. A new expression is proposed to represent this ageing characteristic, which also incorporates a limiting (or maximum available) shaft friction.