Laboratory investigation to determine ageing of pile shaft friction in clay

The shaft capacity of driven piles in clay increases with time even after installation-induced consolidation is completed. However, existing studies have shown that these gains in capacity are variable and cannot be predicted reliably. Projects such as those involving life extension of existing offshore platforms (which often involve increased platform loads) as well as those considering foundation re-use provide the motivation for this paper, which investigates the potential for model-scale testing to replicate the ageing characteristic of shaft friction in a laboratory environment. The study employs a number of model piles installed in reconstituted, high-plasticity Onsoy clay in laboratory pressure chambers. The first-time tension load tests on these piles, performed over the period of 1 year after installation, are compared with a similar series of tests on full-scale driven piles in Onsoy, Norway. Good agreement between laboratory and field experiments is observed when allowance is made for the significantly longer consolidation periods of the full-scale piles. This finding implies that ageing effects of shaft friction in clay can be investigated over relatively short time periods using model piles in laboratory testing chambers.