Abstract:
The development of residual (or locked-in) loads in driven precast piles has been extensively investigated
in recent decades but, contrastingly, cast-in-situ piles are still often falsely assumed to be unaffected. Unlike
precast piles, cast-in-situ piles must be given sufficient time for the concrete to cure and strengthen in the
ground prior to loading. The interaction between the concrete and surrounding soil is complex with several
processes influencing the strains within the pile during this period. Driven cast-in-situ (DCIS) piles are of
particular interest given that residual loads can be potentially developed during both driving and casting
phases. This paper critically reviews four instrumented end-bearing DCIS piles in which temperature and
strains were continuously monitored from installation, with the objective of identifying individual processes
contributing to the measured strains prior to testing. Strains at all depths recorded a net compression and
continued to increase with time up to commencement of load testing. Residual strains in the Avonmouth
test piles were interpreted to be influenced by temperature (internal concrete and ambient soil and air
temperature), increasing concrete density with curing, consolidation of soils due to excess porewater
pressure dissipation, and swelling from groundwater absorption. Several residual load interpretive methods
are evaluated with the Siegel and McGillivray (2009) approach method deemed the most realistic given its
consistency with the skin friction full mobilisation theory of the Unified Design method. The case studies
presented herein provide a unique opportunity to research DCIS piles.