Investigating ageing effects on bored pile shaft resistance in cohesionless soil through field testing

This study investigates the influence of time (ageing) on the uplift capacity of bored piles in cohesionless silty sand through a full-scale field testing programme. Four reinforced concrete piles, two shorter (16 m) and two longer (21 m), were installed and tested under axial tension at two different ageing intervals: 35 days and 165 days post-construction. The load-displacement behaviour, load transfer characteristics, and shaft friction mobilisation were monitored using load cells and embedded strain gauges. Results showed that while all piles exhibited similar ultimate capacities, the aged piles consistently demonstrated stiffer responses and earlier mobilisation of shaft resistance. Extrapolated estimates showed modest increases in estimated ultimate uplift capacity, ranging from 2% to 7%, with ageing. Strain gauge data also indicated more uniform load transfer in the aged piles, suggesting time-dependent improvements in pile-soil interface behaviour. The findings confirm that even in cohesionless silty sand, moderate ageing effects can enhance uplift performance, but the extent of improvement is small and variable. These findings provide a valuable reference for evaluating uplift design assumptions and interpreting field test behaviour in similar soil environments.