Comparison of rapid load pile testing of driven and CFA piles installed in high OCR clay

The current analysis of rapid load tests (RLT) such as Statnamic is normally based upon empirical correlations with static pile tests in similar soils. In certain soil types, such as clays, the number of case studies used to develop analysis and allow selection of appropriate rate effect correction are limited. Due to these limitations, no distinction is made in the selection of correction factors between pile type and pile installation techniques. In clay soils it is well known that driven piles may have a significantly enhanced capacity over cast in situ piles of similar cross-section. To test the effect of pile installation techniques on RLT analysis, RLT testing and static testing were undertaken on precast driven concrete piles and cast in situ CFA piles installed in high plasticity London Clay. The results show that the installation technique does not appear to affect the magnitude of the rate effects, provided modifications are made to the analysis to account for the previously reported differences in static capacity between different installation techniques. Based upon the findings, it is suggested that a distinction should be made in RLT analysis between pile type and installation techniques, and for existing analysis techniques, further case studies based on rate correction parameters are required, especially in clay soils.