Comparing rapid load pile testing for driven and CFA piles in London 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 selection of correction factors does not distinguish between pile type or pile installation technique. In clay soils it is well known that driven piles may have significantly enhanced capacity over cast insitu piles of similar cross-section. To test the effect of pile installation technique on RLT analysis RLT testing and static testing were undertaken on precast driven concrete piles and cast insitu CFA piles installed in high plasticity London Clay. 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 RLT analysis should distinguish between pile type and installation techniques and for existing analysis techniques further case study based rate correction parameter are required, especially in clay soils.