Critical assessment of pile modulus determination methods

The elastic modulus of a concrete pile is an important parameter for the interpretation of load test results. This paper summarizes and assesses the methods available for its determination. Ten methods have been identified of which four are based on laboratory tests and the remainder on in situ pile instrumentation. Six of the methods have been used to interpret the modulus of a concrete pile subject to an axial load test. From the analyses, it was found that creep strains that developed during load-holding periods can have a significant effect on the modulus value if not allowed for when assessing the measured strain values. Based on a comparison of the derived pile loads the secant modulus method was found to be the most satisfactory. The tangent modulus method was also found to be a useful tool for investigating the effect of a partial steel casing — a feature of the method that has not been discussed before. Surprisingly, the theoretically correct transformed area equation had the worst performance, probably because of the chosen method for obtaining the concrete specimens on