Effect of installation method on static and dynamic load test response for piles in sand

Abstract

Static load tests (SLTs) are rarely performed on offshore piles, instead relying on dynamic load tests (DLTs). Evaluation techniques for DLTs were developed originally for solid piles, and caution is needed in applying the techniques directly to open-ended piles, particularly for the large-diameter monopiles used for offshore wind turbines. Centrifuge tests are reported here, investigating the influence of pile installation method and sand relative density for pairs of DLTs and SLTs. The piles were successfully driven to penetration of 3–4·6 diameters, which was much deeper than proved possible to jack the piles. Due to limited hammer energy, loads mobilised during the DLTs were less than 25% of the corresponding SLT values. The soil resistance mobilised at limited displacements was lowest for wished-in-place piles, and also for DLTs conducted on shallowly embedded jacked piles. For driven piles, the DLT and SLT results were relatively consistent, with surprisingly similar values for piles driven into loose and dense sand despite significant differences in cone resistance. Given the potential for low mobilisation of soil resistance in DLTs, care is needed when using DLTs for evaluating the static axial pile capacity of open-ended piles of low length-to-diameter ratio.