Using water injection to remove pile base resistance during installation

摘要

Water injection is currently used to reduce pile installation resistance in a variety of soil conditions. However, the mechanisms governing load reduction remain unclear, and there are uncertainties over the effect of water injection on the long-term behaviour of the installed pile. This paper offers some insights based on centrifuge model tests, with the aim of clarifying the installation mechanism. A novel approach to scaling was required, and the particle size was deemed to scale with enhanced gravity. A three-stage variable permeability mechanism is proposed and validated against a series of instrumented pile installations. Various pile installations were completed using different flow rates and injection geometries to investigate the differing injection effects. Base resistance was eliminated by forming a fluidized region around the pile toe, extending to two pile radii. However, fluidization could not be maintained beyond a critical depth of installation, and base resistance increased thereafter.