Investigation into soil displacement near a jacked-in pile in sand

Abstract

When a pile is driven into soil, the soil is pushed away which results in significant changes in both stress state and strain state. Using Finite Element Code to simulate the pile installation process has been not yet completely successful partly due to the limited knowledge of the governing behavior of the soil around a displacement pile. An investigation into the soil behavior during a static installation of a jacked-in pile in dry sand is conducted in this research. The mechanism of pile installation is studied under a plane strain condition. A measurement method based on (1) digital photography and (2) digital image correlation was applied to observe the soil deformation around the pile during installation. Series of simple tests were performed and proved that the method offers sufficient accuracy concurrent with large number of measurement points within the observation area. A series of four pile installation tests, with stress controlled on the top boundary, is conducted. The influence of initial void ratio and an additional surcharge on soil deformation was examined. The resulting displacement field was used to deduce the strain field around the pile and strain paths during pile installation process. The rigid/nearly-rigid cone of soil is found under the pile tip. Zone of high high volumetric strain and high shear strain locates below the cone and radially extends with respect to the cone. That a zone of high volumetric strain and considerable shear strain occurs along the pile shaft during continued penetration suggests an existence of the shear band. The inwards relaxation of soil elements near the pile shaft is confirmed by the tail at the end of the displacement trajectories and the peak of rotation paths in loose condition. The steady state deformation is also observed in loose assembly only.Geo-EngineeringGeotechnologyCivil Engineering and Geoscience