Installation Effects on Stress and Grading Around Displacement Piles in Sand

A 3D discrete element model (DEM) is used to model earlier calibration chamber experiments that investigated the responses seen when highly instrumented model displacement piles were installed in Fontainebleu sand. The crushable DEM particle model was calibrated against earlier laboratory element tests. The impact of particle breakage on the piles’ behaviour is investigated and it is shown that monotonic and cyclic jacking lead to similar tip resistance trends. The DEM analysis predicts experimental measurements of the stresses developed in the sand surrounding the piles during and after penetration realistically. It also allows micromechanical features to be examined that are hard to detect using experimental or continuum numerical methods. Grain crushing is observed below the pile tip and the analysis of particle stresses and force chains highlight how arching develops around the shaft. Circumferential force chains form around the shaft during the unloading stages of each jack stroke. Comparison between analyses that consider crushable and uncrushable grains indicates that particle crushing induces more marked stress relaxation close to the shaft and more marked circumferential arching.