Micromechanics of Pile Cyclic Response in Sand

A 3D discrete element model is used to investigate the axial cyclic response of a small-scale displacement piles installed in Fontainebleau sand. Calibration chamber experimental results from literature are used to validate the pile penetration phase of the DEM model which is then employed to simulate stress controlled vertical cyclic loading. The crushable DEM particle model is calibrated using high pressure element test data for the same sand. The model predicts the experimental stress measurements surrounding the jacked pile in both penetrating and unloaded conditions. The DEM model is used to assess micromechanical features hard to detect using experimental and continuum numerical methods. Grain crushing within the soil is observed to occur only below the cone during pile penetration. The analysis of particle stresses and force chains highlight how arching develops around the shaft. These arching effects create a sort of shield around the shaft causing the radial stresses to be lower. After pile installation is completed, a numerical parametric study of stress controlled cyclic axial loading of the pile is performed. The results show that depending on the magnitude of the cyclic load stable or metastable pile cyclic response is attained. The cyclic load amplitude also influences in different ways both stress and density profiles around the pile. These results may serve as a step forward to the understanding of installation effects on axial cyclic performance of jacked piles in sand.