On Soil Deformation and Stress Redistribution Around Pressed-in and Vibrated Displacement Pile Tips

Abstract

The experimental study compares soil displacement trajectories around model pile tips obtained from Digital Image Correlation (DIC) for different penetration modes. Monotonic and cyclic quasi-static penetration under plane strainresembling conditions in dry sand and vibratory model pile penetration in saturated sand are investigated. The comparison results agree well although the penetration mode and the degree of saturation differ considerably. In the experiments, the soil below the pile tip is first pushed downwards as the pile approaches and is then moved more and more sidewards. A slight uplift of the grains is observed when the pile tip has passed. Subsequently, a clear trend of the soil adjacent to the pile shaft to move towards the pile is measured in the case of quasistatic cyclic and vibratory penetration. This trend is considered to be an indicator for "friction fatigue", the degradation of shaft friction at a certain depth as the pile penetrates further. A discussion on the comparability with numerical results and on the influence of disturbing boundary effects concludes this contribution.