Densification mechanism of granular soil under dynamic compaction of proceeding impacts

This paper numerically studies the densification mechanism of granular soil under dynamic compaction (DC) of proceeding impacts. Two-dimensional model of material system was established by the coupled discrete element-finite difference method to reveal the dynamic responses at both macro- and microscopic levels. Firstly, normalized crater deformation simulated was compared with existing in-situ experimental data, ensuring that the ground deformation under DC has been reproduced reasonably. Then, the micro-fabric evolutions such as the local porosity, contact normal orientations and displacement paths of tracer particles were analyzed incorporating with the macro- phenomena such as soil deformation and dynamic stresses. In this way the deformation mechanism of soil is explained at the particle scale. The responses of the DEM model show that an extremely compacted soil plug forms and develops under successive impact loading. This results in obvious lateral squeezing effect that forcing the soil outside the tamper radius being compacted. The evolution of contact normal orientations and displacement paths of tracer particles further indicate that the lateral squeezing effect varies with the relative position of measured regions to the tamping point. The significant improvement area mainly lies in the range of 30 degrees intersecting with the tamping point.