Particle scale responses during high velocity impact penetration in dry and saturated sand: A coupled CFD-DEM study

Impact penetration testing enables rapid in situ geotechnical characterization, particularly in inaccessible or hazardous environments. However, the particle-scale penetration response of saturated sand remains insufficiently understood. This study investigated impact penetration into dry and saturated sand at initial velocities of 10-40 m/s using a coupled CFD-DEM model calibrated against laboratory test results. Within the investigated range, the peak cone tip resistance increased approximately quadratically with initial velocity, while saturated sand exhibited higher peak resistance and stronger velocity dependence than dry sand. Particle-scale analyses indicated that saturated sand exhibited smaller particle displacements, a narrower region of velocity disturbance around the cone tip, and more cone-particle contacts. Force chain statistics further showed that, despite a lower local mean interparticle contact force, saturated sand transmitted a larger share of local interparticle normal force through strong force chains. Fluid-particle interaction forces were concentrated near the cone tip and increased markedly with penetration velocity. Their net opposing action on particle motion near the cone tip at peak resistance was consistent with a fluid contribution to the higher penetration resistance in saturated sand. These findings characterize velocity-dependent differences between dry and saturated sand and provide numerical evidence for interpreting impact penetration behavior under the investigated conditions.