Impact-induced pore pressure dissipation in saturated sand: test and theoretical analysis

In practical engineering, transient impact loads such as pile driving are common. In this study the dissipation mechanisms of excess pore water pressure (EPWP) in saturated sand under impact loading were investigated through integrated experimental and theoretical approaches. Controlled impact tests were conducted on one-dimensional soil columns with varying particle sizes (coarse, medium and fine) and impact amplitudes. The results revealed a two-stage dissipation process: stage I, characterised by gradual dissipation due to particle rearrangement, and stage II, marked by relatively rapid dissipation driven by drainage. The duration of stage I is strongly dependent on permeability, following fine sand medium sand coarse sand. A higher load amplitude notably prolonged stage I, especially in the low-permeability fine sand. A distinct ‘solidification front’ between the two stages was found to migrate linearly from the bottom to the top of the soil layer, differentiating impact loading from the non-linear migration observed under cyclic loading. Theoretically, a modified non-linear compression relationship incorporating an atmospheric pressure term (e-σ′/paα) outperformed the traditional semi-logarithmic model in simulating EPWP dissipation in sand. Experimental validation confirmed good agreement with the theoretical predictions. The findings of this work provide a predictive framework for post-liquefaction EPWP evolution, with practical implications for foundation stability assessment and liquefaction mitigation under transient impact loads.