Mechanism of dissipation of excess flow pressures in unsaturated granular soils subjected to seismic excitations

This paper focuses on the response of unsaturated granular soils under cyclic loading and the subsequent dissipation mechanism of excess air and water pressure which can result in the accumulation of water in the upper layer and increase of saturation degree in these zones. A problem that can be the source of structural instability and leading to problems such as capsizing the ships carrying unsaturated iron cargo and landslide failure. The employed numerical model is based on previous developments by the authors of a finite element (FE) approach that considers the hydraulic hysteresis of Soil Water Characteristic Curves (SWCCs) with a mechanical model based on two-surface plasticity to capture the cyclic mechanical response. We demonstrate that the accumulation of water in unsaturated soils subjected to cyclic motions happens during the consolidation stage and our chosen numerical framework can successfully capture this process. It is also shown that the problem can be explained by considering the difference between the dissipation speed of the water and the air phase and the settlement of the unsaturated soil during the consolidation stage.