Janssen effect in submerged granular columns

We experimentally study the effect of an interstitial liquid on pressure saturation in a confined granular column, specifically regarding the Janssen effect. First, we analyze the case of dry grains in a cylindrical container as a reference system. Then, the experiments are carried out in the same container filled with water, considering two scenarios: (i) when the grains are denser than water and sediment under gravity, and (ii) when the grains are less dense than water and rise to the surface due to buoyancy. In the first case, we observe a Janssen-like effect that depends on the particle density ratio to the liquid density. Stress saturation is evident when very dense particles are poured; however, this saturation nearly disappears for grains with a density similar to that of water. We describe these experimental observations using a Janssen-like approach that accounts for the hydrostatic stress introduced by the surrounding fluid. In the second scenario, a buoyancy-driven Janssen effect is found when the pressure is measured at the top of the column, and the model successfully accounts for this phenomenon. Importantly, these results demonstrate the significance of grain-to-grain stress transmission, even for granular columns suspended in a fluid.