During the design phase and the realization of building pits in the saturated soft soils of the Netherlands, often questions show up with respect to the effects of unloading the subsoil. Due to the reduced pressure, the soil will expand which we call “bottom heave” or “swell”. Especially for cohesive soils with a low permeability, it is hard to predict how fast the swell will develop and whether it may result into additional loads on underwater concrete floors and piles.