This paper presents an innovative procedure to model collapsible soil before-during-after inundation using the finite element method. The proposed numerical model can easily be implemented to analyze the case of shallow or deep foundations on/in collapsible soils. The model developed takes into account soil suction reduction resulted from progressive inundation, from two different aspects: soil stress state and its properties, and irrecoverable volume change of the soil. The theories of Unsaturated Soil Mechanics, including Soil Water Characteristic Curve (SWCC), are employed to take into account the effects of inundation on collapsible soil properties. For illustration purpose, numerical modeling of a single pile in collapsible soil before-during-after inundation is presented.