Rainfall infiltration into swelling soils

Water movement through swelling soils exhibits features different from those observed in rigid soils, mainly due to the presence of the envelope-pressure potential. The gouerning equation for soil water movement is the generalized Richards equation, where p is the dry bulk density in some reference state, chosen to be the initial one, po is the mass density of soil water, 9 is the gravimetric water content, D is the soil water diffusivity, z is a material coordinate taken positive upwards, and H is a gravity-envelope-pressure parameter given by: bo the wet bulk density, and 'bw K representing the hydraulic conductivity, V the slope of the shrinkage curve. For a rigid soil H is equal to K, but in deformable soils H is lower than K, becoming negative at high water contents. Rainfall infiltration can be described by integration of (1) in a soil profile, whose initial water content profile is known, subjected to an external flux condition at the soil surface, r being the rate of rainfall