| In order to better understand the effects of the soil hydraulic conductivity at saturation Ks on
the water content dynamics in a layered soil, a steady infiltration process was modeled in a
soil characterised by exponential decreasing of Ks with depth. The soil domain is assumed
finite, unsaturated, and the flux takes place toward the increasing water content direction. At
the bottom of the domain a saturation condition is assumed. By means of analytical solutions
of the Darcy’s law, the profiles of the total (Φ) and matric (Ï) water potential, of the
conductivity (K) and of the effective degree of saturation (s) were determined and compared
with a numerical solution. Two soil classes of constitutive laws were considered, respectively
characterised by (i) a finite and (ii) an infinite slope of K(Ï) as it approaches the soil
saturation.
The obtained profiles stress the high sensitivity of the solution to the K(Ï) model near
saturation, and its effects are furhermore emphasized by the decrease of Ks with
depth. For the second soil class, in fact, a strong reduction of the saturation value
Ks is represented for K, even for very little values of |Ï| which means nearby
saturation conditions. With regard to the first soil class, the flux needs a higher
value of the gradient |dΦ-dx| to take place, and values of Ï are much closer to the
saturation values throughout the soil profile. The flux is therefore sensibly governed by
gravity.
The obtained results can contribute to improve our understanding of the role played
by the upper layers of dishomogeneous soils to control the infiltration processes. |