Numerical modeling and simulation of water transfer in soil with low water contents

In this paper, we present the results of numerical model and simulation of water transfers in soils with low water content. The main objective is to identify the major phenomena which allow to adequately describe water transfer in soil between the filtration of liquid phase and the capillary rise. We have shown that in the superficial layer of soil, the ambient atmosphere has less influence on the transfer phenomena at low water content. The bibliographic works realized on water transfer mechanisms do not allow to draw conclusions at very low water contents that is why the present manuscript brings answers to concerns not yet elucidated. The methodological approach is based on the off-center upstream method for the flux convection and the implicit scheme in time for the discretization using the Finite Volumes method. The numerical resolution of the problem is based on the Newton-Raphson method. Water profiles for different sizes of sample (30 cm, 40 cm, 50 cm and 60 cm) and for initial water contents, w(0), varying from 2 to 7% were obtained at regular time interval of 85,000 s. All the simulation results highlight two distinct domains for water contents w < 4 and three distinct domains for water contents w >= 4%. Indeed the lower limit conditions on the flux of filtration cause an accumulation of water leading to an increase in water contents for initial water contents of 4%, 5%, 6% and 7%. We note the existence of a limiting water content w(lim) = 2.4% representing the hygroscopic limit of the soil.

Automated summary

This paper presents the results of a numerical model and simulation of water transfers in soils with low water content. The main objective is to identify the major phenomena involved in water transfer between filtration and capillary rise in soil. The study shows that the ambient atmosphere has less influence on water transfer in the superficial layer of soil with low water content. Existing literature on water transfer mechanisms does not provide clear conclusions for very low water contents, hence this manuscript provides new insights. The methodology used an off-center upstream method for flux convection and an implicit scheme in time for discretization using the Finite Volumes method. The numerical resolution of the problem was based on the Newton-Raphson method. The simulation results reveal distinct water content domains for different initial water contents, and the existence of a limiting water content representing the hygroscopic limit of the soil.