Caractérisation hydrodynamique du sol in situ par infiltrométrie à disques : analyse critique des régimes pseudo-permanents, méthodes transitoires et cas des sols encroutés

摘要

The work presented here is related to the in situ hydrodynamic characterization of near-saturated soils using tension disc infiltrometers. The study is organized in three parts. The first part reviews existing methods based on the analysis of steady state of axisymmetric infiltration using Wooding's equation. It is shown that techniques which combine information from measurements at a range of surface matric potentials are the most stable and are not limited to quasilinear soils. The second part shows how, in practice, to make use of a simple equation for transient axisymmetric flow to determine capillary sorptivity and hydraulic conductivity without the attainment of steady conditions. A new method for determining sorptivity during the early stages is proposed taking into account the sand contact layer. Several methods are then proposed for estimating unsaturated conductivity, which are numerically tested and compared with classical approaches. It is shown that, for most field situations, the influences of gravity and lateral capillary flow on infiltration are of a similar order of magnitude, which enables both sorptivity and conductivity to be estimated. One of the consequences of the analysis is the proposal of a new time scale for disc infiltrometers that takes account of both gravitational and geometric effects. The third part concerns crusted soils, for which classical methods fail. The use of a minitensiometer coupled with the infiltrometer allows differentiation between infiltration into the crust and into the underlying soil. Using this information, the hydraulic conductivity of the crust is estimated from sorptivity measurements. Values obtained in this way were validated by comparing measured values of runoff with predictions using a two-Iayer infiltration model based on the assumptions of Green and Ampt. It is shown that crusts around one centimeter thick have a large impact on the amount of runoff.