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RESEARCH PRODUCT

Soils with Specific Features

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This chapter deals with some specific features of soil that are relevant for interpretation of infiltration experiments. Infiltration in water repellent soils is first examined. After summarizing the causes of hydrophobicity, phenomena associated to infiltration in water repellent soil, including reduced infiltration rates and irregular wetting front advance, are illustrated. The Water Drop Penetration Time (WDPT), the Molarity of an Ethanol Droplet (MED) and the Repellency tests for quantitative assessment of soil water repellency are presented. Particular attention is given to estimation of subcritical soil water repellency by means of soil sorptivity measurements conducted with infiltrating liquids of different surface tension (e.g., water and ethanol). Infiltration in crusted soil is examined in the second part of the chapter. After examining the different causes of soil surface sealing, water infiltration experiments for crust characterization are presented which include (i) the transient method proposed by Vandervaere et al. (1997) that uses a tension infiltrometer and a minitensiometer placed at the crust-subsoil interface; (ii) the inverse procedure developed by Simůnek et al. (1998) to obtain a complete hydraulic characterization of the two layered crust-subsoil system; (iii) the method proposed by Touma et al. (2011) to estimate the hydraulic resistance of the crust that combines two infiltration experiments conducted before and after removing the sealed layer. Determination of saturated hydraulic conductivity of low permeability soils is the topic of the third part of the chapter. Given that steady-state flow analysis procedures cannot be applied in practice due to the very long times, measurement of conductivity of low permeability soil is based on the transient phase of the infiltration process. In particular, these techniques use early-time transient flow established by constant (early-time constant-head, ECH, technique) or a falling (early-time falling-head, EFH, technique) head of water on the infiltration surface, or realizing an initial constant-head stage followed by a falling-head phase (sequential early-time constant-head/falling-head, ECFH, technique). A falling-head infiltrometer technique for measurement of saturated conductivity of low permeability wet soils is also illustrated. Concepts and related models developed for analysing preferential flow are illustrated in the fourth part of the chapter. In particular, the focus is put on dual permeability models that implement water flow in and between two pore regions, i.e. matrix with slow flow and a fast-flow macropore region. The following subjects are successively presented: conceptual models for the description of preferential flow, related analytical and numerical models, methods for detection of preferential flow during water infiltration experiments, and methods to characterize dual permeability behaviors using water infiltration experiments.