Evaporation rates can be successfully modelled for soil–atmosphere interaction problems by means of a convective vapour flux at the soil surface equal to the product of a driving force (difference between the vapour density at the soil surface and that of the surroundings) and a mass transfer coefficient characterising the resistance of a boundary layer where the transfers take place. While the vapour density at the soil surface can be deduced from solving the coupled heat and moisture transfer equations for the soil below the surface, the determination of the mass transfer coefficients under varying weather conditions is rarely investigated. Laboratory-scale drying tests are performed on a compacted silt specimen, focusing on the influence of atmospheric conditions (relative humidity and wind speed) on the evaporation kinetics and the mass transfer coefficient. Two experimental techniques are used and compared: a drying chamber with relative humidity controlled through saline solutions and a convective microdryer. New insights are given into the prediction of mass transfer coefficients from mass transfer theories. Finally, the results highlight the necessity of testing specimens that are large enough to define relevant mass transfer coefficients for geotechnical applications.

Predictions of the unsaturated shear strength with generalized effective stress-based approaches disregard the non-uniform microstructure of remolded fine-grained soils. The study aims at investigating the adequacy of microstructurally-based effective stress to predict the unsaturated shear strength of remolded fine-grained soils over a wide range of suctions. For that purpose, shear strength data are acquired on a silty clay soil compacted at two different dry densities through suction-controlled triaxial tests and unconsolidated triaxial tests at constant water content. The microstructure of the soil at the as-compacted state is determined with Mercury Intrusion Porosimetry and is directly incorporated in different expressions of microstructurally-based effective stress available in the literature. The experimental data suggest that compared to the generalized effective stress, microstructurally-based effective stress expressions provide better predictions of the unsaturated shear strength, especially at high suctions. Also, the use of microstructurally-based effective stress is particularly relevant for remolded fine-grained soils compacted at high dry densities, i.e. with a low proportion of macropores.

This work aims at investigating the adequacy of microstructurally based effective stress to predict the shear strength of unsaturated soils over a wide range of suction. For that purpose, shear strength data are acquired on a silty clay soil through two types of unsaturated triaxial tests: suction controlled triaxial tests and unconsolidated triaxial tests at constant water content. The microstructure of the soil is determined with Mercury Intrusion Porosimetry and is directly used in different expressions of microstructurally based effective stresses available in the literature. The large range of suction tested allows to determine the most consistent expression of the effective stress to reproduce the experimental observations.