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Extreme, extended wet and dry seasons increase the adverse effects that soil wetting and drying cycles have on the response of shallow geotechnical structures. In expansive soils, volumetric changes due to water content variations may result in the incompatibility of deformations at the soil-structure interface. This study proposes a physical approach and a numerical model to address the soil-atmosphere-structure interactions during soil saturation and desiccation. Experimental desiccation tests were performed on relatively thin, compacted kaolin clay samples that represent the soil-atmosphere boundary. A climatic chamber was used to impose atmospheric conditions of air relative humidity, temperature, wind velocity, and irradiance on the soil surface. Empirical mathematical expressions were obtained to estimate soil desiccation rates as a function of basic atmospheric parameters and soil properties. The experimental desiccation approach was complemented with a coupled thermo-hydro-mechanical (THM) numerical model for unsaturated soils. The coupled THM model calculates water and thermal fluxes, soil volumetric changes, vertical stresses, and the compatibility of soil-structure movements during swelling and shrinking. An example of the capabilities of the numerical model is presented for a full-scale geotechnical problem.

Reusing excavated material in geotechnical engineering reduces the carbon impact of a project. Such materials are usually placed in a compacted state in order to achieve the mechanical and hydric characteristics required to guarantee the safety of the structures. A good geotechnical knowledge of the materials is therefore necessary as well as a good anticipation of their behaviour over time. Indeed, in some situations, as in the case of waste storage, a low hydraulic conductivity is required. The use of crushed rocks rich in clays (argillite), possibly improved by adding bentonite, could be interesting. However, this addition, beneficial in terms of hydraulic conductivity, could be damaging from a mechanical point of view by the development of cracks at the interface atmosphere-compacted soil. For this purpose, samples compacted at the normal Proctor optimum are exposed to a relative humidity of 46% and a temperature of 22.5°C. The thickness, mass and surface condition (cracking) were monitored during the drying process, and measurements were taken in the thickness of the specimen after 29 hours of exposure. The results make it possible to compare the two materials at the same compaction energy. The argillite sample shows a significant shrinkage but no cracks at this scale. On the different hand, with the addition of bentonite, a significant cracking was observed and analysed. These results provide information on the hydromechanical behaviour of unsaturated fine soils at the atmosphere-compacted soil interface.

Erosion of the base layers in rigid pavements is a complex hydro-mechanical process that rapidly reduces the structural integrity of these structures. This research revisits a vertical shaking table testing method to characterise the erosion susceptibility of the materials used on base layers in rigid pavements. The procedure consists of applying a vertical vibration to a cylindrical sample of the material under evaluation, which is partially immersed in water in a cylindrical metallic container with a high-strength concrete base. The vertical movement of the sample causes a radial flow of water on its base, which induces high shear forces that eventually erode the bottom of the sample. The volumetric loss of material from the testing sample under different water velocities and pressure conditions is used to quantify its susceptibility to erosion. After presenting the theoretical principles and the numerical formulation of the hydro-mechanical erosion processes occurring in this test, the experimental method was applied to characterise the erosion susceptibility of five different materials. The results suggest that the vertical shaking experimental technique is more versatile and accurate in quantifying the erosion susceptibility of base materials than available standardised tests. [ABSTRACT FROM AUTHOR]