Analyse à l'échelle microscopique des phénomènes d'humectation et de dessiccation des argiles

Abstract : The drought, emphasised by the current global warming and to come, leads phenomena of shrinkage and swelling of many clayey soils. These phenomena are mainly translated by two major consequences: the modification of the physical properties of the soil which influences directly the agriculture and the deformations leading often differential compaction at the levels of the structures and the buildings. Until today, these phenomena were mainly studied at the mesoscopic level (laboratory classical level) and macroscopic level (buildings scale). Research was led to the microscopic level but in particular contexts (clays intended for the confinement of the radioactive waste). The research work presented in this thesis manuscript constitutes consequently one of the first studies on natural clays, taken in situ from sites affected by the swelling-shrinkage: the Greek montmorillonite and the clay of Romainville. These two clays were subjected to wetting-drying cycles in the Environmental Scanning Electron Microscope (ESEM) in order to quantify the swelling-shrinkage and to study kinetics. An experimental protocol was established, based on the application of the wetting and the drying by stages with regular time of stabilisation and frequency of application. These tests were led in order to analyse: the influence of the mineralogical composition, the study of the effect of scale and the influence of the type of piloting (pressure or temperature). In parallel to these tests, some experiments were led to the mesoscopic level to establish possible links between both levels. They consisted of the study of the evolution of the microstructure, the microporosity and the establishment of the retention curves. The observations made in these two levels led to the development of two methods, voluntarily simplified for ease of implementation and of a fast investigation (preliminary studies, engineering consulting firms). These two methods are, the one analytics, the other numerical, allowing the transition towards the macroscopic level and to be able to estimate the possible shrinkage and the swelling on a given site. The analysis of the results of the tests made in the microscopic level (ESEM tests) leads to the following remarks: the major part of the strains occurs in the high relative humidities; the strains measured in the microscopic level are similar to those measured in the mesoscopic level; the kinetics of swelling and shrinkage are marked by several different phases according to the considered clay; the mineralogical composition, the size of the aggregates and the type of piloting present an influence at the level of the amplitude of the shrinkage - swelling and the kinetics. The analysis of the results of the tests made in the mesoscopic level (laboratory tests) leads to the following remarks: the shrinkage limit (Wr) corresponds to a 13 % moisture content and a void index of 0,52; in the high and medium suctions, the soil presents a compact microstructure with a macroporosity increasing with the suction; in the low suctions, the compact microstructure evolves of sharp outlines of the aggregates in rounder outlines; microorganisms were observed, engendering a very important porosity on the surface, being able to pull an ageing of the ground and the creation of preferential paths for the penetration of the water; with the decrease of the suction, the decrease of the external specific surface and of the microporous volume is observed; the wetting and the drying of samples do not seem to lead no irreversible consequences on the microstructure.
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Theses
Engineering Sciences [physics]. Ecole Centrale Paris, 2011. French. <NNT : 2011ECAP0004>


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Tatiana Maison. Analyse à l'échelle microscopique des phénomènes d'humectation et de dessiccation des argiles. Engineering Sciences [physics]. Ecole Centrale Paris, 2011. French. <NNT : 2011ECAP0004>. <tel-00594238>

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