International audienceThe soil compaction by vehicles is a major factor responsible for physical degradation of cultivated soils. Uniaxial confined compression tests are usually performed to characterise the compaction properties of soil. Two main forms of compression curve have been observed: (i) the bi-linear curve having an elastic rebound curve at low stresses and a linear virgin compression curve at higher stresses; (ii) the S-shaped curve having deviation of the virgin compression curve at high stresses. In the present work, uniaxial confined compression tests were performed on four soils having various textures and different plasticity. Tests were performed on undisturbed and remould samples, at various initial dry bulk densities and water contents. The S-shaped compression curves were observed more frequently when the clay content and/or the initial water content were high. In addition, the S-shaped curves were observed more frequently on remould soils than on undisturbed soils. The difference between the compression of air-filled pores and that of meso-pores storing water subjected to high capillary forces could explain the observed S-shaped curves
S U M M A R YThe damage of a porous rock (Euville oolitic limestone) was studied through uniaxial stresscycling tests. An experimental device, allowing the simultaneous and continuous measurement of strains (in two perpendicular directions) and five elastic wave hree P waves and two S waves) velocities in two different directions under fully controlled hydrous conditions, was developed for the work presented in this paper. Hence, the damage was monitored in a really precise and continuous way through the evolution of dynamic and static elastic moduli. The evolutions of wave velocities and elastic moduli, which reproduce very remarkably the shape of the stress-strains curves, showed that the limestone, initially isotropic, became progressively anisotropic during uniaxial loading due to microcrack damage. Indeed, even if the creation of microcracks is probably scattered and isotropic before the coalescence of microcracks, as shown in past studies, pre-existing microcracks and penny-shaped pores which are perpendicular (or almost perpendicular) to the uniaxial stress direction closed, whereas axially-oriented microcracks opened. The anisotropy of the damage is completely reversible but some of the damage is irreversible. V P(90 • ) , which cannot record the opening of these microcracks, started to decrease just before the macroscopic failure of the sample and can detect, therefore, very precisely the macroscopic failure of the material. The influence of water on the strength and deformation of the Euville limestone was analysed by considering both the hydromechanical and physio-chemical ('Rehbinder effect', intergranular pressure solution and subcritical cracking) effects of water.
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