Etude expérimentale de l'influence du degré de saturation sur le comportement instable du sable de Fontainebleau sous sollicitation cyclique : application aux risques de liquéfaction

Abstract : This work aims to study influence of saturation degree on unstable behavior under cyclic loading, and more specifically against risks of liquefaction. The potential of liquefaction of Fontainebleau sand is evaluated experimentally, in function of its initial degree of saturation. A theoretical frame is established, defining three areas of saturation states: a fully saturated zone, where pore fluid consists only of water; a nearly-saturated zone, where pore fluid consists of water and dissolved or occluded air, and where effects of suction are neglected; an unsaturated zone, where gaseous phase is considered as continuous, and suction is positive. Boundaries of this theoretical frame are defined in terms of saturation degree. Each zone is then experimentally investigated. Cyclic triaxial tests are performed. For each test, initial conditions of saturation are imposed, in agreement with saturation conditions parameters defined in the theoretical frame. For unsaturated zone investigation, a special equipment of Negative Water Column is developed and used in the laboratory in order to obtain initial conditions of suction in the sample. For nearly-saturated zone investigation, initial conditions of saturation are imposed through a calibration curve, linking Skempton coefficient B and saturation degree, previously obtained in the laboratory. Results show that Fontainebleau sand liquefies under cyclic loading, even when initial saturation degree is below 100%. More specifically, every sample tested on the nearly-saturated zone are in a complete state of liquefaction after cyclic loading is applied. Samples on the unsaturated zone did not show any sign of instability, under same conditions of stress applied and density. It seems that distribution pattern of pore fluids within granular material plays a major role regarding potential of liquefaction. In state of stress and density tested in this study, continuous air phase and positive suction prevent granular material from liquefaction. On the contrary, if dissolved or occluded air as a pore fluid delays the onset of instabilities and liquefaction, it does not prevent it.
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Mathilde Vernay. Etude expérimentale de l'influence du degré de saturation sur le comportement instable du sable de Fontainebleau sous sollicitation cyclique : application aux risques de liquéfaction. Génie civil. Université Clermont Auvergne, 2018. Français. ⟨NNT : 2018CLFAC013⟩. ⟨tel-01936782⟩

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