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Transport en fracture et interaction avec la matrice : une expérience analogique

Abstract : We characterize in the laboratory the solute transport in a single fracture, as well as the fracture-matrix interaction during transport. Our experimental setup consists in a 100x5x0.5 cm3 synthetic plexiglass fracture, the lower wall of which is either an impervious plane, or the top boundary of a glass bead piling. A controlled volumetric rate corresponding to fluid velocities in the mm/s range is imposed through the fracture. A localized source of contaminant is simulated in the setup using a custom-made injection setup, and an optical measurement system is used to monitor in time the two-dimensional concentration field inside the fracture. This setup proves to be well-suited to the study of the coupling between flow and transport through density effects in the pre-asymptotic regime. Measuring at regular time intervals the advective mass flux field inside the fracture allows us to determine the mass m(x) that passes through a section of the fracture transverse to the flow, at position x along the fracture. An amount of solute that is trapped at the piling's surface, even without penetration of the solute inside the porous medium, is “seen” by the measurement system as lost-, and therefore, exchanged-, solute mass. Mass losses significant compared to our experimental uncertainty are measured in a geometrical configuration for which the porous wall exhibits a quasi-sinusoidal roughness: in such a configuration, low velocity zones make superficial solute trapping (up to 30% of it) possible. Gravity plays a major role in this process.
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Submitted on : Monday, August 2, 2010 - 10:42:29 AM
Last modification on : Thursday, January 14, 2021 - 11:46:50 AM
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  • HAL Id : tel-00507846, version 1

Citation

Laure Michel. Transport en fracture et interaction avec la matrice : une expérience analogique. Hydrologie. Université Rennes 1, 2009. Français. ⟨tel-00507846⟩

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