Influence of the screen and filter pack permeability on in situ permeability tests

Nadège Baptiste, Robert P. Chapuis

In the proceedings of: GeoManitoba 2012: 65th Canadian Geotechnical Conference

Session: M1D - Hydrogeology

ABSTRACT: Field permeability (slug) tests are frequently performed in observation wells to measure the saturated hydraulic conductivity K of the soil surrounding the filter pack around the well screen. The screen and filter pack have their own ability to allow or slow down seepage, thus they generate head losses. The effect of filter pack and screen is usually ignored when analysing in situ permeability test data. Analytic equations, which have been validated with a numerical model, show that for pervious soils, field permeability tests can underestimate the soil K value due to the influence of screen and filter pack. Moreover, results from water tank tests have shown that gas micro-bubbles can also contribute to the undervaluation of the field K value by acting as obstacles to seepage.

RÉSUMÉ: Des essais de perméabilité in situ sont couramment réalisés obervation afin de mesurer la conductivité hydraulique saturée K entourant un sable filtre et une crépine. Or, les crépines et les sables filtres possèdent leur propre capacité à laisser passer un écoulement et donc générent des pertes de charges. ces deux médias Des équations analytiques, validées par modèle numérique, ont permis de montrer que pour des sols perméables, la valeur K tirée méabilité in situ peut être sous-estimée uence de la crépine et du sable filtre. De plus, modèle réduit ont montré que les microbulles dnt aussi à sous-estimer la valeur K en se comportant comme des obstacles .

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