6533b826fe1ef96bd1284452

RESEARCH PRODUCT

On the use of geophysical methods to characterize heterogeneities of quaternary alluvial deposits. Application to stormwater infiltration.

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Colloque avec actes et comité de lecture. International.; International audience; Stormwater infiltration basins are generally built on geological formations with large values of hydraulic conductivity. Such is the case for quaternary alluvial formations, among which are glaciofluvial deposits. Two geophysical investigation methods, namely ground-penetrating radar and electrical tomography, were tested on an infiltration basin built on a glaciofluvial deposit. Geophysical profiles were calibrated on a trench wall dug in the glaciofluvial formation. A sedimentological study coupled to geophysical measurements behind the trench wall highlights the three-dimensional architecture of the deposit (paleochannels and high energy deposit). A typology of geophysical facies connected to the sedimentary characteristics was thus established. A simple estimation model of saturated hydraulic conductivities was used to quantify the hydraulic properties of glaciofluvial lithofacies. This study shows that sedimentary heterogeneities generate a strong hydraulic heterogeneity, potentially leading to preferential flows. The orientation of paleochannels is a privileged flow direction. Heterogeneity at the scale of lithofacies must be taken into account in the numerical models of water flow underlying stormwater infiltration basins. A preliminary geophysical investigation, coupled to a localized knowledge of alluvial stratigraphy, can be used to define a realistic hydrostratigraphic model.