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- Detection and mapping of ghost-rock features in the Tournaisis area through geophysical methods – an overview
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Detection and mapping of ghost-rock features in the Tournaisis area through geophysical methods – an overview
Abstract
In the context of cover-collapse sinkholes, as in the Tournaisis area, the detection of palaeokarst features allows to delineate, at a local scale, areas that might be subject to future collapse. These areas should therefore be avoided or dealt with in the perspective of earthworks for civil engineering. Before the last decade, karst mapping in this context was often wrongly considered as a cavity detection problem and tackled in this way. A better understanding of these phenomena allows developing more appropriate detection methods. We precise the geological settings and karst context of the Tournaisis. We present the key characteristics of the palaeokarsts and the main contrasts in petrophysical properties expected between alterite (ghost-rock) and bedrock. Given these contrasts and the wide range of overburden thicknesses found in the Tournaisis, we evidence the main advantages and major limitations of potentially effective geophysical investigation methods. We illustrate our purpose by describing some results of electrical resistivity tomography and seismic surveys applied to palaeokarst detection. These results are assessed using numerous geotechnical data and geological knowledge. Finally, we show how these results could be used for geological and geotechnical problem solving in particular trough the design of adapted detection and mapping strategies.
imaging, karst, ghost-rock, geophysics
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About: Olivier KAUFMANN
University of Mons – Faculty of Engineering, Geology and Applied Geology Department, 20 Place du Parc, 7000 Mons (Belgium)
About: John DECEUSTER
University of Mons – Faculty of Engineering, Geology and Applied Geology Department, 20 Place du Parc, 7000 Mons (Belgium)