Since 1999, maps (at 1:10,000 scale) of zones of karstic constraints have been established in the Walloon Region of Belgium (the southern part). These maps sort areas in terms of karstic hazards (negligible, low, moderate and high). They were drawn based on geological settings, field observations, background knowledge and geostatistical forecasts. Nowadays, these maps are used as background documents in physical planning over covered karstic areas. Indeed, the local government now requires to conduct geophysical and/or geotechnical investigations previous to building construction over moderate and high karstic hazard areas. In this context, we conducted several 2D, quasi-3D and 3D resistivity tomography surveys using a total number of electrodes ranging from 100 to 1000. 3D resistivities were measured using a cross-diagonal survey with a combination of dipole-dipole, pole-dipole and equatorial dipole arrays. The<br>inversions were computed within Res2DInv and Res3DInv. The results of these investigations allowed pointing out resistivity anomalies interpreted as effects of karstic features. When possible, boreholes are then drilled over and away from the detected anomalies to confront geophysical results. Finally, geophysical results are used to adapt construction projects.


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