Application of 2D electrical and seismic tomography techniques for investigating landslides

摘要

Providing a ground image, electrical and seismic tomography tests are increasingly used for investigating landslide sites. After a slope failure, these techniques help to understand the geological structure of the site and to design support or remedial treatment. On the other hand, these non-destructive and relatively low-cost methods also contribute to assess the landslide risk in potential unstable areas. Two case histories are presented in this paper. The first one is an instantaneous rock failure of a few thousand cubic meters which affected a railway slope, causing a spectacular train derailment. This slide occurred along a fault plane after heavy rainfalls in a rock massif consisting of a succession of shale and sandstone layers which were folded and fractured during the Variscan orogeny. Seismic tomography profiles were performed perpendicular to the slope in order to assess the quality and strength of the rocky material forming the cutting. The second site is a heap made of Carboniferous shales and resulting from coal mining works, which was affected by an instantaneous landslide of few ten thousand cubic meters during a dry period. Observations between the burning and that the rupture has been initiated at the contact between the burning mass (red coloured) and the unburned shallow part (black coloured). Electrical tomography profiles have allowed to map the burning zones at depth, and they are charactrised by a higher resistivity value and have contributed to assess the slide risk.