Mapping underground cracks using 2D electrical resistivity tomography: the case of the landslide of Kef Essenoun phosphate deposit, Djebel Onk (northeast of Algeria)

The landslide of Kef Essenoun phosphate deposit (northeast of Algeria) occurred on September 2007, when a large mass of rocks detached from the rock mass scale and filled almost entirely the pit (the career). Recently, new cracks oriented N–S and NE–SW with large sizes have appeared in several places near a slide area and even in the alignment of the 2007 slide area. To understand the nature of the deformations recently observed at the surface, and to favor safety measures that can be implemented rapidly, it is essential to obtain maximum information on the deep structure of underground cracks and areas of weakness. Electrical resistivity imaging or tomography (ERT) is well suited for characterizing the bedrock surface thanks to the ability of the technique for detecting resistive features as well as discriminating subtle resistivity variations. For the present investigation, a Wenner transect was conducted through a visible crack area near the landslide area. The electrode spacing was 2 m and the length of the transect was about 60 m. In this case study, the survey results suggest that ERT is a cost-effective tool that can easily be deployed to gather valuable subsurface data and to aid in the detecting and mapping of underground cracks and other subsurface cavities.