Management of sinkhole risks using long term ERT monitoring : a laboratory experiment

Accurate methodologies are required to manage risks linked to land-use planning in covered kart terrains, especially in densely urbanized areas. The main risk lies in the occurrence of sinkholes at the base of buildings or infrastructure. We conducted a laboratory experiment to evaluate the contribution of ERT monitoring in the long term management of such karstic risks. After presenting the design of the laboratory experiment, we detail the selected scenarios and the acquisition protocols tested. The methodology proposed to process the data and manage the inversion results relies on two steps: (1) we estimate the resistivity variations due to measurement and inversion errors based on Monte-Carlo simulations and (2) we define a resistivity changes index for every cell of the 3D model. The methodology is tested on a 3D surface survey including inline dipole-dipole, equatorial dipole and Wenner-Schlumberger arrays. A 10 cm in diameter plastic ball is used to model a 3.5 m sinkhole at depths ranging from the surface to 20 cm, using a water resistivity of 12 Ohm.m. Based on the proposed methodology, we show that this target can be suitably detected when its top reaches 10 cm or less in depth.