Full-3D Electrical Resistivity Tomography (ERT) for mining activity planning and sinkhole assessment: A case study in the Murisengo gypsum quarry

Mining excavation design requires preliminary investigation surveys to identify the location of the exploitable resource. Also, monitoring activities should be planned since the degradation of the mechanical properties of rock volumes may trigger instability. Specifically, the formation of sinkholes in areas with gypsum is a major hazard during excavation work. We studied the Murisengo gypsum quarry, near Turin, Italy, in which a sinkhole of about 70 m in diameter has formed in 2025. To understand the causes of the phenomenon and evaluate residual risk, we aimed to reconstruct the geometry of the top of the gypsum orebody and the physico-mechanical properties of the involved materials. We decided to conduct a coarse, rapid, large-scale geophysical survey to investigate the entire quarry site (20-ha area), focusing on the areas around the sinkhole. The Electrical Resistivity Tomography (ERT) technique was chosen because past research found solid correlations between electrical resistivity and percentage/quality of gypsum. We employed ERT in a full-3D mode, obtaining a 3D resistivity model that depicts the sinkhole as a low-resistivity anomaly. Other low-resistivity areas were correlated to previously documented sinkholes and lower-quality gypsum volumes. The adopted approach demonstrated its effectiveness for two aims. First, it was able to characterize the gypsum unit, indicating which rock volumes contain better quality gypsum and are safer to exploit in the future. Second, it rapidly assessed the emergency situation, detecting the main areas at risk to be further investigated with geotechnical studies.