Geophysical and geological characterisation of karst hazards in urban environments: application to Orleans (France)

Surface or shallow karst constitutes a significant problem for many cities, including Orleans, France. However, the detection of cavities in an urban environment presents numerous difficulties (buried networks, reworked soils, geophysical noise, etc.) A methodology has been developed to respond to this need based on the integration of four complementary methods: geological and geostatistical analysis of existing borehole descriptions, microgravimetry, spectral analysis of surface waves (SASW) and ground penetrating radar (GPR). This combination of different methods, applied to a test sector in the city of Orleans and validated by control borings, made it possible to locate the principal karstic conduits beneath the study area and identify a zone of mechanical weakness associated with one such feature. It also revealed that the presence of buried networks does not create significant gravity anomalies.