A multi-geophysical approach to assess potential sinkholes in an urban area

Sinkholes caused by natural or anthropogenic factors pose as potential safety hazards in urban areas. From April to May 2019, six consecutive ground collapses occurred in Beihuan New Village (Guigang City, China) that affected the livelihoods of residents and caused substantial economic losses. The present study aimed to inves-tigate potential sinkhole areas and determine the formation mechanism of a series of ground collapses in Beihuan New Village using a combined drilling and multi-geophysical approach. Geophysical profiles collected using electrical resistivity tomography (ERT) and ground penetrating radar (GPR) revealed shallow geological struc-tures, potential sinkholes, and karst fracture zones. We also drilled several shallow boreholes along the geophysical survey profiles to obtain accurate hydrogeological information. To precisely identify groundwater runoff zones, cross-hole electrical resistivity tomography (CHERT) surveys of deep boreholes were conducted to locate the initial boundaries of the target anomaly areas delineated using ERT and GPR. The results demonstrated that a combination of geophysical exploration and geological profile analysis could accurately delineate potential sinkholes in urban areas. The locations of sinkholes in the study area were consistent with subsurface karst and groundwater runoff zones inferred from our survey results. Additionally, comprehensive analysis indicated that a depleted groundwater table, heavy seasonal rainfall, and overlying soil characteristics were possibly responsible for sinkhole formation. These findings can assist in prevention of ground collapses in urban areas and mitigation of the damages caused by these collapses.