Investigation of subsurface karst in an opencast mine in southwestern China via surface and cross-borehole electrical resistivity tomography

Subsurface karst features are significantly developed in Guangxi Province, China. This area mainly contains fractured subsurface rock, abundant karst channels, and widely distributed underground fissure networks. Such adverse geological conditions could potentially create hydrogeological hazards such as collapses, water inrush, and mud inrush during infrastructure construction. The Hejing limestone mine is an opencast mine in Pingnan County, Guangxi, that produces cement. Mining activities have altered the seepage fields in this area, causing large amounts of groundwater to flood into the mining pit; this has caused many ground collapses while severely reducing limestone production. More than 24 km of surface electrical resistivity tomography (ERT) profiles have been previously recorded in the region to identify potential karst positions and explore groundwater inrush paths. In this study. we employed surface and cross-borehole ERT surveys to delineate specific groundwater inrush paths on the eastern side of the mine and characterise karst distribution in the study area. Resistivity imaging results revealed some low-resistivity anomaly distributions and provided reliable geological information about the distribution of subsurface karst for future grouting work.