High-Resolution Seismic Reflection Investigation of Subsidence and Sinkholes at an Abandoned Coal Mine Site in South Africa

The high-resolution seismic reflection method was conducted at an abandoned coal mine site located in the Benoni area, near the city of Johannesburg, South Africa, with the aim of investigating the subsidence- and sinkhole-related features that are commonly observed in the area. Like many old abandoned coal mine sites, the study area lacks adequate mine records that show the extent of the underground coal mining activities that took place in the area in the late 1930s. The preliminary geotechnical investigation conducted in the study area using percussion drilling had also confirmed the existence of underlying weathered dolomitic rocks that may give rise to dolomite-related sinkholes and subsidence. The seismic survey has revealed the occurrence of subsidence and sinkhole features in the area to be due to the collapse of the colliery roof into subsurface voids caused by coal extraction that took place at the depth between 7 and 13m, as well as the dissolution cavities that exist within the underlying dolomite formation at the depth of about 50m below the surface. The size of the coal-mining-related voids varies between 10 and 15m and corresponds to the size of the room and pillar mining technique employed in the coal extraction, while the size of the dissolution cavities that exist within the underlying dolomite formation varies from 2 to 10m.