ISSN: 2319-7293
R.M Sethobya1 M. Hobo1, and S. Sebothoma1
The work highlighted herein represents part of efforts made to assist Johannesburg`s West Rand District Municipality in mapping sinkhole and subsidence vulnerability around the town of Venterspost, using geophysical exploration tools. ERT, VES and gravity surveys were conducted to assist in mapping sinkhole vulnerability, using an existing sinkhole as a constraint. Video evidence was also collected using a drone to image the geology within the sinkhole. The Venterspost sinkhole is a known karstic feature which has developed over the past 10 years, and has so far collapsed deep and the actual depth extend is currently unknown. The site was initially earmarked for a school, before the sinkhole developed, prompting for stability assessments to be conducted. Geophysical studies focused on mapping the possible depth extend of this feature, and to identify other areas in close proximity to the sinkhole, which may also develop sinkholes in the near future. Methodology applied includes Electrical Resistivity Tomography (ERT) profiling, Electrical Soundings (VES) and the gravity method. ERT profiles were used to map the lateral changes and disturbances in the local strata, and possibly identify locations of potential risk (sinkhole formation and/ or cavities) at depth. VES soundings were used to define potential sinkhole and subsidence locations with depth, to help classify the material at specific locations of interest within the site. Results of the geophysical surveys conducted mapped the possible extend of the currently existing sinkhole and offered characterisation of the area wherein possible subsidence, sinkholes and other karstic features would possibly form. A high-resolution residual gravity map of the area was created, to map the possible extension and trajectory of the karstic features at depth.The work highlighted herein represents part of efforts made to assist Johannesburg`s West Rand District Municipality in mapping sinkhole and subsidence vulnerability around the town of Venterspost, using geophysical exploration tools. ERT, VES and gravity surveys were conducted to assist in mapping sinkhole vulnerability, using an existing sinkhole as a constraint. Video evidence was also collected using a drone to image the geology within the sinkhole. The Venterspost sinkhole is a known karstic feature which has developed over the past 10 years, and has so far collapsed deep and the actual depth extend is currently unknown. The site was initially earmarked for a school, before the sinkhole developed, prompting for stability assessments to be conducted. Geophysical studies focused on mapping the possible depth extend of this feature, and to identify other areas in close proximity to the sinkhole, which may also develop sinkholes in the near future. Methodology applied includes Electrical Resistivity Tomography (ERT) profiling, Electrical Soundings (VES) and the gravity method. ERT profiles were used to map the lateral changes and disturbances in the local strata, and possibly identify locations of potential risk (sinkhole formation and/ or cavities) at depth. VES soundings were used to define potential sinkhole and subsidence locations with depth, to help classify the material at specific locations of interest within the site. Results of the geophysical surveys conducted mapped the possible extend of the currently existing sinkhole and offered characterisation of the area wherein possible subsidence, sinkholes and other karstic features would possibly form. A high-resolution residual gravity map of the area was created, to map the possible extension and trajectory of the karstic features at depth.