Electrical resistivity tomography to detect ground loosened zone near excavation region in an urban site of ground subsidence, South Korea

Abstract

Ground subsidence in urban environment due to excessive development and deteriorated underground urban facilities is serious social problem. Geophysical surveys were applied to estimate distribution and scale of cavities and subsidence. In this study, electrical resistivity tomography (ERT) was performed near the subsidence occurred on road in urban area. The subsidence arose due to leak of groundwater and soil into neighboring excavation region. The survey line was located between the major subsidence area and excavation region. Since ERT data are affected by rapid topographic change or surrounding structure, influences of the excavation to data were analyzed through field-scale numerical modeling. The effect of excavation should be considered to interpret ERT data, as it can be estimated wrong anomaly. In 2D interpretation, a method of performing inversion after correcting the resistivity data including the effect of excavation was proposed. This method was proved first using the field-scale numerical model including excavation region and subsurface anomaly assuming loosened zone and then applied to field data. In addition, the ERT data were interpreted by using existing a 3D in-house algorithm, which can deal with excavation region. Both of inversion results demonstrated that conductive anomalies of loosen zone appeared stronger in more specific area compared to before considering the excavation effect.