Subsurface cavity detection in a karst environment using electrical resistivity (er): a case study from yongweol-ri, South Korea

ABSTRACT Karst voids were encountered during road construction in Yongweol-ri, South Korea. Attempts to determine the extent of the karst voids through drilling was expensive, time-consuming and too dangerous. An electrical resistivity survey was thus carried out to investigate current subsurface geology beneath the proposed road network. This investigation was aimed at imaging karstic voids and detecting areas prone to ground subsidence through the collapse of cavities beneath a road segment overlying such features. A numerical modelling study preceded the field survey to determine whether the electrical resistivity method could identify such features. The field data set consisted of eleven electric profiles acquired using dipoledipole array; electrical resistivity profiles (100 m and 300 m length) were measured using a dipole-dipole electrode configuration and electrode spacing was kept at 5 m to ensure good coverage of the study area. The resistivity data was inverted using 2D and 3D algorithms based on the least squares smoothness constraint technique. The inverted resistivity images provide a clear view of weathered soils, the distribution of weak areas or karst voids and bed rock. Several low resistivity areas were identified and the subsequent drilling of such anomalous areas led to the discovery of several weak zones or clayfilled underground cavities; the drilling results had excellent correlation with the resistivity images. The electrical resistivity imaging result proved precise and extremely efficient in delineating the karstic void investigation and should be taken into account when choosing an investigation technique to be used at complex geological sites. A remedial action plan involving consolidation grouting work has been suggested prior to road construction. RESUMEN Cuevas kársticas fueron encontrados durante la construcción de unas carreteras en Yongweol-Ri, Corea del Sur. Los intentos para determinar el grado/extensión de las cuevas kársticas a través de perforaciones eran costosos, lentos y muy peligrosos. Así, un estudio de resistividad eléctrica (RE) se llevó a cabo para investigar la geología actual del subsuelo por debajo de la red de carreteras propuesta. La presente investigación fue dirigida a obtener imagen de las cuevas kársticas y la detección de zonas propensas al hundimiento del terreno a través del colapso de las cavidades debajo de un segmento de una carretera encima de las mismas. Un estudio de modelación numérica precedió a la investigación de campo para determinar si el método RE podría identificar tales característ