Evaluation of Three‐Dimensional Electrical Resistivity Array Types for Optimal Detection of Voids in Karstic Limestone

Abstract

Electrical resistivity imaging provides a non‐destructive means for detecting the presence of karst features (e.g., caves, solution cavities, and sinkholes) in limestone terrains. To statistically improve delineation of three‐dimensional (3‐D) heterogeneities, such as caves, a true 3‐D electrical resistivity survey using a 3‐D interpretation model can be used. When conducting 3‐D resistivity investigations in karst terrains, a common problem is determining which of the existing electrode configurations will respond best to material changes in the subsurface, and provides the needed depth and resolution for accurate void delineation. In this study, 3‐D electrical resistivity measurements were collected over the site of Dead Deer Cave in Bexar County, Texas, using various electrode configurations (i.e., dipole‐dipole and pole‐dipole). The entrance to Dead Deer Cave is a pit that connects to a series of vertical and horizontal solution cavities that have been surveyed to a depth of approximately 30 m. The pit has been filled in with rock and dirt, concealing its exact location. Results of 3‐D numeric modeling of the resistivity measurements at Dead Deer Cave indicate that the pole‐dipole array configuration provided the needed depth and resolution for locating the cave entrance as well as the shafts and passages that are beneath the surveyed area.