2.5D Inductively-Coupled Resistivity Assessment of Karst Geohazards AlongRanch to Market 652, Culberson County, Texas.

Differential dissolution of Permian aged evaporite karstic rocks throughout the Gypsum Plain of West Texas has become a major geotechnical problem. This is especially significant in Culberson County due to an increase in heavy vehicular traffic related to increased petroleum exploration, extraction and transportation within the region. The Castile Formation, which is the dominant unit within the study area, consists of gypsum/anhydrite which is highly susceptible to dissolution and karstification by meteoric and groundwater flow. Karstic features along and beneath roadways in the Castile outcrop are common and includes sinkholes, surface subsidence and caves of both epigenic and hypogenic origin. These form potential geohazards to road users and are a major concern forthe Texas Department of Transport (TxDOT) and other administrative bodies.

Traditional methods of conducting karst surveys can be effective in mapping the extent of subsurface features once they are located based on surficial expression. However, these methods are sometimes inadequate in delineating the existence and full extent of subsurface features that are not manifested on the surface. Department of Geology at Stephen F. Austin State University have collaborated with the TxDOT to conduct a comprehensive resistivity study over several miles of roadway along RM 652. Researchers utilized an OhmMapper TR5 resistivity meter, a capacitively-coupled resistivity instrument, to scan and collect 2D resistivity data along sections RM 652. The 2D resistivity scans were inverted using the 3D EarthImager software to produce 2.5D models of the subsurface. This method allowed researchers to better characterize the extent of karst geohazards. The data included in this presentation represents preliminary 2.5D model results from a much more comprehensive study.