Abstract

Geohazard concerns such as sinkholes, subsidence features, and caves are found within evaporite outcrops of the Castile and Rustler formations of the Delaware Basin. The manifestation of karst features from the dissolution of evaporite strata pose a significant geohazard threat to infrastructure, as well as to increased traffic flow from commercial petroleum transportation. The study area is located on the northernmost region of the Chihuahua Desert within the Gypsum Plain of the Delaware Basin, which is the major western subdivision of the Permian Basin. The study focused on a 30 mi (48 km) segment of Farm to Market Road 2185 (FM 2185) in Culberson County, Texas (Fig. 1A).

Capacitively-coupled resistivity methods were used to delineate karst features that pose potential geohazard concerns along the 30 mi (48 km) segment of FM 2185. Figure 1B displays a magnified map of FM 2185 with the Road Markers (RM) labeled, the green box indicates the extent of the 30 mi (48 km) segment traversed from RM 2208 to RM 3780. Data were acquired with the Geometrics OhmMapper G-858 resistivity system, that uses a dipole-dipole TR-5 configuration, composed of five receivers and a transmitter connected by 8.2 ft (2.5 m) coaxial cables with a transmitter offset of 8.2 ft (2.5 m). This geometric configuration enabled resistivity readings up to ∼8.2 ft (2.5 m) deep. Data were processed using MagMap2000 and AGI’s (Advanced Geometrics Inc.) Earthlmager 2D software to produce inverted resistivity sections. This enabled the interpretation of karst related features for improved roadway design.

The OhmMapper G-858 resistivity meter proved to be an effective tool in the rapid delineation of potential geohazards. The 30 mi (48 km) capacitively-coupled resistivity survey of FM 2185 resulted in the discovery of several karst phenomena including potential soil caves, open caves, evidence of probable suffosion, and vertical piping. Figure 2A displays an uninterpreted 300 ft (91 m) inverted resistivity section along RM 2750-2753. The interpreted resistivity section (Fig. 2B) shows possible vertical piping, probable suffosion cave, dry soil conditions, bedrock, and probable moist soil conditions. Compared to a high-resolution color infrared photo of the study area (Fig. 3), the inverted resistivity section displays a positive correlation between the surface vegetation and the resistivity signature.