GEOPHYSICAL CHARACTERIZATION OF GYPSUM KARST GEOHAZARDS IN THE DELAWARE BASIN, WEST TEXAS (Invited Presentation)

Gypsum karst is associated with significant geohazards throughout the Delaware Basin of West Texas and southeastern New Mexico, including common road failures and similar complications during pipeline construction and petroleum operations. Karst phenomena specifically within the Castile Formation are diverse, including: 1) polygenetic gypsum caves; 2) solutionally-widened fractures; 3) intrastratal brecciation; 4) gypsite suffosion; and 5) variably filled/mantled epikarst and sinkholes. Effectively, most Gypsum Plain geohazards do not readily express as dominant surface manifestations; however, incised and collapsed sinkholes in gypsum bedrock provide direct evidence of cavernous porosity, while common suffosion piping attests to extensively soil-mantled karst development. Although the same karst phenomena that are attributed to geohazard manifestations throughout the Gypsum Plain extend to significant depths, generally only those phenomena that occur at shallow depths pose significant geohazard concerns.

Roadway assessment has traditionally relied on ground-penetrating radar to identify anomalies and isolated road failure, but vehicle-mounted systems that enable rapid, large-scale data acquisition generally only image pavement and roadbase conditions, not underlying geologic phenomena. However, capacitively-coupled resistivity has proved effective in delineation of roadbase degradation and shallow geohazard phenomena in the Gypsum Plain. The utilization of a TR-5 OhmMapper with 2.5 meter electrode spacing in a dipole-dipole array and a traverse speed of three kilometers per hour have yielded sub-meter, geohazard detection to depths of five meters. At localized regions of repeated infrastructure failure and/or intense karst development identified through capacitively-coupled resistivity analyses, traditional 2D electrical surveys have been conducted with a Super-Sting (R8/IP) in a dipole-dipole array with electrode spacing dependent on site specific conditions for increased lateral and vertical resolution. The combination of capacitively-coupled and traditional multi-electrode resistive analyses as proven to effectively delineate potential geohazards when coupled with traditional karst surveys.