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Publication Date

April 1993

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Environment

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Presented at 6th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems by Lynn Yuhr and Richard Benson Technos, Inc., 3333 NW 21st Street, Miami, FL 33142 Dwain Butler, US Army Engineers - Waterway Experiment Station, 3909 Hails Ferry Rd., Vicksburg, MS 39180 Abstract: The flat-lying limestones of western Texas are naturally jointed with preferential dissolution occurring along joints and bedding planes. This area has some of the largest air-filled open caves in West Texas and large paleokarst collapse features have been identified throughout a wide region. Aerial photos indicate the presence of extensive joints, lineaments and paleokarst. Site characterization to detect and map such subsurface features using borings alone is inadequate to produce a reasonable level of spatial sampling. This paper addresses the application of surface geophysical techniques, and an assessment of the spatial sampling and instrument sensitivities necessary to define the karst features of interest in this geologic setting. Electromagnetic measurements using a Geonics EM34 were selected because the measurements provide an excellent means of locating dissolution-enlarged joints. Microgravity was selected because it is the only surface geophysical method that will provide the location of karst feature regardless of their shape or fill material as long as there is a sufficient density contrast. While both methods have limitations, as do all methods of site characterization, the combination of gravity and EM measurements are complementary in this application. A known cave system was used to establish the spatial sampling criteria for the detection and characterization of such features. Field tests were then run over two known karst sites; a paleokarst collapse; and a localized doline to provide anomaly signatures in this geologic setting. It is clear that the EM and the gravity techniques are appropriate for detecting and characterizing karst features in this geologic setting. However, one of the key issues in planning and carrying out a geophysical survey, is developing a spatial sampling criteria. This criteria should be based upon an understanding of project objectives, a conceptual geologic model of site conditions and, if possible, existing data from the area of interest. Open Access - Permission by Author(s) (1993) See Extended description for more information.

Subject: topical

Environment

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Article

Genre

Conference Proceeding; serial

Identifier

K26-01054

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