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Multiconfiguration GPR measurements for geometric fracture characterization in limestone cliffs (Alps)

Abstract : Rock-mass fracturing is a key parameter in rock-fall hazard assessment. However, traditional geologic observations can provide information only about discontinuities at the surface. In this case study, detailed ground-penetrating-radar (GPR) measurements (with antennas of 50 MHz, 100 MHz, 200 MHz, and 400 MHz) were conducted on a test site, using different acquisition configurations deployed on vertical cliff faces. Conventional 2D profile data, common-midpoint (CMP) survey data, and transmission data were acquired to evaluate the potential use of radar waves to characterize the geometry and properties of the major discontinuities (fractures) within a Mesozoic limestone massif. Results showed that the continuity and geometry (orientation and dip) of the major observed fractures, which are crucial parameters for assessing rock stability, can be obtained by combining vertical and horizontal profiles measured along the cliff. We used 100-MHz antennae and reached a maximum penetration of 20 m, which limits the technique to rock volumes of a few tens of thousands of cubic meters. We observed significant differences in reflectivity along the detected fractures, which suggests that the fractures' characteristics vary in the rock mass. We used transmission data to obtain a radar velocity image. Although the results were consistent with radar profiles on the cliff, they showed that the technique has little utility, beyond that of more traditional GPR methods, for delineating fractures in a rock mass.
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Submitted on : Monday, January 19, 2009 - 10:35:54 AM
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Mathieu Jeannin, Stéphane Garambois, Colette Grégoire, Denis Jongmans. Multiconfiguration GPR measurements for geometric fracture characterization in limestone cliffs (Alps). Geophysics, Society of Exploration Geophysicists, 2006, 11 (3), pp.B85 à B92. ⟨10.1190/1.2194526⟩. ⟨insu-00354163⟩



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