Localization of deep voids through geophysical signatures of secondary dewatering features

• DOI: 10.1190/geo2020-0491.1
• Publication Date: 2021-03-11T01:28:46Z
• Authors: Dan R. Glaser; Katrina Burch; Dennis L. Brinkley; Philip Reppert
• Keywords: Electrical Resistivity Tomography; Bedrock; Petrophysics; Dewatering; Ground-Penetrating Radar; Geophysical Imaging

Discrete deep targets are a significant challenge for most surface-based geophysical techniques, even when considering high property contrasts. In general, methods lose lateral and vertical resolution with depth as result of the limited acquisition geometry increased signal attenuation. The former can be overcome through use cross-borehole methods, but localization is still needed optimal borehole placement. As such, relatively small, void located near maximum investigation (DOI) very unlikely to detected. Yet, secondary features associated these voids exploited enhanced detection performance. When below groundwater table, amount dewatering pumping required make them functional passageway. This not only removes water from space also surrounding formation, resulting in much larger, if more diffuse, target: an induced table gradient. Many sensing sensitive subsurface moisture content. We have implemented 2D joint-petrophysical mixing model (JPM), using inverted electrical resistivity tomography (ERT) seismic refraction models sense changes Our results validated bedrock, groundwater-surface information, ground-penetrating radar, time-domain reflectometry methods. initial proof concept applied shallow area soil gradient, different surface types bedrock. JPM used generate estimate air, moisture, matrix percent fractions area, providing clear delineation refined hydraulic gradient then laterally locate at or DOI ERT refraction.