Scholarly record

FILLED AND UNFILLED UNDERGROUND VOIDS EVALUATION USING ELECTRICAL RESISTIVITY METHOD

F. Chitea

Abstract

Geoelectrical contrasts generated between underground voids and the surrounding materials, their vertical or horizontal development, geometry and burial depth are key elements for voids detection when investigated by electrical resistivity method from the surface. Nevertheless, the acquisition techniques, the array type selection and profile(s) deployment are equally influencing the survey results. The relations between the mentioned factors were subject to detailed analysis by constructing various synthetic models and simulating the geoelectrical model response when subject to artificial electrical current. In order to reveal the challenging situation when carrying out a real survey, resistivity models situated in inhomogeneous geological environments were constructed, simulating different types of voids, ranging from unfilled voids (model representative for dry karstic voids, mining voids, tunnels or archaeological buried chambers) to partial and complete filled ones (model representative for cavities situated below the water table and abandoned mine works invaded by groundwater), addressing the common real situations concerning the filling materials. Simulation results revealed the limits of geoelectrical approach when the investigated buried voids are covered by conductive rocks. Real field surveys of geoelectrical measurements performed in distinct environments have been chosen as examples of the diversity of situations, which has to be faced when studying underground voids. Selected case studies present examples of dry anthropogenic voids detection as well of shallow and deep-water filled cavities. Following the real case studies and synthetic models results we conclude that caves exploration and mapping of the anthropogenic underground voids can benefit of the non-invasive technologies of investigation, but in most of the cases, the void dimensions are hard to be extracted from the resulted anomalies.

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