Assessment of geoelectrical configurations using reduced physical models for the structural mapping of rock mass and fractured aquifers

Abstract

The identification of geological fractures is important for the solution of several geotechnical and hydrogeological problems. The electrical resistivity method has been used to identify fractures, and this research seeks the optimization of its application in characterizing rock mass and fractured aquifers. A reduced physical model consisting of marble plates buried in saturated sand was built inside an acrylic tank in order to simulate a fractured rock mass covered by saturated soil. The contacts between the plates represent two vertical fracture families, named J1 and J2, which were respectively oriented in the NS and N60°E directions. In the comparison between the electrical arrays, the same parameters were considered, e.g. depth of investigation and number of survey lines, as well as internal and boundary conditions. The experiments were divided in stages E1 and E2. In stage E1, azimuthal surveys were carried out using Wenner, Equatorial Dipole-Dipole and Quadratic arrays. The Equatorial Dipole-Dipole array required the smallest area to relocate cables and electrodes and yielded the best results regarding the interpretation of apparent electrical resistivity ellipses and rock mass anisotropy. It was also accurate in the estimation of the fissural porosity. In stage E2, electrical profiling was carried out via the Dipole-Dipole and Gradient arrays. The latter yielded the best resolution regarding the electrical resistivity anomalies, which allowed the mapping of all fractures present in the surveyed area by means of 2D and 3D analyses. It is believed that these results be of relevance to the characterization of fractures in geotechnical studies and water exploration in fractured aquifers.