PRELIMINARY EVALUATION OF GEOELECTRICAL METHODS FOR THE QUANTIFICATION OF VOLUMETRIC BLOCK PROPORTION (VBP) OF MÉLANGES

Chaotic rock units (including mélanges, broken formations and complex formations) represent some of the most challenging rock masses for technical characterization. The most commonly accepted methods for the parametrization of mechanical properties in these rocks require the quantification of the percentage of rock blocks on the total volume of the rock mass (i.e. the Volumetric Block Proportion – VBP). Traditional methods for the quantification of VBP are often time consuming and expansive, requiring a large number of accessible outcrops and/or drilling boreholes. In this study, we propose an alternative methodology for the estimation of VBP based on indirect (geo-electrical) measures. We considered chaotic units with soft clay-rich (low resistivity) matrix and hard (high resistivity) blocks. In these conditions, geoelectrical surveys are suited for the quantification of matrix percentage. In order to evaluate the applicability of geoelectrical techniques in this context, we realized 31 simulations, following a Monte Carlo stochastic approach. The good direct relationship between VBP and modeled electrical conductivity confirms the suitability of the ERT methodology for the estimation of VBP in chaotic units.