Characterization of electrical anisotropy for cuttability of rocks using geophysical resistivity measurements

The rock hardness, strength, fracturing and anisotropy property parameters are the main factors controlling cuttability of the rocks. The orientations of elongated grains cause considerable variations in hardness, anisotropy and layering parameters of the rocks. The resistivity sounding technique (DES) is used to determine anisotropy resulted by the rock's fracturing, pressure and metamorphism properties. We calculated typical polar diagrams by modelling using various anisotropy values and electrode arrays for comparing with field measurements. Based on the synthetic data it is clearly seen that dipole azimuthal sounding was most determined electrical anisotropy. To understand the reason of these effects and to estimate suitable direction for easily cuttability of the rock, resistivity soundings using dipole azimuthal array were applied on karstified limestones covered with alluvial units around Kozyata quarry, Istanbul. Dipole azimuthal soundings were made on 10°, 55°, 100°, 140° azimuths with spacing r=10-90 meters. The azimuthal diagrams in the ranges of 88-950 ohm-m were indicated characteristic orientations as the anisotrophy indicator at various depth levels within limestone. Based on the azimuthal diagrams, the direction ∼120° (from north) where apparent resistivit considerably decreased to lower values towards deep levels (>15 m) within limestone is interpreted as more suitable extension for easy cuttability.