Evaluating the deformation modulus at representative elementary volume using electrical resistivity tomography

The deformation modulus of rock mass is an essential parameter for evaluating the bearing capacity and deformations. A deformation modulus obtained through conventional approaches, including empirical equations and in situ tests, cannot present the deformation modulus at representative elementary volume (D_REV) due to limited test coverage and technical difficulties in harsh geological or topographic conditions. This study utilized electrical resistivity (ER) tomography and numerical back-analysis to investigate D_REV at the Asmari-Jahrum formation. We employed geoelectrical contrasts to detect proper locations for installing extensometers at excavated galleries. The deformations recorded by extensometer were used to back-calculate the D_REV values by finite difference numerical modeling. We established a correlation between ER and D_REV to predict D_REV, which were 30–80 % more accurate than those obtained through conventional approaches at the study site. The tested area, anisotropy, creep, ER inaccuracies, and plastic deformations are evaluated as statistically significant factors that can influence D_REV. Our methodology provides a systematical approach to assess D_REV, which applies to geoengineering projects within the Asmari-Jahrum formation or similar sedimentary units (ER below 200 Ω⸱m). This methodology is also replicable for other geological formations with harsh geology or limited access without exposing an extreme financial burden or environmental issues.