Geoelectrical reconstruction of microbially induced calcium carbonate bridging in rock fractures for micromechanical assessment

Microbially induced calcium carbonate precipitation (MICP) has gained prominence as a nature-based approach for enhancing geological materials and healing rock fractures. However, the precipitation mode and spatiotemporal evolution of calcium carbonate within optically inaccessible fractures remain difficult to quantify. This study evaluates electrical resistivity tomography (ERT) as a non-invasive method for monitoring MICP precipitation and healing in rock fractures. Results from 24 calibration cells showed that heterogeneous precipitation within fractures precluded a robust correlation between electrical resistivity and the mass of precipitated calcium carbonate. By introducing bridging height as the key intermediate variable, a quantitative calibration with electrical resistivity was established, thereby enabling ERT monitoring of MICP processes in rock fractures and supporting its application in larger-scale models. Subsequently, ERT monitoring was conducted on two large-scale rock fracture models with different roughness to reconstruct the evolution of the resistivity field across successive injection cycles and infer the corresponding mineralization process. The quantitative calibration relationship between electrical resistivity and calcium carbonate bridging height remains valid in large-scale models, and the results indicate that calcium carbonate precipitation was predominantly concentrated at the fracture bottom under gravity-driven transport, whereas localized sidewall bridging developed primarily through adsorption-controlled processes, collectively contributing to the self-limitation phenomenon. The ERT-derived bridging height agreed well with the laser-scanned result, with an error of 6%. Furthermore, an empirical relationship between electrical resistivity and local elastic modulus was established using bridging height as an intermediate variable, providing a basis for calibrated assessment of local micromechanical heterogeneity in healed fractures.