Experimental and Mesoscale Numerical Investigation of Fracture Behavior in MICP-Cemented Sand Under Different Loading Conditions

Microbially induced calcium carbonate precipitation (MICP) can transform a loose sand mass into a cemented porous medium. To elucidate its deformation and failure behavior, we developed a two-dimensional mesoscale finite element model. The model integrates a novel multiphase random particle placement algorithm with a cohesive zone model (CZM) to explicitly represent the heterogeneous microstructure of sand grains and CaCO3. The model was used to simulate crack evolution and mechanical response under uniaxial tension, compression, and direct shear, with the results validated against experimental data. Under uniaxial compression, the simulated peak strength was approximately 2.65 MPa, compared with an experimental average of 2.53 MPa. The proposed model accurately represents the multiphase microstructure and captures the main mechanical response characteristics. The results show that the sand-grain arrangement has a limited influence on peak strength but significantly affects post-peak behavior by controlling crack propagation. The simulations reproduced distinct failure modes: brittle tensile rupture, quasi-brittle shear failure, and mixed quasi-brittle-frictional compressive failure with inclined shear bands. Across all loading conditions, a common mesoscale failure mechanism was identified: microcracks initiate in weak or stress-concentrated regions, propagate along CaCO3-sand interfaces, and coalesce into through-going fractures. This study enhances the understanding of mechanics of MICP-cemented sand and provides a mechanism-oriented mesoscale framework for future analyses.