Reconstruction of pore structure and transformation of failure mode in reef limestone under MICP grouting

Given the high porosity, strong connectivity, and low strength of reef limestone, microbial-induced carbonate precipitation (MICP) reinforcement tests were performed under different grouting cycles. CT-based three-dimensional reconstruction, uniaxial compression, and acoustic emission analyses were employed to elucidate the coupling mechanism between microstructural evolution and macroscopic mechanical behavior. MICP-induced calcium carbonate deposition exhibited distinct scale selectivity, initially occurring in large pores and highly coordinated nodes, which reduced the average pore diameter from 221.26 μm to 75.36 μm and transformed the pore network from a highly connected loose type to a dense isolated one. The elastic modulus increased from 3.27 GPa to 6.21 GPa, and the peak strength approximately doubled, while the failure mode evolved from brittle to brittle–ductile. Acoustic emission analysis revealed a greater proportion of post-peak high-energy events and a frequency shift from high to mid–low ranges, indicating a multi-stage energy dissipation process. A reinforcement variable was introduced to quantify the MICP-induced strengthening, and a structural densification factor was incorporated to establish a constitutive model governed by densification. The study clarifies the coupling mechanism from microscopic densification to macroscopic enhancement, providing theoretical support for the green reinforcement of highly porous rock masses.