Macro–mesoscopic damage evolution and constitutive modeling of bio-reinforced weak interlayer zones under cyclic excavation disturbance

Abstract

The weak interlayer zone (WIZ), characterized by tectonic damage and weak cementation, is significantly impacted by load-induced damage accumulation and stiffness degradation under cyclic loading and unloading conditions, thereby posing a serious threat to the stability of underground cavern excavations. To address this engineering geological issue, a synergistic reinforcement technique combining enzyme-induced calcium carbonate precipitation and fiber reinforcement (EICP-FR) was employed to reinforce the WIZ. The macro-meso correlation between mesoscopic structural characteristics and macroscopic mechanical responses was elucidated through uniaxial cyclic loading–unloading tests combined with quantitative SEM-MATLAB analysis. The peak strength of the WIZ increases to 340% of that of the unreinforced sample, with fatigue life substantially extended. The WIZ evolves from progressive failure of weakly cemented media to ductile failure characteristic of fiber-reinforced composites. The three-dimensional interlocking network of fibers, CaCO₃, and WIZ particles inhibits meso-structural degradation by inhibiting particle breakage, restricting particle reorientation, and reducing pore space complexity. The average particle area is maintained at 125% of that of the unreinforced sample, accompanied by a reduction of 48.7% in the anisotropy ratio and a decrease of 33% in the pore morphology fraction dimension. Based on these findings, a macro-meso energy-based constitutive model was established by physically mapping mesoscopic features to constitutive parameters, providing a high precision (R² > 0.95) theoretical tool for characterizing the non-linear cyclic unloading responses of EICP-FR reinforced WIZ. These outcomes provide a mechanistic framework for controlling WIZ-induced engineering geological hazards in deep underground excavations and assessing cavern-support system stability under excavation disturbances.