New insights into the reinforcement and failure mechanisms of biocemented fracture zone

The fault fracture zone rock mass in slope, tunnel, and dam foundation engineering exhibits a loose structure, low strength, and high permeability, posing a serious threat to engineering safety. This study employs microbial-induced calcium carbonate precipitation (MICP) technology and innovatively integrates computed tomography with SEM-MATLAB image processing to systematically investigate the reinforcement mechanism, failure mechanism, and macro- meso theoretical relationships of biocemented fracture zones. Results show that urease activity dominates the rapid deposition of calcium carbonate in key seepage channels, controlling the formation of an impermeable skeleton. Cementation solution concentration governs the precipitate yield and distribution, determining the depth of mechanical strengthening. Their synergy drives systematic pore structure reconstruction, effectively blocking dominant seepage channels. The overall porosity was reduced by up to 63.9%, the connected porosity decreased to 6.75%, irregularly elongated pores were reduced by 91.75%, geometric tortuosity increased by 1.54 times, and the average coordination number and throat count decreased by 63.37% and 84.32%, thereby reducing the permeability coefficient by two orders of magnitude and increasing the peak compressive strength by 5.58 times. Damage analysis reveals that the calcium carbonate cementation network effectively inhibited particle breakage, reorientation, and pore damage evolution, significantly enhancing the residual strength. The macro- meso quantitative relationships were established by multiple nonlinear regression, with estimation errors below 4.27%, revealing the control effects of geometric tortuosity, average pore equivalent diameter, and average particle area on strength and permeability coefficient. These outcomes provide theoretical guidance for parameter design and process optimization of MICP technology in fracture zone reinforcement.