In order to investigate the dilatancy of irregular columnar jointed rock masses (ICJRM) under unloading conditions, a series of three-dimensional discrete element numerical models of ICJRM with seven column dip angles were established, and the compressive strength typical failure characteristics and dilatancy evolution of ICJRM were obtained through numerical conventional triaxial compression tests under unloading confining pressure conditions. The results show that: The shape of peak deviatoric stress Δσ_1f vs. dip angle β_j curve resembled the letter “J”, where the peak deviatoric stress has the minimum value at β_j =60°, and reached its maximum value at β_j =90°, and the typical failure modes included splitting along the column and columnar joint surface, shear slipping along the columnar joint surface, and the compression-flexure destabilization of the columns; The dilatancy of irregular columnar jointed rock mass under unloading condition was closely related to the initial confining pressure and dip angle, and the corresponding volumetric strain increment obtained larger values when the dip angles ranged from 30° to 60° indicating a significant dilatancy.

Microbially induced calcite precipitation (MICP) has been widely applied for soil reinforcement, but its applications in rock mass permeability reduction have been rarely reported. To explore the plugging mechanism of rock joints using MICP, artificial rock joint specimens made of transparent resin were prepared, and laboratory MICP plugging experiments under six various conditions considering MICP reaction influence factors were performed. Through the plugging experiments, evolution laws of rock joint transmissivity and hydraulic aperture, accompanied with corresponding CaCO₃ distribution images, during plugging processes were obtained. The experimental results showed that the hydraulic aperture of rock joint approximately decreases linearly with grouting cycles during MICP plugging process, and the decreasing rate is closely related to the CaCO₃ distribution that is significantly affected by grouting rate, injection time of fixation, bacterial, and reaction solutions, and standing time. Among the six experimental conditions, both the plugging efficiency and effect are optimal under the fourth experimental condition, where the grouting rate is high and the grouting and standing time is the longest. After only two grouting cycles under the fourth experimental condition, the rock joint transmissivity decreases from 40.51×10^–6 m²/s to 0.52×10^–6 m² /s with a decrease rate of 98.72%, and the hydraulic aperture decreases from 0.367 mm to 0.086 mm with a decrease rate of 76.6%. Furthermore, the CaCO₃ distribution on the upper and lower surfaces of rock joint specimens were observed, and CaCO₃ in rock joints produced by MICP reaction was found to bring cementation strength in a short time, which helps improve mechanical properties of rock joints while reducing rock joint permeability.