Properties of Jointed Rock Mass under Triaxial Compression Based on Microbial-Induced Calcium Carbonate Precipitation

Rock mass is a structural system composed of intact rock and joints. The properties and strength of rock mass determine the macroscopic mechanical properties of rock mass. Enhancing the self-stability of rock mass by improving the integrity of jointed rock mass and the joint strength is a popular research topic in the geotechnical field. As a new reinforcement method for joints, the microbial healing technique has attracted much attention. This study investigated a healing technique for jointed sandstone based on microbial-induced calcium carbonate mineralization, and triaxial compression tests were conducted on the jointed rock mass after healing. Bacillus cohnii (lyophilized powder) was activated in the laboratory, and calcified precipitation was induced in sandstone joints to realize healing and reinforcement of joints. Observations by X-ray diffraction (XRD) and scanning electron microscopy (SEM) indicated that the mineralization products in the joints were microbial-induced calcium carbonate precipitation (MICP) and that the sandstone joints were fully cemented. Finally, triaxial compression tests were conducted on jointed rock specimens after healing to investigate their mechanical properties. The experimental results showed that the deviatoric stress of the specimens after MICP repair increased by 50% compared with that before repair. When the dip angle of the joint surface was 15 degrees-45 degrees, the shear failure along the structural plane was the main failure before repair; after MICP repair, the main failure was shear failure of the rock block. The strength of the rock specimen with microbial-induced calcite precipitation was analyzed theoretically using the Jaeger criterion. It was shown that the microbial-induced calcium carbonate precipitation technique not only can enhance the integrity of rock joints, but also can improve the strength of jointed rock mass remarkably. This study provides new ideas for reinforcement of jointed rock mass.