Influence of bacterial concentration and fissure aperture on improving dynamic mechanical properties of MICP repaired fissured sandstone

Fissured rocks are prevalent in geotechnical engineering and can significantly impact the stability of engineering structures. Microbial-induced carbonate precipitation (MICP) technology provides an eco-friendly solution for repairing fissured rocks. To optimize repair effectiveness, this study first investigated the effects of environmental factors on bacterial growth, urease activity, and calcium carbonate yield. The optimal MICP scheme was determined to be a pH of 9, a temperature of 25 °C, and a cementation solution concentration of 0.5 mol/L. Subsequently, the sandstone specimens with various fissure apertures were repaired using MICP with different bacterial concentrations. Dynamic tests were carried out on the repaired specimens using a split Hopkinson pressure bar system. The experimental results indicate that the dynamic strength of the MICP-repaired specimens positively correlates with strain rate, but decreases with increasing bacterial concentration and fissure aperture. These factors have little effect on the progressive failure behavior. Surface cracks were mainly compression-shear cracks in the repair area and tensile-shear cracks at the end of the specimen. Moreover, the crystal morphology observed by scanning electron microscope indicates that MICP primarily produces vaterite crystals, and lower bacterial concentrations favor the formation of more stable calcite crystals, thereby enhancing the cementitious properties. Furthermore, X-ray computed tomography demonstrates an uneven distribution of calcium carbonate within fissures, with higher filling rates observed at the injection end and at the bottom of the fissures. Lower bacterial concentrations and smaller fissure apertures are conducive to more uniform distribution and increased filling rate of calcium carbonate, with fissure aperture exerting a more dominant influence.