<p>Granite residual soil is widely distributed in southern China, with high permeability, large porosity, and weak cementation. It is highly susceptible to erosion and landslides under heavy rainfall conditions. To enhance the mechanical properties of biocemented granite residual soil, laboratory tests were conducted to investigate the effects of various cementing solution parameters. Different grouting volumes, concentrations, and cycles of biocementation are compared in this study. Results indicated that high single-grouting volumes and high concentrations impeded the improvement of mechanical properties, while increasing the number of cycles was much more effective. Grouting volume was determined to be 1.05–1.2 times of porosity with a concentration of about 1.0 mol/L. Biocemented granite residual soil mainly gained increased shear strength through the increase of cohesive strength, while the internal friction angle played a minor role. The micro- and meso-pores dominated in the evolution of porosity, and its repair effectively influenced the mechanical properties. Moreover, filling pores and cementation of the soil particles improved the loose, porous, and weak bonding state of the soil. Improvement in mechanical properties could be considered varied and caused by the bridging effect, agglomeration, and coating at the microstructural interfaces. Vaterite formed under high solution concentrations and large injection volumes is prone to transformation into calcite, and the volumetric shrinkage associated with this phase transition leads to a deterioration in mechanical performance. This study offers valuable insights into the mechanisms and effectiveness of improving the mechanical properties of biocemented granite residual soil.</p> Graphical Abstract <p></p>