## 4 Results and Discussion
### Effect of Bacterial Solution Concentration on Disintegration  
Figure 7 shows the disintegration curves of different bacterial solution concentrations of OD\({}_{600}\) = 0.25, 0.5, 0.75, and 1.0 with one treatment cycle. At the given cementation solution concentration of 0.4, 0.8, 1.2, and 1.6, the MICP can improve the resisting disintegration ability of granite residual soil after one treatment cycle. However, the improvement is relatively limited. The disintegration time of the sample has been extended, and the sample completely disintegrates. This is because the reaction of the bacterial solution and cementation solution on the surface of the sample forms a small amount of reinforcement layer after one cycle of treatment. However, the reinforcement layer is too small and thin and thus does not create significant improvement. Disintegration curves with three treatment cycles are shown in Figure 8. All samples are the incomplete disintegration type. For the cementation solution concentrations of 0.4, 0.8, and 1.2, the residual mass of disintegration is the highest when the bacterial solution concentration is 0.75. At the same time, it should be noted that the impact of the bacterial solution concentration varies under different cementation solution concentrations. When the cementation solution concentration is 0.4, the reinforcement effects affected by the bacterial solution concentration are 0.75 \(>\) 0.5 \(>\) 1.0 \(>\) 0.25. When the cementation solution concentrations are 0.8 and 1.2, respectively, the reinforcement effects of the bacterial solution concentration are 0.75 \(>\) 1.0 \(>\) 0.5 \(>\) 0.25. When the cementation solution concentration is 1.6, the reinforcement effect is more significant due to the increase in the bacterial solution concentration. However, the difference in the reinforcement effect between 0.75 and 1.0 is not significant. This indicates that the bacterial solution concentration of 0.75 is more suitable for forming a certain thickness layer to reinforce the soil samples. Figure 6: Disintegration process of non-disintegration. Figure 8: Disintegration curves with three treatment cycles of different cementation solution concentrations: (**a**) 0.4, (**b**) 0.8, (**c**) 1.2, and (**d**) 1.6. Figure 7: Disintegration curve with one treatment cycle of different bacterial solution concentrations: (**a**) 0.4, (**b**) 0.8, (**c**) 1.2, and (**d**) 1.6. Due to the short treatment time, the MICP reaction is not fully carried out in one cycle treatment. At a lower cementation solution concentration, when the bacterial solution concentration is greater than 0.5, the reaction can be completely carried out. This will lead to a rapid reaction. If the bacterial solution concentration is too high, a large amount of calcium carbonate crystals is produced to fill the surface pores of the soil. The reinforcement layer only stays on the surface, making it difficult for bacteria and cementitious to continue infiltrating. Disintegration curves with five and seven treatment cycles are shown in Figures 9 and 10, respectively. Some samples exhibit non-disintegration phenomena after five and seven treatment cycles. The effect of the bacterial solution concentration on treated samples varies according to different treatment cycles. After multiple cycles of treatment, the effect of the MICP reaction is limited. A proper combination of the bacterial solution concentration and the cementation solution concentration can achieve good reinforcement under sufficient reaction conditions. A lower bacterial solution concentration is suitable for lower concentration solution concentrations. Meanwhile, when the cementation solution concentration is \(\leq\)1.2, the most suitable bacterial solution is 0.75. When the cementation solution concentration is 1.6, the most suitable bacterial solution is 1.0. However, there is not much of a difference compared to the bacterial solution of 0.75.