## 4 Conclusions  
In this study, MICP technology was utilized to investigate the effect of different reinforcement methods and conditions on the strengthening effect of granite residual soil. The following conclusions can be drawn:  
(1) After culturing the bacteria in a double culture medium, the concentration of the bacteria solution reaches OD\({}_{600}\) = 3.0, and the urease activity is measured to be 31.64 mM/min. The concentration of the bacterial solution and urease activity directly impact the output of calcium carbonate, as well as the stability of crystal shape and appearance. These factors are crucial to strengthening poorly graded soil such as granite residual soil.  
(2) MICP technology can effectively improve the anti-disintegration performance of granite residual soil. The sample disintegration rate of the soaking method is the lowest, reflecting a close correlation between the disintegration rate and the calcium carbonate content generated on the soil surface. Therefore, the granite residual soil slope may achieve shallow consolidation by strengthening through spraying, preventing the surface from peeling and collapsing year by year.  
(3) The peristaltic pump grouting method strengthens the more effectively than the air compressor and immersion method. Compared with the uncured soil, the UCS increased by 513.65%, while the cohesion and internal friction angle increased by 297.98% and 101.75%, respectively.  
(4) A high concentration of cement can lead to one-dimensional consolidation, which is not ideal for deep consolidation of soil samples. To a certain extent, reducing the concentration of cement and increasing the number of grouting rounds can enhance the UCS of the soil sample. After seven grouting rounds, the consolidated soil sample with a cement concentration of 0.5 mol/L showed the highest UCS of 1.602 MPa.  
(5) The pH value of the cementing fluid plays a crucial role in the acceleration of calcium carbonate formation, and the optimal pH range for this process is 6-8. As the pH value increases, the UCS of the soil samples also increases. However, when the pH value is 8-9, the increase in UCS tends to be gentle.  
(6) According to the results of XRD, the diffraction peaks of kaolin and silica in the consolidated soil samples decreased significantly. In contrast, the characteristic diffraction peaks of the calcite crystal type appeared in the range of 29.4-29.6\({}^{\circ}\). The soil sample consolidated with multiple grouting with the peristaltic pump showed the highest peak value of calcite diffraction. Combined with the soil consolidation state observed under SEM, it can be concluded that the peristaltic pump grouting solidification mode produced a large amount of evenly distributed calcium carbonate content, resulting in an optimal consolidation effect.  
(7) In order to achieve the application of MICP in engineering, the grouting test of undisturbed soil samples should be carried out in the next stage. Meanwhile, long-term performance of soil samples, including freezing and thawing, acid rain resistance, long-term creep, and settlement deformation also need systematic study. Importantly, if local bacteria can be extracted and applied in MICP, this may strengthen the environmental adaptability of bacteria and improve the long-term performance of the soil.  
Conceptualization, R.W. and C.H.; Methodology, F.L. ([PERSON]); Investigation, F.L. ([PERSON]); Resources, M.W. and C.H.; Data curation, Z.C.; Writing--review & editing, R.W. and H.L.; Project administration, Q.W. All authors have read and agreed to the published version of the manuscript.  
Natural Science Foundation of Fujian Province of China: 2020J01403; Natural Science Foundation of Fujian Province of China: 2023J011044; Resource Chemical Industry and Technology Foundation of Nanjing of China: N2021Z002; Natural Science Foundation of Fujian Province of China: 2020Y0092; Teachers and Students Co-construction Team of Wuyi University: 2021-SSTD-04.  
Not applicable.