## 3 Test Results and Analysis
### Shearing Strength  
After 7 days of natural air drying, the soil samples were consolidated into a whole by using five methods, as shown in Figure 8. The results show that the soil particles, after strengthening, are evenly distributed using a peristaltic pump for grouting. However, the soil sample grouted with an air compressor was subject to air pressure, and a large number of fine particles sank to the bottom of the sample. It had a significant impact on the uniformity of the soil particles. On the other hand, the soil surface solidified with the immersion method was dense and thick. According to the stress-strain curve obtained from the shear test (Figure 9), the shear strength (Table 5), the internal friction angle, and cohesion (Table 6) of granite residual soil are obtained. It can be seen from the table that a significant improvement in the shear strength of soil solidified with five methods was achieved. The group JR under the  
Figure 8: Soil samples solidified with different grouting methods: (**a**) JR; (**b**) JRY; (**c**) JK; (**d**) JKY; (**e**) JPY. Figure 7: Relationship between disintegration frequency and disintegration rate. same vertical stress shows a maximum cohesion of shear strength of 167.59 kPa and an internal friction angle of 54.15\({}^{\circ}\). These values are 101.75% and 297.98% higher than the uncured group (cohesion: 42.11 kPa, internal friction angle: 26.84\({}^{\circ}\)). The lowest degree of improvement in the strengthening effect is group JPY, with the cohesion and internal friction angle increased by 14.42% and 122.51%, compared with the uncured soil. It can be seen that microbially induced CaCO\({}_{3}\) precipitation can effectively bond soil particles, fill the space between soil particles, increase the surface's roughness, improve the sample's integrity and enhance the friction resistance. Further comparison between the test group of one-time grouting and multiple grouting revealed that multiple grouting with peristaltic pump increased the cohesion by 55.03% and the internal friction angle by 44.86% compared with one grouting. The cohesion increased by 34.79%, and the internal friction angle increased by 53.74% when the air compressor was used for multiple grouting compared to a single grouting. The effectiveness of multiple grouting's strengthening is significant due to the increase in the number of bacteria on the surface or between soil particles with each injection of bacterial liquid. This promotes the precipitation of calcium carbonate between soil particles, resulting in a more apparent bridging effect between soil particles [31]. The cohesion increase of air compressor grouting is lower than that of peristaltic pump grouting, but the friction angle increase is greater. This is due to the fine-grained soil sinking to fill the bottom gap under the air pressure, which affects bacterial adhesion and cementing fluid injection, resulting in a lower adhesive force after soil sample solidification. However, the consolidated soil with coarser particles is formed in areas except for the bottom. The interlocking effect between soil particles and the surface friction and the connection bite force between them are improved. Figure 10 presents the relationship curve between the shear strength and normal pressure of granite residual soil under different normal pressures. The figure demonstrates that the curing effect of groups JPY, JKY, and JRY mainly enhances cohesion. The soaking method used in the group JPY resulted in a one-dimensional surface consolidation, which prevented the bacteria and cementation liquids from entering the soil and forming a complete consolidation body. Groups JKY and JRY had limited bacterial adsorption due to a one-time injection, which affected the amount of calcium carbonate between the soil particles and failed to form a complete consolidated body.