## 3 Test Results and Microscopic Observation Analysis
### Microscopic Observation  
In order to better explore the mechanism of microbial mineralization in the soil-rock mixture and to feel the cementation products of microbial mineralization more intuitively, a set of blank controls was set up. In the blank control group, deionized water was used to replace the cementation reagent and bacterial liquid. Under the condition that other conditions remain unchanged, the samples were dried and then microscopically observed. D1, B3, and the blank control group were selected for microstructure and phase analysis. Observing Figure 10, it can be observed that calcium carbonate crystals are attached to the surface of the sample, which strengthens the bonding of particles at the voids. Observing Figure 11, there are spot-like crystals on the surface of B3, which aggregate on the surface of the silt, connecting the two parts of the silt and the rock. It can be observed from Figure 12 that the surface of the sample is powdery, and there is no crystal at the connection. There is an obvious fracture failure surface in the sample, the failure contact surface is smooth, and there is no \"rough feeling\", as shown in Figures 10 and 11. Observing Figure 13a, the atomic energy percentage of calcium ions in sample D1, it can be found that the percentage content of calcium ions in this sample is 0.54%, which is very small. Observing Figure 13b, the atomic energy percentage of calcium ions in sample B3 is 0.5%, compared with the atomic energy percentage of calcium ions in sample D1. Under the same mass, the calcium ion content of B3 is less than that of D1. Combined with Figure 13c, the calcium ions in the blank control group accounted for 38%, which was less than the percentage of calcium ions in D1 and B3. It is proved that the mineralization of microorganisms can indeed precipitate calcium ions between particles, which provides a theoretical basis for the mineralization of microorganisms. Figure 10: _Cont._Figure 10: SEM micrographs of D1 at different magnifications. (a) 2 \(\upmu\)m; (b) 4 \(\upmu\)m; (c) 10 \(\upmu\)m.  
Figure 11: _Cont_. Figure 11: SEM micrographs of B3 at different magnifications. (**a**) 2 μm; (**b**) 4 μm; (**c**) 10 μm. Figure 12: _Cont._  
Figure 12: SEM micrographs of the blank control group at different magnifications. (a) 2 μm; (b) 4 μm; (c) 10 μm. From the detection results of XRD (Figure 14, Table 3), it can be observed that the three groups of samples have the highest dolomite content, and the dolomite content of D1, B3, and the blank control group is 46.3%, 30%, and 18.7%, respectively. The calcite content is 2.9%, 3.1%, and 3.7%, respectively. Calcium ion is an important constituent element of dolomite and calcite, both of which exist in the form of calcium carbonate. The sum of the content of the two phases can also be regarded as the total content of calcium  
Figure 13: Element distribution of different soil–rock mixture columns. (**a**) D1; (**b**) B3; (**c**) Blank control group. carbonate crystals generated under the action of microbial mineralization. According to Table 3, the calcium carbonate content of the three groups of samples under the action of cementation is as follows: D1 > B3 > blank control group. Combined with the EDS composition analysis results of D1 and B3, the percentage of calcium ions in the sample D1 > B3, it is proved that in the whole process of microbial mineralization, D1 produces more calcium carbonate than B3, with better cementation performance, filling the pores between particles. The compressive capacity of the soil-rock mixture sample is stronger, which is consistent with the mechanical test results. At the same time, it also shows that calcium carbonate is indeed generated under the action of bacterial liquid and cementation reagent, which strengthens the internal connection between soil and rock, fills pores, and increases the strength of the sample. It can be seen that microbial mineralization technology can effectively strengthen the adhesion between soil particles.