# Application of Microbially Induced CaCO\({}_{3}\) on the Reinforcement of Rock Discontinuity
## 3 Results and Discussions  
### Microbial Concentration and Urease Activity  
In Section 2.1, the turbidimetric method was used to indirectly measure the number of bacteria by analyzing the absorbance of the bacterial suspension. This method is based on the fact that cell concentration is directly related to the turbidity of the bacterial suspension, which in turn is related to the value of absorbance (OD\({}_{600}\)). In Figure 8, we can see the lowest concentration of bacterial suspension after the first 48 h expanded culture (shown by a red circle), which is called the \"initial domestication stage\", and the highest concentration after multiple expanded cultures (shown by a black pentagon) for the three domestication schemes. For comparison, the figure also shows the highest bacterial concentration of undomesticated bacteria after being cultured 48 h in a neutral medium, labeled as \"undomesticated\". In Figure 8, \"1/3\" represents the prolonged growth of bacteria in a solution with a 1/3 salt and alkaline concentration during the three-stage domestication process, and so on. Figure 8: Concentration of bacteria at different domestication schemes. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Specimen Type**} & \multirow{2}{*}{**Curing Time/Day**} & \multicolumn{4}{c}{**Test Quantity**} & \multicolumn{1}{c}{**Total**} \\ \cline{3-6}  & & **0.05**\(\sigma_{e}\) & **0.1**\(\sigma_{e}\) & **0.2**\(\sigma_{e}\) & **Quantity** \\ \hline Uncemented & – & 1 & 1 & 1 & 3 \\  & 7 & 1 & 1 & 1 & 3 \\ Undomesticated & 14 & 1 & 1 & 1 & 3 \\  & 28 & 1 & 1 & 1 & 3 \\  & 7 & 1 & 1 & 1 & 3 \\
1/1 & 14 & 1 & 1 & 1 & 3 \\  & 28 & 1 & 1 & 1 & 3 \\  & 7 & 1 & 1 & 1 & 3 \\
3/3 & 14 & 1 & 1 & 1 & 3 \\  & 28 & 1 & 1 & 1 & 3 \\  & 28 & 1 & 1 & 1 & 3 \\  & 7 & 1 & 1 & 1 & 3 \\
5/5 & 14 & 1 & 1 & 1 & 3 \\  & 28 & 1 & 1 & 1 & 3 \\ \hline \hline \end{tabular} Note: “Uncemented” refers to an uncometed specimen. “Undomesticated” means an undomesticated strain that is mixed with the neutral medium. “1/1” indicates a directly domesticated strain mixing with the saline–alkaline medium. “3/3” signifies a three-gradient domesticated strain mixing with the saline–alkaline medium. “5/5” denotes a five-gradient domesticated strain mixing with the saline–alkaline medium. The same conventions apply to the subsequent text.  
\end{table} 
Table 3: Details of uncemented and cemented rock specimens. The key to this experiment is to use urease secreted by _Sporosarcina pasteurii_ to hydrolyze urea to produce carbonate ions, providing raw materials for carbonate precipitation [68; 69]. Therefore, bacterial urease activity is an important indicator of MICP efficiency [70; 71]. In this study, the maximum urease activity of bacteria was measured by the method discussed in Section 2.5 during the expanded culture of the bacteria, and the results are shown in Figure 9.  
In the direct domestication scheme, the maximum concentration of bacterial suspension and the maximum unit urease activity of bacteria after the initial expanded culture was significantly lower, and even after multiple expanded cultures, the increase was limited, but the maximum concentration of bacterial suspension and the maximum unit urease activity of bacteria were still small. This result indicated that a high concentration of saline-alkaline medium had a significant inhibitory effect on the growth and reproduction of _Sporosarcina pasteurii_, which was the same with the maximum unit urease activity of bacteria. For the three-gradient and five-gradient domestication schemes, the maximum concentration of the bacterial suspension and the maximum unit urease activity of bacteria after the initial expanded culture were relatively low in the process of each level of concentration domestication. However, after multiple expanded cultures, the concentration of bacterial suspension and the maximum unit urease activity of bacteria increased rapidly and gradually became stable.