# Application of Microbially Induced CaCO\({}_{3}\) on the Reinforcement of Rock Discontinuity
## 3 Results and Discussions
### Peak Shear Strength  
The graph in Figure 12 displays the peak shear strength of sandstone under three different levels of normal stress after reinforcement by varying strains. The specific strength values are provided in Table 5. A comparison of the increase in the peak shear strength of artificial joints by different strains is presented in Table 6 when compared with uncomented specimens. It is evident that the peak shear strength of strains on joints acquired through the direct domestication method shows a slight increase of between 2.33% and 13.55%. In contrast, both the three-gradient domestication method and five-gradient domestication method effectively led to an increase of between 7.62% and 28.56%. The increase in peak \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Species**} & \multicolumn{3}{c}{**The Percentage Increase**} \\ \cline{2-4}  & **0.05 \(\sigma_{c}\)** & **0.1 \(\sigma_{c}\)** & **0.2 \(\sigma_{c}\)** \\ \hline \(1/1\) & 2.33 & 13.55 & 2.13 \\ \(3/3\) & 18.52 & 22.70 & 7.62 \\ \(5/5\) & 22.11 & 28.56 & 14.19 \\ Undomesticated & 29.64 & 32.19 & 16.93 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Percentage increase in peak shear strength of joints strengthened by different strains. Figure 12: Comparisons of the peak shear strength of artificial rock joints. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Species**} & \multicolumn{3}{c}{**Peak Shear Strength (MPa)**} \\ \cline{2-4}  & **0.05 \(\sigma_{c}\)** & **0.1 \(\sigma_{c}\)** & **0.2 \(\sigma_{c}\)** \\ \hline Uncemented & 3.266 & 5.150 & 10.310 \\ \(1/1\) & 3.342 & 5.848 & 10.530 \\ \(3/3\) & 3.871 & 6.319 & 11.096 \\ \(5/5\) & 3.988 & 6.621 & 11.773 \\ Undomesticated & 4.234 & 6.808 & 12.055 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Peak shear strength of sandstone specimens repaired by different strains. shear strength of the five-gradient domesticated strains in the saline-alkaline environment (14.19% to 28.56%) was comparable to that of undomesticated strains in the neutral environment (16.93% to 32.19%). To compare the effect of different strains obtained from various domestication schemes on reinforcing microbial-induced calcium carbonate precipitation (MICP) on sandstone joints, and to analyze the influence of curing time on peak shear strength, we plotted the relationship between peak shear strength and curing time under three different normal stresses, as illustrated in Figure 13. The key findings are as follows:  
1. The peak shear strength increases rapidly during the early curing period, but the rate of increase slows down gradually with the extension of the curing time. This phenomenon is due to the gradual slowdown in the generation rate of calcium carbonate as urea and nutrients are consumed, and the bacterial population decreases in the absence of a supplemental nutrient solution and bacterial suspension [76,77]. 2. The repair ability of the strain obtained by direct domestication is significantly inhibited by the saline-alkaline environment, resulting in only a small increase in peak shear strength after restoration. 3. The peak shear strength of the specimens repaired after three- and five-gradient domestication showed a significant improvement after 28 days of maintenance, indicating that the gradient domestication program can help bacteria gradually adapt to the saline-alkaline environment. Furthermore, the peak shear strength of specimens repaired by bacteria after five-gradient domestication is slightly higher than that of bacteria after three-gradient domestication, and it is close to the repair strength of undomesticated bacteria in a neutral environment. The above results suggest that the five-gradient domestication method is more effective than other methods. From the mechanical analysis of rock joint reinforcement, it is clear that the key to strengthening rock joints is to use engineering measures to improve their shear strength parameter (\(c\)) and internal friction angle (\(\varphi\)) [13].