## 5 Discussion
At this time, the solute migration of each solution used by MICP technology was hindered the most. Therefore, the solute of each solution can migrate before 7 days if the hydraulic conductivity and porosity of the area covered by MICP solute migration were set to the value after 7 days of perfusion and if the solute of each solution can still migrate to the designed area through the seepage field formed by the reinjection well after 7 days. This condition proved that forming a horizontal curtain by using MICP technology is feasible. (1) Bacterial migration  
According to the analysis results of bacterial migration before, refer to the infusion plan of bacterial solution, bacteria solution (5000 mg/L, OD600 = 1) was injected at an irrigation rate of 400 m\({}^{3}\)/d after the stable seepage field was formed with an irrigation rate of 1000 m\({}^{3}\)/d in the recharging well. From the calculation results, as shown in Figure 25a, it was more difficult for the solution to migrate to the outer ring than to the inner ring after filling the pores with the calcium carbonate produced by the MICP reaction in the early stage. In order to solve this problem, and to minimize the re-addition of bacteria solution, the method of stopping the injection of bacteria solution into the outer ring and continuing the injection of water into the inner ring recharge wells at an irrigation rate of 1000 m\({}^{3}\)/d was adopted to promote the migration of existing bacteria solution outward. The calculation result is shown in Figure 25b. After the slurry injection is stopped, the seepage field formed by the inner ring recharge well continues to promote the migration of bacteria solution to the outside, enabling bacteria to break through the blocking effect caused by the carbonate generated in the earlier stage. However, this method will cause some bacteria solution to leak out, and it is necessary to replenish the bacteria solution. (2) Migration of stationary solution  
Stationary solution (0.05 mol/L, Ca\({}^{2+}\) concentration 2000 mg/L) was injected at an irrigation rate of 400 m\({}^{3}\)/d after the stable seepage field was formed at an irrigation rate of 1000 m\({}^{3}\)/d in the recharging well. As shown in Figure 26a, the migration of the stationary solution injected in the later stage was hindered by the calcium carbonate generated between the pores of the sand particles in the early stage. The cost increased slightly by increasing the injection amount of the fixation solution because the concentration of CaCl\({}_{2}\) solution used was low. Therefore, the method of increasing the injection amount was changed to the fixation solution, with an injection rate of 800 m\({}^{3}\)/d. The results are shown \begin{table}
\begin{tabular}{c c c} \hline
**Time** & **Laboratory Test K(cm/s)** & **Numerical Model K(cm/s)** \\ \hline
0 & \(2.1\times 10^{-3}\) & \(5.0\times 10^{-2}\) \\
1 & \(1.96\times 10^{-3}\) & \(4.67\times 10^{-2}\) \\
2 & \(1.67\times 10^{-3}\) & \(3.98\times 10^{-2}\) \\
3 & \(1.35\times 10^{-3}\) & \(3.21\times 10^{-2}\) \\
4 & \(8.9\times 10^{-4}\) & \(2.12\times 10^{-2}\) \\
5 & \(5.5\times 10^{-4}\) & \(1.31\times 10^{-2}\) \\
6 & \(3.2\times 10^{-4}\) & \(7.62\times 10^{-3}\) \\
7 & \(1.9\times 10^{-4}\) & \(4.52\times 10^{-3}\) \\ \hline \end{tabular}
\end{table} 
Table 7: Hydraulic parameters of different time models. in Figure 26b; Ca2+ migrated to the designated area under the condition of being hindered by increasing the irrigation rate. (3) Migration of cementation solution  
The cementation solution (1.5 mol/L, Ca2+ concentration 60,000 mg/L) was injected at an irrigation rate of 400 m\({}^{3}\)/d after the steady seepage field was formed in the recharging well at an irrigation rate of 1000 m\({}^{3}\)/d. As shown in Figure 27a, the migration of the cementation solution poured in the later period was hindered by the calcium carbonate generated in the pores of the sand particles in the earlier period.