## 6 Conclusions  
An innovative MICP HSRB formation method was developed. _S. pasteurii_ and cementation solution were used in MICP HSRB. Reinjection wells were used to form a stable seepage filled from pit center to outside. MICP HSRB was formed using the seepage field generated by the recharge wells to drive the migration of bacteria solution, stationary solution, and cementation solution into the confined aquifer. The effects of the recharge rate of the inner circle recharge wells, injection rate of bacterial and cementing solution, and the layout of the recharge wells on migration were studied. The conclusions are as follows:  
(1) Under the condition of the same _S. pasteurii_ solution injection rate, the coverage area of bacteria increased with the increase of continuous infusion time. However, the growth rate of coverage area decreased with the increase of time. The effect of continuous infusion gradually decreased with the increase of infusion time. Therefore, when the upper limit of the bacterial covered area is reached, the infusion of bacterial solution can be stopped.  
(2) The main factors affecting the coverage area of bacteria migration were the injection rate of the inner circle reinjection well and the recharge rate of the outer circle bacteria solution. However, increasing the recharge rate of the inner circle recharge well did not increase the migration coverage area of the effective high concentration bacterial solution, but did accelerate the bacterial solution leakage and reduced the effective concentration coverage area. On the contrary, the coverage area of the effective bacterial solution concentration obviously increased by increasing the bacterial solution recharge rate in the outer recharging well. The time spent injecting the bacterial solution should be minimized.  
Figure 27: Horizontal migration diagram of cementation fluid: (**a**) Horizontal migration after 1 day of perfusion; (**b**) horizontal migration driven by seepage field for 1 day after grouting is stopped; (**c**) Legend.  
(3) Increasing the number of reinjection wells with bacterial fluid in the outer ring can effectively increase the coverage area of the bacterial fluid. The condition of constant total amount of reinjection can achieve a better effect to split the amount of one reinjection well into two wells.  
(4) The migration process of solute in the later filling solution was blocked by calcium carbonate generated in the earlier filling slurry of MICP technology. In accordance with a different solution, different methods were adopted to re-drive the seepage field to break through the plugging effect and make the solute migrate to the designated area.  
[PERSON], [PERSON] and [PERSON] carried out the main research task and wrote the manuscript. [PERSON] and [PERSON] proposed the original idea and contributed to the revision of the obtained results and of the whole manuscript. [PERSON] and [PERSON] helped perform numerical simulation. [PERSON], [PERSON] and [PERSON] helped revise the results and manuscript.All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Shanghai Municipal Science and Technology Project (19 DZ1200900); Xiamen Road and Bridge Group (XM2017-TZ0151; XM2017-TZ0117); the project of Key Laboratory of Impact and Safety Engineering (Ningbo University), Ministry of Education (CJ202101); Shanghai Municipal Science and Technology Major Project (2021 SHZDZX0100) and the Fundamental Research Funds for the Central Universities; Key Laboratory of Land Subsidence Monitoring and Prevention, Ministry of Natural Resources of the People's Republic of China (No. KLLSMP202101), Suzhou Rail Transit Line 1 Co., Ltd., China Railway 15 Bureau Group Co., Ltd.  
Not applicable.  
The authors declare no conflict of interest.