## 4 Conclusions  
In this paper, based on calcium carbonate precipitation induced by microorganisms technology, considering the influence of three different factors, such as fine particle content, porosity ratio and cement injection amount, on the curing effect of silt, a series of tests, such as CaCO\({}_{3}\), unconfined compressive strength, permeability, XRD, SEM and so on, show that the macroscopic properties and microstructure of the strengthened silt samples have been improved to varying degrees. 1. After curing by microorganism, the CaCO\({}_{3}\) content of silt increased with the decrease in pore ratio and the increase in fine particle content. Therefore, the CaCO\({}_{3}\) content of silt A with pore ratio of 0.75 and fine particle content of 75% was the highest. There is no linear relationship between the content of CaCO\({}_{3}\) in silt and the injection amount of cementing liquid. When the injection amount of cementing liquid is 150 mL in a single round, the CaCO\({}_{3}\) content is 13%, and when the injection amount is 300 mL, the CaCO\({}_{3}\) content is 19%. 2. By XRD analysis, there are three crystal types of calcium carbonate generated in the biological treatment samples, namely aragonite, vaterite and calcite, among which vaterite and aragonite are the main crystal types. The SEM images of three kinds of biological treatment samples of silt with different fine particle contents were obtained, and the crystal shapes were mainly spherical and acidular clusters, which were consistent with the XRD results. With the decrease in fine particle content, the crystal shape changes from spherical uniform distribution to spherical and acidular cluster distribution. Figure 15: Effect of different fine particle content on permeability coefficient. 3. In the process of calcium carbonate precipitation induced by microorganisms, the capacity of residual bacteria in silt under different conditions is all over 50%. The higher the capacity of residual bacteria is, the higher the content of CaCO\({}_{3}\) in silt after curing. The retention capacity of silt A was affected by silt porosity ratio and fine particle content, and had nothing to do with the injection amount of cementing fluid. The retention capacity of silt A with pore ratio of 0.75 and fine particle content of 75% was the highest, which was 77%. 4. Untreated silt has a certain strength due to its cohesion. After curing by microorganism, the unconfined compressive strength of silt can reach more than 1 MPa. When the content of fine particles is the same, the unconfined compressive strength of silt with a pore ratio of 0.75 is higher than that of silt with a pore ratio of 0.9 because of its small pore volume, large number of pores and strong retention bacteria capacity. There is an obvious correlation between unconfined compressive strength and CaCO\({}_{3}\) content of silt. When CaCO\({}_{3}\) content accumulates to a certain extent, the strength of silt will be significantly improved. 5. The permeability coefficient of untreated silt is in the range of 1.18 \(\times\) 10\({}^{-4}\)-5.37 \(\times\) 10\({}^{-4}\) cm/s. After curing by microorganism, the permeability coefficient of silt is significantly improved. In particular, when the single injection amount of cementing fluid is 300 mL, the permeability coefficient of silt A with pore ratio of 0.75 and fine particle content of 75% is 7.08 \(\times\) 10\({}^{-8}\) cm/s, and the silt is close to the impermeable state. Conceptualization, Z.X. and X.H. ; Data curation, Q.W. ; Formal analysis, Q.W. and Z.X. ; Funding acquisition, Y.Z., J.Z. and Q.T. ; Investigation, Y.Z. ; Methodology, Y.Z. and Q.W. ; Project administration, Q.T. ; Resources, Y.Z. ; Software, Q.W., M.Y. and X.C. ; Supervision, Y.Z., X.H. and J.Z. ; Validation, Q.T. ; Writing--original draft preparation, Y.Z. ; Writing--review and editing, Q.W. All authors have read and agreed to the published version of the manuscript.