Abstract: 【Objective】 Determining the behavior of microbial cementation silt treated by bio-grouting, based on the technology of microbial induced carbonate precipitation(MICP), could provide a basis for developing the MICP technology and applying it for dredger fill silt. 【Method】 Experiments were conducted for cement dredger fill silt specimens by microbial grouting. Unconfined compressive tests, X-ray diffraction analyses(XRD), scanning electron microscope(SEM)observations, mercury intrusion porosimetry(MIP)and some chemical analyses were performed to investigate the difference in strength, mineral component, cementing CaCO₃ content, soil microstructure and pore size distribution of untreated and treated dredger fill silts. 【Result】 After injecting 1 to 6 rounds of Sporosarcina pasteurii(A₆₀₀=1.2)and a cement solution containing a mixture of CaCl₂ and urea(0.1 mol/L)under constant pressure, the unconfined compressive strength of the treated silt specimens increased by 26.8%, 33.0%, 36.4%, 39.6%, 59.8% and 61.8% after the rounds 1 to 6, respectively, compared to the untreated silt specimen. The strength of the treated silt specimens increased with the number of rounds of injection. The cementing CaCO₃ from the microbial grouting was mostly in the calcite phase, which filled the soil pores and cemented the soil particles. The CaCO₃ content had a dominant effect on the strength of the treated silt. The more the CaCO₃ precipitated from the microbial process in the silt, the higher was the strength of the silt. Furthermore, there was a sensitive threshold for CaCO₃ content with respect to strength variation. The cementing efficiency increased significantly when the CaCO₃ content was higher than the threshold, which varied with the genetic type or sedimentary environment of the silt. Compared to the untreated silt, the treated silt had significantly different pore diameter distribution characteristics. After the bio-grouting treatment, the pores in the range 10-300 μm in the silt reduced sharply, and the pores smaller than 10 μm remained almost unchanged. 【Conclusion】 Bio-grouting is an effective method that can be applied for cementing dredger fill silt. The strength of the dredger fill silt treated with microbial grouting is influenced by the CaCO₃ content, and there is a sensitivity threshold for CaCO₃ content with respect to strength variation. The pore size of the dredger fill silt is large enough for the microbial cells of Sporosarcina pasteurii migration. In the dredger fill silt treated by bio-grouting, there is a large reduction in the number of pores with a size over 10 μm.