Abstract:A large amount of the Yellow River silt deposits in the middle and lower reaches of the Yellow River. The Yellow River silt has properties of small fineness modulus, poor particle gradation, and high mud content, which limit the use of the Yellow River silt in engineering. In order to improve the quality of the Yellow River silt and reduce the engineering defects caused by the use of the Yellow River silt, based on the characteristics of silt and microbial induced carbonate precipitation (MICP) technology, the Yellow River silt was quantitatively solidified and analyzed by using SEM and range analysis methods to study the effect of MICP technology on the improvement of Yellow River silt particle size distribution. The results showed that the specific gravity of the particles in the size range of 1 mm to 5 mm after MICP treatment was 45% higher than that of the first solidified sample, 70% higher than that of the initial sand sample in the same interval, and the contact number of particles in unit volume becomes larger, showing a multi particle cluster shape. Through the immersion test, the dispersion degree of coarse particles and aggregates in the sample was only 5%～10%. The optimum condition was that the particle size distribution of the sample was 5%～10%. The improved scheme includes 1∶1 bacterial to gum ratio, 1.5 mol/L cement concentration, 2∶1 urea to calcium source ratio, and CaCl₂ as calcium source, in which the cement concentration was the main factor to improve the particle size distribution. Most of the CaCO₃ crystals generated by mineralization were calcite crystal phase, and a large number of CaCO₃ crystals were superimposed to form a bedding structure, and CaCO₃ bridge was formed between sand particles, and fine particles were absorbed by cementation, thus increasing the size of silty sand and improving the Yellow River silt’s engineering property. This research provides a new idea for improving the Yellow River silt.