Mechanism and Strength Characteristics of Microbially Induced Carbonate Precipitation and Lime Composite Cured Soft Clay

Soft clay is characterized by high compressibility, low permeability, low strength, and high water content, making it a poor substrate for construction. Hence, soil treatment is often required for soft clay. However, the traditional treatment methods, such as stacking and on-site mixing, involve large space, long time, and high cost. In contrast, lime is stable and cheap, but slow to set and harden. In this paper, the microbially induced carbonate precipitation (MICP) and lime composite curing of soft clay was investigated. Tests were carried out on soft clay samples with different lime ratios. By comparing the changes of strength, composition, and microstructure before and after curing, the mechanism of MICP/lime composite solidification of soft clay was systematically studied. The results showed that (1) a reasonable proportion of lime can react with water and CO2 in clay to generate CaCO3, and also promote the induction of more CaCO3 precipitation by microorganisms, contributing to the improved strength of solidified clay; (2) MICP/lime composite curing can effectively reduce water in soft clay and help to improve the strength of solidified soil; (3) MICP and lime were complementary in terms of curing time, leading to continuous improvement of curing effect; and (4) the MICP/lime composite has a good effect on the solidification of soft clay. Under the experimental conditions in this study, the best solidification effect was observed for soft clay with a water content of 30% and a lime ratio of 30%.