Evaporation cracking characteristics and mechanism of silt improved by microbial-induced calcium carbonate precipitation

Abstract Silt readily develops desiccation cracks under evaporation, degrading mechanical properties and triggering hazards like slope instability and foundation deformation. As an eco-friendly soil improvement technique, MICP lacks systematic study on its anti-cracking effect and mechanism. In this study, laboratory drying cracking tests, combined with orthogonal tests and SEM characterization, are performed to explore the evaporation pattern and crack evolution characteristics of MICP-treated silt, quantify the influence weight of process parameters, and reveal the microscopic improvement mechanism. The results demonstrate that MICP-generated calcium carbonate can block water migration pathways, reducing soil evaporation rate and enhancing the water retention capacity. Compared with plain silt specimens, the modified samples achieve a maximum absolute crack ratio reduction of 1.72% points (about 22% relative reduction, achieved by the A3B2C3 group as the optimal combination), a 16% decrease in average crack width, and a markedly delayed crack initiation time. Orthogonal test results indicate that cementation solution concentration is the dominant factor governing the crack ratio, and the bacteria-cementation solution ratio exhibits a noticeable trend, while bacterial suspension concentration has a negligible effect. The optimal parameters are identified as bacterial suspension at OD 600 =1.5, cementation solution at 1 mol/L, and a bacteria-cementation solution volume ratio of 2:1. Calcium carbonate plays a synergistic role via three occurrence modes, enhancing the anti-cracking performance of silt from both hydraulic and mechanical perspectives.