Microbial-induced carbonate precipitation (MICP) is a bio-inspired solution where bacteria metabolize urea to precipitate. This carbonate acts as a bio-cement that bonds soil particles. The existing framework has focused mainly on applying MICP through infiltration of liquid bacterial solutions in existing soil deposits. However, this technique is inefficient in soils with high fines content and low hydraulic conductivity, and thus few studies have focused on the use of MICP in fine soils. The main objective of this study was to evaluate the effect of MICP applied to compaction water in soils containing expansive clays and sandy silts. This approach searches for a better distribution of bacteria, nutrients, and calcium sources and is easy to apply if associated with a compaction process. In soils with expansive minerals, the effect of MICP in swelling potential was explored at laboratory and field scales. In sandy silts, the evolution of the stiffness and strength were studied at the laboratory scale. The treatment at the laboratory scale reduced the swelling potential; nevertheless, no significant effect of MICP was found in the field test. In sandy silts, the strength and stiffness increased under unsaturated conditions; however, subsequent saturation dissolved the cementation and the improvement vanished.

The improvement of soil behaviour by the bacterial precipitation of calcium carbonate has been extensively studied in geotechnical engineering. However, the evolution of bio-cementation bonds under shear conditions is only partially understood. This research presents a micromechanical approach to gain a deeper insight into the interaction between bio-cemented particles. A series of glass bead samples were treated with Microbial Induced Calcite Precipitation (MICP) and then subjected to direct shear tests. A calibrated model based on the Discrete Element Method was used to reproduce the macro-mechanical paths observed in the experiments, allowing the detailed analysis and description of the bond evolution at the microscopic scale in the treated samples. In general, it was found that a higher rate of bond breakage occurred before the peak shear strength was reached, and this was followed by a relatively constant rate of bond breakage associated with a macroscopic softening trend. Tensile stress was identified as the primary fracture mechanism. Finally, it was determined that the bond breakage mechanism is influenced by several factors, such as bond distribution, particle array, and the mechanical parameters of the bond.