Cyclic response of compacted completely decomposed granite soil by microbially induced carbonate precipitation

In this study, the microbially induced calcite precipitation (MICP) was applied to compacted completely decomposed granite (CDG) soil at both the dry and wet sides of its optimum water content, using fixed concentrations of bacterial suspensions and chemical reagents. Scanning electron microscopy (SEM), calcium carbonate content measurements, and cyclic triaxial tests were conducted on the effects of the water content and curing period on the microstructure and mechanical performance of the samples. Testing results indicate that the MICP treatment significantly improves the mechanical performance through calcium carbonate crystals filling structural pores or attaching to the matrix surface, compared to untreated samples. During the 0–6-d active phase, the dry-side permanent strain decreases by more than 12% and that on the wet-side strain by more than 60%. After the 6-d active phase, the permanent strain remains stable due to the completion of calcium carbonate precipitation. The resilient modulus and damping ratio also display the two-phase evolutionary characteristics similar to those of the permanent strain. At a given curing period, the dry-side sample presents a lower permanent strain or a higher resilient modulus compared to the corresponding wet-side sample. Nonetheless, the impact of water content on the damping ratio is not substantial.