Numerical modeling of MICP grouting in homogeneous and layered heterogeneous soils

Abstract

Microbially induced carbonate precipitation (MICP) has been extensively studied through experiments as a potential solution for ground improvement. However, the investigation and optimization of the MICP grouting process remain incomplete due to various experimental limitations, such as budget constraints, equipment availability, time limit, and suitable sites. As a result, the numerical method could be a practical approach, providing a clearer understanding of the hydrological-biological-chemical processes involved, which could help improve the performance of MICP. In this study, a hydrological-biological-chemical coupling model was developed to simulate MICP grouting in both homogeneous and layered heterogeneous soils, which is often found in nature. The model effectively captures the impact of carbonate precipitation on critical aspects of the grouting process, such as flow field, bacterial adsorption, bacterial activity, and soil properties. Additionally, the Péclet and Damköhler numbers were introduced to comprehensively describe the impact of various grouting factors on the distribution of precipitates and the average CaCO3 increment in homogeneous soils. In layered heterogeneous soils, it was observed that some solutions migrate across the interface between the two soil layers, leading to an accumulation of precipitates near the interface and forming a wedge-shaped CaCO3 increment zone in the lower-permeability soil layer. Beyond this wedge-shaped zone, the distribution of CaCO3 is comparable to that in homogeneous soils. These findings suggest that in layered heterogeneous soils, special attention should be given to the area adjacent to the soil interface in the less permeable layer, as the precipitate distribution in other regions mirrors that in corresponding homogeneous soils.