Development of bio-grout injection strategy and design guide using reactive transport model for field-scale soil improvement based on microbially induced calcium carbonate precipitation (MICP)

Abstract

Microbially induced calcium carbonate precipitation (MICP) has garnered huge interest for its potential as an alternative and sustainable ground improvement method as it exploits natural microbiological processes. To this date, there is little or no guidance on the injection strategy to achieve a uniform calcium carbonate distribution at a field scale and most of the MICP method is still limited to lab-scale or meter-scale experimentation. Therefore, this study investigates effect of biochemical factors on spatial distribution of calcium carbonate precipitation at a field scale by using a reactive transport model, and suggests a guide to field-scale MICP treatment strategies for ground improvement. The reactive transport model couples microbial, chemical, hydrological processes associated with MICP, in which the key model parameters are validated with half-meter column experiments. The parametric case study primarily examines the effects of bacterial density in biological solutions, chemical concentration in cementation solutions, and bacterial attachment rate on spatial distribution of precipitated carbonate. The results reveal that the density of attached bacteria has a profound effect on the uniformity in calcium carbonate content around the injection point. Bio-augmentation with low bacterial density facilitates in achieving a homogeneous precipitation due to the slow reactions of urea hydrolysis. The findings in the parametric study leads to the development of preliminary design guide to achieve the uniform distribution of calcium carbonate with the minimal heterogeneity and the minimal over-precipitation and to account for the calcium loss due to the diffusion and solution mixing.