A coupled bio-chemo-hydraulic model to predict porosity and permeability reduction during microbially induced calcite precipitation

Microbially induced calcite precipitation (MICP) provides the potential for developing innovative and environmentally friendly techniques to improve the engineering properties of soil through reduction of permeability in soil and increase of soil stiffness and strength. In the present research work, coupled bio-chemo-hydraulic modelling was developed to enhance the understanding of the coupled processes involved in MICP and to predict the MICP performance in permeability reduction. In the model, an overall kinetically controlled model is adopted to describe the biochemical reactions, where the reaction rate is dependent on the concentration of both bacteria and chemical reactants. Specifically, an effective porosity concept was proposed and implemented in the model to capture the effects of pore throat blockage on permeability reduction caused by precipitated calcite. Correspondingly, the Kozeny-Carman equation was modified to describe the permeability variation during MICP. This model has been applied to simulate two laboratory experiments. The observed changes in chemical components and hydraulic conductivity can be well reproduced in the model. Through comparisons of the effective porosity concept to other commonly used porosity-permeability relationships, it is estimated that effective porosity should be considered to simulate the permeability reduction observed in MICP. Furthermore, a sensitivity analysis of the reaction-related parameters was conducted. The results of the sensitivity analysis indicate that the maximum urease rate has a strong influence on the biochemical hydraulic responses in MICP.