Numerical analysis of microbially induced calcite precipitation and enzyme induced calcite precipitation in calcareous sand: Multi-process and biochemical reactions

Abstract

Microbially induced calcite precipitation (MICP) and Enzyme induced calcite precipitation (EICP) techniques were implemented to reinforce the large-scale calcareous sand in this study. Then a coupled numerical model to predict the biochemical reactions and hydraulic characteristics of MICP and EICP reaction was proposed and verified by physical experiments. Results showed that: This model could describe the variations of bacteria, calcium, calcite, permeability over time reasonably. It is necessary to consider the influence of the calculation domain scale when simulating the convection-diffusion-reaction in the multi-process of MICP and EICP reactions. The numerical and experimental values of calcite content are 0.841 g/cm3 and 0.861 g/cm3 for MICP-reinforced sand, 0.263 g/cm3 and 0.227 g/cm3 for EICP-reinforced sand after 192 h of reaction. The reaction rate krea is an important parameter to control the calcite content. Accordingly, the permeability coefficient of MICP and EICP reinforced calcareous sand decreases by 32% and 18%. Due to the influence of substance transportation and calcite precipitation, the calcite shows a trend of decreasing firstly and then increasing with the enhancing of the initial permeability coefficient in biochemical reactions. The optimal injecting ratio q11: q12 in this study is 100:300 mL/min. The process for the application of MICP and EICP coupled numerical model is also recommended, which provides reference for engineering projects in ground improvement.