Coupled bio-chemo-hydro-mechanical modeling of microbially induced calcite precipitation process considering biomass encapsulation using a micro-scale relationship

Abstract

Geomaterials with inferior hydraulic and strength characteristics often need improvement to enhance their engineering behaviors. Traditional ground improvement techniques require enormous mechanical effort or synthetic chemicals. Sustainable stabilization technique such as microbially induced calcite precipitation (MICP) utilizes bacterial metabolic processes to precipitate cementitious calcium carbonate. The reactive transport of biochemical species in the soil mass initiates the precipitation of biocement during the MICP process. The precipitated biocement alters the hydro-mechanical performance of the soil mass. Usually, the flow, deformation, and transport phenomena regulate the biocementation technique via coupled bio-chemo-hydro-mechanical (BCHM) processes. Among all, one crucial phenomenon controlling the precipitation mechanism is the encapsulation of biomass by calcium carbonate. Biomass encapsulation can potentially reduce the biochemical reaction rate and decelerate biocementation. Laboratory examination of the encapsulation process demands a thorough analysis of associated coupled effects. Despite this, a numerical model can assist in capturing the coupled processes influencing encapsulation during the MICP treatment. However, most numerical models did not consider biochemical reaction rate kinetics accounting for the influence of bacterial encapsulation. Given this, the current study developed a coupled BCHM model to evaluate the effect of encapsulation on the precipitated calcite content using a micro-scale semiempirical relationship. Firstly, the developed BCHM model was verified and validated using numerical and experimental observations of soil column tests. Later, the encapsulation phenomenon was investigated in the soil columns of variable maximum calcite crystal sizes. The results depict altered reaction rates due to the encapsulation phenomenon and an observable change in the precipitated calcite content for each maximum crystal size. Furthermore, the permeability and deformation of the soil mass were affected by the simultaneous precipitation of calcium carbonate. Overall, the present study comprehended the influence of the encapsulation of bacteria on cement morphology-induced permeability, biocement-induced stresses and displacements.