Various Bacterial Attachment Functions and Modeling of Biomass Distribution in MICP Implementations

Microbial induced calcium carbonate precipitation (MICP) offers a robust technique to improve strength and stiffness properties of subsurface soils supporting infrastructures. Several unknown factors, including the MICP reactive transport parameters, however, limit the ability to predict spatial distribution of calcium carbonate (CaCO3) precipitation within a subsurface area and with depth. As it was shown that calcium carbonate distribution is highly affected by biomass profiles in subdomains, five bacteria attachment models (constant-rate, power-law, exponential, gamma distribution, and "c(str) based on colloid attachment theory") were calibrated here using data from both small- and large-scale testing programs. Out of the five models, colloid attachment theory with modified velocity and straining terms was shown to be the most promising approach in yielding the most fitted CaCO3 distribution compared with the experimental data. A new parameter, c(str), was incorporated to modify straining and the constraint peak value of biomass attachment due to straining at distances larger than a 0.14xsample size. Using the results from the numerical simulations, relationships were developed for velocity and straining coefficients of "the c(str) based on colloid attachment theory" (hereafter "colloid attachment c(str)") as a function of bacteria size, soil particle size, sample size, volume of injected bacteria, and soil pore volume.