Exploring Bio-Bentonite Slurry Seepage Control Process in Coarse Sand with Numerical Modeling

Bentonite slurry grouting is an effective method for reducing the permeability of soil, while the Microbially Induced Carbonate Precipitation (MICP) is a perfect choice for stabilizing fine particles to avoid seepage-induced erosion. The combination of MICP and bentonite slurry (bio-bentonite slurry) can thus solve the challenge that bentonite clusters can hardly be entrapped in coarse sand, providing the potential to reduce permeability in coarse sand. Although experiments have been conducted demonstrating the successful seepage control of coarse sand, the whole grouting process is challenging to measure physically. This challenge motivates us to develop a reactive transport model to explore these processes. The proposed numerical model consists of several components designed to describe fluid flow, material transport, bentonite deposition, and CaCO3 precipitation, as well as the operation of valves controlling injections and material concentration. The model parameters are calibrated using a unidirectional grouting test, and the accuracy of the model is further verified through a bidirectional grouting test. Then, the distributions of bacteria, CaCO3, bentonite, and hydraulic conductivity after each treatment cycle, along with the temporal evolution of reaction processes, are discussed. All results provide a comprehensive understanding of the seepage control achieved by the bio-bentonite slurry method in coarse sand.