| Microbial induced calcite precipitation (MICP) is a bio-mediated soil modification technique that harnesses a natural, in situ, biological process (urea hydrolysis) to change the mechanical properties of soil. Bio-mediated soil modification is a currently developing field of civil and environmental engineering that relies on biological systems to improve soil characteristics for geotechnical engineering applications. Motivation for this research is driven by the societal need to find sustainable technologies that require minimal input and have minimal adverse effects to the environment. Additionally, the ground improvement industry has been using technologies (specifically in grouting applications) for decades that require the injection of synthetic materials into the subsurface and although widely used, have resulted in several cases where human and animal health is adversely affected. MICP, driven by microbial urea hydrolysis (ureolysis), has become the focus of many studies as a first foray into developing a bio-mediated soil improvement technology due to the relative ease of investigation in the laboratory. Up-scaling of MICP towards implementation for field applications is the focus of this research.;The study presented herein examines from micro-scale to macro-scale the MICP process for cementing sands, including the identification of the key controllable parameters associated with achieving targeted strength properties, uniformity, and chemical efficiency, as well as the development of the mathematical tools to predict measurable MICP outcomes.;Ureolytic microbes (bacteria that harbor the urease enzyme) induce calcite precipitation by converting urea to ammonia and carbon dioxide, which react in the pore fluid to raise pH and allow calcite precipitation in well-poised geochemical systems. At the micro-scale, bio-mediated calcite was examined for structure and distribution around particles for varying soil types. At the macro-scale, optimization of the treatment technique to achieve uniform distribution was examined in half-meter column experiments where the primary controls were identified. A reactive transport mathematical model was developed in order to analyze MICP in macroscopic one-dimensional flow and a procedure for predicting MICP at column scales is presented. The study culminates by applying lessons learned from the column experiments and numerical modeling to treat a macro-scale three-dimensional experimental model representing a commonly used injection technique for achieving uniformly distributed injectate fluids into a 0.5m × 0.5m × 0.15m target treatment zone.;The purpose of the research presented in this dissertation is two-fold: (1) to provide insight on what makes MICP effective at the micro-scale, (2) identify the primary factors associated with optimizing treatment uniformity and reaction efficiency, (3) develop a capable, robust numerical model to predict MICP, (4) demonstrate effective MICP treatment in a three-dimensional flow regime. Throughout the research, particular attention was given to providing the necessary tools and insight to take MICP to the field scale and recommendations for future application is provided. |
