IMPACT OF SOIL AND GEOCHEMICAL PARAMETERS ON GROUND IMPROVEMENT USING MICROBIAL INDUCED CALCITE PRECIPITATION

Microbial induced calcite precipitation (MICP) is a biomediated ground improvement method that represents a relatively new innovation in the field of ground improvement. Due to its adaptability in urban environments and because microbes are ubiquitous in soils, MICP has emerged as a promising method to treat the soil in challenging urban environments. However, many challenges exist before the technique can be widely applied in practice. Because MICP is a complex process affected by a wide variety of factors, including the soil grain size, the concentration of bacteria, the concentration of reagents, nutrient injection rate, and flow direction, work remains to be done before widespread field implementation. The work performed in this study focused on quantifying the impact of multiple geochemical and soil variables on the performance of MICP as a biocementation method. Experimental investigations were performed at the bench scale to quantify the relationship between soil conditions (grain size ratio, fines content, nucleation sites, iron content, and surface roughness) and the mass of precipitated calcite produced during the treatment process, while the changes in the engineering properties of the treated soil were monitored using geophysical methods. The study compared changes in shear wave velocity of untreated control soils, chemically treated soils, and biologically treated sandy soils using column and batch tests with simulated groundwater conditions. Finally, a field scale demonstration of the MICP treatment method was performed at the Integrated Field-Scale Subsurface Research Challenge (IFRC) uranium mine tailings site in Rifle, Colorado, USA. Field scale treatment and monitoring were performed to demonstrate scale-up of laboratory results, to prove field adaptability, as well as to identify potential problems during field implementation. The study demonstrated that MICP could effectively be implemented at the field scale, with soil shear wave velocity increasing by approximately 50% during in situ treatment. Field tests also demonstrated that changes in the geochemical parameters and the microbial community could be tracked to monitor progression of the treatment scheme. The bench scale laboratory investigations demonstrated that precipitated calcite mass and shear wave velocity increased with silt and colloidal particle content (with controlled distribution), and with particle surface roughness.Ph.D