Stimulating In Situ Soil Bacteria for Bio-Cementation of Sands

Abstract

Microbially induced calcite precipitation (MICP) has advanced rapidly in the past decade; however, its implementation as a prevalent ground improvement technique has been partially limited by the need for cultivation and injection of specific bacterial strains. The future of this technology as a cost-competitive and environmentally conscious alternative is largely dependent on whether native bacteria can be stimulated to facilitate the precipitation of calcite. A research program was implemented to assess the ability of biostimulation treatment solutions to stimulate native ureolytic bacteria in a variety of soils ranging from quarried sands to lacustrine silty-sand deposits using soil specimens prepared in 10.2 cm high by 5.1 cm diameter hollow acrylic cylinders. Treatment solutions were administered in two 10-day phases, a stimulation phase to stimulate native bacteria and a cementation phase during which calcium was added to initiate calcite precipitation. Techniques used to evaluate specimens included pH, unconfined compressive strength, permeability, and calcite content measurements. Results indicate that native ureolytic bacteria can be stimulated in natural soils to precipitate calcite and significantly improve engineering properties. Unconfined compressive strengths were shown to be as high as 5.3 MPa with average calcite contents as high as 13.2%. Additionally, SEM images were taken to provide insight about calcite structure and the presence of bacteria that facilitated this biogeochemical process.