Large-Scale Comparison of Bioaugmentation and Biostimulation Approaches for Biocementation of Sands

Microbially induced calcite precipitation (MICP) is a promising biocementation process that can improve the geotechnical properties of granular soils through the precipitation of calcite. In this study, a large-scale biocementation experiment was completed to evaluate differences in improvement obtained using a bioaugmentation approach with S. pasteurii and a biostimulation approach, which stimulated native ureolytic microorganisms to complete the process. Two identical 1.7-m-diameter soil tank specimens containing a 0.3-m-thick layer of sand were treated using three wells at a well-to-well spacing of 1.2 m. Treatments were applied daily over 12 days and were designed to evaluate differences between tanks by creating a nonuniform spatial distribution of improvement. During treatment, shear wave velocity and biogeochemical changes were monitored spatially and temporally. Post-treatment, cone penetration tests were completed to assess improvement, and samples were obtained for calcite content measurements. Similar final improvement was observed between tanks, with highly cemented regions achieving shear wave velocities over 960 m/s and increases in tip resistances of over 419%. Results suggest that biostimulation may enable comparable biocementation improvement at the meter scale.