Effects of microbially induced calcite precipitation on static liquefaction behavior of a gold tailings sand

Abstract

Loose tailings are susceptible to static liquefaction during which they lose a substantial amount of their strength. This study examines a sustainable technique known as Microbially-Induced Calcite Precipitation (MICP) to improve the static liquefaction resistance of gold mine silty sand tailings. These materials were enriched with Sporosarcina pasteurii, consolidated in a direct simple shearing apparatus, and subjected to several injections of a cementation solution. Calcified tailings were then sheared under constant-volume and constant vertical stress conditions to evaluate their undrained and drained shearing behaviors. Results showed that bio-mineralization can prevent the occurrence of static liquefaction in tailings by reducing their contraction tendency. This is demonstrated by the strong strain-hardening behaviors of the treated tailings specimens compared to the strain-softening and undrained strength loss in specimens of the untreated tailings. Substantial increases in the tailings undrained and drained shear strengths (by up to 30 - 50 kPa), improvements (by up to 5 MPa) in their tangent moduli, and more than 5° rise in their friction angles are observed in the direct simple shear tests following MICP-treatment. The critical state line of tailings is also found to be steeper and shifted to denser void ratios following MICP treatment. These changes reduce liquefaction susceptibility of tailings and enhance their resistance against static liquefaction. Post-treatment acid dissolution further indicates that CaCO3 contents of about 4% to 11% precipitated in the treated specimens. This amount decreases with increasing specimens void ratio. Changes in the microstructural fabric of the cemented tailings particles are also characterized using scanning electron microscopic (SEM) images and X-ray diffraction (XRD) analyses.