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 contractive tendency. This was demonstrated by the strong strain-hardening behaviors of the treated tailings compared to the strain-softening and undrained strength loss in specimens of untreated tailings. Substantial increases of tailings undrained and drained shear strengths (by up to 30 - 50 kPa), improvement (by up to 5MPa) of their tangent moduli, and more than 5° rise in their friction angle were observed in the direct simple shear tests following MICP-treatment. The tailings critical state line was also found to become steeper and shifted to denser void ratios following MICP treatment. These changes reduced tailings liquefaction susceptibility and enhanced their resistance against static liquefaction. Post-treatment acid dissolution further indicated CaCO3 contents of about 4 to 11% precipitated in the treated specimens. This amount decreased with rising specimens void ratio. Changes of the microstructural fabric of cemented tailings particles were also characterized using scanning electron microscopic (SEM) images and x-ray diffraction (XRD) analyses.