Enhancement of Coal Ash Compressibility Parameters Using Microbial-Induced Carbonate Precipitation

Microbial-induced calcium carbonate precipitation (MICP) was experimentally implemented on two coal ash materials (i.e., CA1 and CA3) to investigate the efficacy of the treatment on the hydraulic and compressibility properties of the material. Oedometers used in testing were modified to enable the injection of treatment solutions and to provide the ability to monitor shear wave velocity. The coal ash specimens were treated to reach different levels of shear wave velocity, which corresponded to varying amounts of ${\mathrm{CaCO}}_3$ content. The hydraulic conductivity and shear wave velocity values were assessed throughout the loading process. Results indicate that the MICP treatment decreased the compressibility (compression index decreased by a factor as high as 2), and the hydraulic conductivity (decreased by a factor as much as 0.05). The slope of $\log ({\sigma }_{\mathrm{V}}^{\prime })\text{-}{\mathrm{V}}_{\mathrm{S}}$ relationship (${\beta }^{\prime }$) decreased from 0.31 for the untreated material to 0.01 with treatment. In parallel, the increase in the shear wave velocity after treatment increased the intercept of the relationship between $\log ({\sigma }_{\mathrm{V}}^{\prime })\text{-}{\mathrm{V}}_{\mathrm{S}}$ (i.e., ${\alpha }^{\prime }$) from 38 to $383\mathrm{m}/\mathrm{s}$. The correlation between small-strain and large-strain parameters are explored and discussed.