Investigation on hydraulic conductivity reduction for silty sand by enzyme induced calcium carbonate precipitation considering urease activity and cementing solution concentration

Abstract

This study examined the effects of urease activity and cementing solution concentration on the reduction of hydraulic conductivity in enzyme-induced calcium carbonate precipitation (EICP)-treated silty sand soil. Saturated hydraulic conductivity (K_sat) and induced CaCO₃ mass were utilised to quantify changes in hydraulic conductivity reduction. The mechanisms underlying hydraulic conductivity reduction across varying urease activities and cementing solution concentrations were elucidated from a microscopic perspective through analyses of area, size, and orientation distributions. Key findings include: First, K_sat generally decreased with increasing urease activity, although the rate of decrease diminished at higher activities. The impact of urease activity became negligible when exceeding 23.86 mM·min⁻¹. Second, K_sat exhibited a decreasing trend followed by an increasing trend with varying cementing solution concentrations, with optimal hydraulic conductivity reduction observed at a concentration of 1.0 mol·L⁻¹. Additionally, the induced CaCO₃ mass ($C_{{\mathrm{CaCO}}_3}$) corresponded with the variations in K_sat, highlighting its role as a critical factor in hydraulic conductivity reduction. Moreover, area, size, and orientation distributions significantly influenced variations in hydraulic conductivity reduction. Lastly, the study proposed mechanisms by which urease activity and cementing solution concentration affect hydraulic conductivity reduction. Furthermore, we have compared the relationship between parameter K_sat and $C_{{\mathrm{CaCO}}_3}$ with sandy soil in previous studies, suggesting that the EICP technology is promising for fine-grained soil.