Effect of humic acid on soil solidification by enzyme induced carbonate precipitation

Enzyme induced carbonate precipitation (EICP) is a promising technique in the field of biocementation due to its efficiency and controllability. Although many studies have proved its reliability in different environment, little attention has been paid to the influence of humic substances on the EICP. Humic substances cover most of the surface soil across the world land with vegetation, which varies according to the density of vegetation and climate. To understand the compatibility of this technique to distinct problematic soils, it is important to figure out how humic substances could affect the carbonate precipitation process induced by urease enzyme. Therefore, this study aims to investigate the effects of humic acid (HA), one type of humic substance, on the soil solidification through EICP. For this purpose, HA was added to natural soil with varying addition amounts (0%, 1%, 2%, 4%, 8%, 16%) in soil column solidification tests. The results found that the cementation effectiveness was enhanced by a small amount of HA addition (<4%), while an addition up to 8% greatly inhibited the formation of calcium carbonate. At the same time, soil samples were buffered by HA in a weak acidic condition, thus preventing the emission of undesirable by-product ammonia in the ureolysis process. Therefore, this study makes a contribution to research on enzymatic biocementation by demonstrating the effects of HA on the cementation effectiveness of EICP technique.