Study on the macro-micro mechanisms of mineralized sand columns based on dual-enzymatically induced carbonate precipitation

Enzyme-induced carbonate precipitation (EICP) shows great promise in consolidating loose materials. However, traditional single-enzyme systems have limitations such as low precipitation efficiency, uneven spatial distribution and difficulty controlling reaction rates. This makes it challenging to meet engineering requirements. This study therefore selected Bacillus licheniformis as the target strain, employing a three-step purification process to obtain highly active urease (Ur) and carbonic anhydrase (CA). Experiments were conducted using a single-phase, low-pH grouting method to solidify sand columns using dual-enzymatic induced carbonate precipitation ( D -EICP). The mineralisation characteristics under single-enzyme and dual-enzyme systems were systematically compared using UCS combined with microscopic characterisation techniques such as SEM, XRD, TG, FTIR and BET. The results showed that the UCS and TGA-derived apparent calcium carbonate content (apparent CCC) of the sand column in the dual-enzyme synergistic treatment group reached 1.493 MPa and 8.83%, respectively. Both values were higher than those obtained with the single-enzyme treatments. The dual-enzyme group exhibited a mass loss of only approximately 1.22% below 500 °C and showed more prominent calcite-related features after curing. Together with the results of the apparent CCC, SEM, XRD, FTIR, and BET analyses, these findings suggest that the combined action of Ur and CA was associated with enhanced mineral formation and interfacial cementation under the tested conditions. This enhancement was accompanied by a significant reduction in the BET-derived mesopore volume. The results provide evidence for the enhanced mineralisation and interfacial association of sand columns under the dual-enzyme treatment, thereby providing a theoretical basis and process reference for the engineering application of D -EICP technology.