Kinetically informed optimization of reaction solution formulation for EICP under multi–factor coupling

Enzyme–induced carbonate precipitation (EICP) is a promising and environmentally sustainable soil improvement technique; however, its performance remains difficult to predict due to the coupled effects of multiple controlling factors. Establishing a reliable reaction solution formulation is therefore essential to facilitate the transition of EICP from fundamental research to engineering practice. To this end, a series of standard urease activity tests were conducted to quantitatively elucidate the effects of urease concentration ( C urease ), urea concentration ( C urea ), initial pH (pH 0 ), and reaction temperature ( T ) on the apparent urease activity ( V u,o ) of soybean crude urease (SCU). Based on these results, a predictive model for V u,o , incorporating the combined effects of C urease , C urea , pH 0 , and T , was developed within the framework of Michaelis–Menten kinetics. A C urea range of 0.1–1 M was identified as appropriate for SCU to maintain utilization efficiency. Subsequently, solution-scale mineralization tests were conducted to investigate the influence of the urea-to-calcium ratio ( R U–Ca ) on calcium conversion efficiency ( η ). An R U–Ca ratio of 1:1 is considered appropriate, as it provides a balance between mineralization efficiency and urea utilization. For solution systems using calcium chloride as the calcium source at a concentration of 1.0 M, equal reactant concentrations (1 M) of urea and calcium chloride are recommended for the cementation solution. An SCU solution with V u,o ≥ 15.50 mmol·L -1 ·min -1 (corresponding to a C urease of approximately 100 g/L or higher) is recommended to be mixed with the cementation solution at a 1:1 volume ratio to form the reaction solution, which is sufficient to meet the catalytic requirements of the proposed system. The effectiveness of the proposed reaction solution was further validated through a series of sand column tests. For Fujian sand with particle sizes of 0.2–0.25 mm, a single–cycle EICP treatment satisfies the strength requirements of conventional roadbeds and foundations. The proposed reaction solution formulation exhibits promising potential for engineering application and design of EICP.