Biopolymer-based soil treatment (BPST) and enzyme-induced calcite precipitation (EICP) have attracted attention as sustainable soil stabilization methods. However, the two techniques have distinct advantages and disadvantages. In this study, we propose two composite treatment approaches, including (1) biopolymer-assisted EICP (BAE) and (2) EICP-assisted BPST (EAB) to optimize the advantages and compensate for the disadvantages of BPST and EICP. The effects of the sequence of treatment on stiffness enhancement, elastic recovery, microstructure and calcite distribution, and pH and ammonia behavior were examined, and the distribution of calcites was examined using X-ray computed tomography (CT). The experimental results showed that the stiffness of the BAE-treated soil increased steadily with increasing treatment cycles and time, whereas the EAB-treated soil exhibited a sharp increase in stiffness over time; however, its efficiency gradually decreased with each treatment cycle. BAE was influenced in terms of Poisson’s ratio by both confining pressure and the number of treatment cycles, whereas EAB was affected by only confining pressure. Furthermore, EAB exhibited higher elastic recovery under loading and unloading process, whereas BAE achieved a notable reduction in ammonia gas and neutralization of the soil pH. Based on microstructure analysis using X-ray CT, uniformly distributed calcite precipitation was observed within the pores in EAB, whereas precipitation was concentrated at the edges with less impact on wave velocity in BAE. In conclusion, EAB offers superior stiffness and resilience enhancement, and BAE is effective in reducing ammonia emissions and ensuring long-term environmental stability.
Park et al. (Fri,) studied this question.