Freeze-thaw durability and environmental risk assessment of silty soil improved using EICP combined with magnesite tailings powder.

Enzyme-induced carbonate precipitation (EICP) technology holds significant potential for applications in geotechnical engineering. While prior research has primarily focused on the mechanical enhancement of EICP-treated soils, limited attention has been paid to their long-term stability and durability. This study addresses the deterioration of foundation soils in the seasonally frozen region of the lower reaches of the Yellow River, where repeated freeze-thaw (FT) cycles pose a major challenge. To enhance silt stability under such conditions, a novel approach combining EICP with magnesite mine tailings (MMT) was investigated. The effects of FT cycles on the mechanical properties, physical characteristics, and microstructure of the treated silt were evaluated, alongside an environmental risk assessment. Results showed that prior to FT exposure, the unconfined compressive strength and secant modulus of the treated soil increased by 1.67 and 3 times, respectively, than those of the untreated soil, while apparent porosity and permeability coefficient decreased by 20 % and 93 %, respectively. Under increasing FT cycles and wider FT temperature variations, the EICP-MMT-treated soil maintained lower apparent porosity and higher strength, toughness, and stiffness compared to untreated silt. However, the degree of improvement gradually diminished with increasing number of FT cycles. Furthermore, the treatment significantly reduced the leaching and bioavailability of heavy metals, thereby lowering environmental pollution risks. These findings suggest that EICP-MMT treatment provides a promising strategy for reinforcing road or building foundations in seasonal permafrost regions.