Performance and Mechanism of MICP-Treated Silty Soil Subjected to Freeze–Thaw Cycles

Freeze–thaw deterioration of foundation soil is the main cause of canal slope damages in seasonally frozen areas. Soil treatment is an important means to ensure the safe operation of canals. Using microbially induced calcium carbonate precipitation (MICP) technology, the mechanical properties, permeability characteristics, and microstructure characteristics of untreated and treated silty soil with different cementation solution concentrations, curing ages, and numbers of freeze–thaw cycles were investigated in a series of laboratory tests. The macro- and microindicators are described, and the quantitative relationships were established. The results show that the MICP treatment can significantly improve the physical and mechanical characteristics of silty soil subjected to freeze–thaw cycles. Compared with untreated silty soil, treated silty soil with different cementation solution concentrations and curing ages hade a decrease in freeze–thaw deformation by approximately 70%, a decrease in the permeability coefficient by at least 1 order of magnitude, an increase in compressive strength by about 82%–305%, and an increase in shear strength index by approximately 65.50%. The MICP treatment of silty soil subjected to freeze–thaw cycles demonstrated optimized performance when the cementation solution concentration and curing age were set to 1.00 mol/L and 28 days, respectively. The calcium carbonate generated by the MICP treatment filled the original large pores and cemented the soil particles together. The treated specimens exhibited significantly improved compactness and integrity compared to untreated silty soil during cyclic freeze–thaw processes. This enhancement was particularly evident in porosity parameters, where both initial porosity values and their rate of increase demonstrated near-linear correlations with key physical and mechanical properties of silty soil. Consequently, the dynamic evolution of internal soil porosity well explains the mechanism of MICP treatment in inhibiting the freeze-thaw deterioration of silty soil in seasonally frozen areas.