Freeze-thaw performance and micro-mechanism of canal foundation silt treated by MICP

The freeze-thaw deterioration characteristics of foundation soil are the main cause for damages of canal slopes in seasonally frozen areas. The soil treatment is an important means to ensure the safe operation of canals. Based on the microbially induced calcium carbonate precipitation (MICP) technique, a series of laboratory tests on treated silt with different concentrations, curing ages and freeze-thaw cycles are conducted. The macro-and micro-indices of treated silt, such as volumetric rate, permeability coefficient and porosity, are described, and their quantitative relationships are established. The results show that under different concentrations and curing ages, the treatment can reduce the freeze-thaw deformation by 70%, decrease the permeability coefficient by at least one order of magnitude, increase the compressive strength by 220.17%, and improve the shear strength index by 65.50%. As the concentration is 1.00 mol/L and the curing age is 28 days, the treatment effects of silt under freeze-thaw cycles are the most significant. In addition, the calcium carbonate precipitation induced by the MICP reshapes the microstructure of silt through a series of processes such as filling, cementation and encapsulation, which ensures the integrity of silt subjected to freeze-thaw cycles. It is also the main reason for the good engineering properties of treated silt in freeze-thaw environments.