Regulation of the Mechanical Behavior of Frozen Soil during Warming and Thawing by Ice Nucleation Active Bacteria

Infrastructures in cold regions are suffering thaw subsidence–caused issues because of ice thawing in frozen soil under climatic warming. The loss of crystalline ice and the subsequent reduction of soil load-bearing capacity is responsible for these issues. Alleviation methods are commonly used to maintain the frozen state of soil by releasing the soil inner heat or insulating the external heat input. However, facilitating ice formation actively by using bioresources of frozen soil to improve the soil strength under temperature rising is rarely mentioned. Thus, the effect of ice nucleation active (INA) bacteria Pseudomonas syringae with concentrations of 0–20 g/L on the ice content and the shear strength of frozen soil under temperatures ranging from −5°C to −0.1°C is investigated by conducting nuclear magnet resonance and direct shear tests. A new constitutive model considering P. syringae contributions is established by introducing the coefficient of correction in cemented elements and the correction formula in frictional elements. Results show that adding P. syringae in frozen soil can effectively increase the ice content 3.18%–176.78% and the shear strength 3.16%–64%. P. syringae with a concentration of 1 g/L can slow down frozen soil warming rate and reduce the temperature of warm frozen soil by around 1°C. Adding P. syringae alters stress–strain behaviors of frozen soil from strain-hardening to strain-softening when temperature rises from −1°C to −0.5°C. The predicted values matched well with the experimental data, indicating that the constitutive model can well describe the meso-macroscopic mechanical behavior of frozen soil with P. syringae during warming and thawing.