The artificial ground freezing (AGF) method is a frequently-used reinforcement method for underground engineering that has a good effect on supporting and water-sealing. When employing the AGF method, the mesoscopic damage reduces the strength of the frozen sandy gravel and consequently affects the bearing capacity of the frozen curtain. However, a few studies have been conducted on the mesoscopic damage of artificial frozen sandy gravel, which differs from fine-grained soil due to its larger gravel size. Therefore, based on triaxial compression tests and CT scanning tests, this paper investigates both the mesoscopic damage mechanism and variations in artificial frozen sandy gravels. The findings indicate that there are contact pressures between gravel tips within the frozen sandy gravel, with damage primarily concentrated around these gravels during incompatible deformation within a four-phase medium consisting of ice, water, soil, and gravel. Furthermore, numerical simulation validates that failure typically initiates at delicate contact surfaces between gravel and soil particles. For instance, when the axial strain reaches 8%, the plastic strain at the location of gravel contact reaches 4.6, which significantly surpasses most of the surrounding plastic strain zones measuring around 1.3. Additionally, the maximum local stress within the soil sample is as high as 48 MPa. This failure event is distinct from viscoplastic failure observed in frozen fine-grained soil or brittle failure seen in frozen rock. The findings also indicate that the mesoscopic damage is about 0.3 when the axial strain is 10%. The study's findings can serve as a valuable guide for developing finite element models to assess damage caused by freezing in sandy gravel using AGF method.

Freeze-thaw processes can cause slope instability in areas with short-term frozen (STF) soil, resulting in potential safety risks and huge financial losses to a certain extent, as these processes affect the physical and mechanical properties of the soil. However, their adverse effect on the mesoscopic-level mechanical properties of residual soil has not been adequately investigated. To gain an effective understanding in this regard, a laminated-wall approach was adopted to create a flexible boundary for a triaxial-shear test. Simulated stress-strain curves closely matched experimental results, with a maximum relative error of 7.81% at the peak. Moreover, the experimental data collected from real soil subjected to freeze-thaw cycles were used to calibrate the relation between the macroscopic and mesoscopic parameters. The deterioration of the macromechanical and micromechanical parameters of residual soil primarily occurred in the first four freeze-thaw cycles. For eight freeze-thaw cycles, the damage degree of each microparameter remained the same, reaching approximately 0.37. A freeze-thaw damage model of the mesoscopic parameters of residual soil was then constructed through parameter fitting. Using this model, the impact of frost-thaw on slope deformation behaviors was analyzed. A simulation revealed that displacement primarily occurred at the slope toe and the area of influence expanded with an increasing number of freeze-thaw cycles. As freeze-thaw cycles increased, the stress distribution in the X-direction along the top and surface of a slope became more concentrated, impacting mesoscopic parameters. Conversely, the stress in the Z-direction on the slope dispersed across three slopes after four to eight freeze-thaw cycles, with considerable influence during the initial four cycles. The flexible boundary created using the laminated-wall approach and the freeze-thaw damage model of the mesoscopic parameters facilitated an effective understanding of the freeze-thaw effect on residual soil obtained from an STF area.

The study aimed to investigate the influence of dry-wet freeze-thaw cycles on the mechanical properties of undisturbed loess and evolution of microscopic damage. In order to analyse the stress-strain curves and chang law of strengch index and mesoscopic damage of pores from a macro and meso perspective, the research employed consolidation drainage triaxial shear tests (CD) and nuclear magnetic resonance tests under varying dry-wet freeze-thaw cycle durations. On this basis, the strength distribution of loess was assumed to follow a composite function, a statistical damage constitutive model of loess was established and its applicability was verified. The key findings and observations are summarized as follows. The stress-strain curve of the soil exhibited strain softening, with the degree of softening gradually decreasing with an increase in the number of cycles. The peak value of deviatoric stress decreased with the number of cycles and tended to be stable gradually, and the attenuation degree was most significant at the second cycle, decreasing by 17.6%, 23.2%, 24.5% and 18.1% respectively under different confining pressures. The circulation action led to damage to the cemented block in the soil, resulting in a gradual increase in internal pore area, primarily due to the transformation of small pores into large pores. With an increase in the number of cycles, the internal structure of the soil gradually became more stable.