Abstract: 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.

Key words: dry-wet freeze-thaw cycles, loess, mechanical property, mesoscopic damage, statistical damage constitutive model