Strength Criteria for structural Loess considering coupled dry-wet-frost-thaw Damage mechanisms

The stability of soil slopes in seasonal frozen soil areas is significantly affected by the natural environment. However, at present, there are limited studies on damage identification and mechanical responses under the combined action of multiple factors. By conducting triaxial shear tests (CD) of consolidated drainage with different cycle numbers under the coupling of dry-wet and freeze-thaw, as well as nuclear magnetic resonance and electron microscope scanning tests, the variation laws of mechanical properties and damage and deterioration mechanisms of structural loess were analyzed from a macro-mesoscopic perspective, and the correlation analysis between the pore changes of microscopic particles and strength parameters was carried out. Finally, the strength criterion of structural loess under the coupling of dry-wet and freeze-thaw was established and,its rationality was verified. The results show that the soft/hardening characteristics of the stress-strain curve are related to the number of cycles and the magnitude of confining pressure. With the increase of cycles numbers and confining pressure, the stress-strain curve gradually transitions from softening to hardening characteristics. Under the action of cycles, the strength parameter cohesive force is more damaged than the internal friction Angle, and its deterioration rate is higher. After 10 cycles, the pore area increased by about 40%. The damage of the cementation blocks led to a gradual increase in the pore area. Micro-small pores transformed into large-medium pores, and a new distribution pattern was formed within the soil. The increase law of the mesoscale pores was consistent with the deterioration law of the macroscopic strength parameters. After the dry-wet-freeze-thaw cycle, during the shear action, the cementing elements inside the soil gradually transform into friction elements. The evolution of the part of the soil providing strength is cementing block-cementing block and weak zone - weak zone, forming a new strength-bearing mechanism. This research provides theoretical reference for the stability evaluation and protection of slopes in seasonally frozen areas.