Experimental investigation into shear behavior of loess-red clay composite interface under low-temperature environment

The shear behavior of the double-layer heterogeneous interface between loess and red clay is crucial for better understanding the formation and evolution mechanism of loess-red clay interface landslides in the Loess Plateau. However, the effects of low-temperature environment on the shear behavior of loess-red clay composite interface are given lesser attention. This study conducted freezing and direct shear tests on loess-red clay composites with different moisture contents to investigate the effects of moisture content and low temperature on the shear behavior of the interface. The results indicate that the shear strength of the interface decreases with increasing moisture content. Under high moisture contents (> 14%), the red clay tends to form aggregates, intensifying the double-layer heterogeneity and further decreasing shear strength. With decreasing temperature, the shear strength exhibits a three-stage trend of "increase (unfrozen stage (-2°C~ - 5°C))-decrease (transition zone (-5°C~ - 10°C))-increase (freezing stage (-10°C~ - 20°C))", mainly attributed to water migration and water-ice phase transition evolution under different low-temperature environments. Considering the coupling effects of moisture content and temperature, the shear strength is divided into four intervals using a threshold of 14% moisture content (aggregation formation) and - 10 °C (freezing point). The average shear strength in each interval shows a negative correlation with moisture content, confirming that moisture content is the dominant factor affecting the shear strength of the interface. These findings can facilitate the disaster prevention and control of heterogeneous interface landslides and the security of major engineering construction in seasonal frost and permafrost loess areas.