Experimental study on long-distance shear characteristics of fully weathered granite residual soil

In recent years, with the intensification of global climate change and human engineering activities, mass landslide events triggered by rainfall have become frequent in southeast China, posing serious threats to the lives and property safety of the people. Fully weathered granite residual soil, as the main geological carrier of such landslide disasters, has significant importance for revealing the mechanisms of the formation and evolution of landslide clusters through in-depth study of its mechanical properties. This paper selects fully weathered granite residual soil as the research subject and considers the effects of normal stress (20 kPa, 50 kPa, 100 kPa, 150 kPa), water content (0, 5%, 10%, 20%, and 30%), and shear rate (10°/min, 20°/min, 40°/min, and 80°/min) to conduct a series of ring shear tests. The aim is to explore the mechanical behavior of fully weathered granite residual soil during the landslide initiation and long-distance movement phases, especially its long-distance shear characteristics. Experimental results show that the shear strength of the soil is closely related to its water content; as the water content increases, the shear strength initially decreases, then increases, and decreases again. At a water content of 30%, the soil exhibits significant strain hardening. In addition, the shear strength of the soil is closely related to normal stress, shear rate, and relative density. Specifically, the higher the normal stress, the higher the peak and residual shear strengths of the soil, with a more significant effect on peak shear strength and more pronounced strain softening; the higher the shear rate, the overall downward trend in peak and residual shear strengths, with a greater effect on peak shear strength than on the residual shear strength, and lower the apparent viscosity. The findings of this study provide important theoretical support for the prevention and control of mass landslide disasters within this region.