Non-Negligible Influence of Gravel Content in Slip Zone Soil: From Creep Characteristics to Landslide Response Patterns

The creep mechanical behavior of the slip zone soil is distinctive and assumes a vital role in the identification and prediction of landslide evolution, but the rock content and structure dictate its creep properties. This study examines the Outang landslide in the reservoir region of middle Yangtze River, where the slip zone soil shows considerable variability in particle size distribution, with gravel content varying between 35% and 55%. To investigate the creep characteristics of the slip zone soil, large-scale direct shear creep tests were conducted, focusing on the variations in peak strength and long-term strength under different gravel content conditions. PFC3D numerical simulations were subsequently performed to elucidate the internal mechanisms connecting gravel content, microstructure, and macroscopic mechanical strength. A three-dimensional continuous-discrete coupled model was built to investigate the influence of gravel content on landslide deformation features, accounting for fluctuations in gravel content. The numerical findings indicate that gravel content markedly affects the displacement and deformation characteristics of the landslide. As the gravel concentration rises, landslide displacement progressively diminishes, with elevated gravel content enhancing the structural integrity of the landslide mass. This study underscores gravel content as a pivotal element in landslide deformation and reinforces its significance in assessing landslide stability and forecasting.