Micromechanical characteristics of viscocohesive granular flows down a rough inclined plane

Gravity-driven flows of unsaturated granular materials on inclined planes are ubiquitous in natural hazards such as landslides. The geological hazard flows can behave as a solid-like phase, liquid-like phase, or both phases along the flow height depending on different parameters and triggering conditions. Although extensive research on the granular flows down an inclined surface has been carried out to elucidate the mechanism of such gravitational flows, the micromechanical properties of viscocohesive granular materials simultaneously appearing in different flow phases remain debated. Here, we explore the effects of two principal parameters, namely cohesive stress between grains and liquid viscosity, on the micromechanical behavior of viscocohesive granular flows down an inclined plane in the steady-flowing state. The results showed that the viscocohesive granular flows may or may not be roughly divided into solid-like, liquid-like, and solid–liquid transition regions depending on the magnitude of the cohesive stress and liquid viscosity. In the case of together forming these regions along the height of viscocohesive granular flows, the cohesive stress uniformly affects the density and intensity of the compressive and tensile forces. In contrast, the compressive forces in the solid-like and liquid-like regions show an opposite influence on the liquid viscosity. These complexities may be explained by the intrinsic properties of the liquid binding, the particles’ gravity, and the collisional forces between grains. These observations of the micromechanical properties of viscocohesive granular flows insightfully highlight all phases along the flow height, providing physical origins of geological landslide flows.