Experimental study on the rheological and flow behavior of woody-debris suspensions

Debris flows, composed of water, soil, sand, rocks, and organic materials such as woody debris, are highly destructive phenomena commonly occurring in mountainous regions. The presence of woody debris can significantly modify flow mobility, depositional characteristics, and overall debris-flow dynamics. In this study, woody-debris suspensions composed of clay-silt, water, and woody debris were systematically prepared to investigate the effects of woody-debris proportion (C_vg) and woody-debris size (​L_w) on rheological properties and flow behavior. Rheological parameters were measured using a Brookfield DV-III rheometer. The results show that increasing C_vg​ significantly increases yield stress (τ_B​) and viscosity (μ_B​), whereas increasing L_w leads to a reduction in both parameters. Inclined-channel tests were further conducted to examine flow dynamics. Higher C_vg​ results in lower entry speeds, shorter runout distances, and thicker, wider deposits. In contrast, larger ​L_w generates higher entry speeds, leading to longer runout distances with thinner and narrower deposits. A strong correlation is observed between rheological parameters and flow-test parameters, indicating that inclined-channel tests provide a practical alternative for estimating rheological properties of debris flows containing woody debris.