Investigating the effects of clay/sand content on depositional mechanisms of submarine debris flows through physical and numerical modeling

• Published in: Landslides Vol. 17; no. 8; pp. 1863 - 1880
• Main Authors: Liu, Dingzhu, Cui, Yifei, Guo, Jian, Yu, Zhilin, Chan, Dave, Lei, Mingyu
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.08.2020; Springer Nature B.V
• Subjects: Agriculture; Aspect ratio; Civil Engineering; Clay; Computational fluid dynamics; Debris flow; Density; Deposition; Detritus; Earth and Environmental Science; Earth Sciences; Energy dissipation; Energy exchange; Fluid flow; Flumes; Froude number; Geography; Gravitation; Gravity; Height; Hoisting; Hydroplaning; Kinetic energy; Kinetic energy dissipation; Lifting; Mathematical models; Morphology; Natural Hazards; Numerical models; Original Paper; Potential energy; Rheological properties; Rheology; Sand; Shear stress; Slurries; Three dimensional flow; Three dimensional models; Turbidity; Viscosity; Vortices; Water; Water depth; Wedges; Submarine debris flow; Computational fluid dynamics; Rheology; Herschel-Bulkley model; Flume model
• ISSN: 1612-510X; 1612-5118
• DOI: 10.1007/s10346-020-01387-6

In this study, we carried out a series of physical experiments using a submersed flume model to investigate how sand/clay content influences the depositional mechanism of submarine debris flows. A three-dimensional biphasic numerical model, with a Herschel-Bulkley rheology, was used to back-analyze the physical experiments. The calibrated numerical model was then used in a back-calculation to investigate the effects of viscosity on the deposition process. The results show that as submarine debris flows mix with water during the deposition process, shear stress at the slurry-water interface generates a vortex that leads to a swirl-wedge front head. High-viscosity slurry flows with a swirl-wedge front head travel at a higher aspect ratio and with a greater radius of rotation. Hydroplaning was observed when the front head was lifted by water during flow. The lifting height increased with flow depth fluctuation. Higher viscosity slurry was found to lift more rapidly due to its larger vortex and the decrease in density at the front head over time, both of which promote fluctuation. Although a high-density slurry has a greater lifting height, the ratio of lifting height to front head height is lower, indicating a smaller lifting force influence. Lower density flows have higher kinetic energy as the transfer of potential energy into kinetic energy is more efficient. Kinetic energy dissipation comprises three stages: (1) gravity-dominated coherent flow and hydroplaning lead to a rapid increase in kinetic energy; (2) sharp reduction in kinetic energy as slurry mixes with water, coherence and hydroplaning are reduced, and the influence of the shear stress increases; (3) slurry mixed very well with water, turbidity current dominates the kinetic energy dissipation. High-density slurry dissipates quicker in the last two stages. In stage 3, which dominates the temporal evolution of the debris flow, the Froude number is lower than 1, the flow thins and elongates, and the deposition process of submarine debris flows is dominated by gravity, and the difference of morphology of the different cases become clear.