Abstract
ABSTRACT Sediment gravity flows are natural flows composed by water and sediment in which the gravitational flow acts on the sediment. The distinct physical properties of the cohesive (clay) and non-cohesive (sand) sediment, and the interaction between these particles alter the ability of the flow to resist to the movement (rheology) along time and space, represented by the viscosity of a mixture suspension. Hence, we propose to study the rheological properties of those mixtures and calculate their relative viscosity when used in the physical simulation of turbidity currents. Rheological tests were performed with various mixtures composed by water, clay and/or coal. Two equations are proposed to estimate the relative viscosity as a function of volume concentration of each sediment, the maximum packing fraction and the percentage of clay present in the mixture. The results also show an error close to 20% comparing similar models from the literature, which are satisfactory. The results also demonstrate that caution should be exercised when generalizing the use of a single model to predict the relative viscosity of suspensions. The influence of density (ρ), grain shape, clay percentage (Cclay), volumetric concentration (ϕ) and maximum packaging fraction (ϕmax) should be considered in the formulation of the equations.
Highlights
Sediment gravity flows (SGF) are natural flows in which the gravitational flow acts on the sediment, e.g., turbidity currents and debris flows (Middleton & Hampton, 1973)
We propose a rheological equation from the experimental data of relative viscosity of mixtures composed of kaolin and/or mineral coal, which could be extrapolate to natural sediment gravity flows
The rheological behavior of clay and/or coal mixture suspensions which simulates sediment gravity flows in the laboratory was adjusted to the Newton and Herschel-Bulkley models
Summary
Sediment gravity flows (SGF) are natural flows in which the gravitational flow acts on the sediment, e.g., turbidity currents and debris flows (Middleton & Hampton, 1973). They are the main agent of sediment transport into deep water through events of great magnitude, capable of breaking submarine cables such as the Grand Banks event (Simpson, 1997). Since SGF are composed by sediments with distinct physical properties, such as cohesive (clay) and non-cohesive (sand) sediments, the inner ability of the flow to resist to the movement, i.e., the viscosity of a mixture suspension, can be altered. Sediment gravity flows classification is divided into two groups, mainly because of the rheological behavior of mixture suspensions. All nonNewtonian models imply in non-constant coefficient of viscosity, called apparent viscosity (μap)
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