Is density enough to predict the rheology of natural sediments?

Is density enough to predict the rheology of natural sediments?

Shakeel, A. (TU Delft Rivers, Ports, Waterways and Dredging Engineering; University of Engineering & Technology Lahore)
Kirichek, Alex (TU Delft Rivers, Ports, Waterways and Dredging Engineering; Deltares)
Chassagne, C. (TU Delft Environmental Fluid Mechanics)

2019

Mud is a cohesive material which contains predominantly clay minerals, water, organic matter and some amounts of silt and sand. Mud samples can have complex rheological behaviour, displaying viscoelasticity, shear-thinning, thixotropy and yield stress. In this study, influence of organic matter on the rheological behaviour of different mud samples having similar densities is investigated. Four samples, collected from different locations and depths of Port of Hamburg (Germany) were selected. Two samples with the density of about 1210 kg/m³ and two samples with the density of about 1090 kg/m³ were analysed by different rheological tests, including stress ramp-up tests, flow curves, thixotropic tests, oscillatory amplitude and frequency sweep tests. Two yield stress regions (with two yield stress values stated as “static” and “fluidic” yield stresses) were identified for all the samples, and these regions, corresponding to a structural change of the samples were significantly different from sample to sample due to the differences in organic matter content. For lower density samples, the ratio of fluidic to static yield stress increased from 3 to 4.4 while it increased from 4.4 to 5.2 in case of higher density samples, by increasing the organic matter content. The thixotropic studies showed that the mud samples having lowest organic matter content (VH and KBZ) exhibit a combination of thixotropic and anti-thixotropic behaviours. The results of frequency sweep tests revealed the solid-like character of the mud within the linear viscoelastic regime. Mud samples having higher organic matter content (RV and RT) had a higher complex modulus (417 Pa and 7909 Pa) than the ones with lower organic matter content (13 Pa and 1774 Pa), for a given density. This study demonstrated that the density only is not a sufficient criterion to predict the rheology of different mud. Furthermore, even small amounts of organic matter content change significantly the mud rheological behaviour.

Density
Fluid mud
Natural sediments
Organic matter
Rheology
Thixotropy
Yield stress

http://resolver.tudelft.nl/uuid:08eb8497-e079-4e9f-b22f-a6ed604007c1

https://doi.org/10.1007/s00367-019-00601-2

0276-0460

Geo-Marine Letters, 39 (5), 427-434

Institutional Repository

journal article

© 2019 A. Shakeel, Alex Kirichek, C. Chassagne