Is density enough to predict the rheology of natural sediments?

Ahmad Shakeel,Alex Kirichek,Claire Chassagne

doi:10.1007/s00367-019-00601-2

Ahmad Shakeel, Alex Kirichek + Show 1 more

Open Access

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

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Abstract

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.

Highlights

Mud, found in lake beds, river beds, or coastal seabed, is a cohesive material which contains predominantly clay min-Geo-Mar Lett (2019) 39:427–4342018)
The mud samples analysed in the article exhibit complex rheological behaviours like viscoelasticity, shear-thinning,thixotropy and yield stress
These rheological behaviours, and in particular, the two yield stresses found in the mud systems, are strong functions of density or volume fraction of solids

Summary

Introduction

Found in lake beds, river beds, or coastal seabed, is a cohesive material which contains predominantly clay min-Geo-Mar Lett (2019) 39:427–4342018). Xu and Huhe presented the rheological studies of natural mud at Lianyungang, China using a RS 6000 rheometer with the help of both steady and dynamic measurements (Xu and Huhe 2016). They correlated the yield stress values with the mud volume concentration and fitted the experimental data with an exponential empirical relation. Soltanpour and Samsami compared the rheology of kaolinite and Hendijan mud, northwest part of Persian Gulf (Soltanpour and Samsami 2011) They linked the rheological parameters with the water content in the natural and artificial sediments using exponential relations. The relation between Bingham yield stress and the density of the natural mud sediments was reported in the literature using empirical exponential relations (Carneiro et al 2017; Fonseca et al 2019)

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