Abstract
Natural mud usually exhibits non-Newtonian rheological behaviors like viscoelasticity, thixotropy and yield stress. The history of each mud sample is also an important factor influencing the rheological behavior, as the state of the clay fabric – for a same composition – is dependent on the shear stresses experienced previously by the sample. Several rheological tests including stress ramp-up, oscillatory frequency sweep and structural recovery tests were performed, in order to analyse the rheological fingerprint of the mud samples collected from two different locations of the Port of Hamburg. The yield stress, storage moduli and structural recovery of mud from the same location was studied as a function of density for two series of samples. One series consisted of samples (“natural samples”) taken in-situ as a function of depth (with increasing density as a function of depth) whereas the other one (“diluted samples”) consisted of samples whereby the density was varied by adding in-situ water to the natural sample having the highest density. Significant differences in rheological characteristics were found between the natural and diluted mud samples, that were attributed to the state/composition of the mud's fabric in each situation but also to the structural rearrangements caused by the preparation of diluted samples.
Highlights
Mud consists of clay minerals, water, organic matter, silt and sand
In order to analyse the effect of dilution on the yield stress of mud sediments, stress ramp-up tests were performed at a rate of 0.1–1 Pa/s to determine the yield stress values of natural and diluted mud layers
In case of diluted mud samples from location B, this particular feature is not observed (Fig. 9b) because of the lower densities of these samples as compared to the location A. This behavior shows that the size of the aggregates, formed after dilution, is significantly dependent on both the degree of mixing and the concentration/density of the mud samples. All these results show that the diluted mud samples have signifi cantly different rheological properties yield stresses, storage moduli and structural recovery as compared to the natural mud samples
Summary
Mud consists of clay minerals, water, organic matter, silt and sand. Usually, natural mud exhibits viscoelasticity, shear-thinning, thixotropy and yield stress properties. Van Kessel and Bloom ana lysed the rheological properties of estuarine mud and kaolinite clay samples They investigated the viscoelastic behavior of their samples in oscillatory mode at small strains [6]. Soltanpour and Samsami per formed the comparative rheology of kaolinite clay and Hendijan mud from northwest part of Persian Gulf using frequency sweep and flow curve tests [11] Their results revealed a strong dependence of the rheological parameters on the water content of the samples. Xu and Huhe reported the rheological analysis of estuarine mud at Lia nyungang, China with the help of both steady and dynamic rheological methods [12] They found an exponential increase in the yield stress of their mud samples as a function of increasing volume fraction of solids
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