Rheological properties of sediment suspensions from Eckernförde and Kieler Förde Bays, western Baltic Sea
Faas, R.W.; Wartel, S. (2006). Rheological properties of sediment suspensions from Eckernförde and Kieler Förde Bays, western Baltic Sea. I.J.S.R. 21(1): 24-41 In: International Journal of Sediment Research. IRTCES: Beijing. ISSN 1001-6279, more |  |
| Keywords | Organic matter
Physics > Mechanics > Rheology
Properties > Physical properties > Mechanical properties > Strength > Shear strength
Marine/Coastal |
| Abstract | Local areas of fine-grained organic-rich sediments in Eckernförde and Kieler Förde Bays may experience disturbances which cause fluidization of the substrate and create a dense suspension (fluid mud) which exists temporarily as a component of the benthic boundary layer before becoming incorporated into the permanent bottom. Laboratory studies indicate this material behaves rheologically as a non-Newtonian substance, and both shear thinning (pseudoplastic) and shear thickening (dilatant) flow behavior can occur (often within the same sample) under low to intermediate shear stresses (2 - 40 Pa) and shear rates (0.46 - 122.49 s-1). Detailed granulometric analyses (1/4 phi intervals) of the fraction <63 μm show differences in the silt/clay ratio (clay <2 μm) between the two environments. Little change in the silt/clay ratio is seen in the Kieler Förde sediments (from 0.74 to 0.95); however, at Eckernförde, the ratio changed from 0.73 to 2.19. Fine silt particles are lacking or were removed from the 4 to 16 μm fraction of the Eckernförde but not from the Kieler Förde sediments. Both shear thickening and shear thinning flow was observed in the Eckernförde sediments. Shear thickening flow behavior was not observed in the Kieler Förde sediments. Samples of organic-rich (10 to 20%) interface sediments from both areas were analyzed rheologically prior to, and after removal of organic matter by H2O2 treatment. Reduction in 'apparent' viscosity occurred through the entire range of shear rates and stresses, shear thickening behavior was reduced or became nonexistent, and yield stress decreased significantly compared to the natural samples. The differences in yield stress and flow behavior of dense suspensions result primarily from differences in grain size distributions but the role of organic matter on those properties is very significant and adds to the effects of the grain size distribution of the sediment. |
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