Quantification of the Erosion Resistance of Undisturbed and Remoulded Cohesive Sediments

Abstract

Cohesive sediments besides their typical heterogeneity are characterised by structural discontinuity. Particularly, organic consolidated muds are a good example of sediments that consist of vast aggregates, pore water and gaseous products. The texture of a cohesive sediment bed is a result of a number of mutually affecting factors, such as deposition history, mineral and organic composition, kind of biota and oxygen uptake. The presented work attempts to quantify the effect of sediment physical properties and sediments structure on the sediment erosion potential, considering incipient motion and erosion rate. This quantification is made on the basis of comparative testing of both unremoulded and remoulded samples of a river mud. Due attention is paid to sediment handling to preserve the delicate structure of the sediment for the laboratory experiments. Mud with two degrees of consolidation has been examined in a tilting flume under different flow situations. The test results show a typical increase of erosion strength with dry matter concentration of the mud. It has also been found that the structural properties increase the erosion strength for the less consolidated mud. An opposite effect has been recorded for a more consolidated deposit. As a consequence, due to the sediment structure, the original beds differ much less in erosion resistance in relation to the dry mass concentration than their disturbed analogues. Finally, the erosion resistance of the examined mud is compared with data from the literature.