Consolidation and strength evolution of Dollard mud: Measurement report on laboratory experiments

Consolidation and strength evolution of Dollard mud: Measurement report on laboratory experiments

Merckelbach, L.M.

Civil Engineering and Geosciences

Hydraulic Engineering

1999-01-01

Many harbours in the world suffer from high siltation rates in their basins. To guarantee safe shipping, harbour authorities have to maintain the navigable depth by having dredged large amounts of mud. Some authorities relate the navigable depth to a depth at which the density is equal to a certain value, e.g. 1200 kg/m3. However, the shear strength might be a more direct criterion to relate the navigable depth to. A research project is conducted to develop a model to describe the consolidation behaviour and strength evolution of mud layers. The third series of experiments for this project, executed at Delft University of Technology, are described in this report. The analysis of the data is left for future work. The sedimentation and consolidation of Dollard mud was simulated in segmented consolidation columns. By using segments well-defined and undisturbed samples of the mud bed were obtained. For this reason, more accurate shear vane measurements of the samples could be done than if conventional consolidation columns had been used. Four segmented consolidation columns and one conventional consolidation column were set up. To study the time evolution of the strength of the mud bed, the segmented columns were dismantled at different times. After the dismantling, shear vane tests were carried out and density measurements were done with a conductivity probe. The density profiles of the mud layer in the conventional column were measured with a gamma-ray densimeter. Pore water pressures were measured at several times. From these measurements effective stresses and permeabilities were calculated. Various rheological parameters were derived from four different types of shear vane measurements. Flow curves were also measured. It turned out that significant segregation occurred, resulting in a mud bed formed on top of a layer of approximately 5-8 cm with a relatively large coarse silt fraction and high densities. For the mud layer it turned out that the effective stresses could be approximated by a power law. Furthermore, the rheological parameters turned out to be approximately linearly interrelated, even though the parameters were derived from different types of rheological experiments. Both the relationships between peak shear stress and density, and between peak shear stress and effective stress show time dependency.

consolidation
strength evolution
mud
cohesive sediment
Dollard
experiments
segregation
siltation

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TU Delft, Department of Hydraulic Engineering

Report no. 4-99

Institutional Repository

report

(c) 1999 TU Delft, Department of Hydraulic Engineering