Consolidation and strength evolution of Caland-Beer Channel mud

Abstract

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 second 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 Caland-Beer Channel mud was simulated in segmented consolidation columns. The use of segments made it possible to obtain well-defined and undisturbed samples of the mud bed. 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 could be carried out and density measurements could be 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 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. Small modifications of the experimental set-up are recommended for future experiments.