As regular maintenance and relocation of sediment deposits are highly expensive, Port authorities seek more efficient solutions for reducing the costs and CO2 emissions of maintenance dredging. One solution, water injection dredging (WID), is carried out for maintaining the sediment deposits which predominantly consist of clay and silt. WID has been proven to be a cheaper solution by leaving the sediment in place, eliminating substantial costs for relocation of the dredged sediment.@en

As conventional dredging and relocation of sediment deposits is highly expensive, port authorities seek for more efficient solutions for reducing the costs of maintenance dredging. One of the well-known solutions is water injection dredging (WID). In general, WID is proven to be cheaper than the hopper dredging by leaving the sediment in place, thus, eliminating substantial costs for relocation of the dredged sediment. In autumn 2018, the utility of WID and fluid mud trapping was investigated in the Port of Rotterdam. As a first step, the sediment trap was made in the Calandkanaal. Next, the WID actions were carried out for fluidization of the top layer sediment around the deepening and horizontal transport of the fluidized mud into the sediment trap. The WID actions were monitored by means of multi-beam and single-beam echo-sounding surveying methods at low (15-38 kHz) and high frequencies (200-400 kHz). After WID has taken place, the sediment trap was regularly surveyed for 3 months. Apart of abovementioned echo-sounding surveying methods, different penetrometers were used for monitoring the settling and consolidation processes in the sediment trap. We used Graviprobe, Rheotune and DensX for measuring the shear strength, the yield stress and the density of sediment, respectively. These measurements were compared to the ones in laboratory, where the densities and the yield stresses of sediment samples were measured independently. It was concluded that the water injection dredging method can be efficiently used for fluidizing and transporting weak fluid mud layers. In-situ measuring tools are available for characterizing the behavior of fluidized sediment. Based on our experimental investigation, it can be concluded that new cost-effective port maintenance strategy is feasible in the port.@en

This paper provides a new insight into the surveying strategies that are used (or can be potentially used) in ports and waterways with fluid mud layers. The combination of acoustic methods with other methods, which are based on the density or on the shear strength measurements, is discussed. In particular, the measurements by the DensX, the Rheotune, the Graviprobe and the Rheocable are presented Due to the complexity of mud, the strength of mud exhibits a non-linear relationship with the density due to the thixotropic behaviour (deformation, history and time dependence). Therefore, sampling and measuring procedures, followed by data processing and interpretation of the measurements, have to be standardized by means of recognized practical protocols. In-situ measuring tools are available for characterizing the behaviour of fluid mud. Based on our observations, we can conclude that the new surveying strategies can be potentially developed in the ports and waterways with fluid mud layers.@en

This paper gives an overview of the research that has been conducted to get a better understanding of the navigation in ports and waterways with fluid mud layers. In particular, the up-to-date review of reported full scale experiments that involve real vessels is provided. To study physical processes, the full scale experiments are accompanied by scaled experiments and numerical modelling. This combination provides a valuable insight into ship behavior with respect to different navigation conditions and physical properties of fluid mud. Another aspect of this paper are the surveying methods that can localize the fluid mud layers and potentially provide information about the strength of these layers. Some of these methods were tested on fluid mud produced by water injection dredging in the Port of Rotterdam. It was concluded that the new rheology-based method show a potential for understanding of strength development in fluid mud layers. Finally, some open research questions with respect to the applicability of the navigation through fluid mud are discussed.@en

The objective of this study is to get a new insight into in-situ characterization of fluid mud layers. Water Injection Dredging has been performed to create a fluid mud layer in the 8th Petroleumhaven at the Port of Rotterdam. Four measuring tools, conventional multi-beam echo-sounder, DensX, Graviprobe and Rheocable have been used to monitor the fluid mud layer properties over the time. The results suggest that the currently employed density-based nautical depth criterion has to be revised to ensure more efficient navigation in the vicinity of fluid mud layers@en