The work presented in this thesis investigates the role of flocculation in turbidity flows, with relevance to deep-sea mining but also dredging operations in more shallow waters, as the results are broadly applicable. Deep-sea mining is emerging as an alternative source for critical minerals needed for the transition to clean energy technologies. However, mining activities disturb the seabed, leading to the formation of sediment plumes. These sediment plumes propagate over long distances and impact sensitive marine ecosystems in the area. Similar environmental concerns also arise in the case of dredging projects, where resuspended sediments increase the turbidity in the surrounding waters. These challenges highlight the need for improved understanding of sediment plume dynamics and the processes that control their evolution. Flocculation (the aggregation of small particles into larger ones) could potentially limit turbidity flow propagation. This underpins the work presented in this thesis.


A series of laboratory experiments was designed to study the propagation of turbidity currents under controlled conditions. A lock-exchange flume setup was used to simulate sediment-laden turbidity currents, where detailed investigations of current propagation and floc formation were carried out. The work combines hydrodynamic measurements with advanced particle-sensing techniques to link micro-scale flocculation processes with turbidity current behavior. Experiments were first conducted with clay (illite) in the presence of flocculants (polyacrylamide), and then with a natural clay from the Clarion-Clipperton Fracture Zone (CCZ) that contains organic matter (acting as flocculants). Some experiments were also conducted with non-flocculating quartz as a reference.
The results demonstrate that flocculation can occur rapidly, within tens of seconds, and significantly modifies particle size distributions and settling behavior.

The thesis further explores how seabed characteristics influence turbidity currents. Experiments were performed over beds of different compositions and ages to understand their roles in turbidity flows and floc evolution. The presence of polyacrylamide in the outflow compartment of the lock-exchange flume was found to increase the front velocity when no bed was present, which was attributed to the lubrication effect between the turbidity current and the plexiglass bottom of the flume. It was found that pre-existing beds and their consolidation state affect sediment entrainment and flow propagation. Bed roughness and material type can either enhance or suppress floc formation, thereby altering the mobility of the turbidity current. These findings are directly relevant to operational strategies in dredging and mining, where repeated disturbance of the seabed occurs.

In addition to physical mechanisms, this research also examines the ability of monitoring instruments to detect turbidity current properties, particularly particle size and concentration. Optical Backscatter Sensors (OBS), Acoustic Doppler Velocimeter (ADV), and Laser In-Situ Scattering and Transmissometry (LISST) were used in the lock-exchange setup. Malvern mastersizer and FlocCAM were used to further characterize samples taken at different positions within the lock-exchange flume. The study demonstrates that sensor responses are highly sediment-dependent and that no single instrument can, in situ (lock-exchange) reliably distinguish between primary (unflocculated) particles and aggregates. A combination of lab measurements and in situ sensor techniques is therefore recommended for studying flocculation.

Overall, this thesis provides new experimental insights into the coupling between particle aggregation and turbidity current dynamics. It shows that flocculation, bed interactions, and sensor limitations must all be considered when predicting sediment plume behavior. The outcomes contribute to more reliable assessment and monitoring of environmental impacts associated with offshore engineering activities and offer guidance for future field measurements. The work ultimately strengthens the scientific basis for responsible and sustainable management of deep-sea mining and dredging operations.
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The growing demand for critical metals such as cobalt, nickel, and copper, essential for renewable energy and green technologies, has intensified interest in deep-sea mining of polymetallic nodules. However, such activities generate sediment plumes that may severely impact mining operation and deep-sea ecosystems. The behavior of these plumes is strongly influenced by flocculation, the process through which fine sediment particles aggregate into larger flocs, altering their settling velocity and transport. While flocculation behavior and settling velocities are well documented for the Clarion–Clipperton Zone (CCZ), no data currently exist for the Cook Islands (CI) region. Differences in sediment characteristics may lead to distinct flocculation and settling behavior, highlighting the importance of region-specific data for reliable plume modeling.

This study characterizes the flocculation and settling behavior of deep-sea clay from the CI region to evaluate the applicability of existing CCZ-based plume models. Laboratory experiments were conducted under controlled conditions using jar tests, laser diffraction, rheometry, and imaging techniques to quantify floc size and settling velocity under varying shear and concentration ranges.

The CI clay exhibited non-Newtonian and thixotropic behavior, with a yield stress above the gelling concentration. Floc growth followed a sigmoidal pattern, well described by a logistic growth model. Higher shear rates and clay concentrations were found to limit the floc size. Importantly, flocs of similar size displayed comparable settling velocities, regardless of their formation history.

When compared with CCZ sediments, CI material showed similar gelling behavior but notably slower settling velocities. In addition, floc sizes observed for flocculation under the same conditions also differ. Consequently, plume dispersion in the CI region is likely to be more extensive, and models calibrated for CCZ sediments are not directly transferable. This study provides the first experimental dataset on CI sediment flocculation and settling behavior, offering critical insights for developing region-specific plume models and designing environmentally responsible deep-sea mining operations. ... Read more

Sand utilization has increased over the past decades and is getting a scarce resource globally. In Singapore, no sand is available for construction purposes or land reclamation projects. The increasing scarceness of ''suitable'' sandy building materials around the world forces the dredging industry to consider the usage of alternative ''complex'' materials for land reclamation purposes. However, working with these kinds of ''complex'' materials introduces operational and technical challenges on the estimation of project duration and costs, due to their low permeability, high compressibility and complex consolidation behaviour of this slurry material.

The main involved departments on land reclamation projects are the production department and the geotechnical department. The production department is responsible for ''Production Estimation'' and estimates the rate of which soil can be produced by transporting it from the dredging area to the reclamation area, considering specific equipment choices and costs. The geotechnical department is responsible for ''Reclamation Engineering'' and handles the engineering of the soil brought in by production to be formed into a soil which is eventually usable for the client.

Two reclamation projects of the past; the ''Scandinavia'' and ''Black Sea'' project have proven that Production Estimation and Reclamation Engineering are closely connected when working with ''complex'' material. While working with ''suitable'' sandy materials primarily focuses on minimizing project costs through optimizing Production Estimation, the effects of Reclamation Engineering optimizations increases significantly when dealing with ''complex'' materials. This is due to their long duration of consolidation and the potentially high costs of soil improvements required before the asset can be delivered to the client.
In this context, optimizing Production Estimation by dredging at low initial density comes at the expense of Reclamation Engineering as low initial density often results in longer and more costly consolidation, and vice versa. Therefore, it can be concluded that a trade-off exists in optimizing for Production Estimation and Reclamation Engineering in minimizing project costs.

It becomes evident from the literature review that no specific research is dedicated to investigating the effect of the trade-off between optimizing Production Estimation or Reclamation Engineering in minimizing project costs. Therefore, the main research objective of this thesis is to answer the question:

''How can project costs be minimized by explicitly balancing the trade-off between optimizing for Production Estimation and Reclamation Engineering?''

This thesis provides a new framework for evaluating the effects of the trade-off between Production Estimation and Reclamation Engineering optimizations on total project costs, in order to answer the main research question. This framework couples production estimation models to geotechnical estimation models by OpenCLSim and a large-strain consolidation model. This integral approach enables the simulation of the continuous reclamation construction process, including filling, self-weight consolidation and long-term consolidation under the effect of ground improvement methods. The proposed framework is subjected to a case-study to asses how optimizations on Production Estimation and Production Engineering affect consolidation behaviour and project costs. In this analysis optimizations are implemented by varying initial density coming with hydraulic and mechanical dredging work methods. This thesis evaluates these optimizations in three stages; single production cycle, production - self-weight consolidation analysis, and a full scale case study including long-term consolidation under the effect of ground improvement methods. The full-scale case study is evaluated using a hydraulic work method of 1100 kg/m3 and a mechanical work method of 1300 kg/m3. The production and reclamation models are calibrated by the material characteristics from the case-study, whereas the large-strain consolidation method is calibrated and validated by physical samples from the project site.

Results from the full scale case-study show that utilizing a mechanical method at 1300 kg/m3 (aimed at optimizing Reclamation Engineering) results in a 1,86 more expensive project than using a hydraulic method at 1100 kg/m3 (aimed for optimizing Production Estimation). Almost no differences occur between Reclamation Engineering costs for the two dredging work methods as the case-study material quickly consolidates and converges to a similar compaction profile within a similar time-frame. Consequently, the potential advantage of achieving a higher initial density using the mechanical method is diminished by its lower production rates and high costs. By converging to a similar compaction state within the same duration creates no significant differences between the ground improvement methods needed to force the profile to comply to design requirements. This will lead to almost no differences in costs for Reclamation Engineering. As a result, only optimizations in Production Estimation can lead to minimization of the project costs for the considered case-study material.

Nevertheless, it can be concluded that it is possible to get insights on how to minimize project costs based on the trade-off between Production Estimation and Reclamation Engineering when using a framework which couples their interactions through self-weight (large-strain) consolidation and OpenCLSim. The existence of the trade-off and its magnitude on minimizing project costs depends on the soil type used in the project. ''Complex'' materials that tend towards relatively ''well-consolidating'' seem to reduce the magnitude of the trade-off, while it is believed that more ''poor-consolidating'' materials enhance the magnitude of the trade-off. Therefore, the predictability of the trade-off between Production Estimation and Reclamation Engineering optimizations is closely related to the understanding of production effects (varying initial density and varying duration between layer stacking) on the consolidation behaviour of the slurry material.

The proposed framework in this thesis is believed to be a first step in estimating project costs and duration based on a physics-based approach, compared to the current ''empirical estimations'' that are used to represent physical processes such as large-strain consolidation. The proposed framework could lead to a more integrated understanding between Production Estimation and Production Engineering when using ''complex'' material and more insights on how optimizations between the two departments can minimize project costs.
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Maritime transport facilitates close to 80 % of global trade, standing as an unparalleled cornerstone in international commerce. Projections herald a further increase in maritime activity, due to the low carbon footprint and cost-effectiveness, elevating the need for ensuring navigational safety within ports and waterways. At the heart of safe maritime navigation lies the pivotal concept of maintaining adequate nautical-depth, a threshold where a ship’s keel encounters navigational constraints. However, this necessity inherently demands incessant monitoring and recurring dredging operations, resulting in high costs amounting to millions of euros and, contributing significantly to carbon emissions. These factors underscore an urgent call for optimization of monitoring the nautical-depth to reduce monitoring and dredging costs, and increase marine navigational safety.
Presently, common methods for nautical-depth monitoring rely heavily on acoustic echo sounders, rooted in dated methodologies with limited innovation over nearly a century. Acoustic echo sounders measure the two-way travel time of sound pulses, assuming a known propagation velocity of the acoustic energy. However, accurately approximating the pressure-wave velocity in shallow marine environments poses challenges due to variations in temperature and salinity among different water layers, leading to depth measurement inaccuracies. Furthermore, this method is limited by vessel availability and requires access to quay walls, often occupied by loading or unloading ships.... ... Read more

The Port of Rotterdam experiences large amounts of siltation from the upstream rivers in its basins and canals every year. Furthermore, container vessels increase in size every decade and therefore require a larger navigational depth. These two factors cause the yearly amount of dredged material to increase. Currently, mainly trailing suction hopper dredgers are used to remove the large amounts of sediment, but these vessels come with high costs and operational time. A more time and cost-efficient dredging method is therefore desired.

A potential solution to the increasing problems of costs and operational time by dredgers is the technique of water injection dredging. To make this technique as efficient and effective as possible, this thesis has the objective to measure and analyze flow and sediment properties for different parameter settings of water injection dredging and find the optimal parameter settings of this dredging technique on mud from the Port of Rotterdam. Large-scale experiments have been conducted in the water-soil flume of Deltares, where a jetbar was trailed (or run) over a bed 27 meters long and 0.5 meters deep of port mud while injecting it multiple times with water.
A positive correlation is observed between the production rate and jet momentum. The production is related linearly with the jet momentum using the Vlasblom equation combined with a non-dimensionless empirical fitting parameter per run per traverse velocity.
What is remarkable is that the intrusion depth by the jets increases with ascending runs while the jet parameter settings stay the same. The data shows that the difference between the mass flux by the density current and the mass flux stirred up by the jets when the sediment concentration of an undisturbed bed is assumed, increases between runs when an increased intrusion depth between those runs is observed as well. This indicates that the volume penetrated by the jets contains a smaller amount of sediment than was initially assumed, thus is disturbed by the previous run and is therefore decreased in strength. This decrease in strength results in a larger intrusion depth during the run itself in comparison to the previous run.

The influence of the SOD of the jets is analysed by comparing runs with a SOD to runs without a SOD but with similar remaining jetting parameter settings. When a SOD is applied, the jet pressure applied to the bed is outside the flow development region and therefore the jet pressure decreases with distance from the jet nozzle. The mass of sediment stirred up by the jets, for a SOD of 300 mm, is lower in comparison to a SOD of 0 mm. The density current transports relatively more sediment, however, when a SOD of 300 mm is applied. So, if a large amount of sediment needs to be stirred up, and therefore a large intrusion depth is required, no SOD should be applied and when large horizontal transport by the density current is desired, a SOD outside the flow development region of the jets should be used.
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The nautical bottom is defined as the level where physical characteristics of the bottom reach a critical limit beyond which contact with a ship’s keel causes either damage or unacceptable effects on the controllability and manoeuvrability of ships. The nautical bottom is usually assessed using the density of the bottom fluid mud layer as a criterion. However, for navigability purposes, rheological properties of bottom layers (and in particular yield stress), rather than density, are key parameters. The rheological properties of fluid mud depend on both the density and composition of mud and this composition can vary over time, owing to organic matter degradation.
In this study, the influence of organic matter degradation on the rheological properties of mud is investigated. A total of 129 samples from different locations and mud layers (depths) from the Port of Hamburg were analysed. They were degraded in the laboratory under aerobic and anaerobic conditions for 250 days. The rheological properties of these samples were analysed before and after degradation using a rotational rheometer (HAAKE MARS I).
The rheological properties of the samples before and after anaerobic degradation were significantly dissimilar. On average, the fluidic yield stress decreased by 26 %. This percentage had a strong positive correlation with the total organic carbon contents and degradabilities of the samples under consideration. In contrast, the seasonal variability of the samples did not show any correlation with the rheological properties.
After degradation, the decrease in total organic carbon content is small and could not be correlated to yield stress changes. This leads to conclude that the structural breakdown of organic matter and/or the breakdown of organic bridges between organic matter and clay particles are the reasons for the decrease in strength.
The fluidic yield stresses of the aerobically degraded samples increased by 2 %. The difference with their anaerobically degraded counterparts is suspected to be caused by oxidation, which could add cohesion to the mud. From this study, it can be concluded that intentional organic matter degradation during dredging operations could be very effective in making the mud navigable. ... Read more

Sediment tends to accumulate in small channels in port of Rotterdam which obstructs daily ship navigation and as a result needs to be removed by high-cost dredging operations. The goal of this project was to design a gel product that helps in the sedimentation control in the Rotterdam port area and contributes to the reduction of disposal costs, by offering a feasible, stable and eco-friendly solution. The following steps were followed:
- Technoeconomic evaluation to identify the materials and recipe
- Stability trials to determine critical rheological factors and provide data for CFD study
- Product and application concepts
- Feasibility investigation for the use of Kaumera as a gelation agent and other applications ... Read more

To exploit its socio-economic functions, engineering measures are regularly applied in estuaries. Estuaries are, however, known to be very complex systems. Stemming from this complexity is the generation of a so-called estuarine turbidity maximum (ETM), which poses great siltation problems to the engineering measures. An engineering measure, which is looked upon in this thesis, is a trench accommodating for the construction of a submerged tunnel. Despite the complexity of estuaries, trench siltation rates are predicted in practice by simple empirical engineering tools. However, a lot of uncertainty is associated with the predicted trench siltation rates, as such engineering tools do not capture the complex estuarine mechanisms. These mechanisms are found to dominate the sediment supply to the trench and the subsequent trapping of sediment in the trench. Therefore, in this thesis, it is investigated to which degree of certainty trench siltation rates in estuaries can be predicted, based on a process-oriented and engineering-oriented viewpoint. This is researched according to the implementation of a detailed process-based numerical model, which is considered to be highly accurate. For this purpose, the following case study is adopted: a trench near the ETM of the well-mixed Scheldt Estuary, at Oosterweel, Belgium. The uncertainty of the numerical model is estimated based on a sensitivity analysis, which maps the epistemic uncertainty, and a scenario analysis, which approximates the intrinsic uncertainty. For verification purposes, modelling results are compared with the state-of-the-art theory on trench siltation mechanisms, and estuarine sediment transport and trapping mechanisms. These are thoroughly analyzed in this thesis based on an extensive literature study. Additionally, a link to practice is made by comparison of the degree of certainty and practicality of the numerical model with the engineering tools. It could be estimated, based on the parameter uncertainty, that the epistemic uncertainty of the numerical model equals approximately 1.5 times the expected siltation volumes. A similar uncertainty due to intrinsic uncertainty was estimated, as the trench siltation rates showed a strong dependency on the variation in forcing regarding tide, river and storms at sea. In total, this led to a quantifiable uncertainty in the order of 2.5 times the expected siltation volumes.
Regardless of this uncertainty, great confidence is put in the performance of the numerical model, as in accordance with existing literature of the study area and theory on well-mixed estuary, important mechanisms in the supply of sediment to the trench were found to be: salinity-induced circulation, tidal rectification, Stokes’ drift and river discharge. Additionally, the governing sediment trapping mechanisms of the trench, found by the model, are in line with state-of-the-art literature. In contrast, yet unidentified by literature, the longitudinal salinity gradient over the estuary also seem to dominantly influence the trapping efficiency of the trench, in particular during flood in which it induces a strong decrease in sediment trapping. In comparison, it is believed that engineering tools, applied for trenches in estuaries, are prone to very high epistemic uncertainty caused by model inadequacy. This is because stand-alone application of the engineering tool on the problem gave a significant over-estimation of the siltation volumes, as predicted by the numerical model. Furthermore, the engineering tool was found to behave differently within a tidal cycle, and on changing environmental conditions. Above epistemic uncertainties due to model inadequacy could, however, not be quantifiably supported, as the total quantifiable uncertainty was in the same order of the numerical model. In conclusion, the degree of certainty of the trench siltation rates is believed to be improved significantly using a detailed numerical model instead of engineering tools. However, a huge drawback of the application of detailed numerical models, is the complexity and the impracticality of the numerical model. Therefore, this thesis opts for the development/use of a more sophisticated semi-empirical tool for engineering measures in estuaries. Though, more research is recommended on trenches in both similar and different type of estuaries in order to generalize and confirm the findings of this thesis. ... Read more

The port of Rotterdam is located within the Rhine-Meuse estuary where a substantial amount of fine sediment transport takes place. Therefore, the port of Rotterdam is subject to significant siltation, requiring maintenance dredging to guarantee a sufficient nautical depth of fairways and harbour basins. To optimise the dredging strategy in the port of Rotterdam, a pilot study has been carried out wherein sediment is reallocated in the Rotterdam Waterway, during ebb, instead of offshore in the North Sea. Between May and November 2019, 210,000 tons of sediment has been reallocated. This pilot study has been carried out in the context of the larger EU-Interreg Sediment Uses as Resources in Circular and Territorial Economies (SURICATES) project. The main goals are to re-use the sediment as a resource and to reduce the sailing time of the dredging vessels. Both ideas comply with the Building with Nature philosophy; a concept gaining popularity over recent years in The Netherlands focusing on, amongst others the optimisation of dredging strategies. It is expected that the reallocated sediment is mainly transported offshore, while at the same time some of the sediment will nourish the river banks of the Rotterdam Waterway enhancing its flood resilience. This thesis focuses on understanding the fine sediment behaviour of the SURICATES pilot project on two different scales. This is done by analysing measurements and model hindcasts. The measurement campaign is set-up by Deltares and the Port of Rotterdam. For the model hindcasts an operational hydrodynamic and sediment model is used. On the small scale this is done by focusing on the behaviour of a single disposal over a tidal cycle. The large scale focuses on the cumulative long term behaviour of all sediment reallocations. For the small scale two measurement surveys are analysed. In both surveys it is found that a sediment reallocation executed by bow coupling is subject to mixing up to halfway the water column. Subsequently, the sediment plume is advected around and below the pycnocline. Further measurements in the mid field are lacking, but it is hypothesised that the majority of the sediment settles during subsequent low water slack. For the other execution method, drawing the bottom doors, which is used to reallocate the majority of the sediment, useful measurements are absent. It is hypothesised that the majority of this reallocated sediment is confined in the salt wedge and therefore mainly transported upstream over time. To assess the long term behaviour of the cumulative behaviour of all sediment reallocations, a different measurement campaign is set-up. In this measurement campaign, bed samples are collected prior to and during the pilot study to determine the change of the bed composition. In this campaign an indication for increased sedimentation related to the pilot study is found for nearly all the sample locations. The short term model study is set-up to enhance the understanding of the short term behaviour of a sediment plume, to derive an accurate source term for the sediment disposals and to carry out a sensitivity analysis. This sensitivity analysis is executed to derive the influence of differences in disposal method, timing of disposal, and uncertainties in the model. It is found that the execution method has the largest influence on the critical sediment fluxes on the short term, followed by the timing of disposal. From the long term model hindcast, in which the entire pilot study is hindcasted, it is found that 27% of the total amount of reallocated sediment flows downstream from the location of disposal and 73% upstream. These estimations are in line with the hypothesis and long term measurement results, but a thorough calibration of the results is lacking. To conclude, in this thesis a pilot study utilising a different sediment reallocation strategy in the port of Rotterdam has been investigated. This study shows that majority of the sediment disposed, in the current set-up of the pilot study, is estimated to flow upstream. In the sensitivity analysis, it is predicted that this might be caused by the timing of disposal or method of execution. It is also found that the initial behaviour of the sediment plume and the long term measurement contain a large amount of uncertainties. As most important recommendation for future work an expansion of the current measurement survey is proposed with at least two fixed locations: one downstream and one upstream of the location of disposal. In this way sediment fluxes can be established, which can also be used to verify and calibrate the sediment model. ... Read more

This Master thesis presents an improved model for the transport of fine suspended sediment (SPM) in the Rhine region of fresh water influence (ROFI) and in the Port of Rotterdam. It is known that the transport of SPM in the Rotterdam harbor depends on marine as well as fluvial processes. SPM transport inside the harbor has been modelled in the past, but these studies did not take into account the dynamic nature of SPM concentrations at sea because they employed constant sediment boundary conditions and did not resolve wind waves. At the same time, numerous model studies of SPM transport in the Southern North Sea have been carried out, but none included the Rotterdam harbor as more than a discharge point. This MSc thesis is the first study to combine a North Sea SPM model with a detailed model of the Port of Rotterdam. By doing so, it incorporates the dynamic nature of sediment concentrations in the North Sea, and its effect on sediment transport in the Rotterdam harbor.

A new suspended sediment model of the Rotterdam harbor was set up with the
Delft3D-WAQ software package and the NSC-Course model grid already in use by Port of Rotterdam. A validated hydrodynamic model was available for this grid schematization, and has been used as model forcing. At the open sea boundaries, the validated ZUNO-DD model for SPM transport on the North Sea was used to compute suspended sediment concentrations, which were then applied as boundary conditions. In addition, a wave buoy assimilation technique was used to include the effect of wind
waves on the resuspension of sediment. A set of initial conditions was created by repeating a single spring-neap cycle with calm, virtually waveless conditions until sediment concentrations reached a dynamic equilibrium. A byproduct of this method was that it created a large sediment availability in the bed, which lead to higher than expected resuspension during storms. To investigate the response of the system to variable forcing conditions, three 14 day periods have been selected from measured environmental conditions of the year 2007, containing different combinations of storms and river discharges.

The model shows positive results, but does need improvement. Principally, the episodic nature of siltation in the harbor basins lining the mouth of the Rotterdam Waterway was reproduced. In line with observations, storms at sea correspond to high SPM concentrations at sea, large influxes through the harbor mouth, and increased siltation rates in the harbor basins. Furthermore, differential advection of the salinity structure and the trapping of SPM in the Rotterdam Waterway was observed. However, erosion was also observed, and harbor basins lining the Rotterdam Waterway showed a strong response to events at sea which contradicts observations. This is attributed to
the wave stress assimilation performed on NSC-Coarse grid which generates large wave stresses inside the harbor and causes unwanted resuspension. Three different forcing scenarios were chosen to highlight the differences between marine and fluvial processes, but a clear distinction could not be made. This is expected to be caused by the erroneous wave shear stresses which obfuscate the effects of different siltation mechanisms. It is recommended that this aspect of the model is improved and that the model is reassessed using measurements.
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Deterioration of the ecological quality within the Markermeer, due to the elimination of natural flushing and a resulting increase in turbidity, has created a need to revitalize the region for the benefit of the local wildlife. One major way in which this is being achieved is through the Marker Wadden, designed as a wetland area featuring a combination of islands, marsh-pond areas, mud flats, and sheltered shores which will serve as bird and wildlife spawning area. One of the primary innovations within the Marker Wadden project is the utilization of locally dredged material to form many of the wetland areas. This dredged material −often referred to as mud− is characterized as a soft, cohesive, fine-grained soil material with a mixed sediment composition of clay, silt, fine sand, organic material, water, and often gas (Winterwerp and van Kesteren, 2004). This material has a lot of inherent uncertainties in regards to its behavior and use in construction, stemming from its general non-homogeneity and less predictable/studied behavior. When considering the use of this material to construct areas with specifically designated elevation and strength ranges, the additional strength and settlement effects due to desiccation and crust formation once the material surface has been exposed to atmospheric conditions must be carefully considered. The assessment of this process includes the outlining of a conceptual model emphasizing two distinct stages of desiccation, lab testing to define material behavior during this phase, large-scale testing, and finally an evaluation of an existing numerical model for this process. The conceptual model was then compared and validated in part through both physical, in-situ measurements from a large-scale test setup, as well as to a numerical model developed at Delft University of Technology and further adapted for this process. In addition, the numerical model was utilized as a prediction tool for the Marker Wadden, under various atmospheric conditions and surface water conditions. These effects were evaluated in terms of water content, void ratio, settlement, and strength.

The large-scale test setups −representing three varying degrees of atmospheric conditions and surface water conditions− exhibited similar trends in both the in-situ measurements and modelled results, with increasing levels of active surface water removal and precipitation minimization correlating to increased void ratio profile reduction −and therefore increased desiccation and drying− especially at the surface. However, due to the short-term nature of the large-scale testing, none of the large-scale tests ever reached the second stage of desiccation, and it can be concluded that in the initial stage of desiccation, minimal shear strength development will occur in the surface material. Modelling of variations in surface water conditions show that active removal of surface water promotes faster progression into the second stage of drying, and therefore faster initial development of shear strength. Other significant findings include the long-term stabilization in terms of total additional settlement, and that neither short-term re-submergence of the material surface nor initial seasonal start date will hinder this long-term settlement stabilization. Furthermore, the reality of the large-scale test material, including the presence of increased sand content layers, also highlights the importance of assessing the profile material variation, as deviation between the various in-situ measurement profiles and modelled “uniform” profile results show a high deviation. Modelling of this process is limited to the selection of the proper material input values utilized for the complete profile. During this modelling process, it was determined that the special consideration should be given to how the soil water retention properties are obtained, as well as the hydraulic conductivity relation and values utilized, as small deviations in these inputs impact the model significantly in comparison to other inputs. ... Read more