The current macrostability safety assessment for primary river dike trajectories in the Netherlands is applied to approach the failure probability of a dike during high water events. However, in the current schematization process that is described in the Wettelijk Beoordelings Instrumentarium (WBI) to assess the macrostability, aleatory and epistemic uncertainties are approached ’sufficiently safe’ by applying design values based on expert judgement via a semi-probabilistic assessment. Several primary river dike sections in the Alblasserwaard do not suffice the current safety standard set for the failure mechanism macrostability. The region is composed of a highly complex subsurface with large spatial variation, resulting in large schematization uncertainties for the macrostability assessment of the primary dike trajectories of the Alblasserwaard. With the recent development of full-probabilistic analysis possibilities in software such as D-Stability, it becomes possible to consider uncertainties as a stochastic variable in the macrostability safety assessment. Including schematization uncertainties within the macrostability safety assessment will improve the approximation of the failure probability of the primary dike trajectory. The largest schematization uncertainties in the macrostability safety assessment are currently considered to be the schematization of the subsurface in a vertical soil profile and the uncertainties in the schematization process of the pore water pressures in the dike during high water events. These uncertainties will be included in the calculation process to investigate the influence on the expected reliability of the primary dikes in the Alblasserwaard region. The subsurface schematization uncertainties are investigated by using soil scenarios to investigate the influence of local subsurface schematization in the vertical soil profile. The simplification of the soil profile and position of the soil layers is considered. The pore water pressures are separated into three components: the hydraulic head in the aquifer, the intrusion length, and the phreatic line. Each component will be included as a stochastic variable in the stability analysis. Fragility curves can be applied to describe the distribution function for each pore water pressure component, where the combined fragility curve will provide the combined failure probability and reliability index that includes the schematization uncertainty of the pore water pressures considered.
The soil scenarios can be applied to include schematization uncertainties of the subsurface in the macrostability safety assessment. The analysis showed that the simplification of the subsurface schematization only has a minor influence on the reliability index and failure probability of the case study dike cross-section Kortenhoevendijk. The schematization uncertainties of the pore water pressures can be considered in the macrostability safety assessment by combining the fragility curves of each component describing the pore water pressures underneath the dike. Results of the pore water pressure analysis are that failure probability is improved significantly for case study Kortenhoevendijk by a factor 1000 and case study Bergstoep by a factor 10. The approach to consider schematization uncertainties in the macrostability safety assessment via a full-probabilistic analysis can be used for dike sections prone to the uplift mechanism. This approach provides insight into the influence of schematization uncertainties on the failure probability of a dike cross-section. Including the pore water pressure schematization uncertainties in the macrostability safety assessment can have a significant impact on the outcome of the assessment. Including these uncertainties can make the difference between deciding whether a dike trajectory needs reinforcement, or deciding that reinforcement is not necessary. ... Read more

This thesis examines the role of the concepts of “Build Back Better”, “Disaster Cycle”, and “Sustainability” in water management and the possibility of the interactions between these concepts when designing water management infrastructure. Especially in cases where the disaster cycle is relatively short: 10 to 15 years between disasters.
The case study is on the island of Grand Bahama. The island of Grand Bahama depends on the freshwater groundwater lens for its drinking water. Flooding during hurricanes introduces saline water into that groundwater lens. It is therefore highly probable that the current drinking water production method will not be able to meet the demand in the future. An alternative drinking water supply system should therefore be examined.
To investigate the interactions between the concepts, they are put into a conceptual design process, which uses the methodology “RenewIsland”, and used to set up some preliminary designs. Three Alternatives were made with the methodology “RenewIsland”. These Alternative designs were then subjected to a Multi-Criteria Analysis (MCA).

This thesis substantiates from the process that the interaction between the concepts is possible and that the inclusion of Build Back Better in the Water management decisions gives more possibilities to make balanced choices.
A blueprint has been made for a method to analyze swiftly if an alternative is compatible with the different cycles and phases of a location regarding a disaster and normal circumstances. This thesis also states that the study has to be extended with more research to make it generally applicable. ... Read more

Van Sickle Island, located in the Suisun Marsh in the San Francisco Bay Area, has experienced multiple levee breaches in the past. Due to the large social and economic implications of flooding, questions have arisen about whether the current management of the island is still feasible. This project, therefore, aimed to find the most financially favorable management plan for the upcoming 50 years. First, an understanding of the system was obtained through a site investigation, a multivariate analysis, and a hydrodynamic model. It was concluded that discharge, tide, air pressure, and wind setup all contribute to the water level. These variables were then used as input for a 1-dimensional hydrodynamical model, which quantifies their effect on the water level. Subsequently, four management plans were considered: status quo, raising the levees, conversion into an estuarine wetland, and abandoning the island. To allow for comparison between these management plans, a cost-benefit analysis and a net present value calculation were performed for every plan. One of the major contributors to the costs is risk. Risk is defined as the product of the probability of failure and the consequence of that failure. The failure mechanism assessed is overflow, as this is the most relevant one. To quantify this failure probability, a statistical model was developed. This model includes an extreme value analysis and an event tree. Due to large uncertainties in the behavior of both the levee and the water level over time, the original 50-year lifetime of the management plan was deemed too ambitious. Therefore the lifetime was reduced to 10 years. The conclusion of the cost-benefit analysis and the net present value was to convert Van Sickle Island into an estuarine wetland. This is because it was the only management plan that was profitable after 10 years. The net present value was found to be equal to $14,924,048. ... Read more

River dikes in the eastern part of the Netherlands are characterized by a relatively low daily water table. In the unsaturated zone above the water table, a negative pore pressure (matric suction) is present that binds the soil particles together. Suction can be especially large in soils with small grains, such as clay, and increases the strength of a soil due to higher effective stress. High suction in soils has been proven to significantly increase the stability of dikes. However, due to water level variations and other climatic influences such as precipitation and evapotranspiration, suction in a dike will vary over the year and throughout the cross section. The research described in this report aims at evaluating whether there are parts of a cross-section of a dike where soil suction remains throughout a high water event in a river such that an increase in the strength of the soil can be used in stability analyses. The analysis is centered around a case study of an existing dike in the east of the Netherlands and uses time-dependent unsaturated groundwater flow models to simulate the spatially and temporally varying suction for a number of different initial conditions and climatic influences defined by scenarios. The results show that it is very unlikely that suction in the dike will be lost during the summer months. Due to high evapotranspiration, the water content in the dike is low, which results in a lower water table during a high water event and less infiltration in the dike occurs during precipitation. During winter, the probability that suction is lost throughout the dike cross-section is larger and will occur after heavy precipitation with a long duration where the return period is 1 – 10 years. Although in most scenarios some suction will remain present, the amount of suction during the winter is generally low, between 0.5 and 1 meter, which results in an apparent cohesion of 2 – 4 kPa. A simple stability calculation illustrates that the increase in strength in the dike due to suction does not result in a significant increase in the stability of the dike during high water conditions. ... Read more

New solutions for future flooding problems are becoming more important than ever before. Emergency measures against failure of flood defenses may play an important role in flood risk management and is therefore currently being investigated. One of these measures is the BresDefender, which is a submersible floating pontoon that can be placed on the outer slope of a weakened dike section to prevent or delay failure. The application of the BresDefender can be divided into two scenarios: (1) to stop breach formation and (2) to limit water infiltration into the dike. The latter application scenario is expected to influence the development of the phreatic surface inside the dike, which affects dike safety. This study focuses on this scenario by assessing the effect of this seal on the development of the phreatic surface.

A numerical modelling approach is developed to describe this effect using the finite element method program PLAXIS, with add-on module PlaxFlow, to describe transient groundwater flow problems. This numerical modelling process starts off with the development of a model for a laboratory scale dike. In a previous study at the WaterLab, the phreatic surface level of the dike was measured over time for different degrees of sealing using a steel plate. These measurements are used to calibrate the numerical model, where the connection between seal and dike slope is described with a transmissive interface layer. It is concluded that this interface layer approximates the effect of the seal on the phreatic surface adequately.
The next step is to extent the numerical model to a larger scale dike consisting of heterogeneous soils. This model represents the dike located in the Flood Proof Holland test facility, which consists of a permeable core covered by a low-permeability layer. By modelling this transition from simple to complex, influences of permeability, heterogeneity, and damage of the cover on the phreatic surface are identified.

The effect of a seal on the phreatic surface is also studied using physical model tests of the dike at Flood Proof Holland. The position of the phreatic surface is measured by pressure sensors in standpipes, which are spread over the crest and inner slope of the dike. Different scenarios for the seal are examined: stiff plate, flexible textile, and no emergency measure (reference case). For every scenario, experiments are carried out with and without a damaged location in the outer slope of the dike, which lead to a total of six test cases.
The results of the physical model tests show multiple effects of the seal on the phreatic surface. First, the seal shows a delaying effect on the position of the phreatic surface, which implies that the seal delays the rise of the phreatic surface over time. The time until the phreatic surface reached a steady-state over the entire dike was increased with around 15% for plate cases and around 25% for textile cases when compared to the corresponding reference cases. Second, no decreasing effect on the phreatic surface can be observed, which means that the phreatic surface level in its steady-state condition is not affected by the placement of a seal on the outer slope. Third, the delaying effect is larger for a seal that consists of a flexible textile rather than a stiff plate. The connection between seal and dike cover is proved to be important since leakages underneath the seal influence its performance, especially when the dike is locally damaged.
Last, the textile seal has a three-dimensional effect on the development of the phreatic surface. A certain area of influence can be identified where the phreatic surface is affected. The effect of the phreatic surface is seen to be stronger for locations near the textile and this effect diminishes over time. For the textile case on a damaged dike, an initial decrease of the phreatic level is observed directly behind the textile ranging up to 30 cm.

Overall, the effect of a seal on the development of the phreatic surface is concluded to be relatively small. The effect is only of a time-varying nature and, in three dimensions, the effect diminishes for larger distances. The application of a textile in terms of dike safety shows only a marginal improvement, which occurs only in a limited time period. ... Read more

Coastal and offshore infrastructure must be designed to withstand extreme wave-induced loading conditions. Extreme Value Analysis (EVA) is often employed to infer probabilistic distributions that provide information about extreme design conditions. In traditional practices, EVA is performed under the assumption of stationarity. This means that the probability of extreme events is constant in time. However, hydraulic loading conditions are expected to exhibit temporal variability in severity and frequency as a result of climate change. Therefore, the assumption of stationarity becomes questionable. Nonstationary extreme value analysis (NEVA) for inferring extreme hydraulic loads have become more attractive in recent years. However, the applicability of NEVA models is debatable ansd differs on a case-by-case basis. Large scale oceanic bodies can be characterized by spatially and temporally varying extreme wave characteristics. Clustering analyses have proven to be successful to identify regions exhibiting similar extreme wave characteristics. Creating clusters based on similar extreme wave characteristics can potentially improve extreme value modelling because intra-cluster information can be pooled to derive more accurate extreme value models.

This research presents a practical assessment of the applicability of clustering analysis and non-stationary extreme value modeling of extreme wave statistics at cluster level in the North Sea. The primary objectives of this research are: (1) Study the temporal variability extreme significant wave height (Hm0) and extreme wind speeds (U10) in the North Sea domain, (2) Investigate how hierarchical clustering analysis (HAC) can be employed to cluster grid points that exhibit similar extreme wave characteristics, (3) How the obtained clusters and temporal variability can be employed to derive extreme value models describing extreme Hm0 statistics at cluster level and (4) assess whether NEVA models at cluster level form a practical alternative compared to conventional stationary analysis in the design and risk assessment of hydraulic infrastructure in light of climate change.

Temporal trend analysis of Hm0 in the North Sea showed that the period between 1990 and 2020 can be characterized by a decreasing trend. Between 1950 and 2020, a decrease in Hm0 intensity is observed in the Western regions and an increase is observed in the East. This is reason to believe that the variability in extreme wave climate is cyclical rather than monotonic. There is reason to believe that temporal variations of extreme U10 are responsible for the temporal variability of extreme Hm0. Initial clustering results partition the North Sea domain into 50 clusters based on characteristic values for the significant wave height (Hm0), peak period (Tp), and dominant wave directions (θ1 and θ2). After splitting clusters based on geo-location and merging clusters based on the intra-cluster statistical properties of the wave parameters, 63 clusters are obtained. The identified clusters and temporal variability are used to define NEVA models describing extreme Hm0 statistics at cluster level. Intra-cluster Hm0 observations are detrended before fitting the GEV parameters by means of Bayesian Inference. Informative priors are constructed by pooling the GEV parameter information from the intra-cluster grid points. Potential non-stationarity is accounted for by adding the Theil-Sen parameters (b and b0) to the location parameter (μ∗), making the location parameter a linear function of time. The model parameters subsequently read: Hm0 ∼ GEV (μ∗ + (b · t + b0) , σ∗, ξ∗). Using the extreme Hm0 data from the clustering centroid yields the most promising results for describing extreme Hm0 statistics at cluster level under the condition that the intra-cluster exhibits homogeneous values for b and b0.

The applied HAC analysis presented in this research is not the optimal strategy. The identified clusters exhibit heterogeneous values for b and b0 Because non-stationarity ofHm0 was not accounted for during the HAC analysis. This hinders the performance of the NEVA models at cluster level. Also, whether the derived methodology can be applied for the long-term projection of future extreme wave events in the North Sea is debatable. The non-stationary of extreme Hm0 is best described by a cyclic pattern. Without a thorough understanding of the underlying causes of the non-stationary in Hm0 and without future projections of the extreme wave climate, the applicability of NEVA for deriving extreme Hm0 design conditions in light of climate change cannot be guaranteed. ... Read more

Animal-induced anomalies on a levee surface negatively affect the erosion-resistance of a levee, leading to rapid failure of the inner slope in case of overtopping and/or overflow during high water. Where active prevention techniques of burrows from large animals, such as muskrats, are applied in and around levees in the Netherlands, the identification of smaller burrow holes made by voles and moles and the evaluation of the severity of the damage rely solely on the assessment and experience of the levee inspector.
The Polder2C’s project aims to quantitively assess the impact of animal burrows on the levee surface by conducting experiments at the Living Lab Hedwige and Prosper Polder (LHPP) and this thesis aims to contribute in this by analyzing the experiment results and developing a model for levee inspection that includes uncertainties of the geometrical characteristics of vole and mole burrow systems.
This thesis distinguishes two phases, the first of which focuses on the question: ‘How do animal burrows influence levee performance?’, and it aims to form a foundation for the second phase of the report by focusing on the behavior of burrowing animals and the geometrical characteristics of their burrows by conducting a literature review on existing research on this topic. Guidelines were set up that contribute to the identification of mole and vole burrow system by investigating the main differences between them, with the aim to easily identify separate burrow hole groups in the experiment data. These conclusions could then be used to identify different vole and mole burrow hole groups in data that was collected from several experiments at the Living Lab Hedwige and Prosper Polder (LLHPP) between October 2021 and February 2022 and answer the research question for the second phase, which was: ‘Based on data from levee inspection experiments, which probabilistic model can assess the inspection success rate of animal burrows?’. ... Read more

Terps are artificial dwelling mounds mostly found in the northern regions of the Netherlands, built to provide safe ground against water in such areas affected by flooding, storm surges, and high tides, before the development of dikes. In this thesis, the stability of these terps was evaluated via FEM models and analyses performed on PLAXIS. Results highlight considerable stability risks when the terp slopes are subjected to considerable external loading, such as those exerted by heavy agricultural vehicles being operated in proximity of these.
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A new approach is proposed which uses concepts of both the limit equilibrium method (LEM) and finite element method (FEM) to analyse slope stability. The main limitation of the LEM is that it can give an incorrect display of the initial stresses. The FEM is able to overcome this limitation, however, it uses the shear strength reduction method (SSRM) to determine the safety factor. This SSRM has its limitations as well. It’s a mathematical approach to obtain the factor of safety, without using the strength definitions given by advanced soil models. The proposed method is able to overcome the limitations of both LEM and FEM. It uses a genetic algorithm to search for the most critical slip surface and the safety factor is defined as the as the ratio of the total maximum available shear strength along the slip surface to the total mobilised shear stress. Multiple case studies are performed in this research and the genetic algorithm is able to find a reasonable critical slip surface and safety factor in every example. The proposed method has proven to give reliable results compared to other analysis methods: LEM, FEM and other optimisation methods proposed in literature. ... Read more

Offshore and coastal infrastructure must be designed to withstand loading conditions that among others arise from extreme environmental conditions. Physical processes such as storm surges, tides, currents, and waves play an important role in the design of these structures. Several variables characterize the relevant physical processes (e.g. significant wave height, mean wave period, water level, wind speed) and a thorough analysis of these variables is required when dealing with offshore and coastal dynamics, durability, and reliability assessment.

Traditionally, a critical loading condition is defined by characteristic values of environmental variables that are determined based on the highest loads previously experienced. Modern design methods seek to derive loads that correspond to specified reliability by considering the frequency of a specific loading magnitude.Traditional design approaches do not take into account the interrelations and dependencies among the variables of interest. Hence, wrong representations of the physical processes and unnecessary conservative representations of the design loads might occur. This may severely limit their effectiveness and can lead to expensive and inappropriate decisions. Multivariate frequency analysis approaches currently receive much attention within the academic community, however, advanced statistical concepts such as regular vine copula are slow in being taken up by engineering practice.
This thesis presents a practical assessment and further development of a vine-based methodology, used for the derivation of design values, in continuation of the work performed by Sell´es Valls (2019). Regular vine copulae are advanced statistical models for high dimensional distributions using (conditional) bivariate copulae as building blocks. This study contributes to bridging the gap between the academic community and engineering practice on one hand, and on the other hand, contributes to a better understanding of the potential added value of incorporating dependence information in the design process of coastal and offshore infrastructure. It has a conceptual point of view where the concept of using dependence information by applying advanced statistical techniques is explored and the required adaptations throughout the entire design process are evaluated.
In this research, it is found that the multivariate vine-based methodology can be successfully incorporated in the design process of a breakwater structure, and on average results in minimal required dimensions of elements of the cross-sectional design that turn out to be smaller and the corresponding costs up to 25% lower compared to the univariate traditional approach. This is realized by adapting the framework enabling an offshore-nearshore transformation of the wave conditions using SWAN software. Furthermore, the theoretical framework is extended by introducing Kendall’s measure providing a suitable definition of the critical region from which the critical loading conditions can be obtained. It is concluded that the vine-based approach could act as a tool providing extra information about the behavior of the system and insights on the degree of conservatism of the traditional approach. The considered role of the vine-based methodology in the design process of a breakwater structure (or coastal infrastructure in general) is to provide the practitioner with additional insights supporting the traditional design approach and possibly optimizing the design.
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In this assignment we simulate a two meters wide dike stretch which is subjected to overflow. Three failure mechanisms could occur due to overflow: full erosion of the soil of the dike, macro instability of the levee if too much soil is eroded away, leading to insufficient counterweight on the inside of the levee, and surface slip failure due to reduction of strength of the dike by flow of water in the dike core. Prevention of failure can be achieved by either keeping the water away from the berm surface or holding the soil particles in place while the water flows alongside it. The desired repair is an emergency repair that can placed quickly during a storm, or between two storms to prevent a damaged levee from failing. This is a temporary repair that will later be removed for full reconstruction of the levee. This provides constraints to the installation and repair procedure.
To decide which solution is best, 10 concept solutions are compared based on their score in the Multi Criteria Analysis with 8 weighted criteria. The solution with the highest score is the best solution according to the Multi Criteria Analysis. The selected repair option is to locally cover the damaged area with flexible overlapping sheets of Tyvek®. This is a light and thin material that can easily be transported and cut to size at the location of the repair. These sheets can be easily secured against flow loads using Gripple anchors, while pins are used to keep the Tyvek® in place during windy conditions. An installation plan and cost breakdown was made. Using 3 m wide Tyvek® rolls, the costs would be around 19.19 euros per meter height.
The damaged areas of the levee are covered with Tyvek® which is a waterproof, damp open material. This prevents the penetration of water into the core through the damaged areas. The Tyvek® also prevents the exposed soil from being eroded. Moreover, Tyvek® is a very strong material that won’t be torn off. As there is no strength reduction due to water penetration or further loss of surface material the chance for macro instability is minimized.
First, a design was created, with components dimensioned for a dike stretch in the Hedwigepolder. Subsequently, the design was validated with tests. Including two types of damage. The first was removal of a 2 by 2 m grass layer (0.1 m thick) at the top of the dike and the second was a dug-out step-section across the entire width of the dike with a height difference of 0.5 meters at the toe of the dike. Only the second damage went through the clay layer and into the sand core of dike.
During and after the tests some important observations were made. During all test volumes the plastic sheets were kept in place due to the anchors and pins. Some pins however, came loose due to vibration of the sheets (we presumed the cause of vibration is flow of water between two sheets or turbulence of water). The trench of the lower damage was partly washed away by the water. The erosion of soil in the trench did not result in changing the stability of the top sheet. At the lower damage the plastic sheet was torn off after a tear of 1 m was made with a knife.
Our solution is designed to protect any dike from macro-instability by keeping the water flow away from the berm. This is done by layering multiple sheets of plastic foil over the inner berm, fastened with ground anchors and pins. The solution is a durable and reliable design due to proven waterproof, damp open and UV resistant properties, together with Gripple's demonstrated anchoring capabilities. Another major advantage of our solution is that the repair of the damage is selective, i.e. the solution is applied only to the parts of the levee where damage has occurred. In case of only localized and small damage to the levee, the costs and workload are very minimal compared to other solutions that are applied to the entire surface area of the levee. ... Read more

In the Netherlands the design condition for a dike is surmised to occur during winter where it is assumed that the dike is fully saturated. Preliminary results by Van Duinen (2020) indicate that suction remains present, albeit ever decreasing, during the winter. This means that it would be possible for a dike to dry out during the summer period such that it becomes unsaturated, and that any effects may not have fully disappeared during a normative event.

This problem is two-fold, as (i) the strength of an unsaturated soil is higher compared to a saturated soil, and (ii) it is unknown how the strength associated with the initially unsaturated zone can be modelled in a macro-stability calculation as it varies temporally. This report investigates the strength of the initially unsaturated zone in clay river dikes in the Eastern part of the Netherlands and it explores the opportunities which the better understanding of the strength may present for the factor of safety in a macro-stability calculation

The feasibility and applicability of the SSCC as formulated by Lu and Likos (2006) for conventional geotechnical laboratory tests is investigated. A literature review bundles international knowledge on unsaturated soil behavior which is relevant in the context of dike design. Silty clay samples from the dike trajectory of Ravenstein-Lith were investigated using the SSCC. It can be successfully applied to K0-CAU triaxial test when determining strength parameters using strain-compatibility. Compared to its conventional variant, the saturation stage must be skipped. Samples are air-dried under laboratory conditions to a prescribed volumetric water content which can then be linked to an amount of suction using the SWCC and a comparison can be made with the closed form of the SSCC (Lu et al., 2010).

The SSCC cannot be applied to DSS tests successfully. In DSS tests both slip and a diagonal failure plane was observed. This research was able to pinpoint at which shear strain slip would occur, and hence when tests are valid. DS tests were used to confirm the validity of DSS tests using CCSM.

A case study performed on a representative cross-section found a positive effect on the factor of safety due the additional strength related to the initially unsaturated zone. The FoS increased by at least 1.7% in the most conservative case and at least 5.0% in a scenario supported by field measurements. The current limited number of field measurements restricts a more precise determination. It is advised to perform more of these such that the initially unsaturated zone in a clay river dike can be modelled effectively and reliably with a high degree of certainty.

To conclude, with the application of the SSCC concept, the additional strength produced by considering the initially unsaturated zone in clay river dikes in the Netherlands leads to an opportunity where the dike can be designed more efficiently by reducing conservatism. Thus, taking the initially unsaturated zone in a dike into account can be considered as a valuable contribution to the toolbox of Dutch geotechnical engineers.
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River floods are becoming increasingly devastating because of climate change (more frequent and extreme rainfall), population growth and the increasing economic importance of river basins. This situation requires maintenance and strengthening of flood-defence systems.

Adding certain types of vegetation at precise locations for their positive impact may be a cheaper, more flexible, and more environment-friendly way to strengthen dikes than the traditional increase in height. However, this nature-based (NB) option is not yet widely implemented due to the lack of precise knowledge of the potential of vegetation effects and their uncertainty.

This study uses a probabilistic method to better understand the effects of vegetation by including vegetation in the computation of the failure probabilities of Dutch river dikes. A framework was established to combine all these vegetation effects simultaneously in the computation of the total failure probability, considering different magnitudes of each effect. This enables the consideration of a wide range of vegetation scenarios, from which conclusions were drawn.

Overall, this thesis provides a useful and versatile tool for assessing the influence of vegetation on dikes that has a lot of potential and can be easily enhanced in the future. ... Read more

Internal erosion is a frequent cause of dike failure, also known as piping or backward erosion. Uplift is considered a submechanism of internal erosion, together with heave and piping, where all three submechanisms must occur for the dike to reach a failure condition. The principle of the uplift phenomenon is straightforward: it occurs when high pore water pressures in the aquifer lift the cover layer, which is located at ground surface. If the pressure is great enough, the cover layer begins to float ('opdrijven'), and may also bulge ('opbollen') or crack ('opbarsten'). Currently, the assessment for uplift is based on a vertical equilibrium, which relates to a floating condition of the cover layer. The forming of an exit point for concentrated seepage is presumed to happen simultaneously with the increase in uplift pressure and is therefore not explicitly considered in the current assessment. This thesis aimed to investigate in what way the uplift assessment may be improved, both to describe the complex behavior better and to decrease the need for costly countermeasures. The evaluation of uplift was conducted in two parts: by making explicit what the causes of uncertainty are in the current assessment, as well as by proposing a new model to describe the complete uplift behavior better. It is recommended to evaluate the ‘floating’ and ‘bulging-cracking’ phases directly. In the ‘bulging-cracking’ phase, the forming of an exit point can either occur by a tension or shear failure. ... Read more

The main reason for this research is the possibility of landslides that could trigger a tsunami together with general interest from the oil and gas industry. The goal of this thesis is to find out what the geotechnical properties are of the 7 different locations at the eastern flank of the Rockall bank which is located to the west of Ireland and to the south of Iceland in the Atlantic Ocean. The possible effects of these properties on slope stability are then discussed. This will be done by geotechnically testing the sediments in a laboratory. All standards used during testing can be seen in chapter 3.1.1. The gravity cores used for this research were found to contain parts of sediment that were quite intact together with other more disturbed parts of sediment. The sediments that were found could be classified as silty SAND, clayey SILTS and silty CLAYS which are calcareous to very higly calcareous,from medium to very high plasticity, low to medium-organic and have extremely low to very low undrained shear strengths. Grain size distribtions were found to be gap-graded and well graded and the the sediments were found to be inactive to normal soil based on the Atterberg limits.Geotechnical properties such as gravimetric water contents are found to range from 0.20 to 1.18, the volumetric water contents range from 0.50 to 0.80, a liquidity index from 0 to 3, specific gravities from 2.72 to 2.79, void ratios from 1 to 3, bulk volumetric weights from 14 kN/m3 to 18 kN/m3, dry volumetric weights from 7 kN/m3 to 13 kN/m3, clay contents from 10% to 60%, a silt content of 15% to 60%, a sand content from 8% to 70%, calcite contents from 17.3% to 57.4%, organic matter contents from 2.6% to 9.0%, liquid limits from 0.40 to 0.82 and plastic limits from 0.23 to 0.49. The undrained shear strength for the original and remoulded sediments from the UU DS tests is found to range from 2 kPa to 8 kPa and from 0 kPa to 4 kPa. The undrained shear strengths from original and remoulded sediments from the fall cone test range from 4 kPa to 33 kPa and from 0 kPa to 4 kPa. The undrained shear strengths from the original pocket vane tests range from 5 kPa to 22 kPa. The sensitivities of the sediments measured by the fall cone tests are found to range from 2 to 28 and the sensitivities obtained by direct shear testing are found to range from 0.5 to 4.Based on these undrained shear strengths a failure mechanism similar to that of a direct shear test is found to be more likely on the undisturbed sediments and a failure mechanism like that of a fall cone test is found to be more likely for the remoulded sediments. The non-phyllosilicate minerals that are present are Smectite, Illite, Muscovite, Chlorite and Kaolinite. The phyllosilicate minerals that are present are Quartz, Alkali feldspar, Plagioclase, Calcite, Ankerite, Siderite, Anatase, Rutile, Hematite, Pyrite, Halite and Apatite. This mineral composition can be logically explained by their possible weathering paths and indicates that the possible parent material is Monzogranite type 2 also called Muscovite-metagranite. Magnetic particles are found to be present in all sediments in small amounts that are not quantified. Similar sediments are found to be present from the research of ( Georgiopoulou, Krastel et al., 2019). This confirms the presence of turbidty deposits. These turbidity deposits are indicated to be present at all sites based on the fininng-upward sequences found. Also the presence of lighter interglacial and darker glacial sediments is found. It was also found that the likley reasons for slope instability on the eastern side of the Rockall Bank are the much higher water contents and clay contents of the sediments present compared to the sediments found on eastern side of the Rockall through.The risk of liquefaction upon distrubance is found at sites 1736, 1672, 1988, 1959 and 1604. No risk of liquefaction upon disturbance is found at site 688. The organic matter content is considered to not have an effect on strenght parameters of the sediments present whereas an increase in the amount of foraminifera shells could increase stability of the sediments. Only differential compaction is not found to be a probable factor in lanslide initiation. A long term instability could arise from weathering of Smectite minerals. Erosion could cause slope instability due to sediments with widely varying grain size distributions. The high water content sediments that are present are prone to liquefaction due a disturbance possibly from seismic activity. It is recommended that in future studies a quantification of the marine shell fraction is made. Also a microscope spectrometry is recommended to be done on the sand fraction together with an X-ray diffraction on the <63µm fraction. The most important recommendation is to do a slope stability analysis on the RBSC using the geotechnical properties presented in this thesis. ... Read more

The central Thermo Electrico Antonio Guiteras (CTE Antonio Guiteras) is a thermoelectric power plant located in the bay of Matanzas. In 2017, hurricane Irma passed the north coast of Cuba and destroyed the primary sea defense in front of the CTE, causing major damage to the plant. The power plant is renovated, and a new and improved sea defense is currently being constructed.
The goal of this report is to answer the following question: to what extend is the power plant protected during extreme weather conditions and what improvements are needed to ensure that the power plant can remain operational during these extreme weather conditions?
To determine what the hydrodynamic and meteorological effects are of a extreme weather event such as a tropical cyclone, a synthetic tropical cyclone is created. This synthetic hurricane must generate large significant waves in combination with a big storm surge, to have severe impact on the CTE. It must also have a significant probability of occurrence. To determine this normative synthetic hurricane, multiple synthetic hurricanes are simulated in Delft3D and XBeach and their corresponding return period is determined. As Irma significantly damaged the CTE, this hurricane is taken as the basis for all synthetic hurricane combinations. The hurricanes each vary from Irma in maximum wind velocities, forward speeds and their tracks.
To simulate the physics of hurricane Irma, a spiderweb grid is created at the locations of the hourly best track of Irma. This is then used in the Delft3D model as input for the pressure and wind fields of the hurricane. The output of the Delft3D model is validated with recorded data of observations stations in the Gulf of Mexico. Recorded water levels and wind speeds of buoys near Key West are used for validation. XBeach is used to simulate the nearshore physical processes. XBeach can more accurately predict wave propagation and includes higher order processes in its simulation. As input for the XBeach model, the output of the Delft3D model is used.
After running all the synthetic hurricanes in Delft3D, the five resulting normative hurricanes are run in XBeach. The synthetic hurricane that creates the largest significant wave heights at the project area is taken as a basis for the final design. This normative hurricane gives a maximum significant wave height of 8.8 m with a corresponding storm surge of 1.61 m at the location of the CTE.
With these values a research on the current defense wall is done. Ultimately for a part of the sea defense an adjustment on the existing defense wall is proposed. A second but lower vertical wall with a bigger bullnose is placed in front of the existing one. This creates a triangular shaped stilling basin, from which the water can flow out at the seaside of the wall. For the other part of the sea defense no adjustments on the wall are proposed but an improvement of the existing drainage capacity is proposed. The existing drainage channel, which lies behind this section, is widened and deepened. Additionally, a drainage wall is built around the powerplant, which diverts the overland flow caused by intense rainfall into the drainage channel.
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PIANC has published several working group reports related to the design of fender systems. The work of PIANC WG33 is widely accepted by the industry and has been used to design marine structures worldwide. However, the existing design approach does not distinguish uncertainties in fender engineering, e.g. uncertainties related to vessel sizes, berthing velocities, and berthing angles. This paper aims to show how to take into account some of these uncertainties into fender design using a reliability-based approach. The influence of multiple fenders contact and multivariate dependence between vessel size, berthing velocity, and berthing angle on the failure probability of a fender system was analysed. These correlations were modelled using a Vine-Copula, while the contribution of multiple fenders contact was investigated by performing simulation. Furthermore, the failure probability of the fender system was determined using the First Order Reliability Method and Monte Carlo simulation. The results show that uncertainty in berthing velocity, the effect of multiple fenders contact, and dependence between design variables largely influence the reliability of a fender system. It is highly recommended to incorporate all these aspects into the design approach to accomplish a cost-effective design solution. The key findings of this study can be used to update the existing design approach of fender systems and help to interpret the berthing records collected by Port Authorities. ... Read more

This research focuses on the estimation the failure probability of Shanghai sea-dikes system, taking into account several failure mechanisms. This method follows fully probabilistic approach, in which all relevant parameters for the resistances and the hydraulic loads vary according to specific distributions. ... Read more

The determination of geotechnical parameters from in-situ tests heavily relies on the use of empirical correlations relating field measurements to soil properties. A large number of these correlations can be found across the literature, each of them yielding a different outcome for the parameter value. This results in a high variability of the potential results, which is not necessarily properly accounted for in the current geotechnical engineering practice. A new approach using graphs has recently been proposed by van Berkom [1] to automatically generate multiple parameter values based on a given set of correlations and equations. The present thesis assesses the quality of the estimates obtained from this new graph system and investigates how multiples outcomes can be combined into a unique result. The quality of the parameter’s estimates is appraised both in terms of accuracy or uncertainty, and in terms of validity. The combination of results from multiple methods showed that it is possible to either build confidence or distrust in the combined outcome depending of the consistency of the contributing results. As a result, this framework enabled a quantitative description of the inter-correlations variability. The conceptual framework has been then applied to geotechnical parameters and CPT-based correlations for coarse-grained soils. The range of applicability of the correlations (e.g. soil type, state of consolidation) is a critical factor that actively influences the final outcome of the system. This automatic system demonstrated its ability to produce parameter values relatively close to
the values obtained with the current practices. Further validation is required to assess the overall performance of the system on a broader scale. ... Read more

Deep Soil Mixing is an often-applied technique in the reinforcement of embankments, but little has been done to investigate and understand its behavior when used in excavation projects. The present research presents a database of the results of previous studies on the Deep Soil Mixing technique in Scandinavian soils. An expression that can estimate the improved soil strength when a specific binder content and binder ratio is mixed with the soil is proposed and its pertinence is tested with two full-scale tests. The proposed mathematical expression to predict the improved strength yields a good representation of the available data. The full-scale tests, in which a braced steel sheet pile wall interacts with panels of DSM overlapping columns are used for back-calculating the improved soil strength and stiffness properties. It is observed that the weighted average procedure for calculating properties should be used with care and that the loading conditions affect the strength and stiffness that the improved soil can develop. The drained analysis with a fixed friction angle and a cohesion intercept estimated from the undrained shear strength is the suggested design procedure to assess deep excavations involving improved materials. ... Read more