The design of submerged floating tunnels (SFTs) is a challenging task, as it is often seen as a potential alternative water crossing measure for wide and deepwater environments, and the challenge is to find ways to design and construct it economically and reliably. The aim of this thesis is to provide tools for the design and assessment of SFTs. The approach is divided into three parts: first common overarching topics are addressed, to introduce the subject, but also to introduce common theoretical methods and target reliability concepts for structures and specifically for SFT. The second part is the application of probabilistic design and the use of both non-parametric Bayesian Networks and Vine Copulas, the analysis of traffic loads on an SFT and the quantification of the probability of failure due to bending moments, and a dynamic mooring analysis (DMA) is used on a hypothetical SFT model. The results of the research programme will be utilised to translate them into procedures for design and assess SFT in the first place, and also to use them in other fields of application within the industry. Modern numerical modelling tools in combination with experimental work are used to assess the structural behaviour.

The submerged floating tunnel (SFT) is a conceptual idea that originates from the 19th century. The idea consists of a tunnel tube floating underwater where it is kept at a fixed depth by its buoyancy and by tethers that are anchored to the seabed and or by floating pontoons at the water surface. The tunnel is placed deep enough to avoid extreme weather conditions and to not hinder marine traffic but also not too deep to avoid high hydrostatic water pressures. The dynamic behaviour of this structure differs largely from classic immersed tunnels as it is not embedded in the bed and also from that of (suspension) bridges due to the hydrodynamic environment. This makes the dynamic behaviour of the SFT largely complicated and to this day still raises a lot of questions. This limited understanding contributed to the fact that worldwide not a single SFT has been constructed yet.
For this study, the dynamic response of a tether-supported SFT due to an earthquake will be analyzed. The main goal is to identify the main behaviour of an SFT due to these seismic events, to get an idea of how severe the damage could be and to know which measures in the design could be applied to reduce the impact.
To do so, a case study is introduced where the main dimensions of the tunnel are described. Next, a cross-sectional analysis is performed. This is done both analytically and by the use of the finite element model (FEM). The purpose of these analyses is to verify the input of the FEM. For the analytical model, a singular tether is described as an Euler-Bernoulli beam. By applying the Fourier transform method of analysis, the dynamic behaviour of this tether due to a simplified input signal is obtained. Subsequently, the same tether is modeled as a FEM by the use of DIANA FEA. By performing a time-history analysis for the same simplified input signal, the same results as for the analytical analysis are obtained which verifies the input. After that, the simplified model is used to model the entire tunnel which is used to study the dynamic behaviour of the SFT.
To perform the seismic analyses for the total tunnel, three different accelerograms of three different earthquakes are used. Before applying these signals to the model each of them is scaled to the spectra described by Eurocode to gain a more general input. The model is then used to perform two types of analysis. First, an eigenvalue analysis to gain the eigenperiods of the structure. Next, a time-history analysis to gain the seismic response of the structure. For the time-history analyses, the input is applied in the transverse and in the longitudinal direction, each as a separate analysis. From these analyses, the displacements and tension stresses in both the tunnel elements as in the tethers are obtained.
The last part of the study is used to analyze the effect of different design aspects of the tunnel. By using the case study as a starting point, multiple configurations are tested in where the effect of the number of mooring lines, number of tethers, tunnel alignment, tether inclination and the appliance of base isolation systems are examined.

Over time, degradation processes might cause damage to pattern-placed revetments. Examples of such damages are missing elements, deformation, and the loss of joint filling. However, little is known about the exact consequences of those damages. Therefore, when damage is observed during an inspection, it is estimated based upon experience what the possible consequences are. If the consequences are misjudged, this will lead to inefficient maintenance.
Better insight into the exact consequences of damages will expand the possibilities of how risk-based maintenance can be used to maintain revetments. Consequentially, maintenance interventions can be planned more efficiently, reducing the societal costs incurred due to inefficient maintenance. This study contributes to this topic by investigating whether it is possible to estimate the impact of damages on the stability and reliability of a revetment using a model.
Within the study, first, damages are analyzed based upon a literature review. Next, data of old flume experiments with Basalton and basalt revetments are analyzed to study and quantify damages. This analysis focuses on the uplift of elements, deformation around the wave impact zone (S-profile), and washed-out joint filling. Then, a finite element model (FE-model) is created to simulate the wave impact on pattern-placed revetments. The main focus of the FE-model is to study the uncertainty due to structural changes, which are the damages. The damages quantified during the analysis of the flume experiments are also included in order to be able to assess damaged revetments. Finally, the study uses the FE-model within a sensitivity analysis to study the most important uncertain parameters. Based on the samples used in the sensitivity analysis, response surfaces are fitted to obtain a model that can predict the damage for any set of parameters. Finally, these models are demonstrated in a case study of a coastal dike near Den Helder. An increase of 10 – 100 times of the failure probability has been observed for small deformations, while for medium to large deformations, the failure probability increased by 1000 – 10000 times. For no joint filling or a missing element, the failure probability increased by 10 - 100 times.
This study showed that it is possible to create a finite element model that can estimate the impact damage has on the stability and reliability of a pattern-placed revetment. The obtained results can be used within the daily practise as part of risk-based maintenance as the study provides a way to obtain a first indication of the impact of missing elements, deformation, and washed-out joint filling. Additionally, the developed methodology can be used to obtain the impact of other types of damage. Although Basalton is the primarily investigated type of top layer, analysis of the flume experiments showed that basalt revetments are subject to identical types of damage. Therefore, it is expected that the findings within this study can be applied to a broader range of top layer elements with similar characteristics to Basalton (e.g. basalt, C-Star, and Hydroblocks).

The main focus of this thesis is the influence of different real boundary conditions on the failure mechanism of local buckling of steel tubular piles. The research was started with the theoretical method of describing boundary condition by specifying the degrees of freedom per boundary condition. The method makes use of the radial, meridional and rotational degrees of freedom. This method is also used in the current design code for steel shell structures, the NEN-EN 1993-1-6 \cite{NEN-EN_1993-1-6}. By varying the amount and types of constrained degrees of freedom, eight possible boundary conditions can be generated. Looking to the practical applications, a ninth variant with a non-homogeneous boundary completes a list of nine. From the nine boundary conditions, eight conditions are selected to be included in a FEM model study. The current design code describes only five of the nine conditions, what allows for a comparison of the known and unknown conditions with the prescribed rules. Two types of parameters that influence the local buckling failure mechanism are material and geometrical imperfections. In the study to geometrical imperfections, initial ovalisation, accidental eccentricity and dimples are considered. The effect on the design yield stress of the different imperfections is determined following the calculation methods described by the current design code. The calculated reduction of the design yield stress by specific boundary condition and an increasing imperfection is compared to results of ABAQUS FEM model tests. Residual stresses are investigated on the side of material imperfections. The used residual stresses are validated with a simple FEM ring model test that shows deformations due to the introduced residual stresses. The observed displacements could be compared with measured data of real experiments. A range of 36 different tubes is selected to investigate the influences of the eight different boundary conditions on the buckling failure behaviour. This test range covers a wide range of tubes with cross-section class 3 and 4 known for their sensitivity for local buckling. A base model is generated for all the 288 model tests, 36 tubes with all 8 boundary conditions per tube. The results from all tests are displayed in normalized moment-curvature diagrams. Because of a lack of test data of real experiments with boundary conditions involved, a validation with an analytical method is used that describes a linear and bi-linear part of the moment-curvature relation. Finally the results of the FEM model tests are analyzed per parameter but also the overall behaviour is discussed. From the model results could be concluded that residual stresses hardly influence the moment capacity but causes an increase in the curvature of most boundary condition. Geometrical imperfections cause a decreasing moment capacity and an increasing critical curvature whit an increasing imperfection. The trend of the influence of dimple imperfections is decreasing slightly faster compared to the trend observed from the code calculations. A safety of approximately 20\% is observed between the failure stresses of the test results and the design stresses from the code. With an increasing diameter over thickness (D/t) ratio or yield stress, the moment capacity decreases and the critical curvature increases. The relative influence of the D/t ratio within the tested range is larger compared to the yield stress. To investigate the influence of the different boundary conditions, the effect of all parameters is investigated per boundary condition. Following the test results, all boundary conditions except BC4F show the same influence on the maximum moment and corresponding curvature. Boundary condition BC4F shows a moment resistance reduction of 14\% and a critical curvature reduction of 26\% compared to the other conditions. Small observed differences in the post buckling behaviour between the other different boundary conditions are reported to complete this study.

Due to often existing subsea infrastructure or challenging seabed conditions, engineers are forced to design newnearshore pipeline trajectories that are not always in a straight line. Since subsea tie-in operations are often complex and relatively expensive, alternative methods like pulling pipelines into a curve are worthwhile. By means of this research fundamental knowledge of pipe pull operations into curved trajectories is acquired. This thesis research focuses on the soil - structure interaction between the sliding pipeline and the seabed. A more thorough understanding is obtained of the geotechnical processes that create lateral resistance of the pipeline against the forces applied by the installation vessel. The main goal behind this thesis is to expand the capabilities of pipeline installation by exploring the feasibility of curved pipe pull projects. The research is based on three fundamental elements: 1. An extensive theoretical study 2. A validated numerical soil-structure interaction model 3. A successful physical test campaign of thirty-two experiments The theoretical study of the thesis focuses on the physical processes that play a role during curved pipe pull operations. Research is conducted to gather knowledge of the three main subjects of research, being: 1. Structural behaviour of a concrete covered pipeline 2. Geotechnical behaviour of soil under lateral pipeline displacement 3. Geotechnical behaviour of soil under axial pipeline displacement Since this was the first known research into curved pipe pull operations, influences of dynamic environmental loads are excluded from the scope of research. The second stage of the research focused on creating an engineering model that enabled to predict to what extend partially embedded pipelines can be pulled into a curved trajectory on sandy seabeds. After considering multiple simpler structural models, the final result was a non-linear spring supported tensioned bending beam model. Within this computational prediction model: the lateral soil resistance is modeled by means of a P(Y) spring model, while the pipeline is represented by the tensioned bending beam. The applied lateral soil resistance model is computed based on researches ofWang et al. (2018) and Verley and Sotberg (1994). After themodel was completed, a purpose made test facility was created to pull scaled pipelines into a curved trajectory. During the test-campaign, five different model pipelines were tested on a scale range of 1/11.8 to 1/5.3. The physical test campaign provided valuable experimental data of thirty-two successful drained curved pipe pull tests. By means of the acquired set of experimental data the model was able to be validated. Since the model pipelines differed in diameter, specific weight and bending stiffness, the influence of those parameters is examined. From the fact that the majority of the model pipelines was pulled into a radius that was 0-30% lower than the computed radius,we can state that the numerical model predictions gives awell defined upper limit of the controlled pull radius of pipelines. Along the classified critical curved pulls, the imposed lateral force during the experimentswas within 20% of the maximum predicted force in 86% of the physical tests. From this observation we can conclude that the numerical model captures the maximum lateral pull force with a high accuracy.

The submerged floating tunnel (SFT), also known as the Archimedes bridge or suspended tunnel, is a conceptual idea for a tunnel that floats in the water, supported by its buoyancy. The tunnel would be placed underwater, not too deep in order to avoid high water pressures, but deep enough for it not to be exposed to extreme weather conditions or obstruct shipping traffic. The tunnel is kept in position with tethers that are anchored to the sea bed or floating pontoons at the water surface. This thesis focuses on the tether supported SFT. The dynamic response of a tether supported SFT, in a hydrodynamic environment, is different from the tunnels that are widely used nowadays. The SFT is always in contact with open water in which it is moving due to the hydrodynamic environment. The dynamic response of the tether supported SFT is still a gap in our engineering knowledge and this contributes to the fact that world-wide no tether supported SFT has ever been constructed. Many research has been performed in the last years. A broad range of models has been used to study the dynamic behavior of the tether supported SFT. The key in all these models is to capture the fluid structure interaction. Waves and current exert forces on the tunnel body but at the same time, the presence and motion of the tunnel body affects the wave-current environment. To model the dynamic response of a tethered SFT incorporating fluid-structure interaction, a new model has been developed. The dynamic SFT model describes the cross sectional motion and tether forces of a rectangular tubular tunnel which is pinned down by two inclined tethers, excluding longitudinal effects. The tunnel is forced by waves and current only. When assuming the SFT system to be linear, the motion of the SFT can be seen as a superposition of the motion of the tunnel body in still water and the forces on the restrained tunnel body in waves and current. The tunnel motion in still water is modelled with a dynamic module while the hydrodynamic forces on a restrained tunnel body are computed with a wave force module. The two independent modules are combined in a coupling module which makes it possible to describe the dynamic response of a tether supported SFT in a wave-current environment. The advantages of this model choice are the fast computational time and the convenience of physical interpretation. The wave force module computes the wave-current forces on the restrained tunnel body with a modified Morison formulation. This formulation is capable of computing, besides vertical and horizontal wave-current forces, the rotational wave force. Rotational wave forces are essential in the determination of tunnel roll motion and cannot be determined with the classical Morison theory. Just like the classical Morison theory, the modified Morison formulation does not take into account wave field deformation due to the presence of the tunnel structure. Therefore, for waves that are short compared with the dimensions of the SFT, diffraction effects cannot be taken into account. The absence of the diffraction effect is corrected for by integrating the dynamic pressures, water accelerations and water velocities with respect to the tunnel height and width. It should be noted that the applicability for short waves is only valid in case of structures that are submerged at a depth of at least 1.5-2 times the structure height. For shallowed submergence depths, the diffraction effects in combination with wave deformation become too large which cause prediction errors in the force determination. The force on the restrained SFT due to a uniform current can be modelled with the drag force expression from the classical Morison equation. To correct for the wave current interaction, the hydrodynamic mass coefficients are adapted as function of the Keulegan-Carpenter number. The dynamic module describes the oscillation of the SFT, in still water, with a dynamic system. A free floating tunnel has three degrees of freedom which are roll, sway and heave. This dynamic system assumes the tunnel is connected with two in-extensible tethers. Adding two rigid constrains to the free floating tunnel reduces the SFT to a single degree of freedom system. This single degree of freedom system describes a coupled translational (sway) and rotational (roll) motion around an instantaneous rotational point which can be found at the intersections of the tether axes. When assuming small vibrations, the instantaneous rotational point remains fixed at the intersection of the tether axes when the tunnel is at rest. The moment of inertia of the SFT is obtained by using the Lagrangian approach which is based on energy conservation. Because the structure is submerged in water, added damping and mass terms are used in the equation of motion. The magnitude of these damping and mass terms is calibrated with physical model experiments. The coupling module combines the wave force module and the dynamic module, which makes it possible to formulate a full equation of motion, describing the oscillation of the SFT in a wave current environment. From the equation of motion the sway and roll motions, containing accelerations, velocities and displacements, can be obtained. Apart from the motions, the tether forces can be predicted. The dynamic SFT model is validated with physical model experiments. With this dynamic SFT model, a parametric study has been performed. The first part of the parametric study focuses on the motion of the SFT. The second part examines the tether forces. Furthermore, the slack-taut transition and the safety against fatigue have been investigated. The parametric study does not take into account current. The most important findings and implications are in summary: • Each SFT configuration has a different response to the wave environment. Hence, every configuration has a different critical wave length for which the dynamic response is maximum. This critical wave length is independent of the wave height. It should be noted that the dynamic response is a comprehensive term which consists of many variables. These are; tether forces, sway motions and roll motions of which both motions contain accelerations, velocities and displacements. The most dominant parameters to influence the dynamic response are the buoyance to weight ratio (BWR), tether angle and submergence depth. • The BWR increases the stiffness of the dynamic SFT system which causes a decrease in the roll motions and sway displacement. Due to the stiffness increase, sway accelerations and velocities become larger. The natural frequency of the SFT is increased by increasing the BWR, which makes it more sensitive to shorter waves. • Configurations with large tether angles have the character to be very flexible and sway dominant, while configurations with small tether angles are stiffer and roll dominant. Tether forces for configurations with large tether angles are more sensitive to long waves, while tether forces for configurations with small tether angles are more sensitive to short waves. • A decrease in submergence depth increases all tunnel motions and tether forces, as the tunnel becomes more exposed to the wave environment. The dynamic response of the SFT becomes more sensitive to short waves. • An increase in anchorage depth results in larger tunnel motions. The increase in tether forces is negligible. • Placing the tether connection sideways of the tunnel body results in smaller roll motions and larger sway motions. Lowering the tether connection with respect to the tunnel bottom is favourable for all tunnel motions. The manner of how the tether connection is orientated, with respect to the tunnel body, has small influence on the tether forces. • Increasing the BWR, submergence depth or both reduces the risk of snapping lines and tether fatigue. Configurations with small tether angles have a smaller risk of having line snapping and tether fatigue compared to configurations with large tether angles. This study gives a supplement to the classical Morison theory. Morison’s theory is modified which makes it possible to compute rotational moments due to wave loading. Also the applicability to short waves is enlarged. A new dynamic schematization is developed which makes it possible to describe the dynamic response of a SFT as a single degree of freedom (SDOF) system. The advantages of this dynamic schematization are the fast computational time and the convenience of physical interpretation. The results obtained from this research study can be used as a preliminary design tool. In an early design stage, motions and tether forces can be predicted. Also measures to reduce these motions and tether forces can be investigated using the dynamic SFT model. Design graphs to estimate the snap-taut transition and for safety against tether fatigue are provided. It should be noted that this dynamic SFT model should not be used for detailed computations in later design stages.

The submerged floating crossing (SFC) considered in this study has demonstrated significant sustainability based on provided assumptions. the SFC has appeared to be a sheltered and sound idea appropriate to satisfy its expected capacities and to tackle given environmental conditions. The structure of the proposed SFC is intended to withstand all functional and environmental loads. The results of worst-case scenarios showed the base SFC design have a sufficient robustness to withstand the presumed significant loads. Some major uncertainties were faced throughout the study, which are manageable by means of modern technologies in civil engineering or some organizational arrangements.

In the Netherlands a large variety exists in the used widths of inland port entrances. In addition, multiple entrance layouts are applied. Currently, guidelines are missing for the design of inland port entrances along flowing waters with flow velocities larger than 0.5 m/s. A more generic insight into the minimum required nautical safe entrance width and most efficient entrance layout can reduce the design costs and time. The objective of this research was to find the minimum required nautical safe entrance width for generic situations for inland ports along flowing waters in non-tidal areas. To find this minimum safe entrance width, the most efficient entrance layout was determined. The influence of different design parameters was studied to provide the most efficient situation. Moreover, an insight into the influence of these parameters was needed to determine the effect on the most efficient situation when changing these parameters. A fast-time simulation study was chosen to analyse the influence of different design parameters on the entrance width. A rectangular entrance layout and a mathematical ship model comparable with a loaded CEMT class Va ship were used. Flow velocities between 1.0 and 2.5 m/s were taken into account. Moreover, the influence of the waterway width, entrance width, length and angle were analysed with the simulation study. The fast-time simulation program SHIPMA was used to perform the simulation study. As a result of the simulation study, it was found that the most efficient entrance angle is 120 degrees. Note that this is an entrance orientation in downstream direction. Also from a viewpoint of minimising siltation, this angle is more favourable than an angle of 90 degrees or smaller. The required entrance widths for arrivals sailing upstream and manoeuvring forward into the port are circa 55 and 80 meters, for flow velocities of respectively 1.0 and 2.5 m/s. For the determined most efficient layout, the forward manoeuvres into the port when sailing downstream were replaced by backward manoeuvres. For these backward manoeuvres the required entrance widths are circa 70 and 90 meters, for flow velocities of respectively 1.0 and 2.0 m/s. A linear relation was observed between the flow velocity and the required entrance width. For the most efficient entrance layout, it was found that the sensitivity of the entrance length, width and angle was small. These results are only valid for an available waterway width larger than 90 meters. For smaller waterway widths additional research is required. Furthermore, it should be mentioned that the limitations of the SHIPMA model also apply for the acquired research results. The most important limitation is that human interference was not included in this research. Besides, only a limited amount of design parameters was included in the simulation study. Additional research is required to study the influence of other design parameters on the required entrance width.