Large-diameter monopiles serve as foundations for offshore wind turbines (OWT), and the diameters are now up to 10 meters. These monopiles exhibit lower embedded length-to-diameter (L/D) ratios compared to the conventional monopile that is widely employed in offshore oil and gas platforms. They undergo rotation when subjected to lateral loading like rigid or semi-rigid bodies. This distinct geometry necessitates a different approach to describe the soil reaction that is induced when a lateral load is applied. Previous research introduced a 1D model incorporating four soil spring components to represent four aspects of soil reaction namely lateral soil reaction, distributed moment, base shear force, and base moment. However, questions have arisen regarding the contributions of base components, specifically the base shear force and base moment, to maintaining monopile stability. In response, a series of monotonic loading tests on monopiles in dry sand is conducted to assess the contributions of base shear force and base moment to monopile stability. Following this assessment of base components, parametric analyses are carried out to investigate the effect of pile diameter (D), the L/D ratio, load eccentricity (e), and sand relative density on monopile responses under cyclic and monotonic lateral loading. In this study, the SANISAND-MS material model is employed within 3D Finite Element (FE) software to model ratcheting during cyclic lateral loading. Finally, an investigation is conducted with the aim of constructing a 0D model to represent base shear force and base displacement responses under both monotonic and cyclic lateral loading.

With a fast growing world population, the lack of fresh water is one of the world’s biggest future concerns. Water stress can lead to conflicts, holds back economic growth and has a major impact on human health. Nowadays, more and more countries that lack fresh water sources are using the saline water from the oceans and desalinate it to produce fresh water. The most common way to do this is by the means of Reverse Osmosis (RO). However, one of the biggest negative aspects of desalination is its high energy consumption, mostly provided by fossil fuels. Therefore, a more sustainable solution using renewable energy sources to power a RO system is necessary. Delft Offshore Turbine (DOT) is currently developing a hydraulic drive train wind turbine that converts the aerodynamic power captured from the wind into hydraulic power. With a positive displacement pump, a high pressure water stream is created for centralised electricity production using a spear valve and a Pelton wheel. Using this hydraulic turbine for the purpose of fresh water production with RO can be a well fitted combination. Using wind as an energy source for desalination purposes, however, creates some major challenges, one of which is dealing with the inconsistency of wind. For varying wind speeds, a hydraulic wind turbine is controlled by regulating system pressure hence the pump torque with the spear valve. With a Seawater Reverse Osmosis (SWRO) system with ERD, it is researched how to regulate the flows and pressures for a stable operation. In this thesis, the combination of the hydraulic wind turbine with a Reverse Osmosis system with an Pressure Exchanger Energy Recovery Device (ERD) is being analysed in more detail. For this, a numerical model is used to determine the systems' behaviour and an experimental test setup is designed and constructed to validate the model results. The aim of this thesis is to compare the desalination system performance with a stand-alone system without an ERD, to determine the influence of varying ERD settings on the systems' pressure for potential system pressure and torque controllability, and to investigate how the RO system with an ERD affects the wind turbines stability. The analysis shows a large positive influence on the amount of produced permeate when using an ERD in the RO system. In addition, the power consumption of the RO process can be reduced by up to 80%. A varying input provided by the high pressure pump, for example as a results of varying wind speeds, does not seem to (negatively) affect the efficiency of permeate production. By varying the ERDs' rotational speed, the feed pressure at the membranes inlet hence the pressure at the high pressure pump can be slightly influenced. However, this limited influence is not enough to effectively affect and control the high pressure pumps' torque. On top of that, for the wind turbine to operate in a stable operating region, it seems that the use of an ERD affects the system in such a way that water production can only be realised at fairly high wind speeds. To optimally make use of the hydraulic wind turbine and operate at the highest possible aerodynamic efficiency, a combination of electricity production at low wind speeds and water production with an ERD when wind speeds are sufficient, can be interesting. For this, future research is required.

Part of the innovative character of Jumbo Maritime is a constant search into a more efficient operation of their heavy lift transport vessels. Areas of improvement involve optimizing port time. Currently Jumbo Maritime requires the onboard cranes to open the hold, decreasing effective use of the cranes. Furthermore an expensive load shifting system is needed when a piece of cargo heavier than 900 tonnes has to be loaded on front of aft of the ship, due to crane limitations. In this report a study is done into an integrated solution for both issues experienced by Jumbo Maritime. A system that is able to open the hold and to shift a load to front and aft of the vessel. First, specifications of the new system are defined, after which a literature study is done exploring the options currently available in the industry. After that, multiple concepts are generated, after which an integrated system is selected using a comparison method between concepts. The concept selected consists of a load shifting system using the hatches. Opening of the hold is accomplished by rolling the hatches to the aft where a stacking system is located. First the concept is dimensioned and further designed. The new design incorporates a new seafastening design of the hatches, one of the major challenges encountered in the assignment. The new design is evaluated in structural sense using the finite element analysis program ANSYS to prove its feasibility. After structural feasibility is proven, the design is tested to its functional requirements and implications on operations for Jumbo Maritime are considered. The new system could reduce the minimum opening time of the hold by a factor two and could save around half a million euros on skidding rental costs yearly. As the system is autonomous, the risks involved for humans decrease significantly, beneficial for Jumbo Maritime’s goal of zero Lost Time Injuries. Furthermore the impact on the stability of the vessel is minimal, so there is no impact on cargo loading operations. An economic analysis is conducted to see if it is attractive for Jumbo Maritime to convert the current system onboard of the J1800-class vessels. Considering conversion rates of €4/kg for the structural conversion costs, a total conversion time of 33 days, it is proven that it is beneficial for Jumbo Maritime to convert the current vessels, with an overall value investment ratio of 1.04 and the payback time being 5.3 years. Overall is concluded that a new integrated system for load shifting and hold opening is attractive to further investigate for Jumbo Maritime, both for their current vessels as well as new build vessels.

Throughout the offshore industry large structures installed on the seabed use mudmats as a foundation to provide in sufficient bearing capacity and stability. Due to their size, the mudmats have a significant influence on the hydrodynamic behaviour and installation requirements. It is proposed to change the design of the mudmats from a near solid design to a perforated structure in order to reduce the total loads. When describing the hydrodynamic behaviour of a structure in a body of water, two terms are of importance: the added mass and added damping. For solid flat plates there is much data available to compute the coefficients for models. However the coefficients are influenced by the degree of perforation and the presence of boundaries. Since there is little information available where the presence of a boundary is combined with a perforated structure, it is proposed to conduct experiments to elaborate on the hydrodynamic behaviour of a perforated structure close to an impermeable boundary. A total of six scale models were constructed with a perforation ranging from 0 up to 75%, these models were oscillated in the water with different amplitudes, from 10 mm up to 160 mm. These oscillations were performed at different frequencies, from 0.2 Hz to 2 Hz. These tests were performed in still water and subjected to a uniform current of 5 mm/s and a current of 20 mm/s. All data obtained with these experiments was collected and analysed. The first conclusion drawn from the analysis of the experimental data is that both the added mass as the damping decrease with an increasing perforation. The added damping is found to be larger for high excitation frequencies, however the difference decreases for increasing perforation ratios. The added mass is smaller for high frequencies, but this relative difference does not decrease for larger perforation ratios. Where the damping is not significantly affected by the presence of a current, it is observed that the added mass decreases when a current is present and this effect is larger for lower perforation. The added damping shows linear behaviour when plotted against the amplitude of oscillation, except for experiments where the smallest amplitudes are tested in combination with a low excitation frequency. For the latter experiments a more quadratic behaviour of the damping is observed. The majority of the energy is found at the excitation frequency. For the added damping it is noticed that similar trends are distinguished for the first order and third order, the energy at three times the excitation frequency. At two times the excitation frequency there is only little energy found for the added damping. For the added mass there is no significant trend observed when comparing the first, second and third order energy at the load signal against the perforation. It is however found that there is a similar trend in the dependency of the added mass on the excitation frequency in both the second and third order, although the energy is decreasing for higher orders.

Offshore pipelines represent major items in the oil and gas industry nowadays. These submarine pipelines are usually covered with backfill for protection and a well-known method for this is sand backfilling with a trailing suction hopper dredger (TSHD). Although pipeline installation with a TSHD is a developed technique, there are still some challenges regarding uplift movements of the pipeline during the backfill procedure. This action is called pipeline flotation, which is a frequently occurring problem during the sand backfilling process and the costs for repair measures afterwards are very expensive. Accurate modelling of the sand backfilling process over a pipeline can lead to significant cost reductions by optimising the sand backfilling technique. Pipeline flotation is induced by the development of upward buoyancy forces from the sand-water mixture on the pipeline. If the weight of the pipeline is not sufficient enough, it will experience uplift movements during the backfilling process. The purpose of this research is to develop a better understanding of the mechanism of pipeline flotation. Due to a lack of available field data, it is anticipated that a set of laboratory experiments will provide a better insight into the parameters involved in pipeline flotation during sand backfilling. This research builds on the study Yang (2020), in which a small-scale set-up and 2D calculation model are designed to perform experiments concerning pipeline flotation during sand backfilling. A total amount of 50 experiments is performed with Geba Weiss sand in four different stages: with horizontal discharge, vertically upward discharge, elevated initial pipe positions and increased pipe specific weights. The set of experiments have provided better insight into physical processes that influence pipeline flotation during sand backfilling. The discharge of the sand-water mixture is dominated by its sedimentation and dispersion, so the model is based on empirical equations and the sedimentation theory. The main conclusion regarding the static force balance on the pipe is that the degree of pipe embedment influences the magnitude of an additional frictional force working downwards on the pipe body. A new approach for assessing this frictional downward force, due to the presence of sand that has deposited, is described and added to the model. In the small-scale experiments, this influence plays a significant role in pipe flotation triggering. An undesirable result from the small-scale experiments are the additional hydrodynamic effects from the fluid in the experimental tank, which are induced by the geometrical constraints. A pipe flotation limit was found in the parameter of sand volume concentration in the surroundings of the pipe. This flotation limit was defined at a domain concentration of approximately 7.5% for the experiments with a pipe specific gravity of 1.03. The boundary of flotation for heavier pipes was not achieved in this research, but evidence points towards a significantly higher flotation limit. The discharge flow rate and the total discharged sand volume are the key factors for development of domain concentration in the small-scale experiments. With the acquired data as a strong foundation, additional research regarding pipe flotation during sand backfilling is recommended. As there is still a strong variation in several important input parameters in the small-scale experiments, a Computational Fluid Dynamics (CFD) analysis is suggested to relate the domain concentration to the input parameters at every moment in time. Additional 3D experiments on a larger scale are also recommended to optimise the sand backfilling process and validate the CFD analysis. From this analysis, a prediction can be made regarding the boundary of pipeline flotation on the seabed when discharging with a TSHD. Moreover, additional research regarding the stress and drainage conditions underneath the pipe is proposed to validate the cause and accuracy of the relatively high friction coefficients. Finally, a model could be built to examine the friction force generated on the pipe due to its embedment. With this method, the suggested approach of the frictional resistance due to pipe embedment could be further analysed.

Loose, sandy slopes situated or deposited under water may be susceptible to liquefaction-induced failure. In contrast to 'regular' localised slope failures, flow slides are diffuse, large-scale and potentially disastrous. Earthquake-induced ground vibrations currently dominate the liquefaction engineering scene. In reality, however, many liquefaction failures may be attributed to non-seismic sources of cyclic shear loading, albeit often in less dramatic context. Pile or sheet pile installation form an example. The construction of a new sea lock in IJmuiden brings this issue to the forefront and initiates a series of pile installation tests, conducted in several sandy deposits. The results of these tests are analysed and reveal (1) some key differences with seismic sources of vibration; (2) the importance of the duration and frequency of driving in residual excess pore water pressure (EPP) generation; and (3) the magnitude of spatial and temporal scales on which vibrations and EPPs generally act. The observations from the tests also form the basis for the establishment of a cyclic liquefaction model which simulates vibratory pile driving-induced EPP development. The model is validated using data from the IJmuiden pile installation tests. The cyclic liquefaction model is combined with a constitutive modelling approach for flow, or static, liquefaction behaviour. This enables the creation of a comprehensive strength framework, which allows representative strength parameters, based on the onset of flow liquefaction, to be derived for use in slope stability analyses. This strength framework is rooted in critical state soil mechanics and the related state parameter. A slope stability analysis procedure is advocated in which priority is given to pre-pile installation liquefaction analysis. Given a satisfactorily stable slope, pile installation effects are incorporated, where EPP generation and migration of pore water are considered the dominant contributors to failure. The procedure is applied to a fictional reference slope, where results show significant reduction in safety against global failure during driving. Considering three-dimensional drainage effects, however, suggests that pile installation may only have a minor effect on slope stability, depending on the failure mechanism and volume under examination. From the example stability analysis, some recommendations are made with regard to prevention and mitigation of piling-induced slope failures. Finally, in terms of further study, it must be noted that several major simplifications and assumptions underlie the cyclic liquefaction model and the corresponding method for slope stability analysis, which may be improved upon with more rigorous constitutive modelling and numerical analysis.

Seismic design codes are currently moving from a force-based design approach to a performance-based design approach. For example, in a performance-based design approach it could be specified how many lanes must be available during the lifetime of a bridge given a certain earthquake intensity.The problem with this approach is that it is not specified what the probability must be that the performance criterion is satisfied. This raises the question whether the design codes are acceptably safe or not. Focus is laid on the Canadian Highway Bridge Design Code (CHBDC), in which a total resistance factor approach is used. Because the total resistance factor in the CHBDC is a multiplicative factor, lower resistance factors lead to stronger foundation designs. The goal of this thesis is to calibrate the design procedure in the CHBDC for geotechnical systems under seismic loading, by finding a relationship between resistance factors and the lifetime probabilities of failure of said systems. The resistance factor can then be fine-tuned to a lifetime probability of failure that is consistent with the lifetime probability of failure targeted in static design. As an example problem, the bearing capacity of a shallow foundation on a clay with a pseudo-dynamic earthquake load is tested. The research question that is answered in this thesis is: "What should the resistance factors for geotechnical seismic design be in order to achieve a target lifetime probability of failure that is consistent with static design targets?'' Not every possible combination of soil strengths and forces on the superstructure can be taken into account, and therefore the random finite element method is used in a Monte Carlo simulation. Thousands of realization sare performed for each resistance factor, design return period, and "actual''return period that the designed foundations are tested against. By seeing how many realizations of the Monte Carlo simulation fail given a certain earthquake intensity, the conditional probability of failure given that earthquake intensity can be estimated. The total lifetime probability of failure can then be estimated from the conditional probabilities of failure with the total probability theorem. As part of a parametric study, the lifetime probabilities of failure are estimated for six different scenarios, each of which has different sources of uncertainty.  The resulting lifetime probabilities of failure are interpolated in order to find a resistance factor that targets a lifetime probability of failure consistent with static design targets. Currently, the resistance factor that the CHBDC recommends for geotechnical systems under seismic loading are defined as the static resistance factor for that geotechnical system incremented with 0.20, meaning that compared to static design, weaker foundations are designed for seismic load cases. The resistance factor found in this thesis is closer to the resistance factor for static design than to the resistance factor for seismic design. It should therefore be considered to lower the seismic resistance factor to the value of the static resistance factor so that a sufficient lifetime reliability can be targeted.

The development in harvesting trend of wind energy is evidenced as a result of the Paris convention. Therefore, future wind turbines tend to move towards deeper water, which sets a requirement of larger capacity support structure. The design guidelines of Gravity Based Foundation (GBF) which is capable of supporting deeper water wind turbines lack attention on the cyclic response of the foundation. The undrained capacity of GBF in terms of failure envelope under combined loading is investigated numerically, in order to shed light on the effect of cyclic loads on the capacity of the foundation. A GBF supporting a 5 MW wind turbine on sandy soil domain is designed based on the static conditions. A critical state model called Hypoplastic sand model with intergranular strain concept is adopted to represent the soil domain in 2D. The influence of factors such as relative density (Dr), load characteristics (¿c yc & ¿avg ) and the wave frequency on the pore pressure behaviour are analysed in the event of concluding a critical case. Moreover, it should be noted that the number of cycle is restricted to 50 cycles as a result of limitations in the implicit method. An undrained failure envelope is developed for the critical case, which in comparison with original envelope reveals the expansion in undrained capacity with respect to the number of cycles. It is inferred that the expansion in the capacity is because of the process known as densification which overcomes the effect of pore pressure on the failure envelope. It is also worth noting that the consolidation phase which is used to model the loads has a significant influence on the expansion of the failure envelope.

The starting point of this thesis lies in the area on Groningen, Netherlands. More specifically, induced earthquake activity is observed in this area due to gas extraction activities, which reduce underground gas pressure. In combination with the location’s geomorphology, liquefaction can occur due to earthquake excitations. Furthermore, the area of Groningen is a location with urban activity and infrastructure, such as pipelines, present. The post-liquefaction effect of these pipelines is their uplift, which can lead to failure, along with all its negative consequences. Furthermore, the creation of two different models, capable of describing the soil-structure interaction of pipelines and post-liquefied soil was the main objective of this thesis. The means by which these models were created was the implementation of the spring and dashpot method. More specifically, Kelvin-Voigt models were used for the ground’s behaviour to be modelled. These models required two main parameters to be specified in each case, the spring coefficient (k) and the dashpot coefficient (c). In order for the spring coefficient to be determined, the creation and usage of post-liquefaction p-y curves was deemed necessary while the problem specific dashpot coefficients used, had previously been determined by means of physical modelling. The ground profile consisted of fully saturated loose sand and the pipes investigated had diameters of 110, 160 and 200mm. The first model was a single degree of freedom one, with that being the vertical. As for the second one, it was a multi degree of freedom one. More specifically, it consisted on two degrees of freedom, the vertical and horizontal ones. The results of these models were validated by comparison to previous studies and further investigation of affecting parameters was carried out. More specifically, the way and the degree up to which several parameters of both ground and structure characteristics affect their interaction were investigated. More specifically, the first parameters considered were the pipelines’ diameter as well as their weight, resulting from their geometry and transported material. Next, the effect of the pipelines’ burial depth was considered and then, the effect of the soil’s initial stiffness. Finally, the effect of the dashpot coefficient was investigated for the multi degree of freedom models. A comparison between single and multi-degree of freedom solution results was also carried out. The results of this study were validated by comparison to previous research findings. Most results and conclusions were in complete agreement with the so far existing bibliography. However, what was found to be inaccurate was the previously determined dashpot coefficient for 110mm diameter pipelines and hence, these were left out of scope of study.

Monopiles with large diameter (larger than 6 m) and low aspect ratio (less than 6) are increasingly used in offshore wind farms. These foundations demonstrate a rigid response under lateral loading. The validity of the existing design methods, that are based on small diameter flexible piles, has been questioned by both the industry and researchers. In addition, the monopiles are subjected to both lateral and vertical loads. The influence of vertical load on the lateral design of short rigid monopiles in clay soil is not clear. This study aims to perform a comprehensive study on the influence of vertical load on the lateral response of monopile foundations in clay soil. All analysis in this study was performed using 3D finite element modeling in PLAXIS 3D software. The NGI-ADP constitutive model was adopted to simulate the nonlinear mechanical behaviour of clay. Considered in the analysis is a short rigid pile with a diameter of 10 m (L/D = 3) and a long flexible pile with a diameter of 2 m (L/D = 15). The analyzed clay soil profiles consist of a normally consolidated clay soil and an overconsolidated clay soil with a constant undrained shear strength profile equal to 30 kPa. For each pile in each type of clay soil, a pure lateral loading scenario is performed first to assess the validity of current design methods. Subsequently, a combined loading scenario is performed to assess the influence of vertical loading on the lateral behaviour of rigid monopile in clay soil. Results of the pure lateral loading scenario suggest that current design methods heavily underestimate the lateral capacity of rigid monopile foundations in both clay soil profiles analyzed. According to the findings of this study, it can be concluded that current design methods are not fit to provide an accurate assessment regarding the lateral load response of rigid monopile in clay soil. In order to correctly assess the lateral load response of rigid monopile in clay soil, a method consisting of a 3D finite element model akin to the model used in the research or a PISA design model is advised. A potential third design method, the 1D rotational spring model, is also proposed. Results of the combined loading scenario suggest that the presence of vertical loading causes a decrease in lateral and moment capacity of the rigid pile in both clay soil profiles analyzed. However, the influence is negligible when the vertical load magnitude is smaller than 50% of its bearing capacity. To quantify the influence of vertical load on a monopile foundation, a series of load analysis were performed on a real offshore wind turbine with a 5MW power capacity. It was found that the vertical load on a typical monopile foundation in clay is around 27% of its bearing capacity. According to the findings of this study, it can be concluded that the influence of vertical load on the lateral response of rigid monopiles in clay soil is limited and can be ignored in foundation design.

As a result of population growth and economical prosperity, energy consumption has been on the rise for decades. Present-day projections predict the continuation of this trend with the rapid industrialization of former second world countries. Together with the rise of energy demand, incentives fo the scientific community to quantify the environmental impact of the ever increasing need for energy have gained momentum. It now is clear that continued use of carbon-based energy sources will have a catastrophic, irreversible impact on the global climate. The urgency of this message, which is supported by nearly the entire scientific community, was finally heard in 2012 when the Paris Agreement was drafted. Nearly collectively, the world’s countries are committing themselves to start the transition to durable sources of energy. One of the most promising sources of energy to facilitate the aforementioned transition, is the wind. Europe specifically is home to large patches of sea, which are ideally suited for the construction of offshore wind farms. Due to high construction costs, these endeavors out at sea were, until recently, heavily dependent of governmental support. However, due to advances in technology, wind frams have become profitable enough to be realized without governmental grands. Of the current offshore wind farms, the majority of the budget is allocated to the foundation design, construction and ultimately installation. Monopiles are convincingly the most common foundation type found. Although alternatives under development, it is unlikely for the popularity of this simplistic foundation will diminish in the near future. Especially, as the hollow, large diameter, hollow, steel profiles are finding their way into other foundations types, in example tripods. The installation of the monopiles offshore is mostly done through costly operations involving large hydraulic hammers. Prior to installation, drivability analyses are commissioned which determine the required hammer capacity. The rather simplistic software (in terms of soil representation) used to conduct these calculations, offers limited room for the optimization of the installation process. On the other hand, several full scale experiments have demonstrated that clever manipulation of driving parameters, specifically: (I) hammer weight; (II) driving frequency; (III) falling height/impact velocity; can significantly benefit installation times. This leaves a huge potential for cost savings (several millions EUR) per farm and forms a prime opportunity to stimulate the transition of offshore wind energy towards the mainstream. However, no consensus has been reached on the dynamic processes which positively contribute to the drivability of monopiles, let alone how these processes can be consciously induced in the subsoil. This research sets out to, by means of a parametric experimental study in the centrifuge, evaluate the effects of changes in driving parameters on driving time. Three hypothesis has have been drafted in an attempt to explain the higher efficiency piling operations employing HiLO (high frequency, low falling height) techniques instead of conventional driving, namely: (I) aggravated friction fatigue along the shaft due to an increased number of load cycles as a result of frequency increase; (II) Less dynamic soil resistance following from lower impact velocities, yielding the more efficient usage of available piling energy; (III) accumulation of excess pore water pressures, which reduce the effective stress regime surrounding the pile and thereby benefit piling rates. Through 24 centrifuge experiments, the aforementioned hypotheses are evaluated. During the experiments the effect of changes in driving parameters in monitored. Moreover, water pressure sensors mounted both on the pile shaft and inside the surrounding soil body record the soil response during driving. Results indicate that the dynamic installation of open-ended tubular piles in sandy soil, characterized by a high Rd (¼80%), is associated with the development of excess pore water pressures at larger radial distances from the pile due propagation of seismic waves. However, unlike similar experiments of samples with a lower Rd , the generated excess pore fluid pressures are limited in their magnitude as the soil exhibits no contraction to aid further generation. Moreover, closer to the pile, a transition towards a dilative soil regime is observed, where the increase of driving frequency is arguably related to the accumulation of tensile pore fluid pressures along the shaft, which negatively affects pile drivability. Results indicate the aforementioned adverse effect is partially compensated through the use of a heavy hammer due to subtle difference in soil-structure interaction related to the different geometry of the hammer. Consequently, it seems that HiLo driving is not a technique which guarantees better drivability under all circumstances. Hence, in the quest for optimum drivability, the prevailing soil conditions should play a decisive role in the selection of the best suited pile-hammer combination and driving technique.

Offshore pipelines are considered the arteries of the offshore oil and gas industry and transport hydrocarbon products as well as other fluids. During the installation process of an offshore pipeline, the pipeline is most often located in a trench and covered with backfill material. The burial of the pipeline ensures onbottom stability as well as mechanical protection. With a Trailer Suction Hopper Dredger (TSHD) sand can be deposited in the trench, thereby covering the pipeline in a relatively controlled manner. One major risks associated with this backfilling method is the risk of vertical upward displacement of the pipeline during the backfilling process. The vertical upward movement of the pipe is referred to as pipeline flotation and may result in unprotected or damaged pipes. With the rising use of small diameter and lighter pipelines this risk has become more prevalent. Pipeline flotation is induced by augmented buoyancy which originates from the presence of the water-sand mixture around the pipeline. The particle concentration of the water-sand mixture and the embedment rate of the pipe are leading in the assessment of the buoyancy force acting on the pipeline. The weight of the pipeline is the major force counteracting buoyancy force. In addition, a friction force, resulting from the contact between the pipe and the new formed sand layer around the pipe, counteracts the buoyancy force. The aim of this research is to develop and validate a simplified numerical model for the analysis of offshore pipeline flotation during sand backfilling with a TSHD. The numerical model has been validated against the small-scale physical experiments of Eikhout (2021). The small-scale physical experiments have been developed and used by Yang (2020) and Eikhout (2021) to simulate a simplified sand backfilling process. The numerical model is developed to simulate the sedimentation process and has been developed in the finite element software COMSOL Multiphysics. The model is capable of effectively simulating the simplified backfilling process from the small-scale experiments by Eikhout (2021). Moreover, the sedimentation model is able to simulate the inflow of material over time in the physical domain. The sedimentation process has been modelled with a convection equation in which the settling velocity of the water-sand mixture is described with the hindered settling formulation proposed by Metha (1986). The hindered settling formulation describes the velocity of the suspension as a function of its local particle concentration. The numerical data has been processed and used in a force balance which is able to predict the occurrence or absence of pipeline flotation. The parameters in the hindered settling formulation as well as the numerical settings have been described from a theoretical perspective as well as their practical impact on the numerical solution. After validation against the small-scale physical experiments the numerical model has been used to simulate a more practical scenario. In addition a simplified, spreadsheet friendly, calculation method is proposed.

The current Dutch norms for the macro-stability of ood protection embankments and more specifically the determination of SHANSEP parameters has been subject of debate since its implementation in 2017. The main concerns arise from the apparent over-conservative nature of the guidelines and the apparent underestimation of shear strength of organic and silty clays. In this Master thesis, an assessment of the normalised normally consolidated undrained shear strength is performed for a dike stability reinforcement project between Gorinchem and Waardenburg in the South west of the Netherlands on a problematic clay layer called the `Gorinchem Clay' throughout this thesis. The main goal is the conrmation of the current norms or towards a more optimised and less conservative assessment of the strength parameters and in doing so, discusses one of the most recurrent questions in geotechnical engineering: do some of the measurements from laboratory tests reveal true material behaviour or do the limitations of such laboratory tests produce this particular behaviour? This analysis was performed on Triaxial Compression, Direct Simple Shear and Triaxial Extension tests from which the SHANSEP parameters are derived as input for the available shear strength along a slip surface according to the methodology developed by Ladd (1991) and following the Critical State Soil Mechanics. The structure of this thesis is as follows: rst, a literature study is performed on the strength parameters assessment in chapter 1, the principles of the Critical State Soil Mechanics and the diculties encountered in the determination of the strength parameters from laboratory tests in chapter 2. The laboratory results are then exploited in chapters 4 to 5 according to the current guidelines and more extended methods in which the limitations of the Classical Critical State Soil Mechanics are shown. The next chapters focus on a more fundamental understanding of the considered material consisting of modelling the material behaviour in chapter 6 using a simplied academic constitutive model featuring non-associative elasto-plasticity with mixed volumetric and deviatoric hardening allowing for hardening or softening. The outcomes of this thesis show Critical State conditions as traditionally understood could not be reached reliably for undrained conditions in Triaxial Compression, Triaxial Extension and Direct Simple Shear. The tests showed to be particularly unreliable beyond 10% axial strain in Triaxial Compression and Extension, and beyond 15% shear strain in Direct Simple Shear. The diculties encountered in determining the Critical State friction angle and undrained shear strength were shown to be minimised by performing drained and undrained Triaxial compression tests on slightly over-consolidated soil samples. Additionally, the limitations of the Classical Critical State theory were highlighted and a more advanced constitutive model including a non-associative ow rule and deviatoric hardening was successfully used to predict the behaviour in Triaxial Compression for undrained conditions. The predictions for drained conditions and particularly undrained Triaxial Extension were however limited.

With a rapidly growing population and subsequent technological developments, an increase in demand of rare-earth metals evolves. Land-based deposits seem to be insufficient and shortage impends within the coming decades. Mineral resources from the deep ocean are considered as a possible complement. These minerals occur in various forms. One of these forms is lying on the subsea sediment of the deep ocean; polymetallic nodules. The nodules can be best described as potato shaped objects containing amounts of rare earth minerals like copper, nickel and cobalt. The economic feasibility depends on nodule abundance per square meter. An exploitation region with high prospectiveness in terms of economic feasibility is the Clarion-Clipperton Zone, a region in the centre of the Pacific Ocean. As deep-sea mining implies, the mining site is located at a water depth of approximately 4000m. Characteristics such as these automatically result into challenging conditions. Exploitation of the nodules includes subsea harvesting and vertical transportation towards the sea surface. Activities which are within the scope of Boskalis, appealing their know-how and experience in dredging and marine operations. Currently, most developments are focused on vertical transport by means of hydraulic lifting through a riser. In order to avoid challenges such as flow assurance, riser handling and efficiency, Boskalis proposes an alternative solution; mechanical lifting. Mechanical lifting can be considered as a newcomer in the relative early field of deep-sea mining. However, experience can be gathered from successive deep-sea lowering operations in the oil and gas industry. The objective of this thesis is to investigate the static configuration and dynamic response of the proposed mining system during operation, identify potential showstoppers and in the end asses whether deep-sea mining by mechanical lifting is technical feasible. When simplified, it is merely a matter of collection of nodules in transportation skips and hoisting of these skips towards the sea surface. Nevertheless, within this simple procedure various challenges arise. Therefore a start is made with a proper description of the proposed production method and identification of potential hazards and showstoppers. In complementing the initial research, the project site has been studied in terms of sea floor characteristics and metocean data. These obtained results served as input in further analysis. For example a sheared current is present, influencing the geometry of the hoisting wires. The sheared current phenomenom has been studied in which a quasi-static analysis is performed. The analysis has been carried out by discretization of the hoisting wires in a number of elements with a payload attached at the tip acting as a sinker. Here it became clear that for the applied hoisting setup, the influence of the local current is minimal and the influence of a forward vessel motion significant. When acting in an offshore environment, the vessel motions might affect the deep-sea mining operation as a result of the connection with the nodule collector. Preliminary to a dynamic analysis, typical vessel motions are determined. This is done by selection of an appropriate mining vessel and implementation of a characteristic sea state using a Pierson-Moskowitz spectrum. Vessel motions are calculated with the software package Seaway, resulting in an output in the frequency domain. The suspended hoisting wires are still numerically modelled by a discretization method. Axial analysis for the applied hoisting setup shows significant magnification of the response of the attached payload at full depth (4000m). This hurdle should be overcome by applying heave compensation, which has become a commonplace in this type of marine operations. Transversal motions for the applied setup are expected to be minimal as a result of the submerged state. Conclusively, within this research first insight in technical feasibility is gained, but as a matter of fact yield further valuable questions along the lines of deep-sea technology. Therefore, we can conclude that deep-sea mining by means of mechanical lifting is feasible, but still offers numerous interesting topics in future research exceeding the current standards.

In this master thesis the behaviour of a high speed railway track constructed on top of a pile foundation with settlements under a dynamic load has been analysed. Therefore, a model was developed in the software program DARTS, dynamic analysis of rail track structures. In DARTS the railway track was modelled by stiff and elastic layers, which were loaded by a moving train load. The train was modelled as a mass spring system. The results of DARTS were analysed and validated with field measurements of the HSL. After the validation of the model multiple simulations were performed to analyse the structure for different uncertainties and possible solutions. These simulations showed that the model in DARTS is sensitive for changes of the pile stiffness. The results also show that it is difficult to model permanent displacements in DARTS.

The numerical modelling of a cone penetration test (CPT) has long been a challenging task due to the large deformations associated with the penetration of a CPT. Recent developments in advanced numerical methods have shown promising results in overcoming these difficulties by using the Material Point Method (MPM). In this thesis it is researched whether the MPM is able to reliably produce CPT results in dry sand by using a state-dependent constitutive model. Calibration chamber (CC) tests are modelled for dry sand and results are compared with experimentally performed CC tests in the laboratory. Features regarding the numerical setup and applied boundary conditions which quantitatively influence modelling results are identified and assessed before the model is validated to real CC test data. Validation results show that the model is able to accurately produce cone resistance values for different types of sand for soil states that can be categorised as moderately-dense to dense. Last, it is shown how parameters within the constitutive framework affect the model output and a quantification of the sensitivity of the parameters to model results is presented.

Ground improvement in the form of soil compaction plays a important part in reclamation projects. The development of the Cofra Roller Compaction (CRC), a non-circular impact roller, has proven to be valuable in these projects. However, the heterogeneity of the subsoil causes locally a non-uniform degree of compaction. Traditional compaction control tests are limited in measuring depth, expensive and cause time delay. Therefore, the Continuous Compaction Control (CCC) and Continuous Impact Response (CIR)method were developed in order to provide more real-time information of the compaction based on the response of the drum of the roller. The aim of this study is to develop a semi-empirical energy model which is based on the contact forces of the roller-soil interface as most CCC systems, but also uses field test data as was given in the CIR system to validate this model. The relevant parameters needed for this model were obtained from the field test conducted for the HES Hartel Tank Terminal project in Rotterdam. These included the impact acceleration, the cone resistance, the in situ density, the dynamic modulus and the dynamic plate load test velocity. Two methods are considered in this thesis and both aim to reproduce the measured values from the dynamic plate load test during the field test. The first method considers the acceleration signals and includes double numerical integration of these signals to obtain the displacement, while the other considers modelling the roller as a dynamic plate load test and obtaining the displacement from solving a 2-DOF spring-mass-damper system. However, after analysis of the motion of the roller, it was observed that due to the non-circular shape of the roller, a wedge effect was created where horizontal shearing forces caused loosening of the soil. This inhibited soil compaction up to 0.5 m depth. The impact acceleration signals were thus not representative of the soil compaction. Nonetheless, the DPL-Soil model was proven to be successful in correlating the soil settlement to the dynamic modulus. This study considers a silty sand, so further research should be carried out to obtain correlations for various soils. In order to develop the semi-empirical energy model, it is thus recommended to capture an accurate acceleration response. This can be done by placing accelerometers at a minimum depth of 0.5 m, replacing the 8G accelerometer with e.g. 16G accelerometer and increasing the sampling rate to at least 1000 Hz. In order to filter out the soil variability, a field test with the roller should be performed on a homogeneous sand without fines. Correlations can then be drawn again for the same field tests performed in this thesis. Finite Element Modelling (FEM) could be used to model the interaction between the non-circular shape of the lobe, the rolling motion and the soil. This might form a better correction method for the acceleration signals than those explained in this thesis. Low frequency geophones can be used to measure the velocity directly. This because low frequency data of the accelerometer should be removed and the roller works on a low frequency. The load imparted to the ground could also be measured directly by burying earth pressure cells at a minimum depth of 0.5m and at various depths to get a more accurate representation of the pressure distribution through the soil layers. By using other numerical integration methods such as Simpson’s 3/8 rule and Boole’s rule, the numerical accuracy of the displacement response of the roller could also be improved.

To meet the demand for renewable energy sources, large numbers of offshore windfarms are planned to be constructed in the near future. The majority of the foundations for these offshore wind turbines are large-diameter monopiles. The driving of monopiles into the seabed is conventionally done using a hydraulic hammer, this process is commonly known as piling. Piling causes high noise levels that are damaging to marine life, for example it is known to cause permanent hearing loss to marine mammals. Also smaller fish are known to be affected by this noise. Piling additionally causes fatigue damage to the pile during the installation process requiring over dimensioned monopile foundations. A potential solution to these problems is currently being developed by GBM Works; To install a monopile foundation, a set of vibrating elements is installed at the bottom of the monopile that reduce the resistance of the soil at the tip of the pile. Water is injected upwards on both sides of the pile wall to lubricate the pile-soil interface. In this way, the resistance of the soil is temporarily reduced to such an extent that the monopile foundation penetrates the soil to target depth under its own weight, thereby greatly reducing noise levels and fatigue damage. To determine the feasibility of this installation method, an experimental study has been performed, where a prototype of one oscillating element was constructed and attached to a steel pile. Tests with this prototype were performed at the Maasvlakte, where very dense sand is found with cone resistance values of up to 30 MPa in the test depth range. Multiple experiments were conducted in which the amplitude and frequency of the vibrations were varied. Tests were done for a large range of variables in attempt to optimize the penetration speed. Additionally, based on the test results, a semi-empirical model was built to predict the installation speed of the prototype pile and to identify the influence of the different variables. The experiments show that it is possible to penetrate the prototype pile to its full penetration of 4.5 meters into the soil. Depending on the properties of the applied oscillations and soil conditions, the penetration rates are found between 1 and 5 cm/s. To determine the feasibility of reaching penetration depths that are similar to those of offshore foundation piles, i.e. 30 to 40 meters with larger diameter monopiles, additional experiments are required .The noise levels during the experiments were significantly lower than the noise levels for conventional piling. However, as sound in air propagates differently than in an underwater environment underwater measurements are required to further assess the noise levels of this new installation method for monopile foundations.

The growing interest in the development of offshore wind farms in seismic active areas demands a better insight into the requirements earthquakes impose on the design of wind turbine foundations. The complexity of the soil-structure interaction (SSI) during an earthquake results in large uncertainties in the design process of a monopile foundation. The design codes do not provide a structured framework on how to deal with these uncertainties. On top of this, the design codes are for (offshore) structures in general and do not specify for the large diameter tubulars which are characteristic for the offshore wind energy sector. This thesis presents the investigation into a 1D seismic Winkler foundation that is able to represent the SSI during an earthquake. The model, a beam on nonlinear Winkler foundation (BNWF) coupled with a nonlinear ground response model, is a fast method to determine the structural response for the stochastic seismic and offshore wind load cases. Semi-empirical formulations are used to implement cyclic loading effects into the model. A 3D finite element model of an embedded monopile is developed in parallel with the seismic Winkler foundation for tuning and validation purposes. The resistance of the soil to lateral pile deflections is further investigated to address the uncertainty in the SSI. A 2D horizontal cross-section of the embedded monopile is considered to determine the linear dynamic properties (impedance) of the soil, and a plane strain finite element model is developed to investigate the effect of nonlinear soil behaviour. A combined frequency-time domain extension for the Winkler foundation is developed to incorporate the obtained frequency-dependent foundation properties into a time-domain analysis. It was found that none of the 2D analyses resulted in SSI representation that could be directly applied in a time-domain analysis. Moreover, the large D/L ratio of a monopile activates a global soil response, making an uncoupled 2D analysis inaccurate for the frequency range of interest.

This thesis project has set out to investigate the response in fore-aft direction of a monopile wind foundation supporting an NREL 5MW turbine, offshore the coast of Taiwan, which is affected by weak to strong earthquake ground motion in combination with normal sea state conditions. The soil at the location of the monopile is layered, with sand overlying clay, mud-, sandstone and gravel. Liquefaction, although of great concern in seismic design of piled structures, is not investigated. Two soil-structure interaction models’ responses are compared in this study, one denoted as an elastic and one as an inelastic beam on a nonlinear Winkler spring foundation. The goal of using two different soil definitions was threefold: 1. quantify the effect of inelastic soil-structure behavior on the system’s response, by comparing a nonlinear elastic SSI model with a nonlinear inelastic series hysteretic-viscous damping SSI model, 2. analyze the earthquake intensity level at which nonlinear inelastic effects become dominant, 3. verify whether the elastic response assumption made in design standards is valid and leads to a safe design. Incremental dynamic time-series analysis of the response of a Timoshenko beam finite-element model was conducted, where this model is exposed to co-directional steady wind, regular waves and an as-recorded earthquake signal of increasing intensity. This earthquake record is scaled to different magnitudes, including the Extreme Level Earthquake and Abnormal Level Earthquake as defined by ISO19901-2.