In a bored railway tunnel project in the Middle-East, difficulties in terms of ovalization, water leakages and settlement of several lining rings located in a fault zone were observed at the end of the construction stage. The present research attempted to find the cause for this lining behaviour. The determination of critical loading conditions, the application of the longitudinal beam model and the analytical and numerical modelling (in Plaxis) of a monolith tunnel lining in abrupt ground property transition were analyzed. Thereby, the global lining stiffness reduction due to joints was also considered. The literature review led to the following expected factors that caused difficulties in the Middle-East case: the squeezing and submerged ground conditions, the rock mass disturbance and the improper backfilling of the rings. Additionally, the ring stiffness reduction due to joints was an essential factor for lining behaviour. The geotechnical conditions, the lining design and the observed difficulties in the case were defined in the next section. Critical missing information, such as geotechnical properties of the fault zone material and limited monitoring data, led to essential assumptions. The settlements were expected to be caused by rock mass disturbance and improper backfilling. These altered the water flow during and after the boring operations and led to lowering of the groundwater level and increase of effective stresses. The water leakages were caused by ring ovalization in the soft fault zone, leading to opening of joints. The analysis for this research was divided in 2D transversal, 2D longitudinal and 3D modelling of the lining in and around the fault zone. The 3D model was seen as the integral model, which took into account the transversal and longitudinal behaviour of the lining. However, most of the behaviour of the lining was analyzed by carrying out parametric analysis for both directions in 2D. Moreover, the 2D models were used to validate the results of the 3D model to identify the influence of the third dimension. The assessment of the results from these analyses led to the following conclusions. The behaviour of the tunnel lining in small width fault zones was governed by the transversal action. The ovalization was mainly influenced by the ground stiffness, the vertical to horizontal stress ratio, the backfilling stiffness and the ring stiffness. Using Erdmann's analytical solution, the approximate lining forces can be determined. However, this overestimated the ground pressures acting on the lining, especially in cases where vertical to horizontal stress ratios were not equal to 0.5. This was because the 2D transversal behaviour did not take into account the longitudinal arching effect, which depended mostly on the stiffness ratio between ground types. The final conclusion was that the global reduction of lining stiffness due to the joints led to a discrepancy with regard to the distribution of the longitudinal displacements. A complementary analysis using a numerical model taking into account the joint structure and discontinuous behaviour between rings would probably allow a better prediction of longitudinal displacements.

In 2017 new guidelines concerning macro stability calculations were implemented by the Dutch Ministry of Infrastructure and Environment. These guidelines are formulated in “Wettelijk Beoordelingsinstrumentarium” (WBI). The largest difference with the previous version of the guidelines concerns the material model that is prescribed to determine shear strength parameters. In triaxial tests shear strength parameters are to be determined at ultimate state (25% axial strain), which is assumed to be a good representation of critical state. Critical state is a concept from Critical State Soil Mechanics (CSSM) and assumed to be a good representation of the state reached after large deformations induced by macro instability. Another fundamental assumption in the WBI is the use of the SHANSEP method. This method encompasses a laboratory procedure and a normalisation method. CSSM was originally defined and elaborated under isotropic stress conditions while in engineering practice anisotropic conditions are mostly used.
The goal of this thesis is to investigate the undrained soil behaviour of organic clay in triaxial tests following the SHANSEP procedure and compare the results to the CSSM framework. In order to do so a series of eight K0-consolidated triaxial tests is executed using silty organic Oostvaarders plassen clay, which is assumed to be representative for a typical Dutch soil. A large range of over consolidation ratios is applied (1-20). Both compression and extension tests are executed. The triaxial tests are complemented by two K0-CRS tests and an isotropic compression test to determine relevant soil properties. The results are compared to the CSSM. The qualitative soil behaviour is analysed as well as the actual predicted undrained shear strength Su. Parameter relationships as described by CSSM are tried to be established from the data. The undrained shear strength is predicted by using numerical and analytical formulations of the Modified Cam Clay model, which is the most basic implementation
of CSSM. From the data a clear failure line could be determined in p'-q space. In the triaxial compression tests failure at ultimate state gave very consistent result, a failure line could precisely be determined. In extension failure at peak strength showed the most consistent results. Ultimate state could not be reached under representative stresses because the formation of large shear bands and necking during shearing. A unique p'-q-e relation was much harder to establish. The general trend as described by the CSSM was clearly visible but the uncertainty was rather large. Several factors contributed to the uncertainty. Among which the void ratio determination method that was used to determine the void ratio after the triaxial test, which is prone to errors. The MCC model was not able to model the stress path correctly and p'_0 at failure was not correctly predicted resulting in incorrect Su prediction. The MCC model overestimated Su in compression tests. In extension, however, Su is well predicted by the MCC model. The SHANSEP method turned out to be a very convenient way to normalise the undrained shear strength of the triaxial tests, both in compression and extension. Only at very large OCR Su/σ'_v0 is slightly overestimated.

Monopiles are commonly used as foundations for offshore wind turbine generators (WTGs). Due to the rapid growth of the offshore wind energy sector, there is increasing demand for WTGs of larger capacities which evidently leads to demand for monopiles with larger diameter. An industry standard approach for assessing pile lateral response is the p-y method; however, this method was initially developed and empirically validated for long slender piles and thus its applicability to large diameter monopiles is doubtful.

The joint academia-industry project, Pile Soil Analysis (PISA) project resulted in an improved understanding of the lateral loading response of large diameter monopiles. Based on pile load test (PLT) data and numerical modelling, a method was developed to derive all soil reaction components from advanced finite element method (FEM) calculations to be used in a one-dimensional (1D) design framework.

Cone penetration test (CPT) based approaches have been shown to provide excellent predictions for the response of laterally loaded flexible piles where the p-y response dominates. In this thesis an approach to determine the additional components of the soil reaction curves for rigid monopiles, namely the side and base shear and base moment directly from the CPT is proposed. The results are compared to soil reaction curves are extracted from 3D FEM models, and compared to field tests on monopiles in sand

During the advance of a tunnel boring machine (TBM), the torque applied to rotate the cutterhead must overcome the resisting moments acting on it. Hence, one of the major concerns of TBM design is to determine the torque and power requirements of the excavation machine. The first empirical approach for torque estimation was developed in the 80’s by JSCE. This estimation fits the recorded mean torque for 5-8m diameter projects, but overestimates torque as TBM diameter increases. Newer approaches estimate TBM torque and thrust requirements as sum of multiple components, focusing on the friction between ground and cutterhead. However, the recommended or selected friction coefficients range between a wide interval (typically 0.05-0.75), depending on soil and operational conditions. Consequently, the torque and thrust estimations relying on the above-mentioned friction coefficients can be considerably imprecise, as well. Previous research regarding soil-machine/steel friction coefficients has been collected and studied. Successively, interface shear tests have been performed at TU Delft, to study whether and how friction coefficients could be determined consistently in the laboratory. Three soil types have been examined, ranging from coarse sand to kaolin clay. A metal plate cut out from a worn TBM cutterhead has been added to a direct shear apparatus to test the abovementioned soils. The latter are either water saturated or treaded with bentonite or foam, to assess the influence of conditioners on soil interface friction. Bentonite slurries and foam suspensions have been prepared in the laboratory using common industry products. Overall, in excess of 60 interface shear tests have been performed, considering various permutations of soil, load and conditioning. Results show that lubricated friction coefficients (i.e. when soil samples are conditioned) are up to 25% and 50% lower than for water-saturated conditions, for sand and clay respectively. A direct shear apparatus proves to be useful to study and select friction coefficients for TBM preliminary design, as it provides satisfactory results for non-conditioned and bentonite-conditioned soils. The same apparatus, however, cannot fully capture the lubricating effect of foam on sand. Improved estimation of friction coefficients requires more advanced equipment, or substantial modifications to the direct shear apparatus.

Around 55% of The Netherlands is protected by flood defences like dikes. Flood defences must meet requirements which are based on an allowed flood probability. Safety assessments are performed to check whether flood defences meet these requirements. Uncertainties are explicitly included in safety assessments. Uncertainty in soil behaviour is one of the major contributors to failure probability of dikes. Therefore reduction of this uncertainty in soil behaviour leads to potential savings in reinforcement costs. One of the uncertainties in soil behaviour is the effect of aging on the behaviour of soft clays in compression. Compression behaviour of clay is strongly dependent on the transition from overconsolidated to normal consolidated soil behaviour. This transition phase in plain-strain conditions is indicated by the yield stress. The development of the yield stress due to aging is described by isotach models in terms of creep strains and stiffness parameters. Examples of isotach models are the abc-model and PLAXIS’ Soft Soil Creep model (SSC-model). According to those isotach models, a yield stress induced by aging is similar to a yield stress induced by unloading. This study verifies the development of the yield stress predicted by abc-models based on K0-CRS tests. The test material is remoulded, highly organic, silty clay with a liquid limit of 165% and a plastic limit of 56% (OVP-clay). The determination of the abc-parameters is not straightforward. The value for the creep parameter is easily overestimated due to a slow decrease in excess pore water pressure during a constant stress phase, resulting in stress-dependent strains instead of creep strains. The b-parameter is affected by the gradual transition from overconsolidated to normal consolidated behaviour and by the development of structure during aging. The development of structure is not included in the isotach models and could result in a higher yield stress than predicted by the isotach models. The possible increase of the yield stress due to the development of soil structure is not visible in the test results, but the performed tests indicate softening behaviour after aging phases. The SSC-model simulates no increase in lateral stress during aging. Some studies present data showing that the lateral stresses increase under a constant effective stress in time. Unfortunately, the development of lateral stresses cannot be quantified based on the performed tests due to stick and slip behaviour in the K0-ring during laboratory testing. Based on the test can be concluded that a minimum yield stress in time can be predicted based on isotach models. An important note is that a yield stress is always obtained with respect to a certain isotach which is dependent on the loading rate and the creep parameter. The shift of the yield stress from the imposed isotach to the reference isotach is often significant in laboratory tests, but not taken into account. Effects of development of structure during aging should be further investigated: it influences the behaviour of the soil in compression and affects the yield stress determination.

In the Observational Method Ab Initio approach a flexible design and construction plan is established to allow anticipation to observational feedback during the construction phase. This way, the structural design can be optimized to the in-situ conditions which is beneficial from both safety and economic point of view. In the application of building pits in the soft-soil conditions of the Netherlands the method has the additional value to verify SLS criteria and timely detect unforeseen events. So far limited building pits have been executed via this design strategy. The main reasons for this are the lack of a design procedure and the problematic quantification of safety of the flexible retaining wall design. A strategy for the execution of the Observational Method Ab Initio approach to retaining wall design is described by the CIRIA guideline C760. In this study, the suitability of this 5 step-strategy has been investigated by means of a benchmark. This investigation indicated that, although the CIRIA guideline C760 contains a valuable design strategy, only a qualitative description of safety is provided. Therefore, this study introduces a methodology for real-time measurement-processing with the use of a Bayesian update. The Bayesian update combines the information of the predictive computer model with the information obtained from measurement sets during construction. By describing this information via probability density functions different uncertainties in both the design and construction phase can be weighted in the outcome of the Bayesian update. Consequently, the retaining wall behavior can be re-assessed throughout construction. This methodology is applied to measurement sets gathered at the construction of two different building pits in the Netherlands. Both case studies showed that with the Bayesian update and consequential calibration new parametric distributions can be found. Those parametric distributions describe the retaining wall behavior from which safety definitions in term of a reliability index can be derived. The performance of this methodology for measurement-processing depends on the accuracy of the calculation model and the measurement interpretation. Especially in the case of unexpectedly high and/or fast progressing retaining wall displacements, measurement interpretation is necessary to select the best strategy to redirect the structure. Although this measurement interpretation is a challenge, it is believed that the Observational Method Ab Initio approach complemented with the Bayesian update is a promising design strategy. Its application to the construction of building pits definitely has economic potential and would be favorable for risk management.

Reinforcing levees with traditional methods is becoming more difficult in the Netherlands. Often there is a lack of space near the levee or it is desired that the landscape is maintained. Because of this, alternative methods for reinforcing levees are still sought after (CUR-commissie C141, 2007). In this study, the technical feasibility of a possible alternative reinforcement method for regional flood defences is studied: mass stabilisation. Mass stabilisation is a soil improvement technique with which soft soils are mixed with a binder on site and in-place to create a stronger soil layer (Forsman et al., 2015). It is presumed that mass stabilisation requires no extra space at the levee, does not affect the landscape and requires little transportation of materials. For determining the technical feasibility of applying mass stabilisation for reinforcing regional flood defences, three criteria have been examined. First, the ability of mass stabilisation to solve a stability deficit at levees was examined using two-dimensional stability analyses. Secondly, the achievability of the required effective strength parameters in compliance with Dutch standards was examined in the laboratory. Thirdly, the practicability of mass stabilisation at levees was examined using two-dimensional stability analyses. Although the results of this thesis have shown that mass stabilisation is a technically feasible technique for reinforcing regional flood defences, further studies will be required before a definitive conclusion can be drawn. It is therefore recommended that additional analyses into the practicability are carried out and that the relationship of the properties and the variability thereof between soils stabilised in the laboratory and the field is studied.

The Submerged Floating Tunnel (SFT), also called an Archimedes Bridge, is a state of the art solution for crossing deep and large waters. The concept of a SFT has been around for many decades. However, none has still been build up till today. A general literature study showed a number of ‘blank spots’ which still need to be researched before building the first ever “test” SFT. This Thesis discusses the shore connection of the flexible SFT to the fixed land tunnel and several parameters which influence the design of the End Joint.

This study presents the results of small scale flume experiments on a submerged rectangular cylinder subjected to a current, regular wave and combined wave-current environment. The objective of the study is to gain more knowledge about the hydrodynamics around and the kinematics of a submerged structure, to give a contribute to the research field of the submerged floating tunnel. For this study a rectangular cylinder with an aspect ratio (breadth-depth) of 2.5 is used. Two relative submergence depths (flume depth/model submergence) of 2.75 and 1.63 are tested. For all tests a still water depth of 0.7 m is applied. Waves resulting in very low KC numbers of <1 for regular waves and KC[1+U_c/U_m ]<2 for combined waves-current are generated. To create a combined wave-current environment, a current is created in the flume, to which waves are added by the wave generator. The water velocity is measured in front of the model. To approximate the water velocity at the model, a time/phase shift is added to the velocity signal. Linear wave theory is applied to approximate the amplitudes of the orbital velocities at the depth of the model. For the first part of the study, on the hydrodynamic forces, the cylinder is rigidly fixed in the flume. Due to the inertia dominance for low KC numbers, the relationship between the wave parameters and the hydrodynamic forces is well described by the relationship between the wave parameters and the water particle accelerations. The vertical hydrodynamic forces are found to be larger than the horizontal hydrodynamic forces. The force coefficients from this study are compared to coefficient found in previous studies. The drag coefficients for the only current tests agree well with the results from (Courchesne & Laneville, 1979), (Bearman & Trueman, 1972), (Nakaguchi, 1968) and (Venugopal, 2006). For the regular wave and combined wave-current conditions comparable results are found to those by Venugopal for a rectangular cylinder towed through a wave field (Venugopal, 2008). The drag coefficients in the present study show a similar trend in magnitude as in the study by Venugopal. However, the magnitudes have an opposite sign due to the velocity phase shift method applied in the present study. Nevertheless, the effect of this difference on the total force prediction is insignificant, because of inertia dominance. In general, the Morison equation predicts the measured horizontal force well for regular waves. Adding a current component to the waves results in a larger error between the computed Morison forces and the measured force. However, an increase in the magnitude of the added velocity does not lead to a significant increase of this error. The second part of the study focuses on the same cylinder, only not fixed but held in place by 4 tethers. For these tests a buoyancy to weight ratio of 1.5 is applied. The used tested angles between the tethers and the flume bottom are 30˚ and 70 ̊. The water depth, the wave types and model submergence depths are remained equal to the first part of the study. By comparing the kinematics found in three different configurations, a 30˚ tether angle combined with the largest submergence depth of ds=035 m are found to gives the smallest displacements and accelerations. To reduce the kinematics more, it is recommended to add vertical tethers to limit the vertical movement. In general, dynamic features are seen in the tethered model, influencing the magnitude of the kinematics. To predict the magnitude of the tether forces it is recommended to integrated these features in a structural dynamic model.

Settlement data of the Kiltunnel and the Heinenoordtunnel show that immersed tunnels in the Netherlands have been experiencing much larger settlement than expected when designing the tunnels causing cracks in the concrete and leakages in the joints. Settlements of 8 - 70 mm have been measured at the Kiltunnel and of 7 - 30 mm at the Heinenoordtunnel while settlements in the range of 0 - 1 mm were expected. Both sites are investigated through non-invasive geophysical site investigation method MASW (Multichannel Analysis of Surface Waves) for each 2.5 meter along the length of the tunnel and invasive site characterisation method CPT's (Cone Penetration Tests).The settlement of immersed tunnels is similar to that of a shallow foundation. It can be modelled using the Mayne equation which uses the small strain shear stiffness and the degradation of secant stiffness based on the load compared to the ultimate bearing resistance. The initial settlement can not have caused the settlements that were measured, because the initial settlement have already occurred at this time. The 5% and 95% boundaries of the creep settlements for both tunnels is much smaller than the measured settlements. To see if cyclic loading has an effect on the settlement of the middle section the effect of thermal expansion and contraction of the elements and the cyclic loading of the tides is examined.The expansion of the Gina Gaskets between the flat element and the elements at an angle is between -3 and 3 mm. This expansion and contraction of the Gina Gasket causes a vertical load on each of the edges of the middle element of 268 kN. This means that it does have a small influence on the settlement of both tunnels measured at these joints but does not explain all occurred settlement. For an indication of the settlement of the Heinenoordtunnel and the Kiltunnel under the loading of the tides a few calculations have been performed using an assumed lower bound of 40% and an upper bound of 90% of loading of the tides. At the Heinenoord the lower bound scenario gave results between 4.99 - 7.51 mm, which means that the measured values of around 7 mm are within the range of the results, while the upper bound scenario gave results between 10.05 and 15.57 mm which is larger than the measured values. At the Kiltunnel at location 21 and 23 the lower bound is more accurate, at location 19, 25 and 27 the upper bound is more accurate while for location 29 the measured settlement is somewhere in between the two bounds. At location 19 even the 95 % of the upper bound (21.34 mm) is much smaller than the measured settlement (around 34 mm). The difference in shear wave velocity is not that large and can not explain the large difference in settlement while the information from the CPT's is so limited that it is not possible to determine if there is a difference between location 19 and the other locations.

When engineers at Tunnel Engineering Consultants (TEC) used the Eurocode 2 (EC2) for the verification of flexural cracks in cross sections of immersed tunnel elements, they found out that there was more reinforcement needed for crack width limitation than for tensile strength of the reinforced concrete. This raised questions, namely whether the extra reinforcement is needed, how accurate the EC2 calculates the crack width and what the influence is of the construction height on the crack width?

Are the current rules in the Eurocode 2 for the calculation of flexural cracks too conservative for large thicknesses that are applied in the concrete lining of immersed tunnels?

In this thesis the crack width calculation of the EC2 has been compared with other codes around the world. When these codes are compared with each other it seemed to be that the EC2 is not conservative in comparison with the other codes, however it does not directly mean that this is true.
To check whether the codes, especially the EC2, are conservative, the codes should be compared with laboratory experiments. Since there is little data of experiments available where the cracks are carefully measured, in particular beams with large thicknesses, the finite element program DIANA is used to gain more data sets. A DIANA model is validated with three different experiments with each a different height.

When the EC2 and the DIANA results are compared, a few differences are found. The predicted crack widths in the EC2 are larger than that of the DIANA results. In the EC2 the crack width is the multiplication of the crack strain and crack spacing. If these values are compared, the EC2 gives a smaller crack strain than DIANA and therefore the crack spacing gives an even larger difference than the crack width. Next to that, the influence of the parameters in the EC2 is analysed. In both the EC2 and the DIANA results the cover is the most important parameter for the crack spacing and the steel stress of the reinforcement is the most important parameter for the strain. In all the results there is almost no effect of the construction height visible, except in the crack strain of the DIANA results when the cover is relatively large. A decrease of strain with an increase of height has been detected.

The differences in crack strain can be explained by the fact that the strain in the EC2 is calculated at reinforcement height, but the strain at the outer fibre is needed. In axial loaded cases these strains are the same, but in cases where the cracks appear due to bending moments, which is the case in this thesis, the strain is bigger at outer fibre. Next to that it seemed that influence factors used in the crack spacing calculation are overestimated, but no clear reason is found for this result.

In 2003, it was established that the sea dike between Petten and Camperduin was insufficiently safe.
To ensure the safety of the hinterland against flooding, this part of the Dutch sea defence system needed to be strengthened.
During the design process, the most favourable variant was to construct a dune and beach system in front of the sea dike, which was constructed soon after, and finished in 2015.
This changed the 'hard' sea defence to a 'soft' one, linking the beaches and dunes in the north and south with each other.
Thereby not only increasing the safety of this part of the coast, but also providing a new area reserved for recreation and nature.

The change from a hard to a soft coastal system fundamentally changes the characteristics of the area.
Where the old sea dike was a static structure, the newly constructed sandy beach and dune system is very dynamic in nature.
The change in properties of this coastal defence stretch brings the question how the HD (Hondsbossche Dunes) can best be maintained to ensure its functions as a sea defence now and in the future.
The answer to this question requires insight in the processes relevant to aeolian sediment transport in general, and for the HD in specific.
With the knowledge of what processes are important for coastal dune growth in the HD, a model can be selected to make predictions on the likely development of the HD in the future.

Aeolian sediment transport, much like hydrodynamic sediment transport, can be described as a balance between forcing and resistance against forcing.
The most important factors which govern the dynamics of dune growth as a consequence of aeolian sediment transport are: wind speed and direction, grain size, humidity, sediment availability, beach slope, and vegetation.
Especially vegetation (marram grass) is important, as it stabilizes the dunes with its roots and rhizomes below ground, and by locally decreasing the wind velocity with the biomass above ground.
The above ground component of the marram grass not only stabilizes the present sediment, it also accommodates a sheltering effect for any incoming sand grains.
Dune growth rate is the sum of incoming and outgoing aeolian sediment transport rates.
For a healthy dune system, this must be a positive value, as this process negates the effect of dune erosion as a consequence of storm events.

In the period between 2015-2018, positive dune growth rates have been observed.
An alongshore dune growth velocity gradient has been found, with the highest growth rate being in the south.
This is due to a combination of difference in vegetation health (being poorer in the north), and the orientation of the dunes in relation to the average wind direction (more onshore directed in the south).
The dune growth rate has decreased over time, but has remained positive over the regarded period.
This is due to the eroding beach, which decreases the sediment availability for aeolian transport.
Another factor is the coarsening of the average grain size as a consequence of aeolian transport on the constructed coast, increasing resistance to aeolian transport.
This largely explains the decreasing growth rates of the dunes, along with the fact that beach armoring starts to develop in the HD after construction.

The cellular automaton model DuBeVeg, developed at the University Wageningen, is used to model aeolian sediment transport, and the effect of vegetation in the HD.
This model is chosen over other models like AeoLiS and Aeolus, as DuBeVeg is capable of modeling vegetation growth both in surface area and effectiveness against erosion as a result of vegetation density.
Several improvements have been made to the model.
Non-erodible elements have been implemented, which allows the user to model the effects of the presence of objects such as the old sea dike behind the dunes, or pavement on top of the dunes.
Mass balance has been implemented in the model, with an option to define a sediment flux in the marine area of the model as a consequence of cross-shore and/or long-shore sediment transport.
A dynamic erosion profile on the beach is implemented, based on the erosion profile of Vellinga.
Climate change in the form of sea level rise and changes in wind velocity have been modeled.

Sea level rise affects aeolian transport rate and coastal dune development by influencing the sediment availability on the beach.
Higher water levels increase the reach of hydrodynamic processes, which result in higher beach erosion rates.
To ensure sediment availability for aeolian sediment transport, nourishments are an effective measure.
Higher sea level rise asks for a shorter interval between nourishments to ensure sediment availability.
Higher and lower wind velocities generally result in higher and lower aeolian sediment transport rates respectively.
Higher aeolian sediment transport rates don't necessarily result in higher dune growth rates, as the stabilizing effect of vegetation against aeolian erosion must be present to prevent aeolian transport out of the dune area.
Marram grass has an optimum accretion rate at which the plant grows best, and therefore stabilizes the dune most efficiently at this dune growth rate.
Therefore, an optimum dune growth rate exists.

To ensure the HD can maintain its functions as a sea defence, nature reserve and recreational area, it is important for the dunes to grow under average conditions.
To ensure this, sediment needs to be available on the beach which is ready for aeolian sediment transport toward the dunes.
Enough vegetation needs to be present on the dune surface to protect the dunes against aeolian erosion by sheltering, lowering the local wind velocity at the surface. Thereby inhibiting aeolian transport in the dune itself.
The sediment availability can be ensured by nourishing the beach or foreshore.
The presence of enough healthy vegetation can be ensured by providing the right abiotic conditions for the vegetation to thrive.
Increasing the biodiversity in the area makes the HD more robust to changes in the climate, such as sea level rise and changing wind climates which results in different rates of accretion in the dunes.

Increasing the biodiversity enhances the HD's other functions as a nature reserve and recreational area as well.
Biodiversity helps with the robustness of the ecosystem, and makes the area more enjoyable for recreational purposes.
The nourishments ensure the presence of a wide beach, ensuring enough room is available for a recreational day on the beach.

Soil characterization of the upper 2 meters of the seabed is essential to optimize the design of hydrocarbon fields (mooring systems), wellheads, subsea completions, pipelines, anchors and mudmat foundations (Randolph, 2016). Additionally, it has an increasing importance for geohazard evaluation, particularly in submarine slides. In oceanic developments, where the water depth range from 200 to 3,000 meters, the geotechnical site characterization of the surficial sediments is particularly challenging, as generally extremely low to low strength, normally consolidated fine-grained deposits are encountered. Currently, different in-situ tests and sampling techniques are implemented to determine soil properties at large water depths; however, more accurate measurements are needed to improve the geotechnical designs and reduce project costs.
The preferred in situ tests when testing on extremely low strength clays are the full flow penetrometers, hence, this thesis investigates the fundamental behaviour of a full flow penetrometer by performing monotonic, cyclic and variable penetration rate tests on extremely low strength clays. The methodology followed included the design and construction of the test set-up, the determination of the system compliance, the execution of the penetration tests, the analysis and interpretation of the acquired data and the validation by comparing the results with laboratory vane shear tests.

The response of a shallow foundation has been investigated by numerical simulations in a series of 1g small scale tests using the Finite Element Method. In this numerical study, special attention has been given to the influence of soft boundaries as a measure to counteract boundary effects, since limitations of space were present in the containers used for the experiments. These experiments were carried out on rigid shallow foundations on sand using strongboxes, which are routinely used in the small beam centrifuge at Delft University of Technology. Two soil constitutive laws were used: 1) the well-known linear elastic perfectly plastic model, and 2) a hypoplastic model. Soft boundaries have been modelled as a continuum, while soil-soft boundary interaction has been addressed by zero thickness interface elements. Model parameters have been back-figured from free field experiments, since boundary effects were considered negligible in these kinds of experiments. Finally, comparisons between numerical and experimental data showed hypoplasticity performed better than the elasto-plastic model to reproduce some aspects of mechanical boundary effects.

In this thesis an evaluation of the limit values which are stated in CUR 236 – Micropiles is presented. This evaluation has been done by means of a dataset. The dataset contained information on failure tests performed on four different types of micropiles, and was initially used for research on relations between logged installation aspects and the final capacity of the piles; such relations were however not found. This was mainly caused by the shape in which the data was logged, and the lack of details in the data. During this research, significant differences between raw data and data adapted according the limit values stated in CUR 236, were found. This led to a change in research direction towards the evaluation of the limit values.
Limit values are values that are used to build in additional safety in a design, and thus, to prevent unsafe situations. The values are based on the shape of data in which in general a linear relation between maximum mobilized shear stresses (τ_(mob;max)) and cone resistance (q_c). This relation continues up to a certain cone resistance level, after which τ_(mob;max) does not increase significantly anymore. The point where no significant increase in τ_(mob;max) over q_c was seen, was used as the limit value for the cone resistance. The limit for α_t was chosen to be 2.5% and the limit for τ_(mob;max) 2.5% of the cone resistance limit. Data with values above these limits, has to be reduced to the limit values. (CUR236, 2011)
Differences were thus found between raw data, the same data but then adapted according the limit value method stated in CUR 236, and values stated in CUR 236 Table 6.1. For further investigation on how these differences were caused, the available dataset was combined with data from the appendix ‘Bijlage A. Proefbelastingen’ of CUR 236. This showed that the current limit values did not suit the shape of the data very well. Investigation on the usefulness of the limit values showed that they are useful for the design process by preventing under- and overestimations of the capacity. Limit values are thus useful, but not in their current form. New limit values were therefore proposed based on a statistical analysis of the available data points. Next to limit values, also design values (expectancy and lower bound) are added.
Because no detailed data for all micropile types was available, it is advised to re-elaborate the limit- and design values for the types that were left out of the proposal given in this thesis, in a similar, statistical way. Furthermore is it advised to investigate a different method to estimate the shear stresses that can be mobilized along the anchor body of a micropile, based on a more fundamental approach. Currently are those stresses often based on full-scale tests from which τ_(mob;max) is derived, but bounded by the limit values. A different approach to this might be more time- and cost-effective.

Geotechnical design problems may be characterized by a certain degree of uncertainty, due to insufficient soil data and transformation of test results in soil parameters. In common practice, engineers perform deterministic analyses according to design standards as Eurocode 7, where the uncertainties are taken into account through partial factors for loads and soil properties to attain certain specified target reliabilities. Forcomplexsoilstructureinteractionproblems, partialfactormethodis difficult to adopt, as the design standards consider geotechnical standards with singlefailuremechanism. ThisisespeciallyproblematicforUltimateLimitstatedesigns where both stiffness and strength properties are dominant. With the advent of limit state design philosophy in Eurocodes, the use of reliability methods in Finite Element Analysis for complex situations has become more and more of interest. Reliability analyses allow to explicitly define the single uncertainties in the model by using an appropriate probabilistic distribution for each source of uncertainty. The reliability index and the probability of failure with respect to a predefined condition are calculated. The problem with using reliability based probabilistic design is the absence of simple computational approaches that can be easily implemented. MonteCarlosimulationsarecommonly usedto solvesoil structureinteraction problems. For a large and complex soil-structure interaction problem, it is computationally intensive to complete even a single run. This practical disadvantage can be solved only by a computationally efficient method. A special purpose application to perform probabilistic analysis in PLAXIS 2D, called PROBANA has been recently developed at Plaxis B.V. PROBANA performs direct probabilistic calculations in the finite element framework, using First Order Reliability Method or Monte Carlo Method. In this thesis, PROBANA (FORM) is used to perform reliability analysis for three benchmarks, and the results from PROBANA – FORM are compared with Point Estimate Method (PEM) and other stochastic Methods. The results from FORM are found to be comparable with that of PEM. It is concludedthatPEMislessaccurateduetoassumptionsmadebyPEMintheunderlying output distribution and FORM is more accurate and practical as it is computationally less intensive compared to other stochastic methods such as the Monte Carlo analysis. An extensive comparison of the reliability based method with Eurocode design method shows possibilities to implement reliability methods with EC7. One such approach is proposed, and demonstrated with the benchmarks.

The static liquefaction tank (SL-tank) is a unique large-scale facility that provides a means to simulate the conditions of a submerged soil slope under failure conditions. Static liquefaction (SL) may be defined as a significant loss of soil’s shear strength due to a substantial development of excess pore water pressure under monotonic loads. This complex soil behavior is commonly related to case studies such as submarine flow slides.
The main objective of this project is to use a finite element method (FEM) based on a Hypoplasticity (HP) framework to numerically simulate the experimental data obtained from the Static liquefaction tank facility of Delft University of Technology. A set of Elasto-Plastic (EP) constitutive models were chosen as an initial reference to simulate the SL-tank and afterwards compare their results to the HP framework. The numerical results were analyzed mainly in terms of excess pore water pressure and relating them to experimental data. Additionally, effective stresses, strains and stress paths were examined from the given model outputs.
A fine-cohesion less soil called Geba sand was used in the experimental procedure of the SL-tank, as well as in elements tests performed within this study. The model parameter determination and calibrations were performed by means of element tests, empirical correlations, theoretical formulations, and best-fits from experimental data. Soil behavior at low stresses is of fundamental importance for the performed experiments and numerical simulations in this work.
A potential instability behavior from the given numerical simulations was studied by means of an adopted instability line (IL). The IL criteria is a framework which is commonly illustrated in stress paths as a boundary that delimits a potential susceptibility to soil collapse. Element test data from fine-loose sands, as well as the numerical outputs from this work were used for estimating a potential IL applicable for the scope of this Master’s thesis project.
Results of this investigation showed clear limitations of the hypoplasticity constitutive laws in generating sufficient excess pore water pressures and deformations to trigger static liquefaction. Additionally, boundary effects in the assumed fixity conditions were a main potential issue regarding inaccurate results. Nevertheless, an enhanced model response (HP) was observed in comparison to Elasto-Plastic models.

This study was conducted in the framework of the Leendert de Boerspolder stress test. It focuses on the investigation the performance of the available constitutive models in describing the coupled hydro-mechanical response of peats and organic clays as observed during the stress test. The soil models that are considered are the Mohr-Coulomb model, the Soft Soil model and the Hardening Soil model as are implemented in PLAXIS, a standard commercial finite element code.
The evaluation of the models is performed in two steps. First, the performance of the constitutive models is evaluated by simulating the laboratory tests as single soil element tests with PLAXIS SoilTest facility. Based on the comparison of the numerical results with the laboratory data it is concluded that the HS performs the best compared to the SS and the MC model. In order to achieve good fit it is found that it is necessary to drastically reduce the failure stress ratio, $Rf$ to an average value of 0.15 in contrast to what is mentioned in literature for soft soils. In terms of one-dimensional compression stress path both the HS and SS model are deemed to perform similarly. The MC model is found to reproduce poorly the laboratory tests due to the assumption of linear elasticity - perfect plasticity.
Subsequently, soil models are evaluated through a fully coupled hydro-mechanical simulation of the Leendert de Boerspolder stress test in PLAXIS 2D. The evaluation is done through the comparison of the measured to computed displacements and pore water pressure. It is found that the prediction of the HS model is ``soft'' for peat while the stiffness degradation in the organic clay results in excessive lateral displacements. Response of the SS is found to be better considering both displacements and pore water pressure. The best description of the stress test was found to be possibly by using the SS for the organic clay and the HS for peat. The performance of the MC model is quantitatively good however qualitatively is deemed to be poor. Furthermore, the influence of (a) the soil anisotropy and (b) the interface between organic clay and peat layers are pointed out as factors influencing the outcome of the simulation.
Based on this study, it is concluded that in general the Soft Soil model, at this stage, is recommended for use for both soils. The Hardening Soil model should be used for peat but with caution and mainly when the deviatoric strains are deemed to be important. In this case the calibration should be done focusing on triaxial tests, therefore compromising the oedometric response. Moreover, a high secant stiffness should be considered to describe peat. That might be justifiable due to presence of fibers which under tensioning provide additional stiffness. Moreover, results suggest that the use of the HS model for the organic clay is not justifiable. Finally, the Mohr-Coulomb model should be used only as a rough approximation.

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.