The rapid expansion of offshore wind energy is increasingly pushing projects into seismically active regions, necessitating monopile foundation designs that account not only for typical environmental loads but also for seismic displacement demands. To accurately assess the dynamic response of an offshore wind turbine (OWT) and design its monopile foundation accordingly, it is essential to model the soil-monopile-superstructure interaction with high fidelity. Three-dimensional (3D) finite element (FE) analyses represent the most advanced numerical approach for capturing this complex behaviour. To address this need, this thesis develops a comprehensive FE framework in PLAXIS 3D that integrates free-field site response and soil-structure interaction (SSI) under both linear elastic and nonlinear elastoplastic soil to evaluate the seismic performance of monopile-supported OWTs.
A structured four-step approach is adopted. Step 1 performs one-dimensional (1D), two-dimensional (2D), and 3D site response analyses (SRA) in linear elastic soil, validating the numerical setup against analytical solutions. Step 2 introduces the pile and superstructure, modelled with linear elastic material, in the same medium to assess the dynamic characteristics and their response under steady-state monoharmonic excitation, allowing verification of the SSI model against benchmarks from the literature. To capture more realistic soil behaviour, the framework then incorporates the SANISAND-MS constitutive model, which accounts for nonlinear cyclic sand response, including strain accumulation and stiffness degradation. In Step 3, SRAs with displacement input motions of varying amplitude are performed under both broadband Ormsby and steady-state monoharmonic excitation to evaluate the influence of nonlinearity on free-field response. Finally, Step 4 couples the nonlinear soil with the structure to examine the fully integrated dynamic characteristics under nonlinear SSI conditions.
Overall, the analyses establish best practice boundary conditions and numerical setups for seismic SRA and SSI modelling in PLAXIS 3D for linear elastic soil (Steps 1 and 2), and quantify the transition from inertial to kinematic dominance in the i response of a flexible pile (Step 2). In the nonlinear domain, the results from Step 3 highlight the critical role of loading type in capturing key features of nonlinear free-field response. More specifically, with steady-state monoharmonic excitation of increasing amplitude, the transition from linear to nonlinear behaviour is captured, along with a shift of predominant frequencies to lower values compared to the linear elastic SRA. In contrast, when the same procedure is applied with the broadband impulse load Ormsby wavelet, post-impulse stiffening effects are revealed, expressed as an upshift in resonance frequency. In Step 4, the dynamic characteristics of the monopile-superstructure system are assessed under nonlinear SSI conditions. However, computational cost prevents the execution of full amplitude sweeps, underscoring the practical trade-off between accuracy and run time in high-fidelity 3D nonlinear SSI modelling. Instead, the 1995 Kobe earthquake record is employed to assess the system’s behaviour under real, multi-harmonic excitation. Altogether, the work demonstrates the potential of advanced 3D FE tools to enhance the seismic design of monopiles. ... Read more

The global increase in energy demand coupled with the need to accelerate energy transition has heightened the need for sustainable energy sources, such as wind energy. Offshore wind energy has a number of advantages when compared to onshore, including less turbulent wind, higher wind speeds and less land dispute with other activities, hence playing an important role in this process. However, its foundation design is challenging, particularly under complex geotechnical conditions. One critical risk during pile installation is pile run, a sudden uncontrolled penetration of the pile into the soil that can cause severe financial loss, installation delays and structural damage to the crane and installation vessels.
This research investigates pile run by focusing on the limitations of current static Soil Resistance to Driving (SRD) prediction methods and the influence of soil consolidation on pile driveability. Traditional SRD approaches, such as Alm and Hamre, that relies on CPT data are reviewed critically and their limitations are assessed. Studies show that while this method performs well for clean sands and clays, it is unreliable for soil mixtures and intermediate soils, where discrepancies arise due to different consolidation conditions during CPT testing and driving.
To address these limitations, the study evaluates penetration rate effects by comparing drainage conditions during CPT testing and during driving, using GRLWEAP software to calculate the driving velocities. Adjustments are then made to the SRD predictions applying reduction factors that represent the changes in drainage conditions and loss of soil resistance due to consolidation effects.
This study shows that in regions where unpredicted pile runs occurred the adoption of those reduction factors help in the identification of pile run risk regions. However, a more extensive database of soil tests considering different soil density, fines content, and consolidation state should be analyzed to propose definitive reduction factors that can be widely used for different soil conditions around the globe.
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Scour has become one of the most significant hazards affecting masonry bridges. Existing scour monitoring techniques often fail to meet the requirements for continuous and time-domain tracking of scour evolution. Moreover, existing scour early-warning systems predominantly rely on threshold-based risk assessment and management frameworks. A critical limitation of these systems is the difficulty in accurately defining threshold values, which are often derived from historical monitoring experiences. Given the variability in foundation conditions and river scour characteristics across different bridges, standardized threshold setting is highly challenging. Furthermore, threshold determination often lacks correlation with the health condition of the superstructure, which is an aspect engineers care most about. These deficiencies highlight the urgent need for a more intelligent monitoring framework that can integrate multiple monitoring techniques and facilitate interactive associations between monitoring data and the health condition of the superstructure.

This study explores the use of digital twin (DT) technology to overcome the shortcomings of current monitoring and maintenance strategies. By integrating real-world monitoring measurements with finite element modeling, the DT framework provides the opportunity to simulate "what-if" scenarios under high-fidelity conditions. Such advancements offer novel prospects for detecting scour-induced damage and intervening for the maintenance. This study utilizes DT technology within the context of a scour monitoring project for a masonry bridge in Northern Ireland, United Kingdom. A digital twin-based SHM and maintenance framework is developed to achieve seamless communication between the virtual model and the physical structure using sensor data. The developed model addresses limitations associated with traditional monitoring and maintenance approaches and demonstrates the potential of digital twins in forward model calibration and backward decision-making. ... Read more

This thesis describes the investigation of the lateral monopile response in weak rock and the effect of a zone of crushed rock that is induced by driven installation. The goal of the investigation is to study the impact of the weaker zone around a monopile on the lateral response. The thesis focuses on the modelling of a monopile in a finite element model to examine the effect. The modelled monopile is compared to field tests that were done in previous research to be able to benchmark the model. To full-fill the research objective several steps were taken. The research can be divided into four parts to get to the final conclusion, being a literature review and three different models that are set up. The goal of the literature review and the two model in 2D are to act as a basis for the setup and inputs of the 3D model. The 3D model can then assess the effect of a crushed zone on the lateral capacity and stiffness response of the pile.
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The evolution of ships requires larger depth or larger terrain loads in ports. Therefore, the existing quay walls require reinforcements. An effective way of reinforcing the structure are underwater anchors, requiring holes in existing sheet piles at the location of significant bending moment. Since this is a new area of expertise, the influence of the hole is still unknown. This report discusses a developed finite element model to study the influence of hole weakening of sheet pile and studies the influence of hole weakening on the sheet pile resistance and behaviour with the discussed model.

The 3DSSI model includes soil modelled by the subgrade reaction model (spring model) the steel sheet pile is modelled with shell elements in the finite element software DIANA FEA. The model includes both physical nonlinear and geometrical nonlinear behaviour and captures the soil-structure interaction. Also oblique bending, which is an existing phenomena of older, existing double U-sheet piles, can be captured with interface elements in the 3DSSI model. Nowadays, sheet piles are also designed using the subgrade reaction model and the sheet pile is modelled as a beam with the appropriate stiffness. The 3DSSI model is able to illustrate the 3D behaviour of the sheet pile, without having to model the soil with solid elements as well. This is beneficial with respect to calculation time.

With the 3DSSI model, the hole weakening of sheet piles can be studied. The influence of different parameters on the sheet pile resistance and behaviour is studied. The parameters studied, based on literature findings, are: hole diameter, hole location (level of the hole in depth), hole spacing (hole centre to centre distance in width), hole in-pan (compression zone) or out-pan (tension zone), sheet pile cross-section class 2 and 3 and oblique bending.

The influence of hole weakening on sheet pile behaviour and resistance is studied by finding in the parameter study for each case the load-displacement curve and from this load-displacement curve, the stiffness is derived. The load-displacement curve and stiffness curve include both steel and soil behaviour.
Resulting from the parameter study, the holes significantly reduce the sheet pile resistance and behaviour. The cases with holes in tension show less reduction in resistance and stiffness reduction. The hole diameter is also influencing the results, but the influence of hole location and hole spacing is relatively small. The failure modes are for holes in compression zone is plasticity around the hole and local buckling in the webs. For holes in tension zone, the failure mode is also plasticity around the hole, but also local buckling in the compression flange. For cases including oblique bending and holes in tension zone do not show local buckling in the compression flange, but in the compression web, due to the inclined neutral axis caused by oblique bending.

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The Port of Rotterdam (PoR) is the largest port in Europe and in order to maintain its status, it would need to expand. For the expansion, an extensive survey of the subsurface is needed for the construction of new port areas and its geotechnical structures. As part of designing the geotechnical structures, the subsurface is often modelled as multiple homogeneous soil layers. However the soil properties are in reality heterogeneous and spatially variable. The spatial variability of a soil property is characterized by a mean, a standard deviation and the scale of fluctuation. The scale of fluctuation is the distance over which a soil property is significantly correlated and it is limited to the soil layer of that soil property. Therefore the change in the geological layering of the soil because of external depositional factors such as river, sea and wind can influence the scales of fluctuations and the resulting geotechnical design.

The objective of this thesis is to look at the spatial variability in the vertical direction of the Pleistocene sand from the Kreftenheye and Boxtel Formation in the Port of Rotterdam and see if the river Meuse has any influence on the spatial variability in the vertical direction. An additional question is asked if the spatial variability has any influence on the computation of the pile base capacity for a single foundation pile and what are the implications of the answer to that question. To answer these questions, four sites in the Maasvlakte, Botlek and Pernis were selected and the cone penetration tests (CPTs) taken at the twelve sites were used for this thesis. An empirical method which uses CPT data to identify soil layers was used to identify the Pleistocene sand layer in the CPT data. The first part of the thesis uses the cone resistance data of the CPTs to estimate the spatial variability of the sites. The second part of the thesis focuses on the additional research question by using random field theory. Per site, the mean, standard deviation and vertical scale of fluctuation θ_v were used to generate simulations of cone resistance data. For each combination of standard deviation and θ_v 500 simulations were carried out. For each simulation the pile base capacity was computed with two CPT-based averaging methods, Koppejan method and LCPC method. The coefficient of variation of pile base capacity is used to measure the uncertainty of the computed pile base capacity.

The results show that the range θ_v values are: 0.26 – 2 m in the Maasvlakte, 0.24 – 1.76 m in the Botlek and 0.14 – 1.18 m in Pernis. In terms of the mean θ_v, you see a gradual increase from the upstream area (Pernis) to the downstream area (Maasvlakte). The increase is from 0.27 – 0.63 m in Pernis to 0.64 – 0.80 m in Botlek to 0.84 – 1.86 m in Maasvlakte. However, it is not clear if this is due to the Meuse or due to the existence of sublayers in the geological formation or due to some other factor. Further investigation is needed before a conclusive answer can be given. The answer for the second part is that as long θ_v is significantly larger than the pile diameter D (θ_v ≥ 4D), it does not influence the uncertainty of the computed pile base capacity. However, the mean and standard deviation of cone resistance does influence the uncertainty of the computed pile base capacities. Finally, it is observed that spatial variability does not play a role in the uncertainty of the computed pile base capacity if the coefficient of variation of the cone resistance c_v (q_c) is small (c_v (q_c) ≤ 0.15). The implication for the uncertainty of the computed pile base capacity and therefore the pile design is that one can afford to have a less accurate description of the spatial variability from using fewer CPTs if θ_v ≥ 4D. The same holds true if c_v(q_c) ≤ 0.15.
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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.
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The Dutch pile design method, NEN9997-1, classifies screw and screw-injection piles as fully displacing. For these pile types, the design code prescribes a base factor αp 0.63 and shaft factor αs in sand of 0.009. However, an ongoing TU Delft research programme on these pile types has indicated findings conflicting with NEN9997-1. This thesis investigates whether screw and screw-injection piles should be classified as fully displacing piles and how the design process can be improved, through the interpretation of existing load tests.
The thesis compares measurements of pile load tests to the load-settlement behaviour of fully displacing and (partly) soil replacing piles, including the effect of limiting qc to a maximum of 15 MPa for shaft friction. From appropriately instrumented tests, αp and αs factors are determined and compared to the prescribed factors. Additionally, a shear box test is performed in order to investigate debonding between the grout body and steel tube of a screw-injection pile.
Interpretation of the load tests strongly signify that the load-settlement behaviour of screw and screw-injection piles does not resemble that of fully displacing piles, but rather (partly) soil replacing piles. Determined values of αp range from 0.23 to 0.35, while values for αs in sand range from 0.011 to 0.012. Limiting qc along the shaft is shown to produce less realistic capacity and behaviour predictions when compared to measured test data. The shear box experiments indicate that in dense soils with high qc values, debonding between the grout and steel tube of a screw-injection pile under high load can occur. ... Read more

Wind energy is now a popular competitor among other energy sources all around the world. The offshore wind industry has progressed in recent years, with larger wind turbines being installed in deeper oceans. The construction of such large-scale wind farms necessitates more modern foundation design technologies to increase operational safety while also lowering total structure set-up costs. The environmental load applied to offshore piles are of great complexity. Currents, wind, waves, and even earthquakes are very common dynamic loads in an offshore loading environment. Of course, when a wind turbine is working normally, it also has significant operation loads. The design of offshore wind turbine support structures often involves some universal criteria, e.g., the pull-out capacity of jacket structures on piles. Wind turbine foundation capacity is determined by the qualities of the offshore soil as well as the properties of support structure configurations. Therefore, it is necessary to take account of the potential cyclic impacts of soil-structural interaction to guarantee dependable responses of the wind turbine structure. This thesis aims at evaluating soil−structure interaction of offshore wind turbine foundations under cyclic loading, with emphasis on the tension capacity of axially loaded displacement piles, under different load conditions (cyclic-to-average ratios) on Fontainebleau NE34 sand in France. A newly developed constitutive soil model SANISAND-MS (2018) is applied to model sand stress-strain evolution. In this thesis, the soil is assumed a homogeneous linear elastoplastic material for the sake of simplicity. The SANISAND-MS constitutive model used in this thesis can capture sand ratcheting after considerable cyclic loading cycles. Furthermore, drained and undrained compression triaxial tests performed at DTU GEO−Lab were used to calibrate the model parameters of the constitutive model for Fontainebleau NE34 sand. The finite element model adopted here is built in an open-sourced platform, the OpenSees. The Small-strain approach is adopted in the finite element modelling part. The pile is simplified as a wished-in place which does not include the installation effect and the time effect after the installation and before cyclic tests. Finally, the modelling results are compared to the experiment results recorded by Tsuha et al. (2012). Clear stable, metastable, and unstable response types are recognized in the model results. However, the initial stress state of the sand at the soil-pile interface differs a lot compared to the experiment results. This is the consequence of not including the pile installation effects in the finite element modelling. Recommendations are given to use large-strain soil modelling techniques to include the pile installation process. ... Read more

Almost 4000 MV piles are used as anchorage of quay walls in the port of Rotterdam. The current design method of MV piles in Dutch practice is a CPT-based method that correlates the cone resistance to the shaft friction by a factor α_t. In the port of Rotterdam, the cone resistance is restricted under the assumption that no shaft resistance higher than 250 kPa is mobilised. Consequently, α_t is used in combination with a limiting value for the cone resistance of 18 MPa. Moreover, the value of α_t that is currently used in the port of Rotterdam (1.4%) is derived after limiting the cone resistance at 18 MPa. Since this design method was developed in the 1980s', many more MV piles were tested in the port of Rotterdam. The maximum test load was generally at least two times the characteristic value of the required anchor force. None of these full-scale tests were loaded up to failure and no significant creep effects were observed. Consequently, the design standard was never updated as ultimate bearing capacity remained undetermined. Recently, the Port of Rotterdam has executed failure load tests in the Maasvlakte area. The tests allowed detailed strain readings along the full length of the test piles and offer the possibility to accurately determine the local mobilisation of shaft friction in addition to the ultimate failure load. Apart from describing the successful instrumentation with BOTDA fiber optical sensors (Brillouin Optical Time Domain Analysis), this study addresses the assessment of the obtained data in detail. Multiple relations are considered in this thesis. Analysis of CPT's indicates an increase in cone resistance due to pile installation. Investigation of pile driving data shows that installation energy correlates well with the cone resistance. Soil-structure interaction is analysed and a mobilisation curve is composed. This curve illustrates that mobilisation of shaft friction as a function of displacement of MV (tension) piles is similar to the Dutch standard for small and non-displacement compression piles. This thesis presents proof that limiting the cone resistance based on a maximum shaft friction of 250 kPa is not correct. The derivation of α_t without limiting the cone resistance results in a value of 1.2%. Installation energy proves to be a good indicator of the soil conditions. The piles that give good predictions for the bearing capacity with α_t = 1.2% present similar ratio's between the installation energy and the cone resistance. Future research may establish a consistent relation between CPT-based bearing capacity and pile driving energy to reduce uncertainty. This thesis will contribute to an update on the design method for MV-piles in dense sand layers of the Maasvlakte area. ... Read more

The transition to renewable energy has lead to many new ways of energy production, such as wind and solar energy. For solar energy power, there is an excess of energy during summer and an deficiency of it during winter, which is reversed for the energy consumption. In order to amend this problem, there is an introduction of new ways of energy storage in the form of heat for domestic and industrial use. One of these is the use of Underground Thermal Energy Storage (UTES). These systems make use of the underground to store heat during summer and extract heat during winter by using a fluid as the heat transferring agent. There are many different ways of UTES installation, however there are two which are widely used in the Netherlands: 1) Aquifer Thermal Energy Storage (open systems) which are based on heat-transfer by convection and 2) Borehole Heat Exchangers (closed systems) which are based on heat-transfer by conduction. While the way of transferring heat differs, they both need vertically drilled boreholes to reach a certain storage depth. These boreholes are drilled close to, or underneath, pile-founded buildings. The drilling of boreholes influence in-situ soil stresses around them, which might influence the bearing capacity of the piles. The aim of this thesis is to investigate the influence of installing UTES systems on the bearing capacity of piles. This is done by: 1) investigating the stress changes in sand due to the drilling of boreholes (stress analysis) and 2) the influence of these stress changes on the bearing capacity of piles (bearing capacity analysis). All of the modelling was done in PLAXIS, by using the 2D-axisymmetric model for the first part and the 3D plane strain model for the second part. An advanced soil model for sand was used, with soil mechanical behavior according to the Hardening Soil small strain model. The stress analysis consists out of a parameter sensitivity analysis, including the key parameters: back-fill grout shrinkage and expansion, Over-Consolidation Ratio and Relative Density. After this, the influence of the borehole fluid pressure and borehole diameter on the stress states were investigated. As not all boreholes are drilled perfectly, the last part of the stress-analysis takes into account drilling complications. The bearing capacity analysis includes simulations of static pile load tests of non-displacement piles. Load-displacements curves are produced for several scenario's: 1) perfectly drilled boreholes, 2) boreholes with drilling complications, 3) influence of a soft soil layer and 4) displacement piles and the influence of a varying installation phasing. The results indicate no large effects of perfectly drilled boreholes on bearing capacity of piles located outside a zone of 1.5 times the borehole diameter. For boreholes with drilling complications, the bearing capacity is influenced for piles located in a zone of influence of only several meters (2-6m), depending on the severity of the complication. At last, loaded piles of existing buildings are extremely sensitive for stress changes due to the drilling process, which will cause severe loss of bearing capacity. ... Read more

The low lying areas in the Netherlands often consist of soft and low permeable soils like clay and peat on top of a sand layer. Due to high water pressures at the interface between the permeable sand layer and the low permeable top layers, the effective stresses decrease, which can cause lifting of the low permeable top layers. As a consequence a deep seated long slip surface of the inward dike face can occur. Classical solutions to improve inner slope stability, like decreasing the inner slope or creating a stabilisation berm, are space consuming. Stabilisation columns are expected to improve the inner slope stability within the actual footprint. Various effects of stabilisation columns on inner slope stability are studied. The effects are studied by means of PLAXIS calculations using various modelling techniques. ... Read more

For preparing standardized sand specimens for physical modelling in geotechnics, especially for the geo-centrifuge tests, a “line-style” sand pluviator has been recently developed by TU Delft. Controlling the falling height of sand hopper, the width of hopper’s bottom gap and the relative moving speed between the hopper and the sample box, specimens with bulk relative density ranging from 50% to 100% can be prepared by this automated machine using the coarse Merwede River sand. Besides, the periodic variation of local relative density along depth was observed using the macro-CT scanner and the features of the fabrics were investigated using the micro-CT scanner. It was also proved by a set of shallow foundation modelling tests that the sand specimens having the same bulk relative density but different heterogeneity and fabric features behaved significantly differently and further research works are recommended to explore the influences of these differences. Additionally, a partially substantiated hypothesis was proposed to conclude the general rules of the sand pluviation process, and the reliability of this hypothesis has been proved by a series of tests on the Geba sand. ... Read more

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. ... Read more

Investigating soil response before, during and following large scale, dynamic events like slope failure or impact hammering of monopiles, is challenging. Full scale research into these processes is often conducted in the field, as laboratories don’t offer the required space to conduct these experiments. Apart fromthe monumental costs related to full scale experiments, it is often impossible or impractical to define or portray all boundary conditions, which increases uncertainty. As an alternative to full scale field tests, centrifuge tests on a scaled model are often carried out. When conducting research in the centrifuge, the decrease in geometry is compensated by through the acceleration of the model to N times gravity g. In this way, full scale stress conditions are imposed on the sample. Consequently, the model offers an accurate representation of full scale soil behavior. However, artificial ’gravity’ enhancement impacts a broad range of physical quantities. Scaling laws dictate how physical quantities are affected by conditions in the centrifuge and require careful observation. Yet, the use of scaling laws introduces a discrepancy between the timescale related to dynamic events and diffusive processes. The latter is of particular importance to build-up and dissipation of deviatoric pore fluid pressures. Decreasing the permeability of the soil is generally the best option to eliminate the aforementioned discrepancy. Consequently, instead of water, viscous fluid is used for the centrifuge tests, where the viscosity is increased N times with respect to water. Over the years, various fluids have been developed and utilized in centrifuge experiments. A widely used fluid, consists of aqueous solutions (Hydroxypropyl) Methylcellulose or (HP)MC in short. HPMC molecules form polymeric chains which increase viscosity while largely maintaining the density of the solvent, water. These favorable properties make it a highly sought-after substitute for water in centrifuge experiments. Experience with the fabrication and use of (HP)MC solutions is limited at the centrifuge facility of Delft University of Technology. As part of an initiative to develop in-house knowledge relating to the aforementioned points for physical modeling purposes, this research presents a robust fabrication methodology and maps the viscous properties of HPMC solutions, fabricated usingMethocel® F4M, at various concentrations. Results indicate that advocated preparation methodology enables the fabrication of viscous fluids in the range of 10 to 100 mPa ¢ s of consistent quality. However, overall, the viscosities of the fluids created along the lines of the presented methodology are consistently more viscous than anticipated. Several hypotheses aimed explaining the discrepancy are drafted. However, the nature of the underlying cause remains a topic of debate. Furthermore, it is observed that the HPMC fluids express a substantial degree of shear thinning at high shear rates. The relative decrease in viscosity increases with concentration, causing the viscosities of fluids of different concentration to gradually converge at high shear rates. The latter stresses the importance of quantifying expected shear rates beforehand to prevent behavioral inconsistencies between model and prototype. However, under some circumstances, it is doubtful whether the use of viscous fluids created from Methocel® F4M is suitable to study prototype behavior. In an attempt to facilitate drafting of appropriate recipes for the fabrication of viscous fluid, a general expression is presented to calculate the required concentration, provided the desired viscosity and anticipated shear rate. This generic expression provides adequately describes the experimental data, but requires further tuning in order to fully fulfill its intended purpose. Nonetheless, it provides a valuable indication of the required concentration to obtain a fluid with sought-after properties; thereby shortening the time spent on drafting the ideal fluid recipe. ... Read more

The focus of this research was the implementation of a permanent steel fibre reinforced underwater concrete floor (SFRUCF) as a permanent structural floor. A model was created that can describe the soil structure interaction of an SFRUCF including the highly non-linear behaviour of SFRC. The soil structure interaction of the UCF was modelled in Plaxis 2D with a plate element that includes the behaviour of SFRUC by means of an MN-κ diagram. This model was validated with measured data from the Albert Cuyp garage. It was shown that due to the uplift pressure heave occurred in the clay layer underneath the UCF, which increases the load on the UCF by 10%-30% and should be taken into account in the design. Also the heave from the deep Eemclay was considered. This heave had influence on the total deformations but hardly affected the internal forces in the UCF, justifying the fact that this heave is usually not included in the design of a UCF. A fictive E-modulus is often used to describe the cracked behaviour of steel fibre reinforced concrete. It was shown that using this fictive E-modulus in the building phase leads to an underestimation of the shear forces.
Additionally, a sensitivity analysis was done to show which parameters influence the calculation results, the design and the suitability of a permanent SFRUCF. The suitability of an SFRUCF is determined by the column loads in the final phase and the presence of a stiff raft. It was concluded that an SLS check should be included in the CUR 77 for water tightness, crack width and deformations if an SFRUCF is to be used permanently. The interaction between the raft can be modelled in Plaxis 2D with the plate element that has the behaviour of SFRC. For cases that do not include a stiff raft simpler models can be used such as the Plaxis model with springs or even a beam model with SFRC input. ... Read more

In this thesis the geotechnical bearing capacity of old timber piles in Amsterdam is studied. This is necessary because many structures such as quay walls, bridges and houses in the (historic) city centre of Amsterdam are founded on timber piles with ages ranging between 80 and 300 years old. The assessment of the foundation is currently done using many assumptions, these are needed because the piles are not easily accessible and old construction drawings are not always available or accurate. Furthermore, the effect that bacterial degradation of the wood has on the interface friction between soil and wood has never been studied in detail. In the assessment it is currently assumed that degradation has no effect on the geotechnical bearing capacity (Kalt and Dusseldorp (2018)), while in the old Dapperbuurt tests it was found that old piles had a reduced shaft capacity of 40% (Korff (2013)). The study is split into two parts; firstly a laboratory study into the effect of bacterial degradation on the interface friction between sand and wood has been performed, and secondly a sensitivity analysis into the geotechnical bearing capacity of timber piles in Amsterdam soil has been carried out. ... Read more