In this thesis the performance of five CPT-based p-y models by Novello (1999), Dyson & Randolph (2001), Li, et al. (2014) and Suryasentana & Lehane (2014;2016) is assessed. This is done in part by comparing the measured load-deflection response from a set of lab- and field tests that is representative for offshore monopile structures to the predicted response generated by a MATLAB pile-response model that incorporates the aforementioned p-y models. It is found that with the exception of Suryasentana & Lehane (2014), alle models are more accurate at large- than at small displacements. Furthermore, the models are generally conservative at a groundline displacement of D/100 and unconservative at a groundline displacement of D/10. The latter is likely related to inability of the models to adequately capture the ultimate soil resistance. The strongest found correlation with prediction accuracy is a negative one with pile rigidity at small displacements. The models from Dyson & Randolph (2001) and Li, et al. (2014) generate predictions with the highest mean accuracy, though all models perform relatively poorly when compared to a benchmark from Burd, et al. (2019).
The aforementioned CPT-based p-y models are tested further through a number of new instrumented pile load tests in the TU Delft geotechnical centrifuge and the experimental methods for these tests are evaluated. Image analysis of CT scanned sand samples shows that though there is substantial non-uniformity present in samples prepared through hand raining, this method yields acceptable results and is preferable to preparation using a sand raining machine. Secondly, though soil disturbance does occur as a result of pile installation at 1g, this is not likely to greatly impact the results. A comparison of the load-deflection predictions generated with the p-y models (including API) for these load tests supports the notion that the initial response from the API (2014) model is far too stiff and that it is therefore unconservative in the prediction of the limit states. Furthermore, a modified 5th order polynomial fitting method is found to adequately fit discrete bending moment data and in turn p-y curves are produced. These show that the pu from the models Suryasentana & Lehane (2014;2016) is only reached at shallow depths and does not match the measured ultimate resistance. Finally, at all except the shallowest depths the CPT-based p-y models strongly overestimate p though the resulting prediction of the load-deflection response is more reasonable.
As mentioned previously, the CPT-based p-y models do not perform optimally for the studied experimental cases, especially at small groundline displacements. This can likely be attributed to the fact that they were generally developed from test data on long and flexible piles. Additionally, rigid piles under lateral load develop moments and shear forces at the base that are not taken into account by methods that rely solely on lateral soil resistances (Peralta 2010). To solve these problems the PISA model with additional soil reaction terms was developed and it has been proven to provide better displacement predictions than traditional methods relying on lateral soil resistance (Byrne, et al., 2015a). However, this model is more complex and may not be the most convenient method to use. A less complex alternative has been proposed which uses a simplified rotational pile-soil interaction model to capture the load-displacement behaviour of perfectly rigid piles of varying diameter, stress level and loading eccentricity. Numerical simulations by Wang, et al. (2022) have shown this to work and in this thesis these results are validated using experimental data. The unification of the pile responses is found to work, but is not as successful for the experimental data. This may be due to several factors, the most likely of which are variations is sand density and imperfect rigidity of the model pile. However, the results support use of methods based on the aforementioned simplified rotational pile-soil interaction model, such as the rotational spring model proposed by Wang, et al. (2022).

Tailings are the rock flour which result from the process of mineral extraction at a mine. This waste material is stored in tailings storage facilities, also known as tailings impoundments. These impound­ments gradually grow in size during operation as more tailings are produced and stored over time. These structures are however also prone to failure. Well known failures in the past years are that of the Feijão and Fundão dams in the Minais Gerais state in Brazil. Static liquefaction of the dams has caused mud­streams in which many people were killed and the environment became heavily polluted. This study researched the probability of rainfall­-induced static liquefaction, as meteorological causes have often been named the trigger of failure. The study was limited to upstream raised decommissioned dams in the Minas Gerais state in Brazil. An analysis methodology was established in which the needed rainfall intensity to failure was calculated for different durations of rainfall. In a geohydrological analysis, the Richards equation for unsaturated flow was solved, to model rainfall infiltration. A quasi­-2D procedure was implemented to allow for a computationally efficient solution. Following the results of the geohydrological analysis, a limit equi­librium method was employed to calculate the factor of safety against liquefaction of the dam. In this case, the undrained strength analysis was applied together with an effective stress analysis to model both liquefiable tailings and non­liquefiable tailings in the tailings storage facility. If the factor of safety was equal to a predefined factor of safety associated with failure, the failure intensity was found. The failure intensity was converted to a return period of failure by the application of the Gumbel distributions that are part of the intensity­-duration­-frequency curve of rainfall. These IDF­-curves describe for all possible combinations of intensity and duration the probability of occurrence. Integration of the IDF­-curve for the failure intensities yields the total return period of failure as a single perfor­mance indicator. The analysis was restricted to a period of 5 days of continuous rainfall (storm events) as evaporation effects were not considered and no longer rainfall events were observed in the precipi­tation data used. A series of sensitivity studies was performed to observe how rainfall influences the stability of a tailings dam. It was found that failure is attributed to a loss of suction in the unsaturated zone upon rainfall in­ filtration as well as a loss of strength due to mounding of the water table. Because of the low strengths that liquefiable tailings have, there was the tendency to develop deep slip surfaces below the phreatic surface, causing only marginally stable dams to be prone to failure because of rainfall infiltration. The factor of safety upon rainfall is reduced in the order of 2 to 5 % depending on the parameters used. The strength parameters were of the largest influence. Increasing the friction angle of the non­-liquefiable tailings by 10 % increases the return period of failure by approximately 400 years. The strength ratios used to model the liquefiable tailings are of even larger influence. Adjusting that by only 2 % leads to a jump in the return period of failure of around 1000 years. The chosen boundary conditions for the phreatic surface in the impoundment were also of great influence. A difference of 0.3 meters for the water table for a dam of 20 meters high brings the dam to marginal stability. Given the little sensitivity to storm events, it is recommended to shift focus towards the behaviour of the phreatic surface over longer simulation periods to model the effect of e.g. extremely wet seasons. In addition, construction defects should be considered in which perched water tables could arise, severely decreasing the stability of a tailings dam.

The aim of this research is to find the influence of rapid drawdown on dike stability with the Delta21 project as case study. The Delta21 project is a proposed plan for a waterdefence system in front of the Haringvliet, The Netherlands. Its main element is a water retaining lake with an extensive pumping and turbine system. Whenever other storm surge barriers close, water from inland rivers can be pumped to the sea. The water retaining lake can act as an energy storage system as well by using the turbines to generate electricity at moments of high energy prices. The pumping system has the capacity to reduce the water level with 17.5m in 12hours. The dike surrounding the lake has a gradual slope as the height/width ratio below the water line is 1/20. It consists fully of a homogeneous and permeable fine sand. The estimation of material properties were based on limited CPT data, samples from the adjacent Maasvlakte II and empirical relationships. The rapid decrease of the water level in the lake causes rapid draw down conditions in the dike. Hereby the external hydrostatic pressure is reduced due to unloading effect of removing water, while a delay in the dissipation of pore pressures inside the dike is produced. This causes stress relaxation and slope instability. The research was performed using a numerical model verified with physical modeling in the form of centrifuge tests. For the numerical model the finite element model PLAXIS2D was used. A fully coupled flow deformation analysis was chosen, which can solve the full interaction between deformation, consolidation and groundwater flow simultanously in the same phase. It considers a reduced permeability and degree of saturation in the unsaturated zone. The Hardening Soil small strainmodel was selected as constitutive model due to the potential of capturing hysteresis in the stress-strain regime. Hysteresis could occur as a result of multiple cycles of water level fluctuations. To gain better understanding of the capabilities and weaknesses of the numerical model, it was verified with several physical tests from literature. The first test is a centrifuge test with failure due to increasing hydrostatic pressures within the dike. The moment of occurrence and shape of the failure contour were compared with the numerical model. The second test was a centrifuge test where a dike experiences rapid draw down conditions with the purpose to validate the pore pressure and saturation level. Thirdly, a full scale test of a dike with a changing water level was added, because full scale tests offer the closest resemblance to situations in the field. The field test was modeled to double check pore pressures and saturation. The research aimed to further investigate the development of a failure during rapid draw down, a centrifuge test was performed at 100g. Rapid draw down conditions were simulated on a sand dike with slope 1:1.6 to generate failure. By tracking grains with Particle Image Velocimetry (PIV), correctness of estimating displacement by the numerical model was verified. The addition of pore pressure sensors could give further information on pore pressure development. The numerical model proved to accurately predict positive pore pressures and the moment at which macroscopic failures occur due to drawdown. Negative pore pressures, saturation and development of the failure, in terms of size and deformation could not be accurately approximated. With understanding of the capabilities and weaknesses of the numerical model, the dike of the Delta21 project was modeled. The original design proved to be stable with a FoS of 6.20. Increasing slope angles were modeled resulting in a decreasing FoS. The influence of hysteresis was found to be very small after modelling multiple cycles of changing water level. The positive effect on stability the addition of a high permeable filter layer was modeled. Finally the risk of erosion due to outflow was analytically calculated and proved to be closely related to the numerical results.

In the Netherlands, dikes are the most commonly used structures to retain water and provide safety against flooding. In order to ensure the safety of these dikes against a number of different failure mechanisms such as backwards erosion piping, wave overtopping and macro stability, a detailed safety assessment has been created. The focus of this thesis is on the failure mechanism known as piping. Which consists of three different sub-mechanisms; uplift, heave and backwards erosion piping. The safety assessment against piping consists of a multi-step approach. First an elementary assessment is done, followed by a detailed assessment of the different sub-mechanisms and lastly a final analysis is done using more detailed data and software. Currently, Sellmeijer’s design rule is used in the detailed safety assessment to design against the sub-mechanism backwards erosion piping. His design rule is the starting point of this thesis. Before Sellmeijer was able to derive his design rules, he had to make a number of different assumptions and simplifications. The most significant being, simplifying the three-dimensionality of the piping process to a two-dimensional process, by neglecting the meandering nature of the pipe and excluding the effect of the lateral groundwater flow on the pipe progression. By limiting the problem to twodimensions Sellmeijer derived a mathematical model on which his design rule was based. In his design rule Sellmeijer relates the progression of a pipe to a hydraulic gradient. Over the years, Sellmeijer’s design rule has been adapted three different times. Each adaptation resulted in a more accurate design rule accounting for more and more parameters. However, with each adaptation, Sellmeijer’s design rule did not become more transparent. During the derivation of his design rule, Sellmeijer fails to account for the effect of a leaky layer on the critical hydraulic gradient for pipe progression. This limitation in his design rule is the focus of this thesis. In order to determine if leakage affects the critical hydraulic head for pipe rogression, a study is done using a two dimensional groundwater model in which his design rule is implemented. From these simulations it was observed that the presence of a leaky layer results in an increase in the critical hydraulic head. In the simulations studied, a maximum of 12 % increase is observed. Next an analysis is done on the results of these simulations. On the one hand an attempt is made to determine if and how leakage can be included in Sellemijer’s design rule. The simulations show that the effect of leakage on increasing the critical hydraulic gradient for pipe progression is largely dependent on the hydraulic conductivity of the cover layer. However, in order for a leakage term to be determined, and included in Sellmeijer’s design rule, additional simulations should be done. In MSeep it was also observed that leaky layers significantly impact the groundwater flow under the dike. The effect of this was quantified by looking at the effective depth. Which is defined as the portion of the aquifer which is responsible for groundwater flow towards the pipe and uplift channel. In order to further analyse the effect of leakage on groundwater flow, a number of quasi 3D and 3D scenarios were modelled in iMOD. For these simulations the effective depth, the effective width (in 3D) and the discharge in the well is determined. In this way, the effect of leakage can be quantified. In all three of the models similar trends are observed: a increase in the hydraulic conductivity of the cover layer resulted in the decrease of the effective depth. However, in the full 3D model the impact of leakage on the groundwater flow resulted in a larger range in the results. The results of this thesis, show that derivation of a leakage term would greatly benefit the output of the design rule. As a ’quick fix’ it is recommended to derive a leakage term which can be included in Sellmeijer’s design rule. However, further developments of a 3D model which correctly implements the effect of a pipe on the groundwater flow is also beneficial.

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.

Bioswales contribute to climate resilience, as they positively impact the urban water infrastructure by improving the water balance and water quality. However, current bioretention design ignores the facts that different designs in different soils and climatic locations produce different performance results.
The effect of polder conditions on the hydraulic performance, as well as the effect of different storm-types and initial conditions will be researched in this report. To this end, 5 bioswales located in Rotterdam, The Netherlands are monitored on their hydraulic behaviour. The discharge of the drain, groundwater levels in and at the edge of the bioswale and the water level in the bioswale are monitored for 4 of the bioswales. One bioswale only has groundwater and surface water measurements. The polder conditions resulted in a low volume reduction and faster and stronger reacting drain. However, the peak reduction and peak delay were still quite good due to the low permeability of the top-soil. For smaller storms, even the goal for volume reduction could be met. It was found that the structural porosity governed the infiltration, but large plants can increase the permeability too much. In addition, the textural porosity should start high enough to allow for vegetation development.

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.

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.

The 2011 Great East Japan Earthquake had a devastating impact on the town of Otsuchi in Iwate Prefecture, resulting in 1,234 immediate deaths and 59.6% of residential houses being fully damaged amongst other severe consequences. The post-disaster Reconstruction Plan (2011-2018) of this town focused on rebuilding the previously existing town with large-scale engineered interventions, resulting in a fragmented set of spatial interventions which solve problems in a single faceted way. The management of a post-tsunami reconstruction process should represent a resilient design for the future. This paper demonstrates that a modified land use design, developed and achieved through an interdisciplinary approach, represents a holistic solution to the drawbacks of the reconstruction plan. Through an iterative framework, site-specific strategies are developed at the urban and the building scale that combine safety and livability by finding synergies among disciplinary fields in an integrated manner. The result of this paper is a quantified evaluation of the reduction in flood risk achieved with a new design, making spatially evident the areas in which a refinement is required to mitigate flood damage.
Subject: tsunami; interdisciplinary; resilience; spatial planning; strategy

This MSc thesis was initiated as part of an interdisciplinary project researching post-disaster coastal reconstruction in the Tohoku region of Japan. On March 11, 2011, a highly destructive earthquake induced tsunami hit the north-eastern part of Honshu island, causing enormous damage to numerous small towns along the coast. Since 2011 various studies have been completed to better understand this historical event and explain the nature of tsunamis. However, some researchers have noted the inability of tsunami models, using only an earthquake as a source, to reproduce the timing, frequency and wave heights recorded along the Tohoku coast in March 2011. The differences are especially striking for the Sanriku coast – a relatively small area north of Sendai plain characterised by a ria-type coastline. D. R. Tappin et al. (2014) suggested that a secondary source is required to explain the deviating model results and locally higher tsunami waves, such as a submarine landslide. In low-lying coastal areas, tsunamis are an unavoidable hazard to human lives. A common way of addressing natural disasters of this scale is with timely warning and evacuation, which in turn requires appropriate techniques for prediction of an upcoming disaster. While earthquake induced tsunamis provide a sort of a warning signal, tsunamis generated by a submarine landslide can be much more difficult to predict. Landslide tsunamis are usually concentrated in local areas and do not propagate far, as they are more dispersive than earthquake tsunamis. However, the source of landslide tsunamis is often located on a continental slope near the coastal line. As a result, waves reach the shore in a very short period of time and run-up heights can reach extremely high levels (Harbitz et al., 2006). Thus, landslide generated tsunamis pose a serious hazard to densely populated coastal areas. Within the scope of this thesis, a number of experimental simulations on submarine slope failures were conducted in a so-called static liquefaction tank – a unique testing facility for large scale experiments at the Geo-Engineering Laboratory of TU Delft. To improve the understanding of tsunami generation, this study focuses on the moment of onset of a submarine slope failure and wave generation, linking the processes within failing soil mass to initial characteristics of waves. This study illustrates the connection between these two processes that are usually only considered individually from either a geotechnical or hydraulic perspective.

In this report, an experimental investigation of the influence of currents on submarine slope stability is presented for the Eastern Scheldt storm surge barrier case. Slope instabilities, including liquefaction failures, have been observed in the scour hole slopes near this barrier. The currents above the sloping bed are expected to initiate the liquefaction slope failures. The effects of the excess pore water pressure increase, that is generated by the currents, on the soil response are investigated by triaxial tests. Multiple excess pore water pressure rates are applied on a loose soil sample. The triaxial tests show that higher excess pore water pressure rates result in earlier developments of strains at lower stress ratios. This research is intended as a step towards a better understanding of the initiation mechanism of the liquefaction slope failures near the barrier.

The aim of this project is to elaborate upon the design proposal of a miniature cone penetration test device. The usage of CPTs in the geotechnical centrifuges has proven to be a reliable experimental method. The usage of a CPT in a centrifuge can provide determinant results for many applications of geotechnical experimentation. The usage of cone penetration tests in centrifuge modelling is a significant experimental method in geotechnical engineering. The measurement of cone resistance and pore-pressure during in-flight tests can provide valuable data to correlate with soil properties and material behaviour. Through the years, this method has proven to be reliable and repeatable and has helped in verifying correlations of laboratory measurements and field data. The inexpensive and time-efficient nature of centrifuge testing and the reliability of cone penetration testing complement each other. This method has many relevant applications and acts as an effective tool. A literature study is conducted to obtain practical information on the design process of minia- ture CPTs. The existing designs are studied and their specifics are compared to the boundary conditions of the centrifuge of Delft University of Technology. This apparatus is capable of con- ducting tests at 300 times the gravitational acceleration and can carry samples with widths up to 400 millimeters. Two sets of existing sample containers are considered in this project which define physical dimensional boundaries. These sample containers consist of rectangular and cylindrical boxes with defined dimensions. The existing boundaries are further analyzed with respect to boundary effects derived from previously conducted tests to define design specifications for a potential miniature probe. The definition of such boundaries set the basis of the design proposal. For the rectangular containers a miniature probe with a maximum diameter of 4 millimeters can be used. As for the cylindrical sample containers, miniature probes with maximum diameters of 7.5 and 9.5 millimeters are appropriate to be designed. The analyzed existing designs are then scaled and altered with respect to the determined boundary values and the proposal is further evaluated.
Three miniature CPTs are designed with diameters of 4, 7.5 and 9.5 millimeters. Each design has certain applications and can be used in specific scenarios. All three designs include modular load cells and sub-parts that can be replaced and altered. Each proposed device consists of a modular load cell designed based on required material properties to experience a minimum amount of 500 micro-strain without buckling. The first design, with a cone diameter of 4 millimeters, can be used in any container with a minimum width of 12 centimeters and for soil samples with a maximum average grain size of 200 micrometers. The second design, with a cone diameter of 7.5 millimeters, can be used in containers with a minimum width of 22.5 centimeters and is applicable to soil samples with a maximum average grain size of 270 micrometers. The final design, with a diameter of 9.5 millimeters, is meant to be used in sample containers of widths above 28.5 centimeters and for soil samples with a maximum average grain size of 340 micrometers. The designs are then evaluated with regards to manufacturing costs and feasibility. An estimation is made based on previously designed and patented devices and material catalogues provided by manufacturers. The cost of the first two designs are estimated to amount to 1580 to 2080 Euros, whereas the third design is estimated to cost 3080 to 3580 euros due to temperature compensated pore-pressure sensor that is included in the design. Upon further evaluation, the first design with a diameter of 4 millimeters is chosen as the most feasible and practical concept due to applicability and practicality of the design.

Marine pipelines are widely used for transporting hydrocarbon material. However, they can be damaged by marine geo-hazards such as seabed liquefaction, as they may sink, float or be dragged by the moving soil. One of the triggering mechanism of seabed liquefaction is the increase of seabed inclination as a result of the souring process or human construction activities. Experiments are carried out to simulate seabed liquefaction and to study the drag forces on a shallowly buried gas pipe at a centrifugal acceleration field of 50g. A tilting mechanism is applied to trigger sample liquefaction. A fluidization system equipped at the bottom of the strongbox is designed to prepare fully saturated, loose and uniform samples. Viscous fluid made of Hydroxypropyl Methylcellulose powder is used as the pore fluid. A hollow model pipe is embedded in the sand layer shallowly with a specific embedment ratio. The pipe fixities are made to be adjustable for adjusting pipe locations horizontally and vertically. Strain gauges attached on fixities are used to monitor the loads exerted on the pipe. The effect of the presence of pipes on the sand layer instability is presented. Furthermore, the drag forces acting on the pipe at a specific embedment ratio is discussed.

Wind turbines are nowadays the main means for producing renewable energy in Northern and Western Europe, and therefore research is conducted to secure their efficiency. One of the critical aspects of the windfarms is the foundation type, as it can define the functionality and the cost of each turbine. Monopiles have prevailed as the most efficient foundation, since 75% of the existing wind farms are founded in this way. However, despite their dominance, there are still mechanisms that affect their stability during their lifetime. Scour formation, which is the erosion of the soil around a monopile, is a crucial one that is the topic of this project. More specifically, the effect of the scour formation (both depth and type) in the stiffness and the lateral capacity in sandy soils has been investigated, followed by analyses about the efficiency of the scour protection layers. The methodology that was followed included numerical simulations, which have been performed in the finite element code of PLAXIS 3D. More specifically, 26 simulations have been conducted, in which the vertical load, the scour depth and type and the scour protection length were the parameters that have been investigated. The conclusions drawn could be divided into four categories, the vertical load, the scour depth and type and the scour formation effect in the stiffness and the lateral capacity. It was shown that the increase in the vertical load had a positive influence in the lateral capacity of the soil-monopile system. However, it could be characterized negligible, as the lateral capacity increase was less than 5%. In the next set of results, the scour depth impact in the stiffness and lateral capacity of the soil was investigated. It was observed that for the same type of scouring, the increase of the depth of the scour hole significantly reduced the soil resistance. It is noted though that scour up to 1.0D could be managed except for the global scour case. On the other hand, for larger depths the situation was becoming more critical and in depth of about 2.0D, the loss of the capacity was too great leading to a no-return state, for all scouring types. Then, the type of scouring impact was investigated, as local scour (narrow and wide) or global can occur. It was shown that the narrow type of scour was the most favorable case, which could approach the no scour case for small scour depth, while the global scour case was the most critical, as even in small scour depths could lead to dramatic reduction of the capacity. The main point is that the narrow case and the wide one can be manageable in depths up to 1.5D under certain conditions, while the global type seems to become a no-return case for much smaller erosion depths. The last part included the scour protection effect which was similar to the vertical load effect, as it had a positive influence in the lateral capacity of the soil-monopile system, but in a range of 5 to 15%. Therefore, it could be ignored in the design phase, unless a thicker protection layer is used. The graphs of the evolution of soil pressures and pile deflection clearly indicated that the monopile presents a rigid response, as the pile was rotated in all cases from a certain rotation point. The rigid behavior of the pile states that the API method is outdated as it is based on slender piles and it cannot capture the rotation point and the distribution of soil pressures that occur due to the rigidity of the monopile. The final output of this current report is a design recommendation, depicted in two normalized charts that correlate load and stiffness at failure displacements with the scour depth and type.

The introduction of the new 'Waterwet' led to the retesting of a lot of primary flood defences within the Netherlands, sequentially certifying a lot of levees as unsafe regarding inner slope stability. To test or design a levee an adequate amount of soil investigation is required to indicate the presence of different soil types, stratification and to estimate the relevant soil parameters. The spatial spreading and the fact that the number of cone penetration tests (CPT) and boreholes within a levee to determine geotechnical parameters and stratification are limited, means that the estimated parameters always contain uncertainties. Nevertheless current guidelines do not cover the minimum CPT interval size or the uncertainty in undrained shear strength in longitudinal direction. In this thesis it is analysed how the quantity of CPTs in longitudinal direction affect the estimated undrained shear strength, and how this influences the probability of failure regarding inner slope stability.

A 5 km long levee containing a continuous peat and clay layer along the Markermeer is specified as research area. In this area the CPT interval size in longitudinal direction is 100 m. The inner slope stability is analysed with D-Geo Stability (level I reliability approach) and the Probabilistic Toolkit (level II reliability approach). Although simplifications within the model ensure that only layer thickness and undrained shear strength vary in longitudinal direction, the calculated safety factors still show a lot of fluctuation. The probabilistic stability analysis show that in the considered research area, the undrained shear strength has a larger influence on the probability of failure in comparison to layer thickness, unit weight and outside water level.

As the CPT interval size increases in longitudinal direction, the minimum safety factor could be overseen, which can lead to optimistic reliability estimations. The theory of information entropy is used to analyse the effect of changing CPT interval sizes on the estimation of the undrained shear strength. Information entropy measures the amount of uncertainty/information in a dataset. A new partial factor (the ‘spatial factor’) is proposed based on the normalized entropy. The proposed spatial factor accounts for spatial uncertainty in the estimated undrained shear strength in longitudinal direction and assigns additional safety when the CPT interval size is larger than 100 m for the considered research area. This methodology promotes the collection of additional data, which is thought to be the basic starting point for any partial factor that is assigned to cover epistemic uncertainties.

Failure of slopes has been a frequently occurring hazard, which leads to loss of life and resources. To stabilize the slopes, vegetation has been used, where stump of plant roots act as passive piles by providing mechanical reinforcement. In this research, effect of spacing of trees on load transfer mechanism in a slope has been studied and comparability of passive piles and roots has been investigated. Half portion of an embankment has been taken and simplified instrumented roots were planted in staggered pattern on the slope. Two models with spacing of 3 times the diameter of root and 6 times the diameter of the root were prepared to study the effect of spacing on load transfer mechanism. A model with no reinforcement (fallow) has also been tested. During the test, load was introduced to a foundation at the crest of slope till the slope failed. It was observed that as the spacing increases, load bearing capacity of slopes decreases. As spacing of roots decreases, incidence of failure prolongs. Also, as the spacing of roots decreases, shear failure plane gets deeper in the slope. As these aspects of passive piles were observed, behaviour of roots is comparable to that of passive piles.

As soil behaviour is stress-dependent, a centrifuge model with tilting sample box was developed to generate liquefaction flow slides at higher confining stresses. The design and experimental set-up were based on the large liquefaction tank (de Jager et al., 2017). Fluidisation was used as sample preparation technique to produce a saturated, loose and uniform sand bed. The performance of the fluidisation system was evaluated by experimental investigation of the sample by considering the relative density, uniformity, degree of saturation and the influence of viscous pore fluid. The reproducibility of the initial sample was considered acceptable. A series of centrifuge experiments was conducted where the fluidised sand bed was accelerated to varying gravity levels and inclined to a slope with constant tilting rate. In most tests the soil response was characterised by a rapid liquefaction flow slide and a sudden increase in pore pressures. The moment of failure was consistently influenced by a variation in fluid viscosity and tilting rate, regardless of the gravity level; these effects indicated that instability was caused by the restricted seepage rate during loading. It is believed that the liquefaction potential is governed by the extremely loose and highly contractive top layer, which yields a sudden loss of strength under limited drainage conditions. The pore pressure measurements, which showed no excess pore pressures building up prior to failure, can lead to a misunderstanding of the failure mechanism and false assumption of fully drained conditions. Monitoring the pore pressures is therefore not suitable to predict liquefaction flow slides in submarine slopes. Mitigation of liquefaction should be focussed on densification of the looser part of the sandy slope, which is usually the top layer.

As countries around the world are in a race for clean energy, various renewable energy sources are harvested to meet the energy needs. In Western Europe, wind energy is the primary source of renewable energy. To meet the energy demand, higher capacity wind turbines are being installed in deeper waters. In deep waters, monopile foundations are ineffective due to its inability to withstand large overturning moments. Thus, multi-caisson foundations are preferred in deeper waters. Typically jacket or tripod foundations are preferred as multi-caisson foundation and these foundations are supported by either piles or suction caissons. Suction caissons are preferred due to the ease of installation and removal.Based on the literature, it was understood that various kinds of research are being undertaken throughout the world to better understand the performance of suction caisson foundations. Two main components of suction caisson are researched widely, first being the installation behaviour, and second being the behaviour of caisson during repeated cyclic loading. This thesis seeks to gain further insight on the installation behaviour of the suction caisson. For this purpose, a suction installation apparatus was designed to be used in centrifuge. Various installation characteristics such as flow rate, soil profile has been studied in this thesis and detailed analysis is provided. Extraction tests of caisson were also done at a slow rate to determine the drained tensile capacity, which was used for determining tensile amplitudes in cyclic loading tests.Tripod structures withstand load by ’push-pull’ system, where the windward caisson is pulled out of the soil due to the cyclic environmental loads. This movement is compensated by the push behaviour of the other two caissons. Thus, the tensile capacity ofcaissons plays an important role in the design of caissons in a tripod structure. Windward caisson of a tripod foundation was modelled in this thesis to study the behaviour of the caisson under cyclic loading in tension. Cyclic loading tests were done at 100g using the geo-centrifuge at Delft University of Technology. A series of tests was done for various cyclic loading characteristics such as the average load, frequency and soil profile. Settlement and stiffness response of the suction caisson were obtained for each scenario. A brief discussion of the results is made in this thesis report. Very high settlement was observed when one-way compressive load was applied on the caisson installed in layered sand. A test was also done to study the response of caisson to storm loading where very high tensile amplitudes were used. The results obtained from these tests show the complexity of the response under tensile loads. When the tensile amplitude was more than 50% of the tensile capacity of the caisson, significant uplift of the caisson was witnessed along with a significant reduction in the stiffness of the soil.Finally, Finite Element Modelling (FEM) was done using the geotechnical finite element software - Plaxis 2D to compare the cyclic loading results obtained from centrifuge modelling with FEM. It was observed that the initial settlement behaviour was captured well in plaxis. But after few cycles, no more accumulation of strain was witnessed in the centrifuge tests. However, plaxis failed to capture this behaviour and thus higher settlements were observed in FEM analysis.This thesis can be used as a basis for the design of tripod foundations for OWT using suction caissons. The results obtained from this thesis reinforces previous studies and adds confidence in understanding the tensile behaviour of suction caissons.

Offshore wind farms are rapidly developing in Western Europe as an alternative means of clean energy. The foundation of wind-turbines in the shallow water of the Northern Sea is almost exclusively (over 87%) performed by short rigid monopiles, as an efficient and relatively cheap solution. Scour formation, meaning the soil removal around the pile due to the actions of the waves and currents, is a potential hazard for the functionality and the integrity of the structures supporting the turbines. This thesis investigates the effect of scour formation in the soil-pile capacity and examines the possible contribution of the scour protection layers in the stiffness of the system both under static and cyclic loading. The methodology followed included 18 main static and cyclic centrifuge experiments and 9 basic cyclic numerical analyses. The physical modelling included an aluminum pile, equipped with strain gauges in order to calculate bending moments and ultimately derive the “p-y curves”, which was embedded in a dense dry Geba sand. Numerical analyses have been conducted in PLAXIS 3D, with a symmetrical fully drained model, in prototype scale, with the same set of materials (Geba sand, aluminum pile).
The results have shown that scour formation can diminish the lateral soil capacity in the ultimate limit state (ULS). Scour depth is the most critical characteristic of the scour hole geometry, but the scour width at a specific depth can also make the difference between structure’s integrity and failure. Therefore, the term “local” scour is deemed insufficient, as it cannot be described by a unique geometry. A valid design against scour is recommended to include a series of analyses with combinations of scour depth and width in realistic ranges. Experimental derived “p-y curves” have been compared with the ones proposed by the API method, concluding that the API overestimated both the initial response and the ultimate capacity of the soil reaction. It is proposed to update the existing regulations for the rigid piles and add rotational springs to simulate the effects of the considerable shear developing in the tip of rigid monopiles. The effect of the scour width in the “p-y curves” was observed to be limited in the shallower depth of the pile, as going deeper resulted almost to the same soil response regardless of the type of scour. The cyclic centrifuge experiments focused on the load type, investigating different scenarios of “one-way” and “two-way” load patterns. It was shown that the “one-way” case is more favorable in terms of accumulating deformations compared to the “two-way” case which experienced higher residual displacements, as long as the same maximum load was applied. This was attributed to the smaller dissipation of energy and hence destruction of the soil structure by the “one-way” loading. However, when the maximum load applied in a “two-way” experiment is considerably smaller than the equivalent of the “one-way” test, smaller deformations observed in the “two-way” test, implying the significance of the maximum load. The last section of this thesis, the numerical analyses, focused on the scour protection effect in the mechanical properties of the soil-pile system when subjected to cyclic loading. It was shown that a typical protection layer can highly increase the stiffness of the system and hence decrease the accumulated displacements. The length of the protection layer is not crucial, as change in its magnitude does not alter considerably the reduction of the accumulated displacements, in contrast with the thickness which has a larger impact on the stiffness of the system. It is concluded that scour protection layers can considerably increase the soil resistance around the monopile, allowing for smaller embedment length, so their contribution in the soil-pile stiffness should be taken into account for a more economic design.