1,720,952 research outputs found
Final Report Levee Challenge: Team Hans Brinker
No full textIn this assignment we simulate a two meters wide dike stretch which is subjected to overflow. Three failure mechanisms could occur due to overflow: full erosion of the soil of the dike, macro instability of the levee if too much soil is eroded away, leading to insufficient counterweight on the inside of the levee, and surface slip failure due to reduction of strength of the dike by flow of water in the dike core. Prevention of failure can be achieved by either keeping the water away from the berm surface or holding the soil particles in place while the water flows alongside it. The desired repair is an emergency repair that can placed quickly during a storm, or between two storms to prevent a damaged levee from failing. This is a temporary repair that will later be removed for full reconstruction of the levee. This provides constraints to the installation and repair procedure.To decide which solution is best, 10 concept solutions are compared based on their score in the Multi Criteria Analysis with 8 weighted criteria. The solution with the highest score is the best solution according to the Multi Criteria Analysis. The selected repair option is to locally cover the damaged area with flexible overlapping sheets of Tyvek®. This is a light and thin material that can easily be transported and cut to size at the location of the repair. These sheets can be easily secured against flow loads using Gripple anchors, while pins are used to keep the Tyvek® in place during windy conditions. An installation plan and cost breakdown was made. Using 3 m wide Tyvek® rolls, the costs would be around 19.19 euros per meter height.The damaged areas of the levee are covered with Tyvek® which is a waterproof, damp open material. This prevents the penetration of water into the core through the damaged areas. The Tyvek® also prevents the exposed soil from being eroded. Moreover, Tyvek® is a very strong material that won’t be torn off. As there is no strength reduction due to water penetration or further loss of surface material the chance for macro instability is minimized.First, a design was created, with components dimensioned for a dike stretch in the Hedwigepolder. Subsequently, the design was validated with tests. Including two types of damage. The first was removal of a 2 by 2 m grass layer (0.1 m thick) at the top of the dike and the second was a dug-out step-section across the entire width of the dike with a height difference of 0.5 meters at the toe of the dike. Only the second damage went through the clay layer and into the sand core of dike.During and after the tests some important observations were made. During all test volumes the plastic sheets were kept in place due to the anchors and pins. Some pins however, came loose due to vibration of the sheets (we presumed the cause of vibration is flow of water between two sheets or turbulence of water). The trench of the lower damage was partly washed away by the water. The erosion of soil in the trench did not result in changing the stability of the top sheet. At the lower damage the plastic sheet was torn off after a tear of 1 m was made with a knife.Our solution is designed to protect any dike from macro-instability by keeping the water flow away from the berm. This is done by layering multiple sheets of plastic foil over the inner berm, fastened with ground anchors and pins. The solution is a durable and reliable design due to proven waterproof, damp open and UV resistant properties, together with Gripple's demonstrated anchoring capabilities. Another major advantage of our solution is that the repair of the damage is selective, i.e. the solution is applied only to the parts of the levee where damage has occurred. In case of only localized and small damage to the levee, the costs and workload are very minimal compared to other solutions that are applied to the entire surface area of the levee.Polder2CCivil Engineerin
Grand Bahama after Hurricane Dorian: Interdisciplinary approach to Build Back Better
No full textIn collaboration with the University of the Bahamas, we used the Charette model, the Three-point Approach and the conceptual framework: Build Back Better to propose a solution that involves several aspects: Reduced risk overall, increased social cohesion on the island, improved life quality and reduced costs during reconstruction in the aftermath of a hurricane event. Based on the analysis of the island, the hurricane and the important physical processes, a division between protection method is proposed based on the location on the island: collective andindividual protection.The main vision for the reconstruction of Grand Bahama is to Build Back Better. This is done by taking an interdisciplinary approach and connecting engineering to spatial planning and design. The proposed strategy reduces the risk by taking into account exposure and vulnerability of the general risk approach. The main point of the strategy is to create a resilient urban environment in which vital infrastructure like the airport remains functional. This is done by making a collective protection zone of the economic and social city centre of Freeport, a zone that also offers shelter. Individual protection and evacuation shelters will be given to residents, buildings and facilities in the less densely built areas, east and west of the city.MP31
Human Stability On Slopes Under Overtopping Waves
No full textIn a world affected by climate change and sea-level rise, intense storms are expected to become more frequent in the future. This implies that our coastal protections will be more often and more intensely affected by overtopping waves, potentially endangering the safety of our coastal communities. The objective of the present study is to investigate the hazard to people/pedestrians by postwave overtopping flows over an inclined surface, simulating a coastal dike.Hydraulic Structures and Flood RiskCoastal Engineerin
The investigation of animal burrows in levees: Using experimental data to develop a probabilistic model that aims to improve the efficiency of manual inspection of animal burrows on levees
No full textAnimal-induced anomalies on a levee surface negatively affect the erosion-resistance of a levee, leading to rapid failure of the inner slope in case of overtopping and/or overflow during high water. Where active prevention techniques of burrows from large animals, such as muskrats, are applied in and around levees in the Netherlands, the identification of smaller burrow holes made by voles and moles and the evaluation of the severity of the damage rely solely on the assessment and experience of the levee inspector. The Polder2C’s project aims to quantitively assess the impact of animal burrows on the levee surface by conducting experiments at the Living Lab Hedwige and Prosper Polder (LHPP) and this thesis aims to contribute in this by analyzing the experiment results and developing a model for levee inspection that includes uncertainties of the geometrical characteristics of vole and mole burrow systems. This thesis distinguishes two phases, the first of which focuses on the question: ‘How do animal burrows influence levee performance?’, and it aims to form a foundation for the second phase of the report by focusing on the behavior of burrowing animals and the geometrical characteristics of their burrows by conducting a literature review on existing research on this topic. Guidelines were set up that contribute to the identification of mole and vole burrow system by investigating the main differences between them, with the aim to easily identify separate burrow hole groups in the experiment data. These conclusions could then be used to identify different vole and mole burrow hole groups in data that was collected from several experiments at the Living Lab Hedwige and Prosper Polder (LLHPP) between October 2021 and February 2022 and answer the research question for the second phase, which was: ‘Based on data from levee inspection experiments, which probabilistic model can assess the inspection success rate of animal burrows?’.Civil Engineering | Hydraulic Engineerin
Interaction between a sustainable water management strategy and Build Back Better: Sustainable drinking water management strategy for Grand Bahama Island
No full textThis thesis examines the role of the concepts of “Build Back Better”, “Disaster Cycle”, and “Sustainability” in water management and the possibility of the interactions between these concepts when designing water management infrastructure. Especially in cases where the disaster cycle is relatively short: 10 to 15 years between disasters. The case study is on the island of Grand Bahama. The island of Grand Bahama depends on the freshwater groundwater lens for its drinking water. Flooding during hurricanes introduces saline water into that groundwater lens. It is therefore highly probable that the current drinking water production method will not be able to meet the demand in the future. An alternative drinking water supply system should therefore be examined. To investigate the interactions between the concepts, they are put into a conceptual design process, which uses the methodology “RenewIsland”, and used to set up some preliminary designs. Three Alternatives were made with the methodology “RenewIsland”. These Alternative designs were then subjected to a Multi-Criteria Analysis (MCA). This thesis substantiates from the process that the interaction between the concepts is possible and that the inclusion of Build Back Better in the Water management decisions gives more possibilities to make balanced choices. A blueprint has been made for a method to analyze swiftly if an alternative is compatible with the different cycles and phases of a location regarding a disaster and normal circumstances. This thesis also states that the study has to be extended with more research to make it generally applicable.Civil Engineerin
Reliability Analysis of Foundation Pile Designs from Eurocode 7
No full textRisk-based and probabilistic reliability design methods are starting to be integrated into the daily geotechnical engineering practice, as shown by the current draft of EN1997 (Eurocode 7), which explicitly allows Reliability-based verification of limit states. The semi-probabilistic design methods in EN1997 are a compromise between ease of use and accuracy of the achieved reliability levels. In contrast, EN1990 (Eurocode 0) requires accurate full probabilistic design targets. An assessment to investigate if the semi probabilistic methods from EN1997 comply with the EN1990 reliability targets is therefore necessary since the link between the norms is not explicitly established. In this study, pile foundations serve as an example to assess compatibility between the EN1990 and EN1997. The deterministic Dutch pile design approach by van Mierlo & Koppejan (1956), CPT based design method, is adapted to the semi probabilistic model pile recipe in the EN1997 draft. This thesis assesses what reliability levels are achieved by the model pile design method in draft EN1997 considering the axial bearing capacity and how these compare to the reliability targets in EN1990.Methodology: To assess the performance of the model pile method from EN1997, the design outcome from the semi-probabilistic model pile method is compared to fully probabilistic quantification methods of the resistances and loads. Two probabilistic quantifications are used in the assessment, a Bayesian and a Student-T model. The achieved reliabilities are assessed with both the First Order Reliability Method (FORM) and Monte Carlo Simulation (MCS). Additional insight into the influence of different parameters is provided with sensitivity analysis and the calibration of partial factors. The assessment was applied in two case studies located in the Netherlands. In both case studies, the EN1997 designs resulted in reliability levels in good agreement with the reliability targets stated in EN 1990. This suggests an agreement between the semi-probabilistic and the full probabilistic models if sufficient CPTs are used. In both case studies, EN1997 designs accounted for more model uncertainty than the probabilistic models suggest, thus partial model factor (γRd) in EN1997 may be conservative. EN1997 covers spatial variability and uncertainty due to limited observations with the correlation factor (ζ, a factor that transforms calculated to representative values, and the partial resistance factor (γRc). The coverage of uncertainty with these two factors seems to be rather low, especially for situations with few CPTs available (less than 10), although the results seem to depend strongly on the degree of spatial variability in the CPT field. In the case of homogeneous soil conditions between observations, EN1997 design methods led to over-conservative designs for low numbers of observations. If the variability between limited observations (less than 10 CPTs) was high, designs are assessed to be less reliable than EN1990 requires.Overall, the results suggest good agreement of the semi-probabilistic design methods from EN1997 with the reliability targets defined in EN1990, for designs based on sufficient observations. The sensitivity analysis and isolation of the resistance uncertainty showed for the two cases that the uncertainty of the resistance has the dominating influence on the reliability of the piles, suggesting a low impact of complex stochastic load models. The latter finding suggests that probabilistic treatment of the resistance may be sufficient for assessing pile reliability in practice, while design values could be used for the loads.Civil Engineerin
Evaluating the stability of terps in the Netherlands
No full textTerps are artificial dwelling mounds mostly found in the northern regions of the Netherlands, built to provide safe ground against water in such areas affected by flooding, storm surges, and high tides, before the development of dikes. In this thesis, the stability of these terps was evaluated via FEM models and analyses performed on PLAXIS. Results highlight considerable stability risks when the terp slopes are subjected to considerable external loading, such as those exerted by heavy agricultural vehicles being operated in proximity of these.Geo-Engineerin
Assessment of macro-instability using SHANSEP in RFEM: The application of SHANSEP in combination with RFEM for safety assessment of dikes.
No full textThe Dutch Water board revised their guidelines for the safety assessment of dikes in 2017. A major change for the assessment of macro-stability is the use of the SHANSEP method to estimate the strength of impermeable cohesive layers. The failure probabilities are estimated with a deterministic analysis using limit equilibrium methods. The use of design values and safety factors to account for uncertainty is basic and proven to be conservative leading to over engineering.In this thesis, it is investigated how the SHANSEP method can be incorporated to the more advanced Random Finite Element Method. It is found that three random fields for SHANSEP parameters S,m and POP are required. The random fields do not show particular trends in mean or standard deviation. A random field generator is coded in Python. a simple version of the in-house FEM is modified to read the generated random fields. This code is used to test various geotechnical assumptions. A final version of the assumptions is coded into a more advanced version of the simulator to do the comparison. The output of the FEM code are the FOS and failure mechanism of a single evaluation with a combination of three random fields. A mean and standard deviation of the FOS results are calculated. The probability of failure is estimated by the area under the probability density function of a lognormal distribution for values below unity. The probability of failure of the deterministic case is estimated using the First Order Second Moment method. The results show that the probability of failure is overestimated in a FOSM analysis by one order of magnitude compared to the most conservative RFEM simulation. It is expected that this difference is even higher for the more conservative deterministic approach the Dutch guidelines prescribe. The slip surfaces of RFEM were found to be similar to their deterministic counterpart. The RFEM slip surfaces went through local weak zones in random fields.It is recommended to Dutch policy makers to investigate the use the random finite element method. Although conservatism is preferable in safety assessments, an conservatism of this significance compared to the RFEM approach is unnecessarily costly
Extreme Waves in the North Sea: Deriving extreme wave conditions applying Hierarchical Clustering and Non-Stationary Extreme Value Modelling
No full textCoastal and offshore infrastructure must be designed to withstand extreme wave-induced loading conditions. Extreme Value Analysis (EVA) is often employed to infer probabilistic distributions that provide information about extreme design conditions. In traditional practices, EVA is performed under the assumption of stationarity. This means that the probability of extreme events is constant in time. However, hydraulic loading conditions are expected to exhibit temporal variability in severity and frequency as a result of climate change. Therefore, the assumption of stationarity becomes questionable. Nonstationary extreme value analysis (NEVA) for inferring extreme hydraulic loads have become more attractive in recent years. However, the applicability of NEVA models is debatable ansd differs on a case-by-case basis. Large scale oceanic bodies can be characterized by spatially and temporally varying extreme wave characteristics. Clustering analyses have proven to be successful to identify regions exhibiting similar extreme wave characteristics. Creating clusters based on similar extreme wave characteristics can potentially improve extreme value modelling because intra-cluster information can be pooled to derive more accurate extreme value models.This research presents a practical assessment of the applicability of clustering analysis and non-stationary extreme value modeling of extreme wave statistics at cluster level in the North Sea. The primary objectives of this research are: (1) Study the temporal variability extreme significant wave height (Hm0) and extreme wind speeds (U10) in the North Sea domain, (2) Investigate how hierarchical clustering analysis (HAC) can be employed to cluster grid points that exhibit similar extreme wave characteristics, (3) How the obtained clusters and temporal variability can be employed to derive extreme value models describing extreme Hm0 statistics at cluster level and (4) assess whether NEVA models at cluster level form a practical alternative compared to conventional stationary analysis in the design and risk assessment of hydraulic infrastructure in light of climate change. Temporal trend analysis of Hm0 in the North Sea showed that the period between 1990 and 2020 can be characterized by a decreasing trend. Between 1950 and 2020, a decrease in Hm0 intensity is observed in the Western regions and an increase is observed in the East. This is reason to believe that the variability in extreme wave climate is cyclical rather than monotonic. There is reason to believe that temporal variations of extreme U10 are responsible for the temporal variability of extreme Hm0. Initial clustering results partition the North Sea domain into 50 clusters based on characteristic values for the significant wave height (Hm0), peak period (Tp), and dominant wave directions (θ1 and θ2). After splitting clusters based on geo-location and merging clusters based on the intra-cluster statistical properties of the wave parameters, 63 clusters are obtained. The identified clusters and temporal variability are used to define NEVA models describing extreme Hm0 statistics at cluster level. Intra-cluster Hm0 observations are detrended before fitting the GEV parameters by means of Bayesian Inference. Informative priors are constructed by pooling the GEV parameter information from the intra-cluster grid points. Potential non-stationarity is accounted for by adding the Theil-Sen parameters (b and b0) to the location parameter (μ∗), making the location parameter a linear function of time. The model parameters subsequently read: Hm0 ∼ GEV (μ∗ + (b · t + b0) , σ∗, ξ∗). Using the extreme Hm0 data from the clustering centroid yields the most promising results for describing extreme Hm0 statistics at cluster level under the condition that the intra-cluster exhibits homogeneous values for b and b0.The applied HAC analysis presented in this research is not the optimal strategy. The identified clusters exhibit heterogeneous values for b and b0 Because non-stationarity ofHm0 was not accounted for during the HAC analysis. This hinders the performance of the NEVA models at cluster level. Also, whether the derived methodology can be applied for the long-term projection of future extreme wave events in the North Sea is debatable. The non-stationary of extreme Hm0 is best described by a cyclic pattern. Without a thorough understanding of the underlying causes of the non-stationary in Hm0 and without future projections of the extreme wave climate, the applicability of NEVA for deriving extreme Hm0 design conditions in light of climate change cannot be guaranteed.Civil Engineering | Hydraulic Engineering | Hydraulic Structures and Flood Ris
A probabilistic framework for the quantification of vegetation effects on the failure mechanisms of Dutch river dikes
No full textRiver floods are becoming increasingly devastating because of climate change (more frequent and extreme rainfall), population growth and the increasing economic importance of river basins. This situation requires maintenance and strengthening of flood-defence systems.Adding certain types of vegetation at precise locations for their positive impact may be a cheaper, more flexible, and more environment-friendly way to strengthen dikes than the traditional increase in height. However, this nature-based (NB) option is not yet widely implemented due to the lack of precise knowledge of the potential of vegetation effects and their uncertainty.This study uses a probabilistic method to better understand the effects of vegetation by including vegetation in the computation of the failure probabilities of Dutch river dikes. A framework was established to combine all these vegetation effects simultaneously in the computation of the total failure probability, considering different magnitudes of each effect. This enables the consideration of a wide range of vegetation scenarios, from which conclusions were drawn.Overall, this thesis provides a useful and versatile tool for assessing the influence of vegetation on dikes that has a lot of potential and can be easily enhanced in the future.Civil Engineering | Hydraulic Engineering | Hydraulic Structures and Flood Ris
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