966 research outputs found
Overtopping resistant dike, Sandy dike
No full textAn important element in the ComCoast concept is the overtopable sea defence (often a dike). In this concept the landward (inner) slope of the dike is adjusted in such a way that it can withstand higher overtopping rates. Two new concepts for covering the inner slope, sand cover and perforated mats, are discrebed in this report.Civil Engineering and Geoscience
Innovative concept overtopping dike: Crest Drainage Dike, Theoretical Study
No full textThe ComCoast concept involves measures in seaward and landward direction. One of the options in landward direction is an overtopping dike. In this concept the crest and/or inner slope of the dike is strengthened so that more overtopping of the dike can be allowed. Advantage is that heightening of the dike is not necessary and furthermore this can be combined very well with a wet and brackish zone behind the dike. This zone provides opportunities for nature development, recreation and possible concepts like living in the water (houses on poles). Instead of increasing the revetment strength of the entire inner slope, it is also possible to decrease the overtopping loads at the inner slope without alteration of the cross section of the dike. An alternative where the wave-overtopping load on the inner slope is reduced to an acceptable level by measures taken at the crest of the dike. The concept "Crest drainage dike" consists of a concrete construction in the crest of the dike (in the form of a wide Uprofile). The theoretical study for this solution is discribed in this report.Civil Engineering and Geoscience
Biomarkers of ventricular remodelling in African hypertensives.
No full textIncludes abstract.Includes bibliographical references.There is substantial evidence that the burden of hypertension, hypertension with left ventricular hypertrophy and hypertensive heart failure is very enormous in sub-Saharan Africa. There is therefore the need to look for easier and faster means, compared to electrocardiography and echocardiography of diagnosing and differentiating the different effects of long standing hypertension on cardiac remodelling which ultimately lead to systolic and diastolic dysfunctions as this affects the prognosis, management and treatment modalities of hypertension. We studied 210 subjects who were subdivided into three groups after echocardiography: those without left ventricular hypertrophy (HT) (n=83); those with left ventricular hypertrophy (HTLVH) (n=50) and those with hypertensive heart failure (HHF) (n=77)
Design of a pilot dike on Cat Hai Island
No full textMaster project report. On behalf of, and in cooperation with the TU Delft and the MARD-CWRCT two dike designs are made for a pilot project on Cat Hai Island. Two different types of revetments are used, namely the Dutch block type revetment Basalton and the classic rip-rap revetment. The designs are based on the available boundary conditions, the new Vietnamese guidelines and the Dutch knowledge. The focus points of the technical design are the geometry, the revetment, toe construction and the settlement. Compared to the current Vietnamese dikes, the design is revolutionary due to the presence of an outer berm. Besides the technical part of the design, the logistics and finance for the pilot project is explored. The different possibilities of producing, placing and transporting together with a time and cost estimations are given. In addition a proposal is given for the maintenance schedule and how to monitor the dike. Eventually two optimal dikes are further investigated, this height is based on zero overtopping and the most economical feasible. The crest heights of the old Vietnamese dikes on Cat Hai Island are around 4,80 m and it has a dike footprint width of 40,20 m. The crest height of the Basalton dike will be one meter higher than that of the rip-rap dike and the rip-rap will be one meter higher than then old dike. Because Baslaton has a larger wave runup than a rip-rap dike. Therefor the footprints of both the new Basalton and rip-rap dike are almost twice as large as the old footprint. The reason for this is because of the use of a berm in the outerslope for the Basalton dike. An estimation of the cost of this project is for a riprap dike, roughly 24 billion VND and for the Basalton dike more or less 21 billion VND.Hydraulic EngineeringCivil Engineering and Geoscience
Innovative concept for an overtopping dike
No full textThe ComCoast concept involves measures in seaward and landward direction. One of the options in landward direction is an overtopping dike. In this concept the crest and/or inner slope of the dike is strengthened so that more overtopping of the dike can be allowed. Advantage is that heightening of the dike is not necessary and furthermore this can be combined very well with a wet and brackish zone behind the dike. This zone provides opportunities for nature development, recreation and possible concepts like living in the water (houses on poles). Instead of increasing the revetment strength of the entire inner slope, it is also possible to decrease the overtopping loads at the inner slope without alteration of the cross section of the dike. An alternative where the wave-overtopping load on the inner slope is reduced to an acceptable level by measures taken at the crest of the dike. The concept "Crest drainage dike" consists of a concrete construction in the crest of the dike (in the form of a wide Uprofile). The proposal for this solution is discribed in this report.Civil Engineering and Geoscience
Uncertainties in future dike design
No full textA dike is designed for an extreme event which greatly exceed the situation under daily circumstances. The expected loading during such an event is, however, difficult to estimate. Inherent uncertainties in nature and epistemic uncertainties in models and statistical data impede a clear verdict about the exact loading on a dike. Consequently, incorporating uncertainties in a dike design can have a great impact. One of the aims, following the Delta Decisions of 2015, is to improve the way uncertainties are incorporated in future dike assessment and design models. Conventionally, models become more computationally intensive with the incorporation of each additional uncertainties. Therefore, it is useful to only account for most influential uncertainties. Until new models are established, the Ontwerpinstrumentarium (OI2014) is released for the transitional period. The guideline explains for which extreme event a dike needs to be designed. Looking in more detail to the OI2104, questions can be asked about the underlying assumptions. In this thesis, a modified method of the OI2014 is exhibited by looking into a dike’s location specific dominant failure mechanisms. In so, a better cost-optimal dike design can be realized. Also, a sensitivity is carried out in which currently recognized uncertainties are investigated using the PC-Ring model. In addition, a new statistical wind uncertainty model is built, wherein uncertainty is integrated a priori under the assumption that correlations between random variables do not play a significant role. The model’s implications are evaluated using the Hydra-Zoet model. From this research three main findings can be deduced. Firstly, the proposed methods of the OI2014 do not lead to a cost-optimal dike design. Secondly, addition of statistical wind uncertainty leads to a significant increase of hydraulic boundary conditions for lake systems. Lastly, the prior integration of any random variable has many computational benefits.Hydraulic EngineeringHydraulic EngineeringCivil Engineering and Geoscience
Sandy dike, Comcoast - WP3: Innovative concept of an overtopping resistant dike
No full textAn important element in the ComCoast concept is the overtopable sea defence, often a dike.The landward (inner) slope of the dike is adjusted in such a way that it can withstand higher overtopping rates. One of the concepts to improve the resistance is the "Sandy Dike", a cover of the inner slope with layer sand. The sand will be washed away during extreme overtopping events, but this will not threaten the sability of the dike if the thickness of the sand layer is sufficient. The objective of this study is to elaborate the feasibility of the concept by means of a short theoretical study. In this report a describtion of the relation with its environment, a further developed theorie, a provisional design of the concept and a test case are given.Civil Engineering and Geoscience
Reliability Analysis for Overturning and Sliding of Lacustrine Dikes: The Nezahualcoyotl's Dike Case
No full textBefore the year 1519, the Valley of Mexico was a closed basin and at the bottom of the valley, an extensive system of shallow lakes was formed. Within this lacustrine system, the capital of the Aztec empire, Tenochtitlan, was built. The Aztecs were known for their impressive constructions and complex hydraulic structures, of which the most impressive structure was the Nezahualcoyotl dike. This structure was constructed across Lake Texcoco. Its principal function was to protect the city of Tenochtitlan from high water levels at the lake. However, there is not enough information about the reliability of this dike. Mainly due to two reasons, today there are no remains left of the dike and most of the lacustrine system is drained. In this paper, we present a method to study the reliability of the Nezahualcoyotl dike under two failure modes, overturning and sliding. This is done by following up on the work presented by Torres-Alves & Morales-Nápoles (2020) where they developed a hydrological characterization of the lacustrine system and studied the dike under one failure mode, overflow. The proposed analysis aims to provide a more realistic assessment of the reliability of the dike as a flood defense mechanism.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Hydraulic Structures and Flood Ris
Case Study: Kinderdijk - Schoonhovenseveer: Dike reinforcement lekdijk
No full textThe dike reinforcement project Kinderdijk – Schoonhovenseveer (KIS) is part of the Lekdijk, a primary flooddefense that directly protects two major polders in its hinterland fromflooding by the Rhine: the Alblasserwaard and the Vijfheerenlanden polders. Theinitial expansion of local villages (in the Middle Ages) was concentrated near thedike and around the churches, resulting in ribbon development along the dike (seeFigure 1). Beyond the dike, part of the floodplains is a nature conservationarea. The local population is aging, and village shops, businesses, and localactivities are slowly disappearing. There is a shortage of housing for youngpeople. Policy Analysi
Design of a breach retardant dike
No full textSand dikes have a sand core and a clay layer to protect the core against erosion. It is not unlikely that this layer fails due to several failure mechanisms, exposing the sand core to water. This can be catastrophically when water is overtopping the dike. In case the protective cover fails, water can flow over the core and erode the sand, eventually causing the dike to breach. This breaching process is described and modelled for a better understanding. The BRES-model (BReach Erosion in Sand dikes) was specifically created for sand dikes and is used to simulate this process. It determines, among others, the final breach width, flow rate through the breach and duration of the breaching process. These breach parameters are important for determining rise rates and flow velocities of the water in a polder. By reducing rise rates and flow velocities, which can be achieved by retarding the breaching process, the number of casualties can be reduced. The safety of the inhabitants depends on the mortality during a flood event, i.e. the fraction of casualties of inhabitants in a polder. The safety increases when the mortality reduces, i.e. the amount of casualties decreases. To reach a desired ten times higher safety level, the mortality has to decrease by a factor 10. The breaching process can be retarded in several ways, such as altering the dike shape, increasing the cohesion or strength of the sand core, adding components to the dike or influencing the erosion parameters of sand. Literature research results show that adding a few percent bentonite clay to sand, cementing sand with a biological process or mixing sand with fibres are the most promising options. For these options erosion formulas were determined to implement into the BRES-model. The most promising options were modelled in the BRES-model using a norm dike. The breaching process of this dike was simulated in case it was constructed of sand, mixed with bentonite or fibres, or biologically cemented. The norm dike is the dike which was constructed for the ZWIN’94 experiment. The model simulates the breaching process of these options and the results are compared to each other. From this comparison it is concluded that adding bentonite or polypropylene fibres to sand, or biologically cementing sand lead to similar reductions of the breach parameters. To test the results of the model outcome, laboratory experiments were executed. Sand, sand-bentonite and sand-fibre mixtures were subjected to direct shear, permeability and erosion tests. These tests show that sand-fibre mixtures do not significantly influence the measured parameters of the sand. The sand-bentonite mixtures show a significant reduction of the permeability and erosion velocity compared to sand. The erosion velocities of these mixtures can be modelled in the BRES-model with the Van Rijn-Van Rhee formula. Using the results from the laboratory experiments the effects of bentonite on the breaching process of the norm dike were determined. Even adding a few percent of bentonite reduced the final breach width, maximum breach flow and inundation velocity (rise rate) significantly. For the norm dike it was calculated that 5.4% bentonite is sufficient to reduce the inundation velocity below the threshold value of 0.5 m/h. This results in a reduction of the mortality of approximately a factor ten. Preliminary research indicates it is possible to mix bentonite with sand in-situ, using a Mixed-In-Place technique. A cost indication shows that improving a dike with bentonite using this technique might cost approximately the same as a traditional dike reinforcement. Depending on the circumstances this solution may lead to a decrease of mortality and thus an increase in safety, even by a factor 10.Hydraulic EngineeringCivil Engineering and Geoscience
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