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The aim of this study is the particularisation of the accuracy margins for the determination of the damage level in the experimental plan proposed by Remon Kik at his thesis for the study of Notional Permeability of breakwaters “The experimental research of the permeability factor P”. The evaluation of the proposed technique took place by means of comparisons between different test cases in order to specify the existence of similarities in the statistical behaviour of original tests and their repetitions. Therefore, statistical tests are used to examine the behaviour of the individual tests not only individually, but also in combination with the rest of the test components. For the selected statistical and computational approaches the optimum measurement space step had to be specified. Therefore, a comparison took place between measurements every 5cm and every 10cm. The length of the confidence intervals was used to quantify the difference in accuracy and the two fundamental non parametric tests of Mann-Whitney U/ Wilcoxon W and Kolmogorov-Smirnov (theoretical explanation Appendix B) were applied in order to qualitatively investigate the magnitude of the behavioral change of the distribution due to the addition of the in-between measurements (profile measurements every 5cm). The analysis showed that although the smaller measuring step increased the accuracy at about 10 -30% the differences in absolute damage values were trivial. Furtherupon, differences among tests that occur in the plunging and in the surging area were examined and tendencies were recorded. The outcome showed that an imperceptible difference occurs. The deviation was steadily bigger for the case of tests located in the plunging area (28% in contrast to 21.5% of the surging area), but this difference is considered to be trivial. Finally, the accent was paid in the limitations of the available means and equipment. The observed higher damage values at the sides were investigated. The 13 cross sections of the structure were divided into two groups of side and middle cross sections and comparisons between them were accomplished. Then the influence of the boundary measurements was quantified in order to interpret any existing tendencies of higher damage values and local irregularities that may affect the output of the computations. In fact, the data analysis showed that the variation of damage values at the side cross sections was for all the cases larger than the middle ones. In half of the cases the difference was significant while for the other half, difference occurred, but with a lower magnitude.

Granular filters are used for protection against scour and erosion. For a proper functioning it is necessary that interfaces between the filter structure, the subsoil and the water flowing above the filter structure are stable. Stability means that there is no transport of subsoil material through the filter to the water above the filter, and that no filter material is removed by currents above the filter. Three types of granular filters can be distinguished; 1) Geometrically closed filter structures, 2) Stable geometrically open filter structures, 3) Unstable geometrically open filter structures. This research is focusing on stable geometrically open filter structures. Recently, a desk study has been carried out by Deltares resulting in a new theoretical formula for single layered geometrically open filter structures (CUR, 2010). Hoffmans improved the theoretical formula that had been founded by Deltares (Hoffmans G. , 2012) The goal of this research was to verify the formula found by Hoffmans [2012] for structures loaded by currents (flow parallel to the filter construction). As part of the verification of the design formula ten flume experiments were performed in the Environmental Fluid Mechanic Laboratory at Delft University of Technology. After the execution of the model tests an extensive analysis was made based on the performed model tests and model tests performed in the past (Bakker [1960], Haverhoek [1968], Wouters [1982], Konter et al. [1990], Van Huijstee and Verheij [1991] and Van Velzen [2012]). The analysis showed that the formula is valid for single layered geometrically open filter structures loaded by currents. Two adjustments to the design formula are proposed: 1. The relative layer thickness fits better when related to the nominal diameter of the filter material; 2. The alpha value proposed by Hoffmans [2012] is too high (new alpha values are 30% to 60% lower). The original formula as proposed by Hoffmans [2012] gives unrealistic values for situations with wide graded filter material. Model tests showed that the relative layer thickness is better represented when related to the nominal diameter of the filter material. The design formula can be used for design purposes. The design of a single layered geometrically open filter structure can be schematized in two steps; 1. Firstly, determination of the material that should be used for the top-layer; 2. Secondly, determination of the layer-thickness of the filter/top-layer taking into account filter and base material characteristics.

Interlocking, single layer concrete armour units are placed in a specific grid depending on the type of armour unit. Within this grid, armour units are placed in horizontal rows. The number of horizontal rows of single layer armour units on a breakwater is limited to 20. This limit is proposed in order to prevent major settlements, which might affect the interlocking of the armour units. The limit on the number of rows is based on experience from prototypes and is not yet confirmed in a systematic study. Then number of rows also might have an effect on the load on the first (bottom) row of armour units, which affects the structural integrity of the armour units. The load on the first row of armour units is however unknown. The research presented in this thesis is a study on the load on the first (bottom) row of concrete armour units placed on a breakwater. Both the static load and the dynamic load were examined. The static load is defined as the load on the bottom row of armour units resulting from the higher positioned rows of armour units during conditions without waves. The dynamic load is defined as the load on the bottom row of armour units during conditions with wave attack minus the static load. These loads were studied by physical model tests. The static load was studied in an experiment in which the down slope force on the bottom rows of armour units (Xbloc units of 366 grams) was continuously measured during the placement of 20 rows of armour units on a slope of 37 degrees (slope of 3:4) in a series of 15 tests. The dynamic load was studied in a physical model test in a wave flume. The first row of armour units was placed on a movable frame which was connected to a load cell. The dynamic load was measured during tests with regular waves of 20% to 100% of the maximum wave height corresponding to the used armour unit (Xbloc units of 61.7 gram which were positioned on a typical breakwater slope of 3:4) and a wave period corresponding to an Iribarren number of 3, 4 and 5 for all of the described wave heights. This static load experiment resulted in a relationship of the measured static load on the first row of armour units with the number of rows applied on the slope of the model. From this relationship appeared that the static load approaches a maximum value after 10 rows. An analytical model was developed and validated against the measured results. This model gives an interpretation of the cause of the maximum value. The measurements of the dynamic load showed two clear phenomena. The dynamic load appeared to be a harmonic load with the same period as the waves imposed on the model. The dynamic load is the result of the flow of water along the armour layer. The maximum dynamic load on the first row of armour units occurred simultaneous with the maximum downwash which is in line with expectations. A relation between the downwash velocity and the amplitude of the dynamic load was found. The second observed phenomenon is the increase of the wave averaged load on the first row of armour units during the test. During the tests the harmonic load oscillated around an equilibrium line which showed a positive trend. The measured load after testing was significant higher than the measured load at the beginning of the tests. A relation was found between the wave characteristics and the increase of the load on the first row of armour units.

The design formula for rubble mound breakwaters by Van der Meer has an unclear Notional Permeability term. This term causes a lot of confusion for designers. In the past many people have tried to derive a better formulation for that term by experimental and analytical research. The goal of this study was to obtain a better formulation along a numerical way. This study explores the numerical possibilities and tries to define which direction has to be taken in future research. As a first step, a very simplified case is taken with a vertical homogeneous breakwater which interact with monochromatic waves. In total six different blocks were made of epoxy and elastocoast. Only 4 out of the 6 blocks were tested. Also the porosity (n), laminar friction (α) and turbulent friction constant (β) of the blocks were determined experimentally. This way the experimental results could be compared with computations. These experiments have been done in the large flume of the Environmental Fluid Mechanics Laboratory of the TU Delft. Two types of data were collected: pore pressures and water levels in front and behind the block. The water levels seemed to be the most reliable data. The main deficit of the setup was the wave absorber at the end of the flume. The wave absorber is not able to sufficiently absorb long waves. So the dataset had to be corrected for that effect. The created dataset was in line with results from earlier experiments. Results were compared with an analytical solution and the numerical SWASH model. Comparisons with the analytical solution showed a reasonable fit without any calibration. The SWASH model showed in first instance large deviations using the same dataset. By calibrating the turbulent flow resistance β, it was possible to generate a decent fit. However, the used β constants are 6-10 times higher than the measured β constants. This is physically unrealistic high. Therefore the most likely explanation is an error in the transition between the water and the porous medium. During the experiment discontinuities can occur on this transition while SWASH uses an continuity requirement. Numerical tests were performed on some multi-layered combinations of the different blocks in order to derive a "Vertical P" value in a similar way as Van der Meer determined his P=0.4 structure. The results showed, nevertheless, quite some different patterns as the computations done by Van der Meer. However, taking into account all the problems with calibrating the SWASH model the results for the notional permeability seemed very promising. This numerical method shows the possibility of numerically calculating a notional permeability and should be investigated further in the future.

A Knowledge Management Strategy can help to maintain or improve a knowledge management process. There are two knowledge management strategies; personalization and codification. A personalization strategy focuses on the flow of tacit knowledge through personal contacts while in a codification strategy In codification strategies, explicit knowledge is transferred to information which can be stored in database and can be analyzed independently of the current carriers of the knowledge. Knowledge Management Strategy Conditions can help to determine which knowledge management strategy is best suited for an organization. These (ten) conditions are: Innovation, Networks, Motivation, Attitude, Organization, Community, Sharing, Frequency of repeating tasks, Willingness to follow processes and protocols and the cost-efficiency of a database.

The reshaping of temporary rubble mounds like the core of breakwaters or reclamation bunds is often a concern for contractorsi n the construction stages of marine structures. The formulas found in literature for the prediction of such behavior are few, and they do not provide clear insight on the influence of relevant parameters, in particular the small dimensions and wide stone-size gradation of the material involved, usually consisting of quarry run or resulting from dredging. The previous research in the field of dynamic stability focused on berm breakwaters and gravel beaches. These two typologies of structures define the range to which the rubble mounds considered in this study generally belong. An overview on the design tools provided by the technical literature shows that, whenever the grading was included as a governing parameter, some influence was recognized in the characteristics of the structure (e.g. the permeability) and in the dynamism of the different fractions of stone sizes. However, very wide ranges of the parameter grading were never investigated and a specific analysis in this direction constitutes the main significance of this study. The Delft University of Technology provided the laboratory facilities to carry out physical model tests on a wide graded rubble mound structure representative of the core of a breakwater. The parameter D85/D15, describing the stone-size gradation of the construction material, was varied between the values 2.71 and 17.7, and two different seaward slopes of the model structure were also tested. The reshaped cross-shore profiles measured during the tests showed how if the grading increases the stability of the structure is reduced. This is not always in accordance with the findings of previous researchers, showing how the extrapolation of existing empirical formulas to structures with high values of the ratio D85/D15 do not give reliable results. Instead, the formulas given by van de Meer (1992) to estimate the whole reshaped profile of a dynamic slope predict with good agreement the shape of the measured profiles, although the physical model shows a larger horizontal extension of the displacements. This difference is governed by the grading, being more noticeable as this parameter increases. This result leads to the definition of new formulas, some of them being modifications of the ones given by van der Meer, to describe the geometry of a reshaped profile. The formulas, all including the parameter grading, are derived through curve fitting of the measured data. Also a formula for the direct estimation of the crest recession is given. As a final step, a simple numerical model is proposed in which the new formulas are implemented, constituting a quick way to assess the shape of a slope after a wave attack. As a suggestion for further utilization of the results of physical modeling, a brief comparison is also carried out between the output of the tests and the prediction of the numerical model XBeach (developed mainly at UNESCO-IHE). In conclusion, this research points out how the formulas provided by the technical literature are not reliable in representing the effects of a very wide stone-size gradation in the stability of a rubble mound structure. Physical model tests proved to be a suited way to investigate these effects, as the nature of the phenomena who play a role in the stability does not allow a simple analytical representation. The tests carried out within the present study lead to the implementation of a numerical model of practical use for engineers and contractors: further investigations through laboratory tests are recommended to validate and extend the findings of this study. Another proposed direction for further research is the comparison between the results of physical model tests and the output of numerical models.

Breakwaters are important objects to protect coastal- and harbour areas. To minimalize the probability of failure of breakwaters, a lot of research has been conducted concerning the stability of breakwaters. After Iribarren and Hudson, an influential research is conducted by Van der Meer. The literature research of this report will provide more background information concerning their researches on the stability of breakwaters. Van der Meer tested three sorts of breakwater constructions. The first breakwater structure contained a homogeneous construction (P=0.6) The second and third structure consisted of respectively a construction with impermeable core (P=0.1) and a structure with a filter layer and a permeable core (P=0.5). These variants of breakwaters were constructed with different slopes angles to require as much information possible concerning the stability of breakwaters. Van der Meer discovered two formulas for the stability of breakwaters. The first formula is used for plunging waves while the second formula is used for surging waves.Within these formulas, important factors as damage, wave height and notional permeability are included. The most important parameter of the formulas of Van der Meer is the notional permeability factor P. Van der Meer conducted his research on three different constructions and has designed a fourth construction based on the stability curves. This fourth construction has a value of permeability of 0.4. This value is estimated based on curve fitting. Following the research done by Van der Meer, Kik has subsequently researched the notional permeability of three breakwater constructions. Firstly, Kik repeated the test with a construction of impermeable core (model 1/P=0.08) and the test with the construction of filter layer and permeable core (model 2/ P=0.05) of Van der Meer. Lastly, Kik did a third test existing of a variant of the design of the fourth construction of Van der Meer (model 3 / P=0.35). Concluding from his research, Kik stated that the ‘Root mean square equation’ is a reliable method to determine the notional permeability P. During this research the influence of the thickness of the filter layer on the notional permeability P is studied. This research will also try to answer the question whether other relevant aspects might influence the notional permeability as well. The elaboration of this research is performed in a practical way in a wave flume in the water laboratory of the faculty of civil engineering of the TU Delft. Scale models of the breakwaters were constructed to test the notional permeability of the breakwaters. In the water laboratory three models were tested. Firstly, model 3 of Kik is repeated as model 3A, with a calculated value of notional permeability P 0.38. The construction of model 3A is build with a top layer, filter layer 1, filter layer 2 and a impermeable core. Second, another variant of model 3 of Kik is designed and tested (model 4). However, the measured damage figures were too low and therefore they could not be used to calculate a value for the notional permeability P. The construction of model four is build with a top layer, filter layer 1, filter layer 2 which is thicker as model 3A and an impermeable core. Finally, model 5 is tested with a calculated value of notional permeability of P 0.45. This model is designed from the fourth construction of Van der Meer. The construction of model 5 is build with a top layer, filter layer 1 and a permeable core with the same material of filter layer 2 of model 3A and model 4. The results of this research show that the influences of the notional permeability P exists of the ratio of the armour layer thickness and the thickness of the second filter layer. If the layer thicknesses are equal the value for notional permeability P is 0.38, which follows from model 3A. If the second layer has an infinite thickness (permeable core), the value for notional permeability P is 0.45, which follows from model 5. The value of the notional permeability P of model 5 corresponds to the design calculations of the computer model HADEER. Van der Meer discovered using this computer model that the ratio of dn50a/ dn50f = 5 has a value on the notional permeability P of 0.43 –0.44. During this research, while using two different methods, a value of the notional permeability P of 0.45 was calculated.

Scour formation at the toe of a rubble mound breakwater can lead to abrupt failure. Nowadays, counteraction of scour via geometrically closed filter rules, geotextiles or combinations is the common practice. Alternatively, in specific cases the use of geometrically open filters can save significant amount of time and decrease constructional costs. As a primary step towards this direction, the prediction of scour formation through a geometrically open filter can provide important information. Nevertheless, at this moment the knowledge upon this issue is insufficient and limited. A variety of recommendations occurs in literature, separately for toe design/scour protection and for the application of open filter criteria; however none of the studies treats these subjects combined. Therefore the objective of the present thesis is to get insight into scour formation and development through a breakwater toe lying upon sand and designed as a geometrically open filter. Thereby the research aims in drawing the link between scour characteristics with wave loading and filter configuration properties. In order to accomplish the research objective 2D physical model tests were conducted in the 25m long, 1m deep and 0.6m wide wave flume of DMC, installed in the company’s laboratory. In total, 23 tests were executed with irregular waves (Jonswap spectrum) and by varying wave loading and filter configuration properties. In particular, 5 different filter/base layer combinations were examined and 3 different wave conditions were used to investigate the effects of relative grain diameter, relative filter thickness, grading of filter layer, base layer stability Number and storm duration. Quantification of damage magnitude was accomplished via laser profile measurements of filter and base layer prior and after the execution of each test. Furthermore, wave particle velocity climate was determined via the use of an Electromagnetic Flow Meter (EMS) placed at the center of the toe. Finally, temporal evolution scour was captured through the side glass and was examined by digitizing and analyzing snap-shots from predefined time steps. Test results and observations have revealed the highly spatial character of scour formation. Nevertheless, tests with identical boundary conditions showed a surprising convergence in averaged maximum scour depth magnitude. In addition, in the majority of tests an S-curve erosion/deposition pattern was shaped while erosion started immediately at the downstream side of the box threatening breakwater stability. Equilibrium maximum scour depth was reached for less than half the data set; thus erosion process was still in progress. Based on this, two approaches were developed to investigate temporal evolution of scour. Furthermore, dimensional analysis and literature review have revealed the most important parameters that have significant effect in scour formation; their combination has led to the formation of a prediction tool. However, combination of the results from tests with different base materials would not be possible without the introduction of the base material stability Number (critical Shields’ Number). The derived tool is an empirical expression with limited physical background and range of validity. Additionally, it overestimates maximum scour depth due to a serious model effect; the different buoyancy between filter and base layer that was causing initial damage and damage exaggeration. Nevertheless, it is capable of delineating the relative contribution of each parameter in scour depth formation. For an overall view of scour formation, further research will be needed to provide a more accurate quantification of the interrelation between parameters that play a role in scour formation and development, and to implement the effect of missing parameters. Consequently the use of the derived expression as a scour prediction tool in real life is not yet recommended.

This thesis focuses on wave overtopping at rubble mound breakwaters with a non-reshaping berm. The research was aimed at gaining insight into the influence of a permeable berm on the overtopping behaviour. Moreover it was desired to validate existing prediction methods for the spatial distribution of overtopping for breakwaters with a non-reshaping berm. Wave overtopping was investigated by means of a physical model. The breakwater scale model was divided into 8 collection bins. Overtopped volumes were collected and pumped into floating tanks further down the flume. After the experiment the mass of the floating tanks was measured and the mean overtopping discharge could be determined for 8 horizontal positions on the breakwater. The measured total overtopping discharges cannot be predicted accurately by existing prediction methods. On the basis of experimental data a new prediction method was proposed that achieves an excellent fit for total overtopping. The crest freeboard definition was adjusted to account for the permeability of the crest. The reduction factor accounting for slope roughness was made dependent on the Iribarren number. For Iribarren numbers higher than 6, this method calculates no reduction of overtopping due to slope roughness. The effect of a permeable berm on total overtopping was found to be remarkably different from the effect of an impermeable berm. Permeable berms below Still Water Level (SWL) lead to less reduction of overtopping than impermeable berms below SWL. Berms above SWL lead to wave breaking on the slope in front of the berm. Contrarily to impermeable berms above SWL, a permeable berm above SWL leads to significant reduction of overtopping. The measured spatial distribution of overtopping is associated with a lot of seemingly random behaviour. Large differences were found with the experimental data of Lioutas (2010). It is suspected that the used experiment setup gives rise to significant model effects for the spatial distribution of overtopping. An experiment setup was recommended that is expected to more accurately model the behaviour of the prototype situation. Data on the spatial distribution of overtopping could not accurately be predicted by existing prediction methods. In some cases existing prediction methods provided an upper limit for overtopping (Juul Jensen, 1984) but none led to a good fit with the experimental data. A new reduction factor was found that reduces the amount of scatter and provides a conservative prediction of the experimental data.

The stability formula developed by Van der Meer is used for the design of different kind of rock slopes. In the formula is among a number of other parameters also the permeability of the structure represented. A more permeable structure has the ability to dissipate more water and therefore more energy, this results into a lower required weight of the armour layer. This coefficient, described as the Notional Permeability P, has been determined for three different types of structures. A homogeneous structure, a structure with a permeable core and an impermeable structure. In practice structures are being build who deviate from these standard situations. Therefore there is a demand for values of P about structures other than the known standard situations. In this thesis P values are found by means of physical scale model tests. First of all two reference structures were tested. The permeable and the impermeable structure with known values of P= 0.5 and respectively P=0.1. The values found in this study are almost equal to the values above. The new structure has an impermeable core covered with a thick filter layer. On top of that an under layer is placed and finally there is a double armour layer.