In the past humans used to protect their shores mainly with rocks. In the past decades the shore protections did gently shift to concrete element protections. An example of an often applied concrete armour unit is the Xbloc. This element is quite strong and well investigated. BAM Infraconsult has developed a uniformly placed armor unit, the XblocPlus. The new XblocPlus is placed in a regular pattern, which is easier for contractors to construct. A design detail of a XblocPlus armor layer which still needs some attention is the transition from the slope to the crest. The elements are placed in horizontal rows, locked in place by two elements in the row above and two elements in the row below. However, the upper element is not supported by any element above it, leading to less interlocking. This study focusses on the physical processes which lead to (in)stability of the upper element and tries to increase this stability. First, physical laboratory tests were performed with the main aim to visually observe the failure methods of the upper XblocPlus element. After the initial tests, a computational fluid dynamic model was built with the aim to get a better insight in the load distribution on a single XblocPlus element under wave impact. To increase the stability of the element as much as possible, several increments to the stability of the upper element are proposed. The first method which increases the stability of the element is to cover the back of the element with rock, this changes the rotation point of the element backwards which increases the wave load required to initiate rocking. A second possibility is to face the top of the upper element downward, this does decrease the drag on the element. A third possibility is to face the top of the upper element upward, this leads to a higher drag on the upper element. However, this orientation makes it possible to bury the element in a rock backfill, increasing the weight of the element. This thesis did slightly research the applicability of CFD models to concrete armor design. The main conclusion for this trial is that it is possible to apply numerical models for the design of breakwaters, however physical model tests are still required to validate the obtained data from the numerical model, since the flow around a coastal structure is that complex, it only estimates the loads in the right order of magnitude when not validated. The validity of the model can be increased by calibrating the soil parameters using measured pressures in the different layers of the breakwater. To increase the accuracy of a numerical model, one could construct a three dimensional structure, which requires much computational grid cells, making the computational demand of the system quite high.

Zeeland, located in the south west of The Netherlands, has suffered major casualties and damage due to the flood in 1953. After the disaster, the Dutch Government appointed the so-called Deltacomittee, provided with the task of advising on the execution of the Deltaplan. As part of the Deltaplan, North Sea estuaries has been closed off from the North Sea in order to provide sufficient safety against flooding in the future. The 11000 hectare Lake Grevelingen was one of the closed off North Sea estuaries. Two dams and two islands enclose the lake and prevent fresh water flowing in. Characteristic of former estuaries are deep gullies that remain intact as any kind of sediment transport is prevented. Contact with the North Sea is prevented due to the construction of the Brouwersdam, the western border of Lake Grevelingen. Direct after finishing the construction works of the Brouwersdam, Lake Grevelingen showed reducing oxygen gradients and thus a decreasing water quality, especially at the deep gullies. The construction of a stop lock, the Brouwerssluice, was conducted to prevent the further decrease of the oxygen gradient. Today, more than 40 years after finalizing the Brouwerssluice, the low oxygen gradient tends to rise to shallower areas and reaches critical values. Measures, such as a water inlet system are due to be constructed. Introducing a tidal range of 50 cm has shown to be a valid solution to overcome the decreasing water quality. The tidal range allows thinking of power generation when water flowing in or out Lake Grevelingen. Generating tidal energy produces revenues and provides renewable energy. Therefore, the design of a Tidal Power Plant in the Brouwersdam has become the goal of this thesis. Since caissons were used to close Lake Grevelingen off from the North Sea, as a starting point, it has been determined whether these caissons allow reusing with a new function; forming the powerhouse of a Tidal Power Plant. Mainly due to the concrete cover of the caisson, has shown to be inappropriate. Adapting the caissons becomes expensive and very time-consuming. The starting point of the power plant construction was found in the turbine dimensions. In total six turbine types have been analyzed. Based on their efficiency, fish friendliness and ability to generate power in two directions, two optimal turbine types for low head power generation have been found: free-stream (Tocardo) and a modified bulb turbine (Pentair Fairbanks Nijhuis). Due to the low head differences between lake Grevelingen and the North Sea, maximum energy generation will be required even for very low head differences. Hence, turbines able to generate energy at such low head differences will be required. In the Preliminary turbine design, two turbine types provided the most promising features: The Pentair Fairbanks modified Bulb turbine and the Tocardo free-stream turbine. A total cross-sectional discharge area of 960 m2 would lead to a tidal range of 50 cm at Lake Grevelingen. Applying in total 18 turbines in a squared sluiceway with an inner space of 8.24 meter allows introducing a tidal range of 50 cm at the lake. The free-stream turbine has already proven to generate power in low head environments in previous projects. The PFN modified bulb turbine has not yet been tested on such scale, but due to the expected higher efficiency rate, the energy generation of the PFN lies supposedly much higher than the Tocardo free-stream turbine. Therefore, it has been decided to temporarily apply the free-stream turbine until the PFN turbine has shown to meet the fish friendly requirements while ensuring high efficiencies. With current knowledge, the annual production of the Tocardo and PFN turbine has been estimated at 20 GWh and 80 GWh respectively. The energy production of the freestream turbine is based on the tidal data obtained from 2016. The same tidal data has been applied to the PFN turbine while accounting for the sea level rise as well. Since it is expected the PFN turbine will be in commission at 2030, an estimated sea level rise of 25 cm has been added to the 2016 tidal data. The thickness of the concrete members in the preliminary design has been set at 500 mm. The conceptual design of structural elements has been dedicated to checking the assumption. In total four base cases have been studied, providing local and global forces emerged from uneven bedding of the rubble foundation layer. The rubble foundation layer functions as a bed protection foundation on which the Tidal Power Plant is located. The influence of uneven bedding of the rubble foundation bed has been computed by considering the Tidal Power Plant as a beam on an elastic foundation. Due to an uneven bedding, one-dimensional base cases Hogging and Sagging are introduced. Sagging represents a beam on elastic foundation subject to a reduced foundation stiffness at the midsection of the beam. Hogging has been described as the opposite situation of sagging, a reduced bedding stiffness at the beam edges. The structure’s strength has been determined while applying the hogging and sagging bases cases together with external and local forces. The external forces emerged from the hydraulic pressures in transverse direction and lateral earth pressures in longitudinal direction. The local forces concern the self-weight of an element or locally applied loads, such as the ballast load or road construction. The bending and shear resistance of the concrete members has been checked accordingly. In addition to the forces obtained from hogging and sagging, a coupled 2-dimensional approach has been applied. Two base cases have been considered in the 2-dimensional plane. The uneven bedding induces the rise of torsional moments in the beam on an elastic foundation. The torsional resistance of the concrete members has been checked. Together with local and global one-dimensional forces, the governing reinforcement ratio has been determined for relevant concrete members. Combining the findings of the one-dimensional approach with the two-dimensional approach has resulted in reinforcement ratios exceeding 3%. Comparing this with the 1 % economical reinforcement ratio value, it has been concluded the 500 mm thickness of the concrete member is insufficient. In further analyses, it is recommended to provide a cost estimation including revenues made from the energy production. The feasibility of the Tidal Power Plant will be determined by this cost estimation.

Nowadays, the use of concrete armour units on rubble mound breakwaters designs has become a common practice. Concrete armour units can be placed in a single layer system or in a double layer system and can its placement can be either random or uniform. Recently, Delta Marine Consultants have designed a new armour unit called Xbloc+. This new block is applied as a one layer system and has a regular placement. As Xbloc+ is still under development, preliminary guidance on the performance of this new armour unit is required. This led this research to investigate how Xbloc+ behaves concerning wave overtopping. To analyse wave overtopping, small scale tests were performed in a 2D wave flume. Wave overtopping was measured at a 3Dn distance from the seaward edge of the crest, which is made of rock. In front of the slope there is a flat transition of 0.3m followed by a sloping foreshore of 1/30. In total, 10 series of tests were conducted. In this research, three wave steepness (Sop) were tested (0.02, 0.04 and 0.06) to see the effect of wind waves and swell conditions on the armour layer and tests were performed in two different slope angles (1/2 and 3/4). Each series is formed by several sub tests conducted with increasing wave heights (and wave period in order to maintain a constant wave steepness). Tests were carried out until the failure of the armour slope was reached. Besides, a smooth slope was tested in a 1/2 slope angle to be able to compare smooth and rough results and determine the roughness coefficient of the armour unit more accurately. The test results showed that wave overtopping rates increase exponentially with wave height (Hm0) and wave period (Tm-1,0). Moreover, waves with lower wave steepness (swell conditions) induce higher overtopping discharges as compared to larger wave steepness. Steeper slopes also lead to higher overtopping rates. Therefore, the larger the breaker parameter is, the larger the overtopping discharge results. The influence of the armour roughness and armour permeability is also analysed and it is observed that swell conditions are less affected by these properties. This can be explained by means of the breaker type. Swell conditions are characterized by large surging waves. These waves have a thicker water tongue as compared with other type of breaking (e.g. spilling or plunging) and therefore, they tend to feel the top layer “smoother”. This fact is supported by the analysis of the influence of the roughness coefficient since higher values are obtained for surging waves. In fact, the roughness coefficient ranges between 0.34 and 0.68 showing that, although empirical prediction consider this parameter as a constant, it is dependent on the wave conditions. Concerning the comparison of dimensionless overtopping rate over Xbloc+ armour between test results and empirical prediction, it was found that the present formulae does not give a good estimation due its simplicity. In order to improve the representation of some parameters such as slope angle and wave steepness, correction factors are introduced in the empirical formulae leading to a better fit between prediction and measured data. 

In this MSc thesis it is investigated how the first version of concrete armour unit Xbloc+, Xbloc+ v1, acquires its stability. The stability mechanisms are investigated by conducting two type of physical model tests. First, 23 dry pull-out tests are done to obtain insights into the aspects and mechanisms that influence the armour layer stability. At 8 locations per slope, blocks are pulled out to determine the force needed to extract an armour unit. Tests are done on a 3:4 slope with 2 pull-directions; under an angle of 45 degrees with respect to the slope and perpendicular to the slope. Concrete as well as plastic armour units are tested, both having a different surface roughness. The conclusions of the pull-out tests are verified by means of the second type of model tests; small scale physical hydraulic model tests in a 2D wave flume. In total, 10 tests are conducted; 6 tests with plastic armour units and 4 tests with concrete armour units. Each test starts with a run with a small significant wave height which is increased stepwise in each run until failure occurs. All test sections have a 3:4 slope and are subjected to waves with a 4% steepness. Additionally, the influence of the significant wave height step size for successive runs is investigated. The combination of both physical model tests results in recommendations for a change in design which is expected to lead to a higher stability of an armour layer with Xbloc+ armour units.

In recent years, the use of Xbloc units has increased exponentially. However, the placement of this unit is not always done as randomly as it should be and consequently, the stability of the armor is affected. In order to overcome this problem, Delta Marine Consultants is developing a new armor unit called Xbloc+ that has a regular placement. In this research, the hydraulic performance of version 1 and 2 of this block are analyzed. Small scale tests were performed in a 2D wave flume in order to analyze the damage, rocking and the (partially and fully) displacement of units. In total, 1 series of tests were performed with Xbloc+v1 and 6 series with Xbloc+v2. To analyze the influence of the wave steepness and the slope angle, three wave steepness were tested (Sop = 2%, 4% and 6%) and tests were conducted in two different slope angles (1:2 and 3:4). Each series is formed by several sub tests conducted with increasing wave heights (and wave period in order to maintain a constant wave steepness). Tests were carried out until the failure of the armor slope was reached in order to completely define the failure mechanism. Furthermore, tests after failure where also executed to further investigate the stability of the armor after the damage has started. Results obtained from the laboratory tests provided an overall understanding of how the Xbloc+ performs under certain conditions. It was perceived that the permeability of the armor layer is low as it happens often with single layer units. Thus, the pressure gradient between the underlayer and armor layer is significantly high creating an uplift pressure that leads to a revetment-like failure mechanism. Although the failure mechanism can be related to both slopes used during the laboratory tests, (3:4 and 1:2), the behavior of the armor layer differed completely between slopes. On a steeper slope, the armor layer remained undamaged for wave heights significantly higher than the design wave. However, once one unit was fully displaced, the damage was quite destructive. In contrast, on a milder slope, failure occurred much faster but the damage was not as aggressive. Moreover, after the failure was reached, the structure gained a new level of stability in which remained to provide shelter without reflecting significant damage. Furthermore, the wave height variation did not have much influence as the wave steepness. There was a noticeable difference between the performance of the structure during swell and wind waves. During swell waves, it could be seen that not only failure was achieved faster but it caused much more damage to the structure, while during wind waves the structure had a higher stability.