In this study loading characteristics of rubble mound breakwater crown walls are investigated. This is done using a 2D physical model, testing for overall stability (through sliding) and temporal & spatial distributions of pressure along the face and base of the crown wall. A variety of wave conditions and geometries is used, with special attention for the influence of foundation level on the loading characteristics. This study shows the importance of this parameter and its link to the time lag between the maximum horizontal force and maximum vertical force in a wave impact. Using a new analysis method based on the factor of safety, this time lag is quantified and a reduction factor for the vertical forces is introduced.

This study investigates the capacity of an open inverted filter to stabilize the interface between the sand fill and core fill in a rubble mound breakwater. The strength of this filter relies on the arching mechanism of the base material, which is directly influenced by factors such as stability ratio and effective stresses. These forces arise from porous flow, and its quantification involves both parallel and perpendicular hydraulic gradients.
A full-scale physical model, with a 760 mm open inverted filter, is employed to determine the critical hydraulic gradients required to initiate erosion. The model consists of three compartments, with the central compartment containing the open inverted filter. The two side compartments are filled with water, with one of them featuring a plunger mechanism to induce flow. Pressure sensors and water level gauges are used to measure the hydraulic gradients. In addition to the physical model, a numerical model is developed to gain insights into the flow dynamics within the system.
The tests reveal that an increase in effective stress results in higher critical parallel and perpendicular gradients. Furthermore, the addition of fines at 5% or 10% seems to enhance the critical parallel and perpendicular gradients. A negative correlation was found between SR and 𝑖⊥,𝑐𝑟𝑖𝑡, the results were fitted to a hyperbolic function. The findings further indicate that, even after erosion occurs, a stable interface can be reestablished. Therefore, designing solely for the single largest wave is not imperative.

This study investigates the use of an open filter in a land reclamation structure. The possibility of replacing the geotextile that secures the core-backfill interface with a granular filter has been investigated. This is easier to install and therefore a potential cost-saving. Experiments have been done to determine the influence of various parameters on the interface stability of a geometrically open inverted granular filter. Relationships have been found which can assist in designing such a filter.

This thesis is the third study of a research line that focuses on the interface stability of a rubble mound sand retaining structure. The type of interface considered is a geometrically open granular filter because of its economical and constructional benefits. The stability of an open filter structure in which the base layer is located on top of the filter layer was investigated by the use of physical modeling. The model used was the same waterproof elongated container as used by Van de Ven (2019), after some adjustments were made. Three compartments were allocated in this model. In Compartment A, the water level was controlled by the use of a plunger. This caused water level differences between the compartments and therefore induced a hydraulic gradient (i) in the filter structure that was installed in Compartment B. The hydraulic gradient was considered as the main load parameter for erosion. The main strength parameter was the stability ratio (SR), defined as the sieve diameter for which 15% of themass of the filter material is smaller divided by the sieve diameter for which 85% of the mass of the base material is smaller. During testing, this hydraulic gradient was increased by the plunger until erosion was noted, defining the critical hydraulic gradient (icr) for the filter-base combination tested. Two loading conditions were distinguished, namely the parallel and combined set-up. Besides the SR and these loading conditions, the influence of the characteristic grain size of the base material and the filter layer height on icr was studied. During this thesis, a new phenomenon influencing the icr was observed, which was not included in the research line yet. This was the initial sand saturation of the filter layer. Therefore, the physical model results were split up into unsaturated and partly saturated tests. For the unsaturated parallel configuration, SR = 5.7, 6.7, 12.9 and 13.1 were tested. Results were found for the upper two values. For the lower SR, no erosion was detected resulting in a bottom limit of icr . The partly saturated parallel tests resulted in a reduction of icr up to a minimumof 73%. Projecting this effect into reality could have a significant influence on the stability of an inversed open granular filter in land reclamation structures. However, further research is advised. All found icr in the parallel tests were higher compared to Van de Ven (2019). Besides, it was concluded that a larger characteristic grain size of the base layer and the filter layer thickness did not influence the icr significantly. Furthermore, three unsaturated combined tests were conducted with SR = 6.7 and 12.9. No erosion was noted for SR = 6.7. Erosion was detected twice for SR = 12.9, once in the first test segment – resulting in an upper limit for (icr ) – and once in the second test segment. A reduction of 93% for icr in the combined set-up compared to the unsaturated parallel set-up was noted, implying that an additional load decreases the critical load for the considered filter structure. However, this could also be the results of model installation differences. Lastly, a new physical model was designed and constructed to facilitate the study on the influence of the superimposed load and the filter inclination on the interface stability. A newly developed numerical model has been made to plot design graphs for this new model.

The consortium Projectorganisatie Uitbreiding Maasvlakte (PUMA), consisting out of Van Oord and Boskalis, constructed a hard sea defence for the protection of Maasvlakte 2, which is the expansion of the Port of Rotterdam. This hard sea defence consists of a Dynamic Rock Slope (DRS) with a Block Dam (BD) situated in front of it. The BD is build up out of large concrete blocks which were recycled from Maasvlakte 1. The DRS behind it protects the hinterland through an approximate three to four meter thick layer of quarry rock. When waves travel obliquely through this Block Dam and interact with the DRS, stones are transported in alongshore direction. This process is called Longshore Transport (LT) and will have erosion and accretion of stones to effect along the DRS. In order to maintain the layer thickness of this stone layer, PUMA made a prognosis on LT for the coming 50 years after construction. From this prognosis a nourishment campaign was set-up, consisting of volumes of stone PUMA expected to nourish every 2.5 years. After a maintenance period of five years it was concluded by PUMA that the nourishment volumes were lower than expected. Therefore this thesis assessed where differences in the prognosis of PUMA on LT and the observed LT rates over the period 2013 to 2018 come from. Within their prognosis, PUMA made use of a dimensional LT relation. As this specifically calibrated Longshore Transport relation is only applicable for the computation of LT rates at a structure containing the characteristics of the DRS at Maasvlakte 2, this research looked into the possibilities of using a non-dimensional Longshore Transport relation for the computation of Longshore Transport rates at the DRS of Maasvlakte 2.