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.

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.