Topic LabCoSts 2023 1) Inversed filter, parallel gradient with surcharge.
This is a continuation of project 2021-2 on the stability of an inversed filter. Some problems with the test setup were discovered by the very good student. While the perpendicular gradient was tested well, the parallel gradient appeared not to be tested. Additionally, the load that could be applied by the plunger was not sufficient. Hence a larger plunger will be acquired and installed.
Student Roos Besseling started her study in February 2023.

Topic LabCoSts 2023 2)
This last topic still needs to be determined, and will be decided on by the group. As we are thinking about a continuation of the crest wall setup study, we wait for the results of the (slightly delayed) study 2022-2.

Topic LabCoSts 2021 1) Influence of toe length on toe scour depth
This study is a continuation of 2020-2. A similar setup was built in the lab. A larger range of porosities of the structure and various sand grain sizes were used to increase the range of applicability of the results. This study led to an ICCE poster presentation.

Topic LabCoSts 2021 2) Inverse filters with full-scale top load
Stability of inverse filters with top load is a topic that is of important when creating a land reclamation by placing dredged sand inside rock bunds. To prevent sand loss inside the permeable rock bunds, typically expensive filter layers are constructed. These filter layers are difficult (expensive) to place at lower depths. At these depths the hydraulic loading on the filter interface is very low, such that it is expected that the filters can be made without a geometrically tight filter. To quantify this phenomenon, exploratory tests have been done (Tutein Nolthenius 2018, Van de Ven 2019), which show promising results. Even a somewhat open filter with sand on top of a granular layer, was seen to be stable up to parallel hydraulic gradient (flow parallel to the filter interface) in the order of 1%. For perpendicular gradients (flow through the filter interface) the layer became stable under gradients that were larger than those expected to occur (Van de Ven 2019). As these filters have a large layer of sand on top of them, it is expected that the sand grains will be pushed together, such that the stability will be increased. In a new tests setup this effect will be modelled by applying a hydraulic jack that will apply a top load equal to ca. 10 m of sand.
A MSc student will be trainee with Van Oord while preparing the tests, and guided by representatives from Van Oord (Van Kester). Scope will be discussed biweekly with entire partner group. The tests will be prepared in the Environmental Fluid Mechanics Laboratory of TU Delft, and executed in the structural laboratory, where the jacks are present.
References:
Van de Ven, Daan (2019) Granular open filter in rubble mound sand retaining structures: Physical model tests of a negative geometrically open filter layer. MSc thesis, TU Delft. Link.
Tutein Nolthenius, Raoul (2018) Sandfill-Retaining rubble mound structures: Evaluating the behaviour of sediments at the interface of a rubble mound with a reclamation, by means of physical modelling. Link.

Per jaar (rond september) zullen de projecten worden voorgelegd ter goedkeuring. Voor 2019-2020 zijn door de bedrijven en TUD de volgende specifieke onderzoeksonderwerpen geformuleerd:
Topic LabCoSts 2019-2020 1) Inverse filters
Stability of inverse filters with top load is a topic that is of important when creating a land reclamation by placing dredged sand inside rock bunds. To prevent sand loss inside the permeable rock bunds, typically expensive filter layers are constructed. These filter layers are difficult (expensive) to place at lower depths. At these depths the hydraulic loading on the filter interface is very low, such that it is expected that the filters can be made without a geometrically tight filter. To quantify this phenomenon, exploratory tests have been done (Tutein Nolthenius 2018, Van de Ven 2019), which show promising results. Even a somewhat open filter with sand on top of a granular layer, was seen to be stable up to parallel hydraulic gradient (flow parallel to the filter interface) in the order of 1%. For perpendicular gradients (flow through the filter interface) the layer became stable under gradients that were larger than those expected to occur (Van de Ven 2019).
A MSc student will be trainee with Van Oord while preparing the tests, and guided by representatives from Van Oord (Van Kester). Scope will be discussed biweekly with entire partner group. The tests will be prepared in the Environmental Fluid Mechanics Laboratory of TU Delft.
References:
Van de Ven, Daan (2019) Granular open filter in rubble mound sand retaining structures: Physical model tests of a negative geometrically open filter layer. MSc thesis, TU Delft. Link.
Tutein Nolthenius, Raoul (2018) Sandfill-Retaining rubble mound structures: Evaluating the behaviour of sediments at the interface of a rubble mound with a reclamation, by means of physical modelling. Link.
Topic LabCoSts 2019-2020 2) Influence of toe length on toe scour depth
The guidance on the length of a toe or scour protection in front of a rubble mound breakwater has not been studied often. Scouring patterns have been studie by e.g. Xie (1981). The main study on the influence of the protection on scour was done by Sumer & Fredsøe (2000). They propose a very long rock protection of a quarter wave length, which mostly is not constructed in reality (oral communication of LabCoSts partners). This effect will be better quantified with new tests.
MSc student Casper Jantzen performs his traineeship at Van Oord. Daily guidance by Witteveen+Bos (Kuiper) and Van Oord (Ockeloen). Scope will be discussed with entire partner group. Preparing a first set of tests on the topic for tests in the first half of 2020, which will be followed later by a follow-up study. Scope will be discussed biweekly with entire partner group. The tests will be conducted in the state-of-the-art wave flume of the Environmental Fluid Mechanics Laboratory of TU Delft.
References:
Sumer, B.M. and J. Fredsøe (2000) Experimental study of 2D scour and its protection at a rubble-mound breakwater. Coastal Engineering 40 pp. 59–87
Xie, S.L. (1981) Scouring patterns in front of vertical breakwaters and their influences on the stability of the foundation of the breakwaters. Link.

Topic LabCoSts 2022 1) Closed under-layer under wave attack
Establish design rules exist for granular, geometrically closed filter structures for hydraulic structures. However, this guidance is established for filter layers loaded by uniform flow, either in the parallel or perpendicular direction. For slopes under wave attack stricter rules are used, which are based on very few experiments. Thus the knowledge for sloped, closed filters under wave loading remains limited.
This thesis combines model test results from two historically performed experiment programs on sloped, closed granular filters under wave loading with dedicated new experiments. Based on the test results and existing data sets a new interface stability criterion for sloped, closed granular filters under wave loading will be proposed.

Topic LabCoSts 2022 2) Pressure distribution on elevated crest wall
A crown wall is a L- shaped concrete structure on top of a rubble mound breakwater intended to efficiently reduce wave overtopping and enable transport and other activities on the breakwater on its flat surface. Currently used calculation methods seem to be conservative especially when the vertical distance between the still water level and the base of the crown wall, increases (Bekker 2017). An experimental research is carried out in which the effect of freeboard is examined. Detailed description of the pressure distribution on the wall under wave loading, quantification of the time lag between upward and horizontal forces, and to obtain a dataset for validation of numerical models.
References:
Bekker, J.F. (2017) Experimental research into the effect of freeboard on the stability of a crown wall on a rubble mound breakwater. Link