Coastal structures with open filters under wave loading
Auteur(s) |
M.R.A. van Gent
Publicatie type | Artikel
Permeable coastal structures under wave loading typically contain granular filters in one or more layers. The transition from the armour layer to the filter layer, and transitions between other layers within the structure, are normally geometrically tight to prevent material washout. This requires a limited ratio of the material size of the upper layer and neighbouring layer. An alternative is a geometrically open filter where in principle underlayer material can be transported into the upper layer, but if the hydraulic load at this transition between two layers remains low, the transition can be designed such that no or limited transport occurs. This allows for larger ratios of material sizes, which can reduce the number of filter layers, and can lead to considerable cost savings. Some structures have been constructed in which the transition between the armour layer and the filter layer of rock underneath is an open filter, but proper design guidelines for such open filters are not available yet. Physical model tests for the transition between a layer of rock and an underlayer that consists of sand have been performed and design guidelines have been derived. The developed guidelines based on physical model tests in combination with the numerical modelling lead to valuable insights into the possibilities of this new design approach.