Abstract
Different layer design of a rock slope and under layers has a large effect on the strengths on the rock slope itself. In the stability formula developed of VAN DER MEER [1988] this effect is represented by the term Notional Permeability with symbol P. A more open, or permeable, structure underneath the armour layer has the ability to dissipate more wave energy and therefore requires less weight of the armour layer. The influence of this parameter is thus very important in economic sense. Up until now only three configurations have been tested. In practice often intermediate structures were designed which do not correspond to the standard situations. P-values then have to be estimated in comparison with the known structures, which gives some uncertainty around the P-value. Therefore there is the demand for more validated values of the notional permeability representing other structures. During this study physical scale modelling is used to produce a value of P for a new structure.
Highlights
For the design of the armour layer of randomly placed rubble mound breakwaters usually the choice is made between two formulas; the Hudson formula which is the result of studies in 1953, 1959 and 1961, or the other one which is the well-known formula of Van der Meer introduced in 1988
The second structure was the structure with armour layer on top of a thin filter layer and an impermeable core, Van der Meer found a permeability of P=0.1 for this structure
The new structure has the same stone size ratios between the different layers as the P=0.4 structure defined by Van der Meer, but with the presence of an impermeable layer
Summary
For the design of the armour layer of randomly placed rubble mound breakwaters usually the choice is made between two formulas; the Hudson formula which is the result of studies in 1953, 1959 and 1961, or the other one which is the well-known formula of Van der Meer introduced in 1988. During this study the method of empirical testing is used to determine the value of P for a new structure. Van der Meer was the first one who made a distinct difference between two types of breaking waves with respect to the stability of the breakwater. The first reference structure is the structure with an armour layer on top of a permeable core.
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