Permeable hydraulic structures that consist of rock typically contain a granular underlayer beneath the armour layer. The interface between two rock layers is normally geometrically tight to prevent material washout. However, applying an interface with only minimal loss of material through the layer above could result in a more economical structure. Physical model tests have been performed for the interface between the armour layer and the underlayer. The underlayer consisted of rather small material and various grading widths. Based on these tests guidelines have been derived to design non-standard underlayers beneath rock armoured slopes, under wave loading.
This new CROW-CUR guideline (June, 2021) is presented for the design of an underlayer beneath a rock armour layer and on top of an impermeable/sandy core for structures under wave loading based on physical model tests performed by Deltares in 2016 commissioned by Rijkswaterstaat. In these tests the sandy subsoil was, modelled as fixed and impermeable. Initial publications based on these tests were already published by Van Gent and Wolters (2016) and Van der Meer et al. (2017). This new guideline is developed in a joint effort project of SBRCURnet. First the members of the SBRCURnet committee criticized the results of the physical model tests performed by Deltares in 2016. Thereafter the members of the committee contributed to the discussion about the new guideline. Based on their input the present knowledge paper was written by Deltares. The overall management has been performed by SBRCURnet (now: CROW-CUR).
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