Damage Characterisation of Rock Armoured Slopes

In order to design reliable coastal structures, for present and future scenarios, universal and precise damage assessment methods are required. This study addresses this need, and presents improved damage characterization methods for coastal structures with rock armoured slopes. The data used in this study was obtained from a test campaign carried out at Deltares within the EU Hydralab+ framework. During these tests, advanced measuring techniques (Digital Stereo Photography) were used, which are able to survey the full extension of the structure and identify local variations of damage. The here proposed damage characterisation method is based on three fundamental aspects: clear damage concepts, precise damage parameters and high resolution measuring techniques. Regarding damage concepts, first the importance of the characterization width is studied. For damage parameters obtained from the maximum erosion depth observed in a given width (E3D,m), the measured damage increases continuously with increased characterization width. But for damage parameters obtained from width-averaged profiles (S and E2D), the measured damage reduces with increased characterization width. Second, a new definition of damage limits (damage initiation, intermediate damage and failure) is presented and calibrated. Regarding the damage parameters, the parameter E3D,5, which describes the maximum erosion depth within the characterization width, is recommended as a robust damage parameter for conventional and non-conventional configurations based on three main characteristics: its low bias, its low random error, the ability to distinguish damage levels and is its validity and suitability for all types of structures (conventional and non-conventional). In addition, the results from this study show that the damage measured with the damage parameter E3D,5 presents an extreme value distribution.