Statistical Analysis of the Stability of Rock Armoured Slopes
Marcel van Gent (Deltares)
Ermano De Almeida Sousa (TU Delft - Hydraulic Structures and Flood Risk, Deltares)
B Hofland (TU Delft - Hydraulic Structures and Flood Risk, Deltares)
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Abstract
Physical model tests were performed in a wave flume at Deltares with rock armoured slopes. A shallow foreshore was present. At deep water the same wave conditions were used but, by applying different water levels, the wave loading on the rock armoured slopes increased considerably with increasing water levels. This allows the assessment of effects of sea level rise. Damage has been measured by using Digital Stereo Photography (DSP) which provides information on each individual stone that has been displaced. Two test series have been performed five times. This allows for a statistical analysis of the damage to rock armoured slopes. The statistical analysis demonstrates the need to take the spreading around a mean damage into account in the design of rock armoured slopes. This is important in addition to characterising the damage itself by erosion areas and erosion depths. The relation between damage parameters such as erosion area and erosion depth has been obtained from the tests. Besides tests with a straight slope also tests with a berm in the seaward slopes have been performed. A method to take the so-called length effect into account has been proposed to extrapolate results from physical model tests to real structures. Use is made of standard deviations based on the presented model tests.