Measuring damage in physical model tests of rubble mounds

Abstract

This paper studies novel ways to evaluate armour damage in physical models of coastal structures.High-resolution damage data for reference rubble mound breakwaters obtained under theHYDRALAB+ joint-research project are analysed and discussed. These tests are used to analyse theway to describe damage, the influence of the sequence of testing, and touches on the possibleinfluence of sea level rise. Results of two test programmes were used. Firstly, 3D physical model testscarried out at the University of Porto, in cooperation with Deltares, were used. Here a wide breakwatertrunk was used for statistical reasons. Additionally, 2D test results from LNEC were analysed. Testsfor a sea level rise scenario resulted in less damage to the seaside slope. In addition, clear differencesbetween "cumulative damage" and "rebuild" test series were noticed. However, significant scatter wasalso observed in the result of tests carried out under identical conditions. It was also concluded thatthe damage to the trunk was lower in the tests with short-crested waves. The design values for thedamage depth E2D proposed by Hofland et al. (2011) were partly in line with the experimental resultspresented. Since the relation between S and the depth of damage E does not hold true for nonstandard cases, it seems better to use a parameter based on the local damage depth when testingsuch a structure. The reliability of a damage number for a test on the stability of a trunk can beimproved by either increasing the relative size (width) of the test section or repeating the test.