PSI - Issue 62

Michele Palermo et al. / Procedia Structural Integrity 62 (2024) 593–600 Author name / Structural Integrity Procedia 00 (2019) 000–000

598

6

However, the migration of the dune is delayed by the presence of macro-roughness elements, consequently the scour velocity reduces with respect to the unprotected counterpart. Generally, this phase last up to T * 2  10000. Finally, Phase 3 takes place and is characterized by an increase of the number of elements rolling into the scour pothole, thus contributing to further protect scour surface and reduce scour velocity. Overall, authors found that macro-roughness elements are effective in reducing scour area and volume (i.e., a reduction of more than 50% can occur depending on hydraulic conditions and structure configurations). Furthermore, the kinetics of the scour appears to be slower. As for the maximum scour depth, it is generally smaller, especially for lower values of  A.

Fig. 4. (a) Side and (b) planar views of the experimental apparatus, along with the indication of the main geometric and scour characteristics; (c) picture of the bed morphology at equilibrium; (d) picture of the experimental apparatus before the beginning of a test. All the figures and pictures refer to tests conducted by Pagliara et al. (2015). 4. Comparison of countermeasures efficiency In this section, we compare the effectiveness of sills/gabions and macro-roughness elements in terms of maximum scour depth reduction. To this end, we consider experimental tests conducted by Pagliara et al. (2010a) and Pagliara et al. (2015). More specifically, we selected tests performed under identical hydraulic conditions, characterized by L/D ranging from 0 to 0.5 and different non-dimensional macro-roughness elements diameter D 50 /D (corresponding to different concentrations  ). Comparisons illustrated in Fig. 5 include reference tests (i.e., tests with isolated pier conducted in the absence of debris accumulation, protection sills and macro-roughness elements). Furthermore, since the general behavior is similar, we limited ourselves to show results pertaining to tests conducted with debris 5D. As for the legend of Fig. 5, it is worth remarking that, for instance, “5D” indicates a test with pier and debris accumulation (i.e., without any protection measures), “5D+S1” refers to a test with pier, debris accumulation 5D and sill S1, “D 50 /D=0.5” pertains to a test with pier and downstream macro-roughness elements (i.e., without debris accumulation), and “5D+D 50 /D=0.5” represents a test with pier, debris accumulation and macro roughness elements.