Stability of Accropode(R) and comparison with dolosse

Abstract This paper presents details of irregular wave model tests carried out to determine the hydraulic stability of Accropode(R) under the same conditions that were used to determine the stability of dolosse, that is, for deep water conditions without a specific foreshore. A total of 111 tests were done under 37 different test conditions including slopes of 1:1.33; 1:1.5 and 1:2, and wave periods of 1.25; 1.5 and 1.75 s. Overtopping was prevented by extending the slopes past the highest run-up level and the range of ζ values (Iribarren number) included 2,9 It was found that the stability of Accropode decreases with ζ (Iribarren number) and the minimum stability (Ns = 2.4 for 1% displacement) occurred at the lowest ζ value ( ζ ⋍ 3 ) used in the tests. For the ζ values at which the three slopes were tested, the results show a decrease in stability as the slope is steepened although there was not much difference between the stability on the 1:1.5 and 1:1.33 slopes. The results further indicated that the gentle 1:2 slope has more reserve stability than the steeper 1:1.5 and 1:1.33 slopes. It was found that Accropode are more stable than dolosse (r = 0.33) for ζ>3. However, at the point of minimum stability obtained in the present test ( ζ ⋍ 3 ) the stability of the two armour types is much the same (on a slope of 1:1.5). At this ζ value KD was, respectively, 9 and 12 for 1 and 2% displacement for both dolosse and Accropode. The results of the present tests were compared to those of Van der Meer ∗ and tests done at the First Design Institute of Navigation Engineering in Tianjin, China. The test results were found to be generally compatible, although significant differences did occur. These, however, are mainly due to different test configurations, test procedures and interpretation of test results. It should be mentioned that most of the tests were done at a slope of 1:1.5 while Sogreah prefers a slope of 1:1.33 for Accropode(R). Moreover, since these tests were performed, Sogreah increased the prescribed packing density by some 2.4%.