Hydraulic Performance of Xbloc+ Armor Unit

Abstract

In recent years, the use of Xbloc units has increased exponentially. However, the placement of this unit is not always done as randomly as it should be and consequently, the stability of the armor is affected. In order to overcome this problem, Delta Marine Consultants is developing a new armor unit called Xbloc+ that has a regular placement. In this research, the hydraulic performance of version 1 and 2 of this block are analyzed. Small scale tests were performed in a 2D wave flume in order to analyze the damage, rocking and the (partially and fully) displacement of units. In total, 1 series of tests were performed with Xbloc+v1 and 6 series with Xbloc+v2. To analyze the influence of the wave steepness and the slope angle, three wave steepness were tested (Sop = 2%, 4% and 6%) and tests were conducted in two different slope angles (1:2 and 3:4). Each series is formed by several sub tests conducted with increasing wave heights (and wave period in order to maintain a constant wave steepness). Tests were carried out until the failure of the armor slope was reached in order to completely define the failure mechanism. Furthermore, tests after failure where also executed to further investigate the stability of the armor after the damage has started.
Results obtained from the laboratory tests provided an overall understanding of how the Xbloc+ performs under certain conditions. It was perceived that the permeability of the armor layer is low as it happens often with single layer units. Thus, the pressure gradient between the underlayer and armor layer is significantly high creating an uplift pressure that leads to a revetment-like failure mechanism.
Although the failure mechanism can be related to both slopes used during the laboratory tests, (3:4 and 1:2), the behavior of the armor layer differed completely between slopes. On a steeper slope, the armor layer remained undamaged for wave heights significantly higher than the design wave. However, once one unit was fully displaced, the damage was quite destructive.
In contrast, on a milder slope, failure occurred much faster but the damage was not as aggressive. Moreover, after the failure was reached, the structure gained a new level of stability in which remained to provide shelter without reflecting significant damage.
Furthermore, the wave height variation did not have much influence as the wave steepness. There was a noticeable difference between the performance of the structure during swell and wind waves. During swell waves, it could be seen that not only failure was achieved faster but it caused much more damage to the structure, while during wind waves the structure had a higher stability.