Many rubble mound breakwaters are nowadays made with an armour layer consisting of single layer interlocking elements. The stability of these armour layers could well be influenced by the irregularity of the rock underlayer, as that influences the degree of interlocking. Especially for the new types of regularly placed armour, this might be an important factor for the stability. However, this aspect has not been studied widely yet. Therefore, this paper investigates the influence of irregularities in the underlayer on the stability of a type of single layer breakwater elements. Model tests have been conducted in which the irregularities in the underlayer were systematically varied. The irregularities in the underlayer and the orientations of breakwater elements were measured with 3D-scanning. The breakwater armour unit used in the tests is the XblocPlus. A new failure mechanism, not previously observed for breakwater elements, was found to initiate damage. Causing the armour to be pushed outward by a combined effect of the weight of the upper armour and the excessive hydraulic pressure of the remaining water under the armour layer. Especially large-scale convex (i.e. protruding outwards) undulations in the cross-shore direction influenced the stability of the armour layer. This influence has been quantified.

中文翻译：

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岩石底层的不规则性对 XblocPlus 稳定性的影响

如今，许多碎石堤防波堤都采用由单层互锁元件组成的装甲层制成。这些装甲层的稳定性很可能受到岩石底层的不规则性的影响，因为这会影响互锁程度。尤其是对于新型的定期放置的装甲，这可能是稳定性的重要因素。然而，这方面还没有得到广泛的研究。因此，本文研究了底层不规则对一类单层防波堤元件稳定性的影响。已经进行了模型测试，其中底层的不规则性被系统地改变。底层的不规则性和防波堤元素的方向是用 3D 扫描测量的。测试中使用的防波堤装甲装置是 XblocPlus。发现了一种新的失效机制，以前没有在防波堤元件中观察到，它会引发损坏。在上层装甲的重量和装甲层下剩余水的过高液压的共同作用下，导致装甲被向外推。尤其是跨岸方向的大面积凸起（即向外突出）起伏影响了装甲层的稳定性。这种影响已被量化。向外突出）跨岸方向的起伏影响了装甲层的稳定性。这种影响已被量化。向外突出）跨岸方向的起伏影响了装甲层的稳定性。这种影响已被量化。