Introduction of the Xbloc® breakwater armour unit

Abstract

Over the past two years Delta Marine Consultants has developed a new breakwater armour unit called Xbloc®. The new armour unit has proven to be reliable and easy to use leading to significant cost savings. The new armour development included extensive 2-D and 3-D physical model tests, finite element stress calculations, prototype drop tests, a production and handling analysis, and placement studies.

Whereas originally concrete armour units were simple heavy shapes, the development in the 1960s and 70s focussed more and more on slender shapes. The advantage of slender shapes is the high hydraulic stability caused by improved interlocking. As these shapes turned out to be vulnerable to breakage, a more robust shape was developed in the 1980s. Although this unit combined a relatively high hydraulic stability with a robust shape, a new slender unit was developed in the 1990s with a slightly higher hydraulic stability but a larger vulnerability to breakage. Therefore, the main focus of the DMC armour unit development was to create a unit with a hydraulic stability that is comparable to the present state of the art units, but with a robust shape.

The reliability of the Xbloc® was proven during the physical model tests. The structure proved difficult to damage, even at a significant exceedance of the design wave height. Furthermore the unit provides a large safety margin between the start of damage and failure of the armour layer. The structural stability of the armour unit was proven by the finite element stress calculations and the prototype drop tests.

The Xbloc® is easy to use because of the simple mould, the simple handling and storage methods and especially because of its easy placement on the breakwater slope. The placement of the present interlocking armour units is subject to very stringent specifications about the orientation of each armour unit. Obviously this decreases the speed of construction. No such specifications apply for the placement of the new unit as it easily finds its position on the slope.

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