Development of the Xbloc® breakwater armour unit

Introduction

The development of the Xbloc started with the analysis of the strength and weaknesses of existing armour units (Muttray et al., 2003). Armour units for application on rubble mound breakwaters can be distinguished into two categories:

1. Uniformly placed armour units
2. Randomly placed armour units

Examples of uniformly placed armour units are: Seabee, Hollow cube, Diahitis, Cob and Shed. These units depend mainly on friction to provide hydraulic stability. Presently the uniformly placed armour is mainly applied in situations with relatively mild wave attack and in situations where the armour units do not have to be placed below water. The latter aspect follows from the fact that these blocks need to be placed securely.

Randomly placed breakwater armour units can be divided in blocks which have hydraulic stability by their own weight, and blocks which rely on interlocking to provide hydraulic stability. The first category consists of cubes, Antifer cubes, and parallepedic blocks. As the use of these blocks in the conventional double layer application is not very cost effective due to the large concrete demand, recent application is very limited. Studies are being done on single layer cube armour (d’Angremond, 2002, van Gent, 2002). The interlocking blocks which can be considered are: Tetrapod, Dolos, Tribar, Stabit, Accropode, A-Jacks® and Core-loc®( Coreloc® is a registered trademark of the US Government). From publications of breakwaters constructed over the past 20 years it can be observed that a significant part has been constructed with Accropode armour. In the past five years Core-loc® armour has started to be used instead of Accropode armour. This type of armour is also used for breakwaters in deep water, and exposed to high wave loading.

The development of a new breakwater armour unit by DMC is aimed at an improvement over the present state of the art in armour units. It was thus decided to develop a single layer interlocking armour unit as this has the widest range of application. Desirable properties of the new breakwater armour block are:

• Stability coefficient Kd same as for Accropode and Core-loc®
• Reduced concrete demand compared to Accropode
• Increased structural strength compared to Core-loc®
• Easier placement than Accropode and Core-loc®

In this paper the reasons why the Xbloc® is developed will be discussed. Results from various tests will be presented. A comparison will be made with other single layer interlocking armour units. Finally guidelines for the application of Xbloc® armour units will be given.

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Development-of-the-Xbloc-Breakwater-Armour-Unit-Singapore-2003.pdf