The Xbloc was subjected to an extensive research programme consisting of 2-D and 3-D hydraulic model tests; destructive tests with 4m3 prototype units; analyses of the structural integrity of the blocks using Finite Element calculations; logistic studies of the fabrication, storage and placement of the units; and a comparison of the Xbloc with existing armour units – such as the well-known Accropode and Core-loc.

DMC says it believes that the average saving yielded by using Xbloc units (less concrete needed) can be as much as 15 per cent compared to other single-layer armour units, the difference being due to high stability coefficient of the Xbloc unit and the low packing-density required, both of which result in a lower concrete demand.

As there are no specific requirements on the orientation of the individual units to achieve good interlocking, placement of the units is straightforward reducing both construction time and overall cost.Another key feature of the Xbloc is automatic interlocking – Xbloc units naturally find a stable position on a slope, and DMC says an armoured layer formed using Xblocs is also ‘self-repairing,’ in as much as that, after damage, automatic interlocking reinforces the structure.In 2004, Xblocs were used for a revetment for a shore protection scheme in Indonesia, Reedijk explained, and will be used for a breakwater rehabilitation project in Europe later this year, and to form a breakwater at new marina in Africa.

In addition, notes DMC, 3-D breakwater head tests were successfully completed at Delft Hydraulics towards the end of last year. The tests supplemented the extensive physical model tests already undertaken for the development of the Xbloc and a number of project specific studies.

Previously, the design rule for an Xbloc breakwater head was based on common practice with single layer armour units. The units of the breakwater head were designed with a unit weight which was 125 per cent higher then the unit weight for units on the trunk. The model tests at Delft Hydraulics confirmed that this weight factor can safely be applied for the design of the Xbloc armour layer on a breakwater head.

Tests were also carried out on the Xbloc at the University of Edinburgh, where several single layer armoured units were tested to determine wave overtopping rates on breakwaters as part of the CLASH (Crest Level Assessment of coastal Structures by full scale monitoring, neural network prediction and Hazard analysis on permissible wave overtopping) programme, a research project supported by the European Commission.