An Xbloc is an interlocking concrete block or armour unit designed to protect shores, harbour walls, seawalls, breakwaters and other coastal structures from the direct impact of incoming waves. The Xbloc model has been designed and developed by Delta Marine Consultants (DMC) since 2001 and has been subjected to extensive research by several universities.
Concrete armour units are generally applied in breakwaters and shore protections. The units are placed in a single layer as the outer layer of the coastal structure. This outer layer is called the armour layer. The function of the armour layer in these structures is twofold. Firstly, it must protect the finer material below the armour layer against severe wave action. Secondly, the armour layer must dissipate the wave energy in order to reduce the wave run-up, overtopping and reflection. These two functions require a heavy, but porous armour.
A typical cross section of a breakwater slope is shown in the figure above. The cross section of a shore protection is similar, but instead of a core, the soil material is protected. In both structures, the armour layer is placed on top of a filter layer which covers the fine material in the core of the breakwater (or the soil material of the shore). This filter layer must prevent the fine material washing away through the pores in the armour layer. Near the seabed the armour layer is generally supported by a rock toe.
The Xbloc consists of non-reinforced concrete, similar to other single layer armour units. Although both wooden and steel moulds can be used to construct the Xbloc formwork, steel moulds are preferred as they can be used repetitively to produce large numbers of armour units.
Due to the shape of the Xbloc unit, a relatively simple formwork can be used which is made of a limited number of different steel plates. Since a single Xbloc unit can weigh up to 45 tons, the construction is done as close as possible to the area of application.
Placement and Interlocking Mechanism
The Xbloc armour unit derives its hydraulic stability from its self weight and by interlocking with surrounding units. Due to the highly porous armour layer (layer porosity ~58.7%) constructed with Xbloc units, the energy of the incoming waves will be absorbed. The Xbloc armour layer is therefore able to protect the rock in the under layer from erosion due to waves.
In contrast with the placement of other interlocking concrete blocks, the Xbloc unit does not have very stringent specifications about the orientation of each unit on a breakwater slope. Because of the shape of the Xbloc, each of the 6 sides of the unit is efficiently interlocking. Therefore the blocks easily find a position that fully activates the interlocking mechanism. This increases the rate of placing armour units on a slope.
Due to the random structure and high porosity of an Xbloc breakwater, an artificial reef is created for different kinds of vegetation and animals.
Concrete blocks used for the same purpose are listed below. Like Xbloc, most of these blocks are commercial developments and patented.
Advanced Numerical Study
The Maritime Engineering Division University Salerno (MEDUS) developed a new procedure to study the interaction between breakwaters (submerged or emerged) and waves, by an integrated use of CAD and CFD software.
In the numerical simulations the filtration of the fluid into the porous breakwater, is estimated by integrating the RANS equations, coupled with a RNG turbulence model, inside the voids, not using a classical equations for porous media.
The breakwater armour layer was modelled by overlapping three-dimensional elements and the numerical grid was thickened in such a way to have some computational nodes along the flow paths among the breakwater’s blocks (AccropodeTM, Core-locTM, Xbloc).
- Artificial reef
- Breakwater (structure)
- Coastal management
- Coastal erosion
- Ocean surface wave
- Tetrapod (structure)
- Overview: Shapes of breakwater armour units and year of their introduction 
- British Standards, BS 6349 Code of Practice for Maritime Structures, Part 7, Guide to design & construction of Breakwaters, 1991.
- CIRIA/CUR, Rock Manual, 2007 2
- Research Articles on the Development and Design of Xbloc Breakwater Armour Units 3
- H.J. Verhagen, Classical, Innovative and Unconventional Coastline Protection Methods, Coastal Engineering section, Delft University of Technology, the Netherlands, 2004 4
- ASCE Specialty Conference, Washington D.C. March, Seabees in Service, 1983
- Delta Marine Consultants
- Rock Manual 2007
- MEDUS (Maritime Engineering Division University Salerno)