Offshore breakwaters, or bulkhead, are partially-underwater structures built to lessen the power of waves hitting shores. They provide a safer anchor for boats and reduce coastal erosion. Breakwaters are usually made of large, misshapen cement blocks.
“In Spain, normally, the breakwaters are made out of cubes,” says Moises Santos, technical director of Spanish maritime company SATO, an off-shoot of the IBEX-35 construction company OHL. “In Spain, mound breakwaters with double-layer armors are made of randomly-placed cubes…Concrete blocks have been traditionally used, due to their easy manufacturing, use of simple form works, and efficient stacking,” he says. The typical breakwater blocks are usually haphazard cubes, sometimes made out of re-used materials from old construction sites.
While they have the benefits of quick production and simplicity, the usual blocks lack uniformity and are less predictable in the long term. Breakwaters can become damaged fairly easily and, when facing big tormentas or storms, the water can rise over top, causing major draining problems. The port could overflow, risking the damaging or even sinking of parked boats. If the breakwater damage and storm are both great enough, the mainland could become flooded.
One of the major problems of the traditional blocks is that, when the flat sides of the cubed blocks get wet, they compact and stick together. This leads to sections of the structure becoming weaker and unbalanced. “When the cubes go together, they compact more at the bottom and the ones on top [become] more open. It becomes more at risk for the top to be destroyed by water,” Santos says.
A search for alternatives to the traditional blocks has been going on for more than half a century. Various port construction companies have tested block shapes that resembled flat “X”s and other, stranger shapes. The results have often increased stability, but at a higher price.
The Laboratory of Ports and Coasts at the University of Valencia joined the search for new block shapes in order to reduce cost and to create greater and more predictable stability.
Researchers designed a tiny version of the current Cubipod — a cube, with little pyramidal pods on each of the six faces. In Spanish, it’s called Cubipodo, which means “cube” in Latin, plus “foot” in Greek.
They conducted two small-scale experiments — one with miniatures of the usual bulkhead and one of mini Cubipods, both featuring different colors for the different layers. The traditional blocks shifted, visibly opening at the top and compacting at the bottom, while the Cubipods remained evenly arranged.
In 2007, OHL and its port business SATO collaborated with the university and designed a metal framework to turn the cute prototypes into 16-ton blocks. After numerous drop tests from more than three meters, the new blocks were proven to be much more stable.
Santos also says that, with the Cubipod’s feet, the blocks don’t stick together and that the feet make it homogenous and more structurally stable and predictable.
The first Cubipod project was just finished in the San Andres port in Malaga and the second one will soon open in Galicia’s A Coruña.
Photos: SATO (first two); Jennifer Riggins (of the mold)