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21 November 2011
super-efficient version of its Armorflex erosion-protection block - designed to combat the underwater force of the Indian Ocean – has been developed by concrete building products manufacturer Technicrete.
A total of about 35,000 blocks, assembled into 230 articulated concrete block mattresses, covering an area of more than 3 200m², are to be laid on the sea-bed at Beira port in Mozambique as part of a project to upgrade and deepen the Quay 8 coal export berth to facilitate the movement of larger vessels.
It will be the first time that the new Technicrete Armorflex 405 block has been put into use.
Manufactured at the Technicrete White River plant to a specification set by the Dutch engineering consultancy DHV, the blocks will be laid eight metres below mean sea level in two separate areas near the Beira river mouth. One area of sea-bed to be covered measures 60m x 24m, the other 76.7m x24m.
A heavyweight adaptation of smaller and lighter blocks widely used for flood water and erosion protection, they have a thickness of 220mm compared with the standard Armorflex’s 115mm, and will provide scour protection from tidal forces and the wash from maneuvering ships’ propellers and bow-thrusters.
For the Beira project, individual blocks are laced together with polyrene, a rope made from an exceptionally strong, chafe-resistant mix of polyester and nylon, to form articulated concrete block mats. In all, 230 mats, each made up of 152 blocks and weighing 5,8 tons, will be laid.
A fleet of trucks has already started transporting mats from Technicrete’s White River factory to Beira, and it’s expected that the first load will be lowered onto the seabed by cranes in November.
That will be a delicate operation, as the currents, both from the river flow and the tidal influences, will make the placing of the ACBMs very difficult and time consuming. Divers may not be used as the waters are loaded with silts and the resultant visibility is extremely poor.
“It’s very important that each mat is correctly laid to fit snugly against its neighbour to ensure the desired maximum effect,” says Technicrete product manager Taco Voogt, who has been consulting with DHV and the Contractor on the project.