Avilés, rock dredging

Aviles Rock Dredging

Challenge

The population of Avilés, a city on the northern coast of Spain, has dramatically increased when major factories were established in the 1960’s. Located between the capital Oviedo and the sea, the port of Avilés has been developed land inwards along the Ria de Avilés estuary. At one time, the river was drained and cleared, and the estuary was closed to all navigation. This decision was reversed and the port of Avilés is currently the second largest of the strongly industrialised Asturias region, after Gijón.

In recent years, the Autoridad Portuaria de Avilés has made important investments to improve operations and extend shipping traffic services. With regard to growing demands, the limited draught was seen as a handicap for the commercial running of the port and for its competitiveness. Increasing navigational depth should also increase safety by providing a greater protection against the tidal range. Furthermore, it was hoped this would increase the number of operational hours for bigger ships. However, the local geography and in particular the rocky character of the Cordillera Cantábrica region is a serious impediment, especially since ever deeper layers have to be dredged.

Our solution

The deepening of the access channel to the port of Avilés by rock dredging, is an excellent example of ‘impossible’ projects that become feasible by technological innovation. New technology creates new opportunities and makes its own market. Even then, creative solutions had to be developed to bring this dredging project to a satisfying end.

In 2005, Dredging International had already deepened the harbour from minus 10 m to minus 11,5 m. Although a trailing suction hopper dredger (TSHD) had sufficed to remove loose sediments that were still found at that time, the strongest ocean-going and self-propelled cutter suction dredger (CSD) in the world, d’Artagnan, had even then been necessary for dredging the deeper rock layers. In the second phase of dredging, executed in 2008, only weathered rock was encountered when deepening even further to minus 12,5 m, which required the presence of d’Artagnan all the more. Just a decade earlier, this kind of work would simply have been impossible without blasting. It is only after building the high-tech heavy rock breaker d’Artagnan, that rock dredging at this site and further deepening of the port of Avilés became feasible in the first place.

Creative solutions had to be engineered in order to overcome practical problems. The access channel in Avilés is very narrow and quite busy for that. Commercial traffic and dredging operations interfered and vessels could only hardly overtake. This led to scrupulous timing and frequent consultation with Port Operations, also to reduce idle time for the dredgers and maintain productivity.

Since the CSD anchors could not penetrate the soil in the channel, they were placed onshore where an inventive system prevented damage to the quays. At the Curve of the Port where an environmental sanctuary prevented anchoring onhore, the anchor pattern was optimized and the use of anchors on this side of the channel minimized.

With hardness levels of more than 70 MPa, the dredged rock was very hard indeed and even beyond the design hardness for CSD d’Artagnan. And yet, the target level was reached and the project finalised well within the expectations of the client.

Furthermore, due to the busy activity in the channel and the offshore location of the designated dump area, which was fully exposed to the heavy weather in the Sea of Cantábria, a floating pipeline was not an option. D’Artagnan therefore used its barge loading installation to transport the materials on split hopper barges in the range between 2.000 and 2.500 m³. During the second phase of dredging at Avilés, a total of 178.250 m³ of rock was dredged and dumped offshore.

Do you have a question about this project?