IADC: Facts About Seabed Intervention

The International Association of Dredging Companies (IADC) has announced the Facts About Seabed Intervention study.

Facts About is a series of concise, easy-to-read leaflets which give an effective overview of essential facts about specific dredging and maritime construction subjects. Each leaflet provides a kind of ‘management summary’ for stakeholders who need a quick understanding of a particular issue.

These leaflets are part of IADC’s on-going effort to support clients, consultants and others in understanding the fundamental principles of dredging and maritime construction because providing effective information to all involved parties is an essential element in achieving a successful dredging project.

WHY IS SEABED INTERVENTION NECESSARY?

To place a structure on the seabed securely, the seabed should be as flat and regular as possible. If the seabed is irregular or undulating, the structure, for instance, a pipeline or cable or offshore platform, will suffer the risk of spanning and overstressing. To avoid these and other risks, dredging contractors are asked to intervene to make the seabed flatter or to cover the structure that is being placed to protect it.

Offshore infrastructure installations are often exposed to high external pressures and cold temperatures. They are subject to tidal movements, currents and scour unless buried or trenched in the seabed. Preparation of the seabed is therefore of crucial importance.

HOW OFTEN DOES SEABED INTERVENTION TAKE PLACE?

In recent years the need for seabed intervention has been increasing. Since the late 1940s, gas and oil have been mined from offshore sites. Nowadays these resources are being mined at ever greater depths, often in remote areas. These resources have to be brought on shore and this is frequently done through pipelines laid upon the seabed. These pipelines must often traverse long distances over rough seabed terrain to land-based sites.

For instance, at Sakhalin in Russia, the potential recoverable resources are enormous and the challenges equally as great. This offshore project required the installation and post-trenching of 20 km pipeline crossing of Tatar Strait, the narrow fairway between Sakhalin Island and the Russian mainland, a significant distance to be managed in a harsh climate where the short summers mean a limited working

Post-trenching lowers the pipeline from the level at which it was laid to the final pipeline level. window. Although the main clients for seabed preparation contracts are oil and gas operators for pipe-laying and offshore platforms, the same intervention techniques are applied in other markets, such as cable laying, port construction and in the offshore wind farm industry.

Before foundation towers could be sunk at the Thornton Wind Turbine Farm off the Belgian coast, the seabed had to be levelled and a gravel bed for stabilisation had to be laid. Also at the Le Havre’s Port 2000, the seabed was levelled to a tolerance of approx. 10 cm before the two massive concrete caissons that close off the breakwaters, could be positioned.

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Press Release, September 5, 2013