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Subsea Trenching More Than Just Spade Work


Global Marine Systems Limited has a strong track record in the installation of subsea cables that dates back to 1850. Since then, the company has installed more than 300,000 km of cable – approximately 23% of the world’s total. We take a look at the technology and the techniques behind the process.

The installing of subsea power cables has been a core business activity since the late 1980s. Indeed, Global Marine’s capability is diverse, installing fibre optic, power (from HVDC to HVAC requirements) and composite cables, in both very shallow water depths (less than 10m) through to very deep (over 6000 m).

Clearly, one of the key capabilities with installing any cable is trenching, primarily to ensure protection from the dangers posed by the sea bed terrain itself in certain areas, as well as trawlers, anchors, icebergs or any large objects, such as shipping containers that occasionally fall from vessels. Typically, trenching is performed by ploughing, jetting or cutting the seabed material, and can take place pre- or post-cable laying.

Ploughing forward
The trenching technique of ploughing is a good, general purpose method, as it’s suited to a wide variety of soil types found on the seabed, including granular sand, clays and fractured rock. As a technique, it can produce deep trenches with high quality, straight walls in a single pass. Furthermore, high speeds are possible in softer seabed types, thus reducing the time and costs incurred.

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