A prototype of a newly conceived underwater tracked vehicle for trenching operations has been constructed and tested by TECNOMARE S. p.A.
The project of the vehicle, denominated TM-102, started in 1971 as a research project and led in 1975 to the construction of a prototype which has been successfully tested both in a shipyard dry-dock and at sea.
The vehicle, which is remotely controlled by a surface support vessel through an umbilical cable, can solve the problem of burying cables and pipelines in deep water (up to 200 meters W.D.) and in areas presenting severe ocean graphic conditions, with bottom soil of various characteristics.
The vehicle moves astride the pipe without exerting any stress on the pipe itself and can dig trenches of various shapes.
This paper examines the problems connected with the burying of pipes and cables and describes the TM-102 design criteria.
The TM-102 trenching vehicle's main characteristics and working capabilities, together with the results of the shop and field tests, are presented.
Furthermore, possible developments of the trenching system are indicated.
The continuous expansion of the offshore industry demands systems capable of carrying out earth-moving jobs in deep water. For example, the installation of gravity structures (storage tanks, drilling-production platforms, subsea production systems) may require the execution of various underwater operations for the leveling of the sea bottom. In particular the burial of underwater pipelines and cables is considered, in many cases, an absolutely necessary operation in order to avoid the risks deriving from damage to the lines, which can result in pollution and production losses, in addition to extremely high repair costs.
Among the causes of damage the following can be envisaged: trawler nets, anchors, and acts of sabotage, phenomena of dune migrations or the presence of uneven sea bottoms (with consequent free-span formation).
A system suitable for carrying out successfully general earth-moving jobs and burial operations should satisfy many operational requirements, some of them related to safety reasons and some to operative conditions.
These main requirements are:
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to trench pipes and cables already laid on the sea bottom, by digging the trench beneath the pipe;
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to avoid any risk of damaging pipes and cables;
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to excavate trenches of various depths;
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to move on sea bottoms having various bearing capacities and presenting obstacles (such as stones and protruding rocks) as well as uneven surface;
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to trench soils having various geotechnical characteristics (sand, clay, soft rock);
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to operate in deep water;,
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to operate in areas presenting severe ocean graphic conditions;
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to avoid any risk of injury to the trenching system operators;
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to be capable of burying the pipe, or cable, laid at the trench bottom, with the soil already excavated.
All these requirements have been carefully considered before starting the design of Tecnomare TM-102 trenching vehicle and are the basis of the main choices of the project.
