Hydraulic and earth engineering – Subterranean or submarine pipe or cable laying – retrieving,... – Submerging – raising – or manipulating line of pipe or cable...
Patent
1990-04-17
1991-10-01
Taylor, Dennis L.
Hydraulic and earth engineering
Subterranean or submarine pipe or cable laying, retrieving,...
Submerging, raising, or manipulating line of pipe or cable...
405157, E03B 714
Patent
active
050528599
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to articulated seabed mattresses for the protection and stabilisation of seabed installations such as pipelines.
The use of articulated mattresses in offshore coastal and marine engineering is well known for stabilisation, protection and scour prevention of pipelines, flowline umbilicals, seabed templates, steel and concrete platforms and the like. These mattresses are particularly useful in areas of high bottom current where hydro-dynamic forces are considerable. Thus, for example, a seabed pipeline can be covered with such a mattress so that the pipeline is stabilised by the weight of the blanket thereon and also the adjacent seabed is protected against erosion. Examples of articulated mattresses and their use are given for example in European patent specification 152232A. Generally, these mattresses comprise concrete or similar elements joined together to allow relative articulation.
Subsea stabilisation mattresses can be relatively massive, eg. a mat of 5 m.times.2 m would weigh (in air) over 2.5 tons. However, even so, when they are laid over a seabed pipeline, for example, they can still be prone to movement during a storm or tidal surge. While, in theory, greater stability could be obtained by increasing the mat weight, we have found another way of dealing with this problem.
Further, in addition to stability in extreme storm conditions, a stabilisation mattress should desirably also be capable of withstanding the impact thereon of anchors or trawlboards travelling laterally, or dropped objects travelling largely vertically.
We have now devised a new design of sub-sea mattress which can provide substantial advantages in use over prior known mattresses.
In accordance with one aspect of the present invention, there is provided an articulated mattress for laying on a seabed or the like, which comprises a plurality of concrete or like members articulated together, characterised in that the mattress has a relatively thick region from which its thickness tapers to at least one side edge.
In a simple embodiment, a mattress of the invention is generally wedge-shaped. That is to say, when laid on a horizontal surface, its transverse sectional shape is roughly that of a right-angle triangle. More usually, however, mattresses of the invention will have a shape generally similar to that of a ridge tent, i.e. with a central elongate thick region tapering down on each side to a side edge of the mattress. Another possibility is to have a generally pyramidal shape, i.e. a central thick region tapering down on all sides to the edge(s). In all cases, the upper sloping surface(s) may be generally flat, or generally curved, eg. concave or convex as desired. Whilst the commonest mattress shape in plan is generally rectangular, in fact the mattresses can be of any desired plan shape as required in practice.
By providing the mattress with its own taper from a thin edge to a much thicker region, improved stability can be achieved and also improved ability to withstand lateral impact by dragged anchors or trawlboards, for example, and by dropped objects descending vertically.
The mattresses of the invention taper in thickness from a relatively thick region to at least one side edge. Normally, the tapering extends through at least two of the constituent elements of the mattress.
Conventionally, when a sea-bed pipeline or other object is to be protected, a subsea mattress is laid thereover. In accordance with a highly preferred feature of the present invention, the underside of a mattress is provided with a recessed region in which the object to be protected is received. Such a recessed region is most advantageously provided in the thick region of the mattress. This gives excellent protection to the object and also allows certain further preferred features of the invention to be adopted (described hereinafter).
The mattresses of the invention are constructed from massive elements formed from concrete or other weighty material. The concrete can be adjusted to have a low
REFERENCES:
patent: 4152875 (1979-05-01), Soland
patent: 4171174 (1979-10-01), Larsen
patent: 4242010 (1980-12-01), Gjerde et al.
patent: 4334801 (1982-06-01), Gray
patent: 4696324 (1987-09-01), Petronko
McBee J. Russell
SeaMark Systems Limited
Taylor Dennis L.
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