GB1585860A

GB1585860A - Apparatus for depositing and protecting sediment on the floor of a body of water and a method of installing it

Info

Publication number: GB1585860A
Application number: GB2674876A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-01-11
Filing date: 1976-06-28
Publication date: 1981-03-11

Description

(54) APPARATUS FOR DEPOSITING AND PROTECTING SEDIMENT ON THE FLOOR OF A BODY OF WATER AND A METHOD OF INSTALLING IT (71) I, OLE FJORD LARSEN, Fasan v nget 62, Hjerting, 6700 Esbjerg, Denmark, Danish, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement This invention relates to apparatus for depositing and protecting sediment on the bed of a body of water and, in particular, to suitable apparatus for use in association with underwater pipelines and cables, and for shore protection and the prevention of blocking-up of waterways etc.

My earlier United Kingdom Patents Numbered 1,537,238 and 1,535,170 each disclose apparatus of this kind, having a ridge-like structure the sides of which slope down toward the bed of the body of water with an inclination of the order 1: 2-1: 5.

With the aim of avoiding the risk of damage by dragging anchors or fishing gear and the like, I now propose, in accordance with the present invention, apparatus for depositing and protecting sediment on the bed of a body of water comprising an elon gate cover located on the bed, the cover being a plate-like structure including a longitudinally extending centre portion spaced above the bed and two longitudinally extending side portions being divergent in a direction toward the bed, and means at least partially overlying the longitudinally extending side portions and projecting later ally therebeyond. Other features of the invention are set forth in the appendent claims.

Embodiments of this invention will now be described by way of example with refer ence to the accompanying drawings in which: Fig. 1 is a cross-section of a protective cover Fig. 2 plan view of an alternative cover Fig. 3 a cross-section taken along the line I-I of Fig. 2 Fig. 4 a cross-section of a cover with separate loose edge portions, Figs. 5 and 6 cross-sections of alternative designs of the connection 8 in Fig. 4, on enlarged scale.

Fig. 7 plan view of a cover containing channels 6 Fig. 8 a cross-section taken along the line II-II of Fig. 7 Fig. 9 a cross-section of enlarged scale, taken along the line IIIIII of Fig. 7 Fig. 10 an enlarged longitudinal section of the lower edge of a skirt, taken along the line IV-IV of Fig. 13 Fig. 11 plan view of a hinged connection Fig. 12 a cross-section along the line V-V of Fig. 11 Fig. 13 a cross-section of a cover strengthened by ribs Fig. 14 plan view of a cover with circular ends Fig. 15 a cross-section taken along the line VI-VI of Fig. 14 Fig. 16 a side view of an underwater vehicle carrying a cover Fig. 17 a cross-section taken along the line VII--VII of Fig. 16 Fig. 18 a side view of an underwater vehicle supported on the seated and connected with a surface vessel, and Fig. 19 and 20 are enlarged side views of details of Fig. 18.

The protective cover is a plate like structure and may be designed to have the necessary strength using the minimum material for fabrication, so avoiding unnecessary weight.

As shown in Fig. 4, the portion 1, comprises a thin plate which may be corrugated, the cross-section of the corrugation is being sinuous, trapezoidal, saw-toothed, or any other suitable shape. These corrugations and any other openings or recesses will as a result of the flow of water therethrough, fill with sediment this tending to hold down the cover on the bed.

The thin surface plate 3 (Figs. 1, 13) may be strengthened by ribs 4.

Preferably the cover has one or more skirts 1 on either side of the centerline thereof (Figs. 3, 4, 8, 13). If the cover is divided in symmetrical halves hinged together along the ridge (Figs. 2, 3, 4, 7, 8, 16), the center of gravity of each half should lie over or outside the supporting skirt, for maximum stability. This is especially important if the cover is to protect a pipeline, since only a negligible proportion of the weight of the cover will be transferred to the pipeline, even if initial settlement of the cover takes place.

Damage by dragging ships' anchors and trawlboards may be avoided in different ways. The individual choice being determined by the local conditions, i.e. the bed soil quality, depth of water, number and size of craft passing overhead.

The cover shown in Fig. 1 has at either side a steep face 7 of such height that the flukes of an anchor engaging the cover cannot hook beneath the lower edges thereof. The overall width of the cover between the steep faces 7 should not be much narrower than the width of the upper surface of the cover. Otherwise the scour-preventing effect is lost.

As an extra protection against anchors and trawlboards the edge portions 2 of the cover may be in sections slidable relative to the lower portions 5 (Fig. 4) but suspended by connections 8 so that when one edge portion 2, if hooked by an anchor, it will slide carrying the anchor, without damage to rest of the cover. The displaced section is thereafter repositioned.

The connection 8 may as shown in Fig. 5 or 6. In Fig. 5 the less edge portion 2 has locating rods 9 which fit into corresponding holes 10 in the lower portion 5. The rods 9 prevent lifting of the edge portion 2 from the lower portion 5, but permit turning around the connection 8, or sliding upwards, if the edge portion 2 is hooked by an anchor.

In Fig. 6 the connection 8 is in two parts; an angular plate bolted to the edge portion 2, and an anchoring plate 12 mounted on the lower portion 5, each part being resilient and made, for example, of thin stainless steel plate. Normally a dragging trawlboard will slip over without hooking the edge portion 2. The connection 8 may be designed to resist removal of the edge portion 2 by less powerful impacts, so that only a hooking trawlboard or an anchor of a certain minimum size, but not a regularly moving vertical trawlboard, can remove it.

For example, the lowermost part of the rod 9 may be crooked or formed as a rawlplug, as the surface between the portions 2 and 5 in the connection 8 may be roughened to afford limited frictional resistance.

Alternatively the loose edge portions 13, Fig. 3, may be pivotally hinged in an arc and before disengaging the portion 13, and fall onto the bed on the other side of the ridge.

The arrangement shown in Fig. 2, has a multiplicity of hinged edge pieces 13 which may be held together by a continuous wire 14. When an anchor hooks one of the edge pieces 13, the piece pivots so lifting the anchor over the cover and, when released, is returned to its original position by the weight of adjacent pieces connected thereto by the wire 14.

This effect may be improved, by mounting the edge pieces 13 on intermediate larger pieces 15 alas interconnected in a similar manner.

Another arrangement for prevention of damage comprises longitudinally extending bars 16 (Fig. 1) connected to cross-bars 17 which are hinged to the edge portion of the cover. A dragging anchor will hook the bar 16 and by the pivotal movement of this be lifted to fall on the cover 18. The connection between 16 and 17 being weak in direction away from the pivotal hinge 19, the anchor will thereafter disrupt the connection and pass on without causing other damage.

If the apparatus as shown in Fig. 8 or Fig. 13 is to protect a pipeline or the like, its units may either be so heavy that a dragging anchor will be held fast by the coherent assembly of heavy elements, so that the ship's officers would know that the anchor was foul and remedy the situation without damage to the pipeline. Alternatively, the hinge 20 may be designed so that it separates if the angle between the symmetrical halves decreases to a certain minimum. A Dragging anchor powerful enough to remove one half of the cover therefore will slide across the pipeline on top of this half and be carried over the pipeline without hooking it.

An example of such hinge 20 is shown in Figs. 11-12. One half of the cover includes at intervals bars 21, for example of stainless steel or aluminium. The end of each bar has a cross-piece 22 around which a clamp comprising pins 23 spread by spiral springs or with elastic blades or spring coils can rotate. The opposite half has a divergent recess 24 terminating in a wider cavity 25.

To join the two halves of the cover, the clamp is presses into the recess 24, whereafter on entering the cavity 25, the plus 23 will spread to a position wherein they are held by a tie 27, so preventing separation of the two halves.

Initial relative rotation of the two halves is about the hinge 20 until a thickened portion 26 forming a stop is encountered.

This then acts as a fulcrum for further rotation so placing a strain on the connection eventually resulting in breaking of the tie 27 or the pins or blades 23. To ensure that the skirt 1 will sink into the bed sufficiently to resist prevailing horizontal forces, its lower edge should be indented with a sawtoothed, sinuous, or other configuration, Fig. 10. Depending on th bed conditions (soil quality, surface regularity, etc), the cover may be built of long units so that the number of joints is minimized and maximum resistance to dragging anchors is obtained.

If shorter units are used, the joints may be formed so as to avoid steps between adjacent units. In Figs. 7 and 9 the two triangular transition pieces 28 are pivotally hinged to each other and to the adjacent units of cover forming a ridge when the two units are level. The ridge will flatten to form rather smooth transition between the two units, if one settles deeper into the seabed than the other.

Reduction of the weight of the cover may be obtained by providing cavities 6, (Figs.

4 and 8). Also, valves may be fitted so that after transport and installation during which the reduced weight and increased buoyancy is desirable, water can be admitted to the cavities 6.

For inspection of pipeline or other structure to be protected manholes closed by lids may be provided at intervals along the cover.

For the protection of cables or small diameter pipelines the cover shown in Figs.

14--15 is appropriate, its curved interlocking ends allowing the interconnected cover units to follow any curve of the cable.

Since the upper surface of the unit is transversely corrugated, and the height of the corrugations gradually decreases from the periphery toward the centerline, an anchor will push the periphery downwards into the seabed, so that the unit will turn over and carry the anchor over the cable or pipeline to be protected.

It will be appreciated that installation of the cover constitutes a substantial part of the total cost, so that a rational method of transporting and positioning the cover is important.

If the installation is to take place on the beach or in very shallow water, the cover is towed on the bed.

In deeper water large covers should be transported near the seabed all the way from coast to installation site so that the operation becomes comparatively independent of weather conditions, and the number of possible working days per year is increased.

The wave action near the seabed is minimum and nearly horizontal. Another advantage is that buoyancy effects facilitations handling are maximised.

The cover may be suspended by wires from surface vessels. Alternatively transportation and/or positioning of the cover is effected by means of a manned or unmanned under water vehicle as shown in Figs. 1 1617so 17 so minimizing the need for divers. The vehicle includes of buoyancy tanks, e.g. in the form of longitudinally extending pipes 29 interconnected by lattice members 30. The pipes 29 are preferably made of plastics material so as to obtain maximum buoyancy and -flexibility. Buoyancy is regulated by pumping water in or out of chambers in the pipes 29.

The vehicle may be self-propelled by thrusters 31, or towed by a surface vessel or submarine. For horizontal and vertical manoevering, the vehicle has thrusters 31 acting in different directions but the number of thrusters required can be reduced if they are made rotatable in one or more planes.

The cover 32 may be held by a system of vacuum clutches 33 applied directly on the surface of the cover and allowing simultaneously and instant seizure and release of all the cover units. For adjusting the angle between the symmetrical halves of the cover, the hydraulically operated pistons 34 may be provided. Echosounders mounted on the vehicle monitor the distance between vehicle and seabed and regulate automatically the thrusters to maintain the desired distance.

A sonar system including a display enables the operator to check the position of the vehicle or the row of interconnected vehicles and thereby to direct and navigate the vehicle.

If it is required to protect for instance a pipeline, an automatic system for sideways positioning may be used. When the vehicle with the cover arrives at some point of the pipeline to be protected, as observed using television cameras placed at either end of the vehicle, the positioning system acts to keep the vehicle centered over or at a certain distance to one side of the pipeline until the site of installation has been reached and the cover positioned. The system includes at either end of the vehicle a pair of magnetometers placed symmetrically on either side of the centerline of the vehicle. Any difference between the degrees to which the pipeline absorbs the magnetic fields of the two magnetometers, is registered and a corresponding difference between the two distances between the magnetometers and the pipeline.

For installation of smaller units as shown in Figs. 14--15 the underwater vehicle preferably is supported directly on the seabed by wheels, caterpillars tracks rollers skids or runners 35, Fig. 18.

Such small units may be supplied vertically from a surface vessel 36. Appropriately the elements are lowered to the vehicle in a casing 40 guided by lines 41 connecting the surface vessel with the bottom of the casing 39 on the vehicle. The lines 41 may be made of elastic material, e.g. rubber, to compensate for the vertical motions of the vessel.

The casing 40 is in two interconnected parts 42 and 43 which can move horizontally in relation to each other. When the casing 40 is lowered and strikes the sloping upper surface of the uppermost element in the casing 39, the part 43 will be separate part 42, whereby the lock 44 retaining the element during lowering of the casing will open, so allowing casing 39 where they are located by stepped abutments 54.

The casing 39 on the vehicle carries a stack of elements 46 supported on an inclined plate or beam 47 which is inclined to such degree that the lowermost element 48 by its own weight and/or its coherence to the elements already laid will slide down through an opening 49 at the bottom of casing 39. When the rear end of each element which is formed with a groove (Fig. 7) passes under a tongue on the next element (52) immediately above, the tongue will drop into the groove 50, so that this elements become connected together and are withdrawn in time from the casing 39.

The upper surface of the plate 47 is curved such that the element 48 during its downward slide will cause no upward displacement of the element 52. The said curve therefore should be formed by two symmetrical halves forming a peak 53 under the treading point of the element 52. In an alternative embodiment, instead of replying upon a gravity feed, an endless, horizontal or sloping conveyor belt driven by supporting wheels or caterpillars may be provided at the rear end of the vehicle to eject the elements from the casing 39 to the seabed.

The stepped abutments 24 are preferably inclined such that the lower end of each element is supported chiefly the abutment only a tiny part of the weight of each element is bearing on the element below.

If it is required to protect a pipeline, the vehicle may be guided along the pipeline by rollers as other guide members mounted on the vehicle on either side of the pipeline.

Preferably the vehicle is selfpropelled, e.g.

by means of hydraulic motors powered from the surface vessel or submarine.

The vehicle has the same sensor systems as the vehicle for installation of large covers as described above. The magnetometer system enables it to follow very closely the curves of an existing cable to be protected, even if sections of the cable are covered by sand. On such covered sections the elements are placed on the surface of the sand. If the bed becomes eroded later on, the elements will sink to the level of the cable.

WHAT I CLAIM IS: 1. Apparatus for depositing and protecting sediment on the bed of a body of water comprising an elongate cover located on the bed, the cover being a plate-like structure including a longitudinally extending centre portion spaced above the bed and two longitudinally extending side portions, upper surfaces of the longitudinally extending side portions being divergent in a direction toward the bed, and means at least partially overlying the longitudinally extending side portions and projecting laterally therebeyond for protecting the cover from damage due to dragging ship's anchors, fishing gear, and the like.

2. Apparatus according to in claim 2 wherein the longitudinally extending side portions of the cover are substantially steeper than the remainder of the cover.

3. Apparatus according to claim 1 including means for movably connecting the protecting means to the longitudinally extending side portions.

4. Apparatus according to claim 3 wherein the movable connecting means defines a pivotal connection between the protecting means and the longitudinally extending side portions.

5. Apparatus according to claim 3 wherein the movable connecting means defines a sliding connection between the protecting means and the longitudinally extending side portions.

6. Apparatus according to claim 3 wherein the movable connecting means defines a sliding connection between the protecting means and the longitudinally extending side portions, and the slidable connecting means includes openings in the cover each opening in a direction toward the centre portion, and the slidable connecting means further includes elements carried by the protecting means in slidable relationship to the openings.

7. Apparatus according to claim 3 wherein the movable connecting means defines a sliding connection between the protecting means and the longitudinally extending side portions, and the slidable connecting means being defined by mating lands and depressions disposed in transverse relationship to the longitudinal centerline of the cover.

8. Apparatus according to claim 3 wherein the protecting means comprises a plurality of cover elements disposed along each of the longitudinally extending side portions, and means for articulately connecting together the cover elements along each of the longitudinally extending side portions.

9. Apparatus according to claim 3 wherein the protecting means are a plurality of longitudinally spaced laterally extending elements connected to a longitudinal element at each longitudinal side of the cover and the connections between the longitudinal elements and the laterally extending elements are weaker than the connecting means.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. surface vessel with the bottom of the casing 39 on the vehicle. The lines 41 may be made of elastic material, e.g. rubber, to compensate for the vertical motions of the vessel. The casing 40 is in two interconnected parts 42 and 43 which can move horizontally in relation to each other. When the casing 40 is lowered and strikes the sloping upper surface of the uppermost element in the casing 39, the part 43 will be separate part 42, whereby the lock 44 retaining the element during lowering of the casing will open, so allowing casing 39 where they are located by stepped abutments 54. The casing 39 on the vehicle carries a stack of elements 46 supported on an inclined plate or beam 47 which is inclined to such degree that the lowermost element 48 by its own weight and/or its coherence to the elements already laid will slide down through an opening 49 at the bottom of casing 39. When the rear end of each element which is formed with a groove (Fig. 7) passes under a tongue on the next element (52) immediately above, the tongue will drop into the groove 50, so that this elements become connected together and are withdrawn in time from the casing 39. The upper surface of the plate 47 is curved such that the element 48 during its downward slide will cause no upward displacement of the element 52. The said curve therefore should be formed by two symmetrical halves forming a peak 53 under the treading point of the element 52. In an alternative embodiment, instead of replying upon a gravity feed, an endless, horizontal or sloping conveyor belt driven by supporting wheels or caterpillars may be provided at the rear end of the vehicle to eject the elements from the casing 39 to the seabed. The stepped abutments 24 are preferably inclined such that the lower end of each element is supported chiefly the abutment only a tiny part of the weight of each element is bearing on the element below. If it is required to protect a pipeline, the vehicle may be guided along the pipeline by rollers as other guide members mounted on the vehicle on either side of the pipeline. Preferably the vehicle is selfpropelled, e.g. by means of hydraulic motors powered from the surface vessel or submarine. The vehicle has the same sensor systems as the vehicle for installation of large covers as described above. The magnetometer system enables it to follow very closely the curves of an existing cable to be protected, even if sections of the cable are covered by sand. On such covered sections the elements are placed on the surface of the sand. If the bed becomes eroded later on, the elements will sink to the level of the cable. WHAT I CLAIM IS:

1. Apparatus for depositing and protecting sediment on the bed of a body of water comprising an elongate cover located on the bed, the cover being a plate-like structure including a longitudinally extending centre portion spaced above the bed and two longitudinally extending side portions, upper surfaces of the longitudinally extending side portions being divergent in a direction toward the bed, and means at least partially overlying the longitudinally extending side portions and projecting laterally therebeyond for protecting the cover from damage due to dragging ship's anchors, fishing gear, and the like.

10. Apparatus according to claim 3

wherein each longitudinally extending side portion includes a foot disposed between the longitudinally extending centre portion and a free longitudinal edge of an adjacent longitudinally extending side portion, and the feet project downwardly and away from the longitudinally extending center portion.

11. Apparatus according to claim 3 wherein each longitudinally extending side portion includes a foot disposed between the longitudinally extending centre portion and a free longitudinal edge of an adjacent longitudinally extending side portion, and the feet project downwardly and away from the longitudinally extending centre portion, and the skirts are indented.

12. Apparatus according to claim 3 wherein the cover is formed by symmetrical halves pivotally connected to each other along the longitudinally extending centre portion.

13. Apparatus according to claim 3 wherein the cover is formed of symmetrical halves pivotally connected to each other along the longitudinally extending centre portion, and means for totally separating the halves at a predetermined angle of mutual rotation therebetween.

14. Apparatus according to claim 3 wherein the plate-like structure has a wavy configuration.

15. Apparatus according to claim 3 wherein the plate-like structure has a corrugated configuration the amplitude of which decreases in a direction from the longitudinally extending side portions toward the longitudinally extending centre portion.

16. Apparatus according to claim 3 wherein the protecting means is formed of cementitious material.

17. Apparatus according to any one of claims 3 to 16 including another cover in end-to-end relationship to the first-mentioned cover, and means pivotally connecting the covers together in end-to-end relationship.

18. Apparatus according to claim 17 wherein the last-mentioned connecting means include a pair of transitional elements pivotally connected to each other and to the plate-like structures.

19. Apparatus according to claim 18 wherein the transitional elements are triangular as viewed in top plan.

20. Apparatus according to claim 19 wherein the transitional elements are angularly disposed to each other when said halves are coplanar.

21. Apparatus for depositing and protecting sediment on the bed of a body of water, constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.