EP0200753B1

EP0200753B1 - Erosion-protecting surface covering for laying out on earth surfaces exposed to water

Info

Publication number: EP0200753B1
Application number: EP19850905321
Authority: EP
Inventors: Erik Nielsen
Original assignee: COAST PROTECTION ApS
Current assignee: COAST PROTECTION ApS
Priority date: 1984-10-22
Filing date: 1985-10-22
Publication date: 1989-02-22
Also published as: DE3568360D1; AU4867885A; EP0200753A1; DK153897C; DK153897B; DK502884A; DK502884D0; WO1986002680A1

Abstract

By tightening concrete blocks (1, 4) together around a flexible mat (8) by means of a through-going threaded bolt (6), and with an eye-nut (7) above, there can be built up a covering which can be lowered to the sea bed and protect this against erosion. In order for the covering to be able to lie firmly, the underside of the lower block (4) is made concave, while the top of the upper block (1) is tapered to reduce resistance against current. Finally, the blocks (4) are hexagonal in shape, so that they can be mounted on the mat (8) with the same mutual distance between them.

Description

The invention relates to an erosion-protecting surface covering for laying out on the sea bed, coastal areas and other earth surfaces which are exposed to water, said covering comprising a mat with concrete blocks resting on the top side. Such a covering is known, for example, from FR-A-2 411 269.
Erosion can arise during storms and floods, while harbours are exposed to a bottom erosion which occurs particularly in sailing channels, and at ferry ports where the ferries are so large that the propellers are only a few metres above the sea bed.
When the ships execute the necessary man- aeuvres, the propellers frequently flush sand away from the bottom and from the area near the piling walls, so that the lower ends of the piles are more or less exposed, and thus there is danger of collapse of the quay and its approaches.
In order to moderate the effects of the current from the propellers, it is known to lay mats on the sea bed, self-locking slabs, gabions or the like. The mats are secured by large sea-stones of up to 3 tonnes with eyebolts inserted, which are held together by heavy iron chains through these eyebolts.
However, when such a securing of a strongly- influenced bottom area has taken place, there occurs a violent erosion of the non-secured sea bed along the edges of the mats, whereby the large sea-stones can come to hang freely in their chains over the sea bed, with the risk of the mats being ruined, and thereby the securing of the bottom.
The use of mutually interlocking concrete slabs demands a levelling of the sea bed and a securing of the outer edge area of the concrete slabs, which can be effected by means of large gabions which are buried down in the bottom. These slabs must be controlled and firmly locked by divers. This is an extremely difficult and time-consuming procedure, and in the event of an eventual break in the slabs, repair operations are very difficult and expensive to carry out.
It is also known to lay out a membrane made of synthetic material, steel mesh or asphalt to which concrete elements are affixed or secured. However, this is an expensive and complicated laying- out procedure, in that the construction of. this securing arrangement demands that it be layed out in one continuous course.
It is the object of the invention to remedy these deficiences in the known surface coverings, and at the same time to improve and reduce the cost of bottom securing, and also to make it possible for eventual repairs to be carried out in a good and convenient manner for the divers.
This is achieved by a surface covering where on the underside of the mat, opposite each of the concrete blocks resting on it, there is mounted a further concrete block in such a manner that the mat is clamped between the pairs of opposite-facing concrete blocks. There is thus achieved a protection covering which can remain on the bottom, in that it can normally be laid down completely without levelling of the bottom, with possibility of adapting of the weight of the elements in accordance with the current conditions and the type of bottom. The mat functions as a protection layer against erosion brought about by water currents from above, and gradually it will become an integral part of the sea bottom, the reason being that earth, sand and the like will be deposited under the mat, so that it will finally become embedded in the bottom.
As presented in claim 2, by bolting the concrete blocks together around the mat, the possibility is achieved of constructing the covering in modules on land, and by means of lifting cables through the eyes, the covering can be lowered down into place, where a diver can then assemble adjacent modules in a safe and simple manner.
As presented in claim 3, the providing of a resilient bush in at least the hole in the upper block prevents the formation of cracks and destruction of the blocks by powerful influence from the bolts by dimensional changes, frost and the like.
As presented in claim 4, by providing the concrete blocks with plane assembly surfaces, the greatest possible degree of protection is achieved for the mat and the blocks.
As presented in claim 5, by providing the lower blocks with a hollowed-out bottom, these can suck themselves firmly to the sea bed, and by making the upper blocks tapered, the surface of attack is smaller and therefore less exposed to the influences of the current.
Finally, as presented in claim 6, it is expedient to provide the blocks with a hexagon form, in that they will then be able to be placed at the same mutual intervals in staggered rows on the mat.
The invention will now be described in closer detail with reference to the drawing, where

fig. 1 shows a cross-section of the upper concrete block,
fig. 2 shows a cross-section of the lower concrete block,
fig. 3 shows a cross-section of the blocks bolted together on a mat,
fig. 4 shows the covering from above,
fig. 5 shows the covering with lifting arrangement,. and
fig. 6 shows the assembly of adjacent covering modules.

In the drawing is shown a preferred embodiment of the covering according to the invention. It is built up of hexagon-shaped concrete blocks, as shown in flg. 4, which shows the upper block 1 seen from above, mounted on a mat 8.
The blocks comprise an upper block 1, which is shown in fig. 1, and a lower block 4, which is shown in fig. 2.
The blocks 1, 4 have plane upper and lower sides respectively, so that they can lie up against the flexible loom in the form of the mat 8.
Through the blocks 1 and 4 there are holes through which a bolt 6 with a bent-over head can be inserted with the bent head in a countersinking 5 in the bottom of the lower block 4. The upper block 1 is provided with an elastic bush 2 of synthetic material or rubber for the absorption of possible stresses. As will appear from fig. 3, the parts are tightened together around the mat 8 by means of an eyebolt 7.
The underside of the lower block 4 is also made concave, and it can suck itself firmly to the bottom after the laying out. Furthermore, the upper block 1 is tapered upwards in order to reduce the resistance to current.
Preferably, the blocks are made by being moulded in concrete, and can have a breadth of about 50 cm and thickness of about 15 cm. Moreover, the blocks 1 and 4 are rounded off 3 on the undersides along the side edges in order to make them more resistant to external influences.
As will appear from fig. 4, staggered rows of blocks are secured to the mat, which can be of synthetic fibres or the like. The mat can have a breadth of about 2.5 m and a length of about 6 m. Such an assembled covering will have a weight of about 6,000 kg.
As shown in fig. 5, the laying out can be effected by suspension in a lifting arrangement comprising a yoke 10 with lifting lines 11 and a lifting cable 12 for a crane.
When the covering is placed on the sea bottom, as shown in fig. 6, the mats 8a and 8b can be positioned in such way that they overlap each other, after which a diver can bore holes through the mats and place concrete blocks under and over the mats respectively as shown in the drawing.
In this way, a coherent covering can be built up on the sea bed, and this can be effected in a hitherto unknown simple and effective manner.

Claims

1. Erosion-protecting surface covering for laying out on the sea bed, coastal areas and other earth surfaces which are exposed to water, said covering comprising a mat (8) with concrete blocks (1) resting on the top side, characterized in that on the underside of the mat (8), opposite each of the resting concrete blocks (1), there is mounted a further concrete block (4) in such a manner that the mat (8) is clamped firmly between the pairs of opposite-facing concrete blocks (1, 4).

2. Erosion-protecting surface covering according to claim 1, characterized in that each pair of concrete blocks (1, 4) has a through-going hole and is held together by means of a through-going threaded bolt (6) with a ring-nut (7) above.

3. Erosion-protecting surface covering according to claims 1 and 2, characterized in that a resilient bush (2) is inserted through the hole in the upper concrete block (1).

4. Erosion-protecting surface covering according to claims 1-3, characterized in that the concrete blocks (1, 4) have plane assembly surfaces.

5. Erosion-protecting surface covering according to claims 1-4, characterized in that the underside of the lower concrete block (4) is hollowed-out in a concave manner, while the upper concrete block (1) has sloping side surfaces which make said block (1) tapered.

6. Erosion-protecting surface covering according to claims 1-5, characterized in that the concrete blocks (1, 4) are six-sided in shape, in that the side walls constitute a hexagon.