FR2749330A1 - Submerged barrier to protect maritime areas - Google Patents

Abstract

The barrier (1) is constructed on a submerged base (2) and is made of several caissons (4) attached to one another. The height of the caisson is determined so that whatever the variation in the height of the water (12) they are always completely submerged. Each shock absorbing caisson is a hollow cylinder. The upper third of the caisson which faces the open sea has openings (9) in it allowing water to flow in and out. The base (10) of each caisson can be filled with rubble from a quarry (22) or material from the site (11) up to a certain level, making it stable in its bed (2). The barrier is assembled using piles (5) which fit between shoulders (6) on the outside of the caissons. Transverse tie rods (7) on either side of each pile, pass through the walls of two adjacent caissons and hold them together

Description

 The present invention relates to an underwater structure consisting of a submerged barrier, it also relates to a method of constructing such a barrier.

 The state of the art can be defined by numerous documents.

 The document FR-A-2.712.002 proposes a process which comprises the successive stages consisting first of all in vertically installing on the bottom a lost formwork made up of prefabricated elements comprising two parallel walls, defining between them a space, at least one walls being a self-supporting wall constituted by a perforated plate over its entire surface and then filling said space with concrete loaded with sand and large aggregates, the smallest of the aggregates having dimensions just greater than the openings of the perforated plate. The density of the concrete causes the excess water and the fluid in which the formwork is immersed to be evacuated through the openings and causes the concrete to harden.

 This technique using lost formwork is very conventional. In addition, it contaminates the waters where the dam is built and, being visible, the dam degrades the quality of the landscape.

 The document FR-A-2,708,642 relates to a process and a bolt for the liquid-tight assembly of the bolt halves, lowered in a suspension, of successive membrane sections of an underground curtain. The other half of the puller, composed of an internal profiled element, of a following membrane section, is adjusted with a plane support in one of the halves of the puller, composed of an external profiled element, of one of the membrane sections. An internal groove, which extends essentially along the length of the safe, is formed in the wall of the internal profiled element, this groove passing through the wall of the internal profiled element and extending into the wall of the 'external profiled element, for hermetically welding the internal and external profiled elements together, by applying welding material to the walls of the groove.

 Although its use is rather underground, this process uses profiled elements which can fit into each other; the membranes with which they are associated constituting a curtain. However this technique is not easily transposable to the underwater environment where the conditions, especially due to the swell, are very unfavorable.

 In addition, in traditional dike construction techniques, the work generates muddy water, carrying many impurities from the seabed or construction materials.

 The present invention implements a structure and a construction method which is not very polluting and visible after its construction.

 In addition, it performs four essential functions.

First, it ensures the surge of the swell. Second, it absorbs some of the energy from the swell. Third, it protects the environment by using non-polluting materials.

Always at the level of the environment, it creates a waterproof screen between the open sea and the coast allowing to work without risk of pollution in the protected space. Fourth, it supports a continental shelf or an artificial island.

 To this end, the present invention relates to a structure intended to create a barrier on a submerged bottom, so as to protect a maritime area to allow development, characterized in that it consists of several boxes acting as shock absorbers which are submerged; said boxes are secured to each other by assembly means which also act as a seal between two boxes.

 Each box has a height such that said box is completely submerged whatever the variations in the water level, so as to form an effective but not visible barrier.

 Each damping box is a hollow cylinder.

 The upper part of each box intended to be oriented towards the open sea is, in its upper third, provided with orifices ensuring the entry and exit of water in the area stressed by the swell.

 Each hollow damping box is provided with a bottom so that it can be loaded with all-quarry or backfill with site materials up to a certain height, to be stable in its soil.

 The assembly means are constituted by piles which cooperate with shoulders carried by the outer wall of the boxes and which reinforce the stability of said damping boxes.

 Cross tie rods, located on either side of each pile, connect two adjacent shock absorbing boxes.

 The area where the assembly means are located is delimited from top to bottom and on each side of the pile by cofferdams, the spaces remaining free between the cofferdams are filled in to constitute the final keying.

 According to a particular embodiment, a complementary energy dissipating device is placed in the center of each box.

The present invention also relates to a method of constructing a structure, as developed above, which is characterized in that it consists of
- prepare the soil intended to receive a first box,
- install at least the first two piles,
- position the first box on its soil relative to the first two piles,
- fix the first box to the piles,
- install the other piles, and
- moor the other boxes to the piles.

 The process consists in installing a temporary waterproof shield on the submerged caissons to allow the development of the maritime structure without diffusion and pollution of the embankments towards the open sea, then to remove it once the structure is finished.

 Depending on the case, this process consists, before the installation of each of the first and last caissons, in building an underwater dike which connects the submerged barrier to the coast.

 The attached drawings are given as indicative and non-limiting examples. They represent an embodiment according to the invention. They will allow the invention to be easily understood.

 FIG. 1 represents a top view of a part of the coast fitted with the structure and the construction method of the invention.

 FIG. 2 represents a sectional view along A-A of FIG. 1.

 Figure 3 shows a cross-sectional view of part of a box when it is positioned near a pile.

 Figure 4 shows a view identical to Figure 3, when the box is temporarily moored to the pile.

 5 shows a view identical to Figures 3 and 4, when the two boxes, adjacent to said pile, are permanently fixed.

 The present invention relates to a structure intended to create a barrier 1 on a submerged bottom 2, so as to circumscribe a part of the coastal strip 3 to allow its development.

 This structure can be installed according to a particular process which avoids the spread of embankments towards the sea and thus the pollution of the site.

 This work is well represented in general view in Figure 1. It consists of a succession of boxes 4 acting as dampers of water movements such as swell.

 These caissons 4 are located one behind the other along the coast 3 that we want to arrange, where pontoons are present 18. These 4 therefore circumscribe a strip in which the work will be able to be carried out.

 The essential aim is to obtain, at the end, a more or less complete filling of the liquid space situated between the barrier 1 and the coastal strip 3.

 The free space or spaces between this strip 3 and the barrier 1, constituted by the caissons 4, is or are constituted (s) by stony embankment 20.

 In the part closest to the coastal strip 3, a median or convertible esplanade 16 is set up by which one can access the artificial beach 17, located at water level 12. At this location, the embankments stony 20 are no longer visible under water since rollers 19 are placed at the level of the downward slope in the direction of the caissons 4. Following said rollers 19, riprap 21 are put in place which connect the rollers 19 to the upper end of the caissons 4, while also being above the stony embankments 20.

 As shown in Figure 2, the box 4 consists of a hollow cylinder. The front part of this cylinder, that is to say the one which is situated towards the open sea, has a certain number of orifices 9, especially in the upper part; these orifices 9 making it possible to dissipate part of the energy of the swell, the walls of the cylinder and the body of water contained ensuring the surge of said swell.

 However, the box 4 can have any other external shape, such as a polygonal (hexagonal), oval, etc. shape.

The only necessity lies in the fact that this external shape must be adapted to the swell conditions encountered on the implantation site.

 The components of the caissons 4 can also be multiple, for example made of prestressed concrete or metal.

 The rear part, that is to say that located opposite the coastal strip 3, is for its part waterproof, that is to say devoid of any orifice.

 The box 4, consisting of a hollow cylinder, in fact comprises a bottom 10 which rests on the submerged bottom or soil 2. The soil 2 is of course arranged to allow the reception of said boxes 4. Of course, the presence of the bottom 10 box 4 is not mandatory, the box can be a simple tube.

 The interface between the base of the caisson 4 and the stony embankments 20 is constituted by quarry quarry 22, this quarry quarry can be derived from residues from soil 2.

 In the same way, the boxes 4 are ballasted to avoid any movement. They are therefore filled, initially, with backfill with materials from site 11 on which quarry 22 is added. The height of materials 11 and / or 22 in each box 4 is a function of the presence or not of the orifices 9. If there is no orifice 9, it is possible that the materials 11 and 22 are present up to the top of said box 4.

 I1 is also possible to arrange in the space circumscribed by each box 4, another energy dissipating device, such as a second box or a form comprising concavities.

 However, the juxtaposition of many caissons 4 does not create a barrier 1 all along the coast to be circumscribed 3. Therefore, between each adjacent caisson, it is necessary to put assembly means 5 to 7, like this is shown in Figures 3 to 6. These assembly means are essentially constituted by a pile 5 located between two boxes 4, as can be seen in Figure 5, as well as by two transverse tie rods 7, each located on the side and d another of the pile 5, and finally of a shoulder 6 carried by the external surface of each box 4.

 It is therefore easy to understand the method of manufacturing such a barrier 1.

 Once the submerged funds 2 have been arranged, it is necessary to set up a first box 4, in general it is the box closest to the coast, that is to say located next to an underwater dam 15, as shown in FIG. 1, the construction of the barrier 1 then consisting in adding caissons 4 to go to the other dam 15.

 This thus makes it possible to partially isolate a coastal strip 3 that one wishes to develop.

 This delimitation is partial since the boxes 4 are completely immersed in water, as seen in FIG. 2.

 For this purpose, it should be noted that the current diameter of said boxes 4 is 5 to 20 meters, that their height is between 5 and 40 meters and that the draft above each box 4 is between 1 and 3 meters.

 To return to the process, when the first box 4 is put in place, as shown in FIG. 3, the shoulder 6 of the box 4 is brought into contact with the pile 5. Once this operation is completed, it is moored provisionally via a concrete jaw 23, and via provisional tie rods 24, which are tie rods different from those 7 which are used for final fixing.

 Once secured, the second box 4 is put in place, as shown in FIG. 5, in the vicinity of the first box already in place. Once this is done, the tie rods 7 are placed on either side of the pile 5, then the cofferdams 13 which delimit a space on either side of said pile 5 between the two adjacent caissons 4, and finally the spaces free between the cofferdams 13, are filled with filling materials such as reinforced concrete 14.

 Once this is done for the first two boxes 4, the same operation should be carried out for the following successive boxes 4.

 After the installation of all the boxes 4 and the assembly means 5, 6 or 7, a waterproof shield is put in place at the top of said boxes 4, in order to isolate the circumscribed water from that of the open sea.

 When backfilling, only the confined water will be contaminated and it will be easy to decant it.

 A more detailed view of the barrier 1 constructed by the method is well represented in FIG. 6. It is noted that the angle of presence has orifices 9 in the upper part of the boxes 4 has an opening of between 60 and 1000 in the direction from the sea.

In fact, this angle varies depending on the surface of the outer wall which is stressed by the swell.

 In general, the box 4 is a basic element of the construction system. It is cylindrical in shape, located under water level 12, at rest, and well suited to great depths. These geometric dimensions are determined according to the incident swells and the degree of protection sought.

 It basically has four functions.

 The first function is that which ensures the surge of the swell during contact with its walls and the body of water contained in this cylinder. Therefore, it is necessary to adapt the cylinder diameter and its higher level of level to the swell conditions encountered. The back of the box can be fitted with absorbent horizontal devices to complete the surge function.

 The second function is that of absorbing part of the energy of the swell through the porous wall due to the presence of the orifices 9, as well as to the presence in each box of a dissipative structure d additional energy or to the adapted geometry of the outer wall of the box.

 The third function is an environmental protection function through four major assets. First and foremost, the use of non-polluting materials, for example precast and prestressed concrete which is manufactured in an industrial site. In addition, and secondly, the production of a sealed barrier 1 between the coast 3 and the caissons 4 makes it possible to work without risk of pollution in the protected space. It is thus possible to envisage, in very sensitive sites, the construction of conventional medians, civil engineering works, dikes, islets or beaches, for example. Indeed, the juxtaposition of several caissons linked together by a suitable construction system, and rooted to the coast makes it possible to constitute a waterproof barrier, up to a coast varying from two meters to one meter below the water level 12 During the implementation of the filling process, the space between the coast 3 and the caissons 4, the upper part of the barrier 1 constituted by a waterproof and removable shield put in place only during the duration of the works, not shown in the figures. The third asset for environmental protection is the reduction of nuisance during construction, since 80% of the structure is prefabricated in an industrial complex which can be located far from the work site. The assembly can be transported by sea, since each box 4 can be easily towed. This process eliminates all the nuisances linked to the presence of heavy convoys transporting embankments, riprap blocks, concrete and considerably reduces the time taken to complete the work. There is therefore less public works machinery and therefore less pollution, such as noise, olfactory pollution. The fourth asset consists in the interior layout of the reservation 8 of the box 4, which makes it possible to create real reefs, ensuring the development and protection of the flora and fauna. The heightening of the lagoon located at the rear of the box is ensured by pipes integrated into the box making it possible to connect the body of water to the outside environment. Depending on site conditions, the pipes can be fitted with mechanical agitators which will create a current allowing good regeneration of bathing water, as well as the transport of surface waste to a water reprocessing center.

 Finally, the fourth function of the caisson is to provide support for an artificial continental shelf. Indeed, given its large dimensions imposed by the surge of swells, the structure has great stability ensuring the resumption of significant thrusts, and thus allowing backfilling at the rear of the box even at great depths. The artificial plateau thus created opens up many possibilities such as beaches, coastal development, protection of the coastline against erosion.

 Such a structure makes it possible to envisage coastal development when the bathymetry and the swell conditions are very unfavorable without damaging the environment.

 It can optionally be used for deep water ports, underwater structures, artificial beaches, artificial islands, erosion control structures, damping screens allowing the feasibility of conventional maritime structures such as a dike , breakwater.

REFERENCES
1. Barrier
2. Submerged bottom or soiled
3. Coastal strip or circumscribed maritime area 4. Underwater shock absorber boxes
5. Pious
6. Box shoulders 4
7. Definitive transverse tie rods
8. Reservation of a box 4
9. Holes of each caisson 4 10. Bottom of each caisson 4 11. Embankments of site materials 12. Water level 13. Cofferdams 14. Filling materials or concrete 15. Underwater dike 16. Quay or convertible esplanade 17. Beach 18. Pontoons 19. Pebbles 20. Stony embankments 21. Rock fill 22. All coming from quarry 23. Concrete jaw 24. Temporary transverse tie rods a. Angle of presence of the holes 9 in the upper part of the
boxes 4.

Claims (12)

 1. Work intended to create a barrier (1) on a submerged bottom (2) so as to protect a maritime area (3) to allow its development characterized by the fact  that it consists of several boxes (4) acting as shock absorbers which are immersed; said boxes (4) are secured to each other by assembly means (5 to 7) which also act as a seal between two boxes (4).  2. Structure according to claim 1, characterized by the fact  that each box (4) has a height such that said box (4) is completely submerged whatever the variations in the water level (12) and so as to form a barrier (1) effective but not visible.  3. Structure according to any one of claims 1 or 2, characterized by the fact  that each damping box (4) is a hollow cylinder (8).  4. Structure according to claim 1, characterized by the fact  that the upper part of each box (4) intended to be oriented towards the sea is, in its upper third, provided with orifices (9) ensuring the entry and exit of the water in the area stressed by the swell.  5. Work according to claim 1, characterized in that  that each hollow damping box (4) is provided with a bottom (10) so as to be able to be loaded with all-round quarry (22) or backfill with site materials (11) up to a certain height, to be stable in its soil (2).  6. Structure according to claim 1, characterized in that  that the assembly means are constituted by piles (5) which cooperate with shoulders (6) carried by the outer wall of the boxes (4) and which reinforce the stability of said damping boxes (4).  7. Structure according to claim 6, characterized by the fact  that transverse tie rods (7), located on either side of each pile (5), connect two adjacent damping boxes (4).  8. Work, according to any one of claims 1 or 6, characterized in that  that the area where the assembly means are installed (5 to 7) is delimited from top to bottom and on each side of the pile (5) by cofferdams (13), the spaces remaining free between the cofferdams (13) are filled to constitute the final keying.  9. Work, according to any one of claims 1 to 7, characterized in that  that a complementary energy dissipating device is placed in the center of each box (4).  10. Method for the construction of the structure, according to any one of claims 1 to 9, characterized in that  that it consists of  - prepare the soil (2) intended to receive a first box (4),  - install at least the first two piles (5),  - position the first box (4) on its soil (2) relative to the first two piles (5),  - fix the first box (4) to the piles (5),  - set up the other piles (5), and  - moor the other boxes (4) to the piles (5).  11. Method according to claim 10, characterized in that  that it consists in putting in place a temporary waterproof shield on the submerged caissons (4) to allow the development of the maritime structure without diffusion and without pollution of the embankments offshore, then to remove it once the structure is finished .  12. Method according to any one of claims 10 or 11, characterized in that  that it consists, prior to the installation of each of the first and last caissons (4), in building an underwater dike (15) which connects the barrier (1) submerged to the coast (3).