FR2712002A1 - Method of constructing a dike element on a submerged bottom and use thereof - Google Patents

Abstract

The method comprises the successive steps consisting in: - installing vertically on the bottom (3) a permanent formwork consisting of prefabricated elements comprising two parallel walls (5a, 5b) defining between them a space (6), at least one of the walls being a self-supporting wall consisting of a perforated plate over its entire surface; and - 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 (5a, 5b). The density of the concrete evacuates the excess water and the fluid in which the formwork is immersed, through the openings and causes the concrete to harden.

Description

"Method of constructing a dike element on a submerged bottom and use therefor"
The present invention relates to a method of constructing a dike element on a submerged bottom.

It also relates to the use of a lost formwork for the manufacture of such an element.

 Public works requiring the use of concrete and carried out on banks or submerged bottom, for example on the edges of a river or near the coast, pose important problems of implementation.

Indeed, these works can not generally be conducted directly in the water or in contact with it.

This is the case of structures made using conventional methods requiring the hardening of concrete in the open air. It is then necessary, most of the time, to isolate from water the portion of the bank or the bottom where the work must take place.

 To perform this isolation, the site is generally surrounded with metal plates of very large thickness, for example thirty millimeters. These plates have a characteristic crenellated profile that makes them very resistant to mechanical stresses, mainly due to the pressure and currents of the surrounding water.

 Once the site is circumscribed and isolated from the outside water in a sealed manner, the water inside the site is pumped out. Work can begin when the site is noticeably dry.

 These isolation operations are generally very expensive in terms of equipment and manpower. Indeed, the dimensions and qualities of mechanical strength required for the plates makes their cost very high. In addition, these plates are generally resistant to corrosion, especially in the marine environment, which means that it can not be reused for different jobs and its disposal at the end of operations.

 In addition, given the location of the work, very strict safety rules must be observed.

The plates must be assembled to form a tight assembly and able to withstand very high pressures and currents. The set-up of the whole is therefore long and thorough.

 This is why the present invention aims a method of constructing a dike element on a submerged bottom to overcome these disadvantages by making it faster and less expensive the isolation of a submerged portion, or even to completely eliminate the aforementioned operations by carrying out the work directly in a submerged environment.

 The present invention therefore relates to a method of constructing a dike element on a submerged bottom.

 The term "immersed bottom" should be taken in a broad sense. It designates as well a bank or a bottom, that it is a sea, a river, a pond, an artificial basin, etc.

According to the invention, this method is characterized in that it comprises the successive steps of
- Install vertically in and on the bottom a lost formwork consisting of prefabricated elements comprising two walls defining between them a space, at least one of the walls being a self-supporting wall constituted by a perforated plate over its entire surface; and
filling the said space with concrete loaded with sand and large aggregates, the smaller ones of large aggregates having dimensions just greater than the openings of the perforated plate.

 This method can for example be implemented with the formwork object of French patent applications Nos. 91 13192 and 92 07042.

 The difference in density between the concrete and the liquid medium in which it is to be poured flushes and discharges through the openings of the wall of the formwork the excess water introduced into the composition of the concrete to allow and facilitate its implementation, as well as the liquid in which the work is made.

 Isolation of a portion of bank or bottom is simplified. It is sufficient to circumscribe this portion with formwork elements - which can be relatively light - and to pour the concrete directly inside of them in accordance with the method according to the invention. If the formwork elements are arranged close enough to one another, the concrete can be cast in several elements at once to form a continuous concrete block. The tightness of the assembly is then easy to ensure.

 The walls of the formwork can be kept at a distance from each other by means of spacers whose length can be freely chosen according to the desired thickness for the dike element.

 Thus, when the dike elements are intended to insulate a portion only temporarily, they can be built with a relatively small thickness to destroy or transport after completion of the work.

 The implementation of the method according to the invention is relatively simple and inexpensive compared to the implementation of the slotted profile plates mentioned above.

 In addition, the dike element thus constructed benefits from all the strength qualities of the formwork described in the aforementioned patent applications.

 The method according to the invention has just been briefly described in the context of the construction of dike elements intended to isolate water a bottom or edge portion for the realization of dry work.

 Nevertheless, the method according to the invention can also be used for the construction of definitive dike elements constituting the structure itself, this construction taking place directly in a submerged environment.

Thus, the realization of some concrete works can be done directly in the water without the need to isolate and dry the bottom portion or bank. To this end, we can give the aforementioned spacers a significant length to achieve sufficiently massive elements depending on the work performed.

 According to an advantageous version of the method according to the invention, the two walls are each constituted by a perforated plate over its entire surface.

 In this way, it facilitates the establishment and stability of the formwork in and on the submerged bottom since the formwork open on both sides has only a very low resistance to currents and other movements of water.

 According to another advantageous version, the method comprises the prior step of driving vertically in the bottom at least two piles on only part of their length in order to immobilize them in the bottom, the formwork being then installed so that the piles find between the two walls.

 The piles are embedded in the concrete once the pouring of it completed. This version further strengthens the stability of the dike element, the piles constituting reinforcements to anchor and connect the formwork firmly to the bottom.

 According to a preferred version of the process according to the invention, the perforated plates are expanded metal plates reinforced by stiffeners.

 In particular, such perforated plates have the advantage of presenting a low cost price and of being perfectly adapted to the use in lost formwork, because of their lightness, their mechanical strength and their low grip on currents.

The present invention also relates to the use of a lost formwork consisting of prefabricated elements comprising two walls defining between them a space intended to be filled with sand-laden concrete and large aggregates, at least one of the walls being a self-supporting wall consisting of by a plate perforated on its entire surface by openings just smaller than the dimensions of the smaller aggregates, this use being characterized in that the formwork is intended for the construction of a dike element resting on a submerged bottom
Other features and advantages of the invention will become apparent in the following description of a preferred embodiment of the invention. In the accompanying drawings given by way of non-limiting example:
- Figure 1 is a perspective view showing the result of the implementation of the method according to the invention;
- Figure 2 is a partial perspective view of a formwork used in the method according to the invention;
- Figure 3 is an elevational view showing a dike element constructed;
- Figure 4 is a sectional view of another formwork used in the method according to the invention.

 In the present embodiment and with reference to FIG. 1, the method according to the invention aims at the construction of elements 1 of dike 2 on the submerged bottom 3 of a river, along the shore 4. The dike 2 shaped "U" is intended to come circumscribe a portion 10 of the bank 4 where dry work must be carried out in the vicinity of the water level or below it.

 The elements 1 dike can be built simultaneously or one after the other.

 The process comprises several successive steps.

 Referring to Figures 2 and 3, the first step consists in installing vertically in and on the bottom 3 of the flooded river a lost formwork 20 consisting of prefabricated elements comprising two parallel walls Sa and 5b defining between them a space 6 .

 In the present example, the two walls 5a and 5b are self-supporting walls each consisting of a perforated plate over its entire surface. The perforated plates 5a and 5b may be expanded metal plates reinforced by stiffeners 7.

 The two parallel walls 5a and 5b of the formwork are connected to one another by spacers 8 whose ends are articulated in rotation to the walls 5a and 5b along a vertical axis as is the case in this mode or for example along a horizontal axis.

 These articulation makes it possible to reduce the volume of the formwork by bringing the walls Sa and 5b closer to one another. This facilitates the transport and handling of the formwork.

 The second stage of the process consists, while the place of construction is always invaded by water, to fill the space 6 with concrete loaded with sand and large aggregates, the smaller aggregates having dimensions just greater than the openings perforated plates.

 This filling is done from the top. The poured concrete fills the entire space 6 between the walls Sa and 5b. Under the weight of the concrete, due to the difference in density between the concrete and the liquid in which the structure must be executed, the liquid present between the walls is driven from the formwork. Moreover, all the excess water included in the composition of the concrete to facilitate its implementation, is driven outside the formwork through the openings of the walls Sa and Sb. The aggregates of the concrete are blocked inside because the dimension envisaged for the openings does not allow their exit.

 Such lost forms for concrete are known in particular from French Patent Applications Nos. 91 13192 and 92 07042. Nevertheless, these forms or the like have never been used for the construction of submerged elements. Experience shows that there is no problem of hardening in a submerged environment. As soon as the excess water has been removed, the setting of the concrete, thanks to the cement it contains, begins and continues at a normal rate until complete internal hardening of the dike element 1.

 The shuttering element is installed on the bottom so as to be slightly sunk into it depending on the hardness of the river bed to ensure its seating.

Nevertheless, it is not always easy to drive the formwork deep into the bottom.

 That is why, with reference to FIGS. 1, 2 and 3, the method according to the invention may comprise the preceding step consisting for each element 1 to be driven vertically in the bottom 3 at least two piles 12a and 12b on a part only of their length to immobilize them in the bottom 3, the formwork then being installed so that the piles 12a and 12b are between the two walls Sa and Sb.

 When the concrete is poured into the space 6, the piles 12a and 12b are embedded in the concrete. They reinforce the stability of the dike element 1 by constituting an anchoring thereof in the bottom 3. In Figure 1, the position of the piles at the top of the elements 1 is indicated for the sake of clarity. However, it is not necessary for the piles to extend to the top of the elements 1.

 When the dike element 1 to be constructed must be particularly thick, for example with a thickness greater than 30 cm, a formwork having a greater number of parallel walls can be used as follows.

 Thus, with reference to FIG. 4, the formwork 21, which constitutes a variant of the formwork 4, can be constituted so that between the two formwork walls 5a and 5b and close to those of them constituted by a perforated plate, extends at least one inner wall parallel to the other two.

 In the present example, two inner walls 13a and 13b have been disposed between the walls 5a and 5b. The inner walls 13a and 13b also consist of a perforated plate over its entire surface.

 Of course, the inner walls 13a and 13b are connected to each other and to the outer walls 5a and 5b by suitable spacers 14.

 It will thus be possible to design the lost formwork by arranging as many intermediate perforated walls as necessary according to the mechanical stresses to be expected and the thickness intended for the dike element. As an indication, it will often be useful to have the intermediate walls when the thickness of the formwork exceeds 50 cm. In this way, it constitutes a fractionation in the veil of the final work to achieve.

 The principle of the arrangement of the intermediate walls is nevertheless known in the formwork technique and more details on this point will be found in the aforementioned patent applications.

 The elements 1 are constructed so as to make a dike 2 or a watertight barrier isolating the portion 10 of the bank 4 of the water outside the dike 1.

 When the construction of the dam 2 is completed, the water inside the dike is pumped out to dry the portion 10. The work on the portion 10 can then begin.

 The method according to the invention has been described above as applied to the realization of a dike 2 for isolating a submerged bottom portion to perform dry work.

 Nevertheless, this method is also applicable to the direct construction of concrete structures without the need to isolate the surrounding water from the place of construction.

The structure is then constructed using the formwork elements
above by dimensioning them according to the work to be done, the formwork elements constituting this time the body of the planned construction. It goes without saying that the construction can jointly implement conventional construction means.

 When the construction is carried out in a maritime or fluvial zone subjected to the influence of the tides, one will proceed to the implementation of the work preferably in the slack so as not to be hindered by the tide.

 Of course, we can bring to the invention many modifications and improvements without departing from the scope thereof.

Claims (10)

 1. A method of constructing a dike element (1) on a submerged bottom (3), characterized in that it comprises the successive steps of  - Install vertically in and on the bottom (3) a lost formwork consisting of prefabricated elements comprising two walls (5a, 5b) defining between them a space (6), at least one of the walls being a self-supporting wall constituted by a perforated plate on all its surface; and  filling the said space with concrete loaded with sand and large aggregates, the smaller ones of large aggregates having dimensions just greater than the openings of the perforated plate (5a, 5b).  2. Method according to claim 1 characterized in that the two walls (5a, 5b) are each constituted by a perforated plate on its entire surface.  3. Method according to one of claims 1 to 2, characterized in that it comprises the prior step of driving vertically in the bottom (3) at least two piles (12a, 12b) on only part of their length to immobilize them in the bottom, the formwork being then installed so that the piles (12a, 12b) are between the two walls (5a, 5b).  4. Method according to one of claims 1 to 3, characterized in that between the two walls (5a, 5b) of formwork and close to those of them constituted by a perforated plate, extends at least one wall interior (13a, 13b) parallel to said walls (5a, 5b), said inner wall (13a, 13b) being a perforated plate over its entire surface.  5. Method according to one of claims 1 to 4, characterized in that at least two parallel walls (5a, 5b, 13a, 13b) of the formwork are connected to one another by spacers (8, 14). whose ends are articulated in rotation to said walls.  6. Method according to one of claims 1 to 5, characterized in that said perforated plates are expanded metal plates reinforced by stiffeners (7).  7. Use of a lost formwork consisting of prefabricated elements comprising two walls (5a, 5b) defining between them a space (6) intended to be filled with concrete loaded with sand and large aggregates, at least one of the walls being a self-supporting wall constituted by a plate perforated on its entire surface by openings just smaller than the dimensions of the smaller of the large aggregates, this use being characterized in that the formwork is intended for the construction of a member (1) of a dike resting on a submerged bottom (3).  8. Use according to claim 7, characterized in that the two walls (5a, 5b) are each constituted by a perforated plate over its entire surface.  9. Use according to one of claims 7 to 8, characterized in that between the two walls (5a, 5b) of formwork and close to those of them constituted by a perforated plate, extends at least one wall interior (13a, 13b) parallel to said walls (5a, 5b), this inner wall (13a, 13b) being a perforated plate on its entire surface  10. Use according to one of claims 7 to 9, characterized in that said perforated plates are expanded metal plates reinforced by stiffeners (7).