EP0874941B1 - Automatic wicket for a hydraulic structure such as a river sill, a dam spillway or a protective dyke - Google Patents

Abstract

An automatic flashboard (10) comprises a wall (12) installed on a hydraulic structure (11) so as to be capable of passing from an erect position in which it retains a mass of water to a lowered position in which it allows the water to pass substantially without obstruction, and at least one elongate retaining member (13) for holding the wall (12) in its erect position against horizontal thrust (P1) from the mass of water (25). The retaining element (13) extends between the wall (12) and a reaction point to which it is connected by a connection (15) that can be automatically eliminated when the water reaches a certain level. The flashboard (10) also includes a massive element (16) movably mounted on the structure (11) and coupled to the mass of water so as to be in a stable state so long as the water remains below a predetermined level (N) and to pass into an unstable state and to be moved when the water reaches the predetermined level (N), the connection (15) being eliminated by the massive element moving.

Description

The present invention relates to a rise automatic for hydraulic structure such as threshold in river, weir on a dam or on a dam protection, of the type comprising a structure forming watertight or substantially watertight wall, installed on said hydraulic structure so that it can pass from a first upright position to retain a mass of water at a second lowered position in which said wall lets the water pass through practically without obstruction, and at least one elongated retainer to maintain said wall in its first position against the horizontal thrust exerted by the mass of water, said elongated retaining element being subjected to service, under said push of water, to an effort longitudinal, extending between said wall and a point of reaction balancing said longitudinal force and being connected to the reaction point by a bond which can be removed automatically when water reaches a certain level, so that said wall passes automatically in its second position.

Automatic hikes like this are good known. Usually such automatic increases are installed for example on the crest of a threshold arranged across a river to enhance the river water level above the threshold. They can also be installed on the threshold of a weir of a dam in order to raise the level of the reservoir (reservoir) of the dam. They can be still installed on the threshold of the spillway of a dike bordering a river and intended to protect the regions neighboring against the floods of the river, the spillway being, in the latter case, installed on the dike at a location that is chosen in such a way that, in the event of a flood, the water pours into a reservoir storage or on selected land, safe for other regions around the river. The increases automatic can be of the non-spilling type or overflow type, that is to say, in the second case, that they can pass a certain amount of water over their crest as long as the water level upstream of the rise does not exceed a height predetermined. However, in all cases, the increases must be able to erase automatically if the water level upstream of the rise reaches a predetermined level during a flood, in order to release the mass of water that it retains and thus avoid a flooding of areas around the river or, if applicable if necessary, damage to the dam or dam.

Figure 1 of the accompanying drawings shows schematically, in side elevation, a rise known automatic of the type defined above, which can be considered to represent the state of the closest technique to the present invention. A mockup of this known automatic hike was exhibited on the occasion of the International Congress of Great Dams held in DURBAN, Republic from South Africa in November 1994. The rise known automatic shown in Figure 1 is essentially constituted by a plate 1, vertical or oblique, which, at its base, is articulated on the ridge 2 of the threshold or weir 3 in masonry by means of a hinge 4 or other similar element. Plate 1 is retained in the upright position shown in solid lines in Figure 1 by at least one tie rod 5, one of which end is connected to plate 1, in the region top of it, and the other end of which is connected to the masonry of the threshold or weir 3 at by means of a fastener 6 which is shown larger scale in Figure 2 of the accompanying drawings As shown in Figure 2, the fastener 6 has two parts 6a and 6b, which are respectively fixed to the masonry of the threshold or weir 3 and the tie-rod 5, and a dowel 6c, which is threaded in aligned holes drilled in parts 6a and 6b and which couples these two parts to each other,

In service, the body of water 7 which is retained by the plate 1 pushes on it. The result that the tie rod (s) 5 are under tension and, consequently, that the pin 6c of the fastener 6 is subjected to a shear force. The value of this effort shear is proportional to the value of the tension of tie rod 5, which is itself proportional to the value of the thrust exerted by the body of water 7 on plate 1. The value of this push is itself an increasing function of the level of the body of water 7, i.e. the height of the water above the ridge 2 of the threshold or weir 3. When the value of the shear force reaches and exceeds the shear strength of said dowel 6c by following a rise in the water level, plug 6c is breeze and, under the pressure of the water, plate 1 automatically collapses on crest 2 of the threshold or weir 3 by pivoting about the hinge axis 4 to the position shown in dash in the figure 1.

So, by choosing the diameter and / or the material (usually steel) of pin 60 so that this has an appropriate shear strength, it is possible to make the 6c dowel of the fastener 6 breaks for a predefined water load, so when the water level upstream of the plate 1 reaches a predefined level. However, in the practical experience shows that the water level which will cause ankle rupture 6c is not accurate and can vary in the range of several tens of centimeters. Indeed, even assuming that we uses steel with excellent properties and consistent production quality, the results of rupture tests carried out with samples steel cut from the same steel bar, the diameter has been machined with great precision, usually have a large dispersion.

Despite the apparent simplicity of the rise known automatic described above there is a high probability that plate 1 is triggered prematurely, i.e. folded back into its position low before the water level reaches the level preset, or that plate 1 is triggered too late, i.e. for a higher water level at the predefined level, which is a drawback of the reliability point of view in the first case and a security disadvantage in the second case. It would therefore be highly desirable that the automatic rise can be triggered automatically with greater precision as to water level.

Other hike patterns are described in the US Patent 2,118,535 and in the publication "Engineering for Dams ", W.P. Creager, Volume III, pages 870 to 878, edited by Chapman and Hall, London, 1945. The rise described in US Patent 2,118,535 and the rise shown in Figure 1, pages 872, of the publication "Engineering for Dams" have constructions completely similar, These two increases are essentially constituted by plates or panels vertical which are retained against the push of water by vertical stakes whose lower end is embedded in the masonry of the threshold or weir and on which the downstream face of the vertical plates or panels, on their entire height. Both are increases automatic. The stakes are made up of bars or steel tubes, the cross section of which is chosen from such that the stakes bend or break to a given water load applied to the plates or vertical panels. Regarding the accuracy of the water level which causes the folding or breaking of stakes, these known increases suffer from the same defect that the known automatic rise described above in reference to Figure 1 of the accompanying drawings (see this regard the publication "Engineering for Dams" page 872, 3rd paragraph and page 874, 8th paragraph).

The increase shown in Figure 5, page 877, of the aforementioned publication "Enginnering for Dams" is essentially consisting of one or more panels whose lower end leans against a seat formed on the masonry of the threshold or weir and whose the upper end is attached with a lock to a walkway that passes over the threshold or weir. Each panel consists of a frame metal in which cofferdams are slipped. The metal frame is connected to the gangway by unstretched chains. The lock (s) must be operated by an operator to detach the panels and release the mass of water they retain, from so this rise doesn't work so automatic. We could easily imagine a automation of the operation of this increase in replacing the movable element of the lock with a dowel similar to that described for the known automatic rise described with reference to Figures 1 and 2 of the accompanying drawings. However, even in the latter case, the rise would still suffer from the same defect that the known rise previously described in this which concerns the precision of the water level at which produces the rupture of the shearable anchor.

The rise shown in Figure 6, page 878, of the the aforementioned publication "Engineering for Dams" is essentially consisting of one or more panels which are articulated at their bottom on the masonry of the threshold or weir and which are retained against the push of water by several stays or legs of rigid force arranged on the downstream side of the panels. The still this is not an automatic hike. In Indeed, to allow the panels to fade, it is provided a knotted rope which is threaded through holes drilled in the middle of each stay and using which the struts can be broken and / or retracted by an operator pulling the rope.

In addition, there are automatic increases consisting of one or more massive elements which are placed on the crest of a weir and which are unbalanced and driven off automatically by water when it reaches a predetermined level (patent FR 2 656 354 and 2 671 116), These latest increases have the advantage of operating with a good accuracy with regard to water level for which the removal of the element (s) occurs increase (this precision is of the order of a few centimeters). However, they have the disadvantage that the massive element (s) are lost after they have been chased away by water.

The present invention therefore aims to provide a automatic increase of the type defined in the preamble, which works with better accuracy than increases known automatic machines of the same type, with regard to the water level which triggers the rise.

To this end, the increase according to the present invention is characterized in that it further comprises a massive element which is mounted mobile on said structure and coupled to said body of water so as to be in a stable equilibrium position as long as the water remains below of a predetermined level, and to pass in a unstable state and to be moved when water reaches said predetermined level, and in that the connection between said elongated retainer and the reaction point is removed by the displacement of said massive element.

According to an embodiment of this invention, said massive element can be constituted by a slab installed on said structure so that it can tilt up around a horizontal axis which extends along a first side of the slab and which is perpendicular to the direction of the thrust exerted by the mass of water on the moving wall forming the rise, According to another embodiment of the present invention, the solid element can be mounted so that ability to slide vertically into an open cavity upwards formed in said work. The element elongated restraint can be constituted either by a pulling either by a strut. In both cases, the connection between the tie rod or the strut and the reaction point can be deleted in response to element tilting or sliding movement massive.

la figure 1 montre schématiquement, en élévation latérale, une hausse automatique connue;

la figure 2 montre, à plus grande échelle, un détail de la hausse automatique de la figure 1;

la figure 3 montre schématiquement, en coupe verticale, une hausse automatique selon un premier mode de réalisation de la présente invention;

la figure 3a est une vue semblable à la figure 3, montrant une variante de réalisation du système de déclenchement de la hausse automatique;

les figures 4, 5, 5a et 5b montrent, à plus grande échelle, des variantes relatives au montage de la paroi de la hausse sur l'ouvrage hydraulique;

la figure 6 est une vue en plan de la hausse de la figure 3;

la figure 7 est une vue semblable à la figure 6 dans le cas d'une hausse ayant une paroi non plane, dont la section horizontale a un profil crénelé;

les figures 8 et 9 sont des vues en coupe verticale illustrant le fonctionnement de la hausse de la figure 3;

les figures 10 et 11 montrent, en coupe verticale et à plus grande échelle, deux variantes de réalisation de la liaison détachable reliant le tirant de la hausse au seuil ou au déversoir sur lequel est installée la hausse;

la figure 12 montre, en coupe verticale et à plus grande échelle, un autre mode de réalisation de ladite liaison détachable;

la figure 13 est une vue en plan de la liaison montrée dans la figure 12;

les figures 14 et 15 sont des vues en coupe verticale, respectivement suivant la ligne XIV-XIV de la figure 15 et suivant la ligne XV-XV de la figure 14, montrant encore un autre mode de réalisation de ladite liaison détachable;

la figure 16 est une vue en coupe verticale semblable à celle de la figure XV, montrant encore un autre mode de réalisation de ladite liaison détachable;

la figure 17 est une vue en coupe verticale montrant encore un autre mode de réalisation de ladite liaison détachable;

la figure 18 est une vue en coupe verticale d'une hausse automatique selon un second mode de réalisation de la présente invention;

la figure 19 est une vue en coupe verticale montrant une hausse automatique selon un troisième mode de réalisation de la présente invention.

Other characteristics and advantages of the present invention will emerge more clearly during the following description of various embodiments of the present invention, given with reference to the appended drawings in which:

Figure 1 shows schematically, in side elevation, a known automatic rise;

Figure 2 shows, on a larger scale, a detail of the automatic rise of Figure 1;

Figure 3 shows schematically, in vertical section, an automatic rise according to a first embodiment of the present invention;

Figure 3a is a view similar to Figure 3 showing an alternative embodiment of the automatic raising trigger system;

Figures 4, 5, 5a and 5b show, on a larger scale, variants relating to the mounting of the wall of the rise on the hydraulic structure;

Figure 6 is a plan view of the rise of Figure 3;

Figure 7 is a view similar to Figure 6 in the case of a rise having a non-planar wall, the horizontal section of which has a crenellated profile;

Figures 8 and 9 are vertical section views illustrating the operation of the rise of Figure 3;

Figures 10 and 11 show, in vertical section and on a larger scale, two alternative embodiments of the detachable connection connecting the tie rod to the threshold or to the weir on which the rise is installed;

Figure 12 shows, in vertical section and on a larger scale, another embodiment of said detachable connection;

Figure 13 is a plan view of the connection shown in Figure 12;

Figures 14 and 15 are views in vertical section, respectively along the line XIV-XIV of Figure 15 and along the line XV-XV of Figure 14, showing yet another embodiment of said detachable connection;

Figure 16 is a vertical sectional view similar to that of Figure XV, showing yet another embodiment of said detachable link;

Figure 17 is a vertical sectional view showing yet another embodiment of said detachable link;

Figure 18 is a vertical sectional view of an automatic rise according to a second embodiment of the present invention;

Figure 19 is a vertical sectional view showing an automatic rise according to a third embodiment of the present invention.

As shown in Figure 3, the rise 10 is installed at the top of the masonry 11 of a structure hydraulics which is only partially represented in Figure 3 and which can be for example a threshold in river or weir of a dam or dyke protection against floods. Rise 10 includes, from known manner, at least one panel 12 which, in service normal, is vertical or slightly inclined to vertical and which is mounted so that it can tilt or rotate around a horizontal, virtual axis or real, which extends parallel to the lower edge of the panel 12, near said lower edge. The panel 12 can for example be constituted by a plate metallic, a reinforced or unreinforced concrete plate, a composite structure such as a metal frame in which are embedded or fixed cofferdams, or any other structure forming a tight wall or substantially waterproof. Panel 12 or each panel 12 is retained in its vertical position or substantially vertical by at least one tie 13, by example two tie rods 13 as shown in Figure 6. Each tie 13 can be constituted for example by a metal rod, cable or chain. One of ends of each tie 13 is connected to the panel 12 in the upper region of it, in 14, while the other end of each tie rod 13 is attached to the masonry 11 by a detachable link 15 which several embodiments will be described later.

As shown in Figure 3, the rise 10 has in addition a massive element 16, produced here in the form a rectangular slab (figure 6) which can be example in concrete, reinforced or not, in metal or in material synthetic, armed or not. Slab 16 is laid horizontally on the masonry 11 of the threshold or weir and it can swing up around a horizontal axis A which extends along its side 16a, A this effect, it is provided on masonry 11, just in front of the side 16a of the slab 16, a stop 17 having for example, cross-sectional view, a shape trapezoidal. The stop 17 can extend over the entire length of side 16a of slab 16 or be made in the form of separate studs as shown in the figure 6. Under these conditions, the tilt axis A of slab 16 coincides with the lower edge of its side 16a, Preferably, the abutment (s) 17 are made of masonry and then form an integral part masonry 11 of the threshold or weir, or they may consist of metal parts properly anchored to masonry 11. Good heard, the stop (s) 17 can be replaced by hinges. However, the use of one or more stops 17, in particular in masonry, offer the advantage that they are less prone to corrosion than metal hinges.

The slab 16 has, in its upper surface, near its side 16a, a groove 18 which extends parallel to said side 16a and which has a width more greater than the thickness of the lower edge of the panel 12. The lower edge of the panel 12 is engaged in the groove 18 and presses against the side 18a of the groove 18 which is closest to side 16a of slab 16, as best seen in Figure 4. So, under certain conditions, as we will see later, the panel 12 can swing down around the upper edge B on the side 18a of the groove 18.

Of course, instead of being mounted tilting by compared to slab 16 as described above, the panel 12 can be connected to the slab 16 by a hinge 19 as shown in Figure 5, Similarly, at instead of being mounted tilting or pivoting relative to the panel 16, the panel 12 can be mounted tilting or pivoting in relation to masonry 11, For example, the groove 18 can be formed in masonry 11 in downstream of the stop 17 as shown in FIG. 5a or the hinge 19 or other equivalent means may be attached to the masonry 11 as shown in FIG. 5b, also downstream of the stop 17.

Preferably, a seal is arranged between panel 12 and slab 16 or masonry 11, For example, the gasket can be installed in the bottom of the groove 18 or, as shown in the FIGS. 3 to 5, it may consist of a strip 21, of rubber or other elastomeric material, which is attached by a flange 22 to the upstream face of the panel 12 and extends downward to the upper surface of the slab 16 by covering the groove 18 or the hinge 19. Another seal <not shown) may be also provided between slab 16 and masonry 11, in the region of the side 16b of the slab 16 opposite the side 16a.

We will now describe a first embodiment of the detachable link 15. As shown in the figure 3, the lower end of the tie rod 13 is attached to a fastener 23, which is engaged and retained in a slot 24 arranged between the slab 16 and the masonry 11. The slot 24 extends roughly horizontally under the slab 16 from its side 16b towards its side 16a, the fixing part 23 is here consisting of a metal plate with section elongated rectangular cross section, which when is engaged in the slot 24, has a part which protrudes beyond the side 16b of the slab 16 and at which is attached the lower end of the tie rod 13. As shown in figure 6, the two tie rods 13 extend parallel to each other and are all two attached to the plate 23 which has an equal length or slightly shorter than the length of side 16b of slab 16. However, as indicated by the line mixed in Figure 6, the two tie rods 13 can converge towards each other and be tied into one point of the plate 23, located in the middle of the length on the side 16b of the slab 16. In the latter case, the plate 23 can be significantly longer shorter than that shown in Figure 6.

In operation, the body of water 25 retained by the panel 12 exerts on it a thrust P ₁ , the value of which is an increasing function - of the height h of the water above the crest of the masonry 11 This push P ₁ tends to tilt the panel 12 down around the edge B (FIG. 4 or 5a) or around the hinge axis of the hinge 19 (FIG. 5 or 5b). Under the effect of the thrust P ₁ of the body of water 25 on the panel 12, each of the two tie rods 13 is energized and the tension T of each tie rod is an increasing function of the thrust P ₁ , therefore of the water height h. The tension T of each tie rod is transmitted to the plate 23 which, therefore, tends to tilt upwards around its edge C (see also FIG. 10). Consequently, the plate 23 applies to the slab 16 a force F which is directed upwards and whose intensity is an increasing function of the voltage T. The intensity of the force F also depends on the cosine of the angle between the direction of the tension T and the vertical direction, as well as of the ratio between the distances l ₁ and l ₂ of the points of application of the forces T and F, respectively, compared to the edge C (see figure 10). Under the effect of the force F, the slab 16 tends to tilt upwards around the axis A formed by the lower edge of its side 16a.

On the other hand, the slab 16 is subjected to its own weight P ₂ , to the weight P ₃ of the mass of water located above it and to a force P ₄ which is the result of the thrust P ₁ and of the self-weight of the panel 12. It will be noted that the influence of this last force P ₄ on the balance of the slab 16 can be canceled or made negligible if, by construction, the direction of the force P ₄ intersects the axis A or pass very close to it. In the case of FIGS. 5a and 5b, the force P ₄ is not to be taken into consideration since the panel 12 is supported by the masonry 11 and has no direct action on the slab 16.

As long as the moment of the force F relative to the axis A remains lower than the sum of the moments of the forces P ₂ , F ₃ and possibly P ₄ relative to the axis A, the slab 16 remains in its position equilibrium shown in FIG. 3, When the water height h of the water body 25 increases, for example during a flood, the tension T of the tie rods 13 increases and, consequently, the force F also increases as does the weight P ₃ of the body of water 25 above the slab 16, However, the moment of the force F relative to the axis A increases faster than the antagonistic moment of the weight P ₃ relative to the axis A. This is notably due to the fact that the point of application of the force F on the slab 16 is more distant from the axis A than the point of application of the weight P ₃ on the said slab, and also because the magnitude of the surface of the panel 12 on which the body of water 25 acts and which determines the value of the voltage T, therefore also the value of the force F, is greater o u becomes larger than the surface of the slab 16 on which the body of water acts 25. Consequently, as the height h of the water increases, there comes a time when, for a certain value of the height h of the water corresponding for example to the level N (FIG. 3), the moment of the force F relative to the axis A reaches and exceeds the sum of the moments of the forces P ₂ , P ₃ and possibly P ₄ by relative to the axis A. At this time, the slab 16 is unbalanced and begins to tilt upwards around the axis A. Consequently, the slit 24 widens and the water penetrates under the slab 16 and exerts on the underside of the latter, an upwardly directed pressure which quickly tends to balance the weight P ₃ of the water on the slab 16, thus promoting the tilting of the latter around the axis A, As a result, the slot 24 widens further (see FIG. 8) and, after the slab 16 has tilted a few degrees upwards, the plate 23 is released (see Figure 9). At this time, the panel 12 is no longer retained by the tie rods 13 and, under the thrust P ₁ of the body of water 25, it rocks around the edge B of the groove 18 (FIG. 4 or 5a) or around the axis of articulation of the hinge 19 (FIG. 5 or 5b), Consequently, the panel 12 collapses on the masonry 11 and releases the mass of water 25. At the same time, due to the fact that the slab 16 is no longer subjected to the action of the force F, it falls back under the effect of its own weight P2 and returns to its position of equilibrium as shown in FIG. 9.

In order to avoid the loss of panel 12 after it has tilted, said panel can be connected by at least one short flexible link 26, such as a cable or chain, to a ring 27 anchored to the masonry 11, as shown in Figures 3 and 5a, Instead of the link or links 26, it it is also possible to provide at least one element 28 forming a hook, which is fixed to the downstream face of the panel 12, near the lower edge thereof, and which cooperates with an additional retaining element 29 fixed rigidly to slab 16, as shown in FIG. 4, Of course, it is possible to dispense with these elements when the panel 12 is connected to the slab 16 or to masonry 11 by a hinge like the hinge 19 shown in Figures 5 and 5b.

From the above, it is clear that by appropriately choosing the value of the angle of inclination of the panel 12 relative to the vertical and / or the value of the angle of the tie rods 13 relative to the panel 12 <these angles also determine the value of the tension T), the values of the distances l ₁ and l ₂ (figure 10) which determine with the tension T the value of the force F, as well as the value of the weight P ₂ of the slab 16, it is possible to ensure that the imbalance and, consequently, the tilting of the slab 16 occur when the water upstream of the panel 12 reaches a predetermined level, for example the level N shown in FIG. 3 Under these conditions, when the water reaches the predetermined level N, the wafer 23 is released, the panel 12 swings down and the body of water 25 is released as described above.

The triggering of the automatic rise described above, that is to say the tilting of the panel 12 of its vertical position or substantially vertical to its lowered position, does not result from breaking or bending deformation of several retaining elements of which the breaking or bending strength and the breaking or bending behavior are more or less well controlled, but it results from the displacement of slab 16 due to the fact that it is unbalanced when the water reaches a certain level. The water level for which occurs the triggering of the rise automatic is therefore much more precise than in the previously known automatic increases (figure 1).

Note that the water level N for which product the triggering of the automatic rise can be adjusted by modifying the weight of slab 16. The higher the slab 16 is heavy, the higher the level N. In this Indeed, a ballast 31 can be fixed to the slab 16 (figure 3), Level N can be set either by changing the weight value of ballast 31, either by modifying the position of the ballast 31 on the slab 16, in particular its distance from the tilt axis A. Thus, when multiple automatic raises 10 are arranged side by side, in a manner known per se, as is shown in Figure 6, by adopting weights 31 having different weights and / or different positions on each of the slabs 16 of the increases 10 juxtaposed, it is possible to have the increases be automatically and successively triggered for different predetermined water heights.

In order to further increase the precision of the water level N which will cause the automatic raising 10 to be triggered, means can be provided to create pressure under the slab 16 when the water level upstream of the panel 12 reaches the predetermined level N. For this purpose, a conduit 32 (FIGS. 3 or 3a) is provided, a first end 32a of which opens under the slab 16, while its second end 32b opens on the upstream side of the panel 12 at a level corresponding to the level predetermined N. The duct 32 can extend partly in the masonry as shown in Figure 3, or it can be fixed vertically to the slab 16 as shown in Figure 3a. The slab 16 and the conduit 32 can also be made in one piece by pouring concrete into a suitable formwork. In the case of FIG. 3a, it will be noted that the aforementioned weight P ₂ is the total weight of the slab 16 and of the conduit 32. The latter may for example have a circular cross section (Figures 3 and 6) or an oval cross section or elongated with a hydrodynamic profile such as that shown in phantom in 32c in Figure 3a.

In practice, the upper end 32b of the conduit 32 will open at a slightly lower level, for example a few centimeters, than the predetermined level N in order to obtain a flow of water sufficient to quickly fill the conduit 32 when the water reaches level N. Thus, when water reaches level N, a vertical thrust P ₅ , directed upwards, is applied to the slab 16. This thrust P _{5 is} established in a relatively short period of time, adds to the force F and quickly causes the tilting of the slab 16 upwards around the axis A.

Preferably, the underside of the slab 16 (Figure 4) or the part of the masonry 11 which is located under the slab 16 (Figure 3), or both at the same time (Figure 10) are hollowed out so as to define a chamber 33 into which the end 32a of the conduit 32 opens. In this case, another conduit or channel 34 is provided in the masonry 11 (FIG. 3) or in the lower surface of the slab 16 (FIG. 4) to drain towards the 'downstream the water which is possibly in the chamber 33 and whose presence may be due to a defect in the sealing of the aforementioned seals or else to waves which can cause the pipe 32 to fill before the level mean the water reaches the predetermined level N, It is indeed necessary to avoid that the thrust P ₅ is applied to the slab 16 before the water reaches the predetermined level N. The duct 34 has a passage section more smaller than that of conduit 32 so that the flow in the duct 34 is weaker than in the duct 32 and that the chamber 33 can be quickly filled with water when the water level has actually reached the predetermined level N. In order to minimize the effect of the waves on the filling of the conduit 32 and chamber 33, it is possible to provide for arrangements such as those shown in FIGS. 10a to 10c of the aforementioned patent FR-2 656 354.

The automatic raise 10 described above can be a dumping or non-dumping rise depending on whether the height of panel 12 is chosen such that its upper edge is at a lower level or higher higher than the predetermined level N, respectively, In in the case of an overhanging rise, the panel 12 does not necessarily an essentially flat shape like that shown in Figures 3 and 6, but it can have, seen in horizontal section, a non-linear profile, for example a crenellated profile like that of the panel 12 ' as shown in Figure 7. As is known, this increases the length of the crest of the panel, therefore increasing the flow by. the sheet of water which pours over the crest of the panel for a level given water. So, by adopting a panel whose crest has a non-linear profile, for example crenellated as that of the panel 12 ', it is possible to give the panel 12 'taller than a flat panel having a straight profile ridge should have so that the automatic rise can evacuate a flood with a predefined flow (project flood), without the increase is not triggered automatically, i.e. as long as the water level remains below predetermined level N.

In the case of a pouring rise or in the case of a rise installed on a river threshold, a certain body of water may be present on the downstream side of the panel 12, with a level below the water level of the upstream side of the panel 12. In this case, the body of water downstream of the panel 12 can exert on the downstream face thereof a thrust which partially counterbalances the thrust P ₁ of the water on the upstream face of the panel 12 The thrust exerted on the downstream face of the panel 12 has the effect of reducing the value of the tension T of the tie rods 13, therefore also of reducing the value of the force F which tends to tilt the slab 16 upwards. In this case, this thrust should therefore be taken into account for the calculation of the tension T and the force F. To compensate for the decrease in the value of the force F, it may be necessary, for example, to reduce the weight of the slab 16, or the weight of ballast 31 or to place ballast 31 closer to axis A.

FIG. 10 illustrates an alternative embodiment of the detachable link 15. Here, each tie 13 is constituted at least in part by a flexible element such that cable or chain, and goes around an element of deflection 35, which is fixed on the slab 16 in the region on its side 16b, so that the part end of tie rod 13 which is attached to the plate 23 extends approximately vertically. In these conditions, the moment of tension T of tie rods 13 by relation to the C axis has a greater value than in the case of FIG. 3. The deflection element 35 can be for example constituted by a roller or a pulley or again, as shown, by a fixed cylindrical bar carried by supports 36 fixed to the slab 16.

Figure 11 shows another embodiment of the detachable connection 15. Here, the slot 24 arranged between the slab 16 and the masonry 11 has a cross section in the shape of an inverted L, with a first branch which extends horizontally under the slab 16 from its side 16b to its side 16a (not shown in FIG. 11), and a second branch which extends vertically downwards from the internal end of the first branch. The second branch or vertical branch of the slot 24 has a greater width than that of the first branch or horizontal branch of said slot. As shown in Figure 11, the side 16b of the slab 16 is made in the form of a rounded edge. Here again, each tie rod 13 is constituted, at least in part, by a flexible element such as cable or chain, which passes around the rounded edge 16b of the slab 16. Each tie rod 13 then passes through the horizontal branch of the slot 24 and is attached to the fixing piece 23 'which is engaged in the vertical branch of the slot 24. The fixing piece 23' may for example be constituted by a cylindrical bar having a diameter larger than the width of the horizontal branch of the slot 24, but smaller than the width of the vertical branch of said slot. The detachable link 15 shown in Figure 11 operates as follows. As in the previous embodiments, the tie rods 13, which are under tension, tend to tilt the slab 16 around the axis A (FIG. 3). When the water reaches the predetermined level N, the slab 16 rocks towards at the top, and as soon as the width of the horizontal branch of the slot 24 becomes greater than the diameter of the round section of the bar 23 ′, this bar is extracted from the slot 24 under the effect of the tension of the tie rod 13, so that the panel 12 is no longer retained and can collapse under the pressure P ₁ of the water.

Figures 12 and 13 show yet another mode of the detachable link 15. In this mode each tie rod 13 is attached to one of the ends of a 23 "fastener forming a the sink. A support point 37 for the 23 "lever is provided on one side of the slab 16 at a distance from the side 16a of this, for example near the side 16b of the slab. As shown in Figures 12 and 13, a notch 38 can be formed in side 16b of slab 16 and the fulcrum 37 can be constituted by a bar, by cylindrical example, horizontal axis, which crosses the notch 38 and the ends of which are embedded in the slab 16. Preferably, the lever 23 "comprises, at the place where he is constact with the bar 37, a footprint 39 having for example a shape corresponding to that of said bar 37. A stopper 41 is arranged on the masonry 11 below the bar 37, the stopper 41 can be formed in one piece with masonry 11, or it can consist of a metallic piece properly anchored to the masonry 11, A respective 23 "lever can be associated with each of the two tie rods 13. In this case, the two 23 "levers can be rigidly coupled to each other by a bar transverse 42. However, if the notch 38 is formed in the middle of the length of the side 16b of the slab 16, the two tie rods 13 can be attached to a lever single 23 ".

In service, the tie rod (s) 13 exert on the upper end of the lever (s) 23 "a pull which tends to rotate the said lever (s) 23" in an anticlockwise direction around the point of support constituted by the cylindrical bar 37, and which maintains the lower end of the lever (s) 23 "against the respective stopper (s) 41. It follows that the lever (s) 23" apply to the support point 37, therefore to the slab 16, a force F which tends to tilt it around the axis A (Figure 3). When the water reaches the predetermined level N and the slab 16 tilts up around the axis A, the lower end of the lever 23 "(or of each lever 23") escapes from the stopper 41 by sliding on the latter, so that the fixing part formed by the lever 23 "is released and the panel 12 is no longer retained and can collapse under the pressure P ₁ of the water.

Figures 14 and 15 show yet another embodiment of the detachable link 15. In this embodiment, the lower end of each tie rod 13 (or of the two tie rods 13) is connected to the slab 16, preferably near the side 16b thereof, or to the masonry 11 by a fastener comprising a ring or an eyelet 15a, which is fixed to the tie rod 13, a yoke 15b, which is fixed to the slab 16 as shown in solid lines in FIGS. 14 and 15 or to the masonry 11 as shown in phantom in Figure 15, and a dowel 15c which detachably couples the eyelet 15a and the yoke 15b, The dowel 15c is provided with a ring 43 to which the one end of a flexible link 44, such as a cable or a chain, the other end of which is attached to a ring 45 anchored to the masonry 11. Starting from the ring 45, the link 44 extends entirely first vertically or substantially vertically upwards, then passes around d 'a deflection element 46 fixed to the slab 16 and then extends horizontally or substantially horizontally to the ring 43 in the case where the yoke 15b is fixed to the slab 16. In the case where the yoke 15b is fixed at the masonry 11, the link 44, after having passed around the deflection element 46, extends vertically or substantially vertically downwards, then it passes around another deflection element 47 fixed to the masonry 11, and it then extends horizontally or substantially horizontally to the ring 43 of the pin 15c. In both cases, when the water level reaches the predetermined level N and the slab 16 rocks around the axis A (Figure 3) under the effect of the traction T exerted by the tie rod (s) 13 and / or under the effect of the push P5 of the water which has entered the chamber 33 through the conduit 32 (FIG. 3), the deflection element 46 is raised with the slab 16 and exerts a traction on the link 44. It follows that the pin 15c, pulled by the link 44, is extracted from the ring 15a and the yoke 15b and uncouples these two elements. The panel 12 then no longer being retained, it can collapse under the pressure P ₁ of the water,

When the yoke 15b of the clip 15 is fixed to the masonry 11, this solution has the advantage, by compared to that in which the clevis 15b is fixed to slab 16, that automatic rise 10 is completely insensitive to a possible shock caused by a floating body striking the panel 12 or the or tie rods 13, Indeed, with this solution, the tie rods 13 no longer exert any action on the slab 16, In this case, the tilting of the slab 16 around axis A is caused only by push P5 of the water which enters the chamber 33 via the conduit 32, Consequently, slab 16 must have a more weight weak than in the case where the tie rods 13 exert a action on said slab, more precisely, slab 16 must have a lower density than that of water.

FIG. 16 illustrates an alternative embodiment of the fastener 15 of Figures 14 and 15, In Figure 16, elements that play the same role as those shown in figures 14 and 15 are designated by the same reference numbers. In clip 15 of Figure 16, the ring or eyelet 15a, which is fixed to the tie rod 13, is detachably coupled to the yoke 15b, which is fixed to the slab 16 or to the masonry 11, by means of a hook 15c which can pivot around an axis 15d of the screed 15b. The hook 15c is provided with a ring or eyelet 43 to which the link 44 is attached. In service normal, as long as the water level remains below predetermined level N, the traction T exerted by the pulling 13 on the ring 15a tends to rotate the hook 15c counterclockwise shows around axis 15d and said hook is held resting against the plate 15e of the yoke 15b. When the water reaches the predetermined level N and that the plate 16 tilts up around axis A, the element of deflection 46 (figure 15) exerts on the link 44 a force of traction which pulls this link in the direction indicated by the arrow H in Figure 16. This tensile force has to rotate the lever 15c in the direction clockwise around axis 15d. As soon as the median plane of the ring 15a has crossed the line vertical 48 which passes through the center of the section circular axis 15d, hook 15c opens automatically under the effect of the traction T exerted by pulling on the ring 15a. So we see that just a very small displacement of the slab 16 to cause the detachment of the ring 15a relative to the hook 15c.

In the embodiments described above, the massive element whose displacement causes the removal of the detachable link 15 was constituted by a slab 16 which can tilt around an axis horizontal A. However, the present invention is not limited to the use of a massive element in the form of a tilting slab.

As shown in Figure 17, the massive element can be constituted by a 16 'block, for example in concrete or reinforced concrete, which is mounted so that it can slide vertically in a cavity 49 open towards the high formed in masonry 11. Vertical walls of the cavity 49 can be lined with a coating 51 having a low coefficient of friction with the material constituting the block 16 '. This 16 'block can have, in one of its sides, a notch 24 'which, in normal service, is at least partially closed by one of the vertical walls of the cavity 49 when the block 16 'is in its stable state resting on the bottom of the cavity 49. The lower end of the tie rod 13 or of each of the two tie rods 13 is attached to a piece 23 ’retaining device captive in the notch 24 ′. As in the embodiment of FIG. 11, the fastening piece 23 'can be constituted by a metal bar, preferably cylindrical.

In service, under the effect of the tension T of the tie rod 13, the bar 23 'is subjected to a force which can be broken down into a horizontal component T _H and a vertical component T _v . The horizontal component T _H is absorbed by the masonry 11 or by a metallic reinforcing piece 52 suitably anchored in the masonry 11, The vertical component Tv acts on the block 16 'and tends to lift it, The weight P ₂ of the block 16' is chosen in such a way that the vertical component Tv, the value of which increases when the level of the body of water upstream of the panel 12 increases, reaches and exceeds the sum of the weight P ₂ and the weight of the water column at above the block 16 'when the water reaches the predetermined level N. Under these conditions, the block 16' is raised, the notch 24 'is then released and the bar 23' is released. As a result, the panel 12 is no longer retained and that it can collapse under the pressure P ₁ of the water. A retaining element 53 having a Z-shaped profile can be fixed to the masonry 11 to limit the movement of the block 16 'upwards. However, such a retaining element 53 is not essential. In fact, as soon as the bar 23 'is released, it no longer applies any vertical force to the block 16' which then falls under the effect of its own weight P ₂ on the bottom of the cavity 49.

As in the embodiment of Figure 3 where the solid element is constituted by a slab 16, a chamber 33 communicating with a conduit 32 similar to the conduit 32 of Figure 3 can be arranged under the block 16 'between it and the bottom of the cavity 49. The chamber 33 can be formed either by hollowing out the lower surface of the block 16 ′, or by hollowing out the bottom of the cavity 49, or both. Again, the thrust P ₅ which is applied to the block 16 'when the water upstream of the panel 12 reaches the level N, makes it possible to further improve the precision of the water level which will effectively cause the automatic triggering of the rise .

In the embodiment of FIG. 17, we note that the detachable link 15 which is formed here by the fixing piece 23 'and by the notch 24', can be replaced by a link of the same type as those which have been described above with reference to FIGS. 10 to 16.

In the embodiments which have been described previously, it was assumed that the massive element 16 or 16 'is mostly found (Figures 3, 3a, 4 and 5) or in full (Figures 5a, 5b and 17) on the upstream side of the panel 12. However, the solid element 16 or 16 'can be placed on the downstream side of panel 12 as shown in Figures 18 and 19.

In the embodiment of FIG. 18, the elongated element which retains the panel 12 against the thrust P ₁ of the body of water which is located upstream of this panel 12, is here constituted by at least one forestay or leg of rigid force 13 '. The forestay 13 'has a first support point, at 14, on the downstream face of the panel 12 and a second support point, at 15', on the masonry 11. The support point 14 may for example be constituted by a joint, while the fulcrum 15 'is constituted by a simple stop 54 formed integrally with the masonry 11 or constituted by a metal piece suitably fixed to the masonry 11. However, the joint 14 could be in place of the stop 54 and the stop 54 in place of the articulation 14, The fulcrum 15 'formed by the stop 54 here constitutes the aforementioned detachable connection.

In addition, as shown in FIG. 18, the massive element whose displacement causes the triggering of the rise when the water level upstream of the panel 12 reaches the predetermined level N, can for example be constituted by a block 16 'similar to that described with reference to Figure 17, but devoid of a notch 24', The forestay 13 'passes just above the block 16' so that, when this block is raised, the forestay 13 ' is driven from the fulcrum 15 'constituted by the stop 54, as illustrated in FIG. 18, and that the panel 12 can then collapse under the thrust P ₁ of the water. In this embodiment, the block 16 ′ is moved only by the pressure P ₅ of the water which enters the chamber 33 via the conduit 32 when the water level reaches the predetermined level N. A similar retaining element in element 53 of FIG. 17 may be necessary to limit the displacement of the block 16 'upwards,

In the embodiment of Figure 19, the upper end of the tie rod 13 is connected indirectly to panel 12 by a first arm 55 of a pair of articulated arms 55 and 56. The second arm 56 of said pair of arms is supported directly or indirectly on masonry 11 in 57. In the example shown in Figure 19, the solid element 16 is consisting of a slab similar to that shown in Figure 3 and the second arm 56 is supported on a stop 58 formed on the slab 16 near its side 16a. However, the stop 58 could be formed on the masonry 11. The first arm 55 is articulated, at 14, on the downstream face of the panel 12.

As in the embodiment of Figure 3, a stop 17 for the slab 16 is provided on the masonry 11. The lower end of the tie rod 13 is connected to the masonry 11 by a detachable link 15 similar to that described in connection with Figure 3. However, the detachable link 15 shown in the figure 19 could be replaced by any one connections shown in Figures 10 to 17. From even, slab 16 can be replaced by a block sliding 16 'like that of Figure 17.

In the automatic increases described above, it will be noted that, from the point of view of the transmission of the forces T, F, and P ₅ which are generated by the body of water 25 and applied to the slab 16 or to the block 16 ' , the panel 12, the tie rod 13 and the detachable link 15 constitute a mechanical coupling system between the slab 16 or the block 16 ′ and the body of water 25, while the conduit 32 constitutes a hydraulic coupling system between the slab 16 or the block 16 'and the body of water 25. When the water reaches the predetermined level N, the detachable connection 15 or 15' is removed in response to the movement of the slab 16 or of the block 16 'either under the effect of the mechanical coupling system alone, either under the effect of the hydraulic coupling system alone or even under the effect of the two coupling systems at the same time according to the embodiments described.

Claims (28)

1. An automatic flashboard for a hydraulic structure such as a river sill or a spillway on a dam or protective dyke, comprising a construction forming a water-tight or substantially water-tight wall (12), installed on said hydraulic structure (11) in such a way as to be able to move from a first, raised position for holding back a body of water into a second, lowered position in which said wall (12) allows water to pass virtually without obstruction, and at least one elongate retaining element (13; 13') for holding said wall in its first position against the horizontal thrust (P₁) exerted by the body of water (25), said elongate retaining element (13; 13') being subject, when in operation and under said water thrust, to longitudinal stress (T), extending between said wall (12) and a reaction point compensating said longitudinal stress and being connected to the reaction point by a connection (15) which may be automatically removed when the water reaches a certain level, in such a way that said wall (12) moves automatically into its second position, characterised in that it further comprises a solid element (16; 16') which is mounted movably on said structure (11) and is in relation with said body of water in such a way as to be in a stable position of equilibrium as long as the water remains below a predetermined level (N) and to pass into an unstable state and to be displaced when the water reaches said predetermined level, said connection (15) being removed by displacement of said solid element.
2. A flashboard according to claim 1, characterised in that said solid element consists of a slab (16) installed on said structure (11) in such a way as to be able to swing upwards about a horizontal axis (A) which extends along a first side (16a) of the slab (16) and which is perpendicular to the direction of the thrust (P₁) exerted by the body of water (25) on said wall (12).
3. A flashboard according to claim 1, characterised in that the solid element (16') is mounted in such a way as to be able to slide vertically in a cavity (49) open at the top formed in said structure (11).
4. A flashboard according to any one of claims 1 to 3, characterised in that said elongate retaining element consists of a tension member (13), a first end of which is connected (at 14) to said wall (12), in the upper region thereof, and a second end of which is attached to a securing member (23; 23'; 23") which is engaged and held in a space (24; 24') formed between said solid element (16; 16') and said structure (11) in such a way that, when the tension member (13) is under tension as a result of said thrust (P₁) of the water, the solid element (16; 16') is subject to a force (F; T_v), the value of which increases as a function of the water level and which is oriented in a direction such that it has a tendency to raise said solid element (16; 16'), and, when the water reaches said predetermined level (N), causing raising of the solid element, said space (24; 24') becomes larger and releases the securing member (23; 23'; 23").
5. A flashboard according to claims 2 and 4, characterised in that said space consists of a slot (24), which extends roughly horizontally under the slab (16) from a second side (16b) thereof opposite its first side (16a) towards said first side of the slab, and in that said securing member consists of a plate (23) of elongate rectangular cross section which, when engaged in said slot (24), comprises a portion which projects beyond the second side (16b) of the slab (16) and to which there is attached the second end of the tension member (13).
6. A flashboard according to claim 5, characterised in that said tension member (13) consists at least in part of a flexible element, such as a cable or chain, and passes around a deflecting element (35) fixed to said slab (16) in the region of the second side (16b) thereof, in such a way that the end portion of said tension member (13) which is attached to the plate (23) extends approximately vertically.
7. A flashboard according to claims 2 and 4, characterised in that said space is a slot (24) of inverted L-shaped cross section, a first branch of which extends horizontally under said slab (16) from a second side (16b) thereof opposite its first side (16a) in the direction of said first side, and a second branch of which extends vertically downwards from the inner end of the first branch and is wider than the first branch, in that, on its second side (16b), said slab (16) comprises a rounded edge and in that said tension member (13) consists at least in part of a flexible element, such as a cable or chain, which passes around the rounded edge of said slab (16), then into the first branch of said slot (24) and is attached to said securing member (23') which is engaged in the second branch of said slot (24).
8. A flashboard according to claim 7, characterised in that said securing member (23') has a round section with a diameter which is larger than the width of the first branch of said slot (24) and smaller than the width of the second branch of said slot.
9. A flashboard according to claim 2, characterised in that said elongate retaining element consists of a tension member (13), of which one end is connected (at 14) to said wall (12), in the upper region thereof, and the other end is attached to a first end of a securing member forming a lever (23"), in that a bearing point (37) for the lever (23") is provided on one side (16b) of said slab (16) at a distance from the first side (16a) thereof and in that a stop (41) for a second end of the lever (23") is formed on said structure (11) beneath said bearing point (37) in such a way that, when the tension member (13) is under tension as a result of the thrust (P₁) exerted by the water on said wall (12), the first end of the lever (23") is subjected to a force (T), the value of which increases as a function of the water level and which has a tendency to pivot the lever (23") around said bearing point (37) and holds the second end of the lever (23") against said stop (41), said force (T) being converted by the lever (23") into a force (F) which is applied to the slab (16) and which has a tendency to swing the latter upwards about said horizontal axis (A) in such a way that, when the water reaches said predetermined level (N) and causes swinging of the slab (16) by several degrees upwards, the second end of the lever (23") escapes from the stop (41) by sliding thereover and the securing member forming the lever (23") is released.
10. A flashboard according to claims 3 and 4, characterised in that said space consists of a notch (24') formed in one side of the solid element (16'), said notch (24') being at least partially closed by a vertical wall of said cavity (49) when the solid element (16') is in its stable position resting against the bottom of the cavity (49), and being cleared and and opened when the solid element (16') is raised.
11. A flashboard according to any one of claims 4 to 10, characterised in that at least two tension members (13) are provided which are connected on the one hand to said wall (12) at horizontally spaced points (14) and on the other hand to said securing member (23; 23'; 23").
12. A flashboard according to claim 11, characterised in that the securing member (23; 23'; 23") is common to the two tension members (13).
13. A flashboard according to claims 9 and 11, characterised in that each tension member (13) is attached to a respective securing member forming a lever (23") and in that the two levers (23") are coupled rigidly together by a crossbar (42).
14. A flashboard according to any one of claims 1 to 3, characterised in that said elongate retaining element consists of a tension member (13), a first end of which is connected (at 14) to said wall (12), in the upper region thereof, and a second end of which is connected to the solid element (16; 16') by a fastening (15), in such a way that, when said tension member (13) is under tension as a result of said thrust (P₁) of the water, the solid element (16; 16') is subject to an upwardly directed force, the value of which increases as a function of the water level and which has a tendency to raise said solid element (16; 16'), in that said fastening (15) comprises first and second parts (15a, 15b), which are connected respectively to the tension member (13) and the solid element (16; 16'), and a third part (15c) which is movable and couples the first and second parts of the fastening (15) in detachable manner, and in that a link (44) connects the third part (15c) of the fastening to a fixed point (45) on the structure (11) in such a way that, when the water reaches said predetermined level (N) and the solid element (16; 16') is raised with the first and second parts (15a, 15b) of the fastening (15), the third part (15c) of the fastening is held by said link (44) and uncouples the first and second parts of the fastening.
15. A flashboard according to claim 2, characterised in that the slab (16) has, in its upper surface, a channel (18) which extends at least in part along the first side (16a) of the slab (16) and which is wider than the thickness of the lower edge of said wall (12) which is engaged in said channel (18), in such a way that said wall (12) may swing about the edge (B) of the channel (18) closest to the first side (16a) of the slab (16).
16. A flashboard according to claim 15, characterised in that said wall (12) is connected to a fixed point (27) on the structure (11) by at least one short flexible link (26) such as a cable or chain.
17. A flashboard according to claim 15, characterised in that at least one element forming a hook (28) is fixed to said wall (12) on its face opposite that which holds back the water, close to the lower edge of said wall, and cooperates with a complementary retaining element (29) fixed rigidly to said slab (16).
18. A flashboard according to claim 2, characterised in that said wall (12) is mounted pivotally on the slab (16) by means of a hinge (19) having a horizontal axis of articulation perpendicular to the direction of said thrust (P₁) of the water.
19. A flashboard according to any one of claims 4 to 18, characterised in that the solid element (16; 16') is located at least for the most part on the side of said wall (12) which holds back the water and in that the first end of the tension member (13) is connected directly (at 14) to said wall (12).
20. A flashboard according to any one of claims 4 to 18, characterised in that the solid element (16; 16') is located on the opposite side of said wall (12) from that which holds back the water, and in that the first end of the tension member (13) is connected indirectly to said wall (12) by a first arm (55) of a pair of articulated arms (55, 56), the second arm (56) of said pair of arms resting (at 57) on an abutment provided on said structure (11).
21. A flashboard according to any one of claims 1 to 20, characterised in that a first conduit (32) is provided, a first end (32a) of which opens under said solid element (16; 16'), while its second end (32b) is located on the side of said wall (12) which holds back the water and opens at a level corresponding to said predetermined level (N), in such a way that, when the water reaches said predetermined level (N), said first conduit (32) fills up with water and a vertical, upwardly directed thrust (P_s) is applied to the solid element (16; 16').
22. A flashboard according to claim 21, characterised in that the conduit (32) extends in part into said structure (11).
23. A flashboard according to claim 21, in association with claim 2, characterised in that the conduit (32) is fixed to the slab (16) or is formed in one piece therewith.
24. A flashboard according to claim 21, characterised in that the lower surface of the solid element (16; 16') and/or the part of the structure (11) which is located beneath the solid element is hollowed out in such a way as to define a chamber (33) into which opens the first end (32a) of the first conduit (32).
25. A flashboard according to claim 24, characterised in that a second conduit (34) having a flow cross section smaller than that of the first conduit (32) is provided to drain said chamber (33).
26. A flashboard according to claim 21 or 24, in association with any one of claims 1 to 18, characterised in that said solid element (16; 16') is located on the opposite side of said wall (12) from that which holds back the water, and in that said elongate retaining element consists of a rigid strut (13'), which has a first bearing point (at 14) on said wall (12) and a second bearing point (at 15') on said structure (11) and which passes just above said solid element (16; 16') in such a way that, when the solid element is raised, said strut (13') is driven out of one (15') of its two bearing points (14, 15') and said wall (12) may move from its first to its second position.
27. A flashboard according to any one of claims 1 to 26, characterised in that said wall (12) is substantially flat.
28. A flashboard according to any one of claims 1 to 26, characterised in that said wall (12'), when viewed in horizontal section, has a non-linear profile.

Images