EP0231134B1 - Method for precisely positioning a prefabricated structure by sinking into the sea or into a river, and maritime or fluvial construction obtained by said method - Google Patents

Description

The present invention relates to a method for setting up a prefabricated structure on a sea or river bottom, said prefabricated structure being able to float and, after being floated and towed to the desired site, being stranded on the bottom by ballasting .

In terms of maritime or river works (offshore platforms, submerged tunnels, sub-river crossings, bridges, etc.), prefabricated structures are used whenever possible, which are then floated and washed up at their final location.

We are trying to reduce as much as possible the amount of work to be done at the site of the structure, in favor of prefabrication, because it is done on land or in a form of refit and, therefore, in better conditions of deadlines, costs, quality of the work and safety of the execution staff.

The use of prefabrication is limited, or even made impossible, when the positioning tolerances required for the structure to be built are incompatible with the tolerances that can be achieved by grounding, the latter being from one to several meters. This is particularly the case for bridges with multiple spans, for which the positioning tolerances required for the piers, pylons and spans have an order of magnitude of around ten centimeters. In this case, either the construction in place of the entire structure is used, or a prefabrication limited to a part of the structure, the rest of which is then constructed at the final location, for example prefabrication and grounding of the foundation. with more or less 2 m near, then construction of the pile on the grounded foundation with the required tolerances. An example of limited prefabrication of a foundation, then grounding (sinking) and construction of the rest of the foundation on the site of the structure is described in patent FR 1 277 200. However, in the latter case, given the relatively poor precision with which it is possible to position the prefabricated foundation by grounding, it is sometimes necessary to provide a foundation having dimensions large enough so that, after the latter has been grounded, the bridge pier can then be built on the foundation with a precise position and orientation relative to the other bridge piers already built. This therefore requires having prefabricated foundations having larger dimensions than those which would be strictly necessary to receive a bridge pier. On tour, even if part of the structure can be prefabricated on the ground, a significant amount of work remains to be done on the final site of the structure (construction of the pier, construction or erection of the pylon, installation of the deck or bridge spans, etc.).

In fact, the imprecision of the grounding maneuvers (one to several meters) has several causes. On the one hand, it is practically impossible to completely immobilize a floating structure subjected to the action of waves and currents. The structure that one wishes to immobilize before stranding by mooring lines is in fact subjected to more or less periodic movements, the amplitude of which depends on the stiffness of the moorings and the stresses due to current, swell or in the wind. We can reduce the amplitude of the movements by shortening the mooring lines (or by increasing their stiffness), but then the efforts in the mooring lines also increase and we are quickly limited by the size of the mooring devices (cables, anchors, dead bodies, etc.). On the other hand, the absence of a fixed point makes topographical location operations delicate and imprecise and, consequently, guidance and positioning before stranding. Even in the case where there is a fixed point like 1 "mobile island" or self-elevating platform of patent 1 277 200, the grounding position of the foundation and its orientation remain imprecise, because they depend greatly not only from the stiffness of the lines by which the casing to be suspended is suspended from the mobile island, but also from the precision with which the mobile island had itself been previously stranded on the bottom thanks to its vertically mobile support pillars precision which can only be mediocre for the reasons explained above.

The main object of the present invention is therefore to provide a method for failing a prefabricated structure, in particular a foundation for a bridge pier, with a precise position and orientation on a sea or river bottom.

To this end, the method of the present invention is characterized in that it consists in at least partially surrounding said prefabricated structure by a floating box, while leaving a clearance of several meters between the box and the structure, then, when the floating assembly formed by the caisson and by the structure is at the site where the structure is to be grounded, to give said assembly a suitable approximate position and orientation, then to ground the caisson on the bottom by ballasting, and to ground the structure with a precise position and orientation on the bottom, ballasting said structure and using the stranded box as a fixed point for positioning and orientation of the structure.

• la figure 1 montre moitié en vue de dessus et moitié en coupe horizontale, une fondation préfabriquée pour une pile de pont et un caisson préfabriqué utilisable pour la mise place de la fondation sur un fond marin ou fluvial.
• La figure 2 est une vue en coupe suivant la ligne II-II de la figure 1.
• Les figures 3 à 10 montrent schématiquement, soit en vue de dessus, soit en coupe verticale, diverses phases du procédé de la présente invention.
• La figure 11 montre, en élévation latérale, un élément préfabriqué de pont pouvant être mis en place sur un fond marin ou fluvial par le procédé de la présente invention.
• Les figures 12 à 16 montrent schématiquement certaines des phases de mise en place de l'élément de pont de la figure 11.
• La figure 17 montre schématiquement, en vue de dessus, une autre forme de caisson susceptible d'être utilisée pour la mise en oeuvre du procédé de l'invention.

Other characteristics and advantages of the invention will appear better during the description which follows and which is given with reference to the appended drawings in which:

• Figure 1 shows half in top view and half in horizontal section, a prefabricated foundation for a bridge pier and a prefabricated box usable for the establishment of the foundation on a sea or river bottom.
• Figure 2 is a sectional view along line II-II of Figure 1.
• Figures 3 to 10 show schematically, either in top view or in vertical section, various phases of the process of the present invention.
• FIG. 11 shows, in side elevation, a prefabricated bridge element which can be put in place on a sea or river bottom by the method of the present invention.
• FIGS. 12 to 16 schematically show some of the phases of positioning the bridge element of FIG. 11.
• FIG. 17 schematically shows, in top view, another form of box able to be used for the implementation of the method of the invention.

In Figures 1 and 2, there is shown, by way of example, a prefabricated foundation 1, which is intended to support a bridge pier and which is surrounded, with a large radial clearance (at least 2 meters), by a prefabricated box 2 having, in top view, the shape of a ring, preferably closed. The foundation 1 and the box 2 are in the form of hollow structures, metallic or concrete or partly metallic and partly concrete, comprising compartments 3 and 4, respectively, which allow structures 1 and 2 to float and which are likely to be filled with water or a solid material (sand, gravel, concrete, etc.) for the stranding of said structures. Openings (not shown) may be provided in the lower part of the compartments 3 and in the lower part of the compartments 4, to allow the homologous compartments to communicate with each other. As is known in the grounding techniques, at least some of the compartments 3 and of the compartments 4 are equipped with valves and pumps (not shown) allowing the filling of the compartments 3 and 4 with water (ballasting) or their draining (deballasting).

The foundation 1 and the box 2 are prefabricated on the ground or in the form of a refit. The box 2 can be made in one piece as shown in Figure 1, in which case the foundation 1 and the box 2 are built on the same site, or the box 2 can be built in two parts 2a and 2b (Figures 10 and 17) capable of being detachably attached to each other, in which case the foundation 1 and the box 2 can be built on separate sites. In both cases, the box 2 can be built first, then floated and towed into a basin and washed up on the bottom of the said basin, then, after having evacuated the water contained in the interior space delimited by the box , it can be used as a refit for the construction of the foundation 1.

Once foundation 1 has been built and floated, box 2 is placed around foundation 1 if it was not already there, and it is floated. Next, foundation 1 and box 2 are towed together to the site where foundation 1 is to be stranded on a sea or river bottom. At least during this towing phase, docking defenses 5 (FIG. 4) are placed between the foundation 1 and the box 2 in order to prevent them from colliding. Preferably, during this towing phase, the foundation 1 and the box 2 are also moored to each other by cables (not shown) in order to limit as much as possible the relative movements of the foundation 1 relative to the box. 2.

Once foundation 1 and box 2 have been brought above the site where foundation 1 is to be beached, and while foundation 1 is still moored to box 2, the latter is connected by several mooring lines, for example four lines 6a-6d (FIG. 3) to a corresponding number of anchor points 7a-7d, for example submarine anchor piles previously installed and suitably marked. Although Figure 3 shows only four mooring lines 6a-6d, more lines can be provided if necessary. At its other end, each of the mooring lines 6a-6d is connected to a corresponding winch 8a, 8b, 8c or 8d, respectively, installed on the box 2. In FIG. 3, we have also indicated at 9 and 10 respectively the desired position and orientation for the foundation 1, the axis 10 being for example the longitudinal axis of the point to be constructed. Using the mooring lines 6a-6d and the winches 8a-8d, the position and orientation of the assembly formed by the foundation 1 and by the box 2 are then adjusted, so that they coincide approximately with position 9 and with axis 10. This adjustment operation is also carried out using optical measurement systems, for example laser sighting systems, using fixed points situated on the ground as reference points or structures, for example bridge piers, already in place.

Once the position and orientation of the foundation 1 and the box 2 have been adjusted as indicated above, the grounding operations can then begin. Starting from the position shown in Figure 4, in which the foundation 1 and the box 2 are both floating, the compartments 4 of the box 2 are first filled with water as shown in Figure 5 in order to fail the box 2 on the seabed or river bottom 11. Because of the various factors mentioned above (currents, swell, wind), the grounding accuracy is relatively poor (about plus or minus 2m). It is therefore necessary to fail foundation 1 with much more precise precision and orientation so that they are compatible with the positioning tolerances required for the structure to be built. For this purpose, the quantity of water introduced into the compartments 4 of the box 2 is large enough so that, after being stranded, the box 2 has a stable position on the bottom 11, that is to say so that the currents, swell and wind have no influence on the position of the box 2. Next, the position and orientation of the foundation 1 are adjusted so as to make them coincide with position 9 and with the axis 10 (figure 6). This adjustment can for example be made using mooring lines 12a-12d and winches 13a-13d installed on box 2. The winches 13a-13d may possibly be the same as the winches 8a-8d which had been used previously to carry out the rough positioning of box 2 using the lines 6a-6d. Under these conditions, the position and orientation of the foundation 1 can be adjusted with good precision (about plus or minus 10 cm), that is to say with a precision compatible with the positioning tolerances. required for the construction of the bridge. Indeed, the adjustment of the position and the orientation of the foundation 1 is carried out by using the box 2 as a fixed point since, after being stranded, it is perfectly stable. In addition, since the foundation 1 is now sheltered from the stranded caisson 2, it is no longer subject to the effects of currents and swells. Finally, since the box is relatively close to the foundation 1, the ponds 12a-12d are significantly shorter than the moorings 6a-6d and, therefore, are much more "rigid" than the latter.

It should be noted that the precise adjustment of the position and orientation of the foundation 1 can be carried out while the foundation 1 is still floating (Figure 5) or after the compartments 3 of the foundation 1 have been filled of water (Figure 7). In the second case, one introduces into the compartments 3 of the foundation 1 the quantity of water just sufficient so that the lower part of the foundation is immediately close to the bottom 11, but without being in contact with it.

After the position and orientation of the foundation 1 have been precisely adjusted, it is ballasted with an amount of ballast just sufficient to fail it on the bottom with a low apparent weight. The base, the heel and the level of the foundation 1 are then adjusted. This adjustment operation can be carried out according to any of the known techniques for grounding, for example by means of several jacks 14 (FIG. 8) and / or by means of several cushions 15 (FIG. 2) initially provided at the periphery of the base of the foundation 1. When cushions 15 are used, these are "inflated" by injecting cement therein. Then, after the trim, the heel and the level of the foundation have been adjusted, cement is injected under the foundation 1, between the latter and the bottom 11, in order to create a foundation 16. After the cement has set of the seat 16, the foundation 1 is definitively held in place on the bottom 11 either by gravity, by carrying out an additional ballasting of the foundation 1, for example by filling its compartments 3 with an additional quantity of water or with sand , gravel or concrete as shown in FIG. 9, either by anchoring by means of piles which are driven into the bottom 11 and made integral with the foundation 11.

Then, either the box 2 is left in place after being possibly refocused relative to the foundation 1 in a manner which will be described later, or, if the box 2 is made in two detachable parts 2a and 2b, it can be put back into floatation, by evacuating the water contained in its compartments 4 (figure 9), and its two parts 2a and 2b can be detached from each other, separated from the foundation 1 (figure 10) and reused for the establishment of another structure or foundation in a manner similar to that which has been described above.

In the previously known technique of grounding, the precision of grounding of the foundation was relatively poor, so that, as already indicated above, this required to build the remaining elements of the bridge, in particular the piers and the pylons on the foundations site, after their stranding. Since the process of the present invention makes it possible to ground the foundation 1 with much greater precision than by the previously known grounding technique, it becomes possible to prefabricate on land not only the foundation 1 with the supports 17 (figures 1 and 2) intended to receive the bridge pier, but also the pier itself, the pylon and possibly the bridge deck.

In the case where the foundation has sufficient buoyancy to support the superstructure, it can be prefabricated and assembled on the ground or in a port on the foundation, then the assembly can be towed, positioned and beached as described above.

On the other hand, if the foundation does not have sufficient buoyancy to support the superstructure, the greater buoyancy of the box can be used in the following manner.

For the following description, it will be assumed that the bridge pier is for example constituted by four tubular legs 18 (FIG. 11) having a spacing corresponding to that of the supports 17 of the foundation 1 (FIGS. 1 and 2), and by a support structure 19 for the deck 20 of the bridge. The support structure 19, which is fixed to the upper end of the feet 18, may for example be constituted by a horizontal frame, the sides of which are formed by tubular elements or by appropriate beams. In the example shown in Figure 11, the pylon 21 is constituted by four tubular elements whose lower ends are fixed to the support structure 19 and whose upper ends are joined and fixed to each other so as to form a sort of pyramid. The deck 20 is mounted in double cantilever on the support structure 19 and guy lines 22 are stretched between the deck 20 and the upper end of the pylon 21.

The assembly of the stack 18, 19, of the deck 20, of the pylon 21 and of the shrouds 22 is carried out in a port after the box 2 has been constructed, either while it is still in the form of a refit, or after to have provisionally failed it on the bottom of a basin. The four feet 18 and the support structure 19 are firstly mounted on the box 2 by means of temporary feet 23, the lower ends of which rest on the box 2 at points 24 (FIG. 1) previously fitted for this purpose. , by means of supports 25 (figure 2) adjustable in height and possibly in translation (hydraulic cylinders and sliding shoes). Then, the pylon 21 and the deck 20 are mounted on the support structure 19 and the shrouds 22 are suitably tensioned.

Then, the foundation 1 and the box 2, supporting the superstructure 18-22, are floated and towed to the site where the foundation 1 must be grounded. Then, the foundation 1 is stranded with a precise position and orientation as described above with reference to Figures 3 to 9.

Once the foundation 1 has been definitively stranded, the box 2 is returned to slightly floating by partially de-ballasting its compartments 4, so that the box is lifted a few tens of centimeters above the bottom 11 as shown in the figure 12. Next, the box 2 is refocused with respect to the foundation 1, using the latter as a fixed point. At the same time, the box 2 is suitably oriented in such a way that the feet 18 of the bridge pier come respectively above the supports 17 of the foundation 1 and in such a way that the deck 20 is suitably aligned with the axis 10 (Figure 13), that is to say with the desired longitudinal axis for the bridge if it is the first bridge element which is being laid, or with other bridge elements previously placed square. As shown in FIG. 13, the adjustment of the position and the orientation of the box 2 can for example be carried out by means of the same mooring lines 12a-12d and the same winches 13a13 _d as those which had been used previously for positioning and for the orientation of the foundation 1.

Once the box 2 has been correctly positioned and oriented, its compartments 4 are again filled with water so as to fail on the bottom 11 (FIG. 14). Then, using the adjustable supports 25 (FIG. 15), the level and, if necessary, the position and the orientation of the superstructure 18-22 are precisely adjusted by using the stranded box 2 as a fixed point, such so that the superstructure has an appropriate position, orientation and level in relation to foundation 1 and also in relation to the other bridge elements already in place. These adjustments can be made with precision using the adjustable supports 25 and using optical precision measurement systems, for example laser sighting systems.

Then, the feet 18 of the bridge pier are fixed to the foundation 1, for example by welding, by bolting or by concrete poured in place, as shown diagrammatically at 26 in FIG. 15. Then, the load of the superstructure 18-22 is transferred to the foundation 1, for example by retracting the piston rods of the hydraulic cylinders contained in the adjustable supports 25. Then, the temporary feet 23 are detached from the support structure 19 and from the box 2, and they are then removed and demolished or reused to support other superstructures on other caissons. Similarly, the moorings 12a-12d, the winches 8a-8d, 13a-13d and the adjustable supports 25 are disassembled and removed to be reused with another box.

In the case where the box 2 is in two detachable parts 2a and 2b, the box 2 can be returned to floating, by deballasting of its compartments 4, and its two parts 2a and 2b can be disassembled, separated from the foundation 1 and reused for the establishment of another foundation.

However, the box 2 can advantageously be left in place so as to protect the foundation 1 against collisions likely to occur with ships. In this case, an additional ballasting of the box 2 is carried out, by filling its compartments 4 with an additional quantity of water or with sand, gravel, concrete or other heavy filling material as shown at 27 in FIG. 16. Alternatively, the box 2 could be anchored on the bottom 11 for example by means of piles suitably driven into the bottom 11 and made integral with the box 2. It will be noted that the additional ballasting or the anchoring of the box 2 can be carried out either immediately after the grounding of the box 2 (figure 14) and before the precise adjustment of the position, orientation and level of the superstructure 18-23, that is to say at a time after that this precise adjustment has been made.

FIG. 7 shows, in top view, another form of floating box 2 ′ capable of being used for the implementation of the method of the present invention. As shown in FIG. 17, the box 2 ′ can have a rectangular shape and be composed of a single piece or of two parts 2 ′ a and 2 ′ b detachably fixed to each other so that, when the foundation 1 and the caisson 2 'are built independently of one another on different sites, the caisson 2' can be placed around the foundation 1 after they have been floated.

It goes without saying that the embodiments which have been described above have been given by way of purely indicative and in no way limitative example, and that numerous modifications can be easily made by those skilled in the art without as well depart from the scope of the present invention. Thus, in particular that, if the box 2 or 2 'is formed of two detachable parts, the setting up of the box 2 or 2' around the structure 1 can be carried out not in a port, but outside the port or on the site where the structure 1 must be grounded, the structure 1 and the box 2 or 2 'then being towed separately to the site where they are assembled. Furthermore, although the present invention has been described above in connection with the grounding positioning of a foundation for a bridge pier, the method of the present invention can also be used for positioning by grounding other structures, such as example of the prefabricated underwater tunnel elements. In this case, the box 2 may not completely surround the structure 1 and it can for example be constituted only by the part 2 ′ shown in FIG.

Claims (9)

1. Process for positioning a pre-fabricated structure on a sea or river bottom, the said pre- fabricated structure (1) being capable of floating, and, after being made to float and towed to the desired site, being sunk to the bottom by ballasting, characterised in that it consists in surrounding the said prefabricated structure (1) at least partly by a floating caisson (2, 2') while leaving a play of several metres between the caisson and the structure, then, once the floating unit formed by the caisson and by the structure is at the site where the structure is to be sunk, positioning and orientating the said unit approximately correctly, then sinking the caisson to the bottom by ballasting, and sinking the structure at a precise position and with a precise orientation to the bottom, ballasting the said structure and using the sunken caisson as a fixed point for positioning and orientating the structure.

2. Process according to Claim 1, characterised in that, to sink the structure (1) to the bottom, first the position and orientation of the structure are adjusted using the sunken caisson (2, 2') as a fixed point, then the structure is ballasted to give it an apparent low weight by a quantity of ballast just sufficient to sink it to the sea or river bottom, then the seat, the list and the level of the structure are adjusted, and a cement is then injected below the structure.

3. Process according to Claim 1, characterised in that, to sink the structure (1) to the bottom, it is first ballasted with a quantity of ballast just sufficient for the lower part of the structure to reach the immediate proximity of the sea or river bottom, the position and orientation of the structure on the bottom are then adjusted using the sunken caisson (2, 2') as a fixed point, the structure is ballasted to give it an apparent low weight by an additional quantity of ballast just sufficient to sink it to the bottom, the seat, the list and the level of the structure are then adjusted, and a cement is then injected below the structure.

4. Process according to Claim 2 or 3, characterised in that, after the cement has set, an additional ballasting to the structure (1) is carried out finally to sink it and to keep it definitively in position by gravity.

5. Process according to any of Claims 2 to 4, characterised in that, after the cement has set, the structure (1) is anchored to the bottom to keep it definitively in position.

6. Process according to any of Claims 1 to 5, characterised in that, after the said structure (1) has been sunk to the bottom with a precise orientation and at a precise position, the caisson (2,2') is refloated, separated from the structure (1) and reused to position another structure.

7. Process according to any of Claims 1 to 5, in which the prefabricated structure (1) is a foundation intended to support a non-floating superstructure (18-22) of large height, characterised in that it consists in pre-fabricating the superstructure (18-22) on shore, mounting the pre-fabricated superstructure on the floating caisson (2,2') by means of a provisional support structure (23) and towing to the desired site the unit formed by the floating caisson (2, 2'), the superstructure (18-22) and the foundation (1) if the caisson (2, 2') has already been positioned around the said foundation, and in that, after the foundation (1) has been sunk to the bottom with a precise orientation and at a precise position and after its seat, its list and its level have been adjusted, the ciasson (2, 2') is refloated to a slight extent by removing ballast so as to raise it slightly above the bottom, the position and orientation of the caisson (2, 2') supporting the superstructure (18-22) are then adjusted using the sunken foundation (1) as a fixed point, the caisson (2, 2') is then resunk to the bottom by ballasting, the level of the superstructure (18-22) is then adjusted precisely by using the sunken caisson (2, 2') as a fixed point, so that the superstructure has a position, an orientation and a level which are appropriate with respect to the foundation (1) and, where appropriate, also with respect to other superstructures already installed, the superstructure (18-22) is then reconnected to the foundation (1), the load of the superstructure is transferred and the provisional support structure (23) is detached from the superstructure (18-22) and removed from the caisson (2, 2').

8. Process according to Claim 7, characterised in that, after removing the provisional support structure (23), the caisson (2, 2') is refloated, separated from the foundation (1) and reused to position another foundation.

9. Process according to Claim 7, characterised in that, after the caisson (2,2') has been resunk, it is ballasted further and left in position to serve as a protection against shocks for the foundation (1) in the event of collision with a ship.

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