Device for guiding and vertically holding a monopile and method for installing a monopile using such a device

Abstract

The invention relates to a device (2) for guiding and vertically holding a tubular monopile during its installation in an excavation made in a seabed, which excavation is filled with compacted granular materials and consolidated by a metal reinforcing tube, the device comprising: a support structure (4) mounted on four feet (6) each adjustable in height, a frame (8) for positioning the support structure with respect to the reinforcing tube, having a closed U shape, a cage (14) mounted inside the support structure above the positioning frame in order to receive the monopile, the cage comprising a closed lower portion (14a) and an upper portion (14b) provided with a door (16) to allow lateral insertion of the monopile into the cage, the upper portion of the cage comprising a plurality of damping pads (20) capable of damping the dynamics of the monopile and remaining bearing radially against the monopile when it is inserted into the cage in order to stabilise and modify its inclination, and the lower portion of the cage comprising a plurality of blades (30) capable of bearing radially against the monopile when it is inserted into the cage in order to guide it as it descends into the cage and to modify its inclination.

Description

Description Title of the invention: Device for guiding and vertically maintaining a monopile and method for installing a monopile using such a device Technical Field

[0001] The present invention relates to the general field of the installation of metal monopiles in rocky ground, in particular at sea in a rocky seabed covered with a layer of soft soil.

[0002] A non-limiting example of the field of application of the invention is that of the installation of the foundations of an offshore wind farm. Prior art

[0003] Typically, an offshore wind turbine is installed at sea using a foundation consisting of a very large diameter tubular metal monopile, generally around 7 to 8m in diameter, which is driven around thirty meters deep into the rocky seabed.

[0004] For this purpose, it is known to drill the seabed composed of a bedrock covered by a layer of soft soil with a hole of given diameter and depth to install the pile. This drilling is most often carried out from a barge carrying a drilling and cementing workshop. Cement is then poured into the hole to seal the pile in the hole. When the bearing capacity of the pile thus installed is ensured by the holding of the cement, the pile is released to be able to move the barge carrying the drilling and cementing workshop to the location of the next wind turbine.

[0005] This technique for laying the foundations of an offshore wind farm, however, has many disadvantages. In particular, drilling the hole and installing the pile in it leads to a risk of instability of the walls of the hole in the soft soil layer. Furthermore, this technique results in excessive consumption of cement when sealing the pile in the seabed. In addition, the properties of cement tend to deteriorate in a marine environment and under the cyclical conditions of wave and wind forces on the pile. In addition, this technique requires ensuring the verticality and stability of the pile during its sealing, which requires substantial installation resources and time.

[0006] To overcome these drawbacks, publication WO 2020 / 025864 has proposed a method for installing a tubular metal monopile in rocky soil, comprising successively installing a metal tube up to the roof of the rock with a diameter larger than the borehole to maintain the loose soil layer, drilling the rocky soil to form a cavity of predetermined diameter and depth, filling the cavity with a granular material, arranging the granular material present in the cavity by vibration, and installing the monopile in the cavity by vibro-driving or by ramming. This installation technique is particularly advantageous in that it makes it possible to eliminate the need to seal the monopile with cement with all the drawbacks that this entails. Statement of the invention

[0007] In practice, to implement such an installation technique, there is a need to have a device for guiding and vertically maintaining the monopile during its installation in the excavation made in a seabed and filled with compacted granular materials.

[0008] According to the invention, this need is met by means of a device for guiding and vertically maintaining a tubular monopile during its installation in an excavation made in a seabed, filled with compacted granular materials and consolidated by a reinforcing metal tube, comprising: a support structure intended to be positioned vertically above the excavation made in the seabed and mounted on at least four feet which are each adjustable in height; - a frame for positioning the support structure relative to the reinforcement tube, the positioning frame having a closed U shape, being mounted on a lower part of the support structure and being intended to ensure the positioning of the support structure relative to an upper end of the reinforcement tube; - a cage extending along a longitudinal axis and mounted inside the support structure above the positioning frame in order to receive the monopile, the cage comprising a closed lower part and an upper part provided with a door capable of opening to allow lateral insertion of the monopile into the cage and of closing to maintain the monopile in the cage; - the upper part of the cage comprises a plurality of damping pads distributed around the longitudinal axis of the cage, sized to allow distributed contact with the monopile, and capable of damping the dynamics of the monopile and maintaining radial support against the monopile when it is inserted into the cage in order to stabilize and modify its inclination relative to the longitudinal axis of the cage; and - the lower part of the cage comprises a plurality of blades extending along the longitudinal axis of the cage and distributed around it, said blades being sized to allow distributed contact with the monopile, capable of coming to bear radially against the monopile when it is inserted into the cage in order to guide it during its descent into the cage and to modify its inclination relative to the longitudinal axis of the cage until sufficient ground resistance is reached to naturally maintain the positioning in angle and in translation.

[0009] The device according to the invention has many advantages due to its structure. In particular, this device allows the pre-installation of the support structure above the reinforcement tube, as well as the adjustment of the support structure to the profile of the seabed. In addition, the cage with its upper part equipped with a door allows for lateral insertion of the monopile, which limits the height criteria of the lifting crane.

[0010] During loading of the monopile, the presence of the damping pads in the upper part of the cage allows to absorb the energy of movement of the monopile due to hydrodynamic loads. The monopile is then captured in position and gradually guided in its descent, implementing during the descent, in addition to the damping pads, blades positioned in the lower part of the cage to achieve the required verticality.

[0011] At least some of the shock absorbers positioned at the upper part of the cage can be mounted on a jack so as to allow their position to be modified in a radial direction.

[0012] In this case, the shock absorbers mounted on the jack are preferably two in number and are associated with two diametrically opposed fixed shock absorbers so as to ensure uniform support of the monopile around the longitudinal axis of the cage.

[0013] Each shock absorber positioned at the upper part of the cage may comprise a rigid shield which is intended to bear against the monopile to distribute the contact pressure and limit friction, and which is mounted on a fixed support by means of at least one defense made of elastomer.

[0014] In addition, the shock absorbers positioned at the upper part of the cage can be distributed over at least two rows spaced longitudinally from each other.

[0015] Furthermore, at least some of the blades positioned at the lower part of the cage can be mounted on slides so as to allow their position to be modified in a radial direction.

[0016] Advantageously, the cage door includes buffers intended to absorb shocks and ensure guidance of the monopile during its lateral insertion into the cage.

[0017] Advantageously also, the positioning frame is movable in rotation around two axes perpendicular to the longitudinal axis of the cage and is movable in translation along said longitudinal axis of the cage. This characteristic makes it easier to install the reinforcement tube laterally.

[0018] Advantageously, each foot of the support structure comprises a plate articulated around an axis perpendicular to the longitudinal axis of the cage.

[0019] Preferably, one of the legs terminates at a high end with a ballast receiving cone.

[0020] The support structure may comprise two central columns which terminate at a high end with a cone for receiving a hydraulic lifting tool.

[0021] In addition, the positioning frame of the support structure may include a removable closing bar.

[0022] The invention also relates to a method for installing a tubular monopile in an excavation made in the seabed, comprising successively: - consolidation of the excavation with a metal reinforcement tube, - drilling the seabed to the desired depth, - filling the excavation with granular materials followed by compaction of the granular materials, - the placement on the seabed vertically above the excavation of a device as defined previously, the positioning frame of the support structure being inserted around the upper end of the reinforcement tube, - lifting the monopile from above, - guiding the monopile to insert it inside the cage by passing the lower end of the monopile laterally through the cage door, - lowering the monopile into the cage, - partial driving of the monopile into the compacted granular materials while correcting its inclination relative to the longitudinal axis of the cage to correct verticality defects of the monopile, and - recovery of the device.

[0023] Preferably, the compaction of the granular materials is carried out by vibration and the partial driving of the monopile into the compacted granular materials is carried out by vibro-driving.

[0024] Preferably also, the method comprises, in addition to adjusting the cage to the diameter of the monopile, adjusting the buffers positioned at the upper part of the cage and the blades positioned at the lower part of said cage. Brief description of the drawings

[0025] [Fig. 1] Figure 1 is a perspective view of a device for guiding and vertically maintaining a monopile according to the invention.

[0026] [Fig. 2] Figure 2 shows in detail the positioning frame of the support structure of the device of Figure 1.

[0027] [Fig. 3] Figure 3 shows in detail the shock absorbers of the upper part of the cage of the device of Figure 1.

[0028] [Fig. 4] Figure 4 shows in detail the blades of the lower part of the cage of the device of Figure 1.

[0029] [Fig. 5A] to [Fig. 5D] Figures 5A, 5B, 5C and 5D represent an example of different steps of a method of installing a tubular monopile in an excavation made in the seabed using the device according to the invention. Description of the embodiments

[0030] The invention relates to a device for guiding and vertically maintaining a tubular monopile as shown in Figure 1.

[0031] It finds a particularly advantageous application in the installation of such a monopile in an excavation made in a seabed, filled with compacted granular materials and consolidated by a metal reinforcing tube making it possible to maintain the layer of loose soil as described in particular in publication WO 2020 / 025864.

[0032] According to the invention, the device 2 comprises in particular a support structure 4 which is intended to be positioned vertically above the excavation made in the seabed and which is mounted on at least four feet 6 which are each adjustable in height.

[0033] The device 2 further comprises a frame 8 allowing the positioning of the support structure 4 relative to the reinforcing metal tube (not shown in Figure 1) which is used to consolidate the excavation.

[0034] As shown more precisely in Figure 2, this positioning frame 8 has a U shape and is mounted on a lower part of the support structure 4. It is intended to ensure the positioning of the support structure relative to the upper end of the reinforcement tube.

[0035] For this purpose, the positioning frame 8 comprises a lateral opening 10 for positioning the upper end of the reinforcement tube.

[0036] In addition, the side opening 10 of the positioning frame can be closed by means of a removable closing bar 11.

[0037] Furthermore, to enable adaptation to the surface of the seabed and to facilitate lateral positioning of the reinforcement tube, the positioning frame 8 is advantageously movable in rotation around two axes YY and ZZ perpendicular to the longitudinal axis XX of the support structure and is movable in translation along this longitudinal axis XX.

[0038] For example, a rotation capacity of plus or minus 5° can be given both with respect to the YY axis and with respect to the ZZ axis. This capacity of rotation is for example obtained thanks to the play of the bearings in vertical guides oriented along the XX axis.

[0039] The device 2 also comprises a cage 14 whose longitudinal axis coincides with the longitudinal axis XX of the support structure 4 and which is mounted inside the latter above the positioning frame 8 in order to receive the monopile.

[0040] More precisely, the cage 14 comprises a lower part 14a which is closed and an upper part 14b which is provided with a door 16 capable of opening to allow lateral insertion of the monopile into the cage and of closing to maintain the monopile in the cage.

[0041] The door 16 of the cage 14 includes buffers 18 which are intended to absorb shocks and to ensure guidance of the monopile during its lateral insertion into the cage.

[0042] Furthermore, the upper part 14b of the cage comprises a plurality of damping pads 20 which are distributed around the longitudinal axis XX of the cage. These damping pads 20 are capable of coming to bear radially against the monopile when it is inserted into the cage in order to stabilize and modify its inclination relative to the longitudinal axis of the cage, without stressing the monopile too strongly, thus ensuring its preservation.

[0043] For this purpose, as shown in more detail in Figure 3, at least some of the damping buffers positioned at the upper part 14b of the cage are mounted on a jack so as to allow their position to be modified in a radial direction.

[0044] In the example of Figure 3, the upper part 14b of the cage comprises seven damping buffers 20-1 to 20-7 regularly distributed around the longitudinal axis XX of the cage. Among these damping buffers, two of them (namely the damping buffers 20-1 and 20-7 which frame the opening of the door 16) are mounted on a jack 22 and are associated with two diametrically opposed fixed damping buffers (namely the damping buffers 20-3 and 20-5) so as to ensure uniform support of the monopile around the longitudinal axis XX of the cage.

[0045] The position of the fixed supports 26 is adjustable by means of a slider 100 (figure 3) making it possible to adapt the structure according to the invention to several monopile diameters (for example 3 diameters to be adjusted as required: 7.0m, 7.5m and 7.75m).

[0046] Generally, each shock absorber 20 positioned at the upper part 14b of the cage comprises a rigid shield 24 which is intended to bear against the monopile to distribute the contact pressure and limit friction, and a fixed support 26 on which the rigid shield is mounted by means of at least one defense 28 made of elastomer.

[0047] In the embodiment of Figure 3, the rigid shield 24 of each shock absorber buffer is mounted on the fixed support 26 by means of two elastomer fenders 28.

[0048] In an embodiment not shown in the figures, the shock absorbers which are positioned at the upper part of the cage are distributed over at least two rows spaced longitudinally from each other (i.e. spaced along the longitudinal axis of the cage).

[0049] Still according to the invention, as shown in Figure 4, the lower part 14a of the cage 14 comprises a plurality of blades 30 which extend along the longitudinal axis XX and which are distributed around it.

[0050] These blades 30 are capable of coming to bear radially against the monopile when it is inserted into the cage in order to guide it during its descent into the cage and to modify its inclination relative to the longitudinal axis of the cage (for example of the order of plus or minus 0.25° relative to the vertical). The blades 30 thus ensure a tightening of the guidance, leading to ever more precise control of the angle of the monopile.

[0051] Preferably, there are eight of these blades 30 and at least some of them are mounted on slides 32 so as to allow their position to be modified in a radial direction.

[0052] According to an advantageous arrangement shown in Figure 1, each foot 6 of the support structure 4 comprises a plate 6a articulated around two axes Y'- Y', Z'-Z' perpendicular to the longitudinal axis XX of the cage in order to allow the positioning of the support structure to be adjusted to the surface profile of the seabed.

[0053] According to another advantageous arrangement, one of the feet 6 of the support structure ends at a high end with a ballast receiving cone 34.

[0054] According to yet another advantageous arrangement, the support structure 4 comprises two central columns 36 which each terminate at a high end with a cone 38 for receiving a hydraulic lifting tool.

[0055] At the foot of the central columns 36, the rigidity of the system allows the forces to be transmitted during transport, considering that the structure is secured via the feet of these columns to the deck of the ship.

[0056] In connection with Figures 5A to 5D, an example of the installation of a tubular monopile in an excavation made in the seabed using the device as described previously will now be described.

[0057] According to a preliminary step not shown in the figures, a reinforcing metal tube 44 is placed in the soft soil SM up to the roof of the rock SR, then an excavation 46 is made in the seabed and the rock S-R is drilled to the desired depth. The excavation 46 is then filled with granular materials which are then compacted by vibration as described in publication WO 2020 / 025864, the compacted granular materials coming up to above the seabed but under the upper part of the reinforcing metal tube.

[0058] The device 2 according to the invention is then placed on the seabed vertically above the excavation 46 from a surface installation vessel, the positioning frame 8 of the support structure being inserted around the upper end of the reinforcement tube 44.

[0059] Once correctly positioned and aligned, the cage door 16 is opened to allow the lateral insertion of the monopile 40. For this purpose, the vessel surface installation lifts the monopile 40 from above using a lifting crane (not shown in the figures) and guides it to insert it inside the cage by passing the lower end of the monopile laterally through the cage door (figure 5A).

[0060] The lateral insertion of the monopile into the cage of the support structure makes it possible to limit the lifting height of the monopile (compared to a vertical insertion).

[0061] During this insertion, the buffers positioned at the cage door allow shock absorption and ensure the monopile is guided inside the cage and the shock absorbers distributed in the upper part of the cage allow the monopile to be stabilized vertically, without excessively constraining it. The damping system in fact allows significant dynamics of the monopile to be tolerated and thus allows the use of a floating installation vessel not moored to the ground.

[0062] Once the monopile 40 is inserted into the upper part 14b of the cage, it is guided by means of the lifting crane towards the bottom of the cage (figure 5B). Initially, the monopile 40 passes between the blades of the lower part of the cage, tightening the guidance, then comes to touch the roof of the compacted granular materials filling the excavation 46.

[0063] The monopile 40 is then partially driven into the compacted granular materials, preferably initially by gravity and then by vibratory driving implemented by means of a vibrator 42 mounted on the upper end of the monopile and activated by the lifting crane (figure 5C).

[0064] During this operation of partial driving of the monopile, its inclination relative to the longitudinal axis XX of the cage is corrected in particular by means of the blades of the lower part of the cage so as to correct any defects in the verticality of the monopile.

[0065] When the monopile 40 is sufficiently driven into the ground (the driving depth is about 15m-20m), the participating soil is rigid enough to keep the monopile in a horizontal and angular position. A final adjustment using the shock absorbers and cage blades is then carried out to smoothly finalize the vertical positioning of the monopile to plus or minus 0.25° (figure 5D).

[0066] It should be noted that once this operation of placing the monopile vertical has been carried out, the ground maintains it in a lateral and angular position and the vibratory driving is continued to reach the desired depth, while maintaining verticality.

[0067] In a final step not shown in the figures, the device can be recovered and brought to the surface on the installation vessel.

[0068] Preferably, the method further comprises adjusting the cage to the diameter of the monopile by adjusting the buffers positioned at the upper part of the cage and the blades positioned at the lower part of said cage.

Claims

Demands

1. Device (2) for guiding and vertically maintaining a tubular monopile (40) during its installation in an excavation (46) made in a seabed, filled with compacted granular materials and reinforced by a metal tube (44), comprising: - a support structure (4) intended to be positioned vertically above the excavation (46) made in the seabed and mounted on at least four feet (6) which are each adjustable in height; - a positioning frame (8) of the support structure relative to the reinforcing tube, the positioning frame having a closed U shape, being mounted on a lower part of the support structure (4) and intended to ensure the positioning of the support structure relative to an upper end of the reinforcing tube (44); - a cage (14) extending along a longitudinal axis (XX) and mounted inside the support structure above the positioning frame to receive the monopile, the cage comprising a closed lower part (14a) and an upper part (14b) equipped with a door (16) capable of opening to allow lateral insertion of the monopile into the cage and closing to retain the monopile in the cage; - the upper part (14b) of the cage comprises a plurality of damping pads (20) distributed around the longitudinal axis (XX) of the cage, dimensioned to allow distributed contact with the monopile, and capable of dampening the dynamics of the monopile and maintaining radial support against the monopile when it is inserted into the cage in order to stabilize and modify its inclination relative to the longitudinal axis of the cage; and - the lower part (14a) of the cage comprises a plurality of blades (30) extending along the longitudinal axis (XX) of the cage and distributed around it, said blades being dimensioned to allow distributed contact with the monopile, capable of radially bearing against the monopile when it is inserted into the cage in order to guide it during its descent into the cage and to modify its inclination relative to the longitudinal axis of the cage until it reaches a soil resistance sufficient to naturally maintain the positioning in angle and in translation.

2. Device according to claim 1, wherein at least some of the shock absorber pads (20-1, 20-7) positioned at the upper part of the cage are mounted on a jack (22) so as to allow their position to be changed in a radial direction.

3. Device according to claim 2, wherein the cylinder-mounted shock absorber pads are two in number and are associated with two diametrically opposed fixed shock absorber pads (20-3, 20-5) so as to ensure homogeneous support of the monopile around the longitudinal axis of the cage.

4. Device according to any one of claims 1 to 3, in which each shock absorber positioned at the upper part of the cage includes a rigid shield (24) which is intended to bear against the monopile to distribute the contact pressure and limit friction, and which is mounted on a fixed support (26) by means of at least one fender (28) made of elastomer.

5. Device according to any one of claims 1 to 4, in which the shock absorbers positioned at the upper part of the cage are distributed over at least two rows spaced longitudinally apart.

6. Device according to any one of claims 1 to 5, wherein at least some of the blades (30) positioned at the lower part of the cage are mounted on slides (32) so as to allow their position to be changed in a radial direction.

7. Device according to any one of claims 1 to 6, wherein the door (16) of the cage (14) includes buffers (18) intended to cushion shocks and to provide guidance of the monopile during its lateral insertion into the cage.

8. Device according to any one of claims 1 to 7, in which the positioning frame (8) is mobile in rotation around two axes (Y-Y, ZZ) perpendicular to the longitudinal axis (XX) of the cage and is mobile in translation along said longitudinal axis of the cage.

9. Device according to any one of claims 1 to 8, wherein each foot (6) of the support structure comprises a plate (6a) hinged about an axis (6b) perpendicular to the longitudinal axis (XX) of the cage.

10. Device according to any one of claims 1 to 9, in which one of the feet terminates at a high end with a ballast receiving cone (34).

11. Device according to any one of claims 1 to 10, in which the support structure comprises two central columns (36) which terminate at one upper end with a cone (38) for receiving a hydraulic lifting tool.

12. Device according to any one of claims 1 to 11, in which the positioning frame of the support structure includes a removable closing bar.

13. A method for installing a tubular monopile in an excavation (46) made in the seabed, comprising successively: - the consolidation of the excavation (46) by a reinforcing metal tube (44), - drilling into the seabed to the desired depth, - filling the excavation with granular materials followed by compaction of the granular materials, - the placement on the seabed vertically of the excavation of a device (2) according to any one of claims 1 to 12, the positioning frame (8) of the support structure (4) being inserted around the upper end of the reinforcing tube; - lifting the monopile (40) from above; - guiding the monopile to insert it inside the cage (14) by passing the lower end of the monopile laterally through the door (16) of the cage; - lowering the monopile into the cage; - partially driving the monopile into the compacted granular materials while correcting its inclination relative to the longitudinal axis of the cage to correct any verticality defects in the monopile; and - recovery of the device.

14. Method according to claim 13, wherein the compaction of the granular materials is carried out by vibration and the partial driving of the monopile into the compacted granular materials is carried out by vibro-driving.

15. A method according to any one of claims 13 and 14, further comprising adjusting the cage to the diameter of the monopile by adjusting the pads positioned at the top of the cage and the blades positioned at the bottom of said cage.

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