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

Technical Field

[0001] The present invention relates to the general field of the installation of metallic monopiles in rocky soil, particularly at sea in a rocky seabed covered with a layer of loose soil.

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

[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 about thirty meters deep into the rocky seabed.

[0004] For this purpose, it is known to drill a hole of a specific diameter and depth into the seabed, which consists of a bedrock covered by a layer of loose soil, to install the pile. This drilling is most often carried out from a barge carrying a drilling and grouting rig. Cement is then poured into the hole to secure the pile. Once the load-bearing capacity of the installed pile is ensured by the cement setting, the pile is released so that the barge carrying the drilling and grouting rig can be moved to the location of the next wind turbine.

[0005] This technique for installing the foundations of an offshore wind farm, however, presents numerous drawbacks. In particular, drilling the hole and driving the pile into it carries a risk of instability in the borehole walls within the loose soil layer. Furthermore, this technique leads to excessive cement consumption during the pile anchoring process in the seabed. Moreover, the properties of cement tend to degrade in the marine environment and under the cyclical stresses of waves and wind on the pile. In addition, this technique requires ensuring the verticality and stability of the pile during anchoring, which necessitates significant installation resources and time.

[0006] To overcome these drawbacks, a method for installing a tubular metal monopile in rocky soil was proposed in publication WO 2020 / 025864. This method comprises successively installing a metal tube up to the rock top with a diameter larger than the borehole to retain the loose soil layer; drilling the rocky soil to create a cavity of predetermined diameter and depth; filling the cavity with granular material; arranging the granular material within the cavity by vibration; and installing the monopile in the cavity by vibratory driving or hammering. This installation technique is particularly advantageous because it eliminates the need to seal the monopile with cement, with all the associated disadvantages. NL 2 019 065 describes a device for guiding and vertically supporting a tubular monopile according to the preamble of claim 1. Description of the invention

[0007] In practice, to implement such an installation technique, there is a need for a device to guide and maintain the verticality of the monopile during its placement 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 vertical guidance and support device for a tubular monopile according to claim 1.

[0009] The device according to the invention offers numerous advantages due to its structure. In particular, this device allows for the pre-installation of the support structure above the reinforcement tube, as well as the adjustment of the support structure to the seabed profile. Furthermore, the cage, with its upper section equipped with a door, allows for the lateral insertion of the monopile, thus reducing the required height of the lifting crane.

[0010] During the loading of the monopile, the presence of shock absorbers in the upper part of the cage allows the monopile's kinetic energy to be absorbed by hydrodynamic loads. The monopile is then secured in position and gradually guided down, with blades positioned in the lower part of the cage, in addition to the shock absorbers, being used during the descent to achieve the required verticality.

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

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

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

[0014] In addition, the shock-absorbing pads positioned at the top of the cage can be distributed over at least two rows spaced longitudinally apart.

[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 changed in a radial direction.

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

[0017] Advantageously, the positioning frame is also rotatable around two axes perpendicular to the cage's longitudinal axis and translationally movable along said cage's longitudinal axis. This feature facilitates the lateral installation of the reinforcement tube.

[0018] Even more advantageously, each foot of the support structure includes a plate hinged around an axis perpendicular to the longitudinal axis of the cage.

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

[0020] The support structure may include two central columns which terminate at one upper end with a receiving cone for 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: the consolidation of the excavation with a reinforcing metal tube, drilling into the seabed to the desired depth, filling the excavation with granular materials followed by compacting the granular materials, placing a device as previously defined on the seabed vertically above the excavation, the positioning frame of the support structure being inserted around the upper end of the reinforcing 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, 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 of the monopile, and retrieving the device.

[0023] Preferably, the compaction of 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, the process also includes, in addition to adjusting the cage to the diameter of the monopile, adjusting the pads positioned at the top of the cage and the blades positioned at the bottom of the cage. Brief description of the drawings

[0025] [ Fig. 1 ] There figure 1 is a perspective view of a device for guiding and vertically supporting a monopile according to the invention. Fig. 2 ] There figure 2 shows in detail the positioning framework of the support structure of the device figure 1 . [ Fig. 3 ] There figure 3 shows in detail the shock-absorbing pads of the upper part of the device's cage figure 1 . [ Fig. 4 ] There figure 4 shows in detail the blades of the lower part of the cage of the device figure 1 . [ Fig. 5A] à [Fig. 5D ] THE figures 5A , 5B , 5C And 5D represent an example of different stages of a process for installing a tubular monopile in an excavation made in the seabed using the device according to the invention. Description of the implementation methods

[0026] The invention relates to a device for guiding and vertically maintaining a tubular monopile as shown in the figure 1 .

[0027] 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 reinforcing metal tube allowing the loose soil layer to be held in place as described in particular in publication WO 2020 / 025864.

[0028] According to the invention, the device 2 includes 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.

[0029] Device 2 further includes a frame 8 allowing the positioning of the support structure 4 relative to the reinforcing metal tube (not shown in the figure 1 ) which is used to consolidate the excavation.

[0030] As more precisely depicted on the 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 reinforcing tube.

[0031] For this purpose, the positioning frame 8 includes a lateral opening 10 to position the upper end of the reinforcing tube.

[0032] In addition, the side opening 10 of the positioning frame can be closed by means of a removable closing bar 11.

[0033] Furthermore, to allow adaptation to the surface of the seabed and to facilitate the lateral positioning of the reinforcement tube, the positioning frame 8 is advantageously mobile in rotation around two axes YY and ZZ perpendicular to the longitudinal axis XX of the support structure and is mobile in translation along this longitudinal axis XX.

[0034] For example, a rotational capacity of plus or minus 5° can be given both with respect to the YY axis and with respect to the ZZ axis. This rotational capacity is obtained, for example, through the play of the bearings in vertical guides oriented along the XX axis.

[0035] Device 2 further includes a cage 14 whose longitudinal axis coincides with the longitudinal axis XX of the support structure 4 and which is mounted inside it above the positioning frame 8 in order to receive the monopile.

[0036] More precisely, the cage 14 includes a lower part 14a which is closed and an upper part 14b which is equipped with a door 16 capable of opening to allow lateral insertion of the monopile into the cage and of closing to keep the monopile in the cage.

[0037] The door 16 of the cage 14 includes buffers 18 which are intended to cushion shocks and to guide the monopile during its lateral insertion into the cage.

[0038] 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 designed 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 excessively stressing the monopile, thus ensuring its preservation.

[0039] To that end, as shown in more detail on the figure 3 , at least some of the shock absorber pads positioned at the upper part 14b of the cage are mounted on jacks so as to allow their position to be changed in a radial direction.

[0040] For example, the figure 3 The upper part 14b of the cage comprises seven shock absorbers 20-1 to 20-7 regularly distributed around the longitudinal axis XX of the cage. Among these shock absorbers, two of them (namely the shock absorbers 20-1 and 20-7 which frame the opening of the door 16) are mounted on jacks 22 and are associated with two diametrically opposed fixed shock absorbers (namely the shock absorbers 20-3 and 20-5) so as to ensure homogeneous support of the monopile around the longitudinal axis XX of the cage.

[0041] The position of the fixed supports 26 is adjustable by means of a slide 100 ( figure 3 ) allowing the structure according to the invention to be adapted to several diameters of monopile (for example 3 diameters to be adjusted as needed: 7.0m, 7.5m and 7.75m).

[0042] In general, each shock absorber 20 positioned at the upper part 14b 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 a fixed support 26 on which the rigid shield is mounted by means of at least one fender 28 made of elastomer.

[0043] Based on the example of the implementation of the figure 3 , the rigid shield 24 of each shock absorber is mounted on the fixed support 26 by means of two elastomer fenders 28.

[0044] In an embodiment not shown in the figures, the shock absorbers which are positioned at the top of the cage are distributed over at least two rows spaced longitudinally apart from each other (i.e. spaced along the longitudinal axis of the cage).

[0045] According to the invention, as shown in the 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.

[0046] These 30 blades are designed to radially bear against the monopile when it is inserted into the cage, guiding it during its descent and modifying its inclination relative to the cage's longitudinal axis (for example, by approximately ±0.25° from the vertical). The 30 blades thus ensure tighter guidance, leading to increasingly precise control of the monopile's angle.

[0047] Preferably, these blades 30 are eight in number and at least some of them are mounted on slides 32 so as to allow their position to be changed in a radial direction.

[0048] According to an advantageous provision shown on the figure 1 , each foot 6 of the support structure 4 includes a plate 6a articulated around two axes Y'-Y', Z'-Z' perpendicular to the longitudinal axis XX of the cage in order to allow adjustment of the positioning of the support structure to the surface profile of the seabed.

[0049] According to another advantageous arrangement, one of the 6 feet of the support structure terminates at a high end with a ballast receiving cone 34.

[0050] According to yet another advantageous arrangement, the support structure 4 comprises two central columns 36 which each terminate at one upper end with a cone 38 for receiving a hydraulic lifting tool.

[0051] At the base of the central columns 36, the rigidity of the system allows the forces to be passed on during transport, considering that the structure is secured via the bases of these columns to the deck of the ship.

[0052] In connection with the figures 5A à 5D We will now describe an example of the installation of a tubular monopile in an excavation made in the seabed using the device as described previously.

[0053] 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 top of the rock SR, then an excavation 46 is made in the seabed and the rock SR is drilled to the desired depth. The excavation 46 is then filled with granular material which is subsequently compacted by vibration as described in publication WO 2020 / 025864, the compacted granular material extending above the seabed but below the top of the reinforcing metal tube.

[0054] 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 reinforcing tube 44.

[0055] Once correctly positioned and aligned, the cage door 16 is opened to allow the lateral insertion of the monopile 40. For this purpose, the surface installation vessel lifts the monopile 40 from above using a lifting crane (not shown in the figures) and guides it into the cage by passing the lower end of the monopile laterally through the cage door ( figure 5A ).

[0056] Lateral insertion of the monopile into the cage of the support structure allows the lifting height of the monopile to be limited (compared to a vertical insertion).

[0057] During this insertion process, the buffers positioned at the cage door absorb shocks and guide the monopile inside the cage, while the shock-absorbing buffers distributed throughout the upper part of the cage vertically stabilize the monopile without excessive stress. This damping system effectively allows for significant dynamic movement of the monopile, thus permitting the use of a floating installation vessel rather than one anchored to the ground.

[0058] 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.

[0059] The monopile 40 is then partially driven into the compacted granular materials, preferably initially by gravity and then by vibratory driving implemented using a vibrator 42 mounted on the upper end of the monopile and activated by the lifting crane ( figure 5C ).

[0060] During this partial driving operation of the monopile, its inclination relative to the longitudinal axis XX of the cage is corrected by means of the blades of the lower part of the cage in order to correct any defects in the verticality of the monopile.

[0061] When the monopile 40 is sufficiently driven into the ground (the driving depth is approximately 15m-20m), the participating soil is rigid enough to hold the monopile in a horizontal and angular position. A final adjustment using the damping pads and cage blades is then made to smoothly finalize the vertical positioning of the monopile to plus or minus 0.25° ( figure 5D ).

[0062] It should be noted that once this operation of placing the monopile vertically has been carried out, the soil maintains it in a lateral and angular position and the vibro-driving is continued to reach the desired depth, while maintaining verticality.

[0063] In a final step not shown in the figures, the device can be recovered and brought to the surface on the installation vessel.

[0064] Preferably, the process includes, in addition to adjusting the cage to the diameter of the monopile, adjusting the pads positioned at the top of the cage and the blades positioned at the bottom of said cage.

Claims

1. A device (2) for guiding and vertically maintaining a tubular monopile (40) when it is placed in an excavation (46) made in a seabed, filled with compacted granular materials and consolidated by a metal reinforcement tube (44), comprising: - a support structure (4) intended to be positioned vertically to the excavation (46) made in the seabed and mounted on at least four feet (6) which are each adjustable in height; - a cage (14) extending along a longitudinal axis (X-X) and mounted inside the support structure in order to receive the monopile, the cage comprising a closed low portion (14a) and a high portion (14b) provided with a door (16) able to open to allow lateral introduction of the monopile into the cage and able to close to maintain the monopile in the cage; and - the high portion (14b) of the cage comprises a plurality of damping pads (20) distributed around the longitudinal axis (X-X) of the cage, dimensioned to allow distributed contact with the monopile, and able to dampen the dynamics of the monopile and come radially into abutment against the monopile when it is introduced into the cage in order to stabilize and modify its inclination relative to the longitudinal axis of the cage; characterized in that: - the device further comprises a frame for positioning (8) the support structure relative to the reinforcement tube, the positioning frame having a closed U shape, and being intended to ensure the positioning of the support structure relative to an upper end of the reinforcement tube (44); - the cage (14) is mounted above the positioning frame; and - low portion (14a) of the cage comprises a plurality of blades (30) extending along the longitudinal axis (X-X) of the cage and distributed around it, said blades being dimensioned to allow distributed contact with the monopile, able to come radially into abutment against the monopile when it is introduced 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 reaching a sufficient soil resistance to naturally maintain the positioning in angle and in translation.

2. The device according to claim 1, wherein at least some of the damping pads (20-1, 20-7) positioned at the level of the high portion of the cage are mounted on a cylinder (22) so as to allow modifying their position along a radial direction.

3. The device according to claim 2, wherein the damping pads mounted on a cylinder are two in number and are associated with two diametrically opposite fixed damping pads (20-3, 20-5) so as to make sure to homogeneously maintain the monopile around the longitudinal axis of the cage.

4. The device according to any one of claims 1 to 3, wherein each damping pad positioned at the level of the high portion of the cage comprises a rigid shield (24) which is intended to come into abutment 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. The device according to any one of claims 1 to 4, wherein the damping pads positioned at the level of the high portion of the cage are distributed over at least two rows longitudinally spaced from each other.

6. The device according to any one of claims 1 to 5, wherein at least some of the blades (30) positioned at the level of the low portion of the cage are mounted on slides (32) so as to allow modifying their position along a radial direction.

7. The device according to any one of claims 1 to 6, wherein the door (16) of the cage (14) comprises pads (18) intended to absorb shocks and to ensure guidance of the monopile during its lateral introduction into the cage.

8. The device according to any one of claims 1 to 7, wherein the positioning frame (8) is movable in rotation around two axes (Y-Y, Z-Z) perpendicular to the longitudinal axis (X-X) of the cage and is movable in translation along said longitudinal axis of the cage.

9. The device according to any one of claims 1 to 8, wherein each foot (6) of the support structure comprises a plate (6a) articulated around an axis (6b) perpendicular to the longitudinal axis (X-X) of the cage.

10. The device according to any one of claims 1 to 9, wherein one of the feet ends at a high end with a cone (34) for receiving ballast.

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

12. The device according to any one of claims 1 to 11, wherein the frame for positioning the support structure comprises a removable closing bar.

13. A method for placing a tubular monopile in an excavation (46) made in the seabed, successively comprising: - consolidating the excavation (46) with a metal reinforcement tube (44), - drilling the seabed to the desired depth, - filling the excavation with granular materials then compacting the granular materials, - depositing on the seabed vertically to the excavation a device (2) according to any one of claims 1 to 12, the frame for positioning (8) the support structure (4) being introduced around the upper end of the reinforcement tube; - lifting the monopile (40) from above; - guiding the monopile to introduce 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 verticality defects of the monopile; and - recovering the device.

14. The 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-sinking.

15. The method according to any of claims 13 and 14, further comprising the adjustment of the cage to the diameter of the monopile by setting the pads positioned at the level of the high portion of the cage and the blades positioned at the level of the low portion of said cage.

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