Apparatus for guiding and vertically holding a monopile and method for installing a monopile using such an apparatus

Abstract

Apparatus for guiding and vertically holding a monopile and method of installing a monopile using such an apparatus. The present invention relates to an apparatus (2) for guiding and vertically maintaining a tubular monopile when the tubular monopile is disposed in a bored hole formed in the seabed, filled with a compressed granular material and strengthened by a metal reinforcement pipe, the apparatus comprising a support structure (4) attached to four legs (6) each having an adjustable height, a frame (8) having a closed U-shape for positioning the support structure relative to the reinforcement pipe, and a cage (14) attached inside the support structure above the positioning frame for receiving the monopile, the cage comprising a closed bottom (14a) and a top (14b) provided with a door (16) for enabling introduction of the monopile into the cage from the side, the top of the cage being capable of damping the dynamics of the monopile when the monopile is introduced into the cage and being provided with a plurality of damping pads (20) capable of radially abutting against the monopile to stabilize and change the inclination of the monopile, and the bottom of the cage being provided with a plurality of blades (30) capable of radially abutting against the monopile for guiding the monopile during its descent into the cage and for changing the inclination of the monopile when the monopile is introduced into the cage.

Description

Technical Field

[0001] The present invention relates in particular to the general field of installing metal monopiles in rocky seabeds covered by layers of soft soil in the sea. A non-limiting example of the application field of the present invention is to place the foundation of an offshore wind farm.

Background Art

[0002] Typically, an offshore wind turbine is installed in the sea using a foundation consisting of a tubular metal monopile generally having a very large diameter of about 7-8 m, which is inserted into a rocky seabed at a depth of about 30 m.

[0003] For this purpose, it is known to drill a hole of a given diameter and depth in a seabed composed of bedrock covered by a layer of soft soil and install a pile therein. This drilling is most often carried out from a barge supporting the drilling and cementing equipment. Next, cement is poured into the hole to seal the pile in the hole. Once the bearing capacity of the pile installed in this way is ensured by the action of the cement, the pile is released so that the barge carrying the drilling and cementing equipment can be moved to the location of the next wind turbine.

[0004] However, this method of placing the foundation of an offshore wind farm has many disadvantages. In particular, when drilling a hole and placing a pile therein, there is a risk that the walls of the hole will become unstable in the soft soil layer. Furthermore, this method results in excessive consumption of cement when sealing the pile to the seabed. In addition, the properties of the cement tend to deteriorate under the periodic conditions of the marine environment and the undulations and wind forces on the pile. Moreover, this method requires ensuring the verticality and stability of the pile during sealing, which requires a significant amount of installation means and time.

[0005] To address these drawbacks, a method of installing a tubular metal monopile in rocky ground has been proposed in Patent Document 1. This method involves installing a metal pipe with a diameter larger than that of the drill to the top of the rock to maintain a loose soil layer, excavating the rocky ground to form a cavity of a predetermined diameter and depth, filling the cavity with granular material, arranging the granular material present in the cavity by vibration, and continuously installing the monopile into the cavity by vibration embedding or driving. This installation method is particularly advantageous in that it makes it possible to eliminate the need to seal the monopile with cement and all the associated drawbacks.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In fact, in order to implement such an installation method, when a monopile is placed in an excavation hole formed on the seabed and filled with compressed granular material, a device is required to guide the monopile and keep it vertical.

Means for Solving the Problems

[0008] According to the present invention, this need is met thanks to a device for guiding and vertically maintaining a tubular monopile when the tubular monopile is placed in an excavation hole formed on the seabed, filled with compressed granular material, and strengthened by a metal reinforcement pipe. The device includes: a support structure intended to be vertically positioned in an excavation hole formed on the seabed, the support structure being attached to at least four legs with adjustable heights respectively; A frame for positioning a support structure relative to a reinforcement pipe, the positioning frame having a closed U-shape and being attached to the lower part of the support structure, and being intended to ensure the positioning of the support structure relative to the upper end of the reinforcement pipe, and a frame; A cage extending along a longitudinal axis and attached inside the support structure above the positioning frame for receiving a monopile, the cage having a closed lower part and an upper part provided with a door that can be opened to allow the introduction of the monopile into the cage from the side and can be closed to maintain the monopile within the cage, and a cage; The upper part of the cage comprises a plurality of damping pads distributed around the longitudinal axis of the cage, the damping pads being dimensioned to allow distributed contact with the monopile and being capable of damping the dynamics of the monopile when the monopile is introduced into the cage to stabilize and change the inclination of the monopile relative to the longitudinal axis of the cage, and being capable of radially abutting against the monopile; The lower part of the cage comprises a plurality of blades extending along and distributed around the longitudinal axis of the cage, the blades being dimensioned to allow distributed contact with the monopile and being capable of radially abutting against the monopile when the monopile is introduced into the cage to guide the monopile during its descent into the cage and to change the inclination of the monopile relative to the longitudinal axis of the cage until sufficient soil resistance is reached to naturally maintain the positioning in terms of angle and translation.

[0009] The device according to the present invention has many advantages due to its structure. In particular, this device enables the pre-installation of a support structure on a reinforcement pipe and also enables the adjustment of the support structure to the shape of the seabed. Furthermore, the cage equipped with a door at its upper part allows the introduction of the monopile from the side, thereby limiting the height criteria of the lifting crane.

[0010] During the installation of the monopile, the presence of damping pads at the upper part of the cage makes it possible to absorb the kinetic energy of the monopile due to hydrodynamic loads. The monopile is then captured in place and gradually guided during its descent. During the descent, in addition to the damping pads, blades positioned at the lower part of the cage are also implemented to achieve the required verticality.

[0011] At least some of the damping pads positioned at the height of the upper part of the cage can be attached to a cylinder so that they can change their positions along the radial direction. In this case, the number of damping pads attached to the cylinder is preferably two, and these damping pads are associated with two diametrically opposed fixed damping pads so as to reliably maintain the monopile uniformly around the longitudinal axis of the cage.

[0012] Each damping pad positioned at the height of the upper part of the cage can be provided with a rigid shield intended to abut against the monopile to disperse the contact pressure and limit friction. The rigid shield is attached to the fixed support by at least one fender made of elastomer.

[0013] In addition, the damping pads positioned at the height of the upper part of the cage can be dispersed in at least two rows spaced apart longitudinally from each other. Furthermore, at least some of the blades positioned at the height of the lower part of the cage can be attached to a slide so that they can change their positions along the radial direction.

[0014] Advantageously, the door of the cage is provided with pads intended to absorb shocks and ensure the guidance of the monopile during the lateral insertion of the monopile into the cage. Also advantageously, the positioning frame is rotatably movable about two axes orthogonal to the longitudinal axis of the cage and is translatable along the longitudinal axis of the cage. This feature facilitates the lateral insertion of the reinforcement pipe.

[0015] More preferably, each leg of the support structure comprises a plate articulated about an axis perpendicular to the longitudinal axis of the cage. Preferably, one of the legs terminates at its upper end in a cone for receiving ballast.

[0016] The support structure can comprise two central struts ending at their upper end in a cone for receiving a hydraulic lifting tool. In addition, the frame for positioning the support structure can comprise a removable closing bar.

[0017] The invention also relates to a method of placing a tubular monopile in a borehole formed in the seabed, the method comprising: strengthening the borehole with a metal reinforcement pipe; excavating the seabed to a desired depth; filling the borehole with a granular material and then compressing the granular material; vertically placing in the borehole on the seabed the apparatus defined above, with the frame for positioning the support structure being introduced around the upper end of the reinforcement pipe; lifting the monopile from above; guiding the monopile to introduce it inside the cage by passing the lower end of the monopile laterally through the door of the cage; lowering the monopile inside the cage; partially driving the monopile into the compressed granular material while correcting the inclination of the monopile with respect to the longitudinal axis of the cage to correct for poor verticality of the monopile; and continuously recovering the apparatus.

[0018] Preferably, compressing the granular material is carried out by vibration and driving the monopile partially into the compressed granular material is carried out by vibro - embedding. Preferably, this method further includes adjusting the cage according to the diameter of the monopile by setting pads positioned at the height of the upper part of the cage and blades positioned at the height of the lower part of the cage.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5A

Figure 5B

Figure 5C

Figure 5D

Embodiments for Carrying Out the Invention

[0020] The present invention relates to an apparatus for guiding and vertically maintaining a tubular monopile as represented in Figure 1. The present invention is particularly advantageously applied to placing such a monopile into an excavation hole formed on the seabed and strengthened by a metal reinforcement pipe filled with compressed granular material and capable of maintaining a loose soil layer, as described in particular in Patent Document 1.

[0021] According to the present invention, the apparatus 2 particularly comprises a support structure 4 intended to be positioned vertically in a borehole formed in the seabed, the support structure 4 being attached to at least four legs 6 with adjustable heights respectively.

[0022] The apparatus 2 further comprises a frame 8 enabling the positioning of the support structure relative to a metal reinforcement pipe (not shown in FIG. 1) used to strengthen the borehole. As specifically represented by FIG. 2, this positioning frame 8 has a U-shape and is attached to the lower part of the support structure 4. The positioning frame is intended to ensure the positioning of the support structure relative to the upper end of the reinforcement pipe.

[0023] For this purpose, the positioning frame 8 comprises a lateral opening 10 for positioning the upper end of the reinforcement pipe. In addition, the lateral opening 10 of the positioning frame can be closed by a removable closing bar 11.

[0024] Furthermore, to enable adaptation to the seabed surface and facilitate positioning from the side of the reinforcement pipe, the positioning frame 8 is advantageously rotatable about two axes Y-Y and an axis Z-Z perpendicular to the longitudinal axis X-X of the support structure, and is translatable along this longitudinal axis X-X.

[0025] For example, a rotational ability of about ±5° can be provided for both the axis Y-Y and the axis Z-Z. This rotational ability is obtained, for example, thanks to the clearance of the bearing in a vertical guide directed along the axis X-X.

[0026] The apparatus 2 also comprises a cage 14 whose longitudinal axis coincides with the longitudinal axis X-X of the support structure 4, the cage 14 being attached inside the support structure 4 above the positioning frame 8 to receive the monopile.

[0027] More specifically, the cage 14 includes a closed lower part 14a and an upper part 14b provided with a door 16 that can be opened to allow the introduction of the monopile from the side into the cage and can be closed to maintain the monopile within the cage.

[0028] The door 16 of the cage 14 is provided with a pad 18 intended to absorb shocks and ensure the guidance of the monopile during the lateral insertion of the monopile into the cage. Furthermore, the upper part 14b of the cage includes a plurality of damping pads 20 distributed around the longitudinal axis X-X of the cage. These damping pads 20 can radially abut against the monopile when the monopile is introduced into the cage, so as to stabilize and change the inclination of the monopile with respect to the longitudinal axis of the cage without overly strongly restraining the monopile, thus ensuring its retention.

[0029] For this purpose, as shown in more detail in FIG. 3, at least some of the damping pads positioned at the height of the upper part 14b of the cage are attached to cylinders so that they can change their positions along the radial direction.

[0030] In the example of FIG. 3, the upper part 14b of the cage includes seven damping pads 20-1 to 20-7 evenly distributed around the longitudinal axis X-X of the cage. Among these damping pads, two of them (i.e., the damping pads 20-1 and 20-7 that form the opening of the door 16) are attached to a cylinder 22 and are associated with two diametrically opposed fixed damping pads (i.e., the damping pads 20-3 and 20-5) to securely and uniformly maintain the monopile around the longitudinal axis X-X of the cage.

[0031] The position of the fixed support 26 can be adjusted by a slide 100 (FIG. 3) for adapting the structure according to the invention to several monopile diameters (for example, three diameters set as required: 7.0 m, 7.5 m, and 7.75 m).

[0032] Generally, each damping pad 20 positioned at the height of the upper part 14b of the cage includes a rigid shield 24 intended to abut against the monopile to disperse the contact pressure and limit friction, and a fixed support 26 to which the rigid shield is attached by at least one fender 28 made of elastomer.

[0033] In the exemplary embodiment of FIG. 3, the rigid shield 24 of each damping pad is attached to the fixed support 26 by two fenders 28 made of elastomer. In one embodiment not shown in the figures, the damping pads positioned at the height of the upper part of the cage are dispersed in at least two rows spaced longitudinally from each other (i.e., spaced along the longitudinal axis of the cage).

[0034] Furthermore, according to the present invention, as shown in FIG. 4, the lower part 14a of the cage 14 includes a plurality of blades 30 extending along the longitudinal axis X-X and dispersed around it. These blades 30 can radially abut against the monopile when the monopile is introduced into the cage in order to guide the monopile during its descent into the cage and to change the inclination of the monopile with respect to the longitudinal axis of the cage (e.g., by about 0.25° relative to the vertical). The blades 30 thus ensure enhanced guidance and provide more accurate control of the angle of the monopile.

[0035] Preferably, the number of these blades 30 is eight, and at least some of the blades 30 are attached to slides 32 so that their positions can be changed along the radial direction.

[0036] According to one advantageous configuration shown in FIG. 1, each leg 6 of the support structure 4 includes a plate 6a articulated about two axes Y'-Y', Z'-Z' orthogonal to the longitudinal axis X-X of the cage in order to be able to adjust the positioning of the support structure according to the surface shape of the seabed.

[0037] According to another advantageous configuration, one of the legs 6 of the support structure terminates at its upper end with a cone 34 for receiving ballast. According to yet another advantageous configuration, the support structure 4 comprises two central struts 36 which each terminate at their upper end with a cone 38 for receiving a hydraulic lifting tool.

[0038] Considering that the structure is fixed to the ship's deck through the legs of these struts at the legs of the central strut 36, the rigidity of the system enables the transmission of forces during transportation. With reference to FIGS. 5A to 5D, an example of placing a tubular monopile in an excavation hole formed in the seabed using the device described above will be described next.

[0039] According to one preliminary step not shown in the figures, a metal reinforcement pipe 44 is placed in the soft soil S-M up to the top of the rock S-R, then an excavation hole 46 is formed in the seabed and the rock S-R is excavated to the desired depth. The excavation hole 46 is then filled with a granular material which is then compressed by vibration as described in Patent Document 1, and the compressed granular material reaches above the seabed but below the upper part of the metal reinforcement pipe.

[0040] The device 2 according to the present invention is then placed vertically from an offshore installation vessel into the excavation hole 46 in the seabed, and a frame 8 for positioning the support structure is introduced around the upper end of the reinforcement pipe 44. Once correctly positioned and aligned, the cage door 16 is opened to allow the introduction of the monopile 40 from the side. For this purpose, the offshore installation vessel uses a lifting crane (not shown) to lift the monopile 40 from above and guides the monopile 40 so that the lower end of the monopile passes laterally through the cage door and into the inside of the cage (FIG. 5A).

[0041] By introducing the monopile laterally into the cage of the support structure, the lifting height of the monopile can be limited (compared to vertical introduction). During this introduction, pads positioned at the height of the cage door enable shock absorption, ensure the guidance of the monopile into the cage, and the damping pads distributed at the upper part of the cage enable the monopile to be vertically stabilized without overly restricting the monopile. The damping system actually allows significant dynamics of the monopile, thus making it possible to use a floating installation vessel not moored to the soil.

[0042] When the monopile 40 is introduced into the upper part 14b of the cage, the monopile 40 is guided by the lifting crane towards the bottom of the cage (Figure 5B). The monopile 40 first passes between the blades at the lower part of the cage that reinforce the guidance and then contacts the top of the compressed granular material filling the excavation hole 46.

[0043] Next, the monopile 40 is partially driven into the compressed granular material, preferably first by gravity and then by vibratory driving implemented by a vibrator 42 attached to the upper end of the monopile and operated by a lifting crane (Figure 5C).

[0044] During this operation of partially driving the monopile, the inclination of the monopile with respect to the longitudinal axis X-X of the cage is corrected, in particular by the blades at the lower part of the cage, so as to correct any defects in the verticality of the monopile.

[0045] When the monopile 40 is sufficiently driven into the soil (the driving depth is about 15 m to 20 m), the soil involved becomes rigid enough to maintain the monopile in horizontal and angular positions. Next, the final setting using the damping pads and blades of the cage is carried out to carefully determine the vertical positioning of the monopile to around 0.25° (Figure 5D).

[0046] It should be noted that when this operation of vertically arranging the monopile is carried out, the soil maintains the monopile in lateral and angular positions, and the vibratory driving continues until the desired depth is reached while maintaining verticality.

[0047] In a final step not shown in the figure, the device can be recovered and returned to the surface of the installation vessel. Preferably, the method further comprises adjusting the cage to match the diameter of the monopile by setting pads positioned at the height of the upper part of the cage and blades positioned at the height of the lower part of the cage.

Claims

1. A device (2) for guiding and maintaining a tubular monopile (40) vertically when a tubular monopile is placed in a borehole (46) formed on the seabed, filled with compressed granular material and reinforced by metal reinforcing pipes (44), wherein the device (2) A support structure (4) intended to be positioned vertically in the drilled hole (46) formed in the seabed, the support structure (4) being attached to at least four legs (6) whose heights are adjustable, A positioning frame (8) for positioning the support structure relative to the reinforcing pipe (44), wherein the positioning frame has a closed U-shape, is attached to the lower part of the support structure (4), and is intended to ensure the positioning of the support structure relative to the upper end of the reinforcing pipe (44), A cage (14) extending along a longitudinal axis (X-X) and mounted inside the support structure above the positioning frame to receive the monopile, the cage comprising a closed lower section (14a) and a higher section (14b) having a door (16) that can be opened to allow the monopile to be introduced into the cage from the side and can be closed to keep the monopile inside the cage, and Equipped with, The raised portion (14b) of the cage comprises a plurality of damping pads (20) distributed around the longitudinal axis (X-X) of the cage, the damping pads being sized to allow distributed contact with the monopile, to stabilize and alter the inclination of the monopile with respect to the longitudinal axis of the cage, to dampen the dynamics of the monopile when it is introduced into the cage, and to be able to contact the monopile radially. The lower portion (14a) of the cage comprises a plurality of blades (30) extending along the longitudinal axis of the cage and distributed therearound, wherein the blades are sized to allow distributed contact with the monopile and are radially contactable with the monopile when it is introduced into the cage to guide the monopile during its descent into the cage until sufficient soil resistance is reached to naturally maintain positioning in angles and translations, and to change the inclination of the monopile with respect to the longitudinal axis of the cage.

2. The apparatus according to claim 1, wherein at least some (20-1, 20-7) of the damping pads positioned at the height of the high portion of the cage are attached to a cylinder (22) so that their positions can be changed along the radial direction.

3. The apparatus according to claim 2, wherein the number of damping pads attached to the cylinder is two, and these damping pads are associated with two diametrically opposed and fixed damping pads (20-3, 20-5) to ensure that the monopile is held uniformly in place around the longitudinal axis of the cage.

4. The apparatus according to any one of claims 1 to 3, wherein each damping pad positioned at the height of the high portion of the cage comprises a rigid shield (24) intended to contact the monopile to distribute contact pressure and limit friction, and the rigid shield is attached to a fixed support (26) by at least one fender (28) made of elastomer.

5. The apparatus according to any one of claims 1 to 3, wherein the damping pads positioned at the height of the high part of the cage are distributed in at least two rows spaced apart from each other in the longitudinal direction.

6. The apparatus according to any one of claims 1 to 3, wherein at least some of the blades (30) positioned at the height of the lower part of the cage are mounted on a slide (32) so that their position can be changed along the radial direction.

7. The apparatus according to any one of claims 1 to 3, wherein the door (16) of the cage (14) is provided with a pad (18) intended to absorb shock and ensure guidance of the monopile during lateral insertion of the monopile into the cage.

8. The apparatus according to any one of claims 1 to 3, wherein the positioning frame (8) is rotatable about two axes (Y-Y, Z-Z) perpendicular to the longitudinal axis (X-X) of the cage, and is also rotatable along the longitudinal axis of the cage.

9. The apparatus according to any one of claims 1 to 3, wherein each leg (6) of the support structure is provided with a plate (6a) articulated around an axis (6b) perpendicular to the longitudinal axis (X-X) of the cage.

10. The apparatus according to any one of claims 1 to 3, wherein one of the legs is terminated at the high end with a cone (34) for receiving ballast.

11. The apparatus according to any one of claims 1 to 3, wherein the support structure comprises two central columns (36) terminating at their upper ends with cones (38) for receiving a hydraulic lifting tool.

12. The apparatus according to any one of claims 1 to 3, wherein the positioning frame for positioning the support structure comprises a removable closing bar.

13. A method for placing a tubular monopile in a borehole (46) formed on the seabed, wherein the method is The aforementioned excavated hole (46) is reinforced with a metal reinforcing pipe (44), The seabed is drilled to a desired depth, The process involves filling the aforementioned excavated hole with granular material, and then compressing the granular material. The apparatus (2) according to any one of claims 1 to 3 is placed vertically in the excavation hole on the seabed, wherein the positioning frame (8) for positioning the support structure (4) is introduced around the upper end of the reinforcing pipe, Lifting the monopile (40) from above, The lower end of the monopile is passed through the door (16) of the cage from the side, thereby guiding the monopile to be introduced into the inside of the cage (14). Lowering the monopile into the cage, In order to correct the verticality of the monopile, the monopile is partially driven into the compressed granular material while correcting the inclination of the monopile with respect to the longitudinal axis of the cage. To recover the aforementioned device and A method that includes a series of elements.

14. The method according to claim 13, wherein the granular material is compressed by vibration, and the monopile is partially driven into the compressed granular material by vibratory embedding.

15. The method according to claim 13 further includes adjusting the cage to match the diameter of the monopile by setting the pad positioned at the height of the high part of the cage and the blade positioned at the height of the low part of the cage.

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