EP4650523A1

EP4650523A1 - Foundation structure and associated anchoring method

Info

Publication number: EP4650523A1
Application number: EP24305772.6A
Authority: EP
Inventors: Vincent Lacour; Virginie HURMANE; Josepha GUIOL; Lorenzo MONACO
Original assignee: TotalEnergies Onetech SAS
Current assignee: TotalEnergies Onetech SAS
Priority date: 2024-05-17
Filing date: 2024-05-17
Publication date: 2025-11-19

Abstract

The invention relates to a foundation structure, comprising : a vertical tubular wall (16), including an inner face (26), an outer face (28) and a bottom edge; a base (18) extending downward relative to the bottom edge, the base forming a groove (60) extending along the bottom edge; an injection device (20) for injecting water into the groove; and an extraction device (80) for extracting the injected water from said groove.

The base comprises an inner ring (50) and an outer ring (52), extending respectively from the inner face (26) and from the outer face (28) of the tubular wall, the inner and outer rings being separated by the groove (60); and the injection device comprises a water injection tube (64) extending in the groove, along the bottom edge of the tubular wall, for injecting water into the groove.

Description

The present invention relates to a foundation structure, comprising : a substantially cylindrical tubular wall, said tubular wall extending along a main axis, intended to be vertical; said tubular wall including: an inner face; an outer face; and a bottom edge, joining the inner and outer faces; a base intended to extend downward relative to the bottom edge of the tubular wall, said base and said bottom edge being intended to be anchored in a soil; the base forming a groove extending along the bottom edge of the tubular wall, around the main axis; an injection device for injecting water into the groove; and an extraction device for extracting the injected water from said groove.
The invention especially relates to monopiles for offshore plants, such as wind turbines.
It is known to anchor an offshore monopile into a seabed by hammering said monopile downwards. However, such a method implies high noise levels and may induce soil resistance phenomena, increasing the time and energy necessary to the installation.
Anchoring methods involving water injection are known from the prior art, for example from document CN114592535 . However, water injection may lead to unsuitable soil behavior inducing a phenomenon known as pile run, which corresponds to uncontrollable sinking of the hammered structure into the soil further to soil destabilization.
The aim of the invention is to provide a foundation structure allowing an energy-saving and controllable anchoring.
For this purpose, the invention relates to a foundation structure of the aforementioned type, wherein: the base comprises an inner ring and an outer ring, axially extending respectively from the inner face and from the outer face of the tubular wall, the inner and outer rings being separated by the groove; and the injection device comprises at least a first water injection tube extending in the groove, along the bottom edge of the tubular wall, said first water injection tube comprising at least a first opening for injecting water into the groove.
According to preferred embodiments, the foundation structure may include one or more of the following features, considered alone or in any technically possible combination:

the injection device also comprises at least a first nozzle connected to the first opening of the first water injection tube, said first nozzle being able to inject water in the groove from said first water injection tube;
the base also comprises at least one separator, extending between the inner ring and the outer ring,
the groove is situated between the at least one separator and the bottom edge of the tubular wall, relative to the main axis;
the at least one separator is a blade substantially extending in a plane parallel to the main axis;
the first water injection tube is removable from the groove;
the injection device also comprises at least one water inlet pipe, extending substantially parallel to the main axis and connected to the first water injection tube;
the injection device also comprises a second water injection tube extending in the groove, along the bottom edge of the tubular wall, said second water injection tube comprising at least a second opening for injecting water into the groove, the water inlet pipe being connected to both the first and the second water injection tube;
the extraction device comprises at least one water outlet pipe, extending substantially parallel to the main axis and connected to the groove;
the water inlet pipe and the water outlet pipe are substantially coaxial, the water outlet pipe being preferably around the water inlet pipe.

The invention also relates to a base designed for being assembled to a tubular wall for forming a foundation structure as described above, the tubular wall including: an inner face; an outer face; and a bottom edge, joining the inner and outer faces; the base comprising an inner ring, an outer ring and at least one separator, extending between the inner ring and the outer ring; each of the inner and outer rings comprising an upper part and an intermediate part, aligned along an axis, the upper parts of the inner and outer rings being designed for being fixed to the inner and outer faces of the tubular wall, respectively, so as to form a groove defined by the bottom edge and the intermediate parts of the inner and outer rings.
According to a preferred embodiment, each of the inner and outer rings also comprise a lower part, aligned with the intermediate part along the axis, the at least one separator extending between the lower parts of the inner and outer rings.
The invention also relates to a method for anchoring into a soil a foundation structure as described above, the soil being immersed in a water plan, the method comprising the following steps: placing the base of the foundation structure in contact with the soil, the main axis being vertical; then injecting water into the groove by means of the injection device, so that the soil below the groove is fragmented into soil debris and said soil debris are mixed with the injected water; and simultaneously, extracting from the groove the injected water mixed with the soil debris, by means of the extraction device ;so that the soil is progressively removed from below the base and so that said base and the tubular wall progressively sink into the soil.
According to a preferred embodiment, the injection device injects water into the groove with a pressure superior to 3 bars.
The invention will be easier to understand in view of the following description, provided solely as an example, and with reference to the appended drawings, wherein:

Figure 1 is a schematic view of a foundation structure according to an embodiment of the invention;
Figure 2 is a detailed view of the foundation structure of Figure 1; and
Figure 3 and Figure 4 are detailed, partial views of the foundation structure of Figures 1 and 2.

Figure 1 shows a foundation structure 10 according to an embodiment of the invention. The foundation structure 10 is intended to be anchored in a soil 12.
Preferably, the soil 12 is an underwater soil, being immersed in a water plan 14 such as a sea.
The foundation structure 10 comprises: a tubular wall 16; a base 18; an injection device 20; and an extraction device 22.
The tubular wall extends along a main axis 24, intended to be vertical, and comprises: an inner face 26; an outer face 28; and a bottom edge 30, joining the inner and outer faces. By "bottom edge 30", it is meant that said edge is designed for forming a bottom end of the tubular wall 16.
In the embodiment of Figure 1, the tubular wall 16 comprises an upper portion 32, an intermediate portion 34 and a lower portion 36, aligned along the main axis 24.
Both the upper 32 and lower 36 portions are substantially cylindrical. The lower portion 36 has a larger dimension than the upper portion 32 perpendicularly to the main axis 24.
In the embodiment of Figure 1, the cylinders formed by the upper 32 and lower 36 portions have circular bases, the base of the lower portion 36 having a larger diameter than the base of the upper portion 32. In other embodiments (not shown), the cylinders formed by the upper 32 and lower 36 portions have oval bases or polygonal bases.
The intermediate portion 34 joins the upper 32 and lower 36 portions and has a flared shape. In the embodiment of figure 1, the intermediate portion 34 is frustoconical.
The bottom edge 30 forms a bottom end of the lower portion 36 of the tubular wall 16.
Adjacent to the bottom edge 30, each of the inner 26 and outer 28 faces of the tubular wall 16 is cylindrical. A thickness 38 of the lower portion 36 is defined by a distance between the inner 26 and outer 28 faces.
In the shown embodiment, the bottom edge 30 comprises main sections 40 and junction sections 42, alternatively arranged around the main axis 24.
In the shown embodiment, each main section 40 of the bottom edge 30 extends in a plane perpendicular to the main axis 24; and each junction section 42 comprises two curved strips 44 extending upwards, each curved strip being continuous with an end of one of the main sections 40.
More precisely, in the shown embodiment, the bottom edge 30 comprises three main sections 40, substantially identical to each other; and three junction sections 42, substantially identical to each other.
In another embodiment (not shown), the bottom edge of the tubular wall has a substantially toothed shape or sinusoidal shape around the main axis.
The base 18 is disposed at the bottom end of the tubular wall 16. More precisely, the base 18 is fixed to the tubular wall 16, near the bottom edge 30.
The base comprises an inner ring 50 and an outer ring 52, coaxially arranged around the main axis 24. Preferably, each of the inner and outer rings is substantially cylindrical.
In the shown embodiment, each of the inner and outer rings comprises an upper part 54, an intermediate part 56 and a lower part 58, aligned along the main axis 24.
The upper part 54 of each of the inner and outer rings is in contact with, respectively, the inner face 26 and the outer face 28 of the tubular wall.
In the shown embodiment, the upper parts 54 of the inner and outer rings are continuous. In another embodiment (not shown), the upper part of the inner and/or outer ring is segmented or comprises openings. Such a configuration of the upper parts 54 of the inner and outer rings may allow a more efficient welding of said upper parts to the inner and outer faces of the tubular wall, by providing edges extending in different directions.
The intermediate 56 and lower 58 parts of the inner 50 and outer 52 rings extend downwards from the main sections 40 of the bottom edge 30 of the tubular wall 16. In particular, the intermediate parts 56 of the inner 50 and outer 52 rings are separated by a radial space corresponding to the thickness 38 of the lower portion 36 of the tubular wall.
A groove 60, defined by the intermediate parts 56 of the inner 50 and outer 52 rings and by the main sections 40 of the bottom edge 30, is considered in the following description.
Preferably, the intermediate parts 56 of the inner 50 and outer 52 rings have similar lengths along the main axis 24.
In embodiments of the invention, the base 18 also comprises at least one separator 62, extending between the inner 50 and outer 52 rings.
In the shown embodiment, the base 18 comprises a plurality of separators 62, extending between the lower parts 58 of the inner 50 and outer 52 rings. More precisely, the separators 62 are fixed to the lower parts 58 of the inner 50 and outer 52 rings. Relative to the main axis 24, the groove 60 is situated between the bottom edge 30 of the tubular wall 16 and the separators 62.
In the shown embodiment, each of the separators 62 is a blade substantially extending in a plane including the main axis 24. Preferably, each blade 62 has a convex lower edge 63, intended to be oriented downwards.
In another embodiment (not shown), the separators may have different shapes. One aim of the separators 62 may be to avoid deformation of the inner 50 and outer 52 rings during an anchoring process of the foundation structure 10, as detailed below.
In other embodiments (not shown), the lower parts 58 of the inner 50 and outer 52 rings are not connected to each other. For example, said inner and outer rings may be designed with a thickness sufficient in itself for avoiding deformation.
More precisely, in one of said embodiments (not shown), the at least one separator of the base is situated between the upper part 54 and the intermediate part 56 of each of the inner 50 and outer 52 rings. Preferably, said at least one separator is substantially included in a plane perpendicular to the main axis 24.
In another one of said embodiments (not shown), the base does not comprise separators.
A detailed, partial view of the injection device 20 is shown on Figure 3.
The injection device 20 is configured for injecting water into the groove 60. The injection device 20 comprises at least one water injection tube 64 extending in the groove 60, along at least one main section 40 of the bottom edge 30.
The water injection tube 64 comprises at least one opening 66 for injecting water into the groove 60. Preferably, the water injection tube 64 comprises a plurality of openings distributed along its length.
Preferably, the injection device 20 also comprises at least one nozzle 68, 69 connected to the at least one opening 66 of the water injection tube 64, said nozzle being able to inject water into the groove 60.
Preferably, the injection device 20 also comprises at least one water inlet pipe 70, connected to the at least one water injection tube 64.
More preferably, the at least one water inlet pipe 70 extends substantially parallel to the main axis 24, between an upper end 72 and a lower end 74. In the shown embodiment (Figure 1), the at least one water inlet pipe 70 extends along the lower portion 36 of the tubular wall 16, the upper end 72 being close to the intermediate portion 34.
Preferably, the injection device 20 also comprises a water injection pump 76, connected to the upper end 72 of the water inlet pipe 70. Preferably, the injection device 20 is configured so that the water injection pump 76 injects water from the water plan 14 into the water inlet pipe 70.
More preferably, the injection device 20 is configured so that high-pressure water is injected into the water inlet pipe 70. High-pressure water means pressure higher than 3 bars, preferably higher than 5 bars, more preferably higher than 10 bars, and lower than 1kbar.
Optionally, the injection device 20 also includes an air injection device 78, configured for injecting compressed air in the groove 60, together with the injected water.
The extraction device 22 is configured for extracting from the groove 60 the water injected by the injection device 20.
The extraction device 22 comprises at least one water outlet pipe 80, connected to the groove 60.
More preferably, the at least one water outlet pipe 80 extends substantially parallel to the main axis 24, between an upper end 82 and a lower end 84. In the shown embodiment (Figure 1), the at least one water outlet pipe 80 extends along the lower portion 36 of the tubular wall 16, the upper end 82 being close to the intermediate portion 34.
Preferably, the extraction device 22 also comprises a water extraction pump 86, connected to the upper end 82 of the water outlet pipe 80.
According to an embodiment, the at least one water inlet pipe 70 and the at least one water outlet pipe 80 are substantially coaxial, the water outlet pipe being preferably around the water inlet pipe.
According to another embodiment (not shown), the at least one water inlet pipe and the at least one water outlet pipe are distant from each other.
The injection device 20 and extraction device 22 of the shown embodiment will now be more specifically described. The features of the shown embodiment are preferred features which may be carried out separately or in combination.
In the shown embodiment, the injection device 20 comprises three water inlet pipes 70, substantially identical to each other; and the extraction device 22 comprises three water outlet pipes 80, substantially identical to each other.
Each water outlet pipe 80 extends along the outer face 28 of the lower portion 36 of the tubular wall 16. The lower end 84 of each water outlet pipe 80 includes one of the junction sections 42 of the bottom edge 30 of the tubular wall. More precisely, the curved strips 44 of each junction section 42 partially delimit the lower end 84 of the corresponding water outlet pipe 80.
In an embodiment of the invention (not shown), the inner and/or outer rings of the base 18 comprise radial and/or axial protrusions next to the lower end 84 of the or each water outlet pipe 80, for a water deflecting effect.
Each water inlet pipe 70 extends in one of the water outlet pipes 80. The lower end 72 of each water inlet pipe 70 is disposed near or in the lower end 84 of the corresponding water outlet pipe 80.
Moreover, in the shown embodiment, the injection device 20 comprises six water injection tubes 64, substantially identical to each other. Each water injection tube 64 extends between a proximal end 90 and a distal end 92.
The lower end 72 of each water inlet pipe 70 is connected to the proximal ends 90 of two water injection tubes 64. Said two water injection tubes 64 extend on either side of the corresponding water inlet pipe 70, along adjacent main sections 40 of the bottom edge 30.
More precisely, two distinct water injection tubes 64, connected to different water inlet pipes 70, extend along a same main section 40 of the bottom edge 30. The distal ends 92 of said two distinct water injection tubes 64 face each other in the groove 60.
Moreover, in the shown embodiment, each water injection tube 64 is assembled to a plurality of first nozzles 68 between its proximal end 90 and its distal end 92. Preferably, each first nozzle 68 is configured for emitting a water jet 94 directed towards the proximal end 90 of the corresponding water injection tube.
Optionally, the distal end 92 of each water injection tube 64 is assembled to a second nozzle 69, different from the first nozzles 68. For example, the second nozzles 69 are configured for emitting a forward-oriented water jet.
Optionally, the water inlet pipes 70 are also assembled to nozzles 96 similar to the first nozzles 68 and configured for emitting an upward-directed water jet.
According to an embodiment, the water inlet pipes 70 and water injection tubes 64 are removable from the water outlet pipes 80 and groove 60. According to another embodiment, the water injection tubes 64 are made in one piece with the base 18, for example by 3D-printing.
According to an embodiment, the injection device 20 comprises a water injection pump 76 for each water inlet pipe 70. Alternatively, the injection device 20 comprises a water injection pump 76 connected to more than one water inlet pipe 70.
According to an embodiment, the extraction device 22 comprises a water extraction pump 86 for each water outlet pipe 80. Alternatively, the extraction device 22 comprises a water extraction pump 86 connected to more than one water outlet pipe 80.
According to an embodiment, the foundation structure 10 is a monopile foundation for an offshore wind turbine. For example, the upper portion 32 of the tubular wall 16 is attached to a wind turbine mast.
As an example corresponding to such an embodiment, a height of the tubular wall 16 along the main axis 24 is around 120 m, a diameter of the lower portion 36 is around 10 to 12 m and the thickness 38 of said lower portion 36 is around 150 mm. A weight of such a foundation structure 10 may be between 2.000 and 2.500 tons.
A manufacturing method of the foundation structure 10 will now be described.
First, the tubular wall 16 is manufactured, with the inner 26 and outer 28 faces and the bottom edge 30. In the shown embodiment, the main sections 40 and junction sections 42 of the bottom edge are formed at the bottom end of the lower portion 36 of the tubular wall.
Then, the tubular wall 16 is assembled to the base 18, in order to form the groove 60.
In a first embodiment, the base 18 is provided in separate parts, which are successively fixed to the tubular wall 16. For example, in the shown embodiment, the upper part 54 of each of the inner 50 and outer 52 rings is welded to the inner 26 or outer 28 face, respectively, near the main sections 40 of the bottom edge 30. Then, each of the separators 62 is fixed to the lower parts 58 of the inner 50 and outer 52 rings.
In a second embodiment, the base 18 is provided in one piece, which is then fixed to the bottom end of the tubular wall. For example, in the shown embodiment, the base 18 is provided with the inner 50 and outer 52 rings connected to each other by the plurality of separators 62.
Simultaneously to the assembly of the tubular wall 16 with the base 18, the water outlet pipes 80 are formed along the lower portion 36 of the tubular wall. The lower ends 84 of the water outlet pipes 80 are connected to the groove 60.
Preferably, each water outlet pipe 80 comprises curved plates 97, 98, assembled to the outer face 28 of the tubular wall and to the junction section 42 of the bottom edge 30. Said curved plates include a deflector-shaped plate 97 designed for guiding a water flux from the groove 60 to the water outlet pipe 80, as detailed below.
Moreover, the water inlet pipes 70 and the water injection tubes 64 are disposed in the water outlet pipes 80 and in the groove 60, respectively. In an embodiment, the water injection tubes 64 are disposed along the bottom edge 30 of the tubular wall 16 before the assembly of the tubular wall 16 with the base 18.
Then, the water inlet pipes 70 and the water outlet pipes 80 are connected to a water injection pump 76 and to a water extraction pump 86, respectively.
An installation method of the foundation structure 10 into the soil 12 will now be described. Preferably, the soil 12 is a granular and friable soil, such as a sandy soil.
First, the foundation structure 10 is immersed in the water plan 14 and lowered so that the base 18 comes into contact with the soil 12, the main axis 24 being vertical.
Due to the weight of the foundation structure 10, the lower parts 58 of the inner 50 and outer 52 rings dig in the soil 12. In the shown embodiment, the convex lower edge 63 of the blades 62 also dig in the soil 12.
Then, the water injection pump(s) 76 and water extraction pump(s) 86 are activated. A downward water flux is sent from the water plan 14 to the water inlet pipes 70, preferably with a high pressure, such as a pressure superior to 3 bars. Said 3-bar lower threshold for water pressure during operation corresponds to pressure measurement relative to atmospheric ground pressure. For sake of clarity, if atmospheric ground pressure is 1 bar, absolute pressure within the injection device is 4 bars and relative pressure is 3 bars.
The downward water flux reaches the water injection tubes 64 and the first nozzles 68, generating the water jets 94. Preferably, a velocity of the water jets 94 is superior to 20 m.s^-1.
Said water jets 94 hit soil agglomerates formed between the blades 62, fracturing said soil agglomerates into small size debris. In the case wherein the injection device 20 also includes an air injection device 78, compressed air may be injected in the groove 60 together with water, increasing the soil fragmentation.
Around the water injection tubes 64, the groove 60 is thus filled with water mixed with small-sized soil debris. The direction of the water jets 94 tends to push said mixture towards the closest junction section 42 of the bottom edge 30.
Meanwhile, an upward water flux is generated in the water outlet pipes 80 by the water extraction pump(s) 86. Said upward water flux drives the mixture of water and small-sized soil debris from the groove 60 to the bottom end 84 of the closest water outlet pipe 80. The curved strips 44 of the junction sections 42 and the deflector including curved plate 97 guide the mixture into an upward direction. In case of nozzles 96 with upward water jets assembled to the water inlet pipes 70, said water jets also helps the mixture of water and small-sized soil debris to move upwards in the water outlet pipes 80.
Said mixture then reaches the upper end 82 of the corresponding water outlet pipe 80, out of which it is ejected by the water extraction pump(s) 86. In a first embodiment, the mixture is ejected at the outside of the tubular wall 16. In a second embodiment, the mixture is ejected at the inside of the tubular wall 16.
Therefore, the soil 12 is progressively removed from below the base 18 by the water flux. As a result, the base 18 and the bottom end of the tubular wall 16 progressively sink into the soil 12, anchoring the foundation structure into said soil.
In the embodiment wherein the base 18 comprises blades 62, said blades facilitate the breaking of soil agglomerates before the action of the water jets 94. Moreover, the convex shape of the lower edges 63 may radially push bigger soil fragments away from below the base 16. Moreover, the blades 62 prevent a deformation of the inner 50 and outer 52 rings, maintaining the distance between said rings.
The water flux is substantially confined in the groove 60 and in the water inlet 70 and outlet 80 pipes. Therefore, except for an annular portion immediately below the base 18, the soil 12 is not disturbed by the water flux. In particular, soil behaviors that may result in pile run are thus avoided.
Therefore, during the sinking of the tubular wall 16, the soil 12 applies firmly against the inner 26 and outer 26 faces of said tubular wall, providing a solid anchoring of the foundation structure 10.
When a suitable anchoring depth of the tubular wall 16 is reached, the water injection pump(s) 76 and water extraction pump(s) 86 are stopped and then disconnected from the water inlet 70 and outlet 80 pipes.
In the embodiment wherein the water inlet pipes 70 and water injection tubes 64 are removable, said water inlet pipes 70 and water injection tubes 64 are extracted from the water outlet pipes 80 and groove 60 by pulling the upper end 72 of each water inlet pipe 70. The water inlet pipes 70 and water injection tubes 64 may be reused in another foundation structure 10.

Claims

Foundation structure, comprising:
- a substantially cylindrical tubular wall (16, 36), said tubular wall extending along a main axis (24), intended to be vertical; said tubular wall including: an inner face (26); an outer face (28); and a bottom edge (30), joining the inner and outer faces;

- a base (18) intended to extend downward relative to the bottom edge of the tubular wall, said base and said bottom edge being intended to be anchored in a soil;
the base forming a groove (60) extending along the bottom edge of the tubular wall, around the main axis;

- an injection device (20) for injecting water into the groove; and an extraction device (22) for extracting the injected water from said groove;
the foundation structure being characterized in that:
- the base comprises an inner ring (50) and an outer ring (52), axially extending respectively from the inner face (26) and from the outer face (28) of the tubular wall, the inner and outer rings being separated by the groove (60); and

- the injection device comprises at least a first water injection tube (64) extending in the groove, along the bottom edge of the tubular wall, said first water injection tube comprising at least a first opening (66) for injecting water into the groove.
Foundation structure according to claim 1, wherein the injection device also comprises at least a first nozzle (68, 69) connected to the first opening (66) of the first water injection tube, said first nozzle being able to inject water in the groove from said first water injection tube.
Foundation structure according to claim 1 or 2, wherein the base also comprises at least one separator (62), extending between the inner ring (50) and the outer ring (52).
Foundation structure according to claim 3, wherein the groove (60) is situated between the at least one separator and the bottom edge (30) of the tubular wall, relative to the main axis (24).
Foundation structure according to claim 3 or 4, wherein the at least one separator is a blade (62) substantially extending in a plane parallel to the main axis (24).
Foundation structure according to one of the previous claims, wherein the first water injection tube (64) is removable from the groove (60).
Foundation structure according to one of the previous claims, wherein the injection device (20) also comprises at least one water inlet pipe (70), extending substantially parallel to the main axis (24) and connected to the first water injection tube (64).
Foundation structure according to claim 7, wherein the injection device (20) also comprises a second water injection tube (64) extending in the groove (60), along the bottom edge (30) of the tubular wall, said second water injection tube comprising at least a second opening (66) for injecting water into the groove, the water inlet pipe (70) being connected to both the first and the second water injection tube (64).
Foundation structure according to one of the previous claims, wherein the extraction device (22) comprises at least one water outlet pipe (80), extending substantially parallel to the main axis (24) and connected to the groove (60).
Foundation structure according to claim 9 combined with claim 7 or 8, wherein the water inlet pipe (70) and the water outlet pipe (80) are substantially coaxial, the water outlet pipe being preferably around the water inlet pipe.
Base (18) designed for being assembled to a tubular wall (16) for forming a foundation structure according to one of claims 3 to 5, the tubular wall including: an inner face (26); an outer face (28); and a bottom edge (30), joining the inner and outer faces;
the base comprising an inner ring (50), an outer ring (52) and at least one separator (62), extending between the inner ring (50) and the outer ring (52),

each of the inner and outer rings comprising an upper part (54) and an intermediate part (56), aligned along an axis (24),

the upper parts (54) of the inner and outer rings being designed for being fixed to the inner (26) and outer (28) faces of the tubular wall, respectively, so as to form a groove (60) defined by the bottom edge (30) and the intermediate parts (56) of the inner and outer rings.
Base (18) according to claim 11, wherein each of the inner and outer rings also comprise a lower part (58), aligned with the intermediate part (56) along the axis, the at least one separator (62) extending between the lower parts (58) of the inner (50) and outer (52) rings.
Method for anchoring into a soil (12) a foundation structure (10) according to one of the claims 1 to 10, the soil being immersed in a water plan (14),
the method comprising the following steps:
- placing the base (18) of the foundation structure in contact with the soil, the main axis (24) being vertical; then

- injecting water into the groove (60) by means of the injection device (20), so that the soil below the groove is fragmented into soil debris and said soil debris are mixed with the injected water; and

- simultaneously extracting from the groove (60) the injected water mixed with the soil debris, by means of the extraction device (22);
so that the soil is progressively removed from below the base and so that said base and the tubular wall progressively sink into the soil.
Method according to claim 13, wherein the injection device (20) injects water into the groove (60) with a pressure superior to 3 bars.