FOUNDATION OF AN OFFSHORE STRUCTURE

Abstract

A foundation system for the foundation of an offshore structure includes a monopile having an anchoring portion anchorable in a seabed and a connection portion disposed at the opposite end. A platform structure is connected directly to the connection portion of the monopile or indirectly via a transition piece. The platform structure is disposable above a water surface. The foundation system includes at least two stabilizing devices connected directly to the platform structure or indirectly to the platform structure via the transition piece. The stabilizing devices are attachable to the seabed such that tensile forces or compression forces are transmittable between the seabed and the platform structure. Securing points on the stabilizing devices, together with the connection portion of the monopile, define a plane having a horizontally extending component.

Claims

1. A foundation system for the foundation of an offshore structure, comprising: a monopile, having an anchoring portion anchorable in a seabed, and having a connection portion disposed at an end opposite the anchoring portion; and a platform structure configured for connection at least one of directly to the connection portion of the monopile and indirectly via a transition piece, wherein the platform structure is disposable above a water surface, the foundation system comprising: at least two stabilizing devices configured for connection to at least one of directly to the platform structure and indirectly to the platform structure via the transition piece, wherein the at least two stabilizing devices are attachable to the seabed, such that at least one of tensile forces and compression forces are transmittable between the seabed and the platform structure, wherein the stabilizing devices comprise securing points wherein, together with the connection portion of the monopile, the securing points define a plane having a horizontally extending component.

2. The foundation system of claim 1, wherein the at least two stabilizing devices are each stabilizing pillars configured for displaceable connection to at least one of the platform structure and the transition piece, wherein the at least two stabilizing devices are lowerable onto the seabed from at least one of the platform structure and the transition piece; and the stabilizing pillars are configured to lock to at least one of the platform structure and the transition piece, such that axially oriented compression forces are transmitted thereby to the seabed.

3. The foundation system of claim 1, wherein the at least two stabilizing devices are configured for connection to the seabed, such that tensile forces are transmitted thereby to the seabed.

4. The foundation system of claim 1, wherein the at least two stabilizing devices are each flexible, tensile elements configured for connection to the seabed.

5. The foundation system of claim 4, further comprising a plurality of foundation piles equal in number to the tensile elements, wherein the plurality of foundation piles each comprise a drop anchor connectable to one of the tensile elements, and wherein each drop anchor comprises a column of grouting compound, poured in situ, having a length within the seabed.

6. The foundation system of claim 5, wherein the drop anchor further comprises a mechanism that, when activated, liquefies the seabed in close proximity to the drop anchor, to assist with penetration of the drop anchor into the seabed.

7. The foundation system of claim 4, further comprising a tensioning device configured to apply a force to the tensile elements when the tensile elements are connected to the seabed.

8. The foundation system of claim 1, wherein the platform structure comprises a transformer substation facility.

9. An offshore structure, comprising the foundation system of claim 1, wherein the offshore structure is positioned on the monopile and the at least two stabilizing devices are connected to the seabed.

10. A method for installing a foundation of an offshore structure, comprising: providing a monopile having an anchoring portion anchorable in a seabed and a connection portion disposed at an opposite end; providing a platform structure connectable to at least one of directly to the connection portion and indirectly via a transition piece, wherein the platform structure is disposable above a water surface; anchoring the anchoring portion in the seabed; disposing the offshore structure on the platform structure; providing at least two stabilizing devices that are connectable at least one of directly to the platform structure and indirectly to the platform structure via the transition piece and that are contactable with the seabed such that at least one or tensile and compression forces are transmitted between the seabed and the platform structure, wherein, when the foundation system is in the installed state, securing points of the at least two stabilizing devices, together with the connection portion, define a plane having a horizontally extending component; and bringing the stabilizing devices into contact with the seabed.

11. The method of claim 10 further comprising providing and disposing a drop anchor at a predefined height above the seabed; fastening a tensile element to the drop anchor; fastening a grouting-compound line to the tensile element; dropping the drop anchor, such that it penetrates the seabed; and feeding a hardenable grouting compound into an injection channel produced by the drop anchor upon penetration of the seabed.

Description

[0060] Further advantages, details and features of the invention are disclosed in the following by the exemplary embodiments explained. In detail:

[0061] FIG. 1 shows a schematic representation of an offshore structure, the foundation of which is installed by means of the foundation system according to the invention; and

[0062] FIG. 2 shows an offshore structure that is installed by means of a foundation system according to an alternative embodiment of the present invention.

[0063] In the description that now follows, components that are the same, or features that are the same, are denoted by the same references, such that a description concerning a component that is given with reference to a figure also applies to the other figures, such that repeated description is avoided.

[0064] Represented in FIG. 1 is an offshore structure 1, the foundation of which is installed on the seabed U by means of a foundation system according to the invention.

[0065] It can be seen from FIG. 1 that the foundation system has a monopole 10, having an anchoring portion 11 that can be anchored in the seabed U, and having a connection portion 12 that is opposite the anchoring portion 11. The anchoring portion 11 is set into the seabed U by, for example, ramming or pile jetting. The foundation system according to the invention additionally comprises a platform structure 3 that can be connected to the connection portion 12 of the monopile 10. In the exemplary embodiment represented, the platform structure 3 is connected directly to the monopile 10. It is also possible, however, for the platform structure 3 to be connected to a transition piece that is disposed between the monopile 10 and the platform structure 3. A corresponding transition piece is not represented in the figures.

[0066] It can additionally be seen from FIG. 1 that, placed on the platform structure 3, there is a connection structure 2 in the form of a transformer substation 2. The transformer substation 3 comprises a multiplicity of individual components, which easily cause the weight of the transformer substation to be increased to over 1000 tons.

[0067] However, the present invention is not limited to the connection structure 2 being realized in the form of a transformer substation 2. Thus, according to the invention, the connection structure 2 may also be realized as a wind turbine, or also as a drilling or production platform.

[0068] The foundation system according to the invention comprises at least two stabilizing devices 20. In the case of the exemplary embodiment represented in FIG. 1, the stabilizing devices 20 are realized as supporting feet, or as stabilizing pillars 21. The stabilizing pillars 21 are each connected directly to the platform structure 3, and can be lowered onto the seabed U. In the case of the installation represented in FIG. 1, the stabilizing pillars 21 have already been set down on the seabed U. The installation may be effected in such a manner that the platform structure 3 is placed on the connection portion 12 of the monopile 10, in which case, in this state, the stabilizing pillars 21 are in an upper position, in guide sleeves of the platform structure 3, such that they do not project downward in the direction of the seabed U. Following connection of the platform structure 3 to the monopile 10, the stabilizing pillars 21 are lowered onto the seabed U, such that they are in contact with the seabed U. The stabilizing pillars 21 are then locked to the platform structure 3, such that shear forces can be transmitted onto the seabed U via the respective stabilizing pillars 21.

[0069] Because the guide sleeves on the platform structure 3 are spaced apart from each other in such a manner that they define a plane having a horizontal component of extent, in the present example a horizontal plane, and the stabilizing pillars 21 are disposed at the four corner points of the platform structure 3, horizontal forces that act on the monopile 10 or on the transformer substation 2 can be absorbed by the stabilizing pillars 21. This horizontal action of force may be caused, for example, by wind acting on the monopile 10 and on the transformer substation 2. In addition, horizontal forces due to waves or ship wash are transmitted to the monopile 10.

[0070] Swaying motions of the offshore structure 1, having a foundation installed thus, is consequently counteracted in a reliable manner by the stabilizing pillars 21. The stabilizing pillars 21 also have the effect that the oscillation frequency of the offshore structure is altered in such a manner that the latter is outside of the usual wave frequency spectrum. The resonant frequency of the offshore structure 1 having a foundation installed by means of the foundation system according to the invention is above 0.25 Hz, and usually also above 0.3 Hz.

[0071] In the exemplary embodiment represented, the stabilizing pillars 21 are not connected to the seabed U, or not anchored therein. It is also possible, however, for the stabilizing pillars 21 to be connected to the seabed U, in particular anchored, such that not only compressive forces, but also tensile forces, can be transmitted between the seabed U and the platform structure 3 via the stabilizing pillars 21. A corresponding realization of the foundation system further increases the stability because, in the case of action of force, a stabilizing pillar 21 can absorb compressive forces, and another stabilizing pillar 21, opposite this stabilizing pillar 21, can absorb tensile forces.

[0072] Represented in FIG. 2 is an offshore structure 1, the foundation of which is installed on the seabed U by means of a foundation system according to a further embodiment of the present invention. The stabilizing devices 20 in this case are realized as flexible tensile elements 22, which can be connected to the seabed U. Tensile elements 22, within the meaning of the present invention, are anchor hawsers 22, anchor cables 22, anchor chains 22 or, quite generally, flexible tensile elements 22. Flexible tensile elements 22, within the meaning of the present invention, are tensile elements via which tensile force, but not shear forces, can be transmitted.

[0073] In the case of the exemplary embodiment represented in FIG. 2, there are four tensile elements 22, each connected to the seabed U, which are provided at four corners of the platform structure 3.

[0074] In the case of the exemplary embodiment represented, the foundation system also comprises four drop anchors 31 in the form of four torpedo piles 31, which are each connected to a tensile element 22. The drop anchors 31 are part of foundation piles 30, which, in addition to the drop anchor 31, comprise columns of grouting compound 32.

[0075] The installation of the foundation system proceeds in such a manner that, following connection of the platform structure 3 to the connection portion 12 of the monopile 10, the respective drop anchors 31, with tensile elements 22 connected thereto, are let drop into the seabed U from a predefined height, such that the drop anchors 31 form an injection channel. A hardenable grouting compound, which forms the columns of grouting compound 32 represented in FIG. 2 is then fed into this injection channel.

[0076] Consequently, only tensile forces can be transmitted via the tensile elements 22, with horizontal forces from any direction being able to be compensated, owing to the arrangement of the securing points of the tensile elements 22 on the platform structure 3, because the securing points of the tensile elements 22 on the platform structure 3 define a plane having a horizontal component of extent.

[0077] Preferably, the foundation system additionally comprises a tensioning device, not represented in FIG. 2, by means of which the tensile elements 22 can be tensioned, as a result of which the stability of the offshore structure 1 having a foundation installed by means of the foundation system is further increased.

LIST OF REFERENCES

[0078] 1 offshore structure

[0079] 2 topside/connection structure/transformer substation

[0080] 3 platform structure/platform

[0081] 10 monopile

[0082] 11 anchoring portion (of the monopile)

[0083] 12 connection portion (of the monopile)

[0084] 20 stabilizing device

[0085] 21 stabilizing pillar/stabilizing device

[0086] 22 tensile element/anchor hawser/anchor chain/anchor cable/stabilizing device

[0087] 30 foundation pile

[0088] 31 drop anchor/torpedo pile

[0089] 32 column of grouting compound

[0090] M sea level/surface of sea

[0091] U seabed/ground beneath the sea