FOUNDATION FOR AN OFFSHORE STRUCTURE AND METHOD FOR INSTALLING A FOUNDATION

Abstract

A foundation is for an offshore structure. The foundation includes a wall forming a closed perimeter and a top deck attached to the upper end of the wall, wherein the wall and the top deck define a downwardly open hollow space. The wall includes a plurality of wall sections. Each wall section has a first elongated hollow body and a second elongated hollow body arranged inside the first elongated hollow body. The lower end of the first elongated hollow body is closed by an end member that is provided with an opening through which the lower end of the second elongated hollow body is arranged to extend. A method is for installing a foundation into the ground.

Claims

1. A foundation for an offshore structure, comprising: a wall forming a closed perimeter and having an upper end and a lower end, and a top deck attached to the upper end of the wall, the top deck and the wall defining a downwardly open hollow space, wherein the wall comprises a plurality of wall sections, each wall section comprising a first elongated hollow body having an upper end and a lower end, the lower end being closed by an end member provided with an opening, and a second elongated hollow body having an upper end and a lower end, the second elongated hollow body being arranged inside the first elongated hollow body so that the lower end of the second elongated hollow body extends through the opening and is attached to the end member.

2. The foundation according to claim 1, wherein the wall is a cylindrical wall.

3. The foundation according to claim 1, wherein the foundation comprises means for transferring fluid into and out of the downwardly open hollow space.

4. The foundation according to claim 1, wherein the wall section comprises a bottom pump attached to the lower end of the second elongated hollow body for removing soil, and a riser pipe arranged inside the second elongated hollow body for carrying the soil, a lower end of the riser pipe being attached to the bottom pump.

5. The foundation according to claim 4, wherein the bottom pump comprises a cutter unit for loosening the soil.

6. The foundation according to claim 4, wherein the bottom pump comprises a water spraying unit for fluidising the soil.

7. The foundation according to claim 1, wherein the foundation comprises a plurality of air cushions.

8. The foundation according to claim 1, wherein the wall section comprises a plurality of outer supports attached to an outer surface of the first elongated hollow body.

9. The foundation according to claim 1, wherein the wall section comprises a plurality of inner supports attached between an inner surface of the first elongated hollow body and an outer surface of the second elongated hollow body.

10. The foundation according to claim 1, wherein the end member comprises a conical portion.

11. The foundation according to claim 1, wherein the foundation comprises means for heating and cooling the wall.

12. The foundation according to claim 1, wherein the foundation comprises means for vibrating the wall.

13. A method for installing a foundation according to claim 1, wherein the method comprises: arranging the foundation to float in water, towing the foundation to an installation site, removing fluid from the downwardly open hollow space, using a plurality of bottom pumps attached to the lower ends of the second elongated hollow bodies to remove soil, and using a plurality of riser pipes arranged inside the second elongated hollow bodies to carry the soil.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG. 1 illustrates a foundation according to an embodiment of the invention for an offshore structure, and

[0038] FIGS. 2A-2B illustrate the installation of the foundation of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

[0039] FIG. 1 illustrates a foundation according to an embodiment of the invention for an offshore structure. The foundation is shown from above.

[0040] The foundation comprises a cylindrical wall 101 and a top deck 102 that is attached to an upper end of the cylindrical wall 101. The cylindrical wall 101 and the top deck 102 define a downwardly open hollow space (not shown in FIG. 1), i.e., a hollow space that is open at the bottom of the foundation. An offshore structure is meant to be attached on the top deck 102. The cylindrical wall 101 functions as a load-bearing element that transfers the load of the offshore structure into the ground, such as the seabed.

[0041] The cylindrical wall 101 consists of wall sections 103, which are attached to one another so that they form a closed perimeter. Each wall section 103 comprises a first elongated hollow body 104 and a second elongated hollow body 105 that is arranged inside the first elongated hollow body 104. An upper end of the first elongated hollow body 104 is closed by an upper end member 106 that is provided with an opening through which an upper end of the second elongated hollow body 105 passes. A lower end of the first elongated hollow body 104 is closed by a lower end member (not shown in FIG. 1) that is provided with an opening through which a lower end of the second elongated hollow body 105 passes. The upper end member 106 and the lower end member seal the space between the first elongated hollow body 104 and the second elongated hollow body 105.

[0042] FIGS. 2A-2B illustrate the installation of the foundation of FIG. 1 into the seabed. The foundation is shown as a cross sectional view taken along the line A-A of FIG. 1.

[0043] In FIG. 2A, the foundation is shown floating in water. The foundation is arranged in such a manner that its bottom is towards the seabed. The foundation has been set at a desired height relative to the sea level by controlling the amount of air inside the downwardly open hollow space 107.

[0044] At a desired installation site, the foundation is lowered by removing air and water from the downwardly open hollow space 107 until the lower end of the cylindrical wall 101 comes into contact with the seabed and begins to penetrate into it. After the cylindrical wall 101 has been lowered on the seabed, the soil under the wall sections 103 is removed by using bottom pumps 108 that are attached to the lower ends of the second elongated hollow bodies 105. The lower end member 109 has a conical portion that directs the soil towards the bottom pump 108. The soil is carried away through riser pipes 110, which are arranged inside the second elongated hollow bodies 105. As the soil is removed from underneath the wall sections 103, the cylindrical wall 101 penetrates into the seabed. The soil is removed until the underside of the top deck 102 comes into contact with the seabed. The top of the installed foundation is located above the sea level. The installed foundation is shown in FIG. 2B.

[0045] Only advantageous exemplary embodiments of the invention are described in the figures. It is clear to a person skilled in the art that the invention is not restricted only to the examples presented above, but the invention may vary within the limits of the claims presented hereafter. Some possible embodiments of the invention are described in the dependent claims, and they are not to be considered to restrict the scope of protection of the invention as such.