Method of installing a foundation in the sea bed and such foundation

Abstract

The invention relates to a seabed foundation (1) for an offshore facility, comprising a primary pressure chamber (7) connected to a primary pump (8) and one or more secondary pressure chambers (9) connected to one or more secondary pumps (10). According to an embodiment of the invention, said primary pump is a suction pump and said secondary pump is a pressure pump. The invention further relates to a method (12) of installing said foundation on the seabed (19), which comprises the steps of activating (14) said primary pump to create negative pressure in the primary pressure chamber (7), so that the foundation sinks into the seabed, and activating (15) said one or more secondary pumps (10) to create positive pressures in the secondary pressure chambers (9), so as to control the alignment of the foundation with respect to a substantially horizontal axis (16) during the sinking into the seabed.

Claims

1. A sea bed foundation for an offshore facility, said sea bed foundation having a circumferential side wall substantially defining a cylinder, which cylinder is closed in one end and provided with an opening in the opposite end, thereby defining a primary chamber, said sea bed foundation is hollow, downwardly open and where said side wall defines a skirt, said primary chamber being connected to a primary pump, and wherein said sea bed foundation further comprises one or more secondary chambers, said secondary chambers being separate from the primary chamber, and being downwardly open, but otherwise closed by the sea bed foundation, where said one or more secondary chambers are connected to one or more secondary pumps wherein said primary pump is a suction pump and said secondary pump is a pressure pump, and where an over-pressure created by the one or more secondary pumps increases a resistance against penetration adjacent the one or more secondary chambers, allowing a rest of the foundation to penetrate a bottom at a normal resistance, thereby rectifying an orientation of the foundation.

2. The sea bed foundation according to claim 1, wherein said one or more secondary chambers are externally attached to the skirt.

3. The sea bed foundation according to claim 1, wherein said one or more secondary chambers are integrated in the skirt.

4. The sea bed foundation according to claim 1, wherein said skirt is formed by a number of substantially curved interconnected profiles, said number of substantially curved interconnected profiles being provided with one or more secondary chambers.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A sea bed foundation according to the invention, where a number of substantially curved interconnected profiles is shown.

(2) FIG. 2A sea bed foundation according to the invention, where a primary pump and secondary pumps are shown.

(3) FIG. 3AA sea bed foundation according to the invention, where secondary pressure chambers externally attached to the skirt are shown.

(4) FIG. 3BA sea bed foundation according to the invention, where secondary pressure chambers internally attached to the skirt are shown.

(5) FIG. 4A sea bed foundation according to the invention, where secondary pressure chambers integrated in the skirt are shown.

(6) FIG. 5Schematic illustration of a method for establishing a sea bed foundation according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(7) The invention will be described with respect to the figures. FIG. 1 shows a sea bed foundation 1 having a circumferential side wall (skirt) substantially defining a cylinder, which is closed in one end and provided with an opening in the opposite end.

(8) In this application sea bed refers to waterbottom in general (e.g., sea, lake, etc.), and cylinder refers to a surface created by projecting a closed two-dimensional curve along an axis, which perpendicularly intersects the plane of said curve. Hence, a cylinder according to this definition may for example have circular, elliptical or polygonal cross-sections.

(9) Said sea bed foundation 1 is hollow and downwardly open, and its side wall comprises a wall construction defining a skirt 6 and a primary pressure chamber 7 therein. The primary pressure chamber is connected to a primary pump 8 (FIG. 2) such as a suction pump. The foundation further comprise one or more secondary pressure chambers 9, in this example two secondary pressure chambers, connected to one or more secondary pumps 10 (FIG. 2) such as pressure pumps.

(10) FIG. 1 shows that the skirt 6 may be formed by a number of substantially curved interconnected profiles 11 provided with one or more secondary pressure chambers 9. The one or more secondary pressure chambers may preferably be evenly distributed along the skirt.

(11) In FIG. 2 is illustrated a foundation 1 hovering above a sea bottom 19. The dashed line 16 indicates a substantially horizontal plane, where it is desirable to erect the foundation substantially vertically, i.e. perpendicularly to this plane 16 and not the sea bottom 19. The pressure chambers 7,9 are open downwards (indicated by dashed arrows). As the lower rim of the skirt 6 is buried into the sea bottom, the pressure chambers 7,9 are entirely closedby the foundation structure and the bottom. By creating under pressure in the chambers 7,9 by evacuating the water in the chambers, the foundation structure will sink into the bottom 19. As the foundation 1 sinks into the bottom 19 it may/will encounter various bottom layers, which layers will create more or less resistance against the penetration, thereby causing the foundation structure 1 to come out of perfect alignment. In order to rectify this mis-alignment and make sure that the foundation 1 is placed substantially perfectly vertical, over-pressure is established in the chambers 9 by means of the pump 8. Preferably three chambers are provided such that complete three-axis control is established. The over-pressure created by the pumps 10 will increase the resistance against penetration adjacent the chamber 9, allowing the rest of the foundation to penetrate the bottom at the normal resistance, thereby rectifying the orientation of the foundation.

(12) The embodiments described in order to illustrate the invention are overly simplified in comparison to the real installations. In real life a substantial number of pumps, sensors, sometimes vibrators etc are installed in/on the foundation in order to aid installation, but for the purpose of illustrating the invention only the necessary components are described.

(13) FIG. 3A-B show two embodiments of the invention, where the secondary pressure chambers 9 are arranged externally or internally with respect to the skirt 6.

(14) FIG. 4 shows an embodiment of the invention, where the secondary pressure chambers 9 are integrated in the skirt 6 and divide the skirt in evenly distributed sections 18.

(15) FIG. 1-4 shows two secondary pressure chambers 9 for explicative reasons only. Hence, no limitation regarding the number of secondary pressure chambers has to be drawn from the figures. Foundations including three, four or more secondary pressure chambers 9 are also contemplated within the scope of the invention.

(16) FIG. 5 shows a schematic illustration of a method 12 for establishing a sea bed foundation 1 for an offshore facility. Said method comprises a sea bed foundation 1 according to any of the previous embodiments of the invention. The method comprises the steps of: Positioning 13 a sea bed foundation according to any of the previous embodiments on the sea-bed 19. Activating 14 said primary pump 8 to create negative pressure in the primary pressure chamber 7, so that the foundation sinks into the sea bed 19. Activating 15 said one or more secondary pumps 10 as necessary to create positive pressures in the secondary pressure chambers 9, so as to control the alignment of the foundation with respect to a substantially horizontal plane 16 during the sinking of the foundation 1 into the sea bed 19. Deactivating 17 said primary pump and said secondary pumps when the foundation has reached a desired level in the sea bed.

(17) Said positive pressures (or negative pressures or combinations thereof) may be applied in the one or more secondary pressure chambers 9 with different intensities by the one or more secondary pumps 10.

(18) It should be noted, see FIG. 2 that very often the sea bottom 19 is not even or provides a smooth surface. The sea-bottom may be prepared prior to installing the foundation, for example by removing the top sediment layers. Furthermore the bottom into which the foundation is to penetrate is typically made up of different types of soil such as sand, silt and/or clay and others. This naturally imposes special requirements to the control procedure of setting the foundation and the sinking action carried out by the pumps. The suction in the main suction chamber will have no effect until the lower rim of the skirt 6 has penetrated a certain distance into the sea bottom 19. This initial penetration/sinking of the skirt may be obtained by the foundation structures' own weight. Alternatively the initial sinking may be helped by mechanical means. It is important to assure that the pressure chambers are substantially closed before pressure both under and over pressure is established, as otherwise pressure will only fluidize the surrounding bottom with no or detrimental effect to the setting of the foundation.