METHOD FOR INSTALLING AN ANCHORING SYSTEM

Abstract

The present invention provides a method for installing an off-shore anchoring system comprising drilling a borehole in a seabed, the borehole comprising a first lower portion in communication with a second upper portion. The cross-sectional dimensions of the first lower portion are smaller than the cross-sectional dimensions of the second upper portion. An inwardly protruding abutment surface is provided at a transition point located therebetween. The method further comprises introducing settable locking media into the borehole. The method further comprises subsequently introducing an off-shore anchoring system comprising an anchor pile and a lateral load transition member into the settable locking media within the borehole, such that the anchor pile is located within the first lower portion of the borehole, and the lateral load transition member is located within the second upper portion of the borehole and spaced apart from the anchor pile.

Claims

1. A method for installing an off-shore anchoring system comprising: drilling a borehole in a seabed, the borehole comprising a first lower portion in communication with a second upper portion, in which the cross-sectional dimensions of the first lower portion are smaller than the cross-sectional dimensions of the second upper portion, and in which an inwardly protruding abutment surface is provided at a transition point located therebetween; introducing settable locking media into the borehole; and subsequently introducing an off-shore anchoring system comprising an anchor pile and a lateral load transition member into the settable locking media within the borehole, such that the anchor pile is located within the first lower portion of the borehole, and the lateral load transition member is located within the second upper portion of the borehole and spaced apart from the anchor pile.

2. A method as claimed in claim 1, comprising introducing the settable locking media into the first lower portion of the borehole.

3. A method as claimed in claim 2, in which the settable locking media is introduced into the first lower portion and to not extend beyond the transition point.

4. A method as claimed in claim 1, in which the locking media comprises cement or grout.

5. A method as claimed in claim 1, in which the off-shore anchoring system comprises: an anchor pile comprising a first elongate body having an upper end and a lower end; a lateral load transition member comprising a second elongate body having an upper end, and an opposed lower end positioned adjacent and spaced apart from the upper end of the first elongate body of the anchor pile; and an intermediate portion connecting the lower end of the second elongate body of the lateral load transition member to the upper end of the first elongate body of the anchor pile.

6. A method as claimed in claim 5, further comprising positioning the second elongate body of the lateral load transition member such that at least a portion of the lower end of the second elongate body extends into the first lower portion of the borehole.

7. A method as claimed in claim 1, comprising drilling a first lower portion of the borehole having a cross-sectional dimension of between 300 mm and 500 mm.

Description

BRIEF DESCRIPTION OF FIGURES

[0039] FIG. 1 is a schematic illustration of an anchoring system being inserted into a borehole according to one embodiment of the present invention;

[0040] FIG. 2 is a schematic illustration of a view from below of an anchor system being inserted into a borehole, and subsequently in use, according to the embodiment of FIG. 1; and

[0041] FIG. 3 is a schematic illustration of a view from above of an anchor system being inserted into a borehole, and subsequently in use, according to the embodiment of FIG. 1.

DETAILED DESCRIPTION

[0042] With reference to the Figures, the off-shore anchoring system 1 comprises an anchor pile 2, an intermediate portion 3 and a lateral transition assembly 4.

[0043] The anchor pile 2 comprises a first elongate body 6 having an upper end 7 and a lower end 8.

[0044] The lateral load transition member 4 is spaced apart, by the intermediate portion 3, from the upper end 7 of the first elongate body 6 of the anchor pile 2.

[0045] The lateral load transition member 4 comprises a second elongate body 9 having an upper end 10 configured in use to be in communication with a laterally loaded mooring tether 12, and an opposed lower end 11. The second elongate body 9 is substantially cylindrical in shape.

[0046] The tether 12 has a first end connectable to the upper end 10 of the second elongate body 9 of the lateral load transition member 4, and a second opposed end 13 for connection to a tether termination (not shown) which may for example be a connection point for a main mooring line. The tether 12 is flexible and may be enclosed within a protective outer layer to protect the tether 12 from frictional forces arising as a result of lateral loading forces from the main mooring line causing the tether to move (or cut) through the surrounding geological formation.

[0047] The intermediate portion 3 connects the lower end 11 of the second elongate body 9 of the lateral load transition member 4 to the upper end 7 of the first elongate body 6 of the anchor pile 2. The intermediate portion 3 is rigid and provides the spacing between the upper end 7 of the first elongate body 6 of the anchor pile 2 and lower end 11 of the second elongate body 9 of the lateral load transition member 4.

[0048] The offshore anchoring system 1 is installed by drilling a borehole 5 in a seabed. The borehole 5 comprises a first lower portion 14 in communication with a second upper portion 15. The cross-sectional dimensions of the first lower portion 14 are smaller than the cross-sectional dimensions of the second upper portion 15. An inwardly protruding abutment surface 16 is provided at a transition point located therebetween.

[0049] Settable locking media is introduced into the borehole 5. The settable locking media is introduced into the first lower portion 14 to extend from the lower end 17 thereof towards (preferably up to) the transition point.

[0050] The anchor pile 2 is then introduced into the borehole 5. The anchor pile 2 is received within the first lower portion 14 of the borehole 5 containing the settable locking media. The anchoring system 1 continues to be introduced so that the lateral load transition member 4 is introduced into the second upper portion 15. The lateral load transition member 4 is positioned within the second upper portion 15 of the borehole 5 and abuts the inwardly protruding abutment surface 16 provided at the transition point.

[0051] The cross-sectional dimensions of the second elongate body 9 of the lateral load transition member 4 are greater than the cross-sectional dimensions of the first elongate body 6 of the anchor pile 2. The cross-sectional dimensions of the second elongate body 9 are slightly smaller than the cross-section dimensions of the upper portion 15 of the borehole 5 to ensure a tight fit to enable efficient transmission of lateral forces from the lateral load transition member 6 into the surrounding portions of the borehole.

[0052] The second elongate body 9 of the lateral load transition member 4 comprises side portions 18 extending between the upper and lower ends 10, 11 thereof, configured in use to abut surrounding wall portions of the second upper portion 15 of the borehole 5 to create, in use, hoop stress within the second upper portion 15 of the borehole wall 5 without penetration thereof.

[0053] The method of the present invention provides a simple, reliable installation methodology.

[0054] The anchoring system of the present invention can be used to effectively and reliably anchor a tether, for example mooring line, to provide a taut mooring solution over time. The anchoring system of the present invention may be compatible with a wide range of geological formations.

[0055] The lateral load transition member is located to resist the lateral forces of the loading from a mooring and to transmit the lateral forces of the loading into the surrounding borehole wall portions. In one embodiment, the lateral load transition member is configured to be positioned within the second upper portion of the borehole at a location which has sufficient lateral resistance to prevent penetration of the borehole wall portions by the lateral load transition member. Preferably, the lateral load transition member is configured to be positioned at the highest point within the borehole at which the lateral load transition member will remain stable (i.e. will not penetrate the borehole wall).

[0056] The anchoring system of the present invention may be capable of resisting high loads, for example in excess of 1000 tonnes.

[0057] The anchoring system of the present invention may be used for resisting high angle mooring through to vertically loaded tension leg systems.

[0058] The anchoring system of the present invention enables the lateral forces exerted by the tether to be resisted and transmitted directly into the geological surfaces surrounding the borehole. As a result, the anchoring system of the present invention reduces the forces exerted on the tether, thereby reducing the cutting motion of the tether through the geological surfaces which occurs with conventional anchoring systems. The anchoring system of the present invention therefore reduces the length of tether required and thereby reduces the cost of materials, reduces the potential for damage to occur to the tether as a result of the cutting motion and therefore reduces labour and costs associated with repair and/or replacement of the tether over time. The anchoring system of the present invention reduces the risk of failure of the anchor pile as a result of damage to the tether and thereby provides a more reliable anchoring system.