EP0853575A1

EP0853575A1 - Anchor system

Info

Publication number: EP0853575A1
Application number: EP96935607A
Authority: EP
Inventors: Eldar Lien; Sigurd Ree
Original assignee: Selantic AS
Current assignee: Selantic AS
Priority date: 1995-10-19
Filing date: 1996-10-18
Publication date: 1998-07-22
Also published as: AU7345296A; NO954190D0; WO1997014609A1; NO954190L; BR9611072A; NO301701B1

Abstract

An expanding anchor system consists of a central pile (1) with along the length equiangularly spaced pair of wings (3) and an anchor plate (2), having the mooring line termination points (8) guided on the pile between a top stopper (4) and a bottom stopper (5). When in the upper position, the anchor is fully installed, the wires terminated to the pile head (13), the wings (3) and the anchor plate (2) (system A) and termination ring (7) (system B) are tightened up and form a massive steel and sediment bolt.

Description

ANCHOR SYSTEM

Background.

Seabed teraiination points with predicted holding capacity becomes more and more a necessity for deep water operations. Mooring and anchoring in deep water creates a need for shortening the mooring lines which again creates a need for an anchor system capable of taking vertical line forces. System cost and holding capacity are the most critical design parameters for a deep water anchor systems. Installation method is a key cost element, and generally we can say that a system based on the following design philosophy has a good chance to become commercial attractive;

minimising the need for installation energy, and maximising the pull out force

The expanding principle is welknown through many applications, from expanding nails to anchors. Reference is made to patents like GB 2106849, US 3,154,042, US 3,170,433, US 3,370,566 „„. ^'

We hereby introduces a new expanding pile anchore consisting ofthe following key elements,

the central pile with wings, the anchor plate with the termination point for the anchor line -

Functional description.

Reference is made to drawings Al, A2, A3 and B1,B2, B3, B4 showing the components and the principle.

The anchor consists of a central pile (1). Along the length ofthe pile, there are pair of "hinged" wings (3) equiangulary spaced. These wings are sections of tubes with inner diameter equal to the outer diameter ofthe main tube, so that when folded together, they are encapsulating the main tube. The wings are hinged at the top end. Figure Al, A2 and A 3 shows a system where the anchor plate moves on the pile between two fixed positions, bottom stopper (5) and top stopper (4), so that the wires (6) connected between the anchor plate (2), the wings (3) and the pile (1), pulls the wings(3) out into horizontal position when the anchor plate (2) has moved to its upper position on the pile. For system B, the same will occur, except that the anchor plate (2) will position itself on the seabed, and as the pile (1) penetrates, the wires (6) will force the wings out into the sediment when the termination ring (7) hits the anchor plate (2). Again the termination ring (7) together with the anchor ρlate(2) will force the wings (3) out into the sediment through the wire ropes (6), until they have reach the upper position given by the top stopper (4) on the pile (1) and the wings (3) are then horizontal.

The system is installed by a hammer (9) (electric, hydraulic or hydrostatic operated). The anchor line is terminated to the anchor line termination points (8) on the anchor plate (2), which together with the pile(l) and the wings(3) will form a massive steel - sediment plug. The anchor plate(2) has skirt(l 1) and a suction throttle valve(12) (hatch) which are open during penetration, and are closed automatically when the pile has reached full penetration, enabling this anchor plate(2) to increase the suction created by pulling in the anchor line. This suction and sealing ofthe top sediments, which mostly are very soft, is a key element in the current invention. The lineforce is acting through the anchor plate(2), which again is pulling in the central pile(l). The wings(3) are connected to the wires(6) which again is terminated to the tube head(13) and to the anchor plate(2) (system A) and the termination ring(7) (system B). It all ends up to become a massive steel and sediment bolt. The expanding anchor can be designed so that the static forces can be taken by the sediment rupture friction forces, while the dynamic loading can be taken by the suction rupture force.

When installed, the expanding anchor will tend to reorientate towards the line direction. The horizontal component ofthe line force will try to turn the anchor. The elasticity in the anchor design (wires, wings, tube) combined with local flow in the sediment, will make the anchor turn towards the anchor line direction, until equilibrium is settled. The horizontal capacity ofthe anchor is given by the skirt(l 1) of the anchor plate, the stiffness ofthe pile(l), wires(6) and wings(3). The pile(l) will start turning and mobilising an increasing horizontal capacity. This is given by contribution from the anchor plate(2), which will be forced down into the sediments, as well as resistance against turning from the wings(3). It must be underlined that the wires connected to the wings are terminated in one end to the anchor plate (system A) and the termination ring(7) (system B), and in the other to the tube head(13). The movement ofthe pile, will be a combination of horizontal and vertical displacement, until the anchore has mobilised enough of its potential holding capacity. The anchor is retreavable. By pulling in the central pile(l) through connecting a winch line to the adapter (10), the wings(3) will fold together and the anchor plate(2) follow accordingly.

Anchor design optimisation will be done based on exact geotechnical input, together with line tension and line angle. Pile length, pile diameter and wing length, together with steel cross section thickness in individual components will be chosen in order to achieve the specified holding capacity at lowest possible system weight.

The expanding pile anchor will be a light weight anchor alternative, capable of mobilising large holding capacities.

Claims

Claims.

1. An expanding anchor system, comprising a central pile(l) with along the length equiangulary spaced pair of wings(3) and an anchor plate(2), having the mooring line termination points(8), guided on the pile between a top stopper (4) and a bottom stopper (5), so that when in the upper position, the anchore is fully installed and the wires terminated to the pile head(13), the wings(3) and the anchor plate(2) (system A) and termination ring(7) (system B) are tightened up and form a massive steel and sediment bolt.

2. According to claim 1, an anchor plate(2) containing an anchor line termination point(8) and enabling to seal the top sediments and increase the suction force mobilised by the system.

3. According to claim 1, wings(3) that are hinged on the central pile(l) and also terminated at the other end to a wire(6), so when loaded by the sediments, the wings are supported in both ends.

4. According to claim 1, wires(6) that are parallel to the central pile(l) and terminated to the tube head(13) and at the other end to the anchor plate(2) (system A) or alternatively a termination ring(7) on the pile (system B).

5. According to claim 3, a system locking the wings(3) along the pile(l) during penetration, released when the anchor plate(2) starts moving (sys.A) or the termination ring(7) starts moving (sys.B) on the pile(l).

6. According to claim 1, a central pile(l) made up from short sections, enabling field assembly ofthe complete anchor.

8. According to claim 2, an anchore plate(2) with skirts(l 1) and a suction throttle valve(12) for increasing the suction holding force ofthe anchor system.

9. According to claim 2, an anchor termination point(8), consisting of two points diametrically spaced on the circumference ofthe anchor plate(2).

10. According to claim 2, an anchor plate(2) with a long tube section(14) for good load distribution to the anchor pile, and with stiffeners(15) out to the skirt(l 1), dividing this into sections. 11. According to claim 3, wings(3) that are sections of tubes, cut in two and mounted so that they encapsulate the central pile(l) and with a hinged termination to the wire.

12. According to claim 6, on the top end ofthe pile, an adapter(l θ) for connecting the installation tool(9), and for retrieval ofthe anchor, also a connection for the pull out wire.

13. According to claim 1, a system so when pulling in the pile(l) through the adapter (10), the expanding anchor will fold together and in this way be able to retrieve.

14. According to claim 8, skirts(l 1) with sufficient area to offer horizontal stability ofthe anchor.

15. According to claim 1, a complete anchor system having the elastic flexibility to adjust according to anchor line angle until sufficient holding capacity is mobilised.

16. According to claim 8, an arrangement that automatically closes the suction throttle valve(12) when the anchor plate(2) has reached its top position on the pile.