GB1562075A - Ground anchor for anchoring at least one chaincable to theseabed - Google Patents

Description

(54) A GROUND ANCHOR FOR ANCHORING AT LEAST ONE CHAIN-CABLE TO THE SEABED (71) We, SOCIETE NATIONALE ELF AQUITAINE (PRODUCTION), a French Company, of Tour Aquitaine, 92400 Courbevoie, France, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a ground anchor for use underwater by placement on the seabed, of a type offering a high level of reliability, very easy maintenance, and a wide range of applications including use with floating or semi-submersible rigs for drilling and production purposes in connection with submarine hydrocarbon layers.

Anchoring cables may be attached to the heads of piles driven into the seabed. When such a system is employed, it is impractical to attach more than one cable per pile, and it is difficult to reach the point of attachment, either to check it or to replace certain parts, which can wear out. In addition, when the end of an anchorage cable is attached to the top of the pile, sharp movements are transmitted to the pile, which combined with the pulling forces parallel to the seabed, can overturn the pile and pull it out.

This invention overcomes these drawbacks, by separating the anchoring function, performed by at least one pile, and the cable-attachment function, performed by cable attachment means on an anchor block.

According to the invention there is provided a ground anchor for use underwater comprising an anchor block formed with at least one vertical cylindrical hole, and at least one pile which is cylindrical throughout its length, the number of piles being equal to the number of holes in the block, the crosssection of the or each pile being slightly smaller than the cross-section of the corresponding hole in the block, the upper end of each pile being provided with a projecting rim having dimensions larger than those of the cross-section of the corresponding hole in the block, and said anchor block having dimensions transverse to the vertical hole greater than those axially of the hole and having means thereon remote from the or each hole and towards an edge of the block for connecting or disconnecting one end of an anchoring cable.

The or each pile may comprise a projecting rim adjacent its lower end the outer dimension of said rim being larger than the inner dimension of the corresponding cylindrical hole in the anchor block.

In certain embodiments of the invention, the or each cylindrical hole may contain a tubular lining the inner cross-sectional dimension of which is larger than the outer cross-sectional dimension of the corresponding cylindrical pile.

In such embodiments, the tubular lining may have means for sealing an annular space defined between the lining and the corresponding pile and means for filling the space with settable grouting.

The invention will be described hereafter in a more detailed manner with reference to the appended figures which show, by way of example, but not of limitation, several embodiments of the invention: Figure 1 is an elevational view of a ground anchor comprising a single pile separable from an anchor block; Figure 2 is a sectional view of the anchor shown in Figure 1 along the plane A in Figure 1; Figure 3 is an elevational view of a ground anchor having a single pile which is not separable from an anchor block; Figure 4 is a sectional view of the anchor shown in Figure 3 on the plane A in Figure 3; Figure 5 is an elevational view of a ground anchor having an anchor block for three chain cables and a single pile, and Figure 6 is a plane view of the anchor block shown in Figure 5.

As shown in Figure 1 an anchor block 2 is provided with a central vertical hole 3 of cylindrical circumferential configuration and is arranged to rest on the seabed 1. Block 2 and hole 3 have a common axis of symmetry 22'. The hole 3 contains a tubular lining 4, the inner dimensions of which are slightly larger than the outside dimensions of a pile 5, which slides inside this lining and penetrates the seabed 1. The pile is cylindrical throughout its length. The length of lining 4 is at least equal to the largest transverse dimension of pile 5, in other words, at least equal to the outer diameter of the said pile. In the embodiment shown, lining 4 has a length greater than the thickness of the anchor block 2, and it is held rigidly against the block by means of brackets 6 made of thick metal sheet.

Anchor block 2 may be made of steel, concrete, a metal casing filled with concrete, or built up from individual cells. In general it consists of a thick metal plate or of a set of plates joined together by any suitable means, for example by bolts extending through them.

Internal guide plates 9, consisting of flat vertical strips welded to the inner surface of lineing 4, restrict the clearance between the lining and the outer circumference of pile 5, while leaving enough space for the injection of grouting cement 10, in order to ensure a rigid assembly. Sealing devices and the inlet for injection of cement between the lining and the pile are constructed according to conventional techniques, and are not shown in the Figures.

The top end of pile 5 comprises a circular rim 11, the outer dimensions of which are larger than the inner dimensions of lining 4.

The inner surface of this circular rim 11 forms a projection through which the pile 5 is supported by the upper edge of lining 4.

In cases where rigid assembly of the piles 5 and the block 2 is not considered necessary, the space between lining 4 and pile 5 is reduced to a minimum of a few centimetres, and no provision is made for injecting cement: the pile 5 is simply driven into the seabed, by drilling or vibration driving, until the upper rim comes to rest against the upper edge of the tubular lining 4 or on the anchor block 2.

The anchor block comprises two flat surfaces, to wit: a lower surface 2a, which rests on the seabed, and an upper surface 2b, to which is attached at least one device 7 for at least one anchoring cable 8, and at least two guide columns 12 and 13, of a type known per se, for positioning pile 5 after the block has been depositied on seabed 1. These guide columns are arranged symmetrically with respect to the cen. > e-line 22', and interposed between points provided for connection devices such as 7.

The connection device 7 shown in Figures 1 and 2 is positioned towards the edge of the block 2 remote from the hole 3 and is described in greater detail below, in connection with Figures 5 and 6.

After the plate 2 has been positioned in the seabed, pile 5 can be lowered while being guided until it reaches the level of guide columns 12 and 13, by means of buoy ropes 14 and 15, which connect the tops of these guide columns to buoys on the surface.

Alternatively, pile 5 can be guided until it reaches the level of these columns, by means of an ultrasonic positioning device, which uses reflectors placed on each side of the block at selected locations; such equipment is not shown in the figures.

Figures 3 and 4 schematically illustrate ground anchor with a single pile, designed to be lowered into position together with the anchor block.

This embodiment is substantially the same as that shown in Figures 1 and 2 and comprises a plate 2, tubular lining 4, attachment device 7 for a cable 8, and a pile 5 sliding inside lining 4.

The upper end of the pile 5 comprises a circular rim 11, the outer dimensions of which are greater than the inner dimensions of lining 4. The lower surface of this rim 11 forms a projection which fits against the upper edge of lining 4, when the pile has been driven into the seabed.

The lower end of pile 5 comprises a circular rim 16, the outer dimensions of which are larger than the inner dimensions of tubular lining 4. The upper surface of this rim 16 forms a projection on which the anchor block 2 rests when the ground anchor is being lowered to the seabed.

The position of block 2 during lowering is indicated by a dotted line of 2' in Figure 3.

Figures 2 and 4 show diagrammatically an area 17 designed for the berthing of a manned underwater vehicle or a robot vehicle radio-controlled from the surface. Such vehicles are used in fact for connecting or disconnecting the cable 8, or for carrying out any other operations.

Figures 5 and 6 show an anchor block 2 fitted with attachment devices 7 for three anchoring cables and a pile 5, in elevational and plan view, respectively.

A tubular lining 4 is fixed to a plate 2 and extends therethrough. Lining 4 and plate 2 have a common axis of symmetry 22'. The pile 5 is slidably mounted inside this lining.

The anchor block 2 also comprises three attachment devices 7 distributed about the symmetry axis 22' towards the edge of the block 2 for anchoring cables 8, as well as subsidiary connection devices 26 for an emergency cable (not shown here) and 27 for a cable 28, which carries a hose or electric cable 29.

The anchor block 2 illustrated in Figures 5 and 6 is specially designed for use with a wide-diameter pile 5, which is pile-driven or vibration-driven into seabed 1.

Ground anchors as described herein can be constructed in widely varying forms, to anchor floating or semi-submersible equipment used for drilling or production purposes in connection with underwater oilfields, and for linking such equipment, as well as for any kind of floating equipment used for any other purpose.

WHAT WE CLAIM IS: 1. A ground anchor for use underwater comprising an anchor block formed with at least one vertical cylindrical hole, and at least one pile which is cylindrical throughout its length, the number of piles being equal to the number of holes in the block, the crosssection of the or each pile being slightly smaller than the cross-section of the corresponding hole in the block, the upper end of each pile being provided with a projecting rim having dimensions larger than those of the cross-section of the corresponding hole in the block, and said anchor having dimensions transverse to the vertical hole greater than those axially of the hole and having means thereon remote from the or each hole and towards an edge of the block for connecting or disconnecting one end of an anchoring cable.

2. A ground anchor according to Claim 1, wherein the or each pile has a projecting rim adjacent its lower end, the outer dimension of said rim being larger than the inner dimension of the corresponding cylindrical hole in the anchor block.

3. A ground anchor, according to Claim 1 or 2, wherein the or each cylindrical hole contains a tubular lining the inner crosssectional dimension of which is larger than the outer cross-sectional dimension of the corresponding cylindrical pile.

4. A ground anchor, according to Claim 3, wherein the tubular lining has means for sealing an annular space defined between the lining and the corresponding pile and means for filling the space with settable grouting.

5. A ground anchor for use underwater constructed and arranged substantially as described herein with reference to and as illustrated in Figures 1 and 2, Figures 3 and 4 or Figures 5 and 6 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. and 6 is specially designed for use with a wide-diameter pile 5, which is pile-driven or vibration-driven into seabed 1. Ground anchors as described herein can be constructed in widely varying forms, to anchor floating or semi-submersible equipment used for drilling or production purposes in connection with underwater oilfields, and for linking such equipment, as well as for any kind of floating equipment used for any other purpose. WHAT WE CLAIM IS:

1. A ground anchor for use underwater comprising an anchor block formed with at least one vertical cylindrical hole, and at least one pile which is cylindrical throughout its length, the number of piles being equal to the number of holes in the block, the crosssection of the or each pile being slightly smaller than the cross-section of the corresponding hole in the block, the upper end of each pile being provided with a projecting rim having dimensions larger than those of the cross-section of the corresponding hole in the block, and said anchor having dimensions transverse to the vertical hole greater than those axially of the hole and having means thereon remote from the or each hole and towards an edge of the block for connecting or disconnecting one end of an anchoring cable.

2. A ground anchor according to Claim 1, wherein the or each pile has a projecting rim adjacent its lower end, the outer dimension of said rim being larger than the inner dimension of the corresponding cylindrical hole in the anchor block.

3. A ground anchor, according to Claim 1 or 2, wherein the or each cylindrical hole contains a tubular lining the inner crosssectional dimension of which is larger than the outer cross-sectional dimension of the corresponding cylindrical pile.

4. A ground anchor, according to Claim 3, wherein the tubular lining has means for sealing an annular space defined between the lining and the corresponding pile and means for filling the space with settable grouting.

5. A ground anchor for use underwater constructed and arranged substantially as described herein with reference to and as illustrated in Figures 1 and 2, Figures 3 and 4 or Figures 5 and 6 of the accompanying drawings.