BACKGROUND TO THE INVENTION Conventional sea anchors for holding down structures such as offshore drilling platforms, usually take the form of large concrete blocks placed on the seabed with cables or chains attached. This type of sea anchor requires a significant number of blocks of concrete. The larger the structure, the greater the mass of concrete required to achieve the desired capacity. The other type of conventional sea anchor employs steel tubes which are driven into the seabed. In order to achieve the required capacity, these tubes must be very large and long to increase the surface area and gain the necessary friction, particularly in sandy soils.

The capacity required per anchor point can be as much as 300 tonne or higher. In both conventional forms of sea anchor the time involved in installing the anchor can be significant, which makes the operation very expensive. Part of the difficulty is that weather conditions at sea often only permit small windows of time within which the work can be completed.

SUMMARY OF THE INVENTION The present invention was developed with a view to providing a high capacity anchor that can be quickly installed. It will be apparent that the anchor in accordance with the present invention is not limited in its application to the anchoring of offshore structures, but can also be used onshore for the anchoring of structures on land.

Throughout this specification the term"comprising"is used inclusively, in the sense that there may be other features and/or steps included in the invention not expressly defined or comprehended in the features or steps subsequently defined or described.

What such other features and/or steps may include will be apparent from the

specification read as a whole.

According to one aspect of the present invention there is provided a high capacity anchor comprising : a hollow, elongate body adapted to be driven into soil; a pair of planar members protruding from opposite sides of the elongate body along substantially its full length, each planar member having an inclined surface provided at a rear edge thereof; and, an attachment means fixed to said elongate body for attaching one end of an anchor line to the anchor whereby, in use, when the anchor has been driven into soil along a drive path and a pull force is applied to the elongate body via said anchor line, the anchor pivots away from said drive path, guided by said inclined surfaces, towards a position in which said planar members are oriented substantially perpendicularly to the direction of said pull force wherein further withdrawal of the anchor is inhibited by the resistance offered by the planar members.

According to another aspect of the present invention there is provided a high capacity anchor cluster comprising: a plurality of anchors, each anchor having a hollow, elongate body adapted to be driven into soil, each body being slidably mounted end to end on a drive shaft; each elongate body having a pair of planar members protruding from opposite sides thereof, and an attachment means fixed to the elongate body for attaching one end of a respective anchor line to each anchor; whereby, in use, when the plurality of anchors have been driven into soil on the drive shaft along a drive path, the drive shaft has been removed and a pull force is applied to each elongate body via said respective anchor lines, each anchor pivots away from said drive path towards a position in which it is oriented substantially perpendicularly to the direction of said pull force, wherein further withdrawal of the anchor cluster is inhibited.

Preferably said pair of planar members are each provided with a stabilising fin at an outer extremity thereof to further assist in guiding the anchor as it pivots away from the

drive path. Advantageously said attachment means comprises a pair of lugs fixed side by side to respective sides of said elongate body and each having an aperture provided therein for attaching said anchor line to the lugs. Typically said anchor line is a cable or chain that can be attached to the lugs using a shackle and/or removable pin arrangement.

Typically said elongate body is of circular cross-section and said pair of planar members are co-planar and protrude substantially perpendicularly from an outer wall of the elongate body.

Preferably each of said plurality of anchors are arranged on the drive shaft with its planar members oriented substantially at right angles to the planar members of an adjacent anchor. Advantageously, each anchor is provided with an interlocking means, at each end of its elongate body, adapted to interlock with the interlocking means of an adjacent anchor so as to hold the respective anchors in the correct orientation relative to its neighbour. Advantageously a sacrificial point element is provided at the front end of the drive shaft, said point element being removably attached to the front end of the drive shaft and adapted to remain in the soil when the drive shaft is removed.

According to a further aspect of the present invention there is provided a method of high capacity anchoring of a structure in soil, the method comprising the steps of : driving a plurality of spade anchors along a drive path into soil to a required depth, the anchors being slidably mounted end to end on a drive shaft, and each anchor having an anchor line attached thereto; removing the drive shaft from the soil ; applying a pull force to each of said plurality of anchors via the respective anchor lines, whereby each anchor pivots away from said drive path to a position in which it is oriented substantially perpendicularly to the direction of said pull force wherein further withdrawal of the anchors is inhibited.

According to yet another aspect of the present invention there is provided a high capacity anchor column comprising: a rigid elongate support member adapted to be driven into soil; a pair of anchor members pivotally mounted on respective opposite sides

of the support member and adapted to pivot outwards from a first position, in which the anchor members lie substantially flat against the sides of the support member, to a second position, in which the anchor members extend laterally from the sides of the support member; and, constraining means for constraining said anchor members in the second position whereby, in use, after said support member is driven into soil and a pull force is applied thereto, said anchor members pivot outwards to said second position and are constrained from further movement so as to inhibit further withdrawal of the elongate support member.

Preferably said pair of anchor members is one of a plurality of pairs of anchor members pivotally mounted on the support member at spaced intervals along the length of the support member. Preferably said pair of anchor members are located towards the lowermost end of the support member. Typically said support member is provided with an anchor point adjacent the uppermost end thereof to which a structure may be tethered to anchor it.

Preferably said anchor members are provided with a trip latch for holding them in the first position until a pull force is applied to the support member. Preferably said anchor members are in the form of substantially rectangular anchor plates having an outwardly protruding lip adapted to dig in to the soil when the pull force is applied to the support member, so as to unlatch the anchor plates and cause them to pivot outwards to the second position.

Preferably said constraining means is in the form of a pair of elongate, flexible members, provided on respective sides of each anchor plate and having one end fixed to the anchor plate and the other end fixed to the support member. Typically said elongate, flexible members are in the form of high tensile chains.

Typically said elongate support member is formed from a steel beam, for example, a universal (I) beam or universal (H) column. Alternatively a steel tube may be used.

BRIEF DESCRIPTION OF THE DRAWINGS In order to facilitate a more comprehensive understanding of the nature of the invention, a preferred embodiment of the high capacity anchor and method of anchoring will now be described in detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a plan view of a preferred embodiment of a high capacity anchor in accordance with the present invention; Figure 2 is a side view of the high capacity anchor of Figure 1 ; Figure 3 is an end view of the high capacity anchor of Figure 2 viewed in the direction of arrow A; Figure 4 illustrates a plurality of the anchors of Figures 1-3 mounted end to end on a drive shaft; Figure 5 illustrates an anchor cluster in situ, viewed in side elevation; Figure 6 is a plan view of a second embodiment of a high capacity anchor in accordance with the present invention; Figure 7 is a side view of the high capacity anchor of Figure 6; Figure 8 is an end view of the high capacity anchor of Figure 7; Figure 9 is a perspective view of a preferred embodiment of a high capacity anchor column according to the present invention; and, Figure 10 is a side elevation of the anchor column of Figure 8.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS A preferred embodiment of a high capacity anchor 10 in accordance with the present invention is illustrated in Figures 1-3. The anchor 10 is in the form of a spade anchor and comprises a hollow elongate body 12 of circular cross-section and adapted to be driven into soil or the seabed. A pair of planar members 14 protrude from opposite sides of the elongate body 12 and extend along substantially its full length as can be seen most clearly in Figure 1. A front edge 16 of the planar members is swept back to permit the anchor to be driven into soil or seabed more easily. On the other hand, each planar member 14 is formed with an inclined surface 18 at a rear edge thereof as can be seen most clearly in Figure 2 (omitted from Figure 3 for clarity). The inclined surfaces 18 are like flaps on an aircraft wing, except that they are fixed in position, that guide the trajectory of the anchor as it is first pulled back as will be described further below.

Preferably, each planar member 14 is also provided with a stabilising fin 20 at an outer extremity thereof to further assist in guiding the anchor in its trajectory. In particular, stabilising fins 20 help to inhibit transverse movement of the anchor during tensioning or anchoring.

An attachment means in the form of pair of lugs 22 is fixed to the elongate body 12 for attaching one end of an anchor line 24 (see Figure 5) to the anchor 10. Each lug 22 is welded to the respective sides of the elongate body 12 approximately midway along, and is provided with a aperture 26 therein for attaching the anchor line 24 to the lugs 22 by means of an anchor pin (not shown) or shackle 28 (see Figure 5).

In use, the anchor 10 is driven into soil with an anchor line 24 attached thereto. When the anchor 10 has been driven into the soil to the required depth, a pull force can be applied to the elongate body 12 via the anchor line 24. Initially, the anchor will be oriented substantially parallel to the drive path. However, as the tension on the anchor line is increased and the anchor is drawn backwards towards the surface by the anchor line 24, the anchor 10 begins to pivot away from the drive path, guided by the inclined surfaces 18 and fins 20 towards a position in which the planar members 14 are oriented substantially perpendicularly to the direction of the pull force. Eventually, further withdrawal of the anchor will be inhibited by the resistance offered by the comparatively large surface area

of the planar members 14.

In its more preferred form, a plurality of anchors are provided stacked on top of each other to form an anchor cluster 30 as illustrated in Figure 4. In the illustrated embodiment, four high capacity anchors 10a, lOb, lOc and 10d are slidably mounted end to end on a drive shaft 32. Each of the anchors 10a, lOb, 10c and 10d is substantially identical to the anchor 10 illustrated in Figures 1 to 3. In Figure 4 each of the anchors 10 has been separated from its adjacent anchor for the purposes of illustration, however, in practice each of the anchors would abut against its neighbour, having its planar members 14 oriented substantially at right angles to the planar members 4 of the adjacent anchors 10.

Preferably each anchor is provided with an interlocking means, at each end of its elongate body 12, adapted to interlock with the interlocking means of an adjacent anchor so as to hold the respective anchors in the correct orientation relative to its neighbour. In the illustrated embodiment, the interlocking means takes the form of a pair of projections 34 and matching recesses 36 located'at a front and rear ends respectively of the hollow elongate body 12 (See Figures 1 to 3). The pair of projections 34 are provided at the front end on diametrically opposite sides of the elongate body 12, and the pair of recesses 36, provided on diametrically opposite sides at the rear end of the elongate body 12, are oriented at substantially 90° with respect to the front projections 34. Hence, when the projections 34 on one anchor interlock with the recesses 36 on an adjacent anchor the interlocked anchors will be oriented at substantially right angles to each other.

A sacrificial point element 38 is provided at the front end of the drive shaft 32 and is adapted to assist in driving the whole assembly into the soil. Point element 38 is formed with four barbs 40 which align with the respective planar members 14 of the anchors 10 and effectively cut a path for the planar members 14 as the drive shaft 32 is driven into the soil. Point element 38 is removably attached to the front end of the drive shaft 32 by means of a shear pin (not illustrated) which shears when a load is applied to the drive shaft 32. Hence, once the drive shaft has been driven to the required depth in the soil, it can be withdrawn leaving the point element 38 (and each of the anchors 10) behind in the soil.

in Figure 5. Anchor 10a will travel into the plane of the page, whereas anchor 10c travels out of the plane of the page. Each of the anchor lines 24 may be attached at a central load point above the seabed where a larger cable or chain can carry the full load and be attached to the structure to be secured. By employing a cluster of anchors in the manner illustrated, the total capacity of the anchor cluster will be multiplied by the number of anchors used. Thus, for example, if each anchor 10 has a 75 tonne capacity, the four anchor cluster will have a total capacity of 300 tonnes.

The capacity of the individual anchors 10 can be further increased by increasing the surface area of the wing-shaped planar members 14. Figures 6,7 and 8 illustrate a second embodiment of the anchor 80 having planar members 82 of increased width. Attachment means in the form of a two pairs of lugs 84 are provided intermediate the width of each of the planar members 82 in this embodiment, in order to avoid the need to provide additional bracing or to unduly increase the thickness of the planar members 82. Each pair of lugs 84 is formed with an aperture therein for attaching respective portions of an anchor line (not shown) to the lugs. In other respects the anchor 80 of this embodiment is similar to the anchor 10 of Figures 1 to 5 and will not be described again here.

Each of the anchors 10 may also be recovered by attaching a second line to the front end of the anchor (not illustrated). When a pull force is applied to the second line, the front end of the anchor will be pulled back and the anchor can then move in a straight line and be pulled back through the soil and brought to the surface.

It will be apparent from the above description that the described high capacity anchor has a number of significant advantages, including the following: (i) each anchor can be manufactured from a relatively small mass of high grade steel, greatly reducing the transport and installation costs compared to conventional methods of anchoring; (ii) the use of multiple anchors in a cluster substantially increases the capacity of the anchor with minimal additional weight or effort ;

A method of anchoring a structure in soil using the cluster of high capacity anchors illustrated in Figure 4 will now be described with reference to Figure 5.

Figure 5 illustrates the manner in which a high capacity anchor cluster, comprising four anchors 10, can be installed in a seabed 42. The four anchors 10a, lOb, lOc and 10d are driven into the seabed by means of the drive shaft 32, (as illustrated in Figure 4) to the required depth along a drive path 44. Each anchor 10 has an anchor line 24 attached thereto which is drawn down with the anchors as the drive shaft 32 is driven into the seabed. A large vibrating or impact piling hammer, suitable for working under water, is attached to the other end of the drive shaft 32. The hammer can be lowered into the sea by crane from a barge or other suitable vessel and will drive the shaft into the seabed to the required depth. This may typically be anywhere between 10 to 20 metres, depending on the soil structure. On reaching the required depth, the drive shaft 32 is removed and the point element 38 is left behind in the soil (not illustrated in Figure 5). When the drive shaft has been removed, each of the anchors I Oa, I Ob, I Oc and 10d is free to follow its own trajectory. However, during driving of the drive shaft 32, each anchor must follow the drive path of the drive shaft 32, since it is constrained by the drive shaft which passes through the hollow interior of each of the elongate bodies 12 of the anchors.

A pull force is then applied to each of the anchors 10 via the respective anchor line 24 so that the anchors begin to be drawn backwards along the drive path 44. However, as the tension on the anchor lines 24 increases, each anchor will begin to pivot away from the drive path 44 due to the action of the inclined surfaces 18 on the rear edge of the planar members 14 of the anchors. Hence, for example, anchor 1 Ob will follow a trajectory 46 as illustrated in Figure 5 towards a position in which the planar members 14 are oriented substantially perpendicularly to the direction of the pull force (indicated by arrow B). In this position (as shown in Figure 5) no further outward movement of the anchor lOb along trajectory 46 will occur. Furthermore, further withdrawal of the anchor lOb is inhibited by the resistance offered by the mass or volume of soil located above the planar members 14 of the anchor. Each of the anchors 10a, lOb, 10c and 10d will follow its own trajectory away from the drive path 44, substantially at right angles to its adjacent anchors as shown

(iii) the capacity of the anchor can be tailored to the size of the structure by varying the number of anchors in the cluster and/or changing the transverse dimensions of the planar members; and, (iv) the method of installing the anchors can be implemented using a conventional vibratory or impact hammer.

Figures 9 and 10 illustrate a preferred embodiment of a high capacity anchor column according to the invention. The illustrated embodiment of the high capacity anchor column 50 comprises a rigid elongate support member 52 adapted to be driven into soil.

In the illustrated embodiment, support member 52 is in the form of a steel universal column having a H cross-section. Any suitably rigid and strong elongate member may be employed including, for example, a hollow, steel tubular pile. However, a steel universal beam or column is preferred as the planar surfaces on the beam or column are easier to connect other components to. Towards the lowermost end of the support member 52 a pair of anchor members 54 are pivotally mounted on respective sides of the support member 52. In the illustrated embodiment, two pairs of anchor members are shown, however one or more pairs of anchor members may be adequate depending on the application and soil conditions.

In the illustrated embodiment, the anchor members are in the form of substantially rectangular anchor plates 54 which are pivotally connected to support member 52 by means of hinge connections 56. The hinge connections 56 are respectively welded to the parallel flanges of the anchor beam 52. Anchor plates 54 are adapted to pivot outwards from a first position (as shown in Figure 10) in which the anchor plates lie substantially flat against the sides of the anchor beam 52, to a second position (as shown in Figure 9) in which the anchor plates extend laterally from the sides of the anchor beam 52. Preferably each anchor plate 54 is provided with an outwardly protruding lip 58 which is adapted to dig into the soil when a pull force is applied to the support member, so as to cause the anchor plates 54 to pivot outwards to the second position.

The high capacity anchor column 50 also comprises constraining means in the form of a pair of elongate, flexible members 60 provided on respective sides of each anchor plate for constraining the anchor plates in the second position. In the illustrated embodiment, elongate, flexible members 60 are in the form of high tensile chains having one end fixed to the side of the anchor plate and the other end fixed to the flange of the anchor beam 52.

Preferably chains 60 are fixed at one end to the anchor plates 54 by means of links welded to the upper surface of the anchor plate adjacent the respective side edges, and are fixed to the anchor beam by links welded to the inside faces of the respective parallel flanges of the beam. In this way, when the anchor plates 54 are returned to the first position, as shown in Figure 10, chains 60 are hidden inside the volume of the anchor beam 52 so that they do not protrude outside the cross-sectional area of the anchor beam.

With this arrangement, the chains 60 do not increase soil resistance or otherwise interfere when the anchor column is being driven into soil.

Preferably, each anchor plate 54 is provided with a trip latch 62 for holding the anchor plate in the first position until a pull force is applied to the anchor beam 52 in situ. Trip latch 62 is only intended to hold the anchor plates 54 in the first position during transport of the anchor column 50 and during driving of the anchor column into the soil. However, when the anchor beam 52 has been driven into soil to the required depth, soil resistance against the protruding lips 58 of the anchor plates 54 will cause them to pivot outwards to the second position as soon as a pull force is applied to the anchor beam 52. As the pull force is increased, anchor plates 54 will pivot outwards to the second position until chains 60 become taut, at which point they are constrained from further movement so as to inhibit further withdrawal of the anchor beam 52 from the soil. The relatively large surface area of anchor plates 54 increases the soil resistance to such an extent that it is virtually impossible to withdraw anchor column 50 from the soil without exceeding the cumulative tensile strength of chains 60.

Anchor beam 52 and anchor plates 54 may be of any suitable size or shape as noted above.

Typically, the anchor beam 52 has a cross-sectional area of 500x5OOmm, and each of the anchor plates 54 are approximately lxlm in area. However, these dimensions may be greater or smaller depending on the application. As can be seen most clearly in Figure 10,

anchor plates 54 are typically approximately twice the width of anchor beam 52 and therefore protrude outwards either side of anchor beam 52. This may have a tendency to increase the soil resistance when driving the anchor column 50 into soil. Therefore, cutting blades 64 are preferably provided adjacent the lowermost end of anchor beam 52, angled so as to form a transition between the width of anchor beam 52 and the width of anchor plate 54. Similar cutting blades may be provided in line with the second pair of anchor plates 54, which are preferably oriented perpendicular to the first pair of anchor plates 54 as shown in Figures 9 and 10.

Anchor beam 52 is typically provided with one or more anchor points 70 adjacent the uppermost end of the beam to which a structure may be tethered to anchor it on the sea bed. The anchor column 50 is particularly suited to providing an anchor point that may be subject to lateral loading (in addition to vertical loading). For this purpose, anchor beam 52 may also be fitted with side plates (not shown) welded to the beam in a plane which is substantially parallel to a longitudinal axis of the beam. Such side plates would provide additional soil resistance to any lateral loading on the beam from anchor point 70.

Typically the anchor column 50 is driven into the soil with only the anchor point 70 protruding above the soil surface. However, the anchor column 50 may also be driven into the soil so that it is fully below the soil surface.

Now that a preferred embodiment of the high capacity anchor column has been described in detail, it will be apparent that it provides a number of significant advantages over conventional anchors, including the following: (i) it can be driven into soil using a conventional piling hammer ; (ii) it provides an extremely high capacity anchor point, at relatively low cost; (iii) additional anchor plates can be added to the column to increase its capacity; (iv) it is of simple design and inexpensive to manufacture.

Numerous variations and modifications will suggest themselves to persons skilled in the appropriate arts, in addition to those already described, without departing from the basic

inventive concepts. For example, the shape and size of the planar members provided in connection with the elongate body of the anchor can be varied depending on the required capacity and soil conditions. Furthermore, the cross-sectional shape of the elongate body may be of any suitable shape and does not need to be circular as in the preferred embodiment. Furthermore, in the illustrated embodiments of the anchor column, the anchor plates are of rectangular construction. However, the anchor members may be of any suitable shape or configuration, for example, they may be semi-circular in shape and cupped. Provision may also be made for injecting air, water and grout during installation to increase the capacity of the seabed surrounding the anchor cluster or anchor column.

All such variations and modifications are to be considered within the scope of the present invention, the nature of which is to be determined from the foregoing description and the appended claims.