FIXATION DEVICE AND INSTALLATION METHOD

Abstract

The invention relates to an elongate fixation device (1) for use in subsea anchoring, and a method for installation. The device (1) has a triple nested stem arrangement, the innermost stem (2) of which has a cutter (9) disposed at a distal end and a tapered section (8) located adjacent to and proximally behind the cutter (9). An intermediate stem (3) surrounds at least a central portion of the inner stem (2) and has one or more flareable cutting fingers (7) at its distal end. An outer stem (4) surrounds a proximal portion of the intermediate stem (3). The inner (2) and intermediate (3) stems are coupled by a first releasable coupling (17) which when released allows relative axial motion along a first distance. The outer and intermediate stems are coupled by a second releasable coupling (18) which when released allows relative axial motion along a second distance. The intermediate stem 3 is nested within the outer stem (4), in some cases for at least a majority of the outer stem (4). In some examples, the outer stem (4) has a rotationally driveable portion 10 and the inner stem 2 has a tensioning nut (12) for adjusting the relative axial positions of the inner (2) and outer 4 stems. The tensioning nut (12) and the driveable portion (10) are coupleable to a single rotational drive (23). The invention also relates a method for installation and to installation apparatus (21).

Claims

1. An elongate fixation device for use in subsea anchoring, the fixation device comprising: an inner stem having a cutter disposed at a distal end and a tapered section located adjacent to and proximally of the cutter; an intermediate stem having a generally tubular shape and being shorter than the inner stem, the intermediate stem surrounding a central portion of the inner stem and extending distally towards the taper section, wherein the intermediate stem has one or more flareable cutting fingers at its distal end; and an outer stem having a generally tubular shape and a portion for retaining the fixation device in a substrate, the outer stem further having a third length in an axial direction less than the first length, the outer stem surrounding a proximal portion of the intermediate stem and extending proximally beyond a proximal end of the intermediate stem; a first releasable coupling between the inner and intermediate stems; and a second releasable coupling between the outer and intermediate stems; wherein the inner, intermediate and outer stems are rotationally coupled to one another; wherein the first releasable coupling has a coupled configuration in which relative axial motion between the inner and intermediate stems is prevented and an uncoupled configuration in which relative axial motion between the inner and intermediate stems along a first distance is possible; wherein the second releasable coupling has a coupled configuration in which relative axial motion between the intermediate and outer stems is prevented and an uncoupled configuration in which relative axial motion between the intermediate and outer stems along a second distance is possible; wherein the outer stem has a driving portion for coupling to a rotational drive and the inner stem has a tensioning nut located proximally of the driving portion for adjusting the relative axial positions of the inner and outer stems, the tensioning nut being located on the inner stem and adjustable by coupling to a rotational drive; and wherein the tensioning nut and the driving portion are configured to couple to the same rotational drive.

2. The fixation device according to claim 1, wherein the driving portion is spaced in a distal direction from the proximal end of the outer stem.

3. The fixation device according to claim 1, wherein the proximal end of the outer stem is narrower than the driving portion.

4. An elongate fixation device for use in subsea anchoring, the fixation device comprising: an inner stem having a first length in an axial direction, the inner stem having a cutter disposed at a distal end and a tapered section located adjacent to and proximally of the cutter; an intermediate stem having a generally tubular shape and having a second length in an axial direction less than the first length, the intermediate stem surrounding at least a central portion of the inner stem and extending distally towards the taper section, wherein the intermediate stem has one or more flareable cutting fingers at its distal end; an outer stem having a generally tubular shape and a portion for retaining the fixation device in a substrate, the outer stem further having a third length in an axial direction less than the first length, the outer stem surrounding a proximal portion of the intermediate stem and extending proximally beyond a proximal end of the intermediate stem; a first releasable coupling between the inner and intermediate stems; and a second releasable coupling between the outer and intermediate stems; wherein the first releasable coupling has a coupled configuration in which relative axial motion between the inner and intermediate stems is prevented and an uncoupled configuration in which relative axial motion between the inner and intermediate stems along a first distance is possible; wherein the second releasable coupling has a coupled configuration in which relative axial motion between the intermediate and outer stems is prevented and an uncoupled configuration in which relative axial motion between the intermediate and outer stems along a second distance is possible; and wherein the intermediate stem is nested within the outer stem for at least a majority of the outer stem.

5. (canceled)

6. The fixation device according to claim 1, wherein the relative axial motion between the intermediate and inner stems is restricted to the first distance by a first axial coupling and/or wherein the relative axial motion between the intermediate and outer stems is restricted to the second distance by a second axial coupling.

7.-11. (canceled)

12. The fixation device according to claim 1, wherein the releasable coupling between the inner stem and the intermediate stem and/or the releasable coupling between the intermediate stem and the outer stem comprises a shear pin.

13. The fixation device according to claim 12, wherein both releasable couplings comprise shear pins and the shear strength of the shear pin between the intermediate stem and the outer stem has a greater shear strength than a shear strength of the shear pin between the inner stem and the intermediate stem.

14-16. (canceled)

17. The fixation device according to claim 1, wherein the portion for retaining the fixation device in the substrate comprises a portion which tapers from its proximal end towards its distal end.

18. (canceled)

19. The fixation device according to claim 1, wherein the flareable fingers form part of the distal end of the intermediate stem.

20. The fixation device according to claim 19, wherein the portion of the intermediate stem corresponding to the flareable fingers is coupled to a main body of the intermediate stem via a portion of the intermediate stem which is thinner than the main body of the intermediate stem.

21-40. (canceled)

41. The fixation device according to claim 6, wherein the or each axial coupling is located in a different axial location along the device and/or a different angular location around the device from each releasable coupling.

42. The fixation device according to claim 1, wherein the first distance is larger than the second distance, optionally wherein the first distance is at least as long as a longest cutting finger.

43. The fixation device according to claim 1, further including a remotely operated drive system for installing the fixation device, the remotely operated drive system comprising: a rotational drive; a first connection rotationally driven by the rotational drive for rotationally driving both the outer stem of the fixation device and the tensioning nut; a second connection for coupling to the inner stem of the anchor; a first axial drive for axial movement of the first connection to decouple it from the outer stem while retaining the tensioning nut; and a second axial drive for axial movement of the inner stem relative to the intermediate stem; wherein: the first connection is coupled to the tensioning nut and the driving portion; and the second connection is coupled to the inner stem.

44. The fixation device according to claim 43, wherein the second connection is also rotationally driven by the rotational drive.

45. The fixation device according to claim 43, wherein the first axial drive is in a deployed position, in which the first axial drive is extended in the distal direction.

46. The fixation device according to claim 43, wherein the second axial drive is in a retracted position, in which the second axial drive is retracted and is arranged in a most distal arrangement.

47. A method of installing into a substrate the fixation device according to claim 1, the method comprising the steps of: rotationally driving the driving portion of the outer stem and the tensioning nut with a single rotational drive to cause the outer, intermediate and inner stems to rotate due to their rotational coupling, wherein the rotations of the inner stem causes the cutter to drill into a substrate; drawing the inner stem in a proximal direction relative to the intermediate stem while rotationally driving the intermediate stem, to cause the fingers to flare out and ream an undercut in the substrate; decoupling the rotational drive from the outer stem while retaining the tensioning nut in the rotational drive; and driving the tensioning nut in a distal direction relative to the outer stem.

48. The method according to claim 47, wherein the method is performed using a remotely operated drive system for installing the fixation device, the remotely operated drive system comprising: a rotational drive; a first connection rotationally driven by the rotational drive for rotationally driving both the outer stem of the fixation device and the tensioning nut; a second connection for coupling to the inner stem of the anchor; a first axial drive for axial movement of the first connection to decouple it from the outer stem while retaining the tensioning nut; and a second axial drive for axial movement of the inner stem relative to the intermediate stem; wherein: the first connection is couplable to the tensioning nut and the driving portion; and the second connection is couplable to the inner stem.

49. The method according to claim 48, wherein the drawing step is performed by deploying the second axial drive.

50. The method according to claim 48, wherein the decoupling step is performed by retracting the first axial drive.

Description

[0076] The invention will now be described by way of non-limiting examples with reference to the Figures, in which:

[0077] FIG. 1 shows a prior art fixation device;

[0078] FIG. 2A shows a plan view and side elevation of a fixation device according to the present invention;

[0079] FIG. 2B shows a front elevation of the device of FIG. 2A;

[0080] FIG. 2C shows a section through the device of FIGS. 2A and 2B, in the direction of the arrows along the line A-A in FIG. 2B;

[0081] FIG. 3A shows a sectional view of the fixation device of FIGS. 2A to 2C, and an installation rig, prior to installation in a substrate;

[0082] FIG. 3B shows a sectional view of the device of FIGS. 2A to 2C, and an installation rig, at an early stage of installation in a substrate;

[0083] FIG. 3C shows a sectional view of the device of FIGS. 2A to 2C, and an installation rig, at a later stage of installation in a substrate than that shown in FIG. 3B; and

[0084] FIG. 3D shows a sectional view of the device of FIGS. 2A to 2C, and an installation rig, with the device installed in a substrate.

[0085] In a little more detail, consider FIGS. 2A to 2C. FIG. 2A shows a fixation device 1 from a side elevation at the bottom and a plan view at the top of the Figure. FIG. 2B shows the same device 1 from a front elevation, and FIG. 2C shows the device 1 in sectional view along the line A-A in the direction of the arrows as shown in FIG. 2B. The Figures each show an expected substrate surface position 90, to illustrate the parts of the fixation device 1 which are intended to be anchored within the substrate, and which parts protrude from the substrate. The arrangement of an example of the fixation device 1 will now be described with general reference to these Figures.

[0086] An inner stem 2 runs from the top end of the Figure (also referred to as the proximal end), to the bottom end of the Figure (also referred to as the distal end). Towards the lower end, the inner stem 2 has a tapered section 8, which has a frustoconical shape with its narrowest portion located closest to the proximal end of the device 1 (the proximal end of the device is at the top of e.g. FIGS. 2B and 2C). Located distally of the widest (and distal) end of the tapered section 8 is a cutter 9. The cutter 9 comprises teeth or other cutting surfaces for drilling into rock when the inner stem is rotated and driven into a substrate. The cutter may be shaped to improve the drilling action and may include a particularly durable material so as to optimise the cutting effect; for example, tungsten carbide, silicon carbide, artificial diamond, toughened steels, etc. may be suitable materials. A tensioning nut 12 is mounted to the inner stem 2 by way of a screw thread. The inner stem has a central lumen 13 which can be used to flush debris from the hole formed during the drilling process. An upper end of the inner stem 2 has a coupling 14 for attaching to an installation device, as described in more detail below. The coupling may allow for transmission of rotational force, transmission of axial force, and/or provision of fluid to the lumen 13 for flushing a hole during drilling. As shown, the cutter 9 is formed of cutting materials embedded in a cutting bit. Other examples may include roller cone type bits instead.

[0087] Nested around the inner stem 2 is an intermediate stem 3. The intermediate stem 3 extends along a central portion of the inner stem 2, but leaves the proximal and distal ends of the inner stem 2 uncovered by the intermediate stem 3. At the lower end of the intermediate stem 3 are a plurality of cutting fingers 7, each attached to the intermediate stem 3 by way of a respective hinged connection 16. As above, the fingers may have special cutting portions, shaped to assist in cutting into rock, and including a suitable material such as tungsten carbide, silicon carbide, artificial diamond, toughened steels, etc.

[0088] The intermediate stem 3 is arranged so that relative motion between the inner 2 and intermediate 3 stems (specifically where the relative motion causes the inner stem 2 to move upward or proximally relative to the intermediate stem 3) causes the fingers 7 to interact with the tapered section 8 and flare outwards, in order to ream out an undercut in a substrate, as described in more detail below.

[0089] As shown, relative motion between the inner 2 and intermediate 3 stems is prevented by virtue of a first shear pin 17 which couples the inner 2 and intermediate 3 stems both rotationally and axially by fitting into corresponding holes on each stem. The first shear pin 17 is configured to shear at a particular force, thereby providing a selective coupling, in that the stems 2,3 remain coupled until a suitable force is applied (e.g. by lifting the inner stem 2 relative to the outer stem 3 and applying the required shear force), thus providing a releasable coupling between the inner 2 and intermediate 3 stems. Once the first shear pin 17 has sheared, the two stems 2,3 remain rotationally coupled but can move over a limited axial range relative to one another by virtue of a first slot and pin arrangement 19. Limiting the axial motion in this way can help prevent overextension of the fingers 7 during the installation process, which can damage them.

[0090] Nested around the upper end of the intermediate stem 3 is an outer stem 4. An upper end of the outer stem 3 has a driving portion 10 for coupling to a rotational drive and thereby driving the outer stem 4 to rotate. The driving portion 10 and the tensioning nut 12 are arranged to be driven by the same rotational drive means, as set out in more detail below. Adjacent to the driving portion 10 is a spacing region 11, which is narrower than the driving portion 10, and is arranged not to interact with the rotational drive means. This means that the drive means can overlap the uppermost part of the outer stem 4, without being engaged to rotationally drive the fixation device 1.

[0091] The outer stem 4 is coupled to the intermediate stem by virtue of a second shear pin 18. In part this ensures that, as shown, the outer stem 4 drives the intermediate stem 3, which in turn drives the inner stem 2 by virtue of the rotational coupling between each of the stems. As above, the second shear pin 18 can be configured to shear when a predetermined load is applied, thus providing a releasable coupling between the intermediate 3 and outer 4 stems. This decouples the outer 4 and intermediate 3 stems. As above, even when the second shear pin 18 has sheared, relative motion between the outer 4 and intermediate 3 stems is limited to an axial range by a second slot and pin arrangement 20, while retaining the rotational coupling between the outer 4 and intermediate 3 stems. Allowing a limited range of relative axial motion between the outer 4 and intermediate 3 stems helps to adjust the fixation device 1 to compression of the substrate mass during installation.

[0092] The outer stem 4 is provided with an attachment point 6 for coupling to mooring lines, cables, chains, etc. In turn these can be connected to assemblies to be moored to the water bed, such as rigs, FPSOs, ships, floating energy production devices, etc. In some examples, a structural connection portion for providing a location on which to construct an underwater structure may be provided in addition to, or instead of, the attachment point. In the example shown, the attachment point is provided on a rotating collar 15, which can rotate about the central axis of the fixation device 1 (shown as a dot-dashed line in FIGS. 2A to 2C). This allows moored assemblies to drift with currents or tides, and still to align with the location of the attachment point 6, which swivels freely to follow the location of the moored assembly. Of course, in some examples the attachment point 6 may not rotate relative to the fixation device 1, but be fixed in place instead.

[0093] The outer stem 4 is located primarily around the upper end of the intermediate 3 and inner 2 stems. The outer stem 4 is provided with a tapered portion 5, which narrows towards the lower end of the fixation device 1. This tapered portion 5 helps the device to grip or bear on the substrate as tension is applied to the device via the tensioning nut 12, which when tightened presses downwards against the top of the outer stem 4 while pulling the inner stem 2 upwards. The substrate is gripped and compressed between the tapered portion 5 and the fingers 7 (the fingers 7 being pulled upwards by the tapered section 8 of the inner stem 2 as the inner stem 2 is pulled upwards). In some examples, there may be no tapered portion, and instead the tensioning nut 12 may press against wide plate or indeed a template with feet in the case of a structural connection being provided, which engages with the substrate surface 90 instead.

[0094] Each of the stems 2,3,4 is generally tubular and nested in a triply concentric arrangement. They are formed from any suitable material, specifically one which can withstand the tension forces in gripping the substrate as well as the lateral loading caused by coupling assemblies to the attachment point 6. Corrosion resistant stainless steels, anode protected and coated carbon steels all provide the required level of rigidity and resistance to forces, while being resistant to the harsh conditions found underwater, and being available at a suitable cost. This provides a rigid anchoring pile when installed, and can ensure that the pile can be tensioned and can resist lateral loading, compressive loading (supported against excessing bending or buckling by the rock cavity and tensile loads.

[0095] Note that the first shear pin 17 and the first slot and pin arrangement 19 are angularly aligned, but axially offset from one another. Similarly, the second shear pin 18 and the second slot and pin arrangement 20 are angularly aligned, but axially offset from one another. Finally, the first and second shear pins 17,18 are angularly and axially offset from one another, as are the first and second slot and pin arrangements 19,20. This can help to prevent weak spots being focussed in one place. Of course other arrangements are possible, for example the shear pins 17,18 not being angularly aligned with either slot and pin arrangement 19,20 or each other.

[0096] As shown, the shear pins 17,18 are in fact a pair of diametrically opposed shear pins (but are referred to in the singular for simplicity). Similarly, each slot and pin arrangement 19,20 is actually a pair of diametrically opposed pins and corresponding slots, but is referred to in the singular for simplicity. These arrangements help to ensure that the transmission of rotation between adjacent stems 2,3,4 is smooth and does not focus strain on any one part of the device. In some examples there are different numbers of shear pins 17,18 and slot/pin arrangements 19,20 coupling adjacent stems 2,3,4.

[0097] The fixation device 1 in some examples may be around 1.5 m to 2.5 m long in total and 0.25 m to 0.5 m across the outer diameter of the outer stem 4 (not including any attachment points or structural connection portions).

[0098] Moving on to FIGS. 3A to 3D, the installation of this fixation device will now be described. FIG. 3A shows the fixation device 1 prior to installation, but coupled to a remotely operated installation device 21. The installation device has an upper rotational drive 22 and a lower rotational drive 27 for supplying rotational motions to the fixation device 1, and also two axial drives 25, 26. A first axial drive 25 allows a rotational drive coupling 23 (sometimes referred to as a first connection driven by the rotational drive 22) on the installation device 21 to be moved in an axial direction, for decoupling the rotational drive coupling 23 on the installation device 21 from the driving portion 10 on the fixation device. The second axial drive 26 is coupled to a connection 24 for coupling to the inner stem connection 14, and allows the inner stem to be pulled upwards in the installation procedure. Both sets of axial drives 25,26 are shown as hydraulic rams in this example, but any suitable means could be used, such as pneumatic systems, rack and pinion systems, etc.

[0099] The fixation device 1 and the installation device 21 may be coupled together as shown in FIG. 3A before arrival at the installation site. For example, the coupling may occur on dry land (e.g. on a dock prior to loading onto an installation vessel) or it may occur on an installation vessel itself. Doing so can allow operators to test the functionality of the installation device 21, for example to check that the various rotational and axial actuators are operational and able to move throughout their full range of motion. In any case, once the coupling and testing is complete, the fixation device 1 and installation device 21 are lowered to the water bed in the arrangement shown in FIG. 3A to commence installation.

[0100] In this pre-installation configuration, the fixation device is in the arrangement shown in FIGS. 2A to 2C, and specifically with the fingers 7 flat against the outer surface of the inner stem 2, the shear pins 17,18 intact (with no relative axial or rotational motion possible between any of the stems 2,3,4). The driving portion 10 and the tensioning nut 12 of the fixation device 1 are engaged by the rotational drive coupling 23 of the installation device 21. In this example, each of the driving portion 10, the rotational drive coupling 23 and the tensioning nut 12 are all hex connections. The rotational drive coupling 23 of the installation device 21 is coupled to a rotational drive 22 (e.g. a hydraulic or electric motor), for providing torque to the fixation device 1. In some cases, the upper rotational drive 22 is simply a clutch/brake arrangement, meaning that only a single drive (the lower rotational drive 27) is used to supply rotational motion to the fixation device 1. In other arrangements the upper drive 22 is the primary drive with the lower drive 27 being coupled to it by a clutch/brake arrangement. The following discussion is framed from the point of view of the upper drive 22 being dominant, but the skilled person will recognise that the same considerations would apply to one in which the lower drive 27 is dominant.

[0101] In addition, the inner stem coupling 14 is coupled to an inner stem coupling 24 on the installation device 21. This coupling allows the installation device 21 to impart an axial motion to the inner stem 2. It may also allow rotational motions to be imparted to the inner stem 2, and/or provide fluid for flushing holes drilled by the inner stem 2.

[0102] The installation device 21 starts with the first axial drive 25 deployed, that is, extended in a downward (distal) direction. This forces the rotational drive coupling 23 on the installation device 21 to be towards its lowest extent. The rotational drive coupling 23 on the installation device 21 is coupled to both the driving portion 10 on the fixation device 1, and can be retracted (as it begins in a deployed or extended configuration) to decouple from the driving portion 10 on the fixation device 1 as will be seen later).

[0103] The position of the first axial drive 25 corresponds with the relative axial arrangement of the inner 2 and intermediate 3 stems relative to one another (and held there by the unbroken first shear pin 17). In more detail, the inner stem 2 is held in its most distal (downward) position relative to the intermediate stem 3, as limited by the first slot and pin arrangement 19. This means that when the first shear pin 17 breaks, the inner stem 2 can move only in the proximal (upward) direction relative to the intermediate stem 3 for up to the first axial distance. This corresponds with the first axial drive being 25 at its lowest (distal-most, deployed) state, meaning that it can only drive the inner stem 2 in an upward direction.

[0104] Relatedly, the outer stem 4 is held at its uppermost (most proximal) position relative to the intermediate stem 3 by the unbroken second shear pin 18, as limited by the second slot and pin arrangement 20. When the second shear pin 18 breaks, the outer stem 4 can only move in a downward (distal) direction relative to the intermediate 3 stem (as well as relative to the inner stem 2). This allows the outer stem 4 and its tapered portion 5 and the fingers 7 (and inner stem 2,8) to grip and compress the substrate once installed.

[0105] The second axial drive 26 starts the process retracted, that is, also in its lowest or most distal arrangement, meaning that when deployed it moves in an axially proximal or upward direction. Once more, this means that the second axial drive 26 is able, when deployed, to lift the inner stem 2 upwards, relative to the rest of the fixation device 1.

[0106] When placed on the water bed, the installation device 21 is stabilised to direct the fixation device into the desired area of the water bed. The positioning can be checked using GPS from a surface vessel, for example, where the installation device 21 and fixation device 1 are lowered together to the water bed by a crane, the position of the crane head is a good representation of the position of the fixation device 1. Additionally, the fixation device 1 is arranged to meet the desired area of the water bed at a desired angle. Usually this is approximately directly downwards irrespective of the slope of the substrate forming the water bed, but other angles may be desirable in some cases, for example perpendicular to the local surface, or at an angle to the local surface. The angle at which the fixation device 9 meets the water bed can be altered by changing the pitch and roll of the fixation 1 and installation 21 devices. This can be achieved by providing an installation frame (not shown) which couples to the installation device 21. The orientation of the frame can be adjusted using hydraulic legs on the frame. Alternatively, the fixation device 21 can have an adjustable coupling to the frame, to allow it to change its orientation, while the frame is a simple frame having no moving parts.

[0107] At this stage, installation can begin. Initially, rotation of the rotational drive 22 occurs on a high speed gear. This in turn drives the installation device rotational coupling 23, and in turn rotates the outer stem 4 via the fixation device rotational coupling 10. Since all three stems 2,3,4 are rotationally coupled to one another, the entire fixation device 1 rotates. This means in particular that the inner stem 2 is rotating at the same RPM as the tensioning nut 12, so no relative rotation occurs, and the tensioning nut 12 remains in place, rather than moving up or down along the threaded portions of the inner stem 2. The installation device 21 may have a weight of around 5 metric tons in water, which is enough to drive the fixation device into the substrate. By ensuring that the drilling thrust is suitably limited, for example to no more than 1 to 2 metric tons, the torque is effectively transmitted to the fixation device 1.

[0108] This process continues until the fixation device 1 has been drilled to its intended depth (see e.g. the example of the location of the substrate surface 90 in FIGS. 2A to 2C). During this drilling process, a flushing medium can be forced down the lumen 13 in the inner stem 2, to clear the hole of drilling debris. There may be a delay at this stage while additional flushing medium is forced down the lumen 13 to allow the hole to be fully cleared before proceeding.

[0109] Once drilled to depth, the fixation device 1 is located in a hole in the substrate, having a diameter equal to the diameter of the cutter 9. Since the fingers 7 are flush against the outer surface of the inner stem 2, they fit neatly into the hole drilled by the cutter.

[0110] The next step is to continue to supply rotational force to the fixation device 1 via the driving portion 10 and the rotational drive coupling 23 (and optionally to flush the hole through the lumen 13) while pulling up on the inner stem 2. Due to the coupling of the shear pins 17,18, pulling upwards on the inner stem 2 also pulls the intermediate 3 and outer stems 4 upwards. However, since the rotational drive coupling 23 on the installation device 21 is not axially moved in this motion, the distal (lower) end of the rotational drive coupling 23 on the installation device 21 bears against a shoulder on the outer stem 4 at the lower end of the driving portion 10 on the fixation device 1 and prevents the outer stem 4 (and also the intermediate stem 3 via the second shear pin 18) from moving upwards. This places a shear strain across both shear pins 17,18 as the inner stem 2 is pulled upwards relative to the intermediate stem 3 (this movement is possible due to the initial position of the first slot and pin arrangement 19 which permits upward translation of the inner stem 2 relative to the intermediate stem 3). Similarly, because the first shear pin 17 is initially unbroken, the upward axial force is transmitted from the inner stem 2 to the intermediate stem 3, and causes a strain across the second shear pin 18, where the intermediate stem 3 is forced upwards relative to the outer stem 4. This is equivalent to the desired configuration (discussed in more detail below) where the outer stem 4 is forced downwards relative to the intermediate stem 3, and hence the second slot and pin arrangement 20 would allow the intermediate stem 3 to move upward relative to the outer stem 4, but for the unbroken second shear pin 18. Since this relative motion of the outer stem 4 and the intermediate stem 3 is not intended to occur until later in the installation process, the second shear pin 18 has a greater shear strength than the shear strength of the first shear pin 17. This ensures that the relative timing of the motions is provided in the correct order.

[0111] The overall result of this motion is to rotate the intermediate stem 3 (indeed, all three stems 2,3,4 are rotating together) while the fingers 7 flare outwards by pivoting around their hinges 16 to their position in FIG. 3B. In some cases, the intermediate stem 3 may be continuous down to the fingers, and instead of hinges 16, a preferentially deformable portion may be provided which is e.g. thinner than the rest of the intermediate stem, to preferentially deform and flare the fingers 7 outwards. As the outermost edges of the fingers 7 flare outwards, they ream out a wider portion of the outer all of the hole drilled into the substrate. When this motion is completed, the hole in the substrate remains largely cylindrical or annular (as described above), with a frustoconical portion towards its lower end. Upward forces on the fixation device 1 will now pull the fingers 7 upwards against the downward-facing surface of the frustoconical portion of the hole, and thus resist the removal of the fixation device 1 from the hole. During this motion, both the driving portion 10 on the fixation device 1 and the tensioning nut 12 are retained in the rotational drive coupling 23 on the installation device 21.

[0112] Of course, in some arrangements, the intermediate stem 3 could be forced downwards over the inner stem 2 to flare the fingers with much the same result. However, the arrangement shown in FIGS. 3A to 3D is particularly advantageous as the fact that the inner stem 2 is pulled upwards inside the intermediate stem enables the use of the same drive for both the tensioning nut 12 and the drive coupling 10 because the distal (lower) end of the rotational drive coupling 23 on the installation device 21 bears against a shoulder on the outer stem 4 at the lower end of the rotational drive coupling 10 on the fixation device 1 and prevents the outer stem 2 from moving upwards. Because the rotational drive coupling 23 on the installation device 21 is only required to provide downward axial bracing (i.e. a downward force to prevent upward movement of the outer stem 4) leaves the rotational drive coupling 22 free to lift upwards to easily decouple the rotational drive coupling 10 on the fixation device 1. If instead the rotational drive coupling 23 on the installation device 21 were required to provide an upward bracing force (i.e. to prevent the outer stem 4 moving downwards), for example if the intermediate stem 3 were forced downwards over the inner stem 2, a more complicated drive arrangement would be required, thus complicating the installation procedure. Nonetheless, this may be implemented in some examples. Of course, this arrangement would entail that the starting position of the first axial drive 25 is in its most proximal arrangement (pulled upwards, with the first axial drive 25 deployed) so that the intermediate stem 3 is able to be pushed downward over the inner stem 2 as the first axial drive 25 is retracted. Naturally such an arrangement would require the intermediate stem 3 couples to the installation device 21, to allow the intermediate stem 3 to be pushed, rather than the installation device 21 coupling to the inner stem 2 as in the present example.

[0113] Once the fingers 7 are deployed (i.e. have flared out to the intended extent), rotation of the rotational drive 22 is stopped. Once stopped, the first axial drive 25 is actuated to retract it, and pull back the rotational drive coupling 23 on the installation device 21. This disengages the driving portion 10 on the fixation device 1, but retains the tensioning nut 12. This is the situation shown in FIG. 3C.

[0114] The rotational drive coupling 23 on the installation device 21 is then used on a low speed gear to wind the tensioning nut 12 downwards until it bears against the uppermost part 11 of the outer stem 4. In some cases, instead of high/low gearing, a continuously variable speed and torque drive may be used to provide flexibility during the installation process. During this phase, the rotation of the inner stem 2 may be prevented to allow the tensioning nut 12 to be turned relative to the inner stem 2 and thus to travel along the threaded portion of the inner stem 2. The rotational drive coupling 23 on the installation device 21 continues to drive the tensioning nut 12 downwards, increasing the downward force on the outer stem 4. At a predetermined force, the second shear pin 18 shears and allows the outer stem 4 to move downwards relative to the intermediate stem 3 and compress the substrate between the tapered portion 5 and the fingers 7. Note that until the second shear pin 18 shears, the outer stem 4 is stably held in position, so correct positioning of the outer stem 4 into the hole and controlled tensioning of the inner stem 2 and compression of the substrate can be achieved. The compression of the substrate is controlled over a limited axial range by the second slot and pin arrangement 20. Once the compression stage has been completed, the installation device 21 and fixation device 1 are as shown in FIG. 3D. At this stage, the installation device 21 can be decoupled from the fixation device by breaking the connection between the inner stem coupling 14 on the fixation device 1 and the inner stem coupling 24 on the installation device 21. The rotational drive coupling 23 on the installation device 21 simply slides upwardly off the tensioning nut. The installation device 21 can then be retrieved and reused to install subsequent fixation devices of the type described herein. Various mooring couplings (cables, chains, lines, etc.) can be attached to the attachment point 6 on the fixation device 1 to moor assemblies to the water bed. Indeed, although not shown, the fixation device 1 may further or alternatively include a structural connection portion for providing a location on which to construct an underwater structure.

[0115] Optionally, the installation device 21 may further supply grout or other hardenable materials to the fixation device 1 via the central lumen 13. The grout can be used to displace water and fill the hole with a hardenable material, which can then harden and hold the fixation device 1 firmly in the hole.

[0116] The steps in removal and retrieval of the fixation device 1 from the substrate follow broadly the same steps in reverse. Firstly, any moored assemblies are detached from the fixation device 1. An underwater tensioning device is lowered to the water bed and coupled to the fixation device 1. This tensioning device couples to the inner stem 2 and takes the tension from the inner stem 2. At the same time, the tensioning nut 12 is loosened and driven upwards a distance at least as long as the longest finger 7, in order to allow the fingers 7 to fully collapse. The tensioning device is then removed from the fixation device 1, which allows the inner stem to drop downward (a distance at least as long as the longest finger 7). The fingers 7 are free to act under gravity and hang vertically, flush against the outer surface of the inner stem 2, and thus falling within the outer diameter of the hole.

[0117] Lifting apparatus is then attached to the outer stem 4, and an upward force applied. This causes the intermediate stem 3 to hang as low relative to the outer stem 4 as the second slot and pin arrangement 20 will allow. Similarly, the inner stem 2 hangs as low relative to the intermediate stem 3 as the first slot and pin arrangement 19 will allow, thus ensuring that the fingers 7 remain flush against the outer surface of the inner stem 2. This arrangement allows the entire fixation device to be stably lifted out of the hole and removed from the installation site.

[0118] The present installation method, as seen in FIGS. 3A to 3D, utilises a single drive to impart torque to the fixation device 1 for drilling. This is in contrast to previous rock anchor technology which requires the use of separated drives for the inner and outer concentric barrels to achieve the control requirements for the anchor installation.

[0119] The outer drive in previous anchors is connected via a bayonet type configuration to the fixation device.

[0120] In the present disclosure, the single drive is achieved through the use of a hexagonal internal profile on the bore of the rotational drive coupling 23 of the installation device 21, which is sized to match a corresponding external hexagonal profile on both the top of the outer stem 4 and on the tensioning nut 12 as seen in FIGS. 3A to 3D. This configuration allows the pre-tension nut to be captured within the drive when the fixation device 1 is mounted to the installation device 21 above the water's surface at the start of the installation procedure rather than necessitating a breaking of the outer stem 4 connection after drilling, followed by a subsequent stage to align and engage the tensioning nut 12. This represents a significant simplification to the connection between the fixation device 1 and the installation device 21 and therefore significantly simplifies the installation procedure and reduces overall process time.

[0121] During drilling the torque is transferred between the triple concentric stems 2,3,4 as required for installation by the slot and pin arrangements 19,20 detailed above.