Rock anchor with improved underreaming

Abstract

A cutting finger 104 for a rock anchor (200, Fig 2A), having an upper section 106 having a cutting surface 110 and an upper coupling 108 for pivotably connecting to a main body 102 of the rock anchor

Description

The present invention relates to rock anchors, and specifically to rock anchors arranged to carve out an underream in a substrate to allow gripping of a rock mass. The invention also relates to methods of installing such anchors. Various forms of rock anchor are known in the art. These have a variety of applications for example in mooring floating energy production devices (floating wind platforms, tidal turbine devices), FPSOs, etc. Of particular interest are groutless rock anchors. Typically, these make use of an underreamed bore hole (i.e., a widened portion at the base of the bore hole) to allow the rock anchor to grip a mass of rock between an upper part and a lower part. This arrangement alleviates the need to apply grout to hold the anchor in place. An example of such a groutless rock anchor is disclosed in GB 2513942. In that disclosure, during installation, a rock anchor is first drilled to a set depth. Next, a lower taper at the base of the anchor is pulled upwards, which forces a tapered portion into a set of cutting fingers, forcing the cutting fingers outward. These underream a cone into the rock mass which is wider than the anchor’s drilled diameter. The anchor is then tensioned to the seafloor by pulling against this lower cut cone. The flared fingers also enact the gripping of the rock mass. This arrangement has a number of drawbacks, however. The arrangement is not suitable for adapting to a wide range of anchor sizes. The deployment mechanism is relatively limited and in particular the geometry of the tapered portion places limitations on the maximum angle to which the fingers may be flared outward. The fingers have a high risk of mechanical failure, particularly at their outer edges due to stress concentration which increases along the length of the finger. This arrangement also concentrates radial stresses in the rock mass, risking damage to the gripped mass of rock, which in turn risks failure of the whole installation. Finally, the geometry of the tapered section and the fingers must be carefully controlled to ensure correct operation. This requirement of fine tolerance increases manufacturing cost and installation complexity. The present invention aims to address some or all of these drawbacks. Disclosed herein is a cutting finger for a rock anchor, the cutting finger comprising: an upper section having a cutting surface and an upper coupling for pivotably connecting to a main body of the rock anchor; a lower section having a lower coupling for pivotably connecting to a base portion of the rock anchor; wherein the upper section and lower section are pivotably coupled to one another via a flaring pivot, the flaring pivot coupling a lower portion of the upper section to an upper portion of the lower section. Such fingers may be supplied to retrofit existing rock anchors to provide the benefits discussed in detail below. In other examples, the cutting fingers may be supplied as a separate component, in order to allow an operator to select appropriate fingers (in terms of cutting capability, mechanical strength, size, etc.) for the specific site in which the anchors are to be installed. Also disclosed herein is a rock anchor comprising: an outer stem extending from a proximal end to a distal end along an anchoring axis; an axially displaceable base portion located distally of the distal end of the outer stem; and a cutting finger having a flaring pivot of the type disclosed above, the cutting finger having the upper coupling of the upper section pivotably coupled to the distal end of the outer stem and the lower coupling of the lower section pivotably coupled to the base portion; and wherein the cutting surface is arranged to face outwardly relative to the anchoring axis. That is to say that the cutting finger is disposed between the outer anchor stem and the base plate. This improved cutting finger design leads to a novel deployment mechanism (discussed in more detail below). In brief, the position of the base portion, relative to the distal end of the outer stem, can range from a first distance to a second distance. The first distance is one in which the cutting finger is in a first configuration where the upper and lower sections lie along a common line (i.e., the finger is not deployed). The second distance is less than the first distance and in order to accommodate the length of both the upper and lower sections of the cutting finger, the cutting finger pivots outwardly at the flaring pivot. Starting from the rock anchor in a cylindrical bore hole with the cutting finger in the first configuration, the underreaming process involves gradually transitioning to the second configuration while rotating the outer stem (and correspondingly also the cutting finger since it is attached to the outer stem). As the finger rotates against the rock mass forming the walls of the cylindrical bore, the cutting surface cuts into the rock. As the flaring pivot pivots, the cutting finger is driven outwardly, a conical underream is formed in the rock mass. The pivoting of the flaring pivot continues until the desired angle of the cutting finger is reached. At this stage the outer stem no longer need be rotated, and the rock anchor can be locked in place by preventing the cutting fingers from reverting to (or toward) the first configuration. As is apparent, one can think of the base portion position as defining the angular position of the cutting fingers. Therefore, the cutting fingers can be locked in position by locking the location of the base portion relative to the outer stem. Once this is achieved, the rock anchor cannot be removed other than by mechanical failure of the rock mass or the anchor itself. That said, the rock anchor is easily decommissioned by unlocking the motion of the base portion, returning the fingers to the first configuration, and sliding the rock anchor out of the bored hole. The first configuration has the cutting finger lying closest to the anchoring axis within a substantially cylindrical envelope. The second configuration has the flaring pivot bending the fingers such that the flaring pivot itself (along with the lower part of the upper section and the upper part of the lower section) are further from the anchoring axis than the upper end of the upper section and the lower end of the lower section (which do not move radially during the transition). In general, the cutting fingers are limited so that the upper section extends at most perpendicular from the anchoring axis. There is not usually any benefit in extending the cutting finger further than this i.e., it is not common for the second configuration to have cutting finger angled upwardly such that the lower end of the upper section is above (more proximal than) the upper end. In some cases, the second configuration can even go past this, but there are diminishing returns in doing so, in the sense that the gripping does not get better (it eventually gets worse when the rock mass gets too small) and it requires a more complex design. Any angle involving a deformation from the first configuration up to a horizontal cutting finger angle is certainly beneficial, however, and this is what happens as the base portion is pulled upwardly during the installation process meaning that the process can be stopped at any point in the process and many of the same advantages flow from this. It can be seen that this arrangement can be made in a wide range of sizes, according to this general principle. The deployment mechanism is able to provide cutting fingers flared out at any angle from the anchoring axis, including perpendicular / horizontal arrangements. The anchor results in a load path through the rock of the substrate and thereby providing extremely high mechanical stability. The lower section of the cutting finger flares outwardly and provides support to the cutting surface at least as far out as the flaring pivot, thereby reducing the cantilever effect and improving the mechanical properties of the cutting surface and upper section. This in turn reduces the likelihood of mechanical failure of these parts as well as improving the interface with the rock mass. Finally, the geometry of the cutting fingers is largely a free parameter, allowing them to be formed in any shape which is appropriate for the use, since there is no requirement to be pushed outward by a tapered section. The upper section and / or the lower section of the cutting finger may be substantially rectilinear. This is an easy shape to work with and provides a strong arrangement in both the first and the second configuration. The first configuration using such cutting fingers can allow both the upper and the lower section to lie along a line parallel to the anchoring axis and thereby conform to a generally cylindrical arrangement. The ratio of the length of the upper section to the length of the lower section may be no more than 3. In this context, “length” means the extent of the cutting finger (or its upper and lower sections) in a direction aligned with the anchoring axis when the cutting finger is in the first configuration. This ratio means that, in the second configuration, the upper section is angled at slightly less than 20 degrees from the anchoring axis. In effect there is no minimum value for this ratio, but at a ratio of 1 it is possible to achieve a 90-degree angle, albeit with little supporting effect from the lower portion, which also extends at 90 degrees. A ratio of 0.5 allows a 90-degree angle with a reasonable amount of support against cantilever forces. By the time the ratio has dropped to about 0.1, it has long been possible to achieve a 90-degree angle. In fact, around 0.1 and below, there is little benefit in reducing the ratio further. In fact, for a given available length along the anchoring axis set aside for the cutting finger, all a decrease in this ratio serves to do is dedicate more length to the lower section which necessarily comes at the expense of the upper section. Since the length of the upper section determines the distance the underreaming extends into the rock mass, there is generally little to be gained by decreasing the ratio much further than 0.1 or so. The cutting surface may be integrally formed with upper section, which is a simple way to supply the cutting finger or rock anchor and is resistant to the cutting surface detaching during use e.g., due to mechanical failure. In other examples the cutting surface is removeable element attached to the upper section. This can allow the cutting surfaces to be interchanged to adapt the rock anchor to the specific substrate to be bored. In some examples, the lower end of the cutting surface may be tougher, have greater cutting potential before wearing, etc. This is because, as the finger swings through the arc, the outer (i.e., lower) edge of the cutting surface must cut through more rock than the inner (upper) edge. The cutting surface may extend below the lower end of upper section. That is, when the cutting finger is in the first configuration, the cutting surface extends more distally than the lower end of the upper section, for example past the flaring pivot and even overlapping some or all of the lower section. In some cases, the cutting surface may also be wider than (i.e., extend around a greater angular arc than) the upper section. This allows for improved cutting and in particular the cutting surface being longer than the upper section allows the underreaming to extend deeper into the rock. However, there is a trade-off here in that the further the extension extends past the flaring pivot, the greater the cantilever force on the outer edge of the cutting surface and the greater the risk of mechanical failure. The upper and / or lower sections may be formed from steel (e.g., suitable steel compositions for use for extended periods in fresh- or salt- water) and / or the cutting surface may include tungsten carbide or diamond. The rock anchor may have multiple cutting fingers. For example, between two and eight cutting fingers, preferably between four and six cutting fingers, for example five cutting fingers. There is a trade-off here, as a larger number of cutting fingers reduces the load on an individual cutting finger. However, as will be seen, the fewer cutting fingers there are, the larger the angular separation between adjacent cutting fingers can be made. This in turn allows easier access to the pivoting couplings between the cutting fingers and the outer stem and the base portion. This can make assembly and adjustment far easier. In some cases, the cutting fingers (or at least the cutting surfaces and / or upper sections) may abut one another in the first configuration. In other cases, there may be a gap between adjacent cutting fingers. The plurality of cutting fingers may each be substantially identical to each other cutting finger. In other cases, the cutting fingers may all be different, or there may be groups of different types of cutting fingers. The different types of different cutting finger may be suited to different purposes and arranged appropriately - for example there may be cutting fingers particularly suited to cutting and others being adapted to removal of waste material. These may be alternated around the rock anchor in some examples. The base portion may include a cutter for drilling a bore hole into a rock substrate. For example, this may include any of one or more roller cutters, tricone bits, helical flutes and so forth, depending on the substrate. This allows a single rock anchor to bore the initial cylindrical hole, and then perform the underreaming described above. This is particularly advantageous, because in doing so the rock anchor is already in place in the bored hole as soon as it is formed, ready to underream. This saves installation time and cost. In other examples, the hole is pre-bored by a different drill. The outer stem may be hollow and may provide a lumen through which an inner stem extends to couple to the base portion. This allows the base portion to be controlled from the proximal end of the anchor. For example, the base portion may be moveable by moving the inner stem axially relative to the outer stem. As noted above, this motion causes bending at the flaring pivot to cause the fingers to flare outward. Some designs may have further mechanisms or linkages to ensure that the fingers move outward in the correct manner during base portion motion. The rock anchor may include a mechanism for imparting axial motion to the inner stem relative to the outer stem and / or a mechanism for tensioning the inner stem. The mechanism may be actuable from the proximal end of the rock anchor meaning that it can be used even when the majority of the rock anchor is embedded in the substrate (as in e.g., the installed configuration). This can allow the properties of the anchor (e.g., tension and actuation) to be altered easily for installation and decommissioning purposes. The tensioning and actuation may be performed using the same mechanism. For example, anchors in which the axial motion of the base portion is controlled by pushing / pulling an inner stem and is coupled to the outward motions of the finger(s), moving the base portion spreads out the fingers. In such cases, the mechanism which moves the base portion can be locked to retain the fingers in the second configuration. Prior to locking the base portion, however, the inner stem may be placed under tension to actively grip the rock mass. It will be apparent that the pulling motion which is used to bring the base portion upwards to drive the cutting fingers outward may also be used to provide the tensioning as well. It is often beneficial to locate at least part of this mechanism toward the top of the anchor so that it can be controlled while the anchor is fully embedded in the substrate. The upper part of the rock anchor may also have portions for coupling mooring lines, cables, chains etc. to anchor devices to the substrate (i.e., a water bed, seabed, etc.). The rock anchor may further include a tapered portion for gripping a substrate located at the proximal end of the anchor. This tapered portion acts like the second jaw of a clamp to hold the anchor firmly in the substrate. The tapered portion may further include a further cutting surface for drilling into the substrate. This allows the anchor to be used to drill a top tapered part of the hole, for example by rotating the tapered portion and bearing down on the hole. This leads to an improved interface between the anchor at the top of the hole. Also disclosed herein is a method of installing a rock anchor comprising the steps of: boring a hole into a substrate; and underreaming a lower part of the hole by flaring out at least one cutting finger, the cutting finger(s) being mounted on the rock anchor and comprising an upper section having a cutting surface and a lower section coupled to the upper section via a flaring pivot, the flaring pivot coupling a lower portion of the upper section to an upper portion of the lower section. As noted above this provides a strong and stable underream with a locking mechanism to hold the anchor in place in the bore hole. The method may be performed using any of the cutting fingers discussed above, or indeed any of the rock anchors discussed above. Where the method includes a rock anchor including an outer stem extending from a proximal end to a distal end along an anchoring axis and an axially displaceable base portion located distally of the distal end of the outer stem; then the underreaming may include transitioning from a first configuration in which the base portion is a first distance from the distal end of the outer stem and the or each cutting finger is / are not deployed to a second configuration in which the base portion is a second distance, less than the first distance, from the distal end of the outer stem and the or each cutting finger is pivoted at the flaring pivot to extend outwardly away from the anchoring axis. As described above, this causes the underreaming because, starting from the rock anchor in a cylindrical bore hole with the cutting finger in the first configuration, the underreaming process involves gradually transitioning to the second configuration while rotating the outer stem (and correspondingly also the cutting finger since it is attached to the outer stem). As the finger rotates against the rock mass forming the walls of the cylindrical bore, the cutting surface cuts into the rock. As the flaring pivot pivots, the cutting finger is driven outwardly, a conical underream is formed in the rock mass. The pivoting of the flaring pivot continues until the desired angle of the cutting finger is reached. At this stage, the outer stem no longer need be rotated, and the rock anchor can be locked in place by preventing the cutting fingers from reverting to (or toward) the first configuration. As is apparent, one can think of the base portion position as defining the angular position of the cutting fingers. Therefore, the cutting fingers can be locked in position by locking the location of the base portion relative to the outer stem. Once this is achieved, the rock anchor cannot be removed other than by mechanical failure of the rock mass or the anchor itself. That said, the rock anchor is easily decommissioned by unlocking the motion of the base portion, returning the fingers to the first configuration, and sliding the rock anchor out of the bored hole. The method may include halting the method when the upper section of the or each cutting finger makes an angle of at least 20° with the anchoring axis. In other words, in the second configuration, this 20° angle indicates that the method has reached a point where it can terminate. Of course, larger angles may be used as threshold conditions, if this is desired. The outer stem may be hollow and provides a lumen through which an inner stem extends to couple to the base portion, and may the method include pulling the inner stem proximally to cause the finger(s) to pivot and flex outwardly. As discussed, this is a convenient way to cause the fingers to flare outwardly. The base portion may include a cutter for drilling a hole into the substrate and wherein the same rock anchor is used in the boring step as in underreaming step. This simplifies the installation process as described above. The rock anchor may include a tapered portion for gripping a substrate located at the proximal end of the anchor, the tapered portion further including a further cutting surface for drilling into the substrate, and the method may include providing a tapered portion to a proximal region of the bored hole using the further cutting surface. This operates in broadly the manner described above. The method may further comprise a tensioning step once the cutting fingers have flared out, wherein the tensioning step holds the cutting fingers in their flared configuration. The invention will now be described by way of example only with reference to the Figures, in which: Figures 1A to 1D illustrate the general principles of improved underreaming disclosed herein; Figure 1E shows the concept of Figures 1A to 1D applied to a rock anchor; Figures 2A and 2B illustrate two configurations for the fingers on a rock anchor; Figures 3A to 3C show a first example of a rock anchor; Figures 4A to 4C show a second example of a rock anchor; and Figures 5A and 5B show a sectional view of a rock anchor illustrating the internal operation. In general, corresponding features in one Figure are labelled similarly in each Figure using a three-digit reference numeral, XYZ. Here X refers to the Figure number (all features in Figures 1A to 1E begin with 1, i.e., X=1. YZ is a two-digit number uniquely referring to a given feature, so for example the cutting fingers are always referred to with YZ=04. Thus, the cutting fingers are 104 in Figures 1A to 1E, 204 in Figures 2A to 2B, and so forth. In Figures 1A to 1D, a high-level schematic of the general operation is shown. Here a set of five cutting fingers 104 is arranged around a lower portion of a rock anchor (the bulk of the rock anchor is not visible in these Figures). The lower portion of the rock anchor is broadly cylindrically symmetric around an anchoring axis, A, shown in Figure 1A. Each cutting finger 104 is located between a distal end of an outer stem 102 and a base portion 116. Each cutting finger 104 has an upper coupling 108 to pivotably couple that finger 104 to the distal end of the outer stem 102 and a lower coupling 108 to pivotably couple that finger 104 to the base portion 116. In addition, each cutting finger 104 is formed from an upper section 106 and a lower section 112, such that the lower section 112 is coupled to the base portion 116 via the lower coupling 108 and the upper section 106 is coupled to the outer stem 102 via the upper coupling 108. In addition, the upper section 106 and the lower section 112 are pivotably coupled to one another via a flaring pivot 118. This flaring pivot 118 is actuable to cause the junction between the upper 106 and lower 112 sections (i.e., the lower end of the upper section 106 and the upper end of the lower section 112) to flare outwardly. Although shown mounted on the rock anchor, the disclosure herein extends to the cutting fingers 104 on their own, for example for retrofitting to existing rock anchors. On each cutting finger 104 a cutting surface 110 is provided facing outwardly from the upper section 106. That is, the upper section 106 may include a roughened or otherwise abrasive surface or other elements suitable for cutting into rock or substrate, forming the cutting surface 110. Here the cutting surface 110 is applied directly to the outwardly facing part of the upper section 106. That is to say that the cutting surface 110 is integrally formed with the upper section 106. In other examples, the cutting surface 110 may be removeable and / or replaceable, in order to allow an operator to select appropriate cutting surfaces (in terms of cutting capability, mechanical strength, size, etc.) for the specific site in which the anchors are to be installed. In some examples, the lower end of the cutting surface 110 may be tougher, have greater cutting potential before wearing, etc. This is because, as the cutting finger 104 swings outwardly, the outer (i.e., lower) edge of the cutting surface 110 must cut through more rock than the inner (upper) edge does. The base portion 116 is axially displaceable and is located distally of the distal end of the outer stem 102. The couplings and pivots of the cutting fingers 104 are arranged so that, as the base portion 116 is moved axially (i.e., along the anchoring axis, or vertically in Figures 1A to 1D), the flaring pivot 118 flexes outwardly. This is shown in the progression of Figures 1A to 1D, with progressively more movement of the base portion 116 towards the outer stem 102 (i.e., in a proximal direction) shown. In this way the most distal arrangement of the base portion 116 is shown in Figure 1A, which is associated with the cutting fingers 104 not being deployed and being arranged in a broadly cylindrical arrangement. In Figure 1B, the deployment process has started and the base portion 116 has moved closer to the distal end of the outer stem 102. This has caused the flaring pivot 118 to move outward, away from the anchoring axis. Since the upper 106 and lower 112 sections are coupled to the outer stem 102 and the base portion 116 respectively, they are prevented from also moving outwardly. This causes the upper 106 and lower 112 sections to tilt in opposite directions - the upper section 106 has its upper end retained closer to the anchoring axis than its lower end (the flaring pivot) is, while the lower end of the lower section 112 is retained closer to the anchoring axis than its upper end (also the flaring pivot) is. This process continues in the progression shown in Figures 1C and 1D, in which the base portion 116 moves ever closer to the distal end of the outer stem 102. It can be seen that any of the positions shown in Figures 1B to 1D result in an underreaming which can be used to grip a rock mass and prevent removal of a rock anchor. The situation in Figure 1D illustrates the greatest extent of underreaming, in which the upper sections 106 of the cutting fingers 104 are flared out perpendicularly to the anchoring axis. In other words, depending on the properties of the installation site, the cutting fingers 104 may be flared out to any angle required by the parameters of the installation. This improved design of cutting fingers 104 leads to a novel deployment mechanism (discussed in more detail below). In summary though, the position of the base portion 116, relative to the distal end of the outer stem 102, can range from a first distance to a second distance. The first distance is one in which each cutting finger is in a first configuration where the upper 106 and lower 112 sections lie along a common line (i.e., the upper coupling 108, the flaring pivot 118, and the lower coupling 114 are all approximately the same distance from the anchoring axis). The second distance is less than the first distance and in order to accommodate the length of both the upper 106 and lower 112 sections of the cutting finger 104 in the reduced distance, each cutting finger 104 pivots outwardly at the flaring pivot 118. It can be seen that this arrangement can be made in a wide range of sizes, according to this general principle. The deployment mechanism is able to provide cutting fingers 104 flared out at any angle from the anchoring axis, including perpendicular / horizontal arrangements. The anchor results in a load path through the rock of the substrate and thereby provides extremely high mechanical stability. The lower section 112 of each cutting finger 104 flares outwardly and provides support to the cutting surface 110 at least as far out as the flaring pivot 118, thereby reducing stress generated by cantilever effects and improving the mechanical properties of the cutting surface 110 and upper section 106. This in turn reduces the likelihood of mechanical failure of these parts as well as improving the interface with the rock mass. Finally, the geometry of the cutting fingers 104 is largely a free parameter, allowing them to be formed in any shape which is appropriate for the use. The upper section 106 and the lower section 112 of the cutting finger 104 are formed as substantially rectilinear shapes. This is an easy shape to work with and provides a strong arrangement in both the first and the second configuration. The first configuration using such cutting fingers 104 can allow both the upper 106 and the lower 112 section to lie along a line parallel to the anchoring axis and thereby conform to a generally cylindrical arrangement when not deployed as in Figure 1A. In the examples shown in Figures 1A to 1D, the ratio of the length (i.e., extent in a direction aligned with the anchoring axis when the cutting fingers 104 are un-deployed) of the upper section 106 to the length of the lower section 112 is about 2 / 3. In other designs the ratio may extend as high as 3 - see for example Figure 1E which shows a specific design incorporating the general principles discussed above. Since this ratio is less than 1, there exist deployed (second) configurations such as that shown in Figure 1D, in which the upper section 106 of each cutting finger 104 extends perpendicular to the anchoring axis, although it is not necessary to go this far. For example, in Figure 1E, the upper section 106 is angled at slightly less than 20 degrees from the anchoring axis. In effect there is no minimum value for this ratio, but at a ratio of 1 it is possible to achieve a 90-degree angle, albeit with little supporting effect from the lower portion 112, which also extends at 90 degrees. A ratio of 0.5 allows a 90-degree angle with a reasonable amount of support against cantilever forces. By the time the ratio has dropped to about 0.1, it has long been possible to achieve a 90-degree angle. In fact, around 0.1 and below, there is little benefit in reducing the ratio further. In fact, for a given available length along the anchoring axis set aside for cutting fingers 114, all that a decrease in this ratio serves to do is dedicate more length to the lower section 112 which necessarily comes at the expense of length afforded to the upper section 106. Since the length of the upper section 106 determines the distance the underreaming extends into the rock mass, there is generally little to be gained by decreasing the ratio much further than 0.1 or so. As shown, the device includes five cutting fingers 104, but it is in principle possible to operate the underreaming process with only a single cutting finger 104, or indeed any larger number. For example, there may be between two and eight cutting fingers 104 in other examples, e.g., between four and six cutting fingers. As shown, the cutting fingers 104 (or at least the upper sections 106) abut one another in the first configuration. In other cases, there may be a gap between adjacent cutting fingers 104. The plurality of cutting fingers 104 shown are substantially identical to each other cutting finger 104. In other cases, the cutting fingers 104 may all be different, or there may be groups of different types of cutting fingers 104. The different types of different cutting finger 104 may be suited to different purposes and arranged appropriately - for example there may be cutting fingers 104 particularly suited to cutting and others being adapted to removal of waste material. These may be alternated around the rock anchor in some examples to achieve the desired effect. Consider now Figures 2A and 2B, which show a larger portion of a rock anchor 200 which incorporates a linkage-based cutting finger 204 system similar to those shown in Figures 1A to 1E. Here, a rock anchor 200 is shown, extending vertically in the Figures along the anchoring axis. The top of the Figures shows a proximal end, and the lower part shows the distal end. An outer stem 202 extends from the proximal end to the distal end. As can be seen in the Figures, the distal end includes an arrangement of cutting fingers 204 which operates in much the same manner as those in the previous Figures and will not be described in detail again. In line with that discussion, it can be seen that Figure 2A shows the pre-installation, undeployed, configuration, while Figure 2B shows the cutting fingers 204 flared outwardly, either in their final position, or in transit towards their final position, depending on the specific parameters of the installation. The rock anchor shown in Figures 2A and 2B (as well as in Figure 1E) has a set of cutters 222 on the base portion 216. The cutters 222 can be used to bore the hole into which the anchor 200 fits, prior to beginning the flaring out and underreaming process using the cutting fingers 204. This allows a single rock anchor 200 to bore the initial cylindrical hole, and then perform the underreaming described above. This is particularly advantageous, because in doing so the rock anchor 200 is already in place in the bored hole as soon as it is formed, ready to underream. This saves installation time and cost. In other examples, the hole can be pre-bored by a different drill. Also visible in this view is a tapered portion 220 for gripping a substrate located at the proximal end of the anchor 200. This tapered portion 220 acts like the second jaw of a clamp (the cutting fingers 204 situated in the underream being the first jaw of the clamp) to hold the anchor 200 firmly in the substrate. In some examples, the tapered portion 220 further includes a further cutting surface for drilling into the substrate. This further cutting surface can operate in much the same way as the cutting surface 210 located on the cutting fingers 204, in that it can include a roughened or otherwise abrasive surface or other elements suitable for cutting into rock or substrate. This allows the anchor 200 to be used to drill a top tapered part of the hole (i.e., corresponding in profile to the tapered portion 220). For example, the tapered portion 220 and can be rotated to drive the further cutting surface against the substrate while bearing down on the upper edge of the hole. This means that the full anchor 200 is drilled to depth, the tapered portion 220 begins to form a taper in the upper part of the hole. At full depth, the tapered portion 220 is in contact with a corresponding tapered part of the hole. This leads to an improved interface between the anchor 200 at the top of the hole. In general, the method of use of the anchors 200 described herein includes first boring a hole into a substrate; and subsequently underreaming a lower part of the hole by flaring out at least one cutting finger 204, the cutting finger(s) being of the type described herein and mounted on the rock anchor 200. Starting from the rock anchor 200 in a cylindrical bore hole with the cutting fingers 204 in the first configuration, the underreaming process involves gradually transitioning to the second configuration while rotating the outer stem 202 (and correspondingly also the cutting fingers 204 since they are attached to the outer stem 202). As the cutting finger 204 rotates against the rock mass forming the walls of the cylindrical bore hole, the cutting surface 210 cuts into the rock. As the flaring pivot 218 pivots, the cutting fingers 204 are driven outwardly, and a conical underream is formed in the rock mass. The pivoting of the flaring pivot 218 continues until the desired angle of the upper section 206 of the cutting finger 204 is reached. At this stage the outer stem 102 no longer need be rotated, and the rock anchor 200 can be locked in place by preventing the cutting fingers 204 from reverting to (or toward) the first configuration. As is apparent, one can think of the base portion 216 position as defining the angular position of the cutting fingers 204. Therefore, the cutting fingers 204can be locked in position by locking the axial position of the base portion 216 relative to the outer stem 202. Once this is achieved, the rock anchor 200 cannot be removed other than by mechanical failure of the rock mass or the anchor itself. That said, the rock anchor 200 is easily decommissioned by unlocking the motion of the base portion 216, returning the fingers 204 to the first configuration, and sliding the rock anchor 200 out of the bored hole. The first configuration has the cutting fingers 204 lying closest to the anchoring axis within a substantially cylindrical envelope. The second configuration has the flaring pivot 218 bending the fingers 204 such that the flaring pivot 218 itself (along with the lower part of the upper section 206 and the upper part of the lower section 212) are further from the anchoring axis than the upper end of the upper section 206 and the lower end of the lower section 212 (which do not move radially during the transition). In general, the cutting fingers 204 are limited so that the upper section 212 extends at most perpendicular from the anchoring axis. There is not usually any benefit in extending the cutting finger 204 further than this i.e., it is not common for the second configuration to have cutting fingers 204 angled upwardly such that the lower end of the upper section 206 is above (more proximal than) the upper end of the upper section 206. In some cases, the second configuration can even go past this angle, but there are diminishing returns in doing so, in the sense that the gripping does not get better (it eventually gets worse when the rock mass gets too small and as the underreamed distance decreases) and it requires a more complex design. Any angle involving a deformation from the first configuration up to a horizontal cutting finger 204 angle is certainly beneficial, however, and this is what happens as the base portion 216 is pulled upwardly (proximally) during the installation process meaning that the process can be stopped at any point in the process and many of the same advantages flow from this. Once the desired extent of underreaming has been achieved, a tensioning step may be executed, in which once the cutting fingers 204 have flared out, the base portion 216 is pulled upwardly (proximally). This tensioning step holds the cutting fingers 204 in their flared configuration and resists transitions back toward the first configuration (in which the anchor 200 could be removed from the hole). It can be seen that this arrangement can be made in a wide range of sizes, according to this general principle. The deployment mechanism is able to provide cutting fingers 214 flared out at any angle from the anchoring axis, including perpendicular / horizontal arrangements. The anchor 200 results in a load path through the rock of the substrate and thereby provides extremely high mechanical stability. The lower section of the cutting finger 204 flares outwardly and provides support to the cutting surface 210 at least as far out as the flaring pivot 218, thereby reducing the cantilever effect and improving the mechanical properties of the cutting surface 210 and upper section 206. This in turn reduces the likelihood of mechanical failure of these parts as well as improving the interface with the rock mass. Finally, the geometry of the cutting fingers 204 is largely a free parameter, allowing them to be formed in any shape which is appropriate for the use, since there is no requirement to be pushed outward by a matching part. Figures 3A to 3C and 4A to 4C show similar designs, which each implement the underreaming cutting fingers discussed above. Each of these has certain similarities with the above examples (and which will not be repeated again, for conciseness). In addition, certain features common to both sets of Figures (Figures 3A to 3C and 4A to 4C) are discussed below. In each set of Figures, the outer stem 302, 402 is hollow and provides a lumen through which an inner stem 324, 424 extends to couple to the base portion 316, 416. This allows the base portion 316, 416 to be controlled from the proximal end of the anchor 300, 400. In each example, the base portion 316, 416 is moveable by moving the inner stem 324, 424 axially relative to the outer stem 302, 402. As noted above, this motion causes bending at the flaring pivot 318, 418 to cause the cutting fingers 304, 404 to flare outward. Some designs may have further mechanisms or linkages to ensure that the cutting fingers 304, 404 move outward in the correct manner during base portion 316, 416 motions. The base portion 316, 416 is moveable by virtue of a mechanism for imparting axial motion to the inner stem relative to the outer stem 302, 402. Here this mechanism is a threaded portion at the top of the inner stem 324, 424 and a corresponding nut 326, 426 which can be rotated to force the inner stem 324, 424 upwards or downwards. The mechanism is therefore actuable from the proximal end of the rock anchor 300, 400 meaning that it can be used even when the majority of the rock anchor 300, 400 is embedded in the substrate (as in e.g., the installed configuration). This can allow the properties of the anchor 300, 400 (e.g., tension and actuation) to be altered easily for installation and decommissioning purposes. This same mechanism can be used for tensioning the inner stem 324, 424 and holding the cutting fingers 304, 404 firmly against the upper surface of the underream. In addition, a mechanism to lock the inner stem 324, 424 against rotation may also be included, although this is not shown. The upper part of the rock anchor 300, 400 also has portions for coupling mooring lines, cables, chains etc. to anchor devices to the substrate (i.e., a water bed, seabed, etc.). The mechanism in general can be used in conjunction with a remotely operated vehicle or similar. The simplicity of the threaded inner stem 324, 424 and nut 326, 426 system means that this is a mechanise which can easily be operated remotely in this way. Each of Figures 3A to 3C and 4A to 4C also shows an uppermost portion of the rock anchor 300, 400 which is upstanding from the water bed. This can provide sufficient clearance to allow remote operation and provide a clear location to which remote operation vehicles can couple. The main difference between Figures 3A to 3C and Figures 4A to 4C is in the uppermost portions. In Figures 3A to 3C, a tapered upper section is provided which helps to centrally align remote operated vehicles with the anchoring axis. The tapered upper section can also provide locations to which cables, chains etc. may be coupled. By contrast, in Figures 4A to 4C, a spherical bush is used, to allow for radial interfacing with external devices. Finally, in Figures 5A and 5B, a detailed cross-sectional view of yet a further example is shown. Here it can be seen clearly that the inner stem 524 and outer stem 502 are able to move axially relative to one another to force the cutting fingers 504 outwardly. In some cases, the relative axial motion between these two stems may be temporarily inhibited by supplying the assembled rock anchor 500 with shear pins coupling the two stems 502, 524 to one another. Once the rock anchor 500 is correctly seated in the hole, the shear pins can be forced to shear (optionally as part of the actuation of the flaring cutting fingers 504), and relative axial motion is enabled. Clearly visible in Figures 5A and 5B is the cutting surface 510 extending below (more distally than) the lower end of upper section 506. For example, the cutting surface 510 extends past the flaring pivot 518 and even overlaps some or all of the lower section 512. In some cases the cutting surface 510 may also be wider than (i.e., extend around a greater angular arc than) the upper section 506. This allows for improved cutting and in particular the cutting surface 510 being longer than the upper section 506 allows the underreaming to extend deeper into the rock. However, there is a trade-off here in that the further the extension extends past the flaring pivot 518, the greater the cantilever force on the outer edge of the cutting surface, due to the unsupported length of cutting surface 510, and the greater the risk of mechanical failure. In some cases, as shown in Figure 5A the lower section 512 is angled inwardly, with the flaring pivot 518 located further from the anchoring axis than the lower pivot 514 is. This biases the flaring pivot 518 toward flexing outwardly when the base portion 516 is brought towards the outer stem 502. In general the upper pivot 508 is best located as far outwardly as possible (i.e., at a radial distance as close to the maximum radial dimension of the bore hole) to maximise the distance into the rock which the underreaming process sweeps out. This means that, while the same effect could be achieved by tilting the upper section 506 inward at its proximal end (moving upper pivot 508 inward relative to the flaring pivot 518) this sacrifices some of the underreaming distance, so is not preferred in general. In some cases, both may be tilted, of course, such that the flaring pivot 518 is located furthest out of the three pivots (upper 508, lower 514, flaring 518). This tilting of the upper 506 and lower 512 sections is an example of a passive mechanism for encouraging the cutting fingers 504 to flare outwardly in the intended manner. In other examples, an active mechanism may be used, for example coupling the cutting fingers 504 using e.g. racks and pinions, worm gears, etc. to the mechanism which raises the base portion 516, so that the motion to raise the base portion 516 also exerts an outward force on the flaring pivot 518, to cause the cutting fingers 504 to flare outwards.

Claims

20 11 241. A rock anchor comprising:an outer stem extending from a proximal end to a distal end along an anchoring axis;an axially displaceable base portion located distally of the distal end of the outer stem; anda cutting finger comprising:an upper section having a cutting surface and an upper coupling for pivotably connecting to the outer stem of the rock anchor, wherein the cutting surface:is arranged to face outwardly relative to the anchoring axis; and extends below the lower end of the upper section;a lower section having a lower coupling for pivotably connecting to the base portion of the rock anchor; whereinthe upper section and lower section are pivotably coupled to one another via a flaring pivot, the flaring pivot coupling a lower portion of the upper section to an upper portion of the lower section.

2. The rock anchor according to claim 1, wherein the upper section and / or thelower section of the cutting finger is substantially rectilinear.

3. The rock anchor according to any one of the preceding claims, wherein theratio of the length of the upper section to the length of the lower section is no more than 3.

4. The rock anchor according to any one of the preceding claims, wherein thecutting surface is integrally formed with the upper section.

5. The rock anchor according to any one of claims 1 to 3, wherein the cuttingsurface is a removeable element attached to the upper section.

6. The rock anchor according to any one of the preceding claims, wherein theupper and / or lower sections are formed from steel and / or wherein the cutting surfaces includes tungsten carbide or diamond.

7. The rock anchor according to any one of the preceding claims, havingbetween two and eight cutting fingers.

8. The rock anchor according to any one of the preceding claims, havingbetween four and six cutting fingers.

9. The rock anchor according to any one of the preceding claims, having fivecutting fingers.

10. The rock anchor according to any one of the preceding claims, comprising agap between adjacent cutting fingers.

11. The rock anchor according to any one of the preceding claims, wherein eachcutting finger is substantially identical to each other cutting finger.

12. The rock anchor according to any one of the preceding claims, wherein thebase portion includes a cutter fordrilling a bore hole into a rock substrate.13.The rock anchor according to any one of the preceding claims, wherein the rock anchor has:a first configuration in which the base portion is a first distance from the distal end of the outer stem and the or each cutting finger is / are not deployed; anda second configuration in which the base portion is a second distance, less than the first distance, from the distal end of the outer stem and the or each cutting finger is pivoted at the flaring pivot to extend outwardly away from the anchoring axis.

14. The rock anchor according to any one of the preceding claims, wherein theouter stem is hollow and provides a lumen through which an inner stem extends to couple to the base portion.

15. The rock anchor according to claim 14, wherein the base portion is moveableby moving the inner stem axially relative to the outer stem.

16. The rock anchor according to any one of claims 14 or 15, wherein the anchorincludes a mechanism for imparting axial motion to the inner stem relative to the outer stem and / or wherein the anchor includes a mechanism for tensioning the inner stem.20 11 2417. The rock anchor according to any one of claims 2 to 16, further including atapered portion for gripping a substrate located at the proximal end of the anchor.

18. The rock anchor according to claim 17, wherein the tapered portion includes afurther cutting surface for drilling into the substrate.

19. A method of installing the rock anchor of any preceding claim, comprising thesteps of:boring a hole into a substrate; andunderreaming a lower part of the hole by flaring out the or each cutting finger, the underreaming process further comprising transitioning from a first configuration in which the base portion is a first distance from the distal end of the outer stem and the or each cutting finger is / are not deployed to a second configuration in which the base portion is a second distance, less than the first distance, from the distal end of the outer stem and the or each cutting finger is pivoted at the flaring pivot to extend outwardly away from the anchoring axis.

20. The method according to claim 19, wherein the upper section of the or eachcutting finger makes an angle of at least 20° with the anchoring axis in the second configuration.

21. The method according to any one of claims 19 or 20, wherein the outer stemis hollow and provides a lumen through which an inner stem extends to couple to the base portion, and wherein the method includes pulling the inner stem proximally to cause the cutting finger(s) to pivot and flex outwardly.

22. The method according to any one of claims 19 to 21, wherein the baseportion includes a cutter for drilling a hole into the substrate and wherein the same rock anchor is used in the boring step as in underreaming step.

23. The method according to any one of claims 19 to 22, wherein the rock anchorincludes a tapered portion for gripping a substrate located at the proximal end of the anchor, the tapered portion further including a further cutting surface for drilling into the substrate, and wherein the method includes:providing a tapered portion to a proximal region of the bored hole using the further cutting surface.

24. The method according to any one of claims 19 to 23, further comprising atensioning step once the cutting fingers have flared out, wherein the tensioning step holds the cutting fingers in their flared configuration.20 11 24

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