Field of invention

[01 ] This invention relates to apparatus for and a method of preparing a borehole for a rock anchor. It provides for an expansible packer for sealing an anchor cavity for high pressure grouting for assisting in retaining the anchor.

Background to the invention

[02] An artesian aquifer is a water bearing body that may be present in any rock formation. Highly permeable formations that harbour large natural fissures allow for high flow rates of water, whilst other highly porous/low permeability formations will typically result in lower flow rates. Whenever a hole is drilled for the purpose of installing an anchor for stabilising a rock or foundation formation, it must be waterproof. This means that after the anchor hole is drilled, water must not flow freely from the hole (an artesian aquifer), nor must it retreat once the hole is filled with water. If the hole fails to conform to either of these requirements, the hole must be waterproofed with a suitable sealing material, such as neat cement or bentonite, in a process known as‘grouting’. This requires the sealing material, or grout, to be pumped under pressure into the hole using apparatus referred to as a “grout packer". The process and use of the grout packer apparatus is intended to plug the mouth of the hole to seal it from atmosphere and result in filling the hole and any natural fractures within the surrounding formation with grout under sufficient pressure to penetrate crevices, fractures and similar inconsistencies.

[03] In a highly porous or low permeability formation such as sandstone, additional problems with pressure grouting may occur. Because some rock formations harbour artesian aquifers, a slightly permeable sandstone aquifer drilled to a depth of 10m may produce very low water flows at up to 100kPa. This pressurised water in-flowing into the hole may cause the grout that has been placed into the hole to become displaced. The current industry practice is to drill, then waterproof grout, then redrill. Because the grout viscosity is greater than that of water, and because the rock formation is only slightly permeable, grout cannot be forced into the formation. There is a requirement to remove substantially all the waterproof grout before the anchor is grouted into the borehole. This ensures that an effective bond between the anchor and the borehole wall is achieved once the structural grout is pumped into the hole. During the process of removing all the waterproof grout, the hole is generally unwaterproofed, and water may once again flow into the hole. This results in a hole that will only stay waterproof until it is redrilled. The costs associated with drill/grout/redrill can be more than double the original drilling price.

[04] A tremie line, which is generally constructed from poly pipe, is used to introduce to and place grout at the bottom of a borehole. The grout must be placed at the bottom of the hole so as to displace any water that may be present, upwards. This ensures that the entire column of grout is uniform, with no air or water pockets becoming trapped in the hole.

[05] US patent 4,413,929 discloses a bolt and hole packer for use in an upwardly inclined hole. The packer comprises a bag which is filled with a settable sealing material and is allowed to harden in sealing contact with the hole wall. Clearly, once the sealing material has set, the bag cannot be used again.

[06] Canadian patent publication 2515556 proposes an inflatable cylinder device for plugging an upwardly extending drill hole. It is stated that the cylinder must have enough pressure to seal the plug against the drill hole walls. However, there is no suggestion how the cylinder should be prevented from axially deforming. Axial deformation has the unwelcome outcome of compromising the lateral or radial seal with the surrounding rock wail or shaft lining.

[07] Deforming of the sheath that encases the anchor bar or rod (the terms can be used interchangeably in the context of this invention) can occur when an unacceptably high pressure differential is experienced during an anchor grouting operation, for example when existing concrete has been laid on top of a relatively weak natural rock formation, such as sandstone and over time flowing water has eroded a gap at the interface between concrete and rock. When a hole is drilled across the interface, and the packer has to be inserted below ground level, the inner annulus of the sheath is unconfined. This compromises the integrity of the protective sheath around the rod.

Objects of the invention

[08] It is an object of this invention to address the shortcomings of the prior art and, in doing so, to provide a sealing packer assembly that is suitable for use in rock anchoring applications.

[09] The preceding discussion of the background to the invention is intended to facilitate an understanding of the present invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge in Australia or elsewhere as at the priority date of the present application.

[010] Further, and unless the context clearly requires otherwise, throughout the description and the claims, the words‘comprise’,‘comprising’, and the like are to be construed in an inclusive sense of “including, but not being limited to” - as opposed to an exclusive or exhaustive sense meaning“including this and nothing else.”

Summary of invention

[011] According to a first aspect of the invention, there is provided a re-usable expansible cavity-sealing assembly adapted for sealing an anchor-receiving cavity in a rock or construction for withstanding high pressure grouting, the assembly comprising: a. A flexible gland member having opposite inner and outer ends, between which a fillable chamber is located, the member being beatable radially external to an anchor rod member to be operatively secured in a drilled cavity, and b. Expansion-limiting means adapted for limiting axial expansion of the gland whereby expansion of the chamber is permitted substantially only in a radial direction with respect to the anchor rod member.

[012] High pressure grouting refers to a grouting operation performed in a cavity in which gauge pressure is in a range from 90kPa to 200kPa. Although higher pressures - up to 500kPa - are readily achieved using the assembly of the present invention, where there is significant risk of hydraulic fracture, a pressure of around 100kPa will generally be applied.

[013] Preferably, the gland member is adapted to provide for the chamber to be expansible radially away from and toward the anchor rod member.

[014] In a preferred form of the invention, the expansion-limiting means comprises first and second spaced members between which the gland is operatively located.

[015] Preferably, the first and second spaced members comprise: a. first and second retaining means axially positioned respectively at the inner and outer ends of the gland, and b. connecting means connecting said retaining means together to maintain a maximum spacing between said retaining means.

[016] In a further preferred form of the invention, the connecting means comprises adjustment means operable to adjust the maximum amount of the spacing.

[017] Preferably, the adjustment means comprises engagement means operable to engage with a tremie. The engagement means may comprise a formation for engaging with a tremie line extending from said upper to lower ends.

[018] In an embodiment, the engagement means comprises interacting screw- threaded formations. [019] In a still further preferred form of the invention, the gland member comprises a radially deformable external wall, adapted to deform when the chamber is pressurised with a filler, to cause sealing abutment of the wall with a hole collar surface. The hole collar is also referred to herein as a bore casing. Preferably, the filler is a fluid. Further preferably, the fluid is gaseous.

[020] In a preferred embodiment, the gland member comprises a radially deformable internal annular wall, adapted to deform toward a central axis when the chamber is pressurised with a filler, to cause sealing abutment of the internal wall with a sheath section surrounding the anchor rod member.

[021 ] In use in an embodiment of the invention, two or more assemblies are located in spaced apart relationship on a common anchor bar or rod. Preferably, a protective conduit extends between adjacent assemblies and is located around the protective sheath of the rod.

[022] According to a second aspect of the invention there is provided a method of sealing an anchor-receiving cavity in a formation for withstanding high pressure grouting, the method comprising: a. providing a re-usable expansible cavity-sealing assembly adapted for operatively sealing said cavity for withstanding high pressure grouting, the assembly comprising: i. a gland member having opposite inner and outer ends, between which a fillable chamber is located, the member being beatable radially external to an anchor rod member to be operatively secured in a drilled cavity, and ii. expansion-limiting means adapted for limiting axial expansion of the gland member; b. Introducing filler to the chamber to cause the gland to pressurize the chamber and cause the gland to expand radially into sealing contact with a collar of the cavity, whereby the cavity is sealed to atmosphere; and c. Introducing grouting to the cavity below the assembly and filling the cavity.

[023] In a preferred form of the invention, the method includes exerting pressure on the grout sufficient to waterproof the cavity.

[024] Preferably, the gland member is adapted to allow for the chamber to expand both radially away from and toward the anchor rod member.

[025] In an embodiment, the method comprises exerting gauge pressure in the range from 90kPa to 200kPa. Typically, the gauge pressure, when the assembly is located near the surface, is around 100kPa.

[026] In a preferred form of the invention, the expansion-limiting means comprises first and second spaced members, and the method includes operatively locating the gland between the members, whereby glad expansion is substantially limited to progressing radially in relation to the rod axis.

[027] Preferably, the first and second spaced members comprise: a. first and second retaining means axially positioned respectively at the inner and outer ends of the gland, and b. connecting means connecting said retaining means together to maintain a maximum spacing between said retaining means.

[028] In an embodiment, the method includes operating adjustment means to adjust the maximum amount of the spacing for meeting pressure requirements for grouting.

[029] In a preferred embodiment, the gland member comprises a radially deformable internal annular wall, adapted to deform toward a central axis when the chamber is pressurised with a filler, to cause sealing abutment of the internal wall with a sheath section surrounding the anchor rod member. [030] In a further form of the invention, the method includes locating first and second assemblies in tandem on the same anchor bar, the first assembly having a gland allowing chamber expansion in opposite radial directions and the second assembly having a gland allowing chamber expansion in a single radial direction only, towards a central axis of the bore.

[031 ] Preferably, the method includes causing simultaneous expansion of the chamber of the first assembly in both opposite directions.

[032] In a still further preferred form of the invention, the method includes the step of filling the chamber with a fluid.

[033] In an embodiment the fluid is substantially incompressible.

[034] In a preferred embodiment, the fluid is compressible. Preferably, the fluid is air.

[035] According to a third aspect of the invention there is provided a reusable cavity-sealing kit for use in providing a pressure seal to a collared hole for receiving an anchor device, the kit including a packer assembly in partially assembled form, the assembly including as components: a. A gland member having opposite inner and outer ends, between which a fillable chamber is located, the member being beatable radially external to an anchor rod member to be operatively secured in a drilled cavity and b. Expansion-limiting means adapted for limiting axial expansion of the gland when filled, whereby expansion of the chamber is permitted substantially only in a radial direction with respect to the anchor rod member.

[036] Preferably, the gland member is adapted for the chamber to be expansible radially away from and toward the anchor rod member. [037] In a preferred form of the invention, the expansion-limiting means comprises: a. first and second retaining means axially positioned respectively at the inner and outer ends of the gland, and b. connecting means connecting said retaining means together to maintain a maximum spacing between said retaining means.

[038] In a further preferred form of the kit of the invention, the connecting means comprises adjustment means operable to adjust the maximum amount of the spacing.

[039] Preferably, the adjustment means comprises engagement means operable to engage with a tremie line. The engagement means may comprise a formation for engaging with a tremie line extending from said upper to lower ends.

[040] In an embodiment, the engagement means comprises interacting screw- threaded formations.

[041] The kit may include one or more tremie assemblies adapted for engagement with the formation of the engagement means.

Brief description of drawings

[042] In order that the invention may be readily understood, and put into practical effect, reference will now be made to the accompanying figures. Thus:

Figure 1 shows in a preferred embodiment of the packing assembly of this invention in dissembled, exploded form in (a) and a top view of upper retention plate 44 in (b).

Figure 2 is a perspective view of the packer of Figure 1 without anchor rod and securing nuts in place.

Figure 3 is a cross-sectional view of the assembly of Figure 1 in assembled form, taken along line A-B in Figure 1.. Figure 5 is a cross-sectional side view of an embodiment of a packer for use in tandem with a packer of Figure 4.

Figure 6 illustrates the packer of Figure 4 deployed in tandem with a second, ancillary packer of Figure 5 A partially exploded view of the combination is shown in Figure 5(a), a top view in (b) and the assembled combination in preparation for downhole use in (c).

Detailed description of the invention

[043] The invention, a preferred - but non-limiting - embodiment of which will be described below, provides a packer assembly that may be provided in kit form and is not only reusable, but allows vastly increased grouting pressures to be applied by virtue of having an increased area of sealing contact with the sidewall of a borehole into which an anchor is to be received and grouted in place. The increased area provides an increased friction gripping area for retaining the packer against displacement from the hole as a result of grouting pressure. In cases where the coefficient of friction is too low to allow the force of friction to retain the packer, any conventional method of retainment may be substituted onsite, such as a steel plate fastened to the concrete foundation by an anchor-sleeve device of the kind sold under the brand name DynaBolt and available from Ramset Australia (refer to www.ramset.com.au/Product).

[044] The packer comprises a deformable gland in which is defined a fillable and radially expansible chamber. The chamber has a wall with an external wall surface that sealingly abuts a surrounding borehole wall when the chamber is filled, such as by means of inflation with a fluid. A substance that remains in fluid state, as opposed to a settable compound, is preferred.

[045] Inflation may be by means of a releasable fluid, so that the packer assembly may be deflated and re-deployed at a different site once the grouting has set at a first site. The fluid may be a liquid, for example water, or a gas, for example air or nitrogen. [046] The present invention, rather than relying on the compression of the two plates to increase the diameter of the gland, provides for a fluid, such as compressed air, to be pumped into the packer assembly to inflate it. This gives a far greater area of rubber that has contact with the borehole wall, and therefore provides a much larger sealing surface, resulting in a superior sealing outcome. Meanwhile the spacing between the plates is permitted to reach an acceptable predetermined limit, so that expansion is directed radially outwards. Once the plates have reached their spacing limit, they remain a substantially constant distance apart.

[047] Referring to Figure 1 , illustrating a preferred embodiment of this invention in exploded view, the packer assembly 10 is configured to receive and fit about a screw-threaded anchor bar or rod 12 that passes through it and is secured and tensioned by anchor bar nut 14. In use, the rod extends through a central passage 16 that is defined by the components of the packer assembly, which will be described below. In Figures 2 and 3, like parts found in Figure 1 are like numbered.

[048] The packer assembly has, as its principal component, a gland 18. The gland is made of a flexible, expansible substance. In this preferred embodiment it is a natural rubber compound. Flowever, it will be evident to those skilled in the art that other suitable resilient and flexible materials exist and may be substituted, for example synthetic rubber compounds and flexible plastics. In Figure 3, a cross- section of the packer assembly when assembled, gland 18 is shown to comprise a moulded body 20 having an outer wall 22 behind which is an inner annular recess 24. In use, an outer surface 26 of wall 22 comes into sealing contact with the hole collar 28, which defines the interface with the rock or other formation behind it and into which the assembly is installed temporarily, for sealing against loss of grout under pressure when the hole itself is being sealed.

[049] Gland 18 surrounds tubular casing 30 into which rod 12 is received to pass through and thereby define the annular nature of chamber 24. The assembly is shown in cross-sectional side view in Figure 3, taken along line A-B in Figure 1 (a). Flere it can be seen that the outer wall 22 extends from top to bottom of the packer assembly. This extent and the material of construction of the gland being a flexible rubber has the advantage of maximising the surface for abutting the rock collar surface. The axial extension of wall 22 to cover retention plates 42 and 44 also assists in preventing escape of filling fluid from chamber 24 when wall 22 is radially distorted under inflating pressure in use.

[050] The rod 12 is passed through a corrugated sheath 32 of polyvinyl chloride (PVC) (or a similar substance) which fits coaxially inside an intermediate sheath 34, which in turn fits into previously mentioned casing 30. Intermediate sheath 34 has a flange 36 integrally formed at its lower end. This flange is secured by means of tremie lines 38 to lower and upper retaining plates 42, 44. The tremie lines are externally screw-threaded 45 for receiving fastening nuts 40. The screw threads may be provided along selected portions of the tremie pipes only, or along their entire lengths. It is through the tremie pipes that grouting sealant is introduced to the hole space below the packer assembly and air and water in the space is expelled to allow entry of the grout.

[051 ] Above upper plate 44 is a steel washer 46 through which tremie lines 38 pass, to be fastened with nuts 40. Between lower plate 42 and flange 36 is a lower steel washer 48 having a central aperture that fits about sheath 34 so that it comes into abutment with the flange, when the sheath is drawn into casing 30, when nuts 40 are tightened on tremie lines 38.

[052] Retaining plates 42, 44 each have respective circular projecting surface portions 50, 52, which fit snugly into the upper and lower portions of annular space within casing 30, to stabilise it against relative movement when fitted therein.

[053] Air (or a suitable alternative fluid) is introduced into chamber 24 through valve stem assembly 54, which passes through upper plate 44 and upper steel washer 46.

[054] Each tremie line 38 has a flange portion 56 that is drawn up against the lower surface 58 of flange 36 when nuts 40 are tightened to the selected position along the upper portion 60 of the tremie. At this position, the desired maximum spacing between upper and lower plates 42, 44 is achieved. Tightening or loosening of the screws allows adjustment of the spacing, allowing a means for adjustment of the expansion of and pressure within chamber 24. O-rings 62 surround each tremie line as it passes into and through chamber 24 to ensure fluid sealing is achieved.

[055] It will be appreciated that sheaths 32 and 34 and anchor rod 12 are not shown in Figure 2.

[056] In use, the anchor with rod 12 is inserted into the formation in which the hole defined by collar 28 has been formed. The tremies are then inserted. Packer assembly 10 is placed centrally over the rod and on to the tremies, with the tremies allowed to pass into and through the apertures in the top washer, through the top plate, the chamber, the lower plate 42, washer 48 and flange 36 until flange 36 comes to rest to be supported against further ingress by tremie flanges 56 at a suitable level below the surface of the surrounding formation. Anchor rod 12 has a screw-threaded connector 64 for connecting to a mating thread on an anchor rod extension of like design when extension is required.

[057] Grouting sealant is introduced via one or more of the tremies into the space below the packing and air is pumped into the chamber via valve 54 to achieve sealing abutment between surface 26 and collar 28. At least one of the tremies is temporarily left open to allow air to escape the space to be filled. At an appropriate selected stage the exhaust tremie line is closed to allow pressure grouting to proceed.

[058] The packer of the present invention is an advancement on previous designs in that significantly more pressure may be applied to the grout as it is pumped down the anchor hole during the pressure-grouting process. Previously, with the old packer that was developed, only 20kPa of pressure could be applied before grout would bypass the packer. The new design allows up to 500kPa(g) of grout pressure to be pumped into the rock formation, increasing the range of effective sealing that is available to users of the invention. A preferred range of operation is from 200kPag to 500kPag. More preferably, the range is from 350kPag to 450kPag. However, as previously noted, where there is significant risk of hydraulic fracture, pressures in the range 90kPag to 20GkPag are preferred in susceptible formations, and even more preferably in the range from 9GkPag to 120kPag.

[059] Referring to Figure 4, there is depicted a further embodiment of the invention in a particularly preferred form, where a modified packer 100, having a flexibly resilient gland 1 18 of a synthetic rubber or similar compound, is configured to bear radially, both outwardly against the surrounding bore casing wall 128, and inwardly against the sections of corrugated sheath 132 that protectively isolate an anchor bar 1 12. Tremie lines 138 pass through the packer assembly, for grout transfer and venting purposes.

[060] Gland 1 18 surrounds a section of resiliently flexible tubular casing 130, into which sheath 132 and bar 1 12 are received, to pass through and thereby define an annular inflatable chamber 124. Annular space 124 extends from its radially inner wall 130 to an outer wall 122 having an outer surface 126. It is supplied with inflating fluid, typically air, via an inlet valve 154, providing fluid communication through upper flange 144 with an external supply of compressed air, but which in Figure 4 is obscured by bar 1 12 and sheath 132.

[061 ] When sufficiently inflated and pressurised with compressed air, the chamber 124 expands and gland walls 122 and 130 are pushed respectively radially away from and toward the central axis of the bore, which generally corresponds with the longitudinal axis of anchor bar 1 12. This radial pressure in opposite directions is represented by means of the pairs of directional arrows R1 and R2 and dashed lines denoting radial bulging. Sealing pressure is thus brought to bear on bore casing 128 by the surface of wall 122 and on corrugated sheath or sleeve 132 by flexible wall 130.

[062] As with the assembly described in Figures 1 to 3, axial expansion of chamber 124 in gland 1 18 is substantially prevented in favour of radial expansion by upper and lower retaining flanges 144, 142, which made with complementally shaped formations at the axial ends of gland body 1 18. The flanges are maintained at a constant spacing by screw threaded fasteners and nuts, conveniently found on the tremie lines 138 passing from one to the other.

[063] Referring to Figure 5, there is depicted a further embodiment of the invention in an ancillary form, where a modified packer 200 is shown located at the top end of a bore 28, with anchor rod member 1 12 emerging above ground level 202. Packer 200 has a flexibly resilient gland 218 of a synthetic rubber or similar compound, which is configured to bear radially, in the direction of the arrow, inwardly against corrugated sheath 132 that protectively isolates anchor bar 1 12. Tremie lines 138 pass through the packer assembly, for grout transfer to fillable spaces below the packer, and for venting purposes.

[064] Gland 1 18 surrounds a section of resiliently flexible tubular casing 230, into which sheath 132 and bar 1 12 are received, to pass through and thereby define an annular inflatable chamber 224. Annular space 224 extends from its radially inner wall 230 to an outer wall 222 having an outer surface 226. In this form of the packer of the invention, the outer wall 222 is substantially rigid, made from a metal such as steel or aluminium, or suitable alloys for the conditions of exposure. Chamber 224 is supplied with inflating fluid, typically air, via an inlet valve 254, providing fluid communication through upper flange 244 with an external supply of compressed air (not shown).

[065] When sufficiently inflated and pressurised with compressed air, the chamber 224 expands and flexible gland wall 230 is pushed radially toward the central axis of the bore, which generally corresponds with the longitudinal axis of anchor bar 1 12. This radial pressure direction is represented by means of the directional arrows R. Sealing pressure is thus brought to bear on corrugated sheath or sleeve 132 by flexible wall 230. The flexible wall may be made from any suitable material, such as a synthetic rubber compound able to withstand harsh conditions.

[066] As with the assembly described in Figures 1 to 4, axial expansion of chamber 224 in gland 218 is substantially prevented in favour of radial expansion by upper and lower retaining flanges 244, 242, which made with complementally shaped formations at the axial ends of gland body 1 18. The flanges are maintained at a constant spacing by screw threaded fasteners and nuts 256, conveniently found on the tremie lines 138 passing from one flange to the other. In addition, anchor bar 1 12 is secured relative to upper flange 244 by means of locking nut 240.

[067] Figure 6 illustrates the packer 100 of Figure 4 deployed in tandem with the second, ancillary packer 200. An exploded view of the combination is shown in Figure 6(a), the top view in (b) and the assembled combination in preparation for downhole use in (c). Ancillary packer 200 is located coaxially to be spaced from first packer 100 along the rod 1 12 intermediate the first packer and the open end 106 of the bore casing being sealed (see Figure 5(c)).

[068] The ancillary packer is configured to bear radially inwardly when inflated, so that it creates a seal between its inner annular wall 230 and the PVC corrugated sheath 132, so that pressure within the sheath cavity is maintained and the sheath does not collapse inwardly against the anchor bar. The outer wall 222 of ancillary packer 200 is substantially rigid, the packer being beatable above ground if convenient, the role of this packer not being to seal against the bore casing, but around anchor bar sheathing 132. A sheath cover tube 108 extends between packers 100 and 200, connecting with respective sections 108a, 108b to provide a continuous conduit between the packers enclosing sheathing 132.

[069] In use, the anchor rod or bar 1 12 extends through a central passage 1 16, 216 in each of the packers and is isolated by the sheath 132. Tremie lines 138 extend through the packers to communicate with fillable space 102. Grouting is transferred into space 102 by transfer known means and pressurised within the space below packer 200 to fill crevices and set to hardness.

[070] A series of packers of the kind 100 in Figure 5 may be deployed in tandem below a top packer of the type 200 illustrated in Figure 6, for sealing a bore at different levels. It may not be considered necessary to include type 200 at all, depending on the formation to be anchored and its composition. The tremie lines will extend to the different intermediate spaces located between each pair of packers. Grouting is introduced in stages between the packers to establish separate filled compartments. Different grouting, for example having different setting times, may be introduced into the different compartments. Protective encasing pipes such as 108 in Figure 6 may be installed between successive packers to maintain integrity of the inner sheath that isolates the rod.

[071 ] This invention is advantageous in that the majority of the components of the apparatus are recoverable and reusable. This is not to say that on occasion a packer may not become irretrievably stuck. Its use makes it easy to achieve a watertight seal, in turn making it easily marketable to anyone in the drilling industry, where there are consistently experienced problems associated with the need to install anchors in a waterproof hole. Furthermore, the hole is drilled once and the anchor is installed and pressure grouted in one go. Not only are there considerable costs savings, but an increase in production rates, less mess due to recapturing weak grout, as well as the opportunity to re-batch weak grout for re-use.

[072] These embodiments merely illustrate particular examples of the method, kit and apparatus of the invention that provides means for effective sealing of an anchor hole for pressure grouting. With the insight gained from this disclosure, the person skilled in the art is well placed to discern further embodiments by means of which to put the claimed invention into practice.