AU2016259363A1 - Formation Stabilisation Apparatus - Google Patents

Abstract

Abstract The invention relates to a stabilisation apparatus 10 comprising a rod 12, a retention means 14 and a cap 16. The rod 12 comprises a distal end 18 for receiving the cap 16 and a proximal end 20 for receiving the retention means 14. In the particular arrangement shown in the figures the cap 16 comprises a conical cap 16. The cap 16 comprises a proximal end 24 and a distal end 26. The proximal end 24 is an open end for receiving the distal end 18 of the rod 12; the distal end 26 comprises openings. The openings of the distal end 26 permit delivery of the cementing material into the formation for securing the stabilisation apparatus 10 into the formation. Fig 1 Fig. 1

Description

1 2016259363 16 Nov 2016

FORMATION STABILISATION APPARATUS TECHNICAL FIELD

[0001] The present invention relates to apparatus for stabilising earth formations.

[0002] The invention has been devised particularly, although not necessarily solely, in relation to stabilisation apparatus for insertion into rock formations to stabilise the rock formations, in particular of roof and wail structures of mines.

BACKGROUND ART

[0003] The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

[0004] Mines, such as underground mines or open pit mines, require ground support to impede collapse of the mines, in particular the roof and walls of mines.

[0005] Particular stabilisation apparatus are used for supporting the rock formations of tunnels or shafts drilled during mining procedures. In particular, the stabilisation apparatus are suited for supporting the roofs and walls of mine tunnels or mine shafts of, for example, the underground mines.

[0006] A particular type of stabilisation apparatus comprises a rod and a retaining plate. The rod comprises a pipe section with a tapered end. A slot extends along the longitude of the pipe section. After the stabilisation apparatus has been installed within the earth formation, the support area of the retaining plate abuts the exterior surface of the earth formation that surrounds the opening in which the pipe section has been inserted. The rod when installed within the formation exerts radial pressure against the inner surface of the formation over the full length of the rod. This arrangement secures the earth formation.

[0007] These particular stabilisation apparatus have proven to be suitable for providing ground support to mine structures. However, the installation of these particular stabilisation apparatus can be cumbersome. This is particularly true because the stabilisation apparatus needs to be properly installed from the start. Improper 2 2016259363 16 Nov 2016 installation of the stabilisation apparatus may render the retention plate not suitable for supporting the formation due to, for example, the retention plate does not tightly abutting the exterior surface of the formation to be stabilised. Improper installation can occur, if for example, the borehole that has been drilled into the earth formation has the incorrect diameter - e.g. a diameter that is too big in relation to the diameter of the stabilisation apparatus to be inserted in the borehole. Under these circumstances, the stabilisation apparatus may not snugly fit into borehole and most probably the stabilisation apparatus will fail and the formation may collapse.

[0008] Conventional stabilisation apparatus are not adapted to correct improper installations of the stabilisation apparatus after installation has occurred. In fact, during installation of the conventional stabilisation apparatus, if the stabilisation apparatus have not been improperly installed from the start there are none or relative few options for correcting the installation of the stabilisation apparatus; typically, an option is to drill a new borehole at a location adjacent the improperly drilled borehole, thus weakening the earth formation.

[0009] Furthermore, as indicated before, the rod of the conventional stabilisation apparatus when installed within the formation exerts radial pressure against the inner surface of the formation securing of the rod within the formation. Thus, the conventional stabilisation apparatus are maintained secured within the formation solely by the radial pressure applied against the inner surface of the formation. The radial pressure exerted onto the inner surface may not be sufficient to maintain the stabilisation apparatus secured within the formation; if this this is the case the stabilisation action of the stabilisation apparatus may fail and a collapse of the earth formation may be imminent after failure of the stabilisation apparatus.

[0010] It is against this background that the present invention has been developed. SUMMARY OF INVENTION

[0011] According to a first aspect of the invention there is provided a stabilisation apparatus for providing support to an earth formation, the stabilisation apparatus comprising a rod and retention means reieasabiy attached to the rod, the rod comprising a proximal end for receiving the retention means and a distal end adapted for securing the rod within the formation, wherein the rod is adapted to secure the 3 2016259363 16 Nov 2016 retention means at a particular location along the rod for the retention means to abut a surface of the formation.

[0012] Preferably, the rod comprises an externa! thread and the retention means comprises an interna! thread for screwing the retention means along the rod.

[0013] Preferably, the apparatus further comprises a fastening means for securing the rod within the formation.

[0014] Preferably, the fastening means is attached to the distal end of the rod.

[0015] Preferably, the fastening means comprises a cap.

[0016] Preferably, the cap comprises a proximal end and a distal end, the proximal end being an open end for receiving the distal end of the rod, and the distal end comprising openings for permitting fluid communication between the distal end of the rod and the exterior of the cap.

[0017] Preferably, at least a portion of the cap is attached to the dista! end of the rod.

[0018] Preferably, the cap comprises a conical cap.

[0019] In a particular arrangement of the present embodiment, the apparatus may comprise a retention plate adapted to be attached to a surface of the earth formation.

[0020] Preferably, the retention plate comprises an inner face adapted to be attached to the surface of the earth formation and and outer surface for receiving the retention means.

[0021] Preferably, retention plate comprises an opening for receiving a distai portion of the rod of the apparatus.

[0022] Preferably, the apparatus is adapted to provide cementing materia! into the formation.

[0023] Preferably, the apparatus comprises a passage adapted to provide the cementing material from the exterior of the formation into the interior of the formation.

[0024] In a first arrangement, the rod comprises at least one passage for supplying of the cementing material to the distal end of the rod. 4 2016259363 16 Nov 2016 [0025] Preferably, the passage is fluidly connected to an open end of the proximal end of the rod and to an open end of the distal end of the rod for delivering the cementing material from the exterior of the formation into the interior of the formation.

[0028] Preferably, the open end of the distal end of the rod is fluidly connected to the cap for delivering the cementing material into an interior of the cap.

[0027] Preferably, the interior of the cap is fluidly connected to the openings of the distal end of the cap for permitting fluid communication between the distal end of the rod and an interior of the formation.

[0028] Preferably, the cap comprises a slot extending from the proximal end of the cap to the distal end of the cap, [0029] Preferably, the slot defines a fist edge and a second edge.

[0030] Preferably, a proximal end of the first edge is attached to the distal end of the rod.

[0031] Preferably, a proximal end of the second edge is spaced apart from the distal end of the rod.

[0032] Preferably, the proximal portion of the first edge of the cap is attached to the rod via a plurality of fillets.

[0033] Preferably, the fillets are arranged in a spaced apart relationship with respect to each other.

[0034] Preferably, the fillets comprise weld spots that join together the proximal portion of the first edge of the cap and the distal end of the rod.

[0035] Preferably, the cap is adapted to be selectively displaced between a contracted condition and an extended condition.

[0036] in a second arrangement, the apparatus comprises a rod, a retention means and a cap.

[0037] Preferably, the rod comprises an external thread extending along the length of the rod 5 2016259363 16 Nov 2016 [0038] . Preferably, the external thread is adapted to fastening of the cap to the rod and to screw the retentions means onto the rod, [0039] Preferably, the cap is attached to the distal end of the rod through a nut.

[0040] Preferably, the nut is fastened to an inner surface of the distal end of the cap.

[0041 ] Preferably, the retention means comprises a plug adapted to be screwed onto the proximal end of the rod.

[0042] Preferably, the plug comprises a passage, the passage traversing the plug permitting supply of cementing material into the formation.

[0043] Preferably, the rod comprises a hollow rod for permitting release of fluid pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Further features of the present invention are more fully described in the following description of a non-limiting embodiment thereof. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad summary, disclosure or description of the invention as set out above. The description will be made with reference to the accompanying drawings in which:

Figure 1 is a side view of the stabilisation apparatus in accordance with a first embodiment of the invention;

Figure 2 is a schematic side view of the stabilisation apparatus shown in figure 1;

Figure 3 is a schematic exploded side view of the stabilisation apparatus shown in figure 1;

Figure 4 is a cross-sectionai view of a stabilisation apparatus in accordance with a second embodiment of the invention; and

Figures 5 is a perspective view of the apparatus shown in figure 1 in use. 6 2016259363 16 Nov 2016

It should be noted that the figures are schematic only and the location and disposition of the components can vary according to the particular arrangements of the embodiments of the present invention as well as of the particular applications of the present invention.

DESCRIPTION OF EMBODIMENTS

[0045] Figure 1 shows a particular arrangement of a stabilisation apparatus 10 in accordance with a first embodiment of the invention.

[0046] The stabilisation apparatus 10 shown in figure 2 comprises a rod 12, a retention means 14 and a cap 16. The rod 12 comprises a distal end 18 for receiving the cap 16 and a proximal end 20 for receiving the retention means 14.

[0047] In the particular arrangement shown in the figures the cap 16 comprises a conical cap 16.

[0048] The cap 16 comprises a proximal end 24 and a distal end 26. The proximal end 24 is an open end for receiving the distal end 18 of the rod 12; the distal end 26 comprises openings. As will be described with reference to the method of installation of the stabilisation apparatus 10, the openings of the distal end 26 permits delivery of the cementing material into the formation for securing the stabilisation system 10 into the formation.

[0049] The cap 16 comprises a slot 22. The slot 22 extends from the proximal end 24 of the cap 16 to the distal end 26 of the cap 16. The presence of the slot 22 defines two edges 28 and 30. The first edge 28 comprises a proximal portion 32 that is adapted for attachment to the rod 12, and a distal portion 34 configured to define, in a particular arrangement, a tapered end of the cap 16. A second edge 30 comprises a proximal portion 36 spaced apart from the distal end 18 of the rod 12, and a distal portion 38 configured to define in a particular arrangement, the tapered end of the cap 16.

[0050] The cap 16 is attached to the distal end 18 of the rod 12. In the particular arrangement of figures 1 to 3, the proximal portion 32 of the first edge 28 of the cap 16 is attached to the rod 12 via a plurality of fillets 40. The fillets 40 are arranged in a spaced apart relationship with respect to each other. The fillets 40 comprise welded spots that join together the proximal portion 32 of the first edge 28 of the cap 16 and the distal end 18 of the rod 12. 7 2016259363 16 Nov 2016 [0051] As mentioned before, the proximal portion 36 of the second edge 30 of the cap 16 is spaced apart from the distai end 18 of the rod 12 and not attached to the distal end 18 of the rod 12 defining a free edge 30. This defines a gap between the second edge 30 and the distai end 18 of the rod 12.

[0052] The fact that the second edge 30 is not attached to the distal end 18 of the rod 12 permits that the cap 16 to be selectively displaced between a contracted condition and an extended condition. During insertion of the stabilisation apparatus 10 into the formation, forces may be applied to the cap 16 reducing the diameter of the cap 16 and therefore locating the cap 16 in the contracted condition. If the forces (applied to the cap 16) cease, the cap 16 may increase its diameter by returning to the expanded condition. Displacement of the second edge 28 may occur by variations in the particular profile of the inner surface of the borehole made in the formation for insertion of the stabilisation apparatus 10. As the stabilisation apparatus 10 is inserted into the hole, the diameter of the cap 16 vary due to the variations of the borehole’s inner profile. In this manner, the conical cap is adapted to adjust to the particular profile of the inner surface of the borehole in which the stabilisation apparatus 10 is inserted.

[0053] Further, as will be discussed at a later stage, the rod 12 is adapted to provide cementing material into the borehole of the formation in which the stabilisation apparatus 10 is inserted. For this, the rod 12 comprises a passage adapted to provide the cementing material from the outside of the formation into the borehole.

[0054] During insertion of the cementing material into the borehole of the formation, the diameter of the cap 16 may increase due to the forces applied to the inner surface of the cap 16 as the cementing material is delivered into the formation. The cementing material applies the forces to the inner surface of the cap 16 during exiting of the cementing material through the distai end 18 of the rod 12.

[0055] Moreover, the stabilisation apparatus 10 comprises a retention means 14. The retention means 14 is adapted to conform to any type of external surface of the formation to be stabilised. In a particular arrangement, the retention means 14 comprises a dome plate 48 with its curved side abutting the exterior surface of the formation while the stabilisation apparatus 10 is inserted in the formation. The retention means 14 comprises the dome plate 48 and a fastener 44. 8 2016259363 16 Nov 2016 [0056] Further, the stabilisation apparatus 10 is adapted to displace the retention means 14 along the length of the rod 12.

[0057] In the particular arrangement shown in the figures, the dome piate 48 and the fastener 44 comprises openings receiving the rod 12 and permitting the dome plate 48 and the fastener 44 to move along the length the rod 12. In this manner, the retention means 14 may be selectively displaced between the proximal end 20 of the rod 12 at a particular location spaced apart from the proximal end 20.

[0058] Figure 5 shows the stabilisation apparatus 10 in use. As shown in figure 5, the apparatus 10 is inserted in the earth formation having the retention means 14 adjacent the outer surface of the earth formation. In the arrangement shown in figure 5, the apparatus 10 further comprises a retention piate 42 sandwiched between the earth formation and the retention means 14. The retention plate 42 comprises an inner surface 62 and an outer surface 64. The inner surface 62 is adapted to be attached to the outer surface of the earth formation. The outer surface 64 is adapted to receive the retention means 14. The retention plate 42 comprises an opening for receiving the distal end 18 of the rod 42 during installation of the apparatus 10.

[0059] As will be described with reference to the method of installation of the stabilisation apparatus 10 into the formation, typically, the retention means 14 will be located at a particular location spaced apart from the proximal end of the rod 12 such that the retention means 14 is adjacent to the formation’s exterior surface surrounding the borehole. In particular, the retention means 14 are located at a location such that the dome plate 48 abuts tightly the retention plate 42 attached to the formation’s exterior surface surrounding the borehole -- see figure 5. In this manner, the stabilisation apparatus 10 provides stability to the earth formation.

[0060] In the particular arrangement shown in figure 1, the retention means 14 comprises a dome piate 48 and the fastener 44 comprises a nut 50 having an internal thread. The nut 48 permits securing the retention plate 42 tightly against the exterior surface of the formation after insertion of the stabilisation apparatus 10 into the borehole. In this particular arrangement, the rod 12 comprises an external thread 46 to permit displacing the retention means 14 along the rod 12.

[0061] In a particular arrangement, the dome plate 48 comprises an internal thread permitting the retention piate 42 to be screwed onto and along the rod 12. 9 2016259363 16 Nov 2016 [0062] In an alternative arrangement, the dome plate 48 does not comprises a threaded inner surface; instead, the retention plate 42 is adapted to slide along the rod 12 - in this alternative arrangement, the nut 50 comprises an inner thread for screwing the nut 50 onto and along the rod 12 and displacing the dome plate 48 along the rod 12 together with the nut 50.

[0063] As was mentioned before, the stabilisation apparatus 10 is adapted to deliver cementing material into the formation. For this, stabilisation apparatus 10 comprises a passage for delivering the cementing material.

[0064] In the particular arrangement shown in figures 1 to 3, the rod 12 comprises a passage 52 (see figures 2 and 3) traversing the rod 12 from the proximal end 20 of the rod 12 to the distal end 18. The proximal end 20 and the distal end 18 are open ends allowing supply of the cementing material into the rod 12 through the proximal end 20 and delivery of the cementing material to the cap 16 through the distal end 18 of the rod 12.

[0065] As indicated before, delivery of the cementing material into the cap 16 may increase the dimensions of the cap 16 in the radial direction to secure the stabilisation apparatus 10 within the formation.

[0066] Installation of the stabilisation apparatus 10 includes the steps of drilling a borehole into the formation to define the opening adapted to receive the stabilisation apparatus 10; inserting the stabilization apparatus 10 into the opening; displacing the retention means 14 along the length of the rod 12 until the retention means 14 tightly abuts the formation; and securing the stabilisation apparatus 10 within the formation by delivering cementing material to the cap 16 through the passage 52 of the rod 12.

[0067] In the arrangement where the apparatus 10 comprises the retention plate 42, the retention plate 42 is attached to the surface of the earth formation at a location where the apparatus 10 is to be installed. The borehole may be drilled either prior or after attaching the retention plate 42. The opening of the borehole and the opening of the retention plate 42 concide when the retention plate is attached to the earth formation permitting the rod 12 to be inserted into the opening of the earth formation and that the retention means 14 may abut the retention plate 42 sandwiching the retention plate 42 between the earth formation and the retention means 14. 10 2016259363 16 Nov 2016 [0068] In the first embodiment of the invention, the steps of displacing the retention means 14 along the length of the rod 12 until the retention means 14 tightly abuts the formation is performed by screwing the nut 50 to displace the retention plate until it abuts the exterior surface of the formation. This arrangement is particularly useful because it permits (even after installation of the stabilisation apparatus) securing the retention plate 42 to tightly abut the exterior surface of the earth formation. In this manner, the pressure applied by retention plate 42 against the earth formation may be adjusted during and even after installation of the stabilisation apparatus 10.

[0069] Referring now to figure 4.

[0070] Figure 4 shows a stabilisation apparatus 10 in accordance with a second embodiment of the invention. The stabilisation apparatus 10 according to the second embodiment is similar to the stabilisation apparatus 10 according of the first embodiment and similar reference numerals are used to identify similar parts.

[0071] The stabilisation apparatus 10 shown in figure 4 comprises a rod 12, a retention means 14 and a cap 16, The rod 12 comprises a distal end 18 for receiving the cap 16 and a proximal end 20 for receiving the retention means 14.

[0072] The cap 16 comprises a proximal end 24 and a distal end 26. The proximal end 24 is an open end for receiving the distal end 18 of the rod 12; the distal end 26 comprises openings for delivery of the cementing material into the earth formation for securing the stabilisation apparatus 10 within the formation.

[0073] The rod 12 comprises an external thread 54 extending along the length of the rod 12. As will be described below, the external thread 54 permits (1) fastening of the cap 16 to the rod 12 and (2) screwing the retentions means 14 onto the rod 12.

[0074] The cap 16 is attached to the distal end 18 of the rod 12 through a nut 56. The nut 56 is fastened to the inner surface of the distal end 26 of the cap 16. The rod 12 is attached to the nut 56 by screwing the distal end 18 of the rod 12 to the nut 56.

[0075] Furthermore, the retention means 14 comprises a plug 58 adapted to be screwed onto the proximal end 20 of the rod 12. As was described with reference to the first embodiment of the invention, the retention means 14 is adapted be selectively displaced between the proximal end 20 of the rod 12 and a particular location spaced apart from the proximal end 20, As mentioned before in relation to the method of 2016259363 16 Nov 2016 11 installation of the stabilisation apparatus 10 into the formation, typically, the retention means 14 will be located at a location spaced apart from the proximal end of the rod 12 such that the retention means 14 is adjacent to the external surface of the formation; in particular, the retention means 14 are at a location such that the retention plate 42 tightly abuts the exterior surface of the formation.

[0078] In a particular arrangement, the rod comprises a hollow rod for permitting release of fluid pressure during installation of the stabilisation apparatus 10.

[0077] Moreover, as was mentioned before, the stabilisation apparatus 10 is adapted to deliver cementing material to the cap 16 for securing the stabilisation system 10 into the formation. For this, the stabilisation apparatus 10 comprises a passage 80 for delivering the cementing material.

[0078] In the particular arrangement shown in figure 4, the plug 58 comprises a passage 80. The passage 80 traverses the plug 58 permitting supply of the cementing material into the formation for securing the fastening system 10 into the formation, [0079] Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

[0080] Further, it should be appreciated that the scope of the invention is not limited to the scope of the embodiment disclosed. For example, the retention means 14 of the first embodiment of the invention has been described as comprising a dome plate 48 and a nut 50; in other arrangements, the retention means 14 may comprise a single body having an inner surface adapted to abut the exterior surface of the formation and an internal thread for screwing of the retention means along the rod 12, [0081 ] Throughout this specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims (31)

1. A stabilisation apparatus for providing support to an earth formation, the stabilisation apparatus comprising a rod and retention means releasably attached to the rod, the rod comprising a proximal end for receiving the retention means, and a distal end adapted for securing the rod within the formation, wherein the rod is adapted to secure the retention means at a particular location along the rod for the retention means to abut a surface of the formation.

2. A stabilisation apparatus according to claim 1 wherein the rod comprises an external thread and the retention means comprises an internal thread for screwing the retention means along the rod.

3. A stabilisation apparatus according to claims 1 or 2 wherein the apparatus further comprises fastening means for securing the rod within the formation.

4. A stabiiisation apparatus according to ciaim 3 wherein the fastening means is attached to the distal end of the rod.

5. A stabilisation apparatus according to claims 3 or 4 wherein the fastening means comprises a cap.

6. A stabilisation apparatus according to ciaim 5 wherein the cap comprises a proximal end and a distal end, the proximal end of the cap being an open end for receiving the distal end of the rod, and the distal end of the cap comprises openings for permitting fluid communication between the distal end of the rod and the exterior of the cap.

7. A stabilisation apparatus according to claims 5 or 6 wherein at least a portion of the cap is attached to the distal end of the rod.

8. A stabilisation apparatus according to any one of claims 5 to 7 wherein the cap comprises a conical cap.

9. A stabilisation apparatus according to any one of the preceding claims wherein the apparatus is adapted to provide cementing material into the formation.

10. A stabilisation apparatus according to any one of the preceding claims wherein the apparatus comprises a passage adapted to provide the cementing material from the exterior of the formation into the inferior of the formation.

11. A stabilisation apparatus according to any one of the preceding claims wherein the rod comprises at least one passage for supplying of the cementing material to the distal end of the rod.

12. A stabilisation apparatus according to claim 11 wherein the passage is fluidly connected to an open end of the proximal end of the rod and to an open end of the distal end of the rod for delivering the cementing material from the exterior of the formation into the interior of the formation.

13. A stabilisation apparatus according to any one of claims 5 to 12 wherein the open end of the distal end of the rod is fluidly connected to the cap for delivering the cementing material into an interior of the cap.

14. A stabilisation apparatus according to any one of claims 6 to 13 wherein the interior of the cap is fluidly connected to the openings of the distal end of the cap for permitting fluid communication between the distal end of the rod and an interior of the formation

15. A stabilisation apparatus according to any one of claims 5 to 13 wherein the cap comprises a slot extending from the proximal end of the cap to the distal end of the cap.

16. A stabilisation apparatus according to claim 15 wherein the slot defines a first edge and a second edge.

17. A stabilisation apparatus according to claim 16 wherein a proximal end of the first edge is attached to the distal end of the rod.

18. A stabilisation apparatus according to claims 16 or 17 wherein a proximal end of the second edge is spaced apart from the distal end of the rod.

19. A stabilisation apparatus according to any one of claims 17 to 18 wherein the proximal portion of the first edge of the cap is attached to the rod via a plurality of fillets.

20. A stabilisation apparatus according to claim 19 wherein the fillets are arranged in a spaced apart relationship with respect to each other.

21. A stabilisation apparatus according to any one of claims 19 or 20 wherein the fillets comprise weld spots that join together the proximal portion of the first edge of the cap and the distal end of the rod.

22. A stabilisation apparatus according to any one of claims 5 to 21 wherein the cap is adapted to be selectively displaced between a contracted condition and an expanded condition.

23. A stabilisation apparatus according to any one of claims 5 to 10 wherein the external thread of the rod is adapted for fastening of the cap to the rod and to screw the retentions means onto the rod.

24. A stabilisation apparatus according to claim 23 wherein the cap is attached to the distal end of the rod through a nut.

25. A stabilisation apparatus according to claims 24 wherein the nut is fastened to an inner surface of the distal end of the cap.

26. A stabilisation apparatus according to any one of claims 23 to 25 wherein the retention means comprises a plug adapted to be screwed onto the proximal end of the rod.

27. A stabilisation apparatus according to claim 26 wherein the plug comprises a passage, the passage traversing the plug permitting supply of cementing material into the formation.

28. A stabilisation apparatus according to any of claims 23 to 27 wherein the rod comprises a hollow rod for permitting release of fluid pressure.

29. A stabilisation apparatus according to any one of the preceding claims wherein the apparatus comprises a retention plate adapted to be attached to a surface of the formation.

30. A stabilisation apparatus according to claim 29 wherein the retention plate comprises an inner face adapted to be attached to the outer surface of the earth’s formation and an outer surface for receiving the retention means.

31 .A stabilisation apparatus according to claims 29 or 30 wherein the retention plate comprises an opening for receiving a distal portion of the rod of the apparatus.