ZA201006189B

ZA201006189B - A bearing plate assembly for a rock anchor

Info

Publication number: ZA201006189B
Application number: ZA2010/06189A
Authority: ZA
Inventors: Ian Levitan
Original assignee: Ian Levitan
Priority date: 2010-08-30
Filing date: 2010-08-30
Publication date: 2011-05-25
Also published as: WO2012029012A2; WO2012029012A3; WO2012029012A4; AP2013006783A0

Description

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THIS INVENTION relates to a bearing plate assembly for a rock anchor.

Rock, as referred to herein, is any hard geological formation into which bores may be drilled and rock anchors may be installed.

A rock anchor, as referred to herein, is any rock anchor such as a cable rock anchor or a rock bolt, used for example for stabilizing rock formations or anchoring structural members to rock formations.

A tensile member, as referred to herein, is an elongate member for transferring a tensile force, typically a length of cable or a treaded shaft.

According to a first aspect of the invention there is provided a bearing plate assembly for a rock anchor, the assembly including: a bearing plate pressed to define a central protuberance to a front of the plate; at least one hole defined through the protuberance for receiving therethrough, through a centre of the bearing plate, a tensile member of the rock anchor, and, at positions offset from the centre, a grout tube and a breather tube; and at least one stiffener in the protuberance, secured to the bearing plate, the bearing plate assembly being configured to define, in an operative configuration thereof abutting a face of a rock formation with the centre of the bearing plate in register with a bore in the rock formation, respective paths in the protuberance for the grout tube and the breather tube to pass through the at least one hole and into the bore with respective passages in the tubes open for passage of grout and air, respectively.

Both the bearing plate and the at least one stiffener may be made of steel. The at least one stiffener may be secured to the bearing plate by welding.

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The at least one hole may be a single hole, the plate defining a seat for a fastener about a central part of the hole and the hole including two extension parts, extending radially away from the central part, for the grout tube and the breather tube, respectively.

Alternatively, the at least one hole may include three holes respectively for the tensile member, the grout tube, and the breather tube.

The at least one stiffener may include a pair of stiffeners on opposite sides of the at least one hole. The stiffeners may mirror each other. Each stiffener may be a stiffener rib.

In the case of each stiffener being a stiffener rib, it may include a central portion alongside the centre of the bearing plate and two opposite end portions extending radially away from the centre of the bearing plate. The central protuberance may include ridges extending radially away from the centre of the bearing plate within which the respective end portions of the stiffener ribs are received.

The bearing plate may have a thickness of between 1.6mm and 12mm.

According to a second aspect of the invention there is provided a method of installing a rock anchor, the method including, in the following sequence: providing a rock anchor including: a tensile member; an expanding anchor for anchoring one end of the tensile member in a bore in a rock formation; a bearing plate assembly including: a steel bearing plate pressed to define a central protuberance to a front of the plate; at least one hole defined through the protuberance for receiving therethrough, through a centre of the bearing plate, a tensile member of the rock anchor, and, at positions offset from the centre, a grout tube and a breather tube; and a “2010706189 @® at least one steel stiffener in the protuberance, welded to the bearing plate; inserting the rock anchor into the bore up to a required depth; abutting the bearing plate against a face of the rock formation; tensioning the tensile member and fastening it by means of the fastener; and via a grout tube extending through the bearing plate and into the bore, injecting grout into the bore whilst, via a breather tube extending through the bearing plate and into the bore, allowing air to escape from the bore.

In the method of the second aspect of the invention, the bearing plate assembly may be a bearing plate assembly in accordance with the first aspect of the invention.

The above and further features of the invention will become apparent from the description below of an example embodiment of a bearing plate assembly, in accordance with the first aspect of the invention, and a method of installing a rock anchor, in accordance with the second aspect of the invention, with reference to and as illustrated in the accompanying diagrammatic figures. In the figures:

Figure 1 shows a long section of a bore in a rock formation and a rock anchor installed in the bore, the rock anchor including a prior art bearing plate assembly;

Figure 2 shows a long section of a bore in a rock formation and a rock anchor installed in the bore, the rock anchor including a first embodiment of a bearing plate assembly, in accordance with the first aspect of the invention;

Figure 3 shows a front view of the bearing plate assembly of Figure 2;

Figure 4 shows a rear view of the bearing plate assembly of Figure 2;

Figure 5 shows a side view of the bearing plate assembly of Figure 2 in the direction of arrows V-V of Figure 3; and

Figure 6 shows a rear view of a second embodiment of a bearing plate assembly, in accordance with the first aspect of the invention.

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C In Figure 1, a rock formation 10 has a bore 12 defined therein. A conventional or prior art rock anchor 14 is installed in the bore 12. T he rock anchor 14 includes: a tensile member in the form of a cable 16; an expanding anchor 18 anchoring one end of the cable 16 in the bore 12; a conventional bearing plate assembly 19 bearing against a face 20 of the rock formation 10; and a fastener including a barrel 22 and wedges 24 bearing against the bearing plate assembly 19.

The cable 16 has been conventionally tensioned and then fastened by means of the barrel 22 and wedges 24.

The bearing plate assembly 19 includes a bearing plate 26, defining a central protuberance 28 towards an outside thereof, and a stiffener tube 30 welded centrally to the bearing plate 26 with the stiffener tube 30 received within the protuberance 28.

The cable 16 extends through a hole 32 defined centrally through the bearing plate 26 and a grout tube 34 and a breather tube 36 extend through respective holes 38 and 40 defined through the bearing plate 26. The tubes 34 and 36 are collapsed under pressure exerted by the stiffener tube 30 so that injection of grout into the bore 12 can no longer occur. Clearly then, with the bearing plate assembly 19, injection of grout into the bore 12 can occur only before tensioning of the cable 16.

In Figure 2, a rock formation 42 has a bore 44 defined therein. A rock anchor 46 is installed in the bore 44. The rock anchor 46 includes many parts that are identical to parts of a rock anchor 14 of Figure 1. Identical parts are again designated by the same reference numerals as before and these parts are not described again.

The rock anchor 14 includes a bearing plate assembly 48, in accordance with the first aspect of the invention.

With reference to Figures 3 to 5 generally, the bearing plate assembly 48 includes a square steel bearing plate 50 of 6mm thickness, which has been pressed to

6 2010706189 o define a central protuberance 52 and, conventionally, a raised corner 54 defining therethrough a hole 56 for suspending an object from.

The protuberance 52 includes a domed central portion 58 and four ridges 60 extending radially away from a centre 62 of the bearing plate 50 towards respective corners of the bearing plate 50.

The bearing plate 50 defines through the centre 62 a hole for the cable 16 of

Figure 2. It defines also therethrough two holes 68 and 70 respectively for the grout tube 34 and the breather tube 36 of Figure 2. The holes 68 and 70 are offset from the hole 64 on opposite sides thereof.

With reference particularly to Figure 4, the bearing plate assembly 48 includes also two stiffener ribs 72 mirroring each other about the holes 64, 68, and 70.

Each stiffener rib 72 includes a central portion 74 extending along the centre 62 of the bearing plate 50 and two opposite end portions 76 extending radially away from the centre 62, the respective end portions 72 being received within the respective ridges 60 of the protuberance 52. The stiffener ribs 72 are made of steel plate and are welded to the bearing plate 50.

With reference now particularly to Figure 3, the bearing plate 50 defines around the hole 64 a peripheral seat 78 for the barrel 22 of Figure 2.

With reference now particularly to Figure 2, the cable 16 has been conventionally tensioned and then fastened by means of the barrel 22 and wedges 24.

Due to the configuration of the bearing plate assembly 48, in the operative configuration abutting a face 80 of the rock formation 42, as shown, it defines respective paths 82 and 84 in the protuberance 52 for the grout tube 34 and the breather tube 36 to pass through the respective holes 68 and 70 and into the bore 44 with respective passages in the tubes open for passage of grout and air, respectively. Due to this configuration of the bearing plate assembly 48, it permits injection of grout into the bore 44 after tensioning of the cable 16. The applicant considers this to be a significant advantage over the prior art bearing plate

7 2010706189 ® assembly 19 shown in Figure 1 in that the rock formation 42 is compressed, and, therefore more stable and safer, sooner than would have been the case if grouting had to be performed first. More particularly, the grouting operation is preformed under the said more stable rock formation 42.

The applicant has found that the provision of the stiffener ribs 72 in the configuration shown permits the use of the bearing plate 50 having a thickness of 6mm in applications where omission of the ribs would have required a bearing plate having a thickness of about 12 mm. This amounts to a substantial saving.

Also, the provision of the stiffener ribs 72 does not compromise the option of grouting after tensioning, as is the case with the stiffener tube 30 of the bearing plate assembly 19 of Figure 1.

A method, in accordance with the second aspect of the invention, of installing a rock anchor is exemplified by the installation of the rock anchor 46 of Figure 2, as referred to above. The method includes, in sequence: inserting the rock anchor 46 into the bore 44 up to the depth shown; abutting the bearing plate 50 against a face 80 of the rock formation 42; tensioning the cable 16 and fastening it by means of the fastener comprising the barrel 22 and the wedges 24; and via the grout tube 34 extending through the bearing plate 50 and into the bore 44, injecting grout into the bore whilst, via the breather tube 36 extending through the bearing plate and into the bore, allowing air to escape from the bore.

The bearing plate assembly 48 is also usable with a rock anchor or rock bolt including a tensile member in the form of a threaded shaft.

Figure 6 shows a second embodiment of a bearing plate assembly, in accordance with the first aspect of the invention, designated generally by the reference numeral 86. The bearing plate assembly 86 includes many features that are identical or similar to features of the bearing plate assembly 48 of Figures 2 to 5.

Some such features are again designated by the same reference numerals as before and a description of these features is not repeated here.

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® Instead of the three holes 64, 68, and 70 of the bearing plate assembly 48, the bearing plate assembly 86 includes a single central hole 88. The hole 88 includes a central part 90 for a tensile member of a rock anchor and two laterally extending parts 92 and 94 respectively for a grout pipe and a breather pipe of a rock anchor.

The bearing plate 50 defines about the central part 90 of the hole 88 a seat formation 96 for a fastener of the rock anchor.

The bearing plate assembly 86 and its use in a rock anchor is exactly the same as that of the bearing plate assembly 48, as described above.

Claims

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1. A bearing plate assembly for a rock anchor, the assembly including: a bearing plate pressed to define a central protuberance to a front of the plate; at least one hole defined through the protuberance for receiving therethrough, through a centre of the bearing plate, a tensile member of the rock anchor, and, at positions offset from the centre, a grout tube and a breather tube; and at least one stiffener in the protuberance, secured to the bearing plate, the bearing plate assembly being configured to define, in an operative configuration thereof abutting a face of a rock formation with the centre of the bearing plate in register with a bore in the rock formation, respective paths in the protuberance for the grout tube and the breather tube to pass through the at least one hole and into the bore with respective passages in the tubes open for passage of grout and air, respectively.

2. A bearing plate assembly as claimed in claim 1, in which both the bearing plate and the at least one stiffener are made of steel.

3. A bearing plate assembly as claimed in claim 2, in which the at least one stiffener is secured to the bearing plate by welding.

4. A bearing plate assembly as claimed in any of the preceding claims, in which the at least one hole is a single hole, the plate defining a seat for a fastener about a central part of the hole and the hole including two extension parts, extending radially away from the central part, for the grout tube and the breather tube, respectively.

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5. A bearing plate assembly as claimed in any of claims 1 to 3, in which the at least one hole includes three holes respectively for the tensile member, the grout tube, and the breather tube.

6. A bearing plate assembly as claimed in any of the preceding claims, in which the at least one stiffener includes a pair of stiffeners on opposite sides of the at least one hole.

7. A bearing plate assembly as claimed in claim 6, in which the stiffeners mirror each other.

8. A bearing plate assembly as claimed in any of claims 6 to 7, in which each stiffener is a stiffener rib.

9. A bearing plate assembly as claimed in claim 8, in which each stiffener rib includes a central portion alongside the centre of the bearing plate and two opposite end portions extending radially away from the centre of the bearing plate.

10. A bearing plate assembly as claimed in claim 9, in which the central protuberance includes ridges extending radially away from the centre of the bearing plate within which the respective end portions of the stiffener ribs are received.

11. A bearing plate assembly as claimed in any of the preceding claims, in which the bearing plate has a thickness of between 1.6mm and 12mm.

12. A method of installing a rock anchor, the method including, in the following sequence: providing a rock anchor including: a tensile member; an expanding anchor for anchoring one end of the tensile member in a bore in a rock formation; a bearing plate assembly including:

® a steel bearing plate pressed to define a central protuberance to a front of the plate; at least one hole defined through the protuberance for receiving therethrough, through a centre of the bearing plate, a tensile member of the rock anchor, and, at positions offset from the centre, a grout tube and a breather tube; and at least one steel stiffener in the protuberance, welded to the bearing plate; inserting the rock anchor into the bore up to a required depth; abutting the bearing plate against a face of the rock formation; tensioning the tensile member and fastening it by means of the fastener; and via a grout tube extending through the bearing plate and into the bore, injecting grout into the bore whilst, via a breather tube extending through the bearing plate and into the bore, allowing air to escape from the bore.

13. A method as claimed in claim 12, in which the bearing plate assembly is a bearing plate assembly as claimed in any of claims 1 to 11.

14. A bearing plate assembly as claimed in claim 1, substantially as herein described with reference to and/or as illustrated in any of the accompanying diagrammatic Figures 2 to 6.

15. A method as claimed in claim 12, substantially as herein described with reference to and/or as illustrated in any of the accompanying diagrammatic Figures 2 to 6. DATED THIS 30" DAY OF AUGUST 2010 ’ Q s& ADAMS APPLICANT'S PATENT ATTORNEYS