WO2007112481A1

WO2007112481A1 - A yielding rock bolt

Info

Publication number: WO2007112481A1
Application number: PCT/AU2007/000396
Authority: WO
Inventors: Neville Hedrick
Original assignee: Garford Pty Ltd
Priority date: 2006-04-06
Filing date: 2007-03-29
Publication date: 2007-10-11
Also published as: JP2009532599A; JP5113150B2; AU2007233555B2; MX2008012937A; KR20090019769A; KR101395753B1; AU2007233555A1

Abstract

A yielding rock bolt (10) is arranged to be inserted into a hole in a rock surface, the rock bolt (10) having a shaft (12) formed of a solid metal bar, the shaft (12) having a first end (16) and a second end (18), the shaft (12) having a relatively wide portion (20) adjacent the first end (16) thereof and a relatively narrow portion (22) adjacent the relatively wide portion (20). An anchor member (14) having a longitudinal bore (15) is mounted about the shaft (12) at the relatively narrow portion (22) and adj acent the relatively wide portion (20). The longitudinal bore (15) has at least a portion of lesser dimension than the relatively wide portion (20). The shaft (12) is enclosed in a jacket (36) extending from the anchor member (14) to the first end (16) of the shaft (12), the jacket (36) having an end portion (41) arranged to rupture a container of resin (44) in a bore hole (11) so as to release the contents thereof.

Description

TITLE

"A YIELDING ROCK BOLT"

FIELD OF THE INVENTION The present invention relates to a yielding rock bolt

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention there is provided a yielding rock bolt arranged to be inserted into a hole in a rock surface, the rock bolt having a shaft formed of a solid metal bar, the shaft having a first end and a second end, the shaft having a relatively wide portion adjacent the first end thereof and a relatively narrow portion adjacent the relatively wide portion, an anchor member having a longitudinal bore mounted about the shaft at the relatively narrow portion and adjacent the relatively wide

portion, the longitudinal bore having at least a portion of lesser dimension than the relatively wide portion, wherein the shaft is enclosed in a jacket extending from the anchor member to the first end of the shaft, the jacket having an end portion arranged to

rupture a container of resin in a bore hole so as to release the contents thereof.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of a yielding rock bolt in accordance with the present invention; and

Figure 2 is a longitudinal section of the rock bolt of Figure 1 located in a bore hole. DETAILED DESCRIPTION OF THE DRAWINGS

Referring to the Figures, there is shown a yielding rock bolt 10 comprising a shaft 12 and an anchor member 14 mounted about the shaft 12. The shaft 12 is in the form of a solid

metal bar. The anchor member 14 has a longitudinal bore 15 as can be seen in Figure 2. The bore 15 receives the shaft 12.

The shaft 12 has a first end 16 and a second end 18. Further, the shaft 12 has a relatively

wide portion 20 adj acent the first end 16 and relative narrow portion 22 adjacent the wide portion 20. The anchor member 14 is located adjacent the wide portion 20 at the narrow portion 22.

Further, the shaft 12 is provided with a debonding sheath 24 adjacent the second end 18

thereof. The debonding sheath 24 may be formed of a suitable material such as plastics material. The rock bolt 10 is also provided with a rock face engaging plate 26 adjacent the second end 18 of the shaft 12. The shaft 12 is formed at the second end 18 with a screw threaded portion.

The plate 26 is fitted over the screw threaded portion of the shaft 12. Then a washer 28 is

placed over the second end 18 and a threaded nut 30 is then threadedly engaged with the end 18 to retain the plate 26 and the washer 28 in place.

Further, it is envisaged that the shaft 12 will be provided with a widened portion of increased dimension adjacent the first end 16 such as a welded circle 32 formed of relatively hard material.

As can be seen in Figure 2, the anchor member 14 is provided at the end thereof facing the end 16 with a circumferential step 34. Further, a jacket member 36 is mounted about the shaft 12 between the anchor member 14 and the first end 16. The jacket member 36

has a wall 38 which is generally circular in cross section. The wall 38 defines an open end 40 of the jacket member 36 remote from the end 16. The open end 40 engages with

the step 34 of the anchor member 14.

An opposed end 41 of the wall 38 of the j acket member 36 adj acent the end 16 is inturned

so as to engage with the shaft 12. Further, the end 41 of the wall 38 is formed with a

plurality of outwardly extending fins 42. As can be seen in Figure 2 between the anchor

member 14 and the end 16 the jacket member 36 is spaced apart from the shaft 12.

As can be seen in Figure 2, the rock bolt 10 is, in use, inserted in a bore hole 11 with the

end 16 foremost. Prior to this a flexible container 44 of curable resin material is inserted

in the bore hole 11 at the innermost end thereof.

In operation, as it is being inserted into the bore hole 11, the rock bolt 10 is axially

rotated in known manner by engagement of a rotary apparatus with the nut 30. This also

causes the jacket 36 to rotate axially. The fins 42 move into engagement with the

container 44. The rotational movement of the jacket 36 and the fins 42 causes the fins 42

to rupture the container 44 and release the contents thereof.

As can be seen in Figure 2, the jacket 36 is preferably a snug fit in the bore hole 11 with

only a small clearance therearound. As the rock bolt 10 continues to be inserted into the

bore hole 11₅ the resin is displaced along sides of the rock bolt 10 towards the outer end

of the bore hole 11

Further, as can best be seen in Figure 1, the outer face of the wall 38 is preferably

roughened in some manner. For example, it can be formed with a helical thread as

shown, although other forms of roughening are contemplated. The roughening of the

outer surface of the wall 38, especially the threaded formation shown, counteracts the

tendency of the resin to flow towards the outer end of the bore hole 11, as the rock bolt

10 is inserted and axially rotated. Thus, the rotating wall 38 tends to push the resin inwardly of the bore hole 11. The result of this is that in the course of travelling along

the bore hole 11 the resin becomes thoroughly mixed. This leads to a more predictable

and secure resin bond between the anchor member 14 of the rock bolt 10 and the bore hole 11. The anchor member 14 is preferably formed in the manner described in pending

Australian Patent Application Number 20032087766. The entire disclosure of this patent application is incorporated herein by reference.

As can be seen in Figure 2, the anchor member 14 has a relatively narrow central bore 15 and a relatively wide bore 15 at each end. The anchor member 14 may be manufactured from heat treated steel such as 41/40 steel which has been heat treated to harden it. Further, the bore 15 of the anchor member 14 may be nitrided to prevent molecular welding between the anchor member 14 and the shaft 12.

The rock bolt 10 of the present invention is preferably manufactured by the technique described in relation to Figures 3 to 6 of Australian Patent Application Number

2003287766.

Initially, the shaft 12 is of substantially uniform thickness. Further, the anchor member

14 mounted about the shaft 12 has a longitudinal bore of substantially uniform cross

section throughout its length.

The shaft 12 and the anchor member 14 are placed in a swage press which includes a pair

of swage press members. The swage press members are profiled so as to have relatively

deep mid-portions.

In operation, the swage press members are pressed together in known manner so as to

apply deforming force to the anchor member 14 and the shaft 12. This causes the anchor member 14 to deform inwardly in a mid-portion thereof in a shape complementary to the swage press members.

The deformation of the anchor member 14 causes a complementary deformation of the shaft 12 to occur. Thus, as can be seen in Figure 2, the shaft 12 has an inwardly

deformed portion corresponding in shape to the deformed portion of the anchor member

14.

If movement of rock causes a portion of the rock face to begin to break away, this portion of the rock face is held in place by the rock bolt 10 being secured at the anchor member 14. However, this movement will cause the wide portion 20 of the shaft 12 to be pulled through the anchor member 14. The rock bolt 10 therefore yields as the rock face moves preventing the possibility of sudden failure of the rock face. In this movement the wide portion 20 of the shaft 12 being of larger dimension than a portion of the longitudinal bore 15 of the anchor member 14 is extruded through the anchor member 14. This provides a predictable and substantially constant force on the anchor member 14.

This force continues until the stop 32 engages with the anchor member 14 at which point the force applied to the anchor member 14 is increased considerably because the stop portion 32 will not extrude through the anchor member 14. At this stage the shaft 12 is

subjected to maximum load which is the ultimate tensile strength of the shaft 12.

Modifications and variations such as would be apparent to a skilled addressee are deemed

to be within the scope of the present invention.

Claims

1. A yielding rock bolt arranged to be inserted into a hole in a rock surface,

characterised in that the rock bolt has a shaft formed of a solid metal bar, the shaft having

a first end and a second end, the shaft having a relatively wide portion adjacent the first

end thereof and a relatively narrow portion adj acent the relatively wide portion, an anchor

member having a longitudinal bore mounted about the shaft at the relatively narrow

portion and adjacent the relatively wide portion, the longitudinal bore having at least a

portion of lesser dimension than the relatively wide portion, wherein the shaft is enclosed

in a jacket extending from the anchor member to the first end of the shaft, the jacket

having an end portion arranged to rupture a container of resin in a bore hole so as to

release the contents thereof.

2. A yielding rock bolt according to claim 1, characterised in that the jacket has a

wall which is spaced from the shaft over most of the length thereof and the jacket has an

open end adjacent the anchor member.

3. A yielding rock bolt according to claim 2, characterised in that the anchor

member is formed with a circumferential step facing the jacket and the adjacent open end

of the jacket engages with the step.

4. A yielding rock bolt according to claims 2 or 3, characterised in that the end

portion of the jacket engages with the shaft adjacent the second end thereof.

5. A yielding rock bolt according to claim 4, characterised in that the end portion of

the jacket is provided with at least one external projection.

6. A yielding rock bolt according to claim 5, characterised in that the end portion of

the jacket is provided with a plurality of outwardly extending external fins.

7. A yielding rock bolt according to any one of claims 2 to 7, characterised in that the wall has an outer surface which is roughened.

8. A yielding rock bolt according to claim 7, characterised in that the wall is roughened by being formed with a helical thread.

9. A yielding rock bolt according to any one of the preceding claims, characterised in that a debonding sheath is mounted adjacent the first end thereof and extends as far as the anchor member.

10. A yielding rock bolt according to any one of the preceding claims, characterised in that the first end of the shaft has mounted thereto a rock face engaging plate.

11. A yielding rock bolt according to any one of the preceding claims, characterised in that the rock bolt is provided with means for axial rotation thereof, in use, to facilitate rupture of the container.