WO2020252527A1

WO2020252527A1 - Rock bolt

Info

Publication number: WO2020252527A1
Application number: PCT/AU2020/050613
Authority: WO
Inventors: Dave MALTBY; Adrian ALINGTON; Neville HENDRICK
Original assignee: Garock Pty Ltd
Priority date: 2019-06-17
Filing date: 2020-06-17
Publication date: 2020-12-24
Also published as: AU2020297661A1

Abstract

The present invention provides a yielding rock bolt (10) comprising a tendon in the form of a steel shaft (12) and an anchor member (14), having a longitudinal bore, mounted on the tendon. The anchor member presents a compression zone (50) to the tendon about the longitudinal bore whereby the tendon, upon being moved through the anchor member towards the compression zone, is caused to undergo plastic deformation at the compression zone to reduce in diameter and increase in length, The compression zone is defined by an inclined face (51) provided on the anchor member about the longitudinal bore.

Description

ROCK BOLT

TECHNICAL FIELD

[0001 ] This invention relates to a yielding rock bolt.

BACKGROUND ART

[0002] 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.

[0003] Rock bolt are commonly used in rock surfaces, such as in tunnels of underground mines and other rock wall formations, to stabilise rock strata, and more particularly prevent or at least inhibit disruption or catastrophic collapse of the rock strata in response to seismic disturbances. The rock bolts are secured into holes drilled into the walls and are designed to yield to a certain extent to prevent or at least inhibit collapse. The movement which occurs as the rock bolt yields may provide an indication of potential disruption or collapse of the wall or tunnel.

[0004] In Australian patent AU 2007233555, granted to the present applicant, the contents of which are incorporated herein by way of reference, there is disclosed a yielding rock bolt arranged to be inserted into a bore hole in a rock surface. The yielding rock bolt has a tendon in the form of a shaft, and an anchor member having a longitudinal bore which is mounted on the shaft. The anchor member is swaged onto the shaft, with deformation of the anchor member causing a complimentary deformation of the shaft, as will be understood by a person skilled in the art. One end of the shaft is adapted to receive a rock face engaging plate and the other end of the shaft is enclosed in a jacket extending from the anchor member. The jacket has an end portion arranged to rupture a container of resin inserted into the bore hole in the rock surface, with the resin being displaced along the sides of the rock bolt towards the outer end of the bore hole. If a disturbance causes a portion of the rock face to break away, that portion of the rock face is held in place by the rock bolt being secured to the anchor member. Depending upon the extent of the disturbance, it may be that the shaft is caused to be progressively pulled through the anchor member, whereby the rock bolt yields as the rock face moves, preventing the possibility of sudden failure of the rock face.

[0005] It is against this background that the present invention has been developed. In particular, the present invention seeks to provide an improvement to the rock bolt disclosed in AU 2007233555 or at least offer a useful choice.

SUMMARY OF INVENTION

[0006] According to a first aspect of the invention there is provided a yielding rock bolt comprising a tendon and an anchor member having a longitudinal bore mounted on the tendon, the anchor member presenting a compression zone to the tendon about the longitudinal bore whereby the tendon upon being moved through the anchor member towards the compression zone is caused to undergo plastic deformation at the compression zone to reduce in diameter and increase in length, the compression zone being defined by an inclined face provided on the anchor member about the longitudinal bore.

[0007] The anchor member featuring the inclined face defining the compression zone in effect provides a die through which the tendon is drawn, causing the portion of the tendon passing through the die to undergo plastic deformation to reduce in diameter and increase in length.

[0008] With this arrangement, interaction between the tendon and the anchor member provides a force which yieldingly resists progressive movement of the tendon through the anchor member.

[0009] The inclined face on the anchor member may be angled in the range from about 30 degrees to 50 degrees to the longitudinal axis of the longitudinal bore of the anchor member. More particularly, the inclined face on the anchor member may be angled in the range from about 35 degrees to 42 degrees to the longitudinal axis of the longitudinal bore. Still more particularly, the inclined face on the anchor member may be angled in the range from about 37 degrees to 40 degrees to the longitudinal axis of the longitudinal bore. Preferably, the inclined face on the anchor member is angled at about 38 degrees to the longitudinal axis of the longitudinal bore. [0010] The tendon may comprise a solid shaft, although other arrangements are contemplated including for example a multi-strand steel cable.

[001 1 ] The solid shaft may comprise a steel shaft. The steel shaft may have material grade 8.8 having a yield strength of 680Mpa. The shaft may be 22mm in diameter.

[0012] The anchor member may be manufactured from a high tensile steel; for example, a nickel-chromium-molybdenum medium hardenability general purpose high tensile steel such as 4340 steel.

[0013] The bore of the anchor member may be treated to prevent molecular welding between the anchor member and the tendon. Such treatment may for example comprise nitriding.

[0014] The anchor member may be swaged onto the tendon, with deformation of the anchor member causing a complimentary deformation of the tendon to yieldingly secure the anchored member in position on the tendon.

[0015] One end of the shaft may be adapted to receive a rock face engaging element, such as for example a load plate.

[0016] The other end of the shaft may be enclosed in a jacket extending from the anchor member. The jacket may have an end portion arranged to rupture a container of resin inserted into the hole in the rock surface, with the resin being displaced along the sides of the rock bolt towards the outer end of the hole.

[0017] The tendon may have debonding sleeve extending from the anchor towards the end of the shaft adapted to receive a rock face engaging element.

[0018] The yielding rock bolt in accordance with the present invention may have any one or more features of the yielding rock bolt described and illustrated in aforementioned AU 2007233555, as may be appropriate.

[0019] According to a second aspect of the invention there is provided an anchor member for a yielding rock bolt in accordance with the first aspect of the present invention.

[0020] According to a third aspect of the present invention there is provided an anchor member comprising a body defining a longitudinal bore and an inclined face about the longitudinal bore, the inclined face defining a compression zone operable to cause plastic deformation of a tendon moving through the longitudinal bore whereby the tendon is caused to reduce in diameter and increase in length.

[0021 ] The inclined face on the anchor member according to the third aspect of the invention may be angled in the range from about 30 degrees to 50 degrees to the longitudinal axis of the longitudinal bore. More particularly, the inclined face on the anchor member may be angled in the range from about 35 degrees to 42 degrees to the longitudinal axis of the longitudinal bore. Still more particularly, the inclined face on the anchor member may be angled in the range from about 37 degrees to 40 degrees to the longitudinal axis of the longitudinal bore. Preferably, the inclined face on the anchor member is angled at about 38 degrees to the longitudinal axis of the longitudinal bore.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 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 schematic perspective view of the embodiment of a yielding rock bolt in accordance with the present invention;

Figure 2 features three such yielding rock bolts positioned in side-by-side relation, showing in particular the inner ends thereof;

Figure 3 is a cross sectional representation of the anchor member after the yielding rock bolt has been exposed to a seismic event (steel shaft is not shown);

Figure 4 is a view of a steel shaft of the rock bolt shown in figure 1 removed from the anchor member after a seismic event; and

Figure 5 is a view similar to figure 3 wherein the anchor member is shown embedded in rock. [0023] In the drawings like structures are referred to by like numerals throughout the several views. The drawings shown are not necessarily to scale, with emphasis instead generally being placed upon illustrating the principles of the present invention

[0024] The figures depict several embodiments of the invention. The embodiments illustrate certain configurations; however, it is to be appreciated that the invention can take the form of many configurations, as would be obvious to a person skilled in the art, whilst still embodying the present invention. These configurations are to be considered within the scope of this invention

DESCRIPTION OF EMBODIMENTS

[0025] In the following detailed description, the present invention is described in connection with a preferred embodiment. However, to the extent that the following description is specific to a particular embodiment or a particular use of the present techniques, it is intended to be illustrative only and merely provides a concise description of the exemplary embodiment. Accordingly, the present invention is not limited to the specific embodiments described below, but rather the invention includes all alternatives, modifications, and equivalents falling within the true scope of the appended claims.

[0026] Referring to the drawings, there is shown yielding rock bolt 10 comprising a tendon which, in this embodiment, is in the form of a steel shaft 12 and an anchor member 14 in the form of an annular body having a longitudinal bore 15 which receives the steel shaft 12. Interaction between the steel shaft 12 and the anchor member 14 provides a force which yieldingly resists progressive movement of the steel shaft 12 through the anchor member, as will be explained in more detail later.

[0027] The steel shaft 12 may have a material grade 8.8 having a yield strength of 680Mpa, and is 22mm in diameter. Other suitable materials for manufacture of the steel shaft 12 are of course also contemplated.

[0028] In this embodiment, the anchor member 14 is manufactured from 4340 steel, which is a nickel-chromium-molybdenum medium hardenability general purpose high tensile steel. Other suitable materials for manufacture of the anchor member 14 are of course also contemplated. [0029] The anchor member 14 is swaged onto the steel shaft 12, with deformation of the anchor member causing a complimentary deformation of the steel shaft to yieldingly secure the anchored member in position on the steel shaft.

[0030] The longitudinal bore 15 of the anchor member 14 may be treated to prevent molecular welding between the anchor member and the steel shaft 12. Such treatment may for example comprise nitriding.

[0031 ] The shaft 12 has opposed end sections 16, 18.

[0032] End 16 of the shaft 12 is enclosed in a jacket 36 extending from the anchor member 14. The jacket 36 has an end portion 41 arranged to rupture a container of resin (not shown) inserted into a bore hole in the rock surface, during installation of the rock bolt 10.

[0033] End 18 of the shaft 12 shaft is adapted to receive a rock face engaging element 26, such as for example a load plate.

[0034] The shaft 12 has a debonding sleeve 24 extending from the anchor member towards the end 18. The debonding sleeve 24 prevents the shaft from bonding to other materials such as resin.

[0035] The features described above in relation to shown yielding rock bolt 10 of the present embodiment are similar to corresponding features of the yielding rock bolt described and illustrated in aforementioned AU 2007233555, the contents of which are incorporated herein by way of reference. Accordingly, such features will not be discussed in further detail. Further, it should be noted that the yielding rock bolt 10 of the present embodiment may have any one or more other features of the yielding rock bolt described and illustrated in aforementioned AU 2007233555, as may be appropriate.

[0036] As mentioned above, the anchor member 14 is swaged onto the steel shaft 12, with deformation of the anchor member causing a complimentary deformation of the steel shaft to yieldingly secure the anchored member in position on the steel shaft. Following such deformation, the anchor member 14 is configured to present a compression zone 50 to the steel shaft 12 about the longitudinal bore 15. The compression zone 50 has a cross-sectional area smaller than the cross-sectional area of the steel shaft 12, whereby the steel shaft upon being moved through the anchor member towards the compression zone 50 in response to a seismic event is caused to undergo plastic deformation at the compression zone, reducing in diameter and increasing in length. With this arrangement, interaction between the steel shaft 12 and the anchor member 14 provides a force which yieldingly resists progressive movement of the steel shaft through the anchor member, so providing the yielding function of the rock bolt 10.

[0037] , The compression zone 50 is defined by an inclined annular face 51 provided on the anchor member 14 about the longitudinal bore 15. The features of the compression zone 50 and the inclined annular face 51 of the anchor member 14 are apparent in Figure 3, even though that figure depicts the anchor member after the rock bolt 10 has been exposed to a seismic event; that is, after interaction between the steel shaft 12 and the anchor member 14 to provide the yielding function of the rock bolt 10.

[0038] In practical terms, the anchor member 14 featuring the inclined face 51 defining the compression zone 50 functions as a die through which the steel shaft 12 is drawn, causing the portion of the steel shaft passing through the die to undergo plastic deformation to reduce in diameter and increase in length, as represented in figure 4, As note din figure 4, the section of the steel shaft 12 which has passed through the anchor member 14 as a result of the seismic event has a smaller diameter.

[0039] The inclined face 51 on the anchor member 14 may be angled in the range from about 30 degrees to 50 degrees to the longitudinal axis of the longitudinal bore 15 of the anchor member 14. More particularly, the inclined face 51 may be angled in the range from about 35 degrees to 42 degrees to the longitudinal axis of the longitudinal bore 15. Still more particularly, the inclined face 51 may be angled in the range from about 37 degrees to 40 degrees to the longitudinal axis of the longitudinal bore 15. Preferably, the inclined face 51 is angled at about 38 degrees to the longitudinal axis of the longitudinal bore 15.

[0040] Figure 5 is a view similar to figure 3, and provides a cross sectional view of the anchor member 14 and a portion of the jacket 36 embedded in rock, and after the rock bolt 10 has experienced a seismic event. The steel shaft 12 is not shown but would be represented by the steel shaft shown in figure 4 in which the steel shaft has undergone significant yielding as a result of passing through the anchor element 14. The anchor member 14 and jacket 36 remain in the rock 45 surrounded by the grout/resin 47. [0041 ] The arrangement in which the anchor member 14 is configured to present compression zone 50 to the steel shaft 12 about the longitudinal bore 15, may provide certain advantages over, and an improvement to, the yielding rock bolt described and illustrated in aforementioned AU 2007233555. The advantages and improvement may be attributed (directly or indirectly) to the inclined face 51 defining compression zone 50 functioning as a die through which the steel shaft 12 is drawn, causing the portion of the steel shaft passing through the die to undergo plastic deformation to reduce in diameter and increase in length, so delivering a sustained, predictable and reliable yielding action. This may allow certain components of the yielding rock bolt 10 of the present embodiment to be made smaller and/or from more cost-effective materials than the yielding rock bolt described and illustrated in aforementioned AU 2007233555. For instance, yielding rock bolt 10 of the present embodiment may use a softer steel for the shaft 12 than is the case with the yielding rock bolt of AU 2007233555 (which uses 4140 steel). The use of softer material for the shaft 12 may allow the yielding rock bolt 10 of the present embodiment to be more responsive to seismic activity, commencing incremental movement earlier than would be the case for the rock bolt described and illustrated in aforementioned AU 2007233555, as well as responding to more seismic events. Further, the yielding movement of yielding rock bolt 10 of the present embodiment may be somewhat smoother and more cushioned than the yielding movement of rock bolt described and illustrated in aforementioned AU 2007233555 which typically is somewhat“bouncy”. Still further, it may be possible to install the yielding rock bolt 10 of the present embodiment in a bore hole of smaller diameter than would be the case for a rock bolt described and illustrated in aforementioned AU 2007233555. For instance, it is believed that it may be possible to install the yielding rock bolt 10 of the present embodiment in a bore hole of about 38mm diameter, compared to a bore hole of about 45mm diameter typically required for a rock bolt described and illustrated in aforementioned AU 2007233555. This in itself may provide certain benefits, including a reduction in the time and cost of bore hole drilling, as well as a reduction in the quantity of resin required to install the yielding rock bolt.

[0042] The foregoing disclosure is intended to explain how to fashion and use the particular embodiment described, rather than to limit the true, intended, and fair scope and spirit of the present disclosure. The foregoing description is not intended to be exhaustive, nor to be limited to the precise forms disclosed. [0043] It should be appreciated that various modifications can be made without departing from the principles described herein. Therefore, the principles should be understood to include all such modifications within its scope.

[0044] The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

[0045] The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting.

[0046] As used herein, the singular forms“a”,“an” and“the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0047] Reference to any positional descriptions, such as "top”,“bottom" and“side”, are to be taken in context of the embodiments described and are not to be taken as limiting the invention to the literal interpretation of the term but rather as would be understood by the skilled addressee.

[0048] Spatially relative terms, such as “inner,” “outer,” “beneath”, “below”, “lower”, “above”,“upper” and the like, may be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as“below” or “beneath” other elements or features would then be oriented“above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0049] Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as“first,”“second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

[0050] When an element or layer is referred to as being“on”,“engaged to”,“connected to” or“coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being“directly on,” “directly engaged to”,“directly connected to” or“directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus“directly between,” “adjacent” versus“directly adjacent,” etc ). As used herein, the term“and/or” includes any and all combinations of one or more of the associated listed items.

[0051 ] Additionally, where the terms“system”,“device”, and“apparatus" are used in the context of the invention, they are to be understood as including reference to any group of functionally related or interacting, interrelated, interdependent or associated components or elements that may be located in proximity to, separate from, integrated with, or discrete from, each other.

[0052] 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.

[0053] Furthermore, throughout the specification and the claims that follow, unless the context requires otherwise, the word “include” or variations such as “includes” or “including”, 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

1 . A yielding rock bolt comprising a tendon and an anchor member having a longitudinal bore mounted on the tendon, the anchor member presenting a compression zone to the tendon about the longitudinal bore whereby the tendon upon being moved through the anchor member towards the compression zone is caused to undergo plastic deformation at the compression zone to reduce in diameter and increase in length, the compression zone being defined by an inclined face provided on the anchor member about the longitudinal bore.

2. The rock bolt according to claim 1 wherein the inclined face on the anchor member is angled in the range from about 30 degrees to 50 degrees to the longitudinal axis of the longitudinal bore of the anchor member.

3. The rock bolt according to claim 1 wherein the inclined face on the anchor member is angled in the range from about 35 degrees to 42 degrees to the longitudinal axis of the longitudinal bore.

4. The rock bolt according to claim 1 wherein the inclined face on the anchor member is angled in the range from about 37 degrees to 40 degrees to the longitudinal axis of the longitudinal bore.

5. The rock bolt according to any one of the preceding claims wherein the inclined face on the anchor member is angled at about 38 degrees to the longitudinal axis of the longitudinal bore.

6. The rock bolt according to any one of the preceding claims wherein the tendon comprises a solid shaft or a multi-strand steel cable.

7. The rock bolt according to claim 6 wherein the solid shaft comprises a steel shaft.

8. The rock bolt according to claim 7 wherein the steel shaft is grade 8.8 having a yield strength of 680Mpa.

9. The rock bolt according to claim 7 or 8 wherein the steel shaft is 22mm in diameter.

10. The rock bolt according to any one of the preceding claims wherein the anchor member is manufactured from a nickel-chromium-molybdenum medium hardenability general purpose high tensile steel.

1 1 . The rock bolt according to any one of the preceding claims wherein the bore of the anchor member is treated to prevent molecular welding between the anchor member and the tendon.

12. The rock bolt according to any one of the preceding claims wherein the anchor member is swaged onto the tendon, with deformation of the anchor member causing a complimentary deformation of the tendon to yieldingly secure the anchored member in position on the tendon.

13. The rock bolt according to any one of the preceding claims wherein one end of the shaft is adapted to receive a rock face engaging element.

14. The rock bolt according to claim 13 wherein the other end of the shaft is enclosed in a jacket extending from the anchor member.

15. The rock bolt according to claim 14 wherein the jacket has an end portion arranged to rupture a container of resin inserted into the hole in the rock surface, with the resin being displaced along the sides of the rock bolt towards the outer end of the hole.

16. The rock bolt according to any one of the preceding claims when dependent on claim 13 wherein the tendon has debonding sleeve extending from the anchor towards the end of the shaft adapted to receive the rock face engaging element.

17. An anchor member for a yielding rock bolt in accordance with any one of the preceding claims.

18. An anchor member comprising a body defining a longitudinal bore and an inclined face about the longitudinal bore, the inclined face defining a compression zone operable to cause plastic deformation of a tendon moving through the longitudinal bore whereby the tendon is caused to reduce in diameter and increase in length.

19. The anchor member according to claim 18 wherein the inclined face is angled in the range from about 30 degrees to 50 degrees to the longitudinal axis of the longitudinal bore.

20. The anchor member according to claim 18 wherein the inclined face is angled in the range from about 35 degrees to 42 degrees to the longitudinal axis of the longitudinal bore.

21 . The anchor member according to claim 18 wherein the inclined face is angled in the range from about 37 degrees to 40 degrees to the longitudinal axis of the longitudinal bore.

22. The anchor member according to any one of claims 18 to 21 wherein the inclined face is angled at about 38 degrees to the longitudinal axis of the longitudinal bore.