ROCK BOLT

Abstract

A rock bolt includes a central rod, a tubular outer body provided around the central rod, and an expansion mechanism arranged for radially expanding the leading portion of the outer body. The rock bolt is arranged such that the outer body at installation is pulled into a bore of a formation from the leading portion of the outer body using a driving force applied via the central rod.

Claims

1. A rock bolt comprising: a central rod with a threaded leading portion and a trailing portion; a tubular outer body provided around the central rod along at least a portion of a length of the central rod, said tubular outer body having a leading portion and a trailing portion; a first wedge means attached to the leading portion of the central rod; and a second wedge means attached to the leading portion of the outer body between the first wedge means and the trailing portion of the outer body, wherein the first wedge means and the second wedge means are configured such that the first wedge means is arranged to force the second wedge means radially outwards about a longitudinal axis of the rock bolt upon movement of the first wedge means in a direction towards the trailing portion of the central rod to thereby radially expand the outer body, wherein the leading portion of the outer body is provided with one or more ledge means, and wherein the central rod is provided with a drive means configured to drive the ledge means upon movement of the drive means in a driving direction of the rock bolt to thereby force the outer body in the driving direction via the ledge means.

2. The rock bolt according to claim 1, wherein the ledge means includes one or more protrusions protruding radially inwards within the tubular outer body with respect to the longitudinal axis of the rock bolt.

3. The rock bolt according to claim 2, wherein each protrusion includes an impact surface extending inside the outer body such that the drive means is able to force the impact surface in the driving direction, wherein the impact surface is supported from a leading end-side of the outer body by a support body extending from the impact surface to the outer body.

4. The rock bolt according to claim 3, wherein the impact surface and the support body are formed by a portion of the outer body plastically deformed radially inwards.

5. The rock bolt according to claim 1, wherein the drive means is in a form of drive surfaces on the first wedge means.

6. The rock bolt according to claim 1, wherein the drive means is a drive member provided on the central rod between the second wedge means and the trailing portion of the outer body, and wherein the ledge means is one or more trailing surfaces of the second wedge means.

7. The rock bolt according to claim 6, wherein the drive member is configured to engage the outer body to restrict a relative rotational movement between the drive member and the outer body.

8. The rock bolt according to claim 7, wherein the outer body includes a protrusion extending radially inwards and along the longitudinal axis and being configured to engage with the drive member to restrict the relative rotational movement.

9. The rock bolt according to claim 7, wherein the drive member includes a protrusion extending radially outwards and configured to engage with the outer body to restrict the relative rotational movement.

10. The rock bolt according to claim 6, wherein the drive member includes a nut threaded to the central rod.

11. The rock bolt according to claim 1, further comprising a rock plate and a nut threaded to the trailing portion of the central rod, wherein a washer is provided between the rock plate and the nut for distributing force from the nut to the rock plate, wherein a length of the outer body is such that as the outer body is pulled into a formation at installation of the rock bolt, there is a gap formed between a trailing end of the outer body and the rock plate.

12. The rock bolt according to claim 11, wherein the gap is within a range of 50-100 mm.

13. The rock bolt according to claim 11, further comprising a sleeve fitted around the central rod at the trailing portion of the outer body, wherein a first portion of the sleeve extends within the outer body, and wherein a second portion of the sleeve extends through a central hole of the rock plate and further to the washer a predetermined distance past the trailing end of the outer body.

14. The rock bolt according to claim 13, wherein the sleeve is movable relative to the outer body along the longitudinal axis of the rock bolt, back and forth within an operative range between an inner position and outer position, wherein the outer body and the sleeve are provided with retaining means configured to retain the sleeve within the operative range thereby preventing the sleeve from falling out of the outer body.

15. The rock bolt according to claim 14, wherein the retaining means includes a protrusion of the outer body extending radially inwards into a corresponding elongate recess (29) of the sleeve, wherein the protrusion is movable within confines of the recess as the sleeve moves within the operative range, and wherein the protrusion prevents movement of the sleeve outside of the operative range.

16. The rock bolt according to claim 14, wherein the sleeve is press-fitted to the central rod tight enough for friction between the sleeve and the central rod to prevent the central rod from falling out of the sleeve should the central rod break between the sleeve and the leading portion of the central rod.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0053] FIG. 1a shows a first embodiment of a rock bolt wherein the outer body is driven into a formation via a driving member acting on the trailing portion of second wedges attached to the outer tube.

[0054] FIGS. 1b and c show cross sections of the driving member according to FIG. 1a.

[0055] FIG. 2 shows a second embodiment of a rock bolt, wherein the outer body is driven into a formation forced by a first wedge means attached to the central rod acting on ledge means in the form of protrusions of the outer body extending radially inwards.

[0056] FIGS. 3 and 4 show a front portion of an outer tube provided with ledge means in the form of protrusions extending radially inwards.

[0057] Specifically, FIG. 4 shows a window/through hole in this embodiment adjacent the ledge means, said through hole allowing a first wedge means to extend radially outwards into the space in the through holes, thereby enabling a larger first wedge means.

[0058] FIGS. 5-7 show various embodiments of the ledge means.

[0059] FIG. 5 shows a ledge means provided by through holes in the wall of the outer body availing a leading surface of each respective through holes which the drive means can apply driving force to.

[0060] FIG. 6 shows a ledge means formed by a separate member seated in a through hole of the outer body and optionally welded to the outer body around the circumference of the through hole.

[0061] FIG. 7 shows a ledge means formed by plastic deformation radially inwards of a portion of the wall of the outer body, similar to the ledge means shown in FIGS. 3 and 4 but not open towards the trailing end of the rock bolt.

[0062] FIGS. 8-10 show a trailing portion of a third embodiment of a rock bolt at different stages of installation of the rock bolt in a formation. Specifically, FIG. 8 shows the rock bolt being driven into the formation by a driver socket and a sleeve in an outer position. FIG. 9 shows the rock bolt fully driven into the formation and undergoing pre-tensioning of the rock bolt by rotation of the nut pulling the central rod outwards through the nut. In an alternative embodiment, a blind nut could be used instead, wherein the rotation would instead rely on tensioning the rock bolt by screwing a threaded leading portion of the central rod forwards relatively a first wedge attached by threads to the leading portion of the rock bolt. In FIG. 9, it should be noted that the sleeve has moved forward relatively the outer body/split-tube and that the rock plate is forced against the formation. FIG. 10 shows the rock bolt after failure of the central rod between the sleeve and the leading portion of the central rod. Specifically, it should be noted in FIG. 10 that the sleeve has moved out of the formation together with a trailing portion of the central rod and that a retaining means prevent further movement outwards of the central rod, which is held by friction to the sleeve. A gap is visible between the rock plate and the formation, thereby indicating that the rock bolt is broken.

TABLE-US-00001 1 rock bolt 2 central rod 3 leading portion of central rod 4 trailing portion of central rod 5 outer body 6 leading portion of outer body 7 trailing portion of outer body 8 first wedge means 9 second wedge means 10 longitudinal axis of rock bolt 11 ledge means 12 drive means 13 driving direction of rock bolt 14 radial through holes of outer body 15 drive surfaces on first wedge means 16 drive member 17 trailing surfaces of second wedge means 18 leading end of outer body 19 rock plate 20 nut 21 washer 22 formation 23 trailing end of outer body 24 gap 25 sleeve 26 operative range 27 retaining means 28 protrusion or retaining means 29 elongate recess of retaining means 30 impact surface 31 support body 32 separate member forming impact surface and support body 41 protrusion of outer body 42 protrusion of drive member 43 recess in drive member 44 recess in outer body D predetermined distance

DETAILED DESCRIPTION

[0063] A rock bolt 1 according to an exemplary embodiment will hereinafter be described with reference to the appended drawings.

[0064] As shown in FIG. 2, the rock bolt 1 comprises a central rod 2 with a threaded leading portion 3 and a trailing portion 4. The rock bolt also comprises a tubular outer body 5 provided around the central rod 2 along at least a portion of the length of the central rod 2, said tubular outer body 5 having a leading portion 6 and a trailing portion 7. A first wedge means 8 is threaded onto the leading portion 3 of the central rod 2. The position of the first wedge relatively the central rod 2 can thus be controlled by rotation of the central rod 2, typically by rotating the trailing portion of the central rod 2 via a blind nut attached to the trailing portion of the central rod 2. The rock bolt also comprises a second wedge means 9 attached to the leading portion 6 of the outer body 5 between the first wedge means 8 and the trailing portion of the outer body 7. The first wedge means 8 and the second wedge means 9 are configured such that the first wedge means 8 is able to force the second wedge means 9 radially outwards about the longitudinal axis 10 of the rock bolt 1 upon movement of the first wedge means 8 in a direction towards the trailing portion 4 of the central rod 2 to thereby radially expand the outer body 5, wherein the leading portion of the outer body 5 is forced against the hole in the formation such that the outer body 5 is secured to the formation. The leading portion of the outer body 5 is provided with two opposing ledge means 11 in the form of protrusions extending radially inwards from a tubular portion of the outer body 5, often referred to as a split-tube. In this embodiment the protrusions are formed by plastically deforming portions of the outer body 5 radially inwards as shown in FIG. 3. Each protrusion of the ledge means 11 comprises an impact surface 30 extending inside the outer body 5 such that the drive means 12 is able to force the impact surface 30 in the driving direction. The impact surface 30 is supported from the leading end-side of the outer body 5 by a support body 31 extending from the impact surface 30 to the outer body 5.

[0065] The ledge means 11 may alternatively be configured according to the embodiments shown in FIGS. 5-7 with appropriate changes made to the drive means 12 to interface the ledge means 11.

[0066] For example, the support body 31 and the impact surface 30 may be provided in the form of a separate member 32 attached to the outer body 5 or engaging the outer body 5, as shown in FIG. 6.

[0067] The separate member 32 is typically seated in a through hole of the outer body 5 and may optionally be welded to the outer body 5. However, the separate member 32 may alternatively in other embodiments be attached to the outer body 5 in any other suitable way not necessarily using seating in a through hole of the outer body 5.

[0068] In yet alternative embodiments, the outer body 5 may be manufactured to get the same shape as the outer body 5 and ledge means 11 combination of the embodiment shown in FIG. 6 by forming them together in one piece such as by molding, rather than by adding a separate member to the outer body 5.

[0069] The central rod 2 is provided with a drive means 12 configured to drive the ledge means 11 upon movement of the drive means 12 in a driving direction 13 of the rock bolt 1 to thereby force the outer body 5 in the driving direction 13 via the ledge means 11. In this embodiment, the drive means 12 is provided in the form of drive surfaces 15 on the first wedge means 8 but in other embodiments, the drive means 12 could alternatively be provided on a separate member attached to the central rod 2 at a suitable position along the length of the central rod 2 depending on the position of the ledge means 11 along the length of the outer body 5 as for example shown in the embodiment of FIG. 1a where a drive member 16 in the form of a nut is threaded to the central rod 2. In some examples the drive member 16 as illustrated in FIG. 1a may be configured to engage the outer body 5 to restrict a relative rotational movement between the drive member 16 and the outer body 5. As illustrated in FIG. 1b the engagement may for example be achieved by means of a protrusion 42, such as a lug 42, of the drive member 16, extending radially outwards from the drive member 16 and configured to interlock with a corresponding recess or opening 44 in the outer body 5. FIG. 1c illustrates a further example, wherein the drive member 16 comprises a recess 43 into which a protrusion, such as a tube tab 41, of the outer body 5 may be fitted so as to hinder the drive member 16 from rotating relative to the outer body 5. As a result, the drive member 16 can be ensured to move in the axial direction along the threaded central bolt 2 as the central bolt 2 is rotated relative to the drive member 16. Advantageously, this allows for the drive member 16 to be arranged at a certain distance from for instance the first wedge means 8 during the expansion of the outer body 5, thereby avoiding contact between the first wedge means 8 and the drive member 16.

[0070] The rock bolt 1 further comprises a sleeve 25 fitted around the central rod 2 at the trailing portion 7 of the outer body 5. In this embodiment, the sleeve extends only within the outer body 5 but in other embodiments, the sleeve could alternatively extend outside the trailing end of the outer body 5.

[0071] The sleeve 25 is press-fitted to the central rod 2 tight enough for friction between the sleeve 25 and the central rod 2 to prevent the central rod 2 from falling out of the sleeve 25 should the central rod 2 break between the sleeve 25 and the leading portion 3 of the central rod 2. Such a sleeve is sometimes referred to as a stopper.

[0072] The rock bolt 1 is driven installed into a bore of a formation 22 by applying a driving force to the trailing portion 4 of the central rod 2 via the blind nut. The central rod 2 forces the first wedge means 8 forward and thereby pushes on the ledge means 11 of the outer body 5. The force on the ledge means 11 pulls the outer body 5 into the formation 22, thereby moving the outer body 5 into the formation without buckling of the outer body 5. The present design thus reduces the power needed to force the outer body 5 into the formation 22 as compared to prior art designs which are based on applying driving force directly to the trailing portion 7 of the outer body 5.

[0073] Once the outer body has been pulled sufficiently far into the formation 22, the central rod 2 is rotated by rotation of the blind nut in order to thereby move the first wedge means 8 towards the second wedge means 9, and thereby force the second wedge means 9 radially outward such that the outer body 5 is expanded and anchored to the formation 22.

[0074] In other embodiments, the outer body 5 may additionally be provided with one or more radial through holes 14 and the first wedge means 8 be configured to extend into the radial through holes 14 of the outer body 5 before expansion of the leading portion of the outer tube at installation of the rock bolt. Once, the leading portion of the outer body 5 is expanded, the first wedge means has forced the outer body 5 radially outwards, wherein the wedge means no longer resides in the through holes of the outer body 5. Such a configuration has the advantage that it provides for additional radial expansion of the outer body 5.

[0075] The concept of pulling the outer body into the formation by applying a driving force at its leading portion via the central rod 2 may alternatively be realized in other ways, such as the one mentioned above shown in FIGS. 1a-c where the drive means 12 is provided in the form of a drive member 16 provided on the central rod 2 between the second wedge means 9 and the trailing portion 7 of the outer body 5, and wherein the ledge means 11 is provided in the form of one or more trailing surfaces 17 of the second wedge means 9. In the FIG. 1a-c embodiments, the drive means is a nut threaded to the central rod 2, by the drive means could alternatively have any other suitable form and could alternatively be attached to the central rod 2 in any other suitable way. In yet alternative embodiments, the drive means 12 could be provided in the form of a drive member 16 provided on the central rod 2 between the first wedge means 8 and the leading end 18 of the outer body 5 (not shown in figures).

[0076] Another aspect of the invention relates to how to enable pre-tensioning of the formation by pre-tensioning the central rod 2 of the rock bolt. FIGS. 5-7 relate specifically to a disclosure of how the trailing portion of a rock bolt could alternatively be configured to enable such pre-tensioning. As the skilled person would understand, this type of configuration of the trailing portion of the rock bolt 1 is compatible with the other described alternative embodiments of the leading portion of the rock bolt 1 and can thus be applied to the other embodiments in this disclosure. According to FIGS. 5-7, a rock bolt may thus comprise a rock plate 19 and a nut 20 threaded to the trailing portion 4 of the central rod 2, wherein a washer 21 is provided between the rock plate 19 and the nut 20 for distributing force from the nut 20 to the rock plate 19. The length of the outer body 5 is such that as the outer body 5 is pulled into a formation 22 at installation of the rock bolt 1, there is a gap 24 between the trailing end 23 of the outer body 5 and the rock plate 19.

[0077] The gap 24 may often be within the range of 10-300 mm, but this range being selected according to the length of the rock bolt and the amount of compaction of the formation deemed necessary for pre-tensioning of the formation. The rock bolt 1 comprises a sleeve 25 fitted around the central rod 2 at the trailing portion 7 of the outer body 5, wherein a first portion of the sleeve 25 extends within the outer body 5, and wherein a second portion of the sleeve 25 extends through a central hole of the rock plate 19 and further to the washer 21 a predetermined distance D past the trailing end 23 of the outer body 5.

[0078] The sleeve 25 is movable relative to the outer body 5 along the longitudinal axis 10 of the rock bolt 1, back and forth within an operative range 26 between an inner position and outer position. The outer body 5 and the sleeve 25 are provided with retaining means 27 configured to retain the sleeve within the operative range 26 thereby preventing the sleeve 25 from falling out of the outer body 5. The retaining means 27 comprises a protrusion 28 of the outer body 5 extending radially inwards into a corresponding elongate recess 29 of the sleeve 25, wherein the protrusion is movable within the confines of the elongate recess 29 as the sleeve 25 moves within the operative range 26, and wherein the protrusion prevents movement of the sleeve 25 outside of the operative range 26. In other embodiments, the retaining means could have any other suitable configuration, such as an elongate recess provided in the trailing portion of the outer body 5 and a pin extending through the elongate recess and into the sleeve.