Yield prop

Abstract

Disclosed is a prop comprising a support portion and a yield portion, the support portion being an elongate post and the yield portion being arranged between the support portion and a first end of the prop, wherein the first end includes an open recess that extends along a longitudinal axis of the prop for at least part of a length of the prop defining the yield portion of the prop, and an outer surface of the yield portion has at least one groove, the groove being substantially perpendicular to the longitudinal axis of the prop.

Description

YIELD PROPTechnical Field

[0001] The present invention relates to structural supports and, more particularly, to support prop assemblies for use in mines.Background

[0002] Underground mining environments often experience difficult geological conditions that require both primary and secondary forms of roof support. If designed properly, the secondary support system serves as additional support in the case the primary support system is inadequate whilst also assisting in maintaining the integrity of the immediate roof beam.

[0003] Support prop assemblies are one type of commonly used secondary support system that is used to provide overhanging wall and roof support in underground mines. For example, unmodified timber posts have been used as mine support props. However, support prop assemblies often must exhibit high yield strength and deformation characteristics, and since timber has a limited degree of compression in the direction of its grain, timber poles are generally considered unsuitable for applications involving high compressive loads. In addition, such posts typically offer little to no warning prior to failure of the support.

[0004] Other conventional support prop assemblies enable some measure of deformation by having a reduced cross-sectional area in a region of the timber post, often by tapering one or both ends. In use, the ends of these conventional posts expand radially outward under a compressive load or experience a "brushing" mode of buckling failure that applies a bending moment on the prop and reduces the overall strength of the system. Further, the post often skews to one side, causing it to become ineffective as a load support.

[0005] In the event of closure or convergence of a mine, it may be desirable for a mine support to be capable of yielding vertically under loading when arranged with its long axis upright.

[0006] The present invention seeks to address, or at least partially ameliorate, one or more of the disadvantage of prior support prop assemblies, and / or to at least provide the public with a useful alternative.

[0007] The reference in this specification to any prior publication (or information derived from the prior publication), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that the prior publication (or information derived from the prior publication) or known matter forms liner of the common general knowledge in the field of endeavour to which this specification relates.Summary of the Disclosure

[0008] In a first aspect, embodiments are disclosed of a prop comprising a support portion and a yield portion, the support portion being an elongate post and the yield portion being arranged between the support portion and a first end of the prop, wherein the first end includes an open recess that extends along a longitudinal axis of the prop for at least part of a length of the prop defining the yield portion of the prop, and an outer surface of the yield portion has at least one groove, the groove being substantially perpendicular to the longitudinal axis of the prop.

[0009] In some embodiments, when a compressive load of sufficient magnitude is applied axially to the post the yield portion may be adapted to yield preferentially to the support portion. In some embodiments, an axial load capacity of the yield portion may be between 65 to 85% of an axial load capacity of the support portion. In some embodiments, the axial load capacity of the yield portion may be substantially 75% of the axial load capacity of the support portion. In some embodiments, a mode of failure at the axial load capacity of the yield portion may be yielding. In some embodiments, a mode of failure at the axial load capacity of the support portion may be buckling.

[0010] In some embodiments, the groove may extend around the entire circumference of the outer surface of the yield portion. In some embodiments, the yield portion may be configured to provide a visual indicator of a loading of a roof of a mine in use. In some embodiments, a change in length of the yield portion may provide the visual indicator. In some embodiments, the change in length may be between 0 and 300mm. In some embodiments, the support portion may have a substantially solid core of timber. In some embodiments, the yield portion may have three grooves therearound, each of the grooves being spaced from one another.

[0011] In some embodiments, a tie means may encircle the outer surface of the yield portion substantially perpendicular to the longitudinal axis of the prop intermediate the at least onegroove and at least one of the ends of the prop. In some embodiments, the tie means may be wire ties that are adapted to encircle the yield portion.

[0012] In some embodiments, the prop comprises wood.

[0013] In a second aspect, embodiments are disclosed of a mine support assembly comprising the prop according to any one of the preceding claims and a prestress system, the prestress system comprising at least one wedge adapted to be driven between one of the ends of the prop and a floor or roof of a mine.

[0014] In some embodiments, the prestress system may comprise three wedges, a middle wedge of the three wedges being adapted to be driven between opposing upper and lower wedges of the three wedges. In some embodiments, the at least one wedge may be driven by a hydraulic ram.

[0015] In a third aspect, embodiments are disclosed of a mine support assembly comprising the prop according to the first aspect and a headboard for engaging an uppermost portion of the prop and / or a baseboard for engaging a lowermost portion of the prop.

[0016] In a fourth aspect, embodiments are disclosed of a mine support assembly comprising the prop according to the first aspect, the prestress system according to the second aspect and / or the headboard and / or the baseboard according to the third aspect. In some embodiments, the prop may be arranged upright in a mine having a floor and a roof, the first of the ends bearing against the floor or roof and the opposite end bearing against the other of the floor or roof.

[0017] Other aspects, features, and advantages will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, which are a part of this disclosure and which illustrate, by way of example, principles of inventions disclosed.Description of the Figures

[0018] The accompanying drawings facilitate an understanding of the various embodiments. The invention will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0019] Figures la, lb, 1c, and Id are perspective from above, side, top and bottom views, respectively, of a first embodiment of a prop in accordance with the present disclosure.

[0020] Figure 2 is a close-up perspective view from below of an in-use lower portion of the first embodiment of the prop of Figure 1.

[0021] Figure 3a is close-up side view of segment A-A of Figure lb.

[0022] Figure 3b is section view through B-B of Figure 3a.

[0023] Figure 4 is a close-up side view of an in-use lower portion of a second embodiment of the prop, comprising a tie above the uppermost groove.

[0024] Figure 5 is a close-up side view of an in-use lower portion of a third embodiment of the prop, comprising a first tie above the uppermost groove and a second tie below the lowermost groove.

[0025] Figures 6a and 6b are a plan view and a perspective view from above, respectively, of a first embodiment of a headboard.

[0026] Figure 7 is a perspective view from above of a first embodiment of a baseboard.

[0027] Figures 8a and 8b are a side view and a perspective view from above, respectively, of a first embodiment of the wedges of the prestress system.

[0028] Figure 9 is a perspective view from above of the first embodiment of the baseboard above the first embodiment of the wedges of the prestress system, prior to activation of the prestress system.

[0029] Figure 10 is a perspective view from above of a first embodiment of a hydraulic press frame for activating the prestress system.

[0030] Figure 11 is a perspective exploded assembly view of a first embodiment of a mine support assembly.

[0031] Figures 12a and 12b are a perspective view from above and a side view, respectively, of a first embodiment of the mine support assembly, and with the hydraulic press frame located adjacent the wedges prior to activating the prestress system.

[0032] Figure 12c is a close-up perspective view from above of an in-use lower portion of the first embodiment of the mine support assembly of Figure I la.

[0033] Figures 13a, 13b, 13c, 13d and 13e are side views of a further embodiment of the prop in accordance with the present disclosure under progressively increasing load, where Fig. 12a is prior to the application of a compressive force, Fig. 12b is application of a compressive force that is approaching the yield strength of the prop, Fig. 12c is application of a compressive force that exceeds the yield strength of the prop prior to complete failure of the yield portion, Fig. 12d is application of a compressive force that exceeds the yield strength of the prop after complete failure of the yield portion, and Fig. 12e is application of a compressive force that continues to exceed the yield strength of the prop after complete failure of the yield portion.Detailed Description

[0034] Referring to the figures, the invention is described in relation to a yieldable prop 10 suitable for supporting the roof of an underground mine such as in coal mines, hard rock mines or tunnelling applications. The prop 10 can, in some forms, be manufactured from wood. Where reference is made to timber or lumber herein, this is to be understood as meaning unprocessed wood, or wood that has been processed into uniform and useful sizes including posts, beams, planks etc. The wood can be manufactured such that the grain of the wood extends parallel to the longitudinal axis of the resulting prop 10. Where like reference numerals are used in the following description, the features are considered to be the same unless specified as being otherwise.

[0035] Referring to Figures 1 to 3, the prop 10 is formed from an elongate wooden post that comprises a support portion 20 and a yield portion 30 that are integral with one another intermediate opposing ends 12,14 of the prop 10. The support portion 20 is an elongate post portion, typically comprising a majority of the length of the overall prop 10, and having a specified critical buckling load defined by the maximum axial load capacity of the post for a given height (i.e. effective length) and cross-sectional area. The support portion 20 can be formed to have a substantially solid core of timber, or in some alternative forms can be formed to have a hollow cross-sectional area. As would be understood by a person skilled in the art, whilst the examples herein describe a post having a circular cross-sectional profile,the same principal could be adapted for props formed from other cross-sectional profile shapes such as square, rectangular, ovular, or other polygonal shapes.

[0036] The yield portion 30 is arranged between the support portion 20 and one of the ends 12,14 of the prop 10, for example the in-use lower end 12, although as would be understood by a person skilled in the art, the yield portion 30 could be arranged between the support portion 20 and the in-use upper end 14 of the prop 10. An open cylindrical recess 32 extends through the end 12 of the prop 10 at which the yield portion 30 is arranged. The recess 32 extends substantially centrally from the end 12 along a longitudinal axis Y-Y of the prop 10 at least a part of the length of the prop 10, the interior upper surface 34 of the recess 32 defining the juncture X-X between the yield portion 30 and support portion 20. The thickness tyof the wall of the recess 32 between the outer surface 36 of the yield portion 30 (and prop 10) and the inner surface 38 of the recess 32 can be calculated as the difference between the length of the outer radius r0(i.e. between the longitudinal axis Y-Y and the outer surface 36), and the length of the inner radius n (i.e. between the longitudinal axis Y-Y and the inner surface 38 of the recess 32). A rim 35 is defined by the surface around the recess 32. The bearing surface, defined by the cross-sectional area of the wall thickness tyaround the recess 32, is adapted such that the resulting yield portion 20 produces a yield strength that equates to approximately 75% of the maximum axial load capacity of the support portion 20 of the prop 10 (i.e. the critical buckling load). In some variations, the bearing surface can be adapted such that the resulting yield portion 20 produces a yield strength that is in the range of 65-85% of the maximum axial load capacity of the support portion 20 of the prop 10. As would be appreciated by a person skilled in the art, the size of the yield portion can be adjusted to produce the desired controlled yield effect. As would be appreciated by a person skilled in the art, the cross-sectional shape of the recess can be modified to correspond to the cross-sectional profile of the prop. In addition, as would also be appreciated by a person skilled in the art, the interior walls of the recess can be stepped, straight or angled to provide regions with different yield characteristics (i.e. effectively a plurality of yield portions, each with a different yield strength).

[0037] In use, the stress concentration in the walls around the recess 32 of the yield portion 30 facilitates a controlled yield at the end 12 of the prop 10. The recess 32, and yield portion 30, thus act as a safety feature to provide a visual indicator for determining if the prop 10 is sufficient (i.e. has not yielded) or insufficient (i.e. has yielded) to support the compressive load applied thereto, particularly when an amount of the compressive load is difficult topredict. When a compressive load of sufficient magnitude is applied axially to the prop 10 the yield portion 20 is adapted to yield preferentially to the support portion 30, resulting in a change in the overall length of the prop 10. The change in length, or deflection, of the prop 10 can be in a range of 0mm up to substantially the depth of the recess 32 (i.e. the height from the proximal end 12 of the prop 10 to the interior upper surface 34 of the recess 32). Advantageously, the yield system provided by the disclosed prop 10 allows for deflection of the yield portion 30 of the prop 10 whilst the support portion 20 continues to provide support due to the higher maximum axial load capacity (i.e. the critical buckling load).

[0038] For example, in one form where the total length of the prop is 3.6m from end to end and the cross-sectional diameter of the prop is 150mm in thickness, the recess can have a wall that is 15mm thick and a depth from the proximal end to the interior upper surface of the recess of 100mm. In such forms, the visual indicator of whether the prop is sufficient or insufficient to support the applied compressive load can be provided by a deflection, or change in overall length, of the prop in the range of 0mm (i.e. sufficient) and 100mm (i.e. insufficient). As would be appreciated by a person skilled in the art, in variations, the recess can have a depth in the range of 50 and 300mm calculated based on a diameter of the prop, a thickness of the wall of the recess, and an overall length of the prop.

[0039] The outer surface 36 of the yield portion 30 comprises at least one groove 40 that extends substantially perpendicular to the longitudinal axis Y-Y of the prop 10. In use, the groove 40 interrupts the axially applied compression force along the outer surface 36 of the yield portion 30 and reduce the stress experienced thereat, thereby providing a predictable, and controlled, point along the outer surface 36 of the yield portion 30 at which the yielding can occur. For example, the groove can be a triangular cut having a depth of approximately 5mm. As would be appreciated by a person skilled in the art, the shape, location and depth of the groove / s can be varied to produce the desired controlled yielding and provide a basis for the mode of failure.

[0040] For example, the yield portion 30 can comprise three grooves 40 that are evenly spaced along the length of the outer surface 36 of the yield portion 20 and extend around the entire circumference of the outer surface 36 of the yield portion 20. As would be appreciated by one skilled in the art, the spacing between the grooves and the location of the grooves along the longitudinal length of the prop 10 can be different from one-another, and different spacings between grooves would provide a failure with a different character to one with equal spacing. The grooves 40 are formed such that the depth of each groove 40 is equidistantfrom the longitudinal axis Y-Y around the prop 10. In use, when a compressive load of sufficient magnitude is applied axially to the prop 10, the grooves 40 enable the segments of the yield portion 30 between adjacent grooves 40 to fold relative to one another (for example, see Figures 13a to 13e) such that the deflection of the prop 10 is substantially vertically downwards, with minimal bending moment and rotation of the prop 10. As would be appreciated by a person skilled in the art, the number of grooves can be varied to adjust the yielding, where more grooves provide more folds during failure. Further, as would also be appreciated by a person skilled in the art, the grooves can be spaced along the entire length of the yield portion or contained to a limited portion thereof.

[0041] Referring now to Figures 4 and 5, in some forms a tie means 44 can be used as a secondary controller of the stiffness and predictability of the yield portion 30. The tie means 44 can be a small diameter metal (e.g. stainless steel or cold drawn steel) ring, wire, cord or steel strips that are arranged to confine the yield portion 30 by encircling the outer surface 36 of the yield portion 20, above (e.g. Fig. 4) and / or below (e.g. Fig. 5) the portion of the yield portion 30 that comprises the one or more grooves 40. In some variations, not shown, tie means can be applied to the yield portion intermediate two grooves, providing an additional fixed confinement point thereat. Where a plurality of tie means 44 are arranged on the prop 10, a first of the tie means 44 can locate between the uppermost groove 40 and the in-use upper end 14 of the prop 10, preferably intermediate the uppermost groove 40 and the juncture X-X between the yield portion 30 and support portion 20, whilst a second of the tie means can locate between the lowermost of the grooves 40 and the in-use bottom end 12 of the prop 10. The tie means 44 extend substantially perpendicular to the longitudinal axis Y-Y of the prop 10 and act as a confining reinforcement that can improve the compressive strength and deformation capacity of the yield portion 30. In some forms, tie means 44 can be bent into two full circles around the yield portion 30 of the prop 10 with a small amount of overlap between the ends of the tie means 44 to allow for a weld to be made to hold the tie means 44 intact. The wrapping technique allows for each tie means 44 to surround the outer surface 36 with two loops, except for the region where the ends overlap where three segments of the tie means 44 overlap. The ends of the tie means 44 can be welded to hold the tie means 44 together. In some forms, additional spot welds can be located intermediate the ends of the tie means 44.

[0042] Referring to Figures 6 and 7, the prop 10 can be used as part of a mine support assembly in conjunction with a headboard 50 and / or baseboard 60 that help distributeloading on, and prevent punching into, the mine roof and floor, respectively. The in-use lower surface 52 of the headboard 50 comprises a recessed cut-out 54 having a cross- sectional shape and size that corresponds to that of the in-use upper end 14 of the prop 10, whereby the end 14 of the prop 10 can be received therein. The recessed cut-out 54 prevents side-ways movement of the upper end 14 of the prop 10 in use. The substantially planar in- use upper surface 56 of the headboard 50 is adapted to bear against the roof of the mine in use.

[0043] The in-use upper surface 62 of the baseboard 60 comprises a recessed cut-out 64 having a cross-sectional shape and size that corresponds to that of the in-use lower end 12 of the prop 10, including the recess 32, whereby the end 12 of the prop 10 can be received therein. The recessed cut-out 64 of the baseboard 60 prevents side-ways movement of the lower end 12 of the prop 10 in use. The substantially planar in-use lower surface 66 of the baseboard 60 is adapted to bear against the floor of the mine, or a prestress system 70, in use. In variations, not shown, where the recessed cut-out of the baseboard has sufficient depth, the side walls of the recessed cut-out can act to confine the lower region of the yield portion in place of, or in conjunction with, a tie means.

[0044] Referring to Figures 8 to 12, the mine support assembly can utilise a prestress system comprising one or more wooden wedges 70 that allows an operator to apply a stress to the roof and the floor during installation of the prop 10. The prestress system applies an immediate active support load to the mine roof and may have inherent advantages over a strictly passive roof support system. For example, a prestress system can comprise three wedges, with the upper and lower wedges 70 each having a sloped inward facing surface 72 that engages with, and opposes, an adjacent one of the correspondingly sloped outward facing surfaces 74 of the middle wedge 70'. Each of the wedges 70 have substantially the same width and length, and the combined height of the wedges 70 is sufficient to apply a stress to the roof and the floor of the mine once the prop 10 is installed. A hydraulic ram 80 can be used to drive the middle wedge 70' in between the upper and lower wedges 70 with the hydraulic cylinder 82 providing enough force to the middle wedge 70' to overcome the resistance of the frictional forces between opposing sloped surfaces 72,74 and the compression forces from the prop 10 and / or baseboard 60, located above the wedges 70. The rectangular frame 88 of the hydraulic ram 80 can be dimensioned to correspond to the width and length of the wedges 70, with the length of the wedges also including provision of an additional overlap prior to activation of the prestress system. Once the hydraulic ram 80 hasdriven the middle wedge 70' into place, thereby activating the prestress system, the hydraulic cylinder panel 84 can be removed via a pair of slots 86 adapted on either side of the frame 88, such that the hydraulic ram 80 can be removed from the mine support assembly and reused elsewhere, as needed.

[0045] Variations and modifications may be made to the parts previously described without departing from the spirit or ambit of the disclosure.

[0046] In the foregoing description of preferred embodiments, specific terminology has been resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar technical purpose. Terms such as "front" and "rear", "inner" and "outer", "above", "below", "upper" and "lower" and the like are used as words of convenience to provide reference points and are not to be construed as limiting terms.

[0047] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as, an acknowledgement or admission or any form of suggestion that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

[0048] In this specification, the word “comprising” is to be understood in its “open” sense, that is, in the sense of “including”, and thus not limited to its “closed” sense, that is the sense of “consisting only of’. A corresponding meaning is to be attributed to the corresponding words “comprise”, “comprised” and “comprises” where they appear.

[0049] In addition, the foregoing describes only some embodiments of the invention(s), and alterations, modifications, additions and / or changes can be made thereto without departing from the scope and spirit of the disclosed embodiments, the embodiments being illustrative and not restrictive.

[0050] Furthermore, invention(s) have been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention(s). Also, the various embodiments described above may be implemented in conjunction with other embodiments, e.g., aspects of one embodiment maybe combined with aspects of another embodiment to realize yet other embodiments. Further, each independent feature or component of any given assembly may constitute an additional embodiment.

Claims

CLAIMS:

1. A prop comprising a support portion and a yield portion, the support portion being an elongate post and the yield portion being arranged between the support portion and a first end of the prop, wherein the first end includes an open recess that extends along a longitudinal axis of the prop for at least part of a length of the prop defining the yield portion of the prop, and an outer surface of the yield portion has at least one groove, the groove being substantially perpendicular to the longitudinal axis of the prop.

2. The prop according to claim 1, wherein, when a compressive load of sufficient magnitude is applied axially to the post the yield portion is adapted to yield preferentially to the support portion.

3. The prop according to claims 1 or 2, wherein an axial load capacity of the yield portion is between 65 to 85% of an axial load capacity of the support portion.

4. The prop according to claim 3, wherein the axial load capacity of the yield portion is substantially 75% of the axial load capacity of the support portion.

5. The prop according to claims 3 or 4, wherein a mode of failure at the axial load capacity of the yield portion is yielding.

6. The prop according to any one of claims 3 to 5, wherein a mode of failure at the axial load capacity of the support portion is buckling.

7. The prop according to any one of the preceding claims, wherein the groove extends around the entire circumference of the outer surface of the yield portion.

8. The prop according to any one of the preceding claims, wherein the yield portion is configured to provide a visual indicator of a loading of a roof of a mine in use.

9. The prop according to claim 8, wherein a change in length of the yield portion provides the visual indicator.

10. The prop according to claim 9, wherein the change in length is between 0 and 300mm.

11. The prop according to any one of the preceding claims, wherein the support portion has a substantially solid core of timber.

12. The prop according to any one of the preceding claims, wherein the yield portion has three grooves therearound, each of the grooves being spaced from one another.

13. The prop according to any one of the preceding claims, wherein a tie means encircles the outer surface of the yield portion substantially perpendicular to the longitudinal axis of the prop intermediate the at least one groove and at least one of the ends of the prop.

14. The prop according to claim 13, wherein the tie means are wire ties that are adapted to encircle the yield portion.

15. The prop according to any one of the preceding claims, wherein the prop comprises wood.

16. A mine support assembly comprising the prop according to any one of the preceding claims and a prestress system, the prestress system comprising at least one wedge adapted to be driven between one of the ends of the prop and a floor or roof of a mine.

17. A mine support assembly according to claim 16, wherein the prestress system comprises three wedges, a middle wedge of the three wedges being adapted to be driven between opposing upper and lower wedges of the three wedges.

18. A mine support assembly according to claims 16 or 17, wherein the at least one wedge is driven by a hydraulic ram.

19. A mine support assembly comprising the prop according to any one of claims 1 to 15 and a headboard for engaging an uppermost portion of the prop and / or a baseboard for engaging a lowermost portion of the prop.

20. A mine support assembly comprising the prop according to any one of claims 1 to 15, the prestress system according to any one of claims 16 to 18 and / or the headboard and / or the baseboard according to claim 19.

21. A mine support assembly according to claim 20, wherein the prop is arranged upright in a mine having a floor and a roof, the first of the ends bearing against the floor or roof and the opposite end bearing against the other of the floor or roof.

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