AU669745B2 - Mine roof bolt - Google Patents

Description

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AUSTRALIA

Patents Act 1990 HARVEY D. GILLESPIE

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT

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e Invention Title: "Mine roof bolt" r The following statement is a full description of this invention including the best method of performing it known to me:la MINE ROOF BOLT RELATED APPLICATION The present invention is related to that of my -a t8 4n 93.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to mine roof bolts, and more particularly relates to mine roof bolts constructed of multi-strand steel cable.

2. Description of the Prior Art •coo In the art of mine tunnel roof suppc.rt, there are two major categories of bolting systems wherein mine roof bolts are anchored in bore holes drilled in the mine roof, the bolts' purpose being to reinforce and stabilize the S"unsupported rock formation above the mine tunnel. These two categories of mine roof bolting systems are: (1) tension-type systems, and passive-type systems. In each system, it is common practice to, first, drill a hole through the mine tunnel ceiling into the rock formation above to a depth appropriate for the type of rock AO formation to be supported. A mine roof bolt and roof plate are then anchored in the bore hole to support the mine roof and maintain the rock formation in place.

In a common tension-type mine roof bolt system, an expansion shell type anchor is installed on the threeded end of the bolt. The bolt and expansion shell anchor are inserted up into the bore hole until the roof plate is against the mine roof.

The bolt is then rotated to thread a tapered plug section of the expansion shell down toward the bolt head, in order to expand the jaws of the expansion shell against the interior wall of the bore hole to thereby hold the mine roof bolt in place within the Ie..i: bore hole, the mine roof bolt functioning to support and stabilize the rock formation above the mine tunnel In passive-type mine roof bolt systems, the passive-type bolt is not attached to an expansion S. shell or similar anchor at the free (upper) end of the bolt, but rather is retained in place within the rock formation by a rapid-curing resin adhesive S•material that is mixed in the bore hole as the bolt is rotated and positioned within the bore hole. In 2" theory, the resin adhesive bonds the bolt to the rock formation along the total length of the bolt within the bore hole in the rock formation. It is also common practice to use resin adhesive with a tension-type mine roof bolt to retain the bolt within the mine roof bore hole, at least along the upper portion of the bolt.

In passive-type and some tension-type mine roof bolt systems, one or more resin cartridges are inserted into the bore hole prior to (ahead of) the mine roof bolt. Forcing the mine roof bolt into the bore hole while simultaneously rotating the bolt ruptures the resin cartridge(s) and mixes the resin components within the annulus between the bolt shank and bore hole wall. Ideally, the resin adhesive mixture totally fills the annulus between the bolt shank and bore hole wall at least along the upper portion of tension-type bolting systems, and along the total length of the bolt shank and bore hole wall in passive-type systems. The resin mixture is forced into cracks and crevices in the bore hole wall and into the surrounding rock formation to adhere the bolt to the rock formation.

When extremely long mine roof bolts are S"necessary, it is common practice to attach two or :e S mLore bolt shank sections together by couplers to ."20 result in a "roof bolt" of sufficient length sea. appropriate for the particular type of rock formation. These couplers between bolt sections, being of a larger diameter than the bolt shanks, prevent the mixed resin adhesive from flowing downwardly (resin return) within the bore hole annulus from the first (upper) bolt section to the lower section(s). Therefore, the effective anchoring -4of the bolt to the bore hole wall within the rock formation is, essentially, only along the length of the first (upper) bolt section wherein the resin adhesive totally fills the annulus between the bolt section and the bore hole wall.

To alleviate this problem, it has been common practice simply to drill a larger bore hole in the rock formation that will enable the resin adhesive to flow around the coupler(s) as the bolt is being inserted into and rotated within the bore hole to mix the resin. Although this does effect the desired result (resin return around the coupler(s) within the annulus between the bolt shank and bore hole wall), it creates another problem that, 15 depending on the type of rock formation, may be more dangerous than the problem that is corrected by a larger bore hole. Specifically, the bonding effectiveness of the resin adhesive material to hold eoeeo S"the mine roof bolt in place within the bore hole is 20 *20 considerably weakened by virtue of the increased distance between the bolt shank and bore hole wall, and the sheer volume of resin adhesive material necessary to totally fill the annulus. Additionally, by virtue of their specific makeups, mine roof rock formations that actually require long (fifteen feet or longer) mine roof bolts are more susceptible to movement and shifting within the rock formation, than 5 are more solid rock formations that require only shorter mine roof bolts.

Another common problem with using mine roof bolt sections coupled together in such rock formations that require longer (coupled) mine roof bolts, this shifting of the rock formation (shear) causes the bolt couplers to fracture. When this happens, of course, the effective holding length of the mine roof bolt is instantly decreased. In many instances, there is no or very little resin adhesive material around the broken bolt shank to help stabilise the rock formation. Therefore, in almost all instances, this shortened mine roof bolt is ineffective to safely prevent the mine roof rock formation from further shifting and potential collapse.

An ambodimnt f -he nrscnt ;inven-ion orovidos an

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improved mine roof bolt that does not require an ove zed mine roof bore hole in order to effect full an complete resin return within the annulus between e bolt shank and bore hole wall along the total 1 th of the bolt shank.

In another embodiment e present invention provides an improved mine ro bolt that is available in various lengths with the use of bolt shank couplers that are susce le to fracture when the mine roof rock formation SUMMARY OF THE INVENTION The improved mine roof bolt of the invention of patent No. 661763 is constructed of a length of pre-tensioned, multi-strand steel cable, commonly formed of six individual pre-tensioned steel strands spirally wrapped around a seventh steel strand. The head of the bolt is formed by positioning a twopiece tapered plug around the stranded steel cable at one end, and then slipping a hexagonal or other drive-headed internally tapered collar around the tapered pl g, Pressing the internally tapered hexagonal head collar down around and against the two-piece tapered plug urges serrations on the interior circumference of the plug sections to "bite" into the stranded steel cable to form a rigid hexagonal holt head on the cable that further tightens against the steel strands as tension is applied to the mine roof bolt.

A mine roof bolt in accord with the present invention comprises: 1: a length of multi-strand cable defining a bolt shank; a tapered plug comprising a body portion having an internal bore and a frusto-conical outer surface essentially concentric with said internal bore, said tapered plug being mounted about an end of said cable at said internal bore; an internally tapered drive collar having a frusto-conical inner surface that engages said frusto-conical outer surface of said tapered plug, Goo: and having an outer surface defining a drive head that accepts a driving mechanism for rotating and linearly translating said bolt, wherein said tapered plug is mounted on an end of said cable, and said drive collar is pressed down upon said tapered plug, forcing said tapered plug against said cable, such that said drive collar, said tapered plug, and said cable, when fitted tightly together, define said mine roof bolt; and a sleeve attached to said cable for preventing said [multi-strand] cable from slipping relative to resin adhesive material within a bore hole, said sleeve having radially outwardly proiectilng fins oriented axially relative to said sleeve for centering said sleeve and said cable within the bore hole and for puncturing resin adhesive cart ridges.

The mine roof bolt of the present invention includes a number of einbodinments that enhance its abilitv to be retained withiii the bore hole.

and therefore, to stabilize the rock formation. "B3uttons" or sleeves swaged on the shank cable effect improved bonding of the resin adhesive to the bol shank. An annular dam around the bolt shliank retains the resin adhesive around the shank. minliniizes voids and air pockets ill the resin, and forces the resin into cracks and crevices inll the rock formation. A stiffener sleeve prevenits cable buckles as the bolt is being urged into Ilthe bore hole and also protects the cable from abrasive wear from the mine roof plate as the bolt is being spun into the bore hole. A resin protector cap p'rotects resin cartridges fronm premature rupture by the sharp end of the bolt shank cable, and retainis the resin cartridges in place within the bore hole when the bolt is subsequently withdrawin. A plurality of cap sleNves fit over the boll heads and are iliterconnllected inll a 1mannor to containii bolls that break with 1n the bore hole, An embodiment of the present invention provides aii iimproved mine roof bolt that (loes not requic a i ovesized line roof bore hole inll order to effect full and complete resin return vwithin thle alliulus betwveen the bolt shank and bore hole wall along the total length of thie boll shank.

lin another embodient the present invention provides all improved mine roof bolt that is available inll various lengths without I the use of bolt shank coupllers that are sus ce pliblo to tracIure wlen the mineiI roof rock formiation shifts. A further cibodiment provides all improved Illillne roof having an outer surface that aids inll effecting compilete mixture of tile resill adhesive imatorial, and also includes crovices withini the 11111e roof bolt shank that permit penetiratioi of the resin bonding matorial into the bolt shank for more effective rosin bonding thereto.

A still further embodiment provides an improved mine roof bolt that will easily bend for installation into a bore hole that is considerably deeper than the height of the mine tunnel at the installation location, and will also blend with a shifting rock formation, and fully retain its bonding within the rock formation along the total length of the mine roof bolt without breaking when the rock formation shifts.

Yet another embodiment provides an improved mine roof bolt that includes means for preventing voids in the mixture of resin adhesive material in the annulus surrounding the bolt shank.

A further embodiment provides an improved mine roof bolt that includes means for preventing premature rupture of resin cartridges while positioning the cartridges into the bore hole, Yet a further embodiment provides an imrproved mine roof bolt that IV. includes means on the bolt shank for preventing voids in the resin adhesive material, such means also permitting the resin adhesive to flow around and under the means to further support the mnine roof bolt and the rock form-ation.

A still further embodiment provides an improved inine roof bolt having means for protecting the bolt shank froin abrasive wear from the roof plate as the bolt is being spun into the bore hole.

Another embodiment provides an improved mine roof bolt having means for permnitting the bolt to "yield" within the bore hole at a consistent yielding force as shifting of the rock formation tends to cause the bolt 1' shank to "slip" relative to the resin adhesive.

Still another embodimnent provides an improved mine roof bolt having means for preventing the bolt heads from falling from the bore hole, in the event the bolt fails under extreme load.

Lastly, a "yieldable" cable bolt design incorporates means thait permit the bolt shank to slip or "yield" relative to the resin adhesive within the bore hole while maintaining a consistent resistance force along the shank, even as 9 the shank is pulled outwardly from the bore hole and out of contact with the resin adhesive.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partial sectional view of the improved mine roof bolt embodiment of the invention of patent No. 661763, illustrating the two-piece tapered plug and, in section, the internally tapered hexagonal head collar.

Fig. 2 is an end view of the mine roof bolt of Fig. 1.

Fig. 3 is a perspective view of one section of a two-piece tapered plug.

99* 9**9*9 *t ooze t *oo* 10 Fig. 4 is a perspective view of an alternative embodiment of one section of a two-piece tapered plug.

Fig. 5 is a side elevation view of the mine roof bolt of Figs. 1 and 2 positioned in the mine roof bore hole under the resin cartridge, the mine roof plate, spherical washer, and internally tapered hexagonalha4 being shown in section.

Fig. 6 is a view of the mine roof bolt of Fig. shown in installed position within the mine roof bore 0o hole, with the resin adhesive material thoroughly mixed and completely filling the annulus around the shank of the mine roof bolt.

Fig. 7 is a graph of tensile strergth vs. elongation for a 9/16 inch diameter improved mine roof bolt of Figs.

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I the minc f-bo of the present invention illustrating a number of alternative embodiments.

Fig. 9 is an end view of the se d alternative a' DO embodiment mine roof bolt ta ealong lines 9-9 in Fig. 8.

Fig. 10 is a si elevation view of a resin protector S" cap used with e mine roof bolt of the present invention.

i. 11 is a partial side elevation view of the upper d. .dof tho min roof bolt of Fig. 0 10/1 Fig. 8 is a side elevation view of a mine roof bolt in accord with the present invention illustrating a number of alternative embodiments.

Fig. 9 is an end view of a second alternative embodiment of a mine roof bolt in accord with the present invention taken along lines 9-9 in Fig. 8.

Fig. 10 is a side elevation view of a resin protector cap used with a mine roof bolt of an embodiment of the present invention.

Fig. 11 is a partial side elevation view of th upper end of the min roof bolt of Fig. 8 4**4 *o 4 *oooo o and incorporating the resin protector cap of Fig. 10, shown positioned in a mine roof bore hole prior to puncturing the resin cartridge.

Fig. 12 is a side elevation view of a plastic hex-head cap sleeve for use with an embodiment of a mine roof bolt of the present invention.

Fig. 13 is a top view of the plastic hex-head cap sleeve, taken along lines 13-13 in Fig. 12.

Fig. 14 is a side elevation view of a number of mine roof bolts installed in bore holes in a mine tunnel roof, illustrating the concept of the wire interconnecting the plastic hex-head cap sleeves of adjacent mine roof bolts.

Fig. 15 is a side elevation view of an embodiment of a mine roof S- bolt of my divisional application, illustrating the yieldable concept of the mine roof bolt.

DESCRIPTION OF THE PREFERRED EMBODIMENT

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15 Referring now to the drawings, and initially to Fig. 1, the mine roof bolt of an embodiment of the invention of my patent 661763 is shown, generally illustrated by the numeral 10. The mine roof bolt 10 comprises a shank 12 made up of a length of pre-tensioned steel stranded cabis, which in the embodiment shown, is made up of six peripheral pre-tensioned steel 20 strands 14 spirally wrapped a 0 12 around a central steel strand 16 (more clearly shown in Fig. 2).

At one end of the steel stranded cable is affixed a two-piece tapered plug 20 which comprises two identical diametrically opposed essentially half-cylinders that define the outer surface of a right conical frustum. The frusto-conical outer surface 22 of the two-piece tapered plug 20 is designed to engage a mating inside funnel surface of an internally tapered hexagonal head collar O 26. Although the collar 26 is shown as a hexagonal head, obviously a square head or any other shaped head that accepts a mine roof bolt driver mechanism and boom should function adequately for the intended purpose.

Fig. 2 is an end view of the mine roof bolt of Fig.

oeooo S 1 5 1, and illustrates how the two-piece tapered plug fits S. concentrically around the pre-tensioned steel cable shank of the bolt, and also nests concentrically within the internally tapered hexagonal head collar 26. Note that the individual sections of the two-piece tapered plug are not fully semi-frusto-conical. When functionally positioned within the hexagonalA/4 collar 26 and around the steel cable shank 12, the two individual plug sections 20 define a diametric space 28 between the two plug ::sections to enable the plug sections to be urged together .5 tightly when pressed against the steel stranded cable.

13 Fig. 3 is a perspective view of one section of the two-piece tapered plug 20, and more clearly shows a series of serrations or knurls 30 that define the inner essentially semi-tubular surface of the tapered plug.

These serrations 30 are designed to "bite" into the steel cable defining the roof bolt shank 12 as the two-piece tapered plug 20 is urged further into the hexagonal head collar 26 to define the rigid hex-head of the impruved mine roof bolt.

O Creating this rigid hex-head on the mine roof bolt can be accomplished in either of two ways: By pressing the two-piece tapered plug 20 and steel cable shank 12 into the hexagonal head collar 26 as the mine roof bolt is factory-manufactures; or After having cut the steel cable to the desired length at the mine site, assembling the steel cable, two-piece tapered plug 20, and hexagonal head collar 26, and then tensioning the steel cable against the hexagonal head collar, or otherwise pressing the tapered plug and cable into the collar. In either aO instance, the "head" of the mine roof bolt 10 should be i rigiLd and secure sufficiently to remain intact as the mine oo.ooi S" roof bolt is being inserted into the bore hole, forced up into the bore hole against the resin cartridge(s), and rotated or spun within the bore hole in order to rupture the resin cartridge(s) and mix and distribute the resin adhesive material.

14 Fig. 4 is a perspective view of one section of an alternative embodiment of the two-piece tapered plug, shown at 32. This alternative embodiment tapered plug includes a different type of knurl 34 formed in a diamond pattern resulting from diagonally oriented serrations.

Those skilled in the art will appreciate that this diamond pattern knurl will better retain the tapered plug 32 on the steel cable against both torsion as the improved mine roof bolt 10 is rotated during installation, and against tension as the bolt remains in place within mine roof rock formation to retain the rock formation in place.

Fig. 5 illustrates the mine roof bolt of Fig. 1 and its arrangement as inserted up into a mine tunnel roof bore hole. Assuming that the mine roof bolt has 5 previously been assembled as shown in Fig. i, and the two-piece tapered plug 20 has been pressed into the hexagonal head collar 26 to define a rigid bolt head, the user first places a spherical washer 40 having a partial spherical .urface 42 over the bolt shank and down against ao.. O the hexagonal head collar 26, as shown. Next, the user slips on a dome mine roof plate 44, the through-hol o' S•the roof plate having an angled surface 46 that mates with the partial spherical surface 42 of the spherical washer 0"40.

.n 15 Those skilled in the art will appreciate that this spherical washer 40 and the angled surface 46 of the dome mine roof plate 44 define a "ball and socket" -like arrangement that permits ^te-hoiPmee mine roof bolt and cAoiee mine roof plate to be used in mine tunnel roofs wherein the bore holes are angled or otherwise not normal to the surface of the mine ceiling 48, the mine ceiling surfaces are extremely rough or otherwise uneven, or a combination of and that results in the O0 entrance to the mine roof bore hole not being exactly normal to the mine ceiling surface at the location of the bore hole. Additionally, such an arrangement permits the mine roof bolt 10 to shift slightly as the rock formation above shifts, and still maintain an essentially uniform 15 force distribution against the dome mine roof plate 44.

cx oA-errxoAi<J&e oorrc-rvm eA To this end,Athe inventor has dotgOrle4n-t ha.t, -nam~u;s y, the hexagonal head 26 of the mine roof bolt and the spherical washer 40 may be formed as a single piece. This simplifies installation and more easily 5O maintains the mine roof bolt in alignment with the roof plate during insertion and rotation of the mine roof bolt in the roof bore hole.

ro 16- The spherical washer 40 and dome mine roof plate 44 having been installed on the mine roof bolt 10, the user then inserts a resin cartridge 50 into the bore hole 38, followed by tM mine roof bolt of the present invention.

The user then forces the bolt 1 upwardly into the bore hole 38 under the force of the bolter boom (not shown), while simultaneously rotating the bolt to rupture the resin cartridge 50 and thoroughly mix and distribute the resin adhesive material contained therein. Continued j1O rotation of the mine roof bolt 10 after the dome mine roof plate 44 has been urged up against the mine tunnel ceiling 48, further mixes and distributes the resin adhesive material within the annulus between the steel cable and the mine roof bore hold 38, a.nd causes the resin 5 adhesive material to be forced into the cracks and crevices within the rock formation, and also into the crevices and spaces between the ii1ividual peripheral steel strands 14 of the steel cable. After the resin adhesive material is thoroughly mixed, the assembled bolt 2. is held in place against the mine ceiling 48 as shown in Fig. 6, by the boom, for a period of time sufficient to S°permit the resin to cure.

.eoe.r Fig. 7 is a graph of tensile strength vs. elongation o *for a 9/16 inch diameter cable mine roof bolt of Fig. 1.

When pulled in -17tension until fracture, the mine roof bolt begins to yield at approximately 57,000 pounds of force, and will withstand over 60,00 pounds of force before fracturing.

As the graph of Fig. 7 illustrates, in testing, the fracture of the seven-strand cable mine roof bolt actually occurs in a stepped progression, rather than all at once. Typically, one, two, or three individual cable strands will fail at approximately 60,000 pounds, the remaining four, five, or six strands remaining intact to continue to support the rock formation above the mine roof.

These remaining four to six strands will continue to :o oI withstand from 25,000 to 35,000O pounds of force ee*O 15 before the next set of one, two, or three strands fails in tension. The steel cable strands remaining intact after the second set of strands fails (from one to four) will continue to withstand approximately 35,000 pounds of force before ultimate total failure 20 of the mine roof bolt.

By comparison, a convential 5/8 inch diameter smooth shank mine roof bolt will fail at under approximately 30,000 pounds of force, approximately one-half of the maximum force of approximately 60,000 pounds that a 9/16 inch diameter cable mine roof bolt will withstand before the initial partial failure.

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18 It is important to note that when the 9/16 inch cable mine roof bolt "fails" at 60,000 pounds, its failure is only partial, in that four to six steel strands remind intact through the first "stepped failure". Therefore, the mine roof bolt of, say, Fig. 1 remains intact after initial "failure" to continue to support the rock formation to permiit the rock formation to stabilize with the bolt intact and is still able to withstand approximately 30,000 pounds of force before a subsequent "failure" occurs.

The inventor has also determined in testing, that the multi-strand cable defining the shank of a mine roof bolt as depicted in Fig. 1 fractures adjacent the point of attachment to the two-piece tapered plug, leaving 5 essentially the total length of the steel cable shank remaining in the mine roof bolt bore hold to continue to support the rock formation. This is to be contrasted with conventional mine roof bolts formed of shank sections collared together that generally fracture either at or adjacent a collar. In the event the collar has prevented complete resin return alon 3 the total length of the bolt i section(s), that portion of the mine roof bolt below the eeee..

fracture, if not resin-bonded into the rock formation, is rendered totally ineffective asstructural support, and a5 possibly will even fall out of the bore hole.

19 This aspect of the mine roof bolt permits it to better withstand rock formation lateral movement, in that the cable mine roof bolt will not fracture along the shank or coupler (there is no coupler), but will fracture adjacent the hexagonal head, and will remain intact along essentially its total length of the shank within the bore hole, even following a partial "stepped fracture".

Fig. 8 illustrates a number of alternative embodiments in a mine roof bolt of the present invention, generally illustrated at 60. As in the Figs. 1-7, the mine roof bolt 60 comprises a shank 12 of a length of multi-strand steel cable, which conventionally is made up of six peripheral steel strands 14 spirally wrapped around a central steel strand 16.

ooolo 15 At one end of the stranded steel cable is affixed the two-piece tapered plug 20, which comprises the two identical diametrically opposed tapered semi-cylinders that define the outer surface of a right conical frustum.

The hexagonal head collar 26 is pressed down upon and V. a O around the two-piece tapered plug 20 to define the a. 0 C. C hexagonal bolt head.

ease*: e a e C C Coe C CoC 20 The mine roof bolt 60 includes a number of alternative embodiments that function to enhance its ability to be retained within the bore hole, and therefore to support the rock formation. The first of these b retention enhancements exemplifies an embodiment mine roof bolt of this invention, and comprises one or more sleeves or "buttons" 62 attached to the bolt shank 12 at various points along the cable. These cable buttons 62 take the form of steel cylinders that are swaged down upon the bolt lo shank cable 12. In one embodiment, the steel cylinder has initial dimensions of one inch outside diareter, 5/8 inch inside diameter and one and 1/2 inches in length. When this cylinder is swaged down upon a 0.600 diameter stranded steel cable with 500 tons of force, it deforms down into the interstices between the individual peripheral steel strands of the shank cable, and is transformed into the cylindrical button 62 having a 7/8 inch outside diameter and a length of approximately two inches.

O The steel cylinder that becomes the cable shank button 62 is swaged onto the cable by a piston-ram swaging .evice (not-shown). The swaging device has a stationary semi-cylindrical die mounted on the ram piston for swaging "the steel cylinder onto the cable in diametrical fashion.

As a practical matter, the -21two semi-cylindrical dies are not 100% completely semi-cylindrical. The result is that, when the steel cylinder is swaged onto the shank cable, swaging causes some of the cylinder material to be forced radially outwardly between the dies, forming two diametrically aligned ears or fins 64 that are subsequently trimmed down to a symmetric diammetric distance that corresponds to the inside diameter of the mine roof bore hole. This is best shown in Fig.

9. For example, the previously described steel cylinder that is swaged down to a 7/8 outside diameter and two inch long button 62 would have fins 64 approximately 1/32 inch thick and 1/16 inch long (radial dLnension) for use in a one inch diameter 15 bore hole. Likewise, the buttons, including the 15 fins, can be made to any outside diameter to accommodate the particular bore hole size. These :'".fins 64 serve to center the bolt shank 12 within the bore hole, and also aid in puncturing the resin cartridge 50 and mixing the resin adhesive within the bore hole as the bolt is being rotated and inserted into the bore hole.

It still may be possible that swaging the buttons 62 onto the cable with 500 tons of force would not totally prevent a button from slipping along the cable under extreme tension, as when the supported rock formation shifts. To minimize the 22 possibility of this happening, shallow threads (not shown) may be cut into the cable at locations where buttons are to be swaged. Swaging the buttons onto these "threaded" areas of the bolt shank cable forces the button material into these threads to minimize, if not totally prevent, any axial movement of the buttons along the cable. As an added measure, the cylinders that become buttons may also be formed with internal threads (not shown) that can easily align with the shallow cable threads as the buttons are being swaged onto the cable. This insures optimum grip between the buttons and the cable.

Once the resin adhesive has been thoroughly mixed and has set within the bore hole, the buttons 62 are surrounded by hardened resin, and it is then virtually impossible to retract the mine roof bolt from the bore hole. This is because the resin has worked itself into cracks and crevices within the rock formation in the bore hole, and has also surrounded each of the buttons 62 along the length of the bolt shank cable, forming a 1 O barrier of solid resin around and below the button and into the rock formation.

Fig. 8 also illustrates a second embodiment of the mine roof bolt of the present invention that can be used either by itself or in conjunction with one or more of the buttons 62 along the shank of the bolt in accord with an embodiment of this invention. Specifically, the second embodiment bolt includes a dam 66 mounted on the bolt shank 12.

A preferred and simple construction of this dam 66 takes the form of a plastic or rubber washer of the appropriate outside diameter inch in a 1inch diameter bore hole, for example), and an inside diameter appropriate to enable the washer 66 to fit snugly around the bolt shank 12. A washer 66 of approximately 1/4 inch thick is appropriate to achieve its intended function, that being to retain the mixed liquid resin adhesive within the bore hole along the entire length of the bolt shank above the dam in order to improve the forcing of the resin adhesive into the cracks and crevices of the rock formation within the bore hole, and into the interstices between the individual steel strands of the shank cable, in order to optimise the resin's ability to adhere to both the bolt shank and the bore hole rock formation. A second function of the dam 66 is to ensure a uniform consistency of the 15 resin adhesive along the entire length of the imiine roof bolt shank 12 above the dam, with no air pockets, voids, or other nonuniform areas within the annulus between the bolt shank and the bore hole, The inventor has determined that a preferred manner of retaining the dam 66 in the appropriate functional position along the bolt 20 shank 12 is to utilise a conventional screw-type compression clamp 68 secured tightly to the shank cable at the appropriate location to prevent the dam 66 from slipping downwardly along the bolt shank either as the bolt is being inserted into the mine roof bore hole or as the resin adhesive is being mixed and "returning" downwardly in the annulus between the bolt shank and the bore hole wall under the force of the bolt's being inserted into the bore hole.

Fig. 8 illustrates yet a third alternative embodiment of a mine roof bolt of the present invention. This third embodiment incorporates the use of a stiffener sleeve 70, which takes the form of a metal pipe or cylinder in conjunction with slip prevention means of the present invention. The stiffener sleeve has an inside diameter slightly larger than the outside diameter of th cable (a 5/3 inch inside diameter for a .600 diameter cable, •L "for example), and an outside diameter that is essentially the same as the S. diameter of the bore hole (one inch O.D, or one and 3/8 inches for 15 example. Such an outside diameter the same as the diameter of the bore hole works quite well, inasmuch as, as a practical matter, the actual diameter of the bore hole is generally slightly larger than the indxmd'ted drill S: bit diameter, due to drill bit wobble, etc. The particular outside diameter of the stiffener sleeve 70 also permits the 9 1 sleeve to fit inside the spherical washer 40 and directly against the hexagonal head collar 26.

As those skilled in the art can appreciate, the purpose of the stiffner sleeve 70 is two-fold.

As a stiffner, it prevents the shank cable 12 from buckling as the cable bolt is being inserted into the bore hole, and as the blind end of the shank 12 "bottoms out" against the resin cartridges (not shown in Fig. It should be appreciated that, as the blind end of the bolt shank 12 engages the resin cartridge(s), additional linear force is necessary for further inserting the bolt into the bore hole :against the resistance provided by the resin cartridge(s). But for the stiffner sleeve 70, the 15 bolt shank cable 12 could tend to buckle due to this additional linear force.

The second~~spe of the stiffner sleeve isthat it i a "sleeve" around the shank cable that protects the shank cable from abrasive wear from the dome mine roof plate 44 as the cable bolt is rotated and spun during insertion into the bore hole. It can be appreciated that, but for the stiffner sleeve spinning the bolt into the bore hole with the mine roof plate 44 loose causes the inside edge 46 of the mine roof plate to cut and wear into the outer surface of the peripheral steel strands 14 at the location on the shank cable where the mine roof plate -26- "rides" as the bolt is being spun and inserted into the bore hole.

The inventor has determined that the length of the stiffner sleeve 70 can be anywhere from a minimum of approximately six inches to any desired functional length, typically 10 feet or more. This maximum length, of course, is relative to the overall mine roof bolt length, and may also be in par.

dictated by the amount (total length of cartcidzes) of resin adhesive inserted into the bore hole ahead of the mine roof bolt.

Fig. 10 illustrates a shouldered resin protector plastic cap 72 that functions to (1) protect the resin cartridge from premature rupture as 15 the blind end of the mine roof bolt is being utilized to insert and otherwise "ram" the resin cartridge into the bore hole, and retain the resin cartridge in the blind end of the bore hole, as when subsequent resin cartridges are inserted into the bore hole sequentially.

As shown in Fig 10, the shoulderL_ resin protector cap 72 takes the form of a closed plastic cup that is sized to fit snugly on the end of the bolt shank cable. The resin protector cap 72 includes a cylindrical thin wall 74 having a closed end 76 that enables the resin protector cap to fit snugly on the end of the bolt shank cable. The -27protector cap 72 includes an annular shoulder 78 that is dimensioned to be slightly larger than the inside diameter of the bore hole.

When the resin protector cap 72 is inserted into the bore hole, the annual shoulder 78 is forced downwardly and functions as a one-way mechanism to permit the cap to travel only in one direction (up as shown in Figs. 10 and 11), while essentially preventing movement in the opposite direction (down in the drawings). In this manner, when the resin protector cap 72 is placed on the end of the mine roof bolt shank 12 as shown in Fig. 11, and this combination (bolt shank and resin protector cap) is 9*ee used to insert and urge a resin cartridge 50 up into 15 the blind end of the bore hole, it should be apparent that the resin protector cap will remain in place and retain the resin cartridge in place within the bore hole after the bolt i" withdrawn from the bore hole.

Therefore, the mine roof bolt can be utilized as a 20 plunging device to insert a plurality of resin n eeee cartridges into the bore hole in sequential fashion, each being protected from the sharp edges of the shank cable by the resin protector cap 72, then each 9 9 being subsequently retained in position within the blind end of the bore hole by its own resin protector cap, and therefore prevented by the action of the -28downward direction of the annular shoulder 78 from slipping downwardly within the hole.

Figs. 12 and 13 illustrate a hex-head cap sleeve 80 for use with a plurality of mine roof bolts of the present invention. As shown, the hex-head cap sleeve 80 comprises a hollow, blind hex-shaped closed wall "cylinder" 82 that is dimensioned to fit snugly over the hexagonal head collar 26 of the mine roof bolt. In a preferred embodiment, the closed wall cylinder 82 is approximately 1/4 inch thick, as is •coo Sthe end section that defines the blind end 84.

A 1/4 inch thick semi-circular wing 86 is formed with the outer edge of the blind end 84 of the cap sleeve, diametrically as shown in Figs. 12 and 13. This semi-circular wing 86 includes a through hole 88, for use in indirectly attaching a plurality 00*000 of hex-head cap sleeves together, as will be explained in greater detail hereinbelow with *°reference to Fig. 14.

00** Even though the cable mine roof bolt of the present invention is considerably stronger than a prior art solid steel shank bolt of comparable diameter, the cable mine roof bolt can eventually fail under sufficient force. When these cable bolts have actually failed in testing, failure of the cable shank has almost always been relatively close to the hexagonal head collar 26 where there is little or no -29resin adhesive. Almost consistantly, these cable mine roof bolts have failed in a stepped fashion, as illustrated in Fig. 7, and therefore, are generally retained in the bore hole by the cable strands remaining intact. Occasionally, however, the bolt shank fractures totally at once. When this occurs in a mine tunnel, the broken end of the bolt frequently falls out of the bore hole to the tunnel floor, where it becomes an obstacle to men and equipment. And 10 occasionally when the bolt fails in total, the tapered plug "pops" loose from the hexagonal head collar and cable, both the plug sections and collar separating from the cable, further complicating the situation.

oooeI 15 With this background in mind, Fig. 14 illustrates a plurality of mine roof bolts interconnected in functional position within a mine roof. Each of the bolt hexagonal head collars 26 has affixed thereon a hex-head cap sleeve 80. A suitably strength steel wire 90 is passed through the through holes 88 of each hex-head cap sleeve in a manner to interconnect the cap sleeves, and therefore the hexagonal head collars 26 of adjacent mine roof bolts in order to retain the broken bolt within the bore hole, and thereby, prevent or at least minimize the detrimental effect of the broken cable bolt's falling to the tunnel floor when it breaks.

I

Those skilled in the art will readily appreciate that a plurality of mine roof bolts can be interconnected with a suitable steel wire 90 in continuous patterns that insure that all hex-head cap sleeves 80 are interconnected to at least two adjacent mine roof bolts, so that in the event any bolt within the pattern breaks, the fractured section of broken bolt will be constrained to movemenit limited by the taughtness of the interconnecting wire 10 90 and the broken bolt's proximity to the two adjacent interconnecting bolts within the wire pattern.

As one can appreciate, a downward force at the location of any mine roof bolt results in 15 essentially only a lateral force at each of the adjacent bolt hex-head cap sleeves 80, and only a ~lateral force at each of the remaining hex-head cap sleeves. Because of these lateral only forces, the inventor has determined that it is extremely unlikely that a broken mine roof bolt's falling out of the bore hole would cause the hex-head cap sleeves 80 of adjacent bolts to be pulled off of their respective bolt heads. This is because the force necessary to remove a hex-head cap sleeve 80 from a hexagonal bolt head collar should be axial, and that the forces created by the broken bolt are essentially transverse, thereby effectively operating to "bind" 31 the hex-head cap sleeve 80 more tightly onto its corresponding hexagonal head collar-26.

Fig. 15 illustrates embodiment of o mine nuer~n on y dVV(%iC&C,( CkpAVcAoXv roof bolt of theA.prE-ont -inventi n. The mine roof bolt of Fig. 15 is what is called in the industry a yieldable bolt, in that it is designed to slip or "yield" within the bore hole under substantial force, rather than fail and end up supporting nothing. In some mine roof bolting systems, it is possible for each mine roof bolt to slip 10 within the bore hole a certain amount. This slippage may be either between the bolt shank 12 and the resin adhesive surrounding the shank, or may be between the resin adhesive and the interior wall of the bore hole. In either event, the retaining force of the resin adhesive 15 against the bolt shank is a direct function of the length of direct attachment of the resin adhesive with the bolt i shank. Therefore, as the bolt shank slips out of the resin adhesive, this length of direct attachment is decreased, and the retaining force of the resin adhesive O within the bore hole to retain the bolt shank decreases directly in proportion. For example, assume that a ten foot mine roof bolt is completely surrounded by harder2d resin adhesive. In the event that shifting in the rock formation causes the bolt to "slip" downwardly one foot, the result is that only nine feet of the 32 ten foot bolt shank would now be retained in the resin adhesive within the bore hole, resulting in only 90% of the original resin adhesive bonding force retaining the bolt shank in the bore hole.

SIt would be preferable to utilize a mine roof bo-t that maintained a consistent resistance force along the entire ten foot length of the bolt shank, even after the bolt had "slipped" within the bore hole and otherwise out of the bore hole by a small amount. This fourth :oo i O embodiment of Fig. 15 accomplishes this result by in effect "extending" the length of the bolt shank into an .area in which the bolt shank is not bonded to the resin adhesive along the "extended" portion of the bolt shank.

This is accomplished by covering the extended end of the i. bolt shank with a material that prevents the resin adhesive from bonding to the "extended" end of the bolt i shank, so that the distance along the bolt shank that is in actual and continuous contact with the resin adhesive remains the same, even as the bolt "slips" relative to the e* J bO resin adhesive within the bore hole.

This concept is explained with reference to Fig. A bore hole is drilled to a depth of X. A mine roof bolt of this same length, X, includes a cover material 92 that covers the blind end of the bolt shank 12 down for a distance of approximately 33 two feet from the end of the shank. This particular structure of Fig. 15 also includes a stiffner sleeve that is four feet in length. Therefore, as shown in Fig.

the length of exposed shank cable 12 is Y X 6 feet. This distance, Y, is the length of shank cable that will have the resin adhesive tightly fitted into the annulus around the bolt shank and into the rock formation for resin-bonding the mine roof bolt in the bore hole.

Although the two foot length of bolt shank at the blind 1O end will also have resin adhesive material forced into the annulus therearound, the cover material 92 prevents the

O

*resin adhesive from bonding to the very end two foot section of the bolt shank. As the mine roof bolt "siips" out of the bore hole, the gripping length, Y, of the bolt -15 shank 12 in the resin material remains the same, even e* though the bolt "slips" up to a maximum of two feet within the bore hole. In this manner, this "yieldable concept" of the mine roof bolt of the present invention permits the bolt to "yield" within the bore hole a certain O20 specified amount while maintaining constant the resistance force that retains the bolt within the bore hole.

It should now be apparent to those skilled in the art that a mine roof bolt of the a6pacts of the present invention, not utilizing mine roof bolt shank couplers, does not require an overly large bore hole -34in the mine tunnel roof. Therefore, less potential damage is done to the structural integrity of the rock formation above the mine tunnel. Additionally, less resin adhesive i& required in the bore hole, and therefore the resin that is in the bore hole is more effective. Also, the improved mine roof bolt, not utilizing bolt shank couplers, does not have the problem of bolt or coupler fracture when the mine roof rock formation shifts.

0 The improved mine roof bolt, not utilizing bolt shank couplers, facilitates complete mixture of the resin material and complete distribution of the resin material along the total length of the mine *a %.Go roof bolt shank and mine roof bore hole wall, if desired.

Inasmuch as the improved mine roof bolt of the present invention is constructed of a *.*.multi-strand cable rather than a solid shank, the mine roof bolt will bend sufficiently to follow the path of an irregular bore hole. The multi-strand, flexible cable mine roof bolt can also be bent to facilitate installation into a bore hole that requires a roof bolt that is considerably longer than the height of the mine tunnel at the location of the bore hole, and will also bend rather than break, when the mine roof rock formation shifts.

35 From the foregoing it will be seen that the various aspects of this invention are well adapted to attain their respective ends and objectives herein set forth, together with other advantages which are obvious and which are inherent to the apparatus. It will be understood that certain features and subcombinations are of utility and may be employed with reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. As many possible embodiments may O be made of the invention without departing from the scope of the claims. It is to be understood that all matter herein set forth or shown in the accompanying drawings is 0 to be interpreted as illustrative and not in a limiting sense.

o

Claims (21)

1. A mine roof bolt comprising: a length of multi-strand cable defining a bolt shank; a tapered plug comprising a body portion having an internal bore and a frusto-conical outer surface essentially concentric with said internal bore, said tapered plug being mounted about an end of said cable at said internal bore; an internally tapered drive collar having a frusto-conica! inner surface thai engages said frusto-conical outer surface of said tapered plug, and having an outer surface defining a drive head that accepts a driving mechanism for rotating and linearl) translating said bolt, wherein said tapered plug is mounted on an end of said cable, and said drive collar is pressed down upon said tapered plug, forcing said tapered plug against said cable, such that said drive collar, said tapered plug, and said cable, when fitted tightly together, define said mine roof bolt; and slip prevention means for preventing said multi-strand cable from slipping I b relative to resin adhesive material within a bore hole.

S.2. A mine roof bolt as set forth in claim 1, wherein said multi-strand cable comprises S: a plurality of steel strands spirally wrapped around a central steel strand.

3. A mine roof bolt as set forth in claim 1, wherein said tapered plug comprises two essentially diametrically opposed semi-frusto-conical tapered plug sections. 20

4. A mine roof bolt as set forth in claim 3, wherein each of said tapered plug sections includes a serrated internal bore defining a knurled semi-tubular surface.

A mine roof bolt as set forth in claim 4, wherein the serrations of said serrated internal bore are circumferential.

6. A mine roof bolt as set forth in claim 4, wherein the serrations of said serrated internal bore are angular, defining a diamond pattern.

7. A mine roof bolt as set forth in claim 1, wherein said outer surface of said drive collar defines a hexagonal head essentially concentric with said frusto-conical inner surface. 37

8. A mine roof bolt as set forth in claim 1, wherein said drive collar includes a semi-spherical washer surface on one end thereof.

9. A mine roof bolt as set forth in claim 1, wherein said slip prevention means comprises a sleeve mounted onto said cable.

10. A mine roof bolt as set forth in c'aim 10, wherein said sleeve is swaged onto said cable.

11. A mine roof bolt as set forth in claim 10, wherein said sleeve includes outwardly projecting fins for centering said cable within the bore hole and for puncturing resin adhesive cartridges.

12. A mine roof bolt as set forth in claim 11, wherein said fins extend radially from said sleeve. 1

13. A mine roof bolt as set forth in claim 11, wherein said fins are oriented axially relative to said sleeve. Ol:

;14. A mine roof bolt as set forth in claim 13, wherein said sleeve is cylindrical and wherein said fins are oriented across the diameter of said sleeve.

A mine roof bolt as set forth in claim 1, further comprising a dam for maximizing :the amount of resin adhesive that is concentrated within the blind end of the bore hole around said multi-strand cable.

16. A mine roof bolt as set forth in claim 15, wherein said dam comprises a washer 20 dimensioned to fit tightly around said multi-strand cable and into the bore hole.

17. A mine roof bolt as set forth in claim 15, further comprising stop means for retaining said dam in a predetermirind location on said cable.

18. A mine roof bolt as set forth in claim 17, wherein said stop means is adjustable.

19. A mine roof bolt comprising: a length of multi-strand cable defining a bolt shaft; a tapered wedge comprising a body portion having an internal bore and a frusto-conical outer surface essentially concentric with the internal bore, the tapered wedge being mounted adjacent an end of the cable at the internal bore; a collar having a tapered internal bore that engages the frusto-conical outer surface of the tapered wedge, wherein the tapered wedge is mounted adjacent an end of the cable, and the collar is pressed down upon the tapered wedge, forcing the tapered wedge against the cable, such that the collar and tapered wedge, when fitted tightly together on the cable, define a bolt head of the mine roof bolt, said bolt hea '-ecluding drive means that accept a driving mechanism for rotating and linearly tran '.lhu' Ae mine roof bolt; and slip prevention means for preventing said multi-strand cable from slipping relative to resin adhesive material within a bore hole.

20. A cable bolt comprising- a length of multi-strand cable defining a bolt shaft; a tapered wedge comprising a body portion having an internal bore and a frusto-conical outer slrface essentially concentric with the internal bore, the tapered ,I wedge being mounted adjacent an end of the cable at the internal bore; a collar having a tapered internal bore that engages the frusto-conical outer surface of the tapered vedge, wherein the tapered wedge is mounted adjacent an end of the cable, and the collar is pressed down upon the tapered wedge, forcing the tapered wedge against the cable, such that the collar and tapered wedge, when fitted tightly 1: together on the cable, define a thrust bushing on the cable for receiving thrust 20 compressive forces when the cable bolt is in tension; a drive mechanism attached to the cable to facilitate rotating and linearly translating the cable bolt; and slip prevention means for preventing said multi-strand cable from slipping relative to resin adhesive material within a bore hole. 39

21. A cable bolt comprising: a length of multi-strand cable defining a bolt shaft; a tapered wedge comprising a body portion having an internal bore and a frusto-conical outer surface essentially concentric with the internal bore, the tapered wedge being mounted adjacent an end of the cable at the internal bore: a collar having a tapered internal bore that engages the frusto-conical outer surface of the tapered wedge, wherein the tapered wedge is mounted adjacent an end of the cable, and the collar is pressed down upon the tapered wedge, forcing the tapered wedge against the cable, such S:"that the collar and tapered wedge, when fitted tightly together on the cable, define a thrust bushing on the cable for receiving thrust compressive forces Swhen the cable bolt is in tension; a drive mechanism attached to the cable to facilitate rotating and linearly translating the cable bolt; and slip prevention means for preventing said multi-strand cable from slipping relative to resin adhesive material within a bore hole. S22. A mine roof bolt as hereinbefore described with reference to Figs 8-11 or 15 or the accompanying drawings. *o DATED this 15th day of April 1996 HARVEY D GILLESPIE Patent Attorneys for the Applicant: F.B. RICE CO,. ABSTRACT A passive-type mine roof bolt is constructed of multi-strand steel cable. The bolt head is constructed of a hexagonalor other drive-headed collar having an internally tapered funnel-shaped bore therethrough, and a tapered plug having a frusto-conical outer surface that engages the funnel-shaped inner surface of the drive collar. The tapered plug has an internal bore essentially concentric with the outer frusto-conical surface, and is ego.ei adapted to fit over the steel cable, the hexagonal head drive collar fitting over the tapered plug such that pressing the tapered plug and steel cable into the inner funnel-shaped bore of the hexagonal-head drive collar causes serrations on the internal bore of the tapered plug to be urged down against, and bite into, the steel cable, resulting in a rigid hexagonal head for the cable bolt. The tapered plug is in actuality, a pair of essentially identical diametrically opposed semi-frusto-conical tapered sections that more easily compress together to bite into the multi-strand steel cable. A number of alternative aspects enhance the bolts retention strength in the bore hole to aid in stabilizing the rock formation.