US3306051A

US3306051A - Rock bolt

Info

Publication number: US3306051A
Application number: US343741A
Authority: US
Inventors: George H Howlett
Original assignee: HOWLETT MACHINE WORKS
Current assignee: HOWLETT MACHINE WORKS
Priority date: 1964-02-10
Filing date: 1964-02-10
Publication date: 1967-02-28
Anticipated expiration: 1984-02-28
Also published as: GB1055841A

Description

Feb. 28, 1967 e. H. HOWLETT 3,306,051

ROCK BOLT Filed Feb. 10, 1964 2 Sheets-Sheet 1 INVENTOR GEORGE H. HOWLETT Feb. 28, 1967 e. H. HOWLETT ROCK BOLT 2 Sheets-Sheet 2 Filed Feb. 10, 1964 T T E L W 0.. H H E G R O E G llnited States Patent fifice idfidfiz'il Patented Feb. 28, 1967 3,396,051 RGCK BOLT George H. Howlett, %!21111, Calif., assignor to Hewlett Machine W orl is, a corporation of California Filed Feb. 10, 1964, Ser. No. 343,741 6 Claims. (6!. 61-45) This invention relates generally to devices for providing an anchorage in rock mother earth matter, and more particularly is directed to a rock bolt which is to be sealed from contact with air by a grout substance enclosing the bolt. I

In the construction of tunnels, mine shafts, and the like, it is a well known technique to install rock bolts in the earth extending generally radially to the tunnel in order to assist in supporting the walls thereof. The inner ends of the rock bolts are anchored in the earth, and p ates are secured to the other end of the bolt at the tunnel. The bolt is then placed under tension to support the rock and earth from caving in around the tunnel.

One conventional procedure for installing rock bolts has been to drill an oversized bore into the earth for a predetermined distance, after which the rock bolt is loosely inserted into the here with an anchoring device mounted on its inner end. After the anchor and wall plate are properly positioned, the bolt is placed under tension. Because rock bolts must provide structural support for long periods of time, it is desirable to prevent rusting and deterioration by enclosing the bolt in a concrete grout, thereby preventing contact with the air that otherwise occupies the annular space in the bore surrounding the bolt.

Heretofore, one manner of grouting rock bolts has been to use a bolt formed of tubular construction having a central passageway extending the length of the bolt. A feed tube is inserted into the annular space between the bolt and the bore wall at the outer end of the bore, whereby grout can be passed into this space to fill it from the bottom up. As the grout rises in the annular space, the air formerly in this space is displaced into the inner opening of the aforesaid central passageway, thus releasing it into the atmosphere at the outer end of the bolt. Grout is fed into the bore until it is seen to emerge from the passageway, thus indicating complete evacuation of the bore. In some instances, where the bore and bolt extend downwardly from the surface to be supported the grout can be introduced into the bore through the central passageway so that the bore again will be filled with grout from the bottom up. The air in the latter instance is vented to the atmosphere directly from the annular space rather than through the passageway in the bolt.

The provision of a longitudinal passageway within a rock bolt for venting the bore or feeding grout into the bore has been well known in the art for many years. The only structure heretofore used for providing such passageway, however, has been ordinary tubular steel, this having been considered the simplest and most expedient rock bolt configuration.

The present invention departs from the prior tubular construction, and instead provides the desired passageway by means of an external groove formed in the periphery of the rock bolt. It has been found that by using appropriately configured rollers at the steel mill,

rod or bar stock can be formed with a longitudinal peripheral groove in the same manner as ordinary solid cylindrical stock, at only a nominal added cost. The cost of solid steel stock, however, and accordingly that of the instant grooved stock, is significantly less than that of conventional tubular stock. As compared to the relatively simple high speed rolling process for making solid stock, manufacture of tubular stock mustinvolve a step of piercing the stock either [before or, after rolling, or of welding a seam if the tubular stock is formed from flat sheets.

With the grooved solid core rock bolt, a passageway can be formed in the groove by one of two general means. Either an inexpensive tubular conduit can be disposed and secured in the groove, or a strip of material can be positioned in overlying relation to the groove to define the passageway between the strip and the groove walls. Although the total cost of a rock bolt formed with a passageway disposed Within a peripheral groove is much less than that of conventional tubular stock, there is no difference in tensile strength, reliability, or any other functional characteristics. Furthermore, more than one peripheral groove can be provided as opposed to the single passageway of tubular stock, whereby additional advantages can be achieved with multiple passageways.

Accordingly, an important object of the present invention is to provide a rock bolt having all the advantages and functions of a conventional tubular configuration, but which can be manufactured at a significant reduction in cost as compared to the conventional structure.

Another object of the present invention is to provide an improved method of grouting rock bolts which significantly reduces the cost of this process as compared to conventional techniques. 1

A further object of the present invention-is to pro vide. a rock bolt having multiple passageways whereby concrete grout can be used to anchor a rock bolt in place of conventional mechanical leverage anchoring devices and to provide for successively anchoring and grouting selective portions of the length of the bolt for coordinated prestressing and grouting of the bolt where this procedure is desired.

Still another object of the present invention is to provide a rock bolt which greatly facilitatesthe introduction of grout into the annular space surrounding the bolt When positioned in a bore. a

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of the preferred form of the invention which is illustrated in the drawing accompanying and forming part of the specification. It is understood, however, that variations in the showing made by said drawing and description may be adopted within the scope of the invention as set forth in the claims. 1

Referring to said drawings (2 sheets):

FIGURE 1 is a cross sectional view of a typical tunnel having a plurality of rock bolts installed therein.

.FIGURE 2 is a side elevation of a rock bolt constructed in accordance with the present invention. 7

FIGURE 3 is a side elevation on an enlarged scale of the rock bolt illustrated in FIGURE 2 and with portions of the view broken away and shown in section. l

FIGURE 4 is a cross sectional view of the rock bolt taken substantially on the plane of line 44 of FIG- U'RE 3.

FIGURE 5 is a perspective view of a portion of the rock bolt.

FIGURE 6 is a cross sectional view on an enlarged scale of the rock bolt as illustrated in FIGURE 5.

FIGURE 7 is a fragmentary perspective view of the a modified form of the rock bolt.

FIGURE 8 is a cross sectional view of the rock bolt illustrated in FIGURE 7.

' FIGURE v9 is a side elevation of a modified embodiment of the rock bolt shown disposed in position in a bore.

FIGURE 10 is a cross sectional view of the rock bolt taken substantially on the plane of line 1010 as shown in FIGURE 9.

FIGURE 11 is a side elevation partially in cross sec tion and on an enlarged scale of a coupling splicing two rock bolt members of the type ilustrated in FIGURES 2 to 6.

Rock bolts 11 are used, as generally depicted in FIG- URE 1, for rock and earth reinforcement and support in tunnels or shafts 10.

Preferred embodiment of the invention, there is shown in FIGURES 2 to 6 a reinforcing rock bolt 11 comprising an elongated generally cylindrical member 12, said member 12 having a longitudinally extending groove 13 disposed adjacent the periphery 14 thereof, and means defining a longitudinally extending passageway disposed within said groove subjacent said periphery, said means comprising in the illustrated embodiment a tubular conduit 16 disposed in the groove 13 and having a passageway 17. The member 12 as shown is provided with longitudinally spaced projecting portions 18, which overlie the conduit 16 and serve to secure the conduit in position within the groove. The portions 18 can be formed by peening or rolling over the edge of the groove after the conduit is placed in position.

A rock bolt 19 comprising an alternative embodiment of the invention is shown in FIGURES 7 and 8, and includes a .generally cylindrical member 21 having a longitudinally extending groove 22 disposed adjacent the periphery 23 thereof, and an elongated strip of material 24 secured to the member 21 in overlying relation to the groove 22 to define a passageway 26 between the strip and the walls of the groove. As shown, the groove 22 has a slightly smaller width adjacent the periphery than at the position 27 subjacent the periphery proximate the strip 24. The groove width subjacent the strip at p the position 28 is smaller than at the position 27, and the strip is disposed in the groove subjacent the periphery and has a width larger than the groove at the periphery and at the position 28. The configuration of the groove as just described serves to secure the strip 24 in the position shown. In manufacturing this embodiment of the invention, the groove can be formed with a slightly tapered wall configuration, so that the strip will be maintained in spaced relation to the bottom of the groove. After the strip is inserted in position, the member 21 can be passed through rollers to flatten over the edges of the groove to form the narrower groove width at the periphery as shown, thus retaining the strip 24 in the groove. It will be appreciated that the conduit 16 in the rock bolt 11 can likewise be secured in position by flattening the groove edges with rollers, instead of peening over longitudinally spaced portions of the bolt as described above. Similarly, the longitudinally spaced peened portions can be provided with rock bolt 19 to secure the strip 24 in place.

The installation and grouting of the rock bolt is best described with reference to FIGURES 1 to 4. Rock reinforcement is usually placed as soon after blasting and as close to the working face as possible. A plurality of generally radial holes 32 as shown in FIGURE 1 are.

drilled to a required depth then cleaned of drill cuttings, sludge, and debris. A shell type anchorage device 38 is here shown threadably attached to the inner end 39 of the bolt member 12 and the outer end 41 of the bolt is secured to a wall plate 42 by means of a nut 43. With the anchor 38 fixed securely in the bore, the bolt can be placed under tension by tightening nut 43 for providing the desired support :for the tunnel wall 45.

Where the overall length of the rock bolt needs to be longer than the diameter of the tunnel in which the bolt is to be anchored, a plurality of rock bolts such as

bolts

34 and 36 in FIGURE 11, may be spliced together by a coupler 37. In such case it will be seen that the abutting ends of the two bolt members are provided with beveled or chamfered edges 44 to assure free communication between the peripheral passages in the bolts and an annular chamber 46 surrounding the abutting bolt ends and defined by the coupler body 37. Preferably coupler 37 is a Howlett reinforcing steel coupling such as disclosed in the pending patent application ofGeorge H. Howlett and James W. Howlett, Serial No. 280,357, filed May 14, 1963 now Patent No. 3,253,332. The Howlett coupler provides a convenient connecting means avoiding the necessity of welding while yet affording the gripping and coupling of the adjacent confronting bolt ends to be joined with good continuity of all required physical properties. Briefly, the coupler includes a pair of longitudinally split

sleeves

71 and 72 formed with a pair of external spiral cam lands 73 and 74 of reverse pitch and with serrated

interior surfaces

76 and 77 dimensioned for gripping the peripheries of each of the

bolts

34 and 36 to be joined; a tubular housing 78 formed with a pair of internal spiral cam lands 81 and 82 of reverse pitch extending inwardly from the opposite ends 83 and 84 of the housing 78 and formed to receive in mating threaded fit the cam lands 73 and 74 on

sleeves

71 and 72; the structure being designed upon rotating housing 78 relative to

sleeves

71 and 72, as by means of a wrench, to compress the sleeves into tight gripping engagement with the bolts and to displace the bolts axially toward each other in end to end compression which may approach the yield point of the bolts. The communication of the passageways with the chamber 46, provided by the chamfered edges 44, enables free How from the passageway of one bolt to the passageway of the other, regardless of whether the two passageways are rotationally aligned.

The anchor 38 is seen to include in internal wedge member 47 screwed on to the externally threaded end 39 of the bolt 34. The anchor further includes an outer member 48 having spaced gripping

portions

49, 51 which engage the tapered surfaces of the member 47. Rotation of the bolt 34 causes the member 47 to move downwardly thus forcing the gripping

portions

49, 51 against the bore wall to set them in position. Then as tension is placed on the bolt the wedge action of the anchor increases the radial forces on the gripping portions.

At the outer end 41 of the bolt 31, the nut 43 serves to transmit tension from the bolt to the wall plate 42, thus providing the desired wall support. The plate 42 is seen to have an opening 52 through which the bolt extends and which defines an annular space 53 between the plate and bolt which communicates with the bore 32. A recess 54 is provided in the face 56 of the nut 43, which recess forms an annular space 57 surrounding the bolt and communicating with the aforesaid space 53. A radial bore 58 extends through the nut in communication with the recess 54.

In order to fill the bore 32 with grout, a feed tube (not shown) is coupled to the bore 58 in the nut 43 to supply a liquid concrete grout under pressure into the

annular spaces

57 and 53, and then into the bore 32. As the grout rises in the bore 32, air is evacuated through the passageways in the bolt and vented to atmosphere at the outer end of the bolt. The nut 43 is seen to provide a simple and quick means for introducing grout into the bore 32, as compared with prior methods of drilling a separate hole in the plate 42 for the grout feed tube.

The disposition of a passageway along the periphery of a rock bolt enables more than one passageway to be provided, and as shown in FIGURE three grooves 61 can be formed in a rock bolt 62 with three conduits 63 providing

passageways

64, 66, and 67 in a manner similar to that described with regard tothe rock bolt 11 shown in FIGURES l and 2. The use of the multiple passageways is illustrated in FIGURE 9, wherein the bolt 62 is employed to provide a grout anchor at the inner end of the bolt in lieu of the previously described anchor 38, and also to enable the anchoring and grouting of selective portions of the length of the bolt for coordinated stressing and grouting of the bolt Where this procedure is desired. More particularly, the bolt 62 is inserted into a bore in the earth in the manner described above, but is adapted with an annular flange 68 or the like spaced from the bolts inner end and dimensioned approximately to the diameter of the bore. The passageway 64 terminates just above the flange 68 as shown, with the passageway 66 extending all the way to the top of the bolt. Grout can then be inserted into the passageway 64 at the bottom of the bolt and fed into the annular chamber 69 surrounding the inner end of the bolt, with the air from this chamber being vented through the passageway 66. In this manner, the grout when filled in the chamber 69 serves to anchor the inner end of the bolt in the bore. A relatively short chamber 69 is needed to provide this anchorage, as for example a five foot long chamber for a one inch diameter bolt. After the anchor is set, the bolt can be tensioned in a conventional manner, and the remainder of the bore likewise can be filled with grout in the manner above described as by the introduction of grout through the nut 43-a into the earth bore around the bolt. As shown, the third passage 67 terminates just below the flange 68 so that it provides a vent for the air in the remainder of the bore as it is being filled with grout. The groove in the bolt for the passage 67 can be suitably plugged adjacent the flange 68 so that grout from the chamber 69 does not leak out when the anchor is being formed.

It will be appreciated that the previously described embodiments for forming peripheral passageways in a rock bolt are disclosed only by way of illustration, and that other means may be provided for defining a passageway in the peripheral groove. Thus in the event that a plastic tubular conduit is used, it may be preferable to glue the conduit in the groove as opposed to peening over the groove edges or flattening them by passing the bolt through rollers.

I claim:

1. A reinforcing rock bolt comprising, an elongated generally cylindrical member having threaded portions at its opposite ends and a continuous peripheral groove extending over the length of said member and said threaded end portions, and an elongated strip of material secured to said member subjacent the periphery thereof and said threaded end portions and enclosing the outer portion of said groove to define with the walls of said groove a longitudinally extending passageway over the length of said member.

2. A rock bolt as described in claim 1 wherein said groove has a slightly smaller width adjacent said periphery than at a first position spaced inwardly from said periphery, said groove having a smaller width at a second position spaced subjacent said first position than said width at said first position, and said means including an elongated strip of generally thin flat material disposed in said groove subjacent said periphery and having a width larger than said groove at said periphery and said second position.

3. A reinforcing rock bolt comprising, an elongated generally cylindrical member formed of high tensile strength steel, said member having a continuous elongated groove extending longitudinally over the length and disposed adjacent its periphery and generally parallel to the axis thereof, said member being provided with external threads adjacent at least one end thereof, an elongated tubular conduit disposed in said groove radially inwardly of said threaded portion and subjacent said periphery over said length, said member having longitudinally spaced projecting portions overlying said conduit for securing it in position in said groove, an anchor plate having a hole therein disposed with said cylindrical member extending through said hole adjacent said threaded portion to define an annular space between said plate and member, a nut having an internally threaded bore screwed on said threaded portion and having a surface engaging said plate, said nut having a recess in said face thereof to define a second annular space surrounding said bolt and communicating with said first annular space, and said nut having a radially extending bore communicating with said recess.

4. A spliced rock bolt comprising a pair of elongated generally cylindrical members disposed in axially aligned end abutting relation, said members each having a longitudinal-1y extending groove disposed adjacent the periphery thereof, means defining a longitudinally extending passageway, disposed within each of said grooves and subjacent the periphery of the respective member, coupling means surrounding the abutting ends of each said members and gripping said member peripheries adjacent said abutting ends to secure said members together and to define an annular chamber surrounding said abutting ends, and each of said members having their abutting ends chamfered to provide communication between said passageways and said chamber.

5. A method for anchoring and grouting a rock bolt comprising, forming an open ended bore in earth matter, providing a roll formed steel rod member having a solid cross-section and a diameter substantially less than the diameter of said bore and a continuous longitudinally extending peripheral groove over the length thereof, positioning a member in said groove to provide an elongated conduit extending substantially over the length of said rod member subjacent the periphery thereof and terminating in openings adjacent the ends of said rod member, inserting said rod member into said bore through the open end thereof to define an annular space in said bore surrounding said rod member, sealing off said annular space adjacent said open end of said bore, and passing grout into said space to thereby evacuate the air in said space through said conduit.

6. A method for anchoring and grouting a rock bolt extending through earth matter comprising, inserting into a bore in said earth matter an elongated generally cylindrical bolt member having an inner end first inserted into said bore and an outer end and a diameter substantially less than the diameter of said bore to define an annular chamber between said bolt member and bore and having three longitudinally extending peripheral grooves and means defining an elongated passageway within each of said grooves communicating with said outer end, sealing off said chamber with sealing means positioned adjacent said inner end to form a sealed chamber portion, passing grout from said outer end into a first of said passageways terminating immediately adjacent said sealing means to communicate wit-h said sealed chamber portion, forcing said grout under pressure into said sealed chamber portion, evacuating the air in said chamber through a second of said passageways communicating with said sealed chamber portion through a terminal end thereof disposed substantially at said inner end, filling said sealed chamber portion with grout thereby anchoring said inner end of said bolt in said bore, and subsequently filling the annular chamber between said sealing means and said outer end with grout and evacuating the air therefrom through a third of said passageways References Cited by the Examiner UNITED STATES PATENTS 1,980,668 11/1934 Davis 52 73s 3,204,416 9/1965 Williams 61-45 8 FOREIGN PATENTS 239,150 1962 Australia.

81,491 5/ 1956 Netherlands. 84,9377 1955 Norway. 84,938 1955 Norway.

CHARLES E. OCONNELL, Primary Examiner.

JACOB SHAPIRO, Examiner.

Claims

1. A REINFORCING ROCK BOLT COMPRISING, AN ELONGATED GENERALLY CYLINDRICAL MEMBER HAVING THREADED PORTIONS AT ITS OPPOSITE ENDS AND A CONTINUOUS PERIPHERAL GROOVE EXTENDING OVER THE LENGTH OF SAID MEMBER AND SAID THREADED END PORTIONS, AND AN ELONGATED STRIP OF MATERIAL SECURED TO SAID MEMBER SUBJACENT THE PERIPHERY THEREOF AND SAID THREADED END PORTIONS AND ENCLOSING THE OUTER PORTION OF SAID GROOVE TO DEFINE WITH THE WALLS OF