CA2433932A1 - A self centering cable bolt - Google Patents

Abstract

A self centering cable bolt for use with adhesive grouting materials for insertion into a drilled hole penetrating the face of a rock formation to stabilize the formation comprising a tensionable reinforcing member provided with a plurality of permanent congruent arcuate concavities disposed perpendicular from the axis of the member in a regular spaced relationship along the length of the member at right angles to each other along the member x-y axis.

Description

10 Patent Application of Rock Mongrain For A SELF CENTERING CABLE BOLT' CROSS-REFERENCE TO RELATED APPLCATIONS
Not applicable.
BACK GROUND OF THE INVENTION
Field of the Invention This invention relates to a rock stabilizing apparatus for anchoring unstable rock formations in underground mines and more particularly relates to a self centering tensionable cable bolt adapted to be anchored by cementaceous oh~ resinous grout in a drill hole.
Background of the Invention In underground mines it is important to secure the roof and walls of a tunnel against collapse of unstable rock formations that will hang from stable rock formations.
Such situations may be caused by having to tunnel through naturally fractured rock formations or by blasting operations within the mine. Scaling the roof and walls of a newly formed tunnel is necessary to remove loose rock that could easily collapse.
Scaling is a process whereby a miner uses a long pole to pry and remove loose rock, called scale, from the roof and walls of the tunnel.
After removing the scale it is necessary to anchor the walls and roof of the tunnel to more stable rock formations. This is accomplished through the use o.f devices that are called rock bolts or cable bolts. Holes are drilled into the walls and roof of the tunnel a sufficient distance to penetrate the unstable formations suurounding the roof and walls of the tunnel and enter stable formations. Bolts of adequate length are then inserted into the holes. The inserted end of the bolt is anchored to the stable rock formation using mechanical expansion clamps or hardenable adhesion material such as cement grout or polyester resins.
Rock bolts tend to be a solid length of rebar. It may be a steel rod, from four to 12 feet long and up to one inch in diameter, inserted into open rock faces for roof and wall support in underground mines. Mechanical anchors, epoxy resin, or grout secures the bolts. One example of a typical rock bolt is found in United States Patent 4,051,683 "Method and Apparatus for Supporting a Mine Roof' issued to Koval in 1977. A
cable bolt is a type of rock bolt consisting of pre-stressed, multi-strand steel cable used for supplemental and primary roof support in underground mires. The objective of rock or cable bolting is to improve the shear and tensile strength of the rock mass.
One example of a cable bolt is found in United States Patent 5,785,463 "Combination Cable Bolt System" by Eaton et al issued in 1998. Cable bolts comprise a wire strand or central rope to take axial tensile loads and a plurality of wrapped wires. Since axial tension loads on a cable tend to create a moment which forces rotation in the wire core, the wrapped wires are would so that a counter torque is created.
In order to mix the grouting compound in the drill hole, the cable or rock bolt may be attached to a rotating head and rotated within the drill hole. The cable or rock bolt may be bent to better mix the grouting compound. In some cable bolt installations, as illustrated in Koval, the cable bolt may have a plurality of destranded, unravelled or bulbous sections regularly spaced along their length. These are often referred to as "birdcages". Birdcages are used to provide agitation means in order to improve the mixing of the grouting compound and the bond strength of the resulting anchorage. This can result in displacing the core of the wire rope. Therefore, while birdcages in the cable may provide a useful means for mixing the resin in the drill hole the result may be a weakened cable less able to withstand axial tension. This could potentially lead to failure of the wire core and the cable and place workers in jeopardy.

Therefore, there are disadvantages with using cable bolts having birdcages. To manufacture a cable bolt with a birdcage requires complex and expensive machines to rotate the cable in the opposite direction of the cable lay. much machines are not easily transported to the site of a rock bolting operation and therefore creating cables bolts with birdcages must be done off site. This leads to extra expense in manufacturing such cable bolts. Additionally, the grouting compound, because of its viscosity, may not be able to penetrate the void surrounding the birdcage. This creates undesirable voids in the anchorage.
Another disadvantage of rock and cable bolts presently available is that once they are inserted into the drill hole and grouted, the action of pumping the grout into the drill hole under pressure can result in the axis of the bolt being off set from the axis of the drill hole. This off setting of the drill hole and bolt axis results in an inefficient transfer of forces from the rock structure to the bolt. Therefore it is important that the bolt remain as co-axial as possible with the drill hole to optimize the transfer of tensile and compressive loads between the rock and the bolt.
Another disadvantage of using a straight cable member for the rock bolt is that, once grouted, the member may have sections that are unsupported by grout. That is, void may form between the wall of the drill hole in which the member is placed and the member itself. This is a problem that is difficult to detect during the installation process.

Fence, there is a continued need for an apparatus and method for anchoring unstable rock formations in underground mines using a substantially self centering cable bolt tension member. There is also a need for an apparatus that will promote the support of the member by grout along its entire length. There is also a continued need for an apparatus that is adapted for use with cementaceous and resinous grouting materials, that is simple and inexpensive to manufacture and use; does nol: rely upon deformation of the l0 cable bolt and the resulting loss of axial tensile strength that such deformation causes;
and, maintains itself substantially co-axial with the drill hole to optimize the strength of the reinforcing member.
OBJECTS OF THE INVENTION
It is an object of the present invention to overcome the deficiencies in the prior art.
It is a further objective of the invention to provide a substantially self centering cable bolt that remains substantially co-axial with the drill hole after grouting.
It is a further object of the invention to provide an improved cable bolt and method of manufacturing the same that can be used in anchoring unstable rock formations in underground mines.
Yet another object of the present invention is to provide a cable bolt and method for manufacturing the same that can be transported to a drill site.

Still another object of the invention is to provide a cable bolt for rock stabilizing that does not rely upon birdcaging or other similar deformations in the cable.
Another object of the invention is to ensure that the cable bolt is supported along its entire length by grouting compound.
SZTMMARY OF THE INVENTION
The objects of the present invention are satisfied through the provision of a rock bolting apparatus for use with adhesive grouting material for insertion into a drilled hole penetrating the face of the rock formation. The grouting material may be resinous or cementaceous. The drill hole transverses unstable rock strata and penetrates into stable rock strata in underground mines. The rock bolting apparatus of the present invention comprises a substantially self centering tensionable reinforcing member inserted into the drilled hole. Self centering is accomplished by the member being provided with a plurality of permanent congruent arcuate concavities. The concavities are disposed perpendicular from the axis of the member in an aligned regular spaced relationship along the length of the member. The rock bolt is preferably a cable bolt. Once installed in the drill hole and grouted the concavities act to retain the cable bolt substantially co-axial with the drill hole. This optimizes the ability of the bolt to 'transfer and resist axial loads.
The drill hole in which the reinforcing member is installed is generally 2 inches to 2.5 inches in diameter. Once the reinforcing member is placed into the drill hole, grouting compound is pumped into the drill hole by way of a tube inserted into the drill hole. As the grout is pumped into the drill hole with the member already placed in the drill hole, the grout will act on the member and cause it to move off centre from the axis of the drill hole. It may also contact the walls of the drill hole in the early stages of pumping grout in the drill hole. Ultimately as the drill hole fills with grout, the grout will S exert a pressure against the member concavities that becomes generally equal on both sides of the member. The result is that the grout will act to substantially centre the member within the drill hole. An equal amount of grout will he forced between the sides of the concavities of the member and the walls of the drill hole acting as spacers to keep each of the arcuate concavities spaced away from contacting the sides of the drill hole.
In one embodiment, the alternate concavities are at right angles to each other along the member x-y axis. In a preferred embodiment of the invention there is a parade of arcuate concavities along the length of the member wherein each subsequent concavity is disposed ninety degrees from the previous concavity along the member x-y axis.
I S Generally, the linear distance along the member between the apexes of any two adjacent concavities is one of I2 inches, 18 inches or 26 inches. However, the distance may be any multiple of six inches or it may be varied as demanded by operational conditions.
In one embodiment of the invention the radius of the arcuate concavities is less than the radius of the drill hole. I-Iowever the radius of the arcuate concavities may be a function of the diameter of the member.

Also disclosed in the invention is an apparatus for making the cable bolt described herein. The apparatus comprises a source of wire cable suitable for making cable bolt members; a means for drawing the wire cable from the source of wire cable;
means for measuring the amount of wire cable drawn for the source of wire cable; a cutter for cutting the wire cable into desired lengths; means for disposing a plurality of concavities along axis of the member in a predetermined and spaced manner so that each subsequent concavity is rotated positive 90 degrees or some other desired angle from the previous concavity. The means for disposing a plurality of concavities along the axis of the member comprises: a first ram and die block set disposed along the positive x axis of the member for imparting a first concavity to the member in the negative x direction; a second ram and die block set disposed along the positive y axis of the member for imparting a second concavity to the member in the negative y direction; a third ram and die block set disposed along the negative x axis of the member for imparting a third concavity in the positive x direction; and, a fourth ram and die block set disposed along the negative y axis for imparting a fourth concavity in the positive y direction. 'fhe distance between the ram and die block sets is variable permitting the distance between concavities to be varied. Each ram and die block set comprises: a die block having a concave working surface. The radius of the surface is equal to desired radius ofthe concavity to be imparted to the member. The ram portion of the set also has a radius equal to that of the surface of the die so that when the ram pushes the cable into the die, concavity is formed in the cable.

Also disclosed in the invention is a method of making a cable bolt comprising the steps of: obtaining a section of wire cable of a desired length; defining the number of concavities to be disposed into the wire rope; determining the distance between the apex of the concavities; imparting the predetermined number of concavities into the wire cable each being a predetermined distance apart and each being rotated by positive 90 degrees from the previous concavity; and, cutting the wire cable into a desired length.
Further objects and advantages of this invention will become apparent from a consideration of the following drawings, detailed description and claims.
BRIEF DESCRIPTION OF TI-IE DRAWINGS
Figure 1 is a sectional side view of one embodiment of the invention placed and grouted inside a drill hole in order to stabilize a rock formation.
IS
Figure 2 is an axial view of a preferred embodiment of the invention.
Figure 3 comprises two views of a cable bolt of a preferred embodiment of the invention.
Figure 4 is a perspective view of a preferred embodiment of the invention.
Figure 5 is a sectional side view of a preferred embodiment of the invention installed in a drill hole.

Figure 6 is a view of an apparatus for making a preferred embodiment of the invention.
Figure 7 is a view of a ram and die block set of one embodiment of the invention.
DESCRIPTION OF THE INVENTION
Referring to Figure l, there is shown a preferred embodiment of the invention comprising a cable bolt (10) inserted into a drill hole (12) drilled between stable (14) and unstable (16) rock formations. A fracture line (IS) delineates stable from unstable rock.
The cable bolt (10) is grouted into the drill hole by grout (18). The grout (18) may be a cement grout or a resin grout. Cable bolt ( 10) comprises a length of wire cable having a plurality of permanent arcuate concavities (20, 22, 24, 26) disposed therein.
Each successive concavity is disposed positive 90 degrees from its previous concavity. In other embodiments of the invention, the angle may be more: or less than 90 degrees.
Figure 2 illustrates a preferred embodiment of the invention placed on a three-dimensional x-y-z axis grid where the axis (31) ofthe cable bolt (10) is aligned with the z-axis (30). The view is directly along the z axis (30). Each ofthe arcuate concavities (20, 22, 24, 26) is disposed along the "x" and "y" axes of the grid.
Therefore, in a preferred embodiment of the invention as shown in Figure 2, if concavity (20) is disposed along the negative x axis (32) then concavity (22) will be disposed along the negative y axis (34), concavity (24) will be disposed along the positive x axis (36) and concavity (26) will be disposed along the positive y axis (38).
Referring to Figure 3, there is shown a preferred embodiment of the invention in two perspectives. In Figure 3a, cable bolt (10) is shown oriented along an x-y-z axis grid.
Axis of the cable bolt is co-axial with the z axis. Therefore the observer is looking down onto the cable bolt from the positive y axis direction. Concavity 20 is shown disposed on its side along the negative x axis. Concavity 22 is shown disposed downward along the negative y axis. Concavity 24 is shown disposed along the positive x axis and concavity 26 is shown disposed upwards along the positive y axis . The perspective of Figure 3b is that of Figure 3a turned negative 90 degrees. T herefore concavity 20 is now oriented downwards along the negative y axis; concavity 22 is oriented on its side to the left along the negative x axis; concavity 24 is oriented upwards along the positive y axis; and, concavity 26 is oriented to the right along the positive x axis. Therefore, each successive concavity in the parade of concavities is oriented negative 90 degrees from its adjacent predecessor. The concavities are regularly spaced along the z-axis. In one embodiment of the invention the distance between successive concavities may be a multiple of six inches. However, the spacing between the apexes of the successive concavities may vary to suit operational conditions.
While the preferred embodiment illustrates successive concavities at ninety degrees to its predecessor congruity, it is to be understood that the concavities may repeat axially along the same plane dually or in greater repetitions and may be oriented at angles other than ninety degrees from predecessor to successor concavity, such as 180 degrees. These configurations will be established to suit the operating conditions of the rock bolting operation and all will retain the grouted rock bolt substantially co-axial with the drill hole.
Referring to Figure 4, there is shown a perspective view of a preferred embodiment of the cable bolt (10) shown arcuate concavities (20, 22, 24, 26).
Referring now to Figure 5, there is shown in a sectional side view a preferred embodiment of the cable bolt (10) inserted into a drill hole (12). Concavities (20, 22, 24, 26) are disposed along the length of the bolt. Grout (18) is pumped under pressure into the drill hole (12) so that it surrounds the cable bolt (10). The self centering process works as follows. The radii of the arcuate concavities are all equal and less than the radius of the drill hole. The radii of the arcuate concavities is variable to suit the desires of the operators and the diameter of the drill hole. Referring to Figure Sb, once the grout (18) fills the hole (12), an amount of grouting material (38) will be disposed between the outer surface (40) of the concavity (22) and inner surface (42) of the drill hole ('l2}.
Similarly, as shown in Figure Sc, grouting material will fill the space 46 between the outer surface of concavity (24) and the inner surface of the drill hole. The grout will act with generally equal pressure against the concavities thereby substantially centering the cable bolt within the drill hole. Once the grouting material hardens, the cable bolt will remain centered within the drill hole. As well, the shape of the concavities along the length of the rock bolt promotes a thorough mixing of the grouting compound inside of the drill hole and complete contact of the rock bolt with the grouting compound thus avoiding voids.
Referring to Figure 6, there is shown an apparatus (50) for manufacturing a cable bolt of the invention. The apparatus may be mountable to a transportable platform so that the apparatus may be transported to a drill site within a mine. The apparatus comprises a source of wire cable (52) suitable for making cable bolt members; means (54) for drawing the wire cable (56) from the source of wire cable; means (58) for measuring the amount of wire cable drawn for the source of wire cable; a cutter (60) for cutting the wire cable into desired lengths; and, means for disposing a plurality of concavities along axis of the member in a regularly spaced manner so that each subsequent concavities is rotated a negative 90 degrees from the previous concavity. The cable bolts may then be gathered and stored on a magazine (61).
Still referring to Figure 6, the means for disposing a plurality of concavities along the axis of the member comprise: a first ram and die block set (62) disposed along the negative x axis of the member for imparting a first concavity along the positive x axis; a second ram and die block set (64) disposed along the positive y axis of the member for imparting a second concavity to the member in the negative y direction; a third ram and die block set (66) disposed along the positive x axis of the member for imparting a third concavity in the negative x direction; and, a fourth ram and die block set (68) disposed along the negative y axis for imparting a fourth concavity in the positive y direction. The distance (d) between the ram and die block sets is variable permitting the distance between the apex of the concavities to be varied.
Referring to Figure 7, there is shown a representative ram and die block set of one embodiment of the invention. Cable supply drum (52) is located to the left of the cable (10). The cable is moving left to right. In one embodiment, puller (54) may comprise a pair of opposed pullies (70) and (72) in a frictional engagement with the cable (10). The pullies rotate in a respective counter clockwise and clockwise direction to pull cable from the supply drum. Measuring device (58) measures the length of cable being pulled from the supply drum and pushed into the space between the ram and die block sets (62).
Once the desired length of cable has been pulled from the drum the cutter (60) operates to cut the cable into the desired length. The feed of cable from the supply drum is not continuous and the operation ceases once the desired amount of wire cable has been pushed between the ram and die block sets and 'the cable is cut. The next phase of cable manufacture involves the formation of the arcuate concavities in the cable.
The distance (d) between each die and block set is established by moving each die and block set axially along the cable length to a desired position. The ram and block set comprises a die block (78) having a concave working surface (80). The working surface has a radius equal to desired radius of the concavity to be imparted to the cable. The radius of the arcuate concavity can be adjusted by varying the height of die shoes (82). The higher the die shoes the deep the concavity. Ram (84) is actuated by piston (86). The ram and piston may be air operated or it may be hydraulically operated. Die (88) is fixed to ram (84) and is variable depending on the depth of the concavity desired. In operation, all four ram and die block sets will be actuated simultaneously or in a suitable sequence all controllable by an operator. Once .the concavities are formed in the cable, the formed cable length is ejected from the apparatus and a new cable length is inserted.
The operation is repeated until the desired numbers of cables are made.
The present invention also discloses a method for making a cable bolt having a plurality of arcuate concavities comprising the following steps:
a. obtaining a section of wire cable suitable for rock bolting applications;
b. measuring a desired length of cable;
c. cutting the cable into a desired length;
d. feeding the desired length between a plurality of die and block sets for forming arcuate concavities;
e. compressing cable length between the die and block sets thereby forming the arcuate concavities;
f. ejecting the formed cable bolt.
Although the description above contains many specifications, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Thus the scope of the invention should be determined by the appended claims and their legal equivalents rather than by the examples given.
l5

Claims (20)

1. A self centering tensionable member for use with adhesive grouting material for insertion into a drilled hole penetrating the face of a rock formation, said hole transversing unstable rock strata and penetrating into stable rock strata in underground mines, said member being a predetermined length and having first end, a second end and a plurality of permanent congruent arcuate concavities disposed between said first and second ends in a regular spaced relationship along the axial length of the member so that when the cable is inserted into a drill hole and the hole is grouted the action of grouting the drill hole creates spacers of grouting material between the tips of the arcuate concavities and the walls of the drill hole thereby centering the cable in the drill hole and maintaining the cable co-axial with the drill hole.

2. The member as claimed in claim 1 wherein the member is a length of tensionable wire cable suitable for rock bolting applications.

3. The member as claimed in claim 2 wherein the member includes a parade of arcuate concavities along its length.

4. The member as claimed in claim 3 wherein the radius of the arcuate congruent concavities is less than the diameter of the drill hole.

5. The member as claimed in claim 4 wherein the each successive concavity in the parade of concavities along the member is disposed negative ninety degrees from its predecessor concavity.

6. The member as claimed in claim 5 wherein the linear distance between the apexes of any two adjacent concavities is equal.

7. The member as claimed in claim 5 wherein the linear distance between the apexes of any two adjacent concavities is a multiple of six inches.

8. The member as claimed in claim 7 wherein the radius of the arcuate concavities is a multiple of the diameter of the member.

9. The member as claimed in claim 8 wherein the arcuate concavities parading along the length of the member promotes full contact of the member with grouting material.

10. An apparatus for manufacturing a cable bolt having a plurality of congruent arcuate concavities said apparatus comprising the following components:
a. a source of wire cable suitable for making cable bolt members adaptable to reinforcing rock;
b. a means for drawing the wire cable from the source of wire cable;

c. means for measuring the amount of wire cable drawn for the source of wire cable;
d. a cutter for cutting the wire cable into desired lengths;
e. means for disposing a plurality of concavities along axis of the member in a regularly spaced manner so that each successive concavities is rotated a negative 90 degrees from its predecessor concavity.

11. The apparatus as claimed in claim 10 wherein the components are mounted for axial movement of the cable there through.

12. The apparatus as claimed in claim 11 wherein said means for disposing a plurality of concavities along the axis of the member comprise, in axial alignment:
a. a first ram and die block set disposed along the negative x axis of the member for imparting a first concavity to the member in the positive x direction;
b. a second ram and die block set disposed along the positive y axis of the member for imparting a second concavity to the member in the negative y direction;
c. a third ram and die block set disposed along the positive x axis of the member for imparting a third concavity in the negative x direction; and, d. a fourth ram and die block set disposed along the negative y axis for imparting a fourth concavity in the positive y direction.
wherein the distance between the ram and die block sets is variable by the operator so that the distance between concavities can be varied.

13. The apparatus as claimed in claim 12 wherein each ram and die block set comprises:
a. a die block having a concave working surface said surface having a radius equal to desired radius of the concavity disposed in the member said radius less than the radius of the drill hole;
b. demountable die shoes fixed to the die block so that the depth of said working surface can be varied thereby varying the radius of the concavity disposed in the member;
c. a die mounted to the face of a piston actuated ram said die having a radius equal to that of the radius of the die block; and, d. and demountable die shoes fixed to the face of the die so that the penetrating depth of the die can be varied to match the required depth of the desired arcuate concavities whereby the die is forced into the die block by the piston actuated ram thereby permanently deforming the wire cable disposed between them in the desired shape of an arcuate concavity have a radius less than the radius of the drill hole.

14. The apparatus as claimed in claim 13 wherein the ram is hydraulically operated.

15. The apparatus as claimed in claim 14 wherein the ram is air operated.

16. The apparatus as claimed in claim 15 wherein the apparatus is mountable to a transportable platform so that the apparatus may be transported to a drill site within a mine.

17. A cable bolt made from the apparatus of any one of claims 10 to 16.

18. A method of a manufacturing a plurality of cables bolts suitable for rock reinforcement each of said cable bolts having a plurality of congruent arcuate concavities disposed therein said method comprising the steps of:
a. obtaining a desired length of wire cable suitable for rock bolting applications;
b. cutting the cable into a desired length;
c. feeding the desired length of cable between a plurality of die and block sets for forming arcuate concavities;
d. permanently deforming the cable by compressing the cable length between a plurality of die and block sets imparting a plurality of the arcuate concavities therein, wherein each of the die and block sets is adapted to impart a concavity that is disposed negative ninety degrees from the previous concavity; and, e. ejecting the formed cable bolt.

19. The method as claimed in claim 18 wherein the distance between the concavities disposed in the wire rope are equal, predetermined and variable.

20. The method as claimed in claim 19 wherein the step of feeding the wire cable between the die and block sets stops before the length is cut and commences after the previous length of deformed cable is ejected.