Hollow cable bolt

Abstract

 A hollow cable bolt having a central tube (12) circumscribed by a plurality of wound wires (14). The bolt is inserted into a hole (16) and grout (22) is pumped into the bore of the tube. The grout exits the bolt and flows within the annulus formed between the hole and the bolt.

Description

TECHNICAL FIELD

[0001] The instant invention relates to supporting bolts for underground excavations in general and to cable bolts in particular.

BACKGROUND ART

[0002] Underground excavations are usually supported by, amongst other things, rock bolts and grouted cables inserted into bore holes drilled into the roof and sides of the excavation.

[0003] Rock bolts generally consist of solid bars or hollow metal tubes. They may be tensioned within the hole and grouted to secure the ground.

[0004] Cable bolts, an alternative to rock bolts when conditions allow, are generally flexible, twisted strands of cable that are inserted into the hole and set with grout. They are most useful when large blocks of ground are supported. Cable bolts can supply stronger tensile strength than regular bolting.

[0005] Although rock bolts and cable bolts possess inherent advantages and disadvantages, a useful feature of the cable bolt system is that it is flexible and can be fished into a hole from a portable reel. Usually paired cables are employed. The initial length of each individual cable is generally no concern since they may be cut to length at the site as conditions dictate.

[0006] However, present cable bolt grouting methods, both in mining and civil applications, are labor intensive and have proven difficult to automate. Current methods usually entail pushing one or more bundled cables up drill holes to varying length. An adjacent plastic tube is inserted into these holes, usually also bundled with the cables and is more as a breather and/or a filler tube.

[0007] More specifically, one method uses a filler tube and a breather tube in the hole. Grout is pumped into the filler tube which extends partly into the hole. The collar of the hole is sealed with a plug. The grout percolates to the top of the hole and returns down the breather tube, along with the entrapped air. This indicates that the drill hole and cable are grouted. Usually a grout having a 0.4/1.0 water/cement ratio or higher is used. The problems are that it is difficult to get a proper plug/seal at the opening of the hole. It is labor intensive since the two cables and the two pieces of plastic tubing must be tied or taped together. Grout densities can vary with no indication of completeness. Voids may be created that weaken the bond.

[0008] A second common method employs a dense grout (0.3/1.0 water/cement ratio). The grout is pumped up a feed tube tied to two cables that extends substantially up the length of the hole. The grout then flows downwardly about the annulus formed between the two cables and the hole wall. Pumping is stopped when grout reaches the collar of the hole. The higher density of the grout causes it to remain in the hole until it sets. Plugs are not needed, although a wedge may be employed to keep everything in the hole. The difficulties again include fabrication time. The cables and tube must be taped together. Proper grout density must be maintained. Otherwise, it may drain out before setting.

SUMMARY OF THE INVENTION

[0009] Accordingly, there is provided a hollow cable bolt consisting of a plurality of individual wires spirally wound around a hollow central tube. High density grout is pumped through the bore of the central tube eliminating the need for a plug at the collar of the hole. There is no need to tie the components together. The cable bolt length is not a controlling factor since it may be cut on site.

BRIEF DESCRIPTION OF THE DRAWING

[0010] 

Figure 1 is an elevation of a hollow cable bolt in accordance with the instant invention.

Figure 2 is a view taken along line 2-2 of Figure 1.

Figure 3 is an embodiment of the invention.

Figure 4 is a cross sectional view taken along line 4-4 in Figure 3.

Figure 5 is a view of a prior art cable bolt installation.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

[0011] Figures 1 and 2 show the hollow cable bolt 10. The cable bolt 10 includes a central tube 12 including a bore 40 having a plurality of solid wire strands 14 spirally circumscribing the tube 12.

[0012] The bolt 10 may be cut to any desired length. Although the central tube 12 may be comprised of plastic, preliminary testing indicates that flexible metal tubing 12 is preferable since a plastic tube 12 may allow excessive necking when the bolt 10 is loaded and this significantly reduces the bond strength. The wire strands 14 are preferably preformed metal wire, (steel, copper, etc.) that are spirally woven around the outside diameter of the tube 12. The preformed wire strands 14 will stop the bolt 10 from unravelling when cut. As a result, the bolt 10 can be supplied in precut lengths or taken off a reel and cut to suit the local conditions. Consideration of like material selection for the tube 12 and wire 14 should be borne in mind so that electrical cell activity is reduced.

[0013] Figure 3 and 4 show a simplified installation of the bolt 10. A hole 16 is drilled into the ground 18. Although a side wall installation is shown, it should be understood that the bolt 10 may be used in roofs as well.

[0014] To install the bolt 10, the appropriately sized cable 10 is inserted into hole 16, cut at the hole opening (if necessary) to allow a small segment 26 to extend away from the hole 16, and secured in the hole 16 by a wedge or other suitable means. The grout 20, preferably a high density formulation (at least 0.3/1.0 water/­cement), is pumped into the bore 40 of the central tube 12 and allowed to flow throughout the entire tube 12 and then back around the annulus 22 towards the opening of the hole 16. After the grout 20 sets, a plate or screen holder 24 is slipped over the extension 26 to secure the integrity of the grout 20 and hold the optional screen 28 in place.

[0015] Contrast the simplicity of installing the hollow cable bolt 10 with a current installation as shown in Figure 5.

[0016] Presently, a current system for cable grouting requires that the cables 30 be precut to a predetermined length by the supplier. In most cases, two cables 30, 0.625 inch (1.6 cm) in diameter, each composed of seven wire strands 44 of about 0.2 inch (0.5 cm) diameter are clipped together. These cables 30 are coiled and tied, loaded on a pallet and shipped to the site. At the excavation, the operator must unclip the cables 30 prior to installing them - a dangerous undertaking since the coiled cables act as springs. After they are carefully unclipped, all dirt and grease must be cleaned off the cables, otherwise the grout's bonding capabilities will be degraded. Two cables 30 are then attached to the filler tube 32 by tape 34. The assembly is then inserted into the hole 36 and held in place by a wedge. Grout 38 is pumped through the filler tube 32.

[0017] Besides the difficulties discussed earlier, the current cable bolting system shown in Figure 5 suffers from grout bleeding, grout blockage, and the need for higher pumping pressures. As can be seen from Figure 5, after being pumped upwardly, the group 38 must flow downwardly through many small passages formed between the cables 30, the strands of wire 44 making up the cables 30 and the exterior of the filler tube 32. Sometimes the group 38 will become blocked, leaving voids. Moreover, when the group 38 is pumped under high pressure and through some of the smaller openings, the water component of the grout 38 is sometimes squeezed out of the grout 38 leaving behind a dense cement in pockets that will not flow.

[0018] In contrast, the cable bolt 10 reduces grout problems. Since the wire strands 14 circumscribe the central tube 12, there is a larger area for the grout 30 to flow unimpeded. This results in lower pump pressures, less blockage and less bleeding.

[0019] As a non-limiting example, the flexible central tube 12 may be 1 inch (2.54 cm) outside diameter by 0.75 inch (1.9 cm) inside diameter.The fifteen wire strands 14 are .203 inch (0.5 cm) in diameter. The hole 16 is 2.125 inches (5.4 cm) in diameter.

[0020] In summary, the advantages of the hollow cable bolt 10 over current cable systems include:

1) Less handling of cable.

2) No need for cumbersome taping.

3) Cuttable for any length requirement.

4) Less pump pressure required.

5) Less subject to the debilitating factors of grease and dirt.

6) Safer.

Claims

1. A cable bolt, the bolt comprising a tube and a plurality of wires circumscribing the tube.

2. The bolt according to claim 1 wherein the tube is flexible.

3. The bolt according to claim 1 wherein the wires are wound about the tube and/or wherein the wires are solid strands.

4. The bolt according to claim 1 wherein the tube and the wires are metal.

5. The bolt according to claim 1 including grout disposed within the tube and adjacent to the wires, which grout preferably has a water/cement ratio of about 0.3/1.0.

6. The bolt according to claim 1 wherein a plate is affixed to one end of the bolt.

7. The bolt according to claim 1 disposed within a bore hole or on a reel.

8. The bolt according to claim 1 wherein each wire contacts the tube.

9. A method for installing a cable bolt, the method comprising:

a) opening a hole in a surface;

b) inserting a cable bolt including a tube having a plurality of wires circumscribing the tube into the hole;

c) securing the cable bolt in the hole;

d) introducing grout into the tube and causing the grout to flow into the hole; and

e) setting the grout in the hole.

10. The method according to claim 9 including cutting the cable bolt to a predetermined length.

11. The method according to claim 9 including utilizing a dense grout, which preferably has a water/cement ratio of about 0.3/1.0.

12. The method according to claim 9 including attaching a screen to the bolt.

Drawing