| 1. | A tubular stabilizer having a retainer collar at one end, a tapered region at the opposite end, and a slot or circumferential gap extending along the length of the tube, the stabilizer being characterised in that the outer surface of the tube is provided with a series of undulations extending along the length thereof. |
| 2. | A stabilizer as claimed in claim 1 in which the undulations assume the form of indentations. |
| 3. | A stabilizer as claimed in claim 2 in which the indentations assume the form of grooves extending in a circumferential or helical direction. |
| 4. | A stabilizer as claimed in claim 1 in which the undulations assume the form of raised zones. |
| 5. | A stabilizer as claimed in claim 4 in which the raised zones are in the form of bumps or ridges. |
| 6. | A stabilizer as claimed in any one of the preceding claims in which the stabilizer is made from cut and rolled sheet metal. |
| 7. | A stabilizer as claimed in any one of the preceding claims in which the collar has a circumferential gap coincident with the slot in the stabilizer. |
| 8. | A stabilizer substantially as herein described and exemplified with reference either to Figures 2 and 4 or Figure 5 of the accompanying drawings. |
BACKGROUND TO THE INVENTION Numerous different types of rock or stratum stabilizers have been proposed in the past and these include the well known rock bolts, roof bolts and friction stabilizers with which this invention is concerned. Rock bolts and the like are in modern times, generally grouted into their holes although expansion units can also be used for this purpose. Rock and roof bolts are regarded as being permanent stabilizers whilst the tubular friction stabilizers with which this invention is concerned are usually regarded as being temporary in nature.
The reason for the latter is that the metal from which the tubular stabilizer is produced tends to corrode thus limiting the useful life of the stabilizer.
It is also commonly practised to fill tubular stabilizers with grouting material which assists in maintaining it in position in spite of the fact that the grouting only contacts the surface of the hole itself in the region of the slot extending along the length of the stabilizer.
The collar is generally welded to the outside of the tubular stabilizer and conveniently consists of a torroidal ring which also has a gap in a circumferential direction with the gap being offset by 180 degrees relative to the slot in the tubular stabilizer.
Stabilizers of the type commonly available at present operate effectively and serve a purpose. However, the pull-out resistance is limited and applicant's tests on a 1.2 metre unit indicated that pull-out can occur at about 4 tonnes force, with no grout being present.
OBJECT OF THE INVENTION It is the object of this invention to provide a tubular type stabilizer having improved characteristics and, most particularly, improved pull-out strength and also providing the possibility of achieving improved durability.
SUMMARY OF THE INVENTION In accordance with this invention there is provided a tubular stabilizer having a retainer collar at one end, a tapered region at the opposite end, and a slot or circumferential gap extending along the length of the tube, the stabilizer being characterised in that the outer surface of the tube is provided with a series of undulations extending along the length thereof.
Further features of the invention provide for the undulations to assume the form either of indentations such as inwardly directed grooves extending in a circumferential or helical direction, or for the undulations to be defined by raised zones, such as bumps, ridges or the like; for the stabilizer to be made from sheet metal rolled to form the tubular configuration and provided either before such rolling or afterwards with deformations defining said undulations; and for the
collar to have a circumferential gap which is coincident with the slot in the tubular stabilizer.
Clearly the stabilizer can be made of materials other than metal provided that it exhibits some degree of resilience, and adequate deformability. In the case of metal the material could be a suitable high tensile steel.
It will be understood that the undulations enable the tubular stabilizer to flex along its length more easily into firm contact with the surface of a drilled hole in a rock wall, for example. Tests conducted to date indicate that a 1.2 metre long tubular stabilizer according to the invention and having undulations in the form of spaced circumferential grooves extending inwardly and spaced apart by about 100mm only pulled out at a force of 12 tonnes as opposed to 4 tonnes for the prior art equivalent.
In addition, because of the undulations there are formed spaces between the outer surface of the stabilizer and the inner surface of the hole at a series of positions along the length of the stabilizer. This enables grouting material, where grouting is used, to enter into this space and more firmly mechanically lock the stabilizer to the rock. The fact that grouting material can enter between the outer wall of the hole and the surface of the stabilizer also has the affect of protecting the stabilizer against corrosion and it is envisaged that, at least for a large proportion of applications, a grouted tubular stabilizer according to the invention could be regarded as a permanent stabilizer rather than a temporary one.
In order that the invention may be more fully understood two different embodiments thereof will now be described with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:- FIG. 1 is an isometric view of a prior art tubular stabilizer; FIG. 2 is a similar view of a stabilizer according to the invention;
FIG. 3 illustrates an application of stabilizers in schematic sectional elevation; FIG. 4 is an enlarged sectional elevation of a portion of a stabilizer according to the invention operatively installed in a drilled hole; and FIG. 5 is a longitudinal sectional elevation of a part of the length of an alternative embodiment of the invention.
DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS As indicated under the section headed"Background to the Invention", a tubular stabilizer of the type illustrated in Figure 1 is known. In this case the tubular stabilizer (1) has a smooth outer wall (2) extending along the length thereof and a circumferential gap or slot (3) also extending along the entire length of the stabilizer. The operatively inner end (4) of the stabilizer tapers to allow its introduction into a hole and the operatively outer end (5) has a ring-shaped collar (6) welded to its outer surface. The collar bridges the gap as indicated by numeral (7).
Turning now to the embodiment of the invention illustrated in Figure 2, the basic construction of the stabilizer is the same, the stabilizer (8) being tubular and having a slot (9) extending along its entire length.
However, as provided by the invention, undulations in this case in the form of circumferential grooves (10), are formed in the wall of the tube at spacings of about 100mm apart. In the case that the tubular stabilizer is formed by rolling a flat metal sheet, the grooves could be formed either before or after the rolling or, for that matter, during the rolling operation. Indentations could also be pressed into the tubular stabilizer after it has been formed.
In this embodiment of the invention, as in the case of the prior art, the operatively inner end (11) of the stabilizer is tapered to a narrower end (12) to facilitate insertion of the stabilizer into a drilled hole. The collar (13), however, has its gap (14) in registration with the slot (9) so that the entire outer portion of the stabilizer can be inserted in a hole and flex outwardly without hindrance from the bridge (7) of the prior art stabilizer.
In use, stabilizers (9) according to the invention are introduced into pre-drilled holes (15) in a body of rock (16) as shown in Figure 3. A washer (17) is installed on the stabilizer prior to introduction into a hole so that the collar (13) can bear against the washer to transfer force to the rock surface and retain the rock directly and optionally indirectly through a mesh (18).
The stabilizer is driven into its operative position using a percussion machine such as a pneumatic hammer, conveniently that of a drill, a hydraulic percussion hammer arrangement, or any other suitable percussive instrument. They may even be driven in manually using a suitable hammer.
Turning now more particularly to Figure 4, there is shown the spaces (19) that are formed between the surface (20) of the hole and the outer surface of the stabilizer. In the case that grouting material is introduced into the stabilizer, under pressure, grouting material will enter the grooves via the slot (9) and pass around the grooves to substantially encircle the stabilizer at all positions at which grooves are present. It is anticipated that this will greatly enhance the anchoring of the stabilizer in its operative position and will also contribute significantly towards diminishing corrosion of the stabilizer.
Turning now to the embodiment of the invention illustrated in Figure 5, there is shown an arrangement in which the undulations assume the form of bumps (21) pressed out of the metal before it is rolled to its tubular configuration and these bumps (21) actually engage the wall (22) of the hole (23). The bumps form a gap (24) over substantially part of the outer surface of the stabilizer and grouting material indicated by numeral (25) will enter all of these spaces via the slot during a grouting operation.
It will be understood that numerous variations may be made to the embodiments of the invention described above without departing from the scope hereof. It will be quite apparent that the shape and configuration of the undulations can be varied considerably and that different configurations of undulations may be more appropriate to some rock conditions that other rock conditions. Also, the materials of construction of the stabilizer can be varied as required.