WO2018232426A1

WO2018232426A1 - A method of adapting a rock bolt for improved resin anchoring

Info

Publication number: WO2018232426A1
Application number: PCT/ZA2018/050035
Authority: WO
Inventors: Brendan Robert Crompton; James William Sheppard
Original assignee: Ncm Innovations (Pty) Ltd
Priority date: 2017-06-12
Filing date: 2018-06-12
Publication date: 2018-12-20
Also published as: ZA201803893B

Abstract

The invention provides a method of adapting a rock bolt, which has an elongate metal body which extends between a leading end and a trailing end, to provide the bolt with a positioning and a puncturing formation, the method including the steps of: cutting a pair of slits longitudinally into the leading end of the body, where each slit is cut transverse to the other slit, to provide the leading end with four pie shaped sections and peeling each of a first pair of opposed sections away from the leading end towards the trailing end to provide a pair of bowed positioning formations.

Description

A METHOD OF ADAPTING A ROCK BOLT FOR IMPROVED RESIN ANCHORING

BACKGROUND OF THE INVENTION

[0001] This invention relates to a method of adapting a rock bolt for improved a resin anchoring.

[0002] It is well known in the art to anchor a rock bolt into a rock hole with a grout or a two-part resin. The grout or resin is introduced into the rock hole, ahead of the bolt, by means of grout or resin capsules.

[0003] The rock bolt has to be adapted to puncture the capsule to release the contents. With the two-part resin, the contents have to be thoroughly mixed to achieve optimal setting.

[0004] Strictly, the resin is not an adhesive as it does not adhere the rock bolt to the rock hole. The resin mechanically locks the rock bolt in the rock hole. Thus, there is a reliance upon mechanical interlock with irregularities in the surface of the rock bolt and the rock hole walls to prevent the rock bolt from being pulled from the rock hole. The irregularities on the surface of the rock bolt are provided by a profiled surface.

[0005] Another factor influencing optimal mechanical lock is how efficient the rock bolt is at mixing the two parts of the resin. Typically mixing efficiency decreases in a radial direction from the surface of the rock bolt to the rock hole wall. This means that the larger the ratio between the diameter of rock hole and the rock bolt, i.e. the larger the annular space between the rock bolt and the rock hole wall, the greater the mixing inefficiency towards an outer circumference of the annular space. Potentially, this reduces the load bearing capacity of the rock bolt.

[0006] This factor places a limit on the diametric size of the rock bolt that can be used for a particular hole size. There is economic motive to using as small a rock bolt as possible.

[0007] A resin rock bolt therefore must have features which are a compromise between a mixing and an anchoring function. Unfortunately, the functions are not complementary. Optimising the mixing features tends to decrease the anchoring abilities of the bolt. A typical rock grouted resin anchored rock bolt is profiled with a series of ridges angled at 45^Q. These ridges provide a compromise between anchoring and mixing functionality.

[0008] Another issue in resin bolting is that the rock bolt is very rarely inserted in complete co-axial alignment with the rock hole causing eccentricity of the bolt to the rock hole, about the distal end of the bolt. At the distal end, the annular space is irregular, with a thin and a thick annular arc. In the thin annular arc there is insufficient resin to provide optimal mechanical interlock. Whilst in the thick annular arc, the resin is insufficiently mixed. And with insufficient resin in the small annular arc, the protective barrier provided by the resin is thinned, increasing the chance of acid mine water penetrating to the rock bolt.

[0009] The invention aims, at least partly, to address the aforementioned problems. SUMMARY OF THE INVENTION

[0010] The invention provides a method of adapting a rock bolt, which has an elongate metal body which extends between a leading end and a trailing end, to provide the bolt with a positioning and a puncturing formation, the method including the steps of: a) cutting a pair of slits longitudinally into the leading end of the body, where each slit is cut transverse to the other slit, to provide the leading end with four pie shaped sections; and b) peeling each of a first pair of opposed sections away from the leading end towards the trailing end to provide a pair of bowed positioning formations.

[0011] The method may include the additional step of sharpening a second pair of opposed sections into a penetrating formation.

[0012] The second pair of opposed sections may be sharpened by bevelling or chamfering each section at an outer leading end edge.

[0013] Prior to this step, the method may include the steps of removing material between the sections of the second pair to provide a gap and pushing each of the second pair sections inwardly into the gap.

[0014] From another prespective, the invention provides a method of adapting an end of a resin anchored rock bolt to provide for puncturing and positioning functionality which includes the steps of: (a) providing a resin anchored rock bolt which has an elongate steel body which extends between a leading end and a trailing end;

(b) cutting a pair of longitudinal slits into the leading end of the body, where each slit is cut transverse to the other slit, to provide the leading end with four pie shaped sections;

(c) peeling a first pair of opposed sections towards the trailing end to provide a pair of bowed locating formations; and

(d) forming a second pair of opposed sections into a sharpened penetrating formation.

[0015] It is well known in the art to anchor a rock bolt into a rock hole with a grout or a two-part resin. The grout or resin is introduced into the rock hole, ahead of the bolt, by means of grout or resin capsules.

[0016] The rock bolt has to be adapted to puncture the capsule to release the contents. With the two-part resin, the contents have to be thoroughly mixed to achieve optimal setting.

[0017] The second pair of opposed sections may be sharpened by bevelling or chamfering each section at an outer leading end edge.

[0018] Prior to this step, the method may include the steps of removing material between the sections of the second pair to provide a gap and pushing each of the second pair sections inwardly into the gap.

[0019] A resin bolt is also provided which includes an elongate body which extends between a trailing end and a leading end, which is adapted to a point or a blade, and which has a pair of positioning elements integral with the body at or towards the leading end, each extending laterally from the body in diametrically opposed directions.

[0020] Each positioning element may have even lateral reach.

[0021] Each positioning element maybe a finger-like projection which is bowed, with a free end pointing towards the trailing end.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The invention is further described by way of example with reference to the accompanying drawings in which:

Figures 1 A - 1 F are a sequential series of diagrammatic illustrations of the steps of the method of the invention;

Figure 2 is an isometric view of a penetrating end of a resin bolt made in accordance with the method of the invention ;

Figure 3 is a side on view of the penetrating end of the resin bolt.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0023] Figures 2 and 3 illustrate a resin anchored rock bolt 10 which has an elongate solid steel rod 12 which extends between a leading end 14 and a trailing end (not shown). A leading end section 16 of the rod is adapted, for a puncturing and a positioning function, in accordance with a method of the invention which is described below. The leading end section is formed with a puncturing formation 18 and a pair of diametrically opposed and laterally extending positioning formations, respectively designated 20A and 20B. [0024] The rod of the resin rock bolt 10, in this example, is of typical manufacture with a series of profile ridges 22 formed in an outer surface of the shaft. And, in this particular embodiment, the resin bolt has at least one paddle formation 24 which is integrally formed on the body. The paddle formation not only increases the diametric reach of the rock bolt in mixing the resin content of pre-installed resin capsules (not shown) but also increases the anchoring of the bolt within the rock hole.

[0025] The invention is directed to a method of adapting the leading end section 16 to provide the penetrating formation 18 and the positioning formations 20. The steps of the method are illustrated with reference to Figures 1 A - 1 F.

[0026] To the leading end 14 of the rock bolt body 12, a pair of slits, respectively designated 22A and 22B, are cut in the longitudinal direction to a predetermined depth. Each slit is transverse to the other. In this example, the slits are orthogonally orientated relatively to one another with a point of intersection being at the centre of the end 14. The slits define a first pair of pie shaped sections, respectively designated 28A and 28C, and a second pair of opposed pie shaped sections, respectively designated 28B and 28D.

[0027] In a subsequent step, illustrated in Figure 1 C, the longitudinal sections (28A, 28C) of the first pair are peeled away from the sections of the second pair in a direction towards the trailing end. The sections are bowed outwardly and downwardly to provide the pair of locating formations (20A, 28D). This action is illustrated with directional arrows in Figure 1 C. [0028] An outer facing side of each locating formation 20 is chamfered to provide a respective abutment surface 32 (Figure 3). In use, these surfaces will contact walls of a rock hole, into which the rock bolt is located, in a less resistive manner. [0029] In the next step, illustrated in Figure 1 D, a rectangular or wedge shaped chunk of material is cut away between the sections 28B and 28D of the second pair. Cutting away this material provides a gap 34 between sections of this pair into which the sections are pushed inwardly, as illustrated with directional arrows in Figure 1 D. Contacting one another, as illustrated in Figure 1 E, these sections provide a formation 36.

[0030] Finally, as illustrated in Figure 1 F, an outer leading edge 38 and surface 40 of the sections of the second pair (28B, 28D) may be bevelled or chamfered to sharpen the projecting formation into the sharpened puncturing formation 18. [0031] In use, the rock bolt 10 is inserted into a rock hole (not shown) with the sharpened puncturing formation 18 leading. A tip or bladed edge 42, being the original leading end 14 of the rock bolt body 12, sharpened or pointed, will puncture the frangible walls of the resin capsules, which have been pre-installed into the rock hole, as the bolt advances. [0032] As the bolt advances into the hole, the locating formations (28A, 28D) contact and abut the walls of the rock hole, ensuring that the rock bolt, at least along a leading end portion, is centralized. Positioned relatively concentrically within the hole provides the concomitant benefits of providing a regular annular resin interlock and barrier.

Claims

1 . A method of adapting a rock bolt which has an elongate metal body which extends between a leading end and a trailing end, to provide a bolt with a positioning formation, which methof includes the steps of cutting a pair of slits longitudinally into the leading end of the body, where each slit is cut transverse to the other slit, to provide the leading end with four pie shaped sections; and peeling each of a first pair of opposed sections away from the leading end towards the trailing end to provide a pair of bowed positioning formations.

2. A method according to claim 1 which includes the step of sharpening a second pair of opposed sections to provide a puncturing formation.

3. A method according to claim 2 wherein the second pair is sharpened by bevelling or chamfering each section at an outer leading edge.

4. A method according to any one of claims 1 to 3 which method includes the step of removing material between the sections of the second pair to provide a gap and pushing each of the sections inwardly into the gap.

5. A resin bolt which includes an elongate body which extends between a trailing end and a leading end, which is adapted to a point or a blade, and which has a pair of positioning elements integral with the body at or towards the leading end, each extending laterally from the body in diametrically opposed directions.

6. A resin bolt according to claim 5 wherein each positioning element has even lateral reach.

7. A resin bolt according to claim 5 or 6 wherein each positioning element is a finger-like projection which is bowed, with a free end pointing towards the trailing end.