AU2010235895A1 - Adhesively Fastening Rock Bolts - Google Patents

Description

1 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION STANDARD PATENT "Adhesively Fastening Rock Bolts" The following statement is a full description of this invention, including the best method of performing it known to me: 2 Adhesively Fastening Rock Bolts Field of the Invention 5 This invention concerns, in one aspect, the use of rock bolts to stabilize the ground in civil engineering and mining operations. It is particularly concerned with resin anchored bolts and has particular applicability to roof and wall stabilization in underground mines. 10 Background to the Invention Rock bolts are fastened into holes drilled for that purpose into the rock to be stabilized. Most rock bolts are made of solid steel bar, although some are made of 15 hollow steel bar and others are made from relatively light wall steel tubing. The present invention is particularly adapted to use of rock bolts made from solid bar. The most common method of installing a resin anchored rock bolt is by way of the following steps: 20 1. Drill the hole into the rock about 20cm short of the total length of the rock bolt. 2. Insert into the hole a sausage-like cartridge comprising the separated components of a 2-pack resin adhesive in a frangible casing. 3. Insert the rock bolt and commence rotating it. 25 4. Apply thrust to the rock bolt while it is rotating, so pushing it to the blind end (the far end) of the borehole to rupture the cartridge. The action of thrust and rotation mixes the resin components and shreds the cartridge casing. 5. Stop the rotation for a few seconds, during which time the resin cures. 6. Tension the bolt by applying a washer and tightening a nut on a threaded end 30 of the bolt protruding from the hole.

3 A significant problem in some situations, where the installation is not carried out to the supplier's directions, is the situation known as "gloving". The term is sometimes intended to indicate that fragments of the cartridge casing have become wrapped around the bolt and thus prevented proper adherence of the bolt to the body of resin 5 and thus the wall of the hole. However the term "gloving" may also be used in a broader sense, namely any condition where a portion of unmixed resin and/or a section of intact cartridge adversely affects the transfer of load from the bolt to the rock. Thus gloving in the broader sense includes situations where fragments of the cartridge casing have become wrapped around the bolt and also includes situations 10 where the casing has otherwise become pressed into a form where an isolated pocket still contains a significant quantity of only one part of the reactive mixture so that the pocket fails to react, and creates an inclusion which provides a weakness. Gloving can take place when a pressure front induced over the tip of a rapidly 15 advancing rock bolt applies pressure to the resin cartridge. As the bolt advances into the borehole the induced pressure can cause the film in the cartridge casing to stretch and the cartridge to expand radially. This expansion would normally be satisfactorily constrained by the wall of the borehole but, if the cartridge expands too much (say in weak ground or an oversize hole), the bolt may go inside the cartridge with little 20 shredding of the film. The film remains pressed against the inside of the borehole and the rotating bolt cannot mix or shred the film. Thus, in gloving situations the film may remain against the rock surface, or may wrap itself around the bolt, or may remain unshredded in clumps in the resin matrix. 25 All of these problems can result in the inability of the resin anchor to transfer the full load on the bolt to the rock. Gloving thus creates a major safety issue in mines where the lives of miners are dependent on a sound anchorage between rock bolts and the rock. 30 4 An aim of the present invention is to provide an alternative method and apparatus for installing resin anchored rock bolts whereby gloving is prevented or at least substantially reduced. 5 Summary of the Invention In one aspect the invention provides a method of stablising a zone of rock comprising: (i) drilling a hole into the rock, said hole having a deep end within the hole and an open end at a rock face; 10 (ii) inserting into the hole a frangible cartridge means comprising separate reservoirs having a frangible casing and containing components of a multi component reactive adhesive system; (iii) inserting a rock bolt into the hole such that a leading end of the bolt is towards said deep end of the hole and a trailing end of the bolt is towards said open 15 end of the hole; (iv) thrusting the bolt towards the deep end of the hole and rotating the bolt to thereby rupture said cartridge means, mix the components of the adhesive system, and embed the leading end of the bolt within the mixed components at the deep end of the hole; and 20 (v) allowing the adhesive to set and thereby anchor the bolt within the hole; characterized in that: (i) a cartridge engagement element is inserted into the hole between the bolt and the cartridge means, said engagement element extending further diametrally in the hole than does the bolt; 25 (ii) the engagement element is pressed by the bolt onto the cartridge means to thereby rupture the frangible casing; and (iii) the engagement element presses the frangible casing to the deep end of the hole while allowing the adhesive components to flow past the engagement element and into contact with the bolt. 30 The cartridge means is preferably one or more sausage-shaped containers with the adhesive components in each container being contained in a casing made of a 5 frangible plastics film. Different reactants of the adhesive system may be contained in respective separate such containers such that at least two sausage-shaped containers are required in each hole. However preferably each sausage-shaped container includes all the reactant components in the correct proportions separated by a barrier 5 within the container. The cartridge means is preferably a single container with two separate compartments therein for components of the multi-component reactive adhesive system. The rotation of the bolt may commence before the cartridge means is ruptured or the 10 cartridge means may be ruptured by a thrusting action before rotation commences. Preferably the cartridge engagement element does not rotate in unison with the bolt and, more preferably, the bolt spins freely against the engagement element. Preferably portion of the cartridge engagement element sits around the leading end of 15 the bolt. Preferably the leading end of the bolt is accommodated within a slotted cup forming part of the cartridge engagement element. The cartridge engagement element may be affixed to the cartridge. The bolt may be tensioned after the adhesive is set. 20 In another aspect the invention provides a cartridge engagement element for insertion between an end of a rock bolt and a frangible cartridge of adhesive components placed in a hole drilled into rock, said cartridge engagement element comprising: (i) a leading end adapted to engage the cartridge; 25 (ii) a trailing end adapted to engage the end of the bolt; (iii) one or more circumferential perimeter surfaces adapted to engage the wall of said hole; (iv) one or more sharpened features on said leading end adapted to puncture the casing of said cartridge; 30 (v) one or more bearing faces at the trailing end of the engagement element adapted to receive the end of the bolt and allow the bolt to rotate without rotating the engagement element.

6 In a further aspect the invention provides an assembly comprising a frangible cartridge of adhesive components to one end of which is affixed a cartridge engagement element said assembly being adapted for insertion ahead of a rock bolt 5 into a hole drilled into rock, said cartridge engagement element comprising: (i) a leading end affixed adjacent the cartridge; (ii) a trailing end adapted to engage the end of the bolt; (iii) one or more circumferential perimeter surfaces adapted to engage the wall of said hole; 10 (iv) one or more sharpened features on said leading end adapted to puncture the casing of said cartridge; (v) one or more bearing faces at the trailing end of the engagement element adapted to receive the end of the bolt and allow the bolt to rotate without rotating the engagement element. 15 The sharpened features may be pointed to puncture the cartridge, or may carry sharp edges to both puncture and slice the cartridge. The sharpened features preferably surround a cavity adapted to receive a closure on 20 the cartridge. The engagement element may have, at said trailing end, a socket portion adapted to loosely receive the rock bolt. The socket portion may comprise a skirt. The socket portion may comprise a cup having longitudinal slots in its walls. 25 The engagement element may carry a plurality of legs at its trailing end adapted to, in combination, loosely fit around the rock bolt.

7 Brief Description of the Drawings In order that the invention may be more fully understood there will now be described, by way of example only, preferred embodiments and other elements of the invention 5 with reference to the accompanying drawings where: Figure 1 is a cutaway fragmentary view of a rock bolt in the process of being installed according to one embodiment of the present invention; 10 Figure 2 is a perspective view of a cartridge engagement element according to another embodiment of the present invention; Figure 3 is a view of the leading end of the element in Figure 2; 15 Figure 4 is a view of the trailing end of the element in Figure 2; Figure 5 is a side view of the element in Figure 2; Figure 6 is a cross section view along plane D-D shown in Figure 3; 20 Figure 7 is a cross section view along plane E-E shown in Figure 5; Figure 8 is a perspective view of a cartridge engagement element according to another embodiment of the invention; 25 Figure 9 is a side view of the engagement element in Figure 8; Figure 10 is a perspective view of a cartridge engagement element according to a further embodiment of the invention, and as used as a component in Figure 1; 30 Figure 11 is a view of the leading end of the cartridge element in Figure 10; and 8 Figure 12 is a cross section view along plane G-G shown in Figure 11. Description of the Preferred Embodiment and Other Examples of the Invention 5 Referring to Figure 1, a borehole 2 has been drilled into a zone of rock 3 for the purpose of anchoring a rock bolt 4 so that it can be tensioned to stabilize the zone of rock. The borehole 2 has a deep end 5 within the hole and an open end 6 at the rock face 7. The rock bolt 4 is shown almost fully inserted. Rock bolts have a length which is typically between 2 and 4 metres, depending upon its purpose and the nature 10 of the rock into which it is installed. Slipped onto the leading end 8 of the rock bolt is a cartridge engagement element 9. Between the cartridge engagement element 9 and the deep end 5 of the hole, is a 15 sausage-shaped cartridge 11 containing a multi-component reactive adhesive suitable for fastening the bolt to the rock. The cartridge 11 takes the form of a sausage-shaped bag 13, forming a casing, containing reservoirs of components of a multi-component reactive adhesive system. 20 The bag is made from a plastics film tubing 14 gathered and sealed with a closure 15 at each end to form an umbilicus 17 at each end of the bag. The cartridge 11 has two or more compartments, one compartment for each component in a reactive adhesive formulation. Two-part liquid epoxy adhesives or polyester adhesives are preferred, but three-part systems, or systems with even more parts, may be used. 25 Such cartridges and the resin components therein are well known. A suitable cartridge would be that sold in Australia by Celtite Pty Ltd under the product designation "G9 Duo Speed". 30 The rock bolt 4 shown in Figure 1 is formed from a length of hot rolled ribbed steel bar. To install the rock bolt 4, the borehole 2 is drilled into the zone of rock 3 which is to be stabilized and debris is flushed from the hole. The cartridge It is then fed 9 into the hole 2. The cartridge engagement element 9 is slipped onto the leading end 8 of the rock bolt and both are then fed into the hole 2 whereupon the engagement element on the end of the bolt pushes the cartridge II up to the deep end of the hole. 5 The rock bolt is then rotated by means of the hexagonal nut 19 on a threaded portion 35 on the trailing end 21 of the bolt. The rock bolt rotates but its leading end 8 spins freely within engagement element 9 so that the engagement element does not rotate, To assist the bolt to spin freely, the ribs 10 on the leading end 8 have been removed, 10 by machining or swageing, for a short length to produce a relatively smooth cylindrical surface 12. Such removal may not be necessary in some circumstances. The bolt 4 is then thrust firmly into the hole while maintaining the rotation whereupon sharpened points 23 on the leading end 25 of the engagement element 15 puncture the cartridge 11 all around the umbilicus 17 that the sharpened points 23 surround. A cup-shaped cavity 29 in the leading end of the engagement element cradles the umbilicus 17 and closure 15 from the trailing end of the cartridge. The engagement element 9 presses the bag 13 and the remainder of the casing towards 20 the deep end 5 of the hole while the reactive components of the resin adhesive flow past the engagement element 9 and into the annulus 31 between the rock bolt 4 and the wall 32 of the borehole 2 where high shear conditions induced by the rotating rock bolt ensure good mixing of the reactants. 25 As the engagement element 9 is not rotating (or is perhaps rotating a little but not nearly as fast as the rock bolt) and as the casing of the cartridge does not contact the rock bolt, the plastic film is not substantially shredded and thus does not lead to a gloving condition. No strips of film are entrained in the resin around the bolt to cause a weakness. 30 Any portions of unmixed components, isolated within folds of the film, remain at the end of the hole where they have negligible effect on load transfer from bolt to rock.

10 After an appropriate time of stirring, typically around 30 seconds, the rotation is stopped and the bolt 4 is supported in its fully inserted position for another period, typically 20 or 30 seconds, by which time the adhesive has set. The nut is then tightened against a washer 33 to tension the bolt. 5 The nut 19 incorporates a push-out plug so that it will rotate the bolt to mix the adhesive but, when the adhesive sets the plug pushes out, allowing the nut to run up the threaded portion 35, 10 The cartridge engagement element 40 illustrated in Figures 2 to 7 has a leading end 42 and trailing end 44 at longitudinally opposite ends. Towards the leading end a cylindrical tubular portion forms the main body 46 of the engagement element 10. At the leading end 42 of the cartridge engagement element, the cylindrical body 46 carries an array of teeth 50 which form a serrated rim 48. The serrations 49 are like a 15 saw tooth and are caused to be sharp by means of a beveled face 52 on the inwards surface of each of the teeth 50 so that the leading tip 54 of each tooth is a sharp point. The teeth 50 form a single row completely around the rim 48 and the cylindrical body 46 accordingly has the general shape of a tall crown. 20 Extending radially from the outer wall 55 of the cylindrical body 46 are four support arms 56, each arm being at right angles to its neighbouring arms 56, and each arm 56 having a radially extending web portion 58 and a circumferentially extending flange portion 60 such that the support arms 56 have a T-shaped cross-section and extend outwards from the cylindrical body 46 by the upright of the T. The arms 56 extend 25 longitudinally for about the middle third of the engagement element 40. On the radially outer faces 61 of each flange portion 60 is a circumferential perimeter surface 62 which in use rubs against the wall of the borehole as the element 40 is pushed along the hole. 30 The support arms 56 extend longitudinally of the element 40 to slightly beyond the cylindrical body 46 towards the trailing end 44 of the engagement element. At its 11 trailing end 44 the engagement element 40 has a bolt engagement portion 63 which is cruciform shaped in diametral cross-section as best seen in Figure 4. The bolt engagement portion 63 has its end face 64 at the trailing end 44 of the element. The cruciform-shaped end face 64 forms a bearing face 68 upon which in use a leading 5 end of a rock bolt would bear and rotate. The cylindrical body 46 forms a cup-shaped cavity 59 surrounded by sharpened features on its rim 48. The bottom of the cavity 59 is not fully closed as there are apertures 65 between the arms of the cruciform-shaped portion 63. The cavity 59 10 provides a means to capture the umbilicus 17 and closure 15 from the trailing end of a cartridge being used, while the apertures 65 provide flow paths for liquid adhesive reagents expelled from the cartridge and moving to the annulus 31 between the bolt and borehole wall 32. Resin adhesive also flows past the element 40 by passing along the four annular voids 67 between the flange portions 60 of the support arms 56. The 15 annular voids 67 are too small for large segments of cartridge film to pass through, especially as the film has not been greatly shredded by contact with the rotating bolt. If desired, two or more cartridges 11 may be used in a borehole if a greater volume of adhesive is required. Both ruptured bags are then retained between the deep end 2 of 20 the hole and the engagement element. Referring now to Figures 8 and 9, a different cartridge engagement element 70 is shown therein. It comprises a cylindrical body 76 carrying a serrated rim 78 having teeth 80 at the leading end 72 all generally the same as those described with reference 25 to Figures 2 to 7. However a difference is that the engagement element 70 has at its trailing end 74 a different arrangement for engaging the leading end of a rock bolt. In this embodiment the flange portions 90 of the support arms 86 are extended beyond the bottom 77 of the cylindrical body 76 to form four flattened legs 88. The outward 30 facing surfaces 92 of the legs 88 form a continuation of the peripheral surfaces 91 of the support arms 86. The cavity 96 in the cylindrical body 76 has no formed base in it to retain the umbilicus and closure from the cartridge, but in use the end face of the 12 leading end of the rock bolt would be hard up against the bearing face 94 at base of the cavity 96 so the umbilicus and closure would not escape that way. The legs 88 form a cup like or skirt-like structure with wide slots in its wall. The legs 5 provide a means by which the element 70 may be retained on the leading end of a rock bolt. The addition of the legs 88 when compared with the embodiment shown in Figure 2 provides the advantage that they serve to better support the end of the bolt away from the wall of the hole when the bolt is rotating. This smooths the rotation operation and reduces the propensity of the rotating rock bolt to damage the wall of 10 the hole. Referring to Figures 10 to 12, the cartridge engagement element 100 shown therein is that which can also be seen in Figure 1. The element 100 has a leading end 102 and a trailing end 104 at longitudinally opposite ends. The element 100 has a cylindrical 15 main body portion 111 having a diameter substantially the same as the diameter of a rock bolt it is intended for use with. Rising from the main body portion at the leading end 102 is a smaller diameter cylindrical portion 106 with a serrated rim 108. The rim 108 carries a row of pointed teeth 110 and is the same as the rims described above with reference to the embodiments shown in Figure 2 and 8. 20 The cylindrical portion 106 extends from the leading face 103 of the main body portion 111 for a distance approximately half the diameter of the main body portion. The cylindrical portion 106 is thus about half the length of the corresponding portions described for other embodiments above. 25 The cylindrical portion 100 surrounds a cup-shaped cavity 119 which has a depth about twice the height of the cylindrical portion 106. The cavity 119 thus penetrates well into the main body portion 111. 30 Four flattened legs 118 are spaced equally around the perimeter of the main body portion 111 and extend up the outside surface 117 of the main body portion. The legs 118 extend beyond the trailing face 113 of the main body portion, and have a cross 13 section the shape of a circumferential strip of an annulus the inner diameter of which is the same as the outside diameter of the main body portion 111. The outer surfaces 122 of the legs 118 are the surface which rubs against the borehole wall during installation. The legs 118 serve to locate the element 100 onto the leading end of a 5 rock bolt. The bottom of the cavity 119 is blanked off by a solid wall 105. This wall provides a greater degree of rigidity than the open-bottom arrangement in Figure 8. It also provides a much greater bearing surface for the rock bolt to push against when it is 10 rotating. This can be important when the element 100 is made from an injection moulded plastics material, as narrow bearing surfaces of such materials could fail under the aggressive rotation, loads and rough end of the bolt. Between the legs 118, the smaller diameter of the main body portion creates flow 15 channels 127 which provide means by which the resin bypasses the element 100 when it is being used in the anchoring of a rock bolt. The cartridge engagement elements in their various forms are all preferably made from any suitable injection moulded plastic material. The cartridge engagement 20 elements may be fastened in some manner to the cartridge, such as by hot melt gluing the umbilicus 17 to the bottom 105 of the cylinder body portion 76. In this way a bolt installer in a mine only needs to be concerned about feeding a single unit into the hole instead of ensuring that both the cartridge is in the hole and the cartridge engagement element is slipped onto the leading end of the rock bolt. 25 Suitable sizes for the features when installing a nominal 24mm diameter bolt using a cartridge engagement element as shown in Figures 10 and 11 are: Diameter of borehole 27-28mm Total length of engagement element 37mm 30 Depth of cavity 119 from top of teeth 20mm Length of legs beyond trailing face 113 15mm Diameter through legs 118 25mm 14 Diameter of main body Ill 2 3mm Number of teeth 16 The cartridge engagement elements described may be modified to include a short 5 static mixing portion whereby the reactive components of the resin are given a significant preliminary mixing before being introduced into the annulus bounded by the bolt and the hole wall. Whilst the above description includes the preferred embodiments of the invention, it 10 is to be understood that many variations, alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the essential features or the spirit or ambit of the invention. 15 It will be also understood that where the word "comprise", and variations such as "comprises" and "comprising", are used in this specification, unless the context requires otherwise such use is intended to imply the inclusion of a stated feature or features but is not to be taken as excluding the presence of other feature or features. 20 The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that such prior art forms part of the common general knowledge in Australia.

Claims (20)

1. A method of stabilizing a zone of rock comprising: 5 (i) drilling a hole into the rock, said hole having a deep end within the hole and an open end at a rock face; (ii) inserting into the hole a frangible cartridge means comprising separate reservoirs having a frangible casing and containing components of a multi-component reactive adhesive system; 10 (iii) inserting a rock bolt into the hole such that a leading end of the bolt is towards said deep end of the hole and a trailing end of the bolt is towards said open end of the hole; (iv) thrusting the bolt towards the deep end of the hole and rotating the bolt to thereby rupture said cartridge means, mix the components of the adhesive is system, and embed the leading end of the bolt within the mixed components at the deep end of the hole; and (v) allowing the adhesive to set and thereby anchor the bolt within the hole; characterized in that: (i) a cartridge engagement element is inserted into the hole between the bolt 20 and the cartridge means, said engagement element extending further diametrally in the hole than does the bolt; (ii) the engagement element is pressed by the bolt onto the cartridge means to thereby rupture the frangible casing; and (iii) the engagement element presses the frangible casing to the deep end of 25 the hole while allowing the adhesive components to flow past the engagement element and into contact with the bolt.

2. A method according to claim 1 wherein said cartridge means comprises one or more sausage-shaped containers with the adhesive components in each container 30 being contained in a casing made of a frangible plastics film. 16

3. A method according to any one of the previous claims wherein all the reactants of the adhesive system are contained in each respective said container.

4. A method according to any one of the previous claims wherein said cartridge 5 engagement element does not rotate in unison with the bolt.

5. A method according to any one of the previous claims wherein the bolt spins freely against the engagement element. 1o

6. A method accordingly to any one of the previous claims wherein a portion of the cartridge engagement element sits around the leading end of the bolt.

7. A method according to claim 6 wherein said leading end of the bolt is accommodated within a slotted cup which forms part of the cartridge engagement 15 element.

8. A method according to any one of the previous claims wherein the cartridge engagement element is affixed to the cartridge. 20

9. A cartridge engagement element for insertion between an end of a rock bolt and a frangible cartridge of adhesive components placed in a hole drilled into rock, said cartridge engagement element comprising: (i) a leading end adapted to engage the cartridge; (ii) a trailing end adapted to engage the end of the bolt; 25 (iii) one or more circumferential perimeter surfaces adapted to engage the wall of said hole; (iv) one or more sharpened features on said leading end adapted to puncture the casing of said cartridge; (v) one or more bearing faces at the trailing end of the engagement element 30 adapted to receive the end of the bolt and allow the bolt to rotate without rotating the engagement element. 17

10. A cartridge engagement element according to claim 9 wherein the sharpened features surround a cavity adapted to receive a closure on the cartridge. 5

11. A cartridge engagement element according to claim 10 wherein the sharpened features comprise a row of teeth extending around a rim of said cavity.

12. A cartridge engagement element according to any one of claims 9 to 11 wherein the engagement element has, at said trailing end, a socket portion adapted to 10 loosely receive said rock bolt.

13. A cartridge engagement element according to claim 12 wherein said socket portion comprises a skirt. 15

14. A cartridge engagement element according to claim 12 wherein said socket portion comprises a cup having longitudinal slots in its walls.

15. A cartridge engagement according to any one of claims 9 to 11 wherein said engagement element has a plurality of legs at its trailing end adapted to, in 20 combination, loosely fit around the rock bolt.

16. A cartridge engagement element according to any one of claims 9 to 11 having a plurality of supporting arms extending diametrally therefrom, each said arm having a radially extending web portion and a circumferentially extending flange portion, 25 which said flange portions in use rub against the wall of said hole drilled into the rock.

17. An assembly comprising a frangible cartridge of adhesive components to one end of which is affixed a cartridge engagement element said assembly being adapted 30 for insertion ahead of a rock bolt into a hole drilled into rock, said cartridge engagement element comprising: (i) a leading end affixed adjacent the cartridge; 18 (ii) a trailing end adapted to engage the end of the bolt; (iii) one or more circumferential perimeter surfaces adapted to engage the wall of said hole; (iv) one or more sharpened features on said leading end adapted to puncture 5 the casing of said cartridge; (v) one or more bearing faces at the trailing end of the engagement element adapted to receive the end of the bolt and allow the bolt to rotate without rotating the engagement element. 10

18. An assembly according to claim 17 wherein said sharpened features surround a cavity in which is received a closure on the cartridge.

19. An assembly according to claim 18 wherein said sharpened features comprise a row of teeth extending around a rim of said cavity, 15 Dated this 19th day of October 2010

20 DYWIDAG Systems International Pty Limited by their patent attorneys Morcom Pernat