GB2194828A

GB2194828A - Anchoring dowel

Info

Publication number: GB2194828A
Application number: GB08719496A
Authority: GB
Inventors: Laban Keith Rixon; Robert Burns Tait
Original assignee: Australian Coal Industry Research Laboratories Ltd
Current assignee: Australian Coal Industry Research Laboratories Ltd
Priority date: 1986-08-22
Filing date: 1987-08-18
Publication date: 1988-03-16
Also published as: GB8719496D0

Abstract

An anchoring dowel for rib support or rock bolting applications consists of a tube (10) of plastics material such as PVC. The dowel may be fitted with an internal tension member (17) of fibre reinforced plastics or other material. Grout or resin may be incorporated in a tube and ejected through the end of the tube into the bore during installation. <IMAGE>

Description

SPECIFICATION Mineable strap and bolts FIELD OF THE INVENTION This invention relates to apparatus for the support of side walls (or ribs) of roadways in coal mines. The invention also provides apparatus which is useful for some applications in mine floor and roof support.

BACKGROUND ART Roadway and long wall rib support has conventionally been obtained by the use of steel rock bolts, which have the disadvantage of interfering with later mining. Attempts have been made to use mineable materials and support elements or dowels have been made from wood and fibreglass. U.S. patents 3,302,410 and 3,324,663 of McLean describe the use of dowels in the form of fiberglass rods resin bonded to the strata. U.S. patent 2,667,037 of Thomas et al describes an expansion-type roof bolt comprising a tubular body which allows a quick-hardening cement to be pumped through the body and into the space surrounding the bolt.

An object of the present invention is to provide mineable support elements which, unlike those of the prior art, are tensionable and simple in fitting and tensioning, and which enable choices to be made between strength and cost so that cost effectiveness can be maximised for a particular application.

The invention will be described in relation to two major embodiments, one suitable for light or medium duty and which may optionally be tensioned, and the other for heavy duty applications with tensioning of the dowel.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Fig. 1 shows in side elevation, a light duty rib support dowel according to the present invention; Fig. 2 is an end elevation of the dowel illustrated in Fig. 1; Fig. 3 is a side elevation of a heavy duty rib support dowel embodying the present invention; Fig. 4 is a fragmentary longitudinal crosssection of the dowel of Fig. 3; Fig. 5 is a lateral cross-section of the dowel of Fig. 3, taken on the line 4-4 of Fig.

4; and Fig. 6 is a side elevation of a tensioning adapter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The rib support dowel illustrated in Figs. 1 and 2 comprises a shaft 10 formed as a hollow extrusion of a suitable plastics material such as unplasticised polyvinylchloride. At one end of the shaft 10 a paddle type mixer 11 is provided, in this embodiment consisting of three flats 12 formed by crushing the hot shaft, either during extrusion or as a separate operation, and then allowing the shaft to cool. The star-shaped formation is allowed to spring back somewhat on cooling, leaving a small opening 13 in the end of the dowel for the extrusion of grout during installation, if this is required.

At the other end of the shaft 10 there is provided a loading washer 14 which is fixed to the shaft by means of a closely fitting skirt 15, preferably with the use of an adhesive of cyanoacrylate type, and a retaining head 16, the outer end of which is provided with a shape suitable for attachment to conventional coal mining equipment, this shape typically being a 25 mm square or a 20 mm per side hexagonal.

The retaining head 16 is normally cast in the same material as the shaft 10, but may be machined, moulded or extruded. The head 16 is provided as a press fit over the shaft 10, and like the washer 14, is fixed by adhesive preferably of the cyanoacrylate type.

For light duty applications, the dowel illustrated in Figs. 1 and 2 is designed to carry tensile loads in the range of 4.9 kN to 13 kN, with a nominal outside diameter of 25 mm and wall thickness from 1.7 mm to 3.65 mm. In medium duty applications, for tensile loads of up to 30 kN, the nominal shaft size is increased to 32 mm and wall thicknesses of 2.8 mm to 4.45 mm are employed, giving a strength of 10.9 kN to 17.7 kN.

The load carrying capacity of the dowel system of Figs. 1 and 2 may be increased by the addition of filler material either during manufacture or on installation. The strength, consistency and material used for these fillers can be varied to adjust the dowel load carrying capacity, and such fillers include cementitious grouts, foams, resins, talcs and glass.

The unplasticised PVC employed in the preferred embodiment of the invention illustrated in Figs. 1 and 2 has the following properties: Mechanical Properties at 200 C Density 1430 kg/m3 Direct Tensile Strength 52 MPa Compressive Strength 66 MPa Mobulus of Elasticity 2750 MPa Thermal Properties Specific Heat 1047 J/kg C Coefficient of Expansion 0.0675 mm/m/ C Softening Point 75 C Flame Resistance Self Extinguishing The properties given above relate to normal suspension polymerised polyvinylchloride homopo lymer non-impact modified. It will be appreciated that impact modification and filling can be used to improve the impact resistance of the dowel.

The light or medium duty dowels of the kind illustrated in Figs. 1 and 2 may be installed in a manner similar to that employed with non-tensile dowels in the prior art, by drilling for reception of the dowel, locating the anchoring adhesive and the dowel shaft within the drilled hole, mixing and allowing the adhesive or grout to set, with the loading washer 14 against the face of the rib or against an underlying plate or washer.

The fact that the present dowel is hollow, enables post-grouting to be employed, and also enables injection of anchoring resin after installation of the shaft within the drilled hole, a considerable advantage over prior art dowel constructions.

A most significant consequence of employing as the body of the dowel, a hollow tube of plastics material such as PVC, is the very great extension of which the dowel is capable without failure. The invention in this form is characterised by the use of a tubular body of plastics material capable of significant deformation without failure, but of a diameter sufficient to withstand the necessary torsioned stresses without torsional deformation. The PVC tube referred to satisfies these criteria, as will many other plastics materials.

Illustrated in Figs. 3, 4 and 5, is a heavy duty rib support dowel embodying the present invention. As in the case of the light duty dowel, a hollow shaft 10 of unplasticised PVC is provided at one end with a paddle formation 11. In this case however the dowel additionally comprises a centre member 17 of relatively great tensile strength, and thus the dowel of this embodiment carries tensile loads by means of the member 17, and torque by means of the outer case or shaft 10.

A suitable construction for the end of the dowel of this embodiment, is shown in Fig. 4. An end connector 18 of the same outside diameter as the shaft 10, is fixed to the shaft by the adhesion within the shaft of a reduced diameter portion 19, preferably by cyanoacrylate adhesive. The connector 18 is provided with an axial cavity 20 in which the end of the tensile member 17 is located, and this end of the member 17 is split and wedged at 21. The cavity 20 is then filled with resin to mould the end connector around the split end of the member 17, ensuring that the member 17 is retained in the end connector 18 without significant slippage upon application of the tensioning load.

The important advantage of this construction of dowel is that the outer shaft 10 carries the torque loads applied to the dowel during installation, so that the member 17 can be designed solely to carry tensile forces. This allows the use of a wide range of materials for the member 17, and particularly allows the use of fibre reinforced resins in the form of fibreglass rods, which while well suited to the tensile loads employed, are normally inappropriate for applications such as rib support dowels, due to their sensitivity to torsion loading.

In normal applications a nominally 25 mm outside diameter outer tube 10 of 1.7 mm wall thickness PVC tube will satisfactorily carry a torque of 70 Nm, and of course greater wall thickness can be employed where greater torque loads are encountered.

Materials suitable for the tension member 17 include woven strand rope, extruded, drawn, moulded or machined products such as steel, nylon, kevlar, glass fibre, carbon fibre, boron fibre.

The particular material chosen and the dimensions of the member 17 determine the strength of the rib support dowel.

The end connector 18 may be manufactured from mild steel or chopped glass fibre dough mould, but alternatively other materials such as thermoplastics, thermosets, other metals and composite materials may be employed. Similar materials may be employed for the flaring wedge 21.

It will be appreciated that the tension member 17 is anchored to the shaft 10 at the inner end thereof, by means of a further end connector 18.

The end connector 18 at the outer end of the dowel is shaped to adapt to drilling equipment for the application of torque in installation.

If desired, the dowel system of Figs. 3 to 5 may be pre-tensioned by threading a suitable length of the end connector 18 and driving with a nut 22 which may be pinned or provided with a resin "break out" system to govern the tensioning torque.

Illustrated in Fig. 6, is a tensioning adaptor which may be employed with either of the dowel systems described above, or indeed with prior art systems, to provide pre-tensioning capability.

In this embodiment the tensioning adaptor comprises a moulded or machine formed threaded sleeve 23 which may be placed over the dowel shaft 10 prior to the mounting of the loading washer and retaining head of the light duty dowels, or the end connectors in the case of the heavy duty dowel, the sleeve being fixed to the shaft by a suitable adhesive.

A drive nut 24 engages with the threaded sleeve to enable tensioning of the dowel system to take place upon completion of installation as in the case of the integral tensioning system referred to above in relation to the embodiment of Figs. 3 to 5, the drive nut may use a resin plugged "break out" system or some suitable form of shear pin to govern the torque at which tensioning may begin.

In an alternative form of the invention illustrated in Figs. 7 and 8, the hollow dowel is used as a receptacle for the grout, resin, cement or other fixing material 25. The fixing material may be inserted into the hollow dowel during part of the manufacturing process and ejected once the dowel is in place.

The ejection may be achieved as shown in Fig. 7 by inserting a plunger 26 though the end connector and manually pushing it to the base of the dowel or as shown in Fig. 8 by placing a piston or seal 27 in front of the fixing material and ejecting it with compressed air or water introduced by attachment to the retaining head 16. The use of water as the ejecting medium opens the possibility of using the ejection medium as the catalyst for the fixing material, e.g.

water with cement or purpose-made water set chemicals.

If using two-part resins or similar as the fixing material some form of mixing device at the small hole at the dowel end would be employed. The fixing material, if a two-part resin or similar, may be installed in the dowel inside a divided sheath as is presently used with resin capsules for rock bolts. If this is employed a device may be included in the dowel to puncture the sheath when the ejection medium was applied. Depending upon the nature of the fixing material the holes at each end of the hollow dowel may need temporarily to be plugged at manufacture.

The concept of having a hollow fastener with the fixing material placed inside at manufacture or on site could be appropriate to many fastening systems outside mine rib reinforcement as described. An immediate application is in rock bolting.

Claims

1. A mineable support element for fixing within a bore hole in a rock formation, comprising a body of synthetic plastics material in the form of a hollow tube capable of substantial tensile deformation without failure.

2. A support element according to claim 1, wherein said body is provided at a first, distal end with an integrally formed mixing formation.

3. A support element according to claim 2, wherein said mixing formation comprises a plurality of flats formed by pressing said tube at its end while said tube is hot, thereby plastically to deform said tube.

4. A support element according to claim 3, wherein said mixing formation provides an opening in the distal end of said dowel providing communication between the interior of said dowel and the interior of said bore.

5. A support element according to claim 1, further comprising a loading washer mounted adjacent a second, proximal end of said tube, between retaining sleeve means fixed to said tube and a retaining head fixed to the end of said tube.

6. A support element according to claim 5, wherein said retaining sleeve means comprises a sleeve fixed to said tube by adhesive.

7. A support element according to claim 5, wherein said retaining head is press fitted on to said tube, and fixed thereto by adhesive.

8. A support element according to any preceding claim, wherein said tube consists of unplasticized polyvinylchloride.

9. A support element according to claim 1, further comprising a tension member extending within said tube and fixed at its ends to said tube, said tension member having a tensile strength greater than that of said tube.

10. A support element according to claim 9, further comprising an end connector member fixed to an end of said tube, an end of said tension member being located within an axial cavity within said end connector member, that portion of said tension member within said cavity being deformed therein, said cavity being filled with hardenable material.

11. A support element according to claim 9, wherein said tension member comprises a fibrereinforced plastics material.

12. A support element according to claim 9, wherein said tension member is in a pretensioned condition.

13. A support element according to claim 1, wherein the interior of said tube communicates with- the interior of said bore.

14. A support element according to claim 13, further comprising a hardenable material contained in said tube for ejection therefrom after said element has been placed in said bore.

15. A support element according to claim 14, wherein said material is located at the distal end of said member, a moveable seal being placed at the proximal end of said material.

16. A support element according to claim 14, comprising plunger means insertable within said tube from said proximal end to eject said material.

17. A method of emplacement of a support element according to claim 14, comprising the steps of placing said element within said bore and ejecting said hardenable material into said bore from said tube.

18. A method of emplacement of a support element according to claim 17, wherein said hardenable material comprises a water-setting material, further comprising the steps of introducing water into said tube under pressure to cause said ejection and to mix with said material.

19. A method of emplacement of a support element according to claim 17, wherein said ejection is achieved by introducing a plunger into said tube from the proximal end thereof.