AU2007100836A4 - Improved rock bolt - Google Patents

Description

AUSTRALIA

F B RICE CO Patent and Trade Mark Attorneys Patents Act 1990 PHILLIP HANFORD BOOT COMPLETE SPECIFICATION INNOVATION PATENT Invention Title.

Improved rock bolt The following statement is a full description of this invention including the best method of performing it known to us:- 2 Field of the Invention ;The present invention relates to an improved, typically plastic rock-bolt or rockdowel for use in the reinforcement of earth strata, such as in underground mining and Cc tunnelling in coal mines.

IND Background of the Invention 00 Rock-bolts are used in mining, tunnelling, and in general stabilisation. One use of rock-bolts is in the coal mining industry where underground roadways or tunnels are Sexcavated to facilitate the main mining operation. The tunnels have to be reinforced for safety reasons. Traditionally this has been done with steel rods called rock-bolts or Srock-dowels. Such reinforcement may be of a permanent or temporary nature, and where the reinforcement is of a temporary nature, the reinforced strata may be subsequently excavated/mined.

However, when a steel rock-bolt is used to reinforce this part of the strata, expensive damage can occur to the excavating equipment used in the later excavation and also to equipment used in conveying the excavated material. Because of this problem with steel rock-bolts, fibre reinforced composites (FRP) rock-bolts have become popular, particularly for temporary applications. Such materials have lower shear strength characteristics than steel and will not tend to damage the excavating or conveying equipment. FRP rock-bolts are also used in other applications such a "soil nailing" where the bolts, when used for temporary purposes, can be easily broken or cut up and removed at a later date when or if required.

A typical rock bolt or dowel used in coal mines is usually a rod of 20mm 22mm diameter and varying length from 900mm 1800mm, which is inserted in a predrilled hole of approximately 28mm diameter and encapsulated in a binding cementicious material, usually a resin material.

In many cases, the rod has a threaded end that projects out of the hole where a washer and nut are attached to the rod. After encapsulation, the nut is tightened down to exert a pressure on the strata surface.

The sequence of dowel installation is, firstly a hole is drilled in the strata to the required depth, the drill bit is then removed from the drill chuck and replaced by a socket spanner. A two part resin binding agent contained in a flexible capsule of varying length is inserted into the hole. The capsule keeps the two components separate. Then the dowel, including a plate and a nut partially screwed onto the threaded end is partly inserted into the hole.

The nut is engaged by the drill chuck and spun vigorously whilst being pushed ;further into the hole, thus breaking the capsule and mixing the two resins together. The nut has a cap which prevents it from being screwed further down the dowel thread during the spinning operation, the dowel is then held motionless for a number of seconds whilst the, now mixed, resin solidifies.

IAustralian patent application No 2006202175 describes fibreglass rock bolts and 00 their use in underground coal mining operations in reinforcing the side walls of

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development tunnels.

These days nearly all rockbolts used in coal mines are installed by a powerful hydraulic bolting machine, these machines use drill mechanisms positioned on the N machine.

A typical vertical pattern of rockbolt installation on the tunnel wall is that one bolt is installed approximately half way up (mid point) the vertical wall of the tunnel, another bolt is usually installed approximately towards the top of the tunnel wall section adjacent to the tunnel roof and sometimes a third bolt is installed approximately halfway between the mid point in the tunnel wall and the floor level.

The drill and bolting rigs on these machines do not necessarily drill the hole or install the bolt at a 90 degree angle to the vertical strata surface. Sometimes, the top hole and bolt installation is at quite an angle in fact up to a 45 degree angle from the strata surface.

In addition the distance from the machine platform to the tunnel wall can be too much for the operator to reach, place, push and keep the capsule in the pre-drilled hole.

This presents another problem for the installer in that when he pushes the resin capsule into the top angled hole, gravity may cause the capsule to slip out and fall to the tunnel floor.

The operator then has to prevent the resin capsule from falling by positioning the bolt in the hole and then pushing both bolt and capsule further into the hole until he can attach the drill socket to the nut end of the bolt and hold it in place.

The operator needs a method of attaching or supporting the resin capsule to the end point of the bolt so that he only has to start the other end of the capsule in the hole so that then he can push the capsule into the hole using the bolt.

The operator can then attach the socket end of the drilling mechanism to the nut bolt end and complete the installation.

Most if not all fibreglass bolts have a splayed end oriented at about a 45 degree angle to the longitudinal axis of the bolt to enhance the cutting open of the capsule 4

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casing so that the resin and catalyst can be mixed together, however the use of such a ;splayed end presents two separate problems.

Firstly the splayed end shape cannot assist in the positioning of the capsule in M the hole as described above until the capsule is completely within the hole. Even then, in some cases, the splayed end can wedge between the capsule end and the side of the IN predrilled hole.

O0 Secondly during the spinning and resin mixing phase the splayed end can be counterproductive as the bolt can slip down passed the crimped end of the capsule and can cause or aggravate the "gloving" effect that causes encapsulation failure.

Thus, although the splayed end can cut open the capsule casing it is not a Nsolution to both of these problems.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

Summary of the Invention According to the present invention there is provided a rockbolt or rock dowel having a proximal end and a distal end for inserting in a pre-drilled hole characterised by a recess or hole defined in the distal end of the rockbolt or dowel.

By providing a recess in the distal end or tip of the bolt, the crimped end of the capsule fits snugly into it and therefore supports the capsule at one end, so that when the other end of the capsule is placed in the hole the operator has complete control whilst still standing on the platform of the drilling and bolting machine.

Whilst the recess solves the top bolt installation problem it also serves other functions for example, in both the middle and bottom holes in the tunnel wall the holes are positioned at more positive angles so that the resin capsule cannot fall out. In this situation the capsule is placed into the hole without engaging the bolt end, the nut end of the bolt is then engaged into the socket of the drill machine, the operator then uses the drill mechanism to push the bolt into the hole until it engages the capsule end. In particular, the splayed end of the bolt cannot centrally engage the pointed capsule end and can slip down beside the capsule which is undesirable. In contrast, with the present invention, the recess of the bolt will always engage the pointed crimped end of the capsule and this effect is enhanced as the bolt is turned and spun and pushed further b into the hole. As the capsule end cannot escape, the compressed capsule is easily cut ;open by the bolt and both the resin and the catalyst are forced out, immediately mixed together and travel up the bolt shank. The capsule casing is forced into the bottom of the hole without affecting the encapsulation.

Although the hollow end would work with a square 90 degree cut on the bolt IDend, it is preferred but not essential that the bolt tip be splayed as well but not at a 00 greater angle than 60 degrees. Preferably the angle of the end face of the bolt to the longitudinal axis will be from 300 to 60". The splayed end tip assists as a centering Sdevice further controlling the end of the capsule.

A splayed end also assists in cutting the casing open as the edges around the hollow end are relatively thin and slice through the two casings continually as it is pushed into the hole.

It is important that the point of the splayed end does not engage the capsule before the hollow end captures the capsule shoulders within the hollow section, in this way the capsule shoulders become wedged into hollow section.

The bolt could be made of any suitable material including steel but would preferably be made of a reinforced composite such as fibreglass.

Brief Description of the Drawings A specific embodiment of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:- Fig 1 is a side elevation ofa fibreglass bolt, nut and washer; Fig 2 is an elevation of a typical two part resin capsule with a crimped end; Fig 3 is a section of the resin capsule of Fig 3 showing the larger resin compartment and the smaller catalyst compartment; Fig 4 shows the end of a bolt with a dotted line showing the shape of the hollow section; and Fig 5 is a cutaway drawing showing how the capsule and the hollow section fit together.

Detailed Description of a Preferred Embodiment Fig 1 shows a fibreglass rockbolt bolt 1 with a threaded end proximal la, a washer plate 2 and a nut 3. The bolt has a splayed distal end 4 which is oriented at an angle at of about 60" to the longitudinal axis L of the rockbolt (discussed below with reference to Figure 4).

S6 Fig 2 shows a typical two part resin capsule 5 with resin compartment 5b and a ;catalyst compartment 5a. The capsule includes shoulders Se and a crimped ends 5f at each end of the capsule.

~Fig 3 is a section through the capsule shown the variation between the two compartments 5a the catalyst compartment and 5b the resin compartment. Also shown IDis the capsule casing 5c and the divider 5d which splits the casing 5c into the two 00 discrete compartments 5a and In Fig 4 the splayed end 4 of the bolt is shown at an angle 30 degrees to the transverse direction of the bolt shank or an angle a of 60 degrees to the direction of the 1 0 bolt shank L. A recess or hole 6 is defined in the end 4 shown by a dotted line denoting ri the approximate shape of the recess 6. It can be seen that the recess is generally vshaped in cross-section having a rounded tip or end 6a. The recess is rotationally symmetrical. The volume of the recess is preferably sufficient to enclose the shoulders of the capsule.

Fig 5 illustrates how the end of the capsule 5 fits into the hollow section 6 so that the tapered internal sides of the hollow section 6 engage the capsule shoulders and allow the crimped end 5f to centralize the capsule 5 and bolt 1. This supports one end of the capsule 5 as it is being inserted into a pre-drilled hole (not shown).

As the bolt is spun and pushed into the hole the capsule 5 is compressed and the sharp end 4a of the splayed end 4 pierces the capsule casing 5c in both compartments and 5b. This releases the resin and catalyst from the casing 5c and pushes the casing to the bottom of the hole.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims (4)

1. A rockbolt or rock dowel having a proximal end and a distal end for inserting in a pre-drilled hole characterised by a recess or hole defined in the distal end of the Crockbolt or dowel.

2. A rockbolt or rock dowel as claimed in claim I wherein the distal end of the bolt NO is splayed angle defined between the end face of the bolt and its longitudinal axis is 00 from 30" to 600.

3. A rockbolt or rock dowel as claimed in claim I or claim 3 wherein is made of a Sreinforced composite material comprising fibre embedded in a resin matrix, such as fibreglass. C

4. A rockbolt or dowel as claimed in any one of claims 1 to 3 wherein the recess has a generally v-shaped cross-section. A rockbolt or dowel as claimed in any one of claims 1 to 4 wherein the recess is rotationally symmetrical. DATED this thirty-first day of August 2007 Phillip Hanford Boot Patent Attorneys for the Applicant: F.B. RICE CO.