WO1992009789A1

WO1992009789A1 - Rock bolt

Info

Publication number: WO1992009789A1
Application number: PCT/FI1991/000356
Authority: WO
Inventors: Pertti Saarelainen
Original assignee: Tamrock Oy
Priority date: 1990-11-28
Filing date: 1991-11-27
Publication date: 1992-06-11
Also published as: FI905862A0; AU8927691A; FI905862A

Abstract

The invention relates to a rock bolt (1) comprising a sleeve-like outer bolt portion (2) and an inner bolt portion (3) within the outer bolt portion, which bolt portions can be pushed within each other. The outer bolt portion is provided at its front and rear end with internal threads (5, 11) opposite in screw direction. The inner bolt portion (3) is provided at the front end with adjacent threads (5, 12) opposite in screw direction with respect to each other but equal in screw direction with respect to the thread (4, 11) of the outer bolt portion on that side. The bolt can be installed in a hole by pushing it first into the hole with the portions (2, 3) within each other, whereafter the inner bolt portion is screwed off the outer bolt portion, withdrawn from within the outer bolt portion and attached to the rear end of the outer bolt portion by means of the threads (12, 11).

Description

Rock bolt

This invention relates to a rock bolt compris- ing bolt portions interconnectable by a thread to form an extension of each other.

On supporting rock in cramped places where the length of the bolt, for instance, is greater than the free space of the tunnel in the direction of the hole, the bolting often has to be carried out in dif- ficult ways. The bolts used in such cases are either wire bolts fed into the hole and cut into a suitable length, or a bolt iron on a reel is straightened and fed into the hole and then cut into a suitable length. In these two cases, the bolting requires that a hole should first be drilled by a rock drilling equipment, whereafter the rock drilling equipment is displaced aside for the time required for feeding and supporting the bolt. This makes the work slower and more difficult, and increases the risk of a danger situation as material may be loosened from the rock during the exchange of equipment. Furthermore, it is known to carry out the bolting by using so-called extension rod bolts in which identical bolt portions are interconnected in a sequence by means of threads and pushed into the hole manually or by means of a bolt handling apparatus. This kind of extension bolt structure is complicated and difficult to install manually; on the other hand, an expensive, compli¬ cated apparatus is required for installing it with the bolt handling apparatus, in addition to which the drilling equipment has to be displaced aside for the time required for installing the bolt.

The object of the present invention is to provide a rock bolt which is easy to install and easy to handle both before and during installation. The rock bolt according to the invention is characterized in that it comprises a tubular outer bolt portion and an inner bolt portion capable of being pushed into the outer bolt portion; that one bolt portion is pro- vided at its both ends with threads on the surface facing the other bolt portion, said threads project¬ ing from said surface towards the other bolt portion; that one bolt portion is provided at its one end with at least one thread so that the bolt portions are interconnectable axially immovably with respect to each other by means of the threads and when the inner bolt portion is substantially withdrawn from within the outer bolt portion.

The basic idea of the invention is that the rock bolt comprises two extension portions which can be placed one within the other, so that the rock bolt can first be pushed into the drill hole with its por¬ tions within each other, whereafter the inner bolt portion can be withdrawn from within the outer bolt portion and attached to it by a thread to achieve a continuous, steady rock bolt, which can be pushed in place in the hole and tightened after the hardening of the grout so as to support the rock. The rock bolt according to the invention has the advantage that a short rock bolt can be used in low spaces at the initial stage of the installation, and after the first bolt portion has been inserted into the hole, the bolt is extended so that a bolt structure of suf¬ ficient length for supporting the rock is achieved while the handling of the bolt both before and during installation is easy and simple.

The invention will be described in more detail in the attached drawings, in which

Figure 1 is a schematic sectional view of a rock bolt according to the invention with the bolt portions within each other;

Figure 2 is a schematic view of the rock bolt according to the invention when extended into full length; and Figure 3 is a schematic sectional view of another embodiment of the rock bolt according to the invention.

Figure 1 shows a rock bolt 1 comprising a sleeve-like outer bolt portion 2 and a rod-like inner bolt portion 3 within the outer portion. The forward end of the outer bolt portion is provided with an internal thread 4, and the same end of the inner bolt portion is correspondingly provided with a thread 5 by means of which the inner portion of the bolt can be screwed into the outer portion so that they are axially immovable.- At the rear end of the bolt 1 its inner bolt portion comprises a support flange 6 which is tightened against the end of the outer sleeve-like bolt portion when the rock bolt portions are screwed within each other. It thus locks the bolt portions 2 and 3 axially together, which also prevents their rotation with respect to each other in the possible direction of rotation of the bolt. The inner portion of the rock bolt further comprises a tightening por- tion 8 provided with a thread 7 outward from the flange 6, so that a proper washer 10 intended for supporting the rock can be tightened against the sur¬ face of the rock by means of a nut 9 screwing onto the tightening portion 8. The rear end of the outer portion 2 of the bolt is further provided with a thread 11, and the inner portion 3 of the bolt is further provided with another thread 12 at the back of the thread 5, that is, on the side of the washer 6. The threads 4, 5, 11 and 12 on the respective bolt portion project from the surface towards the other bolt portion, that is, they are outside the surface away from the surface. This is necessary as the un¬ threaded portion of the bolt portions has to be able to move between the ridges of the threads of the other bolt portion. The thread 5 and the thread 12 of the inner bolt portion have reverse screw directions. This means that if the thread 5 is a right-hand thread, the thread 12 is a left-hand thread, and vice versa. Similarly, the threads 4 and 11 of the outer bolt portion 2 are of reverse screw direction so that when the thread 4 is a right-hand thread, the thread 11 is a left-hand thread, and vice versa. The basic idea of the invention is that when the bolt portions 2 and 3 are within each other, they are screwed together so that the threads 4 and 5 are within each other and the washer 6 is pressed against the end of the outer bolt portion 2. The bolt is thereby at shortest and it can be. installed in the hole even in low spaces. After the bolt has been pushed into the hole almost over its unextended length, the outer bolt portion 2 is gripped and the threads 4 and 5 are unscrewed by rotating the inner bolt portion 3 with respect to the outer bolt portion 2. Thereafter the inner bolt portion 3 is withdrawn and rotated in the opposite direction as compared with the opening of the threads 4 and 5, and so the inner bolt portion is tightened when the threads 11 and 12 screw onto each other and is finally locked in position when the thread 5 opposite in direction to the thread 12 reaches the edge of the thread 11. In this situation the thread 5 acts as a locking member which locks the bolts with respect to rotation in the direction of rotation and simultaneously correspondingly axially with respect to each other. Thereafter the entire bolt can be pushed into the hole and, if required, it can be rotated in the hole to promote proper mixing and hardening of the grout. The inner bolt portion 3 may comprise a separate conduit 13 extending through it, through which conduit grout can be introduced into the hole at a suitable stage when the bolt is being installed either when the entire bolt has been pushed into the hole or when the bolt has been pushed into the hole only partly and the bolt portions 2 and 3 are either within each other or withdrawn with respect to each other. The forward end of the outer portion 2 of the bolt may be provided within the area of the thread 4 with an external thread 14, onto which a separate drill bit 15 can be screwed so that the bolt can be used both as a disposable drill rod and as a bolt, and a hole can be drilled by means of it in the rock before the grout is fed into the hole. In such a case it is preferable to make the threads 14 and 5 simultaneously by battering as they must be equal in screw direction to be operative. The bolt 1 may be positioned in the hole either manually or mechanically, whereby the bolt can be extended simply by using the well-known retaining means of a conventional drill centralizer for keeping the outer bolt portion 2 stationary when the inner bolt portion 3 is rotated. After the entire bolt has been pushed into the rock hole, the grout is allowed to harden, whereafter the washer 10 is tightened against the rock surface by means of the nut 9.

Figure 3 shows another embodiment of the rock bolt according to the invention, in which the threads are formed in a different way. In the case of Figure 1 the threads of the outer bolt portion 2 are positioned at its both ends and both threads of the inner bolt portion 3 are positioned at the same end thereof, whereas in the case of Figure 3 both threads 4 and 11 of the first tubular bolt portion 2 are pro¬ vided at the same end thereof, i.e. at its rear end; correspondingly, the threads of the second i.e. inner bolt portion 3 are provided at both ends of the inner bolt portion. Operationally and structurally, this solution is similar to the bolt shown in Figure 1, but, with respect to the bolt shown in Figure 1, the screw directions of the threads are opposite as com¬ pared with the same direction of rotation. Similarly as in Figure 1, the threads 4 and 11 of the first bolt portion 2 and the threads 5 and 12 of the second bolt portion 3 are opposite in screw direction, as shown in Figure 3. A thread 11' of the bolt of Figure 3 also acts as a locking member when the inner bolt portion 3 out of the outer bolt portion 2 and the threads 5' and 4'. are screwed onto each other, so that the thread 5' finally reaches the thread 11' having opposite screw direction as compared to it at the end adjacent to it and is thus prevented from being screwed any further while the bolt portions 2 and 2 are locked to each other also in the axial direction. The bolt of Figure 3 may further be pro¬ vided with an external thread 14 similar to the external thread of Figure 1 at its pull end for the attachment of a possible drill bit 15 when the bolt is to be used as a disposable drill rod.

The invention has been described and shown in the above description and the drawings only by way of example, and it is in no way restricted to them.

Claims

Claims :

1. A rock bolt (1) comprising bolt portions (2, 3) interconnectable by a thread to form an extension of each other, c h a r a c t e r i z e d in that it comprises a tubular outer bolt portion (2) and an inner bolt portion (3) capable of being pushed into the outer bolt portion (2); that one bolt portion (2; 3) is provided at its both ends with threads (4, 11; 5', 12') on the sur¬ face facing the other bolt portion (3; 2), said threads projecting from said surface towards the other bolt portion (3, 2); that one bolt portion (2, 3) is provided at its one end with at least one thread (5, 12; 4', 11') so that the bolt portions (2, 3) are interconnectable axially immovably with respect to each other by means of the threads (4, 5; 11*, 12*; 4', 5'; 11, 12) and when they are substantially withdrawn from within the outer bolt portion (2).

2. A rock bolt according to claim 1, c h a r ¬ a c t e r i z e d in that the threads (4, 11; 5', 12') provided at the ends of one bolt portion (2; 3) are opposite in screw direction, and that the other bolt portion (3; 2) is provided at the same end with two successive threads (5, 12; 4', 11') opposite in screw direction so that when the bolt portions (2, 3) are positioned within each other, they are lockable axially immovably with respect to each other by means of the threads (4, 5; 11', 12') provided in both bolt portions (2, 3) adjacent to one end of the bolt (1), and correspondingly when the inner bolt portion (3) is withdrawn, they are lockable axially together by means of the threads (11, 12; 4', 5') provided in both bolt portions (2, 3) adjacent to the opposite end of the bolt (1).

3. A rock bolt according to claim 2, c h a r ¬ a c t e r i z e d in that the outer bolt portion (2) is provided at its ends with internal threads (4, 11), and the inner bolt portion (3) is provided with adjacent threads (11, 12) at the end close to a drill hole.

4. A rock bolt according to any of the preced¬ ing claims, c h a r a c t e r i z e d in that the inner bolt portion (3) comprises a flange (6) which is pressed against the end of the outer bolt portion (2) close to a drilling machine when the bolt por¬ tions (2, 3) are positioned within each other, the inner bolt portion (3) being screwed into the outer bolt portion (2) by means of the threads (4, 5).

5. A rock bolt according to any of the preced¬ ing claims, c h a r a c t e r i z e d in that when the inner bolt portion (3) is withdrawn from within the outer bolt portion (2), the bolt portions (2, 3) are locked axially together by one of the adjacent threads (11; 5) provided in the same bolt portion (3; 2) and being opposite in screw direction.

6. A rock bolt according to any of the preced¬ ing claims, c h a r a c t e r i z e d in that the outer bolt portion (2) is provided at its forward end with an external thread (14) for the attachment of a drill bit (15) to the forward end of the rock bolt

(1).

7. A rock bolt according to any of the preced- ing claims, c h a r a c t e r i z e d in that a conduit (13) is provided centrally in the inner bolt portion (3) for feeding grout or other medium through the bolt (1) into a drill hole.