GB2206390A

GB2206390A - Deformable rock bolt

Info

Publication number: GB2206390A
Application number: GB08715614A
Authority: GB
Inventors: Peter Frank Reinholt Altounyan
Original assignee: University of Surrey
Current assignee: University of Surrey
Priority date: 1987-07-02
Filing date: 1987-07-02
Publication date: 1989-01-05
Also published as: GB8715614D0

Abstract

A deformable rock bolt (3) has a deformable wall (4) which is pressed against the wall of a hole (1) in strata (2) by fluid injected under pressure through a non return valve 7 to activate a cementitious material (5) and press the wall against the wall of the hole (1) whilst the cement sets. <IMAGE>

Description

IMPROVEMENTS IN DEFORMABLE ROCK BOLTS This invention relates to deformable rock bolts and is particularly concerned with the type of bolt which comprises a hollow longitudinal extending member adapted to be inserted into a predrilled hole in rock strata, the member having at least one part which has a deformable wall, and means for introducing a fluid into the said one part to cause the wall thereof to deform outwards to engage with the strata in which the hole is drilled.

Bolts of the above kind have been used for rock bolting purposes and have the advantage that they have been quick to install and require very little skilled application. However, they suffer from the disadvantage that they have a lower absolute tensile strength than a solid bar and the bond to resistance between the bolt and the rock is less than for a full column resin anchored bolt.

Rock bolting is well known as a technique in which holes are drilled into strata and dowelling or still bolts are inserted into the holes and captured there. Tension can then be applied to the bolt and this results in stress being relieved in the rock and the rock being reinforced.

One of the commonest types of rock bolt apparently in use is the resin bolt where a solid steel bolt is inserted into a predrilled hole in strata along with a two pack resin mixture, the bolt pierces the pack and is rotated to mix the resin which immediately reacts and sets. Once set the bolt is then tensioned externally and secured. The resin bolting technique relies on the resin to engage with the walls of the drilled hole and to fill up any gaps. It is also necessary to ensure that proper mixing takes place quickly to ensure that the resin is properly mixed to obtain the correct setting consistency. This requires some degree of skill on the part of the operator and also requires there to be a stock of both bolts and resin.If reinforcement and rock bolting is not progressing as quickly as possible then there may be difficulties which arise hence the resin has a limited shelf life and if not used within a preset time of manufacture can go off and be ineffective in use. There is also a hazard to personnel from the effects of the resin.

If resin bolting is effectively and correctly done then a good bolt reinforcement is achieved. However the risks of it being improperly done are high and it is necessary to try and find an improved form of bolting which is more reliable and more suitable through application by unskilled personnel. It is because of this that the bolts of the kind referred to above have been employed.

It is our object of the present invention to improve the above kind of bolt and to give a simple and reliable method for its application.

According to the present invention a bolt of the kind comprising a hollow longitudinal extending member adapted to be inserted into a predrilled hole in rock strata includes at least one part which has a deformable wall, means for introducing a fluid into the said one part to cause the wall thereof to deform outwardly is characterised in that the said one part having the formable wall contains therein a cementitious material.

Preferably the fluid to be added is water and the effect of the fluid is such as to cause the cementitious material to mix thoroughly and to set to hold the one part in its deformed state. Preferably a cementitious mixture is of a quality which has a high water to material content to enable the costs of the bolt to be maintained low.

An aperture in the bolt is provided for introducing a fluid to the said part and this aperture may be closed by a valve.

In a variation of the invention a liquid cemenititious mix may be introduced.

The cemenititious material is chosen since it is relatively inexpensive. It will be appreciated that other material such as resins could be used although their costs would be relatively high.

According to a further aspect of the present invention a method of bolting uses a bolt of the kind described and includes inserting it into a predrilled hole inserting a fluid into the hollow part of the bolt to mix the cemenititious material applying a pressure to the fluid to cause the mix to expand the said part and hold the wall of the bolt against the wall of the hole.

One example of the invention and its method of use will now be described with reference to the accompanying diagramatic drawing.

Referring to the drawing this shows a predrilled hole 1 in a rock strata 2 into which a bolt 3 in accordance with the present invention has been inserted. The bolt comprises a deformable hollow wall 4 and contains within the hollow a dry cementitious mix 5.

The end of the bolt 3 extends out of the face 6 of the strata 2 and is sealed with a valve arrangement 7 which comprises a small hole having a non return valve. As shown in the drawing the bolt is a loose fit in the hole 1 and can easily be inserted into it. In order to secure the bolt water is pumped in the direction of the arrow 8 through the valve 7 into the interior of the bolt 3. The force of the water causes a mixing effect with the cementitious material 5 and causes it to mix effectively with the water in order to cure. The pressure which is applied by the water 8 also deforms the wall 4 so that it is pressurised against the side of the wall 1 and establishes a strong bond resistance between the bolt 3 and strata 2.

The cemenititious material is chosen to be a quick setting material having a high water to material ratio. As soon as water reacts with the material 5 it begins to set and as soon as it has set it is able to provide a constant resistance to hold the wall of the bolt against the wall of the strata and thus give a strong bond.

Since the bolt 3 is a fully encapsulated member and only water is required to activate it there is no risk of hazard to personnel through the exposure to chemical substances. The only external material required is water.

Claims

Claims:

1. A deformable rock bolt of the kind comprising a hollow longitudinal extending member adapted to be inserted into a predrilled hole in rock strata includes at least one part which has a deformable wall, means for introducing a fluid into the said one part to cause the wall thereof to deform outwardly characterised in that the said one part having the deformable wall contains therein a cementitious material.

2. A bolt as claimed in Claim 1 in which the fluid to be added is water and the effect of the fluid is such as to cause the cementitious material to mix thoroughly and to set to hold the one part in its deformed state.

3. A bolt as claimed in Claim 1 or Claim 2 in which the cementitious mixture has a high water to material content.

4. A bolt as claimed in Claim 1 or Claim 2 in which an aperture in the bolt is provided for introducing a fluid to the said part, and in which the aperture is closed by a valve.

5. A bolt substantially as hereinbefore described with reference to the accompanying drawing.

6. A method of rock bolting using a bolt as claimed in any preceding claim including inserting the bolt into a predrilled hole, inserting a fluid into the hollow part of the bolt to mix the cementitious material and applying a pressure to the fluid to cause the mix to expand the said part and hold the wall of the bolt against the wall of the hole.