GB2137712A

GB2137712A - Rock bolt assembly

Info

Publication number: GB2137712A
Application number: GB08407602A
Authority: GB
Inventors: Eric Arthur Jackson
Original assignee: PERARD TORQUE TENSION Ltd
Current assignee: PERARD TORQUE TENSION Ltd
Priority date: 1983-04-08
Filing date: 1984-03-23
Publication date: 1984-10-10
Also published as: GB8407602D0

Abstract

A bolt assembly comprises a multiplicity of components 25 each of which has a tapered end (27, fig. 1) and a socket end (29, fig. 1). The socket end has slits 35 to facilitate radial expansion when a tapered end (27) is forced into the socket end by compressive force between nuts 15, 42 on a bolt 40. One component 11 is provided with a recess 17 instead of a socket end and this recess receives one of the nuts 15 so that the nut is held against relative rotation. A resilient collar 20 prevents rotation of this component within a borehole into which the assembly is inserted. <IMAGE>

Description

SPECIFICATION Bolt assembly This invention relates to a bolt assembly which is capable of being secured in a bore formed in rock or other material.

Such bolt asemblies are used in shafts and tunnels, for example, to form an anchor point and/or to consolidate or support rock strata. One known assembly, for providing an anchor point, utilises a radially expansible member around a bolt shank, arranged so that tightening of a shoulder on the shank against the member by means of a nut causes expansion to grip the wall of the bore.

The member has a multiplicity of flexible fingers, which are caused to splay outwardly to effect gripping.

It is usual, to form rock strata supports, to use curable resins, for bonding the bolt assembly to the strata. This is inconvenient, because of the delay necessary to allow for full curing of the resin, before a load can be applied to the bolt assembly.

The present invention provides a bolt assembly, which can serve as a strata support, without use of a resin, so that the delay is avoided. The assembly is also capable of providing controlled release of tension over a long period, due to movement between strata, so that risk of shearing of the assembly is reduced.

The invention also provides a bolt assembly component, which can be used with other such components to vary the length of the bolt assembly. This allows the same component to be used either in an anchor point assembly or in a strata support assembly.

In accordance with this invention, there is provided a bolt assembly comprising a bolt, a nut and means around the bolt shank capable of radial expansion under compressive force between the nut and a shoulder on the bolt, wherein said means comprises first and second elongate generally cylindrical components, the first component having a bearing surface for the nut at one end, or being formed with the nut, and having a frusto-conical external surface adjacent the opposite end, and the second component having a bearing surface for the shoulder at one end and a socket portion adjacent the opposite end for receiving the frusto-conical external surface of the first component, the socket portion being axially slit to facilitate radial expansion of the socket portion by the first component.

The shoulder may be defined by a further nut engaged with the bolt.

At least the first component preferably has a radial projection for gripping the bore sufficiently to resist rotation in the bore when a tightening operation is initiated.

It is preferred that at least one pair of diametrically opposite slits is provided in the socket portion and, advantageously, each slit extends from said opposite end of the second component to an aperture, which reduces the risk of splitting of the component.

In amodification, a third component is provided having a socket portion as in the second component, the end part of the third component opposite to the socket portion having a frustoconical external surface which engages in the socket portion of the second component, the socket portion of the third component being engaged by the first component. The second component and the third component may be of identical construction.

A multiplicity of components of the construction of the third component may be interengaged and interposed between the first and second components.

The invention may also reside in a component for a bolt assembly, the component being of elongate generally cylindrical shape with an axial bore for receiving a bolt shank, one end part of the component defining a socket portion which is slit to facilitate radial expansion, and the opposite end part having a frusto-conical external surface, whereby a plurality of such components can be interengaged, with the frusto-conical external surface of one component engaging in the socket portion of another such component.

Reference is now made to the accompanying drawings, wherein: Figure 1 is an exploded perspective view of a bolt assembly according to the invention, comprising a first component and a second component; and Figure 2 is a side elevation of the bolt assembly showing a first component and a multiplicity of second components.

The first component 11 is generally cylindrical and elongate with an axial bore 12 for receiving the shank of a bolt 40. One end part 13 of the component has a frusto-conical external surface 14 and the opposite end part 1 6 has a recess 1 7 shaped compiementary to a polygonal nut 1 5 for tightly receiving the latter which bears against a shoulder 1 8 defined by the annular bottom of the recess.

An annular resilient skirt 20 projects from said opposite end part 16 at an acute angle to the component axis, so as to extend both outwardly and towards said one end 13 of the component.

The skirt has slits 10 or cut-out portions (e.g. four slits) to increase flexibility.

The second component 25 is also of generally cylindrical shape and is elongate with an axial bore 26. One end part 27 has a frusto-conical external surface 28. The opposite end part defines a socket portion 29. This portion has an enlarged diameter bore portion including a cylindrical portion 30, defining an internal shoulder 31, and a flared end portion 32. The external surface of the socket portion is cylindrical except for an annular, outwardly directed flange 33 of generally triangular cross-section.

The socket portion has, in the example, four axially extending slits 35 extending from the free end to a round aperture 36. The slits comprise two pairs of diametrally opposed slits.

Both components, as illustrated and described are one-piece plastics mouldings made, for example, from polyamide material, such as nylon.

The components may, however, be made from metal.

As shown in Figure 2, a multiplicity of second components 25 can be "stacked" on the shank of the bolt 40 with the frusto-conical surface of one component engaging in the socket portion of the next. A single first component 11 is provided at an end of the "stack", with its frusto-conical surface engaged in the socket portion of a second component. The shank of the bolt 40 is closely received in the bores of the components (except for the enlarged portions 30, 32 of the second components) to avoid crushing of the components.

The nut 1 5, held by the first component 11, is screw-engaged on the bolt and is inserted first in a drilled bore. The skirt 20 grips the bore interior wall sufficiently to resist rotation and the flanges 33 similarly grip the bore due to slight expansion of each of the socket portions by the component part engaged therein.

A washer 41 bears on the end shoulder 37 of the end most second component, opposite to the first component, and the washer is engaged by a nut 42.

Tightening of the nut 42 consolidates the assembly and causes expansion of all of the socket portions to provide a firm grip in the drilled bore. The slits 35 facilitate expansion and the apertures 36 prevent splitting of the second components by extension of the slits.

Where the first component is made of metal, the nut 15 may be an integral part of the component.

Claims

1. A component for a bolt assembly, the component being of elongate generally cylindrical shape with an axial bore for receiving a bolt shank, one end part of the component defining a socket portion which is slit to facilitate radial expansion, and the opposite end part having a frusto-conical external surface, whereby a plurality of such components can be interengaged, with the frustoconical external surface of one component engaging in the socket portion of another such component.

2. A component for a bolt assembly, substantially as herein described with reference to the accompanying drawings.

3. A bolt assembly comprising a bolt, a nut and means around the bolt shank capable of radial expansion under compressive force between the nut and a shoulder on the bolt, wherein said means comprises first and second elongate generally cylindrical components, the first component having a bearing surface for the nut at one end, or being formed with the nut, and having a frusto-conical external surface adjacent the opposite end and the second component having a bearing surface for the shoulder at one end and a socket portion adjacent the opposite end for receiving the frusto-conical external surface of the first component, the socket portion being axially slit to facilitate radial expansion of the socket portion by the first component.

4. A bolt assembly according to Claim 3 comprising a pair of diametrally opposite axial slits in the socket portion.

5. A bolt assembly according to Claim 3 or 4, wherein each slit extends from said opposite end of the second component to an aperture in the socket portion wall.

6. A bolt assembly according to Claim 3, 4 or 5, wherein at least the first component has a radial projection for gripping the wall of a bore to resist rotation of the assembly as the bolt is rotated.

7. A bolt assembly according to any one of Claims 3 to 6, including a third component having a socket portion as in the second component, the end part of the third:component opposite to the socket portion having a frusto-conical external surface which engages in the socket portion of the second component, the socket portion of the third component being engaged by the first component.

8. A bolt assembly according to Claim 7, wherein the second and third components are of identical construction.

9. A bolt assembly constructed substantially as herein described with reference to the accompanying drawings.