GB2138528A

GB2138528A - Rock Bolt Assembly

Info

Publication number: GB2138528A
Application number: GB08407603A
Authority: GB
Inventors: Eric Arthur Jackson
Original assignee: PERARD TORQUE TENSION Ltd
Current assignee: PERARD TORQUE TENSION Ltd
Priority date: 1983-04-16
Filing date: 1984-03-23
Publication date: 1984-10-24
Also published as: GB8407603D0

Abstract

A rock bolt assembly comprises a bolt (20), nuts (21, 23) and axially aligned sleeves (12, 13, 14) around the bolt shank between the nuts, the sleeves having end faces (16, 18) which lie in planes acutely angled to the bolt axis, each end face being in contact with a corresponding end face of another sleeve. Tightening of the nuts on the bolts causes the end faces to slide on each other to cause radial expansion of the assembly for gripping the wall of a bore in which the assembly is inserted. A deformable or frangible inner tube (10) holds the sleeves in axial alignment. <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 assemblies are used in shafts and tunnels, for example, to form an anchor point and/or to consolidate or support rock strata. For heavy duty use, for consolidating rock strata or supporting heavy machinery, it is usual to wedge a bolt assembly in a bore and to fill the remainder of the bore with grout, such as a curable resin.

The strata are, therefore, bonded together and there can be a deep bonded anchorage for supporting heavy machinery. It is necessary, however, to ensure that the bore is properly filled, that the correct grout is used and that the grout is fully cured. Curing takes some time, so there is a delay before bonded bolt assemblies can be utilised as anchorage points.

The present invention provides 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 a pair of axially aligned sleeves having end faces in mutual contact, each said end face lying in a plane at an acute angle to the.sleeve axis, such that under axial compression the end faces slide relative to each other to effect said radial expansion.

It is preferred that deformable or frangible means is provided to hold the sleeves in axial alignment. This means may be an internal tubular member or a thin external covering.

In one embodiment, a multiplicity of pairs of axially aligned sleeves are provided, the sleeves of each pair having said acutely angled faces in mutual contact, the opposite faces of the sleeves being perpendicular to the sleeve axis.

In another embodiment, a multiplicity of axially aligned sleeves are provided including endmost sleeves, each having a first end face perpendicular to the sleeve axis and a second end face in a plane at an acute angle to the axis, and an intermediate sleeve having one end face lying in a plane at an acute angle to the axis and the opposite end face lying in the opposite direction at an acute angle to the axis. Several such intermediate sleeves may be provided in alignment, but it is preferred that groups of said endmost and intermediate sleeves are arranged in alignment.

Where a sufficient number of sleeves is provided, it is preferred that they are relatively differently oriented about the axis, such that the expansion occurs along angularly spaced radii.

Reference is now made to the accompanying drawings, wherein: Figure 1 is an exploded perspective view of a bolt assembly according to the invention; and Figure 2 is an elevation, partly in section, of the bolt assembly.

Referring to Figure 2, there is shown a cylindrical tube 11 of rigid material, such as steel having components cut from it the components comprising sleeves. Figure 1 shows a pair of end sleeves 12, 13 and an intermediate sleeve 14 and Figure 2 shows three such arrangements in alignment in a "stacked" configuration.

Each end sleeve 12, 13 has a first end face 15, perpendicular to the sleeve axis, and a second end face 1 6 extending obliquely to the sleeve axis, and, therefore, of ovate form.

The intermediate sleeve 14 has an end face 1 7 in a plane extending obliquely to the sleeve axis and complementary to the face 16 and the opposite face 1 8 extends in a plane in the opposite direction at the same angle to the sleeve axis, the planes of the faces 17, 1 8 converging towards a median diametral plane through the sleeve. The intermediate sleeve 14 has a regular trapezium form as viewed in elevation.

It is apparent from Figure 2 that, if a compressive axial force is applied to the first faces 1 5 of the end sleeves 12, 13, the intermediate sleeve 14 will move radially out of alignment, due to sliding between the faces 1 6, 1 7 and 1 6, 18, to cause radial expansion of the assembly.

As shown in Figure 2, the assemblies 12, 13, 14 are "stacked" on the shank of a bolt 20. The endmost sleeve 1 3a has a nut 21 welded thereto and screw-engaged on the bolt shank. The sleeves are all held in axial alignment by a cardboard tube 10 extending within the sleeves.

As an alternative, thin plastics material may be heat-shrunk about the sleeves to hold them in axial alignment.

A washer 22 bears against the opposite endmost sleeve 1 2a and a nut 23 can bear against the washer 22. After insertion of the assembly in a bore, the nut 23 is tightened to put the sleeves under compression. Each pair of end sleeves 12, 13 moves radially in the opposite direction to the associated intermediate sleeve 14 to grip the walls of the bore. The cardboard inner tube is disrupted.

As apparent from Figure 2, alternate groups 12, 13, 14 of sleeves are angularly offset by 1 80C to provide more even gripping of the wall bore. In longer assemblies the angular displacement may be smaller than 1 80c. The angular displacement of the groups may progressively increase from one end to the other to cover 3600.

In an alternative arrangement (not shown), there is provided only one pair of end sleeves 12, 13 and a multiplicity of intermediate sleeves 14 between the end sleeves.

In another alternative arrangement, there are no intermediate sleeves 14, but all the sleeves have the same construction as the end sleeves 12, 13. The arrangement is indicated in Figure 2.

If the intermediate sleeve 14 is cut along the dotted line 30, then two sleeves of the same construction as end sleeves 12, 13 are formed.

1. A bolt assembly comprising a bolt, a nut and means around the bolt shank capable of radial

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. 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 assemblies are used in shafts and tunnels, for example, to form an anchor point and/or to consolidate or support rock strata. For heavy duty use, for consolidating rock strata or supporting heavy machinery, it is usual to wedge a bolt assembly in a bore and to fill the remainder of the bore with grout, such as a curable resin. The strata are, therefore, bonded together and there can be a deep bonded anchorage for supporting heavy machinery. It is necessary, however, to ensure that the bore is properly filled, that the correct grout is used and that the grout is fully cured. Curing takes some time, so there is a delay before bonded bolt assemblies can be utilised as anchorage points. The present invention provides 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 a pair of axially aligned sleeves having end faces in mutual contact, each said end face lying in a plane at an acute angle to the.sleeve axis, such that under axial compression the end faces slide relative to each other to effect said radial expansion. It is preferred that deformable or frangible means is provided to hold the sleeves in axial alignment. This means may be an internal tubular member or a thin external covering. In one embodiment, a multiplicity of pairs of axially aligned sleeves are provided, the sleeves of each pair having said acutely angled faces in mutual contact, the opposite faces of the sleeves being perpendicular to the sleeve axis. In another embodiment, a multiplicity of axially aligned sleeves are provided including endmost sleeves, each having a first end face perpendicular to the sleeve axis and a second end face in a plane at an acute angle to the axis, and an intermediate sleeve having one end face lying in a plane at an acute angle to the axis and the opposite end face lying in the opposite direction at an acute angle to the axis. Several such intermediate sleeves may be provided in alignment, but it is preferred that groups of said endmost and intermediate sleeves are arranged in alignment. Where a sufficient number of sleeves is provided, it is preferred that they are relatively differently oriented about the axis, such that the expansion occurs along angularly spaced radii. Reference is now made to the accompanying drawings, wherein: Figure 1 is an exploded perspective view of a bolt assembly according to the invention; and Figure 2 is an elevation, partly in section, of the bolt assembly. Referring to Figure 2, there is shown a cylindrical tube 11 of rigid material, such as steel having components cut from it the components comprising sleeves. Figure 1 shows a pair of end sleeves 12, 13 and an intermediate sleeve 14 and Figure 2 shows three such arrangements in alignment in a "stacked" configuration. Each end sleeve 12, 13 has a first end face 15, perpendicular to the sleeve axis, and a second end face 1 6 extending obliquely to the sleeve axis, and, therefore, of ovate form. The intermediate sleeve 14 has an end face 1 7 in a plane extending obliquely to the sleeve axis and complementary to the face 16 and the opposite face 1 8 extends in a plane in the opposite direction at the same angle to the sleeve axis, the planes of the faces 17, 1 8 converging towards a median diametral plane through the sleeve. The intermediate sleeve 14 has a regular trapezium form as viewed in elevation. It is apparent from Figure 2 that, if a compressive axial force is applied to the first faces 1 5 of the end sleeves 12, 13, the intermediate sleeve 14 will move radially out of alignment, due to sliding between the faces 1 6, 1 7 and 1 6, 18, to cause radial expansion of the assembly. As shown in Figure 2, the assemblies 12, 13, 14 are "stacked" on the shank of a bolt 20. The endmost sleeve 1 3a has a nut 21 welded thereto and screw-engaged on the bolt shank. The sleeves are all held in axial alignment by a cardboard tube 10 extending within the sleeves. As an alternative, thin plastics material may be heat-shrunk about the sleeves to hold them in axial alignment. A washer 22 bears against the opposite endmost sleeve 1 2a and a nut 23 can bear against the washer 22. After insertion of the assembly in a bore, the nut 23 is tightened to put the sleeves under compression. Each pair of end sleeves 12, 13 moves radially in the opposite direction to the associated intermediate sleeve 14 to grip the walls of the bore. The cardboard inner tube is disrupted. As apparent from Figure 2, alternate groups 12, 13, 14 of sleeves are angularly offset by 1 80C to provide more even gripping of the wall bore. In longer assemblies the angular displacement may be smaller than 1 80c. The angular displacement of the groups may progressively increase from one end to the other to cover 3600. In an alternative arrangement (not shown), there is provided only one pair of end sleeves 12, 13 and a multiplicity of intermediate sleeves 14 between the end sleeves. In another alternative arrangement, there are no intermediate sleeves 14, but all the sleeves have the same construction as the end sleeves 12, 13. The arrangement is indicated in Figure 2. If the intermediate sleeve 14 is cut along the dotted line 30, then two sleeves of the same construction as end sleeves 12, 13 are formed. CLAIMS

1. 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 comprising a pair of axially aligned sleeves having end faces in mutual contact, each said end face lying in a plane at an acute angle to the sleeve axis, such that under axial compression the end faces slide relative to each other to effect said radial expansion.

2. A bolt assembly according to Claim 1, comprising deformable or frangible means holding the sleeves in axial alignment and capable of deformation or fracture to permit said radial expansion.

3. A bolt assembly according to Claim 2, wherein the deformable or frangible means comprises an external covering on the sleeves.

4. A bolt assembly according to Claim 2, wherein the deformable or frangible means comprises an internal tube within the sleeves.

5. A bolt assembly according to any preceding claim, comprising a plurality of said pairs of sleeves in axial alignment, with each of at least some of the sleeves having a diametral end face opposite to the acutely angled end face and engaged with a diametral end face of another sleeve.

6. A bolt assembly according to any of Claims 1 to 4, including a sleeve having both opposite end faces lying in planes acutely angled to the axis, said planes converging towards a median diametral plane through the sleeve, these end faces engaging with corresponding end faces of other sleeves.

7. A bolt assembly according to Claim 5 or 6, wherein some of the sleeves are relatively differently oriented about the axis, such that expansion occurs along angularly spaced radii.

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