FIELD OF THE INVENTION

[0001] The invention relates to a rock bolt assembly which is adapted for measuring the strain on a rock bolt shaft as it yields under load when placed in situ.

BACKGROUND OF INVENTION

[0002] To improve mine safety, it is important to be able to assess the integrity of rock wall support, such as installed rock bolts.

[0003] Passive and dynamic forces are imposed on a rock bolt by the surrounding rock mass to which the bolt offers load support. These forces strain the rock bolt. A rock bolt is prone to catastrophically fail when the bolt is subjected to load that exceeds an inherent maximum tolerance level. This event is termed “overload”.

[0004] It would be desirable to be able to monitor a rock bolt and to detect when the rock bolt is approaching overload or maximum strain. An indication that the bolt is approaching its load or strain limit can then be made and action can be taken to avoid this catastrophic failure event.

[0005] Typically, a rock bolt is provided with an elongate electrically conductive element, such as a length of metal wire, which runs along a substantial length of the bolt, originating at an electronic measuring module at a proximal end of the bolt and ending at or towards a distal end of the bolt.

[0006] The problem with a rock bolt configured with an elongate electrically conductive element is that in its extension, it will pass between a spherical seat and a faceplate. At this junction, the element may be functionally impinged ot severed.

[0007] The invention at least partially solves the aforementioned problem.

SUMMARY OF INVENTION

[0001] Hereinafter, the term “spherical” and “spherically” when used to describe a surface is used to describe the surface as being a rounded or convexly curved, despite the surface not being truly spherical.

[0002]The invention provides a strain measuring rock bolt assembly which includes: a yielding rod of a malleable material that extends between a distal end and a proximal end; a spherical seat engaged to the rod that has a body with a first surface, facing the distal end, at least a part of which is spherically shaped, and a second surface, facing the proximal end, the spherical seat including at least one passage which communicates the first surface with the second surface; and an elongate member of an electrically conductive material engaged to the rod along a substantial length of the rod by passing through the passage. [0003] The elongate member may be adapted to elongate as the rod elongates under load as a measure of the load.

[0004] The second surface may be planar.

[0005] The elongate member may be a length of wire of a suitable metal material.

[0006] The assembly may include a processing module. The processing module may be housed in a housing which is engaged to the bolt towards the proximal end.

[0007] The elongate member may connect, at one end, to the processing module and, at an opposed end, may be fixed to the rod towards the distal end.

[0008] The invention extends to an adapted spherical seat for use with a strain measuring rock bolt, which spherical seat includes a body with a spherical surface and a planar surface and at least one conduit which extends between the spherical surface and the planar surface and which is adapted to receive an elongate member of an electrically conductive material.

[0009] From another perspective, the invention of the adapted spherical seat which is used with a rock bolt which is adapted to measure strain by including an electrically conductive elongate member, which spherical seat includes a body with a first surface, at least a part of which is spherically shaped, and a second surface and at least one passage which communicates the first surface with the second surface and which is adapted to receive the electrically conductive elongate member.

BRIEF DESCRIPTION OF THE DRAWINGS [0010] The invention is described with reference to the following drawings in which:

Figure 1A is a diagrammatic representations of a strain measuring rock bolt assembly in accordance with the invention; Figure 1 B diagrammatically illustrates a spherical seat of the assembly; and

Figures 2A, 2B and 2C respectively illustrate the spherical seat in elevation, in longitudinal section and in under plan.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0011]The invention provides a rock bolt assembly 10, which is adapted to measure the strain that a yielding rod 12 of the assembly is subjected to when put in use. This assembly is illustrated in Figure 1.

[0012]The rock bolt assembly 10 includes the yielding rod 12, which is made of a suitable malleable metal material and which extends between a distal end 14 and a proximal end 16, a faceplate 18 and a spherical seat 20. The spherical seat is adapted in accordance with an aspect of the invention.

[0013] The rod is partially externally threaded along a proximal end portion 22.

[0014] The spherical seat 20 has a body 24 which extends in the longitudinal direction of the assembly between a first leading surface 26 and a second trailing surface 28. The trailing surface is largely a planar surface. [0015] The spherical seat 20 is penetrated by a centrally positioned rod- engaging cylindrical aperture 30. The aperture opens at both the first and the second surfaces. Towards the trailing end, the wall of the aperture has a threaded section 31 .

[0016] The leading surface 26 of body is adapted with a rounded or spherical surface section 32 and a tubular surface section 34 (see Figure 2A and 2B). The tubular surface section extends from the spherical surface section in the longitudinal direction.

[0017] A pair of diametrically opposed wire-guiding slots 40 are formed in the tubular surface section 34. Each slot extends in the longitudinal direction and leads to a respective bore 42 at an intersection of the tubular surface section and the spherical surface section. Each bore extends through the body from the spherical surface section 32 to the trailing surface 28.

[0018] The rock bolt assembly 10 is assembled with the threaded section 31 of the aperture 30 of the spherical seat 20 engaging the threaded proximal end portion 22 of the rod 12. The faceplate 18 is engaged with the rod, coming to rest abutting the spherical surface section 32 of the spherical seat 20. A wire 44, or other suitably adapted elongate strain detection element, is fixed or fastened to an exterior surface of the rod 12, extending in the longitudinal direction, with a first end 46 fixed about or towards the distal end 14 of the rod, and an opposed second end 48 connected to a processing module 50. The processing module is housed in a housing 52 which is attached to the proximal end 16 of the rod. The processing module receives electrical input from the wire, the magnitude of which is a function of elongation of the wire and hence the strain imposed on the rod to which the wire is connected. This input is translated into a measure of strain by the processing module, the output of which may be a visual and/or auditory warning that the measure of strain exceeds a predetermined limit.

[0019] Ordinarily, in the wire's extension along a substantial length of the rod, the wire will pass a junction between the spherical seat and the faceplate. At this junction, the wire might be functionally impinged or severed. To avoid this, the wire 44 passes along a respective slot 40 and through a respective bore 42 of the spherical seat.