ROCK BOLT ASSEMBLY COMPRISING A SENSOR ASSEMBLY

Abstract

A sensor assembly for a rock bolt, wherein the rock bolt includes a central rod, a split tube and a wedge anchor assembly fitted around the central rod, a rock plate, and a nut for attachment to an outer end of the central rod. The sensor assembly includes a distance sensor, a bracket for attaching the distance sensor to an outer portion of the split tube, an elongate spacing member configured to be fitted around the split tube between the nut and the rock plate to keep the nut and the rock plate spaced apart. The spacing member has an opening extending along at least a portion of the length thereof, the opening being sized large enough to allow movement of the bracket along a portion of the length of the spacing member with the distance sensor attached to the outer portion of the split tube by the bracket.

Claims

1. A rock bolt assembly comprising: a sensor assembly; and a rock bolt, the rock bolt including a central rod, a split tube fitted around the central rod, a wedge anchor assembly fitted to the central rod, a rock plate having a hole, a nut for attachment to an outer end of the central rod, and a washer for use with the nut, the sensor assembly including a distance sensor, a bracket arranged for attaching the distance sensor to an outer portion of the split tube, an elongate spacing member configured to be fitted around the split tube between the washer and the rock plate to keep the nut and the rock plate spaced apart, wherein the spacing member includes an opening extending along at least a portion of a length of the spacing member, wherein the opening is sized large enough to allow movement of the bracket along a portion of the length of the spacing member with the distance sensor attached to the outer portion of the split tube by the bracket.

2. The rock bolt assembly according to claim 1, further comprising a first unit configured to receive readings from the distance sensor and emit a signal based on the readings from the distance sensor.

3. The rock bolt assembly according to claim 2, wherein the first unit is configured to monitor the readings over a period of time and wherein the signal emitted is indicative of a change in readings monitored over said period of time exceeding a predetermined threshold.

4. The rock bolt assembly according to claim 2, further comprising a base unit configured to be attachable to the nut, wherein the base unit includes a housing configured to contain the first unit.

5. The rock bolt assembly according to claim 4, further comprising an antenna extending outside the housing, wherein the antenna is connected to the first unit.

6. The rock bolt assembly according to claim 2, wherein the distance sensor is an ultrasonic sensor or a laser sensor.

7. The rock bolt assembly according to claim 1, wherein the spacing member is cylindrical.

8. The rock bolt assembly according to claim 7, wherein the opening of the cylindrical spacing member is an elongate slot extending along the spacing member.

9. The rock bolt assembly according to claim 1, wherein a front portion of the spacing member is provided with a chamfered seating portion configured to fit with the hole of the rock plate to align the spacing member with respect to the rock plate.

10. The rock bolt assembly according to claim 1, wherein the bracket is provided with attachment means for attachment to the split tube.

11. The rock bolt assembly according to claim 10, wherein the attachment means comprises a screw.

12. The rock bolt assembly according to claim 1, wherein the distance sensor is an analogue sensor such as a dial gauge or a ruler.

13. The rock bolt assembly according to claim 1, further comprising an alignment means configured to rotationally align the split tube and the spacing member about the longitudinal axis of the central rod bolt.

14. The rock bolt assembly according to claim 1, wherein the outer end portion of the split tube is provided with a hole configured for engagement by the screw.

15. A ground support monitoring system comprising: a plurality of rock bolt assemblies according to claim 1; a monitoring unit configured to receive data emitted by the first units of the plurality of sensor assemblies, and configured to either: relay the received data to a recipient, or analyze the received data by monitoring sensor readings over a period of time and emit a signal indicative of a change in readings monitored over said period of time exceeding a predetermined threshold.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0024] FIG. 1 shows an exploded perspective view of a rock bolt assembly comprising a sensor assembly according to a first embodiment.

[0025] FIG. 2 shows a perspective view of the rock bolt assembly of FIG. 1 as installed in rock (rock not shown) before subsequent crack and movement of rock.

[0026] FIG. 3 shows a perspective view of the rock bolt assembly of FIG. 2 as installed in rock (rock not shown) but after subsequent crack and movement of rock causing elongation of the central rod of the rock bolt. Hence, the distance D1 is smaller than in FIG. 2.

[0027] FIG. 4 shows an end portion of the bolt (rock plate not illustrated) with the alignment means for rotationally aligning the spacing member and the split tube.

[0028]

TABLE-US-00001 1 sensor assembly 2 central rod 3 split tube 4 wedge anchor assembly 5 rock plate 6 nut 7 distance sensor 8 bracket 9 elongate spacing member 10 opening 11 first unit 12 base unit 13 attachment means 14 cable 15 washer 16 alignment means

DETAILED DESCRIPTION

[0029] A sensor assembly 1 according to a first embodiment will hereinafter be described with reference to the appended drawings.

[0030] The sensor assembly 1 is suitable for use with a rock bolt comprising a central rod 2, a split tube 3 for being fitted around the central rod 2, a wedge anchor assembly 4 fitted to the central rod 2, a rock plate 5 with a hole, and a nut 6 for attachment to an outer end of the central rod 2. The rock bolt is mounted to a formation as known in the art by drilling a hole in the formation, inserting the rock bolt, and rotating the nut 6 of the rock bolt to thereby rotate the central rod 2. The wedge anchor assembly 4 causes the rock bolt to be anchored in the formation upon tensioning of the wedge mechanism at rotation of the central rod 2.

[0031] A driver socket (not shown) is used in known manner to hammer the rock bolt into the formation, and the driver socket is subsequently rotated to apply a momentum to the nut 6 at the end of the rock bolt. In the present invention, the sensor assembly 1 is provided for enabling monitoring of elongation of the rock bolt over time which may occur if the rock cracks where the rock bolt is installed such that an outer piece of the rock moves outwards from an inner piece of rock in which the rock bolt is anchored.

[0032] The sensor assembly 1 thus enables detection of rock movement such that proper measures can be taken early on including for example further strengthening of the rock, exchange of bolts or controlled removal of loose pieces of rock.

[0033] The sensor assembly 1 comprises: a distance sensor 7, a bracket 8 for attaching the distance sensor 7 to an outer portion of the split tube 3, an elongate spacing member 9 configured to be fitted around the split tube 3 between the nut 6 and the rock plate 5 to keep the nut 6 and the rock plate 5 spaced apart. The spacing member 9 comprises an opening 10 extending along a portion of the length of the spacing member 9. The opening is sized large enough to allow movement of the bracket 8 along a portion of the length of the central rod 2 with the distance sensor 7 attached to the outer portion of the split tube 3 by the bracket 8. In other embodiments, the opening may alternatively extend along the full length of the spacing member 9.

[0034] Once the rock bolt is anchored, the bracket 8 and distance sensor 7 are attached to the split tube 3 with the bracket 8 extending through the opening 10. As shown in FIGS. 1 and 2, the distance sensor 7 is configured to measure a first distance D1 to the rock plate but could alternatively in other embodiments measure the distance to an object provided at a known and static distance from the rock plate 5. Upon changes in the rock formation, the rock may force the rock plate 5 outwards whilst the split tube 3 remains firmly attached to the rock/formation, causing the central rod 2 to deform by longitudinal extension wherein the first distance D1 is reduced as evident when comparing it in FIG. 1 (before elongation of central rod) and FIG. 2 (after elongation of central rod). FIGS. 1 and 2 also show that the length of the length D2 from the rock plate 5 to the nut 6 is static and that the length D3 of the split tube 3 is static. Hence, at elongation of the central rod 2, the split tube 3 remains substantially static (is not elongated) whilst the rock plate 5 moves outwards. The first distance D1 between the distance sensor 7 and the rock plate 5 is thus reduced since the bracket 8 remains static while the spacing member 9 moves outwards with the rock plate 5. Again, we are discussing relative movements.

[0035] The sensor assembly 1 also comprises a first unit 11 configured to receive readings from the distance sensor 7 and emit a signal based on the readings from the distance sensor 7. The provision of such a first unit 11 enables broadcasting of information based on the readings such that other entities are enabled to remotely listen for the emitted signal and use the information in the signal for initiating appropriate measures to decrease the risk of unwanted further rock movements or rock bolt failure. In other embodiments, the first unit 11 may alternatively be omitted wherein readings have to be collected from each distance sensor 7 by any other suitable means such as by a wired/direct connection.

[0036] The first unit 11 is configured to monitor the readings over a period of time and the signal emitted is indicative of a change in readings monitored over said period of time exceeding a predetermined threshold. Hence, the first unit has an active role in monitoring and interpreting the readings over time wherein the signal emitted is based on local interpretation based on local circumstances. This simplifies the design of any listening systems, reduces the need of transmission of data for analysis, and enables monitoring to be performed locally at each bolt rather than remotely. Hence, different bolts could use different interpretation tactics based on for example their individual dimension and material or based on the local material characteristics or importance of stability of the rock in which they are mounted.

[0037] As shown in FIGS. 1-3, the sensor assembly 1 further comprises a base unit 12 configured to be attachable to the nut 6. The base unit 12 comprises a housing configured to contain the first unit 11. The base unit 12 protects the first unit 11 and holds it to the nut 6. Here, the base unit 12 is connected to the distance sensor 7 by means of a physical cable 14 such that the signal between the readings from the distance sensor are transmittable to the first unit by the cable 14. Further, the use of a cable 14 provides a physical link such that the first unit and the base unit cannot accidently fall apart from the distance sensor upon installation or service. Also, a battery for powering the distance sensor 7 is provided within the base unit 12 and the power transmitted to the distance sensor 7 through the cable 14. The base unit 12 is provided with a central recess configured to fit to the nut 6 by friction/press fit. In other embodiment, the central recess of the base unit 12 is provided with a thread for engaging the large outer thread of the nut shown in the figures.

[0038] The sensor assembly 1 also comprises an antenna (not illustrated) inside the housing. However, the antenna may in other embodiments extend outside the housing. The antenna is connected to the first unit to transmit its signals.

[0039] The distance sensor 7 is an ultrasonic sensor but may alternatively be a laser sensor or any other suitable sensor. Further, the distance sensor 7 may alternatively be an analogue sensor such as a dial gauge or a ruler. If an analogue sensor is used, is requires manual inspection or visual inspection by camera, for example a camera mounted on a robot automatically inspecting the dial or gauge at regular intervals.

[0040] The spacing member 9 is cylindrical and is provided with an elongate slot extending along the spacing member 9. The said slot defines the opening 10 for the bracket to move along.

[0041] A front portion of the spacing member 9 is provided with a chamfered seating portion configured to fit with the hole of the rock plate 5 to align the spacing member 9 with respect to the rock plate 5. In other embodiments, the front portion may have any other suitable shape such as planar or rounded.

[0042] The bracket 8 is provided with attachment means in the form of a screw for attaching the bracket 8 to the split tube. In other embodiments, any other suitable attachment means may be used to attach the bracket 8 to the split tube, such as a rivet, an adhesive, a weld, or a mechanical fastener such as a push button. In other embodiments, the bracket 8 may be integrated with the split tube.

[0043] The second aspect of the invention relates to a rock bolt assembly comprises the sensor assembly 1 and the rock bolt described above.

[0044] The outer end portion of the split tube 3 is provided with a hole configured for engagement by the screw 13. In alternative embodiments, no hole is provided, wherein a hole may have to be manually added at installation of the rock bolt or alternative means for attaching the distance sensor/bracket to the split tube used.

[0045] The third aspect of the invention relates to a ground support monitoring system comprising a plurality of sensor assemblies 1 as described above and a monitoring unit (not illustrated) configured to receive data emitted by the first units 11 of the plurality of sensor assemblies 1. The monitoring unit is also configured to either relay the received data to a recipient or analyze the received data by monitoring sensor readings over a period of time and emit a signal indicative of a change in readings monitored over said period of time exceeding a predetermined threshold. The monitoring unit may be implemented in the form of a computer system operating a software designed to perform the above-mentioned functions of the monitoring unit. The monitoring unit may be provided remotely from the first units as long as the monitoring system is able to receive the data emitted by the first units 11.