Rock bolt assembly including a sensor assembly

Abstract

A sensor assembly for a rock bolt, wherein the rock bolt includes a central rod, a split tube for fitting around the central rod, a wedge anchoring assembly fitted to the central rod, a rock plate having a hole, and a nut for attaching to the outer end of the central rod, wherein the sensor assembly includes: a distance sensor, a bracket for attaching the distance sensor to an outer portion of the split tube, an elongated spacer member configured to fit around the split tube between the nut and the rock plate to keep the nut and the rock plate spaced apart, wherein the spacer member includes an opening extending along at least a portion of the length of the spacer member, wherein the opening is sized large enough to allow the bracket to move along a portion of the length of the spacer member, and wherein the distance sensor is attached to the outer portion of the split tube by the bracket.

Description

Technical Field

[0001] The present disclosure relates to rock bolts for reinforcing formations such as rock formations, and more particularly to techniques for monitoring such bolts over time to detect rock movement. Background Art

[0002] Formations such as rock formations or rock strata are typically reinforced using rock bolts. For example, rock bolts are commonly used to reinforce tunnel roofs and stabilize rock walls, slopes, and dikes. Depending on, for example, the type of formation to be reinforced, various types of rock bolts or anchors are used.

[0003] One common type of rock bolt is a hydraulically expandable rock bolt, which is provided with an expandable body that is driven into the formation and then expanded by introducing a pressurized pressure medium such that the expandable body presses against the wall of the borehole, thereby engaging the formation. A hydraulically expandable rock bolt is known from CZ 25706U1.

[0004] Another type of rock bolt is a friction bolt. Such a rock bolt can be driven into the formation by a driving device such as a jumbo. A mechanically expandable bolt includes an elongate expandable outer body (sometimes referred to as a split tube) and a central rod extending from a tail provided with a nut to a front end within the outer body, the front end being operatively connected to an expansion mechanism that is adapted to expand the outer body when the central rod is rotated.

[0005] When installing a mechanically expandable rock bolt in a formation, the driving device is operated to repeatedly impact the outer body of the bolt, thereby forcing the outer body into the formation. When the bolt has been driven far enough into the formation, the bolt is expanded by rotation of the nut, which causes rotation of the central rod such that the expansion mechanism causes expansion of the outer body. The nut can be a blind nut such that the nut can first be screwed onto the thread located at the tail of the central rod, where the central rod eventually bottoms out in the blind nut, thereby preventing further relative rotation between the central rod and the blind nut. This allows torque to be applied to the nut and further to the central rod for tensioning the expansion mechanism of the bolt. Other means for preventing co-rotation between the central rod and the nut are also feasible, such as thread locking fluid or shear pins, where a standard nut with a through hole can be used instead of the blind nut.

[0006] Ground movement can cause cracks to form in the rock, and the bolts thus prevent the rock blocks from spreading. However, when the rock fractures, the load on the bolts may increase and the bolts may be stretched, thereby increasing the risk of undesirable further rock movement and failure of the rock bolts. Summary of the Invention

[0007] The object of the present invention is to be able to detect rock movement so that appropriate measures can be taken at an early stage in response to the rock movement. According to a first aspect of the present invention, this object is achieved by the sensor assembly of the present invention for a rock bolt. The sensor assembly is for a rock bolt which includes a central rod, a split tube for fitting around the central rod, a wedge anchoring assembly fitted to the central rod, a rock plate with holes, a nut for attaching to the outer end of the central rod, and a washer for use with the nut. The sensor assembly includes: a distance sensor, a bracket for attaching the distance sensor to an outer portion of the split tube, an elongated spacer member which is configured to fit around the split tube between the nut and the rock plate to keep the nut and the rock plate spaced apart. The spacer member includes an opening extending along at least a portion of the length of the spacer member, wherein the opening is sized large enough to allow the bracket to move along a portion of the length of the spacer member, and wherein the distance sensor is attached to the outer portion of the tube by the bracket.

[0008] When the rock bolt is installed in a rock or other formation, the spacer member is fitted between the washer and the rock plate. Then, the nut is rotated to cause anchoring of the bolt by tightening the wedge anchoring assembly. Once the rock bolt is anchored, the bracket and the distance sensor are attached to the split tube, with the bracket extending through the opening. The distance sensor is configured to measure the distance to the rock plate, but in other embodiments could alternatively measure the distance to an object set at a known and static distance from the rock plate. When a change occurs in the rock formation, the rock may force the rock plate outwards while the inner portion of the split tube remains firmly further attached to the rock / formation, causing the central rod to deform by longitudinal extension. During this extension of the central rod, the split tube remains substantially stationary while the rock plate moves outwards together with the spacer member. The distance between the distance sensor and the rock plate thus decreases because the bracket remains stationary while the spacer member moves outwards with the rock plate. We are talking about relative movement.

[0009] The sensor assembly may further include a first unit which is configured to receive a reading from the distance sensor and transmit a signal based on the said reading from the distance sensor. The provision of such a first unit enables information to be broadcast based on the reading, such that other entities can remotely listen for the transmitted signal and use the information in the signal to initiate appropriate measures to reduce the risk of unwanted further rock movement and rock bolt failure.

[0010] The first unit can be configured to monitor the readings over a period of time, and wherein the transmitted signal indicates that the change in the readings monitored over the period of time exceeds a predetermined threshold. Thus, the first signal can play an active role in monitoring and interpreting the readings over time, wherein the transmitted signal is a local interpretation based on the local environment. This simplifies the design of the monitoring system such that tracking can be performed locally at each rock bolt rather than centrally. Thus, different rock bolts can use different interpretation strategies, for example based on their respective sizes and materials, or based on the material of the rock in which they are installed.

[0011] The sensor assembly may further include a base unit configured to be attachable to the nut, wherein the base unit includes a housing configured to accommodate the first unit. The base unit protects the first unit and holds the first unit to the nut.

[0012] The sensor assembly may further include an antenna extending outside the housing, wherein the antenna is connected to the first unit. Providing the antenna outside the housing can increase the signal strength and can reorient the antenna when the sensor assembly is installed onto the rock bolt such that the antenna points in a favorable direction.

[0013] The distance sensor can be an ultrasonic sensor or a laser sensor. Such sensors are readily available at low cost, and are rugged and reliable.

[0014] The spacer member can be cylindrical. The cylindrical shape is easy to manufacture and allows rotation about the central rod, enabling easier assembly onto the rock bolt.

[0015] The opening of the cylindrical spacer member can be an elongate slot extending along the spacer member. The elongate slot is easy to manufacture, for example by milling or extrusion.

[0016] The front portion of the spacer member can be provided with a chamfered seating portion configured to mate with the hole of the rock plate to align the spacer member relative to the rock plate. Thus, the provision of the chamfered seating portion can improve the load distribution.

[0017] The bracket can be provided with attachment means for attachment to the split tube. The attachment means enables the sensor to be manipulated individually until the installation of the rock bolt has been completed, such that the sensor need not be present during the impact driving of the rock bolt into the rock.

[0018] The attachment means can include screws. Screws are readily available and can be easily unscrewed and reassembled for maintenance of the sensor.

[0019] The distance sensor can be an analog sensor, such as a dial gauge or a ruler. The analog sensor operates in a harsh environment with a lot of electrical interference, thus providing a reliable and durable backup in case of failure of the electronic sensor. Some rock bolts can be provided with analog sensors, and nearby sensors can be provided with digital sensors. In addition, an analog gauge or ruler can be provided in the same rock bolt assembly to complement the digital sensor.

[0020] The sensor assembly can also include an alignment device configured to align the split tube and the spacer member about the longitudinal axis of the central rod bolt in a rotational direction. For example, the alignment device can respectively include a protrusion extending from the spacer member or the split tube, and a mating recess in the other of the split tube and the spacer member. The protrusion can be integrally formed with the spacer member or the split tube, or the key can be a separate component positioned between them. If the key is a separate component, corresponding recesses can be provided in both the split tube and the spacer member to hold them in alignment when the key is positioned within the two recesses. By aligning the spacer member and the split tube in the rotational direction, the position on the split tube where the bracket / attachment bracket is to be attached is always aligned with the opening of the split tube through which the bracket will extend in use. Thus, such alignment is useful when installing the bracket and further ensures that the bracket will not be squeezed or damaged by the spacer member when the nut is rotated.

[0021] A second aspect of the present invention relates to a rock bolt assembly including the sensor assembly and a rock bolt as described above.

[0022] The outer end portion of the split tube can be provided with a hole configured to be engaged by a screw.

[0023] A third aspect of the present invention relates to a ground support monitoring system including a plurality of the sensor assemblies as described above and a monitoring unit configured to receive data transmitted by a first unit of the plurality of sensor assemblies. The monitoring unit is also configured to forward the received data to a recipient, or to analyze the received data by monitoring the sensor readings over a period of time and transmit a signal indicating that the change in the readings monitored over the period exceeds a predetermined threshold. Thus, the monitoring system connects a plurality of sensors to a central monitoring unit, which can be configured differently according to local requirements. For example, the central unit can process the data locally, or the central unit can convey / forward the data to a recipient, such as a remote monitoring system that collects data from many geographical locations. The provision of the monitoring unit enables one type of signal to be used between the monitoring unit and the first unit of each rock bolt, and another type of signal to be used for communication with an external system, so that one type of signal can be used for short-range transmission in a complex underground environment, while another type of signal is used for communication with a remote site. Description of the Drawings

[0024] Figure 1 Shows an exploded perspective view of a rock bolt assembly including a sensor assembly according to a first embodiment.

[0025] Figure 2 Shows a Figure 1 rock bolt assembly installed in rock (rock not shown), prior to subsequent rock fracture and movement.

[0026] Figure 3 Shows a Figure 2 rock bolt assembly installed in rock (rock not shown), but after subsequent rock fracture and movement, resulting in elongation of the central rod of the rock bolt. Thus, the distance D1 is less than the distance in Figure 2 .

[0027] Figure 4 Shows an end portion of the bolt (rock plate not shown) with alignment means for aligning the spacer member and the split tube in the rotational direction.

[0028] 1 Sensor assembly 9 Elongated spacer member 2 Central rod 10 Opening 3 Split tube 11 First unit 4 Wedge anchoring assembly 12 Base unit 5 Rock slab 13 Attachment device 6 Nut 14 Cable 7 Distance sensor 15 Washer 8 Bracket 16 Alignment device Detailed Description

[0029] The sensor assembly 1 according to the first embodiment will be described below with reference to the drawings.

[0030] The sensor assembly 1 is adapted for use with a rock bolt that includes a central rod 2, a split tube 3 for fitting around the central rod 2, a wedge anchoring assembly 4 fitted to the central rod 2, a rock plate 5 having holes, and a nut 6 for attachment to the outer end of the central rod 2. As is known in the art, the rock bolt is installed in the formation by drilling a hole in the formation, inserting the rock bolt, and rotating the nut 6 of the rock bolt so as to rotate the central rod 2. When the wedge mechanism is tightened under rotation of the central rod 2, the wedge anchoring assembly 4 anchors the rock bolt in the formation.

[0031] The rock bolt is hammered into the formation in a known manner using a drive sleeve (not shown), and then the drive sleeve is rotated to impart momentum to the nut 6 at the end of the rock bolt. In the present invention, the sensor assembly 1 is provided to be able to monitor the elongation of the rock bolt over time, which may occur when cracks appear in the rock at the location where the rock bolt is installed such that the outer rock mass moves outward relative to the inner rock mass in which the rock bolt is anchored.

[0032] Thus, the sensor assembly 1 can detect rock movement, enabling appropriate measures to be taken at an early stage, including, for example, further strengthening the rock, replacing the bolt, or the controlled removal of loose rock blocks.

[0033] The sensor assembly 1 includes: a distance sensor 7, a bracket 8 for attaching the distance sensor 7 to an external portion of the split tube 3, and an elongated spacer member 9 configured to be assembled 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 spacer member 9 includes an opening 10 extending along a portion of the length of the spacer member 9. The opening is sized large enough to allow the bracket 8 to move along a portion of the length of the central rod 2, wherein the distance sensor 7 is attached to the external portion of the split tube 3 by the bracket 8. In other embodiments, alternatively, the opening may extend along the entire length of the spacer member 9.

[0034] Once the rock bolt is anchored, the bracket 8 and the distance sensor 7 are attached to the split tube 3, wherein the bracket 8 extends through the opening 10. As Figure 1 and Figure 2 shown, the distance sensor 7 is configured to measure a first distance D1 from the rock plate, but in other embodiments, alternatively, it may measure the distance to an object disposed at a known static distance from the rock plate 5. When the rock formation changes, the rock may force the rock plate 5 outwards while 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 decreases, which is evident when comparing Figure 1 (before the central rod elongates) and Figure 2 (after the central rod elongates) the first distance D1. Figure 1 and Figure 2 It is also shown that the length D2 of the length from the rock plate 5 to the nut 6 is static, and the length D3 of the split tube 3 is also static. Thus, when the central rod 2 elongates, the split tube 3 remains substantially stationary (does not elongate), while the rock plate 5 moves outwards. The first distance D1 between the distance sensor 7 and the rock plate 5 thus decreases because the bracket 8 remains stationary while the spacer member 9 moves outwards with the rock plate 5. Again, we are discussing relative motion.

[0035] The sensor assembly 1 further includes a first unit 11 configured to receive readings from the distance sensor 7 and transmit a signal based on the readings from the distance sensor 7. Providing such a first unit 11 enables broadcasting information based on the readings, such that other entities can remotely monitor the transmitted signal and use the information in the signal to initiate appropriate measures to reduce the risk of unwanted further rock movement or rock bolt failure. In other embodiments, alternatively, the first unit 11 may be omitted, where readings must be collected from each distance sensor 7 by any other suitable means (such as by wired / direct connection).

[0036] The first unit 11 is configured to monitor the readings over a period of time, and the transmitted signal indicates that the change in the readings monitored over the period of time exceeds a predetermined threshold. Thus, the first unit has an active role in monitoring and interpreting the readings over time, where the transmitted signal is a local interpretation based on the local environment. This simplifies the design of any listening system, reduces the need for data transmission for analysis, and enables local monitoring at each anchor rather than remote monitoring. Thus, different anchors can use different interpretation strategies, for example, based on their respective sizes and materials, or based on the local material properties or stability importance of the rock in which they are installed.

[0037] As Figures 1-3 shown, the sensor assembly 1 further includes a base unit 12, which is configured to be attachable to the nut 6. The base unit 12 includes a housing configured to accommodate the first unit 11. The base unit 12 protects the first unit 11 and holds the first unit 11 to the nut 6. Here, the base unit 12 is connected to the distance sensor 7 by a physical cable 14 such that signals between the readings from the distance sensor can be transmitted to the first unit through the cable 14. In addition, the use of the cable 14 provides a physical link so that the first unit and the base unit do not accidentally fall off the distance sensor during installation or maintenance. Further, a battery for powering the distance sensor 7 is disposed within the base unit 12, and power is transmitted to the distance sensor 7 through the cable 14. The base unit 12 is provided with a central recess configured to be assembled to the nut 6 by friction / press fit. In another embodiment, the central recess of the base unit 12 is provided with threads for engaging the large external threads of the nut shown in the figure.

[0038] The sensor assembly 1 further includes an antenna (not shown) located within the housing. However, in other embodiments, the antenna may extend outside the housing. The antenna is connected to the first unit to transmit its signal.

[0039] The distance sensor 7 is an ultrasonic sensor, but alternatively, it may also be a laser sensor or any other suitable sensor. Additionally, alternatively, the distance sensor 7 may be an analog sensor, such as a dial gauge or a scale. If an analog sensor is used, manual inspection or visual inspection through a camera, such as a camera mounted on a robot, is required to periodically and automatically check the dial or gauge.

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

[0041] The front portion of the spacer member 9 is provided with a chamfered seating portion which is configured to cooperate with the holes of the rock plate 5 to align the spacer member 9 relative 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 screws for attaching the bracket 8 to the split tube. In other embodiments, any other suitable attachment means (such as rivets, adhesives, welding or mechanical fasteners (such as buttons)) may be used to attach the bracket 8 to the split tube. In other embodiments, the bracket 8 may be integral with the split tube.

[0043] A second aspect of the present invention relates to a rock bolt assembly which includes the above-described sensor assembly 1 and a rock bolt.

[0044] The outer end portion of the split tube 3 is provided with a hole which is configured to engage with the screw 13. In an alternative embodiment, no hole is provided, in which case a hole may have to be manually added when installing the rock bolt or when installing an alternative means for attaching the distance sensor / bracket to the split tube being used.

[0045] A third aspect of the present invention relates to a ground support monitoring system which includes a plurality of the above-described sensor assemblies 1 and a monitoring unit (not shown) which is configured to receive data transmitted by the first unit 11 of the plurality of sensor assemblies 1. The monitoring unit is further configured to forward the received data to a recipient, or to analyze the received data by monitoring the sensor readings over a period of time and to transmit a signal indicating that the change in the readings monitored over the period of time exceeds a predetermined threshold. The monitoring unit may be implemented in the form of a computer system running software which is designed to perform the above-described functions of the monitoring unit. The monitoring unit may be located remotely from the first unit, provided that the monitoring system is able to receive the data transmitted by the first unit 11.

Claims

1. A rock bolt assembly, the rock bolt assembly comprising a sensor assembly (1) and rock bolts (2, 3, 4, 5, 6, 15), the rock bolts including a central rod (2), split tubes (3) for assembling around the central rod (2), a wedge anchoring assembly (4) assembled to the central rod (2), a rock plate (5) having a hole, a nut (6) for attaching to the outer end of the central rod, and a washer for use with the nut (6). The sensor assembly (1) includes: A distance sensor (7). A bracket (8) for attaching the distance sensor (7) to an outer portion of the split tube (3). An elongated spacer member (9) configured to be assembled around the split tube (3) between the washer and the rock plate (5) to keep the nut (6) and the rock plate (5) spaced apart. Wherein the elongated spacer member (9) includes an opening (10) extending along at least a portion of the length of the elongated spacer member (9), wherein the opening (10) is sized large enough to allow the bracket (8) to move along a portion of the length of the elongated spacer member (9), and wherein the distance sensor (7) is attached to the outer portion of the split tube (3) by the bracket (8).

2. The rock bolt assembly according to claim 1, further comprising: A first unit (11) configured to receive a reading from the distance sensor (7) and transmit a signal based on the reading from the distance sensor (7).

3. The rock bolt assembly according to claim 2, wherein, The first unit (11) is configured to monitor the reading over a period of time, and wherein the transmitted signal indicates that the change in the reading monitored over the period of time exceeds a predetermined threshold.

4. The rock bolt assembly according to any one of claims 2 - 3, further comprising a base unit (12) configured to be attachable to the nut (6), wherein the base unit (12) includes a housing configured to accommodate the first unit (11).

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 any one of claims 2-5, wherein, The distance sensor (7) is an ultrasonic sensor or a laser sensor.

7. The rock bolt assembly according to any one of claims 1-6, wherein, The elongated spacer member is cylindrical.

8. The rock anchor assembly according to claim 7, wherein, The opening of the cylindrical elongated spacer member (9) is an elongated slot extending along the elongated spacer member (9).

9. The rock bolt assembly according to any one of the preceding claims, wherein, A chamfered seating portion is provided at a front portion of the elongated spacer member (9), the chamfered seating portion being configured to cooperate with the hole of the rock plate to align the elongated spacer member relative to the rock plate.

10. The rock bolt assembly according to any one of the preceding claims, wherein, The bracket (8) is provided with attachment means (13) for attaching to the split tube.

11. The rock bolt assembly according to claim 10, wherein, The attachment means (13) includes a screw.

12. The rock bolt assembly according to any one of claims 1 or 6 - 10, wherein, The distance sensor is an analog sensor.

13. The rock bolt assembly according to any one of claims 1 - 12 further includes an alignment device configured to align the split tube and the elongated spacer member about the longitudinal axis of the central rod (2) of the bolt in a rotational direction.

14. The rock bolt assembly according to claim 11, wherein, The outer end of the split tube is provided with holes configured to engage with the screws.

15. The rock bolt assembly according to claim 12, wherein, The analog sensor is a dial gauge or a scale.

16. A ground support monitoring system includes a plurality of rock bolt assemblies according to any one of claims 2 - 6, wherein the ground support monitoring system further includes a monitoring unit configured to receive data transmitted by the first unit (11) of the plurality of sensor assemblies (1), and the monitoring unit is configured to: Forward the received data to a recipient, or Analyze the received data by monitoring sensor readings over a period of time and transmit a signal indicating that the change in the readings monitored over the period of time exceeds a predetermined threshold.

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