ARRANGEMENT FOR ROCK BOLTS AND A METHOD FOR THE USE OF THE ARRANGEMENT, AND A REINFORCEMENT SYSTEM COMPRISING SUCH AN ARRANGEMENT

Abstract

An arrangement for a rock bolt that is intended to be embedded in grout in a borehole, a method for using said arrangement, and a reinforcement system including such an arrangement. The rock bolt is equipped with a longitudinal tube with a passage, wherein an extended electrically conducting sensor is introduced into the passage of the tube and the sensor is connected with the anchoring end of the rock bolt, a monitoring arrangement designed to be connected to the rock bolt, that an electrically conducting circuit is formed through the connection of the rock bolt, the sensor and the monitoring arrangement, wherein the monitoring arrangement includes evaluation means intended to evaluate the presence of changes in the condition of the bolt, and signaling means 36 designed for the signaling of the condition of the bolt.

Claims

1. An arrangement for a rock bolt that is intended to be embedded in grout in a borehole, where the rock bolt is equipped with a longitudinal tube with a passage, characterised by an extended electrically conducting sensor that is introduced into the passage of the tube and that the sensor is connected with the anchoring end of the rock bolt, a monitoring arrangement designed to be connected to the rock bolt, that an electrically conducting circuit is formed through the connection of the rock bolt, the sensor and the monitoring arrangement, and that the monitoring arrangement demonstrates evaluation means intended to evaluate the presence of changes in the condition of the bolt, and signalling means designed for the signalling of the condition of the bolt.

2. The arrangement for a rock bolt according to claim 1, where the tube has a wall provided with penetrating openings for the detection of the presence of a cavity.

3. The arrangement for a rock bolt according to claim 1, where the monitoring arrangement is designed to be mounted at the mounting end of the rock bolt.

4. The arrangement for a rock bolt according to any one of claim 1, comprising detection means designed for the detection of changes of position of the sensor.

5. The arrangement for a rock bolt according to any one of claim 1, comprising detection means designed for the detection of whether the circuit is closed.

6. The arrangement for a rock bolt according to claim 1, where the detection means comprises a sliding potentiometer equipped with a sliding contact, whereby the sensor is connected to the sliding contact.

7. The arrangement for a rock bolt according claim 1, where the sensor comprises a thread or wire.

8. The arrangement for a rock bolt according to claim 1, where the signalling means comprises LEDs arranged on the cover of the monitoring arrangement.

9. The arrangement for a rock bolt according to claim 1, where the signalling means comprises communication means for the transmission and/or reception of signals over wireless networks or mobile phone networks to a central presentation unit.

10. The arrangement for a rock bolt according to claim 1, where the monitoring arrangement is designed to be mounted at the mounting end of the rock bolt in a manner that allows it to be removed.

11. The arrangement for a rock bolt according to claim 1, where the rock bolt is designed as a dynamic rock bolt comprising a surrounding sheath along part of the rock bolt.

12. The arrangement for a rock bolt according to claim 1, where the monitoring arrangement comprises a smoke detector.

13. A method for the use of an arrangement for a rock bolt according to claim 1 comprising the steps: the introduction of a sensor into a tube fixed at the rock bolt, the connection of the sensor to the anchoring end of the rock bolt, the introduction of the rock bolt into the borehole that has been filled with grout, the connection of a monitoring arrangement to the rock bolt, the connection of the rock bolt, the sensor and the monitoring arrangement, in order to form an electrically conducting circuit, and the evaluation of the occurrence of changes in the condition of the bolt by an evaluation means, and the signalling of the condition of the rock bolt by signalling means.

14. The method according to claim 13, comprising the step of detecting the presence of a cavity through the supply of medium under pressure to the tube and detecting change of pressure in the medium or a flow of medium.

15. The method according to claim 13, comprising the detection of changes of position of the sensor.

16. The method according to claim 13, comprising signalling when bending e of the rock bolt is detected.

17. The method according to claim 13, comprising signalling when the change of position of the sensor exceeds a predetermined maximum displacement distance smax.

18. The method according to claim 13, comprising the detection of conduction in the circuit, where the lack of conduction indicates breakage of the bolt.

19. The method according to any claim 13, comprising signalling by the signalling means when breakage of the rock bolt is detected.

20. The method according to claim 13, where the signalling comprises the emission of flashing and/or steady light signals at LEDs arranged on the cover of the monitoring arrangement.

21. The method according to claim 13, where the signalling comprises the transmission and/or reception of signals over wireless WiFi networks or mobile phone networks to a central presentation unit.

22. A rock reinforcement system comprising a set of several rock bolts where each one of the bolts is equipped with an arrangement according to claim 1.

Description

DESCRIPTION OF DRAWINGS

[0020] The invention will be described in more detail below with reference to the attached drawings and the subsequent description of an embodiment of the invention, in which:

[0021] FIG. 1 shows schematically the forward end of a rock bolt with a tube and sensor according to one embodiment of the arrangement.

[0022] FIG. 2 shows schematically the end of the rock bolt closest to the opening of the borehole with the monitoring arrangement according to the same embodiment as that shown in FIG. 1.

[0023] FIGS. 3 a-d show schematically the embedding of a rock bolt comprising a tube in a borehole, and shows schematically the investigation of the presence of a cavity in the borehole.

[0024] FIG. 4 shows schematically the forward end of a rock bolt with a tube and sensor according to a second embodiment of the arrangement according to the invention.

[0025] FIG. 5 shows schematically the monitoring arrangement according to one embodiment of the invention.

[0026] FIG. 6 shows schematically the monitoring arrangement according to one embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

[0027] FIGS. 1 and 2 show schematically an embodiment of the arrangement according to the invention. The arrangement according to the invention comprises a rock bolt 1 equipped with a longitudinal tube 2 where the tube has a forward first end 3 arranged at the anchoring end 4 of the rock bolt and a second end 5 arranged at the mounting end 6 of the rock bolt. The tube has a passage 7 and a wall of the tube 8, and is attached at the rock bolt 1 with fastening arrangements 9. The passage 7 extends between the forward end 3 of the tube and the second end 5 of the tube closest to the mounting end 6 of the rock bolt.

[0028] The arrangement according to the invention comprises also an extended sensor 10 that is introduced into the passage 7 of the tube. The sensor 10 consists of a thin loop of electrically conducting material such as wire, which may be of piano wire type, that is introduced into the passage 7 of the tube. The sensor 10 has a forward end 11 that is attached at the anchoring end 4 of the rock bolt with a screw joint 12 or similar, in order to form an electrically conducting connection.

[0029] The passage 7 of the tube may be sealed at the forward end 3 through melt sealing of the tube in order to prevent grout 13 entering the passage 7. The sensor 10 is designed to be longer than the tube 2 and has a connection end 14 intended to be connected to a monitoring arrangement 15 next to the assembly end 6 of the rock bolt. The sensor 10 can be freely displaced inside of the passage 7 of the tube, and is arranged to be parallel with the rock bolt 1. It can in this way follow changes of the rock bolt. If the rock bolt is bent, therefore, the sensor 10 will react in a corresponding manner and be displaced with the anchoring end 4 of the rock bolt. If the rock bolt 1 breaks as a consequence of increased load in a certain region, also the sensor can, under certain circumstances, break, next to the same region.

[0030] FIGS. 3 a-d show schematically the embedding of a rock bolt 1 comprising a tube 2 in a borehole 16, through a portion of grout 13 being injected into the borehole 16 by a nozzle 17, normally a tube. The borehole 16 is filled from the bottom 18 of the borehole, after which the tube is withdrawn as filling continues. The rock bolt 1 is subsequently introduced into the borehole.

[0031] The arrangement according to the invention is illustrated in FIGS. 1 and 2 in association with a rock bolt 1 of ribbed steel type. The rock bolt 1 may be designed also as a cable bolt or a dynamic rock bolt. One type of dynamic rock bolt (not shown in the drawings) is provided with one or several surrounding sheaths whose task is to prevent the bolt becoming fixed embedded in grout 13 along its complete length. This leads to the ability of the bolt to be bent and extended being exploited, whereby the load-absorbing ability of the bolt increases.

[0032] When the bolt 1 with the tube 2 is introduced into the borehole 16, a mounting fitting 20, a washer 21 with a nut 22, is mounted on the protruding assembly end 16 of the rock bolt closes to the borehole 19. It is preferable that the tube 2 be somewhat longer than the rock bolt 1 and protrudes from the borehole 16. The washer 21 of the mounting fitting may be designed with a hole 23 through which the tube 2 with the sensor 10 can be passed.

[0033] Rock material 25 may be constituted in different ways: undiscovered cracks 26 and natural cavities are sometimes present that are filled by an injected portion of the grout 13. This means that the portion of grout that has been injected may be insufficient to fix the rock bolt, which may have as its consequence that the reinforcement system of which the bolt is a part is deficient, and has insufficient load-bearing capacity. When the rock bolt 1 with the tube is introduced into what appears to be a filled borehole 16, empty spaces or cavities 26 may arise along the bolt that are difficult to detect. Such a cavity or cavities 26, usually arises or arise, in particular, at the extreme end, at the deepest part of the borehole. There is in this case the risk that the uppermost part of the bolt is not properly anchored by the grout. If this is the case, a part of the load-bearing capacity of the bolt is lost. Furthermore, the risk for corrosion of the bolt increases, since the rock in itself may be wet.

[0034] FIG. 4 shows schematically a further embodiment of the arrangement where the wall 8 of the tube 2 is provided with a set of openings 27, cuts or slits, that can be closed and that are initially closed (see FIG. 4). These can, however, be opened through the supply of medium 30 under pressure to the passage 7 of the tube, in order to detect the presence of a cavity 26 in the borehole. The openings 27 may be distributed along the complete length of the tube, but are primarily distributed over the forward end 3 of the tube next to the anchoring end 4 of the bolt.

[0035] If the tube 2 is designed with openings 27 for the investigation of the presence of cavities 26, such an investigation is carried out shortly after the bolt has been introduced into the borehole (schematically illustrated in FIG. 2d), in order to determine whether the rock bolt 1 has been correctly embedded and is satisfactorily anchored such that the load-bearing ability of the rock bolt satisfies the desired requirements for load-bearing ability. The investigation concerns primarily the investigation of whether the anchoring end 4 of the rock bolt is well embedded. During the investigation, a medium 30 under pressure is supplied from measuring equipment 28 that has been temporarily connected for this purpose by connection means 29 to the end 5 of the tube that is closest to the opening 19 of the borehole. In the event of a cavity 26 being present in the borehole in direct association with the rock bolt 1 and the tube 2, a change in pressure or a flow of the medium arises that the measuring equipment 28 detects. A fall in pressure or a flow of medium shows that a cavity is present along the rock bolt.

[0036] The arrangement according to the invention comprises also a monitoring arrangement that is mounted at the mounting end 6 of the rock bolt. The monitoring arrangement 15 may be designed to be screwed directly onto the thread 24 of the rock bolt with, for example, a nut 32. The monitoring arrangement 15 is mounted at the bolt such that an electrically conducting connection is formed, for example through the nut 32. In cases in which an investigation of the anchoring of the rock bolt at the bottom end of the borehole through measurement of the presence of cavities 26 is carried out, the monitoring arrangement 15 is mounted at the bolt after such an investigation.

[0037] By connecting the monitoring arrangement 15, the rock bolt 1, and the sensor 10, an electrically conducting closed circuit 33 is formed. FIG. 5 shows one variant of a monitoring arrangement 15 that comprises a detector means 34, an evaluation means 35, a signalling means 36 and a power supply 37.

[0038] The detector means 34 is designed for the detection of changes in the position of the sensor 10. The detector means 34 comprises a linear potentiometer or sliding potentiometer 38 equipped with a sliding contact 39 in order to form an electrically conducting connection of the detector means 34 to the connection end 14 of the sensor 10. The sliding contact 39 can be displaced along the contact surface 40 of the potentiometer, along the longitudinal direction of the sensor 10. The position of the sliding contact 39 is represented by a voltage U that will vary between Umin and Umax, depending on the position of the sensor. The detector means 34 is designed such that the sensor 10 can be displace by a maximum of a predetermined, adjustable displacement distance smax, such as approximately 1-2 cm. Since the sensor 10 is fixed to the anchoring end 4 of the rock bolt and to the monitoring arrangement 15, the sensor is influenced in a corresponding manner and will in this way be displaced at the same time as the rock bolt is extended. If the rock bolt is bent and extended, the sensor 10 and the sliding contact 39 are displaced by a corresponding extent, whereby the potentiometer 38 detects a change dU in voltage.

[0039] The detector means 34 comprises also means 41 to detect conduction in the electrically conducting circuit 33 that consists of the bolt 1, the monitoring arrangement 15 and the sensor 10. If the circuit 33 is closed, the detector means 34 indicates this to the evaluation means 35. If the rock bolt 1 is subject to breakage, the circuit 33 becomes open. In the event that conduction is lacking, the detector means indicates that breakage of the bolt has taken place.

[0040] In the event of displacements in the surrounding rock material 25, forces arise that influence the rock bolt and the sensor 10 that is fixed and connected to the bolt and that runs in the passage 7 of the tube. The rock bolt absorbs the forces and can be deformed, extended and bent through elastic and plastic deformation. The condition of the rock bolt is influenced by this and is changed.

[0041] If the rock material 25 is displaced principally in the longitudinal direction of the rock bolt, the bolt is bent and breakage of the bolt occurs when the load-absorbing ability of the bolt is exceeded. Breakage of the bolt opens the circuit 33 and the monitoring arrangement 15 signals this in an appropriate manner. If the rock material 25 around the rock bolt is displaced in the transverse direction, the bolt and the sensor 10 are sheared off in the same region. The sensor can be removed from the tube and measured in order to give an indication of the location of the break.

[0042] The monitoring arrangement comprises also an evaluation means 35 designed for the reception and evaluation of signals 42 from the detector means 34. The evaluation means comprises data processors for the processing of incoming signals 42 and the production of output signals 51 with respect to the condition of the bolt and changes in the condition of the signalling means 36.

[0043] The signalling means 36 is designed for the signalling of the condition of the bolt, and of changes in its condition.

[0044] FIG. 5 shows that the signalling means 36 comprises LEDs 43.1, 43.2 that can emit flashing or steady light signals in different colours. The LEDs are arranged clearly visible on the cover 44 of the monitoring arrangement.

[0045] The monitoring arrangement according to FIG. 5 is designed to signal several types of change of condition of the rock bolt. In the case in which the evaluation means detects that the displacement s of the sensor 10 and the sliding contact exceeds the predetermined maximum distance smax , the signalling means 36 indicates this through a flashing yellow LED 43.1 in order to signal that the rock bolt has been bent. In the case in which the evaluation means 35 detects that the circuit 33 has been opened, i.e. that the rock bolt has broken, a red LED 43.2 flashes. The signalling means 36 can, of course, be varied and adapted to different situations.

[0046] It is conceivable also that a signal is given if it is detected that the sensor 10 and the sliding contact have been displaced along the contact surface of the potentiometer. It is in this case indicated that the bolt has been bent without breakage of the bolt occurring.

[0047] The signalling means may have also a presentation arrangement 44 or a display that shows the condition of the rock bolt.

[0048] FIG. 6 shows a further variant of a monitoring arrangement that differs from the previous monitoring arrangement in that the signalling means comprises communication means 45 for the transmission and/or the reception of signals over wireless networks such as WiFi or over mobile networks to/from a central presentation unit 46 arranged at another location that is remote from the rock bolt and the monitoring arrangement 15.

[0049] In this variant of the monitoring arrangement 15, the condition of the rock bolt is communicated to the centrally located presentation unit 46. The evaluation means 35 and the signalling means 36 in this variant emit an output signal 47 that indicates whether the circuit 33 is closed or open, i.e. whether the rock bolt is unbroken or broken. Furthermore, the evaluation means 35 may emit an output signal 48 that indicates whether the bolt has become bent or not. The evaluation means 35 may emit also a further output signal 49 that specifies the analogue voltage U of the potentiometer. Since the voltage U varies with the degree of bending e of the bolt, the amount by which the rock bolt has been bent inside the rock is obtained directly. It is preferable that the evaluate means 35 evaluates these incoming signals several times per second and transmits the output signals through the signalling means 36 and a wireless network to the centrally located presentation unit.

[0050] It is preferable that the monitoring arrangement 15 has its own power supply 37, for example through batteries of button cell type, in order to power the monitoring arrangement. Furthermore, the monitoring arrangement has a compact design in order to facilitate its handling and mounting. Furthermore, the manufacturing costs are low.

[0051] In a further embodiment of the arrangement, also other detectors, such as a smoke detector 50 or other appropriate sensors, may be connected to the monitoring arrangement 15 in order to monitor the presence of smoke in the tunnel or mine.

[0052] A further advantage of the monitoring arrangement is that it is possible to reuse it, since it is mounted at the mounting end of the rock bolt and the connection end of the sensor in a manner that allows it to be removed.