WO2017087995A2 - Loss of load indicator device - Google Patents

Loss of load indicator device Download PDF

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Publication number
WO2017087995A2
WO2017087995A2 PCT/ZA2016/000031 ZA2016000031W WO2017087995A2 WO 2017087995 A2 WO2017087995 A2 WO 2017087995A2 ZA 2016000031 W ZA2016000031 W ZA 2016000031W WO 2017087995 A2 WO2017087995 A2 WO 2017087995A2
Authority
WO
WIPO (PCT)
Prior art keywords
load
indicator
passage
rock bolt
indicator member
Prior art date
Application number
PCT/ZA2016/000031
Other languages
French (fr)
Other versions
WO2017087995A3 (en
Inventor
Brendan Robert Crompton
Rual ABREU
Philip John MAXTON
Original Assignee
Ncm Innovations (Pty) Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ncm Innovations (Pty) Ltd filed Critical Ncm Innovations (Pty) Ltd
Publication of WO2017087995A2 publication Critical patent/WO2017087995A2/en
Publication of WO2017087995A3 publication Critical patent/WO2017087995A3/en

Links

Classifications

    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
    • E21D21/00—Anchoring-bolts for roof, floor in galleries or longwall working, or shaft-lining protection
    • E21D21/02—Anchoring-bolts for roof, floor in galleries or longwall working, or shaft-lining protection having means for indicating tension
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
    • F16B13/00—Dowels or other devices fastened in walls or the like by inserting them in holes made therein for that purpose
    • F16B13/04—Dowels or other devices fastened in walls or the like by inserting them in holes made therein for that purpose with parts gripping in the hole or behind the reverse side of the wall after inserting from the front
    • F16B13/045—Dowels or other devices fastened in walls or the like by inserting them in holes made therein for that purpose with parts gripping in the hole or behind the reverse side of the wall after inserting from the front having axially compressing parts allowing the clamping of an object tightly to the wall
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
    • F16B31/00—Screwed connections specially modified in view of tensile load; Break-bolts
    • F16B31/02—Screwed connections specially modified in view of tensile load; Break-bolts for indicating the attainment of a particular tensile load or limiting tensile load
    • F16B31/028—Screwed connections specially modified in view of tensile load; Break-bolts for indicating the attainment of a particular tensile load or limiting tensile load with a load-indicating washer or washer assembly
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
    • F16B2200/00—Constructional details of connections not covered for in other groups of this subclass
    • F16B2200/95—Constructional details of connections not covered for in other groups of this subclass with markings, colours, indicators or the like

Definitions

  • the invention relates to a device that indicates when an installed rock bolt experiences a loss of load.
  • Rock bolts are installed info rock holes, penetrating an excavated wall, to support the wail against disintegration or collapse.
  • a rock bolt provides this support by transferring pre-load, applied to the bolt in installation, to the rock face with a faceplate that is carried on a projecting part of the bolt.
  • Load indicating devices which indicate the achievement of a required preload are commonplace, Such devices typically are located on the projecting part of the bolt, sandwiched between the faceplate and a load applicator such as a nut, and are adapted to deform to indicate achievement of preload.
  • the invention at least partially addresses the aforementioned problem.
  • the invention provides a load loss indicating device which includes a body with a first end and a second end, a passage which extends through the body between the ends and which is adapted to receive a rock bolt, the passage includes a narrow portion and a broad portion divided by a step in the wall of the bore and a resiliency deformable member which locates within the broad portion of the passage to compress when load is applied to the rock bolt and to axially expand when load is released as an indication of loss of load.
  • the resiliency deformable member may be a coiled spring or a ring or cylinder of a resiliency deformable material such as, for example, polyurefhane.
  • the load loss indicating device may include an indicator member which engages with the resiliency deformable member to move relatively to the body between an invisible position, in which the indicator member is contained within the broad portion of the passage, and a visible position in which at least part of the indicator member projects from the body.
  • the indicator member may include a shear formation which is adapted to break away, when the indicator member first moves into the invisible position, to indicate that load was applied to the rock bolt which was subsequently lost.
  • the indicator member may be made of suitable plastics material Preferably, the plastics material is brightly coloured.
  • the body may be made of a metal material.
  • the indicator member may include a plurality of toad loss graduations which are progressively revealed, once the indicator member is in a visible position and there is further movement of the member relatively to the body,
  • the body may include an annular groove in an outer wall of the body which groove is adapted to collapse or deform when a predetermined load is applied to the body,
  • the annular groove may contain a material that is extruded from the groove when the groove collapses or deforms,
  • Figure 1 diagramrnatically illustrates a rock bolt installation which includes a !oad loss indicator device, in accordance with a first embodiment of the invention, interposed on the bolt between a nut and a faceplate;
  • Figure 2 diagrammatically illustrates the rock bolt Installation with the load loss indicator device of Figure 1 in a loss of load position
  • Figure 3 is a sectioned perspective of the load loss indicator of Figure 1 in an expanded loss of load" state
  • Figure 4 is a sectioned perspective of the load loss indicator of Figure 1 in a compressed state
  • Figures 5 to 7 are each a longitudinally sectioned view of a rock bolt installation which includes a load loss indicator device in accordance with a second embodiment of the invention, together sequentially illustrating the indicator moving into a compressed position and then into a loss of toad position; and
  • Figure 8 and 9 are each longitudinally sectioned view of a rock bolt installation which includes a load loss indicator device in accordance with a third embodiment of the invention, DESCRIPTION OF PREFERRED EMBODIMENT
  • Figure 1 illustrates a grouted rock bolt installation 10 which includes a rock bolt 12 which longitudinally extends between a leading end (not shown) and a trailing end 18.
  • the bolt has a threaded end section 18 which extends from the trailing end 18.
  • the rock bolt is installed by Insertion into a rook hole 20. A grout is introduced Into the hole to adhere to the bolt to the rock bolt.
  • a faceplate 22 is received on the rock bolt, forced against a rock wall, such as a hanging wail 24, by action of a load applicator.
  • the load applicator in this example, is a nut 28 which is run along the threaded end section 18, with use of a bolting machine (not shown), into direct or indirect contact with the faceplate 22 to force the faceplate against the wall.
  • the rock bolt 12 carries a toad toss indicator 28 ⁇ , which is in accordance with a first embodiment of the invention, and which is interposed between the nut 28 and the faceplate 22.
  • the load loss indicator device 28A includes a metallic body 30 which has opposed first and second ends, respectively designated 32 and 34. In use, the first end 32 abuts the faceplate 22 and the second end 34 abuts the nut 28.
  • a cylindrical passage 38 extends through the body 30, between the ends (32, 34). At the second end 34, the passage Is stepped inwardly to provide an annular lip 40.
  • a spring coil 42 of complementary circumference is received in the cylindrical passage, in Figure 4, the spring coil is illustrated in the compressed state and, in Figure 3, in an extended state.
  • the coil spring extends between a free end 44 and a supported end 48, The supported end of the cOIL spring rests upon the lip 40.
  • the bad loss indicator device 28A includes an indicator sleeve 48 made of a suitable plastics material which is brightly coloured and which is engaged with the spring 42 to encapsulate at least part thereof, With the spring in the compressed state, as illustrated in Figure 4, the indicator sleeve is positioned wholly within the cylindrical passage in an annular space between the spring and the walls of the passage 38.
  • the body 30 can include an annular rebate 50 formed in an outer wall 52 of the body.
  • a compressible material 54 fills the rebate to extrude therefrom when the rebate collapses on the achievement of the predetermined preload.
  • Figure 5 illustrates a load loss indicator 28B, on the threaded end section 18 of a rock bolt 12, between a nut 28 and a faceplate 22.
  • the rock bolt can be tensioned or loaded by applying torque to the nut as described above with reference to the first embodiment.
  • the cylindrical passage 36 of the body 30 is stepped with a narrow portion 38A towards the first end 32 of the body and a broad recessed portion 388 opening at the second end 38 of the body.
  • a "once-off indicator tab 80 which extends from a lower circumferential edge 82 of the indicator disc 48, breaks away as it comes into contact with an inner edge at the open end 34 of the body. The purpose for this indicator tab will be described below,
  • FIGs 8 and 0 illustrate a load loss indicator 28C, on the threaded end section 18 of a rock bolt 12, between a nut 28 and a faceplate 22,
  • the load loss indicator 28C functions in the same way as the load loss indicator 28B, with the differences being that the indicator 28C does not include the tab 80 and that the indicator 28C has an external surface which is partitioned into, for example, three brightly and differently coloured regions A » 8, and C,
  • Regions A, B and C indicate the degree of the loss of load support.
  • region A can be coloured red to indicate a load range of 0 - 3 ions
  • region B can be coloured yellow? to indicate a load range of 3 - 8 tons
  • region C can be coloured green to indicate a load range of 8 - 10 tons.
  • the 10 ton limit represents the optimal load at which the rock bolt installation 10 is preloaded, [0O3SJ When the nut 28 is tightened to wholly compress the spring 42, fully locating the indicator disc 48 within the recessed portion 388 of the body's passage 38, this is indicative that the 10 ton preload has been achieved.
  • the disc 48 gets exposed as the housing is progressively lifted by the action of the expanding spring 42. Firstly, this progressive lifting will expose the region C (green). When the region G Is fully exposed, a mine ⁇ /orker will know that the load support is at 8 tons, meaning that there has been a toss of 4 tons of load.
  • the disc 48 can be graduated to reflect smaller degrees of load loss.
  • Figure 9 shows the disc 48 being both brightly coloured and graduated.
  • the graduation can also be of varying colours, and can be in the form of indents on the surface of the disc 48,

Abstract

The invention provides a load loss indicating device which includes a body with a first end and a second end, a passage which extends through the body between the ends and which is adapted to receive a rock bolt, the passage includes a narrow portion and a broad portion divided by a step in the wall of the bore and a resiliently deformable member which locates within the broad portion of the passage to compress when load is applied to the rock bolt and to axially expand when load is released as an indication of loss of load.

Description

LOSS OF LOAD INDICATOR DEVICE FIELD OF THE INVENTION
[0001] The invention relates to a device that indicates when an installed rock bolt experiences a loss of load.
BACKGROUND OF THE INVENTION
[0002] Rock bolts are installed info rock holes, penetrating an excavated wall, to support the wail against disintegration or collapse. A rock bolt provides this support by transferring pre-load, applied to the bolt in installation, to the rock face with a faceplate that is carried on a projecting part of the bolt.
[0003] Load indicating devices which indicate the achievement of a required preload are commonplace, Such devices typically are located on the projecting part of the bolt, sandwiched between the faceplate and a load applicator such as a nut, and are adapted to deform to indicate achievement of preload.
[0004] Of equal importance is for there to be an indication that a rock bolt has experienced a loss of this load, for example when the wall disintegrates to an extent that the faceplate is no longer in load support of the wall. With the rock bolt no longer in bad support, the wall may fail at this locality, exposing workers in the area to risk of death or injury.
[0003] In a grouted rock bolt Installation, often there is no obvious visual cue that the rock bolt has lost load support.
[0006] The invention at least partially addresses the aforementioned problem. SUMMARY OF INVENTION
[0007] The invention provides a load loss indicating device which includes a body with a first end and a second end, a passage which extends through the body between the ends and which is adapted to receive a rock bolt, the passage includes a narrow portion and a broad portion divided by a step in the wall of the bore and a resiliency deformable member which locates within the broad portion of the passage to compress when load is applied to the rock bolt and to axially expand when load is released as an indication of loss of load.
[0008]The resiliency deformable member may be a coiled spring or a ring or cylinder of a resiliency deformable material such as, for example, polyurefhane.
[0009]The load loss indicating device may include an indicator member which engages with the resiliency deformable member to move relatively to the body between an invisible position, in which the indicator member is contained within the broad portion of the passage, and a visible position in which at least part of the indicator member projects from the body.
[0010]The indicator member may include a shear formation which is adapted to break away, when the indicator member first moves into the invisible position, to indicate that load was applied to the rock bolt which was subsequently lost.
[0011] The indicator member may be made of suitable plastics material Preferably, the plastics material is brightly coloured.
[0012] The body may be made of a metal material. [0013]The indicator member may include a plurality of toad loss graduations which are progressively revealed, once the indicator member is in a visible position and there is further movement of the member relatively to the body,
[0014] The body may include an annular groove in an outer wall of the body which groove is adapted to collapse or deform when a predetermined load is applied to the body,
[0015] The annular groove may contain a material that is extruded from the groove when the groove collapses or deforms,
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The invention is described with reference to the following drawings in which:
Figure 1 diagramrnatically illustrates a rock bolt installation which includes a !oad loss indicator device, in accordance with a first embodiment of the invention, interposed on the bolt between a nut and a faceplate;
Figure 2 diagrammatically illustrates the rock bolt Installation with the load loss indicator device of Figure 1 in a loss of load position;
Figure 3 is a sectioned perspective of the load loss indicator of Figure 1 in an expanded loss of load" state;
Figure 4 is a sectioned perspective of the load loss indicator of Figure 1 in a compressed state;
Figures 5 to 7 are each a longitudinally sectioned view of a rock bolt installation which includes a load loss indicator device in accordance with a second embodiment of the invention, together sequentially illustrating the indicator moving into a compressed position and then into a loss of toad position; and
Figure 8 and 9 are each longitudinally sectioned view of a rock bolt installation which includes a load loss indicator device in accordance with a third embodiment of the invention, DESCRIPTION OF PREFERRED EMBODIMENT
[0017] Figure 1 illustrates a grouted rock bolt installation 10 which includes a rock bolt 12 which longitudinally extends between a leading end (not shown) and a trailing end 18. The bolt has a threaded end section 18 which extends from the trailing end 18. The rock bolt is installed by Insertion into a rook hole 20. A grout is introduced Into the hole to adhere to the bolt to the rock bolt.
[0018] To complete the installation, a faceplate 22 is received on the rock bolt, forced against a rock wall, such as a hanging wail 24, by action of a load applicator. The load applicator, in this example, is a nut 28 which is run along the threaded end section 18, with use of a bolting machine (not shown), into direct or indirect contact with the faceplate 22 to force the faceplate against the wall.
[0019] In this particular installation 10, the rock bolt 12 carries a toad toss indicator 28Ά, which is in accordance with a first embodiment of the invention, and which is interposed between the nut 28 and the faceplate 22.
[0020] As illustrated in Figure 3, the load loss indicator device 28A includes a metallic body 30 which has opposed first and second ends, respectively designated 32 and 34. In use, the first end 32 abuts the faceplate 22 and the second end 34 abuts the nut 28. A cylindrical passage 38 extends through the body 30, between the ends (32, 34). At the second end 34, the passage Is stepped inwardly to provide an annular lip 40. These features are best illustrated in Figures 3 and 4.
[0021] It is through the cylindrical passage 36 that the rock bolt 12 passes, in use, in assembly of the rook bolt installation 10.
[0022] A spring coil 42 of complementary circumference is received in the cylindrical passage, in Figure 4, the spring coil is illustrated in the compressed state and, in Figure 3, in an extended state.
[0023] The coil spring extends between a free end 44 and a supported end 48, The supported end of the cOIL spring rests upon the lip 40.
[0024] The bad loss indicator device 28A includes an indicator sleeve 48 made of a suitable plastics material which is brightly coloured and which is engaged with the spring 42 to encapsulate at least part thereof, With the spring in the compressed state, as illustrated in Figure 4, the indicator sleeve is positioned wholly within the cylindrical passage in an annular space between the spring and the walls of the passage 38.
[0025] In use, with the load loss indicator device 28A interposed between the nut 26 and the faceplate 22, as Illustrated in Figure 1 , and the faceplate 22 in load support of the hanging wall 24, the coii spring 42 is compressed wholly within the cylindrical passage as illustrated in Figure 4, along with the attached indicator sleeve 48. The coil spring is prevented from expanding into the relaxed extended state due to being constrained between the lip 40 and the faceplate 22. [0026] The grouted rock bolt installation 10 can experience ioss of toad support in that the faceplate is no longer in load supporting contact with the hanging wail 24, due to, for example, the hanging wall disintegrating over time to define a new surface recessed from the original surface of the wall. This is illustrated in Figure 2 with the original face of the hanging wall shown as a dotted line. In such an event, the coil spring is released from compression, by a faceplate that is no longer supportive (see Figures 2 and 3). The spring upwardly pushes on the faceplate and carries the indicator sleeve 48 from the cylindrical passage into an exposed position to visually indicate loss of load support.
[0027] To indicate that the rock bolt installation has been preloaded to an optimally predetermined extent, the body 30 can include an annular rebate 50 formed in an outer wall 52 of the body. A compressible material 54 fills the rebate to extrude therefrom when the rebate collapses on the achievement of the predetermined preload.
[0028] A second embodiment of the invention is now described with reference to Figures 5 to 7, In describing this embodiment, features analogous to those of the first embodiment will bear like reference.
[0029] Figure 5 illustrates a load loss indicator 28B, on the threaded end section 18 of a rock bolt 12, between a nut 28 and a faceplate 22.
[0030] Once the rock bolt is inserted in a rock hole (not shown), the rock bolt can be tensioned or loaded by applying torque to the nut as described above with reference to the first embodiment. In this embodiment, the cylindrical passage 36 of the body 30 is stepped with a narrow portion 38A towards the first end 32 of the body and a broad recessed portion 388 opening at the second end 38 of the body.
[0031] With the toad toss indicator sandwiched, as described, and the faceplate abutting a hanging wail (not shown), the advancing nut will move an indicator disc 48 into the recessed portion 36B. In so doing a poiyurethane spring 42, located within the portion (36B), is compressed as illustrated in Figure 8,
[0032] As the indicator disc 48 advances into the recessed portion 38B, a "once-off indicator tab 80, which extends from a lower circumferential edge 82 of the indicator disc 48, breaks away as it comes into contact with an inner edge at the open end 34 of the body. The purpose for this indicator tab will be described below,
[0033] If pre-load is lost to the rock bolt 12, as is illustrated in Figure 7, the poiyurethane spring will relax and expand in the axial direction, due to the resiliently deformable properties of poiyurethane. No longer heid in compression by pre-load, the spring 42 will push against the disc 48, and the nut 28, lifting the body 30 to reveal the indicator disc 48.
[0034] When the indicator disc 48 moves into a visible position without the indicator tab 80, this indicates that at some stage prior, the rock bolt must have been tensioned in preload. Conversely, if the indicator tab 80 is still part of the indicator disc 48, with the disc in the visible position, it will indicate that the rock bolt was never placed in pre-load. [0035] A third embodiment of the invention is now described with reference to Figures 8 and 9, In describing this embodiment, features analogous to those of the first embodiment will bear like reference,
[0036] Figures 8 and 0 illustrate a load loss indicator 28C, on the threaded end section 18 of a rock bolt 12, between a nut 28 and a faceplate 22,
[0037] The load loss indicator 28C functions in the same way as the load loss indicator 28B, with the differences being that the indicator 28C does not include the tab 80 and that the indicator 28C has an external surface which is partitioned into, for example, three brightly and differently coloured regions A» 8, and C,
[0038] Regions A, B and C indicate the degree of the loss of load support. Using an example, region A can be coloured red to indicate a load range of 0 - 3 ions, region B can be coloured yellow? to indicate a load range of 3 - 8 tons and region C can be coloured green to indicate a load range of 8 - 10 tons. The 10 ton limit represents the optimal load at which the rock bolt installation 10 is preloaded, [0O3SJ When the nut 28 is tightened to wholly compress the spring 42, fully locating the indicator disc 48 within the recessed portion 388 of the body's passage 38, this is indicative that the 10 ton preload has been achieved.
[0040] As the wall 24 recedes through disintegration or collapse towards a new surface (designated 24A), the disc 48 gets exposed as the housing is progressively lifted by the action of the expanding spring 42. Firstly, this progressive lifting will expose the region C (green). When the region G Is fully exposed, a mine ¥/orker will know that the load support is at 8 tons, meaning that there has been a toss of 4 tons of load.
[0041] When region B (yellow) is fully exposed, there is 3 tons of load support, 7 tons of load being lost, And, when region A (red) gets fully exposed a worker will know that there is no load support.
[0042] It will be appreciated that Instead of, or additionally to, using different coloured regions, the disc 48 can be graduated to reflect smaller degrees of load loss. Figure 9 shows the disc 48 being both brightly coloured and graduated. The graduation can also be of varying colours, and can be in the form of indents on the surface of the disc 48,

Claims

1. A load loss indicating device which includes a body with a first end and a second end, a passage which extends through the body between the ends and which is adapted to receive a rock bolt, the passage includes a narrow portion and a broad portion divided by a step in the wall of the bore and a resilientfy deformable member which locates within the broad portion of the passage to compress when load is applied to the rock bolt and to axially expand when load is released as an indication of loss of load,
2. A load loss indicating device according to claim 1 wherein the resiliently deformable member is a coiled spring or a ring or cylinder of a resiliency deformable material.
3. A load loss indicating device according to claim 1 or 2 which includes an indicator member which engages with the resiliently deformable member to move relatively to the body between an invisible position, in which the indicator member is contained within the broad portion of the passage, and a visible position in which at least part of the indicator member projects from the body.
4. A load loss indicating device according to claim 3 wherein the indicator member includes a shear formation which is adapted to break away when the indicator member first moves into the invisible position.
5. A load loss indicating device according to 3 or 4 wherein the indicator member is made of suitabie coloured plastics material.
6. A load loss indicating device according to anyone of claims 3 to 5 wherein the indicator member includes a plurality of load loss graduations which are progressively revealed, once the indicator member is in a visible position and there is further movement of the member relatively to the body.
PCT/ZA2016/000031 2015-11-19 2016-11-03 Loss of load indicator device WO2017087995A2 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
ZA201508536 2015-11-19
ZA2015/08536 2015-11-19
ZA2015/08724 2015-11-30
ZA201508724 2015-11-30

Publications (2)

Publication Number Publication Date
WO2017087995A2 true WO2017087995A2 (en) 2017-05-26
WO2017087995A3 WO2017087995A3 (en) 2017-07-20

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2019211475A1 (en) * 2018-05-04 2019-11-07 Norwegian University Of Science And Technology (Ntnu) Rock bolts
WO2020093092A1 (en) * 2018-11-06 2020-05-14 Lyster Jarrad Clayton Monitoring device

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB950552A (en) * 1961-08-22 1964-02-26 William George Burton Mcclean Improvements in or relating to visual warning devices for indicating loss of tensionin bolts
CA2018970A1 (en) * 1990-06-13 1991-12-13 Gordon R. Friesen Rockbolt load indicator

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
None

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2019211475A1 (en) * 2018-05-04 2019-11-07 Norwegian University Of Science And Technology (Ntnu) Rock bolts
WO2020093092A1 (en) * 2018-11-06 2020-05-14 Lyster Jarrad Clayton Monitoring device

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