WO2003033877A1

WO2003033877A1 - A rock anchor load indicator

Info

Publication number: WO2003033877A1
Application number: PCT/IB2002/004022
Authority: WO
Inventors: Johannes Diderick De Klerk; Christiaan Wilhelm Hauptfleisch; Stanley Nance-Kivell
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-10-15
Filing date: 2002-10-01
Publication date: 2003-04-24
Anticipated expiration: 2004-04-15
Also published as: ZA200202163B

Abstract

The invention relates to a rock anchor. The invention provides a warning device for use in conjunction with a rock anchor. The warning device includes compressible means (34) formed to be installed on a rock anchor in a configuration in which a tensile force operatively exerted on the rod (18) of the rock anchor by a surrounding rock formation is transferred to act as a compressive force on the compressible means (34). The warning device includes also indicator means (36, 110) for indicating when a predetermined magnitude of compressive deformation of the compressible means (34) has operatively occurred. Such deformation may be indicative of a movement within the rock formation. In one embodiment, the indicator means is entirely mechanical. The warning device may be configured to operatively indicate more than one predetermined magnitude of compressive deformation of the compressible means.

Description

ROCK ANCHOR LOAD INDICATOR

THIS INVENTION relates to a rock anchor.

The invention relates particularly to a warning device for use with a rock anchor. It is known in certain fields of geotechnical engineering to support a face of a geological formation by means of geological anchors anchored in the said formation. Examples of such geological anchors are rock anchors that are used in an underground mine to support a roof formation of a tunnel defined in a rock stratum.

A rock anchor typically includes a rod, of which the major portion is unthreaded and an end portion is screw threaded, a bearing plate defining a hole therethrough, and a securing nut. The securing nut may be provided with a washer. The unthreaded portion of the rod is inserted into a blind bore formed in a rock stratum and is then secured to the stratum surrounding the portion of the rod so inserted by suitable securing means, such as grouting, and the like. The screw threaded portion of the rod is left to protrude from the stratum. The bearing plate is located on the protruding portion of the rod via the hole defined therethrough and the securing nut is screwed onto the protruding screw threaded portion to bear against the bearing plate, which is thus caused to bear against the face of the stratum surrounding the bore defined therein. By screwing the securing nut on the rod, the rod is tensioned, normally to a tensile force as near as possible to a predetermined optimum working tensile force for the prevailing conditions.

The current invention provides a warning device to warn a person, such as a mine worker, that the prevailing tensile force in a rod of a rock anchor has reached a predetermined maximum magnitude. In particular, the fact that the prevailing tensile force in a rod of a rock anchor has reached a certain predetermined maximum magnitude, may be indicative that the rock anchor installation is at risk of failure in one of a number of possible failure mechanisms, such as the yielding of its rod in tension, the failure of the rock stratum surrounding the rod, and the like. An increase in the prevailing tensile force in a rod of a rock anchor is caused by factors associated with movements inside the rock stratum, hence threatening rock bursts, and the like.

The warning device of the invention will be defined and described hereinafter with reference to its use in conjunction with a rock anchor of the type described above. It must be understood, however, that the warning device may equally be adapted for use in conjunction with other types of geological anchors of a similar nature to rock anchors.

According to the invention there is provided a warning device for use in conjunction with a rock anchor, the warning device including compressible means formed to be installed on a rock anchor in a configuration in which the prevailing tensile force in the rod of the rock anchor will be transferred to act as a compressive force on the compressible means, and at least one indicator means configured to indicate when a predetermined magnitude of compressive deformation of the compressible means has occurred, in operation of the warning device. As such, in operation of the warning device in conjunction with a rock anchor, there is an ascertainable relation between the magnitude of compressive deformation of the compressible means and the prevailing tensile force in the rod of the rock anchor.

The compressible means may include at least one compressible body.

The warning device of the invention may include a first housing body and a second housing body, both locatable on a rod of a rock anchor and the compressible means may be sandwiched between the two housing bodies. In this configuration, the extent of displacement of the housing bodies relative to each other may be visible or measured, to indicate the magnitude of the compressive deformation of the compressible means. Each housing body may define a plate-like portion defining therethrough a hole for receiving a rod of a rock anchor, the compressible means being sandwiched between the two plate-like portions.

The indicator means may include an indicator formation that can be deformed through relative displacement of the housing bodies, which is associated with compressive deformation of the compressible means, in operation of the warning device. The indicator formation may be an indicator tab which is fixed along an edge thereof with respect to either of the first housing body and the second housing body and which projects therefrom. The warning device may include also a bearing formation for bearing against the indicator tab when a predetermined magnitude of compressive deformation of the compressible means has occurred, the bearing formation being fixed with respect to the other of the first housing body and the second housing body and, in the uncompressed state of the compressible means, being spaced a predetermined distance away from the indicator tab. As such, the said bearing formation may be integrally formed with the first housing body or the second housing body, as the case may be. The indicator tab may be located operatively generally perpendicularly with respect to an axis of a rod of a rock anchor in conjunction with which the warning device is used, and the bearing formation may be spaced away a predetermined distance away from the indicator tab in a direction perpendicular thereto. When displacement of the first body relative to the second body occurs due to compressive deformation of the compressible means, the bearing formation will approach the indicator tab and, when sufficient deformation has taken place, will cause the indicator tab to be deformed to indicate such displacement. The deformation referred to may be in the form of bending of the indicator tab and, as such, the indicator tab will define a leading face and a trailing face on opposite sides thereof. Either one or both of the leading face and the trailing face of the indicator tab may be light reflective to aid visibility thereof and to attract attention thereto.

The compressible means may include at least two compressible bodies, the second compressible body being configured not to be in compression before the first compressible body has deformed to a predetermined magnitude of compressive deformation, in operation of the warning device, and thereafter to be in compression. As such, in operation of the warning device, a force of sufficient magnitude will cause the first compressible body to deform until the second compressible body is in compression. From then, the second compressible body will at least partially bear the total compressive force acting on the compressive means. A sufficient further increase in the magnitude of the compressive force acting on the compressible means may cause the second compressible body to deform. Further compressible bodies may be provided also, each being configured to be in compression only once the previous compressible body has deformed to a predetermined magnitude of compressive deformation.

The first compressible body may be a first tubular member extending substantially between the first and the second housing bodies, and the second compressible body may be a second tubular member, shorter than the first. The tubular members may be located coaxially with respect to each other and be configured for receiving a rod of a rock anchor through the inner tubular member.

The indicator tab may form part of a plate that is located between one of the housing bodies and the compressible means. As such, the plate formation may define therethrough a hole for receiving a rod of a rock anchor.

The indicator means may be configured to indicate that the first compressible body has deformed to the magnitude of compressive deformation at which the second compressible body is in compression, in operation of the warning device. More than one indicator means may be provided. As such, different indicator means and, where applicable, their associated bearing formations, may be configured to indicate different predetermined magnitudes of compressive deformation of the compressible means. Different indicator means may display different colours to render them visually distinguishable.

The indicator means may include an electrically energizable indicator unit and a contact arrangement that are connectable to a power supply in a configuration in which the indicator unit can be energised only when the indicator means is connected to a power supply and the contact arrangement is closed. The contact arrangement may include two electrical contact elements, displaceable towards each other through compressive deformation of the compressible means in a configuration in which they will make contact with each other, thus closing the contact arrangement, only when a predetermined magnitude of compressive deformation of the compressible means has been reached, in operation of the warning device.

The electrical contact elements may each include a contact plate and the compressible means may be sandwiched between the contact plates to form a layered structure. The layered structure may define therethrough, perpendicular to its layers, a hole for receiving a rod of a rock anchor and at least one contact plate may define at least one projection projecting towards the other contact plate, the projection being spaced away a predetermined distance from the other contact plate when the compressible means is in its uncompressed state.

The compressible means may be a compressible body defining therethrough a hole for each projection from a contact plate within which the associated projection is located and within which it is displaceable relative to the other contact plate through deformation of the compressible body, until it makes contact with the other contact plate, in operation of the warning device. The warning device may have more than one indicator unit for indicating when different predetermined magnitudes of compressive deformation of the compressible means have been reached.

The compressible means may be made of a non-conductive material, such as nylon, a plastics material, a ceramics material, or the like. The compressible means may be configured to be installed between a nut and a bearing plate of a rock anchor. Further features of the invention will become apparent from the following description of a warning device, in accordance with the invention, with reference to the accompanying diagrammatic drawings. In the drawings:

Figure 1 shows a diagrammatic cross-sectional view of a first embodiment of a warning device, in accordance with the invention, in a first operative configuration with respect to a rock anchor;

Figure 2 shows a diagrammatic exploded three-dimensional view of the warning device of Figure 1 ;

Figure 3 shows a diagrammatic cross-sectional view of the warning device of Figure 1 , in the same operative configuration as that shown in Figure 1 ; Figure 4 shows a diagrammatic cross-sectional view of the warning device of Figure 1 , in a second operative configuration;

Figure 5 shows a diagrammatic cross-sectional view of a second embodiment of a warning device, in accordance with the invention, in a first operative configuration with respect to a rock anchor;

Figure 6 shows a diagrammatic cross-sectional view of the warning device of Figure 5, in a second operative configuration with respect to a rock anchor;

Figure 7 shows a diagrammatic cross-sectional view of the warning device of Figure 5, in an inoperative configuration;

Figure 8 shows a diagrammatic cross-sectional view of the warning device of

Figure 5, in an inoperative configuration, along the line VIII-VIII of Figure 7; and

Figures 9 to 1 1 show general views of three component parts of the warning device of Figure 5.

In Figures 1 to 4, a first embodiment of a warning device for use with a rock anchor, in accordance with the invention, is designated generally by the reference numeral 1 0.

Figure 1 shows the warning device 1 0 installed on a rock anchor 1 2 supporting a portion of rock stratum 1 4, into which a blind bore 1 6 is formed.

The rock anchor 1 2 includes a rod 1 8, a bearing plate 20 defining a hole 22 therethrough, a securing nut 24, and a washer 26. The rod 1 8 has a screw threaded end portion 28 and an unthreaded portion 30, which constitutes the major portion of the rod. The unthreaded portion 30 of the rod 1 8 is located within the bore 1 6 defined in the rock stratum 1 4 and is secured to the rock stratum surrounding the hole by securing means in the form of grouting 32. The warning device 10 is installed between the bearing plate 20 and the washer 26 in a configuration in which it transfers in compression the prevailing tensile force in the rod 1 8 to the bearing plate 20 via the securing nut 24 and the washer.

With reference particularly to Figure 2, the warning device 1 0 includes compressible means in the form of a nylon material compressible body 34 and indicator means including an electrically energizable unit in the form of a LED 36 and a contact arrangement including two electrical contact elements including contact plates 38 and 40, respectively. The LED 36 and the contact elements 38 and 40 are connected to a power supply in the form of a battery 42. The warning device 10 includes further a plastics material housing comprising a first portion 44 and a second portion 46 matched to fit onto each other and to define, once fitted onto each other, within the housing a space 48 within which the other components of the warning device are housed. The first housing portion 44 defines therethrough a hole 50 through which, when the warning device 10 is assembled, the LED 36 will partially protrude and thus be visible from the outside of the device.

The contact plates 38 and 40 are made of a conductive material. The plates 38 and 40 and the compressible body 34 each has approximately the shape of a conventional- type washer and, in the assembled configuration of the device 10, forms a layered structure in which the compressible body is sandwiched between the said two plates. The plate 38 defines projections 52 projecting in the direction of the plate 40. The compressible body 34 defines therethrough holes 54 within which the projections 52 of the plate 38 are located and within which they are displaceable relative to the plate 40, as will be described in the description below of Figures 3 and 4. The housing portions 44 and 46, the plates 38 and 40, and the compressible body 34 each defines therethrough a hole 56, the holes 56 being aligned when the warning device 10 is assembled, for receiving therethrough a rod of a rock anchor. When the warning device 1 0 is installed on a rock anchor as shown in Figure 1 , the securing nut 24 is screwed on the threaded portion 28 of the rod 1 8 and the rod is thereby tensioned to a tensile force as near as possible to a predetermined optimum tensile force for the prevailing conditions. This force is transferred to the securing nut 24, to the washer 26, to the warning device 1 0, to the bearing plate 20, and to the face 58 of the rock stratum 1 4. A compressive force F equal to the prevailing tensile force in the rod 1 8 is thus exerted on the warning device 10, and particularly also on its compressible body 34.

With particular reference to Figure 3, the compressive force F is exerted on the warning device 1 0 by the washer 26 and the bearing plate 20 in a direction perpendicular to the plates 38 and 40 and the compressible body 34. In the operative configuration of the warning device 10 shown, the rock anchor 1 2 has been installed and tensioned to the predetermined optimum tensile force, as aforesaid. The projections 52 defined by the plate 38 are spaced away from the plate 40. The contact plates 38 and 40 are thus apart and the LED 36 is not energised.

In Figure 4, the compressive force F acting on the warning device 1 0 has increased in magnitude from the configuration shown in Figure 3 and has reached a magnitude at which the compressible body 34 has deformed under compression to a point where the projections 52 from the plate 38 have been displaced within the holes 54 defined through the compressible body to make contact with the plate 40, thus closing the contact arrangement including the contact plates 38 and 40. The housing portion 44 also has been deformed through compression. The said contact arrangement is thus closed and the LED 36 is energised to light up.

It should be appreciated that the magnitude of the force that will close the contact arrangement of the warning device of the invention, and thus energise its indicator means, will be determined by a number of factors, most importantly the shape and configuration of the compressible body and the material of which the body is made. The warning device may thus be configured so that its indicator means is energised at a magnitude of force suited to the particular type of rock anchor with which it is to be used and the particular conditions in which such a rock anchor is to operate.

In Figures 5 to 8, a second embodiment of a warning device, in accordance with the invention, is designated generally by the reference numeral 70.

With reference particularly to Figure 5, the warning device 70 is installed on a rod 72 of a rock anchor 74 between a washer 76 and a bearing plate 78 of the rock anchor 74. The rock anchor 74 includes also a nut 79. As such, the rock anchor 74 is identical to the rock anchor 1 2 of Figure 1 and, as such, will not be described herein in more detail. The warning device 70 includes a first housing body 80 (shown also in Figure 1 0), a second housing body 82 (shown also in Figure 1 1 ), and compressible means including a first compressible body in the form of a first round tubular member 84 and a second compressible body in the form of a second round tubular member 86. The tubular member 86 is located inside the tubular member 84 in a coaxial relation therewith. The tubular member 86 is shorter than the tubular member 84 by a length s1 , say three millimeters, and the rod 72 is received through tubular member 86. In this example, the compressive yield strength of the tubular members 84 and 86 will be assumed to be five tons and eight tons, respectively.

The body 80 includes a plate-like portion 88, defining therethrough a hole 90 through which the rod 72 is received, and four skirt panels (see reference numerals 92 to 98 in Figure 10) projecting peripherally and perpendicularly therefrom, in the general direction of the body 82. The panels 92 and 96 define edge bearing formations 100 and 102.

The body 82 includes a plate-like portion 1 04, defining therethrough a hole 1 06 through which the rod 72 is received, and four guide formations 1 08 (of which only two are shown here) . The guide formations 108 interact with the panels 92 to 96 to guide the displacement of the body 80 with respect to the body 82.

The warning device 80 includes indicator means in the form of two indicator tabs 1 1 0 and 1 1 2 forming part of a plate 1 1 4 that is held between the body 82 and the compressible bodies 84 and 86. The indicator tabs 1 10 and 1 1 2 thus are fixed with respect to the body 82.

The indicator tabs 1 10 and 1 1 2 define leading faces 1 1 6 and 1 20, respectively, and trailing faces 1 1 8 and 1 22, respectively. Each of the faces 1 1 6 to 1 22 has a reflective coating applied thereto (see reference numerals 1 24 and 1 26 in Figure 9) . The various reflective coatings referred to are of different colours to make them visually easily distinguishable.

In Figure 5, the warning device 70 has just been installed on the rock anchor 74. The nut 79 of the rock anchor 74 has been tightened to a torque corresponding to a predetermined optimum maximum prevailing tensile force F in the rod 72 of the rock anchor 74, say four tons. The compressible means comprising the tubular members 84 and 86 are substantially undeformed. The tubular member 86 is in compression, whereas the tubular member 84 is not. The bearing formation 1 00 is a distance s3, say two millimeters, away from the indicator tab 1 1 0. The bearing formation 1 00 is a distance s2, say five millimeters, away from the indicator tab 1 1 2.

In Figure 6, a movement has occurred in the rock formation (not shown) on which the rock anchor 74 is installed. The rock face (not shown) has been displaced and has displaced therewith the bearing plate 78 in the direction of the nut 79 by a distance s1 . The maximum prevailing tensile force F in the rod 72 has increased to a value of say seven tons. The compressive strength of the tubular member 84 has been exceeded and it has deformed in compression to a point where the tubular member 86 is in contact with the body 80. The second tubular member 86 therefore is now in compression and the total compressive force acting on the tubular members 84 and 86 now equals seven tons. The bearing formation 1 00 of the panel 92 has been displaced a distance s1 in a direction towards the indicator tab 1 1 0 and has deformed it by bending it as shown.

When the force F acting on the tubular members 86 and 84 increases further to a value of say ten tons, the tubular member 84 also will yield in compression, causing the bearing formation 102 to deform the indicator tab 1 1 2 to a configuration similar to that of the indicator tab 1 1 0 shown.

As indicated before, Figures 7 and 8 show two diagrammatic cross-sections through the warning device 70 in an inoperative configuration. As such, corresponding features, where designated, are designated again by the same reference numerals as before and a description of these features may be found in the description above of the figures referred to. These drawings together show clearly the configuration of the panels 92 to 98.

Figure 9 shows a diagrammatic view of the plate formation 1 14 including the indicator tabs 1 1 0 and 1 1 2. The plate formation 1 14 defines therethrough a hole 1 28 for receiving the rod 72.

Figures 10 and 1 1 show diagrammatic general views of the bodies 80 and 82 of Figure 1 . Again, corresponding features, where designated, are designated again by the same reference numerals as before and a description of these features may be found in the description above of the relevant figures.

The warning device may thus be configured to indicate a magnitude of compressive deformation of its compressible means suited to the particular type of rock anchor with which it is to be used and the particular conditions in which the rock anchor is to operate. The warning device of the invention also may be adapted particularly for use with different type rock anchors and the invention extends also to such warning devices that are adapted for use with different type rock anchors which still include the main features of the warning device of the invention.

Insofar as a rock anchor may be adapted for use with a warning device, in accordance with the invention, the invention extends also to a rock anchor adapted for the purpose. The invention extends still further to a combination of a warning device, in accordance with the invention, and a rock anchor.

Claims

1 . A warning device for use in conjunction with a rock anchor, the warning device including compressible means formed to be installed on a rock anchor in a configuration in which the maximum prevailing tensile force in the rod of the rock anchor will be transferred to act as a compressive force on the compressible means, and at least one indicator means configured to indicate when a predetermined magnitude of compressive deformation of the compressible means has taken place, in operation of the warning device.

2. A warning device as claimed in Claim 1 , which has a first housing body and a second housing body, both locatable on a rod of a rock anchor, and in which the compressible means is sandwiched between the two housing bodies.

3. A warning device as claimed in Claim 2, in which the indicator means includes an indicator formation that can be deformed through relative displacement of the housing bodies associated with compressive deformation of the compressible means, in operation of the warning device.

4. A warning device as claimed in Claim 3, in which the indicator formation is an indicator tab which has a side that is fixed with respect to either of the first housing body and the second housing body and which projects therefrom, the device including also a bearing formation which is fixed with respect to the other of the first housing body and the second housing body and which provides for the deformation of the indicator tab, in operation of the warning device.

5. A warning device as claimed in any one of Claims 2 to 4, in which the compressible means includes at least two compressible bodies, the second compressible body being configured not to be in compression before the first compressible body has deformed to a predetermined magnitude of compressive deformation, in operation of the warning device, and thereafter to be in compression.

6. A warning device as claimed in Claim 5, in which the first compressible body is a first length of tubing extending between the first and the second housing bodies, and the second compressible body is a second length of tubing, shorter than the first, the lengths of tubing being located coaxially and the inner length of tubing being configured to receive therethrough a portion of a rod of a rock anchor.

7. A warning device as claimed in Claim 5 or 6, in which the indicator means is configured to indicate that the first compressible body has deformed to the magnitude of compressive deformation at which the second compressible means is in compression, in operation of the warning device.

8. A warning device as claimed in any one of the preceding claims, which has more than one indicator means for indicating when different predetermined magnitudes of compressive deformation of the compressible means has been reached, in operation of the warning device.

9. A warning device as claimed in Claim 1 or 2, in which the indicator means includes an electrically energizable indicator unit and a contact arrangement that are connectable to a power supply in a configuration in which the indicator unit will be energised only when the indicator means is connected to a power supply and the contact arrangement is closed, the contact arrangement including two electrical contact elements, displaceable towards each other through compressive deformation of the compressible means in a configuration in which they will make contact with each other, thus closing the contact arrangement, only when a predetermined magnitude of compressive deformation of the compressible means has been reached, in operation of the warning device.

1 0. A warning device as claimed in Claim 9, in which the electrical contact elements each includes a contact plate and the compressible means is sandwiched between the contact plates to form a layered structure, the layered structure defining therethrough, perpendicular through its layers, a hole for receiving a rod of a rock anchor and at least one contact plate defining at least one projection projecting towards the other contact plate, the projection being spaced away a predetermined distance away from the other contact plate when the compressible means is in its uncompressed state.

1 1 . A warning device as claimed in Claim 10, in which the compressible means is a compressible body defining therethrough a hole for each projection from a contact plate within which the associated projection is located and within which it is displaceable relative to the other contact plate through compressive deformation of the compressible body, until it makes contact with the other contact plate, in operation of the warning device.

1 2. A warning device as claimed in any one of the Claims 9 to 1 1 , which has more than one indicator unit for indicating when different predetermined magnitudes of compressive deformation of the compressible means has been reached.

1 3. A warning device as claimed in any one of the preceding claims, in which the compressible means is made of a non-conductive material, such as nylon, a plastics material, a ceramics material, and the like.

14. A warning device as claimed in any one of the preceding claims, in which the compressible means is configured to be installed between a nut and a bearing plate of a rock anchor.

1 5. A warning device for use in conjunction with a rock anchor substantially as described in the specification with reference to and as illustrated in the accompanying drawings.