EP3330482A1

EP3330482A1 - Method and device for installing a cable bolt wrapped in a sheath

Info

Publication number: EP3330482A1
Application number: EP16202248.7A
Authority: EP
Inventors: Federico Scolari; Mark Michael Brandon
Original assignee: DSI Underground IP Holdings Luxembourg SARL
Current assignee: DSI Underground IP Holdings Luxembourg SARL
Priority date: 2016-12-05
Filing date: 2016-12-05
Publication date: 2018-06-06
Also published as: WO2018104212A1

Abstract

The present invention relates to a method for installing a cable bolt (12) in an underground (10), comprising the steps:
• drilling a bore (40) into the underground (10),
• delivering grout material (49) into the bore (40),
• providing a cable (250),
• inserting the cable (250) with its leading end into the bore (40), and
• severing the cable (250) to form a trailing end,

According to the invention, the method comprises the further steps of
• providing a sheath material (251), and
• circumferentially wrapping the sheath material (251) around at least a predetermined length (B) of the cable (250).

The invention furthermore relates to an installation device for carrying out this method, and to a so-obtained cable bolt (12).

Description

The present invention relates to a method for installing a cable bolt in an underground, comprising the steps:

drilling a bore into the underground,
delivering grout material into the bore,
providing a cable,
inserting the cable with its leading end into the bore, and
severing the cable to form a trailing end.

The following discussion of the background of the invention is intended to facilitate the understanding of the invention. Although this discussion refers to the installation of cable bolts in mine tunnels, in particular in the roof of a mine tunnel, this specific application is merely to be understood as an example which by no means is intended to limit the scope of protection of the present invention.
The underground material, e.g. a rock substrate, surrounding a mine tunnel has to be supported and reinforced in order to provide a safe working environment for the miners. In this context, the verb "to support" refers to the fact that underground material located at the surface of the tunnel has to be prevented from falling off the tunnel walls, whereas the verb "to reinforce" refers to the ability of the underground material to support itself even under external loads, e.g. created by mining activities, earthquakes and the like. In other words, the verb "to support" mainly refers to stationary or quasi-stationary conditions, whereas the verb "to reinforce" refers to dynamic conditions.
Generally, so-called primary bolts are used for supporting the underground material, whereas so-called secondary bolts are used for reinforcing the underground material. Usually, secondary bolts are installed following to the installation of the primary bolts. For example, solid bar bolts having a length of less than 2.5 m to 3.0 m are used as primary bolts, whereas cable bolts having a length in the order of 10 m to 30 m may be used as secondary bolts. Cable bolts may, however, also be used as primary bolts.
The most commonly used cable bolts are made from seven wire steel strands having an overall diameter of 15.2 mm.
The present invention relates to the installation of cable bolts, and it should be noted that the facts provided in the above discussion are also valid for the invention.
A generic method is known, for example from DE-A-34 10 100 . The most important advantage of the generic method results from the fact that it allows, even under the limited available space conditions of a mine tunnel, to install bolts having a length exceeding the transverse dimension of the mine tunnel. The disadvantage of the generic method, however, is that the entire length of the bolt is covered by the grout material, preventing the possibility to create a "free length" on the cable, i.e. a section of the cable which is not bonded to the surrounding grout material (e.g. cement or resin).
In this context, it is important to note that tension may be applied to the cable bolts via the trailing end thereof, after the grout material has cured. Before applying tension, usually a rock plate and a cable anchor are placed over the trailing end of the cable. The tension is intended to compress the underground material surrounding the cable bolt in order to increase the ability thereof to resist to external loads. This ability, however, is reduced if the entire length of the bolt is covered by the grout material, as the ability of the cable bolt to act as a spring is reduced. Furthermore, especially in deep mines or tunnels, it is beneficial if cable bolts may absorb a certain rock mass deformation and therefore higher amount of energy, which will not be the case if a stiff, fully bonded cable bolt is used.
In an attempt to address the latter problem, it is furthermore known to deliver the grout material only to a section of the bore adjacent to the bore's bottom end in order to have only a leading end section of the bolt covered by the grout material and to provide a flexible free length of the bolt which may elastically respond to the exertion of external forces. As an alternative, it was suggested to coaxially arrange a sheathing around a predetermined length of the bolt in order to prevent the grout material from contacting the bolt in this section. Whereas the first solution results in a reduced load capacity of the bolt as only limited compression forces may be applied during tensioning, the second solution again limits the length of the bolt to the transverse dimension of the installation site.
It is the object of the present invention to provide a solution to the above-discussed problems.
In view of the above, the method according to the present invention comprises, in addition to the steps of the generic method, the further steps of providing a sheath material, and circumferentially wrapping the sheath material around at least a predetermined length of the cable.
The present invention is based on the new finding that not only a sheathing having a circumferentially closed wall is able to prevent the grout material from contacting the cable. Rather, the inventors found out that, taking the viscosity of the grout material into account, it is also possible to circumferentially wrap the sheath material around the cable without having to take the risk of grout material entering the space between the sheath material and the cable. As a consequence, it is possible to laterally approach the sheath material to the cable, wrap it circumferentially around the cable and to insert the combination of cable and sheath material into the bore. Both, cable and sheath material may be cut to length in dependence on the requirements of the specific bolt installation. In this way, it is possible to create a debonded section of the cable, the length of which advantageously is not limited to the tunnel's transverse dimension.
Preferably the predetermined length covered by the sheath material is shorter than the length of the section of the cable arranged inside the bore. Advantageously a section of the cable adjacent the leading end thereof and/or a section of the cable arranged inside the bore and adjacent to the cable's trailing end arranged outside the bore may be covered by grout material.
An anchoring element may be connected to the section of the cable adjacent the leading end thereof, in order to enhance the mechanical fixation of the cable's leading end section in the grout material. The anchoring element may, for example, be formed by an expansion head including a barrel element intended to surround the cable and at least one wedge element intended to be disposed between the cable and the barrel element in an orientation according to which it is driven into the barrel element due to its engagement with the tensioned cable. This anchoring element will allow an early tensioning of the cable, even before the grout material has cured.
Furthermore, a trailing end section of the cable may be covered by grout material. This allows the cable to take the load generated in this area, which otherwise would be transferred to the rock plate resulting in the risk of overloading the rock plate. Furthermore, grout material has an advantageous effect on the cable bolt's service life, as it prevents or at least limits corrosion processes.
According to the present invention, the cable and/or the sheath material may be supplied from a (respective) reel. This provides full flexibility with respect to the length of each respective cable bolt. In particular, subsequently installed cable bolts could have different lengths.
The sheath material may be supplied as a tube, advantageously as a plastic tube, the tube wall of which has a longitudinal slit. This slit allows the cable to enter into the lumen of the tube where it is protected from contact with the grout material. In order to facilitate the insertion of the cable into the slit tube, a slit-widening tool, e.g. a shoehorn-type tool, may be used. If the tube is made from plastic, the tube shape and the inherent elasticity of the plastic material will allow the slit to automatically close again, when the tube gets out of contact with the slit-widening tool, thus preventing the grout material from contacting the cable. Advantageously medium density polypropylene (PP) or polyethylene (PE) may be used as the plastic material.
Under the external load exerted by the grout material on the tube, the tube wall sections adjacent to the longitudinal edges of the tube wall defining the slit even may overlap further enhancing the separation of grout material and cable.
Although the tube may be a pre-slit tube, it is, according to a further embodiment of the method according to the present invention, conceivable that the tube is slit during the installation process. For example, the tube may be slit after having been supplied from the reel and before being combined with the cable.
Although the sheath material has been described to be formed as a tube, this embodiment is not to be understood as limiting. Rather, it is conceivable that the sheath material is provided as a flexible band material which is circumferentially folded around the cable. During this folding step the edge portions of the band material may be overlapped and/or fixed to each other, e.g. by gluing or welding, in order to provide a sheath preventing grout material from contacting the cable.
In order to make sure that the sheath material will remain in the desired position relative to the cable while being inserted into the bore, it is suggested that the leading end of the sheath material is connected to the cable. For example, this connection may be accomplished using a connection element, e.g. a crimping element. The connection element may be automatically supplied from a connection element stock, e.g. constructed similar to the magazine of a weapon. A connection tool, for example a crimping tool, e.g. including a hydraulically and/or pneumatically activated cylinder-piston device, may be used for fastening the connecting element to the sheath material and the cable.
According to a further embodiment of the present invention, a filling material may be provided in the space between the inner surface of the sheath material and the outer surface of the cable. This filling material may serve several purposes. For example, it may help to stabilize the shape of the sheath material under the influence of an external load exerted e.g. by the grout material. Furthermore, it may, on the one side, lubricate a relative movement of the sheath material and the cable, but, on the other side, dampen such relative movement. A material exhibiting all three characteristics, in particular lubricates relative movement of sheath material and cable under stationary or quasi-stationary conditions, for example while applying tension to the cable bolt, but dampens relative movements under dynamic conditions, for example when the underground material vibrates, e.g. due to mining activities, is grease or wax.
Advantageously, the filling material may be applied to the cable before the sheath material is wrapped around the cable, e.g. by using a filling material application device.
The grout material may be supplied from a grout material supply, e.g. supported by a movable installation device. The grout material supply may either be a container storing a predetermined amount of ready-to-use grout material or a grout material preparing device, e.g. a mixer. The grout material may be cement. However, other grout materials might be used as well, e.g. resin-based grout material, polyurethane, and the like.
In this context, it is furthermore to be noted that, according to the method disclosed by DE-A-34 10 100 , the above-discussed generic steps are carried out in the above-indicated order, i.e. the grout material is delivered into the bore prior to the insertion of the cable into the bore (pre-grouting). However, the present invention is intended to cover also methods according to which the cable is inserted into the bore prior to the delivering of the grout material into the bore (post-grouting).
According to a second aspect, the present invention relates to a device for installing a cable bolt in an underground, in particular using the method according to any preceding claim, the device comprising a drilling unit for drilling a bore into the underground, a grout delivering unit for delivering grout material into the bore, a cable insertion unit for inserting the cable with its leading end into the bore, and a cable severing unit for severing the cable to form a trailing end, a wrapping unit for circumferentially wrapping a sheath material around at least a predetermined length of the cable.
Further embodiments of the installation device according to the present invention as well as the technical advantages thereof may be gathered from the above discussion of the installation method according to the present invention.
According to a third aspect, the present invention relates to a cable bolt comprising a cable and a sheath material having a longitudinal slit and circumferentially wrapped around at least a predetermined length of the cable.
Further embodiments of the cable bolt according to the present invention as well as the technical advantages thereof may be gathered from the above discussion of the installation method according to the present invention.
An embodiment of the invention will now be described in further detail referring to the attached drawings in which:

Figure 1: illustrates an example of an underground of a mine tunnel in which cable bolts according to an embodiment of this invention are installed,
Figure 2: illustrates a device for installing a cable bolt according to the invention,
Figure 3: illustrates the main components of the device of Figure 2,
Figure 4: illustrates a cable bolt according to the invention installed in the underground, and
Figures 5a to 5e: illustrate steps of a method for installing a cable bolt in an underground.

Figure 1 shows an underground 10 of a mine tunnel 11, which is reinforced by for example four secondary bolts 12 in the roof 11 a of the mine tunnel 11 and two secondary bolts 12 in each of the two side walls 11 b. All secondary bolts 12 may be formed as cable bolts, in particular cable bolts according to the invention. Furthermore the underground 10 is supported by for example thirteen primary bolts 14 comprising solid bars.
The cable bolts 12 are installed using a device 20 shown in Figure 2. The installation device 20 may be mounted on a four-wheeled vehicle 22 or a caterpillar vehicle and comprises various units in order to be able to prepare cable bolts 12 on site and install them in the underground 10. These units are inter alia a wrapping unit 24 (shown in more detail in Figure 3), a drilling unit 26, a grout delivering unit 28, a cable insertion unit 30 and a cable severing unit 32.
The wrapping unit 24, as shown in more detail in Figure 3, is arranged on the vehicle 22 and includes a reel 241 supplying a steel strand 250, which is to be used as a cable bolt, and another reel 242 supplying a sheath material 251, which is to be wrapped around the steel strand 250. The sheath material 251 can for example be a plastic tube.
The wrapping unit 24 further comprises a greasing nozzle 245 arranged subsequent to the reel 241 in the feeding direction of the steel strand 250. The greasing nozzle 245 applies grease 48 (see Figure 4) onto the surface of the steel strand 250, which is intended to act as a filling material for filling the space between the inner surface of the sheath material 251 and the outer surface of the steel strand 250.
The wrapping unit 24 further comprises a feeding device 243 for feeding the plastic tube 251 from the reel 242. The feeding device may comprise pulleys. Furthermore, the wrapping unit 24 comprises a cutting tool 244 intended for providing a longitudinal slit in the plastic tube's wall material. For example, the cutting tool 244 can be a slotting knife.
Furthermore, a combining tool 246 is arranged subsequent to the cutting tool 244 and the greasing nozzle 245. The combining tool 246 can for example include a shoehorn widening the slit formed by the cutting tool 244 such that the steel strand 250 provided with the grease may be inserted into the plastic tube 251.
Furthermore, the wrapping unit 24 includes a connection tool 248, which is arranged subsequent to the combining tool 246. The connection tool 248 is intended to attach a connection element 47 to a leading end of the plastic tube 251 wrapped around the steel strand 250. Connection elements 47 might be stored in the vicinity of the connection tool 248 in a connection element stock 247a in order to be supplied to the steel strand 250. The connection tool 248 can be a crimping tool.
Finally, the wrapping unit 24 includes another feeding device 249, which is mounted on an automatic bolting rig (not shown in Figure 3) for feeding the wrapped steel strand 251 into a bore, as will be described below in more detail.
Referring to Figures 2 and 5a, the installation device 20 includes a drilling unit 26 for drilling a bore 40 into the underground 10. The drilling unit 26 may be a conventional drilling unit known in the art, e.g. a drilling unit including a plurality of drill rods 36.
Referring to Figure 2 and 5b, the installation device 20 comprises a grout delivering unit 28 which includes at least one hose 38 and a grout reservoir (not shown) storing grout 49 to be delivered to the bore 40. The hose 38 can be arranged to allow a positioning in the bore 40 in dependence upon the filling level up to which the bore 40 is filled with grout 49.
Referring to Figure 2, 5c and 5d, the installation device 20 further includes a cable insertion unit 30 for inserting the cable bolt 12 with its leading end carrying the anchoring element 50 into the bore 40.
Referring to Figure 2 and 5e, the installation device 20 further comprises a cable severing unit 32 for forming a trailing end of the cable bolt 12 including cutting the cable bolt 12 to length and applying a face plate 52 as well as a tensioning barrel 54 to the trailing end of the cable bolt 12.
When carrying out the method for installing the cable bolt 12 in the underground 10, the installation device 20 operates as follows:

First, as can be seen from Figure 5a, the drilling unit 26 drills a bore 40 at a location where a cable bolt 12 is to be installed into the underground 10 of the mine tunnel. When the bore 40 has the desired length, the drill is removed from the bore 40 and the bore 40 is filled with grout 49 by the grout delivering unit 28, preferably from the inner end of the bore 40 first (see Figure 5b).

By means of the wrapping unit 24 (see Figure 3), the steel cable 250 is prepared as follows: The steel cable 250 is unrolled from the reel 241, while the sheath material 251 is at the same time unrolled from the other reel 242. Before the steel cable 250 is wrapped by the sheath material 251 in the combining tool 246, it is coated with grease or wax as a filling material supplied by the greasing nozzle 245. Downstream (in a feeding direction of the so prepared steel cable 250) of the combining tool 246, the leading end of the sheath material is connected to the cable by means of the connection element 47. Optionally, the leading end of the so prepared steel cable 250 may further be provided with an anchoring element 50 (see Figure 5c).
Then, the cable bolt 12 is inserted into the bore 40 by the cable insertion unit 30 starting with its leading end until the latter reaches the bottom of the bore 40, as shown in Figure 5d.
Now, as may be seen from Figure 5e, the cable bolt 12 is severed by the cable severing unit 32 in order to form a trailing end. Furthermore, a face plate 52 is placed on the trailing end of the cable bolt 12 in order to cover the underground 10 around the bore 40 and a tensioning barrel 54 with tensioning wedges 56 is arranged on the trailing end of the cable bolt 12. Finally, tension is applied to the cable bolt 12 and secured by means of the tensioning barrel 54.
The so obtained cable bolt 12 is shown in more detail in Figure 4. In particular, the cable bolt 12 comprises three zones A to C and optionally a fourth zone D:

Zone A extends from the surface 10a of the underground 10, where the face plate 52 is placed, to the beginning of the sheath material 251. In this zone A, the cable bolt 12 is connected to the underground 10 by means of the hardened grout 49.

Zone C extends from the other end of the sheath material 251 to the end of the bore 40 or, optionally, to the anchoring element 50. Also in this zone C, the cable bolt 12 is connected to the underground 10 by means of the hardened grout 49.
In the optionally provided zone D, the cable bolt 12 is mechanically anchored to the underground 10 using the anchoring element 50.
Finally, zone B corresponds to that section of the cable bolt 12 in which the steel strand 250 is covered by the sheath material 251. Due to this fact, the cable bolt 12 is not connected to the underground 10, and thus can easily move relative to the underground 10, although the space between the outer surface of the sheath material 251 and the underground 10 is filled with hardened grout 49.
It is important to note that zone B, on the one side, enables the cable bolt 12 to effectively respond to dynamic loads, e.g. created by mining activities, earthquakes and the like, as the steel strand 250 wrapped by the sheath material 251 can easily move relative to the underground 10, and, on the other side, allows the cable bolt 12 to be sufficiently tensioned in order to effectively respond to stationary or quasi-stationary conditions, as the hardened grout 49 surrounding the sheath material 251 provides a rigid bridge between zones A and C.
Optionally, the cable bolt 12 may comprise only zones B and C and preferably also zone D, but not zone A. In this case, however, the rock plate 52 is heavily loaded, and thus has to be designed accordingly.

Claims

A method for installing a cable bolt (12) in an underground (10), comprising the steps:
• drilling a bore (40) into the underground (10),

• delivering grout material (49) into the bore (40),

• providing a cable (250),

• inserting the cable (250) with its leading end into the bore (40), and

• severing the cable (250) to form a trailing end,
characterized in that the method comprises the further steps of
• providing a sheath material (251), and

• circumferentially wrapping the sheath material (251) around at least a predetermined length (B) of the cable (250).
The method according to claim 1,
characterized in that a section (C) of the cable (250) adjacent the leading end thereof and/or a section (A) of the cable (250) arranged inside the bore (40) and adjacent to the cable's trailing end arranged outside the bore (40) is/are covered by grout material (49).
The method according to claim 1 or 2,
characterized in that an anchoring element (50) is connected to the section of the cable (250) adjacent the leading end thereof.
The method according to any of claims 1 to 3,
characterized in that the cable (250) and/or the sheath material (251) may be supplied from a reel (241, 242).
The method according to any of claims 1 to 4,
characterized in that the sheath material (251) is supplied as a tube, advantageously as a plastic tube, the tube wall of which has a longitudinal slit.
The method according to claim 5,
characterized in that the slit is opened using a slit-widening tool (246).
The method according to claim 5 or 6,
characterized in that the tube (250) is slit during the installation process, for example after having been supplied from the reel (242) and before being combined with the cable (250).
The method according to any of claims 1 to 7,
characterized in that the leading end of the sheath material (251) is connected to the cable (250), for example using a connection element (47).
The method according to claim 8,
characterized in that the connection element (47) is automatically supplied from a connection element stock (247a).
The method according to any of claims 1 to 9,
characterized in that a filling material (48) is provided in the space between the inner surface of the sheath material (251) and the outer surface of the cable (250).
The method according to claim 10,
characterized in that the filling material (48) is applied to the cable (250) before the sheath material (251) is wrapped around the cable (250).
A device (20) for installing a cable bolt (12) in an underground (10), in particular using the method according to any preceding claim, the device comprising:
• a drilling unit (26) for drilling a bore (40) into the underground (10),

• a grout delivering unit (28) for delivering grout material (49) into the bore (40),

• a cable insertion unit (30) for inserting the cable (250) with its leading end into the bore (40), and

• a cable severing unit (32) for severing the cable (250) to form a trailing end,

• a wrapping unit (246) for circumferentially wrapping a sheath material (251) around at least a predetermined length (B) of the cable (250).
A cable bolt (12) comprising:
• a cable (250) and

• a sheath material (251) having a longitudinal slit and circumferentially wrapped around at least a predetermined length (B) of the cable(250).