Field of the invention

Disclosed herein is a rock bolt for use in stabilising rock masses, particularly via the installation of said bolt in structures such as the walls and ceilings of rock excavations. Also disclosed herein is a method of installing the rock bolt.

Background

It is known to insert rock bolts into correspondingly shaped holes drilled or bored into rock masses for the stabilisation thereof.

In more permanent and/or unstable applications, a setting material such as grout or a resin-catalyst mixture is pumped into the hole to encapsulate the bolt and more strongly anchor the bolt in the preformed hole. This process requires the forming of precisely shaped holes based on the length of the bolt to be inserted. An appropriate amount of resin and catalyst, typically in the form of capsules or cartridges, must also be selected based on the bolt and hole size. The cartridges must then be inserted into the hole in a particular order prior to insertion of the bolt. Additionally, the bolt must be inserted to a particular depth into the hole and rotated at a specific speed for a specific duration to ensure the cartridges are ruptured by the bolt and the resin and catalyst are adequately mixed. There are clearly various parameters that must be carried out correctly in order to properly install such rock bolts; the process is thus relatively time-consuming and quite vulnerable to human error.

Moreover, if one or more parameters of the known process are not chosen or carried out correctly, it can be difficult to address the issue. For example, if the hole has been drilled too deep, or if insufficient resin has been inserted into the hole, this can result in the bolt not being fully encapsulated by resin within the hole, thereby leading to compromised stabilization of the rock mass. Once the bolt is inserted so as to rupture the cartridges and mix the resin, the bolt cannot then be withdrawn if more resin is required. As such, the current process for encapsultaing rock bolts in resin is quite precise and vulnerable to error during installation, which errors may not be addressable once made.

There is a need to address the above, and/or at least provide a useful alternative.

According to a first aspect of the present invention, there is provided a rock bolt having a tubular body that is insertable into a hole preformed in a rock mass for stabilisation thereof, the tubular body being injectable with a setting material for encapsulation of the inserted tubular body, the bolt comprising: a head via which the bolt can be driven into the preformed hole and via which the setting material can be injected into the tubular body; an oppositely disposed outlet through which the injected material can be discharged from the tubular body so as to substantially fill the hole and encapsulate the inserted tubular body; and a bearing plate disposed toward the head configured for engagement against a surface of the rock mass where the tubular body is inserted, the bearing plate comprising one or more through-holes through which the discharged setting material can exude so as to indicate that the inserted tubular body has been encapsulated by the setting material.

In embodiments of the invention, the head is generally bowl-shaped so that the head, relative to the tubular body, defines an upside-down dome through which the setting material can be injected into the tubular body.

In embodiments of the invention, the plate comprises a central aperture configured to slidably receive the tubular body therethrough so that in use, the plate can be slid along the tubular body from the outlet and toward the head. In embodiments of the invention, the head is wider than the central aperture of the plate such that, in use, the plate abuts against the head and is movable relative thereto so that the plate can be tilted to align with the rock mass surface against which it is to be engaged.

In embodiments of the invention, the tubular body comprises one or more circumferentially disposed locating members configured to locate the tubular body in the predrilled hole.

In embodiments of the invention, the tubular body comprises an internal mixing means for mixing the setting material as it is injected into the body.

According to a second aspect of the present invention, there is provided a method of stabilising a rock mass via installation of a rock bolt according to a first aspect of the invention, the method comprising: forming a hole in the rock mass; driving the bolt into the hole such that the bearing plate thereof engages a surface of the rock mass; and injecting a setting material into and through the tubular body of the bolt such that the setting material discharges from the outlet of the bolt and substantially fills the hole, substantially encapsulates the tubular body therein, and exudes through one or more through-holes of the bearing plate.

In embodiments of the invention, forming the hole comprises forming an elongate hole that is deeper than a length of the tubular body of the bolt.

In embodiments of the invention, driving the bolt into the hole comprises urging the head against the plate so as to engage the plate against the surface of the rock mass. In embodiments of the invention, injection of the setting material is substantially ceased when setting material is exudes from the one or more through-holes of the bearing plate.

Brief description of the drawings

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a side cross-sectional view of a rock bolt according to embodiments of the present invention installed in a hole preformed in a rock mass;

Figure 2(a) is a side cross-sectional view of the rock bolt if Figure 1;

Figure 2(b) is a close-up of a head of the bolt of Figure 2(a);

Figure 2(c) is a close-up of an outlet of the bolt of Figure 2(a);

Figure 3(a) is a top perspective view of a bearing plate of a rock bolt according to embodiments of the present invention;

Figure 3(b) is a top view of the bearing plate of Figure 3(a);

Figure 4 is a side cross-sectional view of a bearing plate of a rock bolt according to embodiments of the present invention.

Detailed description

Referring to Figures 1 to 2(c), the rock bolt 2 comprises a tubular body 4 configured for being driven into a hole preformed in a rock mass. In the depicted embodiment, the tubular body 4 has an external diameter of approximately 30mm and an internal diameter of about 20mm, though a range of thicknesses is within the scope of the present specification. The tubular body 4 is substantially hollow and, during installation, is filled with a setting material, such as a resin mixture.

An upper or first end of the bolt 2 comprises a dome-shaped head 6 via which the bolt 2 can be driven, e.g. by a jumbo. The domed head 6 is in fluid communication with the hollow tubular body 4 such that the setting material can be injected via the head 6 and into the tubular body 4.

The tubular body 4 comprises mixing means 8 for promoting mixing of the setting material, such as a resin mixture, as it is injected into the tubular body 4. In the depicted embodiment, an upper end of the tubular body 4 comprises a series of internal fins or blades 8 extending inwardly from an inner wall of the tubular body 4. As the resin mixture is pumped into the bolt via the head thereof, the mixing means 8 helps to promote even and consistent mixing of the resin mixture.

The tubular body 4 may also comprise locating members 10 that help locate and maintain the bolt 2 in the preformed hole during installation. In the figures, the locating members 10 comprise outwardly extending fin-like protrusions 10 extending in the direction of the tubular body 4, the fins 10 being circumferentially spaced around the body 4. Referring to Figure 1, the preformed hole may be slightly wider than the outer diameter of the tubular body 4, and equal to or slightly less than the distance between circumferentially opposed fins 10. In this way, the fins 10 can dig or bite into the walls of the hole and help retain and locate the bolt 2 therein.

Referring to Figure 2(c), a lower or second end of the bolt 2 comprises an outlet end 12 having an opening 13 via which the injected setting material can be discharged from the bolt 2. In use, as setting material is injected into the bolt 2, setting material fills up the tubular body 4 and is also discharged from the outlet 12. The discharged setting material thus fills up the hole so as to encapsulate the tubular body 4 therein.

Referring to Figures 2 to Figure 4, the present bolt 2 also comprises a bearing plate 14 configured to bear against a surface of the rock mass. The depicted bearing plate 14 comprises a lower, larger plate 16 configured to bear directly against the surface of the rock mass. The bearing plate 14 also comprises a smaller, centrally mounted upper plate 18 having an upwardly protruding dome 20. Both plates 16, 18 comprise aligned through-holes 22a, 22b via which the bearing plate 14 can be slid along the tubular body 4, from the outlet 12 and towards the head 6 of the bolt 2.

Referring to Figure 2(b), the domed protrusion 20 of the upper plate 18 is configured to receive and abut against the oppositely oriented dome of the head 6 of the bolt 2. The engagement between the domed protrusion 20 and the domed head 6 allows the bearing plate 14 to be adjusted angularly, relative to a longitudinal axis of the bolt 2. In this way, the angle of the bearing plate 14 can be adjusted, relative to the axis of the bolt 2, to better match the angle of the rock mass surface against which it is to be engaged. To this end, with reference to Figure 2(b), the central through-hole 22b of the lower plate 16 is appreciably larger than the outer diameter of the tubular body 4 so that angular adjustments of the bolt 2 relative to the bearing plate 14 can be accommodated before the tubular body 4 fouls against the lower plate 16.

The domed protrusion 20 of the upper plate 18 is formed with apertures 24 through which setting material can escape or exude from within the preformed hole. In use, after the setting material has substantially filled both the tubular body 4 and the preformed hole, excess setting material will have nowhere else to flow besides out of the preformed hole. Referring to Figure 2(b), the setting material travels along the path a-a' back out through the hole 22(b) of the lower plate 16 and out through the apertures 24 in the domed protrusion 20 of the upper plate 18. Upon sighting escape of the setting material through the bearing plate 14, the installer can be assured that the preformed hole has been filled with the setting material and that the bolt 2 is encapsulated therein.

Escape of the setting material through the bearing plate 14 thus provides the installer with an indication of when to stop injecting the setting material. In this way, there is no need to estimate the amount of setting material needed to encapsulate the present rock bolt 2 before insertion of the bolt 2 into the preformed hole. Provided that the preformed hole is drilled deeper than the depth at which the bolt 2 is installed, the present bolt 2 can be inserted and then injected with setting material until the setting material escapes through the bearing plate 14, which escape indicates the bolt 2 has been encapsulated.

To install the present bolt 2, first, a correspondingly sized hole is drilled or bored into the rock mass. For a bolt 2 with a tubular body 4 with an external diameter of 30mm, a hole having a diameter of about 43mm would be appropriate. The depth of the hole should be greater than the length of the bolt 2, or at least generally greater than the length of the tubular body 4. If not fitted already, the bearing plate 14 can then be slid over the outlet end 12 and onto the tubular body 4 and then brought close to or adjacent to the domed head 6 of the bolt 2. The bolt 2 can then be aligned with and inserted into the preformed hole such that the domed head 6 abuts against the domed protrusion and substantially seals the through-hole 22a thereof. There is no need to spin or drill the bolt 2 into the hole.

Next, a setting material can be injected or pumped into the hollow tubular body 2 via the bolt head 6. The setting material flows such that it fills the tubular body 4, discharges from the outlet 12, fills the preformed hole so as to encapsulate the tubular body 4, and flows back out through the preformed hole along the path a-a' and escapes through apertures 24 in the domed plate 18. The installer can then cease injection of the setting material.

Many modifications of the above embodiments will be apparent to those skilled in the art without departing from the scope of the present invention. For example, while it is envisaged that a length of the present rock bolt 2 may vary from about 1.5 metres to 4.2 metres, other lengths are of course within the scope of the present specification.

Additionally, the bearing plate 14 need not comprise the lower plate 16. For example, the bearing plate 14 could simply be formed from the smaller plate 18 having the domed protrusion 20. Of course, the domed plate 18 may itself be larger than is depicted in the figures, and could also function like the larger plate by providing a larger surface area that bears directly against the surface of the rock mass. In the depicted embodiment, an upper end of the domed-shaped head 6 of the bolt 2 comprises a circumferential ring-shaped flange 26 via which pull testing of the rock bolt 2 can be conducted to ensure the bolt 2 is sufficiently anchored.

Referring to Figure 3(b), the wall defining the through-hole 22a of the upper plate 18 may comprise a series of circumferentially disposed cut outs or slots 28 sized to enable the fins 10 of the tubular shaft 4 to fit through as the bearing plate 14 is slid along the tubular body 4.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.