Self-drilling hybrid rock anchor

A self-drilling rock anchor assembly includes: a friction fit tubular sleeve extending longitudinally between leading and trailing ends; a rod extending through the sleeve between first and second ends, and projecting from each sleeve end; a drill bit member engaged with the rod's first end having an exterior surface part of which tapers towards a back end of the member; a backstop element engaged with the rod's second end having a first drive surface; a load bearing element on the rod between the sleeve's trailing end and the backstop that has a second drive surface. The rod moves relative to the sleeve between a drill position, wherein the drill bit is spaced from the sleeve's leading end, and an insertion position, wherein the sleeve's leading end abuts the bit. The drill and insertion positions are achieved by applying a force to the first and second drive surfaces, respectively.

This application is the U.S. national phase of International Application No. PCT/ZA2019/050024 filed 3 May 2019, which designated the U.S. and claims priority to ZA Patent Application No. 2018/02885 filed 3 May 2018, and ZA Patent Application No. 2018/06341 filed 21 Sep. 2018, the entire contents of each of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to a self-drilling rock anchor.

BACKGROUND OF INVENTION

In ground conditions that are layered or laminated, it is difficult to install a rock bolt that is adapted to radially expand within a rock hole to frictionally fit therein. Such bolts typically have a diameter which is larger than the diameter of the drill hole into which it is inserted to radially compress when inserted and to expand into friction fit when fully inserted in the hole.

The reason for this is that, in such ground conditions, the drill hole begins to close after the drill steel is removed, making it difficult if not impossible to insert the friction fit anchor. In extreme cases, the closure occurs during the drilling operation, making it difficult, sometimes impossible, to retract the drill steel from the drill hole.

The invention at least partially solves the aforementioned problems.

SUMMARY OF INVENTION

The invention provides a self-drilling rock anchor assembly which includes:

a friction fit tubular sleeve which extends longitudinally between a leading end and a trailing end;

a rod which extends through the sleeve between a first end and a second end and which projects from each end of the sleeve;

a drill bit member engaged, or integral, with the first end of the rod having an exterior surface at least part of which tapers towards a back end of the member;

a backstop element engaged, or integral, with the second end of the rod having a first drive surface;

a load bearing element on the rod between the trailing end of the sleeve and the backstop element that has a second drive surface;

wherein the rod is moveable relatively to the sleeve between a drill position, in which the drill bit is spaced from the leading end of the sleeve, and an insertion position, in which the leading end of the sleeve abuts the drill bit; and wherein the drill position and the insertion position is achieved by applying a force to the first drive surface and the second drive surface respectively.

The friction fit tubular sleeve may have a longitudinally extending formation about which the body resiliently deforms.

The longitudinally extending formation may be a slit, longitudinal opening or a channel. The channel may be formed by indentation in a wall of the sleeve.

The rod may include a flushing bore which is longitudinally co-extensive with the rod and which opens at each of the first and second ends to provide a conduit for a flushing medium.

The assembly may include a load indicator on the trailing part of the rod between the backstop element and the load bearing element.

The assembly may include a supporting bush which inserts between the rod and the sleeve at the trailing end to keep the rock concentric to the sleeve.

The sleeve may include a wedge element engaged to the leading end of the sleeve and which is complementary to the exterior surface of the drill bit member.

The load bearing element may include a spherical seat.

The second drive surface may be a rear-facing surface of the load bearing element that faces the second end of the rod and that is adapted in lateral extension to receive force applied in an axial direction.

The backstop element may be a nut.

The first drive surface may be an end surface of the nut, adapted to receive the force applied in axial direction.

Alternatively, the first drive surface may be an outer circumferential surface of the nut, adapted to receive a force applied in a rotary direction.

The invention extends to a method of installing a rock anchor in support of a rock face which includes the steps of:(a) providing the rock anchor which includes a friction fit tubular sleeve which extends longitudinally between a leading end and a trailing end, a rod which extends through the sleeve between a first end and a second end and which projects from each end of the sleeve, a drill bit member engaged, or integral, with the first end of the rod and having an exterior surface at least part of which tapers towards a back end of the member, a backstop element engaged, or integral, with the second end of the rod having a first drive surface and a load bearing element on the rod between the trailing end of the sleeve and the backstop element that has a second drive surface;(b) engaging a face plate with the rock anchor;(c) applying a rotary or percussive force to the first drive surface to cause the drill bit member to bore a hole into a rock face against which the drill bit member is applied;(d) applying a percussive force to the second drive surface to move the sleeve relatively to the rod into the hole until the leading end of the sleeve abuts the drill bit member and a space is opened between the backstop element and the load bearing formation;(e) applying a rotary or percussive force to the first drive surface to cause the drill bit formation to bore deeper into the hole and to move the rod relatively to the sleeve to close the space; and(f) alternating the repeat of steps (d) and (e) until the faceplate is engaged with the rock face in load bearing support, sandwiched between the rock face and the load bearing formation.

In a passive step that follows step (d), the drill bit member is drawn into the sleeve to wedge the sleeve into contact with the hole by action of rock face movement pushing on the faceplate.

The rod may include a flushing bore which is longitudinally co-extensive with the rod and which opens at each of the first and second ends.

The method may include the step of flushing the hole with a flushing fluid introduced through the flushing bore.

The friction fit tubular sleeve may have a longitudinally extending formation about which the body resiliently deforms.

The longitudinally extending formation may be a slit, longitudinal opening or a channel. The channel may be formed by indentation in a wall of the sleeve.

The assembly may include a load indicator on the trailing part of the rod between the backstop element and the load bearing element.

The assembly may include a supporting bush which inserts between the rod and the sleeve at the trailing end to keep the rock concentric to the sleeve.

The sleeve may include a wedge element engaged to the leading end of the sleeve and which is complementary to the exterior surface of the drill bit member.

The load bearing element may include a spherical seat.

The second drive surface may be a rear-facing surface of the load bearing element that faces the second end of the rod and that is adapted in lateral extension to receive force applied in an axial direction.

The backstop element may be a nut.

The first drive surface may be an end surface of the nut, adapted to receive the force applied in axial direction.

Alternatively, the first drive surface may be an outer circumferential surface of the nut, adapted to receive a force applied in a rotary direction.

DESCRIPTION OF PREFERRED EMBODIMENTS

A self-drilling friction fit rock anchor assembly10is illustrated inFIG. 1of the accompanying drawings.

The rock anchor assembly10has an expansible sleeve12which has a generally tubular body14that longitudinally extends between a leading end16and a trailing end18(seeFIG. 1). In this particular embodiment, the body has a slit (not shown) which extends the length of the body. It is about the slit that the sleeve accommodates radial compression and expansion to frictionally fit within a rock hole as will be more fully described below.

The feature of the slit is non-limiting and it is envisaged, within the scope of the invention, that a longitudinally extending formation about which the body is adapted to resiliently deform can be a channel or indented formation formed in a wall of the sleeve body14.

The sleeve body14has a slightly tapered leading end portion20which tapers toward the leading end16to enable the sleeve, and the entire assembly10, to be driven into the rock hole having a smaller diameter than the body. The wall of the sleeve body12is approximately 3 mm, made of structural grade steel or a composite material.

In the embodiment described above, the sleeve body14has a single wall. In an alternative embodiment, the sleeve body also can be made by longitudinally rolling a section of tube into a cross sectional C shape to provide a double walled structure.

The friction bolt assembly10further includes an elongate bored rod22which longitudinally extends between a first end24and a second end26. In assembly, the rod is located partly within the sleeve and partly outside of the sleeve where it extends beyond a leading end16and trailing end18of the sleeve as a leading part28and trailing part30respectively. In this example, the rod is threaded, at least partially, along the leading part and the trailing part, as a means of attachment.

The rod has a flushing bore32which extends the length of the rod and opens at each of the ends (24,26). It is through this bore that a flushing medium, such as water, is passed from the second end to flush a rock hole, drilled by the anchor assembly10, of debris.

The assembly10includes a drill bit34. The drill bit has a generally frusta-conical body36which includes a drill bit end38and an attachment end40and an outer generally frusta-conical surface42between the ends. See in particularFIG. 2A. The drill end38is of standard design, adapted to drill with back and forward hammering action. However, if the ground conditions dictate, the drill bit can be rotary operated.

A threaded aperture44penetrates the body36from the attachment end40(seeFIG. 2A). The leading part28of the rod22engages the drill bit34by threaded engagement with the aperture. Flushing bore extensions46lead from the aperture, exiting at the drill bit end38.

A significant part of the outer surface42tapers inwardly, with the taper ending at the attachment end40.

With the drill bit end38and the taper of the outer surface42, the drill bit34is adapted with dual functionality: to bore a hole and to wedge into the sleeve body14as will be described more fully below.

With reference toFIG. 1, the rock anchor assembly10further includes a closed end nut48, a load indicator50and a spherical seat52, all mounted on the trailing part30of the rod22. The nut is threadingly engaged to the rod, at the second end26. The nut has a blind end54which restrains the nut from travelling along the trailing part of the rod. The blind end only has a small diameter aperture56which is in register with the bore36for fluid communication.

The spherical seat52has a holed base56and a spherical wall58upstanding from the base (seeFIG. 3A). A top edge of the wall is filleted to provide the “spherical seat” onto which a faceplate rests in use as will be described below and as illustrated inFIGS. 3A-3D. Enclosed by the base and the wall, a cup shaped recess60is defined (seeFIG. 1). The seat engages with the rod22which is passed through the hole in the base. The seat is capable of axial movement along the trailing part30of the rod, confined between the sleeve12and the nut48or load indicator50. When the seat is pushed against the trailing end18of the sleeve12, a trailing end portion of the sleeve is frictionally received within the recess58.

Finally, the assembly10includes a centralising support bush72and a circumferential wedge of leaves64which inserts into the trailing end18and leading end16of the sleeve respectively. The bush is supportive in function and prevents the sleeve from collapsing about this end portion when placed under load. The wedge of leaves engages with the outer surface42of the drill bit body36to provide an anchor to the rock anchor assembly10.

With reference toFIGS. 3A to 3D, in use of the rock anchor assembly10, a face plate66is engaged with the rock anchor assembly10, passed over the assembly from the first end24of the rod, to abut the spherical seat52.

The assembly10is installed using a mechanised drilling rig (not shown). Installed in a carousel or feeder of the rig, the assembly is presented to a rock face68, with the drill end38of the drill bit34initially applied to the rock face.

A force (see directional arrow onFIG. 3A) is applied by the rig to the blind end54of the nut48in a percussive or hammering manner. The blind end provides a rod drive surface to which the force, which drives the rod incrementally forward, is applied. This force is rigidly transmitted through the rod to the drill end38of the drill bit34to bore a hole70into the rock face68. This action is illustrated inFIG. 3A.

Periodic flushing of the hole is achieved by introducing a flushing medium through the small diameter aperture56of the nut48, into the bore32and exiting the assembly10at the drill end38through the flushing bore extensions46.

There comes a point in this operation when the leading end16of the sleeve arrives at a mouth72of the rock hole thus formed. At this stage a force (see directional arrow onFIG. 3B) is applied to a rear facing surface74of the base56of the spherical seat52. This surface provides a sleeve drive surface.

Again, the force is applied in a percussive manner by the rig. This force pushes the sleeve forward, relatively to the rod22, into the hole. As the hole has a smaller diameter than the sleeve, the sleeve body14compressively deforms, about the slit, to accommodate passage into the rock hole70. This action, which is illustrated inFIG. 3B, opens a space between the spherical seat52and the nut48or load indicator50. The leading end16of the sleeve is driven against the drill bit34, moving over part the taper of the outer surface42but stopping short of causing the circumferential wedge of leaves64from expanding radially outwardly.

The drill action ofFIG. 3Ais then repeated to increase the depth of the hole70. Here, the rod moves axially relatively to the sleeve, with the drill bit34disengaging from the sleeve12.

The sleeve insertion step ofFIGS. 3B and 3Dalternates with the drill step ofFIGS. 3A and 3Cuntil the rock hole is deep enough to receive the anchor10to a point at which the face plate66engages the rock face68in load bearing support, sandwiched between the rock face and the nut48, the load indicator50and spherical seat52train.

The rock anchor assembly10is capable of mechanically locking within the rock hole. This occurs after the active installation steps when there is inevitable movement of the rock face68outwardly into the excavation. This movement pushes on the face plate66. With the face plate prevented in backward movement relatively to the rod22, the rod is moved axially outwardly relatively to the sleeve, forcing the drill bit34into the sleeve. The tapered outer surface42of the drill bit body36wedges into the leaves64forcing the leaves radially outwardly and causing the sleeve12to frictionally contact with the rock hole70. This is a passive occurrence and is not illustrated.

The self-drilling friction fit rock anchor assembly10of the invention fulfils the need for both increased efficiency, and automation in a mechanized mining development. The assembly is designed to fit onto a mining rig that can install the bolts without stopping mining, and with no need for a secondary operation. These units can be installed in a single operation, with no need for resin, or grout. The assembly is adapted to drill its own hole and thereafter is immediately able to carry load as soon as it is fully installed, with no need for additional operations.

A technical issue, which is overcome by the invention in the choice of material of manufacture, is the need for a hollow bar to flush the drilled rock out of the hole during insertion. However, as this hollow drill steel is to be used as the load bearing element, it needs to satisfy the strength and elongation properties enjoyed by support products and not that of standard off-the-shelf drill steel. Standard off-the-shelf drill steel is intended to efficiently drill multiple holes and as such is very hard and brittle (stiff); not ideal for rock support. Since the envisaged product merely has to drill one hole, the selected hollow drill steel's lack of drilling efficiency is sacrificed for improved elongation properties since this is its long term and primary design consideration.