Hybrid rock bolt and method of use

Abstract

A rock bolt has a tendon extending axialy through a first tube section and a second tube section. The first tube section is adjacent the distal end portion of the tendon, and the second tube section is adjacent the proximal end portion of the tendon. An anchor assembly is connected to the proximal end portion of the tendon, and an expansion mechanism is connected to the distal end portion of the tendon. When the rock bolt is instaled in a borehole and subjected to rock deformation, the second tube section moves axialy away from the first tube section. Additionaly, the tendon may include a holow channel extending axialy through the tendon. The rock bolt may be configured to convey grout through the holow channel and into the borehole. In another configuration, the rock bolt has a single tube and is configured to convey grout through a holow channel and into the borehole.

Description

HYBRID ROCK BOLT AND METHOD OF USECROSS REFERENCE TO A RELATED APPLICATION

[0001] This application claims the benefit of provisional patent application U.S. App. No. 63 / 698,340, filed on September 24, 2025 and entitled “Hybrid Rock Bolt,” and provisional patent application U.S. App. No. 63 / 775,005, filed March 20, 2025 and entitled “Hybrid Rock Bolt and Elongation Indicator and Method of Use,” the entire contents of which are hereby expressly incorporated by reference into the present application.BACKGROUND OF THE INVENTION1. Field of the Invention

[0002] The invention relates to a bolt used in tunnels and mines to reinforce ceilings and walls, typically referred to as a “rock bolt.” More specifically, the present invention relates to a type of rock bolt known as a “hybrid bolt,” which includes an elongated tendon extending through a “friction stabilizer,” such as a hollow tube. The invention also relates to a method of use thereof.2. Discussion of the Related Art

[0003] Without any reinforcement, the ceilings and walls of mines and tunnels are prone to collapse from the dead weight of the rock and / or deformation and even bursting. Rock bolts are typically inserted into the face of the rock to reinforce the ceilings and walls.

[0004] Traditionally, rock bolts are inserted into a borehole in a rock face and then grouted in place with a cementitious or resin grout (generally referred to herein as “grout”). The borehole may be pre-drilled in the rock face, or, in the case of self-drilling rock bolts, formed by the rock bolt itself acting as a drill. Grout may be injected into the annular space surrounding the bolt, sealed in a rupturable cartridge placed in the borehole, or injected through a hollow bolt, such as a self-drilling bolt.

[0005] While grouted rock bolts work well, there can be drawbacks to using grout to secure a bolt within a borehole. For example, when installing a rock bolt in highly fractured ground, the grout leaks into all the cracks in the surface / wall of the borehole. These leaks cause additional grout to be used during installation, increasing costs, and can leave the rock bolt insufficiently secured within the borehole.

[0006] An alternative to grouted rock bolts is rock bolts that are mechanically anchored in the borehole. One such mechanically anchored rock bolt is a friction stabilizer, also referred to as afriction bolt or a split set. Generally, a friction stabilizer is an elongated tube having a C-profile or C-shaped cross-section sized to elastically expand against the borehole surface, mechanically securing the friction stabilizer in the borehole. Friction stabilizers also have some drawbacks, though. For example, friction stabilizers provide minimal yielding and elongation when subject to large amounts of rock deformation.

[0007] Typically, when a large amount of rock deformation is anticipated, a dynamic rock bolt is used. Generally, a dynamic rock bolt includes an elongated tendon, such as a solid rod, that is grouted into a borehole. When subject to rock deformation, the dynamic bolt elongates to accommodate for the deformation while still supporting the rock mass. While effective, dynamic bolts typically require grouting in the borehole. Moreover, dynamic bolts generally offer little to no anchorage within the borehole before being grouted, often requiring the use of expensive rapidsetting grout to secure the bolt in the borehole.

[0008] In some cases, a hybrid bolt may be used, which combines a friction stabilizer with a dynamic bolt. Generally, hybrid bolts include a solid rod extending through a friction stabilizer with a mechanically expanding element attached to the distal / inner end of the rod. Typically, the expanding element includes a wedge, which is pulled into the inner / distal end of the friction stabilizer. This causes radial expansion and increased anchorage of the bolt at the expansion element. The friction stabilizer and mechanically expanding element allow the hybrid bolt to be secured in the borehole without grout. Tensile loads may then be transferred to the tendon when subject to a large amount of rock deformation, causing the tendon to elongate.

[0009] However, traditional hybrid bolts suffer from other deficiencies. For example, a rock mass generally imparts a load on a hybrid bolt when there is a split in the rock, as shown in FIG. 1. Because the C-tube C is a continuous component extending the entire length of the bolt BT in the borehole, the portion of the C-tube that is anchored in the proximal area B pulls on the portion of the C-tube that is anchored in distal area A, where the expansion element E is installed. When the length of the bolt in area B is too great, the load path prevents the load from being transferred to the tendon T. Thus, the tendon T is unable to pull the wedge further into the C-Tube to increase frictional point anchorage to resist this increased tension, nor can the tendon T elongate to accommodate high deformation, tensile, and shear loads.

[0010] Therefore, there is a need for a hybrid bolt that allows for the load caused by rock deformation to be shifted directly to the tendon under a wide range of conditions, allowing anexpansion mechanism to increase its anchorage and for the yielding properties of the tendon to be mobilized without interference from the tensile capacity and anchorage of a friction stabilizer such as a C-tube.

[0011] Further, there is a need for a hybrid bolt that allows for additional anchorage within the borehole.

[0012] Additionally, there is a need for a rock bolt that requires both less grout and the use of less expensive grout.SUMMARY OF THE INVENTION

[0013] The disclosed invention addresses the above-identified issues and improves upon the prior art by providing a rock bolt that allows rock deformation loads to be shifted directly to the tendon, allowing the expansion mechanism to increase its anchorage as a tensile load is applied to the bolt and for the yielding properties of the tendon to be mobilized without unwanted influence by a friction stabilizer’s tensile capacity and anchorage. The rock bolt includes a tendon axially extending through first and second coaxial tube sections. When subject to rock deformation, the second tube section may move axially away from the first tube section, allowing the rock deformation loads to act at least primarily on the tendon rather than a frictions stabilizer tube.

[0014] The disclosed invention may also meet the above-identified needs by providing a hybrid rock bolt that may be grouted within the borehole by injecting grout through a hollow channel in a tendon of the rock bolt and into the borehole. The addition of at least one friction stabilizer tube to the rock bolt may also limit the amount of grout required because the at least one tube may seal many cracks within the borehole wall. Additionally, the rock bolt may be at least temporarily anchored in place prior to grouting, allowing for the use of standard or slow-setting grout. Moreover, the inventive rock bolt having a hollow channel in the tendon also may provide a greater resistance to bending because of the tendon’s increased cross-section without a significant increase in material costs.

[0015] One configuration of the present invention includes a rock bolt having a first and second coaxial tube sections. A tendon extends axially through the first tube section and the second tube section, wherein the first tube section is adjacent the distal end portion of the tendon and the second tube section is adjacent the proximal end portion of the tendon. An anchor assembly is connected to the proximal end portion of the tendon, and an expansion mechanism is connected to the distal end portion of the tendon. The first tube section has a pull-out resistance of at least 3 tons. Whensubject to rock deformation, the tendon is configured to elongate and the second tube section is configured to move axially away from the first tube section. The distal end of the second tube section may be coupled with the proximal end of the first tube section. In one configuration, the distal end of the second tube section moves axially away from the proximal end of the first tube section when the rock bolt is subject to rock deformation.

[0016] The rock bolt may also include a hollow channel extending axially through the tendon from the proximal end portion of the tendon to the distal end portion of the tendon. This rock bolt may be configured to convey grout through the hollow channel and into the borehole.

[0017] The present invention also includes a method of installing a rock bolt, which includes providing a rock bolt having first and second coaxial tube sections. A tendon extends axially through the first tube section and the second tube section. The first tube section is adjacent the distal end portion of the tendon, and the second tube section is adjacent the proximal end portion of the tendon. An anchor assembly is connected to the proximal end portion, and an expansion mechanism is connected to the distal end portion. The method includes inserting the rock bolt into a borehole such that the expansion mechanism is located within the borehole. Once inserted in the borehole, the rock bolt is subjected to rock deformation. In response to the rock deformation, the tendon elongates, the expansion mechanism radially expands, and the distal end of the second tube section moves axially away from the proximal end of the first tube section.

[0018] Another configuration of the present invention includes a rock bolt installed in a borehole. The rock bolt has first and second coaxial tube sections, each abutting a wall of the borehole. A tendon extends axially through the first tube section and the second tube section, wherein the first tube section is adjacent the distal end portion of the tendon and the second tube section is adjacent the proximal end portion of the tendon. An anchor assembly is connected to the proximal end portion of the tendon and is located outside the borehole. An expansion mechanism is connected to the distal end portion of the tendon and is located within the borehole. When the rock bolt is subject to rock deformation, the tendon is configured to elongate, and the second tube section is configured to move axially away from the first tube section.

[0019] Another configuration of the present invention includes a rock bolt having a tube and a tendon. The tendon has a hollow channel extending axially from a distal end portion of the tendon to a proximal end portion of the tendon. The tendon extends axially through the tube. An anchor assembly is connected to the proximal end portion of the tendon, and an expansion mechanism isconnected to the distal end portion of the tendon. This rock bolt is configured to inject grout through the hollow channel and into the borehole. The present invention also includes a method of inserting this rock bolt into a borehole and injecting the grout into the borehole through the hollow channel.

[0020] These and other features and advantages of the invention will become apparent to those skilled in the art from the following detailed description and the accompanying drawings. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Preferred exemplary embodiments of the invention are illustrated in the accompanying drawings in which like reference numerals represent like parts throughout, and in which:

[0022] Figure 1 is a schematic side elevation view of a traditional hybrid bolt installed in a rock and is appropriately labeled “PRIOR ART”;

[0023] Figure 2 is a side elevation view of a rock bolt constructed in accordance with the present invention, the rock bolt having a stopper;

[0024] Figure 3A is an isometric view of the inner or distal end of the rock bolt shown in FIG. 2, illustrating an expansion mechanism;

[0025] Figure 3B is a cross-sectional, side elevation view along line 3B-3B, illustrating the inner or distal end of the rock bolt shown in FIG. 2 and installed in a borehole;

[0026] Figure 3C is a side elevation view of the inner or distal end of the rock bolt shown in FIG. 2;

[0027] Figure 4 is a side elevation view of the outer or proximal end portion of the rock bolt shown in FIG. 2, illustrating an anchor assembly;

[0028] Figure 5 is a side elevation view of a central portion of the rock bolt shown in FIG. 2, illustrating a first tube section and a second tube section coupled together;

[0029] Figure 6 is a side elevation view of the rock bolt shown in FIG. 2 installed in a borehole, illustrating the second tube section moving away from the first tube section due to a fracture in the rock;

[0030] Figure 7 is an isometric view of the central portion of the rock bolt shown in FIG. 6, illustrating the separated first tube section and second tube section;

[0031] Figure 8 is a side elevation view of another rock bolt constructed in accordance with the present invention, the rock bolt having an extended second tube section;

[0032] Figure 9 is a side elevation view of the outer or proximal end portion of the rock bolt shown in FIG. 8;

[0033] Figure 10 is a side elevation view of yet another rock bolt constructed in accordance with the present invention; and

[0034] Figure 11 is a partial, side elevation view of a schematic of another rock bolt constructed in accordance with the present invention.DETAILED DESCRIPTION

[0035] The present invention and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments described in detail in the following description. Terms such as “connecting”, “linking”, “joining”, or the like shall be interpreted broadly and shall not require direct contact between components. Additionally, all ranges shall include all embodiments having sub-ranges within the outer limits of the range. For example, a range of 0-10 shall constitute support for a range of 1-9.

[0036] Generally, the term “distal” shall refer to the direction and / or area associated with the inner end of a borehole. Further, the term “proximal” shall refer to the direction and / or area associated with the outer end of a borehole near the rockface.

[0037] Rock bolts constructed in accordance with the invention may have a central hollow or solid tendon surrounded by first and second coaxial tube sections arranged end to end. The first and second tube sections may be formed from separate tubes that can abut one another or that are separated by an intermediate spacer or sleeve, or a single tube in which a perforated or otherwise weakened portion of the tube separates the first and second tube sections and breaks upon rock deformation. In all cases, the second, proximal tube section can move axially away from the first, distal tube section upon rock deformation.

[0038] FIG. 2 illustrates a rock bolt 100 constructed in accordance with the present invention and installed in a borehole 102. The rock bolt 100 includes a first, inner or distal tube section 110 and a second outer or proximal tube section 120 that are coaxial with one another and arranged end to end. In this configuration, the first tube section 110 and the second tube section 120 are separatetubes. The tube sections 110 and 120 may or may not abut in the absence of tendon deformation. A tendon 140 extends axially through both the first tube section 110 and the second tube section 120. An anchor assembly 150 is connected to the proximal end portion 144 of the tendon 140, and an expansion mechanism 160 is connected to the distal end portion 142 of the tendon 140.

[0039] The tendon 140 is an elongated component having a distal end portion 142 and a proximal end portion 144. When installed in a borehole 102, the distal end portion 142 is located near the inner end of the borehole 102 and the proximal end portion 144 is located near the surface support 106, which is the rockface in FIG. 2. The distal end portion 142 and the proximal end portion 144 of the tendon 140 include threaded portions or sections 148a, 148c with a smooth section 148b located between the threaded sections 148a, 148c. As shown in FIG. 2, the threaded sections 148a, 148c extend to the ends of the tendon 140. In other configurations, not shown here, the entire length of the tendon 140 may be threaded, or intermediate smooth sections may be located between intermediate sections that are threaded, ribbed or otherwise configured to provide a local anchoring effect if the tendon 140 is encased in grout.

[0040] The tendon 140 is configured or capable to of elongating and even yielding when subject to a tensile load. When the rock bolt 100 is installed in a borehole 102 and subject to rock deformation, the tendon 140 may elongate or even yield prior to failure. In one configuration, the tendon 140 is composed of a relatively ductile material, such as a high ductile steel.

[0041] The tendon 140 may be a solid bar or a hollow bar. As best depicted in FIGS. 3A and 3B, the tendon in this configuration is a hollow bar, which has a hollow bore or channel 146 extending axially through the tendon 140. The hollow channel 146 extends from the proximal end portion 144 of the tendon 140 to the distal end portion 142 of the tendon 140. The outer peripheral surface of the tendon 140 defines an outside diameter (OD), and the outer peripheral boundary of the hollow channel 146 defines an inside diameter (ID). The tendon 140 may have an OD that is approximately 20-50 mm, or 30-40 mm, or more typically 28 mm, and an ID from 2 mm to 22 mm, or more typically from 5 mm to 18 mm. The tendon 140 may also have a length from 1.0 m to 3.5 m, or more typically from 1.8 m to 3.0 m.

[0042] The hollow tendon 140 may provide an additional advantage of preventing bending of the tendon 140. The hollow tendon 140 provides a larger cross-section, as compared to a solid rod. This larger cross-section helps prevent bending when subjected to compressive and percussive forces during installation. Providing a similar increase in cross-section with a solid rod wouldrequire an increase in the amount or volume of steel, which would increase costs. Thus, a hollow tendon 140 provides greater bending resistance without increasing the volume of steel.

[0043] As shown in FIG. 2, the tendon 140 extends axially through both the first tube section 110 and the second tube section 120. The first tube section 110 is located adjacent to the distal end portion 142 of the tendon 140, and the second tube section 120 is located adjacent to the proximal end portion 144 of the tendon 140. In one configuration, the first tube section 110 and the second tube section 120 may be composed of a S355 steel, a S420 steel, or an equivalent grade material.

[0044] The first tube section 110 is configured to provide the rock bolt 100 anchorage within the borehole 102. Specifically, as best shown in FIGS. 3 A and 3B, the first tube section 110 is configured to radially compress and resiliendy expand against the borehole wall 104, securing the first tube section 110 within the borehole 102. The first tube section 110 thus has a cross-sectional “C-shape” with a slot 116 extending axially along the first tube section 110. The outside diameter of the first tube section 110 is sized to be equal to or slightly greater than the diameter of the borehole 112. When installed, the C-shape allows the first tube section 110 to radially compress in the borehole 112. The elastic properties of the first tube section 110 then cause the first tube section 110 to resiliently expand against the wall 104 of the borehole, securing the first tube section in the borehole 102. The distal end 112 of the first tube section 110 may also be tapered to allow the first tube section 110 to be inserted into the borehole 102. It should be noted that, instead of taking on the descried C-shape, at least the distal end 112 of the first tube section 110 could have one or more additional slits, scours, or other features that allow the first tube section 110 to radially compress in the borehole 102.

[0045] The second tube section 120 may have a similar cross-sectional C-shape and sizing and / or otherwise be configured to secure the second tube section 120 within the borehole 102. Like the first tube section 110, the second tube section 120 may radially compress and resiliently expand within the borehole 102.

[0046] In one configuration, the first tube 110 may be composed of a heavier gauge than the second tube 120. For example, the gauge of the first tube 110 may be from 2 to 5 mm and, more typically, from 2.2 mm to 3.2 mm, and the gauge of the second tube 120 may be from 1 to 4 mm and, more typically, from 2.2 mm to 3.2 mm. The lengths of the first tube section 110 and the second tube section 120 may be adjusted to suit specific geotechnical conditions to align the jointwith the anticipated location of the rock fracture. One or both of the tube sections 110, 120 may be galvanized.

[0047] As shown in FIGS. 3A-3C, the rock bolt 100 includes an expansion mechanism 160 connected to the distal end portion 142 of the tendon 140. The expansion mechanism 160 is configured to expand radially, causing the expansion mechanism 160 and surrounding portions of the rock bolt 100 to abut the wall 104 of the borehole 104, subsequently anchoring or locking the expansion mechanism 160 in place in the borehole 102.

[0048] The expansion mechanism 160 includes a wedge 162 and at least one wedge insert 164. The wedge 162 is connected to the distal end portion 142 of the tendon 140. As shown in FIGS. 3A-3C, the wedge 162 has a conical or frustoconical shape with a threaded bore extending axially through the wedge 162. The wedge 162 is threaded onto the tendon 140 such that rotation of the tendon 140 relative to the wedge 162 may cause the wedge 162 to move axially relative to the tendon 140. In other words, the wedge 162 may be threaded up and down the distal threaded section 148a of the tendon 140. The outer surface of the wedge, otherwise referred to herein as the outer mating surface 166, is tapered or inclined relative to the axial centerline of the rock bolt 100 over at least part of its length. The outer mating surface 166 is configured to abut the at least one wedge insert 164.

[0049] As illustrated in FIG. 3B, the expansion mechanism 160 includes at least one wedge insert 164, which abuts the outer mating surface 166 of the wedge 162. The wedge insert 164 is at least partially inserted within the distal end 112 of the first tube section 110. The inner surface 168 of the wedge insert 164, which abuts the outer mating surface 166 of the wedge 162, may also be inclined or tapered, mirroring the incline or taper of the outer mating surface. In other words, angles of inclination of the outer mating surface 166 of the wedge 162 and the inner surface 168 of the wedge insert 164 are approximately equal. In one configuration, angle of inclination for the wedge 162 and / or wedge insert 164 is from 3 to 8 degrees, or more typically 5 degrees.

[0050] The rock bolt 100 shown in FIG. 3B includes two semi-circular wedge inserts 164 located radially opposite each other. Each wedge insert 164 may extend through an arc of 25 to 175 degrees and, more typically, of 50 to 125 degrees. Each wedge insert 164 includes a protrusion 170 extending radially outward toward the first tube section 110. The protrusion 170 is inserted in a hole in the first tube section 110, securing each wedge insert 164 to the first tube section 110.

[0051] The expansion mechanism 160 radially expands by pulling the wedge 162 toward the proximal end portion 144 of the tendon 140. This may be accomplished either by rotation of the tendon 140 during installation or from rock deformation. For example, for the later, a fracture in the rock may exert a force on the proximal portion of the rock bolt 100, pulling the distal end portion 142 of the tendon 140 and the wedge 162 toward the proximal end portion 144 of the tendon 140. The wedge 162 is pulled into the distal end 112 of the first tube section 110 and engages with the wedge inserts 164. The angles of inclination of the wedge 162 and / or wedge inserts 164 cause the diameter of the rock bolt 100 at the expansion mechanism 160 to expand radially, causing the expansion mechanism 160 and / or the outer surface of the first tube section 110 near its distal end 112 to abut the wall 104 of the borehole 102. This radial expansion increases the anchorage of the rock bolt 100 in the borehole at the expansion mechanism 160.

[0052] To ensure radial expansion of the expansion mechanism 160, the first tube section 110 exerts a counter force (referred to herein as “pull-out resistance”) against the wedge 162 to allow the wedge 162 to be pulled into the first tube section 110 and further engage the wedge inserts 164. In other words, first tube section 110 resists being pulled out of the borehole 102 when the wedge 162 is being pulled in the proximal direction. A lack of pull-out resistance may cause the expansion mechanism 162 to slip within the borehole 102 without radially expanding. The frictional anchorage produced from the first tube section 110 abutting the wall 104 of the borehole 102 provides the pull-out resistance. The pull-out resistance is proportional to the length of the first tube section 110. In other words, a longer first tube section 110 provides a greater pull-out resistance. A thicker first tube section 110 may also increase the pull-out resistance.

[0053] In the present invention, the first tube section 110 should provide a pull-out resistance of at least 3 tons. “Pull-out resistance” in this regard is defined as the amount of axial force required to remove the first tube section from the borehole. In one configuration, the first tube section 110 provides a pull-out resistance from 3 to 6 tons, or more typically from 4 to 5 tons, or approximately 4.5 tons.

[0054] Additionally, the first tube section 110 has a length of at least 1.0 m. In one configuration, the first tube section 110 has a length of approximately 1.2 to 1.4 m, or more typically 1.4 m. As shown in the configuration depicted in FIG. 2, the first tube section 110 may be longer than the second tube section 120. The first tube section 110 may have a length that is at least 25% of the length of the tendon. In another configuration, the length of the first tube section 110 may be atleast 50% of the length of the tendon, or more typically 75% of the length of the tendon. In yet another configuration, not shown here, the second tube section 120 may be longer than the first tube section 110.

[0055] Referring again to FIG. 3 A, the expansion mechanism 160 may include a keyway that prevents rotation of the wedge 162 relative to the wedge inserts 164. In this configuration, a key 172 protrudes from the outer mating surface 166 of the wedge 162, located within the slot 116 of the first tube section 110. When the tendon 140 is rotated, the key 172 abuts the slot wall 174, preventing the wedge 162 from rotating and allowing the wedge 162 to be threaded up the distal end portion 142 of the tendon 140.

[0056] As shown in FIG. 3C, the first tube section 110 may include a slit 118 extending axially from the distal end 112 of the first tube section 110. The slit 118 is located radially opposite the C-profile slot 116 in the first tube section 110. In combination with the C-profile slot 116, the slit 118 may help prevent deformation of the first tube section 110 when the expansion mechanism 162 radially expands. For example, the radial expansion from the two wedge inserts 164 in this configuration may cause non-uniform expansion relative to the circumference of the distal end 112 of the first tube section 110. This non-uniform expansion may deform or warp the first tube section 110. The C-profile slot 116 and the slit 118 provide openings, allowing the first tube section 110 to expand tangentially from the wedge inserts 164 without deforming or warping the first tube section 110.

[0057] Referring now to FIG. 4, the rock bolt 100 additionally includes an anchor assembly 150, which is connected to the proximal end portion 144 of the tendon 140 and located adjacent the proximal end portion 124 of the second tube section 120. The anchor assembly 150 is configured to secure the rock bolt 100 to a surface support 106, as shown in FIG. 2. The anchor assembly 150 may include a nut 152 and a faceplate 154. As shown in FIG. 4, the anchor assembly 150 may also include a spherical seat 156. The proximal end portion 144 of the tendon 140 extends through a concentric hole in the nut 152, faceplate 154, and spherical seat 156. The faceplate 154 is configured to abut against the surface support 106, either directly or indirectly. The nut 152 is configured to tension the faceplate 154 against the surface support 106. In one configuration, the nut 152 is threaded onto and tightened on the proximal threaded section 148c of the tendon 140, securing the faceplate 154 against the surface support 106. The spherical seat 156 is locatedbetween the nut 152 and the faceplate 154 and is configured to uniformly distribute forces from the nut 152 to the faceplate 154 and vice versa.

[0058] The rock bolt 100 additionally includes a stopper 180. The stopper 180 is mounted onto the proximal threaded section 148c the tendon 140. As shown in FIG. 4, the proximal end portion 124 of the second tube section 120 is connected to the stopper 180. The stopper 180 prevents axial movement of the second tube section 120 toward the proximal end portion 144 of the tendon 140 or generally in the proximal direction. Opposite the second tube section 120, a free length of threads 182 extends from the stopper 180. The nut 152 and the faceplate 154 may travel along the free length of threads 182, which allows the anchor assembly 150 to be tightened against a surface support 106, such as the rockface or welded mesh. This tightening applies a pre-tensioning or clamping force on the surface support 106, removing slack within the system.

[0059] Additionally, the stopper 180 may be configured to transfer tensile forces from the second tube section 120 to the tendon 140. Tensile forces exerted on the second tube section 120 during rock deformation may be transferred from the second tube section 120, through the stopper 180, and to the tendon 140. Absent the stopper 180, these tensile forces would be transferred to the tendon 140 via the faceplate alone. Thus, the addition of the stopper 180 allows for a thinner faceplate 154 to be used.

[0060] Referring to FIG. 5, the proximal end 114 of the first tube section 110 is coupled together with the distal end 122 of the second tube section 120 during installation of the rock bolt 100. Generally, a hybrid bolt is inserted into a borehole 102 via hammering forces on or near the proximal end portion 144 of the tendon 140 and the anchoring assembly 150. In this coupled configuration, the first tube section 110 and the second tube section 120 are coupled together, allowing these hammering or installation forces to transfer from the second tube section 120 to the first tube section 110. The tube sections 110, 120 may be coupled directly or indirectly. Additionally, the tube sections 110, 120 may be concentrically aligned to ensure the transfer of forces from the second tube section 120 to the first tube section 110 and to prevent one tube from slipping into the other.

[0061] In the configuration depicted in FIG. 5, the proximal end 114 of the first tube section 110 is welded to the distal end 122 of the second tube section 120 via multiple weld beads 130. In another configuration, the first tube section 110 and the second tube section 120 may be coupled by rivets. In yet another configuration, not shown here, the first tube section 110 and the secondtube section 120 may be coupled only indirectly. In this indirect configuration, the rock bolt 100 may include an intermediate sleeve located between the proximal end 114 of the first tube section 110 and the distal end 122 of the second tube section 120. The intermediate sleeve may prevent abutting contact between the tube sections 110, 120 while maintaining concentric alignment.

[0062] As shown in FIG. 6, when subjected to rock deformation, the second tube section 120 is configured to move axially away from the first tube section 110, toward the proximal end of the borehole 102. Specifically, the distal end 122 of the second tube section 120 is configured to move away from the proximal end 114 of the first tube section 110, forming a gap 132 between the two tube sections 110, 120 or increasing the thickness of the gap 132 if a gap 132 is already present. A fracture 108 in the rock will cause the length of tube section located in area B to be pulled in the proximal direction. If the first tube section 110 and the second 120 are mechanically coupled together, the length of tube section in area B may pull on the length of tube section in area A. When the pulling force in area B becomes great enough, the second tube section 120 is configured to move away from the first tube section 110, forming or increasing the thickness of a gap 132. When the second tube section 120 moves away, the forces from rock deformation may be transferred primarily to the tendon 140.

[0063] In other words, in the configuration shown in FIG. 6, the weld beads 130 break when the pulling force in area B reaches a threshold. Once weld beads 130 break, the second tube section 120 moves away from the first tube section 110. The tensile forces exerted on the second tube section 120 stop pulling on the first tube section 110 and are transferred to the tendon 140. When the forces are transferred to the tendon 140, the tendon 140 is configured to elongate and activate the expansion mechanism 160, resulting in radial expansion and increased anchorage.

[0064] As illustrated in the configuration shown in FIG. 7, the weld beads 130 between the first tube section 110 and the second tube section 120 are separated. The weld beads 130 may be configured to break or separate at a pre-determined tension or load. For example, the weld beads 130 may be configured to separate from 3 to 7 tons, or more typically from 4 to 5 tons. Other configurations that do not utilize the weld beads 130, such as a configuration using rivets or an intermediate sleeve may also be configured to separate at a pre-determined load or tension.

[0065] In another configuration, a schematic of which is shown in FIG. 11, a rock bolt includes a tendon and a single continuous tube having a first tube section 410 and a second tube section 420. The first tube section 410 is adjacent the distal end portion of the tendon, and the second tubesection 420 is adjacent the proximal end portion of the tendon. The rock bolt has a weakened portion 430 located where the first tube section 410 and the second tube section 420 are joined. The weakened portion 430 may be a perforation, a series of holes, slots or a grove in the continuous tube. When subject to rock deformation, the weakened portion 430 is configured to break. Once the weakened portion 430 breaks, the second tube section 420 is configured to move axially away from the first tube section 410, as shown in FIG. 11.

[0066] In one configuration of the rock bolt 100 shown in FIGS. 2-7, the rock bolt 100 is configured to convey grout through a hollow channel 146 in the tendon 140 and into the borehole 102. In this configuration, the hollow channel 146 is free of any obstruction. Grout is then pumped or injected through the hollow channel 146 from the proximal end portion 144 of the tendon 140. The grout then exits the hollow channel 146 through the distal end portion 142 of the tendon 140 and fills the empty space within the borehole 140.

[0067] The rock bolt 100 may also be compatible with a grout injection assembly, not shown here, having an injection coupler, a pump, and a hose. The injection coupler may be pressed against the proximal end portion 144 of the tendon 140 to create a seal between the tendon 140 and the remainder of the grout injection assembly. In one configuration, the injection coupler is screwed either into the hollow channel 146 or onto the proximal end portion 144 of the tendon 140 to form the seal. Grout may then be pumped through the hose and into the hollow channel 146 of the tendon 140 and subsequently into the borehole 102.

[0068] In this configuration, the rock bolt 100 is configured to be grouted in the borehole 102 after the rock bolt 100 is already anchored within the borehole 102. In other words, the grout provides a redundant point of anchorage to the mechanical anchorage from the expansion mechanism 160, the first tube section 110, and the second tube section 120. The grout may provide a more permanent support for the rock bolt 100 in the borehole 102, as well as may protect the rock bolt 100 from corrosion. Because the rock bolt 100 is anchored or secured in the borehole 102 without grout, there is no urgency for grouting the rock bolt 100. Thus, a standard or slow setting grout may be used, which usually is more cost effective than a rapid-setting grout. Additionally, the rock bolt 100 need not be grouted immediately after installation. For example, the rock bolt 100 may be grouted one or more days or even weeks after the rock bolt 100 is installed in the borehole 102.

[0069] The rock bolt 100 may also limit the leakage of grout in cracks in poor ground because the first tube section 110 and the second tube section 120 seal the majority of the cracks. The first tubesection 110 and the second tube section 120 firmly press against the wall 104 of the borehole 102, sealing cracks in the rock. When installed in a borehole 102, only the slot 116 of the C-shape and small tapered sections of each tube section 110, 120 leave portions of the wall 104 of the borehole 102 exposed. Therefore, the majority of the borehole surface area is sealed.

[0070] FIGS. 8 and 9 depict another configuration of a rock bolt 200 constructed in accordance with the present invention. The rock bolt 200 has an extended second tube section 220 extending to an anchor assembly 250.

[0071] Similar to the rock bolt 100 depicted in FIGS. 2-7, the rock bolt 200 in FIGS. 8-9 includes a tendon 240 extending axially through a first tube section 210 and a second tube section 220. A distal end portion 242 of the tendon 240 is adjacent the first tube section 210 and is connected to an expansion mechanism 260. A proximal end portion 244 of the tendon 240 is adjacent the second tube section 220 and is connected to an anchor assembly 250. The second tube section 220 is configured to move axially away from the first tube section 210 when subject to rock deformation. Additionally, the rock bolt 200 may be configured to convey grout through a hollow channel (not shown) in the tendon 240 and into a borehole.

[0072] In this configuration, the second tube section 220 extends axially to the anchor assembly 250. Specifically the proximal end portion 224 of the second tube section 220 abuts the anchor assembly 250. As shown in FIG. 9, the anchor assembly 250 includes a spherical seat 256 located between a faceplate 254 and a nut 252. The proximal end portion 244 of the tendon 240 extends concentrically through the nut 252, spherical seat 256, and faceplate 254. The nut 252 may be threaded onto the proximal threaded section 248c of the tendon 240.

[0073] The proximal end portion 224 of the second tube section 220 abuts the spherical seat 256, bypassing or otherwise avoiding contact with the faceplate 254. When a load is placed on the rock bolt 200, either during installation or from rock deformation, the loads are transferred between the spherical seat 256 and the second tube section 220, bypassing the faceplate 254. For example, a tensile load exerted from rock deformation on the second tube section 220 is transferred from the second tube section 220 to the spherical seat 256 and subsequently the tendon 240 while transferring little to no load on the faceplate 254. In this configuration, a thinner faceplate 254 may be used. This same effect may be achieved in a similar configuration, not shown here, in which the proximal end portion 224 of the second tube section 220 abuts the nut 252, bypassing the faceplate 254.

[0074] The present invention additionally includes a method of installing a rock bolt in a borehole 102. The borehole 102 is pre-drilled within the rockface. The method includes providing a rock bolt 100, 200 as depicted in FIGS. 2-7 or FIGS. 8-9. For simplicity, the method shall be described with reference to the rock bolt 100 depicted in FIGS 2-7, but the skilled artisan would understand the rock bolt 200 depicted in FIGS. 8-9 would be utilized in a similar manner.

[0075] The rock bolt 100 is inserted into the borehole 102 such that the expansion mechanism 160 is located within the borehole 102. The rock bolt 100 may be inserted into the borehole 102 via hammering forces exerted on the anchor assembly 150. Once inserted in the borehole 102, the rock bolt 100 may be pre-tensioned. Pre-tensioning may include tightening the nut 152 and faceplate 154 of the anchor assembly 150 against the surface support 106, such as the rockface or wired mesh. Additionally, the pre-tensioning may include rotating the tendon 140. The expansion mechanism 160 then radially expands in response to the rotation. Further, the anchorage of the rock bolt 100 within the borehole 102 increases in response to the radial expansion as the expansion mechanism 160 abuts the wall 104 of the borehole 102.

[0076] The method further includes subjecting the rock bolt 100 to rock deformation. In response to the rock deformation, a tensile load is transferred to the tendon 140, causing the tendon 140 to elongate. Additionally, the wedge 162 of the expansion mechanism 160 is pulled in the proximal direction, causing the expansion mechanism 160 to radially expand. As the load on the proximal portion of the rock bolt 100 becomes too great from the rock deformation, the distal end 122 of the second tube section 120 moves axially away from the proximal end 114 of the first tube section 110.

[0077] In another configuration, the method includes a rock bolt 100 having a hollow channel 146. Grout is injected through the hollow channel 146 and into the borehole 102, further securing the rock bolt 100 within the borehole 102.

[0078] FIG. 10 depicts yet another configuration of a rock bolt 300 constructed in accordance with the present invention. The rock bolt 300 includes a single tube 310. A tendon 340 extends axially through the tube 310. An expansion mechanism 360 is connected to a distal end portion 342 of the tendon 340, and an anchor assembly 350 is connected to a proximal end portion 344 of the tendon 340. The tendon 340 has a hollow channel (not shown) extending axially through the tendon 346 from the distal end portion 342 to the proximal end portion 344. In this configuration, the rock bolt 340 is configured to convey grout through the hollow channel and into a borehole. The rock bolt300 may be compatible with a grout injection assembly having an injection coupler, a pump, and a hose.

[0079] The present invention further includes the method of injecting grout through the hollow channel of the rock bolt 300 depicted in FIG. 10.

[0080] Although the best modes contemplated by the inventor of carrying out the present invention is disclosed above, practice of the present invention is not limited thereto. It will be manifest that various additions, modifications and rearrangements of the aspects and features of the present invention may be made in addition to those described above without deviating from the spirit and scope of the underlying inventive concept. The scope of some of these changes is discussed above. The scope of other changes to the described embodiments that fall within the present invention but that are not specifically discussed above will become apparent from the appended claims and other attachments.

Claims

CLAIMSWe claim:

1. A rock bolt comprising : first and second coaxial tube sections; a tendon extending axially through the first tube section and the second tube section, wherein the first tube section is located adjacent a distal end portion of the tendon and the second tube section is located adjacent a proximal end portion of the tendon, wherein the first tube section has a pull-out resistance of at least 3 tons and, when subject to rock deformation, the tendon is configured to elongate and the second tube section is configured to move axially away from the first tube section; an anchor assembly connected to the proximal end portion of the tendon; and an expansion mechanism connected to the distal end portion of the tendon.

2. The rock bolt of claim 1, wherein the tendon has a hollow channel extending axially through the tendon from the proximal end portion of the tendon to the distal end portion of the tendon, and the rock bolt is configured to convey grout through the hollow channel.

3. The rock bolt of claim 1, wherein the first tube section has a length of at least 1.0 meter.

4. The rock bolt of claim 1, wherein the expansion mechanism comprises a wedge connected to the distal end portion of the tendon and a wedge insert abutting an outer mating surface of the wedge and at least partially inserted within a distal end of the first tube section.

5. The rock bolt of claim 1, wherein the anchor assembly comprises a nut and a faceplate.

6. The rock bolt of claim 1, wherein the first tube section is a first tube and the second tube section is a second tube.

7. The rock bolt of claim 6, wherein a distal end of the second tube and a proximal end of the first tube are coupled together.

8. The rock bolt of claim 7, wherein the distal end of the second tube is configured to separate from the proximal end of the first tube when the rock bolt is subject to rock deformation.

9. The rock bolt of claim 1, wherein the first tube section and the second tube section are formed from a continuous tube and are joined at a weakened portion that is configured to break when subject to rock deformation.

10. A method of installing a rock bolt comprising: providing the rock bolt, the rock bolt includingfirst and second coaxial tube sections, a tendon extending axially through the first tube section and the second tube section, wherein the first tube section is adjacent a distal end portion of the tendon and the second tube section is adjacent a proximal end portion of the tendon, an anchor assembly connected to the proximal end portion of the tendon, and an expansion mechanism connected to the distal end portion of the tendon; inserting the rock bolt into a borehole, wherein the expansion mechanism is located within the borehole; and subjecting the rock bolt to rock deformation, in response to the rock deformation elongating the tendon, radially expanding the expansion mechanism, and moving a distal end of the second tube section axially away from a proximal end of first tube section.

11. The method of claim 10, further comprising pretensioning the rock bolt by rotating the tendon; in response to the rotation, radially expanding the expansion mechanism; and in response to the radial expansion, increasing the anchorage of the rock bolt within the borehole.

12. The method of claim 10, further comprising injecting grout through a hollow channel in the tendon and into the borehole.

13. A rock bolt installed in a borehole, the rock bolt comprising: first and second coaxial tube sections that each abut a wall of the borehole; a tendon extending axially through the first tube section and the second tube section, wherein the first tube section is located adjacent a distal end portion of the tendon and the second tube section is located adjacent a proximal end portion of the tendon; an anchor assembly connected to the proximal end portion of the tendon and located outside the borehole; and an expansion mechanism connected to the distal end portion of the tendon and located within the borehole, wherein, when subject to rock deformation, the tendon is configured to elongate and the second tube section is configured to move axially away from the first tube section.

14. The rock bolt of claim 13, wherein a distal end of the second tube section separates from a proximal end of the first tube section.

15. The rock bolt of claim 13, wherein the first tube section has a pull-out resistance of at least 3 tons.

16. The rock bolt of claim 13, wherein the tendon has a hollow channel extending axially through the tendon from the proximal end portion of the tendon to the distal end portion of the tendon, and the rock bolt is configured to convey grout through the hollow channel.

17. A method of installing a rock bolt comprising: providing the rock bolt, the rock bolt including a tube, a tendon having a hollow channel extending axially from a distal end portion of the tendon to a proximal end portion of the tendon, the tendon extending axially through the tube, an anchor assembly connected to the proximal end portion of the tendon, and an expansion mechanism connected to the distal end portion of the tendon; inserting the rock bolt into a borehole such that the expansion mechanism is located within the borehole; and injecting grout into the borehole through the hollow channel of the tendon and into the borehole.

18. A rock bolt installed in a borehole comprising: a tube; a tendon having a hollow channel extending axially through the tendon from the distal end portion of the tendon to the distal end portion of the tendon, the tendon extending axially through the tube; an anchor assembly connected to the proximal end portion of the tendon; and an expansion mechanism connected to the distal end portion of the tendon, wherein the rock bolt is configured to permit the injection of through the hollow channel and into the borehole.

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