ANCHOR BOLT WITH ANTI PROJECTION MECHANISM

Abstract

An anchor bolt for fastening an object in a drilled borehole in a rock mass formation, which is to absorb violent impact loads such as those occurring during earthquakes in an energy dissipating manner. The anchor bolt comprises a split sleeve and a bolt component inserted in the split sleeve that, when pulled outwardly, expends the split sleeve until a key protruding from the surface of the bolt component abuts a ring, thereby informing the operator that appropriate anchoring and pre-tensioning of the anchor bolt in the borehole is reached. Another ring, interfacing with the split sleeve about the entry of the borehole, is designed to force expansion of the split sleeve, preventing a breaking anchor bolt to become a high-speed projectile.

Description

BACKGROUND

(a) Field

The subject matter disclosed generally relates to systems for anchoring solutions for anchoring in boreholes made in rock mass, concrete or alike. More particularly, the subject matter disclosed relates to an anchor bolt offering improved energy absorption including an anti-projection mechanism.

(b) Related Prior Art

Anchors for rock mass support used in mines (open pit or underground) or civil projects (tunnels) are known in various shapes, using different mechanisms and offering different capacities and behavior. If exceptional energy is released by surrounding environment (i.e., seismicity), specialized tendons are required to contain the potential damages to the structure. That specialized tendons needs to be able to react to this exceptional energy since a rigid connection does not exhibit the required energy dissipating behavior.

There is therefore a need for an anchoring element that is able to absorb violent impact loads such as those occurring during seismic event (natural or induced by mining activities i.e., rock burst) in an energy dissipating manner.

SUMMARY

There is described a rock anchor bolt engineered to absorb violent impact loads such as those occurring during seismic events or rock burst in an energy dissipating manner. The rock anchor bolt comprises a split sleeve and a bolt component inserted in the split sleeve that, when pulled outwardly, expends the split sleeve until a key protruding from the surface of the bolt component abuts a ring, thereby informing the operator that appropriate anchoring and pre-tensioning of the anchor bolt in the borehole is reached through torque requirement.

According to an embodiment, there is provided an anchor bolt designed to absorb energy during events with sudden energy released.

According to an aspect, the anchor bolt can adapt in size to the collar of a borehole to allow the friction bolt to generate anchorage to the collar of the borehole.

According to an aspect, the anchor bolt comprises a split sleeve for better performance at borehole collar.

According to an aspect, the split sleeve of the anchor bolt can be radially compressed, allowing the anchor bolt to adapt to different sizes of drill holes.

According to an aspect, contact between an anti-ejection system and a slot in the ring tells the operator through rotation pressure that the system is engaged to its optimum anchoring capacity.

According to an aspect, contact between and anti-ejection system and the slot in the ring dissipates energy, including through friction between the ejection system and the ring slot, to mitigate sudden energy release.

Therefore, in some aspects, the description herein relates to a hybrid bolt designed to be inserted in a borehole having a borehole wall, the hybrid bolt including: a sleeve having a first sleeve-end and an expandable second sleeve-end featuring a longitudinal slit: and a peg having a first peg-end and a second peg-end wherein the peg has a diameter increasing toward the second peg-end thereby providing a frustoconical surface about the second peg-end, wherein the peg is inserted in the sleeve with the first peg-end opposed to the second sleeve-end, and wherein the hybrid bolt, when the peg is pulled towards the first sleeve-end, has the frustoconical surface pushing outwards the second sleeve-end which becomes thereby wedged between the frustoconical surface and the borehole wall.

In some aspects, the description herein relates to a hybrid bolt, further including a wedge ring inserted between the peg and the sleeve at the second sleeve-end, wherein pulling the peg towards the first sleeve-end wedges the wedge ring between the peg and the sleeve.

In some aspects, the description herein relates to a hybrid bolt, wherein the wedge ring includes a longitudinal groove parallel to the slit of the sleeve.

In some aspects, the description herein relates to a hybrid bolt, wherein the wedge ring includes an outwardly extending lip adapted to abut against the second sleeve-end when the peg is pulled towards the first sleeve-end.

In some aspects, the description herein relates to a hybrid bolt, wherein the wedge ring includes a longitudinal body extending within the sleeve, the longitudinal body having a variable thickness increasing towards the first sleeve-end.

In some aspects, the description herein relates to a hybrid bolt, wherein the sleeve has an external diameter decreasing towards the second sleeve-end.

In some aspects, the description herein relates to a hybrid bolt, wherein the sleeve has a slit extending from the first sleeve-end to the second sleeve-end.

In some aspects, the description herein relates to a hybrid bolt, wherein the slit narrows towards the second sleeve-end.

In some aspects, the description herein relates to a hybrid bolt, wherein the sleeve includes a key groove.

In some aspects, the description herein relates to a hybrid bolt, wherein the key groove extends from the first sleeve-end, and the peg includes a body and a key protruding from the body, wherein the key is adapted to take place in the key groove.

In some aspects, the description herein relates to a hybrid bolt, further including an abutting ring slidingly mounted to the first sleeve-end.

In some aspects, the description herein relates to a hybrid bolt, wherein the abutting ring includes a slit.

In some aspects, the description herein relates to a hybrid bolt, wherein the key has a key-width transversal to the peg, and the slit of the abutting ring has a slit-width transversal to the peg narrower than the key-width.

In some aspects, the description herein relates to a hybrid bolt, wherein the abutting ring is adapted to slide into the sleeve.

In some aspects, the description herein relates to a hybrid bolt, wherein the peg includes a weakness between the first peg-end and the second peg-end, wherein the weakness induces a foreseeable location for a breaking point to the peg.

In some aspects, the description herein relates to a hybrid bolt, wherein the weakness consists in one of a hole, of a shaving, of a groove, and of threading.

In some aspects, the description herein relates to a hybrid bolt, wherein the weakness is located between the key and the second peg-end.

In some aspects, the description herein relates to a hybrid bolt, wherein the peg includes a threaded portion extending from the first peg-end towards the second peg-end over a partial length of the peg.

In some aspects, the description herein relates to a hybrid bolt, wherein the peg includes a body, and a key protruding from the body, and a threaded portion extending between the first peg-end and the key.

In some aspects, the description herein relates to a hybrid bolt, further including a mounting nut adapted to be mounted to the peg, the mounted nut adapted to butt off against the abutting ring, pushing the abutting ring inside the sleeve.

Features and advantages of the subject matter hereof will become more apparent in light of the following detailed description of selected embodiments, as illustrated in the accompanying figures. As will be realized, the subject matter disclosed and claimed is capable of modifications in various respects, all without departing from the scope of the claims. Accordingly, the drawings and the description are to be regarded as illustrative in nature and not as restrictive and the full scope of the subject matter is set forth in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present disclosure will become apparent from the following detailed description, taken in combination with the appended drawings, in which:

FIG. 1A is a perspective view of an anchor bolt in accordance with an embodiment;

FIG. 1B is a close-up perspective view of the anchor end of the anchor bolt of FIG. 1A according to detail portion R:

FIG. 1C is a close-up perspective view of the free end of the anchor bolt of FIG. 1A according to detail portion P:

FIG. 2A is a partially exploded perspective view of an anchor bolt in accordance with an embodiment:

FIG. 2B is a close-up perspective view of the free end of an anchor bolt in accordance with an embodiment:

FIG. 3A is a perspective view of a bolt component and a conic ring of an anchor bolt in accordance with an embodiment:

FIG. 3B is a close-up perspective exploded view of the anchor end of the bolt component and the conic ring depicted on FIG. 3A according to detail portion AB:

FIG. 4 is a side elevation view of an anchor bolt mounted with mounting components in a borehole drilled in concrete in accordance with an embodiment:

FIG. 5 is a cross-section of the anchor bolt of FIG. 4 according to cross-section line J-J:

FIG. 6 is a side elevation view of an anchor bolt and mounting components associated therewith mounted in a borehole and in an initial position once hammered in placed in the borehole, with no tension exerted over the anchor bolt, in accordance with an embodiment:

FIG. 7 is a side elevation view of the anchor bolt and mounting components associated therewith of FIG. 6 in a tensioned position following tension being exerted in the anchor bolt through tightening of the hemispherical anchor nut:

FIG. 8 is a side elevation view of the anchor bolt and mounting components associated therewith of FIG. 6 in an over-tensioned position:

FIG. 9 is a cross-section side elevation view of an anchor bolt in an initial position in accordance with an embodiment:

FIG. 10 is a close-up cross-section side elevation view of the anchor end of the anchor bolt depicted on FIG. 9:

FIG. 11 is a side elevation view of a split sleeve of an anchor bolt in accordance with an embodiment:

FIG. 12 is a plan view of the split sleeve of FIG. 11:

FIG. 13 is a cross-section view of the split sleeve of FIG. 12 according to cross-section line N-N:

FIG. 14 is a plan view of the bolt component of an anchor bolt in accordance with an embodiment:

FIG. 15 is an elevation view of the bolt component of FIG. 14:

FIG. 16 is a cross-section view of the bolt component of FIG. 15 according to cross-section line AJ-AJ:

FIG. 17A is an axial elevation view of a conic ring of an anchor bolt viewed from the anchor end of the anchor bolt in accordance with an embodiment:

FIG. 17B is a cross-section view of the conic ring of FIG. 17A according to cross-section line U-U:

FIG. 18A is an axial elevation view of an abutting ring of an anchor bolt viewed from the free end of the anchor bolt in accordance with an embodiment:

FIG. 18B is an elevation side view of the abutting ring of FIG. 18A:

FIG. 19A is an axial elevation view of a mounting nut used to mount an anchor bolt to a borehole in accordance with an embodiment:

FIG. 19B is a side elevation view of the nut of FIG. 19A:

FIG. 20 is an axial schematic view of min-max dimensions of the abutting ring in accordance with an embodiment: and

FIG. 21 is an elevation perspective view of a hemispherical anchor nut adapted to be screwed on anchoring bolt in accordance with an embodiment.

It will be noted that throughout the appended drawings, like features are identified by like reference numerals.

DETAILED DESCRIPTION

The realizations will now be described more fully hereinafter with reference to the accompanying figures, in which realizations are illustrated. The foregoing may, however, be embodied in many different forms and should not be construed as limited to the illustrated realizations set forth herein.

With respect to the present description, references to items in the singular should be understood to include items in the plural, and vice versa, unless explicitly positioned otherwise or clear from the text. Grammatical conjunctions are intended to express any and all disjunctive and conjunctive combinations of conjoined clauses, sentences, words, and the like, unless otherwise positioned or clear from the context. Thus, the term “or” should generally be understood to mean “and/or” and so forth.

Recitation of ranges of values and of values herein or on the drawings are not intended to be limiting, referring instead individually to any and all values falling within the range, unless otherwise indicated herein, and each separate value within such a range is incorporated into the specification as if it were individually recited herein. The words “about,” “approximately,” or the like, when accompanying a numerical value, are to be construed as indicating a deviation as would be appreciated by one of ordinary skill in the art to operate satisfactorily for an intended purpose. Ranges of values and/or numeric values are provided herein as examples only, and do not constitute a limitation on the scope of the described realizations. The use of any and all examples, or exemplary language (“e.g.,” “such as.” or the like) provided herein, is intended merely to better illuminate the exemplary realizations and does not pose a limitation on the scope of the realizations. No language in the specification should be construed as indicating any unclaimed element as essential to the practice of the realizations.

In the following description, it is understood that terms such as “first”, “second”, “top”, “bottom”, “above”, “below”, “interior”, “exterior”, and the like, are words of convenience and are not to be construed as limiting terms.

It will be noted that throughout the appended drawings, like features are identified by like reference numerals.

Referring now to the drawings, and more particularly to FIGS. 1A-C and 2A-B, a hybrid bolt, hereinafter referred to as an anchor bolt 100, is adapted to be inserted to a borehole, first through hammering, and afterward through tightening of a nut, in concrete, rock, or similar material. The anchor bolt 100 is adapted to provide an anchoring solution that tells the user on when the necessary initial tension to be exerted in the anchor bolt 100 during the installation is reached. The anchor bolt 100 is further able to absorb violent impact loads such as those occurring during seismic events or rock burst in an energy dissipating manner.

The anchor bolt 100 has an anchor end 102 and a free end 104 opposed to the anchor end 102, and a body 106 extending in-between. The anchor bolt 100 comprises a bolt component 120, that can be generally called a peg, mounted into a split sleeve 150, the bolt component 120 being longer than the split sleeve 150 and extending beyond the split sleeve 150 in both directions in an initial position. A conic ring 180 takes place between the bolt component 120 and the split sleeve 150 about the anchor end 102. An abutting ring 200 takes place between the bolt component 120 and the split sleeve 150 about the free end 104, butted up by a mounting nut 230.

Referring additionally to FIGS. 3A and 3B, the bolt component 120 comprises a generally cylindrical body 122 between a first position 124 and a second position 126, with the distance between the first position 124 and the second position 126 being longer than the length of the split sleeve 150. Beyond the first position 124 toward the anchor end 102, the bolt component 120 comprises a wedge portion 128 having an increasing conical shape toward the anchor end 102 of the anchor bolt 100 forming therethrough a frustoconical surface. Distant from the first position 124, a key 130 extends axially over the surface of the cylindrical body 122 between a fourth position 132 and a fifth position 134. The key 130 is further protruding radially, having a generally longitudinal portion defining an axial protrusion over the surface of the generally cylindrical body 122 that extends transversally, aka perpendicular to the longitudinal orientation and radial orientation of the bolt component 120 over a transversal width.

Referring additionally to FIGS. 14 to 16, a threaded portion 138 of the bolt component 120 extending between at least a portion of the length between the fifth position 134 and the second position 126 is threaded to have the mounting nut 230. FIGS. 19A-19B, screwed there on such as to be able to abut the abutting ring 200 before the insertion of the anchor bolt 100 in the borehole 302, and an external nut. e.g., hemispherical anchor nut 260. FIG. 21, screwable over the bolt component 120 to exert tension in the anchor bolt 100 after the anchor bolt having been hammered in the borehole 302.

According to an embodiment, the bolt component 120 features, between the positions 124 and 132, a weakness taking. e.g., the form of a hole 136, wherein the nature and dimension(s) of the weakness are selected based on the desired position and characteristics leading to failure of the anchor bolt 100, aka the maximum tension or energy the anchor bolt 100 may undergo before it breaks.

According to another embodiment (not depicted), the weakness is provided through the presence of shaving(s) over the external surface of the anchor bolt 100. According to another embodiment (not depicted), the weakness is provided through the presence of groove(s), wherein number, shape, orientation, location, depth and number of groove(s) may vary with embodiments. According to another embodiment (not depicted), the weakness is provided through the presence of threading.

Accordingly, it is contemplated therethrough that the anchor bolt 100 may comprise a weakness embodiment as a local modification of physical characteristics of material of the anchor bolt 100 is order to induce a foreseeable location for a breaking point to the anchor bolt 100.

Referring now to FIGS. 11 to 13, the split sleeve 150 consists in a generally hollow cylindrical body 152 of an interior dimension adapted to house the generally cylindrical body 122 of the bolt component 120 and being split, aka having a slit that extends over its whole length, thus having a C-shaped cross-section. The generally hollow cylindrical body 152 extends between a first position 154 and a second position 156. Beyond the second position 156 in the direction of the anchor end 102, the split sleeve 150 comprises an expandable anchor portion 160 having a slightly decreasing conical shape toward the anchor end 102. The anchor portion 160 comprises a plurality of slits. e.g., longitudinal grooves 158. e.g., four (4), allowing a level of deformation of the anchor portion 160 when the frustoconical surface of the wedge portion 128 is forced to enter the expandable anchor portion 160.

as depicted particularly on FIGS. 11 and 12, according to an embodiment the longitudinal slit narrows about the anchor end 102.

According to an embodiment, the split sleeve 150 consists in a partially wrapped component. e.g., wrapped over about two hundred and seventy (270) degrees, featuring a longitudinal aperture 164 of a designed dimension allowing the bolt component 120 to be inserted inside the split sleeve 150 thereby and the split sleeve 150 to be compressed until no clearance remains between the split sleeve 150 and the bolt component 120.

Still referring to FIGS. 11 to 13, the split sleeve 150 comprises at least one longitudinal groove 166, preferably opposed to the longitudinal aperture 164, adapted to receive the key 130 of the bolt component 120 and to limit the course of the key 130 during the tensioning operation of the anchor bolt 100, as over-tensioning occurs as will be discussed below in more details.

Referring to FIG. 17A-17B and FIGS. 9-10, the anchor bolt 100 comprises a wedge ring. e.g., conic ring 180, taking place between the bolt component 120, about the wedge portion 128, and the anchor portion 160 of the split sleeve 150. The conic ring 180 is adapted, when pushed by the wedge portion 128 when the bolt component 120 is pulled towards the other end, to force its way inside the anchor portion 160, thereby deforming the anchor portion 160 outwardly so the exterior face of the anchor portion 160 would mate the surface of the borehole to anchor the anchor bolt 100 therein.

According to a preferred embodiment, the conic ring 180 comprises a cylindrical exterior face 182, and a conical interior face 184 thereby a longitudinal body therebetween of variable thickness, providing a conduit sized to insert the generally cylindrical body 122 of the bolt component 120 therein. The conic ring 180 comprises an outwardly extending lip 186 on the wide end of the conical interior face 184. The conic ring 180 features a pair of grooves 190 extending over a substantial portion of the length 192 of the conic ring 180 allowing deformation of the conic ring 180. According to embodiments, the grooves 190 extends over a greater length than 50%. 60%. 70%. 80% or 90% of the total length 192 of the conic ring 180. According to an embodiment, depicted on FIGS. 3A and 3B, the conic ring 180 is made of two pieces that can be assembled around the cylindrical body 122 and maintained in place between the bolt component 120 and the split sleeve 150 once these components are assembled.

Referring to FIGS. 18A-B, the abutting ring 200 is designed to take place between the bolt component 120 and the split sleeve 150 about the free end 104, inserted in the split sleeve 150 and abutted on its lipped face 216 closest to the free end 104 by the mounting nut 230. The abutting ring 200, according to an embodiment, consists in a partially wrapped component covering e.g., about 300 degrees, featuring an aperture 202 sized to insert the bolt component 120 in the abutting ring 200 therethrough. The abutting ring 200 comprises a cylindrical outer face 206 sized to be inserted in the split sleeve 150, and a cylindrical inner face 208 sized to receive the generally cylindrical body 122 of the bolt component 120. The abutting ring 200 comprises an outwardly extending lip 210 designed to be wedged between the extremity of the split sleeve 150 about the free end 104 and the mounting nut 230. The abutting ring 200 features a groove 212 opposed to the aperture 202 that is sized to receive and allow longitudinal displacement of the key 130. The groove 212 is designed, when the abutting ring 200 is mounted between the bolt component 120 and the split sleeve 150 with the lip 210 abutting the split sleeve 150, to limit the course of the key 130 to a distance from the extremity of the split sleeve 150 about the free end 104 as is explained below.

It is worth noting that according to an embodiment the groove 212 is narrower than the key 130 and it features a chamfered entry, thereby having the key 130 generating deformation and friction when the abutting ring 200 pushes against the key 130 such that the key 130 must enter in the groove 212 for the abutting ring 200 to continue its course. That situation provides indication when the correct installation is reached, both through positioning and through torque reading.

Referring to FIGS. 4 and 5, according to a preferred embodiment, the apertures 164, 202 are sized to allow to mount the bolt component 120 into the split sleeve 150 with some deformation of the split sleeve 150 and abutting ring 200.

Referring to FIGS. 4 and 5, as discussed before, the anchor bolt 100 is designed to be mounted through hammering percussion (i.e. hydraulic hammer) in the borehole 302 drilled in the rock mass formation 304 or alike. The borehole 302 is drilled to a recommended diameter of thirty-eight (38) mm but can accommodate irregularities in the borehole 302, or smaller diameter (as small as thirty-five (35) mm) when used in soft rock formation which allow small deformation of the material, for the exemplary anchor bolt 100 having an external normal (no-compressed) diameter of about thirty-nine (39) mm defined by the diameter 168 of the split sleeve 150. The cylindrical body 122 of the exemplary bolt component 120, inserted in the split sleeve 150, has a diameter 140 of about twenty-five (25) mm. The longitudinal aperture 164 of the split sleeve 150 allows the split sleeve 150 to be compressed for insertion in the borehole 302, thereby mating the diameter 308 of the borehole 302 once inserted.

Referring additionally to FIGS. 6 to 8, the anchor bolt 100 is depicted in three typical positions the anchor bolt 100 is able to adopt, with the selected position depending on installation parameters and rock mass conditions.

Depicted on FIG. 6, the anchor bolt 100 is initially, after being inserted, in an initial position when no internal stress is exerted on the anchor bolt 100. For its insertion in the borehole 302, the anchor bolt 100 is hammered in the borehole 302 with the bolt component 120 inserted in the split sleeve 150, the conic ring 180 and the abutting ring 200 interfacing between the split sleeve 150 and the bolt component 120 about the anchor end 102 and at the free end 104, and the mounting nut 230 abutting the lipped face 216 of the abutting ring 200. The wedge portion 128 extends beyond the conic ring 180. The extent of the wedge portion 128 is limited by the key 130 abutting the groove 166. The threaded portion 138 extends beyond the surface of the rock with a washer 240 and a hemispherical anchor nut 260 mounted on the free portion of the anchor bolt 100 out of the rock mass formation 304. To be noted that the distance at which the hemispherical anchor nut 260 is screwed determine the limit penetration of the anchor bolt under hammering, aka without exerted internal tension in the anchor bolt 100. It is further to be noted that other components, not depicted, may also be anchored through the anchor bolt 100, for instance protection grid, anchoring loop and straps, and plates.

Depicted on FIG. 7, the anchor bolt 100 is exerted internal stress by tightening the hemispherical anchor nut 260 until it reaches the tensioned position. More precisely, the hemispherical anchor nut 260 is screwed over the threaded portion 138 with the bolt component 120 moving outward with every revolution of the hemispherical anchor nut 260. As a result, on the anchor end 102, the wedge portion 128 gradually penetrates more in the split sleeve 150, forcing anchoring end of the split sleeve 150 to expand and to abut the surface of the borehole 302. About the free end 104, the mounting nut 230, and the key 130 move also outward, with the key 130 moving in the at least one longitudinal groove 166 away from its bottom until butting off the abutting ring 200. When the key 130 pushes the abutting ring 200 and is blocked thereby, the torque necessary to rotate the hemispherical anchor nut 260 increases, informing the operator that the optimal tensioned position is reached. It is to be noted that this same process applies in a variety of diameters of boreholes. e.g., for the exemplary anchor bolt 100 a borehole diameter of thirty-eight (38) mm in a hard rock mass formation, and a borehole diameter of as low as thirty-five (35) mm in a soft rock mass formation.

Referring additionally to FIG. 20, the schematic depicts that the outer diameter of the abutting ring 200 inserted the split sleeve 150 through hammering percussion to assure anchoring of the split sleeve about the entry of the borehole 302 in various hole dimension (e.g., thirty-five (35) to thirty-eight (38) mm), for instance when installed in a borehole 302 of a smaller diameter, normally performed in soft rock formation. On FIG. 20, the abutting ring 200 is depicted being in its original non-compressed shape 200′, that is greater than the space between the wall of the borehole 302 and the split sleeve 150, to an exemplary compressed shape 200″, limited over a minimum value by the diameter of the bolt component 120 in which the aperture changed from its maximum aperture to its minimum aperture greater than zero (0).

Depicted on FIG. 8, the anchor bolt 100 may adopt additional outward displacement of the bolt component 120 if ground conditions allow (i.e. very soft rock mass or void). If conditions allow it, the wedge portion 128 at the anchor end 102 will penetrate even more in the split sleeve 150, forcing the conic ring 180, and accordingly the split sleeve 150, to increase even more their diameters against with the outside of the split sleeve 150 mating the surface of the borehole. About the free end 104, the outward course of the bolt component 120 would result in the key 130 forcing its way in the groove 212. Since the width of the groove 212. e.g., 5 mm, is smaller than the width of the key. e.g., 10 mm, the key 130 will encounter resistance against that displacement at set torque load for a set length indicating to operator that bolt has passed optimal position. However, the extra course of the key 130 will be stopped by the bottom of the groove 212, in combination with the abutting ring 200 coming in contact with the hemispherical anchor nut 260 or equivalent, preventing any further axial displacement and forcing rotation of the assembly stopped by key 130 sitting against the split sleeve 150 where the over-tensioned position is reached. The measurement of the protruding length 170 combined to sudden high torque load will indicate to the operator that the installation is not correct.

Should the anchor bolt 100 reach failure with high energy absorbency, the hole 136 is designed, by diameter and/or depth, to induce failure at a specific position located beyond the anti-ejection system, aka beyond the key 130 and cooperating components, in the direction toward the anchor end 102. Forced mating of the split sleeve 150 about the abutting ring 200 prevents, through friction between the split sleeve 150 and the wall of the borehole 302 at that position, the freed portion of the anchor bolt 100 to be ejected at high speed. In other words, the forced expansion of the split sleeve 150 of the anchor bolt 100 both about the anchor end 102 and about the entry of the borehole 302 prevents a breaking anchor bolt 100 to be transformed into a high velocity projectile forcibly ejected from the borehole 302.

According to a first realization, the wedge portion 128 has a first diameter about the cylindrical body 122 of twenty-five (25) mm, and a second diameter 142 at its anchor end of thirty-five (35) mm, with the increase being regular and over a length of about fifty-seven (57) mm. The displacement of the key 130 between the initial position and the tensioned position is about thirty-eight (38) mm. Further displacement of the key 130 to reach the over-tensioned position is defined by the length of the groove 212, and is typically of about thirty (30) mm.

In other realizations, the length of the anchor bolt 100, the length of the portion of the anchor bolt 100 extending beyond the surface of the e.g., rock mass formation, distances between the positions, the pressure applied over the surface of the borehole, general resistance of the anchor bolt 100, etc. may be set to different values with changes in the design not departing from the design concept taught through the present exemplary realization.

It must be mentioned that some details of the present design may be omitted, or replaced with alternatives, in alternative designs without substantially affecting the way the present anchor bolt 100 operated.

Therefore, while a preferred embodiment has been described above and illustrated in the accompanying drawings, it will be evident to those skilled in the art that modifications may be made without departing from this disclosure. Such modifications are considered as possible variants comprised in the scope of the disclosure.

Claims

1. A hybrid bolt designed to be inserted in a borehole having a borehole wall, the hybrid bolt comprising: a sleeve having a first sleeve-end and an expandable second sleeve-end featuring a longitudinal slit; anda peg having a first peg-end and a second peg-end wherein the peg has a diameter increasing toward the second peg-end thereby providing a frustoconical surface about the second peg-end,wherein the peg is inserted in the sleeve with the first peg-end opposed to the second sleeve-end, andwherein the hybrid bolt, when the peg is pulled towards the first sleeve-end, has the frustoconical surface pushing outwards the second sleeve-end which becomes thereby wedged between the frustoconical surface and the borehole wall.

2. The hybrid bolt of claim 1, further comprising a wedge ring inserted between the peg and the sleeve at the second sleeve-end, wherein pulling the peg towards the first sleeve-end wedges the wedge ring between the peg and the sleeve.

3. The hybrid bolt of claim 2, wherein the wedge ring comprises a longitudinal groove parallel to the slit of the sleeve.

4. The hybrid bolt of claim 2, wherein the wedge ring comprises an outwardly extending lip adapted to abut against the second sleeve-end when the peg is pulled towards the first sleeve-end.

5. The hybrid bolt of claim 2, wherein the wedge ring comprises a longitudinal body extending within the sleeve, the longitudinal body having a variable thickness increasing towards the first sleeve-end.

6. The hybrid bolt of claim 1, wherein the sleeve has an external diameter decreasing towards the second sleeve-end.

7. The hybrid bolt of claim 1, wherein the slit is extending from the first sleeve-end to the second sleeve-end.

8. The hybrid bolt of claim 7, wherein the slit narrows towards the second sleeve-end.

9. The hybrid bolt of claim 1, wherein the sleeve comprises a key groove.

10. The hybrid bolt of claim 9, wherein the key groove extends from the first sleeve-end, and the peg comprises a body and a key protruding from the body, wherein the key is adapted to take place in the key groove.

11. The hybrid bolt of claim 10, further comprising an abutting ring slidingly mounted to the first sleeve-end.

12. The hybrid bolt of claim 11, wherein the abutting ring comprises a slit.

13. The hybrid bolt of claim 12, wherein the key has a key-width transversal to the peg, and the slit of the abutting ring has a slit-width transversal to the peg narrower than the key-width.

14. The hybrid bolt of claim 11, wherein the abutting ring is adapted to slide into the sleeve.

15. The hybrid bolt of claim 10, wherein the peg comprises a weakness between the first peg-end and the second peg-end, wherein the weakness induces a foreseeable location for a breaking point to the peg.

16. The hybrid bolt of claim 15, wherein the weakness consists in one of a hole, of a shaving, of a groove, and of threading.

17. The hybrid bolt of claim 15, wherein the weakness is located between the key and the second peg-end.

18. The hybrid bolt of claim 1, wherein the peg comprises a threaded portion extending from the first peg-end towards the second peg-end over a partial length of the peg.

19. The hybrid bolt of claim 1, wherein the peg comprises a body, and a key protruding from the body, and a threaded portion extending between the first peg-end and the key.

20. The hybrid bolt of claim 11, further comprising a mounting nut adapted to be mounted to the peg, the mounted nut adapted to butt off against the abutting ring, pushing the abutting ring inside the sleeve.