Frictional mining bolt

A system for mine roof reinforcement includes a bearing plate and a tubular member with an inner surface, an outer surface, first and second free ends, and an enlarged portion disposed proximate one of the free ends. The system also includes a projectile and an insertion member for being received in the tubular member. In addition, a method for inserting a bolt in rock includes: forming a borehole in rock; placing a bearing plate with an opening therein against the rock so that the opening is aligned with the borehole; disposing a tubular member in the borehole and opening so that an enlarged end of the tubular member abuts the plate; and mechanically expanding the tubular member so that an outer wall thereof frictionally engages the rock.

FIELD OF THE INVENTION

The invention is related to a mining bolt and methods of use thereof. In particular, the invention is related to a frictional system for mine roof reinforcement.

BACKGROUND OF THE INVENTION

It is a well established practice in underground mining work, such as coal mining, tunnel excavation, or the like, to reinforce the roof of the mine to prevent its collapse. There are various types of reinforcement apparatus, the most common are of the mining bolt type. Various designs of ming bolts are known.

Split-Set® by Ingersoll-Rand is a mining bolt which is comprised of a c-shaped metal member which is forced into a bore hole and supports the rock by friction. The hollow shape of the Split-Set® bolt allows the bolt to deform rather than break when a rock shift occurs.

Swellex® by Atlas Copco, Inc. of Sweden is a hollow folded c-shaped tube which hydrostatically expands in the bore hole by means of high pressure water. During the swelling process, the Swellex® bolt adapts to fit the irregularities of the bore hole. The hollow shape allows the tube to deform during rock shifts. Unfortunately, the complex shape of the Swellex® mining bolt is expensive to manufacture. Further, the necessary high pressure water tools and fittings add to the expense and complexity of the method.

Spin-Lock® by Williams Co. discloses a rock bolt which has a hollow interior and has open ends for allowing grout to be pumped therethrough. No resin cartridges are disclosed.

Despite these developments, there exists a need for improved mining bolts and methods of use thereof.

SUMMARY OF THE INVENTION

The invention relates to a method for inserting a bolt in rock including: forming a borehole in rock; placing a bearing plate with an opening therein against the rock so that the opening is aligned with the borehole; disposing a tubular member in the borehole and opening so that an enlarged end of the tubular member abuts the plate; and mechanically expanding the tubular member so that an outer wall thereof frictionally engages the rock. The tubular member may have a modulus of elasticity that is greater than a bulk modulus of elasticity of the rock. The method may further include: removing the projectile from the tubular member after expansion thereof. The method may also include one or more of: placing the tubular member in axial tension when the outer wall thereof frictionally engages the rock; disposing a projectile proximate the enlarged end of the tubular member; contacting the projectile with an insertion member; inserting the insertion member into the tubular member to force the projectile into the tubular member; forcing the projectile proximate a free end of the tubular member opposite the enlarged end; and removing the insertion member from the tubular member. In some embodiments, the method additionally may include one or more of: lubricating at least one of the projectile and internal wall of the tubular member; closing the enlarged end of the tubular member; and mechanically coupling the tubular member to the rock.

The tubular member may frictionally engage the rock with an interfacial anchorage strength of between 100 psi and 1000 psi, and may engage the rock with an anchorage strength of between 200 psi and 1000 psi. The tubular member may be mechanically expanded by forcing a projectile against an internal wall of the tubular member. A force of less than 20,000 pounds may be exerted on the projectile to force the projectile to travel in the tubular member, and the force may be between 3,000 pounds and 15,000 pounds. In some embodiments, a force of between 4,000 pounds and 10,000 pounds is exerted on the projectile to force the projectile to travel in the tubular member.

The projectile may be generally spherical in shape, or may have a generally tapered head portion and a generally elongated body portion. The borehole may have a first length and the tubular member may be disposed in a portion of the first length. The tubular member may be mechanically coupled to the rock, for example, by forcing a protruding portion of the tubular member into the rock and/or by a deformable layer disposed on the outer wall. The deformable layer may include sprayed metal and/or a polymer.

A clearance of between 0 inch and 0.2 inch may be formed between the tubular member and borehole prior to expansion of the tubular member. In some embodiments, a clearance of between 0.01 inch and 0.1 inch is formed between the tubular member and borehole prior to expansion of the tubular member.

The invention further relates to a system for mine roof reinforcement including a bearing plate and a tubular member with an inner surface, an outer surface, first and second free ends, and an enlarged portion disposed proximate one of the free ends. The system also includes a projectile and an insertion member for being received in the tubular member. The projectile may be generally spherical. In some embodiments, the projectile and insertion member are integrally formed. The projectile may be generally tapered and the insertion member may be generally elongated. The inner surface of the tubular member may define a first inner diameter or contour that is smaller than an outer diameter of the projectile. The tubular member may be formed of steel.

The outer surface of the tubular member may be textured, may have protrusions thereon, and may be coated with a polymer, elastomer, and/or roughening agent. A fiber-reinforced polymer may be disposed on the outer surface of the tubular member.

At least one of the projectile and the inner surface of the tubular member may be coated with a lubricant. In some embodiments, a lubricant is impregnated in the projectile.

The projectile may have a diameter between about 0.75 inch and 1.5 inch, and in some embodiments the projectile may have a diameter between about 1 inch and 1.375 inch. The inner diameter of the tubular member may be between 70 and 97 percent of the outer diameter of the projectile. In some embodiments the inner diameter of the tubular member is between 85 and 97 percent of the outer diameter of the projectile, and the inner diameter of the tubular member may be between 90 and 97 percent of the outer diameter of the projectile.

The tubular member may have a substantially uniform outer diameter. The outer surface of the tubular member may have a substantially circular cross-section. The tubular member may have at least one generally linear projection extending along the inner surface between the free ends. The at least one projection may be a weld line.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIG. 1, there is shown an exemplary system10for mine roof reinforcement according to the present invention, partially secured in a borehole12in rock14. System10includes bearing plate16with an opening16a, tubular member18, and projectile20. Tubular member18has an inner surface22defining an opening22a, outer surface24and a first free end26a. An enlarged portion28is disposed proximate free end26. Prior to travel of projectile20in tubular member18, a clearance or gap30preferably is disposed between tubular member18and rock14. After travel of projectile20, tubular member18is deformed such that clearance30is decreased. Preferably, enlarged portion28is integrally formed in tubular member18, and is circumferentially disposed about tubular member18. In some embodiments, an increase in the inner diameter of tubular member18is realized proximate enlarged portion28. However, in alternate embodiments, enlarged portion28comprises a circumferential protrusion, or a flange that may form free end26a. In addition, enlarged portion28need not extend about the entire circumference of tubular member18, but may comprise one or more projections for abutting bearing plate16.

Tubular member18preferably is formed of tube having a modulus of elasticity that is greater than a bulk modulus of elasticity of rock14. In the preferred embodiment, tubular member18is formed of steel (welded or seamless), however in alternate embodiments tubular member18is formed of other metallic materials such as aluminum or other alloys, polymer, or another deformable material. Tubular member18may also include one or more layers of a deformable material on outer surface24such as sprayed metal and/or polymer. An elastomer coating, for example, may be applied. One or both of surfaces22,24may include a protective coating such as paint for corrosion resistance. Tubular member18may have a substantially uniform outer diameter and outer surface24may have a substantially circular cross-section. In alternate embodiments, at least one of inner surface22and outer surface24may have a non-circular cross-section, such as hexagonal, square, oval or otherwise oblong.

In some embodiments, tubular member18is provided with one or more portions for mechanically coupling tubular member18to rock14to increase the interfacial strength between outer surface24and rock strata14. For example, outer surface24may be provided with texturing such as one or more helical, circumferential, or longitudinal grooves, a raised or depressed waffle pattern, dimples, a raised weld for example in a spiral pattern, or combinations thereof. The raised weld instead may form at least one generally linear projection extending along the inner and/or outer surfaces22,24, respectively, between free ends26a,26b. Protrusions may also be formed on outer surface24such as small weld spatters for example in the form of raised hemispheres. In yet another alternate embodiment, portions of tubular member18may be pierced or otherwise punched through, so that some of outer surface24extends outward for locking into rock14. Surface roughening may also be in the form of holes drilled into the wall of tubular member18. Various surface treatments may be used to roughen outer surface24, such as shot peening or other deformation techniques. In addition, outer surface24may be painted or otherwise coated with a roughening agent such as a polymer coating that includes glass beads, sand, or metal particles. A polymer reinforced with glass fiber, for example formed with polyesters, may be disposed on outer surface24.

Projectile20preferably is formed of solid, hardened steel, however in alternate embodiments projectile20may be hollow and may be formed of other suitable materials as described with respect to tubular member18. In one preferred exemplary embodiment, projectile20is generally spherical in shape. Advantageously, a spherical projectile20is symmetrical and thus orientation of projectile20is not important during assembly of system10. However, any shape of projectile20that permits suitable expansion of tubular member18may be used. In an exemplary embodiment, projectile20has an outer diameter between about 0.75 inch and 1.5 inch; more preferably, projectile20has an outer diameter between about 1 inch and 1.375 inch. In alternate embodiments, as shown for example inFIG. 1A, a projectile20amay instead be provided with a generally tapered head portion21a(such as a conical shape) and a generally elongated body portion21b, which may be integrally formed. In yet another alternate embodiment, shown inFIGS. 1B and 1C, tapered head portion21aof projectile20amay include linear projections21cor splines disposed thereon for mechanically coupling projectile20ato tubular member18. Other shapes such as hemispheres also may be used for projectile20.

In an exemplary embodiment, the inner diameter of tubular member18is between 70 and 97 percent of the outer diameter of projectile20. More preferably, the inner diameter of tubular member18is between 85 and 97 percent of the outer diameter of projectile20, and may be between 90 and 97 percent thereof.

Turning toFIG. 2, system10is shown prior to anchoring in rock14. A borehole12is formed in rock14, and bearing plate16is placed against rock14such that opening16ais aligned with borehole12in rock14. Tubular member18is inserted in opening16aand borehole12, so that enlarged end28of tubular member18abuts plate16. As shown for example inFIG. 2, borehole12may extend along a first overall longitudinal length and tubular member18may be disposed in a portion of that length. In an exemplary preferred embodiment, a clearance of between 0 inch and 0.2 inch preferably is formed between the tubular member and borehole prior to expansion of the tubular member, and more preferably the clearance is between 0.01 inch and 0.1 inch. The clearance is selected so that tubular member18may be inserted in borehole12by hand or with a roof-bolting machine, as known in the art, and is also a function of the type of rock strata14.

Projectile20is disposed proximate enlarged end28for insertion into opening22a. Inner surface of tubular member18preferably defines an inner diameter or contour that is smaller the largest outer diameter of projectile20. Thus, projectile20and tubular member18are configured and dimensioned so that when projectile20travels along the length of tubular member18, at least a portion of projectile20has a greater width than opening22a, so that the width of opening22amay be expanded to at least frictionally engage surrounding rock14.

A lubricant31may be disposed between projectile20and inner surface22of tubular member18to facilitate travel of projectile20by reducing friction. Lubricant31may be in the form of a coating on at least one of the projectile and the inner surface of the tubular member. In some embodiments, a lubricant is impregnated in projectile20. For example, projectile20may be formed of a material that is oil-impregnated, such as oil-impregnated brass used to form bearings. In other embodiments, lubricant may be coated on a portion or all of inner surface22. Suitable surface coatings include Teflon® (PTFE), galvanizing, and/or grease.

As shown inFIG. 3, an insertion member32may be coaxially aligned with opening22ain tubular member18, with a distal end32athereof configured and dimensioned to abut projectile20. Preferably, insert member32has an outer width less than the inner width defined by inner surface22of tubular member18. In the preferred embodiment, distal end32ais generally flat, but in alternate embodiments distal end32amay be concave, convex, or otherwise shaped for engaging projectile20. Proximal end32bof insertion member32may be enlarged or otherwise configured and dimensioned to receive an external force F applied by a hammer or other device. In some embodiments, projectile20is integrally formed with insertion member32, permitting reuse thereof in expanding multiple tubular members. As can be seen inFIG. 3, application of force F to projectile20causes projectile20to travel in opening22ain tubular member18. Inner surface22of tubular member18defines a first inner diameter or contour that is smaller than an outer diameter or contour of projectile20. Thus when projectile20travels in opening22a, tubular member18is mechanically expanded so that the outer surface or wall24thereof frictionally engages rock14, as seen for example in region34.

Insertion member32preferably has a length along its longitudinal axis such that distal end32amay travel substantially along the length of opening22a, thereby permitting projectile20to travel and finally come to rest proximate second free end26bof tubular member18, where projectile20may seal opening22afor example to provide corrosion resistance. Preferably, insertion member32has a length along its longitudinal axis that is selected so that when projectile20is disposed proximate second free end26bof tubular member18, the proximal end32bof insertion member32abuts first free end26aproximate enlarged portion28. As shown inFIG. 4, substantially the entire opening22aof tubular member18has been mechanically expanded by the passage of projectile20therein.

Referring toFIG. 5, projectile20may travel within opening22asuch that projectile20comes to rest against an upper portion12aof borehole12in rock14. Insertion member32may then be removed therefrom. As a result of the expansion of tubular member18, in an exemplary preferred embodiment, tubular member18frictionally engages rock14with an interfacial anchorage strength preferably between 100 psi and 1000 psi, and more preferably between 200 psi and 1000 psi. Also, a force that is preferably less than 20,000 pounds may be exerted on projectile20to force the projectile to travel in tubular member18; more preferably, this force is between 3,000 pounds and 15,000 pounds, and most preferably the force is between 4,000 pounds and 10,000 pounds.

In a preferred method according to the present invention, borehole12is formed in rock14, and bearing plate16is placed against rock14so that the opening16ain bearing plate16is aligned with borehole12. Tubular member18is inserted in borehole12and opening16aso that enlarged end28of tubular member18abuts plate16. Tubular member18is then mechanically expanded, for example with projectile20, so that outer surface24frictionally engages rock14. Preferably, borehole12is placed in radial compression and hoop tension in the region where tubular member18has been expanded. Such radial compression and hoop tension frictionally retain tubular member18in borehole12because the bulk modulus of elasticity of rock14is lower than the modulus of elasticity of tubular member18. Advantageously, projectile20expands tubular member18against rock strata14and at the same time can effect firm contact between bearing plate6and rock strata14. Tubular member18is placed in axial tension and adjacent rock strata14in compression by a force approximately equal to the force required to effect travel of projectile20in tubular member18. Because of initial compression of rock strata14, some resistance to movement of rock strata14is conferred.

Initially, projectile20may be disposed proximate enlarged end28of tubular member18, and in order to force projectile20into tubular member18, the projectile20may be pushed by insertion member32. Projectile20may be forced through tubular member18to rest proximate free end26bopposite enlarged end28, and then insertion member18optionally may be removed from tubular member18. Also, after expansion of tubular member18, the projectile20optionally may be removed from tubular member18. In addition, at least one of projectile20and inner surface22of tubular member18may be lubricated. Further, enlarged end28may be sealed. Tubular member18also may be mechanically coupled to rock14, for example with projections such as small weld spatters disposed on outer surface24.

As known in the art, a suitable mine roof bolting machine may be used to apply the force needed to propel projectile20in tubular member18. Such machines typically are able to exert forces of at least 10,000 lbs. Alternatively, the necessary force may be exerted by a percussion hammer.

Experimentation was performed to determine the performance of tubular type frictional mining bolts such as those disclosed herein. To simulate the rock found in a mine roof, concrete was prepared using 3 parts limestone gravel, 2 parts silica sand, 1 part Portland cement, and suitable water to create a flowable mixture. The concrete was poured into a pipe100with a flange102coupled to an upper free end100athereof with a circumferential weld104. Pipe100had a longitudinal length L1of about 6 inches (152 mm) and an inner diameter L2of about 6 inches. Flange102had a thickness L3of about ¼ inch (6 mm), and was provided with a central through hole102afor receiving a tubular member, as will be described. Thus, the total longitudinal length of concrete section106was about the same as longitudinal length L1of pipe100, or 6 inches (152 mm), with concrete section106extending to lower free end100bof pipe100.

To test boreholes108of different diameters, DB, solid aluminum bars were machined to 1.260, 1.275, and 1.290 inch (32.0, 32.39, and 32.77 mm, respectively), and were centrally disposed in wet concrete section106. Following curing of wet concrete section106for 4 hours, the aluminum bars were removed and concrete section106was permitted to cure for a minimum elapsed time of 14 days prior to testing.

Welded steel tube110with upper and lower ends110a,110b, respectively, was initially provided with an outer diameter of 1.255 inch (31.88 mm), a wall thickness of 0.093 inch (2.36 mm), and a length L4of 10 inches was used to simulate tubular type frictional mining bolts such as those disclosed herein. Tube110was disposed in borehole108such that a length L5of tube110of about two inches (51 mm) extended beyond each of free ends100a,100b. Central through hole102ain flange102had a diameter of 1.375 inch, so that flange102would not interfere with expansion of tube110. Lower end100bof tube110was swaged along a length L6of about 0.75 inch, and a reinforcing collar112was coupled thereto. Additionally, a weld114was placed in the inside of tube110to partially close lower end110b. The swaging and welding of lower end110bensured that a projectile116traveling from upper end110ato lower end110bcould not exit tube110at lower end110b. Performance testing was undertaken using a universal compression testing machine.

In a first “insertion force” test, a spacer (not shown) with a thickness of about 1.75 inch was placed under concrete section106and abutting flange102so that lower end110bof tube100abutted a bottom platen of the universal compression testing machine. A spherical projectile116in the form of a steel ball having an outer diameter of 1.125 inch was forced into upper end110aof tube110at a rate of about 0.1 inch/minute. Grease was provided between the surface of projectile116and the inner surface of tube108to facilitate movement of projectile116in tube108. The grease was a multipurpose synthetic material with molybdenum-based additives. An insertion member (not shown) in the form of a steel bar having an outer diameter of 1 inch was aligned so that its central longitudinal axis was generally coaxial with the central longitudinal axis of tube110; one end of the steel bar abutted a top platen of the universal compression testing machine, while the other end abutted projectile116. The force FTrequired to push projectile116through the first two inches of tube110proximate upper, unconfined end110awas first measured. Next, the force FCrequired to push projectile116through the section of tube110confined in concrete section106was measured as projectile116traveled toward lower end110bunder the force conferred by the insertion member. When projectile116reached the swaging at lower end110b, the force applied by the universal compression testing machine was stopped.

In a second “anchorage strength” test, a spacer (not shown) with a thickness of about 2.75 inches was placed under concrete section106and abutting flange102so that a gap of about 1 inch was created between lower end110bof tube100and the bottom platen of the universal compression testing machine. With projectile116disposed near the swaging at lower end110b, and with grease provided as described above, a force was again applied by the universal compression testing machine. Initially, until projectile116reached the swaging at lower end110b, the force was about the same as force FT. When projectile116reached the swaging reinforced by collar112at lower end110b, however, a sharp increase in force occurred and the maximum anchorage force FAwas measured when tube110began to slip from concrete section106.

Table I below lists exemplar test data:

TABLE ITestClearanceDBFTFCFANo.(in.)(in.)(lbs.)(lbs.)(lbs.)10.0051.2603,0006,20027,00020.0051.2603,5007,50022,00030.0201.2753,5006,50023,00040.0201.2753,5005,50018,00050.0351.2903,2004,3001,50060.0351.2903,5005,20021,000
As listed in Table I, forces FT, FC, and FAwere the maximum such forces experienced during each test, while the listed clearance was the clearance between the outer surface of tube110and the wall of borehole108. In addition, the force FTvaried plus or minus about 500 lbs. during initial insertion of projectile116.

During test number 6, the outer surface of tube110was roughened by providing approximately 200 small weld spatters (about 0.015 inches high and about 0.060 inches wide) thereon.

The measured outer diameter of tube110after travel of projectile116therein was 1.322 inches.

As a result of the tests described above, it was determined that the maximum anchorage force FAwas quite high for all tested borehole/tube combinations except test number 5 which had a DBof 1.290 inches and a smooth outer surface of tube110. It was also determined that it is desirable to have at least 20,000 lbs. strength per foot of anchorage, which was achieved in the testing with only 6 inches of contact between tube110and concrete section106. Concomitantly, by roughening the outer surface of tube110as described above for test number 6, a dramatic improvement was realized in anchorage strength from 1,500 lbs. to 21,000 lbs. Finally, the required forces FT, FCwere reasonably small and well below the desired maximum of 10,000 lbs.

While various descriptions of the present invention are described above, it should be understood that the various features can be used singly or in any combination thereof. Therefore, this invention is not to be limited to only the specifically preferred embodiments depicted herein.

Further, it should be understood that variations and modifications within the spirit and scope of the invention may occur to those skilled in the art to which the invention pertains. For example, although an upset of flared proximal end32bof insertion member32may be provided to provide suitable surface area to ensure sufficient contact with projectile20, as has been described, in alternate embodiments such a head portion may not be necessary. For example, in some embodiments, projectile20may be pre-inserted and retained in tubular member18, for example proximate flared portion28. A user then may only need to use a tubular insertion member of smaller outer diameter than tubular member18to ram projectile20. In addition, free end26aof tubular member18proximate enlarged portion28may be sealed with a mechanical cap, or alternatively, the wall of tubular member18proximate free end26amay include holes so that hooked objects may be hung therefrom. In yet another alternate embodiment, tubular member18may be provided without an enlarged portion28, and an integrally formed projectile and insertion member may be inserted into tubular member18. In such a case, a flared proximal end32bof insertion member32may be provided to abut bearing plate16to retain plate16against rock14. The system also includes a projectile and an insertion member

Accordingly, all expedient modifications readily attainable by one versed in the art from the disclosure set forth herein that are within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention is accordingly defined as set forth in the appended claims.