Abstract:
In one aspect of the invention, an apparatus and related methods for installation in a borehole formed in a face of a mine passage comprises an elongated bolt including a spiral shaft portion for positioning in the borehole. A hardened, stationary resin nut formed in only part of the borehole, preferably spaced from the distal end thereof, receives the spiral shaft portion of the bolt. Consequently, rotation of the spiral shaft portion within the hardened resin nut serves to move the bolt within the borehole, such as for purposes of tensioning.

Description:
This application claims the benefit of U.S. Provisional Patent App. Ser. No. 60/724,683, filed Oct. 7, 2005, the disclosure of which is fully incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present inventions relate generally to providing support for a face of a passage in a geological structure and, more particularly, to a tensionable spiral bolt associated with a resin nut partially occupying a borehole and related methods. 
     BACKGROUND OF THE INVENTION 
     In recent decades, a number of proposals for supporting the face of a passage in a geological structure, such as the roof in an underground mine, have been made. The typical arrangement employs an anchor, such as an elongated roof “bolt,” that extends into a borehole formed in the face. Federal regulations pertaining to underground mine safety require the placement of these bolts at frequent intervals throughout the mine passage. Consequently, ease of manufacture and use are critical factors in terms of reducing the overall installation cost to the mine owner (which directly correlates to the profitability of the mining operation). 
     Of course, one of the major areas for lowering the manufacturing cost and installation time for such bolts involves reducing the diversity, complexity, and overall number of the parts required. This includes eliminating the need for specialized expansion shells, external nuts, or other attachments to the bolt required in the past to effect proper tensioning. Extensive processing of the bolt shaft typically necessary for accommodating these types of expansion shells or external nuts should also be eliminated, since this activity not only increases manufacturing time and expense, but also tends to weaken the bolt and the resulting assembly. 
     Accordingly, a need exists for an improved bolting apparatus that overcomes the foregoing limitations of the prior art. Specifically, the bolt should be easy and inexpensive to manufacture and install. The bolt would be also be tensionable to compress and provide secure, reliable support for the adjacent strata once installed. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the invention, an apparatus for installation in a borehole formed in a face of a mine passage is disclosed. The apparatus comprises an elongated bolt including a spiral shaft portion for positioning in the borehole. A stationary, hardened resin nut is formed in a portion of the borehole for surrounding at least part of the spiral shaft portion of the bolt. Rotation of the spiral shaft portion within the resin nut thus serves to move the bolt within the borehole, such as during tensioning. 
     In one embodiment, the spiral shaft portion comprises a generally square cross section, and may include approximately 1-2 twists for about every foot in the longitudinal direction. To facilitate rotation within the resin nut, at least part of the spiral portion may include a lubricity or rust-inhibiting agent. Preferably, a colored agent is also applied along at least part of the spiral shaft portion to allow for identification of the bolt for use with the resin nut. 
     The bolt may include a head end and a tail end as well. The tail end for advancing into the borehole may include a taper or point. Preferably, the construction of the bolt is such that it is formed of a single piece of material. A flange may also be provided adjacent the head end, with one side for engaging a plate or like structure adjacent the mine face and the opposite side providing a bearing surface for a device or means for rotating the bolt. 
     In accordance with a second aspect of the invention, an apparatus for installation in a borehole formed in a face of a mine passage is disclosed. The apparatus comprises an elongated bolt including a portion, such as for example a spiral portion, for positioning in the borehole. A stationary, hardened resin nut is also provided for receiving a portion of the bolt. The apparatus further includes means for rotating the bolt relative to the hardened resin nut, preferably in the form of a drill head. 
     In accordance with a third aspect of the invention, an improvement is proposed for use in a borehole formed in a face of a mine passage for receiving a bolt having an elongated shaft for extending into the borehole. The improvement comprises a resin nut formed in a portion of the borehole and having an internal thread surrounding only a portion of the shaft. Preferably, the shaft of the bolt is spiral, whereby rotating the spiral shaft relative to the internal thread serves to tension the bolt. 
     In accordance with a fourth aspect of the invention, a roof bolt is proposed for insertion in a borehole formed in a face of a mine passage. The bolt comprises a shaft having a spiral portion at least partially having a coating selected from the group consisting of a lubricity agent, a rust-inhibiting agent, a colored agent and mixtures thereof. Preferably, the coating is at a distal end of the shaft having a point for insertion in the borehole. 
     In accordance with a fifth aspect of the invention, a method of tensioning a bolt including a spiral shaft portion in a borehole formed in a face of a mine passage is disclosed. The method comprises forming a stationary, hardened resin nut adjacent at least the spiral shaft portion of the bolt. The method further comprises rotating the spiral shaft portion relative to the hardened resin nut. 
     Preferably, the forming step comprises: (1) providing uncured resin within the borehole adjacent the spiral shaft portion of the bolt; (2) rotating the bolt in a first direction to substantially maintain the resin adjacent the spiral shaft portion; and (3) allowing the resin to substantially cure and form the hardened resin nut. Likewise, the step of rotating the bolt preferably comprises rotating the spiral shaft portion in a second direction opposite the first direction upon the substantial curing of the resin. In any case, the method may further include the step of applying a lubricity or rust-inhibiting agent to at least part of the spiral shaft portion. 
     In accordance with a fifth aspect of the invention, a method of installing an elongated bolt having a head end and a threaded or spiral portion in a face of a mine passage having a borehole is disclosed. The method comprises inserting the bolt at least partially within the borehole with the head end spaced from the opening. The bolt is rotated in a first direction and at least partially within an uncured resin within the borehole, and the resin is allowed to substantially cure and form a nut. The bolt is rotated in a second direction opposite the first direction such that the bolt moves through the resin nut with the head end moving closer to the opening of the borehole. Preferably, the head end of the bolt is initially spaced from the open end of the borehole, and the step of rotating the bolt in the second direction advances the head end of the bolt toward the open end of the borehole. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevational view, not to scale, of one possible embodiment of a roof bolt with a spiral portion; 
         FIGS. 1   a  and  1   b  are cross-sections taken along lines  1   a - 1   a  and  1   b - 1   b  of  FIG. 1 , respectively; 
         FIGS. 2-4  are schematic diagrams showing the manner in which the spiral bolt of  FIG. 1  may be tensioned using a resin nut formed in the borehole. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference is now made to  FIG. 1 , which illustrates one embodiment of a bolt  10  for installation in a face F of a mine passage, such as the roof (see  FIG. 2 ) having a borehole H formed vertically therein. Although the bolt  10  and related installation method are described as being used to reinforce and sustain a mine roof, it should be understood that the present invention may be applied to support any one of the other faces of the passage (e.g., a rib) or a different type of geological structure, without limitation. 
     As illustrated, the bolt  10  is preferably an elongated, one-piece structure comprising a head end  10   a , an elongated body or shaft  10   b , and a tail end  10   c . As perhaps best understood with combined reference to  FIGS. 1 and 1   a , the head end  10   a  is adapted for being engaged by a wrench, chuck of a drill head (see  FIG. 2 ), or like device or means for rotating the bolt  10  during installation. Despite being shown as having a portion with a generally square cross-section ( FIG. 1   a ), it should be appreciated that the head end  10   a  of the bolt  10  may take on other cross-sectional shapes (e.g., hexagonal) without impacting the practice of the present invention in any meaningful way. An annular flange  11  is also provided adjacent the head end  10   a  to provide a bearing surface for the means for rotating on one side and the face or intervening structure (such as plate P; see  FIG. 2 ) on the other. 
     In accordance with one aspect of the invention, the shaft  10   b  of the bolt  10  is generally square in cross-section (see  FIG. 1   b ), but is “twisted” along its length to form a spiral or helix. In the illustrated, preferred embodiment, the spiral extends along the entire length of the shaft  10   b  and is left-handed in nature (but could be the opposite as well). Although the number of spirals (twists) per foot (or pitch) of the bolt  10  is not essential to practice of the invention, the arrangement is preferably coarse in nature. For example, each foot of the spiral shaft  10   b  preferably includes between about 1 to 2 complete (e.g., 360°) twists. Most preferably, each complete twist occupies about seven inches of distance in the longitudinal direction, or length, which corresponds to about 1.7 complete twists per linear foot. 
     While it is easier in terms of manufacturing to provide a consistent spiral continuously along the entire length of the shaft  10   b  (such as by simply twisting square bar stock), it will be understood upon reviewing the description that follows that the spiral may be provided along only a portion of the shaft  10   b  (preferably, in such case, along the tail end  10   c , or otherwise away from the head end  10   a ). Alternatively, and especially in cases where the spiral shaft  10   b  is less than one foot in length, the pitch could instead be considered as the thread-to-thread spacing, as is conventional. Using this gauge, the thread-to-thread pitch is preferably greater than ⅞ths of an inch and, most preferably, about two inches (or, stated another way, the spiral repeats in the linear direction about every two inches). 
     Reference is now made to  FIG. 2 , which although not drawn to scale, illustrates schematically the manner in which the bolt  10  of  FIG. 1  is installed in the borehole H. Specifically, the tail end  10   c  of the bolt  10  is inserted through the opening O of the borehole H, which is preferably formed having a diameter close to the width M of the spiral shaft  10   b  (e.g., ¾″ for a 1 inch diameter borehole). The borehole H also preferably has a depth D greater than at least the spiral shaft  10   b , and preferably greater than the length of the entire bolt  10  (e.g., dimension B in  FIG. 1 ) by at least one inch. 
     Using a lift boom associated with a bolting machine or like structure, the bolt  10  is advanced into the borehole H such that the head end  10   a  remains spaced from the adjacent face of the roof a distance equal to or slightly less than the excess depth D of the borehole H (e.g., about two inches). As shown in phantom in  FIG. 2 , a plate P is typically associated with the head end  10   a  of the bolt  10 , and would thus also be spaced from the face F. However, once the bolt  10  is tensioned in the manner described below, this plate P engages the face F and compresses the associated strata (see  FIG. 4 ). 
     Once the bolt  10  is partially inserted, uncured resin (also sometimes referred to as “grout”) is provided adjacent at least a portion of the spiral shaft  10   b  in the associated annulus (which is shown in  FIG. 2  as being greatly oversized for purposes of illustration, but is normally only about ⅛″-¼″ on either side). Most preferably, the uncured resin occupies the annulus adjacent the tail end  10   c  of the bolt  10 , and in the upper portion of the borehole H. Although the uncured resin may be provided from a remote source, such as by way of injection, it is most preferably supplied in the for of a frangible cartridge (not shown), or resin “sausage” in the vernacular. Typically, this type of cartridge is pre-installed in the borehole H and ruptured during insertion of the bolt  10 , thus causing a quick-curing resin to occupy the surrounding borehole H. This “grout” usually comprises two materials (e.g., polyester resin and a catalyst paste) that make contact and react only upon the rupturing of the cartridge. Upon being thoroughly mixed, such as by the rotation of the bolt  10  within the borehole H, the resin then quickly hardens. The hardened resin or grout thus serves to hold the bolt  10  securely within the borehole H. 
     In accordance with another aspect of the invention, the bolt  10  with the spiral shaft  10   b  at least partially surrounded by uncured resin is rotated to effect the desired mixing and/or hardening, such as by using any conventional type of bolting machine. In the illustrated embodiment in which the spiral is left-handed in nature, the rotation is in the opposite, or right-handed, direction (see action arrow R in  FIG. 2 ). Preferably, this rotation is done without simultaneously advancing the bolt  10  within the borehole H any significant amount, such that it remains spaced from the opening O of the borehole H. 
     As should be appreciated, this rotation in combination with the spiral shaft  10   b  serves to create a “pumping” action that substantially holds the uncured resin in place, and may possibly advance or “push” this resin deeper within the borehole H. In other words, the spiral shaft  10   b  of the bolt  10  may essentially function as an auger or screw with flights that maintain the resin at a particular location within the upper end of the borehole H. In any case, the rotation of the spiral shaft  10   b  preferably is such that it prevents the uncured resin from advancing toward the opening O of the borehole H to any significant degree. As a result of this pumping action, once the resin sets or cures (normally, after a period of rest post-mixing), it surrounds only a portion of the spiral shaft  10   b  within the borehole H. The amount of resin supplied will of course depend on the relative sizes of the spiral shaft  10   b  and the borehole H, but is preferably sufficient to cover about 12-18 inches of the shaft  10   b  adjacent the tail end  10   c  or otherwise away from the head end  10   a  (which, of course, still remains spaced from the opening O of the borehole H). 
     Once the resin sets or cures (which normally takes only seconds after mixing), a stationary, hardened resin “nut”  12  is thus formed around at least a portion of the spiral shaft  10   b  in the borehole H. As should be appreciated, this resin nut  12  has an internal thread matching the spiral thread of the adjacent shaft  10   b  and occupied by it. In the case of the left-handed spiral, the bolt  10  may be rotated in a direction opposite the first direction (note action arrow L) and in the same direction as the spiral. The engagement between the spiral shaft  10   b  and the resin nut  12  causes the bolt  10  to advance within the borehole H when so rotated, thus moving the head end  10   a  closer to the adjacent opening O. However, the hardened resin nut  12  remains stationary due to the peripheral contact with the sidewall of the borehole H. 
     This rotation may be completed until any associated engagement hardware, such as a plate P, is brought into secure engagement with the face F (which normally will take less than one complete turn). The appropriate amount of torque is then applied to ensure that the bolt  10  is fully tensioned and the strata compressed or anchored in the desired manner. As noted above, the depth D of the borehole H is made at least slightly greater than the overall length B of the bolt  10  such that the tail end  10   c  can freely advance and does not “bottom out” during the final advance caused by tensioning. 
     Numerous advantages may thus arise from the use of the above-described technique. First of all, the bolt  10  in the preferred embodiment may be made of only one piece of material, and need not include any expansion shells, external nuts, or surface working (e.g., fine threads cut into the surface of the bolt) in order to be effective. Accordingly, no parts require assembly “on-site.” This not only substantially reduces the manufacturing cost, but also facilitates ease of installation and results in a stronger bolt. 
     Additionally, only partial grouting of the borehole is required for effectively practicing the present invention. Thus, substantially less grout is required, as compared to arrangements in which the borehole is fully grouted. A concomitant savings in material cost invariably results (possibly as much as 75%), as well as a reduction in the cost of transporting the grout into the mine and maintaining it in a “ready for use” state. 
     The completed installation of the bolt  10  also advantageously results in the head end  10   a  being positioned extremely close to face F of the mine roof (see  FIG. 4 ). Thus, unlike prior arrangements in which an external nut is threaded onto an exposed shank projecting several inches from the face F, there is very little depending structure of the installed bolt  10  to engage a passing machine or person. This is especially important in narrow mine passages resulting from a low seam height. Moreover, since essentially the entire shaft  10   b  of the bolt  10  is drawn into the borehole H, the overall appearance of the face F is more regular and aesthetically pleasing. 
     Finally, aside from being one piece, the bolt  10  can be manufactured in a relatively easy and inexpensive manner. Standard square bar stock of any suitable width dimension (e.g., ½″, ⅝″, or ¾″ for a 1″ borehole) can simply be forcibly twisted to the desired pitch (whether considered twists per foot, or thread-to-thread spacing) to form the shaft  10   b . The head end  10   a  is typically forged. Conveniently, the twisting can also be completed on a relatively long piece of stock, which can then be cut into lengths corresponding to the shaft  10   b  of the bolt  10 . 
     During manufacturing, the twisting of the bar (which is typically made of steel) may result in the elimination of the exterior surface oxide layer, or “scale,” created during the hot roll process. The absence of the scale allows faster oxidation of the bar, especially when the bolt  10  is stored outdoors and exposed to the elements during the period between manufacturing and ultimate use in the mine. Any deterioration of the surface may inhibit the ability of the shaft  10   b  to turn freely within the resin nut  12  during installation. 
     To ameliorate any such problem, it is possible to coat at least part of the spiral shaft  10   b  (such as the uppermost portion) after manufacture with either a lubricity agent or a rust-inhibiting agent, or both. The partial or full application of such agent(s) is anticipated to ease the installation by allowing the spiral shaft  10   b  to rotate more freely relative to the resin nut  12  during tensioning. Providing any coating agent with a coloring (e.g., a yellow pigment) is also contemplated. As a result, the installer may not only ensure that the coating remains present on an appropriate portion of the shaft  10   b , but also can readily differentiate the spiral bolts  10  for use in the present method from others. 
     During installation, it may also sometimes result that the resin cures not only along a portion of the spiral shaft  10   b , but also within the portion of the borehole H into which the bolt  10  must advance during tensioning (see dashed line Z in  FIG. 4 ). Although this does not preclude installation, it may be helpful to make the tail end of the bolt  10  with a point or taper, as shown. This will help it advance within the resin nut  12 , if such is necessary. 
     Although the pitch of the spiral may be varied, it is also desirable to ensure that the spiral bolts  10  for use in a common installation are consistent. This keeps the installation torque required consistent. Likewise, the spiral shaft  10   b  should also be consistent to facilitate its movement through the resin nut  12  once formed. The pitch of the spiral is also preferably such that there is noticeable movement of the head end  10   a  toward the opening O of the borehole H during installation, thus giving the installer a visual cue that the process is proceeding as expected. 
     The use of conventional types of washers, such as those made of, or coated, with TEFLON or other anti-friction types, is also possible between the head end  10   a  (or flange  11 ) and any associated structure (such as plate P). However, it is believed that the use of such anti-friction washers is less important with this type of arrangement than with conventionally threaded bolts, since conventionally threaded bolts require many revolutions for installation, resulting in greater friction and heat, and less effective tension/torque ratios. 
     The foregoing description of embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The present embodiments were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention.