Patent Publication Number: US-8967916-B2

Title: Mine roof support apparatus and system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/482,851, entitled “Mine Roof Support Apparatus and System,” filed May 5, 2011, which application is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention is directed to a roof support system, and more particularly to a mine cable roof bolt system with a cable portion and a perforated grout tube for distributing grout in a cable bore hole. 
     BACKGROUND OF THE INVENTION 
     Cable systems and cable-type roof bolts have been used in the mining industry to reinforce the mine roof and prevent its collapse. Cable systems generally include a shank formed of a multi-strand cable and a barrel and wedge assembly secured to the cable to provide the necessary support after tensioning or support the bearing plate of the mine roof bolt assembly. The barrel and wedge assembly includes a tubular barrel with a plurality of locking wedges positioned within the barrel surrounding the cable securing the barrel and wedge assembly to the cable. 
     Cable mine roof bolts have been utilized in resin grouted applications. In resin grouted applications, the mine roof bolt is rotated to mix the resin during installation. Examples of cable mine roof bolts designed for resin grouted applications can be found in U.S. Pat. Nos. 5,230,589; 5,219,703 and 5,375,946. 
     To further support the mine roof a steel cable may be connect to the mining bolts to support the rock between the bolting sites. Various types of cabling systems have been introduced. One example is a cable bolting system that consists of a cable which is positioned into a bore hole. Bonding material is then pumped in under pressure around the cable to secure it to the rock. The bonding material must be pumped externally in a separate step after the cable is within the bore hole. The bonding material must completely fill the bore hole in order to ensure proper contact between the rock and the cable. 
     A further design for a cable-type mining support is made by Arnall, Inc. Arnall manufactures a stranded cable a length of which has an open-weave arrangement. (i.e., the strands are not tightly wound). This allows a bonding agent of cementatious grout, which is pumped into a bore hole, to penetrate into and integrate with the cable. 
     The pumping of viscous liquid grout presents challenges that are not easily resolved by the prior art grouted cable mine roof bolts. For example, the grouts used for reinforcing cable type roof bolts are generally fast-setting grouts, which can begin to block flow of grout in the roof bore hole shortly after being injected into the bore hole. In addition, lateral cracks or capillaries in the mine roof adjacent the lower rock strata may divert the pressurized fluidized grout away from the upper column of the cable bore hole, leaving a gap between the lower grouted column and the anchored wedge portion of the mine roof bolt. In many applications, the pressurization of the grout into the cable bore hole is all that is available for controlling the penetration of the grout, particularly to the upper portions of the annular column in which the cable is suspended. 
     What is needed is a method for distributing fluidized grout upwards in a vertical column that allows control of the fluid grout penetration into the full vertical column. 
     SUMMARY OF THE INVENTION 
     In one embodiment is a cable bolt apparatus for supporting a mine roof. The cable bolt apparatus includes a mechanical anchor configured to be driven into a closed end of a bore hole in a rock material. The mechanical anchor is expandable to fix the cable bolt in place in the bore hole. A flexible multi-stranded cable segment is connected at a first end to the mechanical anchor and at a second end to a drive head. A plate disposed adjacent the drive head. The drive head is rotatable to apply torque against the plate for tensioning the cable segment in the bore hole. A seal portion is disposed around the cable segment within the bore hole. A conduit extends into the bore hole for injecting a liquid grout material. At least one mixing element is configured to mix the liquid grout material within the bore hole. The conduit provides a predetermined distribution of the liquid grout material in the bore hole and the seal maintains the liquid grout material within the bore hole while the grout material solidifies and bonds with the rock material. 
     In another embodiment there is disclosed a method for installing a mine cable roof bolt in an underground mine roof for supporting the roof. The method includes the steps of a) drilling a bore hole in a mine roof; b) determining a length of a perforated tubing portion and selecting a perforation pattern for the tubing portion suitable for a predetermined distribution of grout; c) providing an elongated cable bolt and the perforated tubing portion; d) securing the perforated tubing portion to the elongated cable bolt; e) inserting the cable bolt and the perforated tubing portion into the bore hole; f) injecting liquid grout into the tubing portion under pressure; g) anchoring the cable in a closed end of the bore hole via an anchor portion; and h) mixing the resin to form an integrated mechanical anchor between the anchor portion and the resin with the mine roof rock adjacent the bore hole. 
     Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exemplary embodiment of a mine cable roof bolt. 
         FIG. 2  shows one exemplary embodiment of a method for installing a mine cable roof bolt. 
         FIG. 3  shows a stranded wire cable segment with mixing elements disposed therein. 
         FIG. 4  shows another embodiment of a mine cable roof bolt. 
         FIG. 5  shows a mixing element for grout and associated pump arrangement. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a stranded metal cable bolt  10  is shown. Cable bolt  10  includes a cable segment  14 . In one embodiment cable segment  14  may be a multi-strand cable segment constructed from steel wire strands, wire made from steel alloys, or other suitable wire material. Cable segment  14  includes a drive head  16  integrally formed or attached to one end of cable segment  14 . A backer rod  18  made from a compressed rope-like cellular foam is placed along cable segment  14  adjacent drive head  16 . A roof bolt plate  32  is positioned between drive head  16  and backer rod  18 . Backer rod  18  is compressible between roof bolt plate  32  and the mine roof surface  36  when drive head  16  is drawn up against roof bolt plate  32  during the installation process. Backer rod  18  is porous to absorb the polyurethane grout, and seal a bore hole  22  in the mine roof in which cable bolt  10  is inserted. As used herein, grout and resin both refer to polyurethane grouts, epoxy resin grouts, chemical grouts, and injection resin grouts, and similar resin/grout compounds that are well known to persons skilled in the art. 
     Polyurethane grout or other similar compounds are injected into bore hole  22  during the cable bolt installation process. A conduit or tubing portion  11  is affixed to cable segment  14  coaxially along a length of cable segment  14 . Tubing portion  11  may be affixed to cable segment  14  using conventional cable ties  15 , or alternately, using ratchet ties, straps or other suitable binding material. Cable ties  15  retain tubing portion  11  in position adjacent cable segment  14  when cable bolt  10  is inserted into bore hole  22 . 
     Tubing portion  11  provides a conduit for liquid grout that is injected under pressure into bore hole  22 . Tubing portion  11  includes discharge holes  34  that may be predrilled through the wall  31  of tubing portion  11 . Discharges holes  34  provide a predetermined distribution path for the liquefied grout that is injected into bore hole  22  after cable bolt  10  is set in the closed end of bore hole  22 . Discharge holes  34  may be evenly dispersed longitudinally along wall  31 . Alternately, discharge holes may be distributed along wall according to a predetermined arrangement to provide a desired distribution of grout. In one exemplary embodiment, distribution holes  34  may be larger at the top of the tubing than at the bottom. Similarly, tubing portion  11  may have more distribution holes  34  adjacent to the top of tubing portion  11  than at the bottom, thereby allowing greater cross-sectional flow of grout from tubing portion  11  at the top than at the bottom, to compensate for factors that restrict grout flow nearer the top of bore hole  22 . E.g., gravitational force, setting time, roof cracks or capillaries. Cracks/capillaries may draw much of the liquid grout as the grout is injected into bore hole  22 , thus depleting the amount of grout, if any, that is available to fill in the upper end of the bore hole  22  or column. 
     Tubing portion  11  may be, e.g., a ⅜ inch inside diameter hollow brake line tubing that is commercially available, or other suitable type of tubing. Tubing portion  11  may extend the entire length of cable segment  14 , or a portion thereof. The length of tubing portion  11  may be adjusted or selected to suit roof conditions, to direct the flow of grout to areas where a greater concentration of grout may be desired in one section of bore hole  22  for improved roof support. 
     Tubing portion  11  includes an angled tubing segment  25  that extends below the roof surface  36  at a 45° angle to the tube portion  11  axis, through the roof bolt plate  32 , and adjacent drive head  16 . A swivel coupling  26 , e.g., a JIC-type swivel coupling or other quick disconnect type hydraulic coupling, may be attached to angled tubing segment  25  to facilitate the grout injection application. Roof bolt plate  32  is pre-drilled with a slotted or extended hole that will allow drive head  16  to be rotatably threaded to apply torque against roof bolt plate  32  without interference from angled tubing segment  25 . 
     A drive head  16  and a barrel and wedge assembly are disclosed in U.S. Pat. No. 5,829,922 to Calandra, Jr. et al. However, other drive heads  16  integrally formed with cable segment  14 , or otherwise attached to cable segment  14  by welding, swaging, casting, or other suitable method are clearly contemplated for use in association with cable bolt  10 . 
     Cable bolt  10  includes a mechanical anchor  20 , e.g., a multiple prong shell and wedge combination, attached to cable segment  14  via an externally threaded sleeve  21  positioned on an exterior surface of cable segment  14  between the ends of cable segment  14 . Anchor  20  is driven into the closed end of bore hole  20 , wherein the shell portion is compressed against the wedge and expanded into the adjacent rock to fix cable bolt  10  in place. 
     Referring to  FIG. 3 , a stranded wire cable segment is shown with mixing devices  24 ,  245 ,  28  disposed therein. Cable segment  14  of the tensionable cable bolt  10  may also include one or more resin mixing devices such as birdcages  24 . Alternatively, nut cages  245 , or button cages  28  may be used in place of, or in addition to, birdcages  24 . A stiffening sleeve defining a hollow cavity configured to receive cable segment  14  may be positioned adjacent to the drive head  16 . 
     Referring next to  FIG. 4 , in an alternate embodiment, a cable bolt  40  includes a resin tube portion  42  disposed in the top of the bore hole  22  for receiving resin and cable segment  14 . Tubing portion  11  is affixed to cable segment  14  coaxially along a length of cable segment  14  as described above with respect to  FIG. 1 . Tubing portion  11  is provided with one or more internal mixing elements  50  (see  FIG. 5 ) for mixing and injecting resin into bore hole  22 . Mixing elements  50  allow the resin to mix at the point of entry of the tube portion  11 , thus eliminating the need for an external mixing device, e.g., a mixer-packer, as is conventionally used when installing resin bolts. In one exemplary embodiment cable bolt  40  may have three mixing elements  50  per cable bolt  40 , although more or less mixing elements  50  may be used if desired, to accommodate special field conditions. In one embodiment, mixing elements  50  may be used in combination with one or more mixing devices  24 ,  245 ,  28 . 
     An insulation tubing  44  surrounds the bottom section of cable segment  14 , adjacent roof bolt plate  32 . Insulation tubing  44  maintains the polyurethane grout mix in bore hole  22  until the polyurethane grout mix sets. In one exemplary embodiment insulation tubing may be a closed cell pipe tubing insulation having an inside diameter of about 1-⅛″, and about 9″ in length, by way of example and not limitation. Other dimensions for inside diameter and length may be used as suited to the specific dimensions of cable bolt  40 . 
     Mixing elements  50  are disposed on the opposite side of roof bolt plate  32  from bore hole  22 . Mixing elements  50  are in fluid communication with tubing portion  11  through conduits  52 ,  54  and  56 , and supply a fluid mixture of polyurethane grout or other resin mixture to the interior of tubing portion  11 . 
     As shown in  FIG. 5 , a fluid circuit  60  is shown for mixing the chemicals that form the polyurethane grout mix. A first tank  62  containing a first chemical mix and a second tank  64  containing a second chemical mix are each connected to input ports  66 ,  68 , respectively, of a pump  70 . In one embodiment piston pump  70  may be, e.g., a double action piston pump powered pneumatically or hydraulically. First output port  72  of pump  70  is connected to a first inlet  76  of mixing element  50 . Second output port  74  of pump  70  is connected to a second inlet  76  of mixing element  50 . Mixing element  50  may be, e.g., a ½″ tee fitting. An outlet port  80  of mixing element  50  supplies a fluid mixture of first and second chemicals to tubing portion  11 , allowing the chemicals to be mixed adjacent to the point at which the mixture enters the tubing portion. 
     Also disclosed is a method of installing a mine cable roof bolt  10  in a mine roof for supporting the roof. Referring to  FIG. 2 , method  100  generally includes drilling a bore hole in a mine roof at step  102 . Next, at step  104 , the length of a perforated tubing portion is determined and a perforation pattern suitable for a desired distribution of grout is applied to the tubing portion. At step  106 , an elongated cable bolt and the perforated tubing portion are provided, and at step  108 , the perforated tubing section is secured to the elongated cable bolt. Next at step  110 , the cable bolt and the perforated tubing portion are inserted into the bore hole using resin tube cartridges. At step  112  the cable is anchored in the closed end of the bore hole via an anchor portion, i.e., expansion shell located on an end of the cable or resin, or a combination of both. At step  114 , liquid grout is injected under pressure into the perforated tubing section. The method then proceeds at step  116  to rotating the elongated cable in the bore hole. Next at step  118 , a grout or resin is mixed in the bore hole, e.g., by attaching a quick disconnect or similar fitting and pumping grout mix through the fitting, to form an integrated mechanical anchor between the anchor portion and the resin with the mine roof rock adjacent the bore hole. 
     Additional steps of the method may include installing a backer rod around an intermediate portion of the cable roof bolt and tubing portion to seal an entrance of the bore hole at the surface of the mine roof; drawing a roof bolt plate up against the mine roof to compress the backer rod; and drilling a slotted or elongated hole in the roof bolt plate to accommodate an angled stub portion of the tubing portion. 
     In one alternate embodiment, a hollow core rebar-type bolt may be substituted for the cable bolt, and the hollow core used as distribution path for the grout. The hollow rebar bolt may be perforated selectively for customizing the grout distribution for the roof support application. In another embodiment, hollow fiberglass rib bolts, with or without perforations may be used in place of the cable bolt. 
     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.