Patent Publication Number: US-2019178083-A1

Title: Yieldable Bearing Block

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Patent Application No. 62/399,693 filed Sep. 26, 2016, the disclosure of which is hereby incorporated in its entirety by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a mine roof bolting system, and more particularly, a mine roof bolting system including a bearing member that yields or deforms when subjected to a load. 
     Description of Related Art 
     The roof of a mine is conventionally supported by tensioning the roof with mine bolts drilled in the mine roof that reinforce the unsupported rock formation behind the roof. Other structures may also be supported, such as walls or ribs of an underground mine; thus use of the term “roof” herein is also applicable to other such structures. The end of the mine bolt may be anchored mechanically to the rock formation by engagement of an expansion assembly on the end of the bolt with the rock formation. Alternatively, the mine roof bolt may be adhesively bonded to the rock formation with a resin bonding material inserted into the bore hole into which the mine roof bolt is inserted. A combination of mechanical anchoring and resin bonding can also be employed by using both an expansion assembly and resin bonding material. 
     Cable bolts are used in the mining industry, and particularly, hard rock mining as they provide several advantages over conventional mine roof bolts, for example, ease of handling and installation. Cable bolts are substantially easier to fit into a borehole than the elongated rods of conventional rod bolt systems. Regardless of the height limitations in a mine, cable bolts may be adapted to boreholes of any length due to their flexibility. Moreover, the strength capacity of cables typically exceed that of conventional rod bolts. 
     With certain mining conditions, particularly those found in hard rock mining, the rock formation in the mine roof is susceptible to movement or rock burst as a result of mine-induced seismicity, the excavation of perimeter rock, minor seismicities, and the like. Under dynamic loading caused by rock bursts, the conventional mine roof bolts described above are vulnerable to failure. 
     SUMMARY OF THE INVENTION 
     The present invention includes a simple, low cost, and easy to manufacture mine roof bolting system wherein at least a portion of the system deforms to absorb some of the dynamic loading caused by a rock burst or excessive load caused by squeezing ground. 
     The present invention is directed to a mine roof bolting system comprising a bearing member having a first member, a second member spaced apart from the first member, and apertures defined through each of the first and second members; and a mine roof bolt extending through the apertures. When a load is applied to the mine roof bolting system, the bearing member yields. 
     The present invention is also directed to a mine roof bolting system comprising a bearing member comprising a first member defining a first aperture, a second member spaced apart from the first member and defining a second aperture, and a web extending between the first member and the second member and thereby defining a gap between the first member and the second member; and a mine roof bolt extending through the first and second apertures of the bearing member. 
     The present invention is also directed to a method for providing a roof support in an underground mine. The method includes providing a bearing member as described above and inserting a mine roof bolt through the apertures of the bearing member and into a borehole in a mine roof. The bearing member is adapted to yield upon application of a load in excess of a predetermined load. The mine roof bolt may be a cable bolt, a solid bolt, an expandable (inflatable) bolt, or a hollow bolt. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described in further detail with reference to the accompanying figures, in which: 
         FIG. 1  is a perspective view of a yieldable bearing member in accordance with the present invention; 
         FIG. 2  is a cross-section view of the yieldable bearing member of  FIG. 1  taken along line  2 - 2 ; 
         FIG. 3  is a front elevation view of a mine roof bolting system including a bearing plate, the bearing member of  FIG. 1 , and a mine roof bolt; 
         FIG. 4  is a front elevation view of a mine roof bolting system including the bearing member of  FIG. 1  and a mine roof bolt; 
         FIG. 5  is a perspective view of the bearing member of  FIG. 1  after the bearing member has yielded; and 
         FIG. 6  is a load deflection curve comparing yieldable bearing members made in accordance with the present invention. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     The following description is provided to enable those skilled in the art to make and use the described embodiments contemplated for carrying out the invention. For purposes of the description hereinafter, the terms “upper”, “lower”, “vertical”, “horizontal”, “top”, “bottom”, “lateral”, “longitudinal”, and derivatives thereof relate to the invention as it is oriented in the drawing figures. It is to be understood that the specific devices illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments of the invention. Hence, specific dimension and other physical characteristics related to the embodiments disclosed herein are not to be understood as limiting. 
       FIGS. 1 and 2  illustrate a yieldable bearing member made in accordance with the present invention. The yieldable bearing member  10 , also referred to herein as a yieldable bearing block, generally includes a first member  14 , also referred to as a top member, a second member  16 , also referred to as a bottom member, and at least one web  18 ,  20  extending between the top member  14  and the bottom member  16 . 
     The top member  14  may be spaced apart from the bottom member  16  and may be substantially parallel to the bottom member  16 . The top member  14  and the bottom member may each be in the form of a plate which may take any suitable shape including, but not limited to a rectangle, a square, a trapezoid, a parallelogram, a polygon, and a circle. The web  18 ,  20  may extend from a first side  14   a  of the top member  14  to a first side  16   a  of the bottom member  16 . A second web  18 ,  20  may extend from a second side  14   b  of the top member  14  to a second side  16   b  of the bottom member  16 . First sides  14   a ,  16   a  and second sides  14   b ,  16   b  each may include curved portions connecting the top member  14  and the bottom member  16 . The top member  14 , the bottom member  16 , and the two webs  18 ,  20  may combine to define a central cavity  26  such that the yieldable bearing block  10  has a tubular configuration. The central cavity  26  extends along a central axis A from a first end  22  to a second end  24  of the yieldable bearing block  10  such that a gap  30  is formed between an interior surface  32  of the top member  14  and an interior surface  34  of the bottom member  16 . The central cavity  26  may be open, or alternatively, may include a compressible material such as wood, plastic, hard rubber, aerated cement, or the like, to modify the loading/deformation properties of the yieldable bearing block  10 . 
     In one embodiment, the webs  18 ,  20  may extend from respective sides  14   a ,  14   b  of the top member  14  to respective sides  16   a ,  16   b  of the bottom member  16  such that the webs  18 ,  20  are at right angles to the top member  14  and the bottom member  16 . The top member  14  and the bottom member may have the same size and shape and two webs  18 ,  20  may be provided as shown in  FIGS. 1 and 2 . The top member  14 , the bottom member  16 , and the webs  18 ,  20  combine to define a central cavity  26  having a square or rectangular cross-section. 
     In another embodiment, the size and/or shape of top member  14  and the bottom member  16  may be different or the top member  14  may be offset from the bottom member  16  such that the webs  18 ,  20  are angled with respect to the top member  14  and the bottom member  16 . Two webs  18 ,  20  may be provided such that the top member  14 , the bottom member  16 , and the webs  18 ,  20  combine to define a central cavity  26  having a cross-section that is a trapezoid or a parallelogram. 
     In a further embodiment, at least one of the top member  14 , the bottom member  16 , and the webs may be curved. Two webs  18 ,  20  may be provided such that the top member  14 , the bottom member  16 , and the webs  18 ,  20  combine to define a central cavity  26  having a cross-section that is a circle, an ellipse, or a truncated circle having two flat sides and two curved sides. 
     The yieldable bearing block  10  may have a length L measured along the central axis A from the first end  22  to the second end  24 , a width W measured perpendicular to the central axis A between opposing webs  18 ,  20 , and a height H measured perpendicular to the central axis A between the top member  14  and the bottom member  16 . With particular reference to  FIG. 2 , an exterior surface  28  of the yieldable bearing block  10  and the central cavity  26  define a wall thickness  14 ′ of the top member  14 , a wall thickness  16 ′ of the bottom member  16 , and wall thicknesses  18 ′ and  20 ′ of the webs  18  and  20 , respectively. The wall thickness  14 ′,  16 ′,  18 ′,  20 ′ of each wall  14 ,  16 ,  18 ,  20  may be equal to each other such that the yieldable bearing block  10  has a uniform wall thickness T or may be different from each other in order to provide different portions of the yieldable bearing block  10  with different mechanical properties. For example, the yieldable bearing block  10  may have a uniform wall thickness T of 5/16 inch or ⅜ inch. As is further discussed hereinafter, the length L, width W, height H, and wall thickness T of the yieldable bearing block  10  can be manufactured to provide specific yield and tensile properties for various underground mining conditions, for example, hard rock mining. 
     Apertures  36   a ,  36   b  for receiving a fastening mechanism, such as a mine roof bolt  38 , are defined in the top member  14  and the bottom member  16  of the yieldable bearing block  10 . The apertures  36   a ,  36   b  may be positioned substantially at each of the centers of the top member  14  and the bottom member  16 . The apertures  36   a ,  36   b  may be dimensioned to receive an elongated body  40  of a mine roof bolt  38  ( FIGS. 3 and 4 ). For example, the apertures  36   a ,  36   b  may be dimensioned to receive a mine roof bolt  38  having a diameter of 0.6 inch or 0.7 inch. 
     The yieldable bearing block  10  may be produced from any yieldable material having high strength, for example, steel or aluminum. The material may have a minimum yield strength of 46 ksi and a minimum tensile strength of 58 ksi. One such material is rectangular steel tube, for example, a rectangular tube made of ASTM A500-B steel. 
     The yieldable bearing block  10  can be used as part of a mine roof bolting system, such as a mine roof bolting system  100 , shown in  FIG. 3 , including the yieldable bearing block  10 , a bearing plate  42 , and a mine roof bolt  38 , or a mine roof bolting system  200 , shown in  FIG. 4 , including the yieldable bearing block  10  and a mine roof bolt  38 . 
     Referring to  FIG. 5 , the yieldable bearing block  10  is designed to yield, or deform, such that the gap  30  of the yieldable bearing block  10  is reduced when a predetermined load, for example, 15 tons or more or 20 tons or more, is applied to the mine roof bolting system  100  or the mine roof bolting system  200 . 
     Referring to  FIG. 3 , the mine roof bolting system  100  includes the yieldable bearing block  10 , the bearing plate  42 , and the mine roof bolt  38 . The bearing plate  42  may generally include a planar body  44  having a bearing surface  46  for engaging the mine roof R and a contact surface  48  for engaging the top member  14  of the yieldable bearing block  10 . The bearing plate  42  may be made of commercial grade steel. An aperture  50  may be positioned substantially at the center of the planar body  44 . The bearing plate  42  may optionally include one or more rib members  52  surrounding the aperture  50  and positioned between the aperture  50  and a peripheral edge  54  of the bearing plate  42 . It should be appreciated that other bearing plates known in the art may be used in the system  100 . 
     The mine roof bolting system  100  may be installed in a mine roof R to provide support to a rock formation. The mine roof bolt  38  is inserted through the apertures  36  of the yieldable bearing block  10  and the aperture  50  of the bearing plate  42  and into a borehole B. The mine roof bolt  38  may be a solid bolt, such as a solid rebar bolt or smooth bar bolt, a cable bolt, an expandable (inflatable) bolt, a hollow bolt, or any other mine roof bolt designed for supporting rock strata as is known in the art. A drive end  60  of the mine roof bolt  38  may include a drive head that does not tension the bolt or may include a tensioning system. Suitable tensioning systems include an externally threaded bolt with a tensioning nut optionally having a shear pin or breakout portion or the like threaded thereon, a barrel and wedge assembly on a cable bolt or other drive heads as are known in the art for installing mine roof bolts. 
     By way of example, the mine roof bolt  38  may be a cable bolt formed of a selected length of a flexible multi-strand steel cable  56  having an anchor end portion  58  and a drive end portion  60  including a barrel and wedge assembly  61   a  and a drive nut  61   b . Between the anchor end portion  58  and the drive end portion  60 , the cable  56  is flexible and extends a length as determined by the length of the borehole B in the rock formation. A stiffening tube  57  may enclose the flexible multi-strand steel cable  56  at a proximal end thereof, adjacent the barrel and wedge assembly  61   a . A washer  62  may optionally be placed between the bottom member  16  of the yieldable bearing block  10  and the barrel and wedge assembly  61   a  such that the yieldable bearing block  10  does not directly contact the barrel and wedge assembly  61   a.    
     When the mine roof bolting system  100  experiences loading due to a shift in the surrounding rock strata, the yieldable bearing block  10  yields, or deforms, such that the gap  30  of the yieldable bearing block  10  is reduced. As the yieldable bearing block  10  yields, the mine roof bolting system  100  absorbs some of the dynamic load such that the mine roof system  100  can support a greater load than a comparable system not including the yieldable bearing block  10 . 
     Referring to  FIG. 4 , the mine roof bolting system  200  includes the yieldable bearing block  10  and a mine roof bolt  38 . The mine roof bolting system  200  is substantially the same as the mine roof bolting system  100 , but does not include the bearing plate  42 . Instead, the top member  14  of the yieldable bearing block  10  directly engages the mine roof R such that the yieldable bearing block  10  serves a dual function, acting as both the yieldable bearing block  10  and the bearing plate  42 . For example, in the mine roof bolting system  200 , the yieldable bearing block  10  may be at least 36 square inches. 
     When the mine roof system  200  experiences loading due to natural forces of the mine, the yieldable bearing block  10  yields, or deforms, such that the gap  30  of the yieldable bearing block  10  is reduced. As the yieldable bearing block  10  yields, the mine roof bolting system  100  absorbs some of the dynamic load such that mine roof system  200  can support a greater load than a comparable system not including the yieldable bearing block  10 . 
     The following tests were conducted to demonstrate the general principles of the present invention. The invention should not be considered to be limited to the specific tests presented herein. 
     Examples 
     Ten yieldable bearing blocks  10  having a rectangular cross-section and various lengths L, widths W, heights H, and wall thicknesses T, were tested to determine a maximum load and a maximum yield (i.e., maximum deflection) that each of the ten yieldable bearing blocks  10  could withstand prior to failure. A load was applied to the top member  14  of the yieldable bearing blocks  10  using a rod having a 1.75 inch diameter to simulate the housing of a mine roof bolt having a 0.6 inch diameter. The maximum load and deflection achieved before the gap between the top member  14  and the bottom member  16  is at least partially closed as the top member  14  and the bottom member  16  move toward one another under the load as shown in  FIG. 5  was measured. The results of the tests are shown below in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Test results showing maximum load and deflection 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Tube size 
                 Sample 
                   
                   
               
               
                   
                 (W × H × T) 
                 length 
                 Max load 
                 Max deflection 
               
               
                 Test # 
                 (inch) 
                 (inch) 
                 (ton) 
                 (inch) 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 4 × 3 × 3/8  
                 4.5 
                 24 
                 1.95 
               
               
                 2 
                   
                 4.0 
                 22 
                 1.88 
               
               
                 3 
                   
                 3.5 
                 20 
                 1.76 
               
               
                 4 
                 4 × 2 × 5/16 
                 4.5 
                 21 
                 1.21 
               
               
                 5 
                   
                 4.0 
                 20 
                 1.16 
               
               
                 6 
                   
                 3.5 
                 18 
                 1.11 
               
               
                 7 
                 3 × 2 × 5/16 
                 4.5 
                 34 
                 1.22 
               
               
                 8 
                   
                 4.0 
                 33 
                 1.20 
               
               
                 9 
                   
                 3.5 
                 31 
                 1.12 
               
               
                 10 
                   
                 3.0 
                 24 
                 1.06 
               
               
                   
               
            
           
         
       
     
     Load deflection curves comparing the results of the yieldable bearing blocks of Tests 9 and 10 having a length of 3.5 inches and a length of 3 inches, respectively, are shown in  FIG. 6 . The results shown in  FIG. 6  demonstrate that a load up to a predetermined load (e.g., about 25 tons for Test 9 at a length of 3 inches and about 20 tons for Test 10 at a length of 3.5 inches) can be applied before maximum deflection is achieved. A mine roof support system incorporating the yieldable bearing block of the present invention can withstand an added load (e.g., 20-25 tons as shown in Tests 9 and 10), allowing the system to yield upon application of the load. 
     The yieldable bearing block provided herein provides an easy to manufacture and low cost system for increasing the load for which a mine roof bolting system can support. The systems disclosed herein are particularly advantageous in hard rock mining under which dynamic loading is caused by squeezing and rock bursts. 
     While embodiments of the yieldable bearing block are shown in the accompanying figures and described hereinabove in detail, other embodiments will be apparent to, and readily made by, those skilled in the art without departing from the scope and spirit of the invention. Accordingly, the foregoing description is intended to be illustrative rather than restrictive. The disclosure described hereinabove is defined by the appended claims and all changes to the disclosure that fall within the meaning and the range of equivalency of the claims are to be embraced within its scope.