Patent Publication Number: US-8966846-B1

Title: Steel anchored reinforced mine seal

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a reinforced seal cast from a structural material and anchored with steel dowels into the floor and ceiling of a mine passageway. The seal is capable of bidirectionally withstanding an overpressure substantially greater than 20 psi. 
     2. Brief Description of the Prior Art 
     Seals are required in U.S. mine ventilation plans to protect against explosions and are used extensively in mining to isolate worked-out areas. Over the years, tens of thousands of seals have been erected in underground coal mines in the United States. In the 1990s there were a number of explosions of methane and/or coal dust within sealed areas of underground U.S. coal mines. These explosions, believed to be initiated by lightning strikes on the surface, destroyed numerous seals and did considerable damage in the active workings. 
     A response to the above-mentioned disasters was to require that abandoned areas of a mine must be either ventilated or isolated from active workings through the use of seals capable of withstanding a static horizontal pressure of 20 psi. More recently, in response to other mine disasters with fatalities, the standard for mine seals has been substantially increased to require seals to withstand static horizontal pressures of 50 psi or even 120 psi in some instances. 
     Prior art mine seals formed from masonry or concrete are not designed to meet such blast criteria even when hitched into the passageway with roof bolts or grooves into the ribs. There is a need, therefore, for a cost effective and efficient way to construct a mine seal meeting the higher standards for explosion resistance. 
     BRIEF SUMMARY OF THE INVENTION 
     In view of the above, it is an object of the present invention to provide a mine ventilation seal meeting current blast criteria. It is another object to provide a mine ventilation seal that is capable of bidirectionally withstanding overpressures substantially greater than 20 psi, e.g., 50 psi and 120 psi. It is also an object to provide a mine ventilation seal having the above-mentioned characteristics that can be built in a cost effective and efficient way. Other objects and features of the invention will be in part apparent and in part pointed out. 
     In accordance with the present invention, a reinforced slab is anchored with steel dowels into the strata of a mine passageway. The reinforced slab has a pair of spaced apart metal mats formed of vertical and horizontal reinforcing members which are sandwiched between a row of dowels set into the floor and ceiling of the mine passageway and extend into the passageway. A structural material encapsulates the metal mats and dowels to form a plug which has enhanced shear and flexural strength. 
     The invention summarized above comprises the constructions hereinafter described, the scope of the invention being indicated by the subjoined claims. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       In the accompanying drawings, in which several of various possible embodiments of the invention are illustrated, corresponding reference characters refer to corresponding parts throughout the several views of the drawings in which: 
         FIG. 1  is a side elevation of a mine ventilation seal in accordance with the present invention with part of the structural filling material broken away to show internal details; 
         FIG. 2  is a plan view of the mine ventilation seal; 
         FIG. 3  a side view of the mine ventilation seal adjacent a rib of the mine passageway; 
         FIG. 4  is a section taken along the plane of  4 - 4  in  FIG. 1 ; 
         FIG. 5  is a section taken along the planes of  5 - 5  in  FIG. 1 ; 
         FIG. 6  is a section taken along the plane  6 - 6  in  FIG. 1 ; 
         FIG. 7A  is a detail showing inby and outby dowels laced together with a stirrup; and, 
         FIG. 7B  is a detail showing inby and outby dowels laced together with a pair of stirrups. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings more particularly by reference character, a steel anchored reinforced mine seal  10  in accordance with the present invention is shown in a mine passageway  12  with first and second side walls or ribs  14 ,  16 , a floor  18  and a ceiling  20 . Mine seal  10  is formed around a metal structure including first and second metal mats  22 ,  24 , respectively. Each of metal mats  22 ,  24  is composed of vertical and horizontal elongated reinforcing members  26 ,  28 , respectively, laid at right angles to each other. Horizontal reinforcing members  28  extend transverse of passageway  12  and vertical members  26  extend heightwise of passageway  12 . Metal mats  22 ,  24  provide flexural strength to seal  10  and are spaced apart longitudinally of passageway  12  in vertical parallel relationship with horizontal members  28  positioned inboard of vertical members  26 . 
     Reinforcing members  26 ,  28  may be formed as elongated rods or bars and can have any suitable cross-section, for example round, square, or rectangular. When rebar is used for reinforcing members  26 ,  28 , the gauge and grade will depend upon on the flexural strength needed to withstand the overpressure for which seal  10  is designed. For example, when seal  10  is designed to withstand an overpressure of 50 psi from a mine explosion with a maximum seal height of 8 feet and a maximum seal width of 21 feet, vertical members  26  may be #7 rebar, grade 60 on 10 inch centers, and horizontal members  28  may be #5 rebar, grade 60, on 12 inch centers (e.g., MSHA approved 50 psi seal of Precision Mine Repair). If seal  10  is designed to withstand an overpressure of 120 psi, vertical members  26  may be #9 rebar, grade 60, on 12 inch centers, and horizontal members  28  may be #5 rebar, grade 60, on 12 inch centers (e.g., MSHA approved 120 psi seal of Precision Mine Repair). From the above, it will be clear to those skilled in the art that the choice of material for reinforcing members  26 ,  28  (e.g., size and grade) and the spacing between the members is not limited to the above-mentioned examples which are provided by way of example, not limitation. The choice, however, is subject to engineering analyses and MSHA approval. 
     Endmost vertical members  26  should be spaced a distance from ribs  14 ,  16  to allow filling material which is more particularly discussed below to flow around the bars. For like reason topmost horizontal members  28  should be spaced a distance from ceiling  20 . If vertical or horizontal members  26 ,  28  are spliced, the members may be wire tied or mechanical coupled with couplers. 
     The metal structure also includes first and second rows  30 ,  32  of dowels  34  seated in holes  36  drilled into floor  18  and ceiling  20  of passageway  12 . Inby and outby rows of dowels  34  may also be set into side walls  14 ,  16 . The spacing between dowels  34  in first and second rows  30 ,  32  should not be less than one dowel diameter and in most instances is far greater. In PMR&#39;s 50 psi seal approved by MSHA mentioned above, dowels  34  are formed of #8 rebar, grade 60, and placed on 10 inch centers. Holes  36  in floor  18  and ceiling  20  may be aligned vertically with a string line and plumb bob, or equivalent, to assure that the ceiling and floor dowels  34  in each row are aligned vertically. Dowels  34  may also be staggered between rows such that dowels  34  in first and second rows  30 ,  32  are not aligned longitudinally of passageway  12 . In PMR&#39;s approved 120 psi seal  10  no dowels are provided in side walls  14 ,  16  and dowels  34  in floor  18  and ceiling  20  are formed of #9 rebar, grade 60, and set on 14 inch centers. 
     Rows  30 ,  32  of dowels  34  provide bidirectional shear reinforcement bracing seal  10  against lateral movement in passageway  12 . Dowels  34  may be set to a depth and grouted into the strata of passageway  12  such that the pull strength is equal to the full tensile yield strength of the dowel. The depth necessary to develop this pull strength in a particular strata must be determined empirically based on pull-out tests conducted in ceiling and floor strata representative of the seal location. Dowels  34  extend a distance into passageway  12  such that they overlap one or more of horizontal members  28  of metal mats  22 ,  24 . For example, when dowels  34  are set into the strata 2 to 2½ feet, dowels  34  may extend into passageway  12  a distance of 2 feet or more. When vertical members  26  align with dowels  34 , vertical members  26  may be wire tied or mechanically coupled to dowels  34 . In like manner horizontal members  28  may be wire tied to coupled to dowels  34  in side walls  14 ,  16  and the horizontal members align with the dowels. 
     Seal shear and flexural strength of seal  10  may be further improved by lacing dowels  34  together with stirrups  38  as shown in  FIGS. 7A and 7B . As illustrated, one end  40  of stirrup  38  is hooked around a dowel  34  on the inby side of seal  10  while a straight leg  42  overlies a dowel  34  on the outby side of seal  10 . In  FIG. 7A , one stirrup  38  is used to lace together the dowels on the inby and outby sides, whereas two stirrups  38  are used in  FIG. 7B . Stirrups  38  may be formed of the same kind of materials used for the other elements of metal structure or of smaller gauge, for example #4 rebar, 60 grade. 
     The space between metal mats  22 ,  24  may be open to be filled with concrete or supplied with additional reinforcement such as a pair of 3-D building panels  44 ,  46 , sections of which are arranged in side-by-side relationship, as described in PMR&#39;s U.S. Pat. No. 5,879,231 which is incorporated by reference herein. Panels  44 ,  46  add to the flexural strength of seal  10 . As described in PMR&#39;s earlier patent, each panel is formed of a pair of wire grids interconnected by strut wires which pass through a core of insulation and form a truss system. For use in seal  10 , the core of insulation is dissolved away for reasons which will become apparent. 
     As shown in the drawings, an air sampling tube (not shown) and a water drain (not shown) may also be provided in seal  10 . The drain should be equipped to prevent the exchange of air through the pipe. 
     A filling of structural material  48  (shown in FIGS.  1  and  4 - 6 ) is applied to metal structure integrating the metal structure into a reinforced slab which is anchored into the strata of passageway  12  with dowels  34 . Structural material  48  may be normal concrete, high strength concrete, light weight concrete, concrete with special cements and aggregates, polymer modified concrete, special cement mortar, special polymer mortar and other commercially available materials that are sufficient strong when hardened. 
     In seal  10  as shown in the drawings, structural material  48  is applied in the form of gunite or shotcrete. In which case a sheet metal wall  50  is built on the inby side of seal  10  several inches away from dowels  34  as a backstop for the gunite. Wall  50  should be adequately braced against vibration and may be vented to permit escape of air during the gunning operation. Multiple layers of gunite or shotcrete are applied until metal structure is embedded to a depth of several inches. To ensure complete encasement of metal structure, the gunite or shotcrete should be applied with sufficient velocity and plasticity so that the structural material flows around and behind metal structure and overlaps side walls  14 ,  16 , floor  18  and ceiling  20  forming an airtight seal. Layers of shotcrete should be allowed to take an initial, soft set before succeeding layers are applied. If seal  10  is not placed monolithically (i.e., placement of shotcrete layers are interrupted), a bonding agent may be applied to and worked into the fully set concrete prior to additional shotcrete placement. 
     Structural material  48  may also be poured in layers around metal structure. In which case a reusable metal form such as described in U.S. Pat. No. 6,220,785 to Kennedy et al., dry stacked or mortar set cinder blocks or the like may be used. Depending on the nature of the form, the form may be a permanent part of seal  10  or removed after structural material  48  has set. When structural material is poured, a gap may be left along ceiling  20  which may be grouted closed to provide an airtight seal. 
     In use, seal  10  as shown in the drawings is designed to be placed in an area with competent ceiling  20  and floor  18  and is applicable to a wide range of mine geologic formations. Seal  10  should be located at least 10 feet away from the corner of any pillar and may be constructed as follows: 
     1) The area in passageway  12  to be sealed should be cleaned of all loose material on ceiling  20 , ribs  14 ,  16  and mine floor  18  for a distance of several feet on each side of the seal. This may be accomplished with a high pressure air hose. Should weak conditions persist, ribs  14 ,  16  may be reinforced by bolting or grouting. 
     2) A vented or no-vented metal wall  50  is installed in the seal opening. 
     3) Inby dowels  34  are drilled and glued to the depth of the mine seal plan along ceiling  20  and floor  18 . If dowels  34  are provided in side walls  14 ,  16 , the inby dowels  34  along side walls  14 ,  16  are also drilled and glued. 
     4) Vertical members  26  of inby metal mat  22  are installed on centers to plan from rib  14  to rib  16 . Couplers or wire ties may be used to join vertical members  26  to inby dowels  34  where they line up. 
     5) Inby horizontal members  28  are installed on centers to plan from ceiling  20  to floor  18 . If dowels  34  are provided in ribs  14 ,  16 , horizontal members  28  may be coupled to the dowels or wire tied where they line up. 
     6) Two 3-D panels  44 ,  46  are placed next to inby metal mat  22  with space left on the rib sides as well as the ceiling for the installation of stirrups  38 . 
     7) Outby dowels  34  are drilled and glued to the depth of the mine seal plan along ceiling  20  and floor  28  and along ribs  14 ,  16 , if provided. 
     8) Horizontal members  28  of outby metal mat  24  are installed from ceiling  20  to floor  18 . 
     9) Outby vertical members  26  are installed from rib  14  to rib  16 . 
     10) Stirrups  38  are installed lacing inby and outby dowels  34  along ceiling and floor together and lacing inby and outby dowels along ribs  14 ,  16 , if provided. 
     11) Gunite is then applied to the metal structure which includes metal mats  22 ,  24 , 30-D panels  44 ,  46  and inby and outby rows  30 ,  32  of dowels  34  to a depth of 2 inches of gunite over dowels  34  on each side such that metal mats  22 ,  24  are embedded to a depth of about 3 inches. During application, the material and the surrounding air temperature should be maintained at a minimum of 50 degrees F. and thereafter for 7 days after the completion of the work. Rebound material should not be salvaged and reused. 
     12) In some instances, MSHA approval may require a supplemental roof support (not shown) on both the outby and inby side of seal  10  as by cribbing or the equivalent. 
     In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.