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CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. patent application Ser. No. 13/644,604 filed Oct. 4, 2012, which claims the benefit of U.S. Provisional Application Ser. No. 61/544,302 filed on Oct. 7, 2011, and U.S. Provisional Application No. 61/650,643 filed on May 23, 2012, the contents of which applications are herein incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Livestock guards, often referred to as “cattle guards,” are used as an obstacle to prevent livestock from passing through an opening in fencing that surrounds a pasture or the like, and are usually installed where roads or walkways cross a fence line, often at a boundary between public and private lands. Cattle guards are used as an alternative to gates that need to be opened and closed every time a vehicle passes, and are common where roads cross open moorland, rangeland or common land maintained for grazing. 
     Conventional cattle guards in most instances require that a pit be dug adjacent the fence through which the cattle guard is to be installed. The pit is covered by a transverse grid of bars or tubes, normally made of metal and firmly fixed to the ground on either side of the pit with spaces between the bars. The spaces are sufficiently narrow not to prevent a wheeled vehicle from crossing the pit. Cattle will generally not cross the cattle guard since the spaces do not provide adequate footing. 
     For conventional cattle guards that do not require a pit, expensive mechanical features are required. These mechanical features may wear out and also may be subject to mechanical failure. Further, typical cattle guards that do not require a pit are often complex in nature and generally not practical for everyday use. Current cattle guards, as described in the prior art, are pre-assembled and transported to the installation location. The cost of transportation and installation may be high in such circumstances. Therefore, there is a need in the field for cattle guards that may be assembled and installed in a rapid and economical fashion. 
     SUMMARY OF THE INVENTION 
     The several embodiments of the present invention are directed to cattle guard apparatus, systems and methods. 
     In first and second embodiments, the cattle guards are fabricated in situ using a form unit that is transported and placed across the driveway, walkway or other opening in a fence, with the cattle guard unit being used as a form for the depositing of concrete, high-density foam or other settable material capable of providing structural integrity to the form. 
     In the first embodiment, a form unit is shaped by molding a high impact plastic material or shaped from a lightweight metal with elongated hollow rails having spaces between the rails sufficient to deter cattle from crossing the resulting guard. The unit is molded with a series of interior elongated reinforcing rods, preferably formed from a high tensile strength glass fiber, installed both longitudinally and laterally through the molded unit and suspended so as to permit the flow of a settable material into the interior of the unit at the time the cattle guard is being installed. A plurality of openings along the top of each rail permits access to the interior of the unit so that the settable material can be injected therein. Preferably, a removable barrier or blocking such as Styrofoam or similar material is installed in the space between adjacent rails, to prevent the settable material from entering the space during the pour of the settable material into the unit at the installation. 
     In the second embodiment, the cattle guard is installed at a location where heavy equipment such as tractors or the like will not be required to pass through the fence. Accordingly, in the second embodiment the molded form unit has channels into which the concrete or other setting material may be injected, usually without reinforcing rods. 
     In a third embodiment, a basic cattle guard unit is provided having side rails and corners between adjacent side rails with a plurality of guard rails molded with and extending above the side rails. The guard rails are molded at a substantial angle between the side rails and are separated by stringers so as to define intervening grooves between adjacent guard rails. The angular disposition of the guard rails permits vehicles to pass across the top of the unit without destructive loading. Additionally, raised areas at respective corners extend approximately to the same height as the guard rails with directional arrows molded into the unit adjacent one of the raised areas to provide assistance in fitting cattle guard units together. One or more of the cattle guard units are placed in a pit extending through a fence, to restrict the movement of cattle and other animals through the fence. 
     Other features of the various embodiments will be disclosed in greater detail below and in the accompanying drawings. 
    
    
     
       DESCRIPTION OF DRAWINGS 
       For a fuller understanding of the nature and advantages of the present invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which: 
         FIG. 1  is a top perspective view of a form unit used in the construction of a cattle guard in accordance with a first embodiment of the present invention. 
         FIG. 2  is a phantom perspective top view of the unit of  FIG. 1 , illustrating the reinforcing rods installed within the unit. 
         FIG. 3  is a top plan view of the unit of  FIG. 1 , depicting the layout of openings in the unit of  FIG. 1  that permits a flowable media to be injected into the unit and around the reinforcing rods. 
         FIG. 4  is a top perspective view of the unit of  FIG. 1 , illustrating the use of inserts between adjacent rails, to temporarily prevent the fillable material from extending in the space between the rails. 
         FIGS. 5 and 6  illustrate prospective views of a form unit that is utilized to fabricate a cattle guard in accordance with a second embodiment of the invention. 
         FIG. 7  illustrates a side view of the form unit of  FIG. 5 . 
         FIG. 8  illustrates a top view of another version of a cattle guard in accordance with the second embodiment of the invention. 
         FIG. 9  is a side view of the cattle guard of  FIG. 8 . 
         FIG. 10  illustrates a plurality of cattle guards of  FIGS. 8 and 9  that are joined to produce a larger cattle guard installation. 
         FIG. 11  is a perspective view of a form like that shown in  FIG. 6  for fabricating a cattle guard, illustrating the use of temporary blocking during the shipping and pour phases. 
         FIG. 12  is a top plan view of a third embodiment of the present invention. 
         FIG. 13  is a perspective view of an installation of a cattle guard in accordance with the third embodiment, with two units of  FIG. 12  installed in a side-by-side configuration in a walkway W through a fence F. 
         FIG. 14  is a top plan view illustrating the side-by-side installation of  FIG. 12  construction into the walkway of  FIG. 13 . 
         FIG. 15  is a partial perspective view of a portion of a construction illustrating details of a cattle guard construction utilizing multiple units like that shown in  FIG. 12 . 
         FIG. 16  is a partial perspective view of the construction of  FIG. 12 , illustrating certain construction details. 
         FIGS. 17 and 18  are top plan views, respectively, of four unit and eight unit constructions utilizing the basic unit of  FIG. 12 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     It will be understood that this invention is not limited to the particular apparatus, systems or methods described. It is also understood that the terminology used in the description is for the purpose of describing the particular embodiments, and is not intended to limit the scope of the present invention. Unless defined otherwise, all technical terms used herein have the same meanings as commonly understood by one of ordinary skill in the art. Although any methods and materials similar or equivalent to those described herein can be used in the manufacture, practice or testing of embodiments of the present invention, the preferred apparatus, systems and methods are now described. 
     It must also be noted that as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural reference unless the context clearly dictates otherwise. “In situ” (or “the site”) as referenced herein means carrying out at least a part of the method where the cattle guard is to be installed. 
     A first embodiment of the present invention will now be described with reference to  FIGS. 1-4 . 
     Noting  FIGS. 1, 2 and 3 , the first embodiment incorporates a form unit  10  preferably fabricated from a high impact plastic material such as polyethylene that is molded into a member having a hollow interior and hollow channels defining opposing side rails  12 ,  14  and opposing end rails  16 ,  18  with four corners  13 ,  15 ,  17  and  19  between adjacent side and end rails. A plurality of longitudinal intermediate rails  24  are spaced between the two side rails  12 ,  14  and between the end rails  16 ,  18  across a center rail  30 , with each of the rails  12 ,  14  and  24  having a plurality of rectangular openings  32  across the top surface thereof to permit access to the hollow interior of the unit  10  for injecting a setting material such as concrete or a high density foam, as discussed further below. 
     As specifically shown in  FIGS. 2 and 3 , a network of longitudinal reinforcing rods  38  and lateral reinforcing rods  40  are positioned in pairs within the interior of the unit  10 . The longitudinal reinforcing rods  38  are suspended in and extend along corresponding ones of the side rails  20 ,  22  and intermediate rails  24 ; and the lateral reinforcing rods  40  are suspended in and extend along the end rails  26 ,  28  and the center rail  30 . The rods  38 ,  40  may be held in place by a variety of techniques, such as fittings  34  that are spun-welded to the side and end rails. Alternatively, suitable connectors (such as EMT connectors, for example) may also be used to hold the rods  38 ,  40  in place. 
     It will thus be appreciated by one skilled in the art that the molded form unit  10  of  FIGS. 1 and 3  with the internal reinforcing rods  38 ,  40  of  FIG. 2  is appropriately positioned across a fence opening to permit a cattle guard unit having excellent strength and durability to be fabricated in situ by injecting a settable medium  42  ( FIG. 3 ) such as concrete or a high density amorphous foam through the openings  32  along the top of each of the rails  20 ,  22  and  24 , around the grid of reinforcing rods  38 ,  40  and along the length of each rail, including the end rails  26 ,  28  and center rail  30 . Thereafter, the settable medium  42  is permitted to harden and thus create a unified cattle guard system without the difficulties and expense associated with making the cattle guard at a distant location and shipping it to the site. Preferably, the reinforcing rods  38 ,  40  are also lightweight in nature and comprise a high-tensile strength glass fiber rebar. The fillable medium  42  may comprise concrete having an appropriate aggregate content such as chad rock of the type used in pumped concrete applications. As an alternative, a high density settable foam may be used in lieu of concrete. 
     The cattle guard unit made using the form of  FIGS. 1-3  has spaces between adjacent rails  20 ,  22  and  24  that can be passed over by a vehicle, but which discourage cattle from attempting to walk across the unit. The spaces between the adjacent rails  20 ,  22 , and  24  may be wider at the top and become narrower at the bottom. After the molding of the unit  10  and during transportation to an installation site and further during the process of injecting concrete or other appropriate material into the form  10 , it is suitable as shown in  FIG. 4  to place blocking  50 , preferably fabricated of Styrofoam or a similar lightweight material, or temporary barriers along the spaces between adjacent rails  20 ,  22  and  24  to prevent the settable medium  42  from passing through the space between adjacent rails after the medium is injected into the form unit  10  through the openings  32 ; thereafter, the Styrofoam blocking  50  are removed. 
     A second embodiment of the present invention will now be described with reference to  FIGS. 5-11 . 
       FIGS. 5 and 6  illustrate a form unit  110  that is utilized to also construct cattle guards in situ. Form unit  110  is transported and placed in an end-to-end abutting relationship across or in front of an entry way to a site for confining cattle and other livestock. Form unit  110  is preferably rectangular in shape and is generally constructed of lightweight material that can be easily transported and installed. Non-limiting examples of construction material of form  110  are plastic, wood, composite compounds and aluminum. 
     Referring to  FIG. 5 , the unit  110  comprises a series of rails  112  that are also referred to herein as “channels”. Each channel  112  comprises a proximal end  111  and a distal end  113  that are capped with a proximal cap  114  and a distal cap  119  respectively. Each channel  112  comprises a bottom  115 , two opposing sides  116  and  117 , and a front side  121  at the proximal end  111  (as depicted in  FIGS. 5, 6 and 7 ). The sides  116 ,  117  are preferably upwardly convergent and provide a containment volume for cement or other settable medium. A space  118 , on the order of 2″ to 5″ inches, separates each channel  112  from the next, as illustrated in  FIGS. 5 and 7 , where the space  118  may have downwardly convergent sides in that the top has a greater width than at the bottom of the space  118 . 
     As depicted in  FIG. 5 , a connecting compartment  120  is placed across each space  118  and connects each channel  112  to the next. The connecting compartment  120  is preferably a rectangular prism and is configured such that it is placed in the center of a length of the channel  112  in space  118 . Each connecting compartment  120  comprises a bottom  123  (as depicted in  FIG. 7 ), two opposing sides  125  and  127 , a front side  129  and a back side  131  (as depicted in  FIG. 5 ). In each connecting compartment  120 , each of the two opposing sides  125  and  127  are in contact with one of the two opposing sides  116  and  117  of the adjacent channels  112 . This allows for the interconnection of the channels  112  with each other through the longitudinal connecting compartment  120 . A cavity  133  is placed between side  116  of adjacent channel  112  and side  125  of connecting compartment  120 . A cavity  139  is placed between side  117  of adjacent channel  112  and side  127  of connecting compartment  120 . Cavities  133  and  139  allow for the interconnection of connection compartments  120  through each channel  112 , such that concrete or another settable medium can funnel throughout the channels  112  and connecting compartments  120 . 
     In another version of the second embodiment, where circumstances may require it, reinforcement rods  122  are placed in each channel  112 . The reinforcement rods  122  are placed vertically with respect to each other, or one on the top and one directly below, as opposed to being placed side by side of each other. Reinforcement rods  122  run longitudinally along the length of each channel  112  and connect the proximal end  111  to the distal end  113 , as depicted in  FIG. 5 . In yet another aspect of this version, at least two reinforcement rods  124  are placed in a plurality of connecting compartments  120  such that the reinforcement rods  124  run along the width of the connecting compartments  120 , from the side  116  of the first channel  112  to the side  117  of the last channel  112  and through all the connecting compartments  120 . The reinforcement rods  124  are preferably perpendicular to channel  112 , as depicted in  FIG. 5 . 
     Another aspect of this invention is directed to the method for fabricating cattle guards in situ using the form unit  110 , as depicted in  FIGS. 5-7 . 
     A hole at the site of installation of the cattle guard is generally dug corresponding to the depth of the form  110  to allow for leveled and convenient placement. Once the form  110  is placed in an optimal and desirable location, a fillable medium is poured from the top into the form  110 , and the form  110  and its contents or high-density foam are simply left in the ground. The end product is a cattle guard  130 , as depicted in  FIG. 8 . As illustrated in  FIG. 8 , the resulting cattle guard  130  made in the form  110  comprises a series of horizontal, parallel slabs  132 , with at least the opposite ends  150  and  160  acting as a deterrent to cattle and other hoofed animals from passing across the cattle guard  130 . Each slab  132  is produced by pouring wet concrete or other settable amorphous medium into the channels  112  and compartment  120  of form unit  110  in situ. The concrete preferably has a psi of about 5,000. Referring to  FIG. 8 , each slab  132  comprises proximal end  134  and distal end  136 , a bottom  140 , opposing sides  135  and  137 , and a top  142 . The slab  132  also comprises two opposing sides, a front side  135  and a back side  137 . Preferably, the sides  135  and  137  are upwardly convergent. The series of slabs  132  are not overlapping; in fact, space  118  separates each slab  132  from the next, as illustrated in  FIG. 8 . The space  118  is preferably not large enough for a hoof of a hoofed animal to get completely through. Space  118  has downwardly convergent sides in that the width at the top is wider than the width at the bottom so that the hoof will not be able to reach the bottom of space  118  to obtain footing. Likewise, the hoof will be less likely to get stuck under the cattle guard  130 , which might happen were it to pass through the slabs. The top  142  may be rounded in a half-moon shape, which also provides unsuitable footing for hoofed animals and making it virtually impossible for a hoofed animal to walk across. 
     Referring to  FIG. 8 , the cattle guard  130  further comprises a connecting slab  144  which is placed in each space  118  and connects each slab  132  to the next. The connecting slab  144  is preferably rectangular and is configured such that it is placed in the center of a length of the slab  132  in space  118 . In other words, a connecting slab  144  is placed between side  135  of a slab  132 , and side  137  of an adjoining slab  132 . This allows for the interconnection of slabs  132  with each other. 
     Referring to  FIG. 10 , a series of cattle guards  130  can be placed next to each other to form a larger cattle guard  131 . A female connector  146  is placed on the distal end  136  of each slab  132  and a male connector  148  is placed on the proximal side  134  of each slab  132  of the cattle guard  130 . The female connector  146  and the male connector  148  may be switched and placed on proximal end  134  and distal end  136 , respectively. The cattle guards  130  are joined by the interconnection of the female connector  146  with the male connector  148  and the distal end  136  and the proximal end  138  of the first and last cattle guards  130  are capped with an end cap  150  respectively. 
     The dimensions of each cattle guard  130  are preferably on the order of about 8′ long by 6′ wide. The height of the cattle guard is preferably about one foot. 
     The form unit  110  also may have a bottom  115 . This allows for stacking of forms  110  during shipment to reduce cost. In this aspect, the form  110  may be placed on the ground. The proximal end  111 , the distal end  113  and the two opposing sides  116  and  117  are reinforced with bolts and straps, such that these ends and sides maintain their shape during the concrete pour. The concrete may be poured into the ground and the cattle guard  130  is shaped by the surrounding walls. In this arrangement, reinforcement bars  122  and  124  and placed on top of the reinforcement bolts and straps. 
     Noting  FIG. 11 , during shipment of the forms  110  shown in  FIGS. 8-10 , removable blocking  210  is inserted into compartments  120  between the adjacent sides  212 ,  214  that form the slabs  132 . The blocking  210  can be left in place during pouring of the settable material, and then removed before the poured material sets. The blocking  210  may extend substantially a length of each compartment  120  and provide support against the settable material such as concrete. 
     A third embodiment of the present invention will now be described with reference to  FIGS. 12-18 . 
     First noting  FIG. 12 , a basic cattle guard unit  310  in accordance with this embodiment is shown. Cattle guard unit  310  is preferably rectangular in shape and includes side rails  312 ,  314 ,  316  and  318  with four corners  313 ,  315 ,  317  and  319  between adjacent side rails. A plurality of guard rails  320 ,  322 ,  324 ,  326  and  328  are molded with and extend above the side rails  312 ,  314 ,  316  and  318 . The guard rails are molded at a substantial angle, preferably 45 degrees, between the side rails  312 ,  314 ,  316  and  318  and are separated by stringers  330  so as to define intervening grooves  321 ,  323 ,  325  and  327  between adjacent guard rails  320 ,  322 ,  324 ,  326  and  328 . The angular disposition of the guard rails permits bicycles, motor cycles, automobiles and trucks to pass across the top of the unit  310  without destructive loading. Additionally, raised areas  332 ,  334  at respective corners  313 ,  317  extend approximately to the same height as the guard rails  320 ,  322 ,  324 ,  326  and  328 . Directional arrows  336  adjacent one of the raised areas  332  provide assistance in fitting cattle guard units  310  together, as is discussed below with respect to  FIGS. 14, 15, 17 and 18 . 
     The manner in which the basic cattle guard units  310  are fitted together to assist in defining a restriction for cattle and other animals in an opening of a fence will now be described with reference to  FIGS. 13 and 14 . 
     First noting  FIG. 13 , a fence F is provided with an opening defining a walkway W. A pit P is extended into the ground in the opening of the walkway W, and preferably gravel G is placed across the bottom of the pit P. Thereafter, one of more of the cattle guard units  310  are placed into the pit P to restrict the movement of cattle and other animals through the fence F along the walkway W. In the example of  FIGS. 13 and 14 , this is achieved by fitting two of the cattle guard units  310  in the pit P. Noting  FIG. 15 , it is first observed that the guard rails (for example guard rails  320  in  FIG. 15 ) extend above the level of the guard rails  312 ,  314 ,  316  and  318  with the corner raised areas  332  of each cattle guard unit  310  fitting together. The arrows  336  help guide the installation of the cattle guard units  310  in the desired manner. 
     Noting  FIG. 16 , a drain hole  340  is preferably placed in each of the stringers  330  so that the molded plastic cattle guard units do not float when a volume of water fills the pit P of  FIG. 13 . 
     Other construction configurations of the third embodiment invention are shown in  FIG. 17 , which illustrates a use of four cattle guard units  310  in a larger size. Likewise,  FIG. 18  illustrates an eight unit construction for an even larger cattle guard installation. 
     While the invention has been described with respect to certain specific embodiments, it will be appreciated that many modifications and changes may be made by those skilled in the art without departing from the spirit of the invention. It is intended, therefore, that the appended claims cover all such modifications and changes as fall within the true spirit and scope of the invention.

Summary:
Several embodiments of livestock guards are disclosed that utilize pre-fabricated forms that are transported to the installation site and are then either filled with a settable material such as concrete or a settable foam, or alternatively is assembled from basic guard units that are fitted together to define the assembled livestock guard.