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BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to erosion control and, more particularly, to an erosion control or revetment block which can be used to form an interlocking mat or material of similar blocks to prevent erosion due to water movement. 
         [0003]    2. Description of the Prior Art 
         [0004]    Erosion control blocks, so-called revetment blocks, are well known and have been used for years to prevent and or minimize erosion. In general, the revetment blocks are used to minimize erosion caused by the movement of water. The revetment blocks can be used along beaches, bays, lakeshores, waterways, channels, drainage ditches, and the like, so as to be able to revet, depending upon the particular environment, the effects of wave action, water runoff, channeled flow of water, etc. 
         [0005]    Examples of revetment blocks can be found in U.S. Pat. Nos. 4,227,829, 4,370,075, 5,556,228, and 8,123,435, all of which are incorporated herein by reference for all purposes. 
         [0006]    Revetment blocks currently used in erosion control generally comprise a body having a polygonal shape, e.g., square, which have at least two arms which extend from peripheral side edges of the body and at least one and preferably two sockets which extend into the body from peripheral side edges. It will be understood that depending upon the shape of the block, the number of arms and sockets and their relative position on the block can vary. For example, in one common revetment block which is square, there are two arms extending from respective sides of the block at 90° to one another and two sockets extending into the block from respective side edges, the sockets being disposed at 90° to one another. 
         [0007]    It is also common for revetment blocks of the interlocking type as described above to include one or more holes extending through the block, i.e., from the first surface to the second surface. These holes serve the purpose of allowing vegetation to grow from below and through the block and help anchor the block to the surface exposed to the moving water. 
       SUMMARY OF THE INVENTION 
       [0008]    In one aspect the present invention provides a revetment block which can interlock with similarly formed revetment blocks to form a mat or matrix resisting erosion caused by water movement over the mat. 
         [0009]    In yet another aspect, the present invention provides a revetment block having a unique shaped hole(s) for vegetation growth. 
         [0010]    These and further features and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a top plan view of a revetment block according to one aspect of the present invention. 
           [0012]      FIG. 2  is a side, elevational view of the revetment block shown in  FIG. 1 . 
           [0013]      FIG. 3  is a bottom plan view of the block shown in  FIG. 1 . 
           [0014]      FIG. 3A  is a partial, plan view of another embodiment of the vegetation hole(s) used in the revetment block of the present invention. 
           [0015]      FIG. 4  is a view taken along the lines  4 - 4  of  FIG. 1 . 
           [0016]      FIG. 4A  is an elevational view similar to  FIG. 4  showing another embodiment of the vegetation hole(s) used in the revetment block of the present invention. 
           [0017]      FIG. 5  is a top plan view of a mat made using the revetment blocks of the present invention. 
           [0018]      FIG. 6  is an elevational view, partly in section, of a mat made using the revetment blocks of the present invention depicting the ability of the blocks to adapt to uneven or undulating ground contours. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0019]    Referring first to  FIGS. 1-3 , a revetment block, shown generally as  10 , has a generally square body  12  having, a first, e.g., top surface  16 , and an opposite, second, e.g., bottom surface  18 . Body  12  has a first side edge  20 , a second side edge  22 , a third side edge  24 , and fourth side edge  26 . Extending from side edge  20  is an arm  28  while a second arm  30  extends, at 90° to arm  28 , from side edge  26 . A socket  32  extends into body  12  from side edge  24  while a second socket  34  extends, at 90° to socket  32 , into body  12  from side edge  22 . As can be seen from  FIG. 1 , arms  28  and  30  are generally complementary in shape to sockets  32  and  34  for reasons discussed hereafter. Arm  28  has an enlarged head portion  36  distal side edge  20 , head portion  36  being connected to side edge  20  by a narrowed neck portion  38 . In general, arm  28  has a generally dovetail shape when viewed in plan view. Similarly, arm  30 , also having a dovetail shape, has an enlarged head portion  40  which is connected to side edge  26  via narrowed neck portion  42 . Socket  32  has a mouth  44  which opens into an enlarged cavity  46 , socket  32  being generally dovetail shaped when viewed in plan view. Likewise, socket  34  has a mouth  48  which opens into an enlarged cavity  49 , socket  34  having a generally dovetail shape when viewed in plan view. 
         [0020]    There are a plurality of holes, shown generally as  50  which extend through a core  52  of block  10 . Core  52  is defined by four imaginary planes passing through lines indicated as A-A, B-B, C-C, and D-D with intersection points, W, X, Y, and Z wherein said planes are normal to said top and second surfaces  16  and  18 , respectively. Thus, as can be seen, basically the core  52  is the portion of the block  10  which is defined by planes passing through the innermost walls  47  and  51  of the sockets  32  and  34 , respectively, and planes passing through the intersection of the arms  28  and  30  with the side edges  20  and  26 , respectively. As seen, holes  50  are generally symmetrically located within the core  52 . However, it is to be understood that the holes need not be symmetrically positioned and can be arranged in various non-symmetrical orientations as desired. However, generally to ensure that the vegetation growth is uniform, symmetrical placement of holes  50  is normally desired. It will also be appreciated that fewer or more holes can be used if desired and their cross-sectional area can vary widely depending on the number of such holes. 
         [0021]    With reference to  FIG. 4 , it can be seen that holes  50  have a first portion  54  which opens through first surface  16  and a second portion  56  which opens through second surface  18 . As can be best seen with reference to  FIGS. 3 and 4 , first portion  54  has a generally cylindrical cross-section forming a circular opening  58  and second portion  56  has a generally rectangular cross-section forming a square opening  60  through second surface  18  of block  10 . As seen in  FIG. 4 , portions  54  and  56  intersect at a point generally midway through the thickness of block  10 . However, it is to be understood that this intersection point is somewhat arbitrary, e.g., portion  54  could have a greater depth than portion  56  or vice versa. 
         [0022]    At the intersection of portions  54  and  56 , there is formed a ledge  62  which in the embodiment shown in  FIG. 3 , extends peripherally around portion  54 . In any event, it will be recognized that where portions  54  and  56  intersect, second portion  56  will have a greater cross-sectional area than the cross-sectional area of first portion  54  at that intersection so as to form a ledge. 
         [0023]    Referring now to  FIG. 3A , there is shown a variation of a revetment block of the present invention. In all respects, the block  10 A shown in the fragmentary view of  FIG. 3A  is like block  10  with the exception that the holes  50 A of block  10 A have first and second portions, both of which have circular cross-sections, the first portion opening into the first surface (not shown) defining a circular opening  72 , the second portion opening into second surface  18 A having a circular opening  74 . However, again it will be seen that there is a ledge  76  formed at the intersection of the first and second portions of the holes  50 A. Again, as shown in  FIG. 3A , the ledge  76  extends peripherally around the first portion of hole  50 A opening through the first surface of  10 A. 
         [0024]    Referring now to  FIG. 4A , there is shown yet another embodiment of the revetment block of the present invention. The revetment block  10 B, only a portion of which is shown in  FIG. 4A  has a first surface  16 B, a second surface  18 B and a hole  80  having a first portion  82  opening through first surface  16 B, and a second portion  84  opening through second surface  18 B. As can be seen from  FIG. 4A , first portion  82  and second portion  84  have a frusto-shape in elevation wherein frusto-shape means a volume which can be circular or polygonal in cross-section and which varies in cross-sectional area along its length. A ledge  86  is formed at the intersection of the frusto-shaped portions  82  and  84 , the ledge  86  surrounding frusto-shaped portion  82 . It will thus be appreciated that both first and second portions  82  and  84 , respectively could be frustoconical, the first portion could be frustoconical and second portion frustopyramidal, etc. 
         [0025]    It will be apparent that any number of cross-sectional configurations of the holes can be employed, both for the first portion and the second portion, the requirement being that there be a ledge formed at the intersection of the first and second portions. It will also be understood that it is not necessary that the ledge extend in a peripheral fashion around the first portion, i.e., the portion opening through the first surface of the block. Rather, depending on the cross-sectional shape, the ledge could be formed by a series of discontinuous ledges. For example, if the first portion of the hole was circular in cross-section and the second portion of the hole was triangular, the ledge could be formed in three separate portions, it being understood that in such a configuration the triangle defined by the cross-section of the second portion would circumscribe the circle defined by the cross-section of the first portion. Thus, the cross-sectional shapes of the first and second portions can be circular, oval, octagonal, etc. 
         [0026]    Referring now to  FIG. 5 , there is shown a plan view of a mat formed by interlocked blocks  10 . The mat shown generally as  100  depicts how the arm  30  of one block fits into the socket  34  of an adjacent block and the arm  28  of that same block fits into the socket  46  of an adjacent block. As can be seen, the sockets are slightly larger than the arms to permit some degree of freedom of movement laterally between adjacent blocks. Indeed, it can be seen that the blocks can be spread apart in two dimensions some distance to increase the area for vegetation growth. Although the arms fit loosely in the sockets, when moved apart laterally relative to one another, they do not separate because the heads, e.g. head  40  of arm  30  at its widest dimension is wider than the mouth, e.g. mouth  48  of socket  34 . 
         [0027]    Referring now to  FIG. 6 , there is shown how the blocks can be vertically adjusted relative to one another to conform to a contoured or undulating ground surface shown generally as G. This ability of the blocks to articulate in a vertical direction relative to one another again is a function of the fact that the arms fit somewhat loosely in the sockets. 
         [0028]    While not wanting to be bound by any theory, it is believed that the unique configuration of the vegetation holes through the block, e.g., holes  50 , leads to enhanced vegetation retention of the block. In this regard, since, in one embodiment, the enlarged portion of the vegetation holes is adjacent the surface upon which the blocks are laid, vegetation growing up through the holes is believed to form a larger, more complex root structure in the enlarged area of the second portion of the holes, i.e., the portion that opens to the second surface of the blocks. Thus, it is believed the blocks can resist greater shear forces from moving water. 
         [0029]    Although specific embodiments of the invention have been described herein in some detail, this has been done solely for the purposes of explaining the various aspects of the invention, and is not intended to limit the scope of the invention as defined in the claims which follow. Those skilled in the art will understand that the embodiment shown and described is exemplary, and various other substitutions, alterations and modifications, including but not limited to those design alternatives specifically discussed herein, may be made in the practice of the invention without departing from its scope.

Summary:
A revetment block comprising a body having a first surface, a second surface and a plurality of peripherally extending side edges. The body has at least two arms extending laterally outwardly from the respective side edges and at least two sockets extending laterally inwardly from the respective side edges. There is at least one hole extending through the body, the hole having a first and a second portion. The first portion of the hole opens through the first surface of the block while the second opens through the second surface of the block. The first and second portions intersect interiorly of the block. The cross-sectional area of the first portion is less than the cross-sectional area of the second portion at the intersection of the first and second portions. Accordingly, the intersection of the first and second portions forms a ledge.