Abstract:
A block and pad unit for use in forming a seabed mat includes a concrete block having an upper surface, a lower surface and at least four sides extending between the upper and lower surfaces. An opening extends from the upper surface to the lower surface of the block. An abrasive resistant pad is attached to one of the upper surface or the lower surface. The pad includes a base having a lower side adjacent the block and an upper side facing away from the block, an opening aligned with the opening of the block, and a plurality of dome-shaped mounds extending integrally upward from the upper side of the base and distributed about a periphery of the opening of the pad.

Description:
TECHNICAL FIELD 
       [0001]    The present application relates generally to a seabed mat, and more particularly to a non-abrasive pad for an articulated seabed mat. 
       BACKGROUND 
       [0002]    Hydrodynamic forces, which are generated by the bottom currents and waves, create a need for a stabilization technique for underwater pipes and other seabed installations in off shore applications. Seabed mats are often used for such stabilization and protection. The seabed mats can also reduce erosion. 
         [0003]    Concrete has typically been used for the covering because of its strength and strong resistance to the action of natural types of water. However, many underwater pipelines are covered with a thin-filmed epoxy coating that is used as a protection system. If this epoxy coating is scratched, the pipeline is subject to corrosion. Therefore, some mats have utilized pads in conjunction with an articulated mat in an effort to prevent the concrete from scratching or damaging the epoxy coating of the underwater pipelines. 
       SUMMARY 
       [0004]    In an aspect, a block and pad unit for use in forming a seabed mat includes a concrete block having an upper surface, a lower surface and at least four sides extending between the upper and lower surfaces. An opening extends from the upper surface to the lower surface of the block. An abrasive resistant pad is attached to one of the upper surface or the lower surface. The pad includes a base having a lower side adjacent the block and an upper side facing away from the block, an opening aligned with the opening of the block, and a plurality of dome-shaped mounds extending integrally upward from the upper side of the base and distributed about a periphery of the opening of the pad. 
         [0005]    In another aspect, an abrasive resistant pad for connection to a concrete block includes a base having a lower side and an upper side and an opening extending from the upper side to the lower side. A plurality of dome-shaped mounds extend integrally upward from the upper side of the base and distributed about a periphery of the opening. At least two spaced apart collar members extend downward from the periphery of the opening. Each collar member is angled to extend outward from the opening toward a perimeter of the base when moving from the base downward, and each collar member is configured to flex inward. 
         [0006]    In another aspect, a seabed mat includes a plurality of concrete blocks, each block having an upper surface and a lower surface. A first aperture extends between opposed first and second sides of the block and a second aperture extends between opposed third and fourth sides of the block, the first aperture substantially perpendicular to the second aperture. A plurality of cables interconnect the plurality of blocks by passage through the first and second apertures of the blocks. A plurality of abrasive-resistant pads are attached to at least some of the blocks. Each pad includes a base having an upper side facing away from the associated block and a plurality of bulges extend integrally from the upper surface. The bulges are distributed about a perimeter of the pad, each bulge having a footprint having a width that is at least three times a height of the respective bulge. 
         [0007]    The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a plan view of an embodiment of a seabed mat; 
           [0009]      FIG. 2  is a plan view of another embodiment of a seabed mat; 
           [0010]      FIG. 3  is a side view of an embodiment of a block used to form the seabed mat of  FIG. 1 ; 
           [0011]      FIG. 4  is a top view of the block of  FIG. 3 ; 
           [0012]      FIG. 5  is a side view of an embodiment of a abrasive-resistant pad used to form the seabed mat of  FIG. 1 ; 
           [0013]      FIG. 6  is a bottom view of the abrasive-resistant pad of  FIG. 5 ; 
           [0014]      FIG. 7  is a top view of the abrasive-resistant pad of  FIG. 5 ; 
           [0015]      FIG. 8  is a diagrammatic, top view of the pad of  FIG. 5  highlighting footprints of dome-shaped mounds of the abrasive-resistant pads; 
           [0016]      FIG. 9  is a perspective view of the pad of  FIG. 5  connected to the block of  FIG. 3 ; and 
           [0017]      FIG. 10  is a side view of the seabed mat of  FIG. 1  laid over an underwater installation. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Referring to  FIG. 1 , a seabed mat  10  is formed of multiple blocks  12  aligned in rows and columns. As illustrated, each column of blocks  12  is substantially parallel with other columns and each row of blocks is substantially parallel with other rows, however, other configurations are possible. The blocks  12  are interconnected by cables  14 . In some embodiments, a single cable  14   a  is used to connect a pair of adjacent columns of blocks  12  together and another single cable  14   b  is used to connect a pair of adjacent rows of blocks together. The ends of the cables  14   a  extend from the ends of adjacent columns of the blocks  12  and attach to each other to form a loop  16 . A portion of the cables  14   a  also extends from opposite ends of the columns to form loops  18 . The loops  16 ,  18  may be used in lifting, handling and installation of the seabed mat  10 . Non-corrosive compression sleeves  20  are attached to the cables  14   a  where the cables extend from the columns of blocks  12 . Each end of the cables  14   a  is connected by a compression sleeve  20  to the portion of the cable  14   a  extending from the adjacent column, thereby forming double-stranded loops  16 . Cables  14   b  are used to connect adjacent rows of blocks  12  together. The cables  14   b  extend from ends of the rows of blocks  12  and may be connected together in the same or similar fashion as cables  14   a . The compression sleeves  20  may be sufficiently large to prevent them from slipping into the interior of the blocks  12 . Other methods for interconnecting the blocks  12  are also contemplated. For example,  FIG. 2  shows an embodiment where cables  14   b  are tensioned with ends of the cables  14   b  connected by a compression sleeve  20 . 
         [0019]    Each block  12  includes an abrasive-resistant pad  22  connected thereto. As will be described in greater detail below, the pads  22  provide a contact point between the blocks  12  and a seabed or underwater installation overlaid by the pad  22  and the block  12 . The pads  22  include a series of bulges, in the illustrated embodiment, dome-shaped mounds  25  formed of the abrasive-resistant material that reduce the contact area between the blocks  12  and the installation (or other structure in contact with the mat). 
         [0020]      FIGS. 3 and 4  illustrates a block  12  in isolation without the pad  22 . While various shapes may be used, the block  12  (e.g., formed of concrete) is shown as upper and lower trapezoidal-shaped units  23  and includes an upper surface  24 , a lower surface  26  and sides  28 . The upper surface  24  and lower surface  26  are each somewhat square-shaped. An opening  30  extends completely through the block  12  from the upper surface  24  to the lower surface  26 . The shape of the opening  30  can be of any number of shapes; however, the illustrated shape is a square. 
         [0021]    The block  12  includes apertures  32  and  34  that extend between sides  28  of the block. The apertures  32  and  34  run substantially perpendicular to each other and intersect the opening  30 . The apertures  32  and  34  are sized to receive the cables  14  therethrough to interconnect the blocks  12 , for example, as described with reference to  FIG. 1 . Extending inwardly from the upper surface  24  of the block  12  are dowel holes  36 . In this embodiment, there are four dowel holes  36  at the corners of the upper surface  24 . 
         [0022]    Referring to  FIGS. 5 and 6 , the abrasive-resistant pad  22  includes a substantially planar base  38  formed of abrasive-resistant material and self-locking dowels  40  that extend outwardly from a lower surface  43  of the base. The self-locking dowels  40  include fins  42  that extend along the length of the self-locking dowels. The self-locking dowels  40  can have a maximum diameter slightly larger than that of the dowel holes  36  in the block  12  so that the self-locking dowels can be press-fit into the dowel holes thereby securing the pad  22  to the block. 
         [0023]    A collar  44  formed of separate collar members  44   a - 44   d  also extends downward from the base  38 . The collar  44  is associated with an opening  46  extending through the pad  22 . As can be seen most clearly by collar members  44   a  and  44   c  of  FIG. 5 , the collar members  44   a - 44   d  are biased outwardly toward the edges of the pad  22 , but are flexible enough to be urged inward, so that the collar can be press-fit into the opening  30  extending through the block  12 . In one implementation, opposed collar members are oriented non-perpendicular to the base  38  and angled outward such that the planes containing the collar members intersect the base to define an angle Ø of less than 90 degrees, such as between about 90 degrees and 75 degrees (see  FIG. 5 ). The outward bias of the collar members  44   a - 44   d  increases the friction fit between the collar  44  and the block  12 . By separating the collar members  44   a - 44   d  from each other, their flexibility can be increased over a continuous collar. In some embodiments, a continuous collar may be provided instead of the separate collar members. 
         [0024]    Referring to  FIGS. 5 and 7 , the dome-shaped mounds  25  are provided on an upper surface of the pad  22 . The dome-shaped mounds  25  are aligned in single-file, located about the opening  46  and along the peripheral edges of the pad  22  in a spaced-apart fashion. Other arrangements of the dome-shaped mounds  25  are possible, however. 
         [0025]    The dome-shaped mounds  25  each have a round periphery  47  that intersects with the base  38 . The intersection of the periphery  47  with the upper surface  24  defines a footprint  48  of the dome-shaped mounds on the base  38 . In the illustrated embodiment, the footprints  48  are substantially circular.  FIG. 8  illustrates the footprints  48  of the dome-shaped mounds  24 . Each footprint  48  has an area (the shaded region) and a width W. In some embodiments, the area of each footprint  48  is at least two percent (e.g., between about two percent and about five percent) of the total area of the upper surface  24  (not including opening  46 ) of the pad  22 . In one implementation, between 9-16 dome-shaped mounds are provided and the total footprint area of such mounds is between about 30-60 percent of the total area of the upper surface  24 . Additionally, the profile of the dome-shaped mounds  24  is low to the base  38 . In some embodiments, a height H ( FIG. 5 ) of the dome-shaped mounds  24  is less than the width W of their footprint  48 . In one implementation, the width W may be at least about 3 times the height H, such as about six times the height H. 
         [0026]    Referring back to  FIG. 7 , spanning a distance between certain ones of the dome-shaped mounds  24  are connector members  50  which are raised from base  38 . In some embodiments, the connector members  50  may be used as a reinforced location where a fastener (such as a staple) may be applied through the pad material and into a respective block  12 . In other embodiments, the pad  22  may not include the connector members  50 . 
         [0027]    The dome-shaped mounds  24 , connector members  50 , dowels  40  and collar  44  may all be formed integrally with the base  38 , for example, using a molding process. Suitable materials for forming the pads  22  include high-density polyethylene (HDPE), low-density polyethylene (LDPE), polyvinyl chloride (PVC), nylon or mixtures thereof. 
         [0028]    Referring to  FIG. 9 , the pad  22  is shown attached to the block  12 . As can be seen, the pad  22  rests on the upper surface of the block  12 , the dowels  40  received by the dowel holes  36  and the collar  44  located in the opening  30  of the block. The collar  44  can facilitate alignment of the openings  30  and  46 . 
         [0029]    Referring to  FIG. 10 , the assembled seabed mat  10  ( FIGS. 1 and 2 ) is shown laid over an installation, e.g., pipe  50 . Enough space is provided between the blocks  12  of the mat  10  so that the mat can articulate and blanket the pipe  50 . The dome-shaped mounds  24  provide a contact point between the seabed mat  10  and the pipe  50  over-laid by the mat. Particularly, the dome-shaped mounds  24  provide an anti-abrasion material to protect against the creation of defects in the coating of underwater pipeline. 
         [0030]    Additionally, dome-shaped mounds  24  can reduce contact area between the mat  10  and any underlying surface. This can be advantageous, for example, during installation of the mat  10  when it may be moved from one location to another during which the pads  22  may be slid over a surface. Reduced contact area between the pad  22  and the surface can reduce the likelihood that a pad  22  may be torn away from a block  12  during such an installation, removal, repair or readjustment process. 
         [0031]    A number of detailed embodiments have been described. Nevertheless, it will be understood that various modifications may be made. Accordingly, other embodiments are within the scope of the claims.