Abstract:
A retaining wall system and connector therefor. The system can be used with soil reinforcement material. The connector can function to hold the reinforcement material in place in addition to interlocking the blocks together.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a retaining wall block system. The system also includes a connector that is used to interlock blocks together and/or with soil reinforcement materials, such as a geogrid. 
     BACKGROUND OF THE INVENTION 
     In recent years, segmental concrete retaining wall units which are dry stacked (i.e., built without the use of mortar) have become a widely accepted product for the construction of retaining walls. Examples of such products are described in U.S. Pat. No. Re. 34,314 (Forsberg &#39;314) and U.S. Pat. No. 5,294,216 (Sievert). Such products have gained popularity because they are mass produced, and thus relatively inexpensive. They are structurally sound, easy and relatively inexpensive to install, and couple the durability of concrete with the attractiveness of various architectural finishes. 
     The retaining wall system described in Forsberg &#39;314 has been particularly successful because of its use of a block design that includes, among other design elements, a unique pinning system that interlocks and aligns the retaining wall units, allowing structural strength and efficient rates of installation. This system has also shown considerable advantages in the construction of larger walls when combined with the use of geogrid tie-backs hooked over the pins, as described in U.S. Pat. No. 4,914,876 (Forsberg). 
     The construction of modular concrete retaining walls as described in Forsberg involves several steps. First, a leveling pad of dense base material or unreinforced concrete is placed, compacted and leveled. Second, the initial course of blocks is placed and leveled. Two pins are placed in each block into the pin holes. Third, core fill material, such as crushed rock, is placed in the cores of the blocks and spaces between the blocks to encourage drainage and add mass to the wall structure. Fourth, succeeding courses of the blocks are placed in a “running bond” pattern such that each block is centered over the two blocks below it. This is done by placing the blocks so that the receiving cavities of the bottom of the block fit over the pins that have been placed in the units in the course below. As each course is placed, pins are placed in the blocks, the blocks are corefilled with drainage rock, and the area behind the course is backfilled and compacted until the wall reaches the desired height. 
     If wall height or loading conditions require it, the wall structure may be constructed using reinforced earth techniques such as geogrid reinforcement, geosynthetic reinforcement, or the use of inextensible materials such as steel mesh or mat. The use of geogrids are described in U.S. Pat. No. 4,914,876 (Forsberg). After placement of a course of blocks to the desired height, the geogrid material is placed so that the pins in the block penetrate the apertures of the geogrid. The geogrid is then laid back into the area behind the wall and put under tension by pulling back and staking the geogrid. Backfill is placed and compacted over the geogrid, and the construction sequence continues as described above until another layer of geogrid is called for in the planned design. The use of core fill in the blocks is known to enhance the wall system&#39;s resistance to pull out of the geogrid from the wall blocks. 
     Though the pinning system described above can aid in producing a structurally sound wall, there is a desire to provide a block that is as lightweight as possible, relatively inexpensive and easy to produce. In addition it is desirable to have a block that connects well to geogrid reinforcement particularly in the upper section of a retaining wall where the normal load on the connection of the geogrid to the block is limited. 
     SUMMARY OF THE INVENTION 
     This invention is a retaining wall block and system that includes connectors used to align an upper course of blocks over a lower course. The block and connectors can be used with soil reinforcement materials. 
     In one aspect, this invention is a wall block connection system comprising a plurality of wall blocks, each wall block having a top surface, a bottom surface opposed to the top surface, first and second opposing side surfaces, a front face, and a rear face, the front and rear faces, top and bottom surfaces and side surfaces defining a block body, the block body including a head portion including the front face, a rear portion including the rear face, and first and second neck portions defining a core between the head and rear portions adjacent the rear portion, the head portion having at least one cavity defining a first web portion between the cavity and the first side surface and a second web portion between the cavity and the second side surface and a plurality of channel shaped connectors, each connector having first and second side segments connected by a bridge segment, the bridge segment having a pin element extending therefrom and being sized such that during construction of a wall, the first and second side segments straddle a web portion of the block. Each block may further comprise a partition dividing the cavity into first and second cavities. The cross-sectional shape of the pin element may be circular. 
     In another aspect, this invention is a retaining wall having at least a first lower course of blocks and a second upper course of blocks comprising the wall block and plurality of channel shaped connectors described above wherein the bridge segment is accommodated within the recessed region of the web portion so that the pin element extends upwardly into a cavity of a block in the upper course to thereby stabilize the relative positions of the blocks in the upper and lower courses. 
     In a third aspect, this invention is a method of making a retaining wall having at least a first lower course of wall blocks and a second upper course of wall blocks comprising the wall blocks and channel connectors described above, placing the wall blocks to form the first lower course of blocks, positioning the connectors on the blocks in the first course such that the first and second side segments of each connector straddle the first and second web portions and the bridge portion is accommodated within the recessed region of the first and second web portions and the pin element extends upwardly, and placing wall blocks over the first course of blocks to form the second course of wall blocks, the second course of blocks being positioned such that the cavity of each block in the second course of blocks receives an upwardly extending pin element. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: 
     FIGS. 1A and 1B are perspective and top views, respectively, of one embodiment of the retaining wall block of this invention. 
     FIGS. 2A and 2B are perspective and top views, respectively, of another embodiment of the retaining wall block of this invention. 
     FIGS. 3A and 3B are perspective and top views, respectively, of another embodiment of the retaining wall block of this invention. 
     FIGS. 4A and 4B are front and back perspective views of another embodiment of the retaining wall block of this invention. 
     FIGS. 5A and 5B are top and bottom views, respectively, of the block shown in FIGS. 4A and 4B. 
     FIG. 6A is across-sectional view along line a—a of FIG.  5 A and FIG. 6B is a cross-sectional view along line b—b of FIG.  6 A. 
     FIG. 7 is a side view of the block of FIG.  4 A. 
     FIG. 8 is a perspective view of another embodiment of the retaining wall block of this invention. 
     FIG. 9A is a top view of another embodiment of the retaining wall block of this invention; FIG. 9B is a side view of the block of FIG. 9A shown as manufactured with a companion block; FIG. 9C is a side view of the block, and FIG. 9D is a side view of the block with a connector in place. 
     FIGS. 10A and 10B are alternate views of the connector of this invention. 
     FIG. 11 is a partial perspective view of a wall in a running bond pattern constructed from the blocks of FIG.  4 A. 
     FIG. 12 is a top view of a curvilinear row of the blocks of FIG.  4 A. 
     FIG. 13 is a partial perspective view of a wall of the blocks of FIG. 9A with connector and geosynthetic fabric in place. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In this application, “upper” and “lower” refer to the placement of the block in a retaining wall. The lower surface faces down, that is, it is placed such that it faces the ground. In forming a retaining wall, one row of blocks is laid down, forming a course. A second course is laid on top of the first course by positioning the lower surface of one block on the upper surface of another block. 
     The blocks of this invention are made of a rugged, weather resistant material, such as concrete. Other suitable materials include plastic, reinforced fibers, wood, metal and stone. In the blocks of this invention, the front face is substantially parallel to the rear face of the block. The blocks of this invention are provided with a core and one or more cavities that serve to decrease the weight of the block. The core and cavities provide for ease of construction of a retaining wall. In a preferred embodiment, the top surface of the block is provided with a recessed area. This recessed area can receive the transverse bar of a geogrid. Since this transverse bar may be thicker than the rest of the geogrid, the next course of blocks will be level. In addition, this recessed area, in conjunction with one or more cavities, is configured to receive a connector that can be used with a geogrid. 
     Turning now to the figures, several embodiments of the block of this invention will be described. 
     FIG. 1A illustrates block  100   a  in front perspective view and FIG. 1B shows a top view. Block  100   a  has parallel top surface  102   a  and bottom surface  103   a  (not shown), front face  104   a , rear face  105  and first and second side wall surfaces  106   a  and  107   a . Front face  104   a  and rear face  105  each extend from top surface  102   a  to bottom surface  103   a  and side wall surfaces  106   a ,  107   a  each extend from top surface  102   a  to bottom surface  103   a  and from front face  104   a  to rear face  105 . Block  100   a  comprises body  110  which includes front portion  108   a  and back portion  109 . Neck portions  122  and  124  connect front portion  108   a  and back portion  109 . Front portion  108   a  includes at least one front cavity. In the preferred embodiments described herein, the front cavity is two separate cavities. In block  100   a,  cavities  118  and  119  are separated by partition  117 . Partition  117  is optional, however, it provides structural stability and strength to the block. It is not required that cavities  118  and  119  extend the thickness of the block, however, it is typically preferred because of manufacturing constraints. For example, cavities  118  and  119  could be pockets or deep depressions, extending partway through the block, rather than passageways through the block. Preferably, however, the dimensions of cavities  118  and  119  are maximized so that the weight of the block is minimized. Webs  114  and  115  extend between the front cavity and side surfaces  106   a  and  107   a , respectively. 
     Neck portions  122  and  124  are positioned laterally along the width of the block such that their lateral center point is spaced one-quarter of the width of the block away from the widest point of the block. This spacing allows the neck portions of each block to align with the neck portions of blocks above and below the block when a wall is built in a running bond pattern as illustrated in FIG. 11, which facilitates the passage of core fill materials such as crushed stone into the wall structure during construction, and effectively supports the vertical loads of the wall structure. 
     Block body  110  is provided with core  113 . The block is not required to have a core, however, because the presence of a core reduces the weight of the block, a core is highly desirable. In addition, preferably the size of core  113  is maximized. A large core reduces the block&#39;s weight as much as possible and increases the blocks&#39; connection strength to geogrids when the core is filled with core fill material (typically crushed rock). Side wall surfaces  106   a  and  107   a  extend from rear face  105  to front face  104   a  and are of a compound shape. The compound shape results in side voids  111  and  112 . Such side voids are desirable in reducing the weight of the block and because they can be used to add to the stability of a wall, as described further below. 
     An embodiment similar to block  100   a  is block  100   b , shown in FIGS. 2A and  2 B. Identical elements have the same numbers for these two blocks. Front portion  108   b  differs from  108   a  in that there are beveled corners  140 . Thus face  104   b  is smaller than face  104   a . Block  100   b  also is shown with connector  700  in place. 
     In addition, saddle-shaped connector  700  is shown on blocks  100   a  and  100   b  in FIGS. 1A and 2A, respectively. This connector is described further below. 
     Another embodiment of the block of this invention is illustrated in FIGS. 3A and 3B wherein block  200  is shown in perspective and plan views, respectively. Block  200  is similar to block  100   a , except that neck portions  214  and  215  have recessed areas  214   a  and  215   a , respectively, configured to receive saddled-shaped connector  700 . Connector  700  is shown in position on block  200  in FIG,  3 A. Block  200  comprises body  210  which includes front portion  208 , back portion  209  together with neck portions  222  and  224  connect front portion  208  and back portion  209 . Partition  217  separates the front cavity into separate cavities  218  and  219 . Webs  214  and  215  extend between the front cavity and side surfaces  206  and  207 , respectively. 
     Block  200  has parallel top surface  202  and bottom surface  203 , front face  204 , rear face  205  and first and second side wall surfaces  206  and  207 . Front face  204  and rear face  205  each extend from top surface  202  to bottom surface  203  and side wall surfaces  206 ,  207  each extend from top surface  202  to bottom surface  203  and from front face  204  to rear face  205 . Neck portions  222  and  224  are positioned laterally along the width of the block such that their lateral center point is spaced one-quarter of the width of the block away from the widest point of the block. Front face  204  forms part of head or front portion  208 , while rear face  205  forms part of back portion  209 . The block body  210  is provided with core  213 . Side wall surfaces  206  and  207  extend from rear face  205  to front face  204  and are of a compound shape, having side voids  211  and  212 . 
     Block  300   a  is shown in FIGS. 4 to  7 . FIGS. 4A and 4B are front and back perspective views and FIGS. 5A and 5B show top and bottom views, respectively. Block  300   a  has parallel top surface  302  and bottom surface  303 , front face  304   a , rear face  305  and first and second side wall surfaces  306  and  307 . Front face  304   a  and rear face  305  each extend from top surface  302  to bottom surface  303  and side wall surfaces  306 ,  307  each extend from top surface  302  to bottom surface  303  and from front face  304   a  to rear face  305 . As most easily seen in side view in FIGS. 6 and 7, top surface  302  has recessed area  320  extending between the side wall surfaces. Recessed area  320  can receive the transverse bar of a geogrid, as discussed below. 
     Block  300   a  comprises a body  310  which includes front portion  308  and back portion  309 . Neck portions  322  and  324  connect front portion  308  and back portion  309 . Partition  317  separates the front cavity into separate cavities  318  and  319 . Partition  317  is optional, however, it provides structural stability and strength to the block. It is not required that cavities  318  and  319  extend the thickness of the block, however, it is typically preferred because of manufacturing constraints. Webs  314  and  315  extend between the front cavity and the side surfaces  306  and  307 , respectively. Webs  314  and  315  and partition  317  together form recessed region  320 , that is, recessed relative to top surface  302 . The recessed region can be seen in cross section in, for example, FIGS. 5,  6 , and  7 . 
     In addition, front face  304   a  is provided with a desired pattern, design, or texture. For example, a roughened surface, such as the appearance of natural stone, is a desirable appearance. 
     Neck portions  322  and  324  are positioned laterally along the width of the block such that their lateral center point is spaced one-quarter of the width of the block away from the widest point of the block. This spacing allows the neck portions of each block to align with the neck portions of blocks above and below the block when a wall is built in a running bond pattern as illustrated in FIG. 11, which facilitates the passage of core fill materials such as crushed stone into the wall structure during construction, and effectively supports the vertical loads of the wall structure. 
     Front face  304  forms part of head or front portion  308 , while rear face  305  forms part of back portion  309 . The block body  310  is provided with core  313 . The block is not required to have a core, however, because the presence of a core reduces the weight of the block, a core is highly desirable. In addition, preferably the size of core  313  is maximized. A large core reduces the block&#39;s weight as much as possible and increases the blocks&#39; connection strength to geogrids when the core is filled with core fill material (typically crushed rock). Side wall surfaces  306  and  307  extend from rear face  305  to front face  304  and are of a compound shape. The compound shape results in side voids  311  and  312 . Such side voids are desirable in reducing the weight of the block and because they can be used to add to the stability of a wall, as described further below. 
     FIG. 6A is a cross-sectional view along line a—a of FIG.  5 A and shows that core  313  passes from the top to the bottom of the block. Recessed area  320  is shown and discussed further below. FIG. 6B is a cross-sectional view of block  300   a  along line b—b of FIG.  5 A. Cavity  318  is shown extending from the top to the bottom of the block. 
     FIG. 5B shows the bottom view of block  300   a . The bottom surface  303  of block  300   a  is substantially in one plane. FIG. 5B illustrates that the core  313  and cavities  318  and  319  pass through the block. During manufacture of the blocks, it is typical to taper the core and cavities for ease of stripping the block from the mold. That is, for example, the core is slightly larger at the top of the block than at the bottom. 
     An alternate embodiment of the block is shown in FIG.  8 . Block  300   b  is substantially similar to block  300   a  except that front face  4   b  has edges  340   b  that are beveled or chamfered to provide an attractive appearance. In addition, front face  304   b  preferably is provided with a desired pattern, design, or texture. For example, a roughened surface, such as the appearance of natural stone, is a desirable appearance. The block, when made from concrete, preferably has a split or fractured front face appearance. There are several well known manufacturing techniques to accomplish this appearance. 
     Another embodiment of the block of this invention is illustrated in FIGS. 9A to  9 D. The top view of block  400  is shown in FIG.  9 A. Block  400  comprises body  410  which includes front portion  408  and back portion  409 . Neck portions  422  and  424  connect front portion  408  and back portion  409 . Webs  414  and  415  extend between the front cavity and side surfaces  406  and  407 , respectively. 
     Block  400  has parallel top surface  402  and bottom surface  403 , front face  404 , rear face  405  and first and second side wall surfaces  406  and  407 . Front face  404  and rear face  405  each extend from top surface  402  to bottom surface  403  and side wall surfaces  406 ,  407  each extend from top surface  402  to bottom surface  403  and from front face  404  to rear face  405 . Neck portions  422  and  424  are positioned laterally along the width of the block such that their lateral center point is spaced one-quarter of the width of the block away from the widest point of the block. Front face  404  forms part of head or front portion  408 , while rear face  405  forms part of back portion  409 . The block body  410  is provided with core  413 . A Side wall surfaces  406  and  407  extend from rear face  405  to front face  404  and are of a compound shape, having side voids  411  and  412 . 
     Top surface  462  has recessed area  420 . This recessed area is larger than the recessed area as shown in blocks  300   a  or  300   b , as it includes partition  417  and extends between cavities  418  and  419  and the front portion  408  of the block. Neck portions  422  and  424  connect front portion  408  and back portion  409 . Webs  414  and  415  extend between the front cavity and side surfaces  406  and  407  and are provided with indentations  414   a  and  415   a , respectively. That is, indentations  414   a  and  415   a  are recessed even deeper in the block than is recess  420 . Saddle connectors  700  fit in these indentations. 
     The front face of the block preferably has the appearance of natural stone. One way to achieve this is to manufacture the block to have a split front face by forming two blocks together, as illustrated in a side view in FIG.  9 B. Here, blocks B 1  and B 2  are formed in a mold and split along line L to form two identical blocks. 
     Though the blocks illustrated in the Figures may have various dimensions, typical dimensions of this block are about 16 to 18 inches (40.6 to 45.7 cm) wide (i.e., the width of the front face), 12 inches (30.5 cm) deep (i.e., from front face to back face), and 6 to 8 inches (15.2 cm to 20.3 cm) thick (i.e., from top to bottom surface). FIGS. 4 to  7  illustrate block  300   a  and show recessed region  320  to be about 1.37 inches (3.5 cm) wide and about 0.19 to about 0.25 inches (0.5 to 0.63 cm) deep. This region can have any desired dimension, but it has been found that this width and depth is a suitable size to receive a connector. Blocks of the present design typically will be lighter in weight per front face area than prior art blocks. A block of the present design that is 18 inches (45.7 cm) wide and 8 inches (20.3 cm) thick should weigh approximately 72 pounds (32.7 kg), and a block of 18 inches (45.7 cm) wide and 6 inches (15.2 cm) thick should weigh approximately 55 pounds (25 kg). 
     FIGS. 10A and 10B are perspective views of different embodiments of the saddle connector of this invention. Saddle connectors are used to interlock blocks in an upper course with blocks in the next lower course. Two different embodiments of saddle connectors are shown in FIGS. 10A and 10B. The placement of connectors on the blocks and their use in construction of a wall are described further below. The saddle connector illustrated in these figures is about 2 inches (5 cm) wide and fits over webs (e.g.,  114  and  115 ). As illustrated in the Figures, the connector may be used with blocks having no recesses; however, a recessed area to accommodate the connector is preferred. Block  200  has recesses  214   a  and  215   a  designed to fit this connector. Most preferred are blocks having recessed areas such as  414   a  and  415   a  in block  400 . 
     The connector is about 1.5 inches (3.81 cm) deep, though any desired dimension could be used, as long as the connector fits over webs (e.g.,  114  and  115 ). The connector is about {fraction (3/16)} inch (i.e., 0.187 in, 0.48 cm) thick. Connector  700  typically comprises rigid polymeric material such as polyvinyl chloride or polyethylene copolymer. It also may comprise fiberglass, steel, aluminum, or other suitable materials. Connector  700  may be formed by extruding or casting a suitable material into the desired shape. Typically, connectors of the present design are less expensive to produce than alternative, prior art connectors. 
     Connector  700   a  includes a channel-shaped saddle portion  702   a  and a substantially cylindrical pin element  704   a . The pin element defines a longitudinal axis. Saddle portion  702   a  comprises support segments  705   a  and  707   a  joined by bridge segment  709   a . The connector fits over and rests on the surface of a web (i.e.,  314  and  315  of block  300  or  414  and  415  of block  400 ). The length and/or bias of the support segments should be sufficient to hold the connector on a web. Connector  700   b  in FIG. 10B is similar to connector  700   a  except that the shape of the pin element  704   b  is different. Saddle portion  702   b  comprises support segments  705   b  and  707   b  joined by bridge segment  709   b . In cross section, pin element  704   a  has the shape of a circle and pin element  704   b  has the shape of an oval. Any cross-sectional shape of pin element could be used, as long as it serves to connect blocks in adjacent courses together and to attach geogrid to a wall. Also, though the pin element of FIGS. 10A and 10B is centered on bridge segment  709   a / 709   b , the pin element could be at any location on the bridge segment. 
     FIG. 11 illustrates the wall  950  constructed of blocks  300   a . The blocks are arranged in a running bond pattern wherein the shape of side voids  311  and  312  of two adjacent blocks in one course coincides with the shape of core  313  in a block in a lower course. In this way, the side voids vertically align with the cores. Also, webs  314  and  315  rest on webs of the blocks on a lower course, and neck portions  322  and  324  rest on neck portions of the blocks in a lower course, thus transferring loads evenly through the wall structure. This overlap provides continuous cavities in the wall which extends through successive courses of blocks, improving the ease with. These continuous cavities can be filled with core fill material such as crushed rock to encourage drainage and add stabilizing mass to the wall. Continuous cavities also allow for the placement of guardrail posts or fences at the top of a wall, or for the reinforcement of the wall with rebar and concrete grout. 
     The blocks of this invention are designed such that free standing, straight, or curved walls can be formed. FIG. 12 is a top view of a curvilinear or serpentine row  952  of blocks  300   a  and illustrates how the shape of the block permits construction of various curves while maintaining a smooth front face of the wall. The curved walls may have both convex and concave curves, as shown in the figure. 
     During construction of a wall, the blocks illustrated above can be used with reinforcement materials, such as geosynthetic fabrics or relatively more rigid geogrids. 
     Various reinforcement materials are known in the art, and they may be inextensible, such as steel mesh, or extensible geosynthetic materials, such as mats and oriented polymeric materials. Geosynthetics are relatively flexible. Such includes rectilinear polymer constructions characterized by large (e.g., 1 inch (2.5 cm) or greater) openings. In these open structure geosynthetics, polymeric strands are woven or “welded” (by means of adhesives and/or heat) together in a grid. Polymers used for making relatively flexible geosynthetics include polyester fibers. The polyester typically is coated with a polyvinyl chloride (PVC) or a latex topcoat. The coating may contain carbon black for ultraviolet (UV) stabilization. Some open structure geosynthetics comprise polyester yarn for the warp fibers and polypropylene as the fill fibers. Another flexible reinforcing geosynthetic material is fabric, i.e., woven constructions without large openings. These fabrics typically comprise polymers and are referred to as geofabrics. The geofabric can be laid between courses of blocks in a wall, and typically is tied into the wall and held there. When blocks are configured to have pin connectors, for example, a hole or slit is formed in the geofabric at the construction site and the geofabric is held on the blocks by fitting it over the pins. 
     FIG. 13 shows a cut-away view of wall  960  showing geosynthetic fabric  965  laid over connectors  700   a  in position in recesses  414   a  and  415   a  of block  400 . In this case, the connectors not only help secure the geosynthetic fabric, but they also add to the stability of the wall, since the pin elements on the lower course extend into cavities  418  and  419  on the upper course. Geosynthetic fabric  965  extends behind the retaining wall so that it can tie into the earth behind the wall, thus increasing the structural strength of the wall. 
     Geofabrics, such as shown in FIG. 13, are generally more flexible than materials formed from flat polymeric sheets of high density polyethylene (HDPE). These relatively rigid geogrids are commercially available under the trade designation “TENSAR”. Holes are formed in the HDPE sheets and then the sheet is drawn or pulled to orient the polymer and increase the modulus. HDPE geogrids are not readily compatible with many prior art wall systems because HDPE geogrids have a relatively thick transverse bar, which will cause the next layer of blocks to be out of level, unless shimming or other means are utilized to compensate for this tendency. The present invention allows the use of HDPE geogrids without shimming because the transverse bar of the geogrid is laid into the recessed areas of adjacent blocks. A connector can then placed over the geogrid, connecting it to the block. The geogrid will then lie flat and the blocks in an upper course will remain level. 
     Succeeding courses of block are then placed above the reinforcement material. Enhancing the connection strength of the reinforcement material to the block is particularly desirable where the reinforcement material is placed close to the top of a wall. Here the confining pressure of the blocks above the reinforcement material is reduced. In a preferred method of forming a wall with the blocks of this invention, connectors  700  are used (with or without reinforcement material) only in the upper section of a wall to provide optimal connection strength. They are not necessary lower in the wall where there is a higher load on the block resulting in higher connection strength. 
     Blocks of this invention are typically manufactured of concrete and cast in a high-speed masonry block machine. For example, cavities  418  and  419  and core  413  of block  400  all are formed using mold core elements. For ease in manufacturing, these blocks typically are made with the top surface facing up. In this way the recessed area can be easily formed by a stripper shoe head of the mold. An advantage of the present design is that it requires a relatively simple mold. In addition, because the present design does not require the formation of pin receiving holes, it is easier to produce since pin receiving holes need to be kept clear of aggregates and concrete crumbs. Typically, blocks are formed as mirror image pairs joined at front face  404  which are then subsequently split using a block splitter, as known in the art, to provide a rough appearing front surface on the split blocks. The front face may be treated further to chamfer the edges or to give it any other desired appearance. Alternatively, other methods may be utilized to form a variety of front face surface appearances. Such methods are well known in the art. 
     Although particular embodiments have been disclosed herein in detail, this has been done for purposes of illustration only, and is not intended to be limiting with respect to the scope of the appended claims, which follow. In particular, it is contemplated by the inventor that various substitutions, alterations, and modifications may be made to the invention without departing from the spirit and scope of the invention as defined by the claims. For instance, the choice of materials or variations in the shape or angles at which some of the surfaces intersect are believed to be a matter of routine for a person of ordinary skill in the art with knowledge of the embodiments disclosed herein.