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TECHNICAL FIELD OF THE INVENTION  
         [0001]    This invention relates to a masonry block for stacking on other like-shaped blocks in a staggered, interlocking and offset manner to form a gravity-type retaining wall that is particularly suited for integrating into a variety of landscape settings.  
         BACKGROUND OF THE INVENTION  
         [0002]    A variety of masonry block designs have been developed for building gravity-type retaining walls that depend on the weight of the blocks for their stability. Versatile block designs should take several factors into consideration. For walls three feet in height or less, the blocks should form a wall structure that can withstand the pressure of the earth behind the wall. The footprint of the block should be large enough to accommodate soils with relatively low bearing pressures so that the wall will not tilt or sink during use. The setback and height of the block should be such that the combined pressure of the earth and the weight of the wall fall within the footprint of the lowest course of blocks. The block design should also take into account the shape of the blocks, as well as the strength, density and durability of the material forming the block.  
           [0003]    Retaining wall block designs require a mechanism for securing the blocks together to produce a stable wall structure. While the friction between the relatively rough surfaces of stacked blocks can help keep the wall together, this friction is not sufficient in many retaining wall applications. To increase stability, some blocks are designed to be mortared or otherwise adhered together to produce a rigid wall structure. Unfortunately, such retaining walls are prone to cracking due to settling, frost, water buildup behind the wall and earthquakes, as well as the normal use of the wall by people and animals that walk, stand, lean or sit on the wall.  
           [0004]    Other retaining wall block designs incorporate fasteners such as rods, pins or keys to hold and clamp the blocks together. Examples of such block designs are shown in U.S. Pat. Nos. 4,914,876 to Forsberg, 3,390,502 to Carroll, and 4,909,010 to Gravier, the disclosures of which are incorporated by reference herein. A significant problem with these block designs is the expense of the extra components and increased installation costs. These designs can also suffer from unsightly cracks that tend to form in these types of walls.  
           [0005]    Interlocking wall block designs have been developed to overcome the problems associated with the blocks that form rigid retaining wall structures. Interlocking block designs typically have one or more integral projections extending from the upper or lower surface of the block. When stacked, the projection of one block abuts against a surface of another block to help hold the blocks together. The projections also provide a mechanism for offsetting stacked blocks. This offset or setback helps produce a more stable retaining wall that leans into the earth or hill behind the wall to resist the pressure exerted by the earth or hill on the wall. Individual blocks do not need to be rigidly secured by mortar, adhesive, rods, pins or keys, so that the wall is free to flex and accommodate movements in the wall caused by settling, frost, water buildup, earthquakes and normal use. Blocks for retaining walls of this type are described in U.S. Pat. Nos. 5,827,015 to Woolford, 2,313,363 to Schmitt, and 4,565,043 to Mazzarese, the disclosures of which are incorporated by reference herein.  
           [0006]    One problem with conventional interlocking masonry wall blocks is that the thickness of the integral projection is directly related to the amount of setback desired for each course of blocks. A retaining wall application requiring a half-inch setback per course requires blocks with half-inch thick projections. Yet, thin projections are structurally weak and prone to chipping and cracking. While the height of the block can be increased to increase the thickness of its setback, this results in a heavier block that is more difficult to handle. In addition, tall blocks also do not lend themselves to landscaping gradually sloping terrain. Large portions of the block stick out above ground level before a step down at the end of a row or course of blocks can occur. This produces an unsightly wall and results in a waste of material.  
           [0007]    Another problem with conventional interlocking masonry wall blocks is that the integral projection is located along the rear or front edge of the block. As noted above, the setback projection is frequently only a half-inch thick when the blocks are sized for easy handling. Yet, these relatively thin and weak projections are located where they are easily damaged if dropped, improperly stacked or otherwise mishandled. In addition, rear projections are in direct contact with the wetness and acidity of the earth during use, which can cause the projection to deteriorate, weaken and fail over time. Front projections extend upwardly and can collect water between them and the upper course of blocks, which can freeze and crack the projection.  
           [0008]    A further problem with conventional interlocking masonry wall blocks is that the integral projections are relatively short in height to reduce the possibility of chipping and cracking. Although the short projections may be less likely to crack, they do not provide a sufficiently tall abutment to easily and consistently align the block over a lower course of blocks. During construction of a wall, workers have a tendency to leave a gap between the projection and the lower course of blocks or allow the projection to ride-up onto the upper surface of the lower block. These misalignments are not easily detected given the thinness of the projection and its relatively small height. This is especially so for blocks with rear projections that extend down from the lower surface of the block, because the workers are not able to easily see that the blocks are properly aligned. Misalignments can be even more difficult to notice in construction settings where dirt, gravel and other debris are present, and may compact against the setback projection or get on the upper or lower surfaces of the blocks.  
           [0009]    A still further problem with conventional interlocking masonry wall blocks is that they have limited ability to produce serpentine walls with straight, concave and convex portions. The integral projections are sized and shaped to fit into grooves of lower blocks so that the stacked blocks must be oriented a particular way. If a curve is possible, the radius of the curve is constant, so that a true serpentine wall with curves that gradually increase or decrease in radius are not possible. These limitations of conventional block designs prevent the wall from being integrated into the natural contours of the landscape and thus impede the aesthetic value of the wall.  
           [0010]    A still further problem with conventional interlocking masonry wall blocks is that the integral projections do not ensure an even amount of setback for straight and curved portions of the wall. For example, a block with a flange along its front or rear edge produces a wall with discontinuities in the amount of setback between adjacent block as shown in FIG. 14. In addition, the pitch of the wall is also greater in both the concave and convex curved portions of the wall than in the straight portions as shown in FIGS. 14 and 16. This increasing setback and pitch occurs even though a retaining wall may need to be stronger and require more setback in straight portions of the wall than in curved portions.  
           [0011]    A still further problem with conventional interlocking masonry wall blocks is that the blocks require a fixed amount of lateral offset to the right or left of the lower blocks on which they rest. Yet, obstructions at the location where the wall is to be built or the addition of drain pipes in the wall do not always permit each block to be offset a constant amount throughout the entire wall. A block in one course may need to be laterally offset two or three inches to the right or left from the blocks beneath it, and another block in the same or a different course may need to be laterally offset four or five inches from the blocks beneath it. Yet, many interlocking block designs do not allow sufficient flexibility to offset the blocks as needed to accommodate various obstacles or drain pipes. This inflexibility can complicate construction or renders the block unusable for some retaining wall applications.  
           [0012]    A still further problem with conventional interlocking masonry wall blocks is that the integral projection does not provide sufficient resistance to lateral side-to-side movement of the block. Side-to-side movement is only resisted by adjacent blocks in the same course or tier. The side walls of these adjacent blocks abut each other to prevent side-to-side movement. However, should one block in a given course shift or move out of abutting alignment with one of its adjacent blocks, then each of the blocks in that row would be susceptible to shifting as well. Moreover, the blocks that form an end of the wall are not restrained from lateral movement away from its sole adjacent block and could be knocked off the wall altogether.  
           [0013]    A still further problem with conventional interlocking masonry wall blocks is that several different block shapes must be combined to form the straight and curved sections of a serpentine wall. The need for multiple block designs result in increased manufacturing, inventory, shipping and construction costs. The multiple block designs also result in more complicated serpentine wall designs that are not easily integrated to the shape of a specific and unique landscape setting.  
           [0014]    A still further problem with conventional interlocking masonry wall blocks is that they are heavy and difficult to handle. The blocks are typically solid throughout. The openings tend to be small and do not significantly reduce the weight of the block. The excessive weight is compounded by the fact that the block must be tall enough to provide a setback projection or flange that is sufficiently thick to withstand cracking and chipping during transport, construction and use.  
           [0015]    The present invention is intended to solve these and other problems.  
         BRIEF DESCRIPTION OF THE INVENTION  
         [0016]    The present invention relates to an interlocking masonry wall block having an open core and spaced projections that enable stacked blocks to be interlocked, setback and staggered to form a stable gravity-type retaining wall that is particularly suited for landscaping applications. The open core extends completely through the block from top to bottom. The block is formed by front, rear and opposed side walls, each having parallel inside and outside surfaces. One projection extends from the lower surface of each side wall. The front of each projection is forward the inside surface of the front wall to provide the setback when stacked on other like-shaped blocks. Each block is stacked in a staggered manner atop two other blocks. One projection of each block is received by the open core of one of the two lower blocks. The projections abut the inside surface of the front wall of the lower blocks to interlock the blocks together. The block has a preferably trapezoidal shape with a wider front wall to help accommodate the formation of serpentine walls while maintaining a consistent front wall appearance. The block can be used to make serpentine walls with straight and curved portions with a relatively constant pitch.  
           [0017]    One advantage of the present interlocking masonry wall block is that the thickness of the integral projections is not related to the desired amount of setback for each course of blocks. A retaining wall application requiring a half-inch setback per course can have projections that are one or two inches thick. These thicker projections are more structurally sound and not prone to chipping and cracking. The block can be relatively short in height to produce a block that is light weight and easy to handle.  
           [0018]    Another advantage of the present interlocking masonry wall block is that the block can be kept relatively short so that it can be more easily integrated into gradually sloping terrain. The smaller height allows more frequent steps to be incorporated into a particular wall design so the blocks do not rise up above ground level a great deal. This produces a more aesthetically pleasing wall that fits and blends into the natural terrain. The blocks also make more efficient use of material.  
           [0019]    A further advantage of the present interlocking masonry wall block is that the integral projections are located away from the rear and front edges of the block. By locating the projections in this manner, they are less likely to be damaged if the block is dropped or bumped during transport. During shipping, the bottom layer of blocks are inverted to lay flat on the floor, truck bed or shipping pallet. The projections of one block fit into the openings of the other blocks. The various columns and rows of block are arranged flush against adjacent columns and rows of blocks to provide a solid mass of blocks. The projections are also protected by the lower blocks during use so that they are not exposed to the earth and air. This keeps the projections dry and away from the acidity of the earth, which improves the life expectancy of the block and retaining wall formed by the blocks.  
           [0020]    A still further advantage of the present interlocking masonry wall block is that the integral projections are relatively thick and relatively tall. As stated above, the projections can be relatively thick or long because they are not dependent on the desired setback. This increased thickness enables the projections to have an increased height without compromising their structural strength. The projections provide a sufficiently tall abutment to easily and consistently align the block over the lower course of blocks. This reduces the amount of misaligned blocks, and improves the strength and aesthetic uniformity of the retaining wall.  
           [0021]    A still further advantage of the present interlocking masonry wall block is that they produce serpentine walls with varying convex and concave shaped portions. The size and shape of the open cores allow the smaller, spaced projections to fit into the open cores of the blocks of the lower course. Adjacent blocks can be oriented to form a continuous wall with curves and straight portions that gradually increase or decrease in radius.  
           [0022]    A still further advantage of the present interlocking masonry wall block is that the integral projections produce a relatively uniform amount of setback for straight and curved portions of the wall. Even though the setback increases slightly in concave curved portions of the wall and decreases slightly in convex portions of the wall, this change in setback occurs evenly and gradually as the radius of the curve increases. Discontinuities between adjacent blocks are avoided. In addition, the pitch of the wall is relatively constant for straight and curved portions of the wall. The wall leans back a slightly increased amount in concave portion and less in convex portions so that a relatively constant pitch is achieved throughout the entire serpentine wall. This uniform setback and relatively constant pitch enables more courses of blocks to be used in many serpentine walls, and helps produce a more stable serpentine wall where the combined weight of the wall and earth pressure remain within the footprint of the block.  
           [0023]    A still further advantage of the present interlocking masonry wall block is that the integral projections allow the blocks forming one course to have a varying amount of lateral offset with relation to the course of blocks upon which they are stacked. The retaining wall can more easily avoid obstructions, such as a sump pump discharge pipe. The block can also be arranged to allow drain pipes to pass through the middle of the wall. This flexibility also allows one course of blocks to be laterally offset to accommodate the ledge or sill of a building. Thus, the present block facilitates the construction process and the ability to use the block in a wide variety of locations.  
           [0024]    A still further advantage of the present interlocking masonry wall block is that the integral projections provide additional resistance to lateral side-to-side movement of the block. The blocks can easily be stacked so that one of the projections engages the inside surface of one of the side walls of a block beneath it. Accordingly, side-to-side movement is resisted not only by the adjacent blocks in the same course or tier, but by the blocks above and below it as well. Should one block in a given course shift or move out of abutting alignment with one of its adjacent blocks, then the remaining blocks in that row would still be held in place by the blocks above or below it. The projections are particularly helpful in holding the end blocks of the wall in place where the block would otherwise be free to slide laterally and out of place, or off the wall altogether.  
           [0025]    A still further advantage of the present interlocking masonry wall block is that an entire serpentine wall can be built from a plurality of like-shaped blocks. The need for only a single block design results in reduced manufacturing, inventory, shipping and construction costs. The single block design also makes it easier to design a serpentine wall that is integrated to the shape of a specific and unique landscape setting.  
           [0026]    A still further advantage of the present interlocking masonry wall block is its reduced weight. The open core design removes about thirty percent (30%) of the materials and weight of the block so that they are easier to handle during manufacture, shipping and construction. The open core design also reduces material costs which can be passed on to the consumer.  
           [0027]    Other aspects and advantages of the invention will become apparent upon making reference to the specification, claims and drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]    [0028]FIG. 1 is an elevated view of a house built to a unique landscape setting with a gradually sloping and contoured hill that feeds down to the level of the backyard patio of the house and a pre-existing tree.  
         [0029]    [0029]FIG. 2 is an elevated view showing a three foot high serpentine retaining wall constructed from a plurality of the present like-shaped, interlocking masonry wall blocks, and integrated into the natural contours of the hill and unique landscape setting of the house.  
         [0030]    [0030]FIG. 3 a  is a cross sectional view of FIG. 2 taken along line  3   a - 3   a  showing a straight wall section having a pitch of about Ps=5°.  
         [0031]    [0031]FIG. 3 b  is a cross sectional view of FIG. 2 taken along line  3   b - 3   b  showing a high radius, convex curved portion of the wall having a pitch of about Phr=2°.  
         [0032]    [0032]FIG. 3 c  is a cross sectional view of FIG. 2 taken along line  3   c - 3   c  showing a high radius, concave curved portion of the wall having a pitch of about Phr=9°.  
         [0033]    [0033]FIG. 4 is an elevated, front perspective view of the interlocking masonry wall block showing the trapezoidal shape of the upper surface and open core of the block.  
         [0034]    [0034]FIG. 5 is a lowered, front perspective view of the interlocking masonry wall block showing the trapezoidal shape of the lower surface, the open core of the block, and its rectangular shaped integral projections.  
         [0035]    [0035]FIG. 6 is a front view of the interlocking masonry wall block.  
         [0036]    [0036]FIG. 7 is a top view of the interlocking masonry wall block.  
         [0037]    [0037]FIG. 8 is a bottom view of the interlocking masonry wall block showing the orientation of the offset projections relative to the inside surface of the front wall of the block.  
         [0038]    [0038]FIG. 9 is a side view of the interlocking masonry wall block.  
         [0039]    [0039]FIG. 10 is a top view of two courses of the present like-shaped interlocking blocks arranged in a straight configuration with the blocks in the upper course having an offset alignment to create an opening for a drain pipe, the blocks on the right being in about a full right alignment and the blocks on the left being in about a full left alignment.  
         [0040]    [0040]FIG. 11 is a top view of two courses of the present like-shaped interlocking blocks arranged in a concave curve configuration that gradually increases from a low radius curve, through a medium radius curve, to a high radius curve.  
         [0041]    [0041]FIG. 12 is a top view of two courses of the present like-shaped interlocking blocks arranged in a convex curve configuration that gradually increases from a low radius curve, through a medium radius curve, to a high radius curve.  
         [0042]    [0042]FIG. 13 is a top view of a convex shaped retaining wall formed by the present like-shaped, interlocking masonry wall blocks, with a pitch of Ps=1 in the straight section, and about Pmr=0.7 in the medium radius section, and about Phr=0.4 in the high radius section.  
         [0043]    [0043]FIG. 14 is a top view of a convex shaped retaining wall formed by a conventional rear flange, interlocking masonry wall blocks, with a pitch of Ps=1 in the straight section, and about Pmr=1.2 in the medium radius section, and about Phr=1.3 in the high radius section.  
         [0044]    [0044]FIG. 15 is a top view of a concave shaped retaining wall formed by the present interlocking masonry wall blocks with a pitch of Ps=1 in the straight section, and about Pmr=1.4 in the medium radius section, and about Phr=1.8 in the high radius section.  
         [0045]    [0045]FIG. 16 is a top view of a concave shaped retaining wall formed by a conventional, rear flange, interlocking masonry wall blocks with a pitch of Ps=1 in the straight section, and about Pmr=1.4 in the medium radius section, and about Phr=2.0 in high radius section. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0046]    While this invention is susceptible of embodiments in many different forms, the drawings show and the specification describes in detail a preferred embodiment of the invention. It should be understood that the drawings and specification are to be considered an exemplification of the principles of the invention. They are not intended to limit the broad aspects of the invention to the embodiment illustrated.  
         [0047]    [0047]FIG. 1 shows a house  10  with a walkout basement leading to a patio  12  constructed in the backyard of the house. The house  10  has a concrete foundation  14  which transitions to brick  16  along a sill  18  at the top of the foundation. The house is constructed into a hill  20  that levels off to a particular ground level  22  in the backyard of the house. The hill  20  and its terrain  30  and natural plant life  24  form a unique landscape setting  32  around the house  10 .  
         [0048]    The present invention relates to a masonry block  40  for constructing serpentine retaining walls with straight and curved portions, such as the landscape retaining wall  140  shown in FIG. 2. The serpentine wall  140  is easily integrated into a variety of landscape settings  32 . The like-shaped blocks  40  have a setback, as discussed below. A degree of setback is maintained throughout the entire serpentine wall  140 . As discussed below, the setback impacts the degree the wall is pitched or leans into the hill  20 . As shown in FIG. 3 a ,  3   b  and  3   c , the amount of pitch (P) in the wall  140  is somewhat less in convex curved portions of the wall and somewhat greater in concave portions of the wall relative to the pitch in straight portions of the wall.  
         [0049]    An individual block  40  in accordance with the present invention is shown in FIGS.  4 - 9 . The block  40  has a main body  42  with upper  44  and lower  45  surfaces. The upper  44  and lower  45  surfaces are generally parallel to each other. When laid in place on a horizontal supporting surface, the upper  44  and lower  45  surfaces are horizontal as well. The main body  42  includes a front wall  51 , a rear wall  52 , and opposed side walls  53  and  54 . Each wall  51 - 54  is integrally formed to its two adjacent walls during the molding process. Each wall  51 - 54  has an inside  61  and an outside  62  surface. Each wall has a wall width of roughly two (2) inches between its inside  61  and outside  62  surfaces. The upper  44  and lower  45  surfaces of each wall  51 - 54  have a relatively smooth masonry finish. The walls  51 - 54  are solid and form continuous surfaces  44 ,  45 ,  61  and  62 . The outer surface  62  of the front wall  51  is roughened to give it a natural cut or chipped stone finish. A conventional masonry material for landscape retaining wall blocks is used to form the block  40 . A single block  40  weighs about twelve pounds.  
         [0050]    The block  40  has a generally trapezoidal shape as best shown in FIGS. 7 and 8. The inside  61  and outside  62  surfaces of the front  51  and rear  52  walls are parallel, and perpendicular to the upper  44  and lower  45  surfaces. The inside  61  and outside  62  surfaces of the side walls  53  and  54  are also perpendicular or vertical to the upper  44  and lower  45  surfaces. The block  40  has a height of about four (4) inches and a depth of about eight (8) inches. The width of the block at its front wall  51  is roughly twelve (12) inches from the outer surface  62  of each side wall  53  and  54 . The width of the block at its rear wall  52  is roughly ten (10) inches from the outer surface of each side wall  53  and  54 . Each side wall  53  and  54 , and its respective inside and outside surfaces  61  and  62 , converge toward the other at an angle of about seven degrees (7°) as it extends toward the back wall  52 . The outside surface  62  of the front wall  51  has beveled ends  65 . The surface of these ends  65  angle back toward the rear of the block. The outside surface  62  of the angled ends  65  meet the outside surface of the side walls  53  or  54  along edges  67 . The outside surface  62  of the rear wall  52  meets the outside surface of the side walls  53  or  54  along edges  68 .  
         [0051]    The block  40  has an open core or interior  80  that extends completely through the block from its upper surface  44  to its lower surface  45 . The open core  80  is defined by the inside surfaces  61  of the front, rear and side walls  51 - 54 . The open core  80  has a generally trapezoidal shape that is smaller in size and similar to the trapezoidal shape formed by the outer surface  62  or perimeter of the block  40 . The open core  80  has a width at its front of about seven and a half (7½) inches, and a width at its rear of about six and a half (6½) inches. The open core  80  is about four (4) inches deep taken along a line perpendicular to the inside surfaces  61  of the front and rear walls  51  and  52 . The comers  82  of the open core  80  are rounded to a radius of roughly three-quarters (¾) of an inch. One of ordinary skill in the art should readily appreciate that the volume of the core can vary, but is preferably maximized to decrease the weight and material cost of the block without impairing the strength, integrity and manufacturability of the block. Similarly, the actual shape and dimensions of the core  80  can vary, provided the core maintains its ability to receive the lug-shaped projections of another block  40 , as discussed below. The open core  80  should not contain any obstruction that would interfere with the desired ability to receive these lugs.  
         [0052]    Two integral lug-shaped projections  100  and  101  extend from the lower surface  45  of the block  40 . The projections  100  and  101  have front  111 , rear  112  and opposed side  113  and  114  surfaces. These surfaces are generally flat and perpendicular to the lower surface  45  of the block and parallel to the inside and outside surfaces  61  and  62  of the walls  51 - 54 , respectively. Each lug  100  and  101  has a bottom surface  115  that is generally parallel to the lower surface  45  of the block  40 . Each lug  100  and  101  has a width of about one (1) inch from side  113  to side  114 , and a length or thickness of about one and a half (1½) inches from front  111  to rear  112 . Each lug  100  and  101  has a height of about five-eighths (⅝) of an inch, and its comers and vertical edges  117  are rounded to a radius of about seven-sixteenths ({fraction (7/16)}) of an inch. One of ordinary skill in the art should readily appreciate that the size and shape of the lugs  100  and  101  can vary provided they maintain their strength, integrity and manufacturability.  
         [0053]    Each projection  100  and  101  is generally centered between the inside  61  and outside  62  surfaces of its respective side wall  53  or  54 . Each projection  100  and  101  has a portion  118  positioned forward or in front of the inside surface  62  of the front wall  51 . This portion  118  provides an amount of setback  120  for the block  40 . The perpendicular distance between the front surface  111  of each projection  100  and  101  and the inside surface  62  of front wall  51  is the setback dimension  120 . In this embodiment, the setback dimension  120  is shown to be about one-quarter (¼) of an inch. The setback  120  is the same for both projections  100  and  101 . However, it should be understood that the setback dimension  120  could be larger or smaller without departing from the broad aspect of this present wall block invention. Each projection  100  and  101  has a centerline  119 . This centerline  119  is shown perpendicular to the inside and outside surfaces  61  and  62  of the front wall  51 , but could be parallel to the inside and outside surfaces of its respective side wall  53  or  54 .  
         [0054]    The like-shaped blocks  40  are structured to be laterally aligned in an abutting side-by-side engagement, and vertically aligned in a staggered, stacked manner so that one block rests atop two other blocks. When arranged in this manner, the blocks  40  form a multi-tiered wall  140 , such as the wall shown in FIG. 2. The wall  140  is typically constructed one course at a time. Once a lower course  141  is set in place, an upper course  142  is placed on top of it. The blocks  40  can be arranged to form walls  140  having straight wall portions  150  as in FIG. 10, concave curved wall portions  160  as in FIG. 11, and convex curved wall portions  170  as in FIG. 12. The concave portions  160  have a degree of curvature that ranges from a low radius curve  161 , to a medium radius curve  162 , to a high radius curve  163 . Similarly, the convex portions  170  range from low  171 , to medium  172 , to high  173  radius curves. The blocks  40  can be arranged to gradually or rapidly increase or decrease the radius of the curvature of the concave or convex curves  160  or  170 , which enables the wall  140  to conform to the unique landscape setting  30 .  
         [0055]    When erecting a wall  140 , a gravel or sand bed  179  is preferably formed to level the terrain  32  where the first course  141  of blocks  40  is to be laid. In each course  141  or  142 , the front and rear side edges  67  and  68  of laterally adjacent blocks  40  are aligned. The front edges  67  are aligned in abutting engagement in straight wall portions  150  as shown in FIGS. 2 and 13, low radius concave wall portions  161  as shown in FIGS. 11 and 15, and all convex wall portions  170 - 173  as shown in FIGS. 12 and 13. The front and rear edges  67  and  68 , as well as the entire outside surfaces  62  of side walls  53  or  54  of adjacent blocks  40  are flushly aligned in abutting engagement for a medium radius concave wall portions  162  as shown in FIG. 11. High radius concave wall portions  163  are formed by aligning the rear edges  68  of adjacent blocks  40  as shown in FIG. 11. The lower surface  45  of each block  40  in the first or lowest course  141  is placed at the same horizontal level, which is deemed the ground level  22 . In the first course  141 , the projections  100  and  101  can extend into the gravel or sand bed  179 . The upper surfaces  44  of the blocks  40  forming the lower course  141  form a generally horizontal platform upon which the upper course  142  can be stacked. The lower surface  45  of each block  40  in each stacked, upper course  142  is placed on and rests on the upper surfaces  44  of the blocks in the lower course  141  upon which it is placed.  
         [0056]    An interlocking fit is achieved between the like-shaped blocks  40  in adjacent upper  142  and lower  141  courses. Each block  40  in the upper course  142  is laid in a staggered manner relative to the lower course  141  so that the upper block is placed atop two lower blocks. Each block  40  in the upper course  142  is placed so that one of its lug-shaped projections  100  ort  101  extends into and is received by the open core  80  of one of the lower blocks. The other projection  100  or  101  extends into and is received by the open core  80  of an adjacent lower block. The front surface  111  of each lug  100  and  101  of the upper block  40  abuts the inside surface  61  of the front wall  51  of its respective lower block. This abutting engagement between the upper and lower blocks  40  in adjacent courses  141  and  142  forms the interlock that prevents the block in the upper course  142  from moving forward. This interlock enables the blocks  40  in the upper courses  142  to resist the pressure of the earth and hill  20  behind the wall  140 .  
         [0057]    A further aspect of the interlocking fit is achieved by aligning the block  40  in the upper course  142  so that one of its projections  100  or  101  abuts the rounded comer  82  or inside surface  61  of the side wall  53  or  54  of the block in the lower course  141 . When in a full right  181  or full left  182  alignment as shown in FIG. 10, the blocks  40  in the upper course  142  are prevented from sliding sideways or laterally relative to the blocks in the lower course  141 . The block  40  in the lower course  141  experiences a similar resistance to movement in the opposite lateral direction. A block in a middle course may experience a resistance to both right and left movement.  
         [0058]    Adjacent blocks  40  in a particular course  141  or  142  can also be arranged in an offset alignment  185 . One block  40  can be positioned in a fall right alignment  181  and its adjacent block can be position in a full left alignment  182  to form a gap or opening  187  between the two blocks shown as in FIGS. 2 and 10. The maximum amount of offset of the preferred embodiment of the block  40  is about six (6) inches. The ability to laterally offset adjacent blocks  40  to create openings  187  in the otherwise solid wall  140  enables the wall to accommodate drainage pipes, gutter down spouts, sump pump piping or other obstacles, and helps prevent excessive water building up behind the retaining wall.  
         [0059]    As discussed above, the projections  100  and  101  produce an amount of setback  120  between the upper and lower courses of blocks  141  and  142 . When the wall  140  is properly constructed, the blocks  40  in the upper course  142  are set back a predetermined amount  120  from the blocks on which they are placed. In the preferred embodiment, the outer surface  62  of the front wall  51  of the upper block  40  is set back about one quarter (¼) inch from the outer surface of the lower blocks on which it is placed. The setback dimension  120  directly affects the amount or degree of pitch P in the wall  140 . The setback  120  of each block  40  in the upper course  172  is substantially the same when measured along the centerline  119  of each projection  100  or  101 . When the blocks  40  form a straight wall segment  150 , the height of the blocks  40  and the setback amount  120  determine the pitch of the wall. The amount of pitch can vary slightly in an actual construction setting due to the present of dirt or other debris, which can come between the lugs  100  and  101  of the upper block and the inside surface  61  of the front wall  51  of the lower block. When the blocks  40  form a curved wall segment  160  or  170 , the pitch of the wall varies. For example, as shown in FIG. 13, a wall  140  having a pitch in straight wall section of Ps=1.0, should have a reduced pitch in a medium radius convex section  172  of about Pmr=0.7 times Ps, and a high radius convex section  173  of about Phr=0.4 times Ps. As shown in FIG. 15, the wall  140  should have an increased pitch in a medium radius concave section  162  of about Pmr=1.4 times Ps, and a high radius concave section  163  of about Phr=1.8 times Ps. A more consistent pitch is believed to occur with this wall  140  than in other conventional walls, such as the wall shown in FIGS. 14 and 16, because the lug-shaped projections  100  and  101  do not span the entire width of the block  40 , and are located toward the front wall  51  and inwardly from the outside surfaces  62  of the side walls  53  and  54 .  
         [0060]    The top course of blocks  40  in the landscape retaining wall  140  is preferably capped by cap stones  195  to cover the open cores  80  of the blocks  40  that form the top course or portion of a course. These cap stones  195  provide a finished look to the wall. These cap stones  195  can be glued or otherwise adhered to the upper surface  44  of the blocks  40 .  
         [0061]    While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the broader aspects of the invention.

Summary:
The present invention relates to an interlocking masonry wall block having an open core and spaced projections that enable stacked blocks to be interlocked, setback and staggered to form a stable gravity-type retaining wall that is particularly suited for landscaping applications. The open core extends completely through the block from top to bottom. The block is formed by front, rear and opposed side walls, each having parallel inside and outside surfaces. One projection extends from the lower surface of each side wall. The front of each projection is forward the inside surface of the front wall to provide the setback when stacked on other like-shaped blocks. Each block is stacked in a staggered manner atop two other blocks. One projection of each block is received by the open core of one of the two lower blocks. The projections abut the inside surface of the front wall of the lower blocks to interlock the blocks together. The block has a preferably trapezoidal shape with a wider front wall to help accommodate the formation of serpentine walls. The block can be used to make serpentine walls with straight and curved portions with a relatively constant pitch.