Retaining wall blocks and the walls made from such blocks are disclosed, wherein curved landscapes (i.e. curved profiles and sloping embankments) are easily accommodated without the use of mortar. As well, a modular system of blocks and their manufacture are disclosed wherein some blocks are used in vertical orientations and some in horizontal orientations.

This is a continuation of U.S. application Ser. No. 09/530,833, filed Aug. 17, 2000U.S. Pat. No. 6,490,837, the entire disclosure of which is incorporated herein by reference. 


   FIELD OF INVENTION 
   This invention relates to mortarless wall constructions and blocks therefor, particularly suitable to act as retaining walls to secure embankments and terraces. 
   BACKGROUND OF INVENTION 
   To secure earth embankments against sliding and slumping, the retaining wall industry knows various interlocking and mortarless systems. 
   Interlock mechanisms which involve pins and sockets, require close supervision by the labourers and the omission of even one pin may compromise the structural integrity of a course of blocks and thereby the entire wall. Also, these pin and sockets mechanisms do not permit significant lateral movement of blocks for working around curves in the embankment. 
   For large embankments (such as those found near highways), the blocks must be large. Known blocks are solid (i.e. no through core), typically measure in the order of 5′×2½′×2½′ and weigh in the order of 5000 lbs. They are interlocked by large right-angled lugs and corresponding sockets, which severely restricts the ability to create non-90° concave or convex curve wall portions in response to the embankment profile. 
   For the purposes of this invention, the following definitions will be employed. “Batter” is the apparent inclination, from vertical, of the wall face. A “half-bond” is the relationship or pattern created by stacking units so that the vertical joints are offset one half unit from the course below. For orientation, “convex”, “concave”, “left”, “right” are determined from the point of view of a viewer facing the front face of the block or wall portion. “Lateral” means along the longitudinal axis of the block or course of blocks, parallel to the front face. “Filler” is free draining granular material like crushed, angular rock pieces of perhaps ½″ or ¾″ size. 
   SUMMARY OF INVENTION 
   There is provided a block comprising a front wall; a rear wall; first side wall; second side wall opposed to said first side wall; an upper block planar surface; a lower block planar surface; wherein said first side wall and said second side wall extend from said front wall to said rear wall to define a central through core extending through the block from said upper block surface to said lower block surface, said core having a front upper rim and a first front corner at the plane of said upper block surface, proximate intersection of said first side wall and said front wall; a first lug which extends downwardly from said lower block surface adjacent said first side wall, and has (i) a flat side portion flush with said first side wall (ii) a front portion which joins said first lug side surface at an angle of 90° or less. 


   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a top view of a block according to the invention 
       FIG. 2  is a side view of the block of  FIG. 1   
       FIG. 3  is a bottom view of the block of  FIG. 1   
       FIG. 4  is a perspective view of the block of  FIG. 1   
       FIG. 5  is a bottom view of a lug according to the invention 
       FIG. 6  is a top view of another block according to the invention 
       FIG. 7  is a side view of the block of  FIG. 6   
       FIG. 8  is a perspective view of a wall portion constructed from the blocks of  FIGS. 6 and 7 , secured by geogrid 
       FIG. 9  is a perspective view of a wall portion constructed from a variation of the blocks of  FIG. 8 , secured by geogrid 
       FIG. 10   a  is a side view of the wall portion and securing of the geogrid of  FIG. 9   
       FIG. 10   b  is a perspective view of a block and the securing of the geogrid of  FIG. 8   
       FIG. 11  is a top view of another block according to the invention 
       FIG. 12  is a top view of another block according to the invention 
       FIG. 13  is a top view of several courses of a convex wall portion constructed from the blocks of  FIG. 6   
       FIG. 14  is a top view of several courses of concave corner of a wall 
       FIG. 15  is a top view of several courses of convex corner of a wall 
       FIG. 16  is a bottom view of another block according to the invention 
       FIG. 17  is a side view of the block of  FIG. 16   
       FIG. 18  is a top view of several courses of a wall portion constructed of blocks of  FIGS. 16 and 17   
       FIG. 19  is a top view of another block according to the invention 
       FIG. 20  is a bottom view of the block of  FIG. 19   
       FIG. 21  is a front view of a wall portion constructed from the blocks of  FIGS. 19 and 20   
       FIG. 22  is a top view taken along line E—E of the wall of  FIG. 21   
       FIG. 23  is a side view of the wall of  FIGS. 21 and 22  taken along line D—D 
   


   DETAILED DESCRIPTION OF THE INVENTION 
   As shown in  FIGS. 1-4 , block  100  has front wall  110 ; rear wall  130  spaced rearwardly and parallel to front wall  110 ; first side wall  115 ; second side wall  120 ; in a bilaterally symmetrical trapezoidal configuration in top view. The walls define a central through core  150 . There is an upper block planar surface  140  and lower block planar surface  141 . Associated with first side wall  115  and second side wall  120  are respectively lugs  215  and  220  depending integrally and downwardly from lower block surface  141 . 
   In a variation, block  101  is identical to block  100  but, as shown in  FIG. 9 , has no channel equivalent to channel  350 . In that variation, lug  215  is disposed within core  150  of the underjacent block and the most forward rim of front arcuate portion  217  of lug  215  may abut core corner  153  in some applications (not shown). Core  150  of block  101  is of sufficient lateral length that lug  215  or lug  220  of a block  100  of a superjacent course may be shifted laterally left or right (to achieve half-bond or to deviate from half-bond) without changing the resulting batter of the straight wall. Explanations about block  100  are equally applicable to block  101  (except where the context indicates otherwise) and will not be repeated for economy of description. 
   Through core  150  extends downwardly to lower block surface  141  and is shown to taper inwardly although this is optional to facilitate its manufacture. Core  150  has a front upper rim  151  and rear upper rim  154 , both parallel to front wall  110 . Core  150  has first front corner  152  and second front corner  153 , which are arcuately profiled. Through core  150  accommodates filler or vertical reinforcing rod  701  embedded in poured concrete (as will be explained below). 
   As best shown in  FIGS. 2 ,  4  and  8 , block  100  has a horizontal channel  350  which extends vertically downwardly from upper block surface  140  (coinciding with core front rim  151  and core rear upper rim  154 ), horizontally between first side wall  115  and second side wall  120  and intermediately of front wall  110  and rear wall  120 . Channel  350  is not necessary for the construction of a wall but is useful to accommodate reinforcing rods  700  extending from block to block along a course of blocks (as will be explained below in conjunction with  FIG. 8 ) or anchor bars  702  (as will be explained in below conjunction with  FIG. 10   b ). 
   Lugs  215  and  220  provide the engagement means between blocks  100  of one course with blocks  100  of the underjacent course. As best shown in  FIG. 5 , lug  215  is profiled in an approximate cam shape, with a side portion  216  (which is flush with outer face of block side wall  115 ), a front arcuate portion  217  and a rear arcuate portion  218 . 
   As best shown in  FIG. 5 , front arcuate portion  217  of lug  215  meets side portion  216  of lug  215  at 90°. Alternatively, front arcuate portion  217   a  may meet side portion  216  at an angle È greater than 90° to facilitate forming a more convex wall portions. Alternatively, front arcuate portion  217   b  may meet side portion  216  at an angle È less than 90° to facilitate forming a more concave wall portion. È around 90° is a reasonable compromise to achieve turnability and mass (for shear strength). 
   A part of the most forward rim of front arcuate portion  217  of lug  215  approximates a quarter circle. Front arcuate portion  217  is profiled, in part, to be complementary to core corner  153  of a block  100  of an underjacent course (as best shown in  FIGS. 8 and 9  and as will be explained below), and if not complementary, front portion  217  must have at least a forward arcuate portion. The most forward rim of arcuate portion  217  is positioned to lie in the same vertical plane A—A as the front upper rim  151  of core  150  lies, as best shown in  FIGS. 2 and 3 . Lug  220  is identical to lug  215  in all material respects, except that it is disposed as a mirror image of lug  215  on the opposite side of block  100  (i.e. proximate side wall  120 ). The principles involving lug  215  will be described on most occasions below, and, although applicable also to lug  220 , will not be repeated for economy of description. 
   Core corner  153  approximates a quarter circle with a radius approximately equal to the approximate radius of arcuate portion  217 . The exact shape of core corner  153  is not critical and a core with an angular corner is possible. With the presence of channel  350 , only front upper rim  151  of core  150  will contact front arcuate portion  217  and there is no contact between core corner  153  and lug  215 , so corner might be a 90° one. Even with block  101 , core corner  153  need not be arcuately complementary as long as the respective shapes of front arcuate portion  217  and core corner  153  permit lug  215  to turn easily relative to core front rim  151 . At a minimum, lug front portions  217  must be arcuate so it can abut front upper rim  151  of core  150  of the underjacent block  100  and be turnable in a wide range of angles. 
   In this way, block  100  of an upper course creates two pivoting axes relative to the two blocks  100  of the underjacent course. Specifically, the first pivoting axis is at the contact point between lug front portion  217  of lug  215  and front upper rim  151  of core  150  of the left underlying block  100  and the second pivoting axis is at the contact point between lug front portion  222  and front upper rim  151  of core  150  of the right underlying block  100 . This is shown in  FIG. 9  for block  101  and in  FIGS. 8 and 13  for block  300  (a variation of block  100  which will be described below). These two pivoting axes are advantageous for creating convex or concave wall portions. 
   Rear portion  218  of lug  215  may be provided with an arcuate corner approximating a quarter-circle, as shown in FIG.  5 . The exact shape circumscribed by rear portion  218  is subject to design considerations. 
   To facilitate the manufacture of the blocks and lugs, rear portion  218  should extend from front portion  217  transversely to front wall  110 , but other directions are possible. 
   The dimensions of lug  215  affect the shear strength and the turnability of lug  215  within the core of a lower block (as will be explained below). There must be enough mass to provide structural integrity and shear strength to lug  215 . The advantage of increasing the mass is to increase the shear strength of lug  215  in the forward-to-rear direction. This advantage may be offset, in some applications, because the increased mass may make lug  215  less turnable relative to lower blocks. In particular, if the first pivoting axis (i.e. the contact point of lug  215  and front rim  151 ) is near side wall  120  of the lower block  100 , and a concave curved wall is desired, then the arcuate rear portion  218  of lug  215  will provide more turnability towards side wall  120  than a 90° corner rear portion  218  (not shown). In other words, an arcuate rear portion  218  will permit a more concave curve wall portion if desired. 
   Because in block  100 , the most forward rim of front arcuate portion  217  (and similarly, the most forward rim of front arcuate portion  222 ) are disposed in the same vertical plane A—A as front upper rim  151  of core  150  is, then the wall resulting from laying courses of such blocks  100 , is a vertical wall, as shown in FIG.  8 . 
   The trapezoidal shape of block  100  facilitates the formation of a convex wall portion, if desired, as shown in FIG.  13 . But the formation of a straight wall portion or concave wall portion (as shown in  FIGS. 8 ,  9  and  14 ) is in no way hampered by the trapezoidal shape of block  100 . 
   As stated above, known blocks for the application to large embankments are solid (i.e. do not have a through core). One advantage of the blocks of this invention is the provision of a through core  150  to reduce the weight of block  100  and thereby create economic efficiencies in the transport of blocks  100  to the installation site. With a through core like  150 , it is possible to achieve a weight reduction from a solid block of similar dimensions, in the order of one third. At the installation site itself, cores and channels are filled with filler or rods  700  and  701  embedded in poured concrete, as applicable. This creates a good vertical interlock bond (i.e. between superjacent courses of blocks and good tension with the geogrid, discussed below) to increase shear strength which is not available with courses of blocks without through cores. 
   Automatic Offset Block 
   Block  300  (as shown in  FIGS. 6 and 7 ) is used to create a wall portion with a batter. Block  300  is a variation of block  100  which is identical thereto in all material respects except for the relative disposition of the lugs relative to the core. Specifically, block  300  has two lugs  315  and  320  which are identical to lugs  215  and  220  of block  100 , except that they are offset slightly forward of the vertical plane A—A defined by front upper rim  351  of core  150 . The offset forward determines the degree of batter of the resulting wall portion. As shown in  FIG. 8 , the upper course of blocks  300  is offset from the underjacent course of blocks  100  by the amount of offset that the lugs of blocks  300  are offset forward of plane A—A defined by front upper rim  351  of core  150  of the underjacent course of blocks  100 . Specifically, the batter of wall portions involving blocks  300  is defined by the ratio of the extent that front arcuate portion of lug  315  is forward of the vertical plane, to the height of block  300 . 
   For a pleasing appearance, front wall  310  of block  300  is tapered so that the resulting battered wall portion of several courses of blocks  300  may have a flush, tapered appearance. 
   L-Shaped Block 
   Block  400  (shown in  FIG. 11 ) is another shape of block suitable for a corner or end block of a wall portion. Block  400  has an L-shaped channel  450 , which is similar to channel  350  of block  100 , in that it extends from block upper surface from first side wall  425  towards second wall  420  (opposite first side wall  425 ), intermediate of rear wall  430  and front wall  410 , but then it turns towards and terminates at rear wall  430 . 
   Channel  450  accommodates a horizontal reinforcing rod  700  which is appropriately bent to navigate the turn in channel  450 . There is a through core  445  identical to through core  150  of block  100 , to accommodate filler or a vertical reinforcing rod  701  embedded in poured concrete (not shown). Depending integrally and downwardly from first side wall  410  is a lug  415 , profiled and disposed similarly to lug  215  of block  100 , and for economy of description, lug  415  will not be further described. The face of second side wall  420  may be contoured to have an attractive face, as shown. 
   Shown in  FIG. 11  is the offset version (i.e. lug  415  is offset slightly forward of the front rim of channel  450 ) but a non-offset version is possible by aligning lug  415  with the front rim of channel  450 . 
   Block  401  is identical to block  400  in all respects except that the front and rear walls are reversed and the turn in the channel is corresponding reversed, and is shown in  FIG. 15  (in dotted line for clarity). The use of block  400  and block  401  will be explained in conjunction below with the creation of corner wall portions in FIG.  15 . 
   End Block 
   Square block  500  (shown in  FIG. 12 ) is another block which is suitable for employment as a corner or end block. Block  500  is approximately half the length of block  100 . Depending integrally and downwardly from first side wall  510  is lug  515 , profiled and disposed similarly to lug  215  of block  100 , and for economy of description, the description will not be repeated. Opposite first side wall  510  is second side wall  520 , which has no lug depending therefrom. The outer faces of second side wall  520 , as well as of front and rear walls, may be may be contoured to have an attractive face, as shown for second side wall  520 . 
   Block  500  has a through core  545  identical to through core  150  of block  100 , to accommodate filler or a vertical reinforcing rod  701  embedded in poured concrete (not shown). Block  500  has a blind channel  550 , which is similar to channel  350  of block  100 , in that it extends vertically from block upper surface and extends horizontally, intermediate the rear wall and the front wall, from first side wall  510  towards second side wall  520  (opposite first side wall  510 ). However, after extending over core  545  (to permit an unobstructed through core  545 ), channel  550  terminates before reaching second side wall  520 . 
   Block  500  shown in  FIG. 12  is the offset version (i.e. lug  515  is offset slightly forward of the front rim of channel  550 ) but a non-offset version is possible by aligning lug  415  with the front rim of channel  550 . 
   To make a wall with blocks  100 ,  300 ,  400  and  500 , it is advantageous to render the blocks modular by having their lugs offset or aligned with their respective front rims of channels  350 ,  350 ,  450 ,  550 , in a uniform way. 
   Constructing a Wall For a straight wall portion, blocks  100  or blocks  300  may be laid side-by-side in courses and the relationship between courses is a half bond or thereabouts (as shown in FIG.  8 ). Corner or end blocks  400  and blocks  500  are employed as desired. 
   The orientation of the blocks where the lugs face downwardly toward the ground (“downward orientation”) is preferred over the reverse orientation where the blocks are laid with their lugs facing upwardly (“upward orientation”). In the downward orientation, the pivoting axes of a block of an upper course relative to the two associated blocks of the underjacent course, are positioned towards the front wall of the blocks. In the upward orientation, the pivoting axes of a block of a lower course relative to the two associated blocks of the superjacent course, are positioned towards the rear wall of the blocks. Because lugs  215  and  220  of blocks  100  are farther apart in the downward orientation than in the upward orientation, there is possible more lateral shifting from half-bond. Explained another way, in the upward orientation, lugs  215  and  220  are more proximate the respective associated side walls of the two superjacent blocks  100  and hence lower block  100  in upward orientation is more limited in its lateral freedom. As well as lateral freedom, when a curved wall portion is desired, the upward orientation is more limited than the downward orientation. Additionally, the batter in curved portions of the wall will change in an accelerated way with blocks in the upward orientation compared to blocks in downward orientation, and this may be undesirable depending on the application. 
   Both the upward orientation and the downward orientation are possible, and the choice is one of design. Obviously, to lay the bottom course of blocks in the downward orientation, their lugs may be removed with a hammer or saw, or they may be keyed into a foundation by conventional methods. 
   The 90° concave corner using blocks  300 , shown in  FIG. 14 , is created by the transverse meeting of the two wall portions which, in alternating courses, overlap each other at the corner. Specifically, end block  300  of one wall portion is laid past the end block  300  of the other wall portion of the same course, and in the next course, the arrangement is reversed. The lug of a block which is laid past, must be removed. The cores are filled with filler and provide vertical bonding between courses. Because blocks  300  create automatically a batter, each block  300  should be placed laterally towards the corner an appropriate amount from half-bond, to compensate for the fact that the portions of the two wall portions are receding away from each other as they rise because of their respective batters. An appropriate lateral displacement is the amount that lugs  315  and  320  are forward of the plane A—A defined by front core rim  351 . 
   The offset dynamic for a non-90° concave curve wall portion using blocks  300  (not shown), is similar to that of the 90° concave corner using blocks  300 . The radius of the curve of each course increases as the wall rises. In other words, there is an increasingly positive batter. If it is desired to create a more vertical wall, a fraction of the front of front portion of lugs  315  and  320  may be shaved (i.e to approximate lugs  215  and  220  of block  100 ) and lateral offsets towards the center of the curve may be employed. 
   For a non-90° concave curve wall portion using blocks  100 , as the courses of the curve rise, the radius of curvature decreases, i.e., a batter slanted inwardly is naturally created by the fact that blocks  100  are pivoting at two points behind front of the front wall of the block below. 
   The arrangement for a 90° convex corner using blocks  300 , shown in  FIG. 15 , is similar to that for the 90° concave corner using blocks  300 , with a few differences. First, corner block  400  and corner block  401  (shown in dotted lines for clarity) are necessary, which alternate in adjacent courses to overlap each other to form the corner. Secondly, each block  300  should be placed laterally away from the corner an appropriate amount off center, to compensate for the fact that the portions of the wall to the left and right of the corner are moving towards each other because of their respective batters. 
   A non-90° convex curve wall portion using blocks  300  is shown in FIG.  13 . The radius of the curve of each course decreases as the wall rises. In other words, there is an increasingly positive batter. If it is desired to create a more vertical wall, a fraction of the front of front arcuate portions of lugs  315  and  320  may be shaved (i.e to approximate lugs  215  and  220  of block  100 ) to reduce the offset. 
   For a non-90° convex curve wall portion using blocks  100 , as the courses of the curve rise, the radius of curvature increases, i.e., a batter slanted outwardly is naturally created by the fact that blocks  100  are pivoting at two points in front of the front wall of the block below. 
   Corners or turns should be built from the corner or center of the curve, outwardly, i.e. from the central block and proceeding left and right. For blocks with an automatic offset, each block will gain in a concave curve, and fall behind in a convex curve, relative to the blocks below. 
   Geosynthetic Sheet Anchor 
   After laying several courses of blocks, back filling with soil and gravel, and compacting, a geosynthetic sheet is secured to the then upper course of blocks and spread over the backfill, as will be explained below. The process is repeated until a wall of the desired height is obtained. 
   The geosynthetic sheet must be strong enough to resist loads and stiff enough to prevent excessive wall deflection. Examples of suitable geosynthetic sheets include geotextile and geogrid. Geotextile may be a closely woven fabric, like fibreglass, of the closeness sufficient to make industrial sacks. Geogrid  600  is a thin sheet of grid-like structure, resembling a net, which may be woven or constructed from a single sheet with perforations and is shown in  FIGS. 9 ,  10   a  and  10   b . For economy of description, geogrid  600  is shown and described but the applicable principles are equally applicable to geotextile. For economy of description, the principles about wedging geogrid  600  to block  101 , shown in FIG.  9  and described below, are equally applicable to blocks  100 ,  300 ,  400  and  500  with minor modifications and will not be repeated. 
   After cores  150  are filled with filler for a course of blocks  101  and backfilled, as shown in  FIG. 9 , geogrid  600  may be secured by wedging it between adjacent upper and lower courses of blocks at their respective lower and upper surfaces. Geogrid  600  is placed as far forward as possible on the upper surface of blocks  101  of the lower course without exposing it on the face of the wall, and then laid behind the wall on the backfill. Another course of blocks is laid on top. Each upper block is then pulled or pushed forward so that lugs  215  and  220  of the then just laid upper course blocks  101  abut the front upper rims of cores  150  of blocks  101  below. Geogrid  600  is then pulled back and the portion thereof over the backfill is secured with stakes, gravel and soil  601 . Lugs  215  and  220  depress and wedge the corresponding portion of geogrid  600  in associated cores  150  of the lower course blocks, as shown in  FIG. 10   a . The distortion of geogrid  600 , with the filler, provides a good positive connection with good shear strength between blocks  101  and geogrid  600 . Geogrid  600  is thereby anchored. 
   For blocks  100 ,  300 ,  400  and  500  which have channels, to provide even more anchoring of geogrid  600  to block  100 , horizontal bar  702  is disposed in channel  350 , approximate rear wall  130  and core rear upper rim  154 , and geogrid  600  is wedged between bar  702  and rear wall  130 , as shown in  FIG. 10   b . Intermittently, bar  702  is threaded through geogrid  600 . Bar  702  may be of any suitable material of sufficient stiffness but it ideally can be made of stiff plastic which is bendable around corners. In practice, the core of block  100  is filled with filler to a suitable level (at about the level of the bottom of channel  350 ). Then the geogrid  600 /bar  702  combination is placed (as described above), with the front of geogrid  600  resting on the top surface of the front wall (which is not shown in  FIG. 10   b  for simplicity of illustration). Then channel  350  is filled (over the laid geogrid  600 ) with filler to create a good interlock. For channelled blocks  100 ,  300 ,  400  and  500 , the technique of anchoring involving bar  702  is supplemented by the wedging technique described above (with block  101 ). 
   For channelled blocks  100 ,  300 ,  400  and  500 , a wall is formed by a plurality of courses of blocks  100  having channels  350 , wherein reinforcing rods  700  extend horizontally in channels  350  that run from block to block in a course, and reinforcing rods  701  extend downwardly the cores  150  of blocks  100 , as shown in FIG.  8 . For turning a 90° corner, blocks  400  or  401  with L-shaped channels  450  for bent reinforcing rods  700  may be used (not shown). Concrete is poured into the cores and channels, to provide secure interlock between courses. 
   Winged Block 
   Block  800  (shown in  FIGS. 16 and 17 ) is another block which is usually dimensioned smaller than blocks  100  or  300 . Except for smaller dimensions, block  800  is similar to block  100  or  300 . Lug  815 , whose most forward rim of arcuate portion  817  may be aligned with the vertical plane defined by the front upper rim of core  850  (not shown) or slightly forward thereof (being the offset version, as shown in  FIGS. 16 ,  17  and  18 ). Channel  851  provides the same function as channel  350  does for block  100 , and like channel  350 , is optional (if rods  700  or bars  702  are desired to be employed). For simplicity of illustration, channel  851  is not shown for blocks  800 ,  800   a  and  800   b  in FIG.  18 . 
   Being smaller, block  800  is easily gripped, manipulated and laid by hand. There are a few differences with blocks  100  and  300 . Core  850  has a lip  855  which allows the workman to easily grip the block. Wings  860  depend outwardly from each side walls and provide an additional anchor for the block in the backfill. Wings  860  may provide a width to the rear wall equal to that of the front wall, to facilitate the formation of a straight wall portion, as shown in FIG.  18 . 
   Removal of parts of block  800  facilitate the construction of a convex wall portion. As shown in  FIG. 18 , a side wall of block  800  can be removed (block  800   a ) to construct a convex angular, non-90° corner; and also one or both wings  860  can be removed (block  800   b ) to create a convex curve portion. Removal of parts of block  800  is achieved by conventional methods like sawing and is facilitated by the presence of core  850 . Cornerpiece  801  is used to complete the creation of a 90° convex corner. Cornerpiece  801  is approximately rectangular with a central core like other blocks and two of its diagonally opposed corners are profiled to accommodate the side walls of adjacent blocks  800  (i.e. are profiled to fit between two blocks  800  transversely adjacent at a corner. 
   Modular Blocks 
   Another block  900  is shown in  FIGS. 19-23 . Block  900  is made from one mold by conventional means, and may be split by conventional guillotine techniques as follows. 
   There are notches, as shown, to define transverse lines B—B and C—C. Block  900  may be scored along lines B—B and C—C. For best effect of appearance, block  900  is not so scored but the lugs should be scored to facilitate the splitting of block  900  therethrough. 
   If block  900  is split along line B—B, then trapezoidal sub-block  901  and trapezoidal sub-block  902  result (which resemble blocks  100  and  300 ). Sub-block  901  can be further split along line C—C to produce two mini-blocks  901   a  and  901   b . Similarly, sub-block  902  can be further split along line C—C to produce two miniblocks  902   a  and  902   b . Thus block  900  can be split to produce a maximum of four mini-blocks,  901   a ,  901   b ,  902   a  and  902   b.    
   As shown in  FIG. 20 , mini-block  902   a  has lugs  920  and  921 ; mini-block  902   b  has lugs  922  and  923 ; and sub-block  902  has lugs  920  and  923 . Similarly, mini-block  901   a  has lugs  905  and  906 ; mini-block  901   b  has lugs  907  and  908 ; and sub-block  901  has lugs  905  and  908 . 
   Mini-blocks  901   a  and  901   b  have respectively blind channels  951   a  and  951   b . Sub-block  901  has aligned blind channels  951   a  and  951   b  but has an obstruction therebetween. Mini-blocks  902   a  and  902   b  have respectively through channels  952   a  and  952   b . Sub-block  902  has a through channel made of aligned channels  952   a  and  952   b . The dimensions of the channels and lugs are a matter of choice guided by the design considerations described above in conjunction with blocks  100 , but the lug of block  900  should generally be about half of the width of the channel. 
   Thus, from only one mold, it is possible to produce four different sub-blocks of three different sizes: one is a basic unit (sub-block  901  or sub-block  902 ) and two are corner pieces (mini-blocks  901   a  and  901   b , or mini-blocks  902   a  and  902   b ). This is advantageous, as it allows splitting of a single block  900  on the installation site to produce the desired blocks as needed. It is often difficult to estimate accurately exactly how many blocks and their types are needed beforehand, especially with irregular landscape profiles. The conventional alternatives are to overestimate the required quantity and types of blocks and to transport all of them to the installation site (and thereby creating unnecessary waste or transportation costs), or to proceed with a guess of the required quantity and types of blocks and to obtain more blocks when it is apparent that they are needed (and thereby causing delay). 
   Sub-block  902  can be laid over sub-block  901  or sub-block  902  in half bond or near half bond (as shown in FIGS.  21  and  22 ). Sub-block  901  can be similarly placed over sub-block  901  or sub-block  902 . There is no lateral limitation of sub-block  901  being laid over sub-block  902  blocks (because sub-block  902  has aligned channels  952   a  and  952   b  to permit maximum lateral freedom to dispose the lugs). But the interaction of sub-block  902  or sub-block  901  over a sub-block  901  is limited by the relative lengths of channels  951   a  and  951   b  of sub-block  901 . 
   Block  900  is shown in a non-offset version (i.e. the front of the lugs are aligned in the same plane as the front rim of the channel) but offset versions of sub-block  901  and sub-block  902  are possible (offset versions as described for blocks  100  and  300 , for example). 
   A wall made of sub-blocks  901  and  902 , and mini-blocks  901   a ,  902   a , and  902   b , is shown in FIG.  21 . Several courses of the wall along the line E—E of  FIG. 21 , are shown in top view in FIG.  22 .  FIG. 23  shows the wall taken alone line D—D of  FIGS. 22 and 23 . 
   Normally, a motarless wall consists of courses of elongate blocks which are each laid on their elongate sides horizontally, with the engagement means oriented vertically (like the blocks shown in  FIG. 21 , with one exception). According to this invention, a motarless wall can exceptionally include a block  902   a ′ which is block  902   a  oriented vertically and resting on its straight side wall, as shown in  FIGS. 21  to  23 . This allows for improved appearance while not requiring a special block. 
   As shown in  FIGS. 21  to  23 , block  902   a ′ is bracketed on top by sub-block  902 ; by mini-block  902   a  and sub-block  902  on the left, and by block  901   a  and block  902   b  on the right. Block  902   a ′ is wedged from expulsion from the face of the wall (by the abutting of its lugs  920  and  921  against the sloped side wall of mini-block  902   b  and the sloped side wall of mini-block  901   a ). To allow for the placement of block like  902   a ′, its lugs must face the sloped side wall of a neighboring block and not the straight side wall thereof (failing which, the lugs must be removed). The spanning of block  902   a ′ by sub-block  902  is held in place by one lug of sub-block  902  disposed in the channel of block  901   a  on the right and the other lug is disposed in the channel of block  902   a  on the left. 
   The dimensions of block  900  and mini-blocks  901   a ,  901   b ,  902   a  and  902   b  may be set in an advantageous way. Both the length of the face of the front wall of sub-block  901  and the length of the face of the front wall of mini-block  901   a , should be an integer multiple of the length of the face of the front wall of mini-block  901   b  (all lengths considered along line B—B). For example, sub-block  901  may be 15″ long,  901   a  may be 10″ long and  901   b  may be 5″ long. The dimensions are defined by the locations of the notches and lines B—B and C—C defined thereby. 
   All blocks of this invention are of unitary construction, preferably made of high strength, high density concrete made by conventional wet-cast molding or machine precast molding. 
   The dimensions of block  100 ,  300  and  400  may be in the order of 2′×4′×2.′ The channel is about 4″ deep. The lugs are in the order of 6″×3″×1″. 
   The dimensions of block  500  may be in the order of 2′×2′×2′. The lugs are in the order of 6″×3″×1″. 
   The dimensions of block  800  are in the order of 1½′×1′×¾′. The core is in the order of 9¼″×6¼″. The channel is about 1½″ deep. The lugs are in the order 3″×2″×⅜″ to ⅝″ deep. 
   The channel in block  900  is about 1″ deep and width of 4″. Lugs are in the order of 2″×1½″×½″. 
   It will be appreciated that the dimensions given are merely for purposes of illustration and are not limiting in any way. The specific dimensions given may be varied in practising this invention, depending on the specific application. For example, the core must not be excessively large relative to the block walls, for an application where the retained wall retains a parking lot which will suffer constant increases in stress and strain. Otherwise, wall thickness might be reduced to a point that could affect materially the load bearing capabilities of the block in a given application. 
   While the principles of the invention have now been made clear in illustrated embodiments, there will be obvious to those skilled in the art, many modifications of structure, arrangements, proportions, the elements, materials and components used in the practice of the invention, and otherwise, which are particularly adapted for specific environment and operation requirements without departing from those principles. The claims are therefore intended to cover and embrace such modifications within the limits only of the true spirit and scope of the invention.