Erosion control block adapted for use with cellular concrete mattresses

[0002] This nonprovisional patent application claims the benefits of pending provisional patent application bearing the same title, and identified by Ser. No. 60/257,921, filed Dec. 21, 2000.

[0003] The present invention relates in general to erosion control blocks, and more particularly to the type of erosion control block that can be cabled together with other similar blocks, and installed as a mattress by a crane and spreader bar.

[0004] There are numerous types and shapes of erosion control blocks for covering a ground area to prevent erosion of the underlying earth material. An erosion control block is generally constructed of a heavy material, such as concrete, so that the block remains stationary when water flows around or over the block. The shape of erosion control blocks can be made so as to be interlocking, or interengaging, and facilitate the hydraulic stability of the block installed in a waterway, or the like. Interengaging erosion control blocks can be constructed similar to that shown in U.S. Pat. No. 5,484,230 by Rudloff. Interlocking erosion control blocks can be constructed in a manner similar to that shown in U.S. Pat. No. 5,556,228 by Smith. The interlocking type of block prevents lateral removal thereof from another similar block, when moved in any lateral direction. Interengaging erosion control blocks generally provide stability between blocks in one lateral direction, but not a lateral direction perpendicular thereto. The flexibility of interlocking blocks is generally less than that of the interengaging blocks.

[0005] Some erosion control blocks are simply installed by workmen carrying the blocks from a pallet and installing the blocks in a side-by-side relationship. A geotextile is generally layed on the ground before the installation of the erosion control blocks. Depending upon the terrain and other factors, the blocks may simply be interengaged or interlocked together. In other situations, the erosion control blocks are installed in an interengaged or interlocking manner, and thereafter cables are threaded therethrough to provide farther stability to the matrix or mattress of blocks.

[0006] In accordance with other installation techniques, a matrix of erosion control block can be interengaged or interlocked together at the plant, and cabled as a mattress so as to form a flexible unit. In erosion control blocks fabricated for cabling, two or more cable channels are formed through the blocks so that cables can be threaded therethrough. The mattresses can be lifted by the cables and loaded onto a truck or train. The mattress can then be lifted by the cables off a transport truck, or the like, by a large crane and spreader bar assembly, and moved to the site to be protected from erosion. A cellular concrete mattress of erosion control blocks typically includes a matrix of six blocks by thirty-two blocks, which generally measures eight foot by forty foot. A number of such mattresses are installed together so as to provide full coverage over the terrain to be protected from erosion.

[0007] The cabling material is generally a synthetic rope that is threaded through the blocks in an X-direction, as well as a Y-direction, to form the mattress. When installing multiple mattresses of erosion control blocks together, the blocks forming the border of the adjacent mattress are anchored together by splicing the cables. In other words, the end of a cable threaded through the border block of one mattress is spliced to the end of the other cable threaded through the border block of the adjacent mattress. The splicing of the two cable ends includes the utilization of an aluminum sleeve into which the end of each cable is inserted, and then two crimps are made to fasten the cable ends together via the sleeve. It can be appreciated that the border blocks of adjacent mattresses can not be installed in contact with each other, otherwise there would be no room to carry out the splicing operation. As such, the edge or border of one mattress is generally spaced two inches from the border blocks of the adjacent mattress.

[0008] The space between mattresses of erosion control blocks creates a channel through which water can flow in an unimpeded manner. Depending upon the environmental conditions, the flow of water through this channel between the mattresses of erosion control blocks can carry soil with it, thereby forming a pocket under the geotextile material. This is especially prevalent where the mattresses of erosion control blocks are laid on inclined channel banks, where the water flow from the top to the bottom of the grade is swift. When erosion of soil under the geotextile occurs, failures in the erosion control system can occur. In some instances, a sufficient amount of soil is removed through erosion under the geotextile, such that the overlying blocks become suspended by the cables, and bridge the void area. Due to the weight of the blocks, the cables can often break and thereby cause a catastrophic erosion condition.

[0009] From the forgoing, it can be seen that a need exists for a technique for cabling together erosion control blocks so as to avoid water flow channel areas between the mattresses. Another need exists for a erosion control block itself which facilitates the splicing of cables therebetween as well as reduces the speed or volume per unit time of the water that flows in the channel between mattresses. Yet another need exists for a design of erosion control blocks which, when installed adjacent to each other a distance sufficient to allow splicing of cables therebetween, the flow of water between the border blocks is circuitous, thereby reducing possibilities of erosion. A further need exists for a block design where a space between engaged blocks exists, but when the blocks are lifted by a cable to a catenary position, the block edges engage and load forces between blocks are distributed over a larger area of engagement.

[0010] An erosion control block and the method of installation thereof is described below. In one embodiment, the erosion control block is fabricated with a heavy material, and generally in a rectangular shape. Two opposing side edges of the block have semicircular interengaging members. On one side there is formed a semicircular lobe, and on the opposing edge of the block there is formed a semicircular recess. In one embodiment, the lobe and recess are formed so that when fully interengaged, there exists a space between adjacent blocks. As the blocks are lifted by a cable to a catenary position, the lobe of one block becomes disengaged with the recess of a neighbor block, and the adjacent block corner edges become engaged. The corner edges of the blocks are rounded or beveled to provide a larger surface area to distribute the load forces extended between blocks when suspended in the catenary form.

[0011] The other opposing side edges of the erosion control block include edge configurations for providing a circuitous channel when the blocks are installed side-by-side. Two sides edge portions of the erosion control block each include parallel surfaces connected together by an angled edge section. This circuitous channel between adjacent blocks joins the circuitous channel of another adjacent pair of blocks by a lateral water channel. With this arrangement, the channel between the mattress is not straight, but rather is circuitous to thereby impede the flow of water therethrough.

[0012] In the described embodiment, two spaced-apart cable channels are formed between two edges of the block, and another pair of space-apart cable channels are formed between the other two opposing edges. The end of each cable channel, where it terminates at the side edge of the block, opens into a cable cavity to thereby accommodate the use of an anchor button and/or splice sleeve on a cable.

[0013] Further features and advantages will become apparent from the following and more particular description of the preferred and other embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters generally refer to the same parts, components or elements throughout the views, and in which:

[0014] FIG. 1 is an isometric view of an erosion control block constructed according to one embodiment;

[0015] FIG. 2 is a top view of a portion of a mattress of erosion control blocks constructed according to an embodiment of the invention;

[0016] FIG. 3 is a side view of a portion of a block, showing the manner in which a corner of the lobe can be tapered to facilitate flexibility of the mattress of blocks;

[0017] FIG. 4 illustrates the details of a cable channel cavity;

[0018] FIG. 5 shows a portion of two adjacent blocks on the border of two mattresses, with the cable cavities of each block aligned to provide sufficient room for splicing the mattress cable ends;

[0019] FIG. 6 illustrates a number of border blocks of two adjacent mattresses of erosion control blocks, illustrating the circuitous channel between the mattresses;

[0020] FIG. 7 is a top view of a mattress of erosion control blocks suspended by a portion of a spreader bar assembly;

[0021] FIG. 8 is a side view of a spreader bar assembly with a mattress of erosion control blocks suspended therefrom;

[0022] FIG. 9 is a side view of two erosion control blocks of FIG. 1, shown with the semicircular male and female members fully engaged, but with a spacing between the block edges;

[0023] FIG. 10 is a side view of the blocks of FIG. 9, but where one block is flexed to such an extent that the adjacent block edges engage;

[0024] FIG. 11 is a cross-sectional view of the periphera of a mattress as buried in a toe trench;

[0025] FIG. 12 illustrates another embodiment of an erosion control block, where the lobe and recess are formed to allow the edges of the block to engage each other;

[0026] FIG. 13 is a partial cross-sectional view of the engaging edges of the blocks shown in FIG. 12;

[0027] FIGS. 14a-14care respective top, side and frontal views of an erosion control block according to another embodiment;

[0028] FIG. 15 illustrates the mating engagement of two blocks of FIG. 14a,with a space therebetween; and

[0029] FIGS. 16a-16care partial cross-sectional views of two blocks engaged together, at different stages in the process of lifting the same by cables.

[0030] FIG. 1 depicts an erosion control block 10 constructed in accordance with the principles and concepts of the invention. FIG. 2 illustrates a portion of a mattress of erosion control blocks, utilizing the block of FIG. 1. Illustrated is a first block 10 cabled to a second adjacent block 12 by respective cables 14 and 16. The cables 14 and 16 can be of a 20 mm synthetic rope, or other cable suitable for underwater installation. The first block 10 is interengaged with a third block 18, only a portion of which is shown in FIG. 2. Similarly, the second block 12 is interengaged with a fourth block 20, a portion of which is shown. Blocks 10 and 18 are cabled together by a cable 22. Erosion control blocks 12 and 20 are cabled together by cable 26. It should be noted that each block of the mattress is identically constructed. This reduces the decision making by the installers who need not find and/or rearrange different-shaped blocks to form a mattress. A matrix of erosion control blocks can be constructed in the manner shown in FIG. 2, forming a mattress of six blocks by thirty-two blocks. By utilizing interengaging members between blocks, the flexibility of a mattress of cabled blocks is increased.

[0031] With particular reference to erosion control block 10, such block is preferably constructed of a 4000 psi concrete material suitable for underwater usage. In practice, the block 10 can be fabricated using block plant techniques, or other well-known erosion control block forming methods. The block 10 is generally rectangular-shaped, with lateral dimensions of about 15 inches by 15 inches, measured as if the block were square. The thickness of the block 10 can be made to achieve a desired weight of the block. For example, a block having a thickness of about four inches weighs about 50 lbs; a block of about six inches weighs about 63 lbs.; and a block of about eight inches weighs about 95 lbs. Erosion control blocks of different thicknesses can be utilized as a function of the velocity of the water encountered.

[0032] In accordance with an important feature of the invention, the block 10 is fabricated with a semicircular arm or lobe 30 formed as an extension laterally outwardly from edge 32. On the opposite edge 34 of the block 10, there is formed a semicircular recess 36. The lobe 30 of the block 10 can typically interengage with a recess of a neighboring block (not shown). The semicircular recess 36 of block 10 is shown interengaged with a lobe 38 of block 18. The diameter of the semicircular lobe 30 is about 4.125 inches, whereas the diameter by which the recess 36 is formed is about 4.875 inches. The engagement between the lobe of one block and the recess of another block is not an identical mate, but rather includes some slack or play, such as shown in FIG. 2 by the interengagement between the lobe 38 of block 18 and the recess 36 of block 10. In addition, the amount by which the lobe 30 extends outwardly from the edge 32 is greater than the amount by which the recess 36 is formed within the edge 34 of block 10. The mold for forming the block 10 is constructed such that when forming the lobe 38 and the recess 36, the blocks 10 and 18 are separated by about 0.5 inch when the lobe 38 is bottomed out within the recess 36 of block 10. The spacing between the blocks 18 and 10 is shown by reference numeral 40.

[0033] In order to increase flexibility between neighboring blocks of a mattress, if desired, at least a portion of the peripheral rounded edge of the lobe 30 can be beveled or curved, as shown in FIG. 3. Here, the upper circular corner 42 is beveled so that when one block flexes with respect to a neighbor block, sharp edges do not rub or engage with the surfaces of a neighboring block. The blocks of a mattress will necessarily flex when arranged in a mattress and lifted by a spreader bar, such as shown in FIGS. 7 and 8, to be described below. In other modifications of the block 10, the bottom circular edge of the lobe 30 can also be beveled or rounded to reduce the destruction of corner edges when neighboring blocks become engaged under a compressive force.

[0034] With reference again to FIG. 2, there is formed in the block 10 an opening 44 centrally therein, from a top surface of the block to the bottom surface thereof. The opening 44 can be any shape and is for the purpose of allowing vegetation to grow through the block and facilitate anchoring of the block to the ground surface. In practice, the central opening 44 in the block 10 is about 3.5 inches by 6.13 inches. When a number of similar blocks are cabled together, with minimal space therebetween, the overall void area for the mattress of blocks is about twelve percent.

[0035] Four cable channels are formed in the block 10 for threading of the cables therethrough. A first cable channel 46 is formed through the block 10, between edge 32 and edge 34. Similarly, cable channel 48 is formed in the block 10, also between edge 32 and 34. The cable channels 46 and 48 are spaced-apart to accommodate the lobe 30 and the recess 36 therebetween. Each cable channel, for example cable channel 46, opens into a pocket or cavity 50 in a respective side edge of the block 10. In like manner, the other end of the cable channel 46 opens into a cavity 52 formed in the block side edge 34. The cavities 50 and 52 are formed so as to be about 0.75 inch deep into the respective edges 32 and 34, and about 1.5 inches wide. While the cavities 50 and 52 are shown formed from the top surface to the bottom surface of the block 10, such cavities can also be formed as individual pockets formed into the respective edges of the block 10. The cavities 50 and 52 function to allow a crimp button and washer to be secured to the cable 22. For example, the blocks forming the border of a matrix are often constrained from movement on cable 22 by the utilization of the crimp button and washers.

[0036] FIG. 4 illustrates in enlarged form, the manner in which a border block 52 is constrained with respect to a cable 54. A plastic washer 56 is placed flush against the inside surface of the cavity 50, and the cable 54 is threaded through the hole in the washer 56. Next, an aluminum crimpable button 58 is inserted over the cable 54, into engagement with the washer 56. By utilizing a conventional crimping tool, the button 58 is crimped to form one or more indentions 60 so as to securely clamp and anchor the button 58 to the cable 54. In this manner, the block 52 cannot move laterally on the cable, as the block 52 is constrained by the crimped button 58.

[0037] The cavity 50 allows additional space or room between neighboring blocks to allow a workman access to the ends of the cable 54 for installing the button 58 and washers 56 thereon. In practice, the border blocks of one mattress are spaced-apart from the border blocks of another mattress by about two inches or so, such as shown in FIG. 5. Here, there is shown a button 58 crimped to each end of the respective cables of the adjacent mattresses. In addition, the cable ends are spliced together with a double-tubular sleeve 61 that is crimped to the ends of the mattress cables. This anchors one mattress to an adjacent mattress. This spacing is sufficient to allow a workman access to the ends of the respective cables for splicing the same together.

[0038] By utilizing the cable cavities formed in each edge of the block 10, the spacing between border blocks of neighboring mattresses can be smaller, thereby reducing the chances of soil erosion thereunder. As can be appreciated, the unimpeded flow of water through a channel allows an increased flow rate of the water and the higher likelihood of either slope or mattress failure. If the flow of water is impeded in some manner, the flow rate is reduced, thereby reducing the possibility of slope or mattress failure. Those skilled in the art may desire to utilize cable cavities having other shapes and sizes to suit the particular needs required by the installation. Cable cavities 62 and 64 are formed in the respective block edges 32 and 34 of block 10 to accommodate the cable 22 in the same manner described above.

[0039] In addition to opposing block edges 32 and 34, the erosion control block 10 of FIG. 2 further includes other opposing block edges 66 and 68. Formed in the block edges 66 and 68 are respective cable cavities 70, 72 and 74, 76. The cavities 70 and 74 on opposing edges of the block 10 provide terminations for a cable channel 78. Similarly, cavities 72 and 76 formed in opposite edges of the block 10 provide terminations for a cable channel 80. Cable channel 78 has threaded therethrough the cable 14, while cable channel 80 has threaded therethrough cable 16. As such, four cables are threaded through respective channels of each block to provide stability to the block while lifting a mattress with a spreader bar.

[0040] Rather than being straight or linear, the side edge 66 of the block 10 has a first edge portion 66athat is parallel to a second edge portion 66b,but such edge portions 66aand 66bare not formed in the same vertical plane. Rather, edge portion 66ais connected to edge portion 66bby an angled edge section 66c.With this arrangement, the edge portion 66ais offset with respect to the edge portion 66bas shown in FIG. 2. The offset is formed so that the edge portion 66bis closer to the center of the block, as compared to edge portion 66a.

[0041] The opposing side edge 68 of block 10 is similarly formed, with edge portions 68a,edge portion 68band angled edge section 68c.Here, the edge portion 68ais closer to the center of the block 10, as compared to edge portion 68b.The distance across the block 10 between opposing edges 66aand 68ais the same as the distance across the block 10 between 66band 68b.

[0042] The block 10 is formed with offset edge portions on opposing sides thereof to provide two distinct functions. First, the offset edge portions are complementary, as between neighboring blocks within a mattress, such as shown between blocks 10 and 12 in FIG. 2. The spacing between blocks 10 and 12 may exist between border blocks of two adjacent mattresses. If block 10 and block 12 are cabled together in the same mattress, then such blocks would contact each other and there would be little or no spacing. When formed as border blocks between two adjacent mattresses, the blocks 10 and 12 block edge 68ais about one and one half inch from the side edge portion 90aof block 12, and side edge portion 68bof block 10 is about one and one half inch from side edge portion 90bof block 12. Lastly, angled edge section 68cof block 10 is adjacent angled edge section 90cof block 12. However, the spacing between the angled edge sections 68cand 90cis not typically one and one half inch, but rather because of the angled configuration the spacing is less. One function of the offset edge portions of each block is that should one block of one mattress, for example block 20, shift downwardly with respect to adjacent block 10 of another mattress, angled edge section 90cwill engage with angled edge section 68cof block 10, thereby preventing further downward movement of block 12. The stability of the mattress is thereby enhanced.

[0043] With reference now to FIG. 6, another advantage of the erosion control block of the invention is apparent. The thirty-two erosion control blocks in the row 92 are part of one mattress of blocks, and the thirty-two erosion control blocks in row 94 is part of another mattress. The loops in the cables 22 and 26 provide a mechanism for attaching the same to the spreader bar assembly 104. The spacing between the two rows 92 and 94 of blocks in neighboring mattresses constitutes a water channel 96. The ends of the cables extending between the two mattresses are spliced together in the water channel 96, using a splice such as identified by reference numeral 98. Splice 98 is the same as splice 61 of FIG. 5. As noted above, this ties or otherwise anchors the two adjacent mattresses together. In accordance with an important feature, the water channel 96 is circuitous, in that any runoff water cannot flow straight through the channel 96. Rather, any fluid flow between the two mattresses in the water channel 96 must change directions a number of times, thereby reducing the flow rate of water therethrough. The circuitous channel 96 between blocks 10 and 11 is shown in more detail in FIG. 2. In order for water to flow between two border blocks of adjacent mattresses, the water must first be re-routed when flowing through the channel defined by the edge section 68cand 90c.Next, the water must then abruptly change its direction of flow when exiting the water channel of one pair of adjacent blocks 10 and 12 and entering the water channel of the subsequent pair of blocks 18 and 20. This is shown by arrow 98 of FIG. 2. Then, when the water enters the channel of the subsequent blocks, it must again be redirected twice before entering the water channel of the next pair of blocks. As can be seen, when a mattress constitutes a minimum width of about six blocks, the water must change direction many times before passing entirely through the water channel of adjacent mattresses. The possibility of erosion of the soil underlying the blocks is thereby reduced. While only two opposing side edges are shown formed to provide a circuitous water channel between blocks, those skilled in the art may prefer to form all four sides of a block having edge configurations with portions 66a,66band angled edge section 66c.

[0044] FIG. 7 illustrates the top view of a number of erosion control blocks constructed according to the invention, anchored together by numerous cables. Each block of the mattress is constructed in a manner substantially identical to that shown in FIG. 1. The cables at the ends of the mattress are anchored to spaced-apart beams 100 and 102. The ends of the cables can be anchored to the beams 100 and 102 in any conventional manner well known in the field.

[0045] FIG. 8 illustrates a side view of a spreader bar assembly 104 coupled to the beams 100 and 102. The spreader bar assembly 104 includes a structure of heavy duty steel welded together so as to support the weight of the mattress when the spreader bar assembly 104 is lifted by a crane. Typically, an 80-100 ton crane is utilized for lifting the spreader bar assembly 104 by way of a hook or eye 106. As can be seen, the weight of the erosion control blocks constituting the mattress 98 causes it to bow downwardly and form an arc or catenary shape. The erosion control blocks are thus required to flex with respect to each other when suspended by the spreader bar assembly 104 and forced into the catenary shape. In order to prevent destruction of the semicircular lobes 30 due to point contact loading, the upper corners of the lobes can be angled or otherwise rounded, such as shown in FIG. 3.

[0046] The flexibility of the block is shown by example in FIGS. 9 and 10. In FIG. 9, the blocks 10 and 18 of a mattress are shown with the semicircular male member 38 of block 18 fully engaged in the semicircular female member 36 of block 10. When both blocks 10 and 18 are on a generally planar surface, a space 40 exists between the adjacent edges 34 and 35 of the blocks 10 and 18. When the blocks 10 and 18 are angled, such as shown-in FIG. 10, the corner 37 of block 10 can be engaged with the side edge 35 of block 18. The angled orientation can occur when the blocks are picked up by a spreader bar and suspended by the cables threaded therethrough, or when installed on uneven terrain. The blocks can also flex in the opposite direction to a high degree, i.e., greater than 45°, to conform to sharp convex earth terrain such as involved with anchoring the edge of a mattress in a toe trench. In any event, even though the upper corner of the semicircular male member 38 engages with the sidewall of the semicircular female recess 36, the pressure exerted therebetween is reduced by the concurrent engagement of the adjacent side edges 34 and 35 of the blocks 10 and 18. This prevents breakage and chipping of the block members. As can be appreciated, the amount of flexing before the side edges of adjacent blocks engage is a function of the amount of the spacing 40.

[0047] FIG. 11 illustrates the manner in which the periphera of a mattress 130 is anchored in the ground to prevent water from flowing under the mattress 130 and/or the geotextile material. A toe trench 132 is formed in the ground at the periphera of the mattress 130, to a depth of about three feet. The edge or border blocks 134 of the mattress 130 are allowed to overlap into the trench 132. If the mattress 130 has a significant degree of flexibility, then fewer blocks of the mattress are required to reach to the bottom of the trench, as such blocks can be angled downwardly at a sharper angle. On the other hand, if the blocks do not have a significant amount of flexibility, then more blocks must be used for anchoring the mattress 130 in the toe trench 132. Once the edge blocks are installed in the toe trench 132, it is back filled and compacted with dirt.

[0048] FIG. 12 illustrates an embodiment similar to that shown in FIG. 2, but where the block 110 has a semicircular recess 114 which has substantially the same circumferential shape and length as the lobe 116 of block 112. With this configuration of the interengaging members, the side edge 118 of block 110 can engage or otherwise contact the side edge 120 of block 112. The lobe 116 of block 112 can have one or both circular corner edges thereof angled or rounded, such as shown in FIG. 3. Moreover, because of the engagement of the side edges 118 and 120 of respective blocks 110 and 112, such side edges can also include tapered or rounded corner edges, such as shown in FIG. 13. In order to accommodate the flexibility between blocks as shown in FIG. 8, when suspended from a spreader bar 104, the blocks 110 and 112 should preferably include rounded or angled top corner edges 122 and 124. Should it be required that the erosion control blocks flex in the opposite direction, so as to accommodate uneven terrain, the bottom corners of the side edges can also be rounded or angled, such as shown in FIG. 13.

[0049] The invention is susceptible to numerous modifications. For example, the cable cavities 52 and 62 can be eliminated, thereby providing a more sturdy and higher strength block, at least at the diagonal corners. Those skilled in the art may make yet other modifications which will come within the scope of the claims.

[0050] FIGS. 14a-14cillustrate respectively top, side and frontal views of an erosion control block 140, constructed according to another embodiment. The erosion control block 140 is similar to that shown in FIG. 2, with a few exceptions. Diagonal corners 142 and 144 are formed in the block 140 to increase the void area between blocks when a number of such blocks are cabled together to form a mattress. In the embodiment shown in FIG. 14a,the overall void area in a mattress of such type of blocks is about .percent. This includes the void area of the central opening 146, which measures about 3.5 inches by 6.115 inches. The corners 148 of the opening 146 are formed with curvature to facilitate removal of the block 140 from the mold with which it is formed.

[0051] In order to reduce the fragility of the block 140, the cable channel 150 opens into the edge 152 of the block 140, without the use of a corresponding cable cavity. The corner 154 of the block 140 is thus stronger and less susceptible to breakage. The cable channel 156 formed through the block 140 also terminates at the opposite block edge 158 without the use of a cable cavity. In like manner, the corner 160 of the block 140 is less susceptible to breakage. The pair of cable channels 162 and 164 each open into respective opposing cable cavities, much like the embodiment of the block 10 shown in FIG. 1.

[0052] The block 140 is formed with a semicircular recess 166 into block edge 158. A lobe 168 is formed as an extension outwardly from the opposing block edge 152. The lobe 168 has opposing, parallel and linear side walls 170 and 172 that blend into the semicircular portion 174 of the lobe 168. As can be appreciated, when the lobe 168 of the block 140 is engaged within a recess 176 of a neighbor block 178 lying on a planar surface, such as shown in FIG. 15, a space 180 is provided therebetween. This allows flexibility of the blocks when cabled together and lifted off the ground for installation.

[0053] The side edge 152 of the erosion control block 140 is formed with a rounded upper corner 155, such as shown in the enlarged diagram of FIG. 14b.In like manner, the tip portion 182 of the lobe 168 is similarly rounded. The rounded upper corners 155 on the edge 152 as well as on the tip portion 182 of the lobe 168 facilitate the flexibility between engaged blocks, thereby reducing point contact loading of the edges and corresponding breakage or cracking of the blocks. The rounded upper corners 155 of the edge 152 and the tip portion 182 preferably have a radius of about 0.25 inches. Instead of utilizing rounded corners, a chamfer or other geometric shape can be utilized.

[0054] The opposite side edge 158 of the block 140 is similarly formed with a rounded upper corner 159 to reduce breakage of the corner of the blocks when neighboring blocks are engaged and flexed, such as when the cables are lifted for installation of a matrix or mattress of blocks.

[0055] FIGS. 16a-16cillustrate the cooperation between the engaging surfaces/edges of neighboring blocks 140 and 178 of a row of erosion control blocks suspended by cables (not shown) in a catenary form. It is understood that block 178 is cabled by two cables through cable channels 150 and 156 (FIG. 14a) to block 140, as well as to many other similar blocks (not shown) in a row.

[0056] As can be appreciated, when cables are threaded through a number of erosion control blocks on a flat surface, the blocks 140 and 178 are pushed or otherwise forced together into contact with each other, as shown in FIG. 16a.Because the lobe 168 of block 140 is laterally longer than the recess 176 of neighbor block 178, the adjacent edges 186 and 188 of the respective lobe 168 and recess 176 are engaged together. This is also shown in FIG. 15. When both blocks 140 and 178 are lying on a planar surface, there exists a space 180 between the adjacent side edges of the blocks 140 and 178.

[0057] As the blocks 140 and 178 are in the early stage of being lifted by the spreader bar assembly 104 (FIG. 8), the blocks 140 and 178 begin to flex with respect to each other, such as shown in FIG. 16b.Here, the rounded edge 182 of lobe 168 engages the sidewall of the recess 176 of block 178. As noted above, the rounded upper corners 182 reduces point loading on the lobe corner, and facilitate flexing of the blocks during lifting to the catenary form. The rounded upper corner edges of the blocks 140 and 178 move closer to each other. This is shown in FIG. 16b.

[0058] After the spreader bar assembly 140 is lifted higher until all of the blocks are elevated off the ground, the blocks 140 and 178 flex even further, as shown in FIG. 16c.In this fully lifted position, the lobe 168 of block 140 no longer engages with the recess 176 of block 178. Rather, the rounded upper corner edges of the blocks 140 and 178 become engaged to support the force exerted between the blocks. Since there is substantially more surface area between the engaged rounded upper corner edges of blocks 140 and 178, as compared to the area between the recess 176 and lobe 168 (when engaged), the force exerted between engaged blocks 140 and 178 does not result in cracking or breakage of the engaged members.

[0059] After the blocks 140 and 178 have been moved by the crane to the installation side and laid on the area to be protected from erosion, the blocks flex in the opposite direction as shown in FIGS. 16a-16c.If the ground on which the blocks are laid is more or less level, the blocks will assume the position as shown in FIG. 16a.Here, the recess 176 of one block 178 will again engage with the lobe 168 of a neighbor block 140, and a space 180 will exist between the blocks. The space 180 between adjacent blocks can fulfill the requirements for a percentage of void area in a mattress of blocks, or provide an area for vegetation growth to further anchor the blocks to the ground.

[0060] While the erosion control blocks shown in the drawings are each constructed with one lobe and one recess, those skilled in the art may prefer to make blocks each having two recesses and two lobes. In addition, rather than providing side edges with irregular shapes to provide a circuitous space between neighbor blocks, such side edges can be generally linear

[0061] While the preferred and other embodiments of the invention has been disclosed with reference to specific erosion control blocks, and methods of construction thereof, it is to be understood that many changes in detail may be as a matter of engineering choices, without departing from the spirit and scope of the invention, as defined by the appended claims.