Patent Publication Number: US-8123435-B1

Title: Interlocking revetment block with array of vegetation holes

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates in general to erosion control blocks, and more particularly to erosion control blocks with holes therein adapted for anchoring by vegetation growth therethrough. 
     BACKGROUND OF THE INVENTION 
     The erosion of soil on the earth continues to occur as rain and flood waters run from high elevations to lower elevations. Many efforts have been made to reduce the erosion of soil by interrupting the runoff of water, or at least slow down the water flow and thereby reduce the extent of erosion. Erosion control blocks are available for covering watershed areas to protect the underlying soil from being carried with the runoff water. Many styles, shapes and sizes of erosion control blocks are available for placement together to form a mat that covers the ground to be protected from erosion. The use of erosion control blocks is preferred over the use of a slab of concrete, as concrete can crack and settle if the underlying ground is unstable, which it is in many watershed areas. It is also difficult to make a concrete slab that is adapted to slow down the velocity of water that flows thereover. Erosion control blocks of the articulating type continue to conform to the contour of the ground, even when the ground contour changes. 
     Blocks that are simply placed side by side on the ground are helpful in reducing soil erosion, but only in situations where the velocity of the runoff water is low or moderate. Otherwise, the hydraulic lift of the flowing water can cause the blocks to actually lift off the ground and be carried or otherwise moved so that the erosion protection is compromised. Of course, the heavier the block the less likely it is to be moved by high velocity water currents. This solution is costly and often prevents the installation of the heavy blocks by persons who must lift each block and place it into position with others to form the mat. 
     More recently, erosion control blocks have been constructed so as to be laterally interlocking so that horizontal movement is prevented. U.S. Pat. No. 5,556,228 by Smith is an example of a commercially accepted interlocking erosion control block that articulates to conform to the contour of the ground. Such type of block has been accepted by governmental organizations for use on large waterways to halt erosion of the same. 
     In order to further enhance the stability of a revetment block or erosion control block, holes can be formed through the body of the block so that vegetation can grow therethrough and anchor the block to the underlying ground. The use of vegetation to anchor the block or mat of blocks to the ground is advantageous in situations where the mat of blocks is not constantly covered by a substantial depth of water, as vegetation does not grow well under such conditions. Rather, there are many water shed areas where the mat of blocks covers areas that are not under water, but are subjected to substantial water flows during rains and the like. Water ways and other watershed areas comprise such situations, which may be generally dry, but which can carry heavy flows of fast moving water during storms and flood conditions. The interlocking nature of the erosion control blocks together with the anchoring of the same to the ground by vegetation allows the erosion of the underlying ground to be controlled. 
     While the vegetation holes in erosion control blocks allows anchoring thereof by vegetation, such holes can also present a disadvantage. For example, if vegetation does not fully occupy the opening in the block, or if there is no vegetation at all, then the hole in the block can function as a small barrier to the flow of water over the block, and impart a hydraulic lifting force on the block. In other words, the water flowing over the block applies a force to the downstream side of the hole. The resulting water turbulence and the hydraulic forces can impart a force on the block that tends to lift the upstream portion of the block. If the upstream side of the block starts to lift and becomes separated from the ground, then the lifting forces avalanche and can be sufficient to completely lift the entire block from the mat. If this occurs, then the surrounding blocks are more easily dislodged from the mat, whereupon the integrity of the entire mat of blocks can be compromised. If the mat of blocks is installed on a slope that is to be protected from erosion, such as a flume, then the velocity of the water is accelerated due to the downhill grade. With an increased velocity of a large volume of water, the integrity of the mat of blocks must be maintained. 
     Often the erosion control blocks are installed by workmen who can carry one block with a hand, from a skid of blocks to the location where the mat is to be formed. To that end, the blocks must be of a weight that allows an average workman to conveniently carry a block, and the block must be constructed to allow easy gripping of the same with one hand. An average four-inch thick concrete block of the type described above in U.S. Pat. No. 5,556,228 can weigh about 56 pounds, and can be carried with one hand a distance sufficient to install the same in a watershed area. An eight-inch block of the same configuration can weigh about 115 pounds, and can also be carried by a workman with two hands from a skid to the site of installment. Because of the weight, workers generally grasp the arms of the block using two hands. If the blocks are too heavy, they must be carried by wheeled carts or otherwise in order to transport them at the work site. 
     Facilities exist for testing the hydraulic stability of erosion control blocks in order to enable the manufacturer to certify that the blocks can remain stable under specified water flow conditions. Often such certifications are necessary in order for block suppliers and manufacturers to be granted contracts for erosion control projects. These facilities can place the test blocks under actual working conditions in a laboratory setting, where the grade, water depth, volume and velocity can be accurately controlled. As an alternative, blocks can be made physically very large and heavy to assure that they will not be moved under the severest water flow conditions. Such overkill renders the blocks unnecessarily large, heavy and difficult to install. However, once the hydraulic stability characteristics of a block are understood, they can be used in engineering the design of an efficient block that conforms to specified constraints, is easy to handle and install and is cost effective. 
     From the foregoing, it can be seen that a need exists for an interlocking erosion control block that employs an efficient system of vegetation holes therein. Another need exists for an erosion control blocks which employs vegetation holes therein at locations that allow easy grasping of the same by a workman. Yet another need exists for an interlocking erosion control block having plural vegetation holes placed at locations to afford sufficient area for vegetation growth, to allow easy grasping of the block, but not at locations that would affect the structural integrity of the block. 
     SUMMARY OF THE INVENTION 
     Disclosed is an erosion control block that provides interlocking capabilities with neighbor blocks of a mat. According to a feature of the invention, plural holes are formed through the block, from the top surface to the bottom surface to provide vegetation growth, as well as relief of hydrostatic pressure. The holes are constructed with diameters related to the thickness of the block to maximize the hydraulic stability thereof. 
     According to another feature of the invention, the holes are located in the block to also allow a workman to grasp the block using the holes to lift the same. However, the placement of the holes does not compromise the structural integrity of the block. 
     With regard to yet another feature of the invention, the holes are formed in a core square of the block, where the square excludes the arm and socket structures. In a preferred embodiment, five holes are formed in the core square, with two of the holes having a larger diameter than the other holes to allow three fingers of a person&#39;s hand to be inserted therein. 
     Another advantage of the use of multiple holes, is that each hole is tapered to flare out at the bottom of the block to enlarge the open area to the ground to allow a greater degree of vegetation to grow through the block. The tapered holes also facilitate the grasping of the block by a workman. 
     The block can be fabricated with cable channels therethrough, with one diagonal cable channel intersecting plural holes, and the other diagonal cable channel not intersecting any of the holes formed through the block. 
     According to one embodiment, disclosed is a revetment block that includes a body with a thickness defined by a distance between a top surface and a bottom surface of the body of the block, where the block has a plurality of side edges. Further included are at least two arms, where each arm extends from a respective side edge of the body of the block, and each arm has an enlarged end connected to a respective side edge by a narrowed neck portion. Included also are at least two sockets formed inwardly from respective side edges of the body of the block, where each socket has an enlarged cavity connected by a narrowed inlet to the respective side edge of the body of the block. The sockets are adapted for receiving therein an arm of a similarly constructed neighbor block. A plurality of holes are formed through the body of the block. The holes are formed in a core square of the block, where the core square includes a square area that excludes the arms and the sockets. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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, functions or elements throughout the views, and in which: 
         FIG. 1  is a top view of an erosion control block with an arrangement of vegetation holes therein according to the invention; 
         FIG. 2  is a partial side view of the modified arm of the block of  FIG. 1 , taken along line  2 - 2  thereof; 
         FIG. 3  is a side view of the modified socket the block of  FIG. 1 , taken along line  3 - 3  thereof; 
         FIG. 4  is an isometric view of a portion of the interlocking revetment block of  FIG. 1 , illustrating the modified arm constructed according to an embodiment of the invention; 
         FIG. 5  is an isometric view of a portion of the interlocking revetment block of  FIG. 1 , illustrating the modified socket constructed according to an embodiment of the invention; 
         FIG. 6  is a bottom view of the revetment block of  FIG. 1 ; 
         FIG. 7  is a row of a mat of revetment blocks installed according to the invention; 
         FIG. 8  is a top view of the erosion control block illustrating the details of the placement of the vegetation and gripping holes formed therein; and 
         FIG. 9  is a cross-sectional view of the revetment block, taken along line  9 - 9  of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An erosion control block  10  constructed according to the invention is shown in  FIG. 1 . The block  10  includes a full depth socket  12 , a partial thickness arm  14 , a full thickness arm  16  and a partial depth socket  18 . The full depth socket  12  is formed axially into a side edge  20  of the block  10 , and extends from a top surface  20  of the block  10  to a bottom surface  22 , shown in  FIG. 6 . The full depth socket  12  includes an enlarged cavity  24  connected to the edge  20  of the block  10  by a narrowed inlet  26 . The full depth socket  12  includes an inner edge  25 . The full depth socket  12  is the same general shape as the full thickness arm  16 , but somewhat larger in size so that a full thickness arm of a similarly-constructed neighbor block can be fitted into the full depth socket  12  of the block  10 . The arms  14  and  16  are formed orthogonal to each other on respective adjacent side edges  28  and  30  of the block  10 . Similarly, the sockets  12  and  18  are formed orthogonal to each other into respective adjacent side edges  20  and  32  of the block  10 . 
     In the preferred embodiment, the full thickness arm  16  is formed radially outwardly from an edge  30  of the block  10 . The full thickness arm  16  includes an enlarged end  34  connected to the edge  30  by a thinned neck  36 . The full thickness arm  16  extends from the top surface  20  of the block  10  to the bottom surface  22  of the block  10 . The full thickness arm  16  is constructed with a shape and size to fit within a full thickness socket of a similarly-constructed neighbor block. Preferably, the full thickness arm  16  is formed on the block  10  on side edge opposite that of the full depth socket  12 . The arms and sockets are shaped and sized to allow a sufficient degree of articulation between neighbor blocks. 
     The erosion control block  10  is constructed using mold techniques where a wet concrete mixture is poured into a mold and allowed to set. Then, the block  10  is removed from the mold. To that end, the side edges  20 ,  28 ,  30  and  32  can each include a slight taper or draft. In addition, all of the arms and sockets can also be formed with a slight draft so that the block can be removed from the mold. The block  10  can be molded with different thicknesses and dimensions noted herein. The block constructed to a preferred embodiment is about 4.5 inches thick. 
     The block  10  constructed according to the invention also includes a partial thickness arm  14  that extends from the side edge  28  of the block  10 . The partial thickness arm  14  includes an enlarged end  40  connected to the side edge  28  by a thinned neck  42 . The details of the partial thickness arm  14  are also illustrated in  FIGS. 2 and 4 . The partial thickness arm  14  extends to the top surface  20  of the block  10 , but is not coplanar with the bottom surface  22  of the block  10 . To that end, the partial thickness arm  14  is only about 3.25 inches thick, and thus is recessed about 1.25 inches from the bottom surface  22  of the block  10 . Other than the thickness, the size and shape of the partial thickness arm  14  is the same as that of the full thickness arm  16 . 
     Formed in an edge  32  of the block  10  opposite the side edge  28 , is a partial depth socket  18 . The partial depth socket  18  includes an enlarged cavity  44  connected to the side edge  32  of the block  10  by a narrowed inlet  46 . Rather than being formed completely through the block  10 , the partial depth socket  18  is formed from the top surface  20  down into the body of the block about 3.25 inches. This aspect is shown in  FIGS. 3 and 5 . The bottom surface  48  of the partial depth socket  18  is thus about 3.25 inches from the top surface  20  of the block  10 . The portion  50  of the body of the block under the partial depth socket  18  functions to strengthen the block  10 , and especially that portion of the body of the block  10  that extends to the adjacent full depth socket  12 . As can be seen, the partial thickness arm  14  of  FIG. 4  is adapted to fit into a partial depth socket  18  of a neighbor block. 
     The partial thickness arm  14  of one block  10  can be lowered into the partial depth socket  18  of a neighbor block so that the neighbor block is vertically interlocked to the block  10 . A row of four erosion control blocks  10   1 - 10   4  are illustrated in  FIG. 7 . Additional blocks can be added to the row to form a mat of blocks and guard against erosion of the underlying ground when the water is flowing in the direction of arrow  52 . The blocks are installed in the following manner. The down-stream most block  10 , is first installed on the ground or on a geotextile material with the partial thickness arm  14   1  oriented downstream. Then the next block  10 , is installed by lowering it over the block  10   1 , with the partial thickness arm  14 , lowered into the partial depth socket  18   1  of block  10   1 . The next block  10   3  is then installed by lowering it so that the partial thickness arm  14   3  is lowered into the partial depth socket  18   2  of block  10   2 . The next block  10   4  to be installed in the row is installed by lowering the partial thickness arm  14   4  thereof into the partial depth socket  18   3  of block  10   3 . Other upstream blocks can be installed in a similar manner. In addition, another row of blocks can be installed by carrying out the same steps noted above, but in addition to lowering of a partial thickness arm of the block into the partial depth socket of the downstream block, the full thickness arm or the full depth socket of the block being installed is also lowered into the respective full depth socket or over the full thickness arm of the neighbor block in the other row. 
     Much like the conventional revetment block described in U.S. Pat. No. 5,556,228, the erosion control block  10  includes angled corners  54 - 60  to define an octagonal-shaped revetment block  10 . With the angled corners  54 - 60 , a square opening is formed at the location where the angled corners of four blocks meet, and the four blocks form a square. 
     In accordance with an important feature of the invention, the erosion control block  10  is formed with plural, small holes through the block  10  to allow vegetation growth therethrough. As noted above, the growth of vegetation helps anchor the block  10  to the ground and thus the block  10  can withstand substantially more hydraulic lifting forces before being carried away by the water. According to an aspect of the invention, the holes are sized and located to assist an installer in lifting the block  10  and carrying the same with one hand.  FIG. 8  illustrates the top view of the block  10  with five vegetation holes formed therein. The five holes include four holes  62 - 68  formed at the corners of a square  72  defining the core of the block  10 . A fifth hole  70  is formed in the center of the other four holes  62 - 68 . The five holes  62 - 70  are thus positioned like the five dots on a dice. 
     The five holes  62 - 70  are placed in the block at desired locations to accomplish various advantages. The holes  62 - 70  are located within a square identified by the broken line  72 . As noted above, the square defined by the broken line  72  is the core of the block  10 . The broken line  72  is that portion of the block that excludes the two arms  14  and  16  and the two sockets  12  and  18 . Two adjacent sides of the core square  72  are coincident with two respective adjacent side edges  28  and  30  of the block  10 , and two other adjacent sides of the core square  72  are coincident with the inner edges  25  and  45  of the enlarged cavities  24  and  44  of the respective sockets  12  and  18 . The three holes  64 ,  70  and  68  are centered on a diagonal axis  74  which extends through the opposite corners  76  and  78  of the square core  72 . The center hole  70  is located in the center of the core square  72 . The respective centers of the holes  64  and  68  are equidistantly spaced from the center of the hole  70 . In like manner, the three holes  62 ,  70  and  66  are centered on the other diagonal axis  79  which extends through the opposite corners  80  and  82  of the core square  72 . Each hole is tapered so that the opening in the top  20  of the block is smaller than the corresponding opening at the bottom  22  of the block  10 . 
     In the preferred embodiment of the erosion control block  10 , the dimension of each side of the core square is 12.082 inches. The size of the opening of each hole  62 - 70  in the bottom  22  of the block, for example the bottom opening  86  of hole  62 , is 3.0 inches. The spacing  84  between the bottom opening  86  of each hole  62 - 70  is 1.0 inch. Importantly, the diameter of the opening of each hole  62 - 70  in the top  20  of the block  10  is not the same. The holes  62 ,  70  and  66  have top openings all with a diameter of 2.0 inches. In contrast, the holes  64  and  68  have top openings  88  each with a diameter of 2.5 inches. Thus, the holes  64  and  68  have larger openings in the top  20  of the block  10  than the other holes. The effective open area at the bottom  22  of the block  10  is about 35.3 square inches. 
     In accordance with an important feature of the invention, the holes  64  and  68  located adjacent the opposite corners  78  and  76  of the core square  72  have larger openings in the top  20  of the block  10  to facilitate grasping by the fingers of a workman to lift the block and carry the same. More particularly, three fingers of a workman&#39;s hand, even with gloves, can be inserted into the 2.5 inch diameter top opening of the hole  64 , with the thumb on the angled corner  54  and easily pick up the block  10 . Alternatively, the workman can insert the fingers of a hand into the other 2.5 inch diameter opening of the hole  68 , with the thumb in either the socket  12  or socket  18 , and similarly lift the block. The distance between the edge of the hole  64  and the angled corner  54  is suitable to accommodate a person&#39;s hand. Similarly, the distance between the hole  68  and either of the sockets  12  or  18  can also easily accommodate a person&#39;s hand to firmly grasp and lift the block. Moreover, the taper of the holes  64  and  68  facilitates the maintenance of the grasp of the block  10  without it slipping. A block  10  can thus be carried in each hand of the workman. 
     According to another aspect of the invention, the holes  62 - 70  are dimensioned to provide a superior hydraulic stability to the block  10  under severe water flow conditions, and also to allow vegetation to grow therethrough to enhance anchoring of the block  10  to the ground. It is recognized that for best hydraulic performance, there would be no holes in the block, as the downstream edge of each hole allows the water flow to exert a force thereon in a direction tending to lift the block  10 . However, it is also known that the hydrostatic force on an erosion control block can be relieved with one or more holes formed therethrough. Thus, the concern is how many holes should be formed in an erosion control block, and the size thereof, to achieve optimum hydraulic stability, allow the block to relieve hydrostatic pressure, allow easy grasping thereof using the holes, and the placement of the holes to maintain the strength and integrity of the block. 
     As noted above the holes  62 - 70  are tapered so that the larger-size opening is at the bottom  22  of the block  10  to increase the area exposed to the ground to promote vegetation growth therein. The size of each opening of the block  10  at the top  20  is critical to the hydraulic stability of the block. In the preferred embodiment, the average diameter of each hole at the top  20  of the block  10  is ideally attempted to be about half the thickness of the block, namely 2.125 inch diameter for the 4.25 inch thick block  10 . It is realized that it is the top openings of the holes  62 - 70  that are subjected to the force of the water flowing over the block  10 . However, with two holes  64  and  68  having larger diameters (2.5 inches) than the ideal to accommodate the insertion of fingers therein, the other three holes  62 ,  70  and  66  are constructed with slightly smaller openings (2.0 inches) than the ideal. With this construction, it is anticipated that the erosion control block  10  will exhibit superior hydraulic stability and thus remain stable in an interlocked mat when subjected to high velocity water flowing thereover. As noted above, by employing five holes complying with the foregoing criterion, the desired area of vegetation growth in each hole is maximized, without compromising the hydraulic stability of the block  10 . The physical strength and integrity of the block  10  is also maintained. Stated another way, the holes  62 - 70  are spaced in the core square  72  away from the block edges and the cavities so that the block  10  is not weakened at various areas due to the holes  62 - 70 . Nevertheless, the various holes  64  and  68  are placed sufficiently close to the edge of either the block or a socket so as to allow easy grasping by a person&#39;s hand. 
     While the preferred embodiment of the invention employs five holes to achieve a desired vegetation growth area, other numbers of holes can be utilized. If a smaller vegetation area is desired than the four holes  62 ,  64 ,  66  and  68  can be used. If three holes are desired, then either the three holes  62 ,  70  and  66  can be used, or the holes  64 ,  70  and  68  can be used. If two holes are desired, then two of the holes can be used and located in the core square  72 . Preferably, the diameter of the holes, irrespective of the number thereof, should not be larger than about half the thickness of the block, if the optimum hydraulic stability is to be maintained. 
     While not shown, the block  10  can be formed with cable channels therethrough to allow a number of the block  10  to be cabled together, in an interlocked arrangement, and installed on an embankment or other watershed area. One diagonal cable channel can be formed through the block  10  with a bore axially aligned with the diagonal line  74  so as to extend between opposite angled corners  54  and  60  of the block  10 . This diagonal cable channel would extend through the three holes  64 ,  70  and  68 . The second diagonal cable channel would have a bore aligned with the line  90  and would pass through the block  10  between the three aligned holes  62 ,  70  and  66 , and the other hole  68  so as not to intersect with any of the holes in the block  10 . The second cable channel would extend between the diagonal corners  54  and  58 . 
       FIG. 9  is a cross-sectional view taken along the diagonal line  74 , illustrating the details of the holes  68 ,  70  and  64 . Each hole  68 ,  70  and  64  is tapered so as to flare out toward the bottom  22  of the block  10 . The bottom diameter of each hole  68 ,  70  and  64  is the same, but the top diameters are not the same. The diameter of the top openings of the outer holes  64  and  68  is the same, but is larger than the diameter of the top opening of the center hole  70 . As noted above, the larger-diameter holes  64  and  68  allow a workman to better insert multiple fingers, preferably three fingers, therein to grasp the block  10 . 
     While the foregoing illustrates an erosion control block employing interlocking arms and sockets, together with multiple holes therethrough, the various features of the invention can be employed separately. To that end, a block such as disclosed in U.S. Pat. No. 5,556,228 can be constructed with multiple holes to achieve a greater degree of hydraulic stability without sacrificing the area through which vegetation can grow to further anchor the block to the underlying ground. In addition, the features of the invention can be utilized in erosion control blocks of dimensions, shapes and sizes other than that described above. 
     While the preferred and other embodiments of the invention have been disclosed with reference to specific revetment blocks, and associated methods of construction and installation thereof, it is to be understood that many changes in detail may be made as a matter of engineering choices without departing from the spirit and scope of the invention, as defined by the appended claims.