Patent Publication Number: US-8123434-B1

Title: Interlocking revetment block with reinforced sockets

Description:
RELATED APPLICATION 
     This non-provisional patent application claims the benefit of pending provisional patent applications identified as Ser. No. 61/063,530 filed Feb. 4, 2008 and Ser. No. 61/131,679 filed Jun. 11, 2008. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates in general to erosion control blocks, and more particularly relates to interlocking erosion control blocks. 
     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. Disclosed in U.S. Pat. No. 5,020,938 by Scales is a revetment block that employs a number of cavities and a number of tongues that engage the respective tongues and cavities of neighbor blocks to form a mat. While this arrangement provides some degree of vertical interlocking, the blocks can be freely removed from each other in a lateral direction. The hydraulic stability of such type of block is compromised. 
     From the foregoing, it can be seen that a need exists for an erosion control block that is both horizontally interlocking as well as vertically interlocking. Another need exists for an erosion control blocks in which a portion of the neighbor blocks overlie each block and prevent hydraulic forces from lifting the block, which otherwise might be displaced by high velocity flood waters. Yet another need exists for erosion control blocks which, when interlocked together, form an interlocking mat that dissipates the energy of the water flowing thereover. 
     SUMMARY OF THE INVENTION 
     According to the invention, described is an erosion control block that is both horizontally interlocking as well as vertically interlocking. A feature of the erosion control blocks is that a portion of the neighbor blocks overlie each block and prevent hydraulic forces from lifting the block, which otherwise might be displaced by high velocity flood waters. Another feature of the erosion control blocks is that, when interlocked together, an interlocking mat is formed that dissipates the energy of the water flowing thereover. 
     According to one embodiment of the invention, disclosed is a mat of three different types of interlocked revetment blocks, which include a first type of revetment block having a body with a thickness defined by a distance between a top surface and a bottom surface of the body of the first type of block. The first type block has a plurality of side edges. The first type block includes at least two arms, where each arm extends from a respective side edge of the body of the first type block. Each arm has an enlarged end connected to a respective side edge by a narrowed neck portion. At least one arm is a partial thickness arm having a thickness less than the thickness of the body of the first type block. At least two sockets are formed inwardly from respective side edges of the body of the first type block. Each socket has an enlarged cavity connected by a narrowed inlet to the respective side edge of the body of the first type block, and the socket is adapted for receiving therein an arm of a similarly constructed neighbor block. At least one socket is a partial depth socket having the enlarged cavity and the narrowed inlet formed with a depth from the top surface to the bottom surface of the block less than the thickness of the body of the first type block. The mat further includes a second type block, where the first type and second type block each have a first thickness. The first type block and the second type block have different configurations of arms and sockets. A third type block has a thickness greater than the thickness of the first and second type blocks. The first, second and third type blocks each have at least one of an arm or socket for interlocking with a respective socket or arm of a neighbor block of the mat. A mat comprising a plurality of the first type blocks, a plurality of the second type blocks and a plurality of the third type blocks are interlocked together. 
     According to another embodiment of the invention, disclosed is a method of reinforcing a block of the type having arms and sockets. The method includes the operation of forming the block of a heavy material; forming only a pair of arms extending radially outwardly from respective side edges of a body of the block; forming the arms with a radial axis orthogonal to each other; forming one arm having a thickness about the same as a thickness of the body of the block; forming at least one partial depth socket with a depth less than a thickness of the body of the block so that the heavy material covers the socket to a desired depth to thereby provide reinforcement between the sockets; and forming at least one arm as a partial thickness arm with a thickness less than the thickness of the body of the block. 
     According to another embodiment of the invention, 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, and the block has a plurality of side edges. Included also is a full thickness arm that extends radially outwardly from a first side edge of the block. The full thickness arm has a thickness about the same as the thickness of the block. A partial thickness arm extends radially outwardly from a second side edge of the block, and the second side edge is adjacent the first side edge. A radial axis of the full thickness arm is orthogonal to a radial axis of the partial thickness arm. A full depth socket is formed radially inwardly from a third side edge of the block, and the third side edge is adjacent the second side edge of the block. A partial depth socket is formed radially inwardly from a fourth side edge of the block, and the fourth side edge is adjacent the third side edge of the block. A radial axis of the full depth socket is orthogonal to a radial axis to the partial depth socket. A sum of the thickness of the partial thickness arm and a depth of the partial depth socket is about the same as the thickness of the block. The full thickness arm and the partial thickness arm each have an enlarged end. The full depth socket and the partial depth socket each have an enlarged cavity connected to a respective side edge of the block by a narrowed inlet. 
     According to yet another embodiment of the invention, disclosed is a mat of revetment blocks that includes a block having a body with a thickness defined by a distance between a top surface and a bottom surface of the body of the block, and the block has a plurality of side edges. The block further includes only two arms, where each arm extends outwardly from diametric opposite respective side edges of the body of the block, and each arm has an enlarged end connected to a respective side edge by a respective narrowed neck portion. The first arm defines a full thickness arm having a thickness substantially the same as the thickness of the block. A second arm has a partial thickness less than the thickness of the block so that the partial thickness arm extends from one surface of the body of the block but not to the other surface of the body of the block. The block further includes only two sockets, where each socket is formed inwardly from diametric opposite respective side edges of the body of the block, and each socket has an enlarged cavity connected by a respective narrowed inlet to a respective side edge of the body of the block. The socket is adapted for receiving therein an arm of a similarly constructed neighbor block. The first socket defines a full depth socket having a depth about the same as the thickness of the body of the block so that the first socket extends from the top surface to the bottom surface of the block. The second socket has a partial depth with the depth extending from one surface of the body of the block but not to the other surface of the body of the block. A first linear row of side by side blocks of the mat is installed by interlocking full depth arms and full depth sockets of the blocks of the linear first row. A second linear row of side by side blocks of the mat is installed by interlocking a partial depth socket of a block of the second row onto a partial thickness arm of a respective block of the first linear row of blocks. A full thickness arm of one block of the second row is interlocked with a full depth socket of a neighbor block of the second row. Each block of the first linear row interlocked with a corresponding block of the second row defines a respective column of the mat, and the rows and columns of the mat are orthogonal to each other. 
    
    
     
       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 well known in the art; 
         FIG. 2  is a top view of an erosion control block constructed to provide reinforcement between adjacent sockets; 
         FIG. 3  is a partial side view of the modified arm of the block of  FIG. 2 , taken along line  3 - 3  thereof; 
         FIG. 4  is a side view of the modified socket the block of  FIG. 2 , taken along line  4 - 4  thereof; 
         FIG. 5  is a partial cross-sectional view of the modified arm of the block of  FIG. 2 , taken along line  5 - 5  thereof; 
         FIG. 6  is a partial cross-sectional view of the modified socket of the block of  FIG. 2 , taken along line  6 - 6  thereof; 
         FIG. 7  is an isometric view of a portion of the interlocking revetment block of  FIG. 2 , illustrating the modified arm constructed according to an embodiment of the invention; 
         FIG. 8  is an isometric view of a portion of the interlocking revetment block of  FIG. 2 , illustrating the modified socket constructed according to an embodiment of the invention; 
         FIG. 9  is a bottom view of the revetment block of  FIG. 2 ; 
         FIG. 10  is a top view of two revetment blocks of the invention, shown interlocked to provide horizontal and vertical interlocking capabilities; 
         FIG. 11  is the starting row of a mat of revetment blocks installed according to the invention; 
         FIG. 12  illustrates the sequence of installing blocks interlocked to the starting row; 
         FIG. 13  is a top view of an interlocking revetment block constructed according to another embodiment of the invention, with two modified arms and two modified sockets; 
         FIG. 14  illustrates the sequence of installing blocks of the type shown in  FIG. 13 ; 
         FIG. 15  is a mat of erosion control blocks employing blocks of different thicknesses interlocked together to provide a high degree of hydraulic stability; 
         FIG. 16  is a side view of a flume over which the mat of  FIG. 15  is installed; 
         FIG. 17  is another embodiment of a mat of erosion control blocks employing different thickness blocks to provide energy dissipation to water flowing over the mat; and 
         FIG. 18  is yet another embodiment of a mat of erosion control blocks employing different thicknesses blocks to provide energy dissipation to water flowing thereover. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1 , there is shown a top view of an erosion control block  10  described in U.S. Pat. No. 5,556,228 by Smith. This erosion control block  10  has been widely used to provide an interlocking block that resists horizontal separation under high hydraulic loads. The block  10  includes a pair of arms  12  and  14 . The arms, for example arm  12 , includes an enlarged end  16  connected to the side edge of the block  10  by a neck  18 . The arms  12  and  14  are formed orthogonal to each other, on respective side edges  20  and  22  of the block  10 . The block  10  further includes a pair of sockets  24  and  26 . The sockets, for example socket  24 , include an enlarged cavity  26  and a narrowed inlet  28 . The sockets  24  and  26  are formed orthogonal to each other, in respective side edges  30  and  32  of the block  10 . The shape of the sockets  24  and  26  are formed similar to the shape of the arms  12  and  14 . However, the sockets  24  and  26  are somewhat larger than the arms  12  and  14  to provide a desired degree of articulation to accommodate irregularities in the surface of the ground upon which a mat of the blocks  10  are laid. 
     An optional opening  34  is formed through the body of the block  10 , from the top surface to the bottom surface thereof. The opening  34  functions to allow grass and other vegetation to grow through the block  10  and assist in anchoring the block  10  to the ground. The block  10  can be constructed with concrete or another heavy material, of various thicknesses, including a standard thickness of four inches. Other situations may dictate that the block  10  be constructed with a thickness of either six or eight inches. However, the block  10  is not limited to any particular thickness or shape. As can be seen in  FIG. 1 , the revetment block  10  is constructed in an octagonal shape, where the four opposing sides have formed thereon or therein an arm or a socket. The block  10  has angled corners, one shown as reference numeral  36 . Thus, with four sides and four angled corners, the block resembles a polygon with eight side edges. While not shown, the revetment, block  10  can be constructed with cable channels therethrough diagonally, or laterally through the center of the block  10  and through an arm  14  and the opposite socket  24 , or with a second cable channel through the other arm  12  and to the opposite socket  26 . 
     The revetment blocks  10  are constructed of concrete, preferably by block plant techniques. Although, concrete is a strong and heavy material, which characteristics are desired in a revetment block, there is a disadvantage in the use of the revetment block  10 . Through extensive use of the block  10  for commercial purposes, it has been found that during rough handling, or dropping of the block during installation of the same into a mat, the block  10  is subject to breakage. 
     An area of weakness in the revetment block  10  of  FIG. 1  is illustrated by broken line  38 . Here, there is a narrowing in the body of the block  10  between the adjacent sockets  24  and  26 . It can be appreciated that if the block  10  is dropped on other blocks, or where the bottom right corner of the block shown in  FIG. 1  is subject to an upward or downward force, the corner can be broken off the block  10  along line  38 . It can be further appreciated that when a block is broken, it must be replaced. This can be an expensive procedure in replacing a broken block in a mat, especially if the mat is cabled together. In addition, the loss of any block  10  due to breakage during shipping or otherwise, means that the replacement thereof represents an economic loss to the manufacturer. 
     According to an important feature of the invention, a modified revetment block  40  shown in  FIG. 2  is strengthened to provide additional support between the adjacent sockets and thereby reduce the incidences of breakage. The improved block  40  is constructed much like the block  10  of  FIG. 1 , but includes a modified socket  42  that is not formed entirely through the block  40 . Rather, the socket  42  is formed only partially through the body of the block  40 . The socket  42  extends from the bottom surface of the revetment block  42  upwardly, but not to the top surface of the block  40  like the prior revetment block  10  of  FIG. 1 . In one embodiment, the modified socket  42  extends about half way through the block  40 , meaning that the depth of the socket  42  is about half the thickness of the block. This is believed to adequately strengthen the revetment block  40  between the adjacent sockets  42  and  44 . The thickness of the body of the block is the dimension between the top surface and the bottom surface of the body. In the preferred embodiment, the other adjacent socket  44  includes a full depth from the bottom surface of the block to the top surface, much like the sockets  24  and  26  of the  FIG. 1  block. 
       FIGS. 4 and 6  illustrate respective side and cross-sectional views of the modified, or partial depth socket  42 . The top portion of the block  40  is filled in over the socket  42  and covers the same. The socket cavity occupies the bottom portion of the block  40 . The additional material  46  above the socket  42  provides strength to support additional loads to which the corner of the block  40  can be subjected during handling and/or dropping of the block  40 . It is noted that the shape and size of the socket  42  according to this embodiment is substantially the same as that described above in connection with the block of  FIG. 1 . In other words, the socket  42  includes a narrowed inlet  48  between the side edge  52  of the block  40  and an enlarged cavity  50 . The narrowed inlet  48  is illustrated in the isometric view of  FIG. 8 . As will be described below, a reduced-thickness arm  54  is formed on the block  40  for fitting in an interlocking manner into the reduced-depth socket  42 . It is noted that the half-depth socket  42  is centered between opposing side edges  56  and  58 . The sockets  42  and  44  formed in the block  40  have radial axes orthogonal to each other. The depth of the partial depth socket  42  is indicated with arrowed line  43  in  FIG. 4 . 
     As a result of the formation of a partial depth socket  42 , the block  40  constructed according to the invention includes a partial depth arm, shown as numeral  54  in  FIG. 2 . The arm is formed with a shape substantially the same as that of the arm  12  shown in  FIG. 1 . However, the arm  54  has a depth about half the thickness of the block  40 . Thus, for a conventional four inch thick block  40 , the arm  54  has a depth of about two inches. A side view of the partial thickness arm  54  is illustrated in  FIG. 3 , and a cross-sectional view is illustrated in  FIG. 5 . An isometric view of the half-thickness arm  54  is illustrated in  FIG. 7 . The arm  54  extends outwardly from the side edge  60  of the block  40 . 
     In order for the half-thickness arm  54  of one block  40  to fit within the half-depth socket  42  of a neighbor block  40 , the arm  54  is formed to extend from the bottom half of the block  40  to fit within the socket  42  which is also formed in the bottom half of the block  40 : In this manner, neighbor blocks of the invention can be interlocked together by simply lowering a block so that the half-depth socket  42  thereof is lowered over and engaged with the underlying half-thickness arm  54  of another block. The other arm  55  of the block  40  is a conventional full thickness arm. The arms  54  and  55  have radial axes orthogonal to each other. The installation procedure will be described in more detail below. 
     The revetment block  40  is constructed with an opening  62  formed through the block  40 , from a top surface to a bottom surface thereof. A conventional full thickness arm  55  is formed adjacent the half-thickness arm  54 . A conventional full depth socket  44  is formed in the side edge  58  of the block  40  adjacent the half-depth socket  42 . Much like the conventional revetment block  10  shown in  FIG. 1 , the modified revetment block  42  includes angled corners to define an octagonal-shaped revetment block  40 . The opening  62  is centered within a rectangular outline or footprint of the block  40 . Because of the partial thickness arm  54  and the partial depth socket  42 , the block  40  is preferably constructed using a mold and pouring therein the wet concrete. When constructing the block  40  using a mold, the various side edges would have a slight angle or draft to facilitate removal from the mold. 
     Referring now to  FIG. 9 , there is shown the bottom of the modified revetment block  40  of  FIG. 2 . The block  40  includes a full-thickness arm  55  and a full-depth socket  44 . As described above, the block  40  includes the half-depth socket  42  in which the cavity is shown. The half-thickness arm  54  is also shown, although the half that is absent is formed on the top half of the block  40 . 
     According to another embodiment of the invention, the revetment block  40  can be laid on the ground with the bottom thereof facing upwardly, as shown in  FIG. 9 . In other words, during installation the half-depth socket  42  faces upwardly, and the half-thickness arm of a neighbor block in laid downwardly into the upwardly facing half-depth socket  42  of the block  40 . With this arrangement, the block with the partial thickness arm would be installed upstream from the neighbor block. A mat of blocks installed according to this embodiment is illustrated in FIG.  18 . In this and other embodiments described herein, the thickness of the revetment block can be about 4.5 inches, with the thickness of the partial thickness arm being about 3.25 inches, and the depth of the partial depth socket also being about 1.25 inches. The additional portion  46  of the block would thus be about 3.25 inches thick. It may be found that the partial thickness arms of the erosion control block can be made stronger by making them greater than half the thickness of the block  40 , and making the depth of the partial depth sockets correspondingly smaller. 
       FIG. 10  illustrates a pair of modified blocks  40   a  and  40   b  interlocked together. First, the block  40   b  is laid on the surface to be protected from erosion. The bottom of the block  40   b  is on the ground, with the half-thickness arm  54   b  also in contact with the ground. A neighbor block  40   a  is then oriented as shown, and the half-depth socket  42   a  is lowered onto and into engagement with the half-thickness arm  54   b  of block  40   b . With the orientation as shown, the second block  40   a  is oriented so that the half-depth socket  42   a  faces downwardly. It can be seen that the large area of concrete that covers the top half of the half-depth socket  42   a  provides additional strength between the adjacent sockets  44   a  and  42   a , and reduces the likelihood of breakage. As can be appreciated, when the enlarged end of the half-thickness arm  54   b  of one block  40   b  is inserted into the enlarged opening of the half-depth socket  42   a  of the other block  40   a , the blocks are horizontally interlocked and cannot be laterally removed from each other. An additional advantage of the interlocking arrangement between the half-thickness arm  54   b  of one block  40   b  and the half-depth socket  42   a  of the other block  40   a , is that the block  40   b  is vertically interlocked. With this arrangement, the half-thickness arm  54   b  of block  40   b  is held down by the material  46  ( FIGS. 4 and 8 ) that covers the top of the half-depth socket  42   a . As such, when a number of blocks  40  are installed in the interlocking manner noted above, there is both a horizontal and vertical interlocking arrangement. In addition, each of the blocks of the interlocked mat are stronger and less susceptible to breakage. In the event that the erosion control block is installed with the partial depth sockets facing upwardly, then the illustration of  FIG. 10  would be a bottom view of the two neighbor blocks  40   a  and  40   b.    
     The installation of the modified revetment blocks  40  is better understood by referring to  FIGS. 11 and 12 . A first row of blocks  40   a - 40   d  is laid on the ground in the area to be protected from erosion. In practice, the blocks  40  can be laid on a synthetic woven fabric covering the ground. As can be seen, in the first row, the blocks  40   a - 40   d  are interlocked using the full arms  55  engaged within the full sockets  44  of the neighbor blocks. Preferably, the first row of blocks is installed and oriented on the ground so that the half-depth arms  54   a - 54   d  point in an upstream direction. 
     The next row of blocks, which include blocks  40   w - 40   z  of  FIG. 12 , are interlocked with the first row of blocks  40   a - 40   d . The second row of blocks  40   w - 40   z  can be installed, starting from either the right or left of the first row. Each block of the second row  40   w - 40   z  is oriented so that the full arm  55  faces to the left (as depicted in  FIG. 12 ) and the half-depth socket  42  is over the half-thickness arm  54  of the block in the first row to be interlocked therewith. Each block of the second row  40   w - 40   z  is lowered onto the half-thickness arm  54  of the first row blocks  40   a - 40   d  in the manner described until installation of the second row of blocks is completed. Each subsequent row of blocks is installed in the same manner as described above in connection with the second row  40   w - 40   z . An entire mat or section of erosion control blocks can thus be formed. Moreover, when the blocks are installed with the half-thickness arms pointed upstream, the sides of the blocks to which the half-thickness arm is attached is held down by the half-depth socket of the upstream neighbor block. The tendency of water running downstream to hydraulically lift blocks is thus reduced, as the modified block of the invention is vertically interlocked and prevented from being lifted by the adjacent upstream block. 
       FIG. 13  illustrates a modified revetment block  70  constructed according to another embodiment of the invention. The modified block  70  includes a first half-thickness arm  72  and an adjacent, second half-thickness arm  74 . Further included is a first half-depth socket  76  and a second, adjacent half-depth socket  78 . In other words, the block  70  is constructed much like the modified block  40  of  FIG. 2 , except all arms are fabricated in the same orientation and as half-thickness arms, and all sockets are fabricated with the same orientation and as half-depth sockets. 
     The installation of the revetment block  70  is somewhat more complicated than the block  40  shown in  FIG. 2 . Two rows of modified revetment blocks  70   a - 70   d  and  70   w - 70   z  are illustrated in  FIG. 14 . As can be appreciated, the vertical interlocking capability of the revetment block  70  is twice that of the block  40  of  FIG. 2 . Two half-thickness arms of each block are held down by a respective half-depth socket of two other neighbor blocks. The installation of the modified revetment block  70  is somewhat different from that of the block  40 , in that after the first row of revetment blocks  70   a - 70 - d  is laid down, the next row of revetment blocks  70   w - 70   z  must be sequentially laid down from the right to the left in  FIG. 14 . Otherwise, the half-thickness arm of the block to be next laid down in the second row would have to be slid under the half-depth socket of the neighbor block in that row. In any event, it is preferred that the blocks  70  be oriented in the same manner noted above so that the direction of flow of water does not tend to lift the blocks. 
     In order to facilitate a greater degree of articulation of one block with respect to an adjacent interlocked block, a portion of the top surface of a half-thickness arm can be angled downwardly toward the outer edge of the arm so that the arm (and corresponding block) can pivot or articulate about a horizontal axis to a greater degree within a half-depth socket. 
     As noted above, for a four-inch thick revetment block, it is envisaged that the depth of a half-thickness arm can be about two inches, and the depth of a half-depth socket can also be about two inches. For an eight inch thick revetment block, the modified arm can be about six inches thick, and the modified socket can be about six inches in depth. While the thickness of the arm and the depth of the socket are noted above as being of specified dimensions, those skilled in the art may find that other modified arms and sockets can be fabricated with dimensions other than noted above. While the revetment blocks disclosed above are constructed with arms on respective side edges of the block, and a respective cavity on a side edge of the block opposite an arm, this is not a necessity. Those skilled in the art may find it advantageous to construct the revetment block with arms opposite each other, and cavities opposite each other. However, this block configuration is more difficult to install as an interlocking mat. 
     As described above, the interlocking erosion control blocks can be constructed with different thicknesses for use in different situations to achieve the benefits of hydraulic stability, cost, ease of installment, etc. According to an important feature of the invention, blocks of different thicknesses can be employed together to form a mat with thinner and thicker blocks to provide energy or flow dissipation capabilities for water flowing over a mat having an irregular surface contour. 
       FIG. 15  illustrates a mat  80  of erosion control blocks well adapted for use as the floor or bed of a flume to dissipate the energy of water flowing down the grade of the flume. The individual blocks illustrated in  FIG. 15  are shown in simplified form, it being realized that the arms and sockets are structured to provide horizontally interlocking between neighbor blocks. The interlocking arms and sockets can be shaped like those described above, or can be other shapes adapted to provide a horizontal interlocking relationship therebetween. Moreover, some of the arms and sockets are formed with a half depth through the respective blocks, as described above in connection with  FIGS. 2-8 , to provide vertical interlocking capabilities with neighbor blocks. While not shown, the locks of the mat  80  can be constructed with openings therethrough for the growth of vegetation. 
     The partial mat  80  of erosion control blocks can have a pattern that repeats, and thus can be longer and/or wider than shown. The mat  80  includes three different types of blocks, some with different thicknesses, and some with different arrangements of full and partial arms and sockets to provide an energy dissipation surface. It is understood that providing a block itself with an irregular upper surface does assist in dissipating the water energy by slowing down the velocity of the water to a certain extent. However, it is also well understood that if the irregularities in the surface of the block are too close together, then water stagnation can occur, in which event the lower areas simply contain stagnant water and the flowing water passes over the stagnant water without slowing down. According to the mat  80  of erosion control blocks shown in  FIG. 15 , the irregularities in the mat  80  comprise the different thickness blocks where the valleys and peaks are at least a block width apart, thereby reducing areas of stagnant water and providing a reduced velocity to the water flowing thereover. An additional benefit of the arrangement of erosion control blocks is that the hydraulic properties of the small thickness blocks is not compromised, as compared to the thicker and heavier blocks. Thicker and heavier erosion control blocks have a better hydraulic stability, as compared to thinner and lighter blocks. However, the thicker an erosion control block is, the more costly and the more burdensome it becomes to install by manual means. Thus, by using horizontal and vertical interlocking erosion control blocks of different thicknesses and with an arrangement of partial thickness arms and partial depth sockets, a cost effective mat is realized that is also less burdensome to install than the thicker blocks alone, and the hydraulic stability of the mat  80  is not compromised. 
     In one embodiment of the mat  80 , four-inch thick interlocking blocks are employed, as well as eight-inch thick interlocking blocks. A nine-block matrix  84  constitutes six four-inch blocks and three eight-inch blocks. An eight-inch thick block  86  is located in the top row of the matrix  84 , in the middle. The other two eight-inch thick blocks  88  and  90  of the matrix  84  are located in the third row, at the corners. Each eight-inch thick block  86 - 90  is of identical construction, with a pair of partial thickness arms  92  and  94 , a partial depth socket  96  and a full socket  98 , as identified with block  86 . The partial thickness arms and the partial depth sockets of the three eight-inch blocks  86 ,  88  and  90  can be half the thickness of the respective blocks, and thus the same thickness as the neighbor four-inch blocks. The remainder of the blocks in the matrix  84  are four-inch thick interlocking blocks. However, the four-inch thick blocks of the matrix  84  are not of identical construction. Rather, there are two different types of four-inch interlocking blocks utilized in the matrix  84 . In each type of four-inch thick block, the partial thickness arm and the partial depth socket are shown shaded for ease of understanding. 
     Erosion control blocks  100 ,  102  and  104  (connected by V-shaped broken line  112 ) are of a first type, and blocks  106 ,  108  and  110  (connected by V-shaped broken line  114 ) are of a second type. The erosion control blocks  100 ,  102  and  104  are each four inches thick and include two full thickness arms  116  and  118 , a full socket  120  and a partial depth socket  122 , as identified in block  100 . The other type of four-inch blocks  106 ,  108  and  110  each include two full thickness sockets  124  and  126 , a full thickness arm  128  and a partial thickness arm  130 , as shown by block  106 . The partial thickness arms and the partial depth sockets of the four-inch thick blocks can be half the thickness of the respective blocks. 
     The other matrix  132  of nine erosion control blocks is similarly arranged with three eight-inch thick blocks and six four-inch thick blocks. The matrix  132  is connected to the matrix  84 . The two connected matrices  84  and  132  of the example can be installed in a flume where the water flow is in the direction of arrow  134 . Another matrix can be connected in an interlocking manner to the bottom of the matrix  132 , and yet other similar matrices can be connected to the left or right sides of the matrices  84  and  132 . 
     With regard to the interlocking connections of the blocks of the matrix  84 , the block  106 , which is downstream from block  100 , has a partial thickness arm  130  that fits under the partial depth socket  122  of the neighbor upstream block  100 . Thus, the leading edge of the downstream block  106  is held down by the trailing edge of the block  100 , and prevented from being lifted by the hydraulic action of flowing water. The eight inch block  86  has a partial thickness arm  94  that fits into the full depth socket  120  of the neighbor four-inch thick block  100 . The eight-inch block  86  also has a partial depth socket  96  that vertically interlocks with a full thickness arm  136  of downstream four-inch block  104 . It can be appreciated that a partial depth socket of an eight-inch thick block  86  can be four inches thick, and accommodates a full thickness arm  136  of a four-inch thick block  104 . The downstream block  104  is vertically interlocked with the upstream block  86  in a manner much like the neighbor blocks  100  and  106  to prevent the hydraulic lifting of the blocks. 
     The last block in the first row of the matrix  84 , namely the four-inch thick block  102 , includes a four-inch full thickness arm  138  that engages within the eight-inch full depth socket  98  of the eight-inch neighbor block  86 . The four-inch thick block  108 , downstream from the upstream four-inch thick block  102 , includes a partial thickness arm  140  that fits under the partial depth socket  142  of block  102 . With this arrangement, each block  106 ,  104  and  108  in the second row of the matrix  84  has an arm that is vertically interlocked under the partial depth socket of a respective upstream block. This is the case even when all of the blocks in the first and second rows of the matrix  84  are four-inch thick blocks, except for the eight-inch thick block  86 . Thus, water flow over the first two rows of the matrix  84  flows over an uneven surface to prevent stagnant water and to promote energy dissipation of the water by slowing it down. 
     Each four-inch block  106 ,  104  and  108  in the second row of the matrix  84  is interlocked together laterally with full arm and socket connections. The full socket  126  of the four-inch block  106  in the second row is interlocked with the partial thickness arm  144  of the downstream eight-inch block  88 . The partial thickness arm  146  of the four-inch block  110  is interlocked under the partial depth socket  148  of the neighbor upstream block  104 . The partial thickness arm  150  of the eight-inch block  90  is interlocked with the full depth socket  152  of the neighbor upstream four-inch block  108 . In this situation, the downstream lighter weight four-inch block  110  is vertically interlocked under the neighbor upstream block  104 , but the other two heavier eight-inch thick blocks  88  and  90  in the third row are not vertically interlocked with the neighbor upstream blocks, as the heavier eight-inch blocks  88  and  90  are hydraulically more stable than the lighter four-inch block  110 , and do not require a vertical interlocking connection on the leading edges thereof. 
     The four-inch block  110  in the third row of the matrix  84  is interlocked with the neighbor eight-inch block  88  using respective full thickness arms and full depth sockets  154  and  156 . The four-inch block  110  is also interlocked with the other neighbor eight-inch block  90  using a respective full depth socket  158  and partial thickness arm  160 . 
     As noted above, the block arrangement of the first matrix  84  is repeated in the second matrix  132  of the mat  80 . It is also noted that the downstream four-inch blocks  162  and  166  of the first row in the second matrix  132 , are vertically interlocked with the respective neighbor upstream blocks  88  and  90 . The exception for vertical interlocking in the first row of the second matrix  132  is the downstream eight-inch block  164 . In this case, the heavier eight-inch block  164  is hydraulically more stable than the neighbor four-inch blocks by virtue of the heavier weight of such block  164 . The analysis of the improved hydraulic stability of the second and third rows of blocks of the second matrix  132  is the same as set forth above in connection with the corresponding rows of blocks in the first matrix  84 . It is generally necessary only to provide the leading edge of the downstream light-weight blocks in each column with vertical interlocking capabilities so that such leading edge does not tend to be lifted, which would allow water to flow under the block. The laterally located neighbor blocks in a row generally do not need to be provided with vertical interlocking capabilities. However, in all instances, it is preferred to provide all blocks in a mat with horizontal interlocking capabilities, both neighbor blocks in rows and columns. 
     In addition to the improved hydraulic stability of the mat  80  described above, the irregular surface of the mat  80  substantially reduces or eliminates stagnant water pockets in the mat  80 . It can be seen from the mat  80  of  FIG. 15  that the bold outline eight-inch blocks present an impediment to the downstream flow of water thereover. In each column of the mat  80 , every fourth block is an eight-inch block, but staggered from the neighbor columns. In other words, and as can be seen in  FIG. 15 , each matrix  84  and  132 , includes a first row with one eight-inch block, a second row with no eight-inch blocks, and a third row with two eight-inch blocks. Thus, each low elevation surface of the mat  80  is greater than the width a single block. The low elevation surface contour of the mat  80  is where the four-inch blocks are located. 
     In the direction of water flow  134 , there are two four-inch blocks representing the low elevation surface between each eight-inch block. And the adjacent pair of four-inch blocks are staggered for each column in the mat  80  so that a continuous row of eight-inch blocks is not presented to the flow of water. Rather, the water must take a circuitous route down the irregular height blocks in a column of the mat  80 , which thereby dissipates the velocity of the water and reduces the energy and the ability to hydraulically lift the erosion control blocks from the mat  80 . With the arrangement of the three eight-inch blocks  88 ,  90  and  164 , as water flows in the direction of arrow  134 , there is imparted to the water flow a horizontal flow component that makes the overall flow more circuitous. For example, water flowing over the four-inch blocks  100  and  106  in the first column and over the four-inch blocks  102  and  108  in the third column of the mat  80 , flows into the respective eight inch blocks  88  and  90 , and then is funneled somewhat horizontally inwardly toward the center eight-inch block  164 . Because of the arrangement of blocks of the mat  80 , it is believed that optimum energy is dissipated for water flowing over the mat at a depth of about three to four feet. 
       FIG. 16  illustrates a side view of the mat  80  installed in a flume  170 . Typical flumes are about four feet wide, with an incline length of about 30 feet to 120 feet, and with a 2:1 ratio of incline. The radius of curvature of the transitions between the upper and lower horizontal ground portions and the incline is about six feet. Of course, flumes of other dimensions can be employed for erosion protection with the blocks and techniques of the invention. Indeed, the blocks and arrangements illustrated herein are not limited to flumes, but can be used in many other situations to control erosion of soil, sand and the like. 
     The column of blocks illustrated in  FIG. 16  is a side view of the second column of blocks shown in  FIG. 15 . The blocks in the illustrated column, as well as the blocks in each row are spaced apart somewhat from each other to allow flexibility and articulation of adjacent blocks to conform to the contour of the underlying ground, or woven geotextile on which the mat  80  is installed. In the event that the flexibility of the blocks is too limited to be&#39;installed in an interlocking manner over the curved transition between the horizontal ground and the incline, then the appropriate blocks can be grouted together to maintain a rigid interconnection. The broken line  88  represents the eight-inch block of the first column of blocks shown in  FIG. 15 . The broken lines between the blocks of the column shown illustrate the nature of the arm and socket engagement. The blocks at the top horizontal portion of the flume  170  include the eight-inch block  86 , and the two four-inch downstream blocks  104  and  110 . The two four-inch blocks  104  and  110  are vertically interlocked to the respective neighbor upstream blocks  104  and  86 . The water flows over the top of the first eight-inch block  86  and down onto the lower surface contour of the two four-inch blocks  104  and  110 , and then up and over the top of the next eight-inch block  164 . The water then proceeds down the incline of the flume  170  and encounters spaced apart eight-inch blocks that impede the water flow and dissipate the energy thereof. The arrowed line  172  in  FIG. 16  depicts the circuitous up and down path taken by the water flowing over the irregular-surface mat  80 . As noted above, the water flow down the flume  170  also takes a circuitous lateral route that snakes between different columns of blocks, which route also functions to reduce the stagnant water problem and dissipate the energy of the flowing water. 
     While the foregoing block types and arrangements are well adapted for providing a horizontal and vertical interlocking arrangement that vastly improves hydraulic stability and is cost effective, other arrangements and block types are possible and within the scope of the invention. Other configurations and arrangements of four-inch and eight inch blocks to form a mat can be realized which provide a different surface contour than that shown in  FIG. 15 . Moreover, blocks with thicknesses other than four inches and eight inches can be employed to achieve an irregular surface contour to dissipate the energy of the water flowing thereover. 
     In accordance with another embodiment of the invention, illustrated in  FIG. 17  is a mat  180  comprising a repeating matrix of erosion control blocks of different thicknesses to dissipate the energy of water flowing thereover. The first matrix  182  of six blocks is repeated as a second downstream matrix  184 . In this arrangement, there are only two different types of blocks. One type of block  186  is eight inches thick and includes a full arm  188  and a partial thickness arm  190 , and a full depth socket  192  and a partial depth socket  194 . The other type of block  196  is four inches thick and includes a pair of full thickness arms  198  and  200 , and a pair of full depth sockets  202  and  204 . The four-inch block  196  can be an unmodified version of the block described in U.S. Pat. No. 5,556,228, as shown in  FIG. 1  above. 
     There are three eight-inch blocks  186 ,  206  and  210  for each matrix  182  and  184 . Similarly, there are three four-inch blocks  196 ,  208  and  212  for each matrix  182  and  184 . The different type blocks are arranged symmetrically in the mat  180 . Every other block in each row and in each column is either an eight-inch block or a four-inch block. The blocks of the same type occupy different positions in adjacent rows. In other words, the eight-inch blocks in the first row of matrix  182  occupy positions one and three, and in row two position two. The four-inch block in the first row of the matrix  182  occupies the second position and in the second row the four-inch blocks occupy the first and third positions. 
     Much like the matrix  84  of  FIG. 15 , the blocks of the matrix  180  of  FIG. 17  are arranged so that each downstream four-inch block is vertically interlocked with a respective upstream block. For example, the downstream four-inch block  208  includes a full thickness arm  214  interlocked under the partial depth socket  194  of the upstream eight-inch blocks  186 . Similarly, the downstream four-inch block  212  includes a full thickness arm  216  interlocked under the partial depth socket  218  of the upstream eight-inch blocks  206 . Each downstream eight-inch block does not require a vertical interlocking connection with the respective upstream four-inch block, because the eight-inch thick blocks are heavier than the four-inch thick blocks and thus are hydraulically more stable. While this mat  180  of erosion control blocks is well adapted for dissipating the energy of water flowing thereover, such mat is adapted for use where the water depth is expected to be in the range of about one to two feet deep. 
       FIG. 18  illustrates another embodiment of a mat  220  of erosion control blocks adapted to provide horizontal and vertical interlocking, as well as reduction of the energy of the water flowing thereover. The mat  220  is shown with two nine-block matrices  222  and  224 , it being realized that other similar matrices would be employed in practice to cover the ground surface of a specified area. The blocks of the mat  220  are installed on the ground to be protected from erosion, with the water flowing in the direction of arrow  226 . The matrix  222  would be installed first, followed by the upstream matrix  224 . In other words, if the mat  220  were to be installed in a flume, the row of blocks at the top of the matrix  222  shown in  FIG. 18  would be installed first, and then the subsequent rows of blocks of the matrix  222  would be installed upstream therefrom. 
     In the embodiment of the mat  220 , two different types of blocks are employed. In the nine-block matrix  222 , as well as in the matrix  224 , there are six 4.5 inch thick blocks  228 ,  230 ,  232 ,  240 ,  242  and  244  that are each constructed in a similar manner. Lastly, there are three 8.5 inch thick blocks  234 ,  236  and  238  that are each constructed in a similar manner. While not shown, the blocks of the matrices  222  and  224  are constructed like that of  FIG. 9  with vegetation holes formed therethrough. 
     The 4.5 inch set of six blocks  228 ,  230 ,  232 ,  240 ,  242  and  244  each include one full thickness arms  246 , a partial thickness arm  248 , a full depth socket  250 , and a partial depth socket  252 , as shown by block  228 . The 8.5 inch set of three blocks  234 ,  236  and  238  each include a full thickness arm  254 , a partial thickness arm  256 , a full depth socket  258  and a partial depth socket  260 , as shown by block  234 . Preferably, although not by way of necessity, the combined dimensions of a partial thickness arm and the thickness of the additional material  46  ( FIG. 4 ) covering a partial depth socket of a block is about the same as the thickness of that block. In the preferred embodiment, the partial thickness of an arm  248  of the 4.5 inch block  228 , is about 3.25 inches thick. The depth of the partial depth socket  252  of block  228  is about 3.25 inches, and the thickness of the additional material covering the socket  252  is about 1.25 inches thick. The other five blocks of the 4.5 inch set include the same type of partial thickness arms and partial depth sockets. The three 8.5 inch set of blocks  234 ,  236  and  238  each include a partial thickness arm about 7.25 inches thick, a partial depth socket of about 7.25 inches deep, with the thickness of the additional material covering the partial depth socket being about 1.25 inches thick. When installing the blocks of each matrix  222  and  224 , the cavities of the partial depth sockets of each block face upwardly from the ground, and the partial thickness arms of the respective neighbor blocks are laid downwardly into the partial depth sockets. As noted above, the matrix  224  is similarly constructed with the same arrangement of nine erosion blocks. 
     The first row of blocks  242 ,  232  and  244  in the downstream matrix  222  is installed first on the ground to be protected from erosion, and downstream of the other matrices connected to the matrix  222 . The block  242  is laid on the ground. The neighbor block  232  is laid adjacent the block  242  with the full thickness arm  284  interlocked with the full depth socket  286  of block  242 . The block  244  is then laid on the ground with the full thickness arm  290  interlocked with full depth socket  292  of the neighbor block  232 . The blocks  242 ,  232  and  244  of the first row of the matrix  222  can be installed in the reverse sequence. As will be described below, the other blocks of the matrix  222  are installed upstream, or up the grade of the flume. 
     Next, the partial thickness arm  284  of block  236  of the second row is laid down into the partial depth socket  282  of block  242 . The full thickness arm  262  of block  240  is then interlocked with the full depth socket  278  of block  236 , and at the same time the partial thickness arm  264  of the block  240  is laid down into the partial thickness arm  288  of block  232 . The last block in row two of the matrix  222 , namely block  238 , is laid down so that the full thickness arm  280  interlocks with full depth socket  266  of block  240 , and at the same time the partial thickness arm  296  is laid down into the partial depth socket  294  of block  244 . The blocks  236 ,  240  and  238  of the second row can be installed in the reverse sequence. 
     With regard to the third row of the matrix  222 , the block  228  is laid on the ground so that the full thickness arm  248  is laid down into the partial depth socket  272  of neighbor block  236 . The next block  234  is then laid down on the ground so that the full thickness arm  254  interlocks with the full depth socket  250  of block  228 , and at the same time the partial thickness arm  256  of block  234  is laid down into the partial depth socket  268  of block  240 . Lastly, the third block  230  in the third row is laid on the ground so that the full thickness arm  270  interlocks with the full depth socket  258  of block  234 , and at the same time the full thickness arm  276  of block  230  is laid down into the partial depth socket  274  of neighbor block  238 . The blocks  228 ,  234  and  230  of the third row of matrix  222  can be installed in the reverse sequence. 
     As can be seen from the foregoing, the downstream arm of each block is laid down into the upstream socket of the downstream neighbor block to prevent hydraulic lifting of water flowing in the downstream direction, as indicated by arrow  226 . The partial depth sockets of the downstream blocks of the matrix are thus vertically interlocked under the partial thickness arms of the upstream blocks. The hydraulic stability of the matrix  222  is thereby increased. The upstream matrix  224  can be installed in the same manner as the matrix  222  described above. In addition, other similar matrices can be installed to the right and the left of the matrix  222 , as well as matrix  224 , to form mats of desired areas. After a complete mat of blocks has been installed, the partial thickness arms and the partial depth sockets are undetectable to an observer. However, each block is nevertheless vertically interlocked and cannot be lifted out of the matrix of blocks. 
     It can be seen from the foregoing that the different types of mats of revetment blocks can be selected to form a mat. When installing the revetment blocks to form a mat, the specific block must be selected for a particular location in the mat. The blocks can be marked with an indicia during manufacture, or after manufacture, to uniquely identify the different types of blocks. For example, the three different types of blocks in the  FIG. 15  mat could be molded so as to have the numeral “1”, “2” and “3” on the top surface of the respective blocks to aid in selecting the blocks and in repeating the pattern of the blocks already installed. The numerals could be formed as part of the mold, or could be manually stamped thereon before the concrete in the mold has set. The indicia could also be spray painted on the completed blocks or applied in many other ways to visually differentiate the different types of blocks. As yet another method of making the different types of blocks visually different, the blocks could have a different color added to the concrete during mixing of the concrete. Yet other visually distinguishing marks can be applied to the different types of blocks by those skilled in the art. 
     The various embodiments of the erosion control blocks described above include features that facilitate the interlocking relationship between neighbor blocks, as well as features that dissipate the energy of water flowing thereover. It should be understood that the various features can be implemented without employing the particular shapes and sizes of the features. For example, the horizontal interlocking feature of the various blocks can be realized by using arms and sockets with other shapes and sizes. The thicknesses of the various blocks can be other than described above. In addition, the depth of both the arms and sockets of the vertically interlocking feature need not be half the thickness of the respective blocks. Rather, the thickness of a vertical interlocking arm of, for example, a four-inch thick block, can be three inches thick, the depth of a corresponding socket of a four-inch thick block can be one inch. Of course, other dimensions of the partial thickness arm and partial depth socket can be yet other dimensions adapted to address particular problems or issues. 
     While the erosion control blocks of the various embodiments are interlocking and cannot be radially removed from each other, such blocks can nevertheless include cable channels therethrough and be cabled together. The advantage of a cabled mat of blocks is that they can be assembled on level ground and cabled together, and then be lifted with a crane and installed in a river bed, or the like, which is full of water. The cable channels and the cabling of a mat of the blocks can be accomplished in a manner similar to that described in U.S. Pat. No. 6,276,870 by Smith, which is incorporated herein by reference. 
     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.