Abstract:
A connector for joining a soil-reinforcement grid extending through a slot in a block stacked with other blocks to define a mechanically stabilized earth retaining wall, the connector comprising matingly engaged first member having pins that are slidingly received in aligned openings defined in a second member while sandwiching a portion of soil-reinforcement grid therebetween, the grid having apertures through which the pins extend. The soil-reinforcing grid is loaded by being covered with backfill materials. The connector mechanically engages bearing surfaces within a channel in the block such that the tensile loading of backfill covering the soil-reinforcement grid lateral of the wall is distributed by the connector across the block. A method of constructing a mechanically stabilized earth retaining wall is disclosed as well as a connector and blocks useful with such methods and walls.

Description:
TECHNICAL FIELD 
     The present invention relates to earth retaining walls. More particularly, the present invention relates to connectors used in mechanically stabilized earth retaining walls to join laterally extending soil reinforcement sheets to blocks in the earth retaining wall whereby the tensile loading imposed by backfill on the soil reinforcement sheets is transferred to the earth retaining wall. 
     BACKGROUND OF THE INVENTION 
     Mechanically stabilized earth retaining walls are construction devices used to reinforce earthen slopes, particularly where changes in elevations occur rapidly, for example, development sites with steeply rising embankments. These embankments must be secured, such as by retaining walls, against collapse or failure to protect persons and property from possible injury or damage caused by the slippage or sliding of the earthen slope. 
     Many designs for earth retaining walls exist today. Wall designs must account for lateral earth and water pressures, the weight of the wall, temperature and shrinkage effects, and earthquake loads. The design type known as mechanically stabilized earth retaining walls employ either metallic or polymeric tensile reinforcements in the soil mass. The tensile reinforcements extend laterally of the wall formed of a plurality of modular facing units, typically precast concrete members, blocks, or panels, stacked together. The tensile reinforcements connect the soil mass to the blocks that define the wall. The blocks create a visual vertical facing for the reinforced soil mass. 
     The polymeric tensile reinforcements typically used are elongated lattice-like structures often referred to as grids. These are stiff polymeric extrusions defining large sheets. The grids have elongated ribs which connect to transversely aligned bars thereby forming elongated apertures between the ribs. The modular precast concrete members may be in the form of blocks or panels that stack on top of each other to create the vertical facing of the wall. 
     Various connection methods are used during construction of earth retaining walls to interlock the blocks or panels with the grids. One known type of retaining wall has blocks with bores extending inwardly within the top and bottom surfaces. The bores receive dowels or pins. After a first tier of blocks has been positioned laterally along the length of the wall, the dowels are inserted into the bores of the upper surfaces of the blocks. Edge portions of the grids are placed on the tier of blocks so that each of the dowels extends through a respective one of the apertures. This connects the wall to the grid. The grid extends laterally from the blocks and is covered with back fill. A second tier of blocks is positioned with the upwardly extending dowels fitting within bores of the bottom surfaces of the blocks. The loading of backfill over the grids is distributed at the dowel-to-grid connection points. The strength of the grid-to-wall connection is generated by friction between the upper and lower block surfaces and the grid and by the linkage between the aggregate trapped by the wall and the apertures of the grid. The magnitude of these two contributing factors varies with the workmanship of the wall, normal stresses applied by the weight of the blocks above the connection, and by the quality and size of the aggregate. 
     Other connection devices are known. For example, my U.S. Pat. No. 5,417,523 describes a connector bar with spaced-apart keys that engage apertures in the grid that extends laterally from the wall. The connector bars are received in channels defined in the upper and lower surfaces of the blocks. 
     The specifications for earth retaining walls are based upon the strength of the interlocking components and the load created by the backfill. Once the desired wall height and type of ground conditions are known, the number of grids, the vertical spacing between adjacent grids, and lateral positioning of the grids is determined, dependent upon the load capacity of the interlocking components. 
     Heretofore, construction of such mechanically stabilized earth retaining walls has been limited to large high rise walls. This is due in part the need to have sufficient mass of blocks vertically higher in the wall for securing the soil reinforcement grids to the wall. However, there are numerous small scale projects which could benefit from the use of reinforcement grids and mechanically stabilized earth retaining walls. Low height walls provide insufficient normal loading by the mass of the wall above the grid connections. 
     Accordingly, there is a need in the art for an improved connector and block for engaging soil reinforcement grids extending laterally from earth retaining walls. It is to such that the present invention is directed. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention meets the need in the art by providing a connector for being received within a channel defined in blocks stacked side by side in tiers to define an earth retaining wall and being engaged to soil reinforcing grids extending through slots from the channels outwardly of the blocks, to transfer tensile loading imposed by backfill on the soil reinforcing grids to the earth retaining wall. The connector comprises an elongate first member that matingly engages an elongate second member. The first member has a plurality of pins spaced-apart along the longitudinal length thereof. Each pin extends in a first direction from a first side of the first member. The second member has a plurality of openings spaced-apart along the longitudinal length thereof for aligning with the pins. The first member and the second member matingly connect by slidingly receiving the aligned pins within the openings while sandwiching therebetween a soil reinforcement grid having open apertures through which the pins extend. The assembled connector is received in a channel defined in blocks that form the wall, for communicating tensile loading on the soil reinforcement grid to the wall. 
     In another aspect, the present invention provides an earth retaining wall having at least two stacked tiers of blocks placed side by side. Each of the blocks defines a channel extending between opposing sides. The channel defines at least two adjacent bearing surfaces and an opening between the bearing surfaces to a slot extending laterally from the channel to a back side of the block. An elongate connector conforming in cross-sectional shape at least relative to the pair of adjacent bearing surfaces defined in the channel, is received within the channel. The connector comprises an elongate first member that matingly joins an elongate second member. The first member has a plurality of pins spaced-apart along the longitudinal length thereof. Each pin extends in a first direction from a first side of the first member. The second member has a plurality of openings spaced-apart along the longitudinal length thereof for aligning with the pins. A portion of a soil reinforcement grid having a plurality of apertures is sandwiched between the first and the second members and the pins extend through respective apertures. Another portion of the soil reinforcement grid extends from the slot laterally of the blocks. The connector, being engaged to the soil reinforcement grid and received in the channel with the soil reinforcement grid extending through the slot laterally away from the blocks and the extended portion thereof loaded by backfill, mechanically engages the bearing surfaces of the channel to distribute the tensile loading across the wall. 
     In another aspect, the present invention provides a method of constructing an earth retaining wall, comprising the steps of: 
     (a) placing at least two stacked tiers of blocks side by side to define a length of a wall, each of the blocks defining a channel extending between opposing sides thereof, the channel defining at least two adjacent bearing surfaces and opening between the bearing surfaces to a slot extending laterally from the channel to a back side of the block; 
     (b) sandwiching a portion of a soil-reinforcement grid between an elongate first member and an elongate second member that matingly engage together to define a connector, the first member having a plurality of pins spaced-apart along the longitudinal length thereof and each pin extending in a first direction therefrom, the second member having a plurality of openings spaced-apart along the longitudinal length thereof for aligning with the pins, and the soil-reinforcement grid having a plurality of apertures defined therein for being received by the pins while sandwiched between the first and the second members; 
     (c) sliding the connector with the soil-reinforcement grid along the channel with a portion of the soil-reinforcement grid slidingly received within the slot and extending laterally of the wall; and 
     (d) covering the portion of the soil-reinforcement grid lateral of the wall with backfill, 
     whereby the connector, being engaged to the soil-reinforcement grid that is loaded by the backfill, mechanically engages the two bearing surfaces of the channel such that the tensile loading is distributed across the block. 
     Objects, advantages and features of the present invention will become apparent from a reading of the following detailed description of the invention and claims in view of the appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates an exploded perspective view of a connector for engaging open aperture soil reinforcement grids to blocks in earth retaining walls according to the present invention. 
     FIG. 2 illustrates a side view of the connector shown in FIG.  1 . 
     FIG. 3 illustrates in perspective view the connector in FIG. 1 engaged to an open aperture soil reinforcement grid. 
     FIG. 4 illustrates a perspective view of an earth retaining wall in which the connector shown in FIG. 1 engages open aperture soil reinforcement grids for communicating the tensile loading of backfill on the open aperture soil reinforcement grids to the wall. 
     FIG. 5 illustrates an exploded perspective view of an alternate embodiment of the connector illustrated in FIG. 1 for engaging open aperture soil reinforcement grids to blocks in earth retaining walls. 
     FIG. 6 illustrates a design concept for the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now in more detail to the drawings in which like parts have like identifiers, FIG. 1 illustrates an exploded perspective view of a connector  10  for engaging open aperture soil reinforcement grids  12  to blocks  14  in earth retaining walls  16 , according to the present invention as illustrated in FIGS. 3 and 4. The connector  10  assembles from an first member  18  that matingly engages an elongate second member  20 . The first member  18  defines a plurality of pins  22  extending from a first field  24  of the first member. The pins  22  are spaced-apart along the longitudinal length of the first member  18 . Each pin  22  extends in a first direction from a first side of the first member  18 . The first member  18  also defines a second field  26  lateral of the pins  22  along its longitudinal length. The second field  26  is recessed relative to the first field  24 . The transition between the first field  24  and the second field  26  is defined by a wall  28  which forms a stop for a purpose discussed below. The first member defines an exterior bearing surface  30 , a back side  32 , and a front edge  34 . An edge  36  between the bearing surface  30  and the back side  32  is preferably radiused. The front edge  34  is partially radiused to define a tapered edge with the first field  24 . 
     The second member  20  likewise defines an exterior bearing surface  40 , a back side  42 , and a front edge  44 . An edge  46  between the bearing surface  40  and the back side  42  is preferably radiused. The front edge  44  is preferably partially radiused to define a tapered portion. The second member  20  defines a plurality of openings  50  extending from a first field  52 . The openings  50  are spaced-apart along the longitudinal length of the second member  20 . The openings  50  align with the pins  22  of the first member  18 . The second member  20  also defines a second field  56  lateral of the openings  50  along its longitudinal length. The second field  56  is recessed relative to the first field  52 . The transition between the first field  52  and the second field  56  is defined by a wall  58  which forms a stop for a purpose discussed below. FIG. 2 illustrates a side view of the connector  10  shown in FIG.  1 . Each pin  22  defines an oblique surface  60  at a distal end. The angle of the oblique surface conforms to the slope of the bearing surface  40  relative to the first field  52  of the second member  20 . The recessed second fields  26  and  56  cooperatively define opposing walls of a channel  62  in the connector  10 . As best illustrated in FIG. 3, the channel  62  receives an enlarged portion  64  of the soil reinforcement grid  12  as the first member  18  and the second member  20  matingly connect together, as discussed below. 
     FIG. 4 illustrates a perspective view of the earth retaining wall  16  in which connectors  10  engage open aperture soil reinforcement grids  12  for communicating the tensile loading of backfill  70  on the soil reinforcement grids to the wall. The wall  16  comprises a plurality of stacked, interconnected blocks  14  which receive the connectors  10  engaged to the soil reinforcement grids  12  in aligned channels  112  in the blocks  14 . The soil reinforcement grids  12  extend laterally of the wall  16  into the backfill  70  at selected vertical intervals. 
     The sheet-like grid  12  is a stiff extruded planar structure formed by a network of spaced-apart members  72  which connect to spaced-apart transverse ribs  74 . The connection of the members  72  to the ribs  74  define apertures  76  in the lattice-like grid  12 . The apertures  76  define an open space between the adjacent members  72  and ribs  74 . The apertures  76  receive soil, gravel, or other backfill materials for interlocking the grid  12  to the backfill material which is retained by the wall  16 , as discussed below. In a preferred embodiment, the grid  12  is made of synthetic material, such as plastic. 
     The wall  16  comprises at least two tiers  80 ,  82  of the blocks  14 . Two soil reinforcement grids  12  are illustrated extending laterally from the wall  16 . The blocks  14  define a front face  84  for the wall  16 . The blocks  14  in each tier  80 ,  82  are placed side-by-side to form the elongated retaining wall  16 . Soil, gravel, or other backfill material  70  is placed on an interior side  86  of the wall  16 . 
     Each of the blocks  14  are defined by opposing side walls  100 , opposing front face  104  and back face  106 , and opposing top and bottom sides  108 ,  110 . The block  14  defines a channel  112  extending between the opposing sides  100 . In a preferred embodiment, the channel  112  defines a triangular shape in cross-sectional view. In a preferred embodiment, the triangular channel  112  is substantially equilateral. The channel  112  opens to a slot  114  that extends laterally from the channel  112  to the back side  106  of the block  14 . The slot  114  preferably defines opposed tapered edges  115  in the back face  106  (best illustrated in FIG.  6 ). In the illustrated embodiment, the channel  112  has a base surface  116  which is substantially parallel to the front face  104 . In this embodiment, the slot  114  preferably opens to the channel  112  at an apex. The channel  112  defines a pair of bearing surfaces  118 ,  120 , for a purpose discussed below. The opening to the slot  114  is preferably between the two bearing surfaces  118 ,  120 . 
     The blocks  14  are preferably pre-cast concrete. As is conventional with blocks for earth retaining walls, the illustrated embodiment of the block  16  includes matingly conformable top and bottom surfaces  108 ,  110 . In the illustrated embodiment, the top surface  108  defines a raised portion and a recessed portion. The opposing bottom  110  likewise defines a recess portion and an extended portion. The recess portion in the top  108  opposes the extended portion in the bottom  110 . The raised portion in the top surface  108  opposes the recess portion in the bottom surface. When blocks  14  are stacked in tiers  80 ,  82 , the recessed portion of blocks in the lower tier  80  receive the respective extended portion of the blocks  14  in the upper tier  82 . Similarly, the raised portions in the lower tier  80  are received in the respective recesses of the upper tier  82 . In this way, the blocks  14  in vertically adjacent tiers  80 ,  82  are matingly engaged. 
     With reference to FIG. 6, a design for the connector  10  may be described as the combination of the frictional loading between the block  14  and the connector  10  and the pull out frictional loading of the reinforcement grid  12  and the connector  10 . Both components must exceed the pull out force P on the reinforcement grid  12 . This is described as follows, where: 
     P 1  is the pull-out loading for the reinforcement grid  12 , which equals the resisting force of the friction between the connector  10  and the bearing surfaces  118 ,  120  in the block  14 . 
     N is the normal loading between the bearing surface  118 ,  120  and the surfaces  30 ,  40  of the connector  10 . 
     N g  is the loading on the reinforcement grid  12  from the loading N. 
     S is the friction loading between the reinforcement grid  12  and the bearing surfaces  118 ,  120 . 
     S g  is the friction loading between the reinforcement grid  12  and the connector  10 . 
     α a is the angle between the normal load N and a perpendicular line to the reinforcement grid  12 , which is one-half the angle defined by the bearing surfaces  118 ,  120 . 
     φ is the friction angle between the bearing surface  118 ,  120  and the surfaces  30 ,  40  of the connector  10 . This angle controls the self-locking attribute of the apparatus of the present invention. 
     δ is the apparent friction angle of the connector  10  to the reinforcement grid interface. 
     The frictional loading between the block  14  and the connector  10  is described by the following equations: 
     
       
         P 1 =2N sin α+2S cos α  (Eq. 1) 
       
     
     
       
         S=N tan φ  (Eq. 2) 
       
     
     Accordingly, 
     
       
         P 1 =2N (sin α+tan φ cos α)  (Eq. 3) 
       
     
     The mobilized peak pull-out resistance is represented by the frictional load between the reinforcement grid  12  and the bearing surfaces  118 ,  120  of the channel  112  and between the reinforcement grid  12  and the connector  10 . The tensile loading on the reinforcement grid  12  accordingly is resisted by four surfaces of frictional loading. 
     The pull-out resistance of the reinforcement grid  12  within the connector  10  is described by the normal load applying friction in the horizontal direction, which opposes the pull-out force of the reinforcement grid: 
     
       
         N g =N cos α−S sin α  (Eq. 4) 
       
     
     
       
         P 2 =2S g   (Eq. 5) 
       
     
     
       
         P 2 =2N g  tan δ  (Eq. 6) 
       
     
     Combining Eq. 4 and 6, 
     
       
         P 2 =2(N cos α−N tan φ sin α) tan δ  (Eq. 7) 
       
     
     or simplified, 
     
       
         P 2 =2N tan δ (cos α−tan φsin α)  (Eq. 8) 
       
     
     In evaluating failure criterion, the connector  10  within the channel must have sufficient pull-out resistance (i.e., the reinforcement grid  12  must not pull out of the connector  10 ): 
     
       
         P 2 ≧P 1   
       
     
                     tan                 δ     ≥         sin                 α     +     tan                 φ                 cos                 α           cos                 α     -     tan                 φ                 sin                 α                 (     Eq   .              9     )                                              tan                 δ     ≥           tan                 α     +     tan                 φ                        1   -     tan                 α                 tan                 φ                              (     Eq   .              10     )                                tan δ≧tan (α+φ)  (Eq. 11) 
     Accordingly, 
     
       
         δ≧(α+φ)  (Eq. 12) 
       
     
     The reinforcement grid  12  is locked within the connector  10  through the interlocking pins  22 , and the connector  10  achieves ultimate strength bearing against the bearing surfaces as long as the pins  22  are sufficiently strong. Pull-out failure is not anticipated, and thus, Eq. 12 that δ≧(φ+α) holds. 
     With reference to FIGS. 1,  3 , and  4 , Eq. 12 that the connector  10  is used in the wall  16  constructed by placing at least two stacked tiers  80 ,  82  of the blocks  14  side-by-side to define the length of the wall. The blocks  14  are aligned so the channels  112  extend longitudinally through the wall  16  with the slot  114  extending towards the back side of the wall. 
     The connector  10  assembles by sandwiching a portion of one of the soil-reinforcement grids  12  between the first member  18  and the second member  20 . The pins  22  align with the openings  50  which slidingly receive the pins. The pins  22  extend through the respective apertures  76  in the grids  12 . The enlarged portion  64  of the grid  12  is received in the channel  62 . The walls  28 ,  58  define a stop that bears against the enlarged portion  64 . The assembled connector  10  with the soil-reinforcement grid  12  sliding is received in the channel  112 . A portion of the soil-reinforcement grid  12  is slidingly received within the slot  114  and extends laterally of the wall  16 . The lateral portion of the grid  12  is covered with backfill  70 . The tensile loading on the grid  12  causes the connector  10  to move into bearing contact with the bearing surfaces of the channel. The bearing surfaces  30 ,  40  of the first member  18  and the second member  20  engage the bearing surfaces  118 ,  120  and lock the grid  12  to the block  14  and thus to the wall  16 . The connector  10 , being engaged to the soil-reinforcement grid  12  that is loaded by the backfill  70 , mechanically engages the two bearing surfaces of the channel such that the tensile loading is distributed across the block. 
     FIG. 5 illustrates an exploded perspective view of an alternate embodiment  150  of the connector  10  for engaging open aperture soil reinforcement grids  12  to blocks  14  in earth retaining walls  16 , according to the present invention. The connector  150  assembles from a two members  152 . Each member  152  defines a plurality of pins  154  extending from a first field  156  and alternating openings  158 . The pins  154  and openings  158  are spaced-apart along the longitudinal length of the member  150 . The member  150  also defines a second field  160  lateral of the pins  154  and openings  158  along its longitudinal length. The second field  160  is recessed relative to the first field  156 . The transition between the first field  156  and the second field  160  defines a wall  162  which forms the stop for the enlarged portion  64  of the grid  12 . The member  150  defines an exterior bearing surface  166 , a back side  168 , and a front edge  170 . An edge  172  between the bearing surface  166  and the back side  168  is preferably radiused. The front edge  170  is partially radiused to define a tapered edge with the first field  156 . The connector  150  assembles by slidingly receiving the respective pins  154  of one member  152  within the openings  158  of a second one of the members  152 . While the use of the members  152  has longitudinally extending overlap portions at the opposing distal ends of the connector  150 , the common member requires one mold to manufacture rather than two different molds. 
     While this invention has been described in detail with particular reference to the preferred embodiments thereof, the principles and modes of operation of the present invention have been described in the foregoing specification. The invention is not to be construed as limited to the particular forms disclosed because these are regarded as illustrative rather than restrictive. Moreover, modifications, variations and changes may be made by those skilled in the art without departure from the spirit and scope of the invention as described by the following claims.