Patent Publication Number: US-2018038059-A1

Title: Precast concrete bridge unit and headwall assembly and method of production

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. patent application Ser. No. 15/226,978, filed Aug. 3, 2016, which is a continuation-in-part of and claims priority to U.S. patent application Ser. No. 14/751,540, filed Jun. 26, 2015, which applications are herein incorporated by reference in their entirety as if fully set forth herein. 
    
    
     FIELD OF THE INVENTION 
     This invention is directed to precast structures, and more particularly to an improved precast concrete bridge unit and headwall assembly. 
     BACKGROUND OF THE INVENTION 
     In a precast reinforced concrete bridge unit having a headwall it is known to cast the headwall as an integral part of an end bridge unit when the bridge unit is being cast. It is also known to precast the headwall separately with a bottom arcuate abutment or collar which extends continuously across the arcuate top wall of the bridge unit. The collar is secured to the top wall of the bridge unit by bolts or threaded rods which extend into the top wall and are threaded into concrete anchors embedded within the top wall. The continuous arcuate collar provides for attaching the vertical headwall to the bridge unit at the construction site. It is also known to precast a series of concrete counterfoil members that are supported on a headwall and subsequently secured to the top wall of the bridge unit by bolts or threaded rods which extend into the top wall and are threaded into concrete anchors embedded within the top wall. 
     It is desirable for the headwall to be precast separately from the precast bridge unit for significantly reducing the weight of the precast bridge unit and to facilitate shipping the precast bridge unit along a roadway or highway with a semi-truck and low bed trailer vehicle. The separate precast headwall units also facilitate handling and shipping of the headwall units on a semi-truck and trailer vehicle. After all of the bridge units are positioned at the construction site with the aid of a crane, the headwall units are then positioned with the crane and attached to the opposite end bridge units. 
     SUMMARY OF THE INVENTION 
     In accordance with an aspect of the invention, a method of producing a precast concrete bridge and headwall assembly is provided, comprising the steps of: casting a reinforced concrete bridge unit having a top wall connecting opposite side walls; positioning the bridge unit with a first side supported by a horizontal casting surface, wherein the top wall is positioned adjacent a framing unit for the headwall; forming a precast concrete headwall on the casting surface adjacent the top wall with a series of earth anchors at laterally spaced intervals along the top wall between the side walls, each earth anchor formed with: a) a body member extending outward from the headwall to the top wall; and b) a foot member extending laterally outward from the body member engaged on the top wall and including an upper surface generally parallel to the top wall; and removing the headwall and earth anchors as a unit from the bridge unit. 
     A series of earth anchor forms may be releasably attached to the top wall of the bridge unit at laterally spaced intervals between the side walls prior to forming the precast concrete headwall, wherein a bottom edge of the earth anchor forms is located adjacent the framing unit. 
     The earth anchors may be precast simultaneous with precasting of the headwall, forming an integral unit made up of the earth anchors and the headwall. 
     The earth anchors may be precast into the earth anchor forms before the headwall has completely hardened. 
     The earth anchors may be formed without passages in the body member defining connection points to the top wall. 
     The body member may have opposing lateral sides and the foot member may include lateral foot sections that extend laterally outward from each of the lateral sides of the body member. 
     The foot member may include a distal foot section defining a surface that extends from the body member, distal from the headwall, and between the lateral foot sections. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying Drawing Figures, in which like reference numerals identify like elements, and wherein: 
         FIG. 1  is an end view of an assembly of a precast concrete bridge unit and headwall unit constructed and assembled in accordance with the invention; 
         FIG. 2  is a partial perspective view of the bridge unit and casting framework including releasably attached counterfort forms before concrete has been poured; 
         FIG. 2A  is a cross-sectional view taken through a counterfort form and the casting framework and framing unit of  FIG. 2 ; 
         FIG. 2B  is a cross-sectional view taken through a primary bracket in  FIG. 2 ; 
         FIG. 2C  is a cross-sectional view taken through a secondary bracket in  FIG. 2 ; 
         FIG. 3  is a fragmentary cross-sectional view of the bridge unit and headwall and counterfort unit releasably attached to the bridge unit after the concrete has hardened; 
         FIG. 4  is a flow chart illustrating the steps in the method of producing a precast concrete bridge and headwall assembly; 
         FIG. 5  is a partial perspective view of the bridge unit and casting framework including releasably attached counterfort forms in two different sizes before concrete has been poured; 
         FIG. 5A  is a side view of the structure illustrated in  FIG. 5 ; 
         FIG. 6  is a fragmentary cross-sectional view of the bridge unit and headwall and a counterfort unit having a second size releasably attached to the bridge unit after the concrete has hardened; 
         FIG. 7  is a perspective view of the bridge unit and headwall assembly including two different size counterforts; 
         FIG. 8  is a perspective view of the bridge unit and framing unit including releasably attached earth anchor forms illustrating an alternative configuration; 
         FIG. 8A  is an enlarged view of an upper portion of one of the earth anchor forms illustrated in  FIG. 8 ; 
         FIG. 9  is a perspective view of a bridge unit and integral unit comprising a headwall and earth anchors following precasting of the integral unit using the earth anchor forms of  FIG. 8 ; 
         FIG. 10  is a perspective view of the bridge unit and headwall assembly formed using the bridge unit and integral unit of  FIG. 9 ; and 
         FIG. 11  is a cross-sectional elevation view taken along line  11 - 11  in  FIG. 10  through an earth anchor and an adjacent portion of the top wall. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, specific preferred embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention. 
     A method of production of a precast bridge unit and headwall assembly will be described. Referring to  FIG. 1 , a precast reinforced concrete culvert or bridge unit  10  is constructed. The bridge unit  10  includes a top wall  12 , which may have a conventional arcuate configuration, see  FIG. 1 , or which may have a flat construction, and which integrally connects parallel spaced vertical side walls  14  to form an open bottom bridge unit. However, a bridge unit may also be constructed with a bottom wall which also integrally connects the side walls  14  to form a box-type culvert or bridge unit. A separately precast steel reinforced flat concrete headwall  16  projects upwardly from one end of the bridge unit  10  and is supported by a plurality or series of concrete buttresses or counterfort members  18  which preferably are tapered in two directions. For purposes of simplification, each of the counterfort members  18  is illustrated as being identical. However, the counterfort members  18  may be of different sizes, for example, two different sizes, and larger counterfort members may be used on opposite end portions of the headwall  16 , as is discussed in detail below. 
     As shown in  FIGS. 2 and 2A , when the bridge unit  10  is precast, the arcuate top wall  12  is provided with a series of laterally spaced tubular steel first anchor members  22  having internal threads and an end cap or plate, and may further include at least one second anchor member  27  ( FIG. 2A ) for supporting an anchor bracket. The laterally spaced embedded first anchor members  22  and the at least one second anchor member  27  are located a predetermined distance from a first side  38  of the bridge unit  10 . The anchor members  22  are configured to receive a threaded shaft  23 , i.e., a bolt or rod, passing through and supporting a tubular member  25 , as is discussed further below. 
     Referring to  FIG. 2 , after the top wall  12  and side walls  14  of the bridge unit  10  are precast, a series of counterfort forms  24  are releasably attached to the top wall  12  at laterally spaced intervals between the side walls  14 . The counterfort forms  24  may be formed as a sheet metal structure for defining a predetermined counterfort shape. Each counterfort form  24  has two side plates  26 , a lateral plate  28  between the side plates  26 , a bottom edge  30 , a top edge  32 , and forward edges  34 . The lateral plate  28  includes an aperture  29  for passage of the threaded shaft  23 . The counterfort forms  24  are assembled to the top bridge unit  10  such that the forward edges  34  are adjacent the top wall  12  of the bridge unit  10 , the lateral plate  28  is spaced from the top wall  12  of the bridge unit  10 , and the bottom edge  30  is spaced from a horizontal casting surface  40  supporting the first side of the bridge unit  10 . The counterfort forms  24  are each held in position on the bridge unit  10  by one of the threaded shafts  23  extending through the aperture  29  and secured, for example, by two nuts and a washer. In a typical construction, the tubular member  25  may comprise a section of PVC pipe that is positioned within the counterfort form  24  when the counterfort form  24  is assembled to the bridge unit  10  prior to a casting operation. The counterfort form  24  isolates the threaded shaft  23  from concrete formed in the counterfort form  24 . 
     As shown in  FIG. 2 , the bridge unit  10  is illustrated positioned with a first side  38  supported by the horizontal casting surface  40  and a casting framework  42  is constructed above the casting surface  40  adjacent the top wall. The bottom edge  30  of the counterfort forms  24  is located adjacent an upper edge of the casting framework  42 , identified by the dashed line L, with the bottom edge  30  vertically aligned with an intended location of an upper surface of the headwall  16  during a casting operation. The casting framework  42  may be formed of, for example, rebar. Rebar reinforcements  43  may be placed in each of the counterfort forms  24  such that a portion of the rebar reinforcement  43  extends down into the casting framework  42 . For example, one or more rebar reinforcements  43  may be formed as a U-shaped member extending around the outside of the tubular member  25 . The rebar reinforcements  43  may include enlarged ends  55  for increased anchoring and reinforcement strength. A framing unit  44  is placed on the casting surface  40  to define the top end surface and side edge surfaces of the headwall  16 . 
     Referring additionally to  FIGS. 2B and 2C , one or more bracing structures  49  are provided located laterally between adjacent counterfort forms  24 . The bracing structure  49  can comprise a primary bracket  48  located adjacent the casting framework  42 , a secondary bracket  52  releasably attached to the top wall  12  of the bridge unit  10  via a bolt engaged with the at least one second anchor member  27 , and a brace member  54  extending between the primary and secondary brackets  48 ,  52 . The brace member  54  may comprise a rod having opposite threaded first and second ends  56 ,  58  for detachably coupling to the primary and secondary brackets  48 ,  52  via nuts applied to the ends  56 ,  58 . The primary bracket  48  may include a base portion  51  having a plurality of studs  50 , such as four studs  50 , extending downward into the casting framework  42 . The studs  50  preferably comprise Nelson studs for anchoring in the concrete forming the headwall  16 . 
     Prior to formation of the headwall  16 , the primary bracket  48  may be supported by attachment of one or more of the studs  50  to the casting framework  42 , such as by tying the studs  50  via wire to the casting framework  42 . The releasable coupling of the brace member  54  to the primary and secondary brackets  48 ,  52  forms a detachable assembly that permits the bracing structure  49  to be located in position during formation of the headwall  16  for accurate placement of the primary bracket  48 , and allowing disassembly for shipment of the bridge unit  10  and the headwall  16  as separate components. It may be noted that the bracing structure  49  is preferably formed of a corrosion resistant material, such as stainless steel. 
     With the counterfort forms  24 , the brace assembly  49  and the framing unit  44  in position with the top wall  10 , concrete is poured into the framing unit  44  and around the brace assembly  49  to form the headwall  16 . Subsequently, before the concrete of the headwall  16  fully sets, concrete is poured in the counterfort forms  24 . Hence, the top wall  12  with a counterfort form  24  forms a mold cavity for formation of a counterfort member  18 . The concrete for the counterfort members  18  can be poured simultaneous with or as a final stage of pouring of the concrete for the headwall  16 , i.e., immediately following the pouring of the concrete of the headwall  16  while the headwall concrete is still wet. Forming the counterfort members  18  simultaneously with, or substantially simultaneously with, the formation of the headwall  16  is designed to create the counterfort members  18  as integral or unitary with the concrete material of the headwall  16 , defining an integral unit  64 , as illustrated in  FIG. 3 . The construction of the integral unit  64  avoids formation of a seam along the junction between the counterfort members  18  and the headwall  16 . By providing a continuous or seamless junction between the counterfort members  18  and the headwall  16 , the reinforcements  43  are located fully surrounded by concrete material without a pathway for moisture to penetrate from exterior of the counterfort member  18  to the reinforcements  43 . Hence, deterioration caused by oxidation (rust) of the reinforcements  43  can be avoided by the integral construction described herein. 
     Further, upon hardening of the concrete forming the headwall  16 , the at least one primary bracket  48 , previously positioned at least partially within the casting framework  42 , is integrally formed with the headwall  16  via the studs  50 , i.e., the studs  50  are embedded within the hardened concrete of the headwall  16 . A cross-hole  62  is created in each of the counterfort members  18  by way of the threaded shaft  23  and the tubular member  25  such that a diameter D of the cross-hole  62  generally corresponds to the diameter of the tubular member  25 , see  FIG. 3 . After the concrete forming the headwall  16  and counterfort members  18  is set or hardened, the series of counterfort forms  24  can be removed from the top wall  12  of the bridge unit  10 , and the first and second ends  56 ,  58  of the brace member  54  can be disconnected for separation of the headwall from the bridge unit  10 . It may be noted that the removed counterfort forms  24  may be reused in subsequent processes to create additional integral units  64 . 
     Subsequently, the bridge units  10  and integral units  64  can be shipped to a construction site where opposite end bridge units  10  may be installed with a crane on supporting concrete footers, and the integral units  64  can be attached to the top wall  12  of each bridge unit  10  with the threaded shafts  23  to form a bridge unit and headwall assembly. After all of the bridge units and integral units  64  are backfilled with compacted soil, the soil around the attached counterfort members  18  cooperates to provide for a more positive lock of the integral units  64  to the end bridge units  10 . 
     Summarizing the process for formation of the integral units  64 , with reference to  FIG. 4 : a precast bridge unit is initially provided at step S 10 , a series of counterfort forms are attached to the bridge unit at step S 12 ; a casting framework and framing unit are provided at the casting surface adjacent to the bridge unit at step S 14 ; concrete is provided to cast the headwall on the casting surface at step S 16 ; concrete is provide to the series of counterfort forms before the concrete of the headwall has completely hardened at step S 18 ; the counterfort forms are then detached from the bridge unit after the concrete has hardened at step S 20 ; and the integral unit of the headwall and counterfort members is then separated from the bridge unit at step S 22 . 
     Referring to  FIGS. 5, 5A and 6 , an alternative configuration of the bridge unit and headwall assembly will be described wherein structure corresponding to that described above with reference to  FIGS. 1-4  is identified with the same reference number increased by  100 . 
     Referring to  FIG. 5 , a precast reinforced concrete culvert or bridge unit  110  is constructed. The bridge unit  110  includes a top wall  112 , which may have a conventional arcuate construction, as shown in  FIG. 5 , or which may have a flat construction, and which integrally connects parallel spaced vertical side walls  114  to form a bridge unit. A separately precast steel reinforced flat concrete headwall  116  projects upwardly from one end of the bridge unit  110  and is supported by a plurality or series of concrete buttresses or counterfort members  118 ,  118   b.  The counterfort members  118 ,  118   b  may be of different sizes, for example, two different sizes, and larger counterfort members may be used on opposite end portions of the headwall  116 , discussed in detail below. 
     As shown in  FIGS. 5 and 5A , when the bridge unit  110  is precast, the arcuate top wall  112  is provided with a series of first and second laterally spaced tubular steel anchor members  122 ,  122   b  having internal threads and an end cap or plate. The first laterally spaced embedded anchor members  122  are located a first predetermined distance from a first side  138  of the bridge unit  110 . The second laterally spaced embedded anchor members  122   b  are located a second predetermined distance from a first side  138  of the bridge unit  110 . A threaded shaft  123  can be anchored within each of the anchor members  122 ,  122   b  extending outward from the top wall  112 . A tubular member  125  may be positioned over each threaded shaft  123 . 
     After the bridge unit  110  is precast, a series of counterfort forms  124   a,    124   b  are releasably attached to the top wall  112  at laterally spaced intervals between the side walls  114 . Each counterfort form  124   a  may be formed the same as the previously described counterfort form  24 , and includes two side plates  126 , a lateral plate  128  between the side plates  126 , a bottom edge  130 , a top edge  132 , and forward edges  134 . Each counterfort form  124   b  has two side plates  126 , a first lateral plate  128   a  having an aperture  129 , a second lateral plate  128   b,  the first and second lateral plates  128   a,    128   b  being between the side plates  126 , a bottom edge  130 , a top edge  132 , and forward edges  134 . The first lateral plate  128   a  extends generally parallel to the top wall  112  of the bridge unit  110  and the second lateral plate  128   b  angles away from the first lateral plate  128   b  and top wall  112  toward a horizontal casting surface  140 . The second counterfort form  124   b  is taller along the top wall  112  and extends a greater distance from the top wall  112  than the first counterfort form  124   a.  The counterfort forms  124   a,    124   b  are positioned such that the forward edges  134  are adjacent the top wall  112  of the bridge unit  110 , the lateral plates  128 ,  128   a,    128   b  are spaced from the top wall  112  of the bridge unit  110 , and one of the threaded shafts  123  extends through each aperture  129 , and is secured, for example, by two nuts and a washer, to support the counterfort forms  124   a,    124   b  to the bridge unit  110 . 
     The bridge unit  110  is initially provided positioned with a first side  138  supported by the horizontal casting surface  140  and the top wall  112  being adjacent a casting framework  142  and a framing unit  144 . The bottom edge  130  of the counterfort forms  124   a,    124   b  is located adjacent an upper edge of the casting framework  142 , identified by the dashed line L, and framing unit  144 . The casting framework  142  may be formed of, for example, rebar. Rebar reinforcements  143   a,    143   b  may be placed in the respective counterfort forms  124   a,    124   b  such that a portion of the rebar reinforcement  143   a,    143   b  extends down into the casting framework  142 . The rebar reinforcements  143   a,    143   b  may include enlarged ends  155 , or hooks, as illustrated for example by hook  157  in  FIG. 5A , and any combination thereof, for increased anchoring and reinforcement strength. The framing unit  144  is placed on the casting surface  140  to define the top end surface and side edge surfaces of the headwall  116 . 
     The concrete headwall  116  is cast on the casting surface  140  embedding the casting framework  142  within the headwall  116 . Before the headwall  116  completely hardens, the counterfort members  118   a,    118   b  are cast into the counterfort forms  124 ,  124   b,  as seen in  FIGS. 6 and 7  and as described above with reference to the formation of the counterfort members  18 . A cross-hole  162  is created in each of the counterfort members  118 ,  118   b  by way of the threaded shaft  123  and the tubular member  125  such that a diameter D of the cross-hole  162  generally corresponds to the diameter of the tubular member  125 , see  FIG. 6 . After the concrete forming the headwall  116  and counterfort members  118   a,    118   b  sets or hardens, an integral unit  164 , made up of the counterfort members  118   a,    118   b  and the headwall  116 , is formed such that no seam is present between the headwall  116  and the counterfort members  118   a,    118   b,  as illustrated in  FIG. 6 . While two different size counterfort members  118 ,  118   b  are shown in  FIG. 6 , it is understood that more than two different sizes may be used, for example, three or four different sizes. Subsequent to hardening of the material of the integral unit  164 , the series of counterfort forms  124   a,    124   b  is removed from the top wall  112  of the bridge unit  110 . The integral unit  164  is then separated from the bridge unit  110  for shipment to a construction site where the integral unit  164  and bridge unit  110  may be assembled to form a bridge unit and headwall assembly. 
       FIGS. 8-11  illustrate a further alternative configuration of the bridge unit and headwall assembly. Referring initially to  FIGS. 8 and 10 , a precast reinforced concrete culvert or bridge unit  210  is constructed. The bridge unit  210  includes a top wall  212 , which may have a conventional arcuate construction, as illustrated in  FIGS. 8 and 10 , or which may have a flat construction, and which integrally connects parallel spaced vertical side walls  214  to form a bridge unit. A separately precast steel reinforced flat concrete headwall  216  ( FIG. 10 ) projects upward from one end of the bridge unit  210  and is supported by a plurality or series of laterally spaced concrete earth anchors  218  that are configured to buttress the headwall  216  in a manner similar to the counterfort members described above. The earth anchors  218  are formed with a counterfort projection or body member  270  and an integrally formed foot member  272  extending around and laterally outward from the body member  270 , as is described further below. Additionally, the earth anchors  218  may be of different sizes, as described with reference to the counterfort member of the previous configuration illustrated in  FIGS. 5-7 . It may be noted that the earth anchors  218  perform a similar function to the previously described counterfort members, but do not include a mechanical connection to the top wall  212  of the bridge unit  210 , as is described further below. 
     Referring to  FIG. 8 , after the bridge unit  210  is precast, a series of earth anchor forms  224  are releasably attached to the top wall  212  at laterally spaced intervals between the side walls  214 . The earth anchor forms  224  include a body mold structure comprising first and second body member side plates  226   a,    226   b  (see also  FIG. 8A ) laterally spaced apart and parallel to each other. A lateral plate  226   c  extends between and joins the first and second body member side plates  226   a,    226   b.  The lateral plate  226   c  is oriented at an angle relative to a plane defined by the headwall  216  and extends outward toward the top wall  212 . The earth anchor forms  224  further include a foot mold structure comprising first and second foot member side plates  227   a,    227   b  laterally spaced apart and parallel to each other. A lateral plate  227   c  extends between and joins the first and second foot member side plates  227   a,    227   b,  including lateral portions extending between the body member side plates  226   a,    226   b  and respective foot member side plates  227   a,    227   b,  and an upper distal portion that is located outward from an end of the body member lateral plate  226   c.  The body and foot mold structures forming the earth anchor forms  224  define a continuous interior mold area for forming the body member  270  and foot member  227  integral with each other and open at a lower edge  230 . The foot member side plates  227   a,    227   b  and lateral plate  227   c  define a top edge  232  for the earth anchor forms  224 , and the foot member side plates  227   a,    227   b  further define a forward edge  234  for the earth anchor forms  224 . 
     Referring to  FIG. 8 , the bridge unit  210  is initially provided positioned with a first side  238  supported by a horizontal casting surface  240  and the top wall  212  being adjacent a framing unit  244  and associated casting framework (not shown) which may be formed of rebar in a manner similar to the casting framework described for the previous configurations illustrated in  FIGS. 1-7 . The bottom edge  230  of the earth anchor forms  224  is located adjacent an upper edge of the framing unit  244 . The earth anchor forms  224  can be held in place on the top wall  212  by means of a mounting tab  236  extending between the foot member side plates  227   a,    227   b.  The mounting tab  236  may include one or more holes adapted to receive a fastener  239  for temporarily supporting the earth anchor form  224  to the top wall  212 . The framing unit  244  is placed on the casting surface  240  to define a top end surface and side edge surfaces of the headwall  216 . Further, rebar reinforcements (not shown) may be placed in the respective earth anchor forms  224  such that a portion of the rebar reinforcement extends down into the casting framework, as previously described for the counterfort members. 
     In accordance with the present configuration, the earth anchors  218  are not formed with a connecting structure for providing a connection to the top wall  212 . In particular, the earth anchors  218  are formed without passages for accommodating fasteners defining connection points to the top wall  212 , and it is not necessary to provide the top wall with connection structure, e.g., embedded anchor members, for assembly of the headwall  216  to the top wall  212 , as will be described further below. 
     The concrete headwall  216  is cast on the casting surface  240  embedding the casting framework within the headwall  216 . Before the headwall  216  completely hardens, the earth anchors  218  are cast into the earth anchor forms  224 , in a manner similar to that described above with reference to the formation of the counterfort members  18  and  118 . In particular, the earth anchors  218  may be precast simultaneous with the precasting of the headwall  216 , where “simultaneous”, as used herein, encompasses precasting the earth anchors  218  at the same time as precasting of the headwall  216 , as well as shortly after an initial setting of the concrete forming the headwall  216 . That is, it may be desirable to allow an initial firming of the material forming the headwall  216  prior to precasting of the earth anchors  218  in order to provide a supporting layer of material under the earth anchor forms  224 , prior to complete curing of the concrete forming the headwall  216 . In any construction involving the simultaneous formation of the earth anchors  218  with the headwall  216  it should be understood that the material of the earth anchors  218  is formed continuous or integral with the material of the headwall  216  to form a seamless structure including the headwall  216  and earth anchors  218  and defining an integral unit  264  ( FIG. 9 ). Subsequent to complete hardening of the material of the integral unit  264 , the series of earth anchor forms  224  is removed from the top wall  212  of the bridge unit  210 . The integral unit  264  is then separated from the bridge unit  210  for shipment to a construction site where the integral unit  264  and bridge unit  210  may be assembled to form a bridge unit and headwall assembly. 
     Referring to  FIG. 10 , the body member  270  of the earth anchor  218  defines a buttress that extends outward from the headwall  216 , and includes an outer lateral surface  270   c  extending between planar opposing lateral sides  270   a,    270   b.  The outer lateral surface  270   c  extends at a downward angle from the headwall  216  toward the top wall  212 . The foot member  272  defines a base that extends around a lower perimeter portion of the body member  270 . The foot member  272  includes lateral foot sections  272   a,    272   b  that extend laterally outward from the lateral sides  270   a,    270   b  of the body member  270 , and a distal foot section  272   c  defining a surface that extends from the body member  270  distal from the headwall  216  and forming a connecting surface between the lateral foot sections  272   a,    272   b.  The foot member  272  extends a substantial distance out from the body member  270  and preferably extends a distance, in each lateral direction and in the distal direction, at least equal to the lateral width of the body member  270 . 
     As is further seen in  FIG. 11 , the body member  270  and foot member  272  each comprise a planar body wherein the body member  270  is oriented perpendicular to the foot member  272 , defining an earth anchor cross-section having an inverted T-shape. The earth anchors  218  are positioned in contact with the top wall  212  and effect or form a frictional engagement at an interface  235  between the earth anchors  218  and the top wall  212 . The interface  235  is formed without a connecting structure, e.g., without bolts or other linking structure, extending across the interface  235  between the earth anchors  218  and the top wall  210 . Frictional forces between the earth anchors  218  and the top wall  212  resist horizontal movement of the headwall  216  relative to the bridge unit  210 . In particular, the foot member  272  of the earth anchors  218  has an upper surface that is generally parallel to the top wall  212  and that provides a substantial surface for supporting soil S that is layered as a covering over both the top wall  212  and the earth anchors  218 , wherein the weight of the soil S on the foot member  272  increases the frictional forces at the interface  235  to retain the headwall  216  in its horizontal position on the top wall  212 . The layer of soil S on the foot member  272  also operates to weight the earth anchors  218  to retain the headwall in its vertical position, resisting tipping or pivoting of the headwall  216  about its lower edge. The present configuration for the earth anchors  218  can enable a more efficient construction for the bridge unit and headwall assembly in that it permits the bridge unit  210  and headwall  216  to be constructed without placement of anchor members and aligned connecting passages with associated fasteners extending between earth anchors and the top wall. 
     In addition to the above described earth anchors  218 , a low profile earth anchor  246  (see  FIGS. 9 and 10 ) may be provided to facilitate horizontal frictional retention of the headwall  216  relative to the top wall  212 . Due to the short height at the central location of the headwall  216 , a counterfort projection is not needed and only a frictional foot member defined by the earth anchor  246  may be provided. The frictional foot member defined by the earth anchor  246  may be configured as a rectangular member centrally located along the headwall  216 , without a body member, such that a large upper surface is presented for receiving the weight of the soil S and for presenting a substantial frictional engagement surface to the top wall  210 . 
     While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.