Abstract:
A structure for stabilizing an earthen embankment comprises an embankment support for restraining movement of at least a part of the embankment, a flexible fiber geogrid ( 5 ) extending longitudinally through the embankment from a first end portion secured to the support to a second end portion, and anchor means ( 55, 60, 11 ) for securing one of the end portions. The anchor means comprises a pair of anchor rods ( 55, 60 ) extending transversely in relation to the geogrid, and means ( 11 ) for limiting movement of the anchor rods. The end portion secured by the anchor means is wrapped back and forth around the anchor rods so as to tighten thereon when the geogrid is pulled in longitudinal tension away from the anchor means. A method of anchoring a flexible fiber geogrid to a support utilizing such anchor rods is also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to U.S. provisional application No. 60/449,392 filed Feb. 25, 2003, entitled “APPARATUS AND METHOD FOR STABILIZING AN EARTHEN EMBANKMENT”, naming Michael Charles Kallen as the inventor. The contents of the provisional application are incorporated herein by reference in their entirety, and the benefit of the filing date of the provisional application is hereby claimed for all purposes that are legally served by such claim for the benefit of the filing date. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to apparatus and methods for stabilizing earthen retaining walls or embankments. 
     It is well known in the prior art to stabilize earthen embankments with supports and associated geogrids extending rearwardly from the support into the stabilized embankment. This includes embankments with a slope of less than 90 degrees and embankments with a 90 degree slope. In cases where flexible fiber geogrids are used, the geogrid often is wrapped over the face of the support and under the floor of the support But, the time and labor required to instal such geogrids is substantial. 
     Flexible fiber geogrids are available from various sources, for example, Strata Systems, Inc. of Cumming, Ga., U.S. who provide a family of high strength polyester yarn geogrids for soil reinforcement. 
     U.S. Pat. No. 5,975,810 (Taylor et al.) granted on Nov. 2, 1999 discloses apparatus for securing a flexible fiber geogrid to a support without wrapping over the face of the support. In a number of embodiments there is a need to carefully fold the forward end portion of the geogrid back and forth in layers upon itself to provided improved shear strength. The layered end portion is then secured with a retaining rod which is positioned to press against the layers—in effect sandwiching the layers between the rod and the underlying support on which the layers are positioned. In the field, the required aligned folds may be considered awkward and time consuming to achieve. Further, the anchorage does not have a positive hold on the geogrid. The integrity of the anchorage when the geogrid is tensioned appears to be largely dependent upon the compressive grip which the retaining rod imposes on the folded layers. In another embodiment, Taylor et al. describe anchoring a geogrid by means of a retaining rod around which the forward end of a geogrid is folded 180 degrees backwards. However, by itself, the rod does not provide a positive hold on the geogrid. The geogrid is restrained only by the resistance of backfill which is required to be placed over the folded end portion of the geogrid before tension is applied to the geogrid. The sufficiency of the restraint will be dependent on the length of the folded end portion and frictional characteristics of the backfill, the latter of which may vary depending on dampness and other factors. To adjust for such considerations will require particular skill and expertise on the part of those determining what length a folded portion should have to achieve a desired connection strength. 
     Accordingly, there is a need to provide apparatus and a method for positively anchoring a flexible fiber geogrid to a support with a strong, reliable connection which requires minimal labor. 
     BRIEF SUMMARY OF THE INVENTION 
     In a broad aspect of the present invention, there is provided a structure for stabilizing an earthen embankment which comprises an embankment support for restraining movement of at least a part of the embankment, a flexible fiber geogrid extending longitudinally through the embankment from a first end portion secured to the support to a second end portion, and anchor means for securing one of the end portions. The anchor means comprises a pair of anchor rods extending transversely in relation to the geogrid, and means for limiting movement of the anchor rods. The end portion secured by the anchor means is wrapped back and forth around the anchor rods so as to tighten thereon when the geogrid is pulled in longitudinal tension away from the anchor means. 
     In one embodiment, the embankment support comprises a retaining wall and the means for limiting movement of the anchor rods comprises a plurality of anchor bolts, each bolt comprising a shaft extending from one end engaged with the wall to a distal end shaped to form an eyelet, one of the anchor rods extending through each of the eyelets. 
     In another embodiment where the embankment support also comprises a retaining wall, the earthen embankment lies between a rock face and the wall. The means for limiting movement of the anchor rods comprises a plurality of anchor bolts, each bolt comprising a shaft extending from one end engaged with the rock face to a distal end shaped to form an eyelet, one of the anchor rods extending through each of the eyelets. 
     In a further embodiment, the embankment support of the stabilizing structure comprises a floor section and a face section. The floor section extends longitudinally rearwardly from a forward end of the floor section to a rearward end and includes at the rearward end a plurality of transversely spaced hooking members. The face section extends upwardly from the forward end of the floor section to a top end of the face section at an angle corresponding to the slope of the embankment (i.e. up to 90 degrees). The geogrid extends longitudinally rearwardly from the floor section and is anchored thereto by first and second anchor rods extending transverse to the geogrid. Movement of the anchor rods relative to the support is limited by the hooking members when the geogrid is pulled in rearward longitudinal tension. At least in some circumstances, each hooking member preferably defines an inverted U-shaped envelope. In such cases, the geogrid preferably extends from a forward end of the geogrid:
         first forwardly above the first anchor rod, preferably a cylindrical rod, to a position above the second anchor rod, also preferably a cylindrical rod;   then wrappingly around the second anchor rod to a position below the second anchor rod;   then rearwardly to a position above the first anchor rod;   then wrappingly around the first anchor rod to a position below the first anchor rod;   then forwardly to a position below the second anchor rod;   then wrappingly around the second anchor rod to a position above the second anchor rod;   then rearwardly above the first anchor rod and away from the support       

     In another aspect of the present invention, there is provided a method of anchoring a flexible fiber geogrid to a support for stabilizing an earthen embankment, the support comprising an upwardly extending face section and a floor section extending longitudinally rearwardly from the face section. The floor section comprises a plurality of transversely spaced hooking members, and the geogrid comprises longitudinally extending webs sized and spaced to fit between the hooking members. The method comprises:
         positioning a forward end portion of the geogrid atop the floor section such that the longitudinally extending webs of the geogrid extend between the hooking members;   then positioning a first anchor rod atop the end portion of the geogrid rearward of the hooking members in a position where forward movement of the first anchor rod is limited by the hooking members;   then folding the end portion of the geogrid forwardly over the first anchor rod;   then positioning a second anchor rod atop the end portion of the geogrid forward of the first anchor rod in a position where rearward movement of the second anchor rod is limited by the hooking members;   then folding the end portion and the geogrid rearwardly over the second anchor rod.       

     The foregoing structure and method enables a flexible fiber geogrid to be anchored to a support in a quick and efficient manner without imposing undesirable stresses on the geogrid when the geogrid is tensioned in relation to the support. Another key point to note is that unlike the systems of Taylor et al. the strength of the anchoring connection (viz. the “pull-out” factor) will proportionately increase as the longitudinal tension applied to the geogrid is increased. Further, since the anchoring connection of the present invention is not dependent on placing backfill on the connection to provide resistance, the connection is necessarily independent of the quality of backfill that ultimately is added. The frictional resistance which backfill may have to offer is immaterial to the connection strength. 
     The foregoing and other features and advantages of the present invention will now be described with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a representational cross-section elevation view of a vertical earthen embankment stabilized by apparatus in accordance with the present invention. 
         FIG. 2  is a representational cross-section elevation view of a sloped earthen embankment stabilized by apparatus in accordance with the present invention. 
         FIG. 3  is a perspective view illustrating in more detail the linking of the supports shown in  FIG. 1 . Similar linking is present between the supports shown in  FIG. 2 . 
         FIG. 4  is a cross-section elevation view illustrating in more detail the anchoring of a flexible fiber geogrid to an embankment support in accordance with the present invention. 
         FIGS. 5 through 10  are a stepwise progression of perspective views showing a method of achieving the anchoring illustrated in  FIG. 4 . 
         FIG. 11  is a cross-section elevation view illustrating a backfill earthen embankment contained between a retaining wall and a rock face with geogrids extending therebetween, an end portion of each of the geogrids being anchored to the rock face with apparatus in accordance with the present invention. 
         FIG. 12  is a cross-section elevation view illustrating in more detail the manner whereby the geogrids shown in  FIG. 11  are anchored to the rock face shown in  FIG. 11 . 
         FIG. 13  is a cross-section elevation view illustrating a backfill earthen embankment stabilized by a retaining wall and geogrids, the geogrids being anchored to the retaining wall with apparatus in accordance with the present invention. 
         FIG. 14  is a perspective view of an alternative embankment support. 
         FIG. 15  is a cross-section elevation view illustrating the anchoring of a flexible fiber geogrid to the embankment support shown in  FIG. 14 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIGS. 1 and 2  illustrate flexible fiber geogrids  5  anchored to embankment supports generally designated  11 ,  11   a ,  12 ,  12   a . In  FIG. 1 , geogrids  5  and supports  11 ,  11   a  serve to stabilize a vertical earthen embankment of backfill  201 . In  FIG. 2 , geogrids  5  and supports  12 ,  12   a  serve to stabilize a sloped earthen embankment of backfill  202 . 
     Geogrids  5  are anchored to support  11  or  12 , as the case may be, by a preferred anchoring mechanism which is generally designated  15  and which is described below in more detail with reference to  FIG. 4-10 . Each geogrid  5  comprises a plurality of spaced elongated tension members  6  extending from a forward end  7  and intersected at spaced intervals by a plurality of transverse members  8 . For strength, geogrids  5  preferably are fabricated from high density polyester material. 
       FIG. 3  illustrates the structure of supports  11 ,  11   a  in more detail. Note that geogrids  5  and backfill  201  have not been included in  FIG. 3  so as not to obscure the structure. 
     Support  11  comprises a plurality of transversely spaced elongated steel wire members  20 , each extending longitudinally from a hooked rearward end or hooking member  21  (which defines an inverted U-shaped envelope) to a forward end  25 , then upwardly to a hooked upper end  29 . The lowermost horizontally extending portion of wire members  20  together define a floor section of the support. Similarly, the forwardmost upwardly extending portion of wire members  20  together define a face section of support  11  which extends upwardly at 90 degrees relative to the floor section. 
     Support  11  also includes transversely extending steel wire crossbars, namely: rearward crossbar  31 , intermediate crossbar  32  on the floor section, forward crossbar  33  extending proximate forward ends  25  of wire members  20 , and upper crossbar  34 . Each of such crossbars are welded to wire members  20  at their points of intersection therewith to hold wire members  20  in their parallel spaced relationship. As well, to provide added strength, support  11  includes a plurality of diagonal wire braces  40  each of which is hooked at its lower end to intermediate crossbar  32  and at its upper end to upper crossbar  34 . 
     The construction of support  11   a  is substantially the same as that of support  11 . During the process of stabilizing an embankment, support  11   a  of course will be installed first with its geogrid  5  anchored to the support (in the manner described below). Then, embankment backfill sufficient to provide a base for support  11  will be added over the floor section and rearwardly of support  11   a  while leaving hooked upper ends  29  of support  11   a  free to engage forward crossbar  33  of support  11 . 
     As can be seen in  FIG. 3 , forward crossbar  33  of support  11  is engaged by hooked upper ends  29  of support  11   a . The hooked upper ends  29  of support  11  are free ends but may be used to engage the upper crossbar of yet another similar support (not shown) positioned above the level of support  11 . This may be repeated for several levels or tiers of supports and not merely the two levels depicted in  FIGS. 1 and 3 . 
     The only substantive difference between supports  11 ,  11   a  and supports  12 ,  12   a  is that the face section of the latter extends upwardly and rearwardly at an angle of less than 90 degrees relative to the floor section, and is thus suitable for a sloped embankment extending at the same angle. Depending on the job at hand, it will be understood that supports like supports  11 ,  11   a ,  12 ,  12   a  may be combined in the same project. For example, in  FIG. 3 , support  11  or support  11   a  could be replaced by a support like support  12  or with a support having some other angle between its face and floor sections. 
     Apart from the provision of hooked upper ends  29 , the construction of supports  11 ,  11   a ,  12 ,  12   a  is considered to be prior art. The advantage provided by hooked upper ends  29  is to enable supports on successive levels to be quickly linked in the manner shown in  FIG. 3  as construction of a stabilized embankment proceeds and, as each new support is added to the structure, to enable its associated geogrid to be anchored to the support and then tensioned while the support is held in position by the support to which it is linked. 
     Each geogrid  5  is anchored to support  11 ,  11   a ,  12 ,  12   a , as the case may be, by first and second anchor rods (preferably cylindrical rods  55 ,  60 ): see  FIGS. 4-10  for the example of support  11 . When a geogrid  5  is fully anchored to support  11  as shown in  FIG. 4 , each rod  55 ,  60  extends transverse to the geogrid. Rod  55  is positioned rearward of rod  60  outside the inverted U-shaped envelope defined by end  21  and rod  60  is positioned forward of rod  55  within the envelope. As seen in  FIG. 4 , geogrid  5  extends from its forward end  7 
         first forwardly above rods  55  and  60  to a position above rod  60 ;   then wrappingly around rod  60  to a position below rod  60 ;   then rearwardly to a position above rod  55 ;   then wrappingly around rod  55  to a position below rod  55 ;   then forwardly to a position below rod  60 ;   then wrappingly around rod  60  to a position above rod  60 ;   then rearwardly above rod  55  and distantly away from support  11 .       

     When longitudinal tension is applied to geogrid  5  in the direction of arrow  100  ( FIG. 4 ) while support  11  is held in position the geogrid tightens on the rods; rod  55  is pulled by the geogrid forwardly against the rearward side of leg  22  of end  21 ; and rod  60  is pulled by the geogrid rearwardly against the forward side of leg  22 . Thus, both forward movement of rod  55  and rearward movement of rod  60  are limited by leg  22 . 
     It will be note that upward movement of rod  60  is limited because it is contained within the inverted U-shaped envelope defined by end  21 . This is advantageous because when a worker pulls on the geogrid before rods  55 ,  60  are drawn to the final positions shown in  FIG. 4 , rod  60  may otherwise slip up and away from its anchoring position if the manual pulling force includes an upward component relative to support  11 . 
     Reference is now made to  FIGS. 5 through 10  which illustrate a stepwise progression of steps for anchoring geogrid  5  to support  11 . As shown in  FIG. 5 , a forward portion of geogrid  5  is first positioned above support  11  with its forward end  7  directed rearwardly. The forward portion is then lowered in the direction of arrow  101  ( FIG. 5 ) to the position shown in  FIG. 6  where the longitudinal tension members  6  of geogrid  5  fall between hooking members  21 . Although not illustrated, it may be noted that the portion of geogrid  5  not shown in  FIG. 5  typically will be rolled up in a form easy to be unrolled. 
     Next, anchoring rod  55  is located from a position above geogrid  5  as shown in  FIG. 6  to a position atop geogrid  5  as shown in  FIG. 6  (viz. in the direction of arrow  102 ). Then, the forward portion of geogrid  5  as shown in  FIG. 6  is folded forwardly over rod  55  to the position shown in  FIG. 7  (viz. in the direction of arrow  103 ). 
     Next, as indicated in  FIGS. 7 and 8 , anchoring rod  60  is transversely inserted atop the forwardly folded end portion of geogrid  5  and through the inverted U-shaped envelopes provided by ends  21  of support  11 . 
     Next, as indicated in  FIGS. 9 and 10  by arrows  104  and  105 , both the forward portion and the remaining extension of geogrid  5  are folded rearwardly over anchoring rod  60  to the position shown in  FIG. 10 . Geogrid  5  is then situated to be tensioned to the position shown in  FIG. 4  where it is tighened on rods  55 ,  60 . 
     Other structures for supporting earthen embankments are within the scope of the present invention. For example,  FIG. 11  illustrates a case where a backfill earthen embankment  205  lies between a retaining wall  70  comprised of concrete blocks  72  and a rock face  300 . Flexible fiber geogrids  80  progressively installed during the process of adding the backfill each extend longitudinally through embankment  205  from a first end portion  81  held and secured between adjacent blocks  72  to a second end portion  82  secured by a pair of anchor rods  83 ,  84  extending transversely in relation to the geodgrid and anchor bolts  85 . Only one anchor bolt  85  for each geogrid  80  is visible in  FIG. 11 , but it will be understood that a number of such bolts will be used for a given geogrid depending on the width of the geogrid and the load to be carried by the bolts. 
     As best seen in  FIG. 12 , each bolt  85  comprises a shaft  86  extending from one end engaged (e.g. by threading) with rock face  300  to a distal end shaped to form an eyelet  87 . Rod  83  extends longitudinally through eyelet  87  and bears against the inside lower right quadrant thereof. Rod  84  bears against shaft  86  and the outside lower right quadrant of eyelet  87 . Bolt  85  thereby limits movement of rods  83 ,  84 . In much the same manner as shown in  FIG. 5  where the forward end of geogrid  5  is wrapped back and forth around anchor rods  55 ,  60 , end  82  of geogrid  80  is wrapped back and forth around anchor rods  83 ,  84  so as to tighten on the rods when geogrid  80  is pulled in longitudinal tension. (Typically, each geogrid  80  will be pulled and held in tension during construction when its end portion  81  is being secured between adjacent blocks  72 . 
     As another example,  FIG. 13  illustrates a case where a backfill earthen embankment  210  is stabilized by a solid concrete retaining wall generally designated  90 . Flexible fiber geogrids  92  progressively installed during the process of adding the backfill extend from wall  90  into embankment  210 . An end portion  94  of each geogrid is anchored to wall  90  by means of anchor rods  83 ,  84  and anchor bolts  85 , the latter of which are engaged with wall  90  rather than a rock face as in the case of the embodiment shown in  FIG. 11 . Since the anchoring mechanism is otherwise essentially the same as the anchoring mechanism described in relation to  FIGS. 11-12 , it will not be described here in any further detail. 
     As a further example, it should be noted that embankment supports like support  11  can be used but without hooked rearward ends  21 . While considered preferable, such hooked ends are not considered essential. More particularly,  FIG. 14  shows an embankment support  111  which is similar in construction to support  11 , but with a plurality of transversely spaced elongated steel wire members  120  instead of wire members  20 . In the floor section of support  111 , wire members  120  have straight rearward ends rather than hooked rearward ends  21 . Crossbar  31  extends across the top of the straight rearward ends.  FIG. 15  shows the manner whereby a geogrid  5  is anchored to the rearward end of the floor section of support  111  by wrapping the geogrid back and forth around anchor rods  55 ,  60 . Rod  55  abuts against crossbar  31  and against the tops of wire members  120 . Rod  60  abuts against the bottoms of wire members  120 . Movement of the rods  55 ,  60  is thereby limited. 
     Further Variations 
     A variety of modifications, changes and variations to the invention are possible within the spirit and scope of the following claims, and will undoubtedly occur to those skilled in the art. The invention should not be considered as restricted to the specific embodiments that have been described and illustrated with reference to the drawings. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures.