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CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/442,152, having a filing date of Apr. 9, 2012, now U.S. Pat. No. 8,602,692, which is a continuation of U.S. patent application Ser. No. 12/590,184, having a filing date of Nov. 9, 2009, now U.S. Pat. No. 8,235,631, the entire contents and disclosure of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to a temporary or permanent wall for retaining material, and more particularly to a bag used in erecting such a wall. 
     BACKGROUND 
     There have been a variety of methods and techniques developed in the past for building structures that retain material. Some of these structures have been temporary, while others have been intended to be permanent. For example, during times of flooding or expected flooding, temporary levees are sometimes erected using sand bags that are filled and stacked. This type of structure is very labor intensive and is temporary in nature. 
     There have been attempts to develop alternative methods of erecting temporary levees such as those taught in U.S. Pat. No. 6,390,154. However, the shape of the bag and method of using the bag described in that patent restricts the use of the bag to a limited number of environments and filling material. 
     Alternatively, it is known to build retaining walls that require preformed bricks or stones to be stacked and supported so that material is retained such as a hillside or other embankment. Erecting these types of retaining structures is expensive in both the materials and transporting them to the work site. Also, skilled installers are required for all but the simplest structures to ensure the retaining structure has the structural integrity to perform as expected. 
     There remains the need, therefore, for a bag and a system and method for using that bag to build a retaining structure that is flexible in the structures that can be constructed, that is flexible in the variety of material that can be used to fill the bag, that is simple to use, and can reduce the costs of building retaining structure, whether temporary or semi-permanent. 
     SUMMARY 
     The present invention relates to a bag for retaining structures, includes a plurality of cells aligned side-by-side in a continuous manner and configured to be filled with a filling material. Each cell of the bag includes a bottom wall, a first side wall, a second side wall, a back wall, and a front wall, the front wall being longer than the back wall. Furthermore, the first and second side walls each include a) a first corner located where the back wall connects with the bottom wall, said first corner being substantially 90 degrees; and b) a second corner located where a respective top edge of each side wall connects with the rear wall, said second corner being substantially 90 degrees. Embodiments of the present invention also relate retaining structures erected using such a bag. 
     It is understood that other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein it is shown and described only various embodiments of the invention by way of illustration. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modification in various other respects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of a bag, system and method for erecting retaining structures are illustrated by way of example, and not by way of limitation, in the accompanying drawings, wherein: 
         FIGS. 1A and 1B  show, respectively, a side view and a top view of a portion of a bag in accordance with the principles of the present invention; 
         FIG. 2A  shows a top view of a portion of a bag in accordance with the principles of the present invention; 
         FIG. 2B  shows a side-wall deformation of the bag of  FIG. 2A  in accordance with the principles of the present invention; 
         FIGS. 2C and 2D  show alternative side-wall embodiments of the bag of  FIG. 2A  in accordance with the principles of the present invention; 
         FIG. 3  shows a retaining structure erected using the bag of  FIG. 2A  in accordance with the principles of the present invention; 
         FIGS. 4A and 4B  show alternative retaining structures erected using the bag of  FIG. 2A  in accordance with the principles of the present invention; 
         FIG. 5  shows a free standing retaining structure capable of being erected in accordance with the principles of the present invention; and 
         FIG. 6  shows another free standing retaining structure capable of being erected in accordance with the principles of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the invention and is not intended to represent the only embodiments in which the invention may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring the concepts of the invention. 
     In the figures, description and in the claims, the terms “front”, “back”, “side”, “bottom” etc. are used to simplify referring to a particular embodiment of a bag. However, one of ordinary skill will recognize that these terms are relative and that the shape of the bag and its relative dimensions remain the same when viewed from different perspectives or used in different orientations. Thus, use of these terms is not intended to limit embodiments of the present invention to bags having only a single orientation in space. 
       FIGS. 1A and 1B  show, respectively, a side view and a top view of a portion of a bag in accordance with the principles of the present invention. In  FIG. 1A  a cross-sectional view of a bag  100  is depicted. There is a back wall  102 , a bottom wall  104 , and a front wall  106 . The top  108  may include a top wall or be open. If there is a top wall present, then it may be configured in such a way that it connects with either the back wall  102  or front wall  106  to form a flap. Such a flap would be moved out of the way to allow the bag  100  to be filled and then positioned over the bag  100  once it is filled. 
     Of particular benefit to the bag  100  are the relative angles formed by the different walls and their respective lengths. The right angle  110  formed by the back wall  102  and bottom wall  104  adds stability and versatility to the use of the bag  100 . The right angle  111  formed along the top edge of the back wall  102  also provides stability and versatility. 
     Making the bottom wall  104  longer than the back wall  102  provides a shape that adds stability to a structure erected using the bag  100 . By making the bottom wall  104  longer than the back wall  102 , the angles  112  and  113  are formed at each edge of the front wall  106  and the front wall  106  is longer than the back wall  102 . 
     One of ordinary skill will recognize that the bag  100  of  FIG. 1A  may be have a variety of sizes while keeping the relative lengths and angles as discussed above. Thus, embodiments of the present invention are not limited to a particular size of bag  100 . However, the use of ordinary heavy machinery to fill and move a bag  100  makes certain sizes for the bag  100  more practical than others. For example, the top opening  108  may be between one foot to two feet in length and width to accommodate typical front-end loader buckets (or specialized filling equipment). The back wall  102  may vary from about 4 feet to about 8 feet in length and a corresponding bottom wall would vary from about 7 feet to 11 feet in length. These relative dimensions and sizes are provided as examples and not as a limitation of which sizes are contemplated within the scope of the present invention. 
     As for material, the bag  100  can be constructed from polypropylene or similar material that can withstand the elements of a harsh environment. In particular, the material can be a weaved material with the weave spacing and thickness selected based on such things as the type of fill material being used to fill the bag, and the degree to which the bag is intended to retain fluid such as water. In addition, the bag may be coated with a water-proof seal if it is intended to be substantially impervious to water flow. One of ordinary skill will recognize that the specific material of the bag can be selected so as to be suitable for the intended application of use. A material can be selected that is woven or unwoven, impervious to fluid or porous, rugged or biodegradeable without departing from the intended scope of the present invention. 
     The fill material contemplated within the bag  100  includes sand, sand mixed with stones, cement or concrete, and crushed rock of various sizes. Alternatively recycled materials from tires and plastics may also be used that can be condensed to form a solid filling material. 
     In addition to the back wall  102  and side wall  106 , already discussed, the view of  FIG. 1B  also shows a first side wall  116  and a second side wall  118 . The fill material will be delivered to inside the bag  100  through the top opening  108 . 
       FIG. 2A  shows a top view of a portion of a bag in accordance with the principles of the present invention. The bag  200  of  FIG. 2A  shows that adjacent bags  100  are aligned to extend along a first direction. Thus, the bags  100  discussed above can more properly be referred to as bag cells  100  such that a bag  200  is comprised of a plurality of bag cells  100  adjacent to one another. In this arrangement, there is a side wall  202  that is shared by adjacent cells  100 . Thus referring to  FIG. 1B  and  FIG. 2A , the shared wall  202  would correspond to the second side wall  118  of one bag cell  100  and also correspond to the first side wall  116  of an adjacent bag cell  100 . Each such shared wall  202  will have a cross-section that resembles that depicted in  FIG. 1A . 
       FIG. 2B  shows a side-wall deformation of the bag of  FIG. 2A  in accordance with the principles of the present invention. Two adjacent shared walls  202  are shown in the view. In particular, each shared wall is constructed of a material (such as those described above) that is flexible enough to bow out in its center but rigid enough to substantially retain its shape along its edges. 
     For example, when cells  100  are filled with fill material, the top edge  205  (and the bottom edge, not shown) of the shared wall  202  substantially retain their shape but the material of the shared wall  202  stretches or bulges to create the bump  204 . While selecting a material rigid enough to prevent this bump  204  can be accomplished, the bump  204  has benefits. For example, the bump  204  extends into the adjacent bag cell and tends to tie the whole structure together rather than allowing adjacent cells to slip or slide with respect to one another. 
       FIGS. 2C and 2D  show alternative side-wall embodiments of the bag of  FIG. 2A  in accordance with the principles of the present invention. In  FIG. 2C , one or more holes  206  are present in the shared wall  202 , these holes allow filling material in one bag cell to contact with filling material in an adjacent bag cell. In one particular example, if the filling material is cement or concrete, then the holes will allow adjacent cells to tie into one another. 
     In  FIG. 2D , there are one or more protrusions  208  in the shared wall  202 . These protrusions can be located on one side or both sides of the shared wall  202 . 
       FIG. 3  shows a retaining structure erected using the bag of  FIG. 2A  in accordance with the principles of the present invention. The bags  200  extending in a direction perpendicular to the plane of the sheet of paper. A firm foundation  306  is provided for a first bag  200  and then additional bags  200  are stacked on top of a bag underneath. The material to be retained  302  is thus retained by the stack of bags  200 . In particular, a structure can be erected such that the slope of the face  304  of the retaining structure  300  slopes at an angle that is the substantially similar to the angle  112  shown in  FIG. 1A . Thus, by selecting the appropriate lengths and dimensions for the bag cells  100 , a retaining structure  300  having a desired sloping face can be easily constructed. 
     Although not depicted in  FIG. 3 , the bottom walls of the cells in the bags  200  can also be allowed to bulge slightly so that they tie into the bag  200  underneath. This feature provides additional strength and stability to the retaining structure  300 . In constructing the structure  300 , the bags  200  can be filled to different lengths. For example, the bags  200  may be collapsible like an accordion so that pulling (in the direction that the bag extends) on a plurality of folded-up cells will expose and open one cell. This cell can be filled and then the pulling continues to expose and open the next, adjacent cell for filling. If an entire bag  200  is not used when a desired wall length is reached, then the unused cells may be cut away. If, however, additional bags  200  are needed to achieve a desired length, then a bag can be attached to the last cell of a first bag and the pulling, opening, and filling steps continue with the second bag. 
       FIGS. 4A and 4B  show an alternative retaining structures erected using the bag of  FIG. 2A  in accordance with the principles of the present invention. The retaining structures  400  and  420  depicted in these figures illustrate the versatility of the bags  200 . In these structures, the substantially straight back wall is exposed and the slanted front wall is in contact with the retained material  402 ,  422 . The exposed façade  404 ,  424  can then be treated with ornamental, structural (e.g., shotcrete or gunite) or preservative materials as desired. 
       FIGS. 5 and 6  illustrate the versatility and ease of use of bags constructed in accordance with the principles of the present invention. The substantially straight back wall allows construction of free-standing structures such as structure  500  that can act, for example, as a levee. Thus, structure  500  can be constructed without relying on nearby earth or material on one side for its structural strength and integrity. A bag  502  can be filled and then a corresponding back-to-back bag  504  can be filled. These two bags provide a foundation for smaller bags  506  and  508 , which are filled to provide a foundation for even smaller bags  510  and  512 . Although the structure  500  in  FIG. 5  is depicted as symmetrical, the bags can vary in size so that the slope on one outward-facing side is different than the slope on the other outward-facing side. Top flaps  514  and  516  are shown that can be lowered once the bags  510  and  512  are filled. 
     Another alternative structure  600  is depicted in  FIG. 6 . Bags  602  and  604  can be filled and oriented so as to provide a flat outward face (although they could be flipped around as well). Then material  606  can fill in the area between the two bags  602 ,  604 . Sand, sand bags, concrete, etc. can all be used for the material  606 . On top of this base structure other bags can be placed such as bags  608  and  610 . Although not shown, additional bags can continue to be stacked to make a retaining structure of a desired height. 
     The previous description is provided to enable any person skilled in the art to practice the various embodiments described herein. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments. Thus, the claims are not intended to be limited to the embodiments shown herein, but are to be accorded the full scope consistent with each claim&#39;s language, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” All structural and functional equivalents to the elements of the various embodiments described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.”

Summary:
A bag for retaining structures, includes a plurality of cells aligned side-by-side in a continuous manner and configured to be filled with a filling material. Each cell of the bag includes a bottom wall, a first side wall, a second side wall, a back wall, and a front wall, the front wall being longer than the back wall. Furthermore, the first and second side walls each include a) a first corner located where the back wall connects with the bottom wall, said first corner being substantially 90 degrees; and b) a second corner located where a respective top edge of each side wall connects with the rear wall, said second corner being substantially 90 degrees.