Patent Publication Number: US-5525014-A

Title: Horizontally-yielding earth stabilizing structure

Description:
FIELD OF THE INVENTION 
     The present invention relates to earth stabilizing structures and more particularly to a structure having horizontal reinforcing members. The reinforcing members may be wire mesh panels or elongated strips made from metal or any non-extensible material. The reinforcing members may each consist of more than one segment. The reinforcing members are embedded within backfill material to stabilize the earth mass, and may or may not be connected to facing elements. In even greater particularity, the present invention discloses a novel connector for coupling the components of the earth stabilizing structure such that the structure is capable of yielding horizontally to extraordinary horizontal impact loads without failing. 
     BACKGROUND OF THE INVENTION 
     Earth retaining structures are known in the general construction industry for containing backfill or earthen material. These retaining structures prevent the movement of fill material. The structures are particularly useful for retaining earthen material exposed in the construction of roads, highways, interchanges and parking lots. The structures may have facing elements which may be cast-in-place concrete, precast panel masonry units, wood or metal. The facing elements are held in place by reinforcing members which are typically metal strips, welded wire fabric or other non-extensible material. The reinforcing members are connected to the facing elements and extend rearwardly into the fill material. In some applications, facing elements are not used, and an earthen mass is stabilized by use of reinforcing members only. The reinforcing members engage with the fill material by friction, by interlocking, or by a combination of both friction and interlocking with the earthen mass. Many such structures have been rendered unsafe for continued service or have failed because they could not yield horizontally to unexpected loads. A common problem causing such excessive loads is over-compaction of the soil during construction, which in turn subjects the facing elements and reinforcing members to horizontal pressures greater than those considered in the design. Horizontal impact loads are also caused by events such as earthquakes, explosions and vehicle accidents. Attempts have been made to handle these horizontal impact loads by increasing the number of reinforcing members, increasing the strength of the connections between the facing elements and the reinforcing members, and designing the structures to withstand loads well beyond those theoretically expected. Although there has been some success with this approach, it significantly increases the cost of constructing the structures. If a stabilized earth structure is able to yield horizontally without failing in the face of these imposed horizontal stresses, the system would then redistribute the stresses to the earth mass and return to a stable and serviceable condition. A structure that is able to yield horizontally is capable of safely withstanding unexpected horizontal impact loads. Hilfiker, in U.S. Pat. No. 4,343,572, disclosed the use of deformable sections incorporated into welded wire mesh reinforcing members to accommodate horizontal loads. The deformable sections comprise a &#34;zig-zag&#34; in the wires extending rearwardly from the facing elements. The Hilfiker invention has a number of disadvantages. First, it is operative only with welded wire mesh panels. Secondly, it is limited to relief at or near the facing element. Further, it does not afford flexibility in terms of planning for a specific design stress. 
     SUMMARY OF THE PRESENT INVENTION 
     With the foregoing in mind, the principal object of the present invention is to provide an improved connector for a stabilized earth structure that enables the structure to yield horizontally and accordingly to withstand excessive short term forces without failing. 
     Another object of the invention is to provide a connector for an earth stabilizing structure that is capable of use with any type of non-extensible reinforcing member. 
     Yet another object of the invention is to provide a connector for an earth stabilizing structure which may be used to account for anticipated specific excessive loads in design of the structure. 
     A further object of the invention is to provide a yielding connector for an earth stabilizing structure which may be used to relieve stress at any point along a reinforcing member. 
     A still further object of the invention is to provide a yielding connector for an earth stabilizing structure which may be used to relieve stress at any point adjacent to or within the facing elements of the structure. 
     Another object of the invention is to provide a connector for an earth stabilizing structure which may be used to relieve stress at the connection point between the facing element and a reinforcing member. 
     Another object of the invention is to provide a connector for an earth stabilizing structure which provides a means for accounting for excessive horizontal loads in a cost-effective manner. 
     These and other objects of the present invention are accomplished through the use of a connector comprising a slotted metal plate. The slot is shaped so that it has a larger transverse dimension at one end and narrows toward its opposite end. A bolt, pin or connecting arm having a cross-sectional dimension which allows for insertion into the widest end of the slot, but which provides resistance upon movement toward the opposite end of the slot, is inserted through the slot, providing a connection between the metal plate and another component of the earth stabilizing structure. As the bolt, pin or connecting arm is moved toward the narrow end of the slot, it engages the edges of the slot and provides full design strength by mechanical interference. As an additional load beyond the anticipated design load is imposed, the bolt, pin or connecting arm is forced toward the narrow end of the slot, deforming the edges of the slot as it moves. This movement dissipates the extraordinary horizontal load. After slipping, the connection remains in a condition of safe stress. The metal plate may be positioned at any point along a reinforcing member. It may also be positioned on a bracket which provides the connection point between a facing element and a reinforcing member. The plate may be either connected to or integrated within the bracket or reinforcing member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing objects and advantages of the present invention for a yielding connector for an earth stabilizing structure will be more readily understood by one skilled in the art by referring to the following detailed description of a preferred embodiment and to the accompanying drawings which form a part of this disclosure, and wherein: 
     FIG. 1 is a sectional view of an earth stabilizing structure. 
     FIG. 2 is a perspective view of the preferred embodiment of the connector. 
     FIG. 3 is a sectional view of the connector, showing the use of a bolt to connect the metal plate to another component of the earth stabilizing structure. 
     FIG. 4 is a top plan view of the metal plate of the present invention, showing a connecting bolt, pin or arm in its initial position within the slot. 
     FIG. 5 is a top plan view of the metal plate of the present invention, showing the connecting bolt, pin or arm deforming the edges of the slot after the connector has been subjected to an excessive horizontal impact load. 
     FIG. 6 is a sectional view showing a reinforcing member incorporating the metal plate of the present invention, connected to a facing element by a connecting arm. 
     FIG. 7 is a top plan view of the metal plate of the present invention, shown attached to the end of a reinforcing member comprising a wire mesh panel. 
     FIG. 8 is a sectional view of the present invention, showing the metal plate incorporated into the end of a reinforcing member positioned between facing elements and further showing a pin extending through the slot in the metal plate and into the adjacent facing elements to form a connection. 
     FIG. 9 is a sectional view of the present invention, showing the metal plate incorporated into the end of a reinforcing member extending through a facing element, and further showing a pin extending through the slot in the metal plate and along a surface of the facing element to form a connection. 
     FIG. 10 is a sectional view of the present invention, showing two slotted metal plates fastened together with a bolt to form a yielding connection. 
     FIG. 11 is a sectional view of the present invention, showing the metal plate incorporated within segments of a reinforcing member. 
     FIG. 12 is a sectional view of an oversteepened slope without facing elements, showing placement of the metal plate of the present invention on the reinforcing members along a potential failure plane. The dotted line represents the potential failure plane, and the circles represent the position of the yielding connector. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings for a clearer understanding of the invention, FIG. 1 shows an earth stabilizing structure. On the front of the structure is an earth retaining wall 11, formed by a plurality of facing elements 12. Behind the wall 11 is a mass of particulate backfill material 13, which is stabilized by a plurality of horizontal reinforcing members 14 extending rearwardly from the facing elements 12 and embedded in the backfill 13. 
     The connector of the present invention may be used at any point along a horizontal reinforcing member, or at the juncture between a reinforcing member and a facing element. As shown in FIG. 2, it comprises a slotted metal plate 15. The slot is specially shaped to allow the connection to hold at a given design strength, but to yield when subjected to an excessive impact load. In the preferred embodiment, the slot is keyhole-shaped, although the invention would be operative with a slot of any shape that narrows in width from one end to the other. The slot has an initial end 16 and a terminal end 17. The end of the metal plate nearest the initial end of the slot is its juncture end 18, and the end of the metal plate opposite the juncture end is its free end 19. The transverse dimension of the initial end 16 of the slot is greater than the transverse dimension of the terminal end 17. The connector is used with a connecting bolt having a cross-sectional dimension which permits it to be inserted through the initial end of the slot, but which is larger than the transverse dimension of the terminal end of the slot, such that as it moves toward the terminal end of the slot, the bolt engages the side edges 21 of the slot. A connecting pin, rod or arm may alternatively be used in place of the bolt to form the connection. The thickness of the metal plate and the strength of the metal from which it is made determine the resistance provided by the plate. The resistance must be sufficient to hold the bolt at the initial area of engagement with the side edges of the slot, without slipping, at a specific anticipated design load. Both the thickness and strength of the plate may be varied to suit the requirements of a particular job. When the earth stabilizing structure is subjected to an extraordinary horizontal impact load, such as that caused by an earthquake or explosion, the bolt is forced toward the terminal end of the slot, deforming the edges of the slot as it moves. 
     The plate 15 may be welded to the reinforcing member 14, as shown in FIG. 2, or it may be integral with the reinforcing member as shown in FIG. 3. The plate may also be positioned on a bracket extending from, around or through a facing element. 
     FIG. 3 illustrates the use of a bolt 22 to join a reinforcing member 14 incorporating the metal plate 15 of the present invention to a bracket 23 extending from a facing element 12. As shown in FIG. 6, a bracket may be designed to have a laterally extending arm 24 so that the use of a connecting bolt is unneccessary. Likewise, if the slotted plate is attached to or incorporated within the connecting bracket, a reinforcing member with a laterally extending arm may be connected to the bracket without the need for a connecting bolt or pin. 
     FIG. 7 illustrates the metal plate 15 of the present invention connected to a wire mesh panel reinforcing member 14. The plate could alternatively be attached at an end of each of the wires extending rearwardly from the facing element, rather than being positioned between two of the wires as shown in the drawing. In FIG. 8, the end of a reinforcing member 14 incorporating the metal plate 15 of the present invention is shown extending between two vertically adjacent facing elements 12. A pin 26 extends outwardly from the peripheral surface 27 of one of the facing elements 12, through the initial end 16 of the slot in the metal plate 15 and into the peripheral surface 27 of the adjoining facing element 12. FIG. 9 illustrates another means of connecting reinforcing members to a facing element using the present invention. The metal plate 15 is positioned near the end of the reinforcing member 14. The reinforcing member 14 extends through the facing element 12 so that the metal plate 15 extends from the front surface 28 of the facing element 12. A connecting pin 29 is positioned parallel to and adjacent the front surface 28 of the facing element 12 and extends through the initial end 16 of the slot in the metal plate 15. 
     In FIG. 10, the slotted metal plate 15 of the present invention is shown connected by a bolt 22 to another slotted metal plate 15. The bolt 22 extends through the initial ends 16 of the slots in each of the plates 15. This arrangement may be used to join segments of a reinforcing member, or at the juncture between a facing element and a reinforcing member. Forming a connection in this manner increases the distance that the connection will yield when subjected to an excessive impact load. 
     The total distance that the structure will yield horizontally may also be increased by increasing the number of yielding connections. FIG. 11 illustrates the use of the connector at several points along a reinforcing member. As shown, each segment 31 of the reinforcing member 14 has the metal plate 15 of the present invention positioned at one end. 
     In some cases, a stabilized earth structure is constructed without the use of facing elements. In the case of an oversteepened slope, as shown in FIG. 12, the structure is stabilized by embedding horizontal reinforcing members 14 in layers in the fill material 13 of the structure. In such a structure, there is at least one potential failure plane along which the structure may fail if subjected to an excessive load. The connector of the present invention may be positioned at points on the reinforcing members along the potential failure plane, providing the structure with the ability to yield along the failure plane. The ability of the reinforcing members to extend horizontally will increase the impact load that the oversteepened slope may tolerate without failing. 
     While I have shown my invention in several forms, it will be obvious to those skilled in the art that it is not so limited but is susceptible of various changes and modifications without departing from the spirit thereof.