The invention relates to mechanically stabilized earthen wall constructions, in particular, to reinforced retaining walls comprising precast facing elements connected by suitable connectors to reinforcing elements which extend into reinforced soil.
Of the four basic classes of retaining walls, i.e., gravity, cantilever, anchored and mechanically stabilized backfill, the present invention relates primarily to the first and the latter two, although elements of all are included in the improved wall system according to the invention.
By way of background, gravity walls depend upon the weight of the wall itself to prevent overturning and sliding of the wall. A cantilever wall is reinforced in order to resist applied moments and shear forces. Anchored walls resist lateral forces through the use of tieback anchors or soil nails. And mechanically stabilized backfill includes reinforcement members extending backwardly from the front face of the wall into the retained embankment soil to form a coherent mass. Enhanced reinforcement is attained, at least in part, by increased frictional shear resistance and passive resistance which occurs between the soil in the embankment and the reinforcing members. Conventional reinforcing members can be in the form of strips, grids, sheets, rods or fibers which increase the resistance of the soil to tensile forces far beyond those which the soil alone is able to withstand.
Both metallic (steel) and nonmetallic, polymeric (geotextile, geogrid) materials have been used for reinforcement purposes. By definition herein, metallic reinforcements such as steel will be termed "inextensible" or "rigid" materials and nonmetallics such as geogrids and geotextiles will be termed "extensible" or "flexible" materials, owing to their disparate elastic moduli and creep resistance properties, and to be more or less consistent with similar usage in prior literature in this art.
A mechanically stabilized backfill wall system generally comprises four essential components: (1) facing elements; (2) the connection or connectors connecting the facing elements and the reinforcing elements; (3) the reinforcing elements themselves; and (4) the reinforced soil, all of which comprise the reinforced retaining wall system. The facing elements may be precast, modular concrete blocks. The front face of such blocks may be covered with a decorative material, such as slate or the like, which is generally employed solely for aesthetic purposes.
Use of strip or rod reinforcements creates a mechanically stabilized backfill by placing such reinforcements in horizontal planes between successive lifts of soil backfill. Grid reinforcement systems are formed by placing metal or polymeric grid elements in horizontal planes vertically spaced apart in the soil backfill. An example of such a polymeric grid reinforcement is Tensar Geogrid, commercially available from the Tensar Corporation.
Reinforced retaining walls have many uses, particularly in the road building industry wherein these constructions are used to retain embankments and as roadway supports. Further uses of such walls include sea walls, bridge abutments and other, similar configurations.
Several prior retaining wall systems are known. For example, U.S. Pat. No. 4,961,673 discloses a retaining wall construction comprised of a first portion which includes compacted granular fill defining a three dimensional earthenwork bulk form which includes a plurality of tensile members dispersed within the bulk form to enhance the coherency of the mass. The tensile members project from the bulk form and are connected to a second component portion which defines a face construction. The face construction is comprised of a plurality of facing panels connected to tensile members with concrete layers enveloping the connection between the facing panels and the tensile members. See also the references cited in the '673 patent, which disclose many and varied embodiments of reinforced retaining wall systems. A recently issued U.S. patent, U.S. Pat. No. 5,586,841, discloses a modular block wall which includes dry cast, unreinforced modular wall blocks with anchor type, frictional type or composite type soil stabilizing elements recessed therein and attached thereto by vertical rods which also connect the blocks together. The soil stabilizing elements are positioned in counterbores or slots in the blocks and project into the compacted soil behind the courses of modular wall blocks. The many and varied connector means disclosed in that patent, all of which are unrelated to the connectors of the present invention, provide indications of the current state of this art in the retaining wall field.
Mechanically stabilized backfill systems have many advantages over other types of systems including relatively easy and rapid construction, stability of the wall during construction, regardless of height or length, relative flexibility with respect to lateral deformation and differential vertical settlements, and, importantly, economic advantages. Disadvantages may include corrosion of metallic reinforcements (which may be minimized by galvanizing or resin coatings), excessive creep in the case of polymeric reinforcements and the depth and expanse of excavation needed in certain instances.
Objects and advantages of the present retaining wall system are many and varied. The present wall can be constructed as a gravity wall or with reinforced, retaining soil. The retained soil can be reinforced with a specific, designed, combination of reinforcements, all employed in a single wall construction, such as a combination of soil nails or soil anchors, geosynthetic sheets and metallic grids, all designed and specified to produce a safe and economical structure.
According to the invention, the facia may be used as a constructive component, which can transfer loads into the foundation soil without affecting the wall performance, that is, the facia can serve as a foundation to superstructures.
Modular units of the invention may be constructed from a lower foundation level up to a certain designated height employing reinforced backfill, above which height the wall can be constructed as a conventional gravity wall, thus allowing increased construction flexibility, for example permitting unrestricted excavation of the retained soil near the crest of the wall to install utilities, etc.
The connections according to the invention between the reinforcement members and the facing blocks are massive and exceedingly strong, allowing the use of very high strength reinforcements and enabling stable wall construction extending vertically to extreme heights, e.g., 20 meters or more, higher than heretofore achievable. Both rigid walls, allowing for small horizontal displacement of the retained soil, and flexible walls, allowing for appreciable horizontal wall displacements, are possible, providing flexibility in design and allowing for versatility in design options, all while enabling the design of economically attractive high and low walls, optionally having curved facades and corners, and all possessing aesthetically pleasing appearances.
The objects, advantages and specific features of the invention are set forth in detail in the detailed description hereinbelow.