Hydraulic and earth engineering – Earth treatment or control – Shoring – bracing – or cave-in prevention
Reexamination Certificate
2003-05-16
2004-12-07
Pezzuto, Robert E. (Department: 3671)
Hydraulic and earth engineering
Earth treatment or control
Shoring, bracing, or cave-in prevention
C405S262000, C405S286000, C052S605000
Reexamination Certificate
active
06827527
ABSTRACT:
TECHNICAL FIELD
The present invention, as illustrated by its many embodiments, relates primarily to a geosynthetic-reinforced segmental retaining wall (SRW). The components of a wall illustrated herein include a geosynthetic reinforcement loaded at one end and in contact with a locking bar at an opposite end. The locking bar and a section of the geosynthetic reinforcement are then captured between lower and upper segmental units. Such a wall is able to realize the long-term design strength of the geosynthetic reinforcement because the locking bar rotates to engage and hold the entire width of the geosynthetic reinforcement to an interior surface of the segmental units which comprise the wall.
BACKGROUND OF THE INVENTION
The building construction and land development industry requires retaining walls to stabilize substantially vertical sections of earth. Retaining walls can be constructed on-site with poured-in-place concrete or assembled on-site with various segmental units. One type of assembled wall is constructed with pre-manufactured blocks stacked to form an exposed wall face. In practice, a connector is typically located between vertical courses of stacked block and is integral with a solid anchor embedded in the backfill—the tamped earth immediately adjacent to the stacked blocks. The anchor and connector effectively unify the backfill and stacked blocks to create the retaining wall. U.S. Pat. No. 5,921,715 is representative of traditional anchors and connectors.
Recently, improved reinforced-earth systems have emerged as low cost alternatives to the above wall assemblies. In these improved systems the soil is reinforced with geosynthetics; materials made typically from high-tenacity polyester, polypropylene, and high-density polyethylene. Polyester and polypropylene geosynthetics are usually woven into a relatively flexible and dimensionally stable grid or textile matrix. They are referred to as “geogrids” and “geotextiles”, respectively. Polypropylene and high-density polyethylene are also used to manufacture relatively stiff geogrids using an extrusion-based process. As will be understood by those skilled in the art, geosynthetic reinforcements may be “stiff” or may be “flexible.”
The designer of a geosynthetic-reinforced earth retaining wall must consider the strength of the connection—the point at which forces exerted on the segmental unit are transferred to the geosynthetic reinforcement. An objective of the designer is to minimize the relative displacement between the geosynthetic reinforcement and the segmental units. By minimizing the relative displacement, the possibility of bulging, leaning, and other types of undesirable wall movement is reduced. The relative displacement can be reduced by a connection between the unit and reinforcement. Forces which tend to create the displacement include those exerted by soil at the back of the units and those which develop in the plane of the geosynthetic reinforcement. If the forces at the back of the unit can be transferred to the geosynthetic via a connection, the total relative displacement between the unit and geosynthetic can be significantly reduced. Therefore, the strength of the connection between the unit and geosynthetic govern the magnitude of the reduction in relative displacement. Using prevalent standard practice, the relative displacement is reduced to acceptable levels when the peak strength at the connection of the geosynthetic reinforcement and segmental retaining wall unit exceeds the horizontal stress applied to the back of the segmental unit.
If it is not possible with a given type of unit and geosynthetic to develop a connection strength which exceeds the horizontal stress, then the magnitude of the horizontal stress must be reduced. This reduction can be accomplished by decreasing the vertical space between layers of geosynthetic reinforcement. However, a decrease in distance between layers of reinforcement equates to more layers of reinforcement, and results in higher reinforcement costs.
Another objective of the designer is to limit tensile stresses in the plane of the geosynthetic reinforcement to levels below the material's long-term design strength (LTDS). The magnitude of these stresses are a function of geosynthetic reinforcement spacing, soil strength, wall height, and load conditions at the top of the wall. A reinforcement design which is optimal with respect to geosynthetic costs is one in which the LTDS of the geosynthetic exceeds the calculated stresses in the geosynthetic by an amount deemed to provide an adequate factor to safety against tensile rupture.
Thus, the design of the geosynthetic reinforcement for a segmental retaining wall system is primarily controlled by two factors: 1) the peak connection strength between the segmental units and the geosynthetic reinforcement; and 2) the LTDS of the geosynthetic reinforcement. If the peak connection strength is less than the LTDS of the geosynthetic, the connection strength is said to control the reinforcement design. If the peak connection strength is greater than the LTDS of the geosynthetic, the geosynthetic strength is said to control the reinforcement design.
For most combinations of segmental retaining wall units and geosynthetic reinforcement available in today's market, peak connection strength controls the reinforcement design for wall heights in excess of 10 to 15 feet. This limitation exists because the walls rely on one of two mechanisms, or a combination of both, to connect geosynthetic reinforcement to segmental units: 1) friction between the reinforcement and the segmental units; and 2) a dowel which is inserted into the lower and upper segmental units.
For frictional systems, the strength of the connection depends on the coefficient of friction between the geosynthetic and the segmental unit and the normal load applied at the frictional interface. At low to medium normal loads, failure of the connection usually occurs because the reinforcement slips between the segmental units. At high loads, the geosynthetic is often damaged and weakened as slips between the segmental units, and it may fail and rupture.
For dowel-based systems, the dowel passes through an aperture in geogrid reinforcement or between yarns in a geotextile reinforcement. Connection failure of flexible geogrids in dowel systems typically occurs when traverse geogrid members displace or rupture as they pull against the dowel. Similarly, connection failure of geotextiles in dowel systems typically occurs when yarns tear or displace as they pull against the dowel.
To compensate for the relatively inefficient connection of most geosynthetic reinforcement-segmental unit combinations, relatively frequent spacing of geosynthetic reinforcement is required. Because a relatively large amount of geosynthetic material is involved, these combinations can be inefficient with respect to cost. An optimized design is one in which the peak connection strength exceeds the LTDS required of the geosynthetic reinforcement.
It is known to provide a reinforced-earth retaining wall assembled from stacked blocks, which includes a connector bar positioned between vertical courses of block. The connector bar comprises a base and a series of spaced keys that project vertically. The connector bar is positioned in a channel of a lower block, and a geogrid is laid over the bar so as to hook a transverse member around each key. The geogrid is then extended laterally from the connector into the adjacent backfill. An upper block is then stacked over the connector bar to complete the connector assembly.
It is also known to construct a reinforced-earth retaining wall by providing a geosynthetic reinforcement wrapped around a solid body anchor located within a segmental unit. For example, a trough receives an anchor wrapped in a geotextile wherein the trough is then loaded with backfill. Alternatively, the trough may receive an anchor wrapped in a geotextile wherein the anchor is then mechanically fastened to the trough before the trough is loaded with backfill.
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Conkel James E.
Valentine Richard J.
Kilpatrick & Stockton LLP
Pechhold Alexandra K.
Pezzuto Robert E.
The New Castle Group, Inc.
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