BACKGROUND OF THE INVENTION
Various methods have been used to construct precast walls for retaining earth, soil, sand or other fill (generally referred to as soil). A typical precast wall system is disclosed in U.S. Pat. No. 4,914,876, assigned to the Keystone Retaining Wall System, Inc. by Paul J. Forsberg. The Keystone Patent illustrates a typical modular block wall system wherein the wall face is comprised of concrete masonry units connected to geosynthetic wall reinforcement layers. The geosynthetic tensile inclusion members for this type of retaining wall structure are typically referred to as “geogrids.”
A disadvantage of such a system is that a considerable amount of hand labor is required to install the numerous small block facing units of the block wall system. This requirement limits the amount of wall structure that can be completed in any work shift. In addition, if the wall is placed on weak foundation soils, a manifestation of wall settlement is cracking or more significant crushing or crumbling of the facing units. If wall settlement is excessive, the geogrid material can be sheared where it connects to the concrete masonry unit horizontal joints, which can result in wall failure.
Numerous other types of concrete block mechanically stabilized earth wall systems are available. These systems, like the Keystone System previously described, mandate precise grading and compacting of the wall backfill to correspond to increments of the vertical height of the block facing units so that the tensile inclusion materials used to mechanically reinforce the retained wall backfill material can be placed at the horizontal joint elevations of the concrete masonry units. Although the material costs for these types of wall systems are low, the high labor costs for the various stages of wall construction can result in installed price of walls that are substantially higher than the material costs.
Other mechanically stabilized earth walls include walls that use precast concrete panels for the wall facing elements, such as walls disclosed in U.S. Pat. No. 4,961,673, issued to Pagano et al., and U.S. Pat. Nos. 3,421,326; 3,686,873; and 4,116,010 to Vidal. Such wall systems require the use of metal reinforcing strips or steel grids as soil inclusion members in the wall backfill. Those members are connected to the precast wall panels to hold the panels in place and to provide stability for the wall backfill.
A disadvantage of walls that use non-corrosion resistant metal soil reinforcement is that the metal soil tensile inclusion members are subject to corrosion, because the metal is in direct contact with the wall backfill. Numerous catastrophic failures have resulted from the effects of unchecked corrosion on the metal tensile inclusion members for these wall systems. Although soil inclusion members (e.g., metal strips or steel grids) can be galvanized to resist the corrosive effects of the oxidation process, this technique is not effective for all soil types due to the diverse mineral content present in some soils. Other methods, such as epoxy coating of the metal soil inclusion members, have been used to further resist the deleterious effects of potential chemical reactions of the soil minerals with the soil inclusion members. A disadvantage of the epoxy coating, however, is that the coating is easily scratched during the construction, which results in the exposure of the metal soil reinforcement to the corrosive effects of minerals present in the backfill. Also, epoxy coatings increase the costs of these systems.
Another factor that increases the likelihood of premature failure of MSE walls that use steel soil reinforcement is the reduced sliding friction of the soil reinforcing material at the onset of the effects of corrosion. Because corrosion commences from the outside surface of the reinforcing material, the corrosive residue becomes the material that is in contact with the soil following the commencement of corrosion. The interface of the corrosion layer with the steel soil tensile reinforcement member is therefore the weak link. The remaining competent steel material may move with respect to the corrosion layer. Movement between the soil fill and the soil reinforcement may also occur. The ultimate result of this relative movement could be premature wall failure.
Typical wall facing units for existing MSE systems in current use may range in size from 8″×16″ for block systems to 25 to 50 sq. ft. for precast panel wall systems. The concrete masonry block systems, due to the high unit weight and relatively small size of each block, do not require bracing or interlocking to hold the face units in a vertical position as the wall backfill is placed. Since the blocks are heavy (exceeding 100 pounds for some applications), the placement of the blocks is physically demanding, which adds to the placement cost of the facing units. MSE wall systems that use panels for wall facing are large in size compared to the block facing units, and the panels (typically between 25 to 80 sq. ft. in area) are held in place during backfilling operations by interlocking with previously placed or adjacent panels. For some systems, the facing units are “wedged” or leaned by other methods so that the effect of the interaction of the backfill pressure and the metal soil reinforcement will, in theory, force the panels into a plumb or vertical position. Panel placement for these systems requires experienced workers to erect the units so that the resultant structure will be vertical and not leaning either in or out of a vertical plane.
Another broad range of MSE wall types that have been used extensively for permanent and temporary retaining wall applications are wrapped face, or confined fill layers, that form a geotextile MSE wall. These walls are comprised of an assembly of vertically stacked layers of wall backfill confined by closed face sheets of geotextile that are typically placed in horizontal planes within the wall backfill as the backfill is placed and compacted. For temporary walls, the face of these walls is the exposed geotextile material. The geotextile material that retains the fill at the face of each layer is wrapped back into the fill behind the face of the wall. The wrapped back geotextile is imbedded into the backfill material behind the face of the wall for each compaction lift of fill that is placed. One of the difficulties associated with the construction of these types of earth retention structures is that the wrapped back face portion of each backfill layer requires that an external forming system be installed in front of the face of the wall to hold the geotextile face at the proper alignment until the wrap back portion of the geotextile layer is sufficiently imbedded in the backfill adjacent to the wall face. The associated fill pressure prevents the wrap back geotextile from being displaced horizontally. The cost of labor associated with the placement and operation of the external forming system adds to the cost of these types of walls.
Whether the geotextile wall is a temporary or permanent structure, a face forming grid is required during wall construction so that the resultant overall wall face will conform to the wall alignment limits. For permanent geotextile walls, it is necessary to cover the exposed wall face so that the geotextile will be protected from the deleterious effects of prolonged exposure to ultraviolet radiation. Although the geotextile material is corrosion-resistant with respect to the soils and minerals that the material may come into contact with due to the embedment in the wall backfill, the long-term effects of exposure to the sun can result in the ultimate deterioration of the wall face. There are various facing materials that have been used to cover the face of geotextile walls. The facing materials include, for example, sprayed concrete faces, precast or cast-in-place concrete panels. The use of a sprayed concrete faces requires that attachment fasteners, such as lengths of wire or pieces of rebar, be installed in the wall and protrude from the face of the wall to form a connection between the sprayed on concrete and the exposed geotextile surface. The disadvantage of walls with this type of face is that the wall surface is typically not uniform and not aesthetically pleasing. Additionally, if the walls experience any significant long-term settlement, cracking and spalling of the sprayed concrete face can occur.
Precast facing elements have also been attached to wrapped face geotextile walls by the use of long bolts or thread bar anchors that are screwed into the geotextile earth retention structure. Although these methods are adequate to provide U.V. protection, corrosion of the bolts or metal anchors can reduce the life of the wall. The precast facing is also rarely attached accurately, so the resultant wall face may not be uniform in appearance.
Another wall face that has been used for geotextile walls is the option of casting a poured-in-place concrete face over the geotextile textile wall. This approach can result in a uniform aesthetic face, but it does require extensive forming and the associated high field labor and material costs. These additional costs can make walls of this type less competitive than other conventional wall types.
For wall locations where the retaining wall structure is located at the base of a hill or at the toe of an embankment, the cut or excavation required for the base of the wall may make the use of an MSE wall of any type impractical. Depending on the existing slope angle at the proposed wall site and in situ material of the sloping embankment, the excavation limits from the back of the cut may also be very large or require shoring in lieu of excavating massive amounts of material. For applications such as these, cast in place or tied back type retaining walls may be the current choice even though the cost of these walls exceeds the cost of typical MSE wall components.
Cast-in-place, cantilever walls for these applications typically have an extended footing in front of the wall and a shear key. The cost of the shear key and the extension of the footing in front of the wall to offset the lack of the footing behind the wall (under the wall fill) results in a substantially more costly wall than would be the case for a standard configuration cast-in-place wall. By the same token, if a tied back or other top down type of wall is selected for the cut wall site (e.g., due to the high cost of wall excavation), the end result will be a wall with a much higher unit cost than for a typical MSE or cast in place wall.
Another type of cast in place vertical cantilever wall application is for those walls along a channel or for bulkheads to act as erosion control structures along waterways or at the shore of other bodies of water. For channel applications where a vertical wall is required, if the area or right of way behind the proposed wall alignment is at a minimum, a front extension of the wall footing is required at the base of the wall. This situation, as for the previously described wall conditions, adds to the cost of the structure.
Another method that has been used extensively for cantilever wall applications is the double tee wall system that was developed by Colorado Dept. of Transportation in the 1980's. For that design, double tee wall panels are placed on massive cast in place foundations to form a cantilever wall. The mechanism that is used to resist the overturning moments induced on the wall by the fill pressures is the extensive use of post tensioning rods. The rods are typically inserted through the tee stems of the double tee wall panels in the field and threaded into couplers cast into the wall foundation. To achieve the required accuracy for the placement of the couplers in the footing mandates, the use of special forming and highly skilled field personnel is required. Also, the installation of the post tensioning typically requires the use of special contractors in the field. As with the previous systems, should there be a void or incorrect application of grout at the connection point of the wall reinforcement the wall panel connection is subject to corrosion and premature failure.
An additional precast wall system that simulates a conventional cast-in-place cantilever wall is disclosed in U.S. Pat. No. 4,572,711, issued on Feb. 19, 1986 issued to Benson et al. This system requires the use of a precast double tee attached to either a precast or cast-in-place flat footing slab. The implementation of this design has similar shortcomings as those stated for the CDOT tee wall system previously described. Since the footing shown for that post tensioned combination is a flat slab, the size and thickness of the footing is required to be massive, similar to the CDOT cast-in-place footing. Also, the installation of the post tensioning requires specialty contractors.
In addition to the shortcomings stated for the above-mentioned systems, all of these products, with the exception of the Benson patent, require special forms for the production of the wall panels.
There are currently numerous methods available to increase the stability of earthen embankments or to construct retaining walls. Retaining walls are generally constructed by excavating soil or rock at the desired location. Once the soil mass is excavated, the remaining soil mass is typically stabilized to prevent movement of that mass. Slope stability can be increased using soil nails. For example, a slope can be stabilized by drilling holes into an existing embankment, placing steel rods in those holes and then filling the holes with cementations grouts. By concurrently placing the steel rods and cement into an existing embankment, slope stability can be improved so that excavation can be completed in front of that stabilized embankment (i.e. in the plane perpendicular to the orientation of rods placed into the embankment), without risk of the embankment collapsing on the construction site. In another example, rods can also be placed into generally horizontally oriented shafts drilled into existing embankments. Following insertion of the rods into the shafts, concrete or high strength grout is injected into the shafts. The concrete or grout bonds the rods to the shaft, which results in a reinforced structural column within the soil mass of the embankment. There are currently many products that can be used to construct such ground anchored and or soil nailed structures.
Anchored structures can also be used to increase soil stability in situ. Anchored structures are tensioned or loaded so that the load is placed on the face of the in situ soil mass. This face load, which is induced by anchor tensioning, holds the face of the anchors and the in situ material at a predetermined position. In contrast, soil nails are typically not loaded or tensioned when they are installed, but become loaded as the earth in front of the soil nailed structure is removed. A minor amount of movement of a soil nail in situ embankment is typically assumed in design. Movement of the embankment is a manifestation of the stabilizing effect of the soil nails replacing the buttressing effect of the existing in situ material in front of the soil nailed structure.
Soil nails and anchors are prone to corrosion failures. For example, if the steel rods or steel strands are used as nails or anchors, they can corrode through contact with moisture and the soil. To minimize the effects of corrosion, products have been developed to protect metal rods or strands from corrosion. For example, the “Double Corrosion System” offered by the Dywidag-Systems International uses PVC pre-grouted sheathing over metal rods to provide a water tight barrier. Florida Wire and Cable, Inc., offers plastic sheaths over a flexible steel strand for use along soil anchors. Dywidag-Systems International also offers a “Dywidur” bar, which is a non-deformed fiberglass bar bolt. Such a bolt is suitable for use in highly corrosive soil, because it is resistant to corrosion. This bolt does not have significant deformation, so its use is limited in standard grout injection to providing a better bond to the drilled shaft. These products can be effective if installed properly and can offer extended life for the anchored structure.
For anchored structures, corrosion protection is a major consideration. Because metal bars used in such structures are anchored, they are more prone to break under that tension. Therefore, metal bars used in such applications typically have double or triple corrosion requirements to ensure against failure of the anchored slope. Additional corrosion protection adds to the cost of currently available soil reinforcement for anchored slope stability projects.
These and other corrosion-resistant products require proper installation to prevent damage to the corrosion-resistant coating material. The sites for such installations are generally uneven (e.g., mountainous or hilly), which requires heavy equipment. Such installation conditions increase the likelihood that damage might occur to the corrosion-resistant coating material. Because corrosion reduces the service length and load capacity of metal rods or cables, corrosion is a significant problem which limits the useful life of soil nailed or anchored structures.
Another typical application where ground anchors, tie backs or soil nail earth retention structures are used is for the support of temporary site excavations for construction of buildings and other structures. For some locations, such as urban areas, it can be desirable to have the ability to remove or cut through the stabilized earthen wall utilizing tie back ground anchors or soil nails. Future utility placement or maintenance in the streets or other right-of-way areas behind the shoring may necessitate either the removal of or the cutting of trenches through the in situ reinforcement used as shoring. Currently the use of steel materials dominates the types of shoring used. Due to the high shear strength of steel tendons, steel rods, or steel threadbars cutting through the material is both costly and time consuming, resulting in expensive improvements in right-of-way areas behind excavation sites shoring.
In view of these shortcomings of currently available devices for soil nailed or anchored structures, there is a need for soil nails and anchors that provide strength comparable to existing materials while providing improved resistance to corrosion and can be removed or cut if necessary. There is also a need for an economical MSE wall facing that utilizes corrosion resistant tensile inclusion members. There is an additional need for corrosion resistant tensionable rods that can be used to attach other precast concrete wall components to form retaining walls.
SUMMARY OF THE INVENTION
The present invention provides devices to utilize corrosion-resistant, synthetic deformed bar (“SDB”) for use in soil stabilization structures, such as soil nailed or anchored structures, soil tensile inclusion members, or as tensionable tie or as connecting rods. As used herein, the term “bar” refers to a generally elongated synthetic structure which is a generally circular, ellipsoid, square, rectangular, polygonal or other regular or irregular cross section. A typical bar is composed of a synthetic, non-corrosive material, such as a resin. Suitable non-corrosive synthetic resins will include polyester, vinyl ester, epoxy and epoxy derivatives, urethane-modified vinyl ester, polyethylene terephthalate, recycled polyethylene terephthalate, and the like. Suitable resins can also include combination of any of these resins. The synthetic resin can be a complete fiber material, such as a combination of a synthetic resin and a fiber reinforcement. Suitable fiber reinforcements will include E-glass, S-glass, aramide fiber (e.g., Kevlar™), carbon fiber, ceramic reinforcement and the like and combinations of any of these. Suitable fiber composite materials are, for example PSI Fiberbar (Polystructures, Inc., Arkansas) or C-Bar (Marshall Industries). In some applications, the bar can be coated with a corrosion or moisture resistant material.
The SDBs described in the present invention typically have adequate deformations for bonding to cementations grout (hereafter referred to as grout). As used herein, deformations can be corrugations, dimples, protrusions, and the like, on the circumference of the bar. Such deformations provide a larger surface for bonding of the bar surface to cement, concrete, grout or the like (hereafter generally referred to as “grout”). Such increased bonding area allows a stronger bond to be formed between the bar and the grout, thereby taking advantage of the load capacity of the bar. The deformations on the surface of the bar can optionally form a continuous repeating pattern on the surface of the bar. In such an embodiment, the deformation can have a generally relatively consistent spacing and depth (or height) from the bar's surface to provide a predictable field bonding characteristic. The deformations in the SDB also facilitate the connection of attachment devices, such as couplers to join SDB's to achieve longer length SDB's, as may be required for in situ soil reinforcement. The SDB can also have a flared end or a threaded end.
Heretofore SDBs have been used extensively in lieu of standard steel reinforcement (rebar) for both cast in place and precast concrete structures. Prior to the use of SDBs, epoxy coated rebars were another conventional option that could be used for concrete structures placed within a corrosive environment such as for offshore structures. SDBs with an indefinite service life offer many advantages compared to both coated and uncoated steel rebar when used for concrete reinforcement for these types of applications.
Attachment devices are provided to attach the bars to other structural components, which allows the load capacity of the bar to be transmitted to those other components. Attachment devices can be connected to a bar in a variety of ways. An attachment device or coupler can be connected to the bars during manufacture or at the construction site. A bonding agent is used to bond an attachment device to the SDB.
An attachment device can be used to provide a means to transmit in situ earth loads at the face (“face load”) of the retained earthen structure to the in situ soil mass when the bars are used as ground anchors, soil nails or as tie backs. The tensile strength of the bars is then utilized to transfer the face load to the stable portion of the in situ soil mass. The length of the SDB is determined according to the soil anchor design to ensure that soil stability is enhanced. The length is also determined to ensure that the face load can be adequately carried by the SDB and the grout to the in situ soil mass. For some applications, anchor plates, rods or similar devices can be attached to the end of the SDB within the in situ soil mass to increase the loading capacity of the SDB. Attachment devices can also be attached to the portion of the SDB protruding from the face of the soil mass.
Attachment devices on the face or protruding end of the SDB may be composed of a corrosion-resistant material that has adequate tensile strength to transmit any face loading to the in situ portion of the SDB. Such an attachment device can be a corrosion resistant metal, such as, for example, stainless steel, a similarly alloyed steel, a high strength aluminum, or the like. The attachment device can also be formed of a synthetic or conventional material, such as those disclosed above for the bar or can be formed of steel or numerous other steel or similar metal alloys. The preferred synthetic material will have a comparable tensile strength to the material of the SDB.
For soil nailed, ground anchored, or tied back applications utilizing SDBs, a wall can be constructed by excavating a face on the soil mass. Such a face can be substantially vertical or can be at a lesser angle. Following initial face excavation, an exposed cut will exist. The SDBs are typically inserted into shafts placed in the in situ material per the site design. Grout is then injected into the shafts to secure the SDBs. The grout can be inserted according to conventional methods. Attachment devices are then attached to the exposed SDB ends. Alternatively, SDBs having previously bonded or otherwise connected, attachment devices can be placed in the shafts so that the attachment devices protrude from the face of the soil mass. Face reinforcement is then placed onto the exposed in situ soil face and attached to the exposed SDB bar ends or to the attachment devices on the bar ends. An encapsulation, such as field concrete, is then optionally applied over the face reinforcement. Specific designs may require face drainage materials and “shot crete” layers at various phases of construction.
Soil anchor applications have similar construction phases as those of nailed structures except that the nail or anchor soil reinforcements are required to be tensioned after installation. Anchored applications typically require the use of threaded attachment devices to facilitate face tensioning with conventional jacking equipment. These attachment devices are connected as previously described. Tension can be applied to the bars at various phases of the excavation, according to the specific design criteria.
For other “fill” retaining wall applications thin face wall panels attached to either SDB's as described in U.S. patent application Ser. No. 10/047,080 filed on Jan. 14, 2002 or by utilizing wire grid array mats are provided. Such walls can include for example an assembly of thin wall face panels that, with slight modifications to fit the wire grid array mats, are currently used for flat roof ballast paver applications. The grid pattern of the wires used for the wire grid array mats can be also manufactured to closely conform to the dimensions of precast ballast pavers as described by U.S. Pat. No. 4,899,514 dated Feb. 13, 1990 and by U.S. Pat. No. 5,490,360 dated Feb. 13, 1996 or the grids can alternatively match the dimensions of other thin wall face panels. In addition the wire grid array mat sections can be pre-bent to conform to various wall facing geometries. Although wire grid array mats are typically available utilizing standard steel for the wire grids for the retaining wall configurations described for the present invention, it is preferred, although not required, to utilize stainless steel, weathering steel, copper, aluminum or other metal alloys that are relatively unaffected by the deleterious affects of corrosion induced by placing wire grid array mats in contact with soil. Wire grid arrays can also utilize wires that are composed of a synthetic, non-corrosive material, such as a resin. Suitable non-corrosive synthetic resins will include polyester, vinyl ester, epoxy and epoxy derivatives, urethane-modified vinyl ester, polyethylene terephthalate, recycled polyethylene terephthalate, and the like. Suitable resins can also include combination of any of these resins. The synthetic resin can be a complete fiber material, such as a combination of a synthetic resin and a fiber reinforcement. Suitable fibers will include E-glass, S-glass, aramide fiber (e.g., Kevlar™), carbon fiber, ceramic reinforcement and the like and combinations of any of these. The wire shape can be round as is currently commercially available or wires can be of other common shapes i.e. square, rectangular or other common shapes with varying grid patterns in a wire grid array. Hereafter the term “wire”, when used herein, refers to the orthogonally oriented, generally circular shaped continuous flexible rod like members that, when bonded together at orthogonally oriented grid intersection points, form a grid array.
For many of the embodiments of the present invention using thin face wall panels in combination with wire grid array mats, a portion of the wire grid is exposed to view on the face of the thin wall free panel. For other embodiments a portion of the wire grid in contact with the thin wall face panel is cancelled from view and is imbedded in edges of the panels. For configuration with either type of connection, that is in view or concealed, the wire grid array mats typically serve to stabilize and position the thin wall face panels at the face of an MSE wall. Typically the only earth loading imposed on a wire grid array mat is that portion contributed by the soil behind and adjacent to a thin wall face panel. Both the weight of the thin wall face panel and the minor earth loading imposed on the panel is supported by the wire gird array mats attached to the panel.
For all embodiments the wire grid array mats have a rear portion that extends into a reinforced soil mass behind the exposed face of the wall. For walls of minor heights the rear portion of wire grid array mats can be sufficient to act as stabilizing tensile inclusion members to form the MSE wall. Taller walls utilize other common soil reinforcing materials such as welded wire mats, geogrid, or geotextile sheets placed within the soil mass. Flexible metal or synthetic sheets of these types can be used in combination with wire grid arrays for all embodiments of the present invention.
The use of thin wall face panels offers many advantages compared to both concrete masonry unit (CMU) walls or for MSE walls formed with large concrete panels. Although thin wall face panels are comparatively light weight, i.e. approximately 15 pounds per panel for the ballast pavers described in U.S. Pat. No. 4,899,514 dated Feb. 13, 1990 and by U.S. Pat. No. 5,490,360 dated Feb. 13, 1996 they exhibit high strength due to the cross section and high compressive strength of the concrete mix used in paver manufacture. The lightweight and size of approximately 12″×16″×1.5″ facilitates ease of placement resulting in high production rates compared to that of the currently available CMU or panel systems. The substantially higher unit weight of the CMU and panel system face components typically requires lifting equipment to place theses face units. The lightweight of the thin wall facing panels facilitates fast and efficient hand placement of the panels. Additionally, standard wire grid array mats such as welded wire mats can be used for attachment to ballast pavers since the wire grid array spacing can approximate the width of ballast pavers. Different sizes and weights of panels are possible and are within the scope of the present invention as well as is the use of wire grid array mats of varying grid dimensions to correspond to panel sizes selected.
The use of thin wall face panels not only allows for efficient placement with economical costs, but also walls can be configured in numerous wall facial appearances unattainable utilizing other current CMU or panel facing systems. For instance, in one embodiment of the present invention, thin wall face panels can be oriented with an outward batter for tiers of panels providing a planting space within the wall face. The resultant landscaping within the thin wall face panel MSE structure offers aesthetic features not available with other wall systems in current use.
The ballast paver type thin wall face panel is manufactured in conventional high speed concrete roof tile machinery and the outer appearances of the pavers can be manufactured to have a similar appearance to roofing tiles. This colorful effect, along with various texture options, offer additional aesthetic features compared to the limited color and texture options attainable with CMU or panel systems in current use. For certain embodiments of the present invention ballast pavers can be arranged to match the appearance of the ship-lap effect of roofing tiles. This or other wall appearances can also either be constructed with an essentially vertical overall orientation or can be constructed with a batter appearing to lean off of a vertical plane. Either ballast pavers or other thin wall face panels or multiple panels can additionally be arranged in the wall face wherein a lower tier panel edge can utilized to support panels are adjacent upper tier. In certain instances the wire grid array mat may be exposed to view or placed within paver or thin wall face panels edges and the wires are not in view.
Replacement of wall facing elements can be difficult and require substantial reconstruction with currently available CMU and panel MSE wall systems. For certain embodiments of the present invention, either with additional internal bracing or integral bracing of the wire grid array mats, efficient installation and replacement (if needed) of either pavers or other thin wall face panel types is facilitated. By bracing the earth loading of the MSE structure and thereby confining the MSE load to the wire mat, face panels can be removed and replaced over the life of any wall structure without disturbing the integrity of the MSE wall or adjacent thin wall face panels.
The installation and or replacement of thin wall face panels is simply accomplished due to the flexible and resilient nature of the wire grid array mats. The exposed front section of the wire grid array mats can be slightly flexed as needed for panel installation and return to its original position after the paver or individual panel installation. By using a portion of the wire grid array to secure wall facing without additional attachment devices results in efficient placement or replacement of thin wall face panels.
In another embodiment of the present invention thin face wall panels can be installed on opposite sides of wire grid array mats. This configuration has applications for sound or barrier walls typically used in urban areas of high traffic. Utilizing this configuration with the reverse batter (leaning out) wall face geometry allows for the option of planting within the wall face of the sound wall. The result of this internal landscape planting is both an aesthetically pleasing structure with additional sound dampening due to the landscaping.
If a braced wall system is used for any of the thin wall face panel configurations described in the embodiments all or a portion of the MSE wall structure can be constructed prior to the installation of the thin wall face panels. This feature can offer wall construction site logistic advantages since the MSE wall construction can proceed in the field independent of thin wall face panel or ballast paver manufacture and delivery. Additionally the MSE wall can be utilized to surcharge or pre-compress weak or marginal foundation soils under the wall. This effect can induce any wall settlement and preclude future distress since wall foundation settlement, due to-the weight of the wall structure, occurs prior to rather than following wall construction.
For certain retaining wall applications, wherein erosion control structures are utilized to strengthen and elevate existing flood control levees, the use of a “double-sided” precast wall can be desirable. A preferred method to form this type of assembly is by attaching two vertical double tee sections to each opposing end of a horizontal double tee section. When these units are structurally attached by either utilizing synthetic deformed bars, threadbars or steel cable stress strand, as described in U.S. patent application Ser. No. 10/047,080 filed on Jan. 14, 2002, a double-sided counterfort or double tee “H-brace” assembly is formed.
Following assembly of “H-brace” tee units these precast assemblies can be used in combination with precast concrete wall panels placed between adjacent “H-brace” units in the field. The assembly formed can then be backfilled within the parallel walls formed by the panels placed on the flange extensions of the vertical tee components of the “H-brace” assembly of adjacent “H-brace assemblies.
The system can either be used to create a new precast levee or floodwall or be used to elevate an existing earthen fill levee. For use to raise an existing levee, a “slot cut” method can be used that is similar to that excavation system that has been describe for other embodiments contained in U.S. patent application Ser. No. 10/047,080 filed on Jan. 14, 2002. A unique construction feature for elevating existing levees is the limited access attainable due to typically limiting work access from the top of the levee only. Since levee widths are typically narrow (under 30 feet), one-way traffic for equipment may also be mandated. Due to these site constraints, the use of the precast “Hbrace” is advantageous since little if any field concrete or additional fill is required which would entail numerous “two way” deliveries to implement. With the precast tee “H-brace” system an excavator can be the lead piece of equipment that cuts the slots, picks and sets the “Hbrace” units, places excavated fill within and around the “H-braces” and can be used to erect panels between the adjacent “H-brace” units. Although the lower portion of the T face panels can be at a lower elevation than either current or expected high water elevation the base units elevation is typically above the water surface elevation facilitating efficient placement of the units with an excavator. The excavator can typically be the lead piece of equipment on the levee with flatbeds delivering “H-brace” components to the access points of the excavator on the levee. The use of the “H-brace” system offers geotechnical advantages, construction ease, and cost savings compared to other conventional methods used for elevating levees.
Typical concrete cantilever retaining walls or other conventional wall types, impact the wall foundation area inducing an increased vertical load in the in situ soil. Since levees are or will be subjected to flooding and may be in areas of silt or other low load-bearing capacity soil types, it is advantageous to use a floodwall system that has negligible impact on soil bearing capacity. Since the precast concrete “H-brace” assemblies are rigidly cross-tied together and because the unit weight of saturated soil and concrete are similar, a negligible load in induced on the in situ soil with the “H-brace” system. The vertical wall tees can additionally be extended down below the current or expected high water elevation so that the completed “Hbrace” structure has adequate scour protection. The cross-tied assembly also offers seismic advantages compared to a comparable structure utilizing either a conventional cantilever wall or sheet piling.
One of the current approaches used to increase levee height is that of driving sheet piles into the in situ material on opposing sides of the levee. This is time consuming, disturbing construction, especially in urban areas due to continual high impact and vibration as a result of pile driving equipment. Additionally continual, on going corrosion protection can be required to be installed in order to extend the life of the steel sheet pile sections. Epoxy or other corrosion resistant coatings may be required to be applied to the pile sheets which adds to the cost of pile structures. Precast double tee “H-brace” components are not prone to the deleterious effects of corrosion and eliminate these extra costs associated with sheet piling.
These and other objects, features, and advantages of the invention will be apparent from the following description of the invention as illustrated in the accompanying drawings.