Patent Application
20110286795
The present invention relates generally to systems and methods for constructing and repairing roadways, and more particularly, to a system and method for increasing the width of a roadway by incorporating a reverse-oriented retaining wall and subsurface soil nail supports.
In the construction of buildings, bridges, and other man-made structures, it is well-known to place passive supports such as footers, piles, and other subsurface installations for supporting above ground structures. Subsurface supports can be generally classified in two types. Passive supports are those that require the earth around the subsurface support to first shift or move to mobilize the available tensile, bending, or shear capacities of the subsurface supports. Active supports are those that are pre-tensioned to prevent shifts in the earth.
It is known to provide ground strengthening by driving, drilling, or launching elongate reinforcing members, referred to as soil nails, into the ground in a pattern, thus improving the bulk properties of the ground. Soil nails in generally horizontal orientations are used to prevent shifting or other undesirable movement of a particular geological formation. Soil nails installed in vertical orientations can also add to the bearing capacity of a foundation and can be referred to also as mircropiles. When soil nails are pretensioned, they can be referred to as tiebacks or tendons.
In some circumstances, the earth surrounding or under a man-made structure becomes unstable and therefore requires active supports, such as tie-backs, that are pre-tensioned subsurface installations used to restrain movement of the surrounding soil and rock. Recently, soil nails and tie-backs have been used to provide both temporary and permanent excavation support and slope stabilization.
Mountainous terrain provides a challenge for road designers to provide the required roadway width. Two significant regulatory changes over recent years have made roadway construction and maintenance particularly challenging for mountainous areas. The first regulatory change includes Federal and State Highway Safety Standards in which new roads must comply with stricter specifications regarding the size of the roadway width and shoulder, as well as other design specifications, such as the allowable slope, grade, and radius for curves. In some cases, if an existing roadway is repaired or modified, it may have to comply with the more strict design specifications therefore requiring the road to be widened.
The other significant regulatory change is limitations on disruption of the surrounding environment in order to reduce the environmental impact of roads located in State or Federally protected lands. Road widening efforts such as blasting or significant earth removal may not comply with environmental impact standards, thus preventing or greatly inhibiting the ability to widen a roadway.
Therefore, there is a need to provide a system and method for increasing the width of a roadway that complies with current Federal and State regulatory schemes. There is also a need to provide such a system and method that is not cost prohibitive and is relatively easy to install. There is yet another need to provide a system and method for increasing a roadway width in which the solution is adaptable for diverse environments.
In accordance with the present invention, a system and method are provided for increasing roadway widths by incorporating reverse-oriented retaining walls and soil nail supports.
In a preferred embodiment of the invention, the system comprises a retaining wall that serves as the exterior lateral support for a roadway in order to widen the existing roadway. The system of the invention is particularly advantageous for widening a roadway in mountainous or hilly terrain where one lateral side of the road is located adjacent to a vertical drop, such as a cliff or hillside.
The retaining wall is characterized as “reverse-oriented” because when the viewing the retaining wall at a vertical cross-section, the retaining wall extends at a reverse angle with respect to the horizontal plane of the roadway.
The system is constructed with a number of soil nails that tie into the retaining wall from the surrounding geological formation. A first set of nails are placed at a location which defines the position of the reverse-oriented retaining wall and therefore also delimit the additional width of the road to be added with the system. This first set of soil nails can also be referred to as micropiles that act to support the system in compression, shear, and bending. This first set of soil nails may be installed according to various methods, including the use of self-drilling soil nails that may be installed by drilling, or the use of a soil nail launcher which launches the soil nails into the sloping surface. The first set of soils nails are selectively spaced apart from one another along a length that corresponds to the length of the retaining wall to be constructed. A wire mesh material is laid over the first set of soil nails and is tied to the soil nails. A layer of geosynthetic fabric is then placed over the wire mesh material and secured to the wire mesh. The first set of nails, wire mesh, and geosynthetic material form the exterior wall of the retaining wall system. Alternatively, in lieu of geosynthetic fabric and wire mesh, concrete masonry unit (CMU) blocks may be used for the exterior wall of the system. The first set of nails are routed through the interior openings of the CMU blocks, and the CMU blocks are stacked and spaced to form a block wall with mortar placed between the blocks in a conventional brick and mortar construction. The interior cavities of the blocks may also be filled with mortar to further secure the blocks to the first set of soil nails. Unlike a traditional retaining wall; however, the lowermost row of blocks does not have to be supported with separate footers or other types of subsurface supports. Rather, the remaining length of the first set of soil nails embedded into the adjacent slope serve to anchor the blocks. Alternatively, in lieu of CMU Blocks, conventional concrete forming techniques may be used to construct a cast-in-place concrete structural wall centered about the vertical support elements, namely, the first set of soil nails.
A second set of soil nails may be used to further strengthen the roadway extension. The second set of soil nails generally extend at a more horizontal angle as compared to the first set of nails, and the second set of nails may extend further under the existing roadway. The second set of nails may be tied to the first set of soil nails. The second set of nails act primarily in tension, but also may carry shear and bending loads depending upon the horizontal angle. Once each of the sets of soil nails, wire mesh, and fabric are in place, the gap between the retaining wall and existing slope is backfilled with desired materials, including soil, rock, concrete mix, and combinations thereof. Once the backfill material has cured, the upper surface of the backfill may be paved thereby forming the increased roadway width. One or more bearing plates can be connected to any of the sets of nails to further stabilize the second set of nails within the backfill material.
Additional internal support for the retaining wall may be provided by a plurality of shear resisting soil nails, referred to herein as dowels, that are embedded in the existing slope. Typically, the shear resistance soil nails or dowels have a smaller length than the first and second set of nails.
The lateral ends or sides of the retaining wall can taper or reduce in width to terminate as necessary to accommodate the surrounding terrain. The retaining wall may have lateral ends that abruptly terminate because of the abrupt end of a sloping surface adjacent the roadway or the retaining wall may slowly taper to a reduced width taking into account an adjacent sloping surface that does not abruptly end and rather more gradually ends over a distance. In either case, the width of the retaining wall can be adjusted to follow the natural terrain and the existing roadway path.
A roadway barrier may be installed on the upper surface of the roadway extension. Such barriers may include known concrete barriers or other barriers to prevent a vehicle from traveling beyond the outer lateral edge of the roadway extension.
For aesthetic purposes, the exposed surface of the retaining wall may be coated with a cement or plaster material, and painted or stained to match the characteristics of the surrounding environment. The exposed surface may also include a decorative exterior liner that facilitates painting/staining, or may itself be colored and/or textured as to provide the desired appearance.
In one embodiment, the retaining wall takes advantage of the use of form panels, such as used in concrete construction, in which the form panel delimits the exposed surface of the retaining wall. The fill material located against the form panel may include concrete, thereby forming an exterior concrete wall for the retaining wall system. The form panels are removed after the concrete has cured. The use of a decorative exterior liner is particularly advantageous with the use of form panels in which the panels are stripped away to expose the exterior liner.
In order to tie the exposed ends of the soil nails to one another and to otherwise interconnect the parts of the soil nails that extend into the retaining wall, traditional wire or tie rods can be used. Alternatively, the ends of the nails may include couplers that interconnect the ends of the nails with a length of cable that is then used to tie to the other nails or to other structural members in the retaining wall. The desired number and orientation of the cables can be provided for interconnecting the soil nails and to also supplement the structural support provided by the soil nails.
The reverse-oriented retaining wall of the present invention provides significant savings in terms of the amount of required backfill materials as well as construction materials, as compared to traditional construction designs. As one skilled in the art may appreciate, a prior art retaining wall is a vertical installation that commences at the surface of the adjacent sloping surface. In the case of extreme sloping surfaces or cliffs, a retaining wall may often have to be built hundreds of feet below the roadway. A large amount of backfill material is required since the backfill material must fill the entire gap between the retaining wall and the sloping surface. Gaining access to the location where the retaining wall may have to commence may be difficult for large vehicles, thereby increasing the difficulty of constructing the retaining wall. Obstructions may also require the retaining wall to be built a considerable lateral distance from the existing roadway which, increase overall cost and effort in using a retaining wall to widen the road.
Other features and advantages of the present invention will become apparent by a review of the following figures when taken in conjunction with the detailed description.
Once the first set of nails 12 are installed, a wire mesh material 14 is placed over the exposed portions of the soil nails 12. The wire mesh is secured to the soil nails 12 using, for example, adequate wire ties or other hardware. One or more geosynthetic or geotextile layers 16 are then placed over the wire mesh 14, thus forming a semi-permeable layer, which may allow drainage of moisture through the layers. The type of wire mesh 14 and geotextile layer(s) 16 may be selected to match the required design specifications in terms of the strength of the retaining wall 10 as well the degree to which drainage is required. In particular, in wet climates, it may be advantageous to provide more permeable types of geotextile layer(s) 16. The wire mesh material and geotextile layers, either alone or in combination, thereby form a means for forming a barrier that defines the exterior shape of the retaining wall.
In the preferred embodiment of
A second set of soil nails 30 are provided to strengthen the retaining wall, and are preferably anchored to the upper exposed ends 20 of the first set of nails 12. The second set of nails 30 may be two piece soil nails in which an outer portion comprises an outer tube 34, an inner member 36 extends through the outer tube 34 and maintains a spaced concentric relationship with the outer tube 34 as by use of one or more centering features 38. The second set of nails 30 are disposed at a more horizontal angle as compared to the first set of soil nails 12, wherein the horizontal angle is measured as angle A2 from the horizontal. The depth 52 to which the nail 30 is buried in the sloping surface 28 may again vary based on the type of soil/rock formation encountered. The exposed portion of the inner member 36 may include one or more steel bearing plates 40, attached to the inner member 36, and secured in place as by one or more securing nuts 42. The type of soil nail illustrated as soil nail 30 in
The connection between the first 12 and second 30 set of soil nails may be facilitated by use of a longitudinal steel waler or bar 44, in which the free ends of the inner members 36 pass through openings formed in the waler 44. The ends of the inner member 36 are secured to the waler 44 as by securing nuts 46. As best seen in
Additional reinforcement for the system may be provided by a plurality of shear resisting soil nails or dowels 60. As shown, these soil nails or dowels 60 are shortened nails that are dispersed along the slope 28 in a desired pattern. The soil nails or dowels 60 may be installed for example by drilling or launched from a soil nail launching device.
Once the soil nails 12 and 30, wire mesh layer 14, geotextile layer(s) 16, nails/dowels 60 and walers 44 are installed, the generally V-shaped space or gap between the slope 28 and the geotextile layers(s) 16 may be filled with desired materials 49. The materials 49 may include light weight concrete mix, soil, lyme, aggregates, rip wrap, or combinations thereof.
A roadway barrier 70 may be installed to provide the necessary lateral barrier protection to prevent vehicles from driving off the edge of the roadway. In the example of
The increased roadway width is shown as distance 26. This increased roadway width is achieved with a minimum amount of backfill 49, since the lower most point or edge 66 of the retaining wall 10 can commence at an elevation which is a reasonable distance below the roadway, as compared to a traditional retaining wall that may have to extend hundreds of feet below the roadway.
Referring to
The exposed face of the retaining wall 64 may be treated with a layer of sealing material, such as Shotcrete™ or other exterior surface treatments, including other types of concrete, plasters, stains, and paints. The selected sealing/treatment material can match the color and other aesthetic characteristics of the environment, thereby resulting in a natural and non-obtrusive appearing roadway extension.
A considerable amount of time and materials savings may be realized by the system and method of the present invention. The vertical line 48 represents the location of the typical prior art retaining wall that must extend a substantial distance below the roadway, as compared to the retaining wall 10 of the present invention. The prior art retaining wall would also require footers or other subsurface supports to support the retaining wall. The emplacement of these subsurface supports may be particularly time consuming, as compared to the emplacement of soil nails, that can be emplaced by drilling or by a soil nail launcher that is positioned on the existing roadway.
In another aspect of the invention, the retaining wall may be conceptually viewed as a retaining structure that is held in a cantilevered position by subsurface supports which are secured in the underlying geological formation directly under the roadway. This cantilevered structure can be quickly installed with soil nails, which eliminates the prior art disadvantages with respect to footers/pilings and a vertically extending retaining wall.
Once the backfill material 49 has been compacted and/or cured, the roadway surface 56 can be extended onto the increased roadway width 26. A thermal expansion joint 58 may be placed at the location where the roadway extension joins the lateral edge of the existing roadway.
In accordance with the method of the present invention, a roadway width may be increased by incorporating of a reverse-oriented retaining wall. This reverse-oriented or cantilevered retaining wall maintains a reverse-orientation such that the exposed face of the retaining wall has a reverse or concave angle A1, as compared to a traditional vertical retaining wall. The method includes the emplacement of at least two sets of soil nails, a first set that extends substantially parallel to the reverse angle A1 and a second set of soil nails that extend at a more horizontal orientation, such as defined by angle A2. The method further contemplates the use of one or more supporting and barrier layers, such as a wire mesh layer and one or more geotextile layers that define the exterior shape of the retaining wall. The method may also include the use of one or more smaller soil nails or dowels to further provide subsurface support against shearing. Backfill material fills the gap between the existing slope and the retaining wall. The roadway extension can be increased either by increasing the reverse angle at which the first set of soil nails extend, and/or spacing the first set of soil nails further away from the lateral edge of the existing roadway.
The width 26 of the roadway extension can vary based upon the pattern of the first set of soil nails 12 when installed. For example, the roadway width along a particular section of the road may only require minimal widening, while another section of the roadway may require much greater widening. Accordingly, the first set of nails 12 can be selectively spaced either higher or lower upon the sloping surface 28, and the width 26 of the roadway extension would therefore vary depending upon the distance from the upper ends of the first set of nails 12 to the lateral edge of the existing roadway. Because the wire mesh and geotextile material are flexible, changes to the locations of the first set of nails can be accommodated to create a retaining wall that has a limitless number of shapes or orientations. Therefore, the system and method of the present invention are quite adaptable for providing selected roadway width extensions for any areas of a roadway. This flexibility further provides savings both in time and materials in that a nonlinear retaining wall can be built without requiring a complex underlying system of pilings.
In addition to the use of the CMU blocks, the embodiment of
Additionally, this embodiment makes use of a plurality of steel bearing plates 104 that can be tied to the rebar 102. The bearing plates 104 each have a central opening to receive the protruding ends of the second set of nails 30. The ends of the nails 30 may receive securing nuts 106, similar to the securing nuts 46. Accordingly, the lengths of rebar 102 provide additional strength and rigidity to the upper portion of the retaining wall without the need for external anchors or tie downs. The first and second sets of nails in this embodiment are shown as being drilled soil nails with self-drilling bits 24; however, it shall be understood that the soil nails 12 and 30 of this embodiment can also be any of the other soil nail constructions discussed above.
While the system and method of the present invention have been set forth with respect to preferred embodiments, it shall be understood that various other changes and modifications may be made within the scope of the claims appended hereto.
