Hydraulic and earth engineering – Earth treatment or control – Shoring – bracing – or cave-in prevention
Reexamination Certificate
1999-06-09
2001-10-09
Will, Thomas B. (Department: 3673)
Hydraulic and earth engineering
Earth treatment or control
Shoring, bracing, or cave-in prevention
C405S272000, C405S284000, C405S286000, C405S262000
Reexamination Certificate
active
06299386
ABSTRACT:
TECHNICAL FIELD
The invention relates to a method and apparatus for a wall that retains earthen material, and more particularly to a shoring wall for below-grade excavations.
BACKGROUND OF THE INVENTION
Soil nailing is a cost-effective method of in situ ground reinforcement, in which passive, or non pre-stressed reinforcing elements are installed into the ground and attached to a facing of reinforced shotcrete or concrete. The cost effectiveness of soil nailing depends in part on the ability of vertical cuts in the ground to stand unsupported for a sufficient length of time to allow erection of the face reinforcing steel and subsequent application with shotcrete. The length of time that a vertical face can stand unsupported is referred to as “stand-up time.” When the stand-up time of vertical cuts at the face is limited, face stability problems do not allow economical soil nail wall construction. These situations typically require alternative, more costly wall systems, such as soldier piles, sheet piles or tieback walls.
U.S. Pat. No. 3,802,204 to Mason teaches the early use of tendon rods or dowels, inserted into an embankment to aid in the support of a temporary retaining wall, as an alternative to sheet pilings. An additional feature of the Mason '204 retaining wall is that Mason '204 teaches the use of horizontal concrete wale beams that include reinforcing rods. Mason '204 also teaches the use of pneumatically delivered concrete. Pneumatically delivered concrete is also called “shotcrete” or “gunnite,” and can be fiber reinforced for additional strength. However, the wale beams of Mason '204 fail to provide any vertically oriented support for the soil reinforcing rods that extend back horizontally into the excavation. Therefore, there is a need for a retaining wall system that provides a simple and economical, vertical and horizontal support for an excavated wall.
U.S. Pat. No. 4,911,583 to Carey teaches the addition of vertical rods, drilled into the ground along the face of an excavation, to provide an improved retaining wall. The Carey '583 disclosure teaches only the use of vertical rods with soft shale rock or “stiff soil.” The vertical rods are taught by Carey '583 as better able to help define the face of an excavation in these stiff soils, compared to soldier piles. Carey '583 teaches the placement of the vertical rods at two to four foot centers. This placement may eliminate the need for larger diameter soldier piles or wide soldier sheet piles. However, Carey '583 fails to teach any method that is applicable to softer soils. A retaining wall system is needed for soils that are not stable enough to remain in place with simply vertical rods and separate, conventional horizontal anchors.
U.S. Pat. No. 4,952,097 to Kulchin teaches the use of steel plates placed over the proximal ends of soil anchoring rods. The steel plates are mounted next to a grid of rebar so that the tensile strength of the soil anchors provides reenforcement to the rebar grid, which receives shotcrete to form a permanent concrete wall. FIG. 2 of Kulchin '097 shows this grid of rebar used to reinforce the concrete wall. A problem with Kulchin '097 is that the rebar grid relies on the soil anchors for substantially all of the wall's support. To provide the “permanent” retaining wall, as described by Kulchin '097, a substantial footing is also required to prevent the base of the wall from “kicking out,” especially in unstable and high water content soils. The footing is a costly addition to a retaining wall. A permanent retaining wall system is needed that can shore an excavation of unstable soils without the need for additional trenching along the base of the excavated wall for receiving a large and costly foundation.
U.S. Pat. No. 5,456,544 to Barrett et al. teaches a vertical wall support system that includes a horizontal pipe extending from a vertical pipe to form an L-shaped member for supporting a wall, as shown in FIG. 17, therein. The L-shaped member of Barrett '544 requires a foundational layer of concrete and geofabric over-layers to support and maintain the horizontal pipe in position. Such additional reinforcements are undesirable in that they are time consuming and expensive to install and require extensive excavation and backfilling as compared to prior retaining wall systems that primarily rely on the horizontal soil anchors alone. However, these horizontal soil anchors cannot provide an additional level of vertically oriented support, as needed for softer soils. Therefore, a retaining wall system that can bear vertical and horizontal loads is needed that can simply and economically provide horizontal anchoring and vertical support for a shoring wall.
SUMMARY OF INVENTION
The retaining element system of the present invention is designed to improve face stability in poorer quality soils that are not suited to conventional soil nailing. A method for shoring a face of an excavation is provided that includes inserting a plurality of retaining elements substantially vertically into an earthen mass. The earthen mass can be any material or combination of materials, such as soil, clay or rock that requires excavation for the installation of a shoring wall. The earthen mass has an upper surface, which can be referred to as a “grade.” Preferably, this insertion of the retaining elements into the earthen mass is achieved by drilling a plurality of vertical holes, each for receiving one of the plurality of retaining elements. Most preferably, a grout mixture is poured into each of the holes to firmly anchor each of the retaining elements into the earthen material below the grade.
The plurality of retaining elements are placed side by side in a substantially linear arrangement, when viewed along the grade, to define an excavation plane. The excavation plane lies below the grade and because the retaining elements are substantially vertical and the grade is substantially level, the excavation plane is substantially perpendicular to the grade. At least a portion of each retaining element is exposed by excavating along the excavation plane. This exposed surface is the excavated side of the excavation plane. A plurality of soil nails are then inserted into the excavation plane, at the approximate midpoint between a pair of adjacent retaining elements. A tip portion of each soil nail remains exposed on the excavated side of the excavation plane.
This exposed tip portion of each soil nail is employed for attachment to a wale. The wale is a substantially horizontal element that also contacts each retaining element of the pair of adjacent retaining elements on both sides of each soil nail. The wale can be a beam, bracket, or a set of concrete reinforcement bars. The beam or bracket can either be a structural member, formed of steel or the like, or alternatively formed from a precast concrete. The concrete reinforcement bars can then receive a concrete fill to form a solid wale structure.
A lagging matrix can then be constructed proximate to the exposed surface of the excavation plane and preferably attached to the retaining elements along the excavation plane. The lagging matrix is a conventionally constructed system of internal reinforcement bars and supports for a concrete wall. The lagging matrix receives a concrete slurry. The concrete slurry is a concrete mixture that is sufficiently liquid to be deposited or poured into the lagging matrix to form a shoring wall. Preferably, the concrete mixture is pneumatically conveyed shot-crete.
For soils with moderate stability problems along the excavation plane, or cut face, a drill berm is preferably formed along the excavation plane. The drill berm aids in the placement of the soil nails and preserves the earthen material along the excavation plane. The drill berm is then removed after the soil nails are inserted into the excavation plane.
According to an aspect of the invention, a retaining or shoring wall system is described that is simple and economical and provides both vertical and horiz
Byrne R. John
Wolschlag Chris J.
Pechhold Alexandra K.
Stratton Ballew PLLC
Will Thomas B.
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