Ground anchors can be used for Highway Retaining Walls, Slope and Landslide Stabilization, Tiedown Structures

APPLICATIONS OF GROUND ANCHORS
 Highway Retaining Walls
Anchored walls are commonly used for grade separations to construct depressed roadways, roadway widenings, and roadway realignments. The advantages of anchored walls over conventional concrete gravity walls have been described in section 1.2. Figure 8 provides a comparative illustration of a conventional concrete gravity wall and a permanent anchored wall for the construction of a depressed roadway. The conventional gravity wall is more expensive than a permanent anchored wall because it requires temporary excavation support, select backfill, and possibly deep foundation support. Anchored walls may also be used for new bridge abutment construction and end slope removal for existing bridge abutments (see FHWA-RD-97-130, 1998).
 Slope and Landslide Stabilization
Ground anchors are often used in combination with walls, horizontal beams, or concrete blocks to stabilize slopes and landslides. Soil and rock anchors permit relatively deep cuts to be made for the construction of new highways (figure 9a). Ground anchors can be used to provide a sufficiently large force to stabilize the mass of ground above the landslide or slip surface (figure 9b). This force may be considerably greater than that required to stabilize a vertical excavation for a typical highway retaining wall. Horizontal beams or concrete blocks may be used to transfer the ground anchor loads to the ground at the slope surface provided the ground does not “run” or compress and is able to resist the anchor reaction forces at the excavated face. Cost, aesthetics, and long-term maintenance of the exposed face will affect the selection of horizontal beams or blocks.
 Tiedown Structures
Permanent ground anchors may be used to provide resistance to vertical uplift forces. Vertical uplift forces may be generated by hydrostatic or overturning forces. The method is used in underwater applications where the structure has insufficient dead weight to counteract the hydrostatic uplift forces. An example application of ground anchors to resist uplift forces is shown in figure 9c. The advantage of ground anchors for tiedown structures include: (1) the volume of concrete in the slab is reduced compared to a dead weight slab; and (2) excavation and/or dewatering is reduced. Disadvantages of ground anchors for tiedowns include: (1) potentially large variations in ground anchor load resulting from settlement and heave of the structure; and (2) difficulty in constructing watertight connections at the anchor-structural slab interface, which is particularly important for hydrostatic applications; and (3) variations in stresses in the slab. A major uplift slab that incorporated tiedowns was constructed for the Central Artery Project in Boston, Massachusetts (see Druss, 1994).
Although not a highway application, permanent rock anchor tiedowns may be used to stabilize concrete dams (figure 9d). Existing dams may require additional stabilization to meet current safety standards with respect to maximum flood and earthquake requirements. Anchors provide additional resistance to overturning, sliding, and earthquake loadings.