Applications of the Anchoring (Tieback) System
A) Retaining Walls in Highways
Retaining walls stabilized by the tieback method (or anchorage in the soil nailing system) are commonly used in road construction projects with elevation differences, as well as in widening existing roads through excavation or embankment. Compared to conventional gravity concrete walls, anchored retaining walls offer cost advantages.
Traditional gravity walls are significantly more expensive because they require temporary excavation support systems, removal of the backfill soil behind the wall, and large, deep foundations. Anchored retaining walls can also be used for bridge abutments and excavation at the ends of slopes supporting existing bridge foundations (Refer to FHWA – RD-97-130, 1998).
B) Stabilization of Landslides and Slopes
Anchoring elements are often combined with retaining wall components, horizontal beams, or concrete blocks to stabilize slopes and landslides.
Soil or rock anchoring enables deep cuts and excavations for the construction of new highways (Fig. 2-a). Anchoring systems can also provide the high forces required to stabilize soil masses above landslides or sloped surfaces (Fig. 2-b).
These forces can be greater than those needed for vertical cut stabilization in conventional highway retaining wall construction. When the soil remains stable and can bear the anchor’s reaction forces at the excavation side, horizontal beams or concrete blocks can be used to transfer the anchor load into the slope surface. The choice between blocks or beams depends on factors like cost, aesthetics, and long-term maintenance.
C) Tiedown (Anchored Slab) for Uplift Resistance in Excavations
Permanent anchored retaining walls can be designed to resist upward uplift forces caused by hydrostatic pressure or overturning.
This technique is used in projects with a high groundwater table where the structure’s dead weight is insufficient to counteract uplift forces.
Advantages:
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Reduction in slab thickness and weight.
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Less excavation volume and reduced need for dewatering or pumping.
Disadvantages:
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Potential for significant variations in anchor force due to settlement or uplift.
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Difficulty in achieving watertight connections between the slab and anchors.
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Changes in slab stress distribution.
Anchoring in rock is also used for stabilizing concrete dams (Fig. 2-d). To meet current safety standards for seismic and flood loads, additional stabilization may be required for existing dams. Anchoring provides increased resistance to overturning, sliding, and seismic forces.
