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The construction sequence is typically to excavate, nail, and shotcrete the face in increments from the top down. Figure 8.56 shows a schematic of a sequence for underpass widening. Where face stability is a concern, a flashcoat of shotcrete may be applied before nail installation. The most common method of nail installation in

FIGURE 8.56 Construction sequence for soil nailed wall used in widening of underpass. (From Oregon Department of Transportation, with permission)

STEP 7: Place second structural application to full height and architectural finish

FIGURE 8.56 (Continued)

Europe, as in the United States, is the drill-and-grout method. Most commonly, the steel tendon is installed prior to grouting, although this sequence is sometimes reversed...

The stability of a soil nailed structure relies on (1) transfer of resisting tensile forces generated in the inclusions in the active zone into the ground in the resistant zone, through friction or adhesion mobilized at the soil-nail interface, and (2) passive resistance developed against the face of the nail. Ground nailing using closely spaced inclusions produces a composite coherent material. As shown in Fig. 8.54, the tensile forces gen­erated in the nails are considerably greater than those transmitted to the facing.

The design procedure for a nailed retaining structure includes (1) estimation of nail forces and location of the potential sliding surface, (2) selection of the reinforcement type, cross-sectional area, length, inclination, and spacing, and (3) verification that stabilit...

Almost all shotcrete failures in slope stabilization applications have resulted from

inadequate drainage. Therefore, drainage is a critical design and construction element.

Drainage from behind the shotcrete face can be provided by the following methods:

1. Surface interceptor ditch. Excavate a shallow ditch along the crest of the excavation to lead away surface water. Drainage gutters or lined ditches are recommended immediately behind the top of the wall.

2. Prefab geotextile drains. Place 12-in-wide (300-mm) prefabricated geotextile drain strips (Miradrain 6000, Amerdrain 200, etc.) vertically prior to applying the shotcrete. Typical spacings are the same as the horizontal nail spacing...

Soil nailed walls have some similarities with MSE walls but also some fundamental

differences. The main similarities are:

1. The major mechanism in both MSE and soil nailed retaining structures is the development of tensile forces in the reinforcements due to frictional interaction and, consequently, restrainment of lateral deformations of the structures.

2. The reinforced soil mass is separated into two zones based on the points of maximum tension in the reinforcement (Fig. 8.54): an “active” zone close to the facing, where the shear stresses exerted on the surface of the reinforcement are directed outward and have a tendency to pull out the reinforcements, and a “resistant” zone, where the shear stresses are directed inward and prevent the sliding of the reinforcements.

3...