Application of Soil Nailing Retaining Walls

The soil nailing system is highly suitable for vertical or near-vertical excavations. It can be used for highway excavations, slope cutting at the ends of embankments for bridge foundation construction, underpass widening, repairs, stabilization, rehabilitation of existing retaining structures, and tunnel entrances. Past experience has shown that soil nail retaining walls are effective for both temporary and permanent applications, including:

  • Roadway cuts

  • Under-bridge road widening

  • Repair and renovation of existing retaining structures

  • Temporary or permanent excavations in urban environments

Retaining Structures in Excavations

Soil nail retaining walls can serve as retaining structures in both temporary and permanent excavations. This system improves ground stability, while other retaining systems (e.g., tieback or anchored walls) are typically used in more favorable soil conditions. The relatively wide range of facing options also allows for meeting architectural and aesthetic requirements.

In these applications, soil nailing stands out as it reduces excavation volume, minimizes constraints, and limits environmental impacts. It is especially suitable for challenging widening projects in steep terrain or areas with limited access. Figure 1 illustrates examples of soil nail wall applications in both temporary and permanent excavations.

Retaining Structures Beneath Existing Bridge Foundations

In underpass widening projects involving the removal of embankment ends near bridge foundations (Figure 2), soil nail retaining walls offer advantages over tieback systems. Construction costs are generally comparable, but soil nailing avoids the need to stop traffic on the bridge deck.

In tieback systems, limited overhead clearance beneath the bridge requires installing support beams before excavation, leading to traffic disruptions and extra costs. By contrast, reinforcing bars for soil nails are easily available and installable without such complications.

Since the first row of nails is typically placed 1–2 m below the crest of the slope and angled downward (a drawback in embankment-end excavation), interference with bridge girders may occur. This can often be avoided by installing horizontal nails between the girders.

Rehabilitation of Existing Retaining Structures

Soil nailing can also be applied to stabilize or strengthen existing retaining structures at risk of failure. Nails are driven directly through the retaining structure. In this application—slightly deviating from the original philosophy of soil nailing—required ground deformations to mobilize reinforcement capacity come not from removing lateral support during excavation, but from ongoing structural movements.

Relevant applications include:

  • Masonry or reinforced concrete retaining walls showing excessive deformation or structural deterioration due to backfill weaknesses or poor foundation performance.

  • Mechanically stabilized earth (MSE) or crib walls deteriorating from reinforcement corrosion or poor backfill quality.

Typical Suitability of Soil Nailing

Soil nail walls are especially suitable for excavation conditions requiring vertical or near-vertical cuts and have proven effective for both temporary and permanent cases, such as:

  • Roadway cut excavations

  • Under-bridge widening projects

  • Repair and rehabilitation of retaining structures

  • Temporary or permanent excavations in urban areas

Soil nailing is economically attractive and technically feasible when:

  • The soil can stand unsupported in a vertical or near-vertical cut (1–2 m high) for 1–2 days.

  • All nails are above the groundwater table.

  • If nails are below the groundwater table, groundwater does not adversely affect the excavation face, grout–soil bond strength, or long-term nail durability (e.g., no soil chemistry causing corrosion).