What is a Soil Nailed Wall?

A soil nailed wall is an in situ earth retention system used to stabilize existing slopes or excavations.

The Basics: Components and Mechanism

Based on the reference provided, a soil nailed wall is created by:

• Installing passive reinforcement (i.e., no post-tensioning) in existing ground by installing closely spaced steel bars or sections (i.e., nails). These steel "nails" act as reinforcement, increasing the shear strength of the soil mass.
• Placing a front face support. This typically consists of shotcrete, concrete panels, or wire mesh, often with drainage elements, applied to the exposed soil face between the installed nails.
• Grouting the nails. Soil nails are later grouted if they are installed in drilled holes. Grouting secures the nail within the soil mass and transfers load effectively between the soil and the nail.

Unlike anchors which are post-tensioned, soil nails are passive. This means they develop their resistance as the soil mass starts to deform, mobilizing tensile forces within the nail and shear/bearing resistance along the grout-soil interface.

How Soil Nailing Works

The process generally involves constructing the wall from the top down in small stages. At each stage:

1. A shallow excavation is made into the existing soil.
2. Holes are drilled horizontally or at a slight downward inclination into the soil mass.
3. Steel reinforcing bars (the "nails") are inserted into the drilled holes.
4. The holes are filled with grout to bond the nails to the soil.
5. A temporary or permanent facing is applied to the excavated face, typically starting with a layer of shotcrete. Bearing plates are usually installed around the nail heads to transfer load from the facing to the nail.
6. The next layer is excavated below the completed level, and the process is repeated until the desired wall height is reached.

This staged construction sequence allows the soil and nails to work together to create a stable composite mass.

Why Use Soil Nailed Walls?

Soil nailing is a versatile and cost-effective method for various applications:

• Excavation Support: Providing temporary or permanent retention for vertical or near-vertical excavations, especially in urban environments.
• Slope Stabilization: Reinforcing existing unstable slopes to prevent landslides or erosion.
• Roadway Widening: Creating stable cut slopes for expanding transportation corridors.
• Bridge Abutments: Can sometimes be used as an alternative to traditional retaining structures.

Key Benefits often include:

• Cost-Effective: Can be less expensive than other retention systems like soldier pile walls or diaphragm walls, especially for complex geometries or tight sites.
• Adaptability: Suitable for a wide range of soil types (excluding clean sands or very soft clays without modification) and site conditions.
• Minimal Environmental Impact: Construction typically requires smaller equipment and has a smaller footprint compared to some other methods.
• Flexibility: Can easily accommodate irregular shapes or obstacles.

Key Characteristics at a Glance

Here’s a quick summary of the defining features:

Understanding these components and the installation process helps clarify how a soil nailed wall functions as a retaining structure.