?In the external stability assessment of nailed walls, which failure modes are considered

Installation Methods of Nails or Reinforcements in Soil-Nailed Retaining Walls

In the United States, nails (or soil nail reinforcements) are primarily installed using the drill-and-grout method.
However, other installation techniques are briefly outlined below.

Soil nail (or reinforcement) installation methods can be categorized as follows:

1. Drill-and-Grout Nails

Boreholes with diameters of 100 to 200 mm are drilled in the foundation soil, usually spaced about 1.5 m apart.
First, steel reinforcing bars are placed, followed by grout injection.
Drill-and-grout nails are the most common system used in soil-nailed retaining walls. They can be applied for both temporary and permanent stabilization (provided that an appropriate corrosion protection system is considered).

2. Driven (Displacement) Nails

These nails have relatively small diameters (19 to 25 mm) and are driven into the soil under pressure.
Their spacing is generally about 1 to 1.2 m apart.
Installation is faster compared to drill-and-grout nails, but regardless of the thickness of the sacrificial steel, they lack an adequate corrosion protection system.
For this reason, driven nails are typically used only in temporary retaining walls.

3. Self-Drilling Nails

By using hollow steel bars, drilling and grouting can be performed simultaneously.
During drilling, grout is injected through the hollow bar, exiting from the drill bit ports and filling the borehole from top to bottom.
This method uses rotary-percussive drilling techniques.
Self-drilling nails are faster to install than drill-and-grout nails, and unlike driven nails, part of the corrosion protection is provided by the grout.
They are the most common system for temporary soil-nailed walls.

4. Jet-Grouted Nails

In this method, high-pressure grout is used to excavate and advance the borehole to its final depth.
The grout also provides corrosion protection for the steel reinforcement.
In the second stage, reinforcing bars are typically installed using percussive-vibratory drilling methods.

5. Launched Nails

In this method, bare steel bars (without coating) are launched into the soil at very high speed using compressed air.
These bars usually have a diameter of 19 to 25 mm and a length of about 8 m.
This technique enables rapid installation with minimal disturbance to the project environment.
However, it may be difficult to control the penetration depth of the nails.
This method is only used for temporary soil nails.