Soil nailing
A rigid facing (often pneumatically applied concrete, otherwise known as shotcrete) or isolated soil nail head plates may be used at the surface.
[1] Alternatively, a flexible reinforcing mesh may be held against the soil face beneath the head plates.
Soil nail components may also be used to stabilize retaining walls or existing fill slopes (embankments and levees); this is normally undertaken as a remedial measure.
[4] A geotechnical exploration of the subsurface conditions at the site may be appropriate to determine soil strength data, groundwater levels, and soil/bedrock stratifications.
[4]: 15–16 Other difficult conditions include prolonged exposure to freezing temperatures, a climate that has a repeated freeze-and-thaw cycle, and granular soils that are very loose.
[4]: 16 Soil nailing evolved from the New Austrian tunnelling method, which is a system for underground excavations in rock.
This concept of combining passive steel reinforcement and shotcrete has also been applied to the stabilization of rock slopes since the early 1960s.
This program conducted full-scale testing of experimental walls with different configurations and developed analysis procedures for use in design.
[4]: 23 The United States first used soil nailing in 1976 for the support of a 13.7 metres (45 ft) deep foundation excavation in dense silty sands.
Nail length, diameter and spacing typically control external and internal stability of the wall.
[4]: 144 Drainage, frost penetration and external loads such as wind and hydrostatic forces also have to be determined and included in the final examination of the design.
Synthetic drainage mat is placed vertically between the nail heads, which are extended down to the base of the wall where they are most commonly connected to a footing drain.
[3]: 35 A layer of shotcrete is applied and bearing plates are installed before a final facing is put in place to complete the soil nail wall.
[3]: 35 Variations of the steps described above may be necessary to accommodate additional preparation tasks or supplementary activities for specific project conditions.
Verification or ultimate load tests are conducted to verify the compliance of the soil nails with pullout capacity and strengths resulting from the contractor's installation method.
[4]: 163 Creep tests are performed to ensure that the nail design loads can be safely carried throughout the structure's service life.
