Soil Nailing
Passive steel reinforcement installed into existing soil to stabilize slopes and excavations.
Soil nailing is a ground reinforcement technique that stabilizes slopes and excavation faces by installing closely-spaced steel bars (nails) into the soil and applying a structural facing. Unlike tiebacks which are actively tensioned, soil nails are passive reinforcement elements that develop load as the retained soil mass deforms. The technique works by creating a reinforced soil block that acts as a gravity retaining structure. Nails are typically installed at a slight downward angle (10–20° from horizontal) in a grid pattern, then grouted in place. A shotcrete or cast-in-place concrete facing connects the nail heads and prevents surface erosion. Soil nailing is cost-effective for permanent and temporary excavation support, slope stabilization, and retaining wall construction, particularly where top-down construction sequence is required.
Technical Specifications
Common Applications
Installation Process
- 1Excavate soil face in lifts (typically 3–5 foot vertical increments)
- 2Drill nail holes at design spacing and inclination using track-mounted drill
- 3Insert steel bar (nail) with centralizers to full design length
- 4Grout nail hole from bottom up with neat cement grout via tremie
- 5Install bearing plate and hex nut at nail head against excavation face
- 6Apply initial shotcrete layer (3–4 inches) with welded wire mesh reinforcement
- 7Install drain strips between nail rows to relieve hydrostatic pressure
- 8Repeat sequence for each lift until design wall height is reached
- 9Apply final architectural facing if permanent wall (textured shotcrete, MSE panels, or stone veneer)
Frequently Asked Questions
What is the difference between soil nails and tiebacks?
Soil nails are passive elements that develop load as soil deforms. Tiebacks are actively pre-stressed (tensioned) against the wall face during installation. Tiebacks provide immediate support; soil nails require some wall movement to mobilize resistance.
How long do soil nails last?
With proper corrosion protection (epoxy coating, encapsulation, or double corrosion protection per FHWA guidelines), soil nails have a design life of 75–100 years for permanent applications.
Can soil nailing work in all soil types?
Soil nailing works best in soils that can stand unsupported for short periods during excavation lifts — stiff clays, dense sands, weathered rock. It is not suitable for soft clays, loose saturated sands, or soils with high groundwater without dewatering.
What is the maximum height for a soil nail wall?
Soil nail walls have been constructed to heights exceeding 80 feet, though 20–50 feet is most common. Very tall walls may require multiple rows of longer nails and thicker facing sections.
How fast can a soil nail wall be constructed?
Typical production rates are 500–1,500 square feet of wall face per day, depending on nail length, soil conditions, and shotcrete requirements. A 30-foot high, 200-foot long wall might take 3–5 weeks.
Is soil nailing cheaper than other retaining methods?
Soil nailing is typically 20–40% less expensive than conventional cast-in-place retaining walls and comparable to or slightly less than soldier pile and tieback systems. Cost advantage increases with wall height.
What about drainage behind soil nail walls?
Drainage is critical. Geocomposite drain strips are installed between nail rows before shotcrete application. A drainage collection pipe at the wall base carries water to discharge points. Weep holes through the facing provide additional relief.
Can soil nail walls be built in winter?
Yes, but shotcrete application requires temperatures above 40°F and protection from freezing during curing. In cold climates, heated enclosures or accelerated-set shotcrete mixes are used for winter construction.