Soldier Pile & Lagging
Steel beams with timber or concrete lagging for temporary and permanent excavation support.
Soldier pile and lagging is one of the oldest and most economical earth retention systems, consisting of vertical steel H-piles (soldiers) installed at regular spacing (typically 6–10 feet on center) with horizontal timber or concrete planks (lagging) spanning between them to retain the soil face. The soldier piles are installed before excavation begins — either driven, drilled and set in concrete, or augered into pre-drilled holes. As excavation proceeds downward, lagging boards are placed between the pile flanges to retain the exposed soil face. For deeper excavations, tiebacks or internal bracing are added to the soldier piles for lateral support. This system is widely used for temporary excavation support in urban construction, basement excavation, and utility trenching where the soil can stand unsupported for short periods between lagging installation.
Technical Specifications
Common Applications
Installation Process
- 1Install soldier piles at design spacing by driving, drilling, or augering
- 2Begin excavation in front of soldier pile wall
- 3As excavation exposes soil between piles, install lagging boards from top down
- 4Wedge and pack lagging tight against soil to minimize ground loss
- 5Install waler beams at tieback or bracing elevations
- 6Drill and install tiebacks through soldier piles (or install internal bracing)
- 7Continue excavation and lagging sequence to final grade
- 8For permanent walls: install drainage, waterproofing, and cast concrete facing
Frequently Asked Questions
What is the maximum depth for soldier pile and lagging?
Soldier pile and lagging walls can support excavations to 50+ feet with multiple levels of tiebacks or bracing. Without lateral support, cantilever heights are limited to about 12–15 feet depending on soil conditions.
Is soldier pile and lagging watertight?
No — gaps between lagging boards and between lagging and piles allow groundwater seepage. For water-tight applications, sheet piling or secant pile walls are preferred. Drainage systems behind the lagging manage water for most applications.
Can soldier piles be left in place permanently?
Yes — for permanent walls, soldier piles remain in place and a cast-in-place concrete facing is constructed against the lagging. The timber lagging eventually deteriorates but the concrete facing provides permanent retention.
What spacing are soldier piles installed at?
Typical spacing is 6–10 feet on center. Closer spacing (6 ft) is used for deeper excavations or weaker soils; wider spacing (8–10 ft) is used for shallow excavations in competent ground.
How quickly can a soldier pile wall be installed?
Pile installation rates of 4–8 piles per day are typical. Lagging installation keeps pace with excavation — a crew can lag 200–400 square feet per day. A complete wall system for a 30-foot deep, 200-foot long excavation might take 3–6 weeks.
What type of timber is used for lagging?
Douglas Fir or Southern Pine in rough-sawn planks (typically 3×12 or 4×12) are standard. For permanent installations or where fire resistance is required, precast concrete lagging panels are used instead.
Do soldier pile walls cause ground settlement?
Some ground loss (settlement behind the wall) is inherent because lagging installation occurs after soil is exposed. Careful installation, tight packing, and pre-excavation grouting minimize settlement. Typical settlements are 0.1–0.5% of excavation depth.
When are tiebacks needed vs. internal bracing?
Tiebacks are preferred when the excavation interior must remain clear for construction. Internal bracing (struts, rakers) is used when tiebacks cannot extend beyond the property line or when soil conditions don't support adequate anchor capacity.