Tag Archives: safety

Duke University Drilling Anchors Anchored Soldier Pile Wall


Anchor design and installation for excavation support systems

FHWA defines anchors as cement grouted prestressed steel tendons that are installed in soil or rock.

  1. Open Excavations: Anchors are used to provide the horizontal force necessary retain temporary or permanent shoring systems for deep excavations.  They provide an open site, as opposed to internal bracing that would interfere with excavation and building construction.
  2. Limited Movement: They are prestressed – meaning that each row is loaded with the force needed for the full height of the excavation.  In this way movement is limited when compared to non-stressed ground elements such as soil nails.

Photo of an Anchored Soldier Pile Wall
2 Rows of Anchors for a Temporary Soldier Pile Wall


Anchors are typically designed using limit equilibrium analysis.  Think of the sliding block experiment in high school physics lab where you may have calculated what force is required to overcome friction and move a sandpaper block along an incline.  As a wedge of soil (see the curved plane in the diagram above) tries to slide into the excavation, the soil is retained by the embedment of the soldier pile, the force of the ground anchor, and the friction of the ground moving against itself.  Anchors get their capacity from the friction between the grouted nail hole and the ground.  The walls are designed to have a factor of safety of 1.35 to 1.5, meaning 35% to 50% more resisting force than is required to stabilize the wall.

Anchors have an unbonded length and a bonded length.  While the unbonded zone is fully grouted, the steel tendons are encapsulated in a greased sheath, preventing contact with the grout and the ground.  The bonded length is in full contact with the steel tendons and the grout and ground.  The purpose of the unbonded length is to be certain that the wall is restrained by the back portion of the anchor located beyond the failure zone (dashed line).

Diagram showing the active zone and the anchor

Contractors typically install anchors by advancing 6″ to 10″ steel casing to the design length.  With the length of the hole fully cased, steel strands are inserted into the drilled hole.  The hole is then tremie grouted to remove remaining debris or ground water as the casing is extracted.  Once the grout has reached a minimum specified strength (typically 2 to 3 days), the anchors are proof tested and locked off to design load.

    • Drill/case 6″ to 10″ diameter holes
    • Insert steel tendons into the drilled hole
    • Tremie grout as the casing is removed
    • Proof test and lock-off anchor

Duke University Drilling Anchors Anchored Soldier Pile Wall
Drilling Anchors for Sheet Pile Wall

drilling anchors project
Drilling Anchors for a Secant Pile Wall

More Information

Requirements for the Installation of Ground Anchors and Micropiles

Soldier Pile Walls

photo of internally braced soldier pile wall

Soldier Pile Wall Safety

What are some safety considerations when constructing soldier pile walls?

Soldier pile wall safety is about taking care of people first. Here’s how we do it.

Drill Rig Stability

Drill rigs must have a stable base to prevent overturning.  The bearing capacity of the soil must be sufficient to support the rig weight and the added extraction force.  If the ground is soft, possible solutions include undercut and replacement of subgrade soil and/or using crane mats to reduce the contact pressure on the ground.  One hidden, but very dangerous condition is the presence of below grade voids – think fuel tanks or utility tunnels.  Unstable ground conditions can cause a drill to overturn suddenly and disastrously.

photo of drill rig drilling

Drill rigs require a stable base

Fall Protection

During drilling for set soldier piles, barriers must be maintained around the drilled hole to serve as fall prevention.  The barriers must meet OSHA standards for fall protection.  Many shoring contractors use cattle feed panels to create a circle around the drilled hole.  Once the hole is drilled, we place a labeled hole cover over the hole.  Fall prevention must be back in place to remove the hole cover and lower the H-pile and concrete into place.  During drilling activities when employees could be exposed to a fall, they must be tied-off,; but bear in mind that fall protection can get caught in spinning drill tooling creating another serious hazard.

A not so obvious fall hazard is a collapsing hole.  If the hole is not supported with casing and soil collapses into the drilled hole, nearby employees can be exposed to a fall hazard.

Photo showing drill rig drilling to set soldier piles

Drilling to Set Soldier Piles


Wood Lagging

Wood lagging is installed in 5-ft lifts as the excavation progresses.   The boards must be placed by hand.  This is difficult work.  Green wood can be especially heavy.  Employees should work together to place heavy boards and be in good communication to avoid mashed fingers.  Impact resistant gloves can also be helpful.  When cutting the lagging boards with chain saws, employees must have all standard PPE plus chaps, ear muffs, a face shield, and high cut level gloves.

Photo of an Anchored Soldier Pile Wall

Anchored Soldier Pile Wall

Up close photo of wood lagging attached to the face of the front flange.

an up close photo of wood lagging attached to the front face of the front flange on a soldier pile wall

Wood Lagging

Anchor Installation

Drilling anchors presents many hazards but a few of the top ones are hitting utilities, getting caught in rotating drill steel, and mashing fingers.

Utilities locations must be thoroughly understood prior to starting drilling.  While gas and electricity are clearly dangerous; steam lines present a particular hazard.  A punctured steam line has tremendous stored energy due to the heat and pressure.  If punctured, steam would exit at great force and volume causing severe injury or death.  Accurate utility information saves lives.

Avoid injury from rotating drill steel.  Drill rig manufacturers now have stop cables on the sides of the drill masts.  If that cable is touched, the rotation of the drill string stops.  Employees must avoid loose clothing and loose long hair.  Subsurface largely avoids the hazard of the rotating drill steel by using excavators with grapples to load the drill steel.  This keeps employees further from the drill mast and reduces the physical work load.

photo of drilling anchors for a soldier pile wall

Anchor Drilling


As with all construction activities, one of the best preventions is to plan the work and work the plan.  Have operators with the right training and experience.  Be alert at work – sufficient rest, hydration, and avoid distractions such as cell phones.  Plan who will lead each activity, review the hazards and the engineering controls to avoid the hazards.

Be safe out there!

More Information

Requirements for the Installation of Ground Anchors and Micropiles

Soldier Pile Walls