Tag Archives: construction

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

Photo of an Anchored Soldier Pile Wall

Soldier Pile Wall Construction

How are soldier pile walls constructed?
Soldier Pile Installation

Soldier piles are typically steel H-piles or W sections.  The piles may be driven, vibrated, or drilled into place.  Piles are typically driven or vibrated into the ground where soil profiles do not prevent driving and were vibrations can be tolerated by adjacent structures.  On newer pile driving rigs, the input energy and frequency can be adjusted during pile driving to minimize vibration.  Adjacent structures can be monitored for vibration.  However, what often inhibits pile driving is noise and vibration tolerance of the building inhabitants.

Photo of pile being installed with vibratory hammer

Pile Driving with a Vibratory Hammer

Predrilling can be done prior to driving soldier piles to achieve better horizontal alignment and plumbness.  Accuracy is important when the basement wall will be formed against the shoring system.

Photo showing drill rig predrilling prior to diving a solider pile

Predrilling Prior to Pile Driving

When soldier piles cannot be driven or vibrated into the ground due to soil conditions, vibration constraints, or noise restrictions, soldier piles can be set in predrilled holes and backfilled with concrete; i.e. just like setting a fence post.

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.  I’m often asked if the boards “slide down” as the excavation progresses.  Due to the pressure of the ground on the wood lagging, once installed, they will not slide down.  This is especially true once the anchors have been tensioned.

Wood lagging can be installed in several different ways.  Often the top 5-ft of lagging is placed on the backside of the rear flange.  This does two things; it makes setting the 2nd lift faster and allows for easier access should the client require removal of the upper few feet of shoring.  Wood lagging can be installed behind the front flange.  This is often done in soil.  Wood lagging can also be attached with threaded studs or clips to the front flange.  Attaching the front face of the front flange is advantageous in hard soil/partially weathered rock that still requires lagging.

This photo shows wood lagging on the back of the rear flange on the 1st lift, on the back of the front flange on the 2nd lift, and on the face of the front flange on successive lifts.

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

Anchors are typically installed on the 2nd lift of the soldier pile wall at a depth of 8′ to 10′.  The anchors can be angled up to 45 degrees to get below existing utilities.  Additional rows of anchors are installed every 10′ to 15′ feet below the 1st row of anchors.  Note that while steeply angled anchors get below utilities, they increase the vertical load on the soldier piles and that adds stress in addition to the bending stress of the pile.  If possible, flatter anchors are more efficient.

Anchors can be installed directly through a prefabricated hole in the pile or through a waler.  The advantage of drilling directly through the pile is a lower anchor profile.  We have one client that actually mandates this for safety reasons to limit the possible conflict between walers and lowering loads into the excavation.  The advantage of walers is flexibility.  Walers allow the anchor location to be field adjusted and is therefore very helpful when drilling near existing utilities.

Walers can be made using pairs of channels or by putting anchor strands through holes in a W section.

photo of waler for soldier pile wall

Soldier Pile Wall Waler

More Information

Soldier Pile Walls
FHWA Ground Anchors and Anchored Systems
DFI Anchored Earth Retention Committee

Virginia War Memorial Shoring Support

VA War Memorial featured in Foundation Drilling Magazine

Subsurface Construction is honored to have the Virginia War Memorial as a Technical Featured article in Foundation Drilling Magazine July 2018, a publication of the Association of Drilled Shaft Contractors (ADSC). Subsurface designed and constructed a permanent anchored secant pile wall and a temporary soil nail wall for the expansion project.

For the secant pile wall, Subsurface teamed up with the experts at Equipment Corporation of America (ECA) to supplement its own experience with this construction method. From the initial bidding process to the wall’s construction, Subsurface worked closely with ECA’s Gordian Ulrich and Jeff Harmston to assess the appropriate drill rig and tooling needs. Casing was required due to the soft ground, presence of groundwater, and accuracy of the alignment of the piles. Subsurface used a Bauer BG 20 rig with 35-inch sectional casing and an earth auger for secant pile installation. The process alternated between 1-2 days of primary pile construction and 1-2 days of secondary pile construction spaced at 6 ft. on center. The construction of the secant pile wall as a success and was completed two weeks ahead of schedule.

For the temporary shoring, Subsurface designed and installed a hybrid pipe pile and conventional shotcrete soil nail wall had an overall retained height of approximately 35 ft. A primary challenge with design and installation was coordinating the location of soil nails (+/-45 ft. long) to miss existing utilities and soil nails on the opposing side of an outside corner. Subsurface was concerned that despite engineering the nails to miss, slight drilling deviations would inevitably cause damage to previously installed nails. To mitigate this risk, significant effort was spent on the layout of each
soil nail while continuously monitoring during drilling to ensure the original alignment was maintained. In addition, the shotcrete facing was not applied until all drilling within the zone of opposing nails was complete for each lift.

To learn more about the installation, project challenges and modeling/measuring of deflections please read more:

Foundation Drilling Magazine
Duke University Bed Tower Secant Wall

Secant Pile Wall

Subsurface completed a permanent secant pile wall at the VA War Memorial.  The wall serves as a permanent basement wall and supports vertical load from the structure.

Subsurface Construction Company Develops Senior Community Site

Subsurface Helps Develop Senior Community Site

Developer taps into demand created by Triangle’s growing senior population