Auger Cast Piles in North Carolina


What are auger cast piles?

Auger cast piles (ACP) are a type of deep foundation constructed by drilling in-place reinforced concrete piles. The installation process involves:

  • Advancing a hollow stem auger to the desired depth.
  • Pumping grout through the auger as it is withdrawn.
  • Inserting a reinforcement cage into the wet grout to complete the pile.
A photo of a foundation rig drilling an auger cast pile.

Foundation rig drilling an auger cast pile

Advantages of Auger Cast Piles

  • Cost-Effective: Economical solution for deep foundations.
  • Rapid Installation: Quick and efficient construction process.
  • Reliable: Consistent performance in various soil conditions.
  • Vibration-Free: Ideal for sensitive environments and adjacent structures.

Limitations of Auger Cast Piles

  • Unsuitable for Boulders or Debris: Not recommended for soil profiles with boulders or fill with debris.
  • Not Ideal for Karst: Unsuitable for areas with karst geology due to potential voids and irregularities.

Design Process of Auger Cast Piles

  1. Initial Design Considerations

    • Review structure-specific and site-specific conditions.
  2. Comparison and Selection of Deep Foundation Alternatives

    • Consider alternatives, such as shallow foundation systems or ground improvement techniques.
  3. Selection of Pile Length and Assessment of Pile Performance

    • Use Allowable Stress Design (ASD) for geotechnical conditions.
    • Follow LRFD (AASHTO, 2004) for structural design.
    • Determine the required length based on design criteria.
    • Check axial and lateral load capacities.
    • Verification of Pile Group Capacity and Group Settlement Calculations
    • Complete the structural design of the pile.
    • Address any additional project-specific issues.
  4. Review of Constructability

    • Pile length and diameter
    • Penetration into bearing strata
    • Soil mining risk
    • Potential effects on nearby structures
    • Feasibility of construction sequence
  5. Preparation of Plans and Construction Specifications, including Quality Control/Quality Assurance (QC/QA) and load testing requirements.

Construction Process

  1. Drilling: Advance a hollow stem auger to the design pile tip elevation.
  2. Grouting: Extract the auger in a controlled manner while pumping grout under pressure to fill the void.
  3. Reinforcement: Lower the reinforcing steel cage into the wet grout.
  4. Finishing: Adjust grout level to the planned top of pile elevation.

    Other Resources

    FHWA Design and Construction of Continuous Flight Auger Piles, GEC#7

    photo of auger cast pile drill rig

    Auger Cast Pile Design

    Step-by-Step Design Process of Auger Cast Piles (ACP) The design process for Auger Cast Piles ...


    Greg Shenkler, Skanska USA Building

    Subsurface did a great job upfront making sure that we were installing the most effective solutions for our project. And despite a challenging schedule and unexpected underground conditions, the job was still completed ahead of schedule.

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