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• Pumping grout through the auger as it is withdrawn.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.

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