Geotechnical Engineering Circular (GEC) No. 8
Design And Construction Of Continuous Flight Auger Piles
Final
April 2007

PDF Version (15 mb)

• Table Of Contents
• List Of Tables
• List Of Figures
• Technical Support Documentation Page
• Acknowledgements
• Preface
• List Of Abbreviations
• List Of Symbols

Table Of Contents

• Chapter 1: Introduction
  1. Purpose
  2. Background
  3. Relevant Publications
  4. Document Organization
• Chapter 2: Description Of Continuous Flight Auger Pile Types And Basic Mechanisms
  1. Introduction
  2. Construction Sequence
     1. Drilling
     2. Grouting
        1. General Sequence
        2. Start Of Grouting
        3. Withdrawal Of Auger
        4. Grout Vs. Concrete
        5. Reinforcement (Rebar)
  3. Summary
• Chapter 3: Applications For Transportation Projects
  1. Introduction
  2. Advantages And Limitations Of CFA Piles
     1. Background
     2. Geotechnical Conditions Affecting The Selection And Use Of CFA Piles
        1. Favorable Geotechnical Conditions
        2. Unfavorable Geotechnical Conditions
     3. Project Conditions Affecting The Selection And Use Of CFA Piles
  3. Advantages And Limitations Of Drilled Displacement Piles
  4. Applications
     1. Soundwalls
     2. Bridge Piers And Abutments
     3. Retaining Structures
     4. Pile-Supported Embankments
  5. Construction Cost Evaluation
• Chapter 4: Construction Techniques And Materials
  1. Introduction
  2. Construction Equipment
     1. Drilling Rigs
     2. Augers And Drilling Tools
     3. Equipment For Concrete/Grout And Reinforcement Placement
        1. Auger Plug
        2. Pumping Equipment
        3. Finishing The Top Of The Pile
  3. Construction Materials
     1. Grout And Concrete
        1. Cement
        2. Pozzolanic Additives
        3. Water
        4. Aggregate
        5. Fluidifiers For Grout And Water Reducing Admixtures For Concrete
        6. Retarders
        7. Air Entraining Agents
        8. Sampling And Testing
     2. Reinforcing Steel
        1. Reinforcing Steel Materials
        2. Reinforcing Cage/Section
  4. Summary Of Recommended Practices
• Chapter 5: Evaluation Of Static Capacity Of Continuous Flight Augered Piles
  1. Introduction
  2. Development Of Side-Shear And End-Bearing Resistance With Pile Displacement
  3. Recommended Methods For Estimating Static Axial Capacity Of CFA Piles
     1. Cohesive Soils
        1. Recommended Method For Side-Shear And End-Bearing Estimates Using Undrained Shear Strength
        2. Alternative Methods For Side-Shear Estimates Using Undrained Shear Strength
        3. Alternative Method For End-Bearing Estimates Using Dynamic Cone Penetrometer
        4. Alternative Method For Side-Shear And End-Bearing Estimates Using SPT-N Values
        5. Alternative Method For Side-Shear And End-Bearing Estimates Using CPT Values
     2. Cohesionless Soils
        1. Recommended Method For Side-Shear Estimates Using Pile Depth And End-Bearing Estimates Using SPT-N Values
        2. Alternative Methods For Side-Shear Using Pile Depth
        3. Alternative Method For Side-Shear And End-Bearing Estimates Using CPT Values
     3. Other Geo-Materials
        1. Introduction
        2. Vuggy Limestone
        3. Clay-Shale
  4. Static Axial Capacity Of Drilled Displacement Piles
     1. Introduction
     2. Recommended Method Using SPT-N Values Or CPT Data
     3. Amelioration
  5. Group Effects On Static Axial Compression Load Resistance Of CFA Piles
     1. Introduction
     2. Group Efficiencies
        1. Conventional CFA Pile Groups
        2. Drilled Displacement Pile Groups
     3. Settlement Of Pile Groups
        1. Elastic Compression Of The Pile
        2. Compression Settlement In Cohesionless Soils
        3. Consolidation Settlement In Cohesive Soils
     4. Uplift Of Single CFA Piles And CFA Pile Groups
  6. Lateral Resistance And Structural Capacity Of CFA Piles
     1. Behavior And Limitations Of CFA Piles
     2. Lateral Analyses Using The P-Y Method
     3. Lateral Analyses Of CFA Pile Groups
     4. Structural Capacity
        1. Longitudinal Reinforcement
        2. Shear Reinforcement
     5. Concrete Or Grout Cover And Cage Centering Devices
     6. Seismic Considerations
  7. Downdrag In CFA Piles
  8. Example Problems:Axial Capacity Of Single Piles
     1. Conventional CFA Pile In Cohesive Soils
     2. Conventional CFA And Drilled Displacement Piles In Cohesionless Soils
• Chapter 6: Recommended Design Method
  1. Step 1: Initial Design Considerations
     1. General Structural Foundation Requirements
     2. Site Geology And Subsurface Conditions
  2. Step 2: Comparison And Selection Of Deep Foundation Alternatives
  3. Step 3: Select Pile Length And Calculate Performance Under Specified Loads
     1. Limit States For Design
     2. Design Procedures
  4. Step 4: Constructability Review
  5. Step 5: Prepare Plans And Construction Specifications, Set Field QC/QA And Load Testing Requirements
  6. Example Problem
     1. Introduction
     2. Step 1: Initial Design Considerations
        1. General Structural Foundation Requirements
        2. Site Geology And Subsurface Conditions
     3. Step 2: Comparison And Selection Of Deep Foundation Alternatives
     4. Step 3: Select Pile Length And Calculate Performance Under Specified Loads
     5. Step 4: Constructability Review159
     6. Step 5: Prepare Plans And Construction Specifications, Set Field QC/QA And Load Testing Requirements
• Chapter 7: Quality Control (QC) / Quality Assurance (QA) Procedures
  1. Introduction
  2. The Role Of The Inspector
  3. Pre-Construction Planning
     1. Owner-Supplied Information
     2. CFA Contractor Experience
     3. Design Submittals
        1. Design Calculations
        2. Working Drawings
     4. Pile Installation Plan
     5. Testing Plan
        1. Pre-Production Testing
        2. Conformance Monitoring And Verification Tests
        3. Materials Testing
  4. Performance Monitoring And Control During Construction
     1. Monitoring And Control Of The Drilling Phase
     2. Monitoring And Control Of The Grouting/Concreting Phase
     3. Finishing The Pile Top And Installing Reinforcement
     4. Sampling And Testing Of The Grout Or Concrete
  5. Post-Construction Integrity Testing
     1. Use Of Integrity Testing
     2. Integrity Testing By Surface Methods
     3. Integrity Testing Using Downhole Techniques
  6. Load Testing
     1. Considerations In Planning A CFA Pre-Production Test Pile Program
     2. Proof Tests On Production Piles
  7. Summary Of Recommended QC/QA Procedures
     1. Prior To Construction
     2. On-Site Review Of Contractor's Equipment
     3. During Drilling
     4. During Grout/Concrete Placement
     5. During Reinforcement Placement And Pile Top Finishing
     6. Post-Installation
• Chapter 8: Guide Construction Specifications For Continuous Flight Auger (CFA) Piles
  1. Description
     1. Definitions
     2. Related Specifications
     3. Reference Codes And Standards
     4. Available Information
     5. Project Site Survey
     6. CFA Pile Contractors Experience And Submittal Of Experience
        1. Experience Requirements
        2. Experience Requirements And Submittal
     7. CFA Pile Design Requirements
        1. CFA Pile Design Submittals
        2. Design Calculations
        3. Working Drawings
     8. Construction Submittals
        1. Pile Installation Plan
        2. Conformance Testing Plan
     9. Pre-Construction Meeting
  2. Materials
  3. Construction Requirements
     1. Site Preparation And Protection Of Adjacent Structures
        1. Site Preparation
        2. Protection Of Adjacent Structures
     2. Grout Or Concrete
        1. Mix Design - Grout
        2. Mix Design - Concrete
        3. Field Operations
        4. Grout Or Concrete Sampling And Testing
     3. Auger Equipment
     4. Automatic Measurement And Recording Equipment
     5. Drilling
     6. Placement Of Grout Or Concrete
     7. Pile Head Finishing And Protection
     8. Reinforcing Steel Placement
     9. Pile Cut-Off
     10. Inspection And Records
     11. Testing
         1. Pre-Production Testing
         2. Verification Load Testing
     12. Integrity Testing
     13. Unacceptable Piles
  4. Measurement
  5. Payment
• Chapter 9: References
• Appendix A: Comparisons Of Methods For Estimating The Static Axial Capacity Of CFA Piles
  1. Introduction
  2. Methods For Axial Capacity Of CFA Piles
     1. Wright and Reese (1979) Method
     2. Douglas (1983) Method
     3. Rizkalla (1988) Method
     4. Neely (1991) Method
     5. Viggiani (1993) Method
     6. Decourt (1993) Method
     7. Clemente et al. (2000) Method
     8. Frizzi and Meyer (2000) Method
     9. Zelada and Stephenson (2000) Method
     10. Coleman and (2002) Method
     11. O'Neill et al. (2002) Method
  3. Methods For Axial Capacity Of Drilled Shafts Applicable CFA Piles
     1. TxDOT Method (1972)
     2. FHWA 1999 Method.
  4. Methods For Driven Piles Applicable To CFA Piles
     1. Coyle and Castello (1981) Method
     2. American Petroleum Institute (API) (1993) Method
  5. Method For Drilled Shafts And Driven Piles Applicable To CFA Piles
  6. Comparison Of Design Methods For Axial Capacity Of CFA Piles
     1. Comparison of Five Methods in Predominantly Sandy Soils (McVay et al., 1994)
     2. Comparison of Eight Methods in Predominantly Sandy Soils (Zelada and Stephenson, 2000)
     3. Comparison of Four Methods in Mixed Soil Conditions (Coleman and Arcement, 2002)
     4. Comparison of Seven Methods - Sandy and Clay Soils (O'Neill et al., 1999)
     5. Summary of Comparison Study Results for Cohesive Soils
     6. Summary of Comparison Study Results for Cohesionless Soils
• Appendix B: Example Problems: Spreadsheet Solutions For Axial Capacity Of Single Piles With Depth
  1. B.1 Conventional CFA Pile In Cohesive Soil
  2. B.2 Conventional CFA And Drilled Displacement Piles In Cohesionless Soils

List Of Tables

• Table 5.01 Relationship between Undrained Shear Strength, Rigidity Index, and Bearing Capacity Factor for Cohesive Soils for FHWA 1999 Method
• Table 5.02 Soil Conditions Investigated for Drilled Displacement Piles
• Table 5.03 Efficiency (η) for Model Drilled Shafts Spaced 3 Diameters Center-to-Center in Various Group Configurations in Clayey Sand (Senna et al., 1993)
• Table 5.04 P-Multipliers (P_m) for Design of Laterally Loaded Pile Groups
• Table 6.01 Design Consideration for Foundation Selection of CFA and DD Piles
• Table 6.02 Pile Group Settlement Computation
• Table 7.01 General Guidelines for Auger Penetration Rate for CFA Piles
• Table A.01 Soil-Pile Friction Angle, Limiting Unit Side-Shear Resistance, and Limiting End-Bearing Values (API, 1993)
• Table A.02 Total Resistance - Results from Five Methods (McVay et al., 1994)
• Table A.03 Total Resistance - Results from Eight Different Methods (Zelada and Stephenson, 2000)
• Table A.04 Total Resistance - Results from Eight Methods (Zelada and Stephenson, 2000)
• Table A.05 Side-Shear Resistance - Results from Eight Methods (Zelada and Stephenson, 2000)
• Table A.06 End-Bearing Resistance - Results from Eight Methods (Zelada and Stephenson, 2000)

List Of Figures

• Figure 2.01 CFA Pile
• Figure 2.02 Schematic of CFA Pile Construction
• Figure 2.03 Schematic of Typical Drilled Shaft vs. CFA Foundation
• Figure 2.04 Group of CFA Piles with Form for Pile
• Figure 2.05 Effect of Over-Excavation using CFA Piles
• Figure 2.06 Displacement Pile
• Figure 2.07 Hole at Base of Auger for Concrete
• Figure 2.08 Grout Delivered to Pump
• Figure 2.09 Grout at Surface after Auger Withdrawal
• Figure 2.10 Finishing Pile and Reinforcement Placement
• Figure 2.11 Placement of a Single Full-Length
• Figure 2.12 Vibratory Drive Head Used to Install Rebar Cage
• Figure 3.01 Use of CFA Piles for Commercial Building Projects.
• Figure 3.02 Examples of Difficult Conditions for Augured Piles
• Figure 3.03 CFA Piles at Bridge Interchange
• Figure 3.04 Low Headroom CFA Pile Application
• Figure 3.05 Secant Pile Wall with CFA Pile Construction
• Figure 3.06 CFA Piles for Soundwall along Highway
• Figure 3.07 Pilecaps on CFA Piles For A Pile-Supported Embankment
• Figure 3.08 Drilled Displacement Piles Limit Spoil Removal
• Figure 3.09 CFA Pile Foundation for Soundwall
• Figure 3.10 Schematic Diagram of the Foundation on CFA Piles for the Krenek Road Bridge
• Figure 3.11 CFA Piles at the Krenek Road Bridge Site
• Figure 3.12 Comparison of Measured Settlements and Test Pile, Krenek Road Bridge Site.
• Figure 3.13 Secant CFA Pile Wall for a Light Rail System in Germany
• Figure 3.14 Schematic Plan View of a Secant Pile Wall
• Figure 3.15 Drilling CFA Piles through Guide for Secant Wall
• Figure 3.16 Diagram of Pile-Supported Embankment for Italian Railway Project
• Figure 4.01 Typical Crane-Mounted CFA
• Figure 4.02 Photo of Crane-Attached CFA System
• Figure 4.03 Low Headroom CFA Pile
• Figure 4.04 Low Headroom Rig with Segmental Augers
• Figure 4.05 Hydraulic Rig Drilling on M25 Motorway in England
• Figure 4.06 Soilmec Hydraulic CFA Rig with Kelley Extension
• Figure 4.07 Augers for Different Soil Conditions
• Figure 4.08 Auger for Use in Clay with Auger Cleaner Attachment
• Figure 4.09 Cutter Heads for Hard Material and Soil
• Figure 4.10 Hardened Cutting Head
• Figure 4.11 DeWaal Drilled Displacement Pile
• Figure 4.12 Omega Screw Pile
• Figure 4.13 Fundex Screw Pile
• Figure 4.14 Drilled Displacement Piles
• Figure 4.15 Additional Drilled Displacement Piles
• Figure 4.16 Double Rotary Cased CFA Piles
• Figure 4.17 Double Rotary Fixed Drive System
• Figure 4.18 Double Rotary System with Kelly-Bar Extension
• Figure 4.19 Typical Concrete/Grout Pumps
• Figure 4.20 In-Line Flowmeter
• Figure 4.21 Sensor for Concrete Pressure at Auger
• Figure 4.22 Completion of Pile Top Prior to Installation of Reinforcement
• Figure 4.23 Sand-Cement Grout Mixes
• Figure 4.24 Machine-Welded Reinforcement Cage on Project Site in Germany
• Figure 4.25 Use of Steel Pipe to Reinforce a CFA Pile for a Wall
• Figure 4.26 Installation of Reinforcement Cage into Battered CFA Pile
• Figure 5.01 Load-Displacement Relationships.
• Figure 5.02 Relationship for the α Factor with S_u for Calculating the Unit Side-Shear for Cohesive Soils for the Coleman and Arcement (2002) Method.
• Figure 5.03 Unit Side-Shear Resistance as a Function of Cone Tip Resistance for Cohesive Soils - LPC Method
• Figure 5.04 Relationship for the β Factor for Calculating the Unit Side-Shear for Cohesionless Soils for the FHWA 1999 and Coleman and Arcement Methods.
• Figure 5.05 Unit Side-Shear as a Function of Cone Tip Resistance for Cohesionless Soils - LPC Method
• Figure 5.06 Unconfined Compressive Strength vs. Ultimate Unit Side-Shear for Drilled Shafts in Florida Limestone
• Figure 5.07 Correlation of Ultimate Unit Side-Shear Resistance for South Florida Limestone with SPT-N₆₀ Value
• Figure 5.08 Side-Shear Development with Displacement for South Florida Limestone.
• Figure 5.09 Relative Load Capacity vs. Relative Displacement for CFA Sockets in Clay-Shale.
• Figure 5.10 Hyperbolic Model Parameter Q_ult as a Function of the Unconfined Compressive Strength (Q_u) for CFA Sockets in Clay-Shale.
• Figure 5.11 Parameter ρ₅₀/D as a Function of Unconfined Compressive Strength for CFA Sockets in Clay-Shale
• Figure 5.12 Ultimate Unit Side-Shear Resistance for Drilled Displacement Piles for Nesmith (2002) Method
• Figure 5.13 Ultimate Unit End-Bearing Resistance for Drilled Displacement Piles for Nesmith (2002) Method
• Figure 5.14 Overlapping Zones Of Influence in A Frictional Pile Group.
• Figure 5.15 Efficiency (Η) Vs. Center-To-Center Spacing (S), Normalized By Shaft Diameter (B_shaft), for Underreamed Model Drilled Shafts in Compression in Moist, Silty Sand.
• Figure 5.16 Relative Unit Side and Base Resistances for Model Single Shaft and Typical Shaft in a Nine-Shaft Group in Moist Alluvial Silty Sand.
• Figure 5.17 Block Type Failure Mode.
• Figure 5.18 Deeper Zone of Influence for End-Bearing Pile Group than for a Single Pile.
• Figure 5.19 Equivalent Footing Concept for Pile Groups.
• Figure 5.20 Pressure Distribution Below Equivalent Footing for Pile Group.
• Figure 5.21 Typical e vs. Log p Curve from Laboratory Consolidation Testing.
• Figure 5.22 p-y Soil Response of Laterally Loaded Pile Model
• Figure 5.23 Example Deflection and Moment Response of Laterally Loaded Pile Model
• Figure 5.24 Typical Stress-Strain Relationship Used for Steel Reinforcement
• Figure 5.25 Typical Stress-Strain Relationship Used for Concrete.
• Figure 5.26 Variation of Pile Stiffness (EI) with Bending Moment and Axial Load.
• Figure 5.27 The p-multiplier (P_m)
• Figure 5.28 Circular Column (Pile) with Compression Plus Bending
• Figure 5.29 Example Interaction Diagram for Combined Axial Load and Flexure
• Figure 5.30 Examples of Cases of Downdrag.
• Figure 5.31 Potential Geotechnical Limit States for Piles Experiencing Downdrag.
• Figure 5.32 Mechanics of Downdrag: Estimating the Depth to the Neutral Plane.
• Figure 5.33 Mechanics of Downdrag in a Pile Group.
• Figure 5.34 Soil Profile S_u vs. Depth for Example Problem of CFA Pile in Cohesive Soil
• Figure 5.35 Soil Profile SPT-N vs. Depth for Example Problem of CFA Pile and DD Pile in Cohesionless Soil
• Figure 6.01 GULS and Short Term SLS for Axial Load on a Single CFA Pile
• Figure 6.02 Typical Conditions at the Project Site
• Figure 6.03 Idealized Soil Profile for Design
• Figure 6.04 Five-Pile Footing Layout
• Figure 6.05 Computed Lateral Load vs. Deflection
• Figure 6.06 Deflection and Bending Moments vs. Depth for Example Problem
• Figure 6.07 Maximum Bending Moments as a Function of Pile Top Deflection
• Figure 6.08 Bending Moment vs. Curvature for a 18-in. diameter Pile with 6 #7's
• Figure 6.09 Computed Axial Resistance vs. Depth
• Figure 7.01 Operator with Cab Mounted Display Used to Control Drilling
• Figure 7.02 Depth Encoder Mounted on Crane Boom
• Figure 7.03 In-line Flowmeter
• Figure 7.04 Pressure Sensors on Hydraulics to Monitor Rig Forces
• Figure 7.05 Display Panel for Observation by Inspector
• Figure 7.06 Example Data Sheet from Project
• Figure 7.07 Dipping Grout to Remove Contamination
• Figure 7.08 Cleaning the Top of a CFA Concrete Pile
• Figure 7.09 Placement of Reinforcing Cage with Plastic Spacers
• Figure 7.10 Cubes for Grout Testing
• Figure 7.11 Sonic Echo Testing Concept
• Figure 7.12 Sonic Echo Testing of Long Piles
• Figure 7.13 Downhole Sonic Logging Concept (SSL)
• Figure 7.14 Gamma-Gamma Testing Via Downhole Tube
• Figure 7.15 Static Load Test Setup on CFA Piles
• Figure 7.16 Proof Testing of Production Piles with Statnamic (RLT) Device
• Figure 7.17 Effect of Multiple Load Cycles on a CFA Pile
• Figure A.01 β Factor vs. Pile Length (Neely, 1991)
• Figure A.02 α vs. Undrained Shear Strength - Clayey Soils (Clemente et al., 2000)
• Figure A.03 β Factor vs. Depth - Zelada and Stephenson (2000) and FHWA 1999 Methods
• Figure A.04 Ultimate Unit End-Bearing Resistance vs. SPT-N Values - Zelada and Stephenson (2000) and Other Methods
• Figure A.05 Normalized Load-Settlement Relationship for Design of CFA Piles - Clay Soils of Texas Gulf Coast (O'Neill et al., 2002)
• Figure A.06 a vs. Average Undrained Shear Strength along Pile Length (Coyle and Castello, 1981)
• Figure A.07 Unit Side-Shear and End-Bearing Capacities - Cohesionless Soils (Coyle and Castello, 1981)
• Figure A.08 Relationship between SPT-N Values and f (Coyle and Castello, 1981)
• Figure A.09 Summary of Total Resistance - Results from Five Methods (McVay et al., 1994)
• Figure A.10 Summary of Total Resistance - Results from Eight Methods (Zelada and Stephenson, 2000)
• Figure A.11 Summary of Total Resistance - Results from Four Methods (Coleman and Arcement, 2002)
• Figure A.12 Total Capacity - Results from FHWA 1999 Method (Coleman and Arcement, 2002)
• Figure A.13 Total Capacity Results - Coleman and Arcement (2002) Method
• Figure A.14 Effective Lateral Earth Pressure near a CFA Pile during Construction (O'Neill et al., 2002)
• Figure A.15 Total Resistance - Results from Four Methods
• Figure A.16 Comparison of Study Results - Axial Capacity in Cohesive Soils
• Figure A.17 Comparison of Study Results - Axial Capacity in Cohesionless Soils

Technical Support Documentation Page

English to Metric (SI) Conversion Factors

The primary metric (SI) units used in civil and structural engineering are:

• meter (m)
• kilogram (kg)
• second (s)
• Newton (N)
• Pascal (Pa)

The following are the conversion factors for units presented in this manual:

A few points to remember:

1. In a "soft" conversion, an English measurement is mathematically converted to its exact metric (SI) equivalent.
2. In a "hard" conversion, a new rounded metric number is created that is convenient to work with and remember.
3. Use only the meter and millimeter for length (avoid centimeter).
4. The Pascal (Pa) is the unit for pressure and stress (Pa and N/m²).
5. Structural calculations should be shown in MPa or kPa.
6. A few basic comparisons worth remembering to help visualize metric dimensions are:
   • One mm is about 1/25 inch, or slightly less than the thickness of a dime.
   • One m is the length of a yardstick plus about 3 inches.
   • One inch is just a fraction (1/64 inch) longer than 25 mm (1 inch = 25.4 mm).
   • Four inches are about 1/16 inch longer than 100 mm (4 inches = 101.6 mm).
   • One foot is about 3/16 inch longer than 300 mm (12 inches = 204.8 mm).

Acknowledgements

The authors express their appreciation to Mr. Jerry A. DiMaggio, P.E. of the Federal Highway Administration (FHWA), Office of Bridge Technology, Mr. Silas Nichols, P.E., of the FHWA Resource Center, and Mr. Chien-Tan Chang of the FHWA Office of Bridge Technology for providing valuable technical assistance, review, and project overview during this project. The authors thank the following individuals that served on the Technical Working Group for this project:

• Silas Nichols FHWA Resource Center
• Benjamin Rivers FHWA Resource Center
• Khalid Mohamed FHWA Eastern Federal Lands Highway Division
• Rich Barrows FHWA Western Federal Lands Highway Division
• James Brennan Kansas DOT
• Mark McClelland Texas DOT

The authors thank the following organizations and individuals for providing valuable information and reviewing this manual:

• International Association of Foundation Drilling (ADSC-IAFD) - Emerging Technologies Task Force
• Deep Foundations Institute (DFI) - Augered Cast-In-Place Pile Committee

In addition, the authors thank the following organizations and individuals for providing valuable information for the preparation of this document:

• Applied Foundation Testing, Green Cove Springs, Florida
• Bauer Maschinen GmbH, Schrobenhause, Germany
• Berkel and Company Contractors, Inc., Bonner Springs, Kansas
• British Research Establishment, U.K.
• Cementation Foundations Skanska, U.K.
• DGI-Menard, Inc., Bridgeville, Pennsylvania
• Franki Geotechnics B, Belgium
• Jean Lutz, S.A., France
• Morris-Shea Bridge Company, Inc., Irondale, Alabama
• Pile Dynamics, Inc., Cleveland, Ohio
• Societa Italiana Fondazioni (SIF), S.p.A, Italy
• Soilmec, S.p.A., Italy
• Soletanche Bachy, France
• STS Consultants, Vernon Hills, Illinois
• Trevi, S.p.A., Italy
• Prof. A. Mandolini, Second University of Naples, Naples, Italy
• Prof. W. Van Impe, Ghent University, Ghent, Belgium
• Prof. C. Vipulanandan, University of Houston, Houston, Texas
• Prof. Michael O'Neill (deceased), University of Houston, Houston, Texas

Finally, the authors thank Ms. Lynn Johnson, of Geosyntec Consultants, for word processing, editing, and assisting in the layout of the document.

Preface

The purpose of this document is to develop a state-of-the-practice manual for the design and construction of continuous flight auger (CFA) piles, including those piles commonly referred to as augered cast-in-place (ACIP) piles, drilled displacement (DD) piles, and screw piles. An Allowable Stress Design (ASD) procedure is presented in this document as resistance (strength reduction) factors have not yet been calibrated for CFA piles for a Load Resistance Factored Design (LRFD) approach. The intended audience for this document is engineers and construction specialists involved in the design, construction, and contracting of foundation elements for transportation structures.

CFA piles have been used in the U.S. commercial market but have not been used frequently for support of transportation structures in the United States. This underutilization of a viable technology is a result of perceived difficulties in quality control, and the difficulties associated with incorporating a rapidly developing (and often proprietary) technology into the traditional, prescriptive design-bid-build concept. Recent advances in automated monitoring and recording devices will alleviate concerns of quality control, as well as provide an essential tool for a performance-based contracting process.

This document provides descriptions of the basic mechanisms involving CFA piles, CFA pile types, applications for transportation projects, common materials, construction equipment, and procedures used in this technology. Recommendations are made for methods to estimate the static axial capacity of single piles. A thorough evaluation and comparison of various existing methods used in the United States and Europe is also presented. Group effects for axial capacity and settlement are discussed, as well as lateral load capacities for both single piles and pile groups. A generalized step-by-step method for the selection and design of CFA piles is presented. Quality control (QC)/quality assurance (QA) procedures are discussed, and a performance specification is provided. This generic specification may be adapted to specific project requirements.

A list of the references used in the development of this manual is presented. These references include the key publications on the design of augered pile foundations. Existing Federal Highway Administration (FWHA) and American Association of State Highway Officials (AASHTO) publications that include engineering principles related to the subject of CFA piles are also included in the references.

List Of Abbreviations

AASHTO

American Association of State Highway and Transportation Officials

ACI

American Concrete Institute

ACIP

Augered cast-in-place

API

American Petroleum Institute

ASCE

American Society of Civil Engineers

ASD

Allowable stress design

ASTM

American Society of Testing Materials

bpf

Blows per foot

CFA

Continuous flight auger

CIP

Cast-in-place

CSL

Cross-hole sonic logging

DD

Drilled displacement

DFI

Deep Foundations Institute

DLT

Dynamic load test

DOT

Department of Transportation

FDOT

Florida Department of Transportation

FWHA

Federal Highway Administration

GULS

Geotechnical ultimate limit state

GWT

Ground water table

H₂SO₄

Sulphuric acid

IGM

Intermediate geotechnical material

kcf

Kips per cubic foot

kPa

KiloPascal

ksi

Kips per square inch

LPC

Laboratorie Des Ponts et Chausses

LRFD

Load and Resistance Factor Design

MPa

Megapascal

Na₂SO₄

Sodium sulphate

NaCl

Sodium chloride

NGES

National Geotechnical Experimentation Site

NHI

National Highway Institute

pcy

Pounds per cubic yard

pH

Hydrogen potential

ppm

Parts per million

psi

pounds per square inch

PVC

Polyvinyl chloride

QA/QC

Quality Assurance/Quality Control

RLT

Rapid load test

SLD

Service load design

SLS

Service limit state

SPT

Standard penetration test

SSL

Single-hole sonic logging

SULS

Structural ultimate limit state

tsf

Tons per square foot

TSL

Total service load

TXDOT

Texas Department of Transportation

VMA

Viscosity-modifying admixtures

W/C

Water-to-cement ratio

List Of Symbols

A_c

Cross-sectional area of concrete inside spiral steel

A_i

Average cross-sectional area for pile segment "i"

A_g

Gross area

A_g′

Effective area

A_pile

Cross-sectional area of single pile

A_piles

Cross-sectional area of all piles in a group

A_group

Cross-sectional area of pile group, not including overhanging cap area

A_s

Cross-sectional area of reinforced steel

A_v

Effective cross-sectional area in resisting shear

A_vs

Required area of transverse steel

B_shaft

Shaft diameter

B

Width of block

B

Pile diameter

C

Wave propagation velocity

C_c

Compression index

C_r

Recompression index

d

Pile diameter

d_c

Depth of concrete cover

d_b

Diameter of longitudinal bars

d_pile

Distance normal to neutral axis of outer piles

D

Pile diameter

D

Depth of block

D_B

Diameter of pile at the base

D_i

Diameter of pile segment "i"

e

Void ratio

e_o

Initial void ratio

E

Elastic modulus

E_c

Initial tangent slope

E_c

Young's Modulus of concrete or grout

E_e

Average Young's Modulus of equivalent pier within compressible layer

E_i

Average composite modulus for pile segment "i"

EI

Flexural rigidity of pile/beam

E_pile

Average Young's modulus of pile

E_s

Undrained Young's modulus or secant modulus

E_soil

Soil average Young's modulus

E_st

Young's Modulus of geomaterial between piles

f

Side-Shear resistance

f′_c

Concrete compressive strength

f″_c

Ultimate compressive strength

f_max

Ultimate Side-Shear resistance

f_s

Ultimate unit Side-Shear resistance

f_s-ave

Average unit Side-Shear resistance

f_s,i

Unit Side-Shear resistance of segment "i"

f_y

Steel yield stress

F_pile

Axial force on pile

H

Original thickness of layer

i

Generic pile segment number

I_f

Influence factor for group embedment

I_r

Rigidity index

k

Subgrade modulus

K, K_s, K′

Lateral earth pressure coefficient

K_o

In-situ lateral earth pressure coefficient

K_a

Active lateral earth pressure coefficient

K_p

Passive lateral earth pressure coefficient

L

Pile embedment length below top of grade

L

Pile socket length

L_i

Length of pile segment "i"

L_pile

Pile length

M, M_t

Moment

M_overturn

Overturning moment

M_x

Nominal ultimate flexural resistance

N

Number of pile segments

N

SPT blow-count

N_eq

Average equivalent N value

N₆₀

SPT-N value (bpf) corrected for 60% efficiency

N_60′

Average corrected SPT-N value

N_c

CPT cone factor

N_C^*, N_q

Bearing capacity factor

N_TxDOT

Value obtained from the Texas Cone Penetrometer

p

Vertical effective consolidation stress

p

Lateral soil reaction

p_c

Preconsolidation pressure

p_f

Foundation pressure

p_o

Effective overburden or vertical pressure

P

Compressive force

P_a, P_atm

Standard atmospheric pressure

P_m

P-multiplier

P_n

Nominal ultimate axial resistance

P_t

Lateral force

P_x

Axial load

P_x

Nominal ultimate axial resistance

q_c

CPT tip resistance

q_c

Average CPT tip resistance

q_p

Ultimate unit end-bearing resistance

q_u

Unconfined compressive strength

Q

Pile total resistance

Q_i

Average axial load at pile segment "i"

Q_i

Value of load of type "i"

Q_t

Ultimate total load

Q_t, Q_ult, Q_max

Ultimate resistance

r_ls

Radius of rings formed along centroids of longitudinal bars

R

Computed resistance at GULS

R_allowable

Allowable static axial resistance

R_B, R_Bd

End-bearing resistance

R_Block

Resistance of the block

R_S

Side-shear resistance

R_T

Total axial compressive resistance

R_ug

Ultimate resistance of pile group

R_u,i

Ultimate resistance of "i" in pile group

S

Pile spacing

S

Pile slope

S

Longitudinal spacing of reinforcement ties (spiral pitch)

S_group

Total settlement of pile group

S_i

Total settlement

SF

Safety factor

S_R

Stiffness ratio

S_u

Soil undrained shear strength

S_ua

Average undrained shear strength along pile length

S_{u ave}

Average soil undrained shear strength

V

Shear force

V_c

Concrete shear strength

V_n

Nominal shear resistance of concrete section

V_steel

Nominal shear resistance of transverse steel

w

Load along pile length

W

Pile displacement

W_S

Correlation constant

W_T

Correlation constant

x

Coordinate along pile length

y

Lateral deflection at a point with coordinate x

z_soil,i

Thickness of soil layer "i"

z_w

Depth below watertable

Z

Length of block

Z

Depth from ground surface to middle of a soil layer or pile segment (in ft)

Z_m

Depth from ground surface to middle of a soil layer or pile segment (in m)

α

Reduction factor

β

Pile segment factor

β

Reduction factor

γ

Soil unit weight

γ_{soil, i}

Unit weight of soil layer "i"

γ_w

Water unit weight

δ

Soil-to-pile interface friction angle

Δ

Elastic compression of pile

Δp

Change in overburden pressure

ε₅₀

Strain at 50% of compressive strength in compression load tests

ε_y

Yield strain

η

Pile efficiency

η_g

Pile group efficiency

ρ

Pile displacement

σ′_v

Vertical effective stress

Φ

Soil drained angle of internal friction

Φ

Resistance factor

Ψ

Ratio of undrained shear strength and vertical effective stress in soil