Geotechnical Engineering Circular (GEC) No. 8
Design And Construction Of Continuous Flight Auger Piles
Chapter 1: Introduction
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 worldwide and also 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 of 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.
A performance-based approach is presented to allow the specialty contractors greater freedom to compete in providing the most cost-effective foundation system while satisfying the project requirements. The performance specification places a greater responsibility for the resulting foundation performance on the contractor or design-build team. Rather than rigorous prescriptive specifications, a comprehensive testing program is used to verify performance. Full-scale load testing is used to verify the load carrying capabilities of the foundations provided. Automatic monitoring and recording devices are used during construction of both test piles and production piles to establish construction parameters (down-force, torque, grout take, etc.), and to verify that these parameters are met for every production pile. Full-scale load testing may be performed on production piles throughout the project, as selected by the owner.
This document provides descriptions of CFA pile types, materials, construction equipment, and procedures. Quality control (QC)/quality assurance (QA) procedures are discussed. A performance specification is provided in a format that may be adapted to specific project requirements. 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 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.
1.3 Relevant Publications
A list of the references used in the development of this manual is presented in Chapter 9. These references include 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.
1.4 Document Organization
The remainder of this document is organized as follows.
- Chapter 2 - Description of Continuous Flight Auger Pile Types and Basic Mechanisms. This chapter provides a general overview of CFA piles, including a description of the main system components, typical equipment, and the sequence of construction.
- Chapter 3 - Applications for Transportation Projects. This chapter presents advantages and limitations of CFA piles in transportation projects, describes favorable and unfavorable project and geotechnical conditions, and illustrates applications of CFA piles in transportation projects.
- Chapter 4 - Construction Techniques and Materials. This chapter provides details on construction techniques, materials, and recommended practice for the construction of CFA piles in transportation projects.
- Chapter 5 - Evaluation of Static Capacity of Continuous Flight Augered Piles. This chapter presents an evaluation and comparison of various existing methods used in the United States and Europe to calculate the static capacity of CFA piles.
- Chapter 6 - Recommended Design Method. This chapter presents a step-by-step generalized method for the selection and design of CFA piles. An annotated example is included in this chapter.
- Chapter 7 - Quality Control (QC)/Quality Assurance (QA) Procedures. This chapter discusses the use of automated QC/QA equipment and presents guidelines.
- Chapter 8 - Guide Construction Specifications for Continuous Flight Auger Piles. This chapter presents a performance specification for CFA piles.
- Chapter 9 - References. A list of the references used in this document is presented.
- Appendix A - Comparisons of Methods for Estimating the Static Axial Capacity of CFA Piles.
- Appendix B - Spreadsheet Solutions for Axial Capacity of Single CFA Piles.