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

PDF Version (15 mb)

FHWA-HIF-07-039

Table Of Contents

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 (Pm) 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 Su 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 Qult as a Function of the Unconfined Compressive Strength (Qu) 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 (Bshaft), 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 (Pm)
  • 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 Su 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

1. Report No.
 
2. Government Accession No.
 
3. Recipient's Catalog No.
 
4. Title and Subtitle
Geotechnical Engineering Circular No. 8
Design and Construction of Continuous Flight Auger (CFA) Piles
5. Report Date
 
6. Performing Organization Code
 
7. Author(s)
Dan A. Brown, Ph.D., P.E., Steven D. Dapp, Ph.D., P.E., W. Robert Thompson, III, P.E., and Carlos A. Lazarte, Ph.D., P.E.
8. Performing Organization Report No.
 
9. Performing Organization Name and Address
GeoSyntec Consultants
10015 Old Columbia Road, Suite A-200
Columbia, MD 21046-1760
10. Work Unit No. (TRAIS)
 
11. Contract or Grant No.
 
12. Sponsoring Agency Name and Address
Office of Technology Application
Office of Engineering/Bridge Division
Federal Highway Administration
U.S. Department of Transportation
400 Seventh Street, S.W.
Washington D.C., 20590
13. Type of Report and Period Covered
Technical Report
14. Sponsoring Agency Code
 
15. Supplementary Notes
FHWA Technical Consultant: J.A. DiMaggio, P.E., S.C. Nichols, P.E.
16. Abstract

This manual presents the state-of-the-practice for design and construction of continuous flight auger (CFA) piles, including those piles commonly referred to as augered cast-in-place (ACIP) piles, drilled displacement piles, and screw piles. CFA pile types, materials, and construction equipment and procedures are discussed. A performance-based approach is presented to allow contractors greater freedom to compete in providing the most cost-effective and reliable foundation system, and a rigorous construction monitoring and testing program to verify the performance. Quality control (QC)/quality assurance (QA) procedures are discussed, and general requirements for a performance specification are given.

Methods to estimate the static axial capacity of single piles are recommended based on a thorough evaluation and comparison of various methods used in the United States and Group effects for axial capacity and settlement, and lateral load capacities for single piles and pile groups are discussed. A generalized step-by-step method for selecting and designing CFA piles is presented, along with example calculations. An Allowable Stress Design (ASD) procedure is used.

17. Key Words
Continuous flight auger piles, CFA, augered cast-in-place piles, ACIP, drilled displacement piles, screw piles, deep foundation, testing, automated monitoring, performance specification.
18. Distribution Statement
No Restrictions.
19. Security Classification (of this report)
Unclassified
20. Security Classification (of this page)
Unclassified
21. No. of Pages
 
22. Price
 

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:

Quantity From English Units To Metric (SI) Units Multiply by For Aid to Quick Calculations
Mass lb Kg 0.453592 1 lb(mass) = 0.5 kg
Force lb
kip
N
kN
4.44822
4.44822
1 lb(force) = 4.5 N
1 kip(force) = 4.5 kN
Force/Unit Length plf
klf
N/m
kN/m
14.5939
14.5939
1 plf = 14.5 N/m
1 klf = 14.5 kN/m
Pressure, Stress, Modulus of Elasticity psf
ksf
psi
ksi
Pa
kPa
kPa
MPa
47.8803
47.8803
6.89476
6.89476
1 psf = 48 Pa
1 ksf = 48 kPa
1 psi = 6.9 kPa
1 ksi = 6.9 MPa
Length inch
foot
foot
mm
m
mm
25.4
0.3048
304.8
1 in = 25 mm
1 ft = 0.3m
1 ft = 300 mm
Area square inch
square foot
square yard
mm2
m2
m2
645.16
0.09290304
0.83612736
1 sq in = 650 mm2
1 sq ft = 0.09 m2
1 sq yd = 0.84 m2
Volume cubic inch
cubic foot
cubic yard
mm3
m3
m3
16386.064
0.0283168
0.764555
1 cu in = 16,400 mm3
1 cu ft = 0.03 m3
1 cu yd = 0.76 m3

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

Ac
Cross-sectional area of concrete inside spiral steel
Ai
Average cross-sectional area for pile segment "i"
Ag
Gross area
Ag
Effective area
Apile
Cross-sectional area of single pile
Apiles
Cross-sectional area of all piles in a group
Agroup
Cross-sectional area of pile group, not including overhanging cap area
As
Cross-sectional area of reinforced steel
Av
Effective cross-sectional area in resisting shear
Avs
Required area of transverse steel
Bshaft
Shaft diameter
B
Width of block
B
Pile diameter
C
Wave propagation velocity
Cc
Compression index
Cr
Recompression index
d
Pile diameter
dc
Depth of concrete cover
db
Diameter of longitudinal bars
dpile
Distance normal to neutral axis of outer piles
D
Pile diameter
D
Depth of block
DB
Diameter of pile at the base
Di
Diameter of pile segment "i"
e
Void ratio
eo
Initial void ratio
E
Elastic modulus
Ec
Initial tangent slope
Ec
Young's Modulus of concrete or grout
Ee
Average Young's Modulus of equivalent pier within compressible layer
Ei
Average composite modulus for pile segment "i"
EI
Flexural rigidity of pile/beam
Epile
Average Young's modulus of pile
Es
Undrained Young's modulus or secant modulus
Esoil
Soil average Young's modulus
Est
Young's Modulus of geomaterial between piles
f
Side-Shear resistance
f′c
Concrete compressive strength
f″c
Ultimate compressive strength
fmax
Ultimate Side-Shear resistance
fs
Ultimate unit Side-Shear resistance
fs-ave
Average unit Side-Shear resistance
fs,i
Unit Side-Shear resistance of segment "i"
fy
Steel yield stress
Fpile
Axial force on pile
H
Original thickness of layer
i
Generic pile segment number
If
Influence factor for group embedment
Ir
Rigidity index
k
Subgrade modulus
K, Ks, K′
Lateral earth pressure coefficient
Ko
In-situ lateral earth pressure coefficient
Ka
Active lateral earth pressure coefficient
Kp
Passive lateral earth pressure coefficient
L
Pile embedment length below top of grade
L
Pile socket length
Li
Length of pile segment "i"
Lpile
Pile length
M, Mt
Moment
Moverturn
Overturning moment
Mx
Nominal ultimate flexural resistance
N
Number of pile segments
N
SPT blow-count
Neq
Average equivalent N value
N60
SPT-N value (bpf) corrected for 60% efficiency
N60′
Average corrected SPT-N value
Nc
CPT cone factor
NC*, Nq
Bearing capacity factor
NTxDOT
Value obtained from the Texas Cone Penetrometer
p
Vertical effective consolidation stress
p
Lateral soil reaction
pc
Preconsolidation pressure
pf
Foundation pressure
po
Effective overburden or vertical pressure
P
Compressive force
Pa, Patm
Standard atmospheric pressure
Pm
P-multiplier
Pn
Nominal ultimate axial resistance
Pt
Lateral force
Px
Axial load
Px
Nominal ultimate axial resistance
qc
CPT tip resistance
qc
Average CPT tip resistance
qp
Ultimate unit end-bearing resistance
qu
Unconfined compressive strength
Q
Pile total resistance
Qi
Average axial load at pile segment "i"
Qi
Value of load of type "i"
Qt
Ultimate total load
Qt, Qult, Qmax
Ultimate resistance
rls
Radius of rings formed along centroids of longitudinal bars
R
Computed resistance at GULS
Rallowable
Allowable static axial resistance
RB, RBd
End-bearing resistance
RBlock
Resistance of the block
RS
Side-shear resistance
RT
Total axial compressive resistance
Rug
Ultimate resistance of pile group
Ru,i
Ultimate resistance of "i" in pile group
S
Pile spacing
S
Pile slope
S
Longitudinal spacing of reinforcement ties (spiral pitch)
Sgroup
Total settlement of pile group
Si
Total settlement
SF
Safety factor
SR
Stiffness ratio
Su
Soil undrained shear strength
Sua
Average undrained shear strength along pile length
Su ave
Average soil undrained shear strength
V
Shear force
Vc
Concrete shear strength
Vn
Nominal shear resistance of concrete section
Vsteel
Nominal shear resistance of transverse steel
w
Load along pile length
W
Pile displacement
WS
Correlation constant
WT
Correlation constant
x
Coordinate along pile length
y
Lateral deflection at a point with coordinate x
zsoil,i
Thickness of soil layer "i"
zw
Depth below watertable
Z
Length of block
Z
Depth from ground surface to middle of a soil layer or pile segment (in ft)
Zm
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
γsoil, i
Unit weight of soil layer "i"
γw
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
εy
Yield strain
η
Pile efficiency
ηg
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
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Updated: 04/07/2011
 

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