Fundamental Principals Foundation Design

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Fundamental Principles of Foundation Design

Anthony M. DiGioia Jr., PhD, PE, PresidentDiGioia, Gray and Associates, LLC

IEEE TP&C Subcommittee Meeting

Orlando, Florida

January 8 – 11, 2007

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Foundation Design Requires a Blending of

Soil/Foundation Interaction Modelingand

Engineering Judgment

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Foundation Design Process

INPUT DATA

FOUNDATION DESIGN

CONTRACT DRAWINGS AND SPECIFICATIONS

CONSTRUCTION MONITORING

AND AS-BUILT INFORMATION

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SUBSURFACE

INVESTIGATION

Input Data

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PAST SUBSURFACE INVESTIGATIONS

GEOLOGY STUDY

SUBSURFACE

INVESTIGATION

Input Data

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SUBSURFACE INVESTIGATION

Input DataGEOLOGY

STUDYPAST SUBSURFACE

INVESTIGATIONS

STRUCTURE TYPES(Lattice Towers, Poles, H-Frames, Etc.)

AND ROLE(Tangent, Runing Angle, Dead End, Etc.)

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SUBSURFACE INVESTIGATION

Input DataGEOLOGY

STUDYPAST SUBSURFACE

INVESTIGATIONS

STRUCTURE TYPES(Lattice Towers, Poles, H-Frames, Etc.)

AND ROLE(Tangent, Runing Angle, Dead End, Etc.)

MODE OF FOUNDATION LOADS(Moment, Horizontal, Uplift, Compression

and Combinations)

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Input Data

SINGLE POLE STRUCTURES

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Input Data

LATTICE TOWER (FOUR-LEGGED) STRUCTURES

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Input Data

H-FRAME STRUCTURES

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SUBSURFACE INVESTIGATION

Input DataGEOLOGY

STUDYPAST SUBSURFACE

INVESTIGATIONS

STRUCTURE TYPES(Lattice Towers, Poles, H-Frames, Etc.)

AND ROLE(Tangent, Runing Angle, Dead End, Etc.)

MODE OF FOUNDATION LOADS

(Moment, Horizontal, Uplift, Compression and Combinations)

NUMBER, TYPE AND LOCATION

OF BORINGS

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SUBSURFACE INVESTIGATION

Input DataGEOLOGY

STUDYPAST SUBSURFACE

INVESTIGATIONS

STRUCTURE TYPES(Lattice Towers, Poles, H-Frames, Etc.)

AND ROLE(Tangent, Runing Angle, Dead End, Etc.)

MODE OF FOUNDATION LOADS

(Moment, Horizontal, Uplift, Compression and Combinations)

NUMBER, TYPE AND LOCATION

OF BORINGS

LINE DESIGN CRITERIA

Line Reliability Issues Component Reliability

Issues

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SUBSURFACE INVESTIGATION

Input DataGEOLOGY

STUDYPAST SUBSURFACE

INVESTIGATIONS

STRUCTURE TYPES(Lattice Towers, Poles, H-Frames, Etc.)

AND ROLE(Tangent, Runing Angle, Dead End, Etc.)

MODE OF FOUNDATION LOADS

(Moment, Horizontal, Uplift, Compression and Combinations)

NUMBER, TYPE AND LOCATION

OF BORINGS

LINE DESIGN CRITERIA

Line Reliability Issues Component Reliability

Issues

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PI1

PI3 PI2

PI4

PI5

How should you approach obtaining subsurface information and geotechnical design parameters?

• SOIL TYPES

• ROCK TYPES

• DEPTH TO GROUND WATER

• DEPTH TO ROCK

GEOTECHNICAL ISSUES

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PI1

PI3 PI2

PI4

PI5

How should you approach obtaining subsurface information and geotechnical design parameters?

• STRUCTURE TYPES

• STRUCTURE ROLES

• PERFORMANCE CRITERIA

• RELIABILITY LEVEL

STRUCTURE ISSUES

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Ws Ws

GWL

U

H Wc

β

• What geotechnical data do we need?- All cohesive soil- All cohesionless soil- Layered soil conditions

• Free-Standing Lattice Tower; Concrete Spread Footings;Frustrum Design Method

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Ws Ws

GWL

U

H Wc

τ τ

• What geotechnical data do we need?- All cohesive soil- All cohesionless soil- Layered soil conditions

• Free-Standing Lattice Tower; Concrete Spread Footings;Side Friction Design Method

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H

GWL

U

Wcττ

• What geotechnical data do we need?- All cohesive soil- All cohesionless soil- Layered soil conditions

• Free-Standing Lattice Tower; Drilled Shaft;Cylindrical Shear Design Method

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• What geotechnical data do we need?- All cohesive soil- All cohesionless soil- Layered soil conditions

• Tubular Steel Pole; Drilled Shaft;Hansen Design Method

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Foundation Design Process

INPUT DATA

FOUNDATION DESIGN

CONTRACT DRAWINGS AND SPECIFICATIONS

CONSTRUCTION MONITORING

AND AS-BUILT INFORMATION

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Foundation Design Process

INPUT DATA

FOUNDATION DESIGN

CONTRACT DRAWINGS AND SPECIFICATIONS

CONSTRUCTION MONITORING

AND AS-BUILT INFORMATION

ASCE MANUAL 74 RBD METHOD

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• Consider the variability of loadings.• Consider the variability of component

strength.• Vary reliability levels between lines.• Vary reliability levels between line

components.

The ASCE Method allows the designer to:

ASCE Manual 74 Reliability-Based Design (RBD) Method

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The Load Resistance Factor Design (LRFD) equation presented in Section 1 of Manual 74 for weather-related (reliability based) loads is as follows:

ΦCRe > effect of [DL + γ Q50] (1)

in which:

ΦC = strength (resistance) factor which can be selected to adjust the reliability of the component;

Re = the e-th % design strength for the component;DL = dead load effect in the component;γ = load factor applied to the live load effect Q50;

Q50 = load effect produced by combinations of wind velocity, ice thickness, and/or temperature, which has a 50-year return period

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Load Factors to Adjust Line Reliabilityby Factor LRF

40020010050Load Return Period - RP (years)

1.41.31.151.0Load Factor, γ

8421Line Reliability Factor (LRF)

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Strength Factors to AdjustComponent Reliability by Factor CRF forStrength Exclusion Limit, e of 5 to 10%

0.750.901.11CRF, ΦC, for COVR = 50%0.770.881.09CRF, ΦC, for COVR = 40%0.760.871.05CRF, ΦC, for COVR = 30%0.730.851.00CRF, ΦC, for COVR = 10-20%

421Component Reliability Factor

(CRF)

NOTE: COVR = Coefficient of Variation of Resistance

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Foundation Design Process

INPUT DATA

FOUNDATION DESIGN

CONTRACT DRAWINGS AND SPECIFICATIONS

CONSTRUCTION MONITORING

AND AS-BUILT INFORMATION

ASCE MANUAL 74 RBD METHOD

FOUNDATION DESIGN MODEL SELECTION & CALIBRATION

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Hansen Design Model

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0

1000

2000

3000

4000

5000

6000

0 1000 2000 3000 4000 5000

Predicted Nominal Strength - X (kip-ft)

Test

Str

engt

h - Y

(kip

-ft)

Constant COVm

least squares f ity = mm Xy = 1.242 X

Calibration of Hansen Design ModelTP3 Revised, 4-in criteria – Drilled Shafts Under Drained Moment – 20 Tests – Lognormal PDF

RT5 = 0.75 Rnφ5 = 0.75

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MFAD Design ModelThe Schematic Four-Spring Model in MFAD

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0

1000

2000

3000

4000

5000

6000

7000

0 1000 2000 3000 4000 5000 6000 7000

Predicted Nominal Strength - X (kip-ft)

Test

Str

engt

h - Y

(kip

-ft)

Constant COVm

least squares fity = mm Xy = 0.929 X

Calibration of MFAD Design ModelTP3 Revised, 4-in criteria – Drilled Shafts Under Drained Moment – 20 Tests – Lognormal PDF

RT5 = 0.60 Rnφ5 = 0.60

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CAISSON Design Model

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0

1000

2000

3000

4000

5000

6000

0 1000 2000 3000 4000 5000 6000

Predicted Nominal Strength - X (kip-ft)

Test

Str

engt

h - Y

(kip

-ft)

Constant COVm

least squares f ity = mm Xy = 1.017 X

TP3 Revised, 4-in criteria – Drilled Shafts Under Drained Moment – 20 Tests – Lognormal PDF

Calibration of CAISSON Design Model

RT5 = 0.42 Rnφ5 = 0.42

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0.4249.91.0220CAISSON

0.6024.90.9320MFAD

0.7528.91.2420Hansen

φ5(Lognormal

PDF)COVm(%)mmnDesign Model

Summary of Calibration Statistics and Strength Factor Data

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Foundation Design Process

INPUT DATA

FOUNDATION DESIGN

CONTRACT DRAWINGS AND SPECIFICATIONS

CONSTRUCTION MONITORING

AND AS-BUILT INFORMATION

ASCE MANUAL 74 RBD METHOD

FOUNDATION DESIGN MODEL SELECTION & CALIBRATION

LABORATORY TESTING PROGRAM

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Laboratory Testing ProgramCOHESIVE SOILS

•Total Density

•Moisture Content

•Undrained Shear Strength

•Modulus of Deformation

COHESIONLESS SOILS•Total Density

•Moisture Content

•Angle of Internal Friction

•Compaction Characteristics

•Modulus of Deformation

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Engineering Property Correlations –Cohesionless Soils

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Engineering Property Correlations –Cohesive Soils

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Foundation Design Process

INPUT DATA

FOUNDATION DESIGN

CONTRACT DRAWINGS AND SPECIFICATIONS

CONSTRUCTION MONITORING

AND AS-BUILT INFORMATION

ASCE MANUAL 74 RBD METHOD

FOUNDATION DESIGN MODEL SELECTION & CALIBRATION

LABORATORY TESTING PROGRAM

SELECTION OF GEOTECHNICAL DESIGN PARAMETERS

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Selection of Geotechnical Design Parameters

+ =BORING

LOG

SUMMARY of

LAB TEST RESULTS

SUMMARY of

SELECTED GEOTECHNICAL

DESIGN PARAMETERS

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Selection of Geotechnical Design Parameters

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Foundation Design ProcessINPUT DATA

FOUNDATION DESIGN

CONTRACT DRAWINGS AND SPECIFICATIONS

CONSTRUCTION MONITORING

AND AS-BUILT INFORMATION

ASCE MANUAL 74 RBD METHOD

FOUNDATION DESIGN MODEL SELECTION & CALIBRATION

LABORATORY TESTING PROGRAM

SELECTION OF GEOTECHNICAL DESIGN PARAMETER

FOUNDATION DESIGN

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Using the reliability-based design approach, determine D for the Hansen, MFAD and CAISSON design methods.

M50 =1000 kip-ft

D = ?

Groundwater level at surface

Stiff to very stiff clayγT =120 pcfsu = 2.0 ksf

ll = ll = ll ll = ll

Laterally Loaded Drilled ShaftFoundation Design Process

5 FT

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Laterally Loaded Drilled ShaftLognormal PDF

23810.42CAISSON16670.60MFAD13330.75Hansen

The Required Nominal Design Moment

Capacity (1)Φ5Design Model

(1)The nominal design capacity moment required = M50/φ5

Foundation Design Process

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Nominal Moment Capacity (Mn)Versus Embedment Depth

1000

1100

1200

1300

1400

1500

1600

1700

1800

1900

2000

2100

2200

2300

2400

2500

2600

2700

2800

2900

3000

10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 14.0

Embedment Depth (ft)

Nom

inal

Mom

ent C

apac

ity (k

ip-ft

) CAISSON

HANSEN

MFAD

Mn =2381 k-ft

Mn =1667 k-ft

Mn =1333 k-ft

Foundation Design Process

470

100200300400500600700800900

10001100120013001400150016001700180019002000

10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 14.0 14.5 15.0 15.5 16.0

Embedment Depth (ft)

Desig

n Mom

ent C

apac

ity φ

5Mn (

kip-ft)

CAISSON

MFADHANSEN

Design Moment Capacity (Φ5Mn)Versus Embedment Depth

Foundation Design Process

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Summary•FOUNDATION DESIGN REQUIRES A BLENDING

•A WELL-PLANNED SUBSURFACE INVESTIGATION IS CRITICAL

•IMPLEMENTATION OF THE RBD METHOD IN ASCE MANUAL 74 IS RECOMMENDED

•CALIBRATING FOUNDATION DESIGN METHODS PROVIDES A RATIONAL DESIGN FRAMEWORK FOR DEVELOPING STRENGTH FACTORS

•FIELD INSPECTION OF CONSTRUCTION AND GEOTECHNICAL PARAMETER CONFIRMATION ARE CRITICAL

SOIL/FOUNDATION INTERACTION MODELING

ENGINEERING JUDGEMENT

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