design of deep foundations n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
DESIGN OF DEEP FOUNDATIONS PowerPoint Presentation
Download Presentation
DESIGN OF DEEP FOUNDATIONS

Loading in 2 Seconds...

play fullscreen
1 / 45

DESIGN OF DEEP FOUNDATIONS - PowerPoint PPT Presentation


  • 144 Views
  • Uploaded on

DESIGN OF DEEP FOUNDATIONS. George Goble Goble PileTest , Inc. In this lecture I will discuss the deep foundations design process for driven piles and to a lesser degree cast-in-place systems, both geotechnical, structural aspects and some other topics within time limitations.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'DESIGN OF DEEP FOUNDATIONS' - lindsay


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
design of deep foundations

DESIGN OF DEEP FOUNDATIONS

George Goble

Goble PileTest, Inc.

slide2

In this lecture I will discuss the deep foundations design process fordriven piles and to a lesser degree cast-in-place systems, both geotechnical, structural aspects and some other topics within time limitations

slide3

MY BACKGROUNDStructural Engineer – Minor in Soil MechanicsExperience in Construction and Several Years as a Structural DesignerDesigned Several Large Pile FoundationsThirty Years as a College Professor Teaching Structures and Mechanics, Emphasizing DesignResearch on Minimum Cost Structural Designand on the Dynamics of Pile DrivingManaged the Research that Developed Dynamic Methods for Pile Capacity PredictionFounded PDI and GRLNow Have a Bridge Testing and Rating BusinessIn Goble Pile Test, I’m Developing an Easy to Use Dynamic Pile Testing System

why make this presentation
WHY MAKE THIS PRESENTATION?
  • Driven Pile Design is Often Not Well Done
    • Not dangerous but excessively conservative
    • Design process not clearly understood
    • Large cost savings possible
    • Capabilities of modern hammers not recognized
    • Drivability analyses not competently done
    • Many job specs are poorly written
the advantages of the driven pile
THE ADVANTAGES OF THE DRIVEN PILE
  • We know the material that we put in the ground before we drive
  • Because it is driven each pile penetrates to the blow count necessary to get the required capacity
  • Capacity can be determined quite accurately by driving observations, usually conservative (setup)
foundation design process
FOUNDATION DESIGN PROCESS
  • Process is Quite Complex (Unique)
  • Not Complete Until the Driving Criterion is Established in the Field
  • Structural Considerations can be Critical
    • But Structural Properties Are Known in Advance of Pile Installation
  • Factor of Safety (Resistance Factor) Dependent on Methods of Capacity Determination and Installation Quality Control
slide7

BASIS FOR DESIGNSince Early in the 19th Century a Design Approach Called Allowable Stress Design (ASD) Has Been and Is Still Used in Some Codes. The Fundamental Basis?

asd historical background
ASD HISTORICAL BACKGROUND
  • Rational Linear Elastic Analyses Appeared Early 1800’s
  • Linear Elastic Analysis Based on Steel
  • Well Developed by Late 1800
  • Basic Concept – Do not Exceed Yield Stress
  • Produced an Orderly Basis for Design
asd basis
ASD BASIS

STRESS

y

a

STRAIN

Define an ALLOWABLE STRESS

a = Cy

For Steel Beams C = 0.4 to 0.66

Factor of Safety? How is Stress Measured?

allowable stress design
ALLOWABLE STRESS DESIGN
  • “Safe” Stress or Load Permitted in Design
    • Allowable Stress Determined by Multiplying the Yield Stress of the Material by a Safety Margin that is Less than One
    • The Factor Provides Safety Margin
    • Factor Selected by Experience of about 150 Years
strength design
STRENGTH DESIGN
  • Not All Structures Have Linear Load-Stress (or Load-Strength) Relationship
  • Example – Columns, or Concrete
  • Behavior Understood by Late 1800’s
  • But for Columns, Strength is Non-Linear and Dependent on Slenderness Ratio and Can Be Calculated
  • Factor of Safety Introduced
  • Universally Used in Geotechnical Design
  • Still Called ASD
why lrfd
WHY LRFD?
  • First Adopted by ACI Building Code – 1956 in an Alternate Appendix (Strength Design)
  • Adopted 1963 as Equal to ASD
  • Strength Design Necessary for Particularly for Concrete Columns
  • Desirable to Split Safety Margin on Both Loads and Strength
  • Adopted Different Factors on Different Load Types
  • Adopted in Practice in about Two Years
  • All Factors Determined Heuristically
slide13
ASD

Qi = Rn/F.S.

LRFD

γij Qij = k Rnk

Gravity Loads

ASD - D + L

LRFD - ACI: 1.2D + 1.6L

LRFD - AASHTO: 1.25D + 1.75L

understand the limitations
UNDERSTAND THE LIMITATIONS
  • Load and Resistance Factors not Unique
    • Several Factors Selected Based on One Condition
  • Design Process Must Be Well-Understood by Code Developers
  • Strength Data May Be Dependent on Undefined Variables
slide16
ButThere Are Many LoadsAnd Load CombinationsFor Instance,Two Important OnesIn AASHTOStr I = 1.25D + 1.75 L + …Str IV = 1.50 D
summary
SUMMARY
  • LRFD Is an Improvement Based on the Split Safety Margins Alone
    • Both between Load Types and between strength types Strength
  • Load and Resistance Factors non-Unique
  • Clearly Written, Unique Codes Necessary
foundation design process1
FOUNDATION DESIGN PROCESS
  • Combined effort of geotechnical, structural and construction engineer
  • Local contractor may provide input
  • Large design capacity increases are often possible for driven piles
  • Both design and construction practice need improvement
foundation design process2
FOUNDATION DESIGN PROCESS

Establish requirements for structuralconditions and site characterization

Obtain general site geology

Collect foundation

experience from the area

Plan and execute subsurface

investigation

foundation design process3
FOUNDATION DESIGN PROCESS
  • Preliminary loads defined by the structural engineer
  • Loads will probably be reduced as design advances
  • Improved (final) loads must be used in final design
  • (Anaheim Example)
foundation design process4
FOUNDATION DESIGN PROCESS

Plan and execute subsurface

investigation

Evaluate information and

select foundation system

Deep Foundation

Shallow Foundation

cost evaluation
COST EVALUATION

A Cost Evaluation Should Always Be Made If More Than One Deep Foundation System Is Possible. It Is Not Difficult For Deep Foundations And Cost Savings Can Be Very Large.

foundation design process5
Foundation Design Process

Deep Foundation

Drilled Shaft

Driven Pile

Select Drilled Shaft

foundation design process6
Foundation Design Process

Drilled Shaft

Select Shaft Type and

Factor of Safety or Resistance Factor

By Static Analysis, Estimate Unit

Shaft Friction and End Bearing

Select Cross Section and

Length for Required Capacity

(Structural Engineer?)

foundation design process7
Foundation Design Process

Prepare Plans and Specifications

Select Contractor

Verify Shaft Constructability

and Capacity

Install and Inspect Production

Shafts

question

QUESTION

Where does the Strength Variability come from?

foundation design process8
Foundation Design Process

Deep Foundation

Drilled Shaft

Driven Pile

Select Driven Pile

foundation design process9
FOUNDATION DESIGN PROCESS

Define Subsurface Conditions

Select Capacity Determination Method

Select Quality Control Procedures

Determine Safety Factor or Resistance Factor

Determine Working Loads and Loads Times Factor of Safety

Gives Required Ultimate or Nominal Resistance for ASD

For LRFD Determine Loads Times Load Factors

Get Factored Load - Multiply by  Factor to

Get Required Nominal Resistance

Penetration Not Well Defined

Penetration Well Defined

driven pile design process
DRIVEN PILE DESIGN PROCESS
  • Pile Depth is Defined by a Dense Layer or Rock
  • The Length is Easily Selected Based on the Depth to the Layer
  • Select pile type oirjmoi;ernj;som

Penetration Well Defined

foundation design process penetration not well defined
FOUNDATION DESIGN PROCESSPenetration Not Well Defined

Select Pile Type and Size

Determine Unit Shaft Friction and

End Bearing With Depth By Static Analysis

Estimate Required Pile Length

Do a Preliminary Drivability Check

Can The Pile Be Driven To The Required

Depth And Capacity

Is The Pile Satisfactory Structurally

driven pile design process general
DRIVEN PILE DESIGN PROCESSGENERAL
  • Capacity Verification Method
    • More Accurate Methods Justify a Smaller Safety Factor (Larger Resistance Factor)
      • Choices
        • Static load test
        • Dynamic test
        • Wave equation
        • Dynamic formula
driven pile design process general1
DRIVEN PILE DESIGN PROCESSGENERAL
  • Q. C. Method
    • As Q.C. is Improved, Factor of Safety can decrease (Resistance Factor can Increase)
      • e.g., Better Capacity Determination Method
      • Increased Percentage of Piles Statically or Dynamically Tested
      • Critical Piles Tested
driven pile design process general2
DRIVEN PILE DESIGN PROCESSGENERAL
  • Make Pile Static Capacity Prediction
    • Predict Unit Shaft Friction and End Bearing with Depth
    • Prediction Should Be Best Possible
      • Do Not Adjust with Resistance Factor
    • Note Any Minimum Depth Requirements
    • Pile Size Determined With Knowledge of Loads (Costs??)
driven pile design process general3
DRIVEN PILE DESIGN PROCESSGENERAL
  • Pile Size Selection Should Consider Loads
  • Structural Limit State Must Also Be Considered – Lateral Loads
  • Close Structural and Geotechnical Coordination Necessary
  • Maybe Pile Size Selection by Structural Engineer – Foundation Engineer
  • Length Will Be Obvious if Piles to Rock or Dense Layer (Howard Franklin)
driven pile design process1
DRIVEN PILE DESIGN PROCESS
  • At this stage a proposed foundation design is complete
  • All other strength limit states must be checked
  • Drivability must be checked
  • All serviceability limit states also checked
driven pile design process2
DRIVEN PILE DESIGN PROCESS

Evaluate Drivability

Design

Satisfactory?

NO

YES

Prepare plans and specifications

Select Contractor

driven pile design process3
DRIVEN PILE DESIGN PROCESS
  • Drivability usually evaluated by wave equation
    • Must satisfy driving stress requirement
    • Blow count must be reasonable
    • Hammer and driving system assumed
  • If dynamic formula used it will determine required blow count
    • Dynamic formula will not detect excessive driving stresses
driven pile design process4
DRIVEN PILE DESIGN PROCESS

Change

Driving

System

Select Contractor

Contractor Advises Proposed

Hammer and Driving System

Perform Drivability Analysis

Hammer

Satisfactory?

NO

driven pile design process5
DRIVEN PILE DESIGN PROCESS

Hammer

Satisfactory?

YES

Set driving criteria

Drive test pile to criteria

Verify test pile capacity

Capacity/stress

satisfactory?

NO

driven pile design process6
DRIVEN PILE DESIGN PROCESS

Capacity/stress

satisfactory?

NO

YES

Drive production piles

Undertake construction control

and monitor installation

Resolve pile installation problems

and construction procedures

question1

QUESTION

Where does the Strength Variability come from?