AASHTO’s LRFD Specifications for Foundation and Earth Retaining Structure Design (Through 2006...

AASHTO’s LRFD Specifications for AASHTO’s LRFD Specifications for Foundation and Earth Retaining Foundation and Earth Retaining

Structure DesignStructure Design

(Through 2006 Interims and Beyond)(Through 2006 Interims and Beyond)

Jerry A. DiMaggio, P.E.Jerry A. DiMaggio, P.E.

Principal Bridge/Geotechnical EngineerPrincipal Bridge/Geotechnical Engineer

FHWA, Washington D. C. FHWA, Washington D. C.

Existing SpecificationsExisting Specifications

StandardStandard

1717thth Edition Edition

LRFDLRFD

33rdrd Edition Edition

““AASHTO and FHWA AASHTO and FHWA have agreed that all have agreed that all state DOT’s will use state DOT’s will use LRFD for design of LRFD for design of NEW structures by NEW structures by

2007.”2007.”

0-2-2NE60%

PA100%

NY 50%

ME100%

FL100%

OK 100%

WA100%

OR100%

CO 90%

MN 40%

SD 10%

ID 100% WY

MT 35%

0- 24 -10

0-2-2NE

AASHTO LRFD SurveyAASHTO LRFD SurveyMay 2005May 2005

SD ID WY

LAMS AL

AK 95%AK

PRFull Implementation50-90% Partial Implementation

1-10% Partial ImplementationNo Implementation

26-50% Partial Implementation11-25% Partial Implementation

Superstructure: LRFD

Substructure: LRFD/ASD

Foundations: ASD

Earthwork and walls: ASD

Reasons for Not AdoptingReasons for Not Adopting

• Human nature.Human nature.• No perceived benefits.No perceived benefits.• Unfamiliarity with LRFD methods.Unfamiliarity with LRFD methods.• Lack of confidence in the computed Lack of confidence in the computed

results. results. • Perceived errors and inconsistencies. Perceived errors and inconsistencies. • A specification that did not reflect A specification that did not reflect

current design practices.current design practices.

What is FHWA doing?What is FHWA doing?

• Bridge Design examples.Bridge Design examples.• NHI LRFD Training Courses.NHI LRFD Training Courses.• FHWA Technical Assistance.FHWA Technical Assistance.• FHWA/ NCHRP Calibration efforts.FHWA/ NCHRP Calibration efforts.• AASHTO Section 11 and 10 AASHTO Section 11 and 10

Revisions. Revisions.

Bridge Design ExamplesBridge Design Examples

http://www.fhwa.dot.gov/bridge/lrfd/examples.htmhttp://www.fhwa.dot.gov/bridge/lrfd/examples.htm

ConcreteConcrete SteelSteel

NHI LRFD Training CoursesNHI LRFD Training Courses

Course 130082ACourse 130082A

LRFD for Highway LRFD for Highway Bridge Substructures Bridge Substructures and Earth Retaining and Earth Retaining

Structures Structures

FHWA/ NCHRP ActivitiesFHWA/ NCHRP Activities

• NCHRP Project 12-66, Specifications for Serviceability in the Design of Bridge Foundations

• NCHRP Report 507, Load and Resistance Factor Design (LRFD) for Deep Foundations

FHWA/ NCHRP ActivitiesFHWA/ NCHRP Activities

• Publication No. FHWA-NHI-05-052, Development of Geotechnical Resistance Factors and Downdrag Load Factors for LRFD Foundation Strength Limit State Design

Revisions to Section 10Revisions to Section 10• Compiled by a Technical Expert PanelCompiled by a Technical Expert Panel• Review and input from A Technical Review and input from A Technical

Working Group (TWG)Working Group (TWG)• Accepted by AASHTO Subcommittee Accepted by AASHTO Subcommittee

T-15 in June 2005 in Newport, Rhode T-15 in June 2005 in Newport, Rhode IslandIsland

• To be published in 2006 InterimTo be published in 2006 Interim

http://bridges.transportation.org/?siteid=34&c=downloads

•Attachments to Agenda Item 39 Section 3 revisions

•Attachments to Agenda item 40 Section 10 revisions

Topics IncludedTopics Included• Subsurface Subsurface

investigationsinvestigations• Soil and rock Soil and rock

propertiesproperties• Shallow foundationsShallow foundations• Driven pilesDriven piles• Drilled shaftsDrilled shafts• Rigid and flexible Rigid and flexible

culvertsculverts• AbutmentsAbutments• Walls (All types)Walls (All types)

• Integral Integral abutmentsabutments

• MicropilesMicropiles• Augercast pilesAugercast piles• Soil nailsSoil nails• Reinforced slopesReinforced slopes• All soil and rock All soil and rock

earthwork earthwork features. features.

Topics NOT IncludedTopics NOT Included

Section 10 ContentsSection 10 Contents10.1 SCOPE 10.1 SCOPE

10.2 DEFINITIONS10.2 DEFINITIONS

10.3 NOTATION10.3 NOTATION

10.4 SOIL AND ROCK PROPERTIES10.4 SOIL AND ROCK PROPERTIES

10.5 LIMIT STATES AND RESISTANCE FACTORS10.5 LIMIT STATES AND RESISTANCE FACTORS

10.6 SPREAD FOOTINGS10.6 SPREAD FOOTINGS

10.7 DRIVEN PILES10.7 DRIVEN PILES

10.8 DRILLED SHAFTS10.8 DRILLED SHAFTS

PROPERTY INFOPROPERTY INFO

NO SIGNIFICANT CHANGENO SIGNIFICANT CHANGE

UPDATEDUPDATED

UPDATED, CONSISTANTUPDATED, CONSISTANT

REORGANIZED,REORGANIZED,

NEW CONTENTNEW CONTENTNEW CONTENTNEW CONTENT

Section 10.4 Soil and Rock PropertiesSection 10.4 Soil and Rock Properties

GEC 5GEC 5

Sabatini, 2002Sabatini, 2002

Subsurface Subsurface InvestigationsInvestigations

Mayne, 2002Mayne, 2002

Section 10.4 Soil and Rock PropertiesSection 10.4 Soil and Rock Properties

• Soil Strength Soil Strength • Soil Deformation Soil Deformation • Rock Mass Strength Rock Mass Strength • Rock Mass Deformation Rock Mass Deformation • Erodibility of rockErodibility of rock

10.4.6 SELECTION OF DESIGN PROPERTIES10.4.6 SELECTION OF DESIGN PROPERTIES

Section 10.5 Limit States and Section 10.5 Limit States and Resistance FactorsResistance Factors

• Resistance factors revised Resistance factors revised • Additional discussion on the basis for Additional discussion on the basis for

resistance factorsresistance factors• Additional discussion of extreme event Additional discussion of extreme event

considerationsconsiderations

Articles 3.4.1 and 3.11.8Articles 3.4.1 and 3.11.8

MaximumMaximum MinimumMinimum

Piles, Piles, -method-method 1.41.4 0.250.25

Piles, Piles, -method-method 1.051.05 0.300.30

Drilled Shafts, O’neill Drilled Shafts, O’neill and Reese (1999)and Reese (1999)

1.251.25 0.350.35

DowndragDowndrag• Methods for computingMethods for computing• Load FactorsLoad Factors• Use of minimum load factors clarifiedUse of minimum load factors clarified

Section 10.6 Spread FootingsSection 10.6 Spread FootingsEccentricity provisions clarifiedEccentricity provisions clarified

BB′′ = B – 2e = B – 2eBB

LL′′ = L – 2e = L – 2eLL

Q = P/(B’ L’)Q = P/(B’ L’)ML MB

Applies to Applies to geotechnical design geotechnical design for settlement and for settlement and bearing resistancebearing resistance

Section 10.6 Spread FootingsSection 10.6 Spread Footings

Hough methodHough method

Elastic Settlement of Elastic Settlement of cohesionless soilscohesionless soils

vvoc σ'

Δσσ'log

Section 10.6 Spread FootingsSection 10.6 Spread Footings

qqnn = c N = c Ncmcm + + D Df f NNqm qm CCwqwq + 0.5 + 0.5 B NB Nm m CCw w

NOMINAL RESISTANCENOMINAL RESISTANCE

NNc c ssc c iicc NNq q ssq q ddq q iiqq N N s s i i

Shape Correction FactorsShape Correction Factors

COHESIONCOHESIONUNIT WEIGHTUNIT WEIGHT

DEPTHDEPTH WIDTHWIDTH

Bearing Capacity FactorsBearing Capacity FactorsInclination FactorsInclination FactorsShear through overburden Shear through overburden correction factorcorrection factor

Water table correctionWater table correction

Settlement correction factors removedSettlement correction factors removed

Section 10.7 Driven PilesSection 10.7 Driven PilesSettlement of pile groupsSettlement of pile groups

4 new diagrams4 new diagrams

From:From:

Hannigan (2005)Hannigan (2005)

Section 10.7 Driven PilesSection 10.7 Driven Piles

The P-y method specified The P-y method specified for horizontal deflectionfor horizontal deflection

Original c

urvePP

yyModified curve

Modified curve

PPmm * P * P

Spacing (S)Spacing (S) Row 1Row 1 Row 2Row 2 Row 3Row 3

3D3D 0.70.7 0.50.5 0.350.35

5D5D 1.01.0 0.850.85 0.70.7

P-multiplier (PP-multiplier (Pmm))DD

Section 10.7 Driven PilesSection 10.7 Driven PilesField determination of nominal resistanceField determination of nominal resistance

Static load testStatic load test Dynamic load testDynamic load test

Static analysis methodsStatic analysis methods

• Nordlund – Nordlund – Thurman method Thurman method addedadded

Static analysis methodsStatic analysis methods

• Primary use is for pile length estimation Primary use is for pile length estimation for contract drawingsfor contract drawings

• Secondary use for estimation of downdrag, Secondary use for estimation of downdrag, uplift resistance and scour effectsuplift resistance and scour effects

• Should rarely be used as sole means of Should rarely be used as sole means of determining pile resistancedetermining pile resistance

Section 10.7 Driven PilesSection 10.7 Driven PilesComp Str

Ult Cap

0 160 320 480 Blows/ft

16.0ft

Stroke

Tens Str

Requirements for Requirements for driveability analysis driveability analysis have been added and have been added and clarifiedclarified

10.7.3.2 10.7.3.2 PILE LENGTH ESTIMATES FOR PILE LENGTH ESTIMATES FOR CONTRACT DOCUMENTSCONTRACT DOCUMENTS

10.7.6 10.7.6 Determination of minimum pile Determination of minimum pile penetrationpenetration

Section 10.8 Drilled shaftsSection 10.8 Drilled shaftsRefers to driven piles section where possibleRefers to driven piles section where possible• DowndragDowndrag• Group settlementGroup settlement• Horizontal displacement (single and group)Horizontal displacement (single and group)• Lateral squeezeLateral squeeze• Water table and buoyancyWater table and buoyancy• ScourScour• Group resistance (cohesive soil only)Group resistance (cohesive soil only)• Uplift (group and load test sections)Uplift (group and load test sections)• BucklingBuckling• Extreme event limit stateExtreme event limit state

Section 10.8 Drilled shaftsSection 10.8 Drilled shafts

• Static analysis methods Static analysis methods for soil and rock have for soil and rock have been updatedbeen updated

• Consideration of both Consideration of both base and side resistance base and side resistance in rock is now includedin rock is now included

O’Neill and Reese (1999)O’Neill and Reese (1999)

Section 10.8 Drilled shaftsSection 10.8 Drilled shafts

A + BA + B

DisplacementDisplacement

Side ResistanceSide Resistance

Tip ResistanceTip Resistance

Total ResistanceTotal Resistance

BBCCDD

A + DA + D

B + CB + C

ConclusionConclusion

Future EnhancementsFuture EnhancementsOverall stabilityOverall stability• Weight is both a load and a resistanceWeight is both a load and a resistance• Service limit state (should be strength Service limit state (should be strength

limit state)limit state) +

WWTTWWTT

WWTT WWTT

TT TTll ll

ccllN tan N tan

N tan N tan

Future EnhancementsFuture Enhancements

Inclination FactorsInclination Factors• Ignored by many practicing engineersIgnored by many practicing engineers• Based on small scale tests and theoryBased on small scale tests and theory• Effect of embedment (DEffect of embedment (Dff))

• Resistance factors are for vertical loadResistance factors are for vertical load

Nominal bearing resistance of rockNominal bearing resistance of rock• Very little guidance availableVery little guidance available• CSIR Rock Mass Rating System proposedCSIR Rock Mass Rating System proposed• CSIR developed for tunnel designCSIR developed for tunnel design• Includes life safety considerations and Includes life safety considerations and

therefore, margin of safetytherefore, margin of safety• May be conservativeMay be conservative

Pile head fixityPile head fixity• Connection detailsConnection details• Effects of axial loadsEffects of axial loads

Serviceability limitsServiceability limits

NCHRP 12-66 NCHRP 12-66

Due April 2006Due April 2006

What Should I Know and Do?What Should I Know and Do?

• Become familiar with BOTH Become familiar with BOTH the AASHTO standard the AASHTO standard specifications and LRFD specifications and LRFD specs.specs.

• Develop an understanding Develop an understanding of your agency’s current of your agency’s current design practice design practice

• Develop and compare results Develop and compare results for SEVERAL example for SEVERAL example problems with LRFD and problems with LRFD and YOUR standard design YOUR standard design practicepractice

• Translate your current Translate your current practice to an LRFD formatpractice to an LRFD format

• Communicate your findings to Communicate your findings to AASHTO’s SubCommitteee AASHTO’s SubCommitteee membersmembers

AASHTO Section 11AASHTO Section 11

• Design specifications for:• Conventional gravity/semigravity

walls• Non-gravity cantilevered walls• Anchored walls• Mechanically Stabilized Earth (MSE)

walls• Prefabricated modular walls

LRFD Specifications for LRFD Specifications for Foundation/ Earth Retaining Foundation/ Earth Retaining

Structure DesignStructure Design

Questions? Questions?

AASHTO’s LRFD Specifications for Foundation and Earth Retaining Structure Design (Through 2006...

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