AASHTO’s LRFD Specifications for Foundation and Earth Retaining Structure Design (Through 2006 Interims and Beyond) Jerry A. DiMaggio, P.E. Principal Bridge/Geotechnical Engineer FHWA, Washington D. C.

Existing Specifications Standard 17 th Edition LRFD 3 rd Edition

“AASHTO and FHWA have agreed that all state DOT’s will use LRFD for design of NEW structures by 2007.”

0-2-2 NE 60% MO TN NC VA WV 80% PA 100% NY 50% ME 100% IA 5% IL 5% KY FL 100% GA TX 13% OK 100% KS 50% OH WA 100% OR 100% WI CA CO 90% SC 50% NJ MA CT DE MD VT 5% MN 40% MI IN UT 75% ND SD 10% ID 100% WY NMAZ NV MT 35% AR 5% LA MS AL NH RI NE MO TN NC VA WV PA NY ME IA IL KY FL GA TX OK KS OH WA OR WI CA AASHTO LRFD Survey May 2005 CO SC VT MN MI IN UT ND SD ID WY NMAZ NV MT AR LA MS AL AK 95% AK HI PR Full Implementation 50-90% Partial Implementation 1-10% Partial Implementation  No Implementation 26-50% Partial Implementation 11-25% Partial Implementation

Superstructure: LRFD Substructure: LRFD/ASD Foundations: ASD Earthwork and walls: ASD

Reasons 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 results. Lack of confidence in the computed results. Perceived errors and inconsistencies. Perceived errors and inconsistencies. A specification that did not reflect current design practices. A specification that did not reflect current design practices.

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 Revisions. AASHTO Section 11 and 10 Revisions.

Bridge Design Examples ConcreteSteel

NHI LRFD Training Courses Course A LRFD for Highway Bridge Substructures and Earth Retaining Structures

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

Revisions to Section 10 Compiled by a Technical Expert Panel Compiled by a Technical Expert Panel Review and input from A Technical Working Group (TWG) Review and input from A Technical Working Group (TWG) Accepted by AASHTO Subcommittee T-15 in June 2005 in Newport, Rhode Island Accepted by AASHTO Subcommittee T-15 in June 2005 in Newport, Rhode Island To be published in 2006 Interim To be published in 2006 Interim Attachments to Agenda Item 39 Section 3 revisions Attachments to Agenda item 40 Section 10 revisions

Topics Included Subsurface investigations Subsurface investigations Soil and rock properties Soil and rock properties Shallow foundations Shallow foundations Driven piles Driven piles Drilled shafts Drilled shafts Rigid and flexible culverts Rigid and flexible culverts Abutments Abutments Walls (All types) Walls (All types) Integral abutments Micropiles Augercast piles Soil nails Reinforced slopes All soil and rock earthwork features. Topics NOT Included

Section 10 Contents 10.1 SCOPE 10.2 DEFINITIONS 10.3 NOTATION 10.4 SOIL AND ROCK PROPERTIES 10.5 LIMIT STATES AND RESISTANCE FACTORS 10.6 SPREAD FOOTINGS 10.7 DRIVEN PILES 10.8 DRILLED SHAFTS PROPERTY INFO NO SIGNIFICANT CHANGE UPDATED UPDATED, CONSISTANT REORGANIZED, NEW CONTENT

Section 10.4 Soil and Rock Properties GEC 5 Sabatini, 2002 Subsurface Investigations Mayne, 2002

Section 10.4 Soil and Rock Properties Soil StrengthSoil Strength Soil DeformationSoil Deformation Rock Mass StrengthRock Mass Strength Rock Mass DeformationRock Mass Deformation Erodibility of rockErodibility of rock SELECTION OF DESIGN PROPERTIES NEW!

Section 10.5 Limit States and Resistance Factors Resistance factors revised Resistance factors revised Additional discussion on the basis for resistance factors Additional discussion on the basis for resistance factors Additional discussion of extreme event considerations Additional discussion of extreme event considerations

Articles and MaximumMinimum Piles,  -method Piles, -method Drilled Shafts, O’neill and Reese (1999) Downdrag Methods for computing Methods for computing Load Factors Load Factors Use of minimum load factors clarified Use of minimum load factors clarified

Section 10.6 Spread Footings Eccentricity provisions clarified B′ = B – 2e B L′ = L – 2e L Q = P/(B’ L’) Applies to geotechnical design for settlement and bearing resistance

Section 10.6 Spread Footings Hough method Elastic Settlement of cohesionless soils

Section 10.6 Spread Footings q n = c N cm +  D f N qm C wq  B N  m C w  NOMINAL RESISTANCE N c s c i c N q s q d q i q N  s  i  Shape Correction Factors COHESION UNIT WEIGHT DEPTHWIDTH Bearing Capacity Factors Inclination Factors Shear through overburden correction factor Water table correction Settlement correction factors removed

Section 10.7 Driven Piles Settlement of pile groups 4 new diagrams From: Hannigan (2005)

Section 10.7 Driven Piles HtHtHtHt QtQtQtQt MtMtMtMtPy The P-y method specified for horizontal deflection

Section 10.7 Driven Piles Original curve P y Modified curve P m * P P Spacing (S) Row 1 Row 2 Row 3 3D D P-multiplier (P m ) D S

Section 10.7 Driven Piles Field determination of nominal resistance Static load test Dynamic load test

Section 10.7 Driven Piles Static analysis methods Nordlund – Thurman method added Nordlund – Thurman method added

Section 10.7 Driven Piles Static analysis methods Primary use is for pile length estimation for contract drawings Primary use is for pile length estimation for contract drawings Secondary use for estimation of downdrag, uplift resistance and scour effects Secondary use for estimation of downdrag, uplift resistance and scour effects Should rarely be used as sole means of determining pile resistance Should rarely be used as sole means of determining pile resistance

Section 10.7 Driven Piles Requirements for driveability analysis have been added and clarified

Section 10.7 Driven Piles NEW! PILE LENGTH ESTIMATES FOR CONTRACT DOCUMENTS Determination of minimum pile penetration NEW!

Section 10.8 Drilled shafts Refers to driven piles section where possible Downdrag Downdrag Group settlement Group settlement Horizontal displacement (single and group) Horizontal displacement (single and group) Lateral squeeze Lateral squeeze Water table and buoyancy Water table and buoyancy Scour Scour Group resistance (cohesive soil only) Group resistance (cohesive soil only) Uplift (group and load test sections) Uplift (group and load test sections) Buckling Buckling Extreme event limit state Extreme event limit state

Section 10.8 Drilled shafts Static analysis methods for soil and rock have been updated Static analysis methods for soil and rock have been updated Consideration of both base and side resistance in rock is now included Consideration of both base and side resistance in rock is now included O’Neill and Reese (1999)

Section 10.8 Drilled shafts A + B QPQPQPQP QSQSQSQS Displacement Resistance Side Resistance Tip Resistance Total Resistance B C D A A + D B + C

Conclusion

Future Enhancements Overall stability Weight is both a load and a resistance Weight is both a load and a resistance Service limit state (should be strength limit state) Service limit state (should be strength limit state) WTWTWTWT WTWTWTWT WTWTWTWT WTWTWTWT N N T T T T l l clclclcl clclclcl N tan f

Future Enhancements Inclination Factors Ignored by many practicing engineers Ignored by many practicing engineers Based on small scale tests and theory Based on small scale tests and theory Effect of embedment (D f ) Effect of embedment (D f ) Resistance factors are for vertical load Resistance factors are for vertical load Q DfDf

Future Enhancements Nominal bearing resistance of rock Very little guidance available Very little guidance available CSIR Rock Mass Rating System proposed CSIR Rock Mass Rating System proposed CSIR developed for tunnel design CSIR developed for tunnel design Includes life safety considerations and therefore, margin of safety Includes life safety considerations and therefore, margin of safety May be conservative May be conservative

Future Enhancements Pile head fixity Connection details Connection details Effects of axial loads Effects of axial loads HH V

Future Enhancements Serviceability limits NCHRP Due April 2006 DxDxDxDx DzDzDzDz

What Should I Know and Do? Become familiar with BOTH the AASHTO standard specifications and LRFD specs. Become familiar with BOTH the AASHTO standard specifications and LRFD specs. Develop an understanding of your agency’s current design practice Develop an understanding of your agency’s current design practice

What Should I Know and Do? Develop and compare results for SEVERAL example problems with LRFD and YOUR standard design practice Develop and compare results for SEVERAL example problems with LRFD and YOUR standard design practice Translate your current practice to an LRFD format Translate your current practice to an LRFD format

What Should I Know and Do? Communicate your findings to AASHTO’s SubCommitteee members Communicate your findings to AASHTO’s SubCommitteee members

AASHTO 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 Foundation/ Earth Retaining Structure Design Questions?