AASHTO LRFD AASHTO LRFD Section 10.7 and 10.8 Section 10.7 and 10.8

Deep FoundationsDeep Foundations

““BY FAR THIS SECTION HAS BEEN BY FAR THIS SECTION HAS BEEN IDENTIFIED AS THE MOST PROBLEMATIC IDENTIFIED AS THE MOST PROBLEMATIC SECTION OF THE AASHTO LRFD SPECS. SECTION OF THE AASHTO LRFD SPECS.

BY THE STATE DOTS”BY THE STATE DOTS”

10.7DRIVEN PILES10.7.1General10.7.1.1MINIMUM PILE SPACING, CLEARANCE AND EMBEDMENT INTO CAP10.7.1.2PILES THROUGH EMBANKMENT FILL10.7.1.3BATTER PILES10.7.1.4PILE DESIGN REQUIREMENTS10.7.1.5Determination of Pile Loads10.7.1.5.1Downdrag10.7.1.5.2Uplift Due to Expansive Soils10.7.1.5.3Nearby Structures10.7.2Service Limit State Design10.7.2.1GENERAL10.7.2.2TOLERABLE MOVEMENTS10.7.2.3settlement10.7.2.3.1Pile Groups in Cohesive Soil10.7.2.3.2Pile Groups in Cohesionless Soil10.7.2.4HORIZONTAL PILE FOUNDATION MOVEMENT10.7.2.5SETTLEMENT DUE TO DOWNDRAG10.7.2.6lateral squeeze10.7.3Strength Limit State Design10.7.3.1POINT BEARING PILES ON ROCK10.7.3.1.1Piles Driven to Soft Rock10.7.3.1.2Piles Driven to Hard Rock10.7.3.2pile length estimates for contract documents10.7.3.3nominal axial RESISTANCE CHANGE AFTER PILE DRIVING10.7.3.3.1Relaxation10.7.3.3.2Setup10.7.3.4 groundwater effects and BUOYANCY

Deep Foundations OverviewDeep Foundations Overview 10.7 Driven Piles10.7 Driven Piles

Total re-writeTotal re-write

10.8 Drilled Shafts10.8 Drilled Shafts Re-organized + new & updated contentRe-organized + new & updated content

Service Limit State (10.7.2) Service Limit State (10.7.2) Vertical DisplacementVertical Displacement

Additional equivalent footing diagrams addedAdditional equivalent footing diagrams added Horizontal DisplacementHorizontal Displacement

P-y method for analysis of horizontal P-y method for analysis of horizontal displacement now specifically called outdisplacement now specifically called out

P multipliers for group effects updated and P multipliers for group effects updated and specifiedspecified

Overall stabilityOverall stability

Vertical DisplacementVertical Displacement

Horizontal Displacement Horizontal Displacement (P-y method)(P-y method)

HHtt

QQtt

MMttyyPP

yyyy

PropertiesPropertiesA, E, IA, E, I

Original cu

rve

Original cu

rvePP

yyModified curve

Modified curve

PPmm * P * P

PP

Spacing (S)Spacing (S) Row 1Row 1 Row 2Row 2 Row 3Row 33D3D 0.70.7 0.50.5 0.350.355D5D 1.01.0 0.850.85 0.70.7

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

SS

From Table 10.7.2.4-1

Overall StabilityOverall Stability

Strength Limit State (10.7.3)Strength Limit State (10.7.3) Geotechnical ResistanceGeotechnical Resistance

EmphasisEmphasis of pile resistance verification of pile resistance verification during constructionduring construction

De-emphasisDe-emphasis on use of static analysis on use of static analysis methods except for estimation of pile methods except for estimation of pile length for contract drawingslength for contract drawings

Structural ResistanceStructural Resistance AxialAxial Combined bending and axialCombined bending and axial ShearShear

Driven ResistanceDriven Resistance (10.7.7) (10.7.7)

Axial Geotechnical ResistanceAxial Geotechnical Resistance

Static Load TestStatic Load Test

LoadLoadS

ettle

men

tS

ettle

men

t

Pile top settlementPile top settlement

Elastic pile compression

Elastic pile compression

Davidson Method SpecifiedDavidson Method Specified

Dynamic Load Test (PDA)Dynamic Load Test (PDA)

Method & equations are Method & equations are now prescribednow prescribed

Driving FormulasDriving Formulas

Driving FormulasDriving Formulas FHWA Gates MethodFHWA Gates Method

Method & Equation PrescribedMethod & Equation Prescribed

Engineering News MethodEngineering News Method Equation Modified to Produce Equation Modified to Produce

Ultimate Resistance by Removing the Ultimate Resistance by Removing the Built-in Factor of Safety = 6Built-in Factor of Safety = 6

Driving Formula LimitationsDriving Formula Limitations

Design “stresses” Design “stresses” mustmust be limited if a be limited if a driveability analysis is not performeddriveability analysis is not performed

limiting stresses prescribedlimiting stresses prescribed

Limited to nominal resistances below 300 Limited to nominal resistances below 300 tonstons

Geotechnical Safety Factors for PilesGeotechnical Safety Factors for Piles

Design Basis & Design Basis & Const. ControlConst. Control

Increasing Design/Const. Increasing Design/Const. ControlControl

Subsurface Expl.Subsurface Expl. XX X X X X X X X XStatic CalculationStatic Calculation XX X X X X X X X XDynamic FormulaDynamic Formula XXWave EquationWave Equation XX X X X X X XCAPWAPCAPWAP XX X XStatic Load TestStatic Load Test XX X XFSFS 3.503.50 2.752.75 2.252.25 2.002.00 1.901.90

Static Analysis MethodsStatic Analysis Methods Existing Methods RetainedExisting Methods Retained FHWA Nordland/Thurman Method AddedFHWA Nordland/Thurman Method Added

Applicability limited to:Applicability limited to:- - Prediction of pile penetration (used Prediction of pile penetration (used

without resistance factors)without resistance factors)- - Rare case of driving to prescribed Rare case of driving to prescribed

penetration or depth (no field penetration or depth (no field determination of pile axial resistance)determination of pile axial resistance)

Geotechnical Resistance FactorsGeotechnical Resistance FactorsPile Static Analysis MethodsPile Static Analysis Methods

MethodMethod CompComp TenTen

- Method- Method 0.40.4 0.30.3 - Method- Method 0.350.35 0.250.25 - Method- Method 0.40.4 0.30.3Nordlund-ThurmanNordlund-Thurman 0.450.45SPTSPT 0.30.3 0.250.25CPTCPT 0.450.45 0.350.35GroupGroup 0.60.6 0.50.5

From Table 10.5.5.2.2-1

Table 10.5.5.2.2-1 Resistance Factors for Driven Piles

CONDITION/RESISTANCE DETERMINATION METHOD RESISTANCE FACTOR

Nominal Resistance of Single Pile in Axial Compression – Dynamic Analysis and Static Load Test Methods, dyn

Driving criteria established by static load test(s); quality control by dynamic testing and/or calibrated wave equation, or minimum driving resistance combined with minimum delivered hammer energy from the load test(s). For the last case, the hammer used for the test pile(s) shall be used for the production piles.

Values in Table 2

Driving criteria established by dynamic test with signal matching at beginning of redrive conditions only of at least one production pile per pier, but no less than the number of tests per site provided in Table 3. Quality control of remaining piles by calibrated wave equation and/or dynamic testing.

0.65

Wave equation analysis, without pile dynamic measurements or load test, at end of drive conditions only

0.40

FHWA-modified Gates dynamic pile formula (End Of Drive condition only) 0.40

Engineering News Record (as defined in Article 10.7.3.7.4) dynamic pile formula (End Of Drive condition only)

0.10

Table 10.5.5.2.2-2 Relationship between Number of Static Load Tests Conducted per Site and (after Paikowsky, et al., 2004)

Number of Static Load

Tests per Site

Resistance Factor, Site Variability*

Low* Medium* High*

1 0.80 0.70 0.552 0.90 0.75 0.653 0.90 0.85 0.75

> 4 0.90 0.90 0.80

Table 10.5.5.2.2-3 Number of Dynamic Tests with Signal Matching Analysis per Site to Be Conducted During Production Pile Driving (after Paikowsky, et al., 2004)

Site Variability*

Low* Medium* High*

Number of Piles

Located within Site

Number of Piles with Dynamic Tests and Signal Matching Analysis Required (BOR)

< 15 3 4 6

16-25 3 5 8

26-50 4 6 9

51-100 4 7 10

101-500 4 7 12

> 500 4 7 12

Structural Axial Failure ModeStructural Axial Failure Mode

Structural Flexure Failure Structural Flexure Failure ModeMode

Structural Shear Failure Structural Shear Failure ModeMode

Methods for determining Methods for determining structural resistancestructural resistance

Axial compressionAxial compression Combined axial and flexureCombined axial and flexure ShearShear

LRFDSpecifications

Concrete – Section 5Concrete – Section 5

Steel – Section 6Steel – Section 6

Wood – Section 8Wood – Section 8

Driven Performance LimitDriven Performance Limit

Drivability Analysis (10.7.7)Drivability Analysis (10.7.7) Specifically requiredSpecifically required Purpose is to verify that the specified pile Purpose is to verify that the specified pile

can be driven:can be driven: To the required minimum penetrationTo the required minimum penetration To the required ultimate resistanceTo the required ultimate resistance Using a commonly available hammerUsing a commonly available hammer Without exceeding the permissible Without exceeding the permissible

driving stressdriving stress At a reasonable penetration rateAt a reasonable penetration rate

37.5 ksi37.5 ksi

550 kip550 kip

120 bpf120 bpf

Comp Strksi

30

20

10

Ult Cap

200

400

600

800

kips

0 160 320 480 Blows/ft

4.0

8.0

12.0

16.0ft

Stroke

Tens Strksi

Driven Performance LimitDriven Performance Limit

Extreme Event Limit State (10.7.4 )Extreme Event Limit State (10.7.4 )

New section New section with limited with limited guidance guidance regarding regarding extreme events extreme events (no guidance (no guidance previously previously provided)provided)

Piles - Other ConsiderationsPiles - Other Considerations 10.7.5 Corrosion and Deterioration10.7.5 Corrosion and Deterioration

Moved from section 10.7.1 with no major changesMoved from section 10.7.1 with no major changes 10.7.6 Determination of Minimum Pile Penetration10.7.6 Determination of Minimum Pile Penetration

New section combining some of the existing material from section 10.7.1 with additional guidance.New section combining some of the existing material from section 10.7.1 with additional guidance. Downdrag provisions extensively modifiedDowndrag provisions extensively modified

DowndragDowndrag

New provisions in article New provisions in article 3.11.83.11.8 regarding regarding determination of downdrag as a loaddetermination of downdrag as a load

Revisions to load factors pending Revisions to load factors pending additional analysis/researchadditional analysis/research

Prediction MethodPrediction Method MaximumMaximum MinimumMinimum

Piles, Piles, -Tomlinson -Tomlinson 1.4 1.4 --Piles, Piles, -Method-Method 1.051.05 --

Drilled shafts, O’Neill Drilled shafts, O’Neill and Reese (1999) and Reese (1999)

1.251.25 --

10.8 DRILLED SHAFTS10.8 DRILLED SHAFTS Article re-organized to follow section 10.7Article re-organized to follow section 10.7 Most provisions refer back to section 10.7Most provisions refer back to section 10.7 Service limit state provisions removed from Service limit state provisions removed from

strength limit state resistance determinationstrength limit state resistance determination Provisions for resistance determination Provisions for resistance determination

updatedupdated Detailed procedures for evaluation of Detailed procedures for evaluation of

combined side friction and end bearing in rock combined side friction and end bearing in rock added to commentaryadded to commentary

10.8DRILLED SHAFTS10.8.1General10.8.1.1scope10.8.1.2shaft spacing, clearance and embedment into cap10.8.1.3shaft diameter and enlarged bases10.8.1.4batterED shafts10.8.1.5drilled SHAFT resistance10.8.1.6DETERMINATION OF Shaft Loads10.8.1.6.1General10.8.1.6.2Downdrag10.8.1.6.3Uplift10.8.2Service Limit State Design10.8.2.1tolerable movements10.8.2.2 settlement10.8.2.2.1 General10.8.2.2.2 Settlement of Single-Drilled Shaft10.8.2.2.3 Intermediate Geo Materials (IGM’s)10.8.2.2.4 Group Settlement10.8.2.3 HORIZONTAL MOVEMENT OF SHAFTS AND SHAFT GROUPS10.8.2.4 settlement due to downdrag10.8.2.5 lateral squeeze10.8.3 Strength Limit State Design10.8.3.1 general10.8.3.2 ground water table and bouyancy10.8.3.3 Scour10.8.3.4 downdrag

10.8.3.5 NOMINAL axial COMPRESSION resistance of single drilled shafts10.8.3.5.1 Estimation of Drilled Shaft Resistance in Cohesive Soils10.8.3.5.1a Side Resistance10.8.3.5.1b Tip Resistance10.8.3.5.2 Estimation of Drilled Shaft Resistance in Cohesionless Soils

Drilled Shaft Resistance in RockDrilled Shaft Resistance in Rock

Side ResistanceSide Resistance

Tip ResistanceTip Resistance

Total ResistanceTotal Resistance

AABBCCDD

QQPP

QQSS

QQRR = fQ = fQnn = ffqpqpQQpp + f + fqsqsQQss

DisplacementDisplacement

Res

ista

nce

Res

ista

nce

Geotechnical Resistance FactorsGeotechnical Resistance Factors Drilled ShaftsDrilled Shafts

MethodMethod CompComp TenTen

- Method (side)- Method (side) 0.550.55 0.450.45 - Method (side)- Method (side) 0.550.55 0.450.45Clay or Sand (tip)Clay or Sand (tip) 0.50.5Rock (side)Rock (side) 0.550.55 0.450.45Rock (tip)Rock (tip) 0.550.55Group (sand or clay)Group (sand or clay) 0.550.55 0.450.45Load TestLoad Test 0.70.7

AASHTO Table 10.5.5.2.3-1