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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 Additional equivalent footing diagrams addedadded
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
MMttyy
PP
yy
yyPropertiesPropertiesA, E, IA, E, I
Original c
urve
Original c
urvePP
yyModified curve
Modified curve
PPmm * P * P
PP
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
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 X
Static CalculationStatic Calculation XX X X X X X X X X
Dynamic FormulaDynamic Formula XX
Wave EquationWave Equation XX X X X X X X
CAPWAPCAPWAP XX X X
Static Load TestStatic Load Test XX X X
FSFS 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 0.30.3
Nordlund-ThurmanNordlund-Thurman 0.450.45
SPTSPT 0.30.3 0.250.25
CPTCPT 0.450.45 0.350.35
GroupGroup 0.60.6 0.50.5From 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 0.55
2 0.90 0.75 0.65
3 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 Str
ksi
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 Str
ksi
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 shafts
10.8.3.5.1 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
AA
BBCCDD
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 0.450.45
Clay or Sand (tip)Clay or Sand (tip) 0.50.5
Rock (side)Rock (side) 0.550.55 0.450.45
Rock (tip)Rock (tip) 0.550.55
Group (sand or clay)Group (sand or clay) 0.550.55 0.450.45
Load TestLoad Test 0.70.7AASHTO Table 10.5.5.2.3-1
Recommended