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AASHTO LRFD Section 10.7 and 10.8 Deep Foundations “ BY FAR THIS SECTION HAS BEEN IDENTIFIED AS THE MOST PROBLEMATIC SECTION OF THE AASHTO LRFD SPECS.

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Presentation on theme: "AASHTO LRFD Section 10.7 and 10.8 Deep Foundations “ BY FAR THIS SECTION HAS BEEN IDENTIFIED AS THE MOST PROBLEMATIC SECTION OF THE AASHTO LRFD SPECS."— Presentation transcript:

1 AASHTO LRFD Section 10.7 and 10.8 Deep Foundations “ BY FAR THIS SECTION HAS BEEN IDENTIFIED AS THE MOST PROBLEMATIC SECTION OF THE AASHTO LRFD SPECS. BY THE STATE DOTS”

2 10.7DRIVEN PILES General MINIMUM PILE SPACING, CLEARANCE AND EMBEDMENT INTO CAP PILES THROUGH EMBANKMENT FILL BATTER PILES PILE DESIGN REQUIREMENTS Determination of Pile Loads Downdrag Uplift Due to Expansive Soils Nearby Structures Service Limit State Design GENERAL TOLERABLE MOVEMENTS settlement Pile Groups in Cohesive Soil Pile Groups in Cohesionless Soil HORIZONTAL PILE FOUNDATION MOVEMENT SETTLEMENT DUE TO DOWNDRAG lateral squeeze Strength Limit State Design POINT BEARING PILES ON ROCK Piles Driven to Soft Rock Piles Driven to Hard Rock pile length estimates for contract documents nominal axial RESISTANCE CHANGE AFTER PILE DRIVING Relaxation Setup groundwater effects and BUOYANCY

3 Deep Foundations Overview 10.7 Driven Piles 10.7 Driven Piles Total re-write Total re-write 10.8 Drilled Shafts 10.8 Drilled Shafts Re-organized + new & updated content Re-organized + new & updated content

4 Service Limit State (10.7.2) Vertical Displacement Vertical Displacement Additional equivalent footing diagrams added Additional equivalent footing diagrams added Horizontal Displacement Horizontal Displacement P-y method for analysis of horizontal displacement now specifically called out P-y method for analysis of horizontal displacement now specifically called out P multipliers for group effects updated and specified P multipliers for group effects updated and specified Overall stability Overall stability

5 Vertical Displacement

6 Horizontal Displacement (P-y method) HtHtHtHt QtQtQtQt MtMtMtMt y P y yProperties A, E, I

7 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 From Table

8 Overall Stability

9 Strength Limit State (10.7.3) Geotechnical Resistance Geotechnical Resistance Emphasis of pile resistance verification during construction Emphasis of pile resistance verification during construction De-emphasis on use of static analysis methods except for estimation of pile length for contract drawings De-emphasis on use of static analysis methods except for estimation of pile length for contract drawings Structural Resistance Structural Resistance Axial Axial Combined bending and axial Combined bending and axial Shear Shear Driven Resistance (10.7.7) Driven Resistance (10.7.7)

10 Axial Geotechnical Resistance

11 Static Load Test

12 Load Settlement Pile top settlement Elastic pile compression Davidson Method Specified

13 Dynamic Load Test (PDA) Method & equations are now prescribed

14 Driving Formulas

15 FHWA Gates Method FHWA Gates Method Method & Equation Prescribed Method & Equation Prescribed Engineering News Method Engineering News Method Equation Modified to Produce Ultimate Resistance by Removing the Built-in Factor of Safety = 6 Equation Modified to Produce Ultimate Resistance by Removing the Built-in Factor of Safety = 6

16 Driving Formula Limitations Design “stresses” must be limited if a driveability analysis is not performed Design “stresses” must be limited if a driveability analysis is not performed limiting stresses prescribed limiting stresses prescribed Limited to nominal resistances below 300 tons Limited to nominal resistances below 300 tons

17 Geotechnical Safety Factors for Piles Design Basis & Const. Control Increasing Design/Const. Control Subsurface Expl. X X X X X X X X X X Static Calculation X X X X X X X X X X Dynamic Formula X Wave Equation X X X X X X X X CAPWAP X X X X Static Load Test X X X X FS

18 Static Analysis Methods Existing Methods Retained Existing Methods Retained FHWA Nordland/Thurman Method Added FHWA Nordland/Thurman Method Added Applicability limited to: - Prediction of pile penetration (used without resistance factors) - Rare case of driving to prescribed penetration or depth (no field determination of pile axial resistance)

19 Geotechnical Resistance Factors Pile Static Analysis Methods Method  Comp  Ten  - Method  - Method Method - Method Nordlund-Thurman0.45 SPT CPT Group From Table

20 Table Resistance Factors for Driven Piles CONDITION/RESISTANCE DETERMINATION METHODRESISTANCE 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 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 ) dynamic pile formula (End Of Drive condition only) 0.10

21 Table 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* >

22 Table 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) < >

23 Structural Axial Failure Mode

24 Structural Flexure Failure Mode

25 Structural Shear Failure Mode

26 Methods for determining structural resistance Axial compression Axial compression Combined axial and flexure Combined axial and flexure Shear Shear LRFD Specifications Concrete – Section 5 Steel – Section 6 Wood – Section 8

27 Driven Performance Limit

28 Drivability Analysis (10.7.7) Specifically required Specifically required Purpose is to verify that the specified pile can be driven: Purpose is to verify that the specified pile can be driven: To the required minimum penetration To the required minimum penetration To the required ultimate resistance To the required ultimate resistance Using a commonly available hammer Using a commonly available hammer Without exceeding the permissible driving stress Without exceeding the permissible driving stress At a reasonable penetration rate At a reasonable penetration rate

29 37.5 ksi 550 kip 120 bpf

30 Driven Performance Limit

31 Extreme Event Limit State ( ) New section with limited guidance regarding extreme events (no guidance previously provided) New section with limited guidance regarding extreme events (no guidance previously provided)

32 Piles - Other Considerations Corrosion and Deterioration Corrosion and Deterioration Moved from section with no major changes Moved from section with no major changes Determination of Minimum Pile Penetration Determination of Minimum Pile Penetration New section combining some of the existing material from section with additional guidance. New section combining some of the existing material from section with additional guidance. Downdrag provisions extensively modified Downdrag provisions extensively modified

33 Downdrag New provisions in article regarding determination of downdrag as a load New provisions in article regarding determination of downdrag as a load Revisions to load factors pending additional analysis/research Revisions to load factors pending additional analysis/research Prediction Method Prediction MethodMaximumMinimum Piles,  -Tomlinson 1.4- Piles, -Method Drilled shafts, O’Neill and Reese (1999)

34 10.8 DRILLED SHAFTS Article re-organized to follow section 10.7 Article re-organized to follow section 10.7 Most provisions refer back to section 10.7 Most provisions refer back to section 10.7 Service limit state provisions removed from strength limit state resistance determination Service limit state provisions removed from strength limit state resistance determination Provisions for resistance determination updated Provisions for resistance determination updated Detailed procedures for evaluation of combined side friction and end bearing in rock added to commentary Detailed procedures for evaluation of combined side friction and end bearing in rock added to commentary

35 10.8DRILLED SHAFTS General scope shaft spacing, clearance and embedment into cap shaft diameter and enlarged bases batterED shafts drilled SHAFT resistance DETERMINATION OF Shaft Loads General Downdrag Uplift Service Limit State Design tolerable movements settlement General Settlement of Single-Drilled Shaft Intermediate Geo Materials (IGM’s) Group Settlement HORIZONTAL MOVEMENT OF SHAFTS AND SHAFT GROUPS settlement due to downdrag lateral squeeze Strength Limit State Design general ground water table and bouyancy Scour downdrag NOMINAL axial COMPRESSION resistance of single drilled shafts Estimation of Drilled Shaft Resistance in Cohesive Soils aSide Resistance bTip Resistance Estimation of Drilled Shaft Resistance in Cohesionless Soils

36 Drilled Shaft Resistance in Rock Side Resistance Tip Resistance Total Resistance A B C D QPQPQPQP QSQSQSQS Q R = fQ n f qp Q p + f qs Q s Q R = fQ n = f qp Q p + f qs Q s Displacement Resistance

37 Geotechnical Resistance Factors Drilled Shafts Method  Comp  Ten  - Method (side)  - Method (side) Clay or Sand (tip) 0.5 Rock (side) Rock (tip) 0.55 Group (sand or clay) Load Test 0.7 AASHTO Table


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