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AASHTO LRFD Section and 10

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Presentation on theme: "AASHTO LRFD Section and 10"— Presentation transcript:

1 AASHTO LRFD Section 10. 7 and 10

2 10.7 DRIVEN 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 Total re-write 10.8 Drilled Shafts Re-organized + new & updated content

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

5 Vertical Displacement

6 Horizontal Displacement (P-y method)
Qt P Ht Mt y y Properties A, E, I y

7 S P P Original curve Modified curve Pm * P y D P-multiplier (Pm) Spacing (S) Row 1 Row 2 Row 3 3D 0.7 0.5 0.35 5D 1.0 0.85 From Table

8 Overall Stability

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

10 Axial Geotechnical Resistance

11 Static Load Test

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

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

14 Driving Formulas

15 Driving Formulas FHWA Gates Method Method & Equation Prescribed
Engineering News Method 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 limiting stresses prescribed 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 Static Calculation Dynamic Formula X Wave Equation X X X X CAPWAP X X Static Load Test X X FS

18 Static Analysis Methods
Existing Methods Retained 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
Comp Ten  - Method 0.4 0.3  - Method 0.35 0.25  - Method Nordlund-Thurman 0.45 SPT CPT Group 0.6 0.5 Note that the static analysis resistance factors are much less than the field tested resistance factors. Ask Participants why (answer less uncertainty from fielded tested resistance) From Table

Table 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) Engineering News Record (as defined in Article ) dynamic pile formula (End Of Drive condition only) 0.10

21 Number of Static Load Tests per Site
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* 1 0.80 0.70 0.55 2 0.90 0.75 0.65 3 0.85 > 4

22 Number of Piles Located within Site
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) < 15 3 4 6 16-25 5 8 26-50 9 51-100 7 10 12 > 500

23 Structural Axial Failure Mode

24 Structural Flexure Failure Mode

25 Structural Shear Failure Mode

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

27 Driven Performance Limit

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

29 37.5 ksi 550 kip 120 bpf

30 Driven Performance Limit

31 Extreme Event Limit State (10.7.4 )
New section with limited guidance regarding extreme events (no guidance previously provided)

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

33 Drilled shafts, O’Neill and Reese (1999)
Downdrag New provisions in article regarding determination of downdrag as a load Revisions to load factors pending additional analysis/research Prediction Method Maximum Minimum Piles, -Tomlinson 1.4 - Piles, -Method 1.05 Drilled shafts, O’Neill and Reese (1999) 1.25

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

35 10.8 DRILLED 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 a Side Resistance b Tip Resistance Estimation of Drilled Shaft Resistance in Cohesionless Soils

36 Drilled Shaft Resistance in Rock
Total Resistance A Side Resistance B Resistance D C Tip Resistance QS Displacement QR = fQn = fqpQp + fqsQs QP

37 Geotechnical Resistance Factors Drilled Shafts
Method Comp Ten  - Method (side) 0.55 0.45  - Method (side) Clay or Sand (tip) 0.5 Rock (side) Rock (tip) Group (sand or clay) Load Test 0.7 The resistance factors are provided for each method in AASHTO section 10.5 AASHTO Table

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