AASHTO LRFD Section 10. 7 and 10 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”

10.7 DRIVEN PILES 10.7.1 General 10.7.1.1 MINIMUM PILE SPACING, CLEARANCE AND EMBEDMENT INTO CAP 10.7.1.2 PILES THROUGH EMBANKMENT FILL 10.7.1.3 BATTER PILES 10.7.1.4 PILE DESIGN REQUIREMENTS 10.7.1.5 Determination of Pile Loads 10.7.1.5.1 Downdrag 10.7.1.5.2 Uplift Due to Expansive Soils 10.7.1.5.3 Nearby Structures 10.7.2 Service Limit State Design 10.7.2.1 GENERAL 10.7.2.2 TOLERABLE MOVEMENTS 10.7.2.3 settlement 10.7.2.3.1 Pile Groups in Cohesive Soil 10.7.2.3.2 Pile Groups in Cohesionless Soil 10.7.2.4 HORIZONTAL PILE FOUNDATION MOVEMENT 10.7.2.5 SETTLEMENT DUE TO DOWNDRAG 10.7.2.6 lateral squeeze 10.7.3 Strength Limit State Design 10.7.3.1 POINT BEARING PILES ON ROCK 10.7.3.1.1 Piles Driven to Soft Rock 10.7.3.1.2 Piles Driven to Hard Rock 10.7.3.2 pile length estimates for contract documents 10.7.3.3 nominal axial RESISTANCE CHANGE AFTER PILE DRIVING 10.7.3.3.1 Relaxation 10.7.3.3.2 Setup 10.7.3.4 groundwater effects and BUOYANCY

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

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

Vertical Displacement

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

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 10.7.2.4-1

Overall Stability

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)

Axial Geotechnical Resistance

Static Load Test

Load Elastic pile compression Settlement Pile top settlement Davidson Method Specified

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

Driving Formulas

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

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

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 3.50 2.75 2.25 2.00 1.90

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)

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 10.5.5.2.2-1

CONDITION/RESISTANCE DETERMINATION METHOD 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) Engineering News Record (as defined in Article 10.7.3.7.4) dynamic pile formula (End Of Drive condition only) 0.10

Number of Static Load Tests per Site 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 0.85 > 4

Number of Piles Located within Site 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 5 8 26-50 9 51-100 7 10 101-500 12 > 500

Structural Axial Failure Mode

Structural Flexure Failure Mode

Structural Shear Failure Mode

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

Driven Performance Limit

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

37.5 ksi 550 kip 120 bpf

Driven Performance Limit

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

Piles - Other Considerations 10.7.5 Corrosion and Deterioration Moved from section 10.7.1 with no major changes 10.7.6 Determination of Minimum Pile Penetration New section combining some of the existing material from section 10.7.1 with additional guidance. Downdrag provisions extensively modified

Drilled shafts, O’Neill and Reese (1999) Downdrag New provisions in article 3.11.8 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

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

10.8 DRILLED SHAFTS 10.8.1 General 10.8.1.1 scope 10.8.1.2 shaft spacing, clearance and embedment into cap 10.8.1.3 shaft diameter and enlarged bases 10.8.1.4 batterED shafts 10.8.1.5 drilled SHAFT resistance 10.8.1.6 DETERMINATION OF Shaft Loads 10.8.1.6.1 General 10.8.1.6.2 Downdrag 10.8.1.6.3 Uplift 10.8.2 Service Limit State Design 10.8.2.1 tolerable movements 10.8.2.2 settlement 10.8.2.2.1 General 10.8.2.2.2 Settlement of Single-Drilled Shaft 10.8.2.2.3 Intermediate Geo Materials (IGM’s) 10.8.2.2.4 Group Settlement 10.8.2.3 HORIZONTAL MOVEMENT OF SHAFTS AND SHAFT GROUPS 10.8.2.4 settlement due to downdrag 10.8.2.5 lateral squeeze 10.8.3 Strength Limit State Design 10.8.3.1 general 10.8.3.2 ground water table and bouyancy 10.8.3.3 Scour 10.8.3.4 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 Soils 10.8.3.5.1a Side Resistance 10.8.3.5.1b Tip Resistance 10.8.3.5.2 Estimation of Drilled Shaft Resistance in Cohesionless Soils

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

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 10.5.5.2.3-1