Geotechnical - Load and Resistance Factor Design

1 Geotechnical - load and Resistance Factor DesignByMir Zaheer, , Geotechnical Engineer , INDOT Office of Geotechnical EngineeringINDOT Structures Conference -2010 MSE WallsAASHTO Section 11 FHWA GEC 11 FHWA-NHI-10-024 & 25 MSE Walls In LRFD, the external and internal stability of the MSE wall is evaluated at all appropriate Limit states. In the AASHTO-LRFD framework, there are four limit states, which represent distinct structural performance criteria: (1) strength limit states (2) Serviceability limit states (3) extreme event limit states (4) fatigue limit states For most earth retaining system designs, the strength or service limit states control the Design . For walls subject to earthquake or vessel/vehicle impact, the extreme limit states may of MSE walls Using LRFD MethodologyStrength Limit States External Stability Limiting Eccentricity Sliding Bearing Resistance Internal Stability Tensile Resistance of Reinforcement Pullout Resistance of Reinforcement Structural Resistance of face elements Structural Resistance of Face Element ConnectionsService Limit States External Stability Vertical WALL Movements Lateral Wall MovementsGlobal Stability Overall Stability Compound StabilityInternal Stability is the responsibility of the manufacturerLRFD for MSE Walls load Combinations load Factors for Permanent Loads External Stability Resistance FactorsLoads and Combinations Permanent Loads EH = Horizontal Earth Loads ES = Earth Surcharge load EV = Vertical Pressure from dead load of earth fill Transient Loads CT = Vehicular collision force EQ = Earthquake load LL = Vehicular Live load LS = Live load SurchargeLoad Combination Limit State EHESEV LLLSEQ CTStrength I Event I P Event II I

2 P= load Factor for permanent loading. May subscript as P-EV, P-EH EQ= load Factor for live load applied simultaneously with seismic loads Table AASHTO 2007 load Factors for Permanent Loads, PTable AASHTO 2007 Type of load load Factor , PMaximumMinimumDC: Component and EH: Horizontal Earth PressureActive EV: Vertical Earth Pressure Overall Stability Retaining Walls and ES: Earth Note: May subscript as EV-MAX EV-MIN, EH-MAX, EH-MIN, Stability Resistance Factors for MSE WallsStability ModeConditionsResistance Factor , Bearing Resistance Sliding Overall (Global) Stability Where Geotechnical parameters are well defined, and the slope does not support or contain a structural element Where Geotechnical parameters are based on limited information, or the slope contains or supports a structural element MSE Wall Design ExampleMSE Wall Design ExampleMSE Wall Design ExampleMSE Wall Design ExampleMSE Wall Design ExampleMSE Wall Design ExampleCDR = Capacity To Demand RatioMSE Wall Design ExampleMSE Wall Design ExampleIf the sliding, capacity demand ratio, CDR < 1, INCREASE the reinforcement length, L, and repeat the Foundation Design Flow Chart1.

3 Establish Global Project Performance Requirements and Constraints2. Define Preliminary Project Geotechnical Site Conditions3. Determine Substructure Loads and load Combinations at Foundation Level4. Develop and Execute Subsurface Exploration and Laboratory Testing Program for Feasible Foundation System5. Evaluate Information and Determine Foundation Systems for Further Evaluation6. Deep FoundationsShallow FoundationsWithout Ground ImprovementWith Ground ImprovementShallow FoundationsAASHTO SECTION RC/TD -10-001 FHWA-NHI-05-094 Shallow Foundation Design FlowchartDefine Subsurface Conditions and any Geometric ConstraintsDetermine depth of footing based on Geotechnical bearing, scour, and frost protection considerationsDetermine Applicable Loads and load CombinationsFactor Loads for Each CombinationDetermine Design Soil Properties & Resistance FactorsCheck Global Stability at the Service Limit StateDetermine the Nominal Geotechnical Bearing Resistance at the Service Limit StateSize the Footing at the Service Limit StateDetermine the Nominal Bearing & Sliding Resistance at the Strength & Extreme Limit StatesCheck Footing at Strength Limit State for Bearing, Sliding and EccentricityCheck Footing at Strength & Extreme Limit States for Sliding.

4 Eccentricity and Bearing StressPerform Structural Design of Footing Based on Factored Loads and Factored ResistancesLimit States for Spread FootingsDesign of a spread footing must provide adequate Resistance against Geotechnical and structural limit states, , "failure modes. The Geotechnical limit states includethe following: Strength limit state Bearing Resistance Limiting eccentricity SlidingStrength Limit StatesSlidingLimiting EccentricityBearing Resistance Service limit state Settlement Global stability Extreme Event limit state Bearing Resistance Limiting eccentricity SlidingService Limit StatesSettlementOverall StabilityThe structural Design includes considerationof limit states for the following: Flexural Resistance (strength limit) Shear Resistance (strength limit) Crack control (service limit)Horizontal Deformations-Settlements & RotationsBearing Resistance ChartDesign ResourcesLRFD Design -BASICS load Factor combinations to obtain resulting maximum force effects on the foundations are needed for limit states checks.

5 This is done through structure modeling by varying the load factors over the specified rangeService Limit State I-Checks Vertical deformation Settlement Horizontal movements at the top of foundation Rotations at the top of foundation Vertical and horizontal deformations under scour at the Design flood, Q100 Settlements due to downdrag(AASHTO , , & )Requirements for LRFD Design Tolerable vertical and horizontal deformations (movements) are established by the structural designer, based on structural tolerance to total and differential movements, rideability, and economy. (AASHTO )Strength Limit States - Checks Geotechnical lateral Resistance of soil and rock Geotechnical axial compression Resistance Geotechnical axial uplift resistanceAll the above for single and group foundations Structural Resistance checks for axial, lateral and flexure Punching of foundation elements through stronger soil in to weaker soilsAll the above resistances under scour at Design flood, Q100 Axial Resistance when downdrag occurs(AASHTO , , & )Axial Geotechnical ResistanceOverall StabilityMethods for determining structural Resistance Axial compression Combined axial and flexure Shear Concrete AASHTO Section 5 Steel AASHTO Section 6 Structural Axial Failure ModeStructural Flexure Failure ModeStructural Shear Failure ModeLoad & Resistance Factor Design .

6 Deep Foundations (AASHTO & ) Piles Drilled Shafts Shallow Foundations (AASHTO ) Spread Footings MSE Walls & Other Retaining Walls (AASHTO 11) Culverts, Tunnels and other buried Structures (AASHTO 11)DeepFoundationsDriven Piles -AASHTO Shafts - AASHTO Deep Foundations7. Select Driven pile Foundations for Further Evaluation8. Select static Analysis Method and Calculate Ultimate Axial Capacity vs. Depth9. Identify Most Economical pile Types from Ultimate Capacity vs. Depth Charts10. Drivability of pile types to penetration depths and sufficient ultimate capacities 11. Select pile types, ultimate capacities, and pile penetration depths for group sizing12. Evaluate Group axial, Lateral, and Rotational Capacities, Settlement, and performance of pile group configurationEvaluate Other Deep Foundation Systems Drilled ShaftsGeneral Deep Foundation Design Flow Chart for Driven PilesGeotechnical Resistance Factors for Driven PilesCondition/ Resistance Determination MethodAASHTO Resistance FactorModifiedResistance FactorNominal Resistance of Single pile in Axial Compression Dynamic Analysis and static load Test Methods, dynStatic load Test in combination w/ dynamic testing or wave Design MemosGDM 2010-01 Memo listing the Maximum Nominal Soil Resistance for Common pile Types Nominal soil Resistance based on modified Resistance factors Available on the InternetPile SectionPile Area(in2)Rn max (Kips) 10x42 " Pipe pile SEC42016" Pipe pile SEC480 Maximum Nominal Soil Resistance for Common Piles to RockHorizontal Displacement (P-y method)HtQtMtyPyyPropertiesA, E, IPyPm* PPSpacing (S)Row 1 Row 2 Row (Pm)

7 DSFrom Table pile Design -PierExample pile Design -PierEXAMPLE pile LOADSS trengthExtremeValues in pile load TableFactored Loads QF200 K300 K210 KResistance Factor Soil Resistance Rn286 K300 K300 KThe extreme loads control the Design . Hence the pile shall be driven to a nominal capacity that provides the required controlling factored of Resistance Factors:AASHTO LRFD BRIDGE Design SPECIFICATIONS selection of the target reliability assumes a significant amount of redundancy in the foundation system is present, which is typical for pile groups containing at least five piles in the group. For smaller groups and single piles, less redundancy will be present. These smaller pile groups that lack redundancy. Therefore, the Resistance factors specified in Table 1 should be reduced to account for reduced ShaftsAASHTO AND GEC 10 FHWA-NHI-10-0166. Deep Foundations7. Select Drilled Shaft Foundations for Further Evaluation8. Define Subsurface Profile for analysis9. Determine Resistance Factors for Design10.

8 Establish Minimum Diameter and Depth for Lateral Loads11. Establish Diameter and Depth for Axial Loads12. Finalize Structural Design of the Drilled Shafts and Connection to Structure (or cap)Evaluate Other Deep Foundation Systems PilesGeneral Deep Foundation Design Flow Chart for Drilled Shafts10. Establish Minimum Diameter and Depth for Lateral Refine Detailed Subsurface Profiles as needed for each Lateral load Case, including scour, liquefaction, fill, Select Trial Length and Analyze Geotechnical Strength Limit State using Factored Loads (for each case)Check Stability against Pushover FailureYes. Analyze Preliminary Structural Strength Limit State for Flexure using Factored LoadsCheck Moment Capacity with 1 to 2% Longitudinal Analyze Service Limit State (Deformations) using UnfactoredLoadsCheck: Deformations AcceptableYes. Define Minimum pile Length and Diameter based on analysisNo . Return to and Revise DesignNo. Revise Diameter and repeat steps starting at Revise Length and repeat steps starting at Loads Design Process For Drilled Idealized Geomaterial Layer Review Limit States and Factored Axial Force Assign Appropriate Geomaterial Properties to each Subsurface Select Trial Lengths and Establish Nominal Side and Base Evaluate Trial Design for LRFD Strength Limit StatesYes.

9 Evaluate Trial Design for LRFD Service Limit StatesYes. Design CompleteNo. Return to and RedesignNo. Return to and RedesignEstablish Minimum Depths and Diameters for Axial Loads for Drilled ShaftsGeotechnical Resistance FactorsDrilled ShaftsMethod Comp Ten - Method (side) - Method (side) or Sand (tip) (side) (tip) (sand or clay) Table of Resistance Factors for LRFD Design of Drilled Shaft FoundationsDrilled Shaft Resistance in RockSide ResistanceTip ResistanceTotal ResistanceABCDQbQSQR= Qn= qbQb+ qsQsDisplacementResistanceQuestions?EXAM PLE CALCSL imit StateNominal load (kip)ResistanceFactor ( )Factored load (kip)MaximumService Strength Extreme I is controlling. The pile is driven to this maximum nominal load in the pile load Tabl