Abutment Design Example - Michigan Technological University

1 Abutment Design ExampleChris Byrum Doug Parmerlee Example BridgeEvaluate Existing Test Hole DataNot much before 1940 MDOT Housel Soil Mechanics 1940-80sASTM SPT N-modified valuesEvaluate Existing Test Hole DataNot much before 1940 MDOT Housel Soil Mechanics 1940-80sASTM SPT N-modified valuesEvaluate Existing Test Hole DataNot much before 1940 MDOT Housel Soil Mechanics 1940-80sASTM SPT N-modified valuesNew Test HolesIn-Situ Vane-shear and 3 Shelby TubesDesign Shear Strength ProfilesVane onlyFinal SelectionUC only 4* MDOTUsed for: Global Stability, Bearing Capacity, Piling Side Resistance, pile for Piling Tip ResistanceExternal Stability Task 1: Lateral Squeeze Task 2: Global Stability Task 3: Settlement Analyses Task 4:Bearing CapacityFS = 2*Cu +( *Cu)gama*Ds*tan(theta)H*gama Where, Cu =Undrained shear strength of soft layer, psfDs =Thickness of soft soil layer, ftgama =Unit weight of fill soil, psfthe ta =Angle of fill slope, degreesH =Height of fill, ft Also used in the H*gama < 3Cu, or 4 CuLATERAL SQUEEZE ANALYSISP rimary Shear Secondary/Sympathy ShearLaterally SqueezedBulging Uplift AreaEdge of Recent FillH = 6 to 7 feetPrevious ScenarioUtility Contractor Adds WeightRoad = ConditionFailure BackcalculationFS = 2*Cu +( *Cu)gama*Ds*tan(theta)

2 H*gamaComponent 1 Component 2 FSCu = =30ftgama =125pcf3*Cu =540the ta =45degrees4*Cu =720H = *H = FS = 1 Example BridgeFS = 2*Cu +( *Cu)gama*Ds*tan(theta)H*gamaComponent 1 Component 2 FSCu = =100ftgama =120pcf3*Cu =6300the ta =88degrees4*Cu =8400H =46ftgama*H = , Cu =Undrained shear strength of soft layer, psfDs =Thickness of soft soil layer, ftgama =Unit weight of fill soil, psfthe ta =Angle of fill slope, degreesH =Height of fill, Shear strength, Cu, psfLateral SqueezeAbut. BAbut. AGLOBAL STABILITY ANALYSISA butment AAbutment ASet 2% strain force > FS forceAbutment ASet ultimate force > FS forceAbutment ASet Grid Limits > FS forceDecided to add-a-span, use short pile -supported Abutment , on 25+ feet of fill instead of the tall full-height Abutment Change in PlanAbutment AAbutment BAbutment BAbutment BAbutment BARE SPREAD FOOTINGS OK?

3 Bearing CapacityARE SPREAD FOOTINGS OK? Bearing = approx. 5000 -6000 psfApproach Embankment Weight next to Abutment :Abut. A = 48*125 = 6000 psf not likely!Abut. B = 30 * 125 = 3750 psf maybeARE SPREAD FOOTINGS OK? Settlement Management Need to estimate settlement of footings caused by approach embankments And Footing pressures causing settlement serviceability-limit (1-inch and limits) Pre-loads? Lightweight Fills? pile Downdrag?SETTLEMENT MANAGEMENTSETTLEMENT MANAGEMENT515540565590615030006000900012 000 Ele va tio n, ftPressure, psfP0, O verburdenToday s ConditionGroundwater Table515540565590615030006000900012000 Ele va tio n, ftPressure, psfP0, O verburdenGlacial Lake StanleyLake Stanley Dry PeriodGroundwater Table515540565590615030006000900012000 Ele va tio n, ftPressure, psfP0, O verburdenGlacial Lake StanleyPc Assu mptionPreconsolidationPseudo-PcIce Weight on Hard Till515540565590615030006000900012000 Ele va tio n, ftPressure, psfP0, O verburdenGlacial Lake StanleyFooting PressurePc Assu mptionP 0 + DPLoad Effects515540565590615030006000900012000 Ele va tio n, ftPressure, psfP0, O verburdenGlacial Lake StanleyFooting PressurePc Assu mptionP 0 + DP51554056559061502468 Ele va tio n, ftS e ttle me nt.

4 InUc = 100%Uc = 75%Uc = 50%Uc = 25%SETTLEMENT MANAGEMENTWick DrainsWick DrainsWick DrainsExample Bridge14 10 (5-20 years w/o wicks) 6 8 Settlement Estimates Soil Only, no footing pressuresChange in PlanWick Drains Installed throughSand Drainage LayerChange in PlanPre- load to this (6 month wait for T90)Settlement Estimates Change in PlanEPS BlockH-PilesLess than remains (ZERO Downdrag!!!!!)Settlement EstimatesPlacement of EPS and Geogrid behind BridgeWick Drains Installed throughSand Drainage LayerPre- load to Full Height(2 month wait) 7 Settlement Estimates EPS BlockRemove Pre- load , Piles, and Partial EPS Est. Settlement =60% of all-sand pre-loadPiling Analyses Axial Resistance Lateral Resistance: batter vs COM624P Bridge Approach Fill Settlement Downdrag Negative Skin FrictionAxial Capacity: Driven into Shale RockWith about.

5 400 Kip Side Resistance100+ kip Tip/Bottom settlement 515540565590615030006000900012000 Ele va tio n, ftPressure, psfP0, O verburdenGlacial Lake StanleyFooting PressurePc Assu mptionP 0 + DP51554056559061502468 Ele va tio n, ftS e ttle me nt, inUc = 100%Uc = 75%Uc = 50%Uc = 25% "250 ki p320 ki p350 ki p360 ki p515540565590615030006000900012000 Ele va tio n, ftPressure, psfP0, O verburdenGlacial Lake StanleyFooting PressurePc Assu mptionP 0 + DP51554056559061502468 Ele va tio n, ftS e ttle me nt, inUc = 100%Uc = 75%Uc = 50%Uc = 25% "250 ki p320 ki p350 ki p360 ki p220 ki p310 ki p340 ki p355 ki "An extra allowance for elastic pile Rndr= 500 kip HP14x73, 25% settlement remaining:Rn= 500 220(250/400) = kipsQp= ( ) 220 = 52 kips/ pile OUCH!!!!Drive 500 kip pile , only 52 kip available for bridge weight!

6 !!NO GO!!PDA with Dynamic Signal MatchingRsdd= 250/400(DD)..reduced side resistance during drivingStatic Rs = 400 kipsDynamic51554056559061503000600090001 2000 Ele va tio n, ftPressure, psfP0, O verburdenGlacial Lake StanleyFooting PressurePc Assu mptionP 0 + DP51554056559061502468 Ele va tio n, ftS e ttle me nt, inUc = 100%Uc = 75%Uc = 50%Uc = 25% "250 ki p320 ki p350 ki p360 ki p220 ki p310 ki p340 ki p355 ki "An extra allowance for elastic pile Lateral Resistance COM624P Below Footing, inLateral Deflection, in9-kip15-kip20-kip25-kip30-kipLateral LoadFrom LPILE Technical ManualWQpP= soil pressureMVFrom LPILE Technical ManualList of Recs Given To Bridge Engineer Global Stability Settlement Amounts and Rates Spreads versus Deep Foundations Lateral Resistances Special Provisions/Materials Specifications Construction Considerations Water control Surface preparation Temporary Walls Vibrations Geotechnical Instrumentation needed?

7 Doug Parmerlee Overview of Abutment Design ConceptsGeotechnical Engineering During ConstructionGeotechnical Field Monitoring pile Axial Capacity Settlement Rates and Amounts Geosynthetics: Limits/Continuity/Splicing Lightweight Fills: Limits/MaterialsPDA with Dynamic Signal MatchingStatic pile load TestsSoil Pore Pressure DissipationMEId zdx=22 Michigan s State Fossil:MastodonAncient Glacial Lake Beach on top ofGrand Portal Point, Pictured Rocks