Long-Term Cyclic Performance Assessment of Micropile Systems ...

Long-Term Performance Assessmentof Micropiles Subject toCyclic Axial LoadingGary M. WeinsteinISM 2007 Toronto, CanadaSeptember 27, 2007

Summary1. Problem Definition & Research Needs2. Model: Creep & Cyclic Displacement3. Model Validation• * Structural Laboratory (New York)• Calibration Chamber (Paris)4. Conclusions

Industry ApplicationsBridges & HighwaysRailwaysLand-based Arresting Gear(Courtesy of U.S. Navy)Waterfront/HarborsPower

Cyclic StrainA timedependentphenomenaq ,δ , nThe effect of number of load cycles on anchordisplacement for a range of load amplitudes(After Al-Mosawe, 1979)The effect of load cycleson the rate of anchor displacement(After Al-Mosawe, 1979)

Strain Rate Model for Cyclic Strainq , ε , t dεdtacb. . .dε = ε = ε o* ε -β + ε resε(t) =[ ε o (β +1)] 1/ (β+1) x t1/ (β+1)dtThe procedure charts including (a) stress, σ, vs. strain, ε, at constant strain rate (b) strain rate vs. strain, ε atconstant stress (c) residual strain rate vs. stress, σ and (d) strain, ε, vs. cycle number, n at constant stressd

Ecole Nationale des Ponts et ChausséesCERMESCentre d’Enseignement det de Recherche en Mécanique Mdes Sols

CERMESCalibration ChamberFOREVER (1992-2002)- Physical modeling of micropiles and micropile systems- Controlled testing conditions (stress level, density, etc.)- Monotonic & cyclic loading

Calibration ChamberUpper baseplateLateralconfinement Chambred’étalonnageTrancheélémentaired ’un massif avecdesconditions initialesSoil MassifDouble cellwallI D,Lower baseplateσ h et σ v1. Preparation of massif2. Implementation of test protocol3. Initialize data acquisition system4. Jacking of instrumented pile5. Loading of micropile6. Demounting massifSand reservoir(plexiglass)Double grillDiffuser reeldeviceUpper reservoirVerticalconfinementDiffuser (doublegrill)MicropileLower reservoirCalibration Chamber - SchematicSystem of Pluviation

Preassembly of Chamber

Fontainebleau SoilGradation PropertiesSt Rémy-lès-ChevreuseSand D 50 (mm) e max e min ρ s ( g/cm 3 ) ρ d ( g/cm 3 ) ρ dmax ( g/cm 3 )AF 0.21 0.94 0.54 2.65 1.37 1.72

MassifTest No. Designation M s (Kg) I(g/cm 2 /s) I D1 MDRC-02 MDRC-1 225.38 2.72 0.4053 MDRC-1b 224.96 2.71 0.3964 MDRC-1c 224.06 2.70 0.3785 MDRC-3 221.92 2.67 0.3356 MDRC-3a 222.96 2.69 0.3567 MDRC-3b 224.38 2.70 0.3858 CDRC-1 223.96 2.70 0.3769 CDRC-2 224.56 2.70 0.38810 CDRC-3 224.24 2.70 0.38211 FDRC-1 223.94 2.70 0.37612 FDRC-2 225.54 2.72 0.40813 FDRC-2a 223.96 2.70 0.37614 FDRC-3 224.22 2.70 0.38215 FDRC-4 224.64 2.71 0.39016 FDRC-4a 225.28 2.71 0.40317 FDRC-5 225.82 2.72 0.41418 FDRC-6 225.72 2.72 0.41219 FDRC-8 225.83 2.72 0.41420 FLC-1 225.52 2.72 0.40821 FLC-2 225 2.71 0.397ID10.90.80.70.60.50.40.30.20.10y = 0.0851x 2 - 0.4318x + 0.938R 2 = 0.95070 1 2 3I(g/cm2/s)20 testsDensity Index vs. Deposition IntensityMassif Calibration

Pluviation

Application of Vacuum/Counterpressure

Application of Stresses

Principle SchematicJacking pistonTracks fortranslationMTS loadingpistonCellMobile base -translation androtation

Jacking & LoadingHydraulic jackSingle stroke(force transducer)Loading jack(Displacement & forcetransducer at head)Loading of micropileJacking of micropile

Instrumented MicropileMeasure of friction atthe sleeve200 mmForce transducer4 kNInstrumented micropileφ20 mmForce transducer (5kN) –Measure of load at the tip

Test ScheduleTest Number Designation Applied Displacement Rate Cyclic Displacement Rate Frequency Rate Q Peak q p Peak f s Peak δ max δ e δ p q p,res f s,res(mm/min) (mm/cycle) (cycle/min) (kN) (MPa) (kPa) (mm) (mm) (mm) (MPa) (kPa)1 MDRC-0 1 na na 5.06 6.85 68.37 5.13 4.64 4.64 0.88 -0.442 MDRC-1 1 na na 4.38 6.26 60.96 59.80 59.80 59.80 1.13 -1.863 MDRC-1b 1 na na 4.34 6.58 43.06 24.92 24.92 24.92 0.90 -2.484 MDRC-1c 1 na na 4.59 6.31 62.52 24.90 24.90 24.90 0.89 -1.765 MDRC-3 0.2 na na 4.14 5.22 54.22 24.91 24.91 24.91 0.75 -0.486 MDRC-3a 0.2 na na 5.01 5.98 73.07 19.93 19.93 19.93 0.69 -1.547 MDRC-3b 0.2 na na 4.38 5.45 66.03 19.92 19.92 19.92 1.03 -0.638 CDRC-1 1 0.2 5 4.84 4.84 75.91 3.58 3.23 3.23 0.57 0.619 CDRC-2 0.25 0.05 5 4.61 4.01 86.43 2.49 2.23 2.23 0.56 1.1810 CDRC-3 0.02 0.004 5 3.40 3.13 0.96 0.78 0.78 0.5911 FDRC-1 1 1 1 4.69 5.82 67.10 10.98 10.63 10.6312 FDRC-2 1 0.1 10 4.21 4.50 57.57 9.99 9.72 9.72 0.13 0.1813 FDRC-2a 1 0.1 10 1.10 1.1014 FDRC-3 1 0.02 50 3.56 3.89 56.47 10.86 10.66 10.6615 FDRC-4 1 0.004 250 2.55 2.88 54.95 1.07 0.94 0.94 0.83 0.8316 FDRC-4a 1 0.004 250 1.20 1.2017 FDRC-5 1 0.002 500 2.29 2.92 55.34 1.02 0.83 0.83 0.79 0.7918 FDRC-6 1 0.001 1000 2.04 2.79 51.74 1.00 1.00 1.00 0.22 0.2219 FDRC-8 1 0.0004 2500 1.87 2.64 47.63 0.53 0.45 0.4520 FLC-1 1 na na 3.17 4.21 45.07 17.47 17.29 17.2921 FLC-2 1 na na 1.82 3.05 52.22 0.77 0.67 0.67Testing Summary1. Monotonic displacement rate control – Effect of rate2. Cyclic displacement rate control – Effect of frequency3. Cyclic load control – Validation of testing methodology & modelEstablishment of Critical Cyclic Load

Test Control & Data AcquisitionMission ControlLABView EnvironmentMTS FlexTest System

Repeatibility & Rate EffectsForce (kN)432100 100 200 300 400 500 600Displacement of the Point (mm)FDRC-1FDRC-2FDRC-3FDRC-4FDRC-5FDRC-6FDRC-8JackingForce (kN)54.543.532.521.510.500 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2Displacement (mm)ADR = 1mm/min (MDRC-1)ADR = 1mm/min (MDRC-1c)ADR = 0.02mm/min (MDRC-3)ADR = 0.02mm/min (MDRC-3b)Loading

Initial Stiffness (Rate Effects)Force (kN)65432101mm/min.0.1mm/min.0.01mm/min.0 1 2 3 4 5 6 7Displacement (mm)Force (kN)65432101mm/min.0.1mm/min.0.01mm/min.0 0.1 0.2 0.3Relative Displacement (mm)y = 10.416x + 0.8116R 2 = 0.9915y = 10.374x + 0.2936R 2 = 0.9982y = 8.144x - 0.0338R 2 = 0.9986Loading

Cyclic Displacement Rate ControlSleeve Friction (kPa)Tip Resistance (MPa)Force (kN)5100 790648070 5360 450240 330 21201010000 1 2 3 400 1 Displacement 2 (mm)3 44Displacement (mm)MDRC-1c (ADR = 1.0 mm/min)MDRC-1c CDRC-1 (ADR(ADR = 1.01.0 mm/min;mm/min)CDR = 0.20 mm/cycle; F = 5 cpm; N =18 cyclesCDRC-1 CDRC-2(ADR (ADR= =1.0 0.25mm/min;mm/min; CDR CDR= 0.20= 0.05mm/cycle; mm/cycle;F =F 5= cpm;5 cpm;N N=18 = 50cyclescyclesCDRC-2 (ADR = 0.25mm/min; CDR = 0.05 mm/cycle; F = 5 cpm; N = 50 cyclesVariable Applied Displacement Rate

Cyclic Displacement Rate ControlTip Resistance (MPa)Force (kN)7806575705 654 604 55503 453 40352230251 201 15100 5000 1 2 3 4 5 6 7 8 9 10001122334Displacement 45 (mm) 5667788991010DisplacementDisplacement(mm)(mm)MDRC-1c (ADR = 1 mm/min)FDRC-1 MDRC-1cMDRC-1c (ADR (ADR = (ADR 1 = mm/min; = 1 mm/min)1 mm/min) CDR = 1 mm/cycle; F = 1 cpm; N = 11 cycles)FDRC-2 FDRC-1FDRC-1(ADR (ADR(ADR==1 = 1 mm/min; CDR = 1 mm/cycle; F = 1 cpm; N = 11 1mm/min;mm/min;CDRCDR==0.11 mm/cycle;mm/cycle; F =110cpm;cpm;NN==11100cycles)cycles)FDRC-3 FDRC-2 (ADR = 1 mm/min; CDR = 0.1 mm/cycle; F = 10 cpm; N = 100 cycles)FDRC-2 (ADR (ADR = = 11 mm/min; mm/min; CDR CDR = = 0.02 0.1 mm/cycle; F = 50 10 cpm; N = 58 100 cycles) cycles)FDRC-3 (ADR = 1 mm/min; CDR = 0.02 mm/cycle; F = 50 cpm N = 58 cycles)FDRC-3 (ADR = 1 mm/min; CDR = 0.02 mm/cycle; F = 50 cpm N = 58 cycles)Sleeve Friction (kPa)Variable Cyclic Displacement Rate

Cyclic Displacement Rate ControlForce vs. DisplacementForce vs. Displacement (cyclicenvelope)

Cyclic Displacement Rate Control90Sleeve Friction (kPa) .7560453015MDRC-1 (Mono)CDRC-1 (5cpm)FDRC-1 (1cpm)FDRC-2 (10cpm)FDRC-3 (50cpm)FDRC-4 (250cpm)FDRC-5 (500cpm)FDRC-6 (1000cpm)FDRC-8 (2500cpm)FLC-1FLC-200 1 2 3 4 5 6 7 8 9 10 11 12Displacement (mm)Sleeve Friction vs. DisplacementSleeve Friction vs. Displacement

Load Control20Displacement (mm15105FLC-1 (3.15kN)FLC-2 (1.80 kN)01 100 10000Cycle NumberDisplacement vs. Cycle NumberRate of Displacemen(mm/100 cycles)10.10.01FLC-1 (3.15kN)FLC-2 (1.80 kN)0.001100 1000 10000Number of CyclesDisplacement Rate vs. Cycle Number

Load & Rate ControlForce (kN)Cyclic DisplacementRate (mm/cycle)0.10.080.060.040.0200 0.2 0.4 0.6 0.8 1 1.2 1.4Displacement (mm)Displacement Rate vs. DisplacementEstablishment of Critical Cyclic Load0.250.500.751.001.251.501.752.002.252.502.753.003.253.503.754.003.15kN1.80 kN

Conclusions• Experimental Model Evaluation illustrates that model predictions agree with the experimentalresults indicating that long-term behavior of strain-rate dependent and frequency dependent materialsand phenomena such as soil-pile interaction can be predicted using short-term strain rate controlledcyclic compression test results.• The cyclic strain model predicts a Cycle Limit at which the cyclic strain process ends for loads thatare smaller then the Critical Cyclic load. For loads that are greater than the Critical Cyclic Load, themodel predicts linear long-term strain-cycle behavior.• Further research is now required to better understand the effect of in-situ testing conditions (i.e. soilconfinement, ground water, etc.) on the long-term cyclic behavior of micropiles. Full scale loadingtests would be required in order to provide a relevant database for the field evaluation of the strainrate – cyclic creep model and the development of reliable design methods for the assessment of thelong-term performance of rate and frequency dependent phenomena.• Impact on Engineering Practice Existing pile load testing equipment could be used to conduct fullscalefield loading tests using the suggested testing protocol. If successful, testing standards could bedeveloped which could lead to adopting the proposed cyclic strain testing procedure and strain ratecontrolled cyclic strain model as a base line for industry pile testing standards

Research Program SupportSchnabel EngineeringPolytechnic UniversityInternational Association of Foundation Drilling (ADSC)Applied Geotechnical Engineering (AGE)Branlow Piling SolutionsCAT Construction/Traylor GroupCon-Tech Systems LTD.DBM ConstructionGeosystems LPHayward Baker, Inc.IschebeckLayne GeoConstructionMoretrench American Corp.Nicholson ConstructionTEI Rock Drills

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