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Effective-stress Based Dynamic Analysis and C entrifuge Simulation of Earth Dam

Effective-stress Based Dynamic Analysis and C entrifuge Simulation of Earth Dam. Yii-Wen Pan 1 Hui-Jung Wang 1 C.W.W. Ng 2 1 National Chiao-Tung University 2 Hong Kong University of Science and Technology. Contents. Introduction Constitutive Model of Compacted Soil

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Effective-stress Based Dynamic Analysis and C entrifuge Simulation of Earth Dam

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  1. Effective-stress Based Dynamic Analysis and Centrifuge Simulation of Earth Dam Yii-Wen Pan1 Hui-Jung Wang1 C.W.W. Ng2 1National Chiao-Tung University 2Hong Kong University of Science and Technology

  2. Contents • Introduction • Constitutive Model of Compacted Soil • Numerical Analysis and Centrifuge Tests • Comparison of Calculated and Experimental Results • Application • Conclusions

  3. Introduction Dynamic Stress Analysis for Earth Dam • Objectives • Effective-stress modeling for earth dam • Verification by centrifuge models • Purposes of dynamic analysis for earth dam • to evaluate dam response under earthquake • Stress / Acceleration • Liquefaction Potential • Permanent deformation/settlement • Types of analysis • Total stress analysis • Effective stress analysis

  4. Effective Stress Constitutive Models for Soil under Cyclic Loading • Dev= f(Dg, g, No of cycles,…) • e.g., ： Martin-Finn (1975) • dilatancy = f( stress state, state parameters,…) • e.g., Li et al. (2000) • Ueng and Lee (1990) • Du = f(damage parameters) • Du = f(k) orDev= f (k) • e.g., Finn et al.(1981) endochronic model • Park(2000) disturbed state concept • Elasto-plastic model • e.g., Manzari ＆ Dafalias (1997) , Prevost（1985） • Pastor et al, (1990), Iai et al. (2000)

  5. Effective-stress Based Dynamic Analysis • FEM & FDM incorporating effective stress model appropriate for cyclic loading e.g., • Zienkiewicz, et al. (1981, 1984) • Beaty and Byrne (1999) • Dakoulas and Eltaher (1998) • Ming and Li (2003) among others • Application on dynamic response of earth dam • Simulation of failure case e.g., Lower San Fernando Dam – built by hydraulic fill

  6. Typical Behavior of heavily compacted fill e=10-1% ~1% e=10-2% e=10-3%

  7. A Constitutive Model of Compacted Soil • Stress-strain relation • Incrementally linear • Stress-level dependent • Modulus degradation - disturbed state concept • Irrecoverable dilatancy • Assumption • Saturated Soil

  8. DSC ( Disturbed State Concept) Desai and co-workers (1991) • Disturbance due to external loading • RI (Related Intact)FA (fully adjusted ) • Follows a specific rule • Separate Constitutive laws for RI ＆ FA

  9. Constitutive Relations RI State : As Dde =0 Seed-Idriss formula (1970) FA State : As Dde =1 Along the failure line h=M Li and Dafalias (2000)

  10. Intermediate state • For an arbitrary disturbed state • (i.e., for 1>Dde>0) • Accounting for stress history

  11. Modeling Pore Water Pressure Build-up Irrecoverable Dilatancy : slope of phase transformation line C & w: material parameters : shear strain increment : plastic volumetric strain Pore Water Pressure Build-up

  12. Summary of Model • Progressive yielding • 2. • 3. Stress history • 4. Pore pressure build-up

  13. Stress Path Model Behavior Stress-Strain Pore Water Pressure Build-up

  14. Type of parameters Elastic Constants Modulus Related Dilatancy Critical States Parameters Kmax, Gmax β, λ , z C,ω M, ψμ Calibration of Parameters • Parameters • Calibration by optimization (through GA, Nonlinear) • Objective function

  15. Centrifuge Testing • Purposes • Observation of the dynamic response of model earth dam subjected to dynamic loadings • Verification of Numerical Model • Centrifuge tests • Carried out in Hong Kong University of Science and Technology • Capacity : 400 g-tons • Arm radius : about 4.2m • Maximum centrifuge acceleration : 70g • Shaker: max. shaking acceleration 40g

  16. Model Embankment Dam • Detail of the model embankment dam • in rectangular rigid container 712mm x 432mm x 440mm • symmetrical slopes (slope ratio 1:2) • height and base width : 190 mm and 660 mm • Leighton-Buzzard sand with Dr=90% • Carboxy methylcellulose (CMC) as the substituted pore fluid (Dewoolkar et al 1999) • to take time conflict of dynamic and diffusion problems into account • CMC is a water-soluble cellulose ether • odorless, harmless, use in food & pharmacy

  17. Model Embankment Dam Installed miniature sensors: accelometers, pore pressure transducers , LVDTs, Laser sensors

  18. Triaxial Tests • Purpose: • Calibration of parameters for the material as same as the model embankment dam (Dr=90%) • Types of Test • Cyclic triaxial tests • Stress controlled cyclic triaxial tests • sc=0.3、0.5 、1kg/cm2 • Monotonic CU tests • sc= 0.3、0.5、1 kg/cm2

  19. Effective Stress Based Numerical Analysis Dam Construction Modeling Static Stress Analysis Modeling Seepage Analysis (obtain steady state phreatic surface) Stress Analysis after Steady State Seepage (static equilibrium after steady state seepage) Dynamic Analysis (in time domain)

  20. Pore Water Pressure

  21. Acceleration

  22. Settlement

  23. Application in Li-Yu-Tan Dam • Li-Yu-Tan Dam • A well instrumented earth dam. • Data was successfully recorded in Chi-Chi earthquake • Input motion in numerical simulation • Using the recorded bedrock acceleration in Chi-Chi earthquake • Comparison of the numerical results and the recorded data in Chi-Chi earthquake

  24. Results of Static Analysis Mesh Vertical Stress Horizontal Stress Vertical Deformation Horizontal Deformation

  25. Steady-state Flow Pore Water Pressure Vertical Stress Horizontal Stress Vertical Deformation Horizontal Deformation

  26. Results of Dynamic Analysis Pore Water Pressure Vertical Stress Horizontal Stress Vertical Deformation Horizontal Deformation

  27. Acceleration history in bedrock & Crest m/sec2 sec

  28. Comparison of Numerical Results and Recorded Data • Maximum settlement • Recorded settlement < 10 cm • Calculated settlement ~10cm • Horizontal deformation • Downstream slope moves toward downstream, and vice versa • Agree with the trend of instrumented data • Amplification of acceleration • About 3 times at crest • Close to the recorded data

  29. Conclusions • Heavily compacted fill in an earth dam behaves like a very dense soil. • An effective stress based constitutive model for compacted fill was proposed. • This model takes into account • Progressive degradation • Stress-level dependency • Effects of stress history & Stress history • Pore water pressure build-up

  30. Conclusions (con’d) • A numerical model for an effective stress based analysis was • developed for dynamic analysis of earth dam • verified by the results of centrifuge tests • Effective stress analysis for a well instrumented earth dam • using the Chi-Chi earthquake data • numerical and instrumented results were consistent

  31. Thank youfor Attention

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