Effective-stress Based Dynamic Analysis and Centrifuge Simulation of Earth Dam

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) or Dev 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
e10-1 1
e10-2
e10-3
7
A Constitutive Model of Compacted Soil

• Stress-strain relation

1. Incrementally linear
2. Stress-level dependent
3. Modulus degradation - disturbed state concept
4. 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 hM
Li and Dafalias (2000)
10
Intermediate state

• For an arbitrary disturbed state
• (i.e., for 1gtDdegt0)

• 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
Model Behavior
Stress Path
Stress-Strain
Pore Water Pressure Build-up
14
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 12)
• height and base width 190 mm and 660 mm
• Leighton-Buzzard sand with Dr90
• 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
Installed miniature sensors accelometers, pore
pressure transducers , LVDTs, Laser sensors

• Model Embankment Dam

18
Triaxial Tests

• Purpose
• Calibration of parameters for the material as
  same as the model embankment dam (Dr90)
• Types of Test
• Cyclic triaxial tests
• Stress controlled cyclic triaxial tests
• sc0.3?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 lt 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 (cond)

• 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