An Overview of Seismic Design of Earth Dams and Embankments
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An Overview of Seismic Design of Earth Dams and Embankments Sudhir K Jain October 2013. Outline. Performance of Earth Dams in 2001 Bhuj earthquake Introduction to Seismic Design Principle Dynamic Soil Properties Site Effects Liquefaction Embankment Analysis.

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An overview of seismic design of earth dams and embankments sudhir k jain october 2013

An Overview of Seismic Design of Earth Dams and Embankments

Sudhir K Jain

October 2013

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Outline

Outline

  • Performance of Earth Dams in 2001 Bhuj earthquake

  • Introduction to Seismic Design Principle

  • Dynamic Soil Properties

  • Site Effects

  • Liquefaction

  • Embankment Analysis

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Performance of Earth Dams in 2001 Bhuj earthquake

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


2001 bhuj earthquake

2001 Bhuj Earthquake

  • Magnitude 7.7

  • Maximum MSK Intensity X

    • Bhuj in Seismic Zone V of Indian seismic map

  • 8.46 am on 26 January 2001

    • More than 13,805 dead; 1,67,000 injured

    • 300,000 houses destroyed; 700,000 houses damaged

  • Numerous multistorey RC buildings collapsed

    • 130 such buildings collapsed in Ahmedabad ~225km from epicenter

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


2001 bhuj earthquake contd

2001 BhujEarthquake (contd…)

  • 2 year drought; reservoirs at very low levels

  • 16 (out of 20) medium dams damaged

    • 5 severely

  • 80 (out of 165) minor dams damaged

    • 14 severely

  • Damage consisted of

    • Liquefaction beneath engineered fill

    • Slope displacements

    • Longitudinal cracking at crests, cracking and movements on upstream faces

    • Damage to outlet towers, spillways, parapet walls, …

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Tappar Dam

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Tappar Dam

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Tappar Dam

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Fatehgadh Dam

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Fatehgadh Dam

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Fatehgadh Dam

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Kaswati Dam

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Kaswati Dam

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Kaswati Dam

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Rudramata

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Rudramata

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Intake tower

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Spillway

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Piers

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Some Remarks on

Seismic Design Principles

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Seismic design principle

Seismic Design Principle

  • Large earthquakes are infrequent as compared to smaller earthquakes

  • Should a structure meant for 50 years be designed to remain undamaged for an earthquake that may occur once in 500 years?

  • The criteria is:

    • Minor (and frequent) earthquakes should not cause damage

    • Moderate earthquakes should not cause significant structural damage (but could have some non-structural damage)

    • Major (and infrequent) earthquakes should not cause collapse

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Seismic design principle1

Seismic Design Principle …

  • A well designed structure can withstand a horizontal force several times the design force due to:

    • Energy dissipation in a variety of ways, e.g., ductility

    • Overstrength

    • Redundancy

  • In many cases, limited deformation may be acceptable, e.g., slopes, retaining walls.

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Site specific design criteria

Site Specific Design Criteria

  • Seismic design codes meant for ordinary projects

  • For important projects, such as nuclear power plants, dams and major bridges site-specific seismic design criteria are developed

    • These take into account geology, seismicity, geotechnical conditions and nature of project

  • Site specific criteria are developed by experts and usually reviewed by independent peers

  • A good reference to read on this:

    • Housnerand Jennings, “Seismic Design Criteria”, Earthquake Engineering Research Institute, USA, 1982.

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Shaking is not the only issue

Shaking is not the only issue!

  • Ground shaking can affect the safety of structure in a number of ways:

    • Shaking induces inertia force

    • Soil may liquefy

    • Sliding failure of founding strata may take place

    • Fire or flood may be caused as secondary effect of the earthquake.

  • Fault rupture may pass through the structure

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Direction of ground motion

Direction of Ground Motion

  • During earthquake shaking, ground shakes in all possible directions.

    • Direction of resultant shaking changes from instant to instant.

  • Structure must withstand maximum ground motion occurring in any direction.

  • Peak ground acceleration may not occur at the same instant in two perpendicular directions.

  • Hence for design, maximum seismic force is not applied in the two horizontal directions simultaneously.

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Direction of ground motion1

Direction of Ground Motion …

  • On average, peak vertical acceleration is one-half to two-thirds of the peak horizontal acceleration.

  • Structures experience vertical acceleration equal to gravity (g) at all times.

  • Vertical acceleration is a concern for:

    • Stability issues (e.g., slopes)

    • Large span structures

    • Cantilever members

    • Prestressed horizontal members

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Dynamic Soil Properties

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Dynamic soil properties

Dynamic Soil Properties

  • Behaviour of soil complex under static loads. Even more complex under dynamic loads

  • Need for simple methods to characterize complex behaviour

  • Analysis techniques:

    • Equivalent linear models

    • Cyclic non-linear models

    • Advanced constitutive models

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Shear modulus

Shear Modulus

  • Soil stiffness depends on strain amplitude, void ratio, mean principal effective stress, plasticity index, over consolidation ratio, and number of loading cycles

  • Shear Modulus

    • Tangent modulus

    • Secant modulus

  • Shear modulus varies with strain level. It is high at low strains

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Shear modulus1

Shear Modulus …

Figure: Hysteretic stress-strain response of soil subjected to cyclic loading

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Dynamic properties

Dynamic Properties

  • Shear modulus decreases with strain increase

  • Damping increases with strain increase

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Maximum shear modulus g max

Maximum Shear Modulus (Gmax)

  • Can be obtained in a number of ways: shear wave velocity, laboratory tests, and empirical relationships

  • Shear wave velocity obtained from geophysical tests at strains lower than about 3x10-4%

    Gmax= ρvs2

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Soil properties

Soil Properties

Exploration data converted to shear modulus:

Gmax = 65N[Seed, and Idris 1983]

Gmax = 1000[35(N60)0.34] (σ’)0.4[Seed,Wong,andIdris, 1986]

Gmax= 1000[20(N1,60)0.33] (σ’)0.5[Seed,Wong,andIdris, 1986]

Gmax= 325(N60)0.68[Imai, and Tonouchi, 1982]

Gmax= K (N60)0.66[PWRI, 1998]

Where,

N60 = SPT value, uncorrected for over-burden pressure

N1,60 = SPT value, corrected for over-burden pressure

σ’= Effective soil pressure

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Soil properties1

Soil Properties …

Eqn (1)

Eqn (5)

Eqn (2)

Eqn (4)

Eqn (3)

  • Small strain Shear Modulus (Gmax)

    • Tends to vary significantly, depending on which relationship is used

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Ground motion along depth

Ground Motion Along Depth

  • Peak amplitude of underground motion is smaller than that at the surface

  • Variation of amplitude depends on

    • Earthquake characteristics

      • Frequency content

    • Type of soil and its distribution along depth

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Ground motions along depth

Ground Motions Along Depth …

Vertical distribution PGV

Vertical distribution PGA

Vertical distribution PGD

Figure: Distribution of peak amplitude of ground motion along depth, (Kanade, 2000)

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Ground motions along depth1

Ground Motions Along Depth …

Artificially generated time history [SIMQKE -1]

Known Spectrum

Back calculated time history [SHAKE 2000]

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Ground motions along depth2

Ground Motions Along Depth …

Response time history [SHAKE 2000]

Response time history [SHAKE 2000]

Response time history [SHAKE 2000]

Assumed earthquake

Corresponding response spectrum [SMSIM]

Artificially generated time history [SIMQKE-1]

Figure: Schematic representation of procedure used for artificially generated time histories for earthquake motion

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Underground structures

Underground Structures

  • When seismic waves hit the ground surface, these are reflected back into ground

  • The reflection mechanics is such that the amplitude of vibration at the free surface is much higher (almost double) than that under the ground

  • Codes allow the design spectrum to be one-half if the structure is at depth of 30m or below.

    • Linear interpolation for structures and foundations if depth is less than 30m.

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Site Effects

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Site effects

Site Effects

  • Motion at the base rock different from that at the top of soil.

  • Local amplification of the earthquake motion due to the soil profile at the site.

  • Site Effect.

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Mexico earthquake of 1985

Mexico Earthquake of 1985

  • Earthquake occurred 400 km from Mexico City

  • Great variation in damages in Mexico City

    • Some parts had very strong shaking

    • In some parts of city, motion was hardly felt

  • Ground motion records from two sites:

    • UNAM site: Foothill Zone with 3-5m of basaltic rock underlain by softer strata

    • SCT site: soft soils of the Lake Zone

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Mexico earthquake of 19851

Mexico Earthquake of 1985 …

Time (sec)

  • PGA at SCT site about 5 times higher than that at UNAM site

    • Epicentral distance is same at both locations

Figure from Kramer, 1996

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Mexico earthquake of 19852

Mexico Earthquake of 1985 …

  • Extremely soft soils in Lake Zone amplified weak long-period waves

    • Natural period of soft clay layers happened to be close to the dominant period of incident seismic waves

    • This lead to resonance-like conditions

  • Buildings between 7 and 18 storeys suffered extensive damage

    • Natural period of such buildings close to the period of seismic waves.

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Site response amplification

Site Response Amplification

Depends on:

  • Soil properties (shear modulus, damping)

  • Soil depth

  • Contrast in soil properties

    • More amplification if greater contrast

  • Intensity of ground motion

    • Soil is elastic at low strains

    • Shear modulus decreases and damping increases as soil strain increases

    • More amplification for weak motion

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Site response amplification1

Site Response Amplification …

Figure: Relationship between maximum acceleration on rock and on soft sites (Idriss, 1990, 1991).

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Site response amplification2

Site Response Amplification …

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Site response amplification3

Site Response Amplification …

Figure:Procedure for modifying ground motion parameters from a seismic hazard analysis to account for the effects of local site conditions

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Site response amplification4

Site Response Amplification …

Figure:Two hypothetical soil deposit overlying rigid bedrock: (a) site A; (b) site B. Soils are identical, except the s-wave velocity of the soil at site B is four times greater than that at site A.

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Site response amplification5

Site Response Amplification …

Figure: Amplification functions for sites A and B. Note that the softer soil at site A will amplify low-frequency input motions much more strongly than will the stiffer soils of site B. At higher frequencies, the opposite behaviourwould be expected.

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Soil effect

Soil Effect

Period (sec)

  • Recorded earthquake motions show that response spectrum shape differs for different type of soil profile at the site

Fig. from Geotechnical Earthquake Engineering, by Kramer, 1996

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Soil effect1

Soil Effect …

Spectral Acceleration Coefficient (Sa/g)

Period (s)

  • This variation in ground motion characteristic for different sites is now accounted for through different shapes of response spectrum for three types of sites.

Fig. from IS:1893-2002

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Soil effect2

Soil Effect …

  • Modern Codes (e.g., IBC) classify the soil type based on weighted average (in top 30m) of:

    • Soil Shear Wave Velocity, or

    • Standard Penetration Resistance, or

    • Soil Undrained Shear Strength

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Liquefaction

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Liquefaction

Liquefaction

  • In case of loose or medium dense saturated soils, liquefaction may take place.

  • Sites vulnerable to liquefaction require

    • Liquefaction potential analysis.

    • Remedial measures to prevent liquefaction.

    • Else, deep piles are designed assuming that soil layers liable to liquefy will not provide lateral support to the pile during ground shaking.

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Liquefaction analysis

Liquefaction Analysis

  • Difficult to obtain undisturbed samples

  • Approach based on in-situ tests preferred

  • SPT and CPT based procedures are popular

  • Simplified procedure of Seed and Idriss used with SPT values

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Liquefaction analysis example

Liquefaction Analysis (Example)

North Bank: Rail and Road : At Center of Embankment : Water Level 1.0 m below GL

h

h

g

g

g

amax/g

0.60

1.00

0.98

21.00

1.85

0.85

M

7.00

w

emb

w

emb

sub

%

e

'

u

C

C

(N

)

r

K

CSR

CSR

CSR

FS

CSR

D

g

s

s

K

K

D Rng

Depth

%Fine

Avg.N

0

N

60

l

60

d

m

eq

7.5

L

liq

eql

sat

v

v

V

a

s

0.0-1.5

0.75

8.20

1.85

40.24

0.00

40.24

6.22

2.00

1.00

12.44

0.67

1.09

1.00

0.66

0.26

0.15

0.11

0.42

0.37

1.95

0.03

1.5-3.0

2.25

8.00

1.85

43.01

1.23

41.79

8.80

2.00

1.00

17.60

0.65

1.09

1.00

0.64

0.26

0.24

0.17

0.64

0.38

1.95

0.03

3.0-4.5

3.75

8.30

1.85

45.79

2.70

43.09

12.08

1.50

1.00

18.16

0.63

1.09

1.00

0.63

0.26

0.21

0.15

0.56

0.38

1.93

0.03

4.5-6.0

5.25

8.50

1.85

48.56

4.17

44.40

16.30

1.31

1.00

21.43

0.61

1.09

1.00

0.62

0.26

0.26

0.18

0.68

0.38

1.50

0.02

6.0-7.5

6.75

6.15

1.85

51.34

5.64

45.70

20.68

1.18

1.00

24.45

0.58

1.09

1.00

0.62

0.26

0.31

0.21

0.81

0.38

1.18

0.02

7.5-9.0

8.25

8.00

1.85

54.11

7.11

47.01

24.47

1.08

1.00

26.53

0.56

1.09

1.00

0.60

0.25

0.35

0.23

0.92

0.39

1.00

0.02

9.0-10.5

9.75

6.40

1.85

56.89

8.58

48.31

27.72

1.01

1.00

27.90

0.54

1.09

1.00

0.59

0.25

0.41

0.27

1.07

0.38

0.88

0.01

10.5-12.0

11.25

6.40

1.85

59.66

10.05

49.62

24.75

0.94

1.00

23.35

0.52

1.09

1.00

0.58

0.24

0.30

0.19

0.78

0.38

1.36

0.02

12.0-13.5

12.75

6.40

1.85

62.44

11.52

50.92

26.00

0.89

1.00

23.17

0.49

1.09

1.00

0.58

0.24

0.30

0.19

0.81

0.37

1.34

0.02

13.5-15.0

14.25

6.40

1.85

65.21

12.99

52.23

30.63

0.85

1.00

25.92

0.47

1.09

1.00

0.57

0.23

0.31

0.19

0.84

0.37

1.05

0.02

15.0-16.5

15.75

6.40

1.85

67.99

14.46

53.53

33.25

0.81

1.00

26.86

0.45

1.09

1.00

0.57

0.22

0.35

0.22

0.97

0.36

1.00

0.02

16.5-18.0

17.25

7.33

1.85

70.76

15.93

54.84

36.13

0.77

1.00

27.97

0.43

1.09

1.00

0.56

0.21

0.36

0.22

1.02

0.35

0.50

0.01

18.-19.5

18.75

7.00

1.85

73.54

17.40

56.14

39.00

0.74

1.00

29.03

0.40

1.09

1.00

0.55

0.21

0.45

0.27

1.31

-

-

-

19.5-21

20.25

7.00

1.85

76.31

18.87

57.45

44.63

0.72

1.00

32.04

0.38

1.09

1.00

0.55

0.20

(N

)

Greater than 30 hence

l

60

soil is Non - Liquefiable

TOTAL

D

0.23

rd is calculated at the center of depth range below top of embankment

Units : Tons & Meters

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Embankment Analysis

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Issues for Embankments

  • Slope failure due to

    • Inertial loading, and/or

    • Softening of material strength or liquefaction

  • Fault displacement under the foundation

    • Not being addressed here

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Slope stability of embankments

Slope Stability of Embankments

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

Sudhir K. Jain


Two methods

Two Methods

  • Pseudo-static slope stability analysis

    • Factor of safety concept

  • Permanent deformation analysis as per Newmark’s sliding block approach

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

Sudhir K. Jain


Pseudo static analysis

Pseudo-Static Analysis

  • Complex ground shaking replaced by a single constant unidirectional pseudo-static acceleration

  • Ensure adequate factor of safety against sliding

    How to choose seismic coefficient and factor of safety?

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

Sudhir K. Jain


Seismic coefficient for pseudo static method

Seismic Coefficient(for Pseudo-Static Method)

  • Terzaghi (1950)

    • 0.1g for severe earthquake (RF Intensity IX)

    • 0.2g for violent, destructive earthquake (RF X)

    • 0.50g for catastrophic earthquake

  • Mercuson (1981)

    • Seismic coefficient should be one-third to one-half of the PGA the embankment is subjected to

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

Sudhir K. Jain


Seismic coefficient contd

Seismic Coefficient contd…

  • Hynes and Franklin (1984)

    • Embankment with yield acceleration (FOS=1.0) of

      • one-half the PGA will experience permanent deformation of less than 0.3m.

      • Deformation limited to 1.0m if yield acceleration is greater than one-sixth of Peak Average Acceleration

        • Based on upper bound graph

        • See figure for the concept of peak average acceleration

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

Sudhir K. Jain


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Permanent Seismic Deformation (Hynes and Franklin, 1984)

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Concept of Average Acceleration (Kramer, 1996)

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Concept of Average Acceleration (Kramer, 1996)

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Newmark s sliding block model

Newmark’s Sliding Block Model

  • Developed originally for evaluation of seismic slope stability

  • Motivated by concerns about realistic ground motions that are much higher than the traditional design based on pseudo-static stability analysis

  • If FOSslid < 1.0

    • What will happen? Will the structure collapse?

    • Not, if the permanent deformation is within an acceptable limit

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Newmark s sliding block model1

Newmark’s Sliding Block Model …

Time (s)

W

N

T

Kh(t)W

θ

Figure:Development of permanent displacement for actual earthquake ground motion

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Newmark s sliding block model2

Newmark’s Sliding Block Model …

Deformations accumulate when the rigid body acceleration exceeds the yield acceleration.

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Ambraseys and menu 1988

Ambraseys and Menu (1988)

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

Sudhir K. Jain


Yegian et al 1991

Yegian et al (1991)

  • Neq = equivalent number of cycles

  • T = predominant period of input motion

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

Sudhir K. Jain


Makdisi and seed 1978

Makdisi and Seed (1978)

  • Determine yield acceleration

    • Standard slip circle analysis.

  • Determine earthquake induced average acceleration

  • Determine permanent seismic vertical deformation

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

Sudhir K. Jain


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Comparisons of Peak Base and Crest Accelerations Recorded at Earth Dams (Harder, 1991)

  • Peak base acceleration known for the site

  • Obtain peak crest acceleration.

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Variation of Maximum Acceleration with Depth of Sliding Mass (Makdisi and Seed, 1978)

  • Depth of sliding obtained from stability analysis.

  • Obtain Peak Average Acceleration

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Permanent Displacement versus Normalized Yield Acceleration for Embankments (Makdisi and Seed, 1978)

Read permanent displacement: Not a unique number, but a range.

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Example

Example

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

Sudhir K. Jain


Assuming no liquefaction in sub soil

Assuming No Liquefaction in Sub-Soil

  • Static load (only self weight): FOS=1.99

  • Pseudo-static: Yield coeff (FOS=1.0) is 0.275g

  • FOS Approach by:

    • Terzaghi (1950): Yield coeff. should be >0.20g

    • Mercuson (1981): Yield coeff. > 0.2g-0.3g

    • Hynes and Franklin (1984): Yield coeff of 0.1g will give permanent deformation less than 1m.

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

Sudhir K. Jain


Assuming no liquefaction in sub soil1

Assuming No Liquefaction in Sub-Soil

  • Permanent Deformation by Newmark’s Sliding Block Concept

    • Makdisi and Seed (1978) approach: 5 -15 mm

    • Ambraseys and Menu (1988): 39 mm

    • Yegian et al. (1991): 30mm

  • Permanent deformation of about 40mm should generally be acceptable.

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

Sudhir K. Jain


Liquefaction of sub soil

Liquefaction of Sub-Soil

  • Liquefied soil layers may not transmit significant amount of shear waves.

  • Will the embankment be stable under its own weight?

  • Liquefied soil layers will loose considerable amount of strength.

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

Sudhir K. Jain


Liquefaction of sub soil1

Liquefaction of Sub-Soil

  • Residual strength of liquefiable soil strata considered as per Seed and Harder (1990)

  • FOS against self weight:

    • 1.39 for North Embankment

    • 1.18 for South Rail Embankment

    • 1.31 for South Road Embankment

  • Embankment will be stable due to its own weight after foundation soils have liquefied

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

Sudhir K. Jain


An overview of seismic design of earth dams and embankments sudhir k jain october 2013

Relationship between Corrected ‘Clean Sand’ Blow Count (N1)60 and Undrained Residual Strength (Sr) (Seed and Harder, 1990)

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


Liquefaction of sub soil2

Liquefaction of Sub-Soil

  • Conservative Assumptions:

    • Liquefaction occurs early during shaking

    • Base of embankment still sustains PGA of 0.60g

  • Deformations computed for 0.60g but with residual strength of liquefiable soils

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013


More reading materials

More Reading Materials

  • IITK-GSDMA Guidelines for Seismic Design of Earth Dams and Embankments

  • Available at www.nicee.org

Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

Sudhir K. Jain


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