Geotechnical Earthquake Engineering · Seismic analysis/design of retaining walls mainly consists...

Geotechnical Earthquake

Engineering

by

Dr. Deepankar Choudhury Humboldt Fellow, JSPS Fellow, BOYSCAST Fellow

Professor

Department of Civil Engineering

IIT Bombay, Powai, Mumbai 400 076, India.

Email: [email protected]

URL: http://www.civil.iitb.ac.in/~dc/

Lecture – 34

IIT Bombay, DC 2

Module – 8

Site Response Analysis

Example # 1

Case Study

on

Seismic Ground Response Analysis

for Mumbai, India

D. Choudhury, IIT Bombay, India

Ref.: V. S. Phanikanth, Deepankar Choudhury and G. R. Reddy

(2011); "Equivalent-linear seismic ground response analysis of

some typical sites in Mumbai", Geotechnical and Geological

Engineering, Springer, Vol. 29(6), 1109-1126.

4

EQUIVALENT LINEAR GROUND

RESPONSE ANALYSIS FOR MUMBAI

Mangalwadi site near Girgaon (MBH#1, MBH#2);

Walkeswar site (WBH#1, WBH#2) ; and

BJ Marg near Pandhari Chawl site (BBH#1, BBH#2

& BBH#3)

Equivalent-linear Ground response Analysis for some

typical Mumbai Soil sites:


Typical bore hole data at soil site MBH#1 at Mumbai [Phanikanth et al. 2011, Geotech. and Geological Engg., Springer]


Acceleration-time history of

4 different input motions [Phanikanth et al. 2011, Geotech.

and Geological Engg., Springer]


Output Acceleration-time history at GL for soil site MBH#1 at

Mumbai when input was 2001 Bhuj motion

[Phanikanth et al. 2011, Geotech. and Geological Engg., Springer]

Software used, DEEPSOIL v3.5beta (2008)


Acceleration response spectra at ground level with 5% damping for

soil site MBH#1 at Mumbai under various earthquake motions [Phanikanth et al. 2011, Geotech. and Geological Engg., Springer]


Typical soil amplification for earthquake acceleration at various

soil sites in Mumbai under different earthquake motions [Phanikanth et al. 2011, Geotech. and Geological Engg., Springer]


Acceleration Response Spectra for site MBH#1 at various layers

for input motions (a) Bhuj 2001 (b) Loma Prieta 1989 (c) Loma

Gillory 1989 (d) Kobe 1995 [Phanikanth et al. 2011, Geotech. and Geological Engg., Springer]


Comparison of frequencies and validation of model for

ground response analysis in Mumbai subjected to 2001 Bhuj motion [Phanikanth, 2011, Ph.D. Thesis., IIT Bombay]


Seismic Zonation Map of India as per BIS 1962 and 1966


Seismic Zonation Map of India as per BIS 1970 and 1984


Seismic zonation map of India [as per IS 1893 – Part 1 (2002)]

with highlight on Soil Characterization

• Only 3 types of soil!!!

Soft soil

Medium soil

Hard rock

• Characterization of Soil Based

on SPT ‘N’ Value, irrespective of

soil type !!

• No DYNAMICS (for soil

characterization) is involved!!!

Soil Classification for Seismic Design in USA (NEHRP-2003)

Choudhury (2010) in Structural Longivity, 3(2), 155-170.

Dr. Deepankar Choudhury, IIT Bombay

Soil Classification as per Eurocode 8 (2004)


Comparison of Soil Classification as per

Modern Seismic Codes Worldwide


Soil Amplification Factor for various control Periods

for different subsoil class for

Earthquake Type 1 (Ms > 5.5) as per Eurocode 8

Soil Amplification Factor for various control Periods

for different subsoil class for

Earthquake Type 2 (Ms < 5.5) as per Eurocode 8

Example # 2

Case Study

on

Seismic Ground Response Analysis

for Four Ports in Gujarat, India


Ref.: Jaykumar Shukla and Deepankar Choudhury (2012); "Seismic

hazard and site-specific ground motion for typical ports of Gujarat",

Natural Hazards, Springer, Vol. 60(2), 541-565.

Location of selected

Ports in Gujarat, India

7/11/2013

67, E 68, E 69, E 70, E 71, E 72, E 73, E 74, E 75, E

19, N

20, N

21, N

22, N

23, N

24, N

25, N

26, N

F18

F17

F14 F15

F13

F12 F25A F5

F2

F1

F4

F3F6

F7

F8

F10

F9

F33

F35

F34

F37

F38 F42

F41

F43

F45 F46

F31

F32

F24

F49F23

F48

F24

F26

F21

F28

F29

F30

Kandla port site

Mundra port site

Hazira port site

Dahej port site

Fn Fault line

Legend

0 N

Shukla and Choudhury (2012) in Natural Hazards, 60(2), 541-565.

Uniform Hazard Spectra for

Kandla and Mundra port sites

• UHS obtained are for rock sites

• Compared with of IS:1893 -Part 1 (2002)

specified spectra for rock sites – MCE Spectra

• As per IS:1893 – Part I (2002), Design Basis

Earthquake can be taken as 50% of MCE.

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

0.0

0.5

1.0

1.5

2.0

2.5

Retrun Period 2475 years



IS 1893 (2002)- Zone V

Sp

ectr

al A

ccel

erat

ion

(g

)

Spectral Period (s)

Kandla Port Site

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

0.0

0.5

1.0

1.5

2.0

Sp

ectr

al A

ccel

erat

ion

(g

)

Spectral Period (s)

Mundra Port Site




IS 1893 (2002)- Zone V


Stiff Clay

Typical Geotechnical Characterization

0 200 400 600 800 1000 1200

25

20

15

10

5

0

200 400 600 800

40

35

30

25

20

15

10

5

0

Average (used in present study) Imai, 1977 (for all soils) Jinan, 1987 (for all soils)

Imai and Yoshimura, 1970 (for all soils)) Imai and Tonouchi, 1982 (for all soils) Iyisan (for all soils)

Jafari et al., 1997 (for all soils) Yokota et al., 1991 (for all soils) Seed and Idriss, 1981 (for all soils)

Athanasopoulos, 1995 (for all soils) Kiku, 2001 (for all soils)

Dep

th (

m)

Shear Wave Velocity (m/sec)

Kandla Port siteB

Mundra Port site

Dep

th (

m)

Shear Wave Velocity (m/sec)

Silty Clay

Stiff Clay

Silty Sand

Stiff Clay

Sandy

Gravel

Silty Sand

Dense

SiltySand

Shear wave velocities are estimated from 10

empirical correlations and then averaged.

0 20 40 60 80

40

35

30

25

20

15

10

5

0

0 20 40 60 80 100

Mundra port site

Dep

th (

m)

SPT N-Value

Borehole 1

Borehole 2

Kandla port site A

Borehole 1

Borehole 2

Site characterization from available

geotechnical investigations

Shukla and Choudhury (2012) ASCE GSP No. 225, 1650-1659.

Typical synthetic time

history for Kandla Port

0 10 20 30 40 50 60 70 80 90 100

-0.8

-0.4

0.0

0.4

0.8

Spec

tral

Acc

eler

atio

ns (g

)

Time (sec)

Bhuj Earthquake 2001 (recorded at Ahemedand passport office, N-W component)

Level 3 ground motion(2475 years return period)

Level 2 ground motion(475 years return period)

Level 1ground motion(72 years return period)

Kandla Port


Ground Response Analysis

0.01 0.1 1 10

0.1

1

10

Pse

ud

o-

Acc

eler

atio

n (

g)

Period (sec)

Layer 1, Damping: 5.0%




Kandla Port - Level 3 ground motions

0.1 1 10

0.0

0.5

1.0

1.5

2.0

2.5

Kandla Port - Level 3 ground motions

Am

pli

fica

tio

n r

atio

Frequency(Hz)

Layer 1 to Bedrock

Layer 2 to Bedrock

Layer 3 to Bedrock

Layer 4 to Bedrock

Layer

NO

Avera

ge

SPT-

value

Description Modulus reduction

curve and damping

curve selected

1 10 Soft clay Sun et al. (1988)

2 17 Stiff clay Vucetic and Dobry

(1991)

3 35-40 Medium silty

sand

Idriss (1990), upper

range

4 50 Stiff to very stiff

clay

Vucetic and Dobry

(1991)

• Ground Response analysis is carried out using

equivalent liner model using SHAKE91 (Schnabel et al.,

1972).

• Modulus reduction curves and damping curves are

selected based on the Soil properties

• Typical results in form of Pseudo-acceleration response

spectra and transfer function (amplification factor)


Important observations Contributing faults:

• Kandla port :F13, F25A, F14 ; Mundra port:F25A and F13 ; Dahej port : F33 and

F30; Hazira port : F34

• IS:1893 part 1:2002, underestimates the seismic ground motions for the two port sites

of Kachchh region however for Dahej and Hazira ports they are in agreement.

Ground

Motion

level

Peak ground accelerations (g) IS:1893

Part 1 (2002 )

Mundra

port site

Kandla

port site

Hazira

port site

Dahej

port site

Zone V Zone III

Level 1 0.07 0.12 0.05 0.04 ---

Level 2 0.19 0.25 0.10 0.10 0.18 0.08

Level 3 0.33 0.40 0.17 0.18 0.36 0.16

Peak ground accelerations obtained for port sites

IIT Bombay, DC 26

End of

Module – 8

IIT Bombay, DC 27

Module – 9

Seismic Analysis and

Design of Various

Geotechnical Structures

IIT Bombay, DC 28

Seismic Design of

Retaining Wall

Introduction

Retaining walls

› are built for the purpose of holding back earth which would

otherwise move downwards.

› knowledge of seismic earth pressure is very important for

design of retaining structures in the earthquake prone areas.

D. Choudhury, IIT Bombay, India 29

Typical Retaining wall sections commonly used in practice (Source:http://www.stonescapecontracting.com/images/images/walls/Retaining_Walll_Type_Function_lg.jpg)

Earth Pressures on Retaining Walls


Earth pressures-

› at rest earth pressure

› active earth pressure

› passive earth pressure

Earth pressure conditions

Failure of Retaining Walls


Failure of gravity retaining wall

(Source: http://www.geofffox.com) (Source: http://www.parmeleegeology.com/)

Retaining walls may fail during an earthquake, if they are not

designed to resist additional destabilizing earthquake forces.

Seismic Analysis and Design of Retaining Walls

Seismic analysis/design of retaining walls mainly consists of

› Determining magnitude of additional destabilizing forces that act during an earthquake

› Determining seismic active and passive earth pressures due to all destabilizing forces (static + seismic)

› Design section based on above parameters using

1. Force based approach

2. Displacement based approach – for performance based

design


Pseudo-static Method

33

Theoretical background of seismic coefficient lies in the

application of D´Alembert´s principle of mechanics.

Example of elementary seismic

slope stability analysis

(Towahata, 2008)

D’Alembert’s principle of

mechanics

Towhata, I., (2008), Geotechnical Earthquake Engineering, Springer,

Tokyo, Japan.


Conventional Seismic Design of Retaining Walls

Pseudo-Static Approach Proposed by Mononobe-Okabe (1929)

Questions: Value of kh and kv to be used for design?

Soil amplification?

Variation of seismic acceleration with depth and time?

Effect of dynamic soil properties? etc.

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