recent r & d activities in geotechnical earthquake

Recent R & D Activities in Geotechnical Earthquake Engineering

at IIT Bombay

by

Dr. Deepankar ChoudhuryAssociate Professor

Department of Civil Engineering I I T Bombay, Powai, Mumbai. http://www.civil.iitb.ac.in/~dc

Presentation at IIT Bombay, organized by IRCC on October 7, 2009for IIT Bombay Young Investigator Awardee of 2007

Why this Area of Research ?

List of Major Historic EarthquakesList of Major Historic Earthquakes

6.91,00,000Gujarat, India20017.35,472 Kobe19957.162 California19898.19,500 Mexico City19857.87,00,000 China19769.2131 Alaska19649.52,230 S. Chile19607.9700San Francisco19068.05,30,000China1556

MagnitudeDeathsLocationYear

D. Choudhury, IIT Bombay, India

Nishinomia Bridge 1995 Kobe earthquake, Japan

Flow failures of structures - caused by loss of strength of underlying soil

Earthquake Destruction: Liquefaction


Kirishima Bridge, Japan

Vibration Isolation

Earthquake Resistant Construction


Sand blow in mud flats used for salt production southwest of Kandla Port, Gujarat

Earthquake Destruction: Liquefaction

D. Choudhury, IIT Bombay

Design As Per Seismic Code

• Using pseudo-static approach to evaluate stability of retaining walls.

• Compute seismic earth pressure using Mononobe-Okabe equations.

• Dynamic increment of earth pressure will act at mid height of the wall.

• Effect of dry, partially submerged and saturated backfill is considered.

• Range of permissible displacement is not specified.

• Soil amplification is not considered.

IS 1893: 1984, Part 3 (Bridges and Retaining Walls)


Design As Per Seismic Code

IS 1893: 2002, Part 1

Only 3 types of soil!!!

Soft soilMedium soilHard rock

Characterization of Soil Based on SPT ‘N’ Value, irrespective of soil type !!


Soil Classification for Design Standard in USA


• Based on modified pseudo-static analysis.

• Compute seismic earth pressure using Richards and Elms (1979) model.

• Permissible displacement for sliding and rocking movement of the wall are considered.

• Included non-linear behaviour in base soil and backfill.

• The point of application of the dynamic earth pressure increment is at mid-height of the wall.

• Soil amplification is considered.

Eurocode 8 – 1998


Earthquake Engineering Research in India

Three major Shake Tables of about 50 ton capacity with multi-directional shaking

Seismological recording stations – several 100s

Research Institutes/Organizations – 7 IITs, IISc, SERC, NGRI, CPRI, NIDM, GSI, CWC, CWPRS, BMTPC etc.

Information Centre – National Information Centre for EarthqaukeEngineering (NICEE)

Journal/Society – Indian Society of Earthquake Technology (ISET)


Damages to Geotechnical Structures during Earthquake



Preamble and Background

o Waterfront retaining walls or seawalls subjected to both earthquake and tsunami are common.

o Evaluation of seismic earth pressures, hydrodynamic wave pressures with other forces are important for design of seawall.

o Researches on individual topics like effects of earthquake on retaining wall and hydrodynamic wave force on waterfront wall iscommonly available.

o Dynamic effects of earthquake like shear and primary wave velocities, time period, soil amplification etc. are not considered in the conventional pseudo-static methods.


Available LiteratureOn Earthquake On Tsunami/Hydrodynamics

Mononobe-Okabe (1926, 1929)Richards and Elms (1979)Saran and Prakash (1979)Prakash (1981)Nadim and Whitman (1983)Steedman and Zeng (1990)Ebeling and Morrison (1992)Kramer (1996)Kumar (2002)Choudhury and Subba Rao (2005)Choudhury and Nimbalkar (2006)And many others…………..

Westergaard (1933)Fukui et al. (1962)Ebeling and Morrison (1992)Mizutani and Imamura (2001)CRATER (2006)And few others……



Proposed Design Techniques for Waterfront RetainingWall subjected to Earthquake and Tsunami

(1) For Tsunami attacking the wall (passive case)

(a) Against Sliding mode of failure(b) Against Overturning mode of failure

(2) For Tsunami receding away from wall (active case)

(a) Against Sliding mode of failure(b) Against Overturning mode of failure


Case 1(a): Passive Case – Pseudo-static

Choudhury, D. and Ahmad, S. M. (2007) in Applied Ocean Research, Elsevier, U.K., Vol. 29, 37-44.

Case 1(b): Passive Case – Pseudo-dynamic

Soil amplification is considered.

Frequency of earthquake excitation is considered.

Time duration of earthquake is considered.

Phase differences between different waves can be considered.

Amplitude of equivalent PGA can be considered.Considers shear and primary wave velocities traveling during earthquake.

Advantages

Choudhury and Nimbalkar (2005)

Choudhury, D. and Nimbalkar, S. (2005), in Geotechnique, London, U.K., Vol. 55, No. 10, 949-953.

ah(z, t) = ah sin [ω{t – (H – z)/Vs}]

av(z, t) = av sin [ω{t – (H – z)/Vp}]

Seismic passive earth pressure by pseudo-dynamic model

Choudhury and Nimbalkar (2005)


H

h0

( ) m(z)a (z, t)dz hQ t = ∫ [ ]2

2 Hcosw (sin sin )4 tan

ha w wtg

λ γπ ζ λ ζ

π α+ −=

where, λ = TVs is the wavelength of the vertically propagating shear wave and ζ = t-H/Vs.

H

v0

( ) m(z)a (z, t)dz vQ t = ∫ [ ]2

2 Hcos (sin sin )4 tan

va tg

η γπ ωψ λ ωψ ω

π α= + −

The total (static plus dynamic) passive resistance is given by,

where, η= TVp, is the wavelength of the vertically propagating primary wave and ψ = t – H/Vp.

ah(z, t) = ah sin [ω{t – (H – z)/Vs}]

where ω = angular frequency; t = time elapsed; Vs = shear wave velocity;Vp = primary wave velocity

sin( ) cos( ) sin( )cos( )

h vpe

W Q QP α φ α φ α φα δ φ

+ − + − +=

+ +

av(z, t) = av sin [ω{t – (H – z)/Vp}]and


20

( ) sin( )( )tan cos( )

cos( ) sintan cos( )

sin( ) sintan cos( )

pepe

h

s

v

p

dP t zp tdz

k z ztV

k z ztV

γ α φα α δ φ

γ α φ ωα α δ φ

γ α φ ωα α δ φ

+= =

+ +

⎛ ⎞+− −⎜ ⎟+ + ⎝ ⎠

⎛ ⎞+− −⎜ ⎟⎜ ⎟+ + ⎝ ⎠

The coefficient of seismic passive resistance (Kpe) is given by,

The seismic passive earth pressure distribution is given by,

where and


Typical non-linear variation of seismic active earth pressure

1.0

0.8

0.6

0.4

0.2

0.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6

kv=0.5kh, φ=300, δ=φ/2,H/λ=0.3, H/η=0.16

z/H

pae/γH

kh=0.0 kh=0.1 kh=0.2 kh=0.3

Choudhury, D. and Nimbalkar, S. (2006), in Geotechnical and Geological Engineering, Springer, 24(5), pp. 1103-1113

Effect of amplification factor on seismic active earth pressure

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0.2

0.4

0.6

0.8

1.0

kh = 0.2, kv = 0.0, φ = 330, δ = 160 fa=1.0 fa=1.2 fa=1.4 fa=1.8 fa=2.0K

ae

H/TVs

ah(z, t) = {1 + (H – z).(fa – 1)/H}ah sin [ω{t – (H – z)/Vs}]

Nimbalkar, S. and Choudhury, D. (2008), in Journal of Earthquake and Tsunami, 2(1), pp. 33-52.


Experimental Validation

Using

Geotechnical Dynamic Centrifuge Facility

24D. Choudhury, IIT Bombay, India

Experimental Validation using Dynamic Centrifuge Facility


Comparison of proposed pseudo-dynamic method with existing pseudo-static method

Dynamic moment increment, Z

, where M (Z, t) = p (z, t) cos (Z - z) dz3 3 ae0

MH

δγ

∫

0.0

0.2

0.4

0.6

0.8

1.00 0.05 0.1 0.15 0.2 0.25

Dynamic moment increment

z/H

Mononobe-Okabe method

Present method

Centrifuge test results(Steedman and Zeng, 1990)

φ = 370, δ = 200, kh = 0.184, kv = 0, fa = 2, G = 57 MPa, T = 1.0 s

26

Typical Design Charts for Factor of Safety

Choudhury, D. and Ahmad, S. M. (2008), in Journal of Waterway, Port, Coastal and Ocean Engg., ASCE, USA.

Behaviour of Reinforced Soil-Wall used as

Waterfront Retaining Structure

28D. Choudhury, IIT Bombay, India

Slope in Kagoshima, Japan

Slope Stability using Earth Anchors

Earthquake Resistant Construction

29

Mitigation: Typical Reinforced Soil-Wall used as Waterfront Retaining Structure during Earthquake

Ahmad, S. M. and Choudhury, D. (2008), in Geotextiles and Geomembranes, Elsevier, U.K., Vol. 26(4), pp. 291-301.

Seismic Design of Shallow Foundations

Choudhury and Subba Rao (2006)Choudhury, D. and Subba Rao, K. S. (2006) in International Journal of Geomechanics, ASCE, USA, Vol. 6(3), 176-18

Design Charts for Seismic Bearing Capacity Factors

qud = cNcd + qNqd + 0.5γBNγd

( ) ( )

αtan 1

αtan 1

- α sin cos

mK - - α sin

cosK

k1 N

21

222

pqd21

pqd1

h qd

⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢

⎣

⎡

+=

φφ

φφ

Choudhury, D. and Subba Rao, K. S. (2006) in International Journal of Geomechanics, ASCE, USA, Vol. 6(3), 176-18

Seismic Behaviour MSW Landfills

Equivalent-linear analysis of MSW landfill sections during earthquake motionsusing DEEPSOIL

Choudhury, D. and Savoikar, P (2009) in Engineering Geology, Elsevier, Vol. 107, pp. 98-110.

Typical Results by Choudhury and Savoikar (2009)

Variation of MHA with depth for 40m high landfill on type (ii) foundation

Variation of spectral amplification with frequency for 40m high landfill.

Choudhury, D. and Savoikar, P (2009) in Engineering Geology, Elsevier, Vol. 107, pp. 98-110.

Deepankar Choudhury, IIT Bombay, India

* Continuous update of Design codes in India is Essential following latest research findings.

* Closed-form design solutions using simple and realistic earthquake analysis for design of seawall, foundation, railway subgrade, reinforced soil-wall etc. subjected to earthquake.

* Reinforced soil slope provides more stability to the existing slope under earthquake conditions compared to the un-reinforced slope, provided the property and length of reinforcement is properly designed.

Concluding Remarks / Future Needs

Hope to build ‘STABLE Earthquake Resistant’Geotechnical Structures

Deepankar Choudhury, IIT Bombay, India

* PhD Scholars: Dr. S. Nimbalkar, Dr. S. M. Ahmad, Mr. P. Savoikar and other current students at IIT Bombay.

* M.Tech. Students: Former and present students at IIT Bombaywho carried out M.Tech. dissertation under my supervision.

* Collaborators in India: Prof. K. S. Subba Rao, Prof. T. G. Sitharam of IISc Bangalore & Prof. M. R. Madhav of J.N.T.U.

* Collaborators from Abroad: Prof. J. D. Bray of UC Berkeley, Prof. B. Indraratna of UoW Australia, Prof. C. F. Leung of NUS Singapore, Prof. R. Kitamura of KU Japan.

* Funding Agencies: AERB, BRNS, INAE, DST, IRCC-IITB.

Acknowledgements

Contact Email: [email protected]

[email protected]

recent r & d activities in geotechnical earthquake

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