recent r & d activities in geotechnical earthquake
TRANSCRIPT
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
D. Choudhury, IIT Bombay, India
Kirishima Bridge, Japan
Vibration Isolation
Earthquake Resistant Construction
D. Choudhury, IIT Bombay, India
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)
D. Choudhury, IIT Bombay
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 !!
D. Choudhury, IIT Bombay
Soil Classification for Design Standard in USA
D. Choudhury, IIT Bombay
• 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
D. Choudhury, IIT Bombay, India
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)
D. Choudhury, IIT Bombay, India
Damages to Geotechnical Structures during Earthquake
D. Choudhury, IIT Bombay, India
D. Choudhury, IIT Bombay, India
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.
D. Choudhury, IIT Bombay, India
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……
D. Choudhury, IIT Bombay, India
D. Choudhury, IIT Bombay, India
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
D. Choudhury, IIT Bombay, India
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)
Choudhury, D. and Nimbalkar, S. (2005), in Geotechnique, London, U.K., Vol. 55, No. 10, 949-953.
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
Choudhury, D. and Nimbalkar, S. (2005), in Geotechnique, London, U.K., Vol. 55, No. 10, 949-953.
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
Choudhury, D. and Nimbalkar, S. (2005), in Geotechnique, London, U.K., Vol. 55, No. 10, 949-953.
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.
D. Choudhury, IIT Bombay, India
Experimental Validation
Using
Geotechnical Dynamic Centrifuge Facility
24D. Choudhury, IIT Bombay, India
Experimental Validation using Dynamic Centrifuge Facility
D. Choudhury, IIT Bombay, India
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]