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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 – 38
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IIT Bombay, DC 2
Module – 9
Seismic Analysis and
Design of Various
Geotechnical Structures
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IIT Bombay, DC 3
Seismic Design of
Waterfront Retaining Wall
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D. Choudhury, IIT Bombay, India
Applications on Waterfront Retaining Wall / Seawall
-A soil retaining armoring structure, generally massive
- To defend a shoreline against wave attack
-Designed primarily to resist wave action along high value
coastal property
(source: www.mojosballs.com/main.htm)
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D. Choudhury, IIT Bombay, India
Available Literature On Earthquake
On Tsunami/Hydrodynamics Mononobe-Okabe (1926, 1929)
Madhav and Kameswara Rao (1969)
Richards and Elms (1979)
Saran and Prakash (1979)
Prakash (1981)
Nadim and Whitman (1983)
Steedman and Zeng (1990)
Ebeling and Morrison (1992)
Das (1993)
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
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D. Choudhury, IIT Bombay
Design Solutions for Waterfront Retaining Walls (Sea
Walls) subjected to both 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
Ref: PhD Thesis of Dr. Syed Mohd. Ahmad (2009) at IIT Bombay. India.
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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.
CRATER (2006)
Combined effects of tsunami and earthquake
On rigid waterfront retaining wall
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Case 1(a): Passive Case – Pseudo-static (Results)
Choudhury, D. and Ahmad, S. M. (2007) in Applied Ocean Research, Elsevier, U.K., Vol. 29, 37-44.
Factor of safety
against sliding
Factor of safety
against overturning
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Design solutions for Active Case (pseudo-static)
proposed by Choudhury and Ahmad (2007)
Factor of Safety against Sliding Failure:
Factor of Safety against Overturning Failure:
Choudhury, D. and Ahmad, S. M. (2007) in Ocean Engineering, Elsevier, U.K., Vol. 34(14-15), 1947-1954.
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Typical Results by Choudhury and Ahmad (2007)
Choudhury, D. and Ahmad, S. M. (2007) in Ocean Engineering, Elsevier, U.K., Vol. 34(14-15), 1947-1954.
Factor of Safety against Sliding
Factor of Safety against Overturning
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Active Case with Pseudo-dynamic method
Forces acting on typical seawall subjected to
earthquake and tsunami (active case)
Choudhury and Ahmad (2008) in Jl. of Waterway, Port, Coastal and Ocean Engg., ASCE, Vol. 134, 252-260.
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Comparison of Results
Choudhury and Ahmad (2008) in Jl. of Waterway, Port, Coastal and Ocean Engg., ASCE, Vol. 134, 252-260.
Choudhury and Ahmad (2008)
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IIT Bombay, DC 13
Seismic Design of
Reinforced Soil-Wall
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A week after the 1995 Kobe Earthquake
24 Jan. 1995 The wall survived!
GRS RW for a rapid
transit at Tanata
Ref: Tatsuoka (2010)
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Typical Design of Earthquake Resistant
Reinforced Soil-Wall (Internal Stability)
Nimbalkar, S.S., Choudhury, D. and Mandal, J.N. (2006), in Geosynthetics International, ICE London, 13(3), 111-119.
Nimbalkar et al. (2006)
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Typical Design of Earthquake Resistant
Reinforced Soil-Wall (Internal Stability)
Nimbalkar, S.S., Choudhury, D. and Mandal, J.N. (2006), in Geosynthetics International, ICE London, 13(3), 111-119.
Reinforcement strength and length required as per Nimbalkar et al. (2006)
For H = 5 m, = 300
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Comparison of Results
Nimbalkar, S.S., Choudhury, D. and Mandal, J.N. (2006), in Geosynthetics International, ICE London, 13(3), 111-119.
Nimbalkar et al. (2006)
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Typical Design of Earthquake Resistant
Reinforced Soil-Wall (External Stability)
Choudhury, D., Nimbalkar, S.S., and Mandal, J.N. (2007), in Geosynthetics International, ICE London, 14(4), 211-218.
Choudhury et al. (2007) Overturning stability
Sliding stability
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Typical Design of Earthquake Resistant
Reinforced Soil-Wall (External Stability)
Choudhury, D., Nimbalkar, S.S., and Mandal, J.N. (2007), in Geosynthetics International, ICE London, 14(4), 211-218.
Choudhury et al. (2007)
Length of Reinforcement for
Overturning stability
Length of Reinforcement for
Sliding stability
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Comparison of Results
Choudhury, D., Nimbalkar, S.S., and Mandal, J.N. (2007), in Geosynthetics International, ICE London, 14(4), 211-218.
Choudhury et al. (2007)
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IIT Bombay, DC 21
Seismic Design of
Waterfront Reinforced
Soil-Wall
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Typical Reinforced Soil-Wall used as
Waterfront Retaining Structure during Earthquake
(Pseudo-dynamic approach)
Ahmad, S. M. and Choudhury, D. (2008), in Geotextiles and Geomembranes, Elsevier, U.K., Vol. 26(4), 291-301.
Ahmad and Choudhury (2008)
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Typical Results for Reinforcement Strength
Ahmad and Choudhury (2008)
Ahmad, S. M. and Choudhury, D. (2008), in Geotextiles and Geomembranes, Elsevier, U.K., Vol. 26(4), 291-301.
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Typical Reinforced Soil-Wall used as
Waterfront Retaining Structure during Earthquake
(External Stability)
Choudhury, D. and Ahmad, S. M. (2009) in Geosynthetics International, ICE London, U.K., Vol. 16, No. 1, pp. 1-10.
Choudhury and Ahmad (2009)
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Typical Result for Length of Reinforcement
Choudhury, D. and Ahmad, S. M. (2009) in Geosynthetics International, ICE London, U.K., Vol. 16, No. 1, pp. 1-10.
Choudhury and Ahmad (2009)
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IIT Bombay, DC 26
Reinforcement required for Soil-Wall used as
Waterfront Retaining Structure during Earthquake
(Pseudo-static approach, Ahmad and Choudhury, 2012)
Ahmad, S. M. and Choudhury, D. (2012), in Ocean Engineering, Elsevier, Vol. 52, 83-90.
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IIT Bombay, DC 27
Seismic Design of
Shallow Footings
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Choudhury, D. and Subba Rao, K. S. (2005), in Geotechnical and Geological Engg., Springer, Vol.23, pp.403-418
Choudhury and Subba Rao (2005)
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D. Choudhury, IIT Bombay, India
Choudhury and Subba Rao (2005)
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D. Choudhury, IIT Bombay, India
qud = cNcd + qNqd + 0.5 BN d
Design charts given by
Choudhury and Subba Rao (2005)
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D. Choudhury, IIT Bombay, India
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D. Choudhury, IIT Bombay, India
Comparison of Results
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Shallow Strip Footing embedded in Sloping Ground
under Seismic Condition
Choudhury and Subba Rao (2006) Choudhury, D. and Subba Rao, K. S. (2006), “Seismic bearing capacity of shallow strip footings embedded in slope”,
International Journal of Geomechanics, ASCE, USA, Vol. 6, No. 3, pp. 176-184.
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Deepankar Choudhury, IIT Bombay
Design Equations proposed by Choudhury and Subba Rao (2006)
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Deepankar Choudhury, IIT Bombay
Typical Design Chart for Ncd
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Deepankar Choudhury, IIT Bombay
Typical Design Charts for Nqd and N d
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Design Charts for Seismic Bearing Capacity Factors
qud = cNcd + qNqd + 0.5 BN d
αtan
1
αtan
1
- α sin cos
mK - - α sin
cos
K
k
1 N
21
22
2
pqd2
1
pqd1
h
qd
Choudhury, D. and Subba Rao, K. S. (2006) in International Journal of Geomechanics, ASCE, USA, Vol. 6(3), 176-184.
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Deepankar Choudhury, IIT Bombay
Typical Results to Show Effects of Ground Slope and Embedment
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Seismic Bearing Capacity of Shallow Strip Footing
Using Pseudo-Dynamic Approach
Model and forces
considered by
Ghosh and
Choudhury (2011)
Ghosh, P. and Choudhury, D. (2011) in Journal Disaster Advances, Vol. 4(3), 34-42.
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Seismic Bearing Capacity Factor & Comparison
Using Pseudo-dynamic approach
Ghosh and Choudhury (2011) – Pseudo-Dynamic Approach
Ghosh, P. and Choudhury, D. (2011) in Journal Disaster Advances, Vol. 4(3), 34-42.
Effect of Soil Amplification
on Bearing Capacity Factor
Comparison of present result with other methods
= 300
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IIT Bombay, DC 23
Seismic Stability of Finite
Soil Slopes
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24 Deepankar Choudhury, IIT Bombay
CLASSICAL THEORIES in Seismic Slope Stability
Terzaghi’s method (1950)
Newmark’s sliding block analysis (1965)
Seed’s improved procedure for pseudo-static
analysis (1966)
Modified Swedish Circle method (1968)
Modified Taylor’s method (1969)
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Terzaghi (1950)
25 Deepankar Choudhury, IIT Bombay
Pseudo-Static method of Seismic Analysis
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Pseudo-Static method of Seismic Analysis
The selection of the seismic coefficient kh takes considerable experience and judgment.
Guidelines for the selection of kh are as follows:
1. Peak ground acceleration: The higher the value of the peak ground acceleration amax,
the higher the value of kh that should be used in the Pseudo-static analysis.
2. Earthquake magnitude: The higher the magnitude of the earthquake, the longer the
ground will shake and consequently the higher the value of kh that should be used in the
pseudo-static analysis.
3. Maximum value of kh: When items 1 and 2 as outlined above are considered, keep in
mind that the value of kh should never be greater than the value of amax/g.
4. Minimum value of kh: Check to determine if there are any agency rules that require a
specific seismic coefficient. For example, a common requirement by many local
agencies in California is the use of a minimum seismic coefficient kh 0.15 (Division of
Mines and Geology 1997).
5. Size of the sliding mass: Use a lower seismic coefficient as the size of the slope
failure mass increases. The larger the slope failure mass, the less likely that during the
earthquake the entire slope mass will be subjected to a destabilizing seismic force acting
in the out-of-slope direction. Suggested guidelines are as follows:
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27 Deepankar Choudhury, IIT Bombay
Pseudo-Static method of Seismic Analysis
a. Small slide mass: Use a value of kh = amax/g for a small slope failure mass.
Examples would include small rockfalls or surficial stability analyses.
b. Intermediate slide mass: Use a value of kh = 0.65amax/g for slopes of moderate
size (Krinitzsky et al. 1993, Taniguchi and Sasaki 1986). Note that this value of
0.65 was used in the liquefaction analysis.
c. Large slide mass: Use the lowest values of kh for large failure masses, such as
large embankments, dams, and landslides. Seed (1979) recommended the
following:
kh = 0.10 for sites near faults capable of generating magnitude 6.5 earthquakes.
The acceptable pseudo-static factor of safety is 1.15 or greater.
kh = 0.15 for sites near faults capable of generating magnitude 8.5 earthquakes.
The acceptable pseudo-static factor of safety is 1.15 or greater.
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Pseudo-Static method of Seismic Analysis
Terzaghi (1950) suggested the following values: kh = 0.10 for “severe” earthquakes, kh
= 0.20 for “violent and destructive” earthquakes, and kh = 0.50 for “catastrophic”
earthquakes.
Seed and Martin (1966) and Dakoulas and Gazetas (1986), using shear beam models,
showed that the value of kh for earth dams depends on the size of the failure mass. In
particular, the value of kh for a deep failure surface is substantially less than the value of
kh for a failure surface that does not extend far below the dam crest.
Marcuson (1981) suggested that for dams kh = 0.33amax/g to 0.50 amax/g, and consider
possible amplification or deamplification of the seismic shaking due to the dam
configuration.
Hynes-Griffin and Franklin (1984), based on a study of the earthquake records from
more than 350 accelerograms, use kh = 0.50amax/g for earth dams. By using this seismic
coefficient and having a psuedo-static factor of safety greater than 1.0, it was concluded
that earth dams will not be subjected to “dangerously large” earthquake deformations.
Kramer (1996) states that the study on earth dams by Hynes-Griffin and Franklin
(1984) would be appropriate for most slopes. Also Kramer indicates that there are no
hard and fast rules for the selection of the pseudo-static coefficient for slope design, but
that it should be based on the actual anticipated level of acceleration in the failure mass
(including any amplification or deamplification effects).
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Terzaghi’s Wedge Method (1950)
N normal force acting on the slip surface, kN
T shear force acting along the slip surface, kN. The shear force is also known as the resisting force
because it resists failure of the wedge. Based on the Mohr-Coulomb failure law, the shear force is equal
to the following:
For a total stress analysis: T = cL + N tan , or T = suL
For an effective stress analysis: T = c′L + N′ tan ′
where L length of the planar slip surface, m
c, shear strength parameters in terms of a total stress analysis
su undrained shear strength of the soil (total stress analysis)
N total normal force acting on the slip surface, kN
c′, ′ shear strength parameters in terms of an effective stress analysis
N′ effective normal force acting on the slip surface, kN
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Terzaghi’s Wedge Method (1950)
cossin
tansincos
hv
hvab
FFW
FFWcl
forcedriving
forceresistingFS
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Newmark’s Sliding block analysis (1965) in Geotechnique
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Newmark’s Method (1965)
csotk
tkFS
h
h
)(sin
tansin)(cos
ky = tan( - )
arel(t) = ab(t) – ay = A – ay to t to + t
t
t
oyrelrel
o
ttaAdttatv )()(
t
t
oyrelrel
o
ttaAdttvtd2
2
1)()(