Geotechnical Earthquake Engineering

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1 Geotechnical Earthquake Engineering by Dr. Deepankar Choudhury Humboldt Fellow, JSPS Fellow, BOYSCAST Fellow Professor Department of Civil Engineering IIT Bombay, Powai, Mumbai , India. URL: Lecture 38

2 Module 9 Seismic Analysis and Design of Various Geotechnical Structures IIT Bombay, DC 2

3 Seismic Design of Waterfront Retaining Wall IIT Bombay, DC 3

attack -Designed primarily to resist wave action along high value coastal

4 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 D. Choudhury, IIT Bombay, India (source:

5 On Earthquake 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.. Available Literature On Tsunami/Hydrodynamics Westergaard (1933) Fukui et al. (1962) Ebeling and Morrison (1992) Mizutani and Imamura (2001) CRATER (2006) And few others D. Choudhury, IIT Bombay, India

6 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. D. Choudhury, IIT Bombay

7 Case 1(a): Passive Case Pseudo-static CRATER (2006) Combined effects of tsunami and earthquake On rigid waterfront retaining wall Choudhury, D. and Ahmad, S. M. (2007) in Applied Ocean Research, Elsevier, U.K., Vol. 29,

8 Case 1(a): Passive Case Pseudo-static (Results) Factor of safety against sliding Factor of safety against overturning Choudhury, D. and Ahmad, S. M. (2007) in Applied Ocean Research, Elsevier, U.K., Vol. 29,

9 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),

10 Typical Results by Choudhury and Ahmad (2007) Factor of Safety against Sliding Factor of Safety against Overturning Choudhury, D. and Ahmad, S. M. (2007) in Ocean Engineering, Elsevier, U.K., Vol. 34(14-15),

11 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,

12 Comparison of Results Choudhury and Ahmad (2008) Choudhury and Ahmad (2008) in Jl. of Waterway, Port, Coastal and Ocean Engg., ASCE, Vol. 134,

13 Seismic Design of Reinforced Soil-Wall IIT Bombay, DC 13

14 A week after the 1995 Kobe Earthquake GRS RW for a rapid transit at Tanata The wall survived! Ref: Tatsuoka (2010) 24 Jan. 1995

15 Typical Design of Earthquake Resistant Reinforced Soil-Wall (Internal Stability) Nimbalkar et al. (2006) Nimbalkar, S.S., Choudhury, D. and Mandal, J.N. (2006), in Geosynthetics International, ICE London, 13(3),

16 Typical Design of Earthquake Resistant Reinforced Soil-Wall (Internal Stability) For H = 5 m, = 30 0 Reinforcement strength and length required as per Nimbalkar et al. (2006) Nimbalkar, S.S., Choudhury, D. and Mandal, J.N. (2006), in Geosynthetics International, ICE London, 13(3),

17 Comparison of Results Nimbalkar et al. (2006) Nimbalkar, S.S., Choudhury, D. and Mandal, J.N. (2006), in Geosynthetics International, ICE London, 13(3),

18 Typical Design of Earthquake Resistant Reinforced Soil-Wall (External Stability) Sliding stability Choudhury et al. (2007) Overturning stability Choudhury, D., Nimbalkar, S.S., and Mandal, J.N. (2007), in Geosynthetics International, ICE London, 14(4),

19 Typical Design of Earthquake Resistant Reinforced Soil-Wall (External Stability) Length of Reinforcement for Sliding stability Choudhury et al. (2007) Length of Reinforcement for Overturning stability Choudhury, D., Nimbalkar, S.S., and Mandal, J.N. (2007), in Geosynthetics International, ICE London, 14(4),

20 Comparison of Results Choudhury et al. (2007) Choudhury, D., Nimbalkar, S.S., and Mandal, J.N. (2007), in Geosynthetics International, ICE London, 14(4),

21 Seismic Design of Waterfront Reinforced Soil-Wall IIT Bombay, DC 21

22 Typical Reinforced Soil-Wall used as Waterfront Retaining Structure during Earthquake (Pseudo-dynamic approach) Ahmad and Choudhury (2008) Ahmad, S. M. and Choudhury, D. (2008), in Geotextiles and Geomembranes, Elsevier, U.K., Vol. 26(4),

23 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),

24 Typical Reinforced Soil-Wall used as Waterfront Retaining Structure during Earthquake (External Stability) Choudhury and Ahmad (2009) Choudhury, D. and Ahmad, S. M. (2009) in Geosynthetics International, ICE London, U.K., Vol. 16, No. 1, pp

25 Typical Result for Length of Reinforcement Choudhury and Ahmad (2009) Choudhury, D. and Ahmad, S. M. (2009) in Geosynthetics International, ICE London, U.K., Vol. 16, No. 1, pp

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, IIT Bombay, DC 26

27 Seismic Design of Shallow Footings IIT Bombay, DC 27

28 Choudhury and Subba Rao (2005) Choudhury, D. and Subba Rao, K. S. (2005), in Geotechnical and Geological Engg., Springer, Vol.23, pp

29 D. Choudhury, IIT Bombay, India Choudhury and Subba Rao (2005)

30 Design charts given by Choudhury and Subba Rao (2005) q ud = cn cd + qn qd BN d D. Choudhury, IIT Bombay, India

31 D. Choudhury, IIT Bombay, India

32 D. Choudhury, IIT Bombay, India Comparison of Results

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.

33 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

34 Design Equations proposed by Choudhury and Subba Rao (2006) Deepankar Choudhury, IIT Bombay

35 Deepankar Choudhury, IIT Bombay Typical Design Chart for N cd

36 Typical Design Charts for N qd and N d Deepankar Choudhury, IIT Bombay

37 Design Charts for Seismic Bearing Capacity Factors N qd 1 k h K cos pqd1 sin α1 - mk pqd2 - sin cos tan α tan α 1 2 α 2-2 q ud = cn cd + qn qd BN d Choudhury, D. and Subba Rao, K. S. (2006) in International Journal of Geomechanics, ASCE, USA, Vol. 6(3),

38 Typical Results to Show Effects of Ground Slope and Embedment Deepankar Choudhury, IIT Bombay

39 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),

40 Seismic Bearing Capacity Factor & Comparison Using Pseudo-dynamic approach = 30 0 Comparison of present result with other methods Effect of Soil Amplification on Bearing Capacity Factor Ghosh and Choudhury (2011) Pseudo-Dynamic Approach Ghosh, P. and Choudhury, D. (2011) in Journal Disaster Advances, Vol. 4(3),

41 Seismic Stability of Finite Soil Slopes IIT Bombay, DC 23

42 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) Deepankar Choudhury, IIT Bombay 24

43 Pseudo-Static method of Seismic Analysis Terzaghi (1950) Deepankar Choudhury, IIT Bombay 25

44 Deepankar Choudhury, IIT Bombay Pseudo-Static method of Seismic Analysis The selection of the seismic coefficient k h takes considerable experience and judgment. Guidelines for the selection of k h are as follows: 1. Peak ground acceleration: The higher the value of the peak ground acceleration a max, the higher the value of k h 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 k h that should be used in the pseudo-static analysis. 3. Maximum value of k h : When items 1 and 2 as outlined above are considered, keep in mind that the value of k h should never be greater than the value of a max /g. 4. Minimum value of k h : 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 k h 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: 26

45 Pseudo-Static method of Seismic Analysis a. Small slide mass: Use a value of k h = a max /g for a small slope failure mass. Examples would include small rockfalls or surficial stability analyses. b. Intermediate slide mass: Use a value of k h = 0.65a max /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 k h for large failure masses, such as large embankments, dams, and landslides. Seed (1979) recommended the following: k h = 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. k h = 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. Deepankar Choudhury, IIT Bombay 27

46 Pseudo-Static method of Seismic Analysis Terzaghi (1950) suggested the following values: k h = 0.10 for severe earthquakes, k h = 0.20 for violent and destructive earthquakes, and k h = 0.50 for catastrophic earthquakes. Seed and Martin (1966) and Dakoulas and Gazetas (1986), using shear beam models, showed that the value of k h for earth dams depends on the size of the failure mass. In particular, the value of k h for a deep failure surface is substantially less than the value of k h for a failure surface that does not extend far below the dam crest. Marcuson (1981) suggested that for dams k h = 0.33a max /g to 0.50 a max /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 k h = 0.50a max /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). Deepankar Choudhury, IIT Bombay 28

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 = s u L For an effective stress analysis: T = c L + N tan where L

47 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 = s u L 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 s u 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 Deepankar Choudhury, IIT Bombay 29

48 Terzaghi s Wedge Method (1950) FS resisting driving force force cl ab W W F F v v cos sin F F h h sin cos tan Deepankar Choudhury, IIT Bombay 30

49 Newmark s Sliding block analysis (1965) in Geotechnique D. Choudhury, IIT Bombay, India 31

50 Newmark s Method (1965) cos FS sin k h ( t)sin tan k h ( t) cso k y = tan( - ) a rel (t) = a b (t) a y = A a y t o t t o + t rel t t v ( t) a ( t) dt o rel A a y t t o d rel ( t) t t o v rel ( t) dt 1 2 A a y t t o 2 Deepankar Choudhury, IIT Bombay 32

Geotechnical Earthquake Engineering

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: dc@civil.iitb.ac.in