1 / 91

An Overview of Seismic Design of Earth Dams and Embankments Sudhir K Jain October 2013

An Overview of Seismic Design of Earth Dams and Embankments Sudhir K Jain October 2013. Outline. Performance of Earth Dams in 2001 Bhuj earthquake Introduction to Seismic Design Principle Dynamic Soil Properties Site Effects Liquefaction Embankment Analysis.

deepak
Download Presentation

An Overview of Seismic Design of Earth Dams and Embankments Sudhir K Jain October 2013

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. An Overview of Seismic Design of Earth Dams and Embankments Sudhir K Jain October 2013 Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  2. Outline • Performance of Earth Dams in 2001 Bhuj earthquake • Introduction to Seismic Design Principle • Dynamic Soil Properties • Site Effects • Liquefaction • Embankment Analysis Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  3. Performance of Earth Dams in 2001 Bhuj earthquake Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  4. 2001 Bhuj Earthquake • Magnitude 7.7 • Maximum MSK Intensity X • Bhuj in Seismic Zone V of Indian seismic map • 8.46 am on 26 January 2001 • More than 13,805 dead; 1,67,000 injured • 300,000 houses destroyed; 700,000 houses damaged • Numerous multistorey RC buildings collapsed • 130 such buildings collapsed in Ahmedabad ~225km from epicenter Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  5. 2001 BhujEarthquake (contd…) • 2 year drought; reservoirs at very low levels • 16 (out of 20) medium dams damaged • 5 severely • 80 (out of 165) minor dams damaged • 14 severely • Damage consisted of • Liquefaction beneath engineered fill • Slope displacements • Longitudinal cracking at crests, cracking and movements on upstream faces • Damage to outlet towers, spillways, parapet walls, … Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  6. Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  7. Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  8. Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  9. Tappar Dam Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  10. Tappar Dam Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  11. Tappar Dam Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  12. Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  13. Fatehgadh Dam Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  14. Fatehgadh Dam Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  15. Fatehgadh Dam Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  16. Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  17. Kaswati Dam Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  18. Kaswati Dam Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  19. Kaswati Dam Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  20. Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  21. Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  22. Rudramata Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  23. Rudramata Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  24. Intake tower Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  25. Spillway Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  26. Piers Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  27. Some Remarks on Seismic Design Principles Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  28. Seismic Design Principle • Large earthquakes are infrequent as compared to smaller earthquakes • Should a structure meant for 50 years be designed to remain undamaged for an earthquake that may occur once in 500 years? • The criteria is: • Minor (and frequent) earthquakes should not cause damage • Moderate earthquakes should not cause significant structural damage (but could have some non-structural damage) • Major (and infrequent) earthquakes should not cause collapse Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  29. Seismic Design Principle … • A well designed structure can withstand a horizontal force several times the design force due to: • Energy dissipation in a variety of ways, e.g., ductility • Overstrength • Redundancy • In many cases, limited deformation may be acceptable, e.g., slopes, retaining walls. Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  30. Site Specific Design Criteria • Seismic design codes meant for ordinary projects • For important projects, such as nuclear power plants, dams and major bridges site-specific seismic design criteria are developed • These take into account geology, seismicity, geotechnical conditions and nature of project • Site specific criteria are developed by experts and usually reviewed by independent peers • A good reference to read on this: • Housnerand Jennings, “Seismic Design Criteria”, Earthquake Engineering Research Institute, USA, 1982. Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  31. Shaking is not the only issue! • Ground shaking can affect the safety of structure in a number of ways: • Shaking induces inertia force • Soil may liquefy • Sliding failure of founding strata may take place • Fire or flood may be caused as secondary effect of the earthquake. • Fault rupture may pass through the structure Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  32. Direction of Ground Motion • During earthquake shaking, ground shakes in all possible directions. • Direction of resultant shaking changes from instant to instant. • Structure must withstand maximum ground motion occurring in any direction. • Peak ground acceleration may not occur at the same instant in two perpendicular directions. • Hence for design, maximum seismic force is not applied in the two horizontal directions simultaneously. Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  33. Direction of Ground Motion … • On average, peak vertical acceleration is one-half to two-thirds of the peak horizontal acceleration. • Structures experience vertical acceleration equal to gravity (g) at all times. • Vertical acceleration is a concern for: • Stability issues (e.g., slopes) • Large span structures • Cantilever members • Prestressed horizontal members Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  34. Dynamic Soil Properties Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  35. Dynamic Soil Properties • Behaviour of soil complex under static loads. Even more complex under dynamic loads • Need for simple methods to characterize complex behaviour • Analysis techniques: • Equivalent linear models • Cyclic non-linear models • Advanced constitutive models Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  36. Shear Modulus • Soil stiffness depends on strain amplitude, void ratio, mean principal effective stress, plasticity index, over consolidation ratio, and number of loading cycles • Shear Modulus • Tangent modulus • Secant modulus • Shear modulus varies with strain level. It is high at low strains Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  37. Shear Modulus … Figure: Hysteretic stress-strain response of soil subjected to cyclic loading Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  38. Dynamic Properties • Shear modulus decreases with strain increase • Damping increases with strain increase Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  39. Maximum Shear Modulus (Gmax) • Can be obtained in a number of ways: shear wave velocity, laboratory tests, and empirical relationships • Shear wave velocity obtained from geophysical tests at strains lower than about 3x10-4% Gmax= ρvs2 Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  40. Soil Properties Exploration data converted to shear modulus: Gmax = 65N [Seed, and Idris 1983] Gmax = 1000[35(N60)0.34] (σ’)0.4 [Seed,Wong,andIdris, 1986] Gmax= 1000[20(N1,60)0.33] (σ’)0.5 [Seed,Wong,andIdris, 1986] Gmax= 325(N60)0.68 [Imai, and Tonouchi, 1982] Gmax= K (N60)0.66 [PWRI, 1998] Where, N60 = SPT value, uncorrected for over-burden pressure N1,60 = SPT value, corrected for over-burden pressure σ’ = Effective soil pressure Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  41. Soil Properties … Eqn (1) Eqn (5) Eqn (2) Eqn (4) Eqn (3) • Small strain Shear Modulus (Gmax) • Tends to vary significantly, depending on which relationship is used Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  42. Ground Motion Along Depth • Peak amplitude of underground motion is smaller than that at the surface • Variation of amplitude depends on • Earthquake characteristics • Frequency content • Type of soil and its distribution along depth Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  43. Ground Motions Along Depth … Vertical distribution PGV Vertical distribution PGA Vertical distribution PGD Figure: Distribution of peak amplitude of ground motion along depth, (Kanade, 2000) Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  44. Ground Motions Along Depth … Artificially generated time history [SIMQKE -1] Known Spectrum Back calculated time history [SHAKE 2000] Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  45. Ground Motions Along Depth … Response time history [SHAKE 2000] Response time history [SHAKE 2000] Response time history [SHAKE 2000] Assumed earthquake Corresponding response spectrum [SMSIM] Artificially generated time history [SIMQKE-1] Figure: Schematic representation of procedure used for artificially generated time histories for earthquake motion Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  46. Underground Structures • When seismic waves hit the ground surface, these are reflected back into ground • The reflection mechanics is such that the amplitude of vibration at the free surface is much higher (almost double) than that under the ground • Codes allow the design spectrum to be one-half if the structure is at depth of 30m or below. • Linear interpolation for structures and foundations if depth is less than 30m. Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  47. Site Effects Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  48. Site Effects • Motion at the base rock different from that at the top of soil. • Local amplification of the earthquake motion due to the soil profile at the site. • Site Effect. Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  49. Mexico Earthquake of 1985 • Earthquake occurred 400 km from Mexico City • Great variation in damages in Mexico City • Some parts had very strong shaking • In some parts of city, motion was hardly felt • Ground motion records from two sites: • UNAM site: Foothill Zone with 3-5m of basaltic rock underlain by softer strata • SCT site: soft soils of the Lake Zone Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

  50. Mexico Earthquake of 1985 … Time (sec) • PGA at SCT site about 5 times higher than that at UNAM site • Epicentral distance is same at both locations Figure from Kramer, 1996 Short course on Seismic Design of Earth and Rock-fill Dams / October 15-18, 2013

More Related