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Liquefaction final


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liquefaction ,problems and solutions

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Liquefaction final

  1. 1. Liquefaction: A MAJOR CAUSE OF STRUCTURAL FAILURE DURING EARTHQUAKE Prakash Paudel Graphic Era University
  2. 2. INTRODUCTION What is liquefaction? Relation with earthquakes
  3. 3. DEFINITION: phenomen on where in a mass of soil loses a large percentage of its shear resistance when subjected to monotonic, cyclic, or shock loading, and flows in a manner resembling a liquid until the shear stresses acting on the mass are as low as the reduced shear resistance
  4. 4. Soil grains Soil at normal water pressure Liquefied soil
  5. 5. To understand the this phenomenon some basics required regarding: Total stress, Pore water pressure Effective stress
  6. 6. Case Total Pressure Pore Pressure Effective Pressure Figure- 1 475 150 325 Figure- 2 475 250 225 Figure-1 Figure-2 Total stress, Pore water pressure and Effective stress
  7. 7. General Ground Failure Resulting From Soil Liquefaction: Sand boils Lateral spreads Loss of bearing capacity Ground settlement Flow failures of slopes Ground oscillation
  8. 8. Lateral spread at Budharmora ((Bhuj, 2001)
  9. 9. Loss of bearing strength Large deformation occur within the soil allowing the structure to settle & tip e.g., 1964 Niigata earthquake, Japan-Most spectacular bearing failure--Kawangishicho apartment complex, several four story building tipped as much as 60 degree
  10. 10. Chile earthquake 1960 : An island near Valdivia- Mag. 9.5 Large settlements and differential settlements of the ground surface-Compaction of loose granular soil by EQ
  11. 11. Japan earthquake 1964: Niigata- Mag. 7.5 Settlement and tilting of structures-liquefaction of soil
  12. 12. Flow failure •Most catastrophic ground failure •Lateral displacement of large masses of soil • Mass comprised of completely liquefied soil or blocks of intact material riding on a layer of liquefied soil •Flow develop in loose saturated sand or silts or relatively steep slope (>3 degree)
  13. 13. Liquefaction Mitigation Selection of method for site improvement will depend on:  Location, Area,Depth,Volume of soil Soil types, properties Site conditions Anticipated Earthquake loading  Structure type and condition Economic and social effects of structure Availability of necessary materials Availability of equipments and skills
  14. 14. Liquefaction Mitigation Techniques: Soil Improvement Methods  Dewatering:- Permanent dewatering systems lower ground water levels below liquefiable soil strata, thus preventing liquefaction . Because lowering of water table increases the effective stress in the soil This alternative also involves an ongoing cost for operating the dewatering systems
  15. 15.  stone columns:- Stone columns works like drains
  16. 16.  excavation of poor soil:-
  17. 17. Placement of additional fill:-
  18. 18. Densification of soil :- Various methods of compaction
  19. 19. Smooth Wheeled Roller Sheep foot Roller Pneumatic Tyred Roller
  20. 20. Grid Roller Pad Foot / Tamping Rollers
  21. 21. Dynamic compaction Vibro compaction
  22. 22. Compaction Grouting Compaction by pile Driving
  23. 23. Anchored pile :-
  24. 24. Liquefaction Resistant Structures
  25. 25. Deep Foundation Aspects