Download - Liquefaction final
Liquefaction:
A MAJOR CAUSE OF STRUCTURAL FAILURE DURING EARTHQUAKE
Prakash PaudelGraphic Era University
INTRODUCTION
What is liquefaction?
Relation with earthquakes
DEFINITION:
phenomenon 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
Soil grains Soil at normal water pressure
Liquefied soil
To understand the this phenomenonsome basics required regarding:
Total stress, Pore water pressure Effective stress
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
General Ground Failure Resulting From Soil Liquefaction:
Sand boils
Lateral spreads
Loss of bearing
capacity
Ground settlement
Flow failures of slopes
Ground oscillation
Lateral spread at Budharmora ((Bhuj, 2001)
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
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
Japan earthquake 1964: Niigata- Mag. 7.5Settlement and tilting of structures-liquefaction of soil
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)
Liquefaction MitigationSelection of method for site improvement will depend on:
Location, Area,Depth,Volume of soilSoil types, propertiesSite conditionsAnticipated Earthquake loading Structure type and conditionEconomic and social effects of
structureAvailability of necessary materialsAvailability of equipments and skills
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
stone columns:-Stone columns works like drains
excavation of poor soil:-
Placement of additional fill:-
Densification of soil :-Various methods of
compaction
Smooth Wheeled Roller Sheep foot Roller
Pneumatic Tyred Roller
Grid Roller
Pad Foot / Tamping Rollers
Dynamic compaction
Vibro compaction
Compaction Grouting
Compaction by pile Driving
Anchored pile :-
Liquefaction Resistant Structures
Deep Foundation Aspects