4. 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
6. To understand the this phenomenon
some basics required regarding:
๏Total stress,
๏Pore water pressure
๏Effective stress
7. 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
8. General Ground Failure Resulting
From Soil Liquefaction:
Sand boils
Lateral
spreads
Loss of
bearing
capacity
Ground
settlement
Flow failures
of slopes
Ground
oscillation
11. Loss of bearing strength
๏ถLarge deformation occur within the soil allowing
the structure to settle & tip
๏ถe.g., 1964 Niigata earthquake, Japan-Most
spectacular bearing failure--Kawangishicho
apartment complex, several four story building
tipped as much as 60 degree
12.
13. 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
14. Japan earthquake 1964: Niigata- Mag. 7.5
Settlement and tilting of structures-liquefaction of soil
15. Flow failure
โขMost catastrophic ground failure
โขLateral displacement of large masses of soil
โข Mass comprised of completely liquefied soil or blocks of intact
material riding on a layer of liquefied soil
โขFlow develop in loose saturated sand or silts or relatively steep
slope (>3 degree)
16.
17.
18. Liquefaction Mitigation
๏ถSelection of method for site improvement will
depend on:
๏ง Location, Area,Depth,Volume of soil
๏งSoil types, properties
๏งSite conditions
๏งAnticipated Earthquake loading
๏ง Structure type and condition
๏งEconomic and social effects of
structure
๏งAvailability of necessary materials
๏งAvailability of equipments and skills
19. Liquefaction Mitigation Techniques:
๏ถSoil Improvement Methods
๏ฑ 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