Transcript IN THE NAME OF ALLAH , THE BENEFICENT ,THE MERCIFUL

SOIL LIQUEFACTION:
PHENOMENON,
HAZARDS ,
REMEDIATION
Dr. Farhat Javed
Associate Prof. Military College of Engg, Risalpur
AIM
• HIGLIGHT THE IMPORTANCE OF
LIQUEFACTION IN ENGINEERING
PRACTICE
SEQUENCE OF PRESENTATION
• Introduction
• Liquefaction phenomenon
• Hazards Associated with Liquefaction
• Evaluation of Liquefaction Potential
• Remediation
• During an earthquake seismic waves travel
vertically and rapid loading of soil occurs
under undrained conditions i.e., pore water
has no time to move out. In saturated soils
the seismic energy causes an increase in
pore water pressures and consequently the
effective stresses decrease. This results in
loss of shear strength of soil and soil starts
to behave as a fluid. This fluid is no longer
able to sustain the load of structure and the
structure settles. This phenomenon is
known as liquefaction.
The Phenomenon is associated with:
• soft
• young
• water-saturated
• uniformly graded
• fine grained sands and silts
During liquefaction these soils behave as viscous fluids
rather than solids .
This can be better demonstrated by a video clip in
which a glass container with saturated sand is resting on
a vibrating table.
STRUCTURE
GLASS
CONTAINER
SATURATED
SAND
• The phenomenon of liquefaction can
be well understood by considering
shear strength of soils. Soils fail under
externally applied shear forces and the
shear strength of soil is governed by
the effective or inter-granular stresses
expressed as:
Effective stress = (total stress - pore
water pressure)
σ’ = σ - u
Shear strength τ of soil is given as :
τ=
c + σ’tan φ
It can be seen that a cohesionless
soil such as sand will not posses
any shear strength when the
effective stresses approach zero and
it will transform into a liquid state.
Assemblage of
particles
Contact forces between particles
give rise to normal stresses that are
responsible for shear strength.
This box
represents
magnitude of
pore water
pressure
During dynamic loading there is an increase in water
pressure which reduces the contact forces between the
individual soil particles, thereby softening and weakening
the soil deposit.
Increase in pore
pressure due to
dynamic loading
HAZARDS ASSOCIATED
WITH LIQUEFACTION
PHENOMENON
Historical Evidences
• 1964 Nigata (Japan)
• 1964 Great Alaskan earthquake
• Seismically induced soil liquefaction
produced spectacular and devastating
effect in both of these events, thrusting
the issue forcefully to the attention of
engineers and researchers
When liquefaction occurs, the strength of the soil
decreases and, the ability of a soil deposit to suppo
foundations for buildings and bridges is reduced ….
overturned apartment complex buildings in Niigata
in 1964.

Liquefied soil also exerts higher pressure on retaining walls,which can
cause them to tilt or slide. This movement can cause settlement of the
retained soil and destruction of structures on the ground surface
Kobe
1995

Retaining wall damage and lateral spreading, Kobe 1995

Increased water pressure can also trigger landslides and cause the
collapse of dams. Lower San Fernando dam suffered an underwater slide
during the San Fernando earthquake, 1971.

Sand boils and ground fissures were observed at various sites in Niigata.

Lateral spreading caused the foundations of the Showa bridge in Nigata
,Japan to move laterally so much that the simply supported spans
became unseated and collapsed

Liquefaction-induced soil movements can push foundations out of place
to the point where bridge spans loose support or are compressed to the
point of buckling
•1964 Alaskan earthquake.
The strong ground motions that led to collapse of the Hanshin Express way also caused
severe liquefaction damage to port and wharf facilities as can be seen below.
1995 Kobe
earthquake, Japan
Lateral spreading caused 1.2-2 meter drop of paved surface and local flooding, Kobe
1995.
Alaska earthquake,
USA,1964
1957 Lake Merced slide
modest movements during liquefaction produce tension
cracks such as those on the banks of the Motagua River
following the 1976 Guatemala Earthquake.
Damaged quay walls and port facilities on Rokko Island.
Quay walls have been pushed outward by 2 to 3 meters with 3
to 4 meters deep depressed areas called grabens forming
behind the walls, Kobe 1995.
1999 Chi-Chi (Taiwan) earthquake
over 2,400 people were killed, and 11,000 were injured
1999 Chi-Chi (Taiwan) earthquake
1999 Chi-Chi (Taiwan) earthquake
1999 Chi-Chi (Taiwan) earthquake
1999 Chi-Chi (Taiwan) earthquake
1999 Chi-Chi (Taiwan) earthquake
1906 sanfransisco USA earthquake
Road damaged by lateral spread,
near Pajaro River, 1989 Loma Prieta earthquake
Liquefaction failure of shefield dam (1925, california USA)
Liquefaction failure of Tanks at Nigata, Japan)
.
Chi-Chi earthquake
Among the 467 foundation damage cases reported, 67 cases (14%
were caused by earthquake-induced liquefaction.
• Evaluation of
Liquefaction Potential
• The evaluation of liquefaction
potential of soils at any site requires
parameters pertaining to:
• cyclic loads due to an earthquake
• and
• soil properties which describe the soil
resistance under those loads.
Normal Field Conditions
Where
σv’ = effective vertical
stress
K0= at-rest earth
pressure coefficient
K0σv’ = effective
horizontal stress
During
Earthquake
• Two tests can be used to simulate
field stress conditions
•
•
•
Cyclic direct shear test
Cyclic triaxial test
Cyclic Direct Shear Test
Cyclic Triaxial Test
Relation between
cyclic direct shear and cyclic triaxial
test
(τh/σv) direct shear = Cr (1/2 x σd/σ3’ )triaxial
where; τh = horizontal shear stress
(τh/σv) = cyclic stress ratio CSR
σv = vertical stress
σd = deviator stress
σ3’ = effective confining pressure
Cr = Correction faactor obtained from
figure given on next slide
• If relative density in lab is different from field
then the equation is modified as follows:
(τavg/σv’)= Cr(1/2 x σd/σ3’)triaxial at RD1 x RD2/RD1
• Where RD1 is relative density in lab and RD2
is relative density in field
Generally cyclic triaxial test is conducted at various cyclic stress
ratios CSR = (1/2 x σd/σ3’) on undisturbed or remolded specimen
till liquefaction occurs, and corresponding number of stress cycles
is determined. A graph is plotted between CSR and number of
stress cycles.
This graph can be used to read out CSR
corresponding to any number of stress cycles and
this value is used in following relationship to
determine shear resistance that will be mobilized
at any depth.
(τavg/σv’)= Cr(1/2 x σd/σ3’)triaxial at RD1 x RD2/RD1
If cyclic tiaxial testing can not be conducted then this
Graph can be used to determine CSR from Mean grain
Size D 50
Results of Standard Penetration
Test can also be used to determine
CSR from this curve.
Subsequently shear resistance of
soil against cyclic loading can be
determined by:
 = CSR x σv ‘
Where,
σv‘ is effective vertical stress
DETERMINATION OF
SHEAR STRESSES
INDUCED BY CERTAIN
EARTHQUAKE IN THE
FIELD BY SIMPLIFIED
PROCEDURE
Since soil prism is assumed to be a rigid body therefore
a correction factor “rD” must be applied as soil is not
rigid.
τ
Where,
= rD (h amax )/g
τ
=
amax
g
h
=
=
=
=

rD
shear stress induced during an earthquake
unit weight of soil.
maximum acceleration due to earthquake
acceleration due to gravity
height of soil prism
= stress reduction factor , a function of depth
of point being analyzed. It can be obtained from next
slide
For an actual earthquake event
Acceleration v/s time relationship
(accelerogram) looks like
During an earthquake the
induced cyclic shear stresses
vary with time. On the contrary
in the laboratory shear test the
specimen is subjected to a
uniform cyclic shear stress.
To incorporate this effect a
multiplication factor of 0.65 has
been suggested.
• Seed et al have recommended a
weighted procedure to derive
the number of uniform stress
cycles Neq (at an amplitude of
65% of the peak cyclic shear
stresses i.e. τcyc=0.65 τmax) from
recorded strong ground motion
This Table can be used to determine
equivalent number of stress cycles for an
earthquake of certain magnitude.
The effect of non uniform stress cycles is incorporated
by determining equivalent number of stress cycles for
an earthquake and shear stresses induced during an
earthquake are computed by the following equation:
τ
Where,
= 0.65 rD (h amax )/g
τ
=
amax
g
h
=
=
=
=

rD
shear stress induced during an earthquake
unit weight of soil.
maximum acceleration due to earthquake
acceleration due to gravity
height of soil prism
= stress reduction factor , a function of depth
of point being analyzed. It can be obtained from next
slide
Maps like these
Can be used to
Determine max
Ground
acceleration
• After determining the cyclic shear
stresses induced by an earthquake
and
the shear resistance mobilized at the
point under consideration, a graph
is plotted between depth and the
stresses determined above.
•If
induced cyclic shear
stresses are more than
shear resistance
mobilized, liquefaction
will occur.
•RESEARCH ON
KAMRA SAND
Soil Stratification developed after SPT and Boring
Compacted Earth Fill
SAND LAYER
0.5 m
SILT LAYER
Sampling being done in Test Pit
RELATIVE DENSITY DETERMINATION AT
CMTL WAPDA LAHORE
Vibrating Table for relative density
Mould for relative density
Lab Relative Density =53 %
Relative Density From SPT
correlations =52.8 %
EVALUATION OF LIQUEFACTION
SEISMICITY OF KAMRA CITY
PHA at
Kamra =
0.24 g
Sr. No
Fault
Name
1
Khairabad
Fault
Distance
From
Length Kamra
(km)
(km)
Magnitude
of earthquake
From equation
logL=1.02M – 5.77
370
8.2
3
It is concluded that an
earthquake of Magnitude 7 can
occur at Kamra with peak
horizontal acceleration of 0.24 g
Evaluation of Liquefaction potential
•Standard Penetration Test (SPT)
•Cyclic Triaxial Test.
Hypothesis If water table rises and sand gets saturated then
liquefaction will occur under magnitude 7 earthquake
Evaluation Of Liquefaction On the basis
of SPT
Point
Depth
(m)
Shear stress
mobilized in
field
τ avg
(KN/m2)
τ = 0.65 rD (h amax
)/g
A
1.50
4.17
Shear
Resistance
τr (KN / m )
2
Remarks
 = CSR x σv ‘
3.24
τavg > τr
(Liquefaction will occur)
B
1.75
4.89
3.24
τavg > τr
C
2.00
5.58
4.13
τavg > τr
(Liquefaction will occur)
(Liquefaction will occur)
ANALYSIS ON THE BASIS OF
CYCLIC TRIAXIAL TEST.
Analysis on the basis of triaxial was based on the method
proposed by SEED AND IDRIS
Shear resistance was computed from the following formula
(τ(τavg/σv’)= Cr(1/2 x σd/σ3’)triaxial at RD1 x RD2/RD1
Cr(1/2 x σd / σ3’ )triaxial x RD2/RD1
τh = Cr(1/2 x σd / σ3’ ) x σv’ x RD2/RD1
0.57
0.255
Analysis By Cyclic Triaxial Test
point
Shear
stress
mobilized
Depth in field
(m) τ avg
(KN/m2)
τ = 0.65 rD (h amax
)/g
A
1.50
4.17
Shear
resistance
by
Triaxial
τr (KN / m2 ) Remarks
(τavg/σv’)=Cr(1/2 x σd/σ3’)triaxial at RD1 x RD2/RD1
4.08
τavg > τr
(Liquefaction will
occur)
B
1.75
4.89
4.46
τavg > τr
(Liquefaction will
occur)
C
2.00
5.58
5.20
τavg > τr
(Liquefaction will
It
is concluded on the basis of
these results that the sand
will liquefy under the event of
an earthquake of Magnitude
7.
REMEDIATION
HOW CAN LIQUIFACTION HAZARDS BE
REDUCED?
Avoid Liquefaction Susceptible
Soils
 Build Liquefaction Resistant
Structures
 Improve the Soil

Avoid Liquefaction Susceptible
Soils

historical Criteria


Soils that have liquefied in the past can liquefy
again in future earthquakes.
Geological Criteria
Saturated soil deposits that have been
created by sedimentation in rivers and lakes
deposition of debris or eroded material or
deposits formed by wind action can be very
liquefaction susceptible.

Man-made soil deposits, particularly those
created by the process of hydraulic filling

Compositional Criteria
D10 sizes ranging from 0.05 to 1.0 mm
AND
a coefficient of uniformity ranging from 2 to 10.
 Uniformly graded soil deposits
 Angularity of particles

Silty soils are susceptible to liquefaction if they
satisfy the criteria given below.




Fraction finer than 0.005 mm< 15%
Liquid Limit, LL < 35%
Natural water content > 0.9 LL
Liquidity Index < 0.75
State Criteria


Relative density, Dr
Increasing confining pressure
HOW CAN LIQUIFACTION HAZARDS BE
REDUCED?
Build Liquefaction
Resistant Structures
Build Liquefaction Resistant Structures

It is important that all
foundation elements
in a shallow
foundation are tied
together to make the
foundation move or
settle uniformly, thus
decreasing the
amount of shear
forces induced in the
structural elements
resting upon the
foundation.
Build Liquefaction Resistant Structures

A stiff foundation
mat is a good type
of shallow
foundation, which
can transfer loads
from locally liquefied
zones to adjacent
stronger ground.
Build Liquefaction Resistant Structures

Buried utilities, such as
sewage and water pipes,
should have ductile
connections to the
structure to
accommodate the large
movements and
settlements that can
occur due to liquefaction.
The pipes in the photo
connected the two
buildings in a straight
line before the
earthquake
Build Liquefaction Resistant Structures
HOW CAN LIQUIFACTION HAZARDS BE
REDUCED?
Improve the Soil
Vibroflotation
Vibroflotation
Improve the Soil

Dynamic Compaction
Stone Columns
Generally, the stone column ground improvement method is
used to treat soils where fines content exceeds that
acceptable for vibrocompaction

Compaction Piles
Compaction Grouting


Compaction grouting is a ground
treatment technique that involves
injection of a thick-consistency soilcement grout under pressure into the soil
mass, consolidating, and thereby
densifying surrounding soils inplace. The injected grout mass occupies
void space created by pressuredensification. Pump pressure, as
transmitted through low-mobility grout,
produces compaction by displacing soil
at depth until resisted by the weight of
overlying soils.
Improve the Soil


Drainage techniques
Improve the Soil


Drainage techniques
Improve the Soil
Verification of
Improvement

A number of methods can be used to verify
the effectiveness of soil improvement. In-situ
techniques are popular because of the
limitations of many laboratory techniques.
Usually, in-situ test are performed to evaluate
the liquefaction potential of a soil deposit
before the improvement was attempted. With
the knowledge of the existing ground
characteristics, one can then specify a
necessary level of improvement in terms of
insitu test parameters.