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IN THE NAME OF ALLAH , THE BENEFICENT ,THE MERCIFUL

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SOIL LIQUEFACTION: PHENOMENON, HAZARDS , REMEDIATION Dr. Farhat Javed Associate Prof. Military College of Engg, Risalpur AIM HIGLIGHT THE IMPORTANCE OF LIQUEFACTION ... – PowerPoint PPT presentation

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Title: IN THE NAME OF ALLAH , THE BENEFICENT ,THE MERCIFUL


1
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2
  • SOIL LIQUEFACTION PHENOMENON, HAZARDS ,
    REMEDIATION
  • Dr. Farhat Javed
  • Associate Prof. Military College of Engg,
    Risalpur

3
AIM
  • HIGLIGHT THE IMPORTANCE OF LIQUEFACTION IN
    ENGINEERING PRACTICE

4
SEQUENCE OF PRESENTATION
  • Introduction
  • Liquefaction phenomenon
  • Hazards Associated with Liquefaction
  • Evaluation of Liquefaction Potential
  • Remediation

5
  • 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.

6
  • 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.

7
STRUCTURE
GLASS CONTAINER
SATURATED SAND
8
LIQUEFACTION PHENOMENON
9
  • 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)
  • s s - u

10
  • Shear strength t of soil is given as
  • t c stan f
  • 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.

11
Contact forces between particles give rise to
normal stresses that are responsible for shear
strength.
Assemblage of particles
This box represents magnitude of pore water
pressure
12
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
13
  • HAZARDS ASSOCIATED WITH LIQUEFACTION PHENOMENON

14
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

15
When liquefaction occurs, the strength of the
soil decreases and, the ability of a soil deposit
to support foundations for buildings and bridges
is reduced . overturned apartment complex
buildings in Niigata in 1964.
16
  • 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
17
  • Retaining wall damage and lateral spreading, Kobe
    1995

18
  •  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.

19
  • Sand boils and ground fissures were observed at
    various sites in Niigata.

20
  • 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

21
  • 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.

22
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
23
Lateral spreading caused 1.2-2 meter drop of
paved surface and local flooding, Kobe 1995.
24
Alaska earthquake, USA,1964
25
1957 Lake Merced slide
26
modest movements during liquefaction produce
tension cracks such as those on the banks of the
Motagua River following the 1976 Guatemala
Earthquake.
27
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.
28
1999 Chi-Chi (Taiwan) earthquake over 2,400
people were killed, and 11,000 were injured
29
1999 Chi-Chi (Taiwan) earthquake
30
1999 Chi-Chi (Taiwan) earthquake
31
1999 Chi-Chi (Taiwan) earthquake
32
1999 Chi-Chi (Taiwan) earthquake
33
1999 Chi-Chi (Taiwan) earthquake
34
1906 sanfransisco USA earthquake
35
Road damaged by lateral spread, near Pajaro
River, 1989 Loma Prieta earthquake
36
Liquefaction failure of shefield dam (1925,
california USA)
37
Liquefaction failure of Tanks at Nigata, Japan)
38
Chi-Chi earthquake.   Among the 467 foundation
damage cases reported, 67 cases (14 were caused
by earthquake-induced liquefaction. 
                                                
                                                  
                             Figure 1. Foundation
damage survey after the 1999 Chi-Chi earthquake
(NCREE, 2000
39
  • Evaluation of Liquefaction Potential

40
  • 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.

41
Normal Field Conditions
  • Where
  • sv effective vertical stress
  • K0 at-rest earth pressure coefficient
  • K0sv effective horizontal stress

42
During Earthquake

43
  • Two tests can be used to simulate field stress
    conditions
  • Cyclic direct shear test
  • Cyclic triaxial test

44
Cyclic Direct Shear Test
45
Cyclic Triaxial Test
46
Relation between cyclic direct shear and cyclic
triaxial test
  • (th/sv) direct shear Cr (1/2 x sd/s3
    )triaxial
  • where th horizontal shear stress (th/sv)
    cyclic stress ratio CSR
  • sv vertical stress sd deviator
    stress s3 effective confining pressure
  • Cr Correction faactor obtained from figure
    given on next slide

47
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48
  • If relative density in lab is different from
    field then the equation is modified as follows
  • (tavg/sv) Cr(1/2 x sd/s3)triaxial at RD1 x
    RD2/RD1
  • Where RD1 is relative density in lab and RD2 is
    relative density in field

49
  • Generally cyclic triaxial test is conducted at
    various cyclic stress ratios CSR (1/2 x sd/s3)
    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.

50
  • 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.
  • (tavg/sv) Cr(1/2 x sd/s3)triaxial at RD1 x
    RD2/RD1

51
If cyclic tiaxial testing can not be conducted
then this Graph can be used to determine CSR
from Mean grain Size D 50
52
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 sv   Where,   sv is effective vertical
stress
53
  • DETERMINATION OF SHEAR STRESSES INDUCED BY
    CERTAIN EARTHQUAKE IN THE FIELD BY SIMPLIFIED
    PROCEDURE

54
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55
  • Since soil prism is assumed to be a rigid
    body therefore a correction factor rD must be
    applied as soil is not rigid.
  • t rD (?h amax )/g
  • Where,
  • t shear stress induced during an earthquake
  • ? unit weight of soil.
  • amax maximum acceleration due to earthquake
  • g acceleration due to gravity
  • h height of soil prism
  • rD stress reduction factor
    , a function of depth of point being analyzed.
    It can be obtained from next slide

56
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57
  • For an actual earthquake event
    Acceleration v/s time relationship
    (accelerogram) looks like

58
  • 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.

59
  • 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. tcyc0.65 tmax) from recorded
    strong ground motion

60
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61
  • This Table can be used to determine
    equivalent number of stress cycles for an
    earthquake of certain magnitude.

62
  • 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
  • t 0.65 rD (?h amax )/g
  • Where,
  • t shear stress induced during an earthquake
  • ? unit weight of soil.
  • amax maximum acceleration due to earthquake
  • g acceleration due to gravity
  • h height of soil prism
  • rD stress reduction factor
    , a function of depth of point being analyzed.
    It can be obtained from next slide

63
Maps like these Can be used to Determine
max Ground acceleration
64
  • 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.

65
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66
  • If induced cyclic shear stresses are more than
    shear resistance mobilized, liquefaction will
    occur.

67
  • RESEARCH ON KAMRA SAND

68
Soil Stratification developed after SPT and Boring
69
Compacted Earth Fill
SAND LAYER
0.5 m
SILT LAYER
70
Sampling being done in Test Pit
71
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
72
  • EVALUATION OF LIQUEFACTION

73
SEISMICITY OF KAMRA CITY
74
PHA at Kamra 0.24 g
75
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76
Sr. No Fault Name Length (km) Distance From Kamra (km) Magnitude of earthquake From equation logL1.02M 5.77
1 Khairabad Fault 370 3 8.2


77
It is concluded that an earthquake of Magnitude 7
can occur at Kamra with peak horizontal
acceleration of 0.24 g
78
Evaluation of Liquefaction potential
  • Standard Penetration Test (SPT)
  • Cyclic Triaxial Test.

79
Hypothesis If water table rises and sand gets
saturated then liquefaction will occur under
magnitude 7 earthquake
80
Evaluation Of Liquefaction On the basis of SPT
Point Depth (m) Shear stress mobilized in field t avg (KN/m2) Shear Resistance tr (KN / m2 ) Remarks
A 1.50 4.17 3.24 tavg gt tr (Liquefaction will occur)
B 1.75 4.89 3.24 tavg gt tr (Liquefaction will occur)
C 2.00 5.58 4.13 tavg gt tr (Liquefaction will occur)
t 0.65 rD (?h amax )/g
? CSR x sv
81
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
(t(tavg/sv) Cr(1/2 x sd/s3)triaxial at RD1 x
RD2/RD1 Cr(1/2 x sd / s3 )triaxial x RD2/RD1

th Cr(1/2 x sd / s3 ) x
sv x RD2/RD1
82
0.57
83
0.255
84
Analysis By Cyclic Triaxial Test
point Depth (m) Shear stress mobilized in field t avg (KN/m2) Shear resistance by Triaxial tr (KN / m2 ) Remarks
A 1.50 4.17 4.08 tavg gt tr (Liquefaction will occur)
B 1.75 4.89 4.46 tavg gt tr (Liquefaction will occur)
C 2.00 5.58 5.20 tavg gt tr (Liquefaction will occur)
(tavg/sv)Cr(1/2 x sd/s3)triaxial at RD1 x
RD2/RD1
t 0.65 rD (?h amax )/g
85
  • It is concluded on the basis of these results
    that the sand will liquefy under the event of an
    earthquake of Magnitude 7.

86
  • REMEDIATION
  • HOW CAN LIQUIFACTION HAZARDS BE REDUCED?

87
  • Avoid Liquefaction Susceptible Soils
  • Build Liquefaction Resistant Structures
  • Improve the Soil

88
  • Avoid Liquefaction Susceptible Soils

89
  • 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

90
  • 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 mmlt 15
  • Liquid Limit, LL lt 35
  •  Natural water content gt 0.9 LL
  •  Liquidity Index lt 0.75

91
  • State Criteria
  • Relative density, Dr
  • Increasing confining pressure

92
Build Liquefaction Resistant Structures
HOW CAN LIQUIFACTION HAZARDS BE REDUCED?
93
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.

94
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.


95
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


96
Build Liquefaction Resistant Structures

97
Improve the Soil
HOW CAN LIQUIFACTION HAZARDS BE REDUCED?
98
Vibroflotation
99
Vibroflotation
100
Improve the Soil
  • Dynamic Compaction

101
Stone Columns
  • Generally, the stone column ground improvement
    method is used to treat soils where fines content
    exceeds that acceptable for vibrocompaction

102
Compaction Piles
103
Compaction Grouting
  • Compaction grouting is a ground treatment
    technique that involves injection of a
    thick-consistency soil-cement grout under
    pressure into the soil mass, consolidating, and
    thereby densifying surrounding soils in-place. 
    The injected grout mass occupies void space
    created by pressure-densification.  Pump
    pressure, as transmitted through low-mobility
    grout, produces compaction by displacing soil at
    depth until resisted by the weight of overlying
    soils.

104
Improve the Soil
  • Drainage techniques

105
Improve the Soil
  • Drainage techniques

106
Improve the Soil
107
Verification of Improvement 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.

108
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109
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