IN THE NAME OF ALLAH , THE BENEFICENT ,THE MERCIFUL

1
(No Transcript)
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
(No Transcript)
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
(No Transcript)
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
(No Transcript)
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
(No Transcript)
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
(No Transcript)
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
(No Transcript)
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
?
109
?