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. Effective stress = (total stress - pore water pressure)
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

10. τ = c + σ’tan φ Shear strength τ of soil is given as :
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
Lateral spreading caused 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
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. Among the 467 foundation damage cases reported, 67 cases (14%
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
σv’ = effective vertical stress
K0= at-rest earth pressure coefficient
K0σv’ = 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
(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

48. 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

49. 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.

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.
(τavg/σv’)= Cr(1/2 x σd/σ3’)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 σv ‘
Where,
σv‘ is effective vertical stress

53. DETERMINATION OF SHEAR STRESSES INDUCED BY CERTAIN EARTHQUAKE IN THE FIELD BY SIMPLIFIED PROCEDURE

55. τ = shear stress induced during an earthquake
Since soil prism is assumed to be a rigid body therefore a correction factor “rD” must be applied as soil is not rigid.
τ = rD (h amax )/g
Where,
τ = 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

57. For an actual earthquake event. Acceleration v/s time relationship
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
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. τcyc=0.65 τmax) from recorded strong ground motion

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

62. τ = shear stress induced during an earthquake
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 = 0.65 rD (h amax )/g
Where,
τ = 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.

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 Vibrating Table for relative density
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

76. Sr. No
Fault
Name
Length (km)
Distance
From
Kamra
(km)
Magnitude
of earthquake
From equation
logL=1.02M – 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. τr (KN / m2 ) Evaluation Of Liquefaction On the basis of SPT
Point
Depth
(m)
Shear stress mobilized in field
τ avg (KN/m2)
Shear Resistance
τr (KN / m2 )
Remarks A
1.50
4.17
3.24
τavg > τr
(Liquefaction will occur) B
1.75
4.89 C
2.00
5.58
4.13
τ = 0.65 rD (h amax )/g
 = CSR x σv ‘

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
(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

82. 0.57

83. 0.255

84. Analysis By Cyclic Triaxial Test
point
Depth
(m)
Shear stress mobilized in field
τ avg (KN/m2)
Shear resistance by
Triaxial
τr (KN / m2 )
Remarks A
1.50
4.17
4.08
τavg > τr
(Liquefaction will occur) B
1.75
4.89
4.46 C
2.00
5.58
5.20
(τavg/σv’)=Cr(1/2 x σd/σ3’)triaxial at RD1 x RD2/RD1
τ = 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. HOW CAN LIQUIFACTION HAZARDS BE REDUCED?
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 mm< 15%
Liquid Limit, LL < 35%
 Natural water content > 0.9 LL
 Liquidity Index < 0.75

91. State Criteria
Relative density, Dr
Increasing confining pressure

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

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. HOW CAN LIQUIFACTION HAZARDS BE REDUCED?
Improve the Soil

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. ?