This document summarizes a student project on liquefaction of soil. It includes an introduction defining liquefaction and factors that affect it. Methods for determining liquefaction are described, including the IS Code method and Idriss and Boulanger method. Borehole data from a site in Patna is presented, showing soil strata with depth. Calculations of cyclic stress ratio and factor of safety against liquefaction are shown for the site using SPT data from boreholes. Factors of safety are presented in tables for different depths, magnitudes, and methods.

1. LIQUEFACTION OF SOIL
Submitted by
Ayush Kumar (1603012)
Under the guidance of
Dr. Shiva Shankar Choudhary
(Assistant Professor)
DEPARTMENT OF CIVIL ENGINEERING
NATIONAL INSTITUTE OF TECHNOLOGY PATNA
JUNE 2020
Presentation submitted in fulfilment of requirement
Bachelor of Technology

2. CONTENT
1. Introduction
2. Factors Affecting Liquefaction
3. Effects of Liquefaction
4. Types of Failures
5. Methods to Determine Liquefaction
6. Cross Section of Soil Strata at IGIMS Patna Site
7. Calculations and Observation Tables
8. Graph Between SPT N Value vs Depth
9. Graphical Comparison of FOS Values
10. Conclusion
11. References

3. 1. Introduction
What is Soil Liquefaction:
Fig 1.liquefaction in Nishishiro,Japan Fig 2. Source: IOPScience
• Liquefaction is the phenomena when there is loss of
strength in saturated and cohesion-less soils because of
increased pore water pressures and hence reduced effective
stresses due to dynamic loading. It is a phenomenon in
which the strength and stiffness of a soil is reduced by
earthquake shaking or other rapid loading.

4. • It is the process that leads to soil suddenly losing strength,
most commonly as a result of ground shaking during a large
Earthquake (Fig2).
• Technical definitions : Soil liquefaction occurs when
the effective stress (shear strength) of soil is reduced to
essentially zero. This may be initiated by either
monotonic loading or cyclic loading . In both cases a soil in a
saturated loose state, and one which may generate significant
pore water pressure on a change in load are the most likely to
liquefy. As pore water pressure rises, a progressive loss of
strength of the soil occurs as effective stress is reduced.
Liquefaction is more likely to occur in sandy or non-plastic
silty soils, but may in rare cases occur in gravels and clays.

5. • Shear Strength, τ = c + σn tanφ
• Effective stress gives more realistic behaviour of soil, shera
strength can be expressed as : τ = c’ + (σn - u) tanφ’
• During the ground motion, due to an earthquake, static pore
water pressure may be increased by an amount udyn, then
τ = c’ + (σn - u + udyn) tanφ’. Let us consider a situation when
{u + udyn = σn } , then [τ = c’].
In cohesionless soil , c’ = 0, hence [ τ = 0 ].
Hence , soil losses its strength due to loss of effective stress.

6. Fig 3.

7. 2. Factors Affecting Liquefaction
1. Soil Type
2. Grain size and its distribution
3. Initial relative density
4. Vibration characteristics
5. Location of drainage and dimension of deposit
6. Surcharge load
7. Method of soil formation
8. Period under sustained load
9. Previous strain history
10. Trapped Air

8. 3. Effects of Liquefaction
1. Loss of Bearing strength: The ground can liquefy and lose its
ability to support the structure.
2. Lateral Spreading : The ground can slide down very gentle
slopes. It is mainly cause by cyclic mobility. It damage the
foundations of buildings, pipelines, railway lines.
Lateral Spreading at Kutch (Bhuj) in 2001 Earthquake.
Fig 4.

9. 3. Flow Failures : Flow Failures are the most catastrophic ground
failures caused by liquefaction. These failures commonly
displaces large masses of soil laterally. It developes in loose
saturated sands or silts on relatively steep slopes.
4. Flotation : Light structures that are burried in the ground ( like
pipelines sewers , nearly empty fuel tanks ) can float to the
surface when they are surrounded by liquefied soil.Fig 3.
Fig 5. Fig 6. Lifted up Manhole

10. 4. Types of Failures in Liquefaction
1. Overturning : It is a phenomenon in which the static
equilibrium is destroyed by static or dynamic loads in a soil
deposit with low residual strength. It occurs when the static
shear stresses in the soil exceed the shear strength of the
liquefied soil.
• It causes Overturnig of large
lateral loads on foumdation.
Foundation must also be able to
resist horizontal loads , bending
moment induced.
Fig 7. 1964 Nigata, Japan

11. 2. Cyclic Mobility : It is a liquefaction phenomenon, triggered by
cyclic loading, occuring in soil deposits with static shear
stresses lower than the soil strength.
• Deformation due to cyclic mobility develop incrementally
because of static and dynamic stresses that exist during
earthquake.
• Lateral spreading, a common result
of cyclic mobility, can occur on gently
sloping and on flat ground close to
rivers and lakes.
Fig 8. Source: Wikipedia

12. 3. Sand Boiling : A sand boil is sand and water that come out
over the ground surface during an earthquake as a result of
liquefaction at shallow depth.
• The damage of Port structure ( at Kushiro Port )
Fig 9. Kushiro port, Japan

13. 5. Methods to Determine Liquefaction
1. IS Code method
2. Idriss and Boulanger Method
The above methods involve calculation of Cyclic Stress
Ratio(CSR) and Cyclic Resistance Ratio (CRR).
• CRR is usually correlated to to an in-situ parameter such as
CPT penetration resistance, SPT blow count, or shear wave
velocity, Vs. An overview of the stress-based approach that
has been used with SPT data is presented in this section.
• Let us discuss some important parameters of these methods.

14. 5.1 IS Code Method
Calculation of CSR
amax = peak ground acceleration (PGA) preferably in terms of g
rd = stress reduction factor.
σvo = Total overburden Pressure
σ’vo = Effective Overburden Pressure
If value of PGA is not available, the ratio (amax/g) may be taken
equal to seismic zone factor Z . In our discussion, it is 0.25.
(Eq.1)

15. Calculation of CRR
CRR7.5= standard cyclic resistance ratio for a 7.5 magnitude
earthquake obtained using values of SPT or CPT or shear wave
velocity
MSF = magnitude scaling factor given by following equation:
This factor is required when the magnitude is different than 7.5.
The correction for high overburden stresses Kσ is required when
overburden pressure is high (depth > 15 m) and can be found
using following equation:
(Eq.2)
(Eq.3)
(Eq.4)

16. • Kα is required only for sloping ground and is not required in
routine engineering practice. Therefore, in the scope of this
standard, value of Kα shall be assumed unity.
SPT (Standard Penetration Test) blow count N60, for a
hammer efficiency of 60 %.
Therefore, FOS =
(Eq.5)
(Eq.7)
(Eq.6)

17. 5.2 Idriss and Boulanger Method
Calculation of CSR
M= magnitude of the earthquake
Where Pa= atmospheric earth pressure (100kPa)
(Eq.8)
(Eq.9)
(Eq.10)
(Eq.11)

18. Calculation of CRR
FC = % Fine Content .
FOS =
(Eq.12)
(Eq.13)

19. Depth
(m)
0.00
3.00
1.50
7.50
4.50
6.00
9.00
10.50
12.00
13.50
15.00
16.50
6.Cross Section of Strata at IGIMS Patna Site 1.BH1
18.00
19.50
21.00
22.50
24.00
25.50
27.00
28.50
30.00
31.50
33.00
34.50
36.00
37.50
39.00
40.00
Silty Clay with Low
Plasticity
Silty Clay with Medium
Plasticity
Clayey Sand
Silty Sand
Silty Sand
Log Strata Log Strata
Depth
(m)

20. Depth
(m)
0.00
3.00
1.50
7.50
4.50
6.00
9.00
10.50
12.00
13.50
15.00
16.50
18.00
21.00
22.50
24.00
25.50
27.00
28.50
30.00
31.50
33.00
34.50
36.00
37.50
39.00
40.00
Log Strata Log Strata
Depth
(m)
19.50
2.BH2
Silty Clay with Medium
Plasticity
Silty Clay with High
Plasticity
Silty Sand
Silty Sand

21. Depth
(m)
0.00
3.00
1.50
7.50
4.50
6.00
9.00
10.50
12.00
13.50
15.00
16.50
18.00
21.00
22.50
24.00
25.50
27.00
28.50
30.00
31.50
33.00
34.50
36.00
37.50
39.00
40.00
Log Strata Log Strata
Depth
(m)
19.50
3.BH3
Silty Clay with High
Plasticity
Silty Clay with Medium
Plasticity
Clayey Sand
Silty Sand
Silty Sand

22. Depth
(m)
0.00
3.00
1.50
7.50
4.50
6.00
9.00
10.50
12.00
13.50
15.00
16.50
18.00
21.00
22.50
24.00
25.50
27.00
28.50
30.00
31.50
33.00
34.50
36.00
37.50
39.00
40.00
Log Strata Log Strata
Depth
(m)
19.50
4.BH4
Silty Clay with Low
Plasticity
Silty Clay with Medium
Plasticity
Silty Clay with Low
Plasticity
Silty Sand
Silty Sand
Clayey Sand

23. 7. Calculations and Observation Tables
Some relevant informations and assumptions :-
• The following calculations have been done on the basis of soil data
observed at the IGIMS Patna site.
• There are Four Bore Holes under consideration for determination of
liquefaction possibility.
• Ground Water Table (GWT ) has been assumed to be at the ground
level , and effective vertical pressure is calculated in accordance
with it.
• Peak ground acceleration is assumed to be 0.25.
• CRR calculation has been done on the basis of SPT data.
• Three different Magnitude of Earthquake (Mw) has been taken ,
Mw=6.5, Mw=7.0, Mw=7.5.
• FOS <1 Then Soil is assumed to be liquefy.
• Termination depth of BH is 40 m.

24. S.No. Depth FOS Values FOS Values
(m) IS Code Method Idriss and Boulanger Method
Mw=6.5 Mw=7.0 Mw=7.5 Mw=6.5 Mw=7.0 Mw=7.5
1 1.5 0.53 0.51 0.37 0.65 0.55 0.41
2 3 0.88 0.73 0.61 1.11 0.81 0.59
3 4.5 0.65 0.54 0.45 0.77 0.66 0.51
4 6 0.77 0.64 0.53 0.94 0.71 0.59
5 7.5 0.97 0.74 0.67 1.12 0.89 0.71
6 9 1.14 0.77 0.55 1.39 0.85 0.61
7 10.5 1.21 1.14 0.78 1.41 1.19 0.85
8 12 1.98 1.64 1.21 2.31 1.75 1.31
9 13.5 2.1 1.67 1.13 2.38 1.88 1.22
10 15 2.52 2.1 1.45 2.84 2.31 1.49
11 16.5 3.55 3.12 3.15 3.18 1.95 1.59
12 18 NL NL NL 3.24 2.32 1.88
13 19.5 NL NL NL 3.38 2.72 2.19
14 21 NL NL NL 4.43 3.55 2.84
15 22.5 NL NL NL 5.06 4.83 3.84
16 24 0.12 0.1 0.09 6.69 5.88 5.45
17 25.5 3.18 2.63 2.2 NL NL NL
18 27 4.68 3.87 3.24 NL NL NL
19 28.5 6.05 4 4.19 NL NL NL
20 30 7.35 5.08 5.1 NL NL NL
1.BH1

25. S.No. Depth FOS Values FOS Values
(m) IS Code Method Idriss and Boulanger Method
Mw=6.5 Mw=7.0 Mw=7.5 Mw=6.5 Mw=7.0 Mw=7.5
1 1.5 0.53 0.44 0.37 0.71 0.58 0.48
2 3 0.86 0.8 0.58 0.98 0.81 0.61
3 4.5 0.68 0.55 0.95 0.86 0.74 1.05
4 6 0.98 0.69 0.57 1.18 0.88 0.61
5 7.5 0.9 0.75 0.62 1.21 0.83 0.68
6 9 1.23 1.15 0.85 1.68 1.31 0.94
7 10.5 1.11 0.98 0.74 1.48 1.13 0.79
8 12 1.88 1.54 1.37 2.32 1.72 1.32
9 13.5 2.15 2.05 1.41 2.58 2.27 1.52
10 15 2.71 2.21 1.54 3.42 2.44 1.64
11 16.5 NL NL NL 3.61 2.61 2.13
12 18 NL NL NL 4.39 3.56 2.89
13 19.5 0.78 0.65 0.54 9.18 7.39 5.95
14 21 1.83 1.52 1.27 NL NL NL
15 22.5 2.87 2.38 1.99 NL NL NL
16 24 4.07 3.37 2.82 NL NL NL
17 25.5 5.65 4.67 3.92 NL NL NL
18 27 6.81 5.63 4.72 NL NL NL
19 28.5 7.86 6.5 5.45 NL NL NL
20 30 7.35 7.46 5.1 NL NL NL
2.BH2

26. S.No. Depth FOS Values FOS Values
(m) IS Code Method Idriss and Boulanger Method
Mw=6.5 Mw=7.0 Mw=7.5 Mw=6.5 Mw=7.0 Mw=7.5
1 1.5 0.44 0.36 0.35 0.61 0.44 0.49
2 3 0.73 0.61 0.51 0.66 0.65 0.5
3 4.5 0.95 0.88 0.75 1.21 0.94 0.87
4 6 0.66 0.54 0.46 0.78 0.67 0.57
5 7.5 0.72 0.62 0.5 0.83 0.85 0.61
6 9 0.93 0.77 0.64 1.06 0.9 0.76
7 10.5 0.81 1.23 1.03 0.95 1.33 1.09
8 12 1.61 1.5 1.25 1.97 1.63 1.19
9 13.5 2.21 2.31 1.54 2.58 2.54 1.61
10 15 2.88 2.52 2.21 3.21 2.74 2.43
11 16.5 NL NL NL 4.2 3.43 2.8
12 18 NL NL NL 9.37 7.6 6.15
13 19.5 2.36 1.95 1.64 NL NL NL
14 21 3.37 2.79 2.34 NL NL NL
15 22.5 4.17 3.45 2.89 NL NL NL
16 24 4.7 3.88 3.26 NL NL NL
17 25.5 5.96 4.67 4.13 NL NL NL
3.BH3

27. S.No. Depth FOS Values FOS Values
(m) IS Code Method Idriss and Boulanger Method
Mw=6.5 Mw=7.0 Mw=7.5 Mw=6.5 mw=7.0 Mw=7.5
1 1.5 0.44 0.36 0.3 0.55 0.41 0.29
2 3 0.81 0.67 0.56 0.79 0.61 0.49
3 4.5 0.98 0.88 0.45 1.12 0.95 0.46
4 6 0.83 0.69 0.57 0.93 0.75 0.62
5 7.5 0.97 0.8 0.67 1.25 0.68 0.7
6 9 1.05 0.87 0.73 1.52 0.96 0.69
7 10.5 0.88 0.74 0.83 1.36 1 0.86
8 12 1.23 1.28 1.07 1.51 1.27 1.12
9 13.5 1.3 1.07 0.9 1.74 1.31 1.02
10 15 1.77 1.47 1.23 2.21 1.97 1.18
11 16.5 3.98 3.29 2.76 2.43 2.13 1.31
12 18 NL NL NL 3.65 2.96 2.39
13 19.5 1.1 1.1 1.1 9.48 7.63 6.14
14 21 1.05 1.05 1.05 NL NL NL
15 22.5 2.44 2.44 2.44 NL NL NL
16 24 3.14 3.29 2.18 NL NL NL
17 25.5 3.97 4.43 2.76 NL NL NL
4.BH4

28. 8. Graph Plotted Between SPT N Value vs Depth
0
2
4
6
8
10
12
14
16
0 10 20 30
Depth(m)
SPT N value
0
2
4
6
8
10
12
14
16
0 10 20 30
Depth(m)
SPT N value
1. (BH1) 2. (BH2)
0
2
4
6
8
10
12
14
16
0 10 20 30
Depth(m)
SPT N value
0
2
4
6
8
10
12
14
16
0 5 10 15 20
Depth(m)
SPT N value
3. (BH3) 4. (BH4)

29. 9.Comparison of FOS values between IS Code & Idriss and Boulanger
0
3
6
9
12
15
0 1 2 3 4
Depth(m)
FS value
IS code
Idriss and
Boulanger
(2006)
Mw =6.5
0
3
6
9
12
15
0 1 2 3 4
Depth(m)
FS value
IS code
Idriss and
Boulanger
(2006)
Mw =7.0
0
3
6
9
12
15
0 1 2 3 4
Depth(m)
FS value
IS code
Idriss and
Boulanger
(2006)
Mw =7.5
BH1
2.1. 3.

30. 0
3
6
9
12
15
0 1 2 3 4
Depth(m)
FS value
IS code
Idriss and
Boulanger
(2006)
Mw =6.5
0
3
6
9
12
15
0 1 2 3 4
Depth(m)
FS value
IS code
Idriss and
Boulanger
(2006)
Mw =7.0
0
3
6
9
12
15
0 1 2 3 4
Depth(m)
FS value
IS code
Idriss and
Boulanger
(2006)
Mw =7.5
BH2
5.4. 6.

31. 0
3
6
9
12
15
0 1 2 3 4
Depth(m)
FS value
IS code
Idriss and
Boulanger
(2006)
Mw =6.5
0
3
6
9
12
15
0 1 2 3 4
Depth(m)
FS value
IS code
Idriss and
Boulanger
(2006)
Mw =7.0
0
3
6
9
12
15
0 1 2 3 4
Depth(m)
FS value
IS code
Idriss and
Boulanger
(2006)
Mw =7.5
BH3
7. 8. 9.

32. 0
3
6
9
12
15
0 1 2 3 4
Depth(m)
FS value
IS code
Idriss and
Boulanger
(2006)
Mw =6.5
0
3
6
9
12
15
0 1 2 3 4
Depth(m)
FS value
IS code
Idriss and
Boulanger
(2006)
Mw =7.0
0
3
6
9
12
15
0 1 2 3 4
Depth(m)
FS value
IS code
Idriss and
Boulanger
(2006)
Mw =7.5
BH4
10. 11. 12.

33. CONCLUSION
• It has been observed that from the calculated FOS, with respect to CRR
and CSR, decreases as the Magnitude of Earthquake (Mw) increases in all
the Four Bore Holes which is in accordance with the past studies. Analysis
has been done in accordance with SPT data provided at the IGIMS Patna
Site.
• Since Water Table has been assumed to be at the ground level, so there is
slightly more calculated FOS value as compared to the Water Table below
the Ground Level , which is obvious because there will be more Pore
Water Pressure in case of WT at the ground level which decreases the
Effective Vertical Pressure and Soil becomes more prone to the
Liquefaction which is obviously dangerous for the structure.

34. • According to the IS Code if FOS < 1 soil is assumed to be liquefy.
• Graphical comparison has been done above between IS Code & Idriss and
Boulanger Method upto the depth of 15m .
• On this basis we can easily conclude that the calculated FOS value
obtained from Idriss and Boulanger method is slightly more than that of IS
Code method at different Magnitude of Earthquake and this difference
decreases as Magnitude of Earthquake increases and tends to be almost
equal at higher Magnitude. From these graphs we can easily find upto
which depth Liquefaction is possible.

39. REFERENCES
• M. Idriss and R. W. Boulanger, “Semi-empirical Procedures for Evaluating Liquefaction
Potential During Earthquakes”, Proceedings of the 11th ICSDEE & 3rd ICEGE, pp 32 – 56,
January 7 – 9, 2004.
• Jin-Hung Hwang and Chin-Wen Yang, “A Practical Reliability-Based Method for Assessing
Soil Liquefaction Potential”, Department of Civil Engineering, National Central University.
• Adel M. Hanna, Derin Ural and Gokhan Saygili, “Evaluation of liquefaction potential of
soil deposits using artificial neural networks”.
• Adel M. Hanna, Derin Ural, Gokhan Saygili, “Neural network model for liquefaction
potential in soil deposits using Turkey and Taiwan earthquake data”, Soil Dynamics and
Earthquake Engineering 27 (2007) 521–540
• Chapter 2: soil liquefaction in earthquakes
• Sladen, J. A., D‟Hollander, R. D., and Krahn, J. _1985_. „„The liquefaction of sands, a
collapse surface approach.‟‟ Can. Geotech. J., 22, 564– 578.
• Finn, W. L., Ledbetter, R. H., and Wu, G.: Liquefaction in silty soils: design and analysis,
Ground failures under seismic conditions, Geotechnical Special Publication No 44, ASCE,
Reston, 51–79, 1994
• Castro, G., (1975) Liquefaction and cyclic mobility of saturated sands. Journal of the
Geotechnical Engineering Division, ASCE, 101 (GT6), 551-569.