Liquefaction of soil

Calculation of Liquefaction Possibility of Soil at Igims Patna Site.

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 Introduction Factors Affecting Liquefaction Effects of Liquefaction Types of Failures Methods to Determine Liquefaction Cross Section of Soil Strata at IGIMS Patna Site Calculations and Observation Tables Graph Between SPT N Value vs Depth Graphical Comparison of FOS Values Conclusion 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 + σ n tan φ Effective stress gives more realistic behaviour of soil, shera strength can be expressed as : τ = c’ + ( σ n - u) tan φ ’ During the ground motion, due to an earthquake, static pore water pressure may be increased by an amount u dyn , then τ = c’ + ( σ n - u + u dyn ) tan φ ’. Let us consider a situation when {u + u dyn = σ n } , 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 Loss of Bearing strength : The ground can liquefy and lose its ability to support the structure . 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 IS Code method 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 a max = peak ground acceleration (PGA) preferably in terms of g r d = stress reduction factor. σ vo = Total overburden Pressure σ ’ vo = Effective Overburden Pressure If value of PGA is not available, the ratio ( a max /g) may be taken equal to seismic zone factor Z . In our discussion , it is 0.25. ( Eq.1)

15. Calculation of CRR CRR 7.5 = 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 K σ is required when overburden pressure is high (depth > 15 m) and can be found using following equation: (Eq.2) (Eq.3) (Eq.4)

16. K α is required only for sloping ground and is not required in routine engineering practice. Therefore, in the scope of this standard, value of K α shall be assumed unity . SPT (Standard P enetration T est) blow count N 60 , 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 1. (BH1) 2. (BH2) 3. (BH3) 4. (BH4)

29. 9 .Comparison of FOS values between IS Code & Idriss and Boulanger M w =6.5 M w =7.0 M w =7.5 BH1 2. 1. 3.

30. M w =6.5 M w =7.0 M w =7.5 BH2 5. 4. 6.

31. M w =6.5 M w =7.0 M w =7.5 BH3 7. 8. 9.

32. M w =6.5 M w =7.0 M w =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.

35. 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.