PRESENTATION ON

LIQUEFACTION AND

LIQUEFACTION POTENTIAL

BY: Mahesh Raj Bhatt ME in Structural Engineering , Kathmandu University

1. LIQUEFACTION: What is liquefaction When does it occur Liquefaction of soil How it works Shear strength of soil Types of liquefaction2.LIQUEFACTION POTENTIAL How to identify Liquefaction analysis Prediction Mitigations3. CONCLUSIONS:

LIQUEFACTION:

In soil mechanics term “liquefied” first used byAllen Hazen (1918), In reference toFailure of Calaveras Dam in California.

Attention of engineer after -1964 Alaska Earthquake(Mw=9.2) good Friday earthquake - 1964 Niigata Earthquake( Ms=7.5) Japan -1989 loma-Prieta Earthquake and others.

In soil mechanics the term "liquefied" was first used by Allen Hazen[1] in reference to the 1918 failure of the Calaveras Dam in California.

attention of engineers after 1964 Niigata earthquake and 1964 Alaska earthquake. 1989 Loma Prieta earthquake, and in Port of Kobe during the 1995 Great Hanshin earthquak

What is Liquefaction?

A phenomenon whereby a saturated or partially

saturated soil substantially loses strength and stiffness in response to an applied stress, usually

earthquake shaking or other sudden change in stress condition, causing it to behave like a liquid.

When does it occurs??

-when the effective stress of soil is reduced to essentially zero, which corresponds to a complete loss of shear strength

May be initiated by –  Monotonic Loading– Cyclic loading–Shock loadings(EQs)

Liquefaction of soil:

Soils behave like a liquid. How and why?To understand the above phenomenon:• some basics required regarding:

Total stress, (σt)Pore water pressure (u) Effective stress (σeff )

σt= σeff + u σeff = σt- u

How It Works??

• When the seismic waves pass through the soil, the vibrations cause the individual grains in the soil to –move around and – re-adjust their positions

• This ultimately results in a decrease in volume of the soil mass as– the grains pack more tightly together – a reduction in porosity

Soil loose its strength because of loss of effective stress

Saturated sand in ground vibration, -it tends to compact and decrease in volume ; -if no drainage, decrease in volume results -increase in pore water pressure

IF Pore water pressure=overburden pressure

THANeffective stress = zero,

-sand looses strength completely and develops a liquefied state.

How pore pressure increase

Spring water analogy of soil layer

Shear strength of soil

Shear strength, τ = c + σt tanøEffective stress gives more realistic behaviour of soil,

Shear strength can be expressed as τ = c1 + (σt –u)tanø1

During the ground motion due to an earthquake, static pore pressure may by an amount udyn, then

τ = c1 + (σn –u + udyn)tanø1

Let us consider a situation when u + udyn= σn, then τ = c1

In cohesion less soil, c1= 0, hence τ = 0 (sand)

Influence of soil condition on liquefaction potential

Liquefaction damage 1964 Niigata japan

Alaska Earthquake (1964)

Types of liquefaction:

1. Flow liquefaction 2. Cyclic Liquefaction: τ static> τliquid state τ static< τliquid state

-flow of soil mass -spreading of mass -slope ϴ >3 degree - slope ϴ <3 degree -steep area -level area -flow/often movement -lateral spreading - ground oscillation

Flow failure

Lateral spreading

Liquefaction potential/evaluation of liquefaction hazards

Is the soil susceptible to liquefaction?If so , will liquefaction be triggered?If so , will damage occur? ANSWER IS We Should evaluate potential liquefaction hazards

How to identify??a. Historical Criteria- earlier earthquake data/Maps/documents availaleb. Geological Criteria• Saturated soil deposits that have been created by – sedimentation in rivers and lakes (fluvial or alluvial

deposits), – deposition of debris or eroded material (collegial deposits), – or deposits formed by wind action (Aeolian deposits) can be very liquefaction susceptible.

c.Compositional Criteria -soil types clay/sand/silt -composition of soils

Critical aspects of hazard evaluationsusceptibility initiation effects

yes no -monotonic loading

-alteration of Ground Motion

-historical criteria

Hazard do not exist(End)

-cyclic loading -sand boiling

-geological criteria -development of flow Liquefaction

-settlements

-Compositional criteria-state criteria

-evaluation of liquefaction

-instability-flow failures-deformation failures

LIQUEFACTION ANALYSIS

• Objective: does soil liquefy During Earthquake?• Assumption: Soil act as rigid body - moves horizontal with amax exerted by EQ

At force equilibrium:Horizontal seismic force = Max. shear force at the base of column

(τmax)Horizontal seismic force = Mass x Accl.= [(γt .z)/g]amax = σvo (amax/g)

= τmax

Mass = W/g = (γt .z)/g = σvo /g

If effective vertical stress = σ’vo ,

Then (τmax / σ’vo ) = (σvo / σ’vo )(amax/g)In reality, during an earthquake, soil column does not act as a rigid

body(τmax / σ’vo ) = rd (σvo / σ’vo )(amax/g)rd ~ 1- 0.012z , also depends upon the magnitude of the earthquake

Conversion of irregular earthquake record to an equivalent series of uniform stress cycle by

τav = τcyc = 0.65τmax = 0.65 rd (σvo / σ’vo )(amax/g)To felicitate liquefaction analysis, define a dimensionless

parameterCSR or SSR = τcyc / σ’vo = 0.65 rd (σvo / σ’vo )(amax/g)CSR = Cyclic stress ratio, SSR = Seismic stress ratioFS = Factor of safety against liquefaction = CRR/CSRCRR= Cyclic resistance ratio

Time history of shear stress during earthquake for liquefaction analysis

Represents liquefactionresistance of soilData used: EQ ~ 7.5,Line represents dividing line Three lines contain- 35, 15 or ≤ 5 % fineData to the left of each line indicate field liquefaction Data to the right of each line indicate no liquefaction FS = CRR/CSRFS = Factor of safety against liquefaction

CYCLIC RESISTANCE RATIO (CRR)

can liquefaction be predicted??• NOT BUT• Possible to identify areas giving detailed information

that have the potential of liquefaction• Liquefaction susceptibility: (Controlling factor: soil type, density and water) table

• Liquefaction opportunity:

(Frequency of earthquake occurrence, intensity of seismic ground shaking)

How to mitigate Liquefaction: a. Improving soil properties BY: Vibro-compaction Dynamic compaction Compacting grouting Stone columnsb. Lowering ground water table:c. Ground surface correction.d. BE CAREFULL ABOUT HAZARD MAPING.

Vibro-Compaction

Dynamic compaction:

Compaction grouting

CONCLLUSIONS:Liquefaction is most important earthquake

caused hazard all over the world.Attention and researched should be increased

in it.Hazard mapping are compulsory in Nepal. (terai and valley regions) - pokhara valley is most susceptible in Nepal.Implementation of mapping should be kept in

mind by all.

Bibliography:• http://publication.hils.org.np/hilspub/index.php/IJLE/article/download

/97/48• https://en.wikipedia.org/wiki/Soil_liquefaction• http://www.slideshare.net/jagadanand/liquefaction-of-soil?qid=28563

337-882f-4bb0-adef-ae2c8d7707e1&v=&b=&from_search=1• https://theses.lib.vt.edu/theses/available/etd-219182249741411/unre

stricted/Chp07.pdf• epa.ohio.gov/portals/34/document/guidance/gd_660_chapter_5.pdf• Geotechnical earthquake engineering Steven L . Kramer. Pearson 2007.• Seismic analysis of structures T. K, Datta. John Wiley & Sons (Asia)

Pte Ltd, 2 Clementi Loop, 2010

THANK YOU !!!!

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