liquefaction i and ii

7/21/2019 Liquefaction I and II

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Liquefaction

Ajanta SachanAssistant ProfessorCivil EngineeringIIT Gandhinagar

Liquefaction

Why does the Liquefaction occur?

When has Liquefaction occurred in the past?

How can Liquefaction hazards be reduced?


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What is Liquefaction ?

Li uefaction occurs in saturated soilsAll pores are completely filled with water;Soil is no more thirsty!!

The water in the pores exerts the pressureon soil articles called Pore Pressure thatinfluences how tightly the soil particles are

pressed together

Why does the Liquefaction occur?

Prior to an earthquake: the pore pressure is low

Earthquake shaking causes pore pressure to Increase:Undrained Condition!!

Pore pressure = Overburden press/Confining stressEffective stress is Zero;

NO S ear Strengt !!

Soil particles starts readily move with respect to each otherdue to zero shear strength.LIQUEFACTION occurs!!


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Mechanism: Why does the Liquefaction occur?

Soil grains in a soil deposit

The small contact forces arebecause of the high waterpressure.

In an extreme case, theporewater pressure may

The length of the arrows represent thesize of the contact forces betweenindividual soil grains

of the soil particles losecontact with each other. Insuch cases, the soil has verylittle strength, and behaveslike a liquid; calledLiquefaction".

When has Liquefaction occurredin the past?

Alaska Earthquake, USA, 1964

Niigata Earthquake, Japan, 1964

Loma-Prieta Earthquake, USA, 1989

Kobe Earthquake, Japan, 1995

- , ,

Bhuj Earthquake, India, 2001

Many More!!


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Liquefaction: Lateral Displacement

Alaska Earthquake, USA, 1964: Displacement of Houses& cracked highway

Liquefaction: Tilting of Buildings

Niigata Earthquake, Japan, 1964:Tilting of apartment buildings at Kawagishi-Cho


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Liquefaction: Collapse of Expressways

Kobe Earthquake, Japan, 1995:Collapse of Hanshin Expressway &collapse of Nishinomiya bridge

Bhuj Earthquake, India, 2001: Damage to rail-road and highway; sandboiling due to liquefaction


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,California, 1989

Failed river dike, California, 1989

Sand boils in a house at Shetou,Taiwan, 1999

an o s n a room n unya- n uan nTown, Taiwan, 1999


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Sand boils in Loma Prieta Earthquake, 1989, California

Liquefaction-induced settlement at Taichung Port, Taiwan, 1999


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1964 Niigata EQMulti span BridgeMovement of Bridge Piers due to Lateral Spreading

1964 Niigata EQTilting of BuildingLoss of Bearing Capacity


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Where does Liquefactioncommonly occur?

Soils susceptible

0.002 200632.360.075

BoulderClay Silt Sand Gravel Cobble

ranu ar so s orCohesion less soils

o es vesoils

o que ac on

Fine grainsoils

Coarse grainsoils

. ; co e

Grain size (mm)

Where does Liquefaction commonly occur?

Liquefaction occurs in saturated soil only, its effects are most commonly- , , ,

and oceans. Port and wharf facilities are often located in areas susceptible toliquefaction, and many have been damaged by liquefaction in pastearthquakes.

Most ports and wharves have major retaining structures, or quay walls, toallow large ships to moor adjacent to flat cargo handling areas. When the soilbehind and/or beneath such a wall liquefies, the pressure it exerts on the wallcan increase greatly - enough to cause the wall to slide and/or tilt toward the

water.

Liquefaction also frequently causes damage to bridges that cross rivers andother bodies of water. Such damage can have drastic consequences, impedingemergency response and rescue operations in the short term and causingsignificant economic loss from business disruption in the longer term.


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Liquefaction Susceptible Soil

Soil

Loose (sometimes dense too)

Saturated

Why not in Dense Soil ??(negative pore pressure generationduring shearing!!)

Without EQ With EQ

k k

kk

Shear Stress Increase inprincipal stress

Liquefaction: Principal Stress

Normal

Stress

0

WithoutEQ

k

With EQ


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Under EQ ground motion

-

Shear Stresses in Soils under Earthquakes

-

Transmitted upwards

Loose cohesionless soils tend to densify and settle

Pore water is forced out from the voids

Shaking duration too short for pore water to drain

Pore water ressure increases

Effective stress reduces

In critical state, soil looses stiffness & shear strength

Liquefaction: Flow Liquefaction

Flow Liquefaction Onl in loose to moderatel dense ranular soils silt sands

sands and gravels) with poor drainage

Soil stratum softens causing large cyclic shear deformations

In loose materials, associated loss of shear strength may causeflow failure

For sharp slopes (>~5 %), landslides on a large scale

Hundreds of meters of motion of soil mass

eq

strength

After Flow FailureAfter Flow FailureBefore Flow FailureBefore Flow Failure


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C clic mobilit

Liquefaction: Cyclic Mobility

In both loose and dense soils

Gentle slopes (


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Liquefaction at depth

Separation of layers

Large Ground Oscillations

Ground soil layers jostleback and forth

Ground waves

Lateral spreading due toflow liquefaction and/orcyclic mobility

TiltingLarge GroundOscillations

Uplift

Subsidence

LateralSpreading

Li uefied underl in soil su ortin the

Loss of Bearing Capacity

structure

Subsidence of heavier structures

Uplifting of lighter structures


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Liquefaction Hazard

Seismic History Criterion

8

from EQ source

Magnitude

Distance from hypocenter

Local sub-surface conditions

tude

7

9

Distance from EQ

Magn

5

6

2 5 10 50 100 500

Earthquake Magnitude

OREarthquake Intensityis used for Designing theStructures??

Liquefaction Hazard

Seismic history of the site Densifying

Better inter-locking between particles

Increased shear resistance

Earthquake ground shaking characteristics Intensity

Duration

Structure should beEarthquake ResistantOREarthquake Proof..??


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Liquefaction Potential: Research

Referred as Simplified Procedure to

(Seed & Idriss, 1971; ASCE)

Largely empirical evolved over last 30 yrs

Research reviewed and recommended in 2workshops, NCEER 1996 and NCEER/NSF1998

Summary report in ASCE journal of

Geotechnical and Geo-environmental Engg.,October 2001Title: Liquefaction Resistance of Soils

Earthquake loading is characterized by theamplitude of an equivalent uniform cyclic stress

Liquefaction Potential Evaluation usingCyclic Stress Approach (Youd et al., Oct 2001, ASCE)

Liquefaction resistance is characterized by anequivalent uniform cyclic stress required toproduce liquefaction in the same number of cycles

For Liquefaction evaluation: compare loading andresistance.

Loading: Equivalent stress induced by Earthquake

es s ance: ress requ re or que ac onLiquefaction ResistanceORLiquefaction SusceptibleORLiquefaction Prone /Liquefiable SoilsSAME??


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0Cyclic Shear Stress

Initiation of Liquefaction

Zone of Liquefaction

Depth

Equivalent stress inducedby earthquake

Stress requiredfor Liquefaction

Evaluation of Liquefaction potential

d

voav ra

CSR'

max

' 65.0

kkkCRRCRR m 5.7

onLiquefacti;0.1; ss FIfCSR

CRRF

vovo

CSR = Cyclic Stress RatioSeismic demand on the Soil due to Earthquake

CRR = Cyclic Resistance RatioCapacity of Soil to resist Liquefaction


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Characterizing Earthquake Load

a

Irre ular time histor of shear stress is converted to an

vog

onacceleratigrounda

equivalent series of uniform stress cycles at an amplitude of65% of peak shear stress (Seed et al. 1975).

voavg

a

max65.0

Stress Reduction Coefficient, rd

dvoav rg

a

max65.0

rd= 1.0 0.00765z for z 9.15m (2a)rd= 1.174 0.0267z for 9.15m < z 23m (2b)


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Cyclic Stress Ratio (CSR)

Seismic demand on the soil

Seed & Idriss (1971)

d

vo

vo

vo

av rg

aCSR

'

max

' 65.0

'

vo

vo

Effective vertical overburden stresses

Total vertical overburden stresses

Capacity of soil to resist

Cyclic Resistance Ratio (CRR)

Liquefaction case historiesused to characterize CRR interms of measured in-situ testparameters (Whitman 1971)

Parameter generally used

BoundaryLiquefactionObserved

m5.7

CPT

Shear Wave Velocity (SWV)

Field Test Parameter

No LiquefactionObserved

CRR


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SPT Correlations

CRR7.5 for SPT data

or . eq or

Corrected Blow

Count (N1)60normalized for 100

kPa overburden

pressure and hammer

efficiency of 60%

Correction factors fornon-standard SPT

values(Youd et al. 2001)

CRR7.5 for CPT data

CPT Correlations

CRR for M7.5 eqk for

Normalized cone tip

resistance

Correction factors for

grain characteristics,

csNc

q 1

an t n ayer e ect

(Youd et al. 2001)


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CRR7.5 for Shear

SWV Correlations

wave velocity data

CRR for M7.5

Earthquake for

normalized shear

wave velocity

Correction actors

(Youd et al. 2001)

Earthquake Magnitude

Correctiono 7.5

forEarthquake

Magnitudeother than

7.5 (km)

kkkCRRCRR m 5.7


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Overburden Pressure

Correction to

7.5 overburdenstresses, Correction factor for

CRR7.5 to extrapolatefor soil layers withoverburden

k

pressures greaterthan 100 kPa

Simplified procedureis valid for depthsless than 15 m.

kkkCRRCRR m 5.7

Correction to CRR7.5

Initial Static Shear

or n a s a c s ear, Correction factor for

CRR7.5 to account forinitial static shear stressconditions such as due topresence of embankment,heavy structures, etc.

k

kkkCRRCRR m 5.7


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Factor of safety against liquefaction

CSR

CRRFs

0

ofLiquefaction

Cyclic Shear Stress0

Fs1

Zone

Depth

CSR CRR

Depth

Example: Liquefaction potentialEvaluation Problem:

SPT data and sieve analysis

Expected earthquake M7.5 & Seismic Zone V

Depth(m)

Soil ClassificationPercentagefines

0.75 9 Poorly Graded Sand and Silty Sand (SP-SM) 11


60N

. oor y ra e an an y an -






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Liquefaction potential at depth 12.75 m

Example: Liquefaction potentialEvaluation

2 4.0m a x g

a, 5.7wM

kPav 9.2355.1875.12

3/5.1 8 mk Ns a t ,3/8.9 mk Nw

....

2.669.2350' uvv

= 169.7kPa

d

vo

vo

vo

av rg

aCSR

'

max

' 65.0

Liquefaction potential at depth 12.75 m


Compute stress reduction factor

Compute CSR

834.00267.0174.1 zrd

' .vvdmaz

18.07.169/9.235834.024.065.0 CSR


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Li ue action otential at de th 12.75 m


Compute CRR

Read value corresponding to (N1)60 =14 (after overburdencorrection) and fines content of 8%

kkkCRRCRR m 5.7

.5.7

0.1

k0.1mk

For vertical effective stress of 169.7 kPa = 1.7 atm 87.0

k

Li ue action otential at de th 12.75 m


Compute CRR (N = 17, N =14 ) (fines = 8%)

kkkCRRCRR m 5.7

12.087.011143.0 CRR

Compute Fs

67.018.0

12.0

CSR

CRRFs


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Repeat for all depths


Depth

%

fines (kPa) (kPa)

0.75 11.0 13.9 13.9 9 2.00 18 0.99 0.15 0.22 0.22 1.47

3.75 16.0 69.4 69.4 17 1.13 19 0.94 0.15 0.29 0.29 1.93

6.75 12.0 124.9 117.5 13 0.98 13 0.95 0.16 0.16 0.16 1.00

v'v

60N NC

601N dr CSR 5.7CRR CRR

sF

9.75 8.0 180.4 143.6 18 0.90 16 0.91 0.18 0.19 0.17 0.94

12.75 8.0 235.9 169.7 17 0.83 14 0.83 0.18 0.14 0.12 0.67

15.75 7.0 291.4 195.8 15 0.80 12 0.75 0.17 0.13 0.11 0.65

18.75 6.0 346.9 221.9 26 0.77 20 0.67 0.16 0.23 0.17 1.10

Liquefaction Potential fordifferent soils using SPT


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Ground Improvement Techniquesto overcome Liquefaction

Measures to Overcome Liquefaction

2) Stone Columns (De-watering)

3) Compaction (Densification of soil)

5) Anchored Piles

6) Liquefaction Resistant Structures


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Increasing surcharge

1) Vertical Stress Increase

Surchar e Surchar e

Factor of Safety against Liquefaction

a d

vovo

rg ''

.

Before Surcharge After Surcharge

25.140' vo

vo

17.1

2040' vovo

CSR

CRRFs


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Surcharge


Vertical Stress Increase

ExpectedZone ofLiquefaction

DepthEquivalent stressinduced by EQwithout surcharge

Equivalent stressinduced by EQwithout surcharge

Equivalent stressinduced by EQwith surcharge

Equivalent stressinduced by EQwith surcharge

Stress requiredfor Liquefaction

2) Stone Columns

Drainage or De-watering

Excess Pore WaterPressure release

Seepageflow

Columns


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Stone Columns

LiquefiableLiquefiableSandSand

DrainsDrains

57


Stone Columns


Stress required for Liquefactionwith stone columnsStress required for Liquefactionwith stone columns

Stress required for Liquefactionwithout stone columnsStress required for Liquefactionwithout stone columns

Depth

Equivalent stressinduced by EQ


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3) Compaction (Densification of soil)

a. Roller Compaction

b. Dynamic Compaction

c. Vibro-compaction (vibro-floatation)

d. Compaction Grouting

e. Compaction by Pile Driving

3a) Roller Compaction

Rubber T re Roller

Smooth wheel vibratory roller


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3b) Dynamic Compaction

Big weightsroppe rom m,

compacting theground.

61

Craters formedin compaction

Used for cohesionless deposits of sand and gravel with not morethan 20% silt or 10% clay

3c) Vibro-floatation

Crators are formed during vibratory motion. Sand /gravel isadded to the crator formed.

Vibrator

OriginalLoose SoilOriginal

Loose Soil

Compacted andrefill material

Compacted andrefill material

Vibro-Compaction


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Compaction0

Cyclic Shear Stress

Vibro-floatation


Stress required for Liquefactionwith densificationStress required for Liquefactionwith densification

Stress required for Liquefaction

without densification

Stress required for Liquefaction

without densification

Depth

Equivalent stressinduced by EQ

3d) Compaction Grouting

Stiff, low mobilit rout isslowly injected into loosesoils under high pressure

grout does not enter the soilpores, but forms a bulb thatcompacts and densify thesoil by forcing it to occupy

http://www.spsrepair.com/www.spsrepair.com/tabid/497/Default.aspx

less space


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3e) Compaction by Pile Driving

deposit, compacts the sand within area

covered by 8 times around it

Increase in the stiffness of soil stratum

due to pile driving

Removal of soil layers thatcan li uef

4) Removal of Liquefiable soil

Soil layerwith potential

Soil layerwith potential

o que yo que y Original GL

New GL

Loweringthe

ground


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Piles are anchored in

5) Anchored Piles

bed rock

Liquefiable LayerLiquefiable Layer

Bed RockBed Rock

6) Liquefaction Resistant Structures

A structure that ossesses ductilit , has the abilitto accommodate large deformations, adjustablesupports for correction of differential settlements,and having foundation design that can span softspots; which can decrease the amount of damage astructure may suffer due to liquefaction.

To achieve these features in a building, followingaspects need to be considered:a. Shallow Foundation Aspectsb. Deep Foundation Aspects


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6a) Shallow Foundation Aspects

All foundation elements in a shallow

the foundation move or settle uniformly,thus decreasing the amount of shear forcesinduced in the structural elements restingupon the foundation.(For example: The well-reinforced perimeter andinterior wall footings should be tied together toenable them to bridge over areas of localsettlement and rovide better resistance a ainstsoil movements.)

A stiff foundation mat is a good type ofshallow foundation, which can transferloads from locally liquefied zones toadjacent stronger ground.

,and water pipes, should haveductile connections to the

structure to accommodate thelarge movements andsettlements that can occur dueto liquefaction.

6b) Deep Foundation Aspects

Piles driven through a potentially liquefiable Piles should be connected to the cap

soil layer to a stronger layer not only have tocarry vertical loads from the superstructure,but also resist the horizontal loads and bendingmoments induced lateral movements if thatlayer liquefies. Sufficient resistance should beachieved by piles of larger dimensions and/ormore reinforcement.

in a ductile manner which couldallow some rotation to occurwithout a failure of the connection.If the pile connections fail, the capcannot resist overturning momentsfrom the superstructure bydeveloped vertical loads in piles.


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Liquefaction Induced Lateral Spreading


Mechanism (Zhang et al. 2004) Lateral spreads occurs due to residual shear strains in liquefied

layers.

Residual shear strains depends on Maximum cyclic shearstrains.

Thicker Liquefied layer Greater Displacement

Increase in cyclic shear strain Greater Displacement

Soil Properties and Earthquake Characteristics

Cyclic Shear strain and Thickness of Liquefied soil layers


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Mechanism (Zhang et al. 2004) Continued At a given relative density of soil; A limited amount of shear

strain could be developed in soil; regardless of the number ofstress cycles applied.

Maximum Cyclic shear strain can be obtained using:

Factor of Safety obtained during Liquefaction PotentialEvaluation

Relative density of soil for given earthquake loadingconditions

Maximum Cyclic

Liquefaction Induced Lateral Spreadingusing SWV

Factor of Safetyagainst Liquefactionfor different relativedensities for CleanSands(Based on data from Ishiharaand Yoshimine 1992; Seed


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Relative Density Calculations:


SPT (Empirical Eq: Seed 1979; Skempton 1986; Kulhawy & Mayne 1991)

CPT (Empirical Eq: Tatsuoka et al.1990)

42)(;)(.14 6060 11 NNDr

kPaqqD NcNcr 200);log(7685 11

The above equations are for clean sands.

Assumption:It is assumed that the effect of graincharacteristics or fines content on lateral spreading issimilar to its effect on liquefaction triggering. (Zhang et al.

2004)

Lateral Displacement Index (LDI):


LDI : Integration of calculated maximum cyclic shear strain valueswith depth.

dzLDIZ

.max

0 max

maxz = Maximum depth below all the potential liquefiable layerswith a Fs


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Lateral displacements for the available case histories for (Zhang et al. 2004) :(a) Gently sloping ground without a free face(b) Level ground with a free face(c) Gently sloping ground with a free face


Shear Wave Velocity (SWV)e o re , :

dzLDIZ

.max

0 max

hD = Lateral Displacement

)(23.0)( LDILDICD hh


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Thank You

liquefaction i and ii

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