liquefaction of soil

Liquefaction of soilLiquefaction of soil

ByDr. J.N.JhaProfessor

Department of Civil EngineeringGuru Nanak Dev Engineering College

LudhianaEmail: [email protected]

Chile earthquake 1960 : Chile earthquake 1960 : An island near Valdivia- Mag. 9.5An island near Valdivia- Mag. 9.5 Large settlements and differential settlements of the Large settlements and differential settlements of the ground surfaceground surface--Compaction of loose granular soil by Compaction of loose granular soil by EQEQ

Japan earthquake 1964: Japan earthquake 1964: Niigata- Mag. 7.5Niigata- Mag. 7.5Settlement and tilting of structuresSettlement and tilting of structures--liquefaction of soilliquefaction of soil

Alaska earthquake 1964:Mag. 9.2Alaska earthquake 1964:Mag. 9.2 Major landslideMajor landslide--combination of dynamic stresses and induced combination of dynamic stresses and induced pore water pressurepore water pressure

Caracas earthquake 1967: Mag. 6.6Caracas earthquake 1967: Mag. 6.6Response of building during EQ found to depend on the Response of building during EQ found to depend on the thickness of soil under the building.thickness of soil under the building.

Observed Damage from Earthquakes Observed Damage from Earthquakes

Chile earthquake 1960 : An island near Valdivia

Large settlements and differential settlements of the ground surface-Compaction of loose granular soil by EQ

Japan earthquake 1964: Niigata

Settlement and tilting of structures-liquefaction of soil Alaska earthquake 1964: Turnagain heights landslide

Major landslide-combination of dynamic stresses and induced pore water pressure

Caracas earthquake 1967

Response of building during EQ found to depend on the thickness of soil under the building.

What is the inference ? Influence of local soil condition on shaking and damage intensity

during earthquake Require a careful attention by Engineers

Seismic wavesSeismic waves

Arrival of Seismic waves at site

Motion of Ground (Description): Displacement, Velocity, AccelerationMotion of Ground : Depends on •Amount of energy release,•Type of slip at fault rupture•Geology along the travel path from fault rupture to earth surface•Local Soil

Influence of local soil conditions on Influence of local soil conditions on Acceleration(Cause for damage during EQ) Acceleration(Cause for damage during EQ) Some Basic Information : Acceleration Response Spectrum

A graph showing the maximum accelerations induced in structures with fundamental period ranging from 0 to several seconds

Velocity Response Spectrum

A plot showing relationship between maximum velocity with fundamental period of the structure

Relation between Velocity Spectrum (Sv )and Acceleration Spectrum (Sa )

Sv ≈ (T/2 π)Sa T = fundamental period of the structure

Value of horizontal peak ground acceleration = 0.6g ?

Physical meaning :Movement of the ground can cause a maximum horizontal force on a rigid structure equal to 60% of its weight

Site approximately same distance from the zone of energy release

Development of Peak/Max. AccelerationDevelopment of Peak/Max. Acceleration

Sites (Increasing order of softness)

Period (sec)(Maximum spectral acceleration)

A 0.3

B 0.5

C 0.6

D 0.8

E 1.3

F 2.5

Clay (soft): Moulded easily at natural water content and readily excavated Clay (firm): Moulded by substantial pressure at natural water content and excavated with a spadeOut of six four spectra obtained from the same city in the same EQ at a considerable distance from the epicenterTo eliminate the influence of different amplitudes of surface acceleration, plot made between period and normalized acceleration (Spectral Acceleration/Maximum Ground Acceleration

velopvelop

Clay layer : Amplified seismic shock of glacial till (Both event) Peat deposits : Amplified seismic shocks (Only for distant shock)

•Time taken for each complete cycle of oscillation is called FUNDAMETNAL NATURAL PERIOD (T) of the building•Time taken by the wave to complete one cycle of motion is called PERIOD OF EQ WAVE (0.03 to 33 seconds)•Short EQ wave have large response on short period buildings• Long EQ wave have large response on long period buildings

Building Response variation during Earthquake

•T (Inherent property of the building) depends on the building flexibility and mass,Any alteration made to the building will change its “T”• Bldg (3-5 storey); damage intensity higher in area with underlying soil cover 40-60 m thick and minimal in areas with larger thickness of soil cover•Bldg (10-14 storey); damage intensity maximum when soil cover in the range of 150-300m and small for lower thickness of soil cover•Soil plays the role of filter allowing some ground waves to pass through and filtering the rest.

Damage potential coefficient varies with building characteristics and soil depth

Relationship between building characteristics, Relationship between building characteristics, soil depth and damage potential coefficient (Ssoil depth and damage potential coefficient (Svv/k)/k)

Structure Fundamental period

Damage intensity (Dr)

2 to 3 storey 0.2 sec Remains same regardless of soil depth

4 to 5 storey 0.4 sec Max. damage intensity expected at soil depth of about 20 to 30 m

10 to 12 storey 1.0 sec Damage intensity expected to increase with soil depth up to 150 m or so

15 to 20 storey Damage intensity even greater for soil depth of 150 to 250 m & relatively low for soil depth up to 80 m or so

Liquefaction of SoilLiquefaction of SoilSoils behave like a liquid. How and why?To understand the above phenomenon:• some basics required regarding: Total stress, Pore water pressure Effective stress

Total stress, Pore water pressure and Effective Total stress, Pore water pressure and Effective stressstress

Case Total Pressure

Pore Pressure

Effective Pressure

Figure- 1 475 150 325

Figure- 2 475 250 225

Figure-1 Figure-2

Liquefaction of SoilLiquefaction of Soil

Shear strength, τ = c + σn tanø

Effective stress gives more realistic behaviour of soil,

Shear strength can be expressed as τ = c1 + (σn –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 cohesionless soil, c1= 0, hence τ = 0 Soil loose its strength because of loss of effective stress Saturated sand when subjected to ground vibration, it tends to compact and decrease in volume ; if

drainage is unable to occur, the tendency to decrease in volume results in an increase in pore water pressure and when this becomes equal to the overburden pressure effective stress becomes equal to zero, sand looses its strength completely and it develops a liquefied state.

φΦγ

Influence of soil conditions on Influence of soil conditions on liquefaction potentialliquefaction potential

Liquefaction Damage: Liquefaction Damage: 19641964 Niigata, Niigata, JapanJapan

Tokachi-oki Earthquake:Tokachi-oki Earthquake:20032003

The Damage of Sewerage StructuresThe Damage of Sewerage Structureskushiro (Town)

Lifted up manhole and gushed soil during liquefaction Lifted up manhole

The Damage of Sewerage StructuresThe Damage of Sewerage Structures

Failure ModeFailure Mode (notice : this is only concept)(notice : this is only concept)

Replaced Soil (Liquefied)

Lift-up Force

Crack or Residual Strain

Sand Boiling Sand Boiling

ManholeFlexible Pipe

Rigid Pipe

Residual Strain

Original Soil (Liquefied)

The Damage of Embankment The Damage of Embankment StructuresStructures

ToyokoroToyokoro

Collapsed EmbankmentCollapsed Embankment

Place where Embankment was collapsedPlace where Embankment was collapsed

Abashiri River Abashiri River (1)(1)

Shibetsu River Shibetsu River (6)(6)Kushiro River Kushiro River (5)(5)

Kiyomappu River Kiyomappu River (2)(2)Tokachi River Tokachi River (66)(66)

Under investigationLateral Spread was observed

( ) : the number of collapsed points

Tokachi RiverTokachi River


ToyokoroToyokoro

Liquefied SoilLiquefied Soil

Collapsed EmbankmentCollapsed Embankment


Liquefied SoilLiquefied Soil

Failure ModeFailure Mode (notice : this is only concept)(notice : this is only concept)

Liquefied Stratum

Embankment

Settlement

Land Slide

Lateral Spread


The Damage of Port Structures The Damage of Port Structures (at (at Kushiro Port)Kushiro Port)

KushiroKushiro

Settlement behind Quay WallSettlement behind Quay Wall

Trace of Sand BoilingTrace of Sand Boiling

Alaska Earthquake (Alaska Earthquake (19641964))

Caracas (Caracas (19671967))

Alaska 2002Boca del Tocuyo, Venezuela, 1989

Lateral spread at Budharmora (Lateral spread at Budharmora (Bhuj, 2001Bhuj, 2001))

Arial view of kandla port, Marked line sows ground crack and sand ejection (Gujrat Earthquake 2001)

Adverse effects of liquefactionAdverse effects of liquefaction

Most catastrophic ground failureLateral displacement of large masses of soilMass comprised of completely liquefied soil or blocks of intact material riding on a layer of liquefied soilFlow develop in loose saturated sand or silts or relatively steep slope (>3 degree)

Flow failure

Lateral SpreadLateral Spread

Lateral displacement of large superficial blocks of soil as a result of liquefaction of subsurface layerDisplacement occurs in response to combination of gravitational and inertial forces generated by an earthquake Develop on gentle slope (<3 degree) and move forward free face Displaced ground-Break up internally causing fissures, scarps etc in the form of surface failure

Ground oscillationGround oscillation

Liquefaction at depth-decouple overlaying soil layer from the underlying ground

Allowing in upper soil to oscillate back and forth and up and down in the form of ground wave

Oscillation accompanied by opening and closing of fissures and fractures of rigid structure (Pavements, Pipelines)

Loss of bearing strengthLoss of bearing strength

Large deformation occur within the soil allowing the structure to settle & tip

e.g, 1964 Niigata earthquake, Japan-Most spectacular bearing failure-Kawangishicho apartment complex, several four story building tipped as much as 60 degree

Soil conditionsSoil conditions in Areas where in Areas where LiquefactionLiquefaction has has occurredoccurred: Case Study: : Case Study: Niigata EarthquakeNiigata Earthquake

Survey of damaged structure(Liquefaction Zone)Survey of damaged structure(Liquefaction Zone)

Zone Damage Soil Characteristi

cs

Water table

Remark

A No damage (Coastal

dune area)

Dense Sand soil up to

depth of 100 ft

At great depth from

ground level

1. Type of structure:

Same2. Extent of

damage: Different

3. Reason:i) Characteristic

s of under lying sand: Different

ii) Type of foundation: Different

B Relatively light damage

(Low land area)

Medium to light Sand soil up to depth of

100 ft

Depth of water

table less than ‘A’

C Damage and Liquefaction

(Low land area)

Medium to light Sand soil up to depth of

100 ft

Depth of water

table less than ‘A’

But similar to

‘B’

Standard Penetration Resistance Test (Zone-B & C)Standard Penetration Resistance Test (Zone-B & C)

Average Penetration Resistance: Same up to 15 ft in zone B & CAverage Penetration Resistance: More below 15 ft depth in zone-B (Sand in zone-B are denser than those in zone- C)Sand below 45 ft in both zone: Relatively dense & unlikely to be involved in liquefactionConclusion: Difference in Penetration resistance of sand in depth range from 15 ft to 45 ft is responsible for the major difference in foundation and liquefaction behaviour in two zones

Soil Foundation condition and Building Soil Foundation condition and Building Performance (Zone-C)Performance (Zone-C)

Variation of Penetration resistance with depth falls within shaded area Standard Penetration Resistance: Top 25 ft: Generally less than 15 and sometimes less than 5

Classification of extent of damage for each Classification of extent of damage for each building (Zone-C) building (Zone-C)

Buildings Foundation: Supported on Shallow spread footing foundations (Number: 63)

Buildings Foundation: Supported on Piles ( 122) Extent of damage due to foundation failure:• Category-I to Category-IV Category-I:No damage to Building

(Tilt: upto 20 min, Settlement: upto 8 inch) Category-IV: Heavy damage to Building

(Tilt: upto 2.3 degree, Settlement: upto 3 ft) Conclusion: N =28 at the base of the foundation ,

required, To prevent major damage.

Relationship between depth of pile, ‘N’ of sand Relationship between depth of pile, ‘N’ of sand at pile tip and Extent of Damage (Zone-C)at pile tip and Extent of Damage (Zone-C)

Case StudyCase Study:: Gujrat Earthquake, 2001 Gujrat Earthquake, 2001

Soil Condition

S.No. Region Type of Soil

1 Ahmedabad and Surrounding region

Alluvial belt

2 Bhuj and Surrounding region

Silty sand

3 Coastal area (Kandla) Soft clay

4 South Gujrat Expansive Clay

Condition of soil before and after Condition of soil before and after earthquakeearthquake

Relative density (D) of sand with depth before and after earthquake

D vs depth of layer of three section charaterized by predominant period Tp of microseismic vibrations

Change in density observed Increase in density observed upto 5m depth from ground

surface Decrease in density from 10-15m depth from ground

surface Change in density of sand under saturation during

vibration cause for liqufaction and possible reason for large differential settlement at Ahmedabad

Damage in Zone A-Minor, Zone B- Moderate, Zone C- Heavy

Direct co-relation between quality of ground, dynamic characteristics and anticipated consequences of earthquake

Case Study: Others sitesCase Study: Others sites

Site Soil Property Standard Penetration

Mino-Owari,Tonankai and Fukui Earthquakes

D10~ 0.05 to 0.25 mmUniformity coefficient < 5

<10 (upper 30 ft)

Jaltipan Earthquake D10~ 0.01 to 0.1 mmUniformity coefficient ~2 to 10

Alaska Earthquake D10~ 0.01 to 0.1 mmUniformity coefficient ~2 to 4

< 20 to 25

What are the options for liquefaction What are the options for liquefaction mitigations?mitigations? Strengthen structures to resist predicted ground

movements (if small)

Select appropriate foundation type and depth including foundation modification of existing structure

Stabilize soil to eliminate the potential for liquefaction or to control its effects

Counter measures against LiquefactionCounter measures against Liquefaction

Densification Vibrofloatation Blasting Stabilization of soils Filtration (drainage) Lowering of Ground water Table Application of dead weight Mitigation of lateral flow by providing baffle walls

Uttarkashi Earthquake, 1991Uttarkashi Earthquake, 1991

Site: National Highway (NH-58)at Byasi (30 km from Rishkesh towards Badrinath in Garhwal Himalaya): Agency: BRO

Geo-synthetic Retaining Wall (Height-11m, Length- 19.5 m)

Location of Existing Retaining Wall of the area

Cross-section(Retaining Geogrid Reinforced Cross-section(Retaining Geogrid Reinforced

cohesionless backfill)cohesionless backfill)

Field Performance of wallField Performance of wall

4 O.P. Fixed in the Wall: To monitor the lateral movement of wall top away from backfill using Electronic Distance Meter for a period of 36 months

Average Lateral Deflection of wall with Average Lateral Deflection of wall with timetime

Stable equilibrium: 700 daysMajor part of total lateral movement (60~70%) : Short span of 45 daysActive earth pressure exerted on wall due to ground shaking by Uttarkashi earth quake 1991Cost: 79% of the cost of retaining wall with conventional earth fill

Hyogoken Nambu Earthquake Hyogoken Nambu Earthquake 19951995

Height of wall – 4 to 8 mConventional Retaining Wall – suffered maximum damage Geo-synthetic reinforced soil retaining wall –Performed very well (due to relatively high ductility of the wall)

Preloading for Grain Silos at city THESSALONIKI in north Greece•The continuity of settlement time curve was not upset , atleast not appreciably earthquake in 1978 •The time rate of settlement versus time curves does not show however a kink

Preloading for oil tanksPreloading for oil tanks

Site:500 km from the sea shore on a coastal alluvial Plain, 5 km south west of THESSALONIKI in Northern Greece, area moderately seismic active

Pre-loading-Aug. 1979 to June, 1980 Table: Change in the Variation caused by Pre Loading

Depth Range (Metre) SPT Resistance (Bloe/0.3m)B A

0 - 5.5 6 22

5.5 - 8.0 22 34

8.0 - 26.0 10 39 B- Before Preloading, A – After Preloading

Rokko & Port (Kobe)Rokko & Port (Kobe)

Ground improvement : Pre loading /Vertical drain/Sand compaction pile

Untreated ground: N - 8 to 15 Subsidence: 30 to 100 cm. (Avg. 50) Treated ground: N - 25 or more Subsidence: less than 5 cm.

SAFETY AGAINST LIQUEFACTIONSAFETY AGAINST LIQUEFACTION

Zone Depth below ground level

‘N’ value

III, II, I Up to 5 m 15

III, II, I Up to 10 m 25

I and II (For important structure) Up to 5 m 10

I and II (For important structure) Up to 10 m 20

Liquefaction AnalysisLiquefaction Analysis

Objective: To ascertain if the soil has the ability or potential to liquefy during an earthquake

Assumption: Soil Column move horizontally as a rigid body in response to maximum horizontal acceleration amax exerted by the earthquake at ground surface

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 assuming the following:

τav = τcyc = 0.65τmax = 0.65 rd (σvo / σ’vo )(amax/g)

To felicitate liquefaction analysis, define a dimensionless parameter

CSR or SSR = τcyc / σ’vo = 0.65 rd (σvo / σ’vo )(amax/g)

CSR = Cyclic stress ratio, SSR = Seismic stress ratio

FS = Factor of safety against liquefaction = CRR/CSR

CRR= Cyclic resistance ratio

Time history of shear stress during earthquake for liquefaction analysis

Cyclic resistance ratioCyclic resistance ratio

Represents liquefaction

resistance of soil

Data used: EQ ~ 7.5,

Line represents dividing line

Three lines contain- 35, 15 or ≤ 5 % fine

Data to the left of each line indicate field liquefaction

Data to the right of each line indicate no liquefaction

FS = CRR/CSR

FS = Factor of safety against liquefaction

Foundation (Guidelines)Foundation (Guidelines) Strip foundations under masonry bearing wall Necessary to ensure bond of masonry in each row and also in all corners

and intersections. Depth of bond not less than one third the height of block.

All the individual footings or pile caps shall be connected by reinforced concrete ties at least in two direction approximately at right angles to each other or by means of reinforced concrete slabs

Footing of foundation of building or its section should be at one level. If level is different, transition of foundation from a lower level to a higher level be made in steps

Foundation of adjoining section of a building should have the same depth over a distance of not less than 1m from the joint. Steps should have a slope not more than 1:2 and height of not more than 50 cm.

Damp course of masonry wall should be made of cement mortar. Use of water proof membrane is not permitted.

For building with no basement the ties or the slab may be placed at or below the plinth level and for building with basement they may be placed at the level of basement floor

Incase of reinforced concrete slab the thickness shall not be less than (1/50)th of clear distance between the footing but not less than 10cm in any case.

The foundation with grillage on concrete pile reaching solid earth may be recommended for earthquake resistant buildings (including multistory) even when ground conditions are unfavourable

Foundation of modern building that Foundation of modern building that survived earthquakesurvived earthquake

(a) Concrete slab without piles (b) The same at deeper depth(c ) Concrete foundation grillage on wood built up piles(d) The same but with concrete piles(e) Foundation grillage suspended by bolts on concrete piles(f) 1 – Street Level; 2 – Level of compacted soil

Can Liquefaction be predicted?Can Liquefaction be predicted?

Occurrence of liquefaction can’t be predicted Possible to identify areas giving detailed information that have the

potential for liquefaction Mapping of liquefaction potential on a regional scale Maps exists for many regions in USA and Japan Liquefaction potential map: complied by superimposing a

liquefaction susceptibility map with liquefaction opportunity map liquefaction susceptibility: capacity of soil to resist liquefaction

(Controlling factor: soil type, density and water table) liquefaction opportunity: A function of the intensity of seismic

shaking or demand placed on the soil

(factor affecting opportunity: Frequency of earthquake occurrence, intensity of seismic ground shaking)

Criteria for liquefaction potential mapCriteria for liquefaction potential map

Area known to have experienced liquefaction during historic earthquakes

Area containing liquefaction susceptible material that are saturated , nearly saturated or expected to become saturated

Area having sufficient existing geotechnical data indicating the soil are potentially liquefiable

Area underlain with saturated geologically young sediments (< 1000 to 15000 year old)

Is it possible to prepare for liquefaction ?Is it possible to prepare for liquefaction ?

Possible to identify areas potentially subject to liquefaction with hazard zone map

Emphasis in terms of developing appropriate public policy or selecting mitigation technique in area of major concern

Use of hazard map by public and private owners the seriousness of expected damage and most vulnerable structure

Using this map local government could designate liquefaction potential areas, and require by ordinance, site investigation and possible mitigation techniques for properties in these area particularly underground pipes and critical transportation routes

AcknowledgementsAcknowledgements

The author wishes to gratefully acknowledge the various sources used during the preparation of this presentation which have aided and enhanced the quality either in the form of information, data, figure, photo, graph or table.

Any Question ………..

The End

Thanks for your attention

liquefaction of soil

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