earthquake hazards: effects and its mitigation

Earthquake Hazards: Effect and

its Mitigation

Dr. J. N. JhaProfessor and Head (Civil Engineering)

Guru Nanak Dev Engineering College, Ludhiana

About 500,000 quakes occur every year: About 100 are

potentially dangerous

(Magnitude> 6 on Richter Scale )

On an average 2 major quakes occur annually

(Magnitude> 8 on Richter Scale )

Very large quakes occur perhaps once in a decade:

Releases nearly all the Earth’s seismic energy

90% of the seismic energy released between 1900 &

1975 was by 10 great quakes only.

Energy released during the 2001 Bhuj (India) earthquake

is about 400 times (or more) that released by the 1945

Atom Bomb dropped on Hiroshima!!

Tectonic hazards: earthquakes

Over 40 countries are under threat from major

destructive quakes

The biggest losses occur where major quakes

coincide with concentrations of people and

structures

Kobe earthquake in the year 1999 resulted in

economic losses of US$ 200 bn

Gujarat earthquake in the year 2001 may have

affected over 100,000 people

Tectonic hazards: earthquakes

List of Major Historic Earthquakes

Year Location Deaths Magnitude

1556 China 5,30,000 8.0

1906 San Francisco 700 7.9

1960 S. Chile 2,230 9.5

1964 Alaska 131 9.2

1976 China 7,00,000 7.8

1985 Mexico City 9,500 8.1

1989 California 62 7.1

1995 Kobe 5,472 6.9

2001 Gujarat, India 16480 6.9

2004 Sumatra, Indonesia 2,30,210 9.3

2005 Pakistan 75000 7.6

2010 Haiti 46,000- 316,000 7.0

2011 Japan 15760 9.0

Some Past Earthquakes in India

7.8

8

8.2

8.4

8.6

8.8

9

9.2

9.4

9.6

1900 1920 1940 1960 1980 2000 2020

Magnitude

Year

Great (M > 8) Earthquakes Since 1900

Chile1906

List of major historic earthquakes

Where do earthquakes occur?

Source: wikipedia

Tectonic hazards: Critical issues

Seismic risk maps are not available for most of the

regions

All earthquakes do not occur along plate

boundaries

Precise prediction of earthquake (date and location

of earthquake ) not possible even today.

Vulnerability to earthquakes has increased

dramatically

More damages due to earthquake is occurring

because of increasing urbanization

Size of quake

Distance from epicenter

Depth of quake

Duration of shaking

The local geology

Meteorological

conditions

Construction

practice

Building code

enforcement

Factors determining the destructiveness of a

quake?

Earthquake damage in downtown Port-au-Prince (Source: wikimedia)

15

Major Earthquake Hazards

Ground Motion: Shaking of structures results in damage or

total collapse

Liquefaction: Happens in loose saturated cohesionless soils in

which the firm soil is converted into a fluid state which has

no shear strength and thus structures found on these soils fail

due to loss of bearing capacity of the ground

Landslides: Vibrations during earthquake trigger large slope

failures

Fire, Dust and Pollution : Indirect effect of earthquakes (large

scale damage triggered by EQ to gas pipe line and power

lines)

Tsunamis: large waves created by the instantaneous

displacement of the sea floor during submarine earthquakes

Frequency of shaking differs for different seismic waves.

High frequency body waves shake low buildings more.

Low frequency surface waves shake high buildings more.

Intensity of shaking also depends on type of subsurface material.

Unconsolidated materials amplify shaking more than rocks do.

Buildings respond differently to shaking depending on the

construction styles and materials

-Wood is more more flexible, holds up well

-Earthen materials, unreinforced concrete are very vulnerable to shaking.

Earthquake Destruction: Ground Shaking

Different Types of Waves

Arrival of Seismic waves at site

19


Collapse of Buildings

Image of Bachau in Kutch region of Gujarat after earthquake

20


Building design: Buildings that are not designed for earthquake loads suffer more

Image of a collapsed building in Ahmedabad during Bhuj earthquake

21


Causes failure of lifelines

Source: google images

22

Earthquake Destruction: Landslides

La Conchita, California- landslide and debris flow in1995Source: wikipedia

Alaska Earthquake 1964: Major landslide

25

Annual Landslide Costs

0 1 2 3 4

Japan

Italy

USA

India

China

Ex USSR

Spain

Canada

Sweden

New Zealand

Norway

Country

Annual Landslide Cost (1990 US$ Billion)

Global: US$ 10-20 Billion

Source: wikipedia

26

Earthquake Destruction: Liquefaction

Buildings founded on saturated cohesionless soils are

vulnerable – Nigata, JAPAN 1964

Source: http://www.ce.washington.edu

29


Flow failures of structures are caused by loss of strength of underlying soil

Nishinomia Bridge 1995 Kobe earthquake, Japan


Sand Boil: Ground water rushing to the surface due to liquefaction

Sand boils in Gujarat earthquake


Sand boils that erupted during the 2011 Canterbury earthquake, New Zealand.

Source: wikipedia


Lateral Spreading: Liquefaction related phenomenon

Fissures caused by lateral spreading during Haiti earthquake

Source: wikipedia


Lateral spreading in the soil beneath embankment causes the embankment to be pulled apart, producing the large crack down the center of the road.

Cracked Highway, Alaska earthquake,

1964



Liquefied soil exerts higher pressure on retaining walls,which can cause them to tilt or slide.



Increased water pressure causes collapse of dams

Source: wikipedia

36


τ = c + σn tanø

τ = c’+ (σn –u)tanø’

During an earthquake,

static pore pressure `u’ may

increase by an amount udyn

τ = c’+ [(σn – (u + udyn)]tanø’

Let us consider a situation

when u + udyn= σn, then τ = c’

In cohesionless soil, c’= 0,

hence τ = 0

Earthquake Destruction: Fire

Earthquakes sometimes cause

fire due to broken gas lines,

contributing to the loss of life

and economy.

The destruction of lifelines and

utilities make impossible for

firefighters to reach fires started and

make the situation worse

eg. 1989 Loma Prieta

1906 San Francisco

2011 Japan

Source: International Business Times

38

Earthquake Destruction: Fire

Northridge, 1994

Source: wikimedia

What is a tsunami?

Definition: a ‘gravity wave’

in the sea (or other body of

water) produced by sudden

displacement of the seafloor

and the water column above

it

Damaging tsunami waves

propagate much further than

damaging earthquake waves

Tsunami can cause

simultaneous catastrophic

losses on opposite sides of

ocean basins

soo-NAH-mee or Harbor Wave is a Japanese word: tsu means harbor & nami means wave

http://www.youtube.com/watch?v=vT07YWKvehA&feature=fvwrel

http://www.youtube.com/watch?v=vT07YWKvehA&feature=fvwrel

Tsunami Movement: ~600 mph in deep water

~250 mph in medium depth water

~35 mph in shallow water

Earthquake Destruction: Tsunami

Source: USGS public domain

53

At least 1500 (possibly ~3000) active volcanoes

Around 50 erupt annually

Over 82,000 people killed in 20th century

Two eruptions killed over 20,000

500 million people threatened

Perhaps 150 volcanoes monitored

Earthquake Destruction: Volcanoes

Etna (Sicily)Source: wikipedia

Earthquake Destruction: Volcanoes

•Geo-morphological changes are often caused by an earthquake:

e.g., movements--either vertical or horizontal--along geological

fault traces; the raising, lowering, and tilting of the ground

surface with related effects on the flow of groundwater;

•An earthquake produces a permanent displacement across the

fault.

•Once a fault has been produced, it is a weakness within the rock,

and is the likely location for future earthquakes.

•After many earthquakes, the total displacement on a large fault

may build up to many kilometers, and the length of the fault may

propagate for hundreds of kilometers.

Geo-morphological Changes

Mitigation Options

•Avoiding the hazard

•Building Earthquake resistant structures

•Ground Improvement

56

Mitigation Options: Avoiding hazard

Where the potential for failure is beyond the acceptable level and notpreventable by practical means, the locations of seismic threat can beavoided and the structures should be relocated sufficiently far awayfrom the threat.

57

Mitigation Options: Earthquake Resistant Structures

Methods to increase capacity/ Decrease demand:

•Special Construction materials•Special Foundation Techniques•Special Construction Techniques

Seismic demand should be less than the Computed capacity

‘Seismic demand’ is the effect of the earthquake on the structure.‘Computed capacity’ is the structure’s ability to resist that effectwithout failure.

58

Building Earthquake resistant structures

Affect of Architectural Features on Building during EQ

Behaviour of Brick Masonary Houses during EQ

Effect of Earth Quake on RC Building

Affect of Architectural Features on Bld during EQ

• Horizontal Movement is very large in tall building(Ht /Base)• Damaging effects are many in long buildings• Horizontal seismic force becomes excessive in case of building with large plan area (force

to be carried by column/wall)

Size of the Building

• Bld. With simple geometry in plan performs well during EQ• Bld. With U,V,H & +shape sustains significant damage• L-Shaped Building- Can be converted in simple plan into 2 rectangular block using

separation joint at the junction• column/wall carries equally distributed load in case of simple plan

Horizontal layout of the building

Vertical layout of buildings

• EQ force travels through the shortest path alongthe height of the building(Developed at different floor level of the bld.)

• Any discontinuity in this load transfer path resultsin poor performance of the bld

• Bld. With vertical set backs causes a sudden jumpin earthquake force at the level of discontinuity

• Bld. With fewer column/wall in a particular storeyor with unusually tall storey tend to damage orcollapse

Contd………

Vertical layout of buildings

• Building with open ground story tends to damage during EQ(2001 –Bhuj EQ-Ahmedabad)

• Unequal height of the column along the slope caused illeffects like twisting and damage is more in shorter column

• Building with hanging and floating column havediscontinuities in load transfer path

• Building with RCC Walls that stops at an upper level getsseverely damaged

Affect of Architectural Features on Bld during EQ

Suggestions• Architectural features detrimental to EQ response of building should be avoided.

If not, they must be minimised• In case irregular features included in building, higher level of engineering efforts is

required in structural design• Decision made at the planning stage on building configuration are very important• Building with simple architectural feature will always behave better during EQ

Behaviour of Wall• All walls if joined properly to the adjacent wall ensures

good seismic performance• Walls loaded in weak direction take advantage of the

good lateral resistance offered in their strong direction• Walls need to be tied to the roof and foundation to

reserve their overall integrity

Behaviour of Brick Masonary Houses during EQ

Box Action in Masonary Bld.• Separate block can oscillate independently and even

hammer each other (If too close during EQ)• Adequate gap required betn such blocks• Gap not necessary if horizontal projections in Bld are small• An integrally connected inclined stair case slab acts like a

cross brace betn floors• It transfers large horizontal forces at the roof and the lower

level (Area of Potential Damage)

Simple Structural Configuration required for Masonary

Building

Horizontal and Vertical Band necessary in Masonary

Building

Contd………

Strength Hierarchy

Effect of Earth Quake on RC Building

• Building to remain safe during EQ :----Column should be stronger than Beam--Foundation should be stronger than Column--Connection between beams & Column and Columns & Foundation should not fail

Reinforcement and Seismic Design

Reinforcement and

Seismic Design

Reinforcement and Seismic Design

How do Beam Column Joins in RC bld Resist EQ

EQ behaviour of Joints Three stage procedure for providing

horizontal ties in the joints

Beam and column in the open ground storey are required to be designed for 2.5 times the forces obtained from bare frame analysis

Soft Storey

Special Construction Materials

Some of the special materials:

Rubber, lead, copper, brass, aluminum, stainless steel, fibre-reinforced plastics and shape-memory alloys

These materials absorb a part of seismic energy and thereby reduces theeffect of earthquake on structure.

These materials are strategically used to modify the force–deformationresponse of structural components and/or enhance their energydissipation potential.

76

Mitigation Options: Special Construction Techniques

•Base Isolation Systems

•Energy Dissipation Systems

•Active Control Systems

Special construction techniques are adapted to reduce the seismicdemand on the superstructure by sharing the earthquake loadsthrough non-conventional structural elements.

Some of these Techniques Include:

77

Base Isolation Systems

In base-isolated systems, the superstructure is isolated

from the foundation by certain devices, which reduce the

ground motion transmitted to the structure. These devices

help decouple the superstructure from damaging

earthquake components and absorb seismic energy by

adding significant damping .

78

Passive Energy Dissipation Systems

Various Energy Dissipating Devices (EDD) are used to dissipate

the seismic energy. These devices are like ‘add-ons’ to

conventional fixed-base system, to share the seismic demand

along with primary structural members.

79

Active Control Systems

They control the seismic response through appropriate adjustments within

the structure, as the seismic excitation changes. In other words, active

control systems introduce elements of dynamism and adaptability into the

structure, thereby augmenting the capability to resist exceptional

earthquake loads.

A majority of these techniques

involve adjusting lateral strength,

stiffness and dynamic properties of

the structure during the earthquake

to reduce the structural response

80

Mitigation Options: Ground Improvement

Earthquake damage is greater in poorer soil areas, and significant life and

property losses are often associated with soil-related failures.

Buildings and lifelines located in earthquake-prone regions, especially

structures founded upon loose saturated sands, reclaimed or otherwise

created lands, and deep deposits of soft clays, are vulnerable to a variety of

earthquake-induced ground damage such as liquefaction, landslides,

settlement, and ground cracking.

Recent experiences show that engineering techniques for ground

improvement can mitigate earthquake related damage and reduce losses.

81

Mitigation Options: Ground Improvement

Fundamental approaches of Ground Improvement to mitigate earthquake

damages are either to increase capacity of soil or to decrease the

earthquake demand on the soil using several techniques.

Increasing Capacity Decreasing Demand

Soil Densification

Providing drains for rapid

dissipation of pore pressures

Grouting

Soil Reinforcement

82

Ground Improvement: Soil Densification

Soil densification techniques:

•Compaction

•Vibro-replacement (Vibroflotation & Stone Columns)

•Blasting

•Grouting

•Compaction Piles

83

Field Compaction

• Pneumatic rubber tired roller

Different types of rollers (clockwise from right):

Vibratory roller

Smooth-wheel roller

Sheepsfoot roller

84

Dynamic Compaction

- pounding the ground by a heavy weight

Suitable for granular soils and landfilles

Crater created by the impact

Pounder (Tamper)

(to be backfilled)

85

Source: http://www.geoforum.com

Dynamic Compaction

Pounder (Tamper)Mass = 5-30 tonneDrop = 10-30 m

86


Dynamic Compaction

87


Ground Densification: Vibro-Compaction

Vibro-Compaction also knows as VibroFlotation is used to densify clean, cohesionless soils. The action of the vibrator, usually accompanied by water jetting, reduces the inter-granular forces between the soil particles, allowing them to move into a denser configuration, typically achieving a relative density of 70 to 85 percent. Compaction is achieved above and below the water table.

88


vibrator makes a hole

in the weak groundhole backfilled ..and compacted Densely compacted stone

column

Vibroflotation

89


Vibroflotation

90


Ground Densification: Vibro-Compaction

91

• Generally used to improve density of silty sands-sandy gravels (non-cohesive soils)

• Makes use of dynamic/undrained loading conditions to cause liquefaction-induced settlement

• Sudden dynamic loading breaks cohesion and any cementation

• Shockwave temporarily liquefies soil layer

• Settlement occurs as excess pore water pressure approaches zero.

• Typical vertical strain between 2% and 10%

Ground Densification: Blasting

92

Aftermath of blasting

For densifying granular soils

Ground Densification: Blasting

93

Grouting is is a technique whereby a slow-flowing water/sand/cement mix is

injected under pressure into a granular soil.

The grout forms a bulb that displaces and hence densifies, the surrounding

soil.

Compaction grouting is a good option if the foundation of an existing

building requires improvement, since it is possible to inject the grout from the

side or at an inclined angle to reach beneath the building.

Jet grouting involves the injection of low viscosity liquid grout into the pore

spaces of granular soils. This creates hardened soils to replace loose

liquefiable soils.

Soil Densification: Grouting

94

Soil Densification: Compaction Grouting

Compaction Grouting uses displacement to improve ground conditions.

A highly viscous aggregate grout is pumped in stages, forming grout bulbs, which displace and densify the surrounding soils.

Used for loose soils, liquefiable Soils and collapsible Soils

95

Soil Densification: Cement Grouting

Cement Grouting, also known as Slurry Grouting, is the intrusion of microfine cement slurry (fine portland cement mixed with a dispersant and larger quantities of water) into fine sand and finely cracked rock under pressure

96

Jet Grouting

Grout is pumped through the rod and exits the horizontal nozzle(s) at high velocity [approximately 200m/sec]. This energy breaks down the soil matrix and replaces it with a mixture of grout slurry and in-situ soil (soilcrete). Jet grouting is most effective in cohesionless soils.

97

Jet Grouting

98

Ground Densification: Deep soil mixing

Deep Mixing Method is the mechanical blending of the in situ soil with cementitious materials using a hollow stem auger and paddle arrangement. These materials could be Cement or Fly ash or Ground Blast Furnace Slag or Lime or Additives or Combination of these. Soil mixing has the ability to strengthen soft and wet cohesive soils in a very short time period to permit many types of construction projects.

99


Ground Improvement: Vertical Drains

The installation of prefabricated vertical drains provides shortened drainage paths for the water to exit the soil. Drainage remediation methods mitigate liquefaction hazards by enhancing the rate of excess pore pressure dissipation. The most common methods of drainage remediation are through the use of gravel, sand or wick drains. Drains are suitable for silts or clays.

100


Ground Improvement: Vertical Drains

Primary consolidation settlement will already be achieved during the construction period by using vertical drains

101

Earthquake drains

102

Earthquake DrainsSM

Earthquake Drains are prefabricated in the field to project specifications. The drain is fitted with a sacrificial

endplate. The completed drains are fed into the installation mandrel and driven to treatment depth. When the

mandrel is withdrawn, the endplate anchors in the soil leaving the drain in-place. 103

Earthquake Drains

• Dissipates excess pore pressures as they generate during a

seismic event

• Can be used to retrofit existing structures

• approximately one third the cost of traditional stone

columns

• installation times approximately one third to one half of

that for stone columns.

104

Earthquake drains

FINS: Transmit vibratory

motion to the soil for

densification

STEEL CASING: Protects

drain from driving stresses

PREFABRICATED

DRAIN

Figure 2.1: Cross section of casing and prefabricated drain

105

Earthquake drains

106

Earthquake drains

107Source: google images

Geosynthetic Reinforced Soil Retaining walls

Seismic wave action in GRS

Wall

Geosynthetics allow for the movement of the

earth to pass through the reinforced soil mass

similar to a wave passing through a body of

water.

Once the wave passes, the water returns to its

original state. As the wave of ground

movement passes through the soil mass, the

geosyntetic reinforcement flexes with the

movement of the earth but returns to its

prequake position

108

Performance of GRS walls during earthquakes

The wall was completed in 1992 for a total length was about 300 m. It was deformed and moved only slightly during the devastating earthquake that occurred in Japan, while more than half of the wooden houses in front

of the wall collapsed totally. This type of geogrid-reinforced soil retaining wall was broadly employed to reconstruct the damaged conventi onal type retaining walls after the earthquake since it performed so well.

Kobe , Japan - MW6.9

109

Turkey Earthquake of August 17, 1999

Mechanically stabilized earth wall within a few meters of the primary fault rupture. Although subjected to differential settlement, it suffered only minor

damage.

110

Rehabilitation of Koyna Bridge abutment in

Maharashtra, India, located on SH 78 in

seismic Zone-IV was done using geosynthetic

reinforced wall technique encapsulating the

cracked return wall.

The project was completed in the year1996 and

its performance in seismic Zone-IV, which is

vulnerable to frequent earthquake, is very

satisfactory in spite of repeated after shocks,

including recent ones

Koyna Bridge Abutment: GRS technique Employed

111

Forecasting Earthquakes: Earlier Methods

Strange Animal BehaviorStress in the rocks causes tiny hairline fractures. Cracking of the rocks emits high pitched sounds and minute vibrations imperceptible to humans but noticeable by many animals.

Unusual Weather Conditions and Clouds

A few scientists claim to have observed clouds associated with a seismic event, sometimes more than 50 days in advance of the earthquake.

Foreshocks

Foreshocks are minor tremors of the earth that precede a larger earthquake originating at approximately the same location. Unusual increase in the frequency of these foreshocks are sign for an earthquake.

Changes in water level

porosity increases or decreases with changes in strain, causing fluctuations in ground water level

112

Forecasting Earthquakes: Recent Developments

Changes in Seismic Velocities

Earthquakes are often accompanied by temporal changes in seismic wave velocities in the region

Radon Emission

Emission of radon gas as a quake precursor is recently being explored by the geophysicists for developing a worldwide seismic early warning system

The Van Method

The method is based on the detection of "seismic electric signals" (SES) via a telemetric network of conductive metal rods inserted in the ground. Researchers have claimed to be able to predict earthquakes of magnitude larger than 5 using this method.

Geodetic Measurements

Laser geodimeter measures changes in distance across the fault between points. Changes in distances may indicate a precursor to an upcoming earthquake. 113

Prediction of Earthquakes

Seismic hazard map of the San Francisco Bay Area, showing the probability of a major earthquake occurring by 2032

114Source: USGS public domain

Earthquake prediction has taken a scientific turn in late 1970s.

The first successful prediction was made in China in winter 1975 for the city of Haicheng(population about 1 million).

Scientists observed changes in land elevation and ground water levels in that region over a period of time. A regional increase in foreshocks had triggered a low-level alert.

Based on the reports from scientists, Chinese officials had ordered the evacuation of the city. On February 4, 1975, earthquake of magnitude 7.3 struck the region. Only very small fraction (2,041 people) died in this event. The number of fatalities and injuries would have exceeded 150,000 if no earthquake prediction and evacuation had been made.

First Successful Prediction

115

Acknowledgements

• The author wishes to acknowledge all the various sources used

during the preparation of this presentation which aided and

enhanced the quality either in the form of information, graph

data, figure, photo, or table.

Any Question ………..?

Thanks for your attention