Applied Soil Dynamics [GE-503A]

MSc Geotechical Engineering

Lectures # 6 and 7

by
Dr. Jahanzaib Israr
Civil Engg. Dept. – UET Lahore
Email: jisrar@uet.edu.pk
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Tentative Topics to be Covered
 Introduction to Soil Dynamics/Earthquake Engineering
◦ Basic Earth Features and Earthquake Principles
◦ Common Earthquake Effects/Damages
 Wave Propagation in Elastic Medium
◦ Idealization of Wave Propagation
◦ Amplification of Ground Motion
 Dynamic Response Analysis
◦ Introduction to Seismic Response Analysis
◦ Significance of Outcrop Motion
◦ Dynamic Response Analysis on Elastic Ground
 Dynamic Properties of Soils
◦ Element Tests (Cyclic Response of Soil)
◦ Model Tests (Shaking Table/Centrifuge)
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Tentative Topics (contd…)
 Geotechnical Earthquake Engineering
◦ Site Investigation for GEE
◦ Liquefaction Analysis
◦ Earthquake-Induced Settlements
◦ Bearing Capacity Analysis
◦ Slope Stability Analysis
◦ Retaining Wall Analysis
◦ Other GEE Analyses
(Surface Rupture, Pavements, Pipelines, Response Spectrum)
 Seismic Microzonation
 Site Improvement Methods to Mitigate Earthquake
Effects
◦ Site Improvement
◦ Foundation Alternatives

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Further Details:
 Geotechnical Earthquake Engineering (Ikuo Towhata)
 Geotechnical Earthquake Engineering Handbook (Robert W. Day)
 Geotechnical Earthquake Engineering (Steven L. Kramer)
 Principles of Soil Dynamics (Braja M. Das)
 Soil Behaviour in Earthquake Geotechnics (Kenji Ishihara)
 United States Geological Survey (USGS)
http://www.usgs.gov/natural_hazards/
 Japan Meteorological Agency (JMA)
http://www.jma.go.jp/en/quake/
 Pakistan Meteorological Department (PMD)
http://www.pakmet.com.pk/seismic/index.htm
 Journal Papers from “Soil Dynamics and Earthquake Engineering”
 Publications on Geotechnical EQ Engineering
http://www.geotechlinks.com/gee.php

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Prerequisite For This Course
 Geotechnical Engineering
 Engineering Geology
 Geophysics
 Seismology
 Structural Engineering
 Risk Analysis
and Last but not the least….
 Mathematics

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Engineering Geologist Geotechnical Engineer
 Location and nature of  Response of soil and rock
faults (Active/Inactive) materials for the design
 Historical records of earthquake
earthquakes  Determination of dynamic
 Design earthquake loading from design EQ
parameters (PGA &  Recommendations for
Magnitude) seismic design of structures

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Importance of Geotechnical Earthquake Engineering
* Current job market requires transportable skills
* Increase in worldwide seismic activities

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Course Objectives
To identify the most common problems that engineers
encounter in the field of soil dynamics or earthquake
engineering. These include,
 Seismic induced ground movements and wave propagation;
 Design of foundations for heavy or vibrating machinery;
 Analyze the changes of the bearing capacity of foundations under dynamic loads;
 The change in load capacity of deep foundations under dynamic loads;
 Analyze the changes of settlement behavior due to dynamic loads;
 Increased lateral earth pressures due to dynamic loads;
 Determine the potential for a soil to “liquefy” when subjected to dynamic loads;
 Determine the potential for collapse of earth embankments under dynamic
loads.

Our job as engineers, is to first identify the level of risk, and then
economically mitigate most of the hazards.
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1.1 Surface of the Earth
Orbital Characteristics
 Orbital period 365.256 days Average orbital speed 107,200 km/h
 Inclination 7.155° to Sun's equator

Physical Characteristics
 Mean radius 6,371.0 km (Equator: 6,378.1 km,Pole: 6,356.8 km)
 Surface area 5.10 x 1008 km2 (Land: 29.2 %, Water: 70.8 %)
 Volume 1.08×1012 km3 Mass 5.97×1024 kg Mean density 5.52 g/cm3
 Equatorial rotation velocity 1,674.4 km/h, Axial tilt 23°26'21"
 Surface temp. Min -89.2 °C, Mean 14 °C, Max 57.8 °C

Atmosphere
 Surface pressure: 101.325 kPa (MSL)
 Composition: nitrogen 78.08%, oxygen 20.95%, argon 0.93%
carbon dioxide 0.038%, water vapor ~ 1% (varies with climate)
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Earth’s Topography

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1.2 Internal Structure of the Earth
1. Continental crust
2. Oceanic crust
3. Upper mantle
4. Lower mantle
5. Outer core
6. Inner core
A: Mohorovičić discontinuity
B: Gutenberg discontinuity
C: Lehmann discontinuity

Depth Component Density

(km) Layer (g/cm3)
0–35 Crust 2.2–2.9
35–60 Upper mantle 3.4–4.4
35–2885 Mantle 3.4–5.6
2885–5155 Outer core 9.9–12.2
5155–6371 Inner core 12.8–13.1 11
 The crust is markedly separated from the mantle by a discontinuous boundary,
called the Mohorovicic discontinuity. This boundary serves an important role in
reflecting and refracting seismic waves.

 The mantle is 2,850 km thick. It is divided into the upper mantle, which is only 650
km thick, and the lower mantle which is 2,200 km thick. No earthquakes have
been recorded to originate in the lower mantle. This layer exhibits a uniform
velocity and appears to be a chemically homogeneous. The mantle has
temperatures in excess of 2,200 oC, which explains why it is in a viscous and
semi-molten state. This material behaves as a solid when subjected to a rapidly
applied stress, such as an earthquake wave. On the other hand, layer behaves
as a fluid to a long-term applied stress. The mantle has an average specific
gravity of 4 to 5.

 The mantle is separated from the core by another boundary, called the Gutenberg
discontinuity.

 The core is divided into outer and inner cores. The outer core is about 2,260
km thick, primarily made of iron with a specific gravity of 9 to 12. In the outer,
or liquid core the velocity of the S-waves drop to zero. The inner, or solid core
is about 1,220 km thick. It is very dense, with a specific gravity of about 15, made
up of both iron and nickel, with temperatures above 3,000 oC.
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1.3 Earthquake Basics
1. Continental Drift
2. Plate Tectonics
3. Plate Boundaries
4. Faults
5. The Elastic Rebound Theory
6. Seismograph
7. Earthquake Types & Common Design Terminologies
8. Seismic Waves
9. Magnitude and Intensity of Earthquake

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 1.3.1 Continental Drift
(Taylor 1910, Wegener 1915, Gubbins 1990)

Evidence of Continental
Drift

• Similar plant and animal

fossils found around
different continent shores

• Areas of maximum seismic

activity along the plate
boundaries

• Geology of ocean bottoms

is found to be very recent

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1.3.2 Plate Tectonics

 The Earth’s surface consists of a number of large intact blocks called plates.
There are six continent sized-plates: African, American, Antarctic, Australia-
Indian, Eurasian and Pacific. There are also 14 sub-continent plates, such as,
Caribbean, Philippine, etc.

 These plates move along each others boundaries which break off smaller
platelets or microplates. This deformation occurs slowly and continuously in
what is called aseismic deformation.

 However, when deformation is rapid or spasmodically, it leads to the

formation of earthquakes, and are called seismic deformation. Because these
occur at the boundaries of the plates, this is the area of concentrated
earthquake activity.

 Plate tectonics thus predicts the geometry of the plate movement (“its
kinematics”) but not the cause.

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The location of the major tectonic plates.The arrows indicate the direction
of the plate movement. 16
The dots represent the epicenters of significant earthquakes. Notice how they
are intimately related to the boundaries of the major plates.
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The cause of the plate movements is
found through a very complex analysis
of the thermo-mechanical equilibrium,
as reported by Hager in 1978. The
thermal flow between very hot core
and the very cool crust. This process
takes place through the convection
currents of the semi-molten rocks of the
mantle. The uprising hot currents help
drag the bottom of the plates in
various directions. Other effects lead
to ridge push and slab pull.

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1.3.3 Plate Boundaries
There are three types of plate boundaries:
1) Divergent or Spreading ridge boundary,
2) Convergent or Subduction zone boundary, and
3) Transform fault boundary.

1) Divergent or Spreading Ridge Boundary

In certain parts of the crust, the boundaries are moving apart at rates of 2 to
18 cm/year, due to the rise of fresh molten basalt from the underlying mantle.
Every year 3 km2 of new crust are formed.

Resulting EQs are relatively

small and occur at shallow
depths

When a divergent boundary

occurs within a continent, it
is called as rifting.
Examples:
Mid-Atlantic ridge
East African rift 19
2) Convergent or Subduction Zone Boundary

 The 3 km2 per year produced by the spreading rifts are cancelled by the loss of
crust at other areas through the process of subduction. At these points, one
plate “subducts” or plunges beneath the other plate. This happens often at the
edge of continents.
 Ocean crusts are colder and denser than continental crusts, and therefore the
ocean plate tends to go under the continental plate.
 This subduction zone is called the trench boundary. The earthquake is
generated in the sloping Benioff zone at the interface of the subducting and the
overriding plates.
 As the subducting plate sinks it becomes warmer and more ductile, and
therefore, less capable of producing earthquakes. Earthquakes have not been
recorded deeper than 700 km, thereby supporting this theory.
 Types of convergent boundaries:
◦ Oceanic-continental subduction zone
◦ Oceanic-oceanic subduction zone
◦ Continent-continent collision zone

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In terms of the seismic energy released at
subduction zones, it has been determined
that the largest earthquakes and the
majority of the total seismic energy
released during the past century have
occurred as shallow earthquakes at
subduction zone–plate boundaries
Oceanic-continental subduction zone
(Pacheco and Sykes 1992).
(e.g. Peru-Chile trench)

Oceanic-oceanic subduction zone

(e.g. Aleutian Islands)

Continent-continent collision zone

(e.g. Himalaya Mountains)

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3) Transform Fault Boundary

Transform faults occur when one plate passes laterally the other plate,
without creating or loosing surface crust. These fracture zones may be
traced by thousands of kilometers, although a small zone may produce
earthquakes. (e.g. The San Andreas fault, California)

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Once a fault has formed at a plate boundary, the
shearing resistance for continued movement of the
fault is less than the shearing resistance required to
fracture new intact rock. Thus faults at the plate
boundaries that have generated earthquakes in the
recent past are likely to produce earthquakes in the
future. This principle is the basis for the
development of seismic hazard zoning maps.
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1.3.4 Faults
A fault is defined as a fracture or a zone of fractures in rock along which
displacement has occurred. (Faults can be aseismic)
Fault Length: few meters to kilometers)
Depth: surface to 40km

The “strike” is the compass heading of a

horizontal line drawn on the fault plane.

The “dip” is measured in a direction

perpendicular to the strike and is the angle
between the inclined fault plane and a
horizontal plane (0o-90o).

The strike and dip provide a description of the orientation of the fault plane in
space. For example, a fault plane defined as N70oW 50oNE would indicate a
strike of North 70° West and a dip of 50° to the Northeast.

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Types of Faults

1) Strike-slip fault (Transform fault)

The fault movement is parallel to the
strike (e.g. San Andreas fault)

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2) Dip-slip fault
The fault movement is in the direction of dip
(perpendicular to the strike)

Fault scarp
Fault line

Footwall Hangingwall
Hangingwall Footwall
Fault plane
Normal fault: The Hangingwall moves When the horizontal component of
downward relative to the Footwall. the dip slip movement is compressive,
Normal faulting is associated with tensile a reverse fault takes place.
stresses in the crust and results in the This results in a horizontal shortening
horizontal lengthening of the crust. of the crust.
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Thrust fault: Oblique-slip fault:
When the dip of a reverse fault When a fault experiences slip in
is less than or equal to 45o. both dip and strike directions.

Active faults:
Faults that have moved in the "recent" geologic past (i.e., during last
11,000 years), or that have a certain average slip rate per year (i.e., 1 mm/year).
This definition, in terms of age or slip rate can vary, depending upon the specific
project and/or the governing agency.

Inactive or dead faults:

Faults that have not moved in the recent geologic past and are
judged to no longer be capable of producing earthquakes.
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Example Problems
Example-1
The engineering geologist has determined that a fault plane is oriented 5NW 34W.
The engineering geologist also discovered a fault scarp, and based on a trench
excavated across the scarp, the hangingwall block has moved upward with respect
to the footwall block. In addition, the surface faulting appears to have occurred
solely in the dip direction. Based on this data, determine the type of fault.

Example-2
Based on the displacement
of rock strata shown in the
figure, what type of fault is
it?

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1.3.5 The Elastic Rebound Theory
High precision GPS instrumentation is now permitting the recording of tiny
movements along fault lines.
The California Division of Mines and Geology has recorded the shortening
movements of chords 17and 19, lengthening of 20 and 23. Chord 21 has not moved.

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As the plates move against each other, shear stresses increase and are stored as
elastic strain energy in the rocks at the boundaries. When the shear stress
reaches the value of the shear strength, the rock fails and the accumulated strain
energy is released.

What happens when the strain energy is released depends on the rock?

If the rock is weak and ductile, the strain energy is released slowly and the fault
movement occurs aseismically.

If the rock is strong and brittle, the failure occurs rapidly. The rapid release of the strain
energy forms heat and stress waves (an earthquake)!

The study of this process is called the theory of elastic rebound,

and was proposed originally by Reid in 1911.
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1.3.6 Seismograph
Most earthquakes are caused by the release of energy due to sudden
displacements on faults. The major earthquake is characterized by the buildup of
stress and then the sudden release of this stress as the fault ruptures.

A seismograph is an instrument that records, as a function of time, the motion of the

earth’s surface due to the seismic waves generated by the earthquake. The actual
record of ground shaking from the seismograph, known as a seismogram, can
provide information about the nature of the earthquake.

UD

NS

EW

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An instrument that records the acceleration of the ground
during an earthquake, also commonly called an
accelerometer.

Units:
Gal (cm/s2) or as a ratio of “acceleration due to gravity, g”

Integration

Integration

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Worldwide Seismic Monitoring Network of USGS

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34
Seismic Monitoring Network of Japan
(JMA)

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Seismic Monitoring Network of Pakistan
(PMD)

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1.3.7 Types of EQ and Common Terminologies
 Plate Boundary Earthquakes
“Earthquake that occurs along a fault associated with an active plate boundary.
(e.g.The San Andreas Fault)”.
* 90% of the world’s earthquakes occur along plate boundaries.
* Frequent occurrence, relatively well understood behavior, as per plate tectonic
theory.
Subduction zone earthquake - type of plate-boundary EQ
These earthquakes typically located very deep (up to 600 km depth recorded).
Some of world's largest earthquakes are of this type.
(e.g. The 1985 Mexico City Earthquake)

 Intra-Plate Earthquake
“Earthquake that occurs along a fault within the stable region of a plate's interior”.
* Infrequent occurrence, often poorly understood.
* There are many uncertainties about intra-plate earthquakes. The causative faults
for historical intra-plate earthquakes in the central and eastern US are typically at
depths of less than about 25 km, and involve shear failure of brittle rocks.
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Common EQ Design Terminologies
Maximum Credible Earthquake
Largest earthquake that, based on all known geologic and seismological data, can
be reasonably expected to occur in a region.

Maximum Considered Earthquake (MCE)

The maximum level of ground motion that is considered as reasonable to design building
to resist. In national codes, the MCE is defined as the ground motions with a 2% probability of
being exceeded in 50-years (2,500-yr. motion). Terminology typically used in building codes for
design.

Maximum Probable Earthquake (MPE)

Typically, the largest historical earthquake for the region. Alternatively, it is sometimes
considered the 100-year earthquake motion or the 50%/50-year earthquake.

Operating Basis Earthquake (OBE)

The earthquake for which the structure is to remain operational, and damage is
readily repairable following the event. The OBE is an event likely to occur during the lifetime
of the structure. The OBE is often defined as the motion with a 50% probability of exceedance
during the life of the structure, or sometimes. Terminology typically used in design of dams,
power plants (including nuclear), etc.
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Safe Shutdown Earthquake (SSE)
Earthquake that produces the largest motions for which a structure, its systems and
components are designed to remain functional enough to be shut down safely. SSE can be taken as
2%/50 yr (2,500 yr.) motion but not greater than OBE. Terminology typically used in design of dams,
power plants, etc.

Design Basis Earthquake (DBE)

The earthquake used for design. For the engineering design of new buildings, the DBE is
typically established by factoring the MCE motions by 2/3, or alternatively, by using a conservative
estimate of a deterministic analysis .

Safety Evaluation Earthquake (SEE)

Earthquake motion with a 2% probability of chance of occurring in 50 years (“2,500-yr.
motion”). Terminology used mainly for bridge design. “Essential” bridges are only designed for SEE,
whereas bridges deemed “critical” are designed for both the SEE & FEE. After an SEE, critical
bridges shall provide service almost immediately, and damage—including yielding of reinforcement,
concrete spalling, and limited yielding of structural steel—shall be easily repairable. Service of
“essential” bridges is recoverable and damage repairable. Service of “normal” bridges is impaired
and damage significant.

Functional Evaluation Earthquake (FEE)

Earthquake motion with a 10% probability of chance of occurring in 50 years (“500-yr.
motion”). Terminology is used mainly for design of bridges. Only used for design of bridges deemed
“critical.” Following an FEE, critical bridges shall provide immediate service and suffer negligible
damage. 39
Epicenter: Point on earth’s surface above hypocenter.

Hypocenter (or Focus): Point in earth where fault rupture actually initiates.
Intensity – oldest measure of earthquake size, based on subjective interpretation
by people who experience an earthquake.

Intensity: Oldest measure of earthquake size, based on subjective interpretation

by people who experience an earthquake.

Magnitude: Measurement of the “size” of an earthquake. Earthquake magnitude

is based on some measurement of the ground shaking by instruments.Various
scales have been used to define magnitude.

1. Shallow-focus: 0 to 70 km deep OBSERVER

(constitute about 75% of all earthquakes)

Epicentral distance
2. Intermediate-focus: 70 to 300 km deep / FOCUS

(constitute about 22% of all earthquakes) Hypocentral distance

3. Deep-focus: 300 to 700 km deep

(constitute about 3% of all earthquakes)

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Locating the Epicenter of the Earthquake

Seismic waves are measured with a seismometer. At least three seismographs

are needed to clearly define the position of the earthquake’s epicenter.
The distance d from the seismometer and the focus of the earthquake is;

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Attenuation:
Decay or reduction of earthquake energy with distance from the zone of energy
release.

Soil amplification:
Process by which ground shaking is amplified in certain earth materials. Soil
amplification is often a big problem in soft soils such as clays. In the 1985 Mexico
City and 1989 Loma Prieta, CA Earthquakes, soil amplification was responsible for
much of the damage.

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1.3.8 Seismic Waves
Earthquakes produce body waves and surface waves.
Body waves
These waves travel though the interior of the earth as p-waves (3-8Km/s) and s-waves
(2-5 Km/s).

P-waves are also known as primary, compression or longitudinal waves.

These waves involve successive compression and rarefaction of the material
through which the waves pass. Sound waves are similar to P-waves, and the
material particles travel in the same direction as the wave. Also like sound waves,
p-waves travel through both solids and fluids.

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S-waves are also known as secondary, shear or transverse waves.

They move through materials causing transverse deformations. The direction of

movement of particles is transverse to the direction of travel of the wave.
S-waves have two orthogonal components: the SV (vertical) and the SH
(horizontal).
The speed of S-waves varies with the stiffness of the material. Since fluids do not
have shear strength, S-waves can not travel through them. Earth solids are stiffest
in compression, therefore the p-waves travel faster than other waves, and are the
first to arrive at a recording station.

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Seismic Waves through interior of the Earth

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Surface-waves are the type that develop when the body waves emerge at the surface.
The two most important surface waves are the Rayleigh and the Love waves.

Rayleigh waves are the product of the interaction of p and SV waves at the Earth’s
surface, whereas Love waves (transverse shear waves) are the interaction between
SH waves with soft surface materials.

The importance of surface waves increases at distances greater than twice the
thickness of the earth’s crust. At these distances, surface waves rather than
body waves will produce the peak ground motions. 46