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AG 2211 – APPLIED GEOLOGY
III SEMESTER
E-LEARNING MATERIAL
BY,
G.KARTHIKEYAN B.E.,M.TECH.,(Ph.D)
ASSISTANT PROFESSOR
DEPARTMENT OF CIVIL ENGINEERING
NPR COLLEGE OF ENGINEERING & TECHNOLOGY
AG 2211 APPLIED GEOLOGY
3003
OBJECTIVE
At the end of this course the student shall be able to understand about geological formations, classification
and morphology of rocks, and the importance of the study of geology for civil engineers with regard to
founding structures like dams, bridges, buildings, etc. The student shall also be able to appreciate the
importance of geological formation in causing earthquakes and land slides.
UNIT I GENERAL GEOLOGY
9
Geology in Civil Engineering – Branches of geology – Earth Structures and composition – Elementary
knowledge on continental drift and plate technologies. Earth processes – Weathering – Work of rivers, wind
and sea and their engineering importance – Earthquake belts in India. Groundwater – Mode of occurrence –
prospecting – importance in civil engineering
UNIT II MINERALOGY
9
Elementary knowledge on symmetry elements of important crystallographic systems – physical properties of
minerals – study of the following rock forming minerals – Quartz family. Feldpar family, Augite, Hornblende,
Biotite, Muscovite, Calcite, Garnet – properties, behaviour and engineering significance of clay minerals –
Fundamentals of process of formation of ore minerals – Coal and petroleum – Their origin and occurrence in
India.
UNIT III PETROLOGY
9
Classification of rocks – distinction between igneous, sedimentary and metamorphic rocks. Description
occurrence, engineering properties and distribution of following rocks. Igneous rocks – Granite, Syenite,
Diorite, Gabbro, Pegmatite, Dolerite and Basalt Sedimentary rocks sandstone, Limestone, shale conglo,
Conglomerate and breccia. Metamorphic rocks. Quartizite, Marble, Slate, Phyllite, Gniess and Schist.
UNIT IV STRUCTURAL GEOLOGY AND GEOPHYSICAL METHOD
9
Attitude of beds – Outcrops – Introduction to Geological maps – study of structures – Folds, faults and joints –
Their bearing on engineering construction. Seismic and Electrical methods for Civil Engineering investigations
UNIT V GEOLOGICAL INVESTIGATIONS IN CIVIL ENGINEERING
9
Remote sensing techniques – Study of air photos and satellite images – Interpretation for Civil Engineering
projects – Geological conditions necessary for construction of Dams, Tunnels, Buildings, Road cuttings, Land
slides – Causes and preventions. Sea erosion and coastal protection.
TOTAL: 45 PERIODS
TEXT BOOKS
1. Parbin Singh, “Engineering and General Geology”, Katson Publication House, 1987.
2. Krynine and Judd, “Engineering Geology and Geotechniques”, McGraw-Hill Book Company, 1990
REFERENCES
1. Legeet, “Geology and Engineering”, McGraw-Hill Book Company 1998
2. Blyth, “Geology for Engineers”, ELBS, 1995
UNIT – I
Introduction to Course
Geo – derived from Greek word means – Earth , Logy study of .
The earth has evolved (changed) throughout its history, and will continue to evolve.
Earth – 4.6 billion years 9715469641 old, human beings have been around for only the past 2
million years.
Why study the earth
We‘re part of it. Dust to Dust. Humans have the capability to make rapid changes. All
construction from houses to roads to dams are effected by the earth and thus require some
geologic knowledge. All life depends on the earth for food and nourishment. The earth is
there everyday of our lives.
Energy and mineral resources – depend on for our lifestyle come from the earth
Geologic Hazards - Earthquakes, Volcanic eruptions , hurricanes, Landslides, - affect us any
time. A better understanding of the earth is necessary to prepare these eventualities.
Minerals – Element – substance that cannot be separated in to simpler forms of matter by
ordinary chemical means
Two or more elements – Compound
Physical properties of Minerals
Depends on – degree of aggregation , degree of Cohesion , senses, light. Magnetism, heat ,
electricity.
Properties – External appearance and internal structure, Cleavage fracture, hardness, Sp.gr ,
Tenacity, Colour, Streak, Lusture, Transparency, Fluorescence, Phosphorescence
External appearance – definite geometric shapes bounded –smooth planes – well defined
solids – Crystals.
Crystallography –study of crystals
Geology, What is it?
Geology is the study of the Earth. It includes not only the surface process which have shaped
the earth's surface, but the study of the ocean floors, and the interior of the Earth. It is not
only the study of the Earth as we see it today, but the history of the Earth as it has evolved to
its present condition.
Important point:
The Earth has evolved (changed) throughout its history, and will continue to evolve.
The Earth is about 4.6 billion years old, human beings have been around for only the
past 2 million years.
Thus, mankind has been witness to only 0.043% of Earth history.
The first multi-celled organisms appeared about 700 million years ago. Thus, organisms have
only been witness to about 15% of Earth's history.
Thus, for us to have an understanding of the earth upon which we live, we must look at
processes and structures that occur today, and interpret what must have happened in the past.
One of the major difficulties we have is with the time scale. Try to imagine 1 million years-That's 50,000 times longer than most of you have lived. It seems like a long time doesn't it?
Yet, to geologists, 1 million years is a relatively short period of time. But one thing we have
to remember when studying the earth is that things that seem like they take a long time to us,
may take only a short time to earth.
Examples:
A river deposits about 1mm of sediment (mud) each year. How thick is the mud after
100 years? -- 10 cm hardly noticeable over your lifetime.
What if the river keeps depositing that same 1 mm/yr for 10 million years? Answer
10,000 meters (6.2 miles). Things can change drastically!
Earth Materials and Processes
The materials that make up the Earth are mainly rocks (including soil, sand, silt, dust). Rocks
in turn are composed of minerals. Minerals are composed of atoms, Processes range from
those that occur rapidly to those that occur slowly Examples of slow processes
Formation of rocks
Chemical breakdown of rock to form soil (weathering
Chemical cementation of sand grains together to form rock (diagenesis)
Recrystallization to rock to form a different rock (metamorphism)
Construction of mountain ranges (tectonism)
Erosion of mountain ranges
Examples of faster processes
Beach erosion during a storm.
Construction of a volcanic cone
Landslides (avalanches)
Dust Storms
Mudflows
Processes such as these are constantly acting upon and within the Earth to change it. Many of
these processes are cyclical in nature.
Hydrologic Cycle
Rain comes from clouds - falls on surface, picks up sand, silt and clay, carries
particles to river and into ocean. Water then evaporates to become clouds, which
move over continents to rain again.
Rock Cycle
Most surface rocks started out as igneous rocks- rocks produced by crystallization from a
liquid. When igneous rocks are exposed at the surface they are subject to weathering
(chemical and mechanical processes that reduce rocks to particles). Erosion moves particles
into rivers and oceans where they are deposited to become sedimentary rocks. Sedimentary
rocks can be buried or pushed to deeper levels in the Earth, where changes in pressure and
temperature cause them to become metamorphic rocks. At high temperatures metamorphic
rocks may melt to become magmas. Magmas rise to the surface, crystallize to become
igneous rocks and the processes starts over.
External Processes
Erosion- rocks are broken down (weathered) into small fragments which are then carried by
wind, water, ice and gravity. External because erosion operates at the Earth's surface. The
energy source for this process is solar and gravitational.
Internal Processes
Processes that produce magmas, volcanoes, earthquakes and build mountain ranges. Energy
comes from the interior of the Earth, Most from radioactive decay - nuclear energy.
Principle of Uniformitarianism
Processes that are operating during the present are the same processes that have operated in
the past. i.e. the present is the key to the past. If we look at processes that occur today, we can
infer that the same processes operated in the past.
Problems:
Rates -- rates of processes may change over time for example a river might deposit 1 mm of
sediment /yr if we look at it today. but, a storm could produce higher runoff and carry more
sediment tomorrow. Another example: the internal heat of the Earth may have been greater in
the past than in the present -- rates of processes that depend on the amount of heat available
may have changed through time.
Observations -- we may not have observed in human history all possible processes.
Examples: Mt. St. Helens, Size of earthquakes.
Perhaps a better way of stating the Principle of Uniform itarianismis that the laws of nature
have not changed through time. Thus, if we understand the physical and chemical laws of
nature, these should govern all processes that have taken place in the past, are taking place in
the present, and will take place in the future.
Energy
All processes that act on or within the Earth require energy. Energy can exist in many
different forms:
Gravitational Energy -- Energy released when an object falls from higher elevations to lower
elevations.
Heat Energy -- Energy exhibited by moving atoms, the more heat energy an object has, the
higher its temperature.
Chemical Energy -- Energy released by breaking or forming chemical bonds.
Radiant Energy -- Energy carried by electromagnetic waves (light). Most of the Sun's energy
reaches the Earth in this form. Atomic Energy -- Energy stored or released in binding atoms
together. Most of the energy generated within the Earth comes from this source.
Heat Transfer
Heat Moves through material by the following modes:
Conduction - atoms vibrate against each other and these vibrations move from high
temperature areas (rapid vibrations) to low temperature areas (slower vibrations).- Heat from
Earth's interior moves through the solid crust by this mode of heat transfer.
Convection - Heat moves with the material, thus the material must be able to move. The
mantle of the Earth appears to transfer heat by this method, and heat is transferred in the
atmosphere by this mode.
Radiation - Heat moves with electromagnetic radiation (light) Heat from the Sun or from a
fire is transferred by this mode
Geothermal Gradient
Temperature and pressure increase with depth in the Earth. Near the surface of the Earth the
rate of increase in temperature (called the Geothermal Gradient) ranges from 15 to 35oC per
kilometer. Temperature at the center of the Earth is about 4500oC
The Earth -- What is it?
The Earth has a radius of about 6371 km, although it is about 22 km larger at equator than at
poles.
Internal Structure of the Earth:
Density, (mass/volume), Temperature, and Pressure increase with depth in the Earth.
Compositional Layering
Crust - variable thickness and composition
Continental 10 - 50 km thick
Oceanic 8 - 10 km thick
Mantle - 3488 km thick, made up of a rock called peridotite
Core - 2883 km radius, made up of Iron (Fe) and small amount of Nickel (Ni)
Layers of Differing Physical Properties
Lithosphere - about 100 km thick (deeper beneath continents)
Asthenosphere - about 250 km thick to depth of 350 km - solid rock, but soft and
flows easily.
Mesosphere - about 2500 km thick, solid rock, but still capable of flowing.
Outer Core - 2250 km thick, Fe and Ni, liquid
Inner core - 1230 km radius, Fe and Ni, solid
All of the above is known from the way seismic (earthquake waves) pass through the Earth as
we will discuss later in the course.
Surface Features of the Earth
Oceans cover 71 % of Earth's surface -- average depth 3.7 km. Land covers remaining surface
with average of 0.8 km above sea level
Ocean Basins
Continental Shelf, Slope, and rise
Abyssal Plains
Oceanic ridges
Oceanic Trenches
Plate Tectonics
Tectonics = movement and deformation of the crust, incorporates older theory of continental
drift.
Plates: are lithospheric plates - about 100 km thick, which move around on top of the
asthenosphere.
Plate Boundaries
Divergent Boundaries occur at Oceanic Ridges, where new Oceanic lithosphere is formed
and moves away from the ridge in opposite directions Continental rifting may create a new
divergent margin and evolve into an oceanic ridge, such as is occurring in East Africa and
between the African Plate and the Arabian Plate.
Convergent Boundaries occur where oceanic lithosphere is pushed back into the mantle,
marked by oceanic trenches and subduction zones. Two types are possible When two plates of oceanic lithosphere converge oceanic lithosphere is subducted beneath
oceanic lithosphere.
When ocean lithosphere runs into a plate with continental lithosphere, the oceanic lithosphere
is subducted beneath the continental lithosphere.
Continental Collisions: may occur at a convergent boundary when plates of continental
lithosphere collide to join two plates together, such as has occurred recently where the Indian
Plate has collided with the Eurasian Plate to form the Himalaya Mountains. Transform
Boundaries occur where two plates slide past one another horizontally. The San Andreas
Fault, in California is a transform fault.
Plate tectonics explains why earthquakes occur where they do, why volcanoes occur where
they do, how mountain ranges form, as well as many other aspects of the Earth. It is such an
important theory in understanding how the Earth works that we cover it briefly here, but will
return for a better understanding of later in the course.
Groundwater
Groundwater is water that exists in the pore spaces and fractures in rock and sediment
beneath
the Earth's surface. It originates as rainfall or snow, and then moves through the soil into the
groundwater system, where it eventually makes its way back to surface streams, lakes, or
oceans.
Groundwater makes up about 1% of the water on Earth (most water is in oceans).
But, groundwater makes up about 35 times the amount of water in lakes and streams.
Groundwater occurs everywhere beneath the Earth's surface, but is usually restricted to
depths less that about 750 meters.
The volume of groundwater is a equivalent to a 55 meter thick layer spread out over the
entire surface of the Earth.
The surface below which all rocks are saturated with groundwater is the water table.
The Water Table
Rain that falls on the surface
seeps down through the soil
and into a zone called the zone
of aeration or unsaturated
zonewhere most of the pore
spaces are filled with air. As it
penetrates deeper it eventually
enters a zone where all pore
spaces and fractures are filled
with water. This zone is called
thesaturated zone. The surface
below which all openings in
the rock are filled with water
(the top of the saturated zone)
is called the water table.
The water table occurs everywhere beneath the Earth's surface. In desert regions it is always
present, but rarely intersects the surface.
In more humid regions it reaches the surface at streams
and lakes, and generally tends
to follow surface topography.
The depth to the water table
may change, however, as the
amount of water flowing into
and out of the saturated zone
changes. During dry seasons,
the depth to the water table
increases. During wet seasons,
the depth to the water table
decreases.
Movement of Groundwater
Groundwater is in constant motion, although the rate at which it moves is generally slower
than
it would move in a stream because it must pass through the intricate passageways between
free
space in the rock. First the groundwater moves downward due to the pull of gravity. But it
can
also move upward because it will flow from higher pressure areas to lower pressure areas, as
can be seen by a simple experiment illustrated below. Imagine that we have a "U"-shaped
tube
filled with water. If we put pressure on one side of the tube, the water level on the other side
rises, thus the water moves from high pressure zones to low pressure zones.
The same thing happens beneath the surface of the Earth, where pressure is higher beneath
the
hills and lower beneath the valleys
Groundwat
The rate of groundwater flow is controlled by two properties of the rock: porosity and
permeability.
Porosity is the percentage of the volume of the rock that is open space (pore space). This
determines the amount of water that a rock can contain.
In sediments or sedimentary rocks the porosity depends on grain size, the shapes of
the grains, and the degree of sorting, and the degree of cementation.
Well-rounded coarsegrained sediments usually have higher porosity than finegrained ,
because the grains do
not fit together well.
Poorly sorted sediments usually have lower
porosity because the fine-grained fragments tend
to fill in the open space.
Since cements tend to fill in the pore
space, highly cemented sedimentary
rocks have lower porosity.
In igneous and metamorphic rocks porosity is usually
low because the minerals tend to be intergrown,
leaving little free space. Highly fractured igneous and
metamorphic rocks, however, could have high
porosity
Permeability is a measure of the degree to which the pore spaces are interconnected, and
the size of the interconnections. Low porosity usually results in low permeability, but
Groundwater
high porosity does not necessarily imply high permeability. It is possible to have a highly
porous rock with little or no interconnections between pores. A good example of a rock
with high porosity and low permeability is a vesicular volcanic rock, where the bubbles
that once contained gas give the rock a high porosity, but since these holes are not
connected to one another the rock has low permeability.
A thin layer of water will always
be attracted to mineral grains due to the unsatisfied ionic charge on
the surface. This is called the force
of molecular attraction. If the size
of interconnections is not as large
as the zone of molecular attraction,
the water can't move. Thus, coarse-grained
rocks are usually more
Permeable than fine-grained rocks,
and sands are more permeable than
clays.
Movement in the Zone of Aeration
Rainwater soaks into the soil where some of it is evaporated, some of it adheres to grains in
thesoil by molecular attraction, some is absorbed by plant roots, and some seeps down into
the saturated zone. During long periods without rain the zone of aeration may remain dry.
Movement in the Saturated Zone
In the saturated zone (below the water table) water percolates through the interconnected pore
spaces, moving downward by the force of gravity, and upward toward zones of lower
pressure.Where the water table intersects the surface, such as at a surface stream, lake, or
swamp, the groundwater returns to the surface.
Recharge Areas and Discharge Areas
The Earth's surface can be divided into areas
where some of the water falling on the surface
seeps into the saturated zone and other areas
where water flows out of the saturated zone
onto the surface. Areas where water enters the
saturated zone are called recharge areas,
because the saturated zone is recharged with
groundwater beneath these areas. Areas where
groundwater reaches the surface (lakes,
streams, swamps, & springs) are called
discharge areas, because the water is
discharged from the saturated zone. Generally,
recharge areas are greater than discharge
areas.
Groundwater
Page 4 of 8 10/20/2003
Discharge and Velocity
The rate at which groundwater
moves through the saturated
zone depends on the
permeability of the rock and
thehydraulic gradient. The
hydraulic gradient is defined
as the difference in elevation
divided by the distance between two points on the
water table.
Velocity, V, is then:
V = K(h2 - h1)/L
where K is the coefficient of permeability.
If we multiply this expression by the area, A, through which the water is moving, then we get
the discharge, Q.
Q = AK(h2 - h1)/L,
which is Darcy's Law.
Springs and Wells
A spring is an area on the surface of the Earth where the water table intersects the surface
and water flows out of the ground. Springs occur when an impermeable rock (called an
aquiclude) intersects an permeable rock that contains groundwater (an aquifer). Such
juxtaposition between permeable and impermeable rock can occur along geological
contacts (surfaces separating two bodies of rock), and fault zones.
A well is human-made hole that is dug or drilled deep enough to intersect the water table.
Wells are usually used as a source for groundwater. If the well is dug beneath the water
table, water will fill the open space to the level of the water table, and can be drawn out
by a bucket or by pumping. Fracture systems and perched water bodies can often make it
Groundwater
Page 5 of 8 10/20/2003
difficult to locate the best site for a well.
Aquifers
An aquifer is a large body of permeable material where groundwater is present in the
saturated
zone. Good aquifers are those with high permeability such as poorly cemented sands, gravels,
and sandstones or highly fractured rock. Large aquifers can be excellent sources of water for
human usage such as the High Plains Aquifer (in sands and gravels) or the Floridian Aquifer
(in porous limestones) as outlined in your text. Aquifers can be of two types:
Unconfined Aquifers - the most common type of aquifer, where the water table is
exposed to the Earth's atmosphere through the zone of aeration. Most of the aquifers
depicted in the drawings so far have been unconfined aquifers.
Confined Aquifers - these are less common, but occur when an aquifer is confined
between layers of impermeable strata. A special kind of confined aquifer is an artesian
system, shown below. Artesian systems are desirable because they result in free flowing
artesian springs and artesian wells.
Changes in the Groundwater System
When discharge of groundwater exceeds recharge of the system, several adverse effects can
occur. Most common is lowering of the water table, resulting in springs drying up and wells
having to be dug to deeper levels. If water is pumped out of an aquifer, pore pressure can be
reduced in the aquifer that could result in compaction of the now dry aquifer and result in
land
subsidence. In some cases withdrawal of groundwater exceeds recharge by natural processes,
and thus groundwater should be considered a non-renewable natural resource.
Groundwater
Page 6 of 8 10/20/2003
Water Quality and Groundwater Contamination
Water quality refers to such things as the temperature of the water, the amount of dissolved
solids, and lack of toxic and biological pollutants. Water that contains a high amount of
dissolved material through the action of chemical weathering can have a bitter taste, and is
commonly referred to as hard water. Hot water can occur if water comes from a deep source
orencounters a cooling magma body on its traverse through the groundwater system. Such hot
water may desirable for bath houses or geothermal energy, but is not usually desirable for
human consumption or agricultural purposes. Most pollution of groundwater is the result of
biological activity, much of it human. Among the sources of contamination are:
 Sewers and septic tanks
 Waste dumps (both industrial and residential)
 Gasoline Tanks (like occur beneath all service stations)
 Biological waste products- Biological contaminants can be removed from the
groundwater by natural processes if the aquifer has interconnections between pores that
are smaller than the microbes. For example a sandy aquifer may act as a filter for
biological contaminants.
 Agricultural pollutants such as fertilizers and pesticides.
 Salt water contamination- results from excessive discharge of fresh groundwater in
coastal areas.
Groundwater
Geologic Activity of Groundwater
Dissolution - Recall that water is the main agent of chemical weathering. Groundwater isan
active weathering agent and can leach ions from rock, and, in the case of carbonate
rocks like limestone, can completely dissolve the rock.
Chemical Cementation and Replacement - Water is also the main agent acting during
diagenesis. It carries in dissolved ions which can precipitate to form chemical cements
that hold sedimentary rocks together. Groundwater can also replace other molecules in
matter on a molecule by molecule basis, often preserving the original structure such as in
fossilization or petrified wood.
Caves and Caverns - If
large areas of limestone
underground are dissolved
by the action of
groundwater these cavities
can become caves or
caverns (caves with many
interconnected chambers)
once the water table is
lowered. Once a cave forms, it is open to the atmosphere and water percolating in can
precipitate new material such as the common cave decorations like stalagtites (hang from
the ceiling), stalagmites (grow from the floor upward), and dripstones, and flowstones.
Sinkholes - If the roof of a cave or cavern
collapses, this results in a sinkhole.
Sinkholes, likes caves, are common in areas
underlain by limestones. For example, in
Florida, which is underlain by limestones, a
new sinkhole forms about once each year,
gobbling up cars and houses in process.
Karst Topography - In an area where the main type of weathering is dissolution (like in
limestone terrains), the formation of caves and sinkholes, and their collapse and
coalescence may result in a highly irregular topography called karst topography (see
pages 404 - 406 in your text).
Groundwater
EARTHQUAKES AND THEIR STUDY
Most of us must have personally experienced earthquakes, and are, therefore, aware of them.
Earthquake is something which causes the shaking of the Earth ; and as such, all our
buildings and structures erected on the Earth's surface start trembling, as and when a quake
comes. An earthquake, is therefore, defined as a natural vibration of the ground (or the
Earth's crust) produced by forces, called earthquake forces or seismic forces.
Many the these vibrations are very feeble, and may not even be felt to any appreciable extent,
by human beings. Some other vibrations, however, may be very severe, and may cause the
collapse and rupture of buildings and other structures, bringing large scale destruction and
disaster in its wake.
Before we discuss the various possible causes of earthquakes in our next article, we shall like
to define two very important technical terms that are associated with earthquakes. These
terms are focus and epicentre.
The focus is the place beneath the Earth's surface from where an earthquake originates, and
the point or line on the Earths' surface immediately above the focus is called the epicentreor
epicentral line (Refer Fig. 6.6). The focus is also sometimes termed as seismic centre. The
point which is diametrically opposite to the epicentre is called anticentre.
In fact, the term epicentre is important as it represents the point on the Earth, where the
earthquake waves reach for the first time, after they are generated from the focus. The area
around the epicentre will be subjected to earthquake vibrations, and is generally indicated as
epicentral area.
Earthquake foci are generally distributed in three general depth ranges. Shallow earthquakes
originate within about 60 kilometres of the surface ; Intermediate earthquakes have foci
between 60 to 300 kilometres down; and the Deep seated earthquakes originate at depths
below 300 kilometres, or so. The deepest focus ever recorded was about 700 kilometres. In
the case of shallow focus, the area affected is smaller compared to that in a deeper focus ; this
is because, in the latter case, the earthquake waves assume a wider dispersion. The deep focus
earthquakes are generally very rare: and most of the million earthquakes occurring in a year
are, generally shallow. Nevertheless, it is generally difficult to know the focus quite
accurately, and therefore, most frequently, only epicentral area is indicated. The shallow
earthquakes which originate at depths up to about 35 km are generally more damaging than
the others.
Causes of Earthquakes and Their Types:
Our ancestors used to believe that the earthquakes were the manifestations of God's wrath.
The first nearly scientific approach to find out a suitable cause for an earthquake was made
by our philospher Aristotle (384—322 B.C.), the Einstein of his days, who explained that
earthquakes were the result of entrapped air escaping from the Earth's interior. Modern
earthquake theories are, however, based on factual data and study of actual earthquakes of the
world.
Depending upon the possible cause of an earthquake, earthquakes are now-a-days generally
classified into two categories, i.e.
(1) Tectonic earthquakes ; and
(2) Non-tectonic earthquakes.
The Tectonic Earthquakes:
The tectonic earthquakes are perhaps caused by the slippage or movement of the rock masses
along a rupture or break called a fault. These are generally very severe, and the area affected
is often very large. The non-tectonic type of earthquakes include earthquakes caused by a
number of easily understandable processes, such as ; volcanic.eruptions; superficial
movements like landslides ; subsidence of the ground below the surface, etc. All such
processes may introduce vibrations into the ground by jerks, etc.
There is, thus, not much controversy on the possible causes of non-tectonic earthquakes.
However, nothing can be said with absolute certainty regarding the origin of the tectonic
earthquakes. Most probably, as pointed out above, these tectonic earthquakes are caused by
the occasional movements of the crustal blocks along the fractured planes, called the faults.
Faulting is a phenomenon which has been found associated with most of
the severe earthquakes of the world. As such, it can generally be considered as the immediate
cause of many tectonic earthquakes. Whether "faulting is due to earthquakes" or "earthquakes
are due to faulting" is infact among the most complicated geological problems that still await
perfect solution.
The modern well known Elastic rebound theory explains as to how faulting takes place, and
how it leads to earthquakes. However, this theory does not account for the force which
produced faulting, but it explains only the manner in which the rocks yield to these forces.
Ultimately, it may be added that these unknown tectonic forces which cause faulting are the
same as those which produce fold mountains and other structural features of the Earths' crust.
The elastic rebound theory is explained below :
The Elastic Rebound Theory. According to this theory, the rocks of the Earths' crust like
any other elastic solid, would undergo elastic deformation* when subjected to unequal
frictional forces or stresses (either compression or tension). But this deformation is possible
only up to a certain limit, i.e. till the breaking point or elastic limit* is reached. As and when
the stress exceeds the frictional resistance of the rock block, it will break, producing rupture
in the rock. This rupture takes the form of faulting, when the rupture is produced by a stress
which was building up rapidly ; and then there occurs a relative movement on either side of
the plane of rupture. Such movements always involve sudden release of enormous amount of
elastic energy (which was stored in the folded rocks) making it possible for the rock block to
acquire new positions of least strain. where all the three stages have been explained quite
clearly). The elastic energy so released may produce powerful seismic waves, which travel in
all directions from the place of faulting, and which induce shaking movements in material
through which they travel, thus producing earthquake shocks.
*When a solid like rubber, wooden Stick, rock blocks, etc. is squeezed (by compression) or
stretched (by tension) it deforms according to certain physical laws which depend on the
inherent properties of the solid itself. The squeezing or stretching force on a unit is called a
stress, and the deformation of the solid yielding to the stress is called strain. Elastic materials
are those in which stress is directly proportional to the strain. Thus, a rubber band if stretched
to twice its original length (L) required a pull equal to say P, then a pull equal to 2P and 3P
respectively will be required to produce a stretching equal to twice or thrice of its original
length. But the band cannot be stretched indefinitely because eventually it will break. This
limiting point is called elastic limit, and the earlier * deformation is called elastic
deformation. When the force or stress exceeds the elastic limit, the solid continues to deform
without any additional stress. Such deformation is called plastic deformation, The stress
value where deformation changes from elastic to plastic, is called yield point. Ultimately with
plastic deformation, the solid ruptures or breaks. Moreover, it has been found by experiments
that in some solids, like rocks, if the stress is applied very slowly, the material will deform
plastically at stress values far below the "normal yield point". But when the stress in built up
rapidly, the material ruptures or breaks shortly after the yield point is reached. This explains
as why rocks will be folded under certain conditions and faulted under others.
This theory, thus, explains to some good enough extent, as to how tectonic earthquakes do
occur. Tectonic earthquakes are quite common; and here in India, all the earthquakes are
generally of this nature.
Earthquake Waves, Their Recording and Types:
The energy released during faulting, produces seismic waves, which can be detected by
sensitive and delicate instruments, called seismographs, installed at specially designed
seismographic stations. The record of seismic waves is called seismogram.
By the study of a lot of such data collected on various actual earthquakes of the world, it has
now become possible to differentiate between different types of waves that are generated in
an earthquake.
Basically, two classes of waves are produced during an earthquake. One group, called the
body waves (consisting of P-waves and S-waves), travels downward into the Earth; whereas,
the other group, called the surface waves (popularly called L-waves), travels along the
surface of the Earth's crust. Since it is only the L waves that pass through the Earth's surface,
the entire destruction] caused during an earthquake will be caused by these L-waves only.
The other kinds of waves (i. e. P and S waves) are helpful in detecting the origin and
epicentre of an earthquake, and for estimating the interior of the earth*.
All these three types of waves obey the laws of reflection and refraction, as they pass
through, the Earth's materials of varying density. The P and S waves, though move towards
the interior of the Earth, yet some of the wave energy is reflected upward to the surface by
certain underlying layers, and thus recorded by the seismographs—located at different
distances from the shot point (i.e. the focus).
A brief description of these waves is given below:
P-Waves (i.e. Primary Waves).The P-waves are com-pressional in nature, and travel like
sound waves. The particles thus vibrate in longitudinal direction (i.e. in the direction of
propagation of the waves) with a push and pull* effect, and these waves are, therefore, also
called as longitudinal waves or compressipnal waves or push and pull waves. The velocity of
such a wave depends upon the resistance of a medium to compression, and hence they travel
with greater velocities in rocks which are rigid, compact and dense.
The P-waves are the fastest of all the three types ; and are, therefore, first to be reached at the
seismograph stations (Refer Fig, 6.8). Also they are capable of passing through solids, liquids
as Well as gases.
S-waves (i.e. Secondary Waves).These waves are transverse or distortional like those of light
waves. The particles, therefore, travel in a direction at right angles (i.e. transverse) to the
direction of propagation of the wave. The velocity of S-wave is controlled by the resistance
of a medium to shear. Due to this reason, these waves, though capable of passing through
solids, yet cannot pass through liquids, as liquids donot have any distortional elasticity. These
waves travel slower than the P-waves, and are second to be recorded at the seismographic
stations (Refer Fig, 6.8).
L-waves (Le. Long Waves).These waves travel alongthe Earth's surface, following a
circumferential path. They are also called surface waves, because their journey is confined
only to the surface layers of the Earth. In other Words, they do not travel towards the interior
of the Earth from the point of origin of disturbance.
The behaviour of these waves is similar to that of sea waves. One type of L-waves involves
both vertical and horizontal motions ; whereas another type involves only horizontal motions.
These waves are the slowest to travel, and therefore, reach in the last at the seismographic
stations (Refer Fig. 6.8). These waves are responsible for causing all the damage done on the
surface by an earthquake.
Travel Time Curves and Locating the Epicentre
The distance from a seismograph station to the place of origin of an earthquake can be
determined by the time interval between the arrivals of the first P and S waves. The more
distant the earthquake's focus, the longer is the S.P. interval. This is somewhat similar to a
type of problem in which two cars start together and move down the same road at constant
rates, of say 40 km/hr and 30 km/hr, respectively. The faster car will, therefore, arrive at a
station first, and if it arrives say 6 hrs ahead of the slower car, then eventually one can easily
calculate that they have travelled a distance of 720 km.*
It, thus, follows that the distance of focus from the recording station depends upon the S.P
interval. Moreover, since the epicentre of an earthquake is the immediate vertical reflection
of its focus, the S.P. interval will also, in the same way, depend upon the distance of the
station from the epicentre(i.e. the epicentral distance). The greater is the S-P interval, the
larger is this distance.
By a study of the records of a number of past earthquakes in a given region, scientists have
been able to plot certain curves called the travel-time curves, such as shown in Fig. 6.9. Such
travel time curves can be used to analyse a future earthquake in the given region, and thus to
determine its epicentre and depth of focus, etc.
Locating the Epicentre by Three Circle Method.
In this method, standard tables or travel time curves, relating the epicentral distance (i.e. the
distance of the epicentre from the seismograph station) with the S.P. interval are used. The SP interval at a station being known, the epicentral distance is known. However, by analysing
the record of a single seismograph station, although we can know the epicentral distance, but
we cannot ascertain its location as the direction of this is not known. This job of locating the
epicentre can be completed easily, provided such records are available from atleast three
seismological stations. These stations should, of course, be conveniently located. By knowing
the S-P intervals for the same earthquake at these three different stations, we can find out the
three corresponding
values of the 'epicentral distance'. With each of the three stations marked on a map or a globe,
three circles, can be drawn with radii equal to the epicentral distance of each, and the point of
inter-section will represent the epicentre (Refer Fig. 6.10).
To illustrate, let us suppose that a particular earthquake was recorded at three widely
separated seismograph stations A, B and C, as marked on a map or globe. The S-P interval
recorded at these three stations was, say, 15 seconds, 20 seconds and 30 seconds,
respectively. The respective corresponding epicentral distances from these stations are now
worked out from standard tables or curves, as say 130 km, 160 km and 240 km. Now, with A,
B and C as centres and the respective distances as radii (i.e. 130, 160 and 240 km), circles are
drawn on the map to the given scale. The epicentre is finally located at the point of intersection of the three circles, say at point E (Refer Fig. 6.10).
Seismographs or Seismometers
As stated earlier, a seismograph is an instrument which receives and records the earthquakes
waves. Different designs have been prepared for seismographs. A seismograph may be
designed to record only the horizontal motion of the ground, or only the vertical motion of
the ground, or both. Moreover, the seismographs may be provided with ordinary paper and
pencil device for recording the waves, or may be provided with photographic papers which
may record the waves under dark room conditions by using a thin beam of light reflected
through a mirror ; or may be electronised or computerised in the advance stages.
Ordinarily, a good seismological station would generally have two horizontal seismographs
mounted at right angles (usually one to record the North-South horizontal movements, and
the other to record the East-West horizontal movements), and one vertical instrument to
record the vertical movements of the ground. These three seismographs can give a complete
picture of the ground motions in three directions.
Even today, simple pendulum type seismographs are used quite frequently, although a lot of
improved electronised and computerised systems have been developed. The essential part of
such a seismograph is a pendulum (or heavy weight), which normally remains at rest, but
starts swinging either horizontally (to and fro) or vertically (up and down) during an
earthquake. Moreover, the horizontal motion of the ground may be recorded either by a
pendulum which swings in a vertical plane, or by a pendulum which swings in a horizontal
plane.
A simplest type of a seismometer is shown in Fig. 6.11. It uses a heavy mass (m) as a
pendulum suspended from the top, as shown. The mass of the pendulum tends to stand still,
as the supporting frame moves during the horizontal motion of the ground, caused by an
earthquake. As the ground and frame moves to one side, gravity pulls on such a pendulum,
and the pendulum tends to follow the motion of the ground, and to continue to swing after the
ground comes to rest. This horizontal motion of the ground can, thus, be recorded by
observing the relative position of a pointer on the mass and a scale attached to the ground, as
shown.
This particular arrangement (Fig. 6.11) will record the horizontal motion of the ground by a
pendulum which swings horizontally (i.e. to and fro), but in a vertical plane. A better system
for earthquake observations is obtained by swinging the pendulum in a horizontal or nearly
horizontal plane instead of a vertical plane, as shown in Fig. 6.12 (a).
When the pendulum swings in a horizontal plane and about a vertical axis [Fig. 6.12 (a)], it
has no tendency to return to any particular position. But, if the plane is
slightly tilted, the pendulum will be acted upon by a small component of gravity, and if
deflected, it will return slowly to its original position Damping is easily provided by a plate
attached to the mass and extending into a cup of Oil on the ground. Such a horizontal
pendulum is the basic principle of most earthquake seismometers, whether recording
horizontal ground motion, or vertical ground motion.
In order to make the seismometer indicate the ground motion accurately, it is necessary that
the rate at which the pendulum returns to its rest position, is very slow, which means that the
natural period of oscillation of the pendulum must be long. The seismometer indicates clearly
only those ground oscillations that have periods shorter than the natural pendulum period. If
the period of the ground motion is longer than that of the pendulum, the inertial mass tends to
move the ground, and motion is not accurately indicated.
Vertical motion of the ground can be detected by swinging the pendulum in a horizontal
plane about a horizontal axis (i.e. the pendulum moving up and down about the horizontal
axis), as shown in Fig. 6.12 (b). The pendulum, in such a case, is supported against gravity by
a spring. A long weak spring can be used to keep the natural period of the pendulum long, or
the spring can be adjusted so that it tends to increase, whenever relative movement of the
ground and inertial mass occurs. A diagonal spring, such as shown in Fig. 6.12 (b), is the
commonest type. In this case, when the ground rises, the angle 9 decreases, and althought the
spring is stretched, the restoring moment about the axis of rotation of pendulum is increased
very little. Similarly, if the ground drops, although the length of the spring and hence its
tension decreases, 0 increases, preventing a large decrease in the torque of the spring. A small
restoring moment, thus, results in a long period of oscillation, and high sensitivity to the
ground motion.
In order to obtain a permanent record of the ground motion with time, etc., it is,.necessary to
attach some sort of recording arrangement with the pendulums of the types shown in Fig.
6.12 (a) and (6). This can be done by attaching a pen or stylus to the pendulum arm and
letting it write a record on a rotating drum covered with a paper. A clock is also provided,
which starts running as soon as the first shock is experienced, and the pendulum is thrown
into motion. restrain to the relative movement of the ground and pendulum. This makes it
difficult to record small ground movements, Moreover, since the ground motion is usually
very small, it is always desirable to amplify it, and the amplification provided by such a
mechanical recorder is only in the ratio of the distance of the recording stylus top from the
axis of motion (L2) to the distance of the centre of oscillation of the pendulum arm from the
axis of rotation {L1).
These shortcomings can be removed (i.e. greater amplification obtained without the
disadvantage of friction between pen nib and paper) by using photographic recording. In such
a recording, a mirror is mounted on the seismometer, and a beam of light is reflected from it
on the recording drum, which is wrapped round by a photographic paper. The recording drum
can be placed at a large distance from the seismometer, thus making the length of the
recording arm much greater than the length of the pendulum, and hence giving the desired
amplification for recording small motions. Moreover, in such a case, since the light beam is
deflected through twice the angle the pendulum rotates, it gives another amplification factor
of 2.
Seismographs will record all the three types of waves during an earthquake. Firstly, the Pwaves will be received ; followed by S-waves after a small interval of time ; and L-waves are
recorded in the end. .
A seismograph is generally suitable only as long as the vibrations are not of a very high
intensity—which may throw the instrument out of balance. Hence, for recording high
intensity earthquakes in highly seismic regions, special strong motion instruments are to be
installed.
Intensity and Magnitude of an Earthquake:
Intensity of an Earthquake.Intensity of an earthquake may be defined as the rating of an
earthquake based on the actual effects produced by the quake on the Earth. These observed
effects may eventually range from simple harmless vibrations to mild jerks capable of
disturbing movable things and causing some damage to structures, to complete overturning
and collapse of buildings and subsidence of crustal segments. All these effects will no doubt
depend partly upon the number of jerks and tremors, but will mainly depend upon the
maximum rate of change of the movements of the ground, i.e. by its maximum acceleration.
Hence, now a days, it is customary to express the intensity of a quake by the maximum
acceleration of the ground. This value can be estimated from seismograph records.
Initially, a scale of earthquake intensity with ten divisions was given by Rossi and Forel,
which was based entirely on the sensation of the people and the damage caused. However, it
was modified by Mercalli and later by Wood and Neumann. The present day intensity scale
which takes into account the range of maximum acceleration of the ground is given as
follows. EINSTEIN COLLEGE OF ENGINEERING DEPT OF CIVIL ENGG EINSTEIN
COLLEGE OF ENGINEERING DEPT OF CIVIL ENGG
Name of the Effects
Magnitude (M)
Table
6.1. Maximum
observed
corres-ponding
Intensity Scale Acceleration of shock
the ground in
to
highest
For
mm/sec2
inten-sity
Earthquakes
reached
with
Approximately
Corresponding
Magnitudes
Inten-sity class
(1)
(2)
(3)
(4)
(5)
I
10
Imperceptible
Recorded only 3.5 to
by
sensitive
seismographs
II
25
Feeble
Recorded by all
seismographs, and
may be felt by some
sensitive persons at
rest.
III
50
Slight
Commonly felt 4.3
by all people at
rest, especially
on
upper
floors.IV
100
Moderate
Commonly felt 4.3 to
by all people 4.9
either at rest or
in motion ;
V
250
VI
500
VII
1000
VIII
2500
IX
X
5000
7500
nocking
of
loose objects
in-cluding
standing
vehicles
Fairly strong
Generally felt ;
most
sleeping
persons
are
awakened ; ringing
of bells
Strong
Trees sway and 4.9 to 5.5
all suspended
objects swing ;
fall of weak
plasters
:
general panic ;
damage
by
overturning
and falling of
loose objects.
Very strong
Damages
to 5.5 to 6.2
buildings
producing
cracks in walls,
etc., fall of
chimneys
;
general alarm
and panic.
Destructive
Car
drivers 6.2 to
seriously
7.0
disturbed
;
masonry
fissured
;
poorly
constructed
buildings
damaged.
Ruinous
Some
houses
collapse
where
ground begins to
crack ; pipes break
open.
Disastrous
Ground cracks 7 to 7.3
badly;
many
buildings
destroyed
;
railway lines
bent
;
landslides
occur on steep
slopes.
UNIT - II
1.Rock types and rock cycle
2.Geological and engineering definitions of rocks
3.Basic Mineralogy
4.Engineering Geology considerations
Geology is the study of the earth, from different perspectives,
it studies
Composition
–
Mineralogy, petrology
Surface expression
–
Geomorphology
Structure
–
Structuralgeology
Internal activities
–
Global geophysics
–
Formation process
Ancient Life
-
The physical nature of the earth and its interaction with
engineering construction -Engineering Geology.
Stratigraphy, geochronology
Paleontology
What is a ‘rock’?
In Geology, ‗Rock‘ is defined as the solid material forming the outer rocky shell or crust of the earth. There
arethree major groups of rocks by its origin:
(1) Igneous rocks: cooled from a molten state;
e.g., granite, basalt …;
(2) Sedimentary rocks: deposited from fluid medium;
the products of weathering of other rocks in water;
e.g., sandstone, mudstone…;
(3) Metamorphic rocks: formed from pre-existing rocks by the action of heat and pressure.
e.g., dolomite, marble …;
Rock Cycles
Plate Tectonic Settings of Volcanoes and Igneous Rocks
hyolite
anite
Andesite
Diorite
e
Basalt
Gabbro
Andesite
Diorite
Thus, in pure geological sense rock is defined as the
essential part of the earth‘s crust. Geologists concern about the origin, classification, history, and the spatial aspects
of rocks. So, geologically speaking, ice, sand, marble, coal, basalt, can be simply regarded as rocks. However, the
Engineering Geologists have a different, and relatively narrower view of rocks.
The Engineering Definition of Rocks
Rock is the hard and durable material.
The Engineering Definition of Rocks (cont.)
By an excavation point ofview, Rocks are the earth materials that cannot be excavated without blasting.
This definition clearly excludes other kinds of earth materials such as soils, and glacial tills, etc.
Here is another engineering definition of rocks:
The earth materials that do not slake when soaked into water.
For example, a thick loess deposit is regarded as rock geologicallyand regarded as soil in engineering.
Basic Mineralogy of Rocks
Rocks are formed with minerals. What is a mineral?
1) a naturally occurring chemical element or compound;
2) formed by inorganic processes;
3) with an ordered arrangement or pattern for its atoms –
crystalline structure;
4) possesses a definite chemical composition or range of compositions.
The opposite of mineral property is amorphous, i.e., the property of non-crystal, order-less property possessed by glass,
volcanic glass, etc.; oil or coal can neither be regarded as minerals by their organic involvement.
Basic Mineralogy of Rocks (cont.)
So we can simply express the mineral as
mineral = composition + crystalline structure
For two minerals if the composition are the same but the structures are different, they can be called a pair of polymorphs. The
common examples for polymorphs include
1) pyrite/marcasite (FeS2 , isotropic vs anisotropic iron atom spacing);
2) diamond/graphite (C, the same composition of carbon but different structure);
3) Calcite/aragonite (CaCO3);
4)quartz/cristobolite(SiO2).
Mineralogy Identification for Engineering Purposes
From an engineering point of view, certain properties of minerals, especially when they are introduced into or encountered with
another mineral, are of special concern to engineers. For example,
gypsum in a limestone can become swelling when water presents;
pyrite (the fool‘s gold) in shale can be deteriorated by acidwater;
swelling clays in shale can become wetting and cause instability problem of a slope.
Thus, fundamental mineralogical acknowledge is needed when identifying engineering material is needed.
Mineralogy Identification
Minerals can be identified by its color;
streak (strip);
luster; hardness; specific weight;
cleavage; fracture;
crystal form; magnetism;
tenacity;
diaphaneity;
striation;
chemical reaction.
Color
•
Minerals are colored because certain wave lengths of light are absorbed, and the color results from a combination of those
wave lengths that reach the eye.
• Some minerals show different colorsalong different crystallographic axes.
Mineral identification by colors can be deceptive!!
Flourite
FlouriteFlourite
Streak
• The streak of a mineral is the color of the powder left on astreak plate
(piece of unglazed porcelain) when the mineral is scraped across it
Luster
•
Luster refersto how light is reflected fromthe surface of a mineral.The two main types of luster are metallic and
nonmetallic.
• Types of nonmetallic luster
adamantine, vitreous, pearly, greasy, silky, earthy
Rosequartz - greasy
Quartz- vitreous
Chrysolite -silky
Apophyllite-pearly
Cuprite - adamantine
Bauxite - Earthy
Hardness
•
The hardness of a mineral is its ―scratchability‖,
determined by Moh‘s hardness scale. The hardest
mineral known, diamond, was assigned the number
10.
Minerals
Level of
Hardness
Talc
1
Gypsum
2
Calcite
3
Fluorite
4
Apatite
5
Orthoclase
6
Quartz
7
Topaz
8
Corundum
9
Diamond
10
Tools
Finger nail
Copperpenny
Glass
Specific Gravity
•
Specific gravity is the "heaviness" of a mineral. It is defined as a number that expresses the ratio
of the weight of a mineral and the weight of an equal volume of water.
• The specific gravity depends on:
• the kind of atoms that comprise the mineral
• how the atoms are packed together
•
Common rock-forming minerals (quartz, feldspar, calcite, etc.) have specific gravity near
2.7
Cleavage
• Cleavage is the ability of a mineral to break along preferred planes
• Minerals tend to break along certain planes where atomic bonds are weak
• Minerals can have one, two plane or three plane cleavages.
Copper - none
Crystalforms
• Crystal forms are displays of well-formed crystal faces by a mineral
•
Crystal faces formed during crystallization process vs. cleavagefaces formed when mineral breaks.
Beryl -hexagonal
-
Diamond- octahedron
Basic Mineralogy of Rocks
There are more than 2000 naturally occurred mineralshave been discovered; only a bit more than 100 are commonand used in
college mineralogy.However, of the 100 common minerals only about 25 are abundant rock-forming minerals. The main types of
minerals are:
metallic
minerals;
nonmetallicminerals;
carbonateminerals;
sulfateminerals;
sulfideminerals; silicateminerals; oxide minerals;
clay minerals.
Sulfide Minerals
•
Pyrite: ―Fool‘s gold‖, minor ore of sulfur for sulfuric acid, causes staining on surface of concrete due to oxidation or
presence of sulfate ions.
• Molybdenite: Nearly 50% of all molybdenum is used in making steel.
•
Sphalerite: The most important ore mineralof zinc which is used to make brass, electric batteries, and zinc white.
Sphalerite
Pyrite
Molybdenite
OxideMinerals
Hematite:
Chromite:
Fe2O3
-resistanttothealtering affects of high
- causes staining and popouts on thetemperatures and pressures
- component in the bricks and linings of
concrete surface
blast furnaces
majorconstituentin
stainlesssteel
Ilmenite:
- major ore of titanium (aluminumlikemetal;light weight, non-corrosive,
able to withstand temperature extreme,
has many applications in high tech
airplanes,missiles,space vehicles)
Silicates
• Most important of all mineral classes because:
- 25% of the known minerals and nearly 40%
of the common ones are silicates
- Nearly 90% of the igneous rock-forming minerals are silicates,
which means that they make up over 90% of the Earth's crust
- Bricks, stones, concrete and glass are either silicatesor derived
from silicates
Silicon-OxygenTetrahedron
•
Important silicate groups: Ferromagnesians, nonferromganesians,
feldspar (orthoclase, plagioclase), Quartz
Ferromagnesians
• Contain Fe orMg
• Olivines:Olivine:(Mg,Fe)2SiO4
-found mostly in igneous rock
-olivine‘s variety, peridot, has same chemical composition as molten magma
inEarth‘s mantle. Thus, peridot is considered the most common mineral by volume in the
Earth
-industrial uses as refractory sands and abrasives, an ore of magnesium
• Pyroxenes: Augite
• Amphibole: Hornblende
• Micas:biotite
ugite
BiotiteHornblende
Olivine
Nonferromagnesians
• Contain Ca, K, Na
• Soft, flaky, platy, one prominent cleavage minerals
•
Serpentine: many industrial applications, including brake linings and fireproof fabrics and as an ornamental
stone.
• Muscovite: used in heat and electrical insulator for industrial purposes
uscovite
serpentine
Feldspars(Si O )
3 8
• By compositions, feldspars is the most common rock-forming silicates
• Orthoclase: - contains K
- used in porcelain industry
• Plagioclase: - contains Ca, Na
- Industrially important in glass and ceramic industries; potteryand enamelware; soaps; abrasives;
bond for abrasive wheels; cements and concretes; insulating compositions; fertilizer; poultry grit; tarred roofing
materials; and as a sizing (or filler) in textiles and paper.
Orthoclase
albite
Quartz Minerals(SiO group)
2
Rose
•
Second common rock-forming mineral
•
silica for glass, electrical components, optical
lenses, abrasives, ornamental stone, building
stone, etc.
• Chert: - variety of Quartz,
- found in sedimentary rock
Rock
crystal
Rock Crystal
smoky
Amethyst quartz
- when used as an aggregate material, it
easily breaks and pop out when exposed to
freezing and thawing. Thus, it reduces the
strength of concrete.
Carbonateminerals(CO group)
3
• Calcite: - fizzes with acid
calcite
- Primary component in cave formation,
react with carbon dioxide
in sea and air, thus, acts like carbon
dioxide filter for the planet
- used in cements and mortars,
production of lime,
limestone is used in the steel industry; glass industry,
ornamental stone, chemical and optical use
•
Aragonite
Aragonite: minor constituent of limestone which is
used in cement and in steel production, ornamental
carvings
• Dolomite: ―Dolomite problem‖
Dolomite
Sulfate Minerals(SO group)
4
• Gypsum: -common in sedimentary rock in high saline water.
- used in plaster, wall board, some cements, fertilizer, paint filler, ornamental stone
Gypsum
Anhydrite
• Anhydrite: -water-free form of gypsum
- in the manufacture of some cement, a source of sulfate for sulfuric acid
- causes cracks in structure due to property of swelling when wet and converting to gypsum
ClayMinerals
• Very fine-grained minerals, common in soil
• Clay = kaolinite, halloysite, illite (non swelling clays), vermiculite, smectite
(swelling clays)
•
Smectite: used in drilling mud since it has property of swelling when exposed to water
•
Kaolinite: made up high-grade clay, used in manufacture of ceramic products, rubber industry, refractories
• Illite: chief constituent in shales
Smectite
illite
Halloysite
Kaolinite
vermiculite
Rock Identification
Rocks are identified mostly by its texture;
mineral composition;
field relationships;
color; hardness; specific weight;
crystal form; magnetism;
Apparently, some techniques used in identifying minerals can also be used to classify the rock type.
UNIT- III
Rock Properties forEngineering
Rock are significant for two major reasons in engineering:
(1) As building materials for constructions;
(2) As foundations on which the constructions are setting;
For the consideration of rocks as construction material the engineers concern about:
(a) Density to some extent (for calculating the weight, load to the foundation, etc.);
(b) Strength; (c) Durability;
For the consideration of rocks as the construction
foundation the geological engineers concern about the rock‘s:
(a) Density; (b) Strength;
(c) Compressibility;
Engineering concerns of different rocks:
(a) Igneous;
(b) Sedimentary; (c) Metamorphic;
The Identification Chart of the Igneous Rocks
Engineering Considerationsof Igneous Rocks
(1)Fine-grainedigneousrockscannotbeusedasaggregatesin
silicareaction.Solutionsinclude:
Portlandcementdueto
volumeexpansioncausedbytheAlkali-
(a)Canbeusedinlowalkalicement;
(b)Non-reactiveaggregatesgowiththehighalkalicement; (c)Addpozzolans,coal-ashes,etc. intheaggregate-cement
mixtureto minimizethereaction.
(2)Coarse-grainedigneousrocks(e.g.,granite,syenite,etc.)
arenot
foraggregatesforconstructionsbecauseitslowabrasion
resistance;butfine-grainedigneousrocks(e.g., basalt)aregood froaggregates(e.g., basaltaspavingaggregatesgoeswith
asphalt.
(3)Sitingoffoundationsneedsto avoidweatheredrocks(e.g., dams, bridgepiers,etc.);
(4)Igneousrocksaregoodfordimensionstone(tombstoneetc.)
becausetheirresistanceto weatheringbutneedavoidfractures.
The Nathan Hale
Monument in Coventry, Connecticut. Built in
1851 with granite blocks quarried fromQuincy, MA.
Sedimentsand SedimentaryRocks
Sedimentsarepiecesof loosedebristhat havenotbeenlithified.
Sedimentsaresoil,withtheengineeringdefinition.Sedimentsare thecombinationofgravels,sands,silts, andclays;
Sedimentaryrocksarelithifiedsedimentsthat
heldtogetherby
varioustypesof
ironoxide;orbycompactionof themineralgrainsintoanindurate mass.
cementingagents,suchascalcite,quarts,and
Therearethreewaysinlithification:
compaction-reductionof poresize;cementation-poresfillingbybindingagents;crystallization
newmineralscrystallizedinpores.
-
SedimentaryRocks
(1)95%of thevolumeof thecrust(thefirst 10milesindepthof the earth)areigneousandmetamorphicrocks;
(2)However,it isabout75%of thesurfaceof theeartharecoveredby sedimentaryrocks;
(3)Consequently,engineersaremostlikelyendupwithworkingmore oftenonsedimentaryrocks.
Sedimentaryrockscomposedof mineralgrainsorcrystalsthat havebeendepositedinafluidmedium,andsubsequentlylithified
to formrocks.Of thesedimentaryrocksontheearth‘ssurface,
46%areshale,32%aresandstoneand22%arelimestone.
Conglomerateis a clastic sedimentary rock that forms from the cementing of rounded cobble
and pebblesized rock fragments. Conglomerate is formed by river movement or ocean wave
action. The cementing agents that fill the spaces to form the solid rock conglomerate are
silica, calcite, or iron oxides.
Chertis a very hard sedimentary rock that is usually found in nodules in limestone. Chert is
light gray to dark gray in color. It probablyformed from the remains of ancient sea sponges or
other ocean animalsthat have been fossilized. Silica has replaced the tissue forming the
sedimentary rock.
Limestone is the most abundant of the non-clastic sedimentary rocks. Limestone is
produced from the mineral calcite (calcium carbonate) and sediment. The main source of
limestone is the limy ooze formed in the ocean.
Sandstone is a clastic sedimentary rock that forms from the cementing together of sand
sized grains forming a solid rock. Quartz is the most abundant mineral that forms sandstone.
Calcium carbonate, silica, or iron has been added to the water that is in contact with the sand
grains.
Engineering Considerationsof SedimentaryRocks
(1)ThesedimentaryrocksalsohavetheAlkali-silicareactionproblem
rockswiththisproblemarechertandgraywacke.
whenusedasaggregateswithPortlandcement.Thesedimentary
(2)Fine-grainedsedimentaryrockslikelimestoneanddolomitearethe
andquartzsandstonearenotacceptable;
bestforbeingusedasaggregates;siltstone,shale,conglomerate,
(3)Streamandterracegravelcontainsweakpieces,theyarenotgood
cancausepop-outsat theconcretesurfaceafterfreeze-thaw cycles;
foraggregatesinconcrete.Weatheredchert,shale,andsiltstone
(4)Coarse-grainedlimestoneisnotgoodforaggregatesbyreducing particlesize;
(5)Sinkholeproblemincarbonateterrainsdueto thehigh dissolvabilityof limestoneanddolomite.
Engineering Considerationsof MetamorphicRocks
(1)ThemetamorphicrocksalsohavetheAlkali-silicareactionproblem
whenusedasaggregateswithPortlandcement.Themetamorphic
rockswiththisproblemareargillite,phyllite,impurequartzite,and granitegneiss;
(2)Coarse-grainedgneisscanbeabradedseverelywhenusedas aggregates;
(3)Formetamorphicrocksthestabilityof rockmassgreatlyaffected bythefoliationorientation;
(4)Marbleasametamorphicrockfromcarbonatesedimentaryrocks
reservoirs,sinkhile collapse,solutioncavities,andchannels.
cancausesimilarproblems,eg.,
leakageof
UNIT-IV STRUCTURAL GEOLOGY
1. Folds
2. Faults
3. State of stress and Faulting
4. Stress perturbation caused by tectonic features
Research Methodologies:
Traditionally, geological knowledge has come to us by a process of induction. This is the reasoning from some particular
geologic observations or individual cases of geologic phenomena to a general conclusion.
In contrast, In Physics, it is more often to usededuction
(as suggested by Albert Einstein):
Reasoning from a known principle that applies to a general construct in order to explain a particular geologic phenomenon
observation.
There are Four ingredients in this approach:
1, general boundary conditions;
2, geometry of the structure;
3, constitutive behavior of the materials;
4, specific boundary conditions and initial condition.
Atypical example of the deduction approach is
the classic mathematic physics.
Physics + constitutive relations + boundary conditions + initial conditions.
Îboundary value problems.
The structural Problems:
Structural Geology studies rocks that have been deformed by earth stresses. These studies include descriptions of
1, Position;
2, Attitude;
3, Sequence.
From observations and infer the cause and process of the deformation.
Examples:
Horizontal and vertical movement in sedimentary rocks;
Intrusion of magma bodies in forming igneous rocks;
The induction approach applied to structural
geology is the observations of rock deformation:
folding:
Ductile, or plastic deformation, a slow process, with relative hot and soft materials;
faulting:
brittle, a rapid to instantaneous process, with relatively cold material, usually caused by compressive
force.
Material
Property
Geological example
Rubber
elastic
response
of
rocks to the
passage
of
seismic waves
Clay
plastic
deformation in
a ductile shear
Honey
viscous
flow of lava
ne
Glass
brittle
fractured rocks
Ductile deformation: folding
Folding:
ductile, or plastic deformation, a slow process, with relative hot and soft materials.
West, Figure 10.2)
(West, Figure 10.3)
(West, Figure 10.6)
(West, Figure 10.7)
West, Figure 10.8)
t=Wsinθ
West, Figure 10.9)
Brittle deformation: types of rock fractures:
Fractures:
narrow openings along which the rock mass has lost grain to grain contact.
Joints:
rock fractures along which no movement has occurred parallel to the joint surface, perpendicular
movement may occur – joints are simple Mode I openings.
Types of rock fractures (cont.):
Shear zones:
rock fractures along which some movement has occurred but not a great amount, at the level of a few
centimeters. Usually, shear zone occurs in weak materials with rich of water, and in great depth.
Faults:
fractures along which significant movement has occurs, much more than that associated with shear
zones. The level of displacement is on the order of meters to kilometers, even to hundred kilometers.
Global plate tectonics, seismicity, and stress
regimes
World Stress Map
State of stress in the crust:
Lithostatic:
all 3 principle stresses are equal to σv=ρgz, rarely occurs;
Reverse faulting regime:
the 2 horizontal stresses are all greater than the vertical stressσv=ρgz;
Strike slip faulting regime:
the maximum horizontal stress is greater than, and the minimum horizontal stress is less than the
vertical stressσv=ρgz;
Normal faulting regime:
the 2 horizontal stresses are all smaller than the vertical stressσv=ρgz;
Stress-Depth
relationships for the three states of stress
Both engineering community and Geological science
community recognize the magnitude of the vertical stress has a depth dependence of ρgz.
However, in engineering community, it is a common
practice to assume the horizontal stress is about 1/3 of the vertical stress, if there is no (and usually very
hard to measure) horizontal stress data. Their
rationale is:
ν
σ=
v
0.25
σ=
σ
−ν
σ
v
=
v
0.75
3
If the engineers keep this idea to a greater depth it is definitely untrue. If it is true, there will never be reverse faulting
in the earth crust.
‘Standard state’: σh=σv;
‘Perfect lateral constraint’: σh=σv/3;
The stress in the crust is closer to the standard state.
Fault geometry:
FaultingGeometry
Hanging
Strike;
Dip;
North
x
a
u
dv
Rake.
b
East
z
y
a:Strike;b:Rake;d:Dip;u:SlipVector;v:FaultNormal
wall;
Foot
wall;
Types of faulting:
1, normal faulting:
hanging wall goes downward;
2, reverse faulting:
hanging wall goes upward;
3, strike slip faulting:
The 2 walls go horizontally in the opposite directions against each other;
left-lateral strike slip;
right-lateral strike slip.
GPS observations of
crustal deformation in the San Francisco
Bay area crossing the
San Andreas fault
Field recognition of faults:
1, Landform features:
Offset/truncation of geologic features such as mountain chains, valleys, and flow channels;
2, Abnormal stratigraphic sequences:
repetition or omission;
3, Fault plane features: polished rock surface; fault gauge;
drag of bed.
The surface
expression of the San Andreas Fault at the Carrizo
Plains, CA.
The Kunlun Fault, Tibet Plateau
The clay formed by fault gauge
Offset of a flow channel caused by the fault generated by
the 1993 Cocosili Earthquake, Tibet plateau.
Stress perturbation caused by some geologic
features
Stress perturbation caused by a dense rift
pillow
The horizontal displacement field superimposed with the contour of the vertical displacement on surface in the New Madrid seismic
zone. The unit of the color bar is in meters. The maximum horizontal displacement is 14 m.
The trajectory of the horizontal principal stress superimposed with the contour of the
horizontal shear strain expressed bythe engineering shear strain on surface.
UNIT - V
1.1 DEFINITION AND PROCESS OF REMOTE SENSING
"Remote sensing is the science of acquiring information about the Earth's surface without actually
being in contact with it. This is done by sensing and recording reflected or emitted energy and processing,
analyzing, and applying that information."
In much of remote sensing, the process involves an interaction between incident radiation and the
targets of interest. This is exemplified by the use of imaging systems where the following seven elements
are involved. However that remote sensing also involves the sensing of emitted energy and the use of nonimaging sensors.
1. Energy Source or Illumination (A) – the first
requirement for remote sensing is to have an
energy source which illuminates or provides
electromagnetic energy to the target of interest.
2. Radiation and the Atmosphere (B) – as the
energy travels from its source to the target, it
will
come in contact with and interact with the
atmosphere it passes through. This interaction may take place a second time as the energy travels from the
target to the sensor.
3. Interaction with the Target (C) - once the energy makes its way to the target through the atmosphere, it
interacts with the target depending on the properties of both the target and the radiation.
4. Recording of Energy by the Sensor (D) - after the energy has been scattered by, or emitted from the
target, we require a sensor (remote - not in contact with the target) to collect and record the
electromagnetic radiation.
5. Transmission, Reception, and Processing (E) - the energy recorded by the sensor has to be transmitted,
often in electronic form, to a receiving and processing station where the data are processed into an image
(hardcopy and/or digital).
6. Interpretation and Analysis (F) - the processed image is interpreted, visually and/or digitally or
electronically, to extract information about the target which was illuminated.
7. Application (G) - the final element of the remote sensing process is achieved when we apply the
information we have been able to extract from the imagery about the target in order to better understand
it, reveal some new information, or assist in solving a particular problem.
1.2 ELECTROMAGNETIC RADIATION
The first requirement for remote sensing is to have an energy
source to illuminate the target (unless the sensed energy is
being emitted by the target). This energy is in the form of
electromagnetic radiation. All electromagnetic radiation has
fundamental properties and behaves in predictable ways
according to the basics of wave theory.
Electromagnetic radiation consists of an electrical field (E) which varies in magnitude in a direction
perpendicular to the direction in which the radiation is traveling, and a magnetic field (M) oriented at right
angles to the electrical field. Both these fields travel at the speed of light (c). Two characteristics of
electromagnetic radiation are particularly important to understand remote sensing. These are the
wavelength and frequency.
The wavelength is the length of one wave cycle, which
can be measured as the distance between successive wave
crests. Wavelength is usually represented by the Greek letter
lambda (λ). Wavelength is measured in metres (m) or some
factor of metres such as nanometres (nm, 10-9 metres),
micrometres (μm, 10-6 metres) (μm, 10-6 metres) or
centimetres (cm, 10-2 metres). Frequency refers to the number
of cycles of a wave passing a fixed point per unit of time. Frequency is normally measured in hertz (Hz),
equivalent to one cycle per second, and various multiples of hertz.
Wavelength and frequency are related by the following formula:
Therefore, the two are inversely related to each other. The shorter the wavelength, the higher the
frequency. The longer the wavelength, the lower the frequency. Understanding the characteristics of
electromagnetic radiation in terms of their wavelength and frequency is crucial to understanding the
information to be extracted from remote sensing data.
1.3 THE ELECTROMAGNETIC SPECTRUM
The electromagnetic spectrum ranges from the shorter wavelengths (including gamma and x-rays)
to the longer wavelengths (including microwaves and broadcast radio waves). There are several regions of
the electromagnetic spectrum which are useful for remote
sensing.
Ultraviolet or UV
For
most
purposes,
the
ultraviolet
or
UV
portion of
the
spectrum
has
the
shortest
wavelengths which are practical for
remote
sensing. This radiation is just beyond the
violet
portion of the visible wavelengths, hence
its
Some Earth surface materials, primarily
rocks
minerals, fluoresce or emit visible light
when
illuminated
name.
by
and
UV
radiation.
Visible Spectrum
The light which our eyes - our
"remote sensors" - can detect
is part of the visible spectrum. It is
important to recognize how
small the visible portion is relative to the rest of the spectrum. There is a lot of radiation around us which is
"invisible" to our eyes, but can be detected by other remote sensing instruments and used to our
advantage. The visible wavelengths cover a range from approximately 0.4 to 0.7 μm. The longest visible
wavelength is red and the shortest is violet. Common wavelengths of what we perceive as particular
colours from the visible portion of the spectrum are listed below. It is important to note that this is the only
portion of the spectrum we can associate with the concept of colours.
�Violet: 0.4 - 0.446 μm
�Blue: 0.446 - 0.500 μm
�Green: 0.500 - 0.578 μm
�Yellow: 0.578 - 0.592 μm
�Orange: 0.592 - 0.620 μm
�Red: 0.620 - 0.7 μm
Blue, green, and red are the primary colours or wavelengths of the visible spectrum. They are defined as
such because no single primary colour can be created from the other two, but all other colours can be
formed by combining blue, green, and red in various proportions. Although we see sunlight as a uniform or
homogeneous colour, it is actually composed of various wavelengths of radiation in primarily the
ultraviolet, visible and infrared portions of the spectrum. The visible portion of this radiation can be shown
in its component colours when sunlight is passed through a prism, which bends the light in differing
amounts according to wavelength.
Infrared (IR)
The next portion of the spectrum of interest is the infrared (IR) region which covers the wavelength
range from approximately 0.7 μm to 100 μm - more than
100 times
as wide as the visible portion. The infrared region can be
divided
into two categories based on their radiation properties -
the
reflected IR, and the emitted or thermal IR. Radiation in
the
reflected IR region is used for remote sensing purposes in
ways very
similar to radiation in the visible portion. The reflected IR
covers
wavelengths from approximately 0.7 μm to 3.0 μm. The
thermal
IR region is quite different than the visible and reflected IR
portions,
as this energy is essentially the radiation that is emitted
from the
Earth's surface in the form of heat. The thermal IR covers
wavelengths from approximately 3.0 μm to 100 μm.
Microwave
The portion of the spectrum of more recent interest to remote
sensing is the microwave region from about 1 mm to 1 m. This covers the
longest wavelengths used for remote sensing. The shorter wavelengths
have properties similar to the thermal infrared region while the longer wavelengths approach the
wavelengths used for radio broadcasts.
1.4 ENERGY INTERACTIONS WITH THE ATMOSPHERE
Before radiation used for remote sensing reaches the Earth's surface it has to travel through some
distance of the Earth's atmosphere. Particles and gases in the atmosphere can affect the incoming light and
radiation. These effects are caused by the mechanisms of scattering and absorption.
Scattering
Scattering occurs when particles or large gas molecules present in
the atmosphere interact with and cause the electromagnetic radiation to
be redirected from its original path. How much scattering takes place
depends on several factors including the wavelength of the radiation, the
abundance of particles or gases, and the distance the radiation travels
through the atmosphere. There are three (3) types of scattering which take place.
Rayleigh scattering
Rayleigh scattering occurs when particles are very small compared to the wavelength of the
radiation. These could be particles such as small specks of dust or nitrogen and oxygen molecules. Rayleigh
scattering causes shorter wavelengths of energy to be scattered much more than longer wavelengths.
Rayleigh scattering is the dominant scattering mechanism in the upper atmosphere. The fact that the sky
appears "blue" during the day is because of this phenomenon. As sunlight passes through the atmosphere,
the shorter wavelengths (i.e. blue) of the visible spectrum are scattered more than the other (longer)
visible wavelengths. At sunrise and sunset the light has to travel farther through the atmosphere than at
midday and the scattering of the shorter wavelengths is more complete; this leaves a greater proportion of
the longer wavelengths to penetrate the atmosphere.
Mie scattering
Mie scattering occurs when the particles are just about the same size as the wavelength of the
radiation. Dust, pollen, smoke and water vapour are common causes of Mie scattering which tends to
affect longer wavelengths than those affected by Rayleigh scattering. Mie scattering occurs mostly in the
lower portions of the atmosphere where larger particles are more abundant, and dominates when cloud
conditions are overcast.
The final scattering mechanism of importance is called
nonselective scattering. This occurs when the particles are much
larger than the wavelength of the radiation. Water droplets and large
dust particles can cause this type of scattering. Nonselective
scattering gets its name from the fact that all wavelengths are
scattered about equally. This type of scattering causes fog and clouds to appear white to our eyes because
blue, green, and red light are all scattered in approximately equal quantities (blue+green+red light = white
light).
Absorption
Absorption is the other main mechanism at work
when
electromagnetic radiation interacts with the atmosphere. In
contrast
to scattering, this phenomenon causes molecules in the
atmosphere to absorb energy at various wavelengths.
Ozone,
carbon dioxide, and water vapour are the three main
atmospheric constituents which absorb radiation.
Ozone serves to absorb the harmful (to most living things) ultraviolet radiation from the sun.
Without this protective layer in the atmosphere our skin would burn when exposed to sunlight. Carbon
dioxide referred to as a greenhouse gas. This is because it tends to absorb radiation strongly in the far
infrared portion of the spectrum - that area associated with thermal heating - which serves to trap this heat
inside the atmosphere. Water vapour in the atmosphere absorbs much of the incoming longwave infrared
and shortwave microwave radiation (between 22μm and 1m). The presence of water vapour in the lower
atmosphere varies greatly from location to location and at different times of the year. For example, the air
mass above a desert would have very little water vapour to absorb energy, while the tropics would have
high concentrations of water vapour (i.e. high humidity).
Because these gases absorb electromagnetic energy in very specific regions of the spectrum, they
influence where (in the spectrum) we can "look" for remote sensing purposes. Those areas of the spectrum
which are not severely influenced by atmospheric
absorption and thus, are useful to remote
sensors, are called atmospheric windows. By
comparing the characteristics of the two most
common energy/radiation sources (the sun and
the
earth) with the atmospheric windows available to
us, we
can define those wavelengths that we can use
most
effectively for remote sensing. The visible portion
of
the
spectrum, to which our eyes are most sensitive, corresponds to both an atmospheric window and the peak
energy level of the sun. Note also that heat energy emitted by the Earth corresponds to a window around
10 μm in the thermal IR portion of the spectrum, while the large window at wavelengths beyond 1 mm is
associated with the microwave region.
1.5 RADIATION - TARGET INTERACTIONS
Radiation that is not absorbed or scattered in the atmosphere can reach and interact with the
Earth's surface. There are three (3) forms of interaction that can take place when energy strikes, or is
incident (I) upon the surface.
These are: absorption (A); transmission (T); and reflection (R). The total incident energy will interact with
the surface in one or more of these three ways. The proportions of each will depend on the wavelength of
the energy and the material and condition of the feature.
Absorption (A) occurs when radiation (energy) is absorbed into the target while transmission (T) occurs
when radiation passes through a target. Reflection (R) occurs
when
radiation "bounces" off the target and is redirected. In
remote
sensing, we are most interested in measuring the radiation reflected from targets. We refer to two types of
reflection, which represent the two extreme ends of the way in which energy is reflected from a target:
specular reflection and diffuse reflection. When a surface is smooth we get specular or mirror-like
reflection where all (or almost all) of the energy is directed away from the surface in a single direction.
Diffuse reflection occurs when the surface is rough and the energy is reflected almost uniformly in all
directions. Most earth surface features lie somewhere between perfectly specular or perfectly diffuse
reflectors. Whether a particular target reflects specularly or diffusely, or somewhere in between, depends
on the surface roughness of the feature in comparison to the wavelength of the incoming radiation. If the
wavelengths are much smaller than the surface variations or the particle sizes that make up the surface,
diffuse reflection will dominate. For example, finegrained sand would appear fairly smooth to long
wavelength microwaves but would appear quite rough to the visible wavelengths. Let's take a look at a
couple of examples of targets at the Earth's surface and how energy at the visible and infrared wavelengths
interacts with them.
Leaves: A chemical compound in leaves called chlorophyll
strongly absorbs radiation in the red and blue wavelengths
but reflects green wavelengths. Leaves appear "greenest"
to us in the summer, when chlorophyll content is at its
maximum. In autumn, there is less chlorophyll in the leaves,
so there is less absorption and proportionately more
reflection of the red wavelengths, making the leaves appear
red or yellow (yellow is a combination of red and green wavelengths). The internal structure of healthy
leaves act as excellent diffuse reflectors of near-infrared wavelengths. If our eyes were sensitive to nearinfrared, trees would appear extremely bright to us at these wavelengths. In fact, measuring and
monitoring the near-IR reflectance is one way that scientists can determine how healthy (or unhealthy)
vegetation may be.
Water: Longer wavelength visible and near infrared radiation is absorbed more by water than shorter
visible wavelengths. Thus water typically looks blue or blue-green due to stronger reflectance at these
shorter wavelengths, and darker if viewed at red or near infrared wavelengths. If there is suspended
sediment present in the upper layers of the water body, then this will allow better reflectivity and a
brighter appearance of the water. The apparent colour of the water will show a slight shift to longer
wavelengths. Suspended sediment (S) can be easily confused with shallow (but clear) water, since these
two phenomena appear very similar. Chlorophyll in algae absorbs more of the blue wavelengths and
reflects the green, making the water appear more green in colour when algae is present. The topography of
the water surface (rough, smooth, floating materials, etc.) can also lead to complications for water-related
interpretation due to potential problems of specular reflection and other influences on colour and
brightness. We can see from these examples that, depending on the complex make-up of the target
that is being looked at, and the wavelengths of radiation involved, we can observe very different responses
to the mechanisms of absorption, transmission, and reflection. By measuring the energy that is reflected
(or emitted) by targets on the Earth's surface over a variety of different wavelengths, we can build up a
spectral response for that object.
By comparing the response patterns of different features we may be able to distinguish between them,
where we might not be able to, if we only compared them at one wavelength.
For example, water and vegetation may reflect somewhat similarly in the visible wavelengths but are
almost always separable in the infrared. Spectral response can be quite variable, even for the same target
type, and can also vary with time (e.g. "green-ness" of leaves) and location. Knowing where to "look"
spectrally and understanding the factors which influence the spectral response of the features of interest
are critical to correctly interpreting the interaction of electromagnetic radiation with the surface.
Types of Platform:
Ground-based platforms:
Ground, vehicles and/or towers => up to 50 m
Examples:
DOE ARM (Atmospheric radiation Program):
NASA AERONET (AErosol Robotic NETwork
Airborne platforms:
airplanes, helicopters,
high-altitude aircrafts, balloons => up to 50 km
Examples:
NCAR, NOAA, and NASA research aircrafts
Spaceborne:
rockets, satellites,
shuttle => from about 100 km to 36000 km
Space shuttle: 250-300 km
Space station: 300-400 km
Low-level satellites: 700-1500 km
High-level satellites: about 36000 km
NASA current and planned Earth‘s observing satellite missions:
NOAA weather satellites: http://www.noaa.gov/satellites.html
NPOESS (National Polar-orbiting Operational Environmental Satellite System):
Types of Orbits
Different orbits serve different purposes. Each has its own advantages and disadvantages. There
are several types of orbits:
1. Polar
2. Sun Synchronous
3. Geosynchronous
Polar Orbits
The more correct term would be near polar orbits. These orbits have an inclination near 90
degrees. This allows the satellite to see virtually every part of the Earth as the Earth rotates
underneath it. It takes approximately 90 minutes for the satellite to complete one orbit. These
satellites have many uses such as measuring ozone concentrations in the stratosphere or
measuring temperatures in the atmosphere.
Sun Synchronous Orbits
These orbits allow a satellite to pass over a section of the Earth at the same time of day. Since
there are 365 days in a year and 360 degrees in a circle, it means that the satellite has to shift its
orbit by approximately one degree per day. These satellites orbit at an altitude between 700 to
800 km. These satellites use the fact since the Earth is not perfectly round (the Earth bulges in the
center, the bulge near the equator will cause additional gravitational forces to act on the satellite.
This causes the satellite's orbit to either proceed or recede. These orbits are used for satellites that
need a constant amount of sunlight. Satellites that take pictures of the Earth would work best with
bright sunlight, while satellites that measure longwave radiation would work best in complete
darkness.
Geosynchronous Orbits
Also known as geostationary orbits, satellites in these orbits circle the Earth at the same rate as
the Earth spins. The Earth actually takes 23 hours, 56 minutes, and 4.09 seconds to make one full
revolution. So based on Kepler's Laws of Planetary Motion, this would put the satellite at
approximately 35,790 km above the Earth. The satellites are located near the equator since at this
latitude; there is a constant force of gravity from all directions. At other latitudes, the bulge at the
center of the Earth would pull on the satellite.
Geosynchronous orbits allow the satellite to observe almost a full hemisphere of the Earth. These
satellites are used to study large scale phenomenon such as hurricanes, or cyclones. These orbits
are also used for communication satellites. The disadvantage of this type of orbit is that since
these satellites are very far away, they have poor resolution. The other disadvantage is that these
satellites have trouble monitoring activities near the poles. See the picture below.
.
1.10 SPATIAL RESOLUTION, PIXEL SIZE, AND SCALE
For some remote sensing instruments, the distance between the target
being imaged and the platform, plays a large role in determining the detail of
information obtained and the total area imaged by the sensor. Sensors
onboard platforms far away from their targets, typically view a larger area,
but cannot provide great detail. Compare what an astronaut onboard the space
shuttle sees of the Earth to what you can see from an airplane. The astronaut
might see your whole province or country in one glance, but couldn't
distinguish individual houses. Flying over a city or town, you would be able to see individual buildings and
cars, but you would be viewing a much smaller area than the astronaut. There is a similar difference between
satellite images and airphotos. The detail discernible in an image is dependent on the spatial resolution of
the sensor and refers to the size of the smallest possible feature that can be detected. Spatial resolution of
passive sensors (we will look at the special case of active microwave sensors later) depends primarily on
their Instantaneous Field of View (IFOV). The IFOV is the angular cone of visibility of the sensor (A) and
determines the area on the Earth's surface which is "seen" from a given altitude at one particular moment in
time (B). The size of the area viewed is determined by multiplying the IFOV by the distance from the ground
to the sensor (C). This area on the ground is called the resolution cell and determines a sensor's maximum
spatial resolution. For a homogeneous feature to be detected, its size generally has to be equal to or larger
than the resolution cell. If the feature is smaller than this, it may not be detectable as the average brightness
of all features in that resolution cell will be recorded. However, smaller features may sometimes be
detectable if their reflectance dominates within a articular resolution cell allowing sub-pixel or resolution cell
detection.
Most remote sensing images are composed of a matrix of picture elements, or pixels, which are the
smallest units of an image. Image pixels are normally square and represent a certain area on an image. It is
important to distinguish between pixel size and spatial resolution - they are not interchangeable. If a sensor
has a spatial resolution of 20 metres and an image from that sensor is displayed at full resolution, each pixel
represents an area of 20m x 20m on the ground. In this case the pixel size and resolution are the same.
However, it is possible to display an image with a pixel size different than the resolution.
Many posters of satellite images of the Earth have their pixels averaged to represent larger areas,
although the original spatial resolution of the sensor that collected the imagery remains the same. Images
where only large features are visible are said to have coarse or low resolution. In fine or high resolution
images, small objects can be detected. Military sensors for example, are designed to view as much detail as
possible, and therefore have very fine resolution. Commercial satellites provide imagery with resolutions
varying from a few metres to several kilometres. Generally speaking, the finer the resolution, the less total
ground area can be seen. The ratio of distance on an image or map, to actual ground distance is referred to as
scale.
If you had a map with a scale of 1:100,000, an object of 1cm length on the map would actually be an object
100,000cm (1km) long on the ground. Maps or images with small "map-to-ground ratios" are referred to as
small scale (e.g. 1:100,000), and those with larger ratios (e.g. 1:5,000) are called large scale.
Spectral Resolution
Spectral resolution describes the ability of a
sensor
to define fine wavelength intervals. The finer the spectral
resolution, the narrower the wavelength range for a
particular channel or band.
Black
and
white
film
records
wavelengths extending over
much,
or all of the visible portion of the electromagnetic spectrum. Its spectral
resolution is fairly coarse, as the various wavelengths of the visible spectrum are not individually
distinguished and the overall reflectance in the entire visible portion is recorded. Colour film is also sensitive
to the reflected energy over the visible portion of the spectrum, but has higher spectral resolution, as it is
individually sensitive to the reflected energy at the blue, green, and red wavelengths of the spectrum. Thus, it
can represent features of various colours based on their reflectance in each of these distinct wavelength
ranges.
Many remote sensing systems record energy over several separate wavelength ranges at various
spectral resolutions. These are referred to as multi-spectral sensors and will be described in some detail in
following sections. Advanced multi-spectral sensors called hyperspectral sensors, detect hundreds of very
narrow spectral bands throughout the visible, near-infrared, and mid-infrared portions of the electromagnetic
spectrum. Their very high spectral resolution facilitates fine discrimination between different targets based
on their spectral response in each of the narrow bands.
Radiometric Resolution
While the arrangement of pixels describes the spatial structure of an image, the radiometric
characteristics describe the actual information content in an image. Every time an image is acquired on film
or by a sensor, its sensitivity to the magnitude of the electromagnetic energy determines the radiometric
resolution. The radiometric resolution of an imaging system describes its ability to discriminate very slight
differences in energy The finer the radiometric resolution of a sensor, the more sensitive it is to detecting
small differences in reflected or emitted energy.
Imagery data are represented by positive digital numbers which vary from 0 to (one less than) a
selected power of 2. This range corresponds to the
number
of bits used for coding numbers in binary format. Each
bit
records an exponent of power 2 (e.g. 1 bit=2 1=2). The
maximum number of brightness levels available depends
on
number of bits used in representing the energy recorded.
Thus, if
a sensor used 8 bits to record the data, there would be
28=256
digital values available, ranging from 0 to 255. However,
if only
4 bits were used, then only 24=16 values ranging from 0
to
would be available. Thus, the radiometric resolution
the
15
would
be much less. Image data are generally displayed in a range of grey tones, with black representing a digital
number of 0 and white representing the maximum value (for example, 255 in 8-bit data). By comparing a 2bit image with an 8-bit image, we can see that there is a large difference in the level of detail discernible
depending on their radiometric resolutions.
Temporal Resolution
In addition to spatial, spectral, and radiometric resolution, the
concept of temporal resolution is also important to consider in a
remote sensing system. The concept of revisit period, which refers to
the length of time it takes for a satellite to complete one entire orbit
cycle. The revisit period of a satellite sensor is usually several days.
Therefore the absolute temporal resolution of a remote sensing system
to image the exact same area at the same viewing angle a second time is equal to this period. However,
because of some degree of overlap in the imaging swaths of adjacent orbits for most satellites and the
increase in this overlap with increasing latitude, some areas of the Earth tend to be re-imaged more
frequently. Also, some satellite systems are able to point their sensors to image the same area between
different satellite passes separated by periods from one to five days. Thus, the actual temporal resolution of a
sensor depends on a variety of factors, including the satellite/sensor capabilities, the swath overlap, and
latitude. The ability to collect imagery of the same area of the Earth's surface at different periods of time is
one of the most important elements for applying remote sensing data. Spectral characteristics of features may
change over time and these changes can be detected by collecting and comparing multi-temporal imagery.
For example, during the growing season, most species of vegetation are in a continual state of
change and our ability to monitor those subtle changes using remote sensing is dependent on when and how
frequently we collect imagery. By imaging on a continuing basis at different times we are able to monitor the
changes that take place on the Earth's surface, whether they are naturally occurring (such as changes in
natural vegetation cover or flooding) or induced by humans (such as urban development or deforestation).
The time factor in imaging is important when:

persistent clouds offer limited clear views of the Earth's surface (often in the tropics)

short-lived phenomena (floods, oil slicks, etc.) need to be imaged

multi-temporal comparisons are required (e.g. the spread of a forest disease from one year to the
next)

the changing appearance of a feature over time can be used to distinguish it from nearsimilar
features (wheat / maize)
UNIVERSITY QP / QB
QUESTION BANK
UNIT I
1.
2.
3.
4.
5.
6.
7.
What is meant by weathering? Describe its effects on rocks and their constituents.
Write an essay on ‗River as a Geological Agent‘
Describe the various methods adopted in costal protection.
Discuss the various theories that explain the origin of the earth.
Write a essay on the interior of the earth.
Give an account on views of the age of the earth.
Write notes on : a) Exfoliation 2) River Piracy 3) Differential Erosion 4) Run off 5)
Barchans 6) Atoll 8) Spit and bar 9) Seismogram and seismograph 10) River terraces.
8. Give a detailed account of the following : a) Formation of soils. b) Reclamation of desert
lands c) Coral Islands
9. Distinguish between the following group of features:
(a) a young and mature valley
(b) a glaciated and river valley
(c) a submerged and emerged coast line
UNIT II
1) Describe the tests you would perform in trying to identify a mineral in the field.
2) What are the rock forming minerals? Give a general account of their Chemical and
Physical properties.
3) Define the term ‗crystal‘.
4) What are symmetry elements in crystals?
5) Describe the following groups of minerals a) Quartz group b) Felspar group c) Mica
group
6) Compare and contrast the minerals of Pyroxene group to that of Amphibole group.
7) Write short notes on :
a) kinds of luster b) Twincrystals c) Moh‘s scale of hardness d) Flourescence e)
Cleavage and parting f) Walker‘s steelyard balance.
8) Mention the most distinguishing physical properties of the following minerals.
Amethyst, Olivine, Talc, Labradorite, Galena
9) Explain how will you distinguish the following pairs of minerals.
a.
b.
c.
d.
Pyrite and chalcopyrite
Beryl and Apatite
Hornblende and Augite
Calcite and Gypsum
e. Muscovite and talc
10) Give the principle ores, their physical properties, Chemical composition and
distinguishing characters of the following metals.
a. Iron b. Copper c. Manganese d. Zinc e. Aluminum f. Lead
UNIT III
1) Explain the three principal kinds of rocks?
Explain the basis of their classification.
Describe their chief characteristics with example.
2)
3)
4)
5)
6)
7)
8)
Give the difference between Plutonic and Volcanic rocks.
Classify the secondary rocks and describe an example from each.
Write an essay on metamorphism.
What are the important intrusive igneous forms ? Explain with neat sketches.
Give a detailed account of the surfacial features of the sedimentary rocks.
What are the different kind of folds?
Explain the following structural features with sketch.
a. Anticlinorium b. Unconformity c. Horst d. Overlap e. Pitching fold.
9) How will you distinguish the following groups of features.
a)
b)
c)
d)
e)
Dip and Strike
Anticlinal fold and Synclinal fold
Outlier and Inlier
Dip fault and Strike fault
Fault and joint
UNIT IV and V
1.
2.
3.
4.
5.
6.
Describe and classify building stones.
Explain how durability of stones is ascertained.
What are the essential qualities of a good building stone.
What physical test is conducted to determine whether a rock is good for building purpose.
Give an account of the physical properties that go to make a good building stone.
Name and fully describe the physical properties of important rock types that are used as
building stone.
7. Define : a) Water table b) Aquifer c) Permeability of a rock
8. What are the important factors which you will consider in selecting a site for a well?
9. What is meant by ―ground water‖ ? How is it surveyed and explored ?
10. Describe the condition when the under ground water is lifted to the surface by its own
pressure.
11. Give an account of the origin, occurrence and circulation of ground water.
12. How does a tube well differ from an artesian well ?
13. What are the geological factors which you will consider in selecting a site for a tube well
and an artesian well.
14. Briefly explain how you will survey the under ground water resources of any city with
water supply from other sources.
15. What are the geological factors which influence the choice of site for a reservoir ?
16. Discuss the suitability of various geological structures and rock types of reservoirs.
17. What are artificial lakes?
18. Give an account of the Geological factors that influence the location of artificial lakes.
19. What is ― River valley project‖ ?
20. Explain geological and related criteria in the construction of earth dam.
21. What are the geological requirements which will have to be investigated for selecting a
site for a tunnel.
22. What type of lining would you suggest for tunnel driven in a) Unconsolidated b)
Consolidated rocks.
23. Explain briefly the distinction between Landslide and creep.
24. Write shot geological note on a) Landslide b) Artesian well
25. Write the geological factors which affect the stability of hill sides.
26. What precaution will you take against the natural changes to which roads on hill station
are subjected as a consequence of the action of geological agencies.
27. Write short essay on the utilization aspect of geology in engineering.
PART –A
ANSWER ALL THE QUESTIONS
(10 x 2 = 20)
1. Describe the internal structure of the earth.
2. Give the earthquake belts of India.
3. Draw and explain the axial position of the normal class of the tetragonal system.
4. Define laws of symmetry in crystallography.
5. List the tests to be carried out to determine the properties of building stones.
6. What is black granite? List its uses.
7. With the help of a diagram, explain dip and strike of rocks.
8. Describe the anticline fold with neat sketch.
9. List the various coastal protection structures.
10. What is the application of remote sensing in civil engg projects?
PART-B
ANSWER ALL THE QUESTIONS
11. a) Give a brief account of
i)
The importance of geology in civil engg
(5 x 16 = 80)
(8)
ii)
The internal structure and constitution of the earth
(8)
(OR)
b) Describe in detail of the geological work of sea with note on coastal protection (16)
12. a) Give a brief account on various physical properties of minerals that help in their
Identification, and give the suitable examples.
(16)
(OR)
b) Explain the physical properties, mode of occurrence and uses of quartz family.(16)
13. a) Give a detailed account on classification of rocks and explain the texture, structure of
Igneous rocks with examples.
(16)
(OR)
b) List the various rocks that are used as building materials. Also give examples (16)
14. a) What are faults? Describe the important types of faults with neat diagram.
(16)
(OR)
b) Explain the uses of seismic methods in civil engg investigations.
(16)
15. a) How the landslides are occur? Give an account on causes and types of landslides,
Explain the landslide mitigation measures
(16)
(OR)
b) Write notes on
i) Problems associated with reservoirs.(8) ii) Complicated regions for roads and
Remedies for them.
(8)