General Geology Acknowledging Dr.V.Nagarajan. UNIT I General Geology CONTENTS Geology in Civil...
If you can't read please download the document
General Geology Acknowledging Dr.V.Nagarajan. UNIT I General Geology CONTENTS Geology in Civil Engineering Branches of geology, Earth Structures and composition,
UNIT I General Geology CONTENTS Geology in Civil Engineering
Branches of geology, Earth Structures and composition, Elementary
knowledge on continental drift and plate technologies. Earth
processes and Ground Water Weathering, Work of rivers, wind and sea
and their engineering importance and Earthquake belts in India.
Mode of occurrence of Ground water, Prospecting & importance in
civil engineering. 2
Slide 3
UNIT I General Geology Geo logy Earth Science It is concerned
with engineering properties of geological materials, including
strength, compatibility, porosity and permeability Present is the
key to the past Branches of Geology 1.Study of composition of earth
mineralogy 2.Study of earth structure 3.Study of earth surface
features 4.Study of earth history 5.Engineering Geology 3
Slide 4
UNIT I General Geology 1.Study of composition of earth
mineralogy a. Mineralogy b. Petrology c. Economic Geology d.
Hydrology and ground water e. Geochemistry f. Geochemical Problems
2.Study of earth structure a. Geodesy b. Geophysics c. Structural
Geology d. Volcanology 3.Study of earth surface features a.
Geomorphology / Physical Geology 4.Study of earth history a.
Historical Geology b. Palaeontology c. Astrogeology 5.Engineering
Geology 4
Slide 5
UNIT I General Geology 5
Slide 6
6
Slide 7
7
Slide 8
8
Slide 9
9
Slide 10
10
Slide 11
UNIT I General Geology 11
Slide 12
UNIT I General Geology 12
Slide 13
UNIT I General Geology 13
Slide 14
UNIT I General Geology 14
Slide 15
UNIT I General Geology 15 Earth Processes It refers to the
geological events, such as weathering, deposition, erosion,
earthquakes, volcanic eruptions and mountain building, that shape
and reshape the surface of the earth. Deep Earth Processes i. Heat
-Radioactive decay. -Gravitational energy released during accretion
and formation of earth ii. Mantle convection iii. Gravitational
forces associated with density differences, due to hot less-dense
magma from mantle. This affect plate movement.
Slide 16
UNIT I General Geology Transformation of rocks into soil 16
Weathering of Rock Soft-weathered rock Soil-forming processes Hard
Rock Soil
Slide 17
UNIT I General Geology Rock Cycle 17
Slide 18
UNIT I General Geology Weathering Total sum of decomposition
and disintegration 18 Magma Magma Solidification Formation of Rocks
& Minerals Deposition Weathering of Rocks Landforms of
weathering eg. Soil, caves etc. Sediment Production Land formation
by erosion processes eg. River, valley etc. Erosion Process
Landform formation by deposition of sediments eg. Sand bars,
glacial, deltas, etc. Sediment Transportation Deposition of
Sediments Decomposition of rocks and minerals Erosion of sediments
by wind, water and ice Decomposition of sediments by wind water,
water and ice
Slide 19
UNIT I General Geology Types of weathering 1.Physical
Weathering 2.Chemical Weathering 3.Biological Weathering 1.Physical
Weathering / Mechanical weathering Caused by the effect of changing
temperature on rocks i.Freeze thaw a. water seeps into cracks of
rock, freezes and expands b. Most effective in jointed rocks c.
Volume expands by 9% in volume d. Alternate freeze thaw results in
spilt of rocks and it breaks off ii. Exfoliation a. Cracks develop
parallel to land surface as a result of uplift and erosion b. Rocks
get peeled off in sheets rather than eroded grain by grain Physical
weathering does not lead to alternation of rocks 19
Slide 20
UNIT I General Geology 2. Chemical Weathering Process of
mineral alternation due to chemical reactions Process :
Carbonation, Hydration, Hydrolysis, Oxidation and ion exchange in
solution i. Carbonation a. Carbon di oxide reacts with rocks, which
contains calcium carbonate (limestone and chalk) b. It takes place
when rain combines with carbon di oxide or organic acid to form
weak carbonic acid with calcium carbonate c. Decrease in
temperature ii. Hydrolysis a. Water combines with substances in
rocks, which is softer than original rock b. Silicate and
Carbonates are affects the minerals c. Pure water ionizes and
reacts with silicate minerals iii. Oxidation a. Oxygen combines
with other element to form new rocks b. New rock softer and easy to
break Temperature is in equilibrium - minerals in rock formed
beneath the surface 20
Slide 21
UNIT I General Geology 3. Biological Weathering/Organic
Weathering Biological process of weathering that breaks down the
rock i.Physical penetration and growth of roots and digging
activity of animals ii.Release of chelating compounds and
acidifying molecules 21
Slide 22
UNIT I General Geology Factors affecting weathering 1.
Composition of rocks Acidic rocks weather more quickly than basic
rock. Limestone and chalk are soluble in rain water and subjected
to carbonation - solution 2. Climatic condition Moisture,
temperature, wind and air pressure determines the weathering action
by making it more rapidly 3. Topography and vegetation By exposing
rocks to sun, wind and vegetation 4. Grain Size Rate of weathering
is high in coarse grain soil than fine grain soil 5. Human activity
Industrial activity and human development 22
Slide 23
UNIT I General Geology Erosion Wearing away of earths surface
material by any natural process and its transportation by natural
agencies ( Wind and running water) Agents of Erosion 1. Water
Erosion Hydraulic action of the water itself moves the sediments,
water acts to corrode sediments by removing ions and dissolving
them and particles in the water strike bedrock and erode it 2. Wind
Erosion Occur in the place where there is less rainfall. Movement
of material by the wind and occurs when the lifting power of moving
air is able to exceed the force of gravity 3. Glacial Erosion
Wearing-down and removal of rocks and soil layers by a glacier. The
erosion work of glaciers is accomplished through the processes of
abrasion, plucking and polishing 4. Water Erosion Wind blows over
the ocean and sea surface. Top layers move faster than the lower
layers and tumbles over it. Erosion of sand is more easier for the
waves as compared to rock. 5. Gravity Erosion Gravitational erosion
causes mass movement of rock and sediments due to the force of
gravity. Different form of gravitational erosion include avalanche,
landslide, debris flow, mudflow and sinkhole formation 23
Slide 24
UNIT I General Geology PLATE TECTONICS 24
Slide 25
UNIT I General Geology PANGAEA Most species exist for a limited
period of geological time and then become extinct. Within the
fossil record there are also instances of mass extinctions.
Evidence of six mass extinctions can be seen in the fossil record.
There are two primary events that are believed to have contributed
to these mass extinctions. The movement of the Earth's surface via
continental drift is one such event. Plate tectonics provides the
explanation for why continental drift occurs. The earth's crust is
made up of many different plates that move around independently of
each other. Where the plates collide with each other, mountains can
be formed and there are earthquakes. Mount Everest is getting
measurably taller each year because of this activity. The current
direction of the drift of the plates has been determined using GPS
data from satellites. By assuming that the plates have always been
moving in the directions they are moving now, all the plates would
have been connected together as a huge supercontinent called
Pangaea. 25
Slide 26
UNIT I General Geology Plate Tectonics is a geologic theory
explaining the movements and forces in the Earth crust. Earth's
surface is made up of tectonic plates. A tectonic plate is a large
section of land made of the Earth's crust and the upper layer of
the Earth's mantle. Tectonic plates vary in size and shape. The
theory of plate tectonics was first formulated by the scientist
Alfred Wegener at the beginning of the 20th century. According to
this theory, the Earth's crust is divided into about 28 large,
slowly- moving plates, called tectonic plates. The movement of
tectonic plates is called plate tectonics. All continents, oceans
and islands sit on tectonic plates. Scientists are still arguing
about the exact number of tectonic plates, so different sources
might have different numbers. Tectonic plates are constantly moving
and interacting with each other, generating enormous and very
powerful forces. These forces are the main and the strongest
'shapers' of the Earth's landforms. Plate tectonics cause
continents to move and shake and volcanoes to erupt. 26
Slide 27
UNIT I General Geology Continental drift Continental drift is
the movement of the Earth's continents relative to each other by
drifting across the ocean bed. The speculation that continents
might have 'drifted' was first put forward by Abraham Ortelius in
1596. The concept was independently (and more fully) developed by
Alfred Wegener in 1912. The theory of continental drift was
superseded by the theory of plate tectonics. The hypothesis that
the continents had once formed a single landmass before breaking
apart and drifting to their present locations was first presented
by Alfred Wegener to the German Geological Society on 6 January
1912. 27
Slide 28
UNIT I General Geology Types of Plate boundaries There are
three types of boundaries between lithospheric plates: 1.
Convergent boundary plates converge, or come together. If a plate
of oceanic lithosphere collides with thicker and less dense
continental lithosphere, the denser oceanic plate will dive beneath
the continent in a subduction zone. 2. Divergent boundary two
plates diverge or move apart New crust or lithosphere is formed. 3.
Transform fault boundary plates slide past one another with no
creation or destruction of lithosphere 28
Slide 29
UNIT I General Geology 29
Slide 30
UNIT I General Geology Implications of Plate Tectonics 30
Oceanic lithosphere is constantly being created at divergent plate
boundaries, destroyed at convergent plate boundaries, and offset at
transform plate boundaries Oceans are temporary features In the
past 600 million years, Atlantic has opened, closed and reopened
(we are now witnessing only the latest opening event)
Slide 31
UNIT I General Geology Types of Convergent Boundaries 31
Oceanic-oceanic convergence -subduction of oceanic lithosphere
under another plate of oceanic lithosphere -molten material from
subducting slab rises to form an island arc (e.g. Japan)
Oceanic-continental convergence -subduction of oceanic lithosphere
under a continental lithosphere -molten material from subducting
slab rises to form an continental arc (e.g. Cascades with Mt. St.
Helens) Continent-continent collision -where two pieces of
continental lithosphere meet (intervening ocean becomes completely
closed) -continental lithosphere cant be subducted, so basically
shortens -Earths highest mountain belts produced in this way (e.g.
Himalayas)
Slide 32
UNIT I General Geology 32 Model for sea-floor spreading showing
expansion of ocean ridges (divergent) and arc- trench (convergent)
systems. Three lithospheric plates are shown moving over the weak
low-velocity zone of the upper mantle. Magmas are produced in arcs
by heating along the subduction zone. Deep earthquakes are
concentrated in the relatively cool, brittle downgoing slab.
Shallower earthquakes occur under the spreading ridges.
Slide 33
UNIT I General Geology Importance of India's Seismic Zoning Map
This kind of map is mainly used by the Department of Disaster
Management of the different state governments in the country. This
map helps them in planning for a natural disaster like earthquake.
An Indian seismic zoning map assists one in identifying the lowest,
moderate as well as highest hazardous or earthquake prone areas in
India. Even such maps are looked into before constructing any high
rise building so as to check the level of seismology in any
particular area. This in turn results in saving life in the long
run. Following are the varied seismic zones of the nation, which
are prominently shown in the map: Zone - II: This is said to be the
least active seismic zone. Zone - III: It is included in the
moderate seismic zone. Zone - IV: This is considered to be the high
seismic zone. Zone - V: It is the highest seismic zone. Indian
Standard Code Available IS 1893 Criteria for earth resistance
structure IS 4326 Code of Practice for earth quake resistance
33
Slide 34
UNIT I General Geology 34
Slide 35
UNIT I General Geology Geological work of Water >>
Approximately 75 % of earths surface is covered with water. Out of
which 97% is salt water, 2% is glacier ice at north and south poles
and 1% is fresh water >> Water present in earth ->
channels, streams, rivers, lakes, ground water, sea and oceans
>> Hydrological cycle components like evaporation,
transpiration, condensation, precipitation and runoff ->
reaching sea 1.Geological work of running water 2.Geological work
of ground water 3.Geological work of sea and ocean 4.Geological
work of Glaciers 35
Slide 36
UNIT I General Geology 1. Geological work of running water
a.River Profile b.River Meanders c.Oxbow lake d.Levees e.Gorges and
Canyons f.Deltas a.River Profile Longitudinal profile and it is
function of lithology of area through which stream flows,
discharge, amount and texture of channel, regional gradient Flow
and discharge depends upon climate, geologic and geomorphic
properties of river drainage basin area Water in river is
accumulated from precipitation of ground water 36
Slide 37
UNIT I General Geology b. River Meanders River flowing over
gently in sloping ground, begin to curve back and forth across the
land scape It forms when moving water in a stream erodes the outer
banks, widens its valley and deposit it on inner curve in further
down stream Its sinuosity is very high i.e > 1.5 Deepest part of
the channel is outside the bed. The water flows faster in these
deeper section and erodes the material. The water flow slowly in
shallow depth and it cannot carry much sediments Helps in under
standing the reason behind change in river flow over time,
direction and flow of river Coriolis force generate erosion on one
bank and deposit of sediment on the opposite bank and secondary
currents cause flow erode portion until redistribution of velocity
forming tortous water course 37
Slide 38
UNIT I General Geology c. Oxbow Lake Crescent shaped lying
alongside, formed due to erosion and deposit of soil along the
river course Area : Flat, low-lying plains, rivers often empties
into another body of water Have high sinuosity and opportunity for
longer lake formation River with lower sinuosity characterised by
fewer cutoffs and shorter oxbows due to shorter distance of their
meanders (Constantine and Thomas, 2008) 38
Slide 39
UNIT I General Geology d. Leeves Embankment raised to prevent a
river from overflowing which runs along banks of river or canal Can
be man made or naturally formed Natural : due to sediments settle
on river bank, raising the level of the land around the river
Artificial : to prevent flooding, to slow down the natural course
of watercourse. usually built by piling the earth on cleared and
levelled surface It is made from stones laid in horizontal rows
with bed of spetchel Formation of Natural Leeves 39
Slide 40
UNIT I General Geology e. Gorges and Canyons Deep, narrow
valley with steep rocky sides Canyon: formed by erosion caused by
rivers. Cliff of canyons are made of harder rock. These are recent
addition of rocks. Formed mainly due to physical weathering Gorges:
small and narrow than Canyon Canyons Gorges 40
Slide 41
UNIT I General Geology f. Deltas Low-lying landform at mouth of
a river, known for fertile soil and abundant vegetation River
reaches a lake or sea. Flow is slow and have less power to carry
sediments River drop so much sediment that waves and tides cant
carry. It builds up in layer forming delta. Area: Flat and plain
above water Tide dominant delta : Long and narrow offshore basin or
islands at mouth of the river Wave dominant delta : triangle in
shape River dominant delta : birds foot 41
Slide 42
UNIT I General Geology 2. Geological work of ground water Found
beneath the earths surface and occupies cracks and pores within
rock material. Can cause erosion because the GW begins to wear away
the materials and soil in ground Formation of acid is possible and
possibility to dissolve the minerals a.Formation of Karst
Topography b.Formation of caves c.Karst Valley a.Formation of Karst
Topography Landscape are characterised by numerous caves,
sinkholes, fissures and underground streams. It is formed by
dissolving action of water. Karst landscape develop where bedrock
is comprised of extremely soluble calcium carbonate rock and mainly
where bed rock is limestone Karst landscape constitute only about
10 to 20 % of earths surface (Palmer, 1991) 42
Slide 43
UNIT I General Geology 43 Active Process of Karst
Topography
Slide 44
UNIT I General Geology b. Formation of caves Underground
passages and chambers are commonly known as caves or caverns It is
seen in areas where limestone is abundant and rainfall is
sufficient ground water may be significant erosion agent producing
large cavities and caves The cave thus formed mainly depend upon
the lime in the limestone. Formation begins when rainwater absorbs
carbon di oxide as it falls on the atmosphere. 44
Slide 45
UNIT I General Geology c. Karst Valleys Blind Valley: Abrupt
end of karst formation Half blind Valley: Surface is occasionally
present downstream of sinkpoint Allogenic Valley : Deep gorge like
valley formed as a stream flows from non krastic region into
karstic region Dry Valley: Well developed valley without any
stream. de as it falls on the atmosphere. 45
Slide 46
UNIT I General Geology 3. Geological work of sea and ocean
(Stagnant Water) Approximately 70 to 75 % of earth is ocean and
sea. Processes of hydraulic action, corrosion and attrition play
vital role in sea and oceanic water formation Geological features
a.Coral reefs b.Deep water clastic reefs a.Coral Reefs Built on
hard surface and found in oceans and lagoons. It is type of marine
ridges or mounds formed as a result of accumulation, deposition and
compaction Great barrier reef is the largest coral reef in world
Types of coral reefs : Fringing,Barrier reefs and Atoll b. Deep
water Clastic reefs Deposited on continental slope between neritic
and abyssal zone Deepwater deposit provide excellent reservoirs of
oil and gas world wide Thick and sandy turbid layers to form
excellent oil and gas reservoirs burried deeply beneath the sea
floor. 46
Slide 47
UNIT I General Geology 4. Geological work of Glaciers Glaciers
themselves do relatively little significant erosion because ice is
so soft. Under the weight of an ice sheet thousands of feet thick
continental glaciers detach material from the surface by crushing
the underlying bedrock. Once the material is loosened from the
surface, ice can quarry (also known as plucking) the rock by
freezing around and into fractures, then lifting it from the
surface. The rock embedded in the ice gouges and smoothes bedrock
surfaces by abrasion. Striations are fine scratches left in bedrock
by abrasion. At a larger scale, linear grooves are ground into the
bedrock in the direction of ice movement. Episodic movement leaves
crescent-shaped marks called chatter marks gouged into the bedrock.
The constant abrasion of exposed rock also creates polished
bedrock. Glacial drift is the general term applied to materials
eroded from the surface and deposited by glaciers. Glaciers
transport the embedded material towards the front of the glacier as
if they were on a conveyor belt, or is deposit directly beneath the
ice. Most material is embedded in the lowest few meters of the
glacier and along its sides. Little drift material is lodged in the
interior as flow through most of the glacier is laminar, except at
the nose where thrust faulting of the ice occurs. When the ice
becomes so burdened by its load of soil and rock fragments, it
deposits the mixture of fine and coarse textured material in place
as glacial till. Till is distinguished by its lack of sorting.
47
Slide 48
UNIT I General Geology Mode of soil transportation through
water Rain fallGroundwater 48
Slide 49
UNIT I General Geology Hydrogeological Investigations: This
enable to predict the influence of GW upon engineering works i.e as
a source of water supply. The location and thickness of aquifer
horizons and zones, their confinement and their hydrogeological
boundaries. The GW levels,their variation over area and fluctuation
with time. The storage and transmissive characters of the ground.
Quality of the GW. Sub surface Investigations are required to
confirm: The GW level The depth, thickness and lateral extent of
aquifers and aquicludes. The permeability of these zones and the
storage of the aquifers Chemistry of the aquifers and their
contained water, Temp, if required. 49
Slide 50
UNIT I General Geology Geophysical methods suitable for most
bore holes and commonly used in Hydrogeology 50 S.No Logs for
defining condition of Strata 1B.H.MeterCalipers: reveals fractures,
cavities, strata boundaries 2Electrical- Potential Self potential :
for boundaries and type of strata. 3RadiationNeutron for porosity
Gamma for density 4Visual Television- for visual Logs for defining
fluid conditions 5TemperatureReveals permeable horizons intersected
by bore- hole 6FlowAs for temperature 7 Electrical- Potential
Conductivity: for fluid composition salinity.
Slide 51
UNIT I General Geology Importance of Geology in Different Civil
Engineering Projects 1.Systematic knowledge of construction
materials, their structures and properties such as quality of
stones, lime, cement, etc. 2.Knowledge of foundation engineering
like assessment of soil, rate of erosion, transportation and
erosion by surface and ground water which helps in soil
conservation, river control, coastal and harbours. 3.Knowledge
about nature of rocks, necessary for all tunnelling and dam
projects, construction of roads and in determining the stability of
cuts and slopes. 4.Foundation problems of dams bridges and
buildings are directly related with geology. The location of
bridge, tunnel and dam construction site are decided after detailed
geological survey 5.All water resources engg projects ->
subsurfcae lithology, quality and discharge capacity 6.Geological
map and section help in planning engineering projects 7.Any
geological structure like faults, joints, beds, folds, solution
channels, dyke and fractures -> if found check for stability
8.Knowledge of natural diasters -> earthquake, flooding and
drought 9.Pre-geological survey ->reduces the cost of
engineering works 51