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General Geology
Acknowledging
Dr.V.Nagarajan
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.
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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.
2.
3.
4.
5.
Study of composition of earth mineralogy
Study of earth structure
Study of earth surface features
Study of earth history
Engineering Geology
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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
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UNIT I General Geology
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.
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UNIT I General Geology
Transformation of rocks into soil
Hard Rock
Soft-weathered rock
Soil
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Rock Cycle
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Weathering
Total sum of decomposition and disintegration
Magma
Magma Solidification
Formation of Rocks & Minerals
Weathering of Rocks
Decomposition of
rocks and minerals
Landforms of weathering
eg. Soil, caves etc.
Sediment Production
Erosion Process
Erosion of sediments by
wind, water and ice
Land formation by erosion
processes eg. River, valley etc.
Decomposition of
sediments by wind
water, water and ice
Landform formation by
deposition of sediments
Sediment Transportation
Deposition
eg. Sand bars, glacial, deltas, etc.
Deposition of Sediments
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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
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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
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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
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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
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UNIT I General Geology
Erosion
Wearing away of earth’s 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
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UNIT I General Geology
PLATE TECTONICS
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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.
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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, slowlymoving 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.
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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.
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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
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UNIT I General Geology
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UNIT I General Geology
Implications of Plate Tectonics
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)
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UNIT I General Geology
Types of Convergent Boundaries
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 can’t be subducted, so
basically shortens
-Earth’s highest mountain belts produced in this
way (e.g. Himalayas)
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UNIT I General Geology
Model for sea-floor spreading showing expansion of ocean ridges (divergent) and arctrench (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.
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UNIT I General Geology
Importance of India's Seismic Zoning Map
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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:
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Zone - II: This is said to be the least active seismic zone.
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Zone - III: It is included in the moderate seismic zone.
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Zone - IV: This is considered to be the high seismic zone.
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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
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UNIT I General Geology
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UNIT I General Geology
Geological work of Water
>> Approximately 75 % of earth’s 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.
2.
3.
4.
Geological work of running water
Geological work of ground water
Geological work of sea and ocean
Geological work of Glaciers
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UNIT I General Geology
1. Geological work of running water
a.
b.
c.
d.
e.
f.
River Profile
River Meanders
Oxbow lake
Levees
Gorges and Canyons
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
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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
It’s 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
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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)
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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
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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
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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 can’t 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 : bird’s foot
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UNIT I General Geology
2. Geological work of ground water
Found beneath the earth’s 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 earth’s surface (Palmer, 1991)
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UNIT I General Geology
Active Process of Karst Topography
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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.
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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.
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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.
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UNIT I General Geology
4. Geological work of Glaciers
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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.
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UNIT I General Geology
Mode of soil transportation through water
Rain fall
Groundwater
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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.
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The GW levels,their variation over area and fluctuation with time.
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The storage and transmissive characters of the ground.
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Quality of the GW.
Sub surface Investigations are required to confirm:
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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.
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UNIT I General Geology
Geophysical methods suitable for most bore holes and
commonly used in Hydrogeology
S.No
Logs for defining condition of Strata
1
B.H.Meter
Calipers: reveals fractures, cavities, strata
boundaries
2
ElectricalPotential
Self potential : for boundaries and type of strata.
3
Radiation
Neutron – for porosity
Gamma – for density
4
Visual
Television- for visual
Logs for defining fluid conditions
5
Temperature
Reveals permeable horizons intersected by borehole
6
Flow
As for temperature
7
ElectricalPotential
Conductivity: for fluid composition salinity.
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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
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