Engineering Geology Unit 3.pdf

ADITYA
Structural Geology
(UNIT-III)
P Shiva Kumar
Sr. Assistant Professor
Department of Civil Engineering

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Unit-3 Outcomes
At the end of the Course, Student will be able to:
CO 1 : Illustrate the Outcrop, Strike and Dip.
CO 2 : Illustrate the types and mechanism of folding.
CO 3 : Illustrate the types and mechanism of faulting.
CO 4 : Illustrate the joints and unconformities.
CO 5 : Understand the importance of structural
geology and stratigraphy for civil engineers.
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Engineering Geology
P Shiva Kumar, Sr. Assistant Professor, CE

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Contents
Structural Geology
• Strike, Dip and Outcrop.
• Study of common geological structures associating with the
rocks such as Folds.
• Faults.
• Joints and Unconformities- parts, types.
• Mechanism and their importance in Civil Engineering.
• Engineering properties of rocks.
Stratigraphy
• Introduction & Formations in India.
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Engineering Geology

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Engineering Geology
Module 1 : Introduction to Structural Geology and
Folds.
Module 1 : Introduction to Structural Geology and
Folds.

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Introduction to Structural Geology and Folds.
P. Shiva Kumar

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Learning Outcomes
At the end of this lecture, Student will be able to:
LO 1 : Understand the occurrence and types of
secondary rock structures.
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Structural geology is the study of factors such as origin, occurrence,
classification, type and effects of various secondary structures like folds, faults,
joints, rock cleavage, the attitude of secondary rock formations and how they
are different from those primary structures such as bedding and vesicular
structure, which develop in rocks at the time of their formation.
OR
The study of three dimensional distribution of rocks formations with respect to
their deformational histories.
The understanding of the dynamics of the stress areas in the rock formations can
reveal the important events or prevailing conditions of past history of regional
geology of that rock formations.

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Economical Importance of Structural Geology:
• The study of geologic structures has been of prime importance in
economic geology.
• Folded and faulted rock strata commonly form traps for the
accumulation and concentration of fluids such as petroleum and
natural gas.
• Veins of minerals containing various metals commonly occupy faults
and fractures in structurally complex areas.
• Deposits of gold, silver, copper, lead, zinc, and other metals, are
commonly located in structurally complex areas.
• Structural geology is a critical part of engineering geology, which is
concerned with the physical and mechanical properties of natural
rocks.

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Geologic structures are
important for understanding:
1) The locations of earthquakes
(faults).
2) The formation of mountains
(faults and folds). Orogeny and
Epeirogeny .
3) How to locate natural
resources (oil, gold, etc.) by using
geophysical exploration.

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Primary rock structures Secondary rock Structures
Formed from origin of the rock: Formed out of local and regional deformations.
Igneous rock Structures : Intrusive and extrusive
like vesicular, amygdale, columnar, pillow, flow,
dykes, sills, bysmalith, batholiths, lenticulars etc.,.
( growth of formations)
The deformations are fractures: Cracks, fissures,
faults and joints.
Sedimentary rock structures: strata or stratum,
ripple marks, tracks and trails.
( impressions on beds)
The deformations produce in the direction of
forces acting on the rock formations, referred as
attitude of bedding.
Metamorphic rock structures: Gneiss, schist,
granulose and Cataclastic.
( alteration of parent rocks in presence of
pressure and temperature)
The common deformational features are: Folds,
Faults, Joints and Unconformities.

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STRUCTURAL GEOLOGY
Horizontal bedding is modified by:
• Faults: Result of brittle deformation (shallow in crust).
• Folds: Result of plastic deformation (deep in crust).

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The three types of stress:
• Compressive stress – Forces squeeze or push toward one
another from opposite directions (cause shortening or
flattening).
• Tensional stress – Forces pull away from one another in
opposite directions (cause stretching or extension).
• Shear stress – Forces that are offset from one another and
operate in parallel but opposite directions.

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Outcrop, strike and Dip of formations:
An outcrop is the exposed rock, so named because the exposed rock "crops out."
STRIKE is the direction of the line formed by
the intersection of a rock surface with a
horizontal plane.
DIP is the acute angle that a rock surface
makes with a horizontal plane.

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Folds: A fold is a flexure or foliation caused only in sedimentary beds due to compressional and shear
forces.
Parts of folds are :
1. Anticline
2. Syncline
3. Axis
4. Axial plain
5. Hinge
6. Inflection plane
7. Limbs
8. Bedding plain
The inflection points are points of zero curvature, where the sense of curvature changes from a convex
to a concave line.

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Types of Folds

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Geoanticlinal and Geosynclinals

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Synclinal fold Anticlinal fold

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Recumbent Fold
Isoclinal Fold
Dome
fold

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Mechanisms of Folding
• Folding of rocks takes place by different ways of accommodation of
stress. In many cases, slips or shear occur in between the beds.
• The process is similar to slipping of cards which occurs when the set is
fold. If they are not allowed to slip over one another, folding of the set
cannot take place.
• This is the way in which folding generally occur in the case of hard and
competent rock like quartzite's.
• In another kind of folding, folds are characterized by thinning of the
limbs and thickening of crest and troughs. This takes place commonly in
weak and incompetent rocks like shales
• Three distinct mechanisms have been identified for the folding of
rocks: bending (across the fold), buckling ( along the fold parallel to
beds), and passive folding ( at grain level instead of single bed level).

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Causes and Effects of Folding
• Most of the important folds, as already pointed out, are due to tectonic
causes. But a few folds of a minor type are due to non-tectonic causes,
• Mainly, the compressive and shear type of tectonic forces are responsible
for the folding phenomenon. Igneous intrusion of viscous magmas such
as laccoliths and lopoliths also contribute to folding.
• Non-tectonic causes like landslides, creeping, differential compaction,
isostatic setting and glaciations too are responsible for some folds. These
are minor in terms of frequency of occurrence and magnitude.

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Effects of Folding
• When a folded area is affected by weathering and erosion, interesting
topographic features are produced as follows, immediately after
folding, anticlines by virtue of their upward bending appear as hills
and synclines due to downward warping appear as valley.
• During folding in the crest portions, the geological formation are
subjected to tensional forces and hence numerous fractures appear
there. Because of these fractures, crest portions are eroded quickly
leading to conspicuous degradations locally.
• On the other hand, trough portion are highly compressed and hence
offer a greater resistance to erosion. Thus, they stand out in the long
run at a greater elevation, while the adjacent parts degrade fast. The
net result of this response to erosion is that the anticlines will change
over to valleys, while synclines change 'over to hills.

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After completion of module 1 the student is now able to understand
formation of secondary rock structures and mechanism of folding.
Summary

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Engineering Geology
Module 2 : Faults, Mechanism and Effects
Module 2 : Faults, Mechanism and Effects

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Faults, Mechanism and Effects
P. Shiva Kumar

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Learning Outcomes
LO 1 : Understand the occurrence and types of
faults.
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Depending upon the nature and magnitude of stresses and the types of the rocks, the rock bodies
may get fractured into different parts , and relative displacement of blocks may occur for
different distances. These are varying from a few centimeters to many meters and this
displacement may occur in any direction.
The deformation is bending it is referred as fold, while if it is a fracture it is fault.
Various stages showing
mechanism of folding leading
to faulting.

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Fault can be defined as a linear or curvy linear, straight line or planar fracture formed due to
deferential stress developed by loading of rocks and tectonic forces in tight plutonic
environment.
Terminology of fault:
1. Foot wall
2. Hanging wall
3. Slip
4. Fault plane
5. Hade
6. Heave
7. Throw
8. Strike and dip of fault

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https://upload.wikimedia.org/wikip
edia/commons/5/53/California_Dep
artment_of_Conservation_-
_Earthquake_Shaking_Potential_for_
California.jpg
The San Andreas fault line
formed about 30 million
years ago as the North
American plate engulfed
nearly all of the Farallon
plate. ... This fault is one of
the largest faults in the
world, running more than
800 (1,287 kms) miles from
the Salton Sea to Cape
Mendocino. It carves the
state in two.

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Displacement(slip) was measured as the distance along the fault
between the mapped terminations of a given stratigraphic layer(
between bedding planes) at the fault surface. (such as is done in
Williams and Chapman, 1983, and others)
Absolute displacements represents of the faults which are measured
when slip take place where one is static and other one is displacing,
while relative displacements are measured along with the direction of
deformations has both footwall and hanging wall displaces. (In
perspective of loss of friction and tectonic movements).

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Possible absolute slips

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Classification of faults based on
1. Type of displacement along the fault plane.
2. Relative movement between footwall and hanging wall.
3. Type of slip involved.
4. Mutual relation of attitudes of fault plane and adjacent beds.
5. Inclination of fault plane.
6. Mode of occurrence of faults.

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1. Type of displacement along the fault plane. 2. Relative movement between footwall and hanging wall.

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2. Relative movement between footwall and hanging wall.

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3. Type of slip involved.

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4. Mutual relation of attitudes of fault plane and adjacent beds.
Adjacent Strike slip
faults
Adjacent dip slip faults Oblique or diagonal
slip faults

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5. Inclination of fault plane.
High angle fault is gravity or
normal fault
Low angle fault is reverse fault
also know as thrust faults
6. Mode of occurrence of faults.

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Miscellaneous faults

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Step faults and parallel faults
Parallel faults have same strike
and dip amounts
Step faults are normal faults which
are similarly to parallel faults with
regular intervals of faulting.

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Engineering consideration of faults
• Faults cause very much shearing and crushing of rocks located in
the fault zone making the rocks weak on one hand and porous,
permeable on the other hand.
• So following general conclusions can be drawn:
I. The faulted rocks will form weak foundations for the dams.
II. The fault zones will provide easy pathways for the water and
causes leakage when left untreated in the dams.
III.Once the fault zone becomes lubricated with water, the
probability of further slipping becomes high. This may create
critical condition within the foundation.
IV.Faulting products like gouge and breccia create additional
problems.

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Fault gouge and breccia

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Causes of faulting
1. Tensional stress is when slabs of rock are pulled apart. ...
2. Compressional stress is when slabs of rock are pushed together. ...
3. Shear stress is when slabs of rock slide past each other horizontally
in opposite directions.
Evidence of faults
1. Visible displacement of rocks.
2. Pulverized rock and
“Slickensides”.
3. Key beds cut out by faulting
reappear elsewhere.

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1. One of the main effects of the faults on topography is that they very often result in the
development of distinct types of steep slopes which are aptly called fault scarps. Three types of
fault associated scarps are often recognized- fault scarps, fault-line scarps and composite-fault
scarps.
2. Locating buildings, tanks, and pipelines and assessing the seismic shaking and tsunami hazard to
infrastructure and people in the vicinity.

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After completion of module 2 the student is now able to understand the
occurrence and types of faults.
Summary

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Engineering Geology
Module 3 : Joints in rocks
Module 3 : Joints in rocks

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Joints in rocks
P. Shiva Kumar

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Learning Outcomes
LO 1 : Understand the occurrence of joints.
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Joints are the planar structure and simply known as crack along bed/rock without
displacement.
Joints/Fracture is a planar or sub planar discontinuity which causes movement ,and change
in mechanical properties of rock and minerals.
Joints:- A fracture without measurable shear displacement (cracks or tensile fractures)
Fault:- A fracture with measurable displacement.
Parts of joints

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Classification of Joints – Based on geometry

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Classification of Joints – Based on dip

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Classification of Joints – Based on origin

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Type of joints identified in common rocks
1. Columnar joints
2. Pillow joints

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Sheet joints
block joints

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Flaggy lime stone
Flaggy sandstone

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RECOGNITION OF JOINTS
1. Flat or smooth surface, joint surface are develop.
2. Gap between joints.
3. block has been displaced due to faulting the joint may be observed in the field but it is necessary
data in order to convey other end to make pertinent analysis .
Importance of joints
1. Mineral exploration in mining industries.
2. Granite industries for quarrying rock blocks.
3. To find the ground water flow in hydrogeological aspect. Joints acts as permeable layer
for aquifer, oil and gas reservoir, it helps in secondary migration of hydrocarbon.
4. Bed rock analysis for construction of tall building in hill area. In hilly region joints get
easily lubricated due to moisture and start sliding causes landslides.
5. To understand the geology and geomorphology of local area control weathering and
erosion.
6. Joints are important to the economic and safe development of petroleum ,
hydrothermal and groundwater resources and the subject of intensive research relative to
development of these resources.

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occurrence of joints.
Summary

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Engineering Geology
Module 4 : Unconformity
Module 4 : Unconformity

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Unconformities
P. Shiva Kumar

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Learning Outcomes
LO 1 : Understand the occurrence of Unconformities.
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• Unconformity is one of the common geological structure found in rocks.
• It is a product of diastrophism ( Folding and faulting of earth crust leading to formation
of mountains, planes, plateaus and they can divide the streams and change the pattern
of flow).
• Diastrophism can also be referred as geo-tectonics.
• An unconformity is a contact between two rock units in which the upper unit is usually
much younger than the lower unit.
• Unconformities are typically buried erosional surfaces that can represent a break in the
geologic record of hundreds of millions of years or more.
• For example, the contact between a 400 million year old sandstone that was deposited
by a rising sea on a weathered bedrock surface that is 600 million years old is an
unconformity that represents a time hiatus of 200 million years.
• The sediment and/or rock that was deposited directly on the bedrock during that
200 million year span was eroded away, leaving the “basement” surface exposed. There
are three kinds of unconformities: disconformities, nonconformities, and angular
unconformities.

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In geology, the law of
superposition or order of
superposition, states that the
sequence of layers observed
in sedimentary rocks marks
the time of deposition of
the layers. The lowest layer
is the oldest layer of
deposition and the ones
above it are successive
younger layers of deposition
according to the law of
superposition definition.

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An unconformity is surface formed with a disturbance in deposition or with a time gap in deposition
of two conformable series . They occur at three basic types of contacts:
• Depositional contacts, where a sediment layer is deposited over preexisting rock.
• Fault contacts, where two units are juxtaposed by a fracture on which sliding has occurred.
• Intrusive contacts, where one rock body cuts across another rock body.
Parts of unconformities:

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Formation of unconformities
There are two important points in the formation of unconformities:-
1. When there occurs break in deposition of sedimentary beds, there may or may not
occur unconformity due to geological action of weathering and Erosion.
2. First formed set of conformable beds may or may not get inclined or angular due to
the tectonic up-liftment or depressed due to subsidence.
Types of Unconformities
Based on factors like:-
• How many beds are there in the formation,
• The attitude of bedding,
• The extent of the formation,
• And based on types of rocks the unconformities are named.

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1. Non-conformity is when the underlying
formations are igneous or metamorphic and the
overlying deposited formations are sedimentary,
such unconformities are referred non-
conformities.

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2. Angular unconformities occurs
when underlying and overlying
strata of the sedimentary rock
formations is not parallel.

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3. Disconformity occurs when the disturbance in the successive formation of two conformable
series at their contact are (at bedding plane) is just a erosional surface with the presence of
any of the rocks like conglomerates, breccia, bauxite, laterite with a time difference between
to conformable sets referred to be “Haitus”.

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4. A Para-conformity is a type of unconformity
in which strata are parallel; there is no
apparent erosion and the unconformity
surface resembles a simple bedding plane.
5. A buttress unconformity is one in which the
younger, overlying rocks are cut by the contact. This
relationship occurs because the younger sediments are
deposited against the older rocks as they stood out in
topographic relief.

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6. Regional and local unconformities: Regional unconformities occur for several square
kilometres of area appearing to be a size of a mountain, while local unconformities occur
at very small areas less than few square meter of formations.
Recognition of unconformities
1. Difference in attitude of two adjacent beds ( may be or may not be disconformity).
2. Difference in nature, age and types of fossils in adjacent sets of rock.
3. Occurrence of conglomerate, residual soil, laterite, bauxite along the unconformity
surface.
4. Considerable difference in degree of metamorphism of two adjacent sets of beds.
5. Stratigraphic correlation and lithological peculiarities ( difference in attitude of the
formations, textural, structural and mineralogical compositions).

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occurrence of unconformities.
Summary

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Summary
From this unit – 3 students are now able illustrate and
understand the occurrence of minerals and rocks,
their identification.
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Thank you

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