Geology introduction civil engineering

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INTRODUCTION
 Geology, one of the core science disciplines with
physics, chemistry, and biology, is the search for
knowledge about the Earth, how it formed,
evolved, and how it works. Geology is often
presented in the broader context of
Geosciences; a grouping of disciplines
specifically looking for knowledge about the
interaction between Earth

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Types of GEOLOGICAL
STRUCTURES
 Foliation
 Folds
 Faults
 Joints
 Unconformities

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 geologic structures up until now, we have
focused our attention mostly on!
 flat-lying rocks, i.e. sedimentary or volcanic
layers!not all

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Geological structures.
 dynamically produced patterns or
arrangements of rock or sediment that result
from forces acting within the Earth

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Strike
 Direction of a line formed by the intersection of
a foliation plane & a horizontal plane.
 It is a horizontal line on a surface of rock beds.
 If the beds are not horizontal, lines joining the
points with same elevation (on one foliation
plane) are called strike lines.
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Measuring the strike
 Strike is usually reported as a measurement of
compass direction. Due north is considered to be
000°, due east is 090°, due south is 180 °, due west
270°, northwest 045° etc.
 The compass was held parallel to the strike line &
the orientation read relative to magnetic north.
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By definition, a strike line trends in 2
directions exactly 180° apart. It is needed to
specify only one direction. By convention, the smaller
of the 2 numbers is considered.
Line 1 strikes at 45°, line 2 strikes at 55°, and line 3
strikes at 60°.
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10
N 300 E N 550 W
900
00

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Dip
 The amount and direction of inclination is
also used to describe orientation of bedding.
 The dip is defined as the amount of
inclination measured from the horizontal
plane downwards.
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Measurement of dip
 The dip is reported as degrees measured
downward from a horizontal plane.
 By convention, the dip of an inclined bed
cannot exceed 90°.
 Beds with dips of 90° are said to be vertical.
Beds that have been overturned have
technically been rotated more than 90°, but
their dips are still reported as less than 90°.
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 The long side of the symbol records the strike
direction (N45°E) and the smaller tick shows the
direction of dip (SE).
 The number gives the amount of dip (30°)
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Determination of strike
 A strike line joins points of equal elevation on a
particular bedding plane.
 The strike line is always at right angles to the dip
direction.
 In determining the strike line, two points of equal
elevation of a particular boundary of a bed on a
geological map are located.
 The line formed by joining these two points will give a
strike line. Its altitude will be the same as that of the
corresponding contour.
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(A) Determination of strike & dip directionon a map
(B) Determination of dip by graphical method
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Determination of dip direction
 The dip will be at right angles to the strike
direction.
 In order to find the dip direction, a line xy is
drawn at right angles to the strike lines.
 Dip direction is from the strike of higher
elevation to that of lower elevation. It is
indicated by the arrow on the xy line.
 Amount of dip
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What are Folds?
 Warps in rock layers and occur bended upwards,
downwards, or sideways.
 Compression forces are the main causes of folds.
 Folds are important causes of mountain formation.
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Fold Terminology
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crest

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Folds
 Can be defined as the curved or zig-zag
structure shown by rock beds.
 They consist of arches & troughs alternatively &
generally occur in groups.
 Two main types.
 Anticline
 Syncline
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Anticline
 An up-fold where the
limbs dip away from the
axis of fold on either side.
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Syncline
 A down-fold where the limbs dip towards the axis of fold
on either side.
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Geometry of a fold
 Fold axis – Line joining planes of sharpest
folding.
 Axial plane – Includes axis and divides the fold
symmetrically as possible
 Plunging fold – If the fold axis is not horizontal,
fold is called plunging.
 Plunge – Angle between horizontal plane & axis
 Limbs – Sloping sides of a fold
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Plunging folds
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Classification of folds
 Symmetrical fold – Axial plane is vertical, limbs
dip in opposite direction in the same angle
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 Asymmetrical fold - Axial plane is inclined, Limbs dip
in opposite direction at different angles
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 Overturned fold – An asymmetrical fold whose one limb
is turned past the vertical. Axial plane is inclined & both
limbs dip in the same direction.
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 Recumbent fold - The folding is so intense both
limbs become almost horizontal. The Axial plane also
becomes nearly horizontal.
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Recumbent folds
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Overturned folds
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Fault
fault, in geology, a planar or gently curved fracture in
the rocks of the Earth’s crust, where compressional or
tensional forces cause relative displacement of the
rocks on the opposite sides of the fracture
Faults may be vertical, horizontal, or inclined
at any angle

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• When rocks slip past each other in faulting, the
upper or overlying block along the fault plane is
called the hanging wall, or headwall;
• the block below is called the footwall.
• The fault strike is the direction of the line of
intersection between the fault plane and the
surface of the Earth.
• The dip of a fault plane is its angle of inclination
measured from the horizontal.
• Faults are classified according to their angle of
dip and their relative displacementz

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There are three kind of fault call as,
• Normal dip-slip faults
• Reverse dip-slip faults
• Strike-slip faults

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Normal fault
Normal dip-slip faults are produced by vertical
compression as the Earth’s crust lengthens. The hanging
wall slides down relative to the footwall. Normal faults
are common; they bound many of the mountain ranges
of the world and many of the rift valleys found along
spreading margins of tectonic plates

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Reverse dip-slip faults
Reverse dip-slip faults result from horizontal
compressional forces caused by a shortening, or
contraction, of the Earth’s crust. The hanging wall moves
up and over the footwall.

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Strike-slip fault
Strike-slip (also called transcurrent, wrench, or
lateral) faults are similarly caused by horizontal
compression, but they release their energy by rock
displacement in a horizontal direction almost
parallel to the compressional force

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Joints

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TYPES OF JOINT
 Tension Joints – Due to tensional forces. Relatively open
& have rough & irregular surfaces.
 Shear Joints – Due to compression forces involved in
folding & faulting of rocks. Rather clean cut & tightly
closed.
 Strike Joints – Run parallel to the strike of the country
rocks.
 Dip Joints – Run parallel to the direction of dip of the
country rocks.

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JOINTS…
 Advantages
 Good source of ground water
 Disadvantages
 In rock quarries blasting become difficult & rock quality is poor
 Outer & Inner breaks in tunnels
 More liable to landslides, rockslides & mudflows
 Foundation problems
 Excavation need more supports

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UNCONFORMITIES

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Unconformities
 An unconfAormity is an old erosion
surface which separates younger series
of rocks from the older series.
 Angular Unconformities
 Disconformities
 Nonconformities

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Development of an
Unconformity
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Angular Unconformity
 An unconformity in which the upper and lower
layers are not parallel
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Disconformities
An unconformity in which the upper and lower layers
are horizontal
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Disconformi
ties

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Nonconforty
 When bedded
sedimentary
rocks overlie the
non-bedded
igneous mass,
the structure is
called
“Nonconforty”.
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Angular unconformity on San Miguel Island, May, 2004

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Nonconformity in Canada Halcon, February,
2007

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Tilted nonconformity, Canada Halcon, February, 2007