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1. INTRODUCTION

1.1 Definition and Concept

Engineering geology is an interdisciplinary field in which pertinent studies

in geology and other geosciences areas are applied toward the solution of

problems involved in engineering works and resources uses. Geology is the

study of the earth, its history, its exterior as well as interior and the processes

that act up on it. Geology is also referred as the earth science or geoscience.

The word Geology comes from the Greek geo, “earth”, and logia, “The study

of”. Geologists seek to understand how the earth is formed and evolved into

what it is today, as well as what made the earth capable of supporting life.

Geology is the study of the changes that the earth has undergone as its

physical, chemical and biological systems have interacted during its billions

years history.

1.2. Requirement of geological study in the field of civil engineering

Nepal is a mountainous country. Since the Himalayan range is a result of

collision of Tibetan and Indian Plates, the zone is the most active tectonic

zone. The area is widely known for its structural deformation. Due to this

Nepal is suffering from different types of geohazards and instabilities. The

rapid construction of infrastructure such as roads, irrigation canals and dams,

without due relating geology and engineering may cause failure of such

infrastructures. So the study of geology is necessary in civil engineering.

Study of Geology helps in mining, town planning, in irrigation, buildings,

transportation, hydropower, industries etc.

2. Location

To study the geological structures we choose Malekhu of Nepal as the right

place. It lies in the Dhading district of Nepal.

3. Objectives of the Field Visit.

To Study and Identification of Rocks and minerals.

To Study the different Geological structures.

To Handling of the Geological Compass.

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To Measurement of the attitude of planar feature like joint, bedding,

foliation etc.

To study the geological works of physical agents.

To Study of features developed by activities of physical agents.

4. Methodology

We went to the site and observe the geological structures and recognize the

structure and its composition with along its formation. Although the

methodology used for the projects differs from one to the other, all these

projects have three basic similarities. First, they all require an evaluation of

the site geology, i.e. rock types, extent of each rock unit, extent and type of

weathering, etc. This is usually done by conducting detailed site exploration

and investigation using surface mapping, boreholes, trenches, or geophysical

survey. Site exploration and investigation is usually conducted in several steps

(preliminary, advanced, etc.). Second, all the aforementioned projects require

an assessment of the engineering properties (strength, deformability,

permeability, etc.) of the soils and rocks involved in the projects. This is done

by testing rock or soil samples in the laboratory and by field testing. Finally,

engineers need to take into account possible geologic hazards and their impact

on existing and future structures. In general, geological hazards can be divided

into hazards from geological materials (reactive minerals, asbestos, gas

hazards), and hazards from geological processes (volcanoes, earthquakes,

landslides and avalanches, subsidence, floods, coastal erosion).

5. Study and Identification of Rocks and Minerals

Rock is defined as naturally forming hard and compact solid aggregate,

assemblage of minerals forming earth’s crust. Minerals can be defined as the

naturally occurring inorganic substance with fixed composition. There are

three types of rock, they are:-

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5.1 Igneous Rock:

Form from hot, molten (liquid) rock material that originated deep within

Earth. Only igneous rocks have this origin. Hot, liquid rock is called magma.

(At Earth’s surface magma is known as lava.) We have learned that Earth’s

temperature increases as we go deeper within the planet. In some places

within Earth, it is hot enough to melt rock. When this molten rock rises to or

near Earth’s surface where it is cooler, the liquid rock material changes to

solid rock. Igneous rocks are especially common around volcanoes and in

places where large bodies of rock that have melted and then solidified

underground have been pushed to the surface. So the rock formed by the

cooling and crystallization of magma is known as igneous rock and the

process is known as magmatism.

Figure: Igneous Rock

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5.2 Sedimentary Rock:

Within Earth’s crust, igneous rock is the most common rock type. However,

most of the surface of our planet is covered with a relatively thin layer of

sedimentary rocks. Unlike igneous rocks, it is difficult to give a precise

definition of sedimentary rocks. Most sedimentary rocks are made of the

weathered remains of other rocks that have been eroded and later deposited as

sediment in layers. Over time, the sediments are compressed by the weight of

the layers above them. In addition, the layers may be cemented by mineral

material left by water circulating through the sediments. The cementing

material is usually silica (fine-grained quartz), clay, or calcite. All sedimentary

rocks are formed at or near Earth’s surface. Although this description applies

only to the classic, or fragmental, group of sedimentary rocks, these are the

most common rocks of sedimentary origin. Fossils are any remains or

impressions of prehistoric life. If fossils are present in a rock, the rock is almost

certainly a sedimentary rock. The processes that create igneous and

metamorphic rocks usually destroy any fossil remains.

We can recognize sedimentary rocks because they are usually composed of

particles, often rounded particles, compressed and cemented into layers. Shale,

the most common rock on Earth’s surface, is made of particles of sediment too

small to be visible without magnification. Shale breaks easily into thin layers.

Identification of Sedimentary rock.

Random orientation of rocks and sediments.

Sediments are cemented by fine matrix.

Have thick bedding plane.

Cross Sectional View of Sedimentary Rock

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5.3 Metamorphic Rock

Metamorphic rocks are formed by subjecting any rock type—sedimentary

rock, igneous rock or another older metamorphic rock—to different

temperature and pressure conditions than those in which the original rock was

formed. This process is called metamorphism; meaning to "change in form".

The result is a profound change in physical properties and chemistry of the

stone. The original rock, known as the protolithic, transforms into other

mineral types or else into other forms of the same minerals, such as

by recrystallization.[ The temperatures and pressures required for this process

are always higher than those found at the Earth's surface: temperatures greater

than 150 to 200 °C and pressures of 1500 bars. Rocks compose 27.4% of the

crust by volume.

The three major classes of metamorphic rock are based upon the formation

mechanism. An intrusion of magma that heats the surrounding rock causes

contact metamorphism—a temperature-dominated transformation. Pressure

metamorphism occurs when sediments are buried deep under the ground;

pressure is dominant and temperature plays a smaller role. This is termed

burial metamorphism, and it can result in rocks such as jade.. Where both heat

and pressure play a role, the mechanism is termed regional metamorphism.

This is typically found in mountain-building regions.

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5.4 Description of Rocks Identified in the field.

Right Bank of Malekhu Khola about 1.5 km upstream

S.N. Sample No. A B C

1. Color Shiny grey White White

2. Texture Crystalline crystalline Crystalline

3. Structure/

Cleavage

Foliation/ Schistocity

cleavage

Random

Orientation

Foliation

4. Specific Gravity Medium High High

5. Mineral

Composition

Chlorite, Muscovite,

Biotite, Quartz, Granite

Muscovite, Biotite,

Plajiaclasez, quartz

Calcite

6. Acid test/Hammer

scratch test

Not done Not done Vigorously

react with acid

7. Rock types Metamorphic rock Igneous rock Metamorphic

rock

8. Rock Name Schist rock Granite Marble

9. Engineering

properties

a) Strength

b) Drillability

c) Blastibillity

Medium

High

Low

High

Low

High

High

High

High

10. Uses -For dry wall -For dam,

-kitchen slab,

-foundation of

megastructure

-flooring

-aggregate

11. Geological

Formation

Raduwa formation Agra granite Bhaise Dobhan

formation

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Left Bank of Malekhu Khola about 1 km upstream

S.N. Sample No. D E F

1. Color Grey Shiny grey Milky white

2. Texture Crystalline Amorphous Crystalline

3. Structure/ Clevage Foliation Foliation/ Slaty

perfect

Bedding

4. Specific Gravity High Medium High

5. Mineral

Composition

Quartz Clayminerals,

mica

Dolomite

6. Acid test/

Hammer scratch test

Hammer

scratched by rock

Not done

Sample

scratched by

hammer

7. Rock types Metamorphic

rock

Metamorphic Sedimentary

rock

8. Rock Name Quartzite Slate Limestone

9. Engineering

properties

d) Strength

e) Drillability

f) Blastibillity

High

Low

High

Low

High

Low

High

High

High

10. Uses -for aggregate

-for railing

-roofing -aggregate

-cement

manufacture.

11. Geological

Formation

Dunga quartzite Benighat slate Malekhu

limestone

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Right Bank of Malekhu Khola about 1 km downstream

S.N. Sample No. G H

1. Color Greenish grey Grey

2. Texture Crystalline Non-crystalline

3. Structure/ Cleavage Foliation Foliation/ Slaty

cleavage

4. Specific Gravity High High

5. Mineral Composition Amphibole group of

mineral

Clay minerals,

serrate, mica

6. Acid test/

Hammer scratch test

Not done Not done

7. Rock types Metamorphic rock Metamorphic rock

8. Rock Name Amphibolite Phyllite

9. Engineering properties

g) Strength

h) Drillability

i) Blastibillity

High

Low

High

Medium

High

Low

10. Uses -As a construction

materials

-For dry wall

-For flooring

11. Geological

Formation

Robang formation Robang Formation

6. Geological structures

Structure geology deals with the mechanism and types of deformation of rock

or earth’s crust due to the distribution of stress generated through various

geological processes such as earthquake, volcano etc.

6.1 Beds and Beddings:-

Beds refers to the layers of sedimentary rock that possess almost planar top

and bottom surfaces and beddings are the planar top and bottom surface of

the beds. These are the plane of weakness.

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If thickness of beds is >100cm very thick beeded

30-100 cm thick

10-30 cm medium

1-10cm thin

<1 lamination

6.2 Types of geologic structures:

(1) Primary structures: those which develop at the time of formation of the rocks

(e.g. sedimentary structures, some volcanic structures, etc.).

(2) Secondary structures: which are those that develop in rocks after their

formation as a result of their subjection to external forces.

(3) Compound structures: form by a combination of events some of which are

contemporaneous with the formation of a group of rocks taking part in these

"structures".

Stress: is the force applied over a given area of the rock mass. It is of three

different kinds:

(1) Compressional stress which tends to squeeze the rock

(2) Tensional stress, which tends to pull a rock apart

(3) Shear stress, which results from parallel forces that act on different

parts of the rock body in opposite directions.

Strain: Is the change in the shape or size of a rock in response to stress. A rock

is said to deform elastically if it can return to its original size once the stress is

removed. Plastic deformation on the other hand, results in permanent changes in

the size and shape of the rock, even after the stress is removed. Plastic

deformation of a rock is also known as ductile deformation. After deforming

plastically for some time, a rock which continues to be subjected to stress may

finally break, a behavior known as brittle deformation.

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6.3 Factors affecting how a rock deforms:

6.3.1 Depth: Lithostatic pressure + heat

6.3.2 Time

6.3.3 Composition

6.3.4 Fluids

Therefore, a rock may undergo ductile deformation when subjected to stress at

certain depths within the earth where pressures and temperatures are relatively

high, or if fluids are abundant, but the same rock may undergo brittle deformation

at shallower depths.

6.4 Measuring geological structures:

Strike: (direction)

Dip: (direction & angle)

6.4.1 Secondary structures

Types of secondary geologic structures:

Folds, which are a form of ductile deformation, and (b) fractures, represented by

faults and joints which generally result from the brittle behavior of rocks in

response to stress.

I- Folds

Folds are bends or flexures in the earth's crust, and can therefore be identified by

a change in the amount and/or direction of dip of rock units. Most folds result

from the ductile deformation of rocks when subjected to compressional or shear

stress. In order to understand and classify folds, we must study their forms and

shapes, and be able to describe them. The following definitions are therefore

essential for the description of a fold:

Hinge line: Is the line of maximum curvature on a folded surface. The hinge line

almost always coincides with the axis of the fold defined as a line lying in the

plane that bisects a fold into two equal parts.

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The axial plane: is an imaginary plane dividing the fold into two equal parts

known as limbs. It is therefore the plane which includes all hinge lines for

different beds affected by the same fold.

The crest: of a fold can be considered the highest point on a folded surface.

The trough: is the lowest point on a folded surface.

The interlimb angle: Is the angle between two limbs of the same fold. It is

measured in a plane perpendicular to that of the fold axis.

The angle of plunge: of a fold is the angle between the fold axis and the

horizontal plane, measured in a vertical plane. The direction of plunge of a fold

is the direction in which the fold axis dips into the ground from the horizontal

plane.

The median surface: Is the surface that passes through points where the fold

limb changes its curvature from concave to convex.

The amplitude: of a fold: is the vertical distance between the median surface and

the fold hinge, both taken on the same surface of the same folded unit.

The wavelength: of a fold system is the distance between two consecutive crests

or troughs taken on the same folded surface.

A. Classification of folds

Folds may be classified based on the direction of dip of their limbs, the inclination

of their axial planes, the value of their interlimb angle, their plunge, and their

general shape and effects on the thickness of the folded layers. In order to describe

a fold correctly, one may have to use more that one of these classifications; e.g.

recumbent anticline, open syncline, tight plunging anticline.... etc.

(a) Classification based on the direction of dip of the limbs:

When both limbs of a fold dip away from the fold axis, the fold is called an

antifoam. If both limbs dip towards the fold axis, the fold is known as a synform.

If the relative ages of the folded units are known, such that the oldest units occur

in the core of the antifoam, the antifoam is called "anticline". Similarly, if the

youngest units occur in the "center" of a synformal structure, it is known as a

syncline.

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A monocline is a single step-like bend in a rock unit, and is often caused by

vertical displacement. A dome consists of uparched rocks that dip in all directions

away from the central point. A basin is a downward in which the layers dip in all

directions from all sides towards the center. A fold is described as isoclinal if

both limbs dip in the same direction at the same angle.

(b) Classification based on the inclination of the axial plane:

A symmetrical (or upright) fold is one in which the axial plane bisects the fold

(and is vertical). If the axial plane is inclined at an angle < 45° (measured from

the vertical plane), the fold is said to be inclined. If the angle of inclination of the

axial plane is > 45° (from the vertical plane), then both limbs of the fold will dip

in the same direction, and the fold is known as inverted or overturned. If the

axial plane is horizontal, the fold is known as recumbent.

(c) Classification based on the value of the interlimb angle:

(1) Open folds: those with an interlimb angle > 70°

(2) Closed folds: with interlimb angles between 30 and 70°

(3) Tight folds: with interlimb angles < 30°

(4) Isoclinal folds: have zero interlimb angles.

II- Faults

A fault is a fracture in the earth's rock units along which there has been an

observable amount of movement and displacement. Unlike folds which form

predominantly by compressional stress, faults result from either tension,

compression or shear. In order to correctly describe a fault, it is essential to

understand its components:

1. The fault plane: Is the plane of dislocation or fracture along which

displacement has occurred. The fault plane therefore separates one or more

rock units into two blocks.

2. The Hanging wall and footwall blocks: If the fault plane is not vertical, then

the block lying on top of the fault plane is known as the hanging wall block,

whereas that lying below this plane is known as the footwall block.

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3. The downthrown and upthrown blocks: The downthrown block is the one

that has moved downwards relative to the other block, whereas the upthrown

block is that which registers an upward relative movement.

4. The Dip of the fault plane is the angle of inclination of the fault plane

measured from the horizontal plane perpendicular to its strike.

5. Fault Throw: Is the vertical displacement of a fault.

6. Dip slip: Is the amount of displacement measured on the fault plane in the

direction of its dip.

7. Strike slip: Is the amount of displacement measured on the fault plane in the

direction of its strike.

8. Net slip: Is the total amount of displacement measured on the fault plane in

the direction of movement.

N.B. In measuring the slip or throw of a fault, the displacement has to be

measured using the same surface of the same unit affected by that fault.

B. Types of Faults

- Normal fault: Is a fault in which the hanging wall appears to have moved

downwards relative to the footwall (i.e. downthrown block = hanging wall

block).

- Reverse fault: Is a fault in which the hanging wall appears to have moved

upwards relative to the footwall (i.e. upthrown block = hanging wall

block). Because the displacement in both normal and reverse faults occurs

along the dip of the fault plane, they may be considered types of dip slip

faults.

- Thrust fault (or thrust): Is a reverse fault in which the fault plane is dipping

at low angles (< 45°). Thrusts are very common in mountain chains (fold

and thrust belts) where they are characterized by transporting older rocks

on top of younger ones over long distances.

- Strike slip (wrench, tear or transcurrent) fault: Is a fault in which the

movement is horizontal along the strike of the fault plane. Strike slip faults

are either dextral or sinistral. When viewed on end , a dextral fault (also

known as right lateral fault) is one in which the block on the observer's

right hand side appears to have moved towards him, whereas a sinistral

strike slip fault (also known as left lateral) is one in which the block on the

observer's left hand side appears to have moved towards him.

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- Oblique slip fault: is one in which the displacement was both in the strike

and dip directions (i.e. the displacement has strike and dip components).

Keep in mind that an oblique slip fault can also be either normal or reverse.

From this classification of faults, it can be seen that normal faults result

predominantly from tensional stress, reverse faults and thrusts from

compression (or shear), and strike slip faults from tension, compression or

shear.

C. Fault Associations and Fault Systems

Faults often occur in groups. If two normal faults have parallel strikes and

share the same downthrown block, a trough-like structure results which is

known as a graben. A horst is an uplifted block bounded by two normal

faults that strike parallel to each other (and which share the same upthrown

block the horst). Grabens and horsts are common in areas of very early

rifting (e.g. the East African Rift Valley). Step faults are several faults with

parallel strikes and a repeated downthrow in the same direction giving the

area an overall step - like appearance. They are common in rifted areas (e.g.

on the flanks of the Red sea).

D. Geomorphological features associated with faults:

Fault planes often result in the exposure of units that erode easily along the

fault trace resulting in the development of valleys or the control of stream

flow. In other cases, faults cause the offset of streams, causing them to bend

sharply when they intersect the fault plane. The topography may also be

strongly influenced by faulting so that the fault plane can be identified on

the ground by a sudden and sharp change in elevation, known as a fault

scarp.

E. Recognition of movement along fault planes

Movement along a fault plane can often be recognized by the following

criteria:

- Fault drag: where small - scale folding or warping of units takes place

as a result of the dragging forces along the fault plane.

- Fault breccia and fault gouge: As a result of movement along the fault

plane, rocks are often broken up into sharp angular pieces known as

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breccia. The fragments may be further crushed into powder - like

material, known as fault gouge.

- Slickensides: As a result of movement and friction along the fault

plane, this plane may become highly polished or abraded with striations

that are known as slickensides.

III- Joints

Joints are fractures in the rocks characterized by no movement along their

surfaces. Although most joints are secondary structures, some are primary,

forming at the time of formation of the rocks.

A. Types of joints

- Columnar joints: Are joints that form in basalts. When the basaltic lava

cools, it contracts giving rise to hexagonal shaped columns.

- Mud cracks: Are joints that form in mud. As the mud loses its water,

it contracts and cracks.

- Secondary joints: Are joints that form in rocks as a result of their

subjection to any form of stress (compression, tension or shear). Joints

that are oriented in one direction approximately parallel to one another

make up a joint set. Rocks often have more than one set of joints with

different orientations, which may intersect, and are then known as joint

systems (Fig. 9). Note that tensional stress usually results in one set of

joints, whereas compression may form more than one set.

- Sheet joints: Are joints that form in granitic rocks in deserts causing

them to break into thin parallel sheets. These joints form when the rocks

expand as a result of the rapid removal of the overlying rock cover,

possibly due to faulting or quarrying. This process is called exfoliation.

6.4.2 Compound Structures

A. Unconformities

An unconformity is a surface (or contact) along which there was no

fracturing (i.e. not a fault or joint) and which represents a break in the

geologic record. An unconformity therefore indicates a lack of continuity

of sedimentary deposition in an area, resulting in rocks of widely different

ages occurring in contact with each other. Unconformities usually result

from changes in the sedimentary history of an area, which may be due to

vertical movements (e.g. uplift followed by erosion and deposition),

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deformation (also followed by deposition), changes in sea level (which

may be due to climatic changes, among other things), ...etc.

In many cases, unconformities represent a buried erosional surface. In such

cases, erosion of the older units results in their fragmentation into smaller

pieces. As soon as deposition resumes, these fragments may consolidate to

form a rock known as breccia (if the fragments are angular) or

conglomerate (if the fragments are rounded). Because the breccia or

conglomerate occur at the base of the younger units lying on top of the

unconformity surface, and because their fragments are derived from the

units below this surface, the conglomerates or breccias are known as basal

conglomerates or basal breccias.

B. Types of unconformities

- Angular unconformities: are those in which the angle of dip of the

younger layers is different from that of the older ones.

- Disconformities: are those in which the units above and below the

unconformity surface are parallel to each other, but not continuous in

deposition or age.

- Nonconformities: are those in which plutonic or metamorphic rocks

are covered by sedimentary or volcanic units.

Fig :-Unconformility

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7. Geological compass

Geological compass is defined as the combination of the compass and the

inclinometer. The compass gives the direction whereas the inclinometer gives

the Inclination of the plane to the horizontal.

There are four types of geological compass, they are:-

7.1 Clinometer compass

It is an instrument for measuring angles of slope (or tilt), elevation or

depression of an object with respect to gravity. It is also known as a tilt meter,

tilt indicator, slope alert, slope gauge, gradient meter, gradiometer, level

gauge, level meter, declinometer, and pitch & roll indicator. Clinometers

measure both inclines (positive slopes, as seen by an observer looking

upwards) and declines (negative slopes, as seen by an observer looking

downward) using three different units of measure: degrees, percent, and topo.

Astrolabes are inclinometers that were used for navigation and locating

astronomical objects.

Figure: Clinometer Compass

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7.2 Brunton Compass

A Brunton compass, properly known as the Brunton Pocket Transit, is a type

of precision compass made by Brunton, Inc. of Riverton, Wyoming. The

instrument was patented in 1894 by a Canadian-born Colorado geologist

named David W. Brunton. Unlike most modern compasses, the Brunton

Pocket Transit utilizes magnetic induction damping rather than fluid to damp

needle oscillation. Although Brunton Inc. makes many other types of magnetic

compasses, the Brunton Pocket Transit is a specialized instrument used widely

by those needing to make accurate degree and angle measurements in the field.

These people are primarily geologists, but archaeologists, environmental

engineers, and surveyors also make use of the Brunton's capabilities. The

United States Army has adopted the Pocket Transit as the M2 Compass for use

by crew-served artillery.

The Pocket Transit may be adjusted for declination angle according to one's

location on the Earth. It is used to get directional degree measurements

(azimuth) through use of the Earth's magnetic field. Holding the compass at

waist-height, the user looks down into the mirror and lines up the target,

needle, and guide line that is on the mirror. Once all three are lined up and the

compass is level, the reading for that azimuth can be made. Arguably the most

frequent use for the Brunton in the field is the calculation of the strike and dip

of geological features (faults, contacts, foliation, sedimentary strata, etc.). If

next to the feature, the strike is measured by leveling (with the bull's eye level)

the compass along the plane being measured. Dip is taken by laying the side

of the compass perpendicular to the strike measurement and rotating horizontal

level until the bubble is stable and the reading has been made. If properly used

and if field conditions allow, additional features of the compass allow users to

measure such geological attributes from a distance.

Figure: Brunton Compass

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7.3 Clark Compass

Advanced than other.

Figure: Clark Compass

7.4 Digital Compass

Compatible with PCs.

Figure: Digital Compass

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8. Attitude measurement of the plane

8.1 Foliation Plane:-

These are very thin layer of planes.

8.2 Joint plane:-

These planes are formed by the breaking down of the

Planes.

8.3 Attitude:

Orientation of the planar feature of the rock is called attitude. It Includes strike

and dip.

a) Strike: - Horizontal trend of inclined plane is called strike.

b) Dip:-

I) Dip Direction: It is the inclination direction of the plane.

ii) Dip amount: It is the angle between inclined and horizontal

plane.

For the measurement of the attitude we should keep the compass

perpendicular to the bedding of which we are measuring and then we

should bring the bubble on the center in the compass. After that

readings should be taken and tabulated as follows:

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Figure: Strike and Dip

S.N. Dip

direction

Dip

amount

Attitudes (dip dirn / Dip

amt.)

Remarks

1 168 86 168/86 Bedding plane

2 162 86 162/86 Bedding plane

3 164 87 164/87 Bedding plane

4 167 86 1676/86 Bedding plane

5 159 86 159/86 Bedding plane

6 167 84 167/84 Bedding plane

7 168 73 168/73 Bedding plane

8 246 71 246/71 Joint plane

9 73 63 73/63 Joint plane

10 175 87 175/87 Bedding plane

11 145 80.5 145/80.5 Bedding plane

12 153 85 153/85 Bedding plane

13 141 87 141/87 Bedding plane

14 153 79 153/79 Bedding plane

15 144 89 144/89 Bedding plane

16 234 59.5 234/59.5 Joint plane

17 254 56 254/56 Joint plane

18 252 61 252/61 Joint plane

19 229 57 229/57 Joint plane

20 242 65 242/65 Joint plane

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9. Geological works of physical agents

The process of disintegration of rocks by the action of physical agents such as

wind, river water, glaciers etc. is geological works. They are by following

process:

9.1 Erosion

Erosion is the breaking down of material by an agent. In the case of a river,

the agent is water. The water can erode the river’s channel and the river’s

load. A river’s load is bits of eroded material, generally rocks that the river

transports until it deposits its load.

A river’s channel is eroded laterally and vertically making the channel

wider and deeper. The intensity of lateral and vertical erosion is dictated

by the stage in the river’s course, discussed in more detail but essentially,

in the upper stage of the river’s course (close to the source of the river)

there is little horizontal erosion and lots of vertical erosion. In the middle

and lower stages vertical erosion is reduced and more horizontal erosion

takes place.

There are several different ways that a river erodes its bed and banks. The

first is hydraulic action, where the force of the water removes rock

particles from the bed and banks. This type of erosion is strongest at rapids

and waterfalls where the water has a high velocity. The next type of erosion

is corrasion1. This is where the river’s load acts almost like sandpaper,

removing pieces of rock as the load rubs against the bed & banks. This sort

of erosion is strongest when the river is transporting large chunks of rock

or after heavy rainfall when the river’s flow is turbulent.

Corrosion is a special type of erosion that only affects certain types of

rocks. Water, being ever so slightly acidic2, will react with certain rocks

and dissolve them. Corrosion is highly effective if the rock type of the

channel is chalk or limestone (anything containing calcium carbonate)

otherwise, it doesn’t have much of an effect.

Cavitation is an interesting method of erosion. Air bubbles trapped in the

water get compressed into small spaces like cracks in the river’s banks.

These bubbles eventually implode creating a small shockwave that

weakens the rocks. The shockwaves are very weak but over time the rock

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will be weakened to the point at which it falls apart. The final type of

erosion is attrition. Attrition is a way of eroding the river’s load, not the

bed and banks. Attrition is where pieces of rock in the river’s load knock

together, breaking chunks of rock off of one another and gradually

rounding and shrinking the load.

9.2 Transportation

When a river erodes the eroded material becomes the river’s load and the

river will then transport this load through its course until it deposits the load.

There are a few different ways that a river will transport load depending on

how much energy the river has and how big the load is.

The largest of particles such as boulders are transported by traction. These

particles are rolled along the bed of the river, eroding the bed and the particles

in the process, because the river doesn’t have enough energy to move these

large particles in any other way.

Slightly smaller particles, such as pebbles and gravel, are transported

by saltation. This is where the load bounces along the bed of the river because

the river has enough energy to lift the particles off the bed but the particles

are too heavy to travel by suspension.

Fine particles like clay and silt are transported in suspension, they are

suspended in the water. Most of a river’s load is transported by suspension.

Solution is a special method of transportation. This is where particles are

dissolved into the water so only rocks that are soluble, such as limestone or

chalk, can be transported in solution.

9.3 Deposition

To transport load a river needs to have energy so when a river loses energy it

is forced to deposit its load. There’s several reasons why a river could lose

energy. If the river’s discharge is reduced then the river will lose energy

because it isn’t flowing as quickly anymore. This could happen because of a

lack of precipitation or an increase in evaporation. Increased human use

(abstraction) of a river could also reduce its discharge forcing it deposit its

load.

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If the gradient of the river’s course flattens out, the river will deposit its load

because it will be travelling a lot slower. When a river meets the sea a river

will deposit its load because the gradient is generally reduced at sea level and

the sea will absorb a lot of energy.

9.4 The Hjulström Curve

A Hjulström curve is a special type of graph that shows how a river’s velocity

affects it competence and its ability to erode particles of different sizes.

There’s a lot going on the graph but it’s fairly easy to read once you get the

hang of it:

There’s two curves on the Hjulström Curve, a critical erosion velocity curve

and a mean settling velocity curve. The critical erosion curve shows the

minimum velocity needed to transport and erode a particle. The mean settling

velocity shows the minimum speed that particles of different sizes will be

deposited by the river. The shaded areas between the curves show the

different process that will be taking place for particles that lie in those shaded

areas.

As an example, a river flowing at 10cms-1 will transport clay, silt and sand

particles but will deposit gravel, pebble and boulder particles. Conversely, a

river flowing at 100cms-1 will erode and transport large clay particles, silt

particles, sand particles and most gravel particles. It will transport all but the

largest of pebbles and will deposit boulders.

The easiest way to read the curve is to draw a horizontal line from the velocity

you’re trying to read and seeing which shaded area it crosses the particle size

you’re interested in. This will tell us whether that particle is eroded,

transported or deposited at that velocity.

There’s a few interesting things to note about the Hjusltröm Curve. The first

is that clay sized particles don’t appear to have a mean settling velocity. This

is because these particles are so fine that a river would have to be almost

perfectly stationary in order for them to fall out of solution. In addition, the

small particles seem to have an erosive velocity that’s the same as the velocity

for larger particles. This is because smaller particles are cohesive, they stick

together, making them harder to dislodge and erode without high velocities.

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Figure: The Hjulström Curve

For this mainly three things happens, they are:

A. Erosion by river water

River erosion can be carried out by five ways, they are:

a) Hydraulic action - with the help of water current

b) Abrasion - by collision

c) Attrition - breaking during collision.

d) Cavitation - by making holes.

e) Corrosion - by chemical effect.

B. By wind

Wind erosion occurs in three ways, they are:

a) Deflation

b) Abrasion

c) Attrition

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C. By Glaciers

It occurs by two ways:

a) Plucking

b) Abrasion

9.5 Features developed by the activities of physical agents

1. Pothole

It is a type of failure in an asphalt pavement, caused by the presence of water

in the underlying soil structure and the presence of traffic passing over the

affected area. Introduction of water to the underlying soil structure first

weakens the supporting soil. Traffic then fatigues and breaks the poorly

supported asphalt surface in the affected area. Continued traffic action ejects

both asphalt and the underlying soil material to create a hole in the pavement.

2. Waterfall

It is a place where water flows over a vertical drop in the course of a stream

or river. Waterfalls also occur where melt water drops over the edge of a

tabular iceberg or ice shelf.

Waterfalls are commonly formed when a river is young. At these times the

channel is often narrow and deep. When the river courses over resistant

bedrock, erosion happens slowly, while downstream the erosion occurs more

rapidly. As the watercourse increases its velocity at the edge of the waterfall,

it plucks material from the riverbed. Whirlpools created in the turbulence as

well as sand and stones carried by the watercourse increase the erosion

capacity. This causes the waterfall to carve deeper into the bed and to recede

upstream. Often over time, the waterfall will recede back to form a canyon or

gorge downstream as it recedes upstream, and it will carve deeper into the

ridge above it.[The rate of retreat for a waterfall can be as high as one and

half meters per year.

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Fig: Formation of waterfalls

3. River Valley

A valley formed by flowing water, or river valley, is usually V shaped. The

exact shape will depend on the characteristics of the stream flowing

through it. Rivers with steep gradients, as in mountain ranges, produce

steep walls and a bottom. Shallower slopes may produce broader and

gentler valleys, but in the lowest stretch of a river, where it approaches its

base level, it begins to deposit sediment and the valley bottom becomes a

floodplain.

4. Floodplain

Flood plain is an area of land adjacent to a stream or river that stretches

from the banks of its channel to the base of the enclosing valley walls and

experiences flooding during periods of high discharge. It includes the

floodway, which consists of the stream channel and adjacent areas that

actively carry flood flows downstream, and the flood fringe, which are

areas inundated by the flood, but which do not experience a strong current.

In other words, a floodplain is an area near a river or a stream which floods

when the water level reaches flood stage.

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5. Terrace

Is a step-like landform. A terrace consists of a flat or gently sloping

geomorphic surface, called a tread that is typically bounded one side by a

steeper ascending slope, which is called a "riser" or "scarp." The tread and

the steeper descending slope (riser or scarp) together constitute the terrace.

Terraces can also consist of a tread bounded on all sides by a descending

riser or scarp. A narrow terrace is often called a bench. The sediments

underlying the tread and riser of a terrace are also commonly, but

incorrectly, called terraces, leading to much confusion. Terraces are

formed in various ways.

6. Oxbow lake

It is a U-shaped body of water formed when a wide meander from the main

stem of a river is cut off, creating a free-standing body of water. This

landform is so named for its distinctive curved shape, resembling the bow

pin of an oxbow. In Australia, an oxbow lake is known as a billabong, from

the indigenous language Wiradjuri.

The word "oxbow" can also refer to a U-shaped bend in a river or stream,

whether or not it is cut off from the main stream.

7. River delta

It is a landform that forms at the mouth of a river, where the river flows

into an ocean, sea, estuary, lake, or reservoir. Deltas form from deposition

of sediment carried by a river as the flow leaves its mouth. Over long

periods, this deposition builds the characteristic geographic pattern of a

river delta.

8. Point bar

It is a depositional feature made of sand and gravel that accumulates on the

inside bend of streams and rivers below the slip-off slope. Point bars are

found in abundance in mature or meandering streams. They are crescent-

shaped and located on the inside of a stream bend, being very similar to,

though often smaller than, towheads, or river islands.

Point bars are composed of sediment that is well sorted and typically

reflects the overall capacity of the stream. They also have a very gentle

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slope and an elevation very close to water level. Since they are low-lying,

they are often overtaken by floods and can accumulate driftwood and other

debris during times of high water levels. Due to their near flat topography

and the fact that the water speed is slow in the shallows of the point bar

they are popular rest stops for boaters and rafters. However, camping on a

point bar can be dangerous as a flash flood that raises the stream level by

as little as a few inches (centimetres) can overwhelm a campsite in

moments.

A point bar is an area of deposition whereas a cut bank is an area of erosion.

Point bars are formed as the secondary flow of the stream sweeps and rolls

sand, gravel and small stones laterally across the floor of the stream and up

the shallow sloping floor of the point bar.

9. Braid Bars

They are landforms in a river that begin to form when the discharge is low

and the river is forced to take the route of less resistance by means of

flowing in locations of lowest elevation. Over time, the river begins to

erode the outer edges of the bar, causing it to become a higher elevation

than the surrounding areas. The water level decreases even more as the

river laterally erodes the less cohesive bank material resulting in a widening

of the river and a further exposure of the braid bar. As the discharge

increases, material may deposit about the braid bar since it is an area in the

river of low velocity due to its increased elevation in relation to

surrounding areas. During times of extremely high flow, the bars may

become covered; only to resurface when the flow decreases. Most braid

bars do not remain stable or in one location. However, vegetation

succession on braid bars can increase the stability of the landform. They

are commonly composed of sand or gravel and typically occur in braided

rivers.

10. Moraine

Is any glacially formed accumulation of unconsolidated glacial debris (soil

and rock) which can occur in currently glaciated and formerly glaciated

regions, such as those areas acted upon by a past glacial maximum. This

debris may have been plucked off a valley floor as a glacier advanced or it

30

may have fallen off the valley walls as a result of frost wedging or

landslide. Moraines may be composed of debris ranging in size from silt-

sized glacial flour to large boulders. The debris is typically sub-angular to

round in shape. Moraines may be on the glacier’s surface or deposited as

piles or sheets of debris where the glacier has melted. Moraines may also

occur when glacier- or iceberg-transported rocks fall into a body of water

as the ice melts.

a. Drumlin,

From the Irish word droimnín ("little ridge"), first recorded in 1833, is an

elongated hill in the shape of an inverted spoon or half-buried egg formed

by glacial ice acting on underlying unconsolidated till or ground moraine.

11. Kame

Is a geomorphological feature, an irregularly shaped hill or mound

composed of sand, gravel and till that accumulates in a depression on a

retreating glacier, and is then deposited on the land surface with further

melting of the glacier. Kames are often associated with kettles, and this is

referred to as kame and kettle topography.

12. Esker

Is a long, winding ridge of stratified sand and gravel, examples of which

occur in glaciated and formerly glaciated regions of Europe and North

America. Eskers are frequently several kilometers long and, because of

their peculiar uniform shape, are somewhat like railway embankments.

13. Kettle

In geology, depression in a glacial outwash drift made by the melting of a

detached mass of glacial ice that became wholly or partly buried. The

occurrence of these stranded ice masses is thought to be the result of

gradual accumulation of outwash atop the irregular glacier terminus.

Kettles may range in size from 5 m (15 feet) to 13 km (8 miles) in diameter

and up to 45 m in depth. When filled with water they are called kettle lakes.

Most kettles are circular in shape because melting blocks of ice tend to

become rounded; distorted or branching depressions may result from

extremely irregular ice masses.

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Two types of kettles are recognized: a depression formed from a partially

buried ice mass by the sliding of unsupported sediment into the space left

by the ice and a depression formed from a completely buried ice mass by

the collapse of overlying sediment. By either process, small kettles may be

formed from ice blocks that were not left as the glacier retreated but rather

were later floated into place by shallow melt water streams. Kettles may

occur singly or in groups; when large numbers are found together, the

terrain appears as mounds and basins and is called kettle and kame

topography.

14. Dune

It is a hill of sand built by either wind or water flow. Dunes occur in

different forms and sizes, formed by interaction with the flow of air or

water. Most kinds of dunes are longer on the windward side where the sand

is pushed up the dune and have a shorter "slip face" in the lee of the wind.

The valley or trough between dunes is called a slack. A "dune field" is an

area covered by extensive sand dunes. Large dune fields are known as ergs.

Some coastal areas have one or more sets of dunes running parallel to the

shoreline directly inland from the beach. In most cases the dunes are

important in protecting the land against potential ravages by storm waves

from the sea. Although the most widely distributed dunes are those

associated with coastal regions, the largest complexes of dunes are found

inland in dry regions and associated with ancient lake or sea beds.

Dunes also form under the action of water flow (fluvial processes), and on

sand or gravel beds of rivers, estuaries and the sea-bed.

15. Loess

It is a clastic, predominantly silt-sized sediment, which is formed by the

accumulation of wind-blown dust.

Loess is an aeolian sediment formed by the accumulation of wind-blown

silt, typically in the 20–50 micrometer size range, twenty percent or less

clay and the balance equal parts sand and silt that are loosely cemented by

calcium carbonate. It is usually homogeneous and highly porous and is

traversed by vertical capillaries that permit the sediment to fracture and

form vertical bluffs.

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10. River Channel Morphology

10.1 Meandering River Channel

Formation of natural levees by spill-over of sediment during floods. Next

to the channel mostly sand is deposited (highest flow velocities), and sand

compacts less than the mud that is deposited farther away. Thus, over time

these near-channel sand deposits will over time rise above the (more

compacted) floodplain and form natural levees.

10.1.1 Overview of features associated with meandering streams.

A meandering stream migrates laterally by sediment erosion on the outside

of the meander (that is part of the friction work), and deposition on the

inside (helicoidal flow, deceleration, channel lag, point bar sequence,

fining upwards). Adjacent to the channel levee deposits build up, and

gradually raise up the river over the floodplain (mainly fine sediments). If

the climate is humid the floodplain area beyond the levees may be covered

with water most of the time, and may form a swamp (backswamp). Rivers

that want to enter the main stream may not make it up the levee, and empty

either into the backswamp (filing it up gradually) or flow parallel to the

stream for a long distance until they finally join (Yazoo streams). Meanders

may cut into each other as they grow (neck cutoffs), and then the river

shortcuts (growing meanders reduce the slope, cutoffs are a means to

increase the slope again, feedback loop) and the old meander is abandoned

and slowly fills with fine sediment during floods (oxbow lakes). Also, as a

river builds up its levees and raises itself over the floodplain, the slope and

the transport power of the stream decrease, the channel fills gradually with

sediment, and finally (often during a flood) the river will breach its levee

(this process is called avulsion) and follow a steeper path down the valley.

Figure: Meandering River Streams

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10.1.2 How meanders grow

Laterally through erosion (outside bend) and sediment deposition (inside

bend, point bar). When the loops get too large and consume too much

energy (friction), the river will eventually find a less energetically "taxing"

shortcut, and a part of the old channel will be abandoned and becomes

an oxbow lake.

Figure: Process of growing River Meandering

10.2 STRAIGHT RIVER CHANNELS

Straight channels, mainly unstable, develop along the lines of faults and

master joints, on steep slopes where rills closely follow the surface

gradient, and in some delta outlets. Flume experiments show that straight

channels of uniform cross section rapidly develop pool-and-riffle

sequences. Pools are spaced at about five bed widths. Lateral shift of

alternate pools toward alternate sides produces sinuous channels, and

spacing of pools on each side of the channel is thus five to seven bed

widths. This relation holds in natural meandering streams.

Figure: straight Channel River

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10.3 Braided River Channel

Is one of a number of channel types and has a channel that consists of a

network of small channels separated by small and often

temporary islands called braid bars or, in British usage, aits or eyots.

Braided streams occur in rivers with high slope and/or

large sediment load.[1]Braided channels are also typical of environments

that dramatically decrease channel depth, and consequently channel

velocity, such as river deltas,alluvial fans and peneplains. Alluvial

fans and peneplains.

Braided rivers, as distinct from meandering rivers, occur when a threshold

level of sediment load or slope is reached. Geologically speaking, an

increase in sediment load will over time increase the slope of the river, so

these two conditions can be considered synonymous; and, consequently, a

variation of slope can model a variation in sediment load. A threshold slope

was experimentally determined to be 0.016 (ft/ft) for a 0.15 cu ft/s

(0.0042 m3/s) stream with poorly sorted coarse sand.[1] Any slope over this

threshold created a braided stream, while any slope under the threshold

created a meandering stream or— for very low slopes—a straight channel.

So the main controlling factor on river development is the amount of

sediment that the river carries; once a given system crosses a threshold

value for sediment load, it will convert from a meandering system to a

braided system. Also important to channel development is the proportion

of suspended load sediment to bed load. An increase in suspended sediment

allowed for the deposition of fineerosion-resistant material on the inside of

a curve, which accentuated the curve and in some instances caused a river

to shift from a braided to ameandering profile The channels and braid bars

are usually highly mobile, with the river layout often changing significantly

during flood events. Channels move sideways via differential velocity: On

the outside of a curve, deeper, swift water picks up sediment

(usually gravel or larger stones), which is re-deposited in slow-moving

water on the inside of a bend.

Figure: Braided River Channel

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11. Conclusion

The report has been prepared with including the important topics and is prepared

with sketches on site observation and their description also. From the field ,we

are able to study and identify about the rocks ,minerals and the various types of

geological structures like bedding, graded bedding ,joint, fault, thrust ,fold and

unconformity. As we also able to use the geological compass during the

investigation of rock structures. By using this also we had measured the attitude

of planner features like joint, bedding and foliation. We studied the river channel

morphology, how they forms and various types of river channel like straight,

meandering and Braded River. We also understand the features developed by this

types of river.