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Rajiv Gandhi Proudyogiki Vishwavidyalaya, Bhopal B.Tech Syllabus 1 st Semester Civil Engineering Course Content Subject: Basic Civil Engineering & Engineering Mechanics Code: BT- 2004 1. SURVEYING AND FIELD WORK: 1. Linear measurements : Chain and Tape Surveying, Errors, Obstacles, Booking and Plotting, Calculation of Areas. 2. Angular Measurements : Bearing, Prismatic Compass, Local Attraction, Bowditch’s Rule of correction, traverse open and closed, plotting of traverse, accuracy and precision. 3. Levelling : Types of Levels, Levelling Staff, Measurements, recording, curvature and refraction correction, reciprocal levelling, sensitivity of level. 4. Contours : Properties, uses, plotting of contours, measurement of drainage and volume of reservoir. 5. Measurement of area by planimeter. 2. BUILDING MATERIALS : 1. Bricks : Manufacturing, field and laboratory test, Engineering properties. 2. Cement : Types, physical properties, laboratory tests 3. Concrete and Mortar Materials : Workability, Strength Properties of Concrete, Nominal Proportion of Concrete, Preparation of Concrete, Compaction Curving. Mortar : Properties and Uses. Reference Books: 1. S. Ramamrutam & R.Narayanan; Basic Civil Engineering, Dhanpat Rai Pub. 2. Prasad I.B., Applied Mechanics, Khanna Publication. 3. Punmia, B.C., Surveying, Standard book depot. 4. Shesha Prakash and Mogaveer; Elements of Civil Engg & Engg. Mechanics; PHI 5. S.P,Timoshenko, Mechanics of stricture, East West press Pvt.Ltd. 6. Surveying by Duggal Tata McGraw Hill New Delhi. 7. Building Construction by S.C. Rangwala- Charotar publications House, Anand. 8. Building Construction by Grucharan Singh- Standard Book House, New Delhi 9. Global Positioning System Principles and application- Gopi, TMH 10. R.C. Hibbler Engineering Mechanics: Statics & Dynamics. 11. A. Boresi & Schmidt- Engineering Mechines- statics dynamics, Thomson’ Books 12. R.K. Rajput, Engineering Mechanics S.Chand & Co.

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Page 1: Rajiv Gandhi Proudyogiki Vishwavidyalaya, Bhopal B.Tech …saitmoodle.in/wp-content/uploads/2017/08/Basic-Civil... · 2017-10-23 · R.C. Hibbler – Engineering Mechanics: Statics

Rajiv Gandhi Proudyogiki Vishwavidyalaya, Bhopal

B.Tech Syllabus 1st Semester Civil Engineering

Course Content

Subject: Basic Civil Engineering & Engineering Mechanics Code: BT- 2004

1. SURVEYING AND FIELD WORK:

1. Linear measurements : Chain and Tape Surveying, Errors, Obstacles, Booking and

Plotting, Calculation of Areas.

2. Angular Measurements : Bearing, Prismatic Compass, Local Attraction, Bowditch’s

Rule of correction, traverse open and closed, plotting of traverse, accuracy and precision.

3. Levelling : Types of Levels, Levelling Staff, Measurements, recording, curvature and

refraction correction, reciprocal levelling, sensitivity of level.

4. Contours : Properties, uses, plotting of contours, measurement of drainage and volume of

reservoir.

5. Measurement of area by planimeter.

2. BUILDING MATERIALS :

1. Bricks : Manufacturing, field and laboratory test, Engineering properties. 2. Cement

: Types, physical properties, laboratory tests 3. Concrete and Mortar Materials :

Workability, Strength Properties of Concrete, Nominal Proportion of Concrete, Preparation of

Concrete, Compaction Curving. Mortar : Properties and Uses.

Reference Books:

1. S. Ramamrutam & R.Narayanan; Basic Civil Engineering, Dhanpat Rai Pub.

2. Prasad I.B., Applied Mechanics, Khanna Publication.

3. Punmia, B.C., Surveying, Standard book depot.

4. Shesha Prakash and Mogaveer; Elements of Civil Engg & Engg. Mechanics; PHI

5. S.P,Timoshenko, Mechanics of stricture, East West press Pvt.Ltd.

6. Surveying by Duggal – Tata McGraw Hill New Delhi.

7. Building Construction by S.C. Rangwala- Charotar publications House, Anand.

8. Building Construction by Grucharan Singh- Standard Book House, New Delhi

9. Global Positioning System Principles and application- Gopi, TMH

10. R.C. Hibbler – Engineering Mechanics: Statics & Dynamics.

11. A. Boresi & Schmidt- Engineering Mechines- statics dynamics, Thomson’ Books

12. R.K. Rajput, Engineering Mechanics S.Chand & Co.

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St. Aloysius Institute of Technology, Jabalpur

Semester: 1st Sem Subject: Basic Civil Engineering Subject Code: BT-2004

SURVEYING:-

UNIT –I: LINEAR MEASUREMENTS

1. Introduction to Surveying

The objective of this lesson is to deal with the introduction and basics of surveying (importance,

objectives, divisions, classifications and principles).

Surveying is defined as the science of making measurements of the earth specifically the surface

of the earth. This is being carried out by finding the spatial location (relative / absolute) of points

on or near the surface of the earth.

Different methods and instruments are being used to facilitate the work of surveying.

The primary aims of field surveying are :

• to measure the horizontal distance between points.

• to measure the Vertical elevation between points.

• to find out the Relative direction of lines by measuring horizontal angles with reference to any

arbitrary direction and to find out Absolute direction by measuring horizontal angles with

reference to a fixed direction. These parameters are utilised to find out the relative or absolute

coordinates of a point / location.

Importance of Surveying to Civil Engineers

The planning and design of all Civil Engineering projects such as construction of highways,

bridges, tunnels, dams etc are based upon surveying measurements.

Moreover, during execution, project of any magnitude is constructed along the lines and points

established by surveying.

Thus, surveying is a basic requirement for all Civil Engineering projects.

Other principal works in which surveying is primarily utilised are

• to fix the national and state boundaries;

• to chart coastlines, navigable streams and lakes;

• to establish control points;

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• to execute hydrographic and oceanographic charting and mapping; and

• to prepare topographic map of land surface of the earth.

Objectives of Surveying

• To collect field data;

• To prepare plan or map of the area surveyed;

• To analyse and to calculate the field parameters for setting out operation of actual

engineering works.

• To set out field parameters at the site for further engineering works.

Divisions of Surveying

The approximate shape of the earth can best be defined as an oblate or tri-axial ovaloid. But,

most of the civil engineering works, concern only with a small portion of the earth which seems

to be a plane surface. Thus, based upon the consideration of the shape of the earth, surveying is

broadly divided into two types.

Geodetic Surveying- In this branch of surveying, the true shape of the earth is taken into

consideration.

This type of surveying is being carried out for highly precise work and is adopted for surveying

of large area.

Plane Surveying- In this method of surveying, the mean surface of the earth is considered to be

a plane surface. This type of survey is applicable for small area (less than 200 square kilometer).

Thus for most of the Civil Engineering projects, methods of plane surveying are valid.

Fundamental assumptions in Plane surveying

• All distances and directions are horizontal;

• The direction of the plumb line is same at all points within the limits of the survey;

• All angles (both horizontal and vertical) are plane angles;

• Elevations are with reference to a datum.

Classifications of Surveying

Based on the purpose (for which surveying is being conducted), Surveying has been classified

into:

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• Control surveying : To establish horizontal and vertical positions of control points.

• Land surveying : To determine the boundaries and areas of parcels of land, also known as

property survey, boundary survey or cadastral survey.

• Topographic survey : To prepare a plan/ map of a region which includes natural as well as

and man-made features including elevation.

• Engineering survey : To collect requisite data for planning, design and execution of

engineering projects. Three broad steps are

1) Reconnaissance survey : To explore site conditions and availability of infrastructures.

2) Preliminary survey : To collect adequate data to prepare plan / map of area to be used for

planning and design.

3) Location survey : To set out work on the ground for actual construction / execution of the

project.

• Route survey : To plan, design, and laying out of route such as highways, railways, canals,

pipelines, and other linear projects.

• Construction surveys : Surveys which are required for establishment of points, lines, grades,

and for staking out engineering works (after the plans have been prepared and the structural

design has been done).

• Astronomic surveys : To determine the latitude, longitude (of the observation station) and

azimuth (of a line through observation station) from astronomical observation.

• Mine surveys : To carry out surveying specific for opencast and underground mining

purposes.

Principles of Surveying

The fundamental principles upon which the surveying is being carried out are

working from whole to part.

after deciding the position of any point, its reference must be kept from at least two

permanent objects or stations whose position have already been well defined.

The purpose of working from whole to part is

to localise the errors and

to control the accumulation of errors.

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This is being achieved by establishing a heirarchy of networks of control points. The less precise

networks are established within the higher precise network and thus restrict the errors. To

minimise the error limit, highest precise network (primary network) of control points are

established using the most accurate / precise instruments for collection of data and rigorous

methods of analysis are employed to find network parameters. This also involves most skilled

manpower and costly resources which are rare and cost intensive.

Operations in Surveying

Operations in surveying consists of :

Planning

Field Observation

Office Works

Setting out works

Exercise 1

Ex.1-1 State two primary divisions of surveying.

Ex.1-2 Enumerate the fundamental parameters of surveying measurement?

Ex.1-3 State the basic principles of surveying.

Ex.1-4 State the basic assumptions of plane surveying.

2. Measurement of Horizontal Distance

Objective of this lesson is to explain the methods, problems and mistakes occuring in direct

measurement of distance.

Introduction

The horizontal distance between points, projected onto a horizontal plane, is required to be

measured in order to prepare plan or map of the area surveyed.

Methods of measurement

In surveying there are several methods for measurement of distance. These are

1. Direct methods;

2. Optical methods; and

3. Electronic method.

In any work, the choice of a method depends on many factors like field condition, accuracy

required, availability of resources (instruments, time, skill, fund etc). Following table

summarizes the principal methods, instrument required, precision, use, errors of measurement

of distance.

Salient Methods of Measuring Distance

Method Instrument Relative Use

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Required Precision

(A) Direct Measurement of distance

Taping Tape, pegs, plumb

bob

1 / 3000 to 1 /

5000

Traverse for land surveys and topographic surveys

and during combustion.

(B) Optical Measurement of distance

Stadia Tacheometer 1 / 300 to 1 /

2000

Location of detail for topographic mapping, rough

traverse, checkingmore amount measurement.

(C) Electromagnetic measurement of Distance

EDM EDM Equipment 0.2 mm ± 1

ppm

Traverse, Triangulation and trilateration for control

surveys of all relative precision is defend as the

ratio of the type anf for allowed stand and

deviations to the distance type and for contraction

surveys.

Direct Measurement

When the distance between points / stations are measured directly, usually by using tape, is

known as direct method.

Ranging

When the distance to be measured is more than a tape length, a straight line is required to be laid

between the points/ stations along which measurements are to be carried out. The process of

laying out a straight line between points is known as ranging.

Direct Ranging - When the end stations are inter visible, ranging is being carried out directly.

The intermediate points are placed at distances having interval less than one tape length. The

intermediate points are found by moving a ranging pole in transverse direction and thus, points

are selected in such a way that the end points and the intermediate points lie in a straight line. In

this method, two flags, one ranging pole and a bunch of pegs are required in a team of at least

one surveyor and one assistant.

Indirect Ranging - When the end stations between which a straight line is to be laid, are not inter

visible, indirect method of ranging is being adopted. It is being carried out either by reciprocal

method or by random line method.

.

Taping

Taping involves measurement of the distance with tapes (steel/linen), either by placing it on the

ground or sometimes by getting it suspended between points. Additional equipments employed

during taping are plumb bob, the hand level, pegs/ pins and range pole (or flag or ranging rod)

etc. The precision of distance measured with tapes depends upon the degree of refinement with

which measurements are taken.

Mistakes in Taping

During taping, mistakes generally made by individuals (usually inexperienced) are:

1. Adding or dropping a full length of tape

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2. Adding or dropping a part of the length of tape

3. Other points incorrectly taken as 0 or 30 meter marks on tape

4. Reading numbers incorrectly

5. Calling numbers incorrectly or not clearly

3. Errors in Measurement of Distance

Objective of this lesson is to explain the different errors/corrections involved in direct

measurement.

Introduction

The length of a tape is standardized at certain temperature and pull to amend distance be

measured in horizontal along a plane surface. But ideal condition is hardly obtained during field

observation. Thus, it is usual that the observations taken in the field are fraught with errors.

These are of various types depending on the origin and nature. These are required to be

determined and necessary corrections are to be applied before making use of the measurements

for further works.

Types of Errors

Depending on the nature, errors present in the measurement of distance have been classified into two

types: Systematic error and random error.

Systematic Errors

Systematic errors (in taping) are caused due to: non-standard length of tape, slope in terrain,

variations in temperature during measurement, variations in tension, sag, incorrect alignment of the

tape etc.

Random Errors

Distance measured depends on observations and on the determination of quantities such as

temperature t, tension or pull p, slope angle q or elevation difference h. Each of these quantities is

subject to random errors which when propagated through the corresponding relations result in random

errors in the distance. Thus the random errors cause random variation in the distance corrected for

systematic errors. The random errors are of much lower magnitude than the systematic errors. The

different sources of random errors in taping, designated by their standard error and these are: sv

(standard error due to the plumbing of the tape ends), sm (standard error due to the marking the

supported tape ends), sp r(standard error due to uncertainty in the value of the applied pull or tension),

sh (standard error in determining either the slope angle q or elevation difference h), st (standard error

in determining the temperature).

Chaining: Chaining is a term which is used to denote measuring distance either with the help of a chain

or a tape and is the most accurate method of making direct measurements. For work of ordinary

precision, a chain can be used, but for higher precision a tape or special bar can be used. The distances

determined by chaining form the basis of all surveying. No matter how accurately angles may be

measured, the survey can be no more precise than the chaining. Instruments for Chaining: The various

instruments used for the determination of the length of line by chaining are as follows: i. Chain or tape

ii. Arrows iii. Pegs iv. Ranging rods v. Offset rods vi. Plumb bob

Chain: Chains are formed of straight links of galvanized mild steel wire bent into rings at the ends and

joined each other by three small circular or oval wire rings. These rings offer flexibility to the chain.

The ends of the chain are provided with brass handle at each end with revolve joint, so that the chain

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can be turned without twisting. Tallies are provided at every 10 or 25 links for facility of counting. The

length of a link is the distance between the centers of two consecutive middle rings, while the length of

the chain is measured from the outside of one handle to the outside of the other handle.

Various Types of Chain Metric Chains: Metric chains are generally available in lengths of 5, 10, 20

and 30 metres. To enable the reading of fractions of a chain without much difficulty, tallies are fixed at

every metre length for chains of 5 m and 10 m lengths and at every five-metre length for chains of 20

m and 30 m lengths. In the case of 20 m and 30 m chains, small brass rings are provided at every metre

length, except where tallies are attached.

Gunter’s Chain or Surveyor Chain: Gunter’s Chain or 66 ft. Chain: Divided into 100 links, each link is

of 0.66 ft. or 7.92 inches. Also called Surveyor’s chain. Engineer’s chain and Gunter’s chain are

commonly used in our country. It was previously used for measuring distance in miles and furlongs (10

Gunter’s chain = 1 furlong 80 Gunter’s chain = 1 mile).

Engineer's Chain: The engineer's chain is 100 ft. long and consists of 100 links, each link being 1 ft.

long. Tallies are provided at every 10 links, then central tally being round. Revenue Chain: The

revenue chain is 33 ft long and consists of 16 links each link being 2 ft long. It is mainly used in

cadastral survey. Steel Band or Band Chain: The steel band consists of a long narrow strip of blue

steel, of uniform width of 12 to 16 mm and thickness of 0.3 to 0.6 mm. Metric steel band are available

in lengths of 20 or 30 metres. It is graduated in meters, decimeters and centimeters on one side and has

0.2 m links on the other. It is used in projects where more accuracy is required.

Tapes: Tapes are available in a variety of materials, lengths and weights. The different types of tape in

general use are discussed below: Cloth or Linen Tape: These are closely woven linen or synthetic

material and are varnished to resist the moisture. These are available in 10 to 30 m in length and 12 to

15 mm in width. The disadvantages of such a tape include: (1) It is affected by moisture and gets

shrunk; (2) Its length gets altered by stretching; and (3) It is likely to twist and does not remain straight

in strong winds.

Metallic Tape: It is a linen tape with brass or copper wires woven into it longitudinally to reduce

stretching. As it is varnished, the wires are not visible. These are available in 20-30 m length. It is an

accurate measurement device and is commonly used for measuring offsets. As it is reinforced with

wires, all the defects of linen tapes are overcome.

Steel Tapes: These are 1 to 50 m in length and are 610 mm wide. At the end of the tape a brass ring is

attached, the outer end of which is zero point of the tape. Invar Tape: This is made of an alloy of

nickel (36%) and steel, having very low coefficient of thermal expansion (0.122 x 10-6 / 0C). These

are available in lengths of 30, 50 and 100 m and in a width of 6 mm.

Pegs: Wooden pegs are used to mark the positions of the stations or terminal points of a survey line.

They are made of stout timber, generally 2.5 cm or 3 cm square and 15 to 60 cm long, tapered at the

end. They are driven in the ground with the help of a wooden hammer and kept about 4 cm projecting

above the surface.

Arrows (Chain pin): Arrows are made of stout steel wire. An arrow is inserted into the ground after

every chain length measured on the ground. Arrows are made of good quality hardened and tempered

steel wire 4 mm in diameter and are black enameled. The length of arrow may vary from 25 cm to 50

cm (generally 40 cm). One end of the arrow is made sharp and other end is bent into a loop or circle for

facility of carrying.

Ranging Rods: Ranging rods have a length of either 2 m or 3 m, the 2 metre length being more

common. They are combined at the bottom with a heavy iron point, and are painted in alternative

bands of either black and white or red and white or black, red and white in succession, each band being

20 cm depth so that on occasion the rod can be used for rough measurement of short lengths. Ranging

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rods are used to range some intermediate points in the survey line. They are circular or octagonal in

cross-section of 3 cm nominal diameter, made of well-seasoned, straight grained timber. The rods are

almost invisible at a distance of about 200 metres; hence when used on long lines each rod should have

a red, white or yellow flag, about 30 to 50 cm square, tied on near its top.

Offset Rod: An offset rod is similar to a ranging rod and has a length of 3 m. They are round wooden

rods, shod with pointed iron shoe at one end, and provided with a notch or a hook at the other. The

hook facilitates pulling and pushing the chain through hedges and other obstructions. The rod is mainly

used for measuring rough offsets nearby. It has also two narrow slots passing through the centre of the

section, and set at right angles to one another, at the eye level, for aligning the offset line. Plumbing

Bob: While chaining along sloping ground, a plumb-bob is required to transfer the points to the

ground. It is also used to make ranging poles vertical and to transfer points from a line ranger to the

ground. In addition, it is used as centering aid in theodolites, compass, plane table and a variety of

other surveying instruments.

Types of Errors occurring in Chain Surveying

Types of Errors:

1. Cumulative error

2. Compensative error

Cumulative error

These errors always accumulate in one direction and are serious in nature. They affect the survey work

considerably.

They make measurements too long or too short.

These errors are of two types and are known as systematic errors.

They are classified as follows:

1. Positive error

2. Negative error

Positive error

These errors make the measured length more than the actual length which results into wrong

calculations by the Surveyor.

The following are some of the positive errors:

The length of chain is shorter than the standard length due to bending of links, removal of

connecting rings and knots in links.

The temperature is lower than at which the tape was calibrated.

Not applying sag correction.

Sag takes place due to self weight of the chain.

Incorrect alignment

Negative errors

These errors make the measured length less than the actual length.

Following are some of the negative errors: Length of chain or tape greater than its standard length due to flattening of rings, opening of ring joints

and temperature being higher than at which it was standardised.

Compensative errors

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These errors occur in either direction and are likely to compensate.

These occur in following situations:

Incorrect holding of chain

Displacement of arrows

Adding or omitting a full length of chain

Reading wrongly

Booking wrongly

4. OBSTACLES IN CHAIN SURVEYING There are 3 types of obstacles

1. Obstacle to ranging

2. Obstacle to chaining

3. Obstacle to both ranging & chaining.

a) Obstacle to Ranging: The type of obstacle in which the ends are not inter visible is quite common except in flat country. These may be two cases.

i) Both end of the line may be visible form intermediate points on the line

ii) Both ends of the line may not be visible from intermediate points on the line

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b) Obstacle to chaining but not ranging

There may be two cases of this obstacle

i) When it is possible to chain round the obstacle ex: a pond

ii) When it is not possible to chain round the obstacle ex: a river

c) Obstacles to both chaining & ranging

A building is the typical example of this type of obstacle the problem lies in prolonging the line beyond the obstacle & determining the distance across it. Method A: Choose two points A & B to one side & Erect perpendicular AC and BD of equal length join CD & prolong it past the obstacle choose two points E and F on CD and erect CG and FH equal to that of AC and BD. Join GH and prolong it. Measure DE, BG = DE.

5. Methods used for the calculation of areas in Surveying:

1. Midpoint Ordinate Rule

2. Average Ordinate Rule

3. Simpson’s rule

4. Trapezoidal rule

Midpoint-ordinate rule

The rule states that if the sum of all the ordinates taken at midpoints of each division multiplied

by the length of the base line having the ordinates (9 divided by number of equal parts).

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Midpoint ordinate rule | Method for calculating area in Surveying

In this, base line AB is divided into equal parts and the ordinates are measured in the midpoints

of each division.

Area = ([O1 +O2 + O3 + …..+ On]*L)/n

L = length of baseline

n = number of equal parts, the baseline is divided

d = common distance between the ordinates

Example of the area calculation by midpoint ordinate rule

The following perpendicular offsets were taken at 10m interval from a survey line to an irregular

boundary line. The ordinates are measured at midpoint of the division are 10, 13, 17, 16, 19, 21,

20 and 18m. Calculate the are enclosed by the midpoint ordinate rule.

Given: Ordinates

O1 = 10

O2 = 13

O3 = 17

O4 = 16

O5 = 19

O6 = 21

O7 = 20

O8 = 18

Common distance, d =10m

Number of equal parts of the baseline, n = 8

Length of baseline, L = n *d = 8*10 = 80m

Area = [(10+13+17+16+19+21+20+18)*80]/8

= 1340sqm

Average Ordinate Rule

The rule states that (to the average of all the ordinates taken at each of the division of equal

length multiplies by baseline length divided by number of ordinates).

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Average Ordinate Rule

O1, O2, O3, O4….On ordinate taken at each of division.

L = length of baseline

n = number of equal parts (the baseline divided)

d = common distance

Area = [(O1+ O2+ O3+ …. + On)*L]/(n+1)

Here is an example of a numerical problem regarding the calculation of areas using

Average Ordinate Rule The following perpendicular offsets were taken at 10m interval from a survey line to an irregular

boundary line.

9, 12, 17, 15, 19, 21, 24, 22, 18

Calculate area enclosed between the survey line and irregular boundary line.

Area = [(O1+ O2+ O3+ …. + O9)*L]/(n+1)

= [(9+12+17+15+19+21+24+22+18)*8*10]/(8+1)

= 139538sqm

Simpson’s Rule

Statement

It states that, sum of first and last ordinates has to be done. Add twice the sum of remaining

odd ordinates and four times the sum of remaining even ordinates. Multiply to this total sum

by 1/3rd of the common distance between the ordinates which gives the required area.

Where O1, O2, O3, …. On are the lengths of the ordinates d = common distance

n = number of divisions

Note:

This rule is applicable only if ordinates are odd, i.e. even number of divisions.

If the number of ordinates are even, the area of last division maybe calculated separated and

added to the result obtained by applying Simpson’s rule to two remaining ordinates.

Even if first or last ordinate happens to be zero, they are not to be omitted from Simpson’s rule.

The following offsets are taken from a chain line to an irregular boundary towards right side of

the chain line.

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Chainage 0 25 50 75 100 125 150

Offset

‘m’

3.6 5.0 6.5 5.5 7.3 6.0 4.0

Common distance, d = 25m

Area = d/3[(O1+O7) + 2 (O3+O5)+4(O2+O4+O6)]

= 25/3[(3.6+4)+2(6.5+7.3)+4(5+5.5+6)]

Area = 843.33sqm

Area Calculation - Trapezoidal Rule

In trapezoidal method, each segment of the section is divided into various trapezoids and

triangles.

Trapezoidal Area A = 1/2 X a X (b1+b2)

Triangle area A = a * b/2

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Example 1:

Intersection Point

In the above example, intersection point is between 351 and 354

Filling Height=0.1 @ distance 351

Cutting depth=0.2 @ distance 354

Length from 351 to 354 =3

Distance from 351 to intersection point = 3*[0.1/ (0.1+0.2)] =1 i.e., intersection point is at 352

Cutting Area – Sum of Area of Segment 1, 2, and 3

Sl. No. Easting Initial

Level

Final

Level

Difference Calculation Area (Sq.

meters)

1 345 20.70 20 0.70

2 348 20.50 20 0.50 Segment 1: Area of Trapezoid =

½ * (b1 + b2) * a = ½ * (0.70 +

0.50) * 3

1.80

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3 351 20.10 20 0.1 Segment 2: Area of Trapezoid =

½ * (b1 + b2) * a = ½ * (0.50 +

0.10) * 3

0.90

4 352 20.00 20 0 Segment 3: Area of Triangle = ½

* b * h = ½ * 0.1 * 1

0.05

Total 2.75

Filling Area – Sum of Area of Segment 4, 5, 6, and 7

Sl. No. Easting Initial

Level

Final

Level

Difference Calculation Area

(Sq.

meters)

1 352 20.00 20 0.00

2 354 19.80 20 0.20 Segment 4: Area of Triangle = ½

* b * h = ½ * 0.2 * 2

0.20

3 357 19.40 20 0.60 Segment 5: Area of Trapezoid =

½ * (b1 + b2) * a = ½ * (0.20 +

0.60) * 3

1.20

4 360 19.10 20 0.90 Segment 6: Area of Trapezoid =

½ * (b1 + b2) * a = ½ * (0.60 +

0.90) * 3

2.25

5 363 19.00 20 1.00 Segment 7: Area of Trapezoid =

½ * (b1 + b2) * a = ½ * (0.90 +

1.00) * 3

2.85

Total 6.50

UNIT II: ANGULAR MEASUREMENTS

1. Traversing:

In traversing , the frame work consist of connected lines. The length are measured by a chain or a

tape and the direction measured by angle measuring instruments.Hence in compass surveying

direction of survey lines are determined with a compass and the length of the lines are measured

with a tape or a chain. This process is known as compass traversing.

2. Principle of Compass Surveying

The principle of compass surveying is traversing; which involves a series of connected lines.The

magnetic bearing of the lines are measured by prismatic compass.Compass surveying is

recommended when the area is large, undulating and crowded with many details. Compass

surveying is not recommended for areas where local attraction is suspected due to the presence

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of magnetic substances like steel structures, iron ore deposits, electric cables , and so on. A

compass is a small instrument essentially consisting of a graduated circle, and a line of sight.

The compass can not measures angle between two lines directly but can measure angle of a line

with reference to magnetic meridian at the instrument station point is called magnetic bearing of

a line.

3. Types of Compass- Prismatic and Surveyor’s Compass

Cylindrical metal box: Cylindrical metal box is having diameter of 8to 12 cm. It

protects the compass and forms entire casing or body of the compass. It protect compass

from dust, rain etc.

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Pivot: pivot is provided at the center of the compass and supports freely suspended

magnetic needle over it.

lifting pin and lifting lever: a lifting pin is provided just below the sight vane. When the

sight vane is folded, it presses the lifting pin. The lifting pin with the help of lifting lever

then lifts the magnetic needle out of pivot point to prevent damage to the pivot head.

Magnetic needle: Magnetic needle is the heart of the instrument. This needle measures

angle of a line from magnetic meridian as the needle always remains pointed towards

north south pole at two ends of the needle when freely suspended on any support.

Graduated circle or ring: This is an aluminum graduated ring marked with 0ᴼ to 360ᴼ

to measures all possible bearings of lines, and attached with the magnetic needle. The

ring is graduated to half a degree.

Prism : prism is used to read graduations on ring and to take exact reading by compass. It

is placed exactly opposite to object vane. The prism hole is protected by prism cap to

protect it from dust and moisture.

Object vane: object vane is diametrically opposite to the prism and eye vane. The object

vane is carrying a horse hair or black thin wire to sight object in line with eye sight.

Eye vane: Eye vane is a fine slit provided with the eye hole at bottom to bisect the object

from slit.

Glass cover: its covers the instrument box from the top such that needle and graduated

ring is seen from the top.

Sun glasses: These are used when some luminous objects are to be bisected.

Reflecting mirror: It is used to get image of an object located above or below the

instrument level while bisection. It is placed on the object vane.

Spring brake or brake pin: to damp the oscillation of the needle before taking a reading

and to bring it to rest quickly, the light spring brake attached to the box is brought in

contact with the edge of the ring by gently pressing inward the brake pin

The following procedure should be adopted after fixing the prismatic compass on the tripod for

measuring the bearing of a line.

Centering : Centering is the operation in which compass is kept exactly over the station

from where the bearing is to be determined. The centering is checked by dropping a small

pebble from the underside of the compass. If the pebble falls on the top of the peg then

the centering is correct, if not then the centering is corrected by adjusting the legs of the

tripod.

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Leveling : Leveling of the compass is done with the aim to freely swing the graduated

circular ring of the prismatic compass. The ball and socket arrangement on the tripod will

help to achieve a proper level of the compass. This can be checked by rolling round

pencil on glass cover.

Focusing : the prism is moved up or down in its slide till the graduations on the

aluminum ring are seen clear, sharp and perfect focus. The position of the prism will

depend upon the vision of the observer.

Observing Bearing of a line:

Consider a line AB of which the magnetic bearing is to be taken.

By fixing the ranging rod at station B we get the magnetic bearing of needle wrt

north pole.

The enlarged portion gives actual pattern of graduations marked on ring.

Surveyor’s Compass:

It is similar to a prismatic compass except that it has a only plain eye slit instead of eye

slit with prism and eye hole.

NORTH

OBJECT B

A

SOUTH

LINE OF SIGHT

90

180

270

0

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This compass is having pointed needle in place of broad form needle as in case of

prismatic compass.

Surveyor’s Compass

Working of Surveyor’s Compass

1) Centering

2) LEVELING

3) OBSERVING THE BEARING OF A LINE

First two observation are same as prismatic compass but third observation differs from

that.

3) OBSERVING THE BEARING OF A LINE : in this compass ,the reading is taken

from the top of glass and under the tip of north end of the magnetic needle directly. No

prism is provided here.

Bearings:

The bearing of a line is the horizontal angle which it makes with a reference

line(meridian).

Depending upon the meridian , there are four type of bearings they are as follows:

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1) True Bearing: The true bearing of a line is the horizontal angle between the true

meridian and the survey line. The true bearing is measured from the true north in the

clockwise direction.

2) Magnetic Bearing: the magnetic bearing of a line is the horizontal angle which the

line makes with the magnetic north.

3) Grid Bearing: The grid bearing of a line is the horizontal angle which the line makes

with the grid meridian.

4) Arbitrary Bearing: The arbitrary baring of a line is the horizontal angle which the

line makes with the arbitrary meridian.

Designation of Bearing

The bearing are designated in the following two system:-

1) Whole Circle Bearing System.(W.C.B)

2) Quadrantal Bearing System.(Q.B)

Whole Circle Bearing System:

The bearing of a line measured with respect to magnetic meridian in clockwise direction

is called magnetic bearing and its value varies between 0ᴼ to 360ᴼ.

TRUE MERIDIAN

MAGNETIC MERIDIAN

TRUE BEARING

MAGNETIC BEARING

A

B

MN

TN

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The quadrant start from north an progress in a clockwise direction as the first quadrant is

0ᴼ to 90ᴼ in clockwise direction , 2nd 90ᴼ to 180ᴼ , 3rd 180ᴼ to 270ᴼ, and up to 360ᴼ is 4th

one.

Quadrantal Bearing System:

In this system, the bearing of survey lines are measured wrt to north line or south line

which ever is the nearest to the given survey line and either in clockwise direction or in

anti clockwise direction.

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Reduced Bearing

When the whole circle bearing is converted into Quadrantal bearing , it is termed as

“REDUCED BEARING”.

Thus , the reduced bearing is similar to the Quadrantal bearing.

Its values lies between 0ᴼ to 90ᴼ, but the quadrant should be mentioned for proper

designation.

Conversion of WCB to RB

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Fore Bearing and Back Bearing:

The bearing of a line measured in the forward direction of the survey lines is called the

‘fore bearing’(F.B.) of that line.

The bearing of a line measured in direction backward to the direction of the progress of

survey is called the ‘back bearing’(B.B.) of the line.

Computation of Angles:

Observing the bearing of the lines of a closed traverse, it is possible to calculate the

included angles, which can be used for plotting the traverse.

At the station where two survey lines meet, two angles are formed-an exterior angles and

an interior angles. The interior angles or included angle is generally the smaller

angles(<180ᴼ).

FB of line AB

BB of line AB

A

NORTH

NORTH

Θ1

Θ2

B

FB of AB = Θ1(from A to B) BB of AB= Θ2(from B to A)

Remembering following points: 1) In the WCB system ,the differences

b/n the FB and BB should be exactly 180ᴼ. Remember the following relation :

BB=FB+/-180ᴼ

+ is applied when FB is <180ᴼ

- is applied when BB is >180ᴼ

2) In the reduced bearing system the FB and BB are numerically equal but the quadrants are just opposite.

A

B

C

D

EXAMPLES

A

E

F

BB

/_A

EXTERIOR ANGLE B

FB

A

M

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Meridian:

Bearing of a line is always measured clockwise wrt some reference line or direction. This

fixed line is known as meridian.

There three types of meridian:

1) Magnetic meridian: The direction shown by a freely suspended needle which is

magnetized and balanced properly without influenced by any other factors is known as

magnetic meridian.

2) True meridian : True meridian is the line which passes through the true north and

south. The direction of true meridian at any point can be determined by either observing

the bearing of the sun at 12 noon or by sun’s shadow.

3) Arbitrary meridian: In case of small works or in places where true meridian or

magnetic meridian cannot be determined, then ,any direction of a prominent object is

taken as a reference direction called as arbitrary meridian.

4. Local Attraction: A compass shows the direction of the magnetic meridian on the principle of magnetism. Any

magnet attracting material, when is brought near to the compass needle, needle will deflect from

the true magnetic north.

In that case, you will not read the true north direction and if you take the bearings of the lines in

such condition there comes a error in the readings and that error is known as the local attraction.

Materials which are most likely to be present there, while you are doing the compass surveying,

are such as an iron chain, metallic wrist band or ear rings(metallic) that one might be wearing.

Other things such as an electric pole or electric wires may also produce local attraction. The

needle is attracted to these objects, so this will deviate from the true direction of the magnetic

meridian.

If local attraction is available at a station then all the readings taken from that station will have

the same amount of the error, and we have to correct the readings to get the true results.

BB

B

C

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There are methods to get the corrections to be applied on the erroneous readings in the

traversing. The two methods which are used in general will be discussed here briefly.

(1) In first method we have to find out the stations where no local attraction exists. To find out

this we have to look for a line where the difference between the fore bearing and the back

bearing is exactly equal to 180 degrees. If we find such line then that means the two end stations

of that line are free from any local attraction. After finding that line we apply the correction to

the bearings of the other lines.

(2) In the second method we find the line where there is no local attraction. We know that even

if the local attraction is present at every station the measured included angles will not be

incorrect and we can calculate them correctly. With the help of the readings from the stations

which are free from local attraction and the correct included angles we can find out the bearings

of all the lines.

If we do not find any line where the both stations are free from the local attraction, we have to

take the line where the error is minimum and then apply the mean correction to both the stations

and then take them as the correct readings.

5. Bowditch Rule

A widely used rule for adjusting a traverse that assumes the precision in angles or directions is

equivalent to the precision in distances. This rule distributes the closure error over the whole

traverse by changing the northings and eastings of each traverse point in proportion to the

distance from the beginning of the traverse. More specifically, a correction factor is computed

for each point as the sum of the distances along the traverse from the first point to the point in

question, divided by the total length of the traverse. The correction factor at each point is

multiplied by the overall closure error to get the amount of error correction distributed to the

point's coordinates. The compass rule is also known as the Bowditch rule, named for the

American mathematician and navigator Nathaniel Bowditch (1773-1838).

The compass rule is based on the assumption that all lengths were measured with equal care

and all angles taken with approximately the same precision

It is also assumed that the errors in the measurement are accidental and that the total error in

any side of the traverse is directly proportional to the total length of the traverse

The compass rule may be stated as follows: The correction to be applied to the latitude (or

departure) of any course is equal to the total closure in latitude (or departure) multiplied by

the ratio of the length of the course to the total length or perimeter of the traverse. These

correction are given by the following equations:

cl = CL (d/D) and cd = CD (d/D)

where:

cl = correction to be applied to the latitude of any course

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cd = correction to be applied to the departure of any course

CL = total closure in latitude or the algebraic sum of the north and south latitudes

(NL + SL)

CD = total closure in departure or the algebraic sum of the east and west

departures (ED + WD)

d = length of any course

D = total length or perimeter of the traverse

To determine the adjusted latitude of any course the latitude correction is either added to or

subtracted from the computed latitude of the course

A simple rule to remember is: If the sum of the north latitudes exceeds the sum of the south

latitudes, latitude corrections are subtracted from the north latitudes and added to the

corresponding south latitudes. However, if the sum of the south latitudes exceeds the sum of

the north latitudes, the corrections are applied in the opposite manner

Compute the Coordinates for the traverse defined in Example 29.1 by applying correction to

consecutive coordinates by Bowditch's method.

Solution :

Adjustment of Coordinates of a closed-loop traverse using Bowditch's Rule

Sides

Length

( dij )m

Azimuth

( i )

Consecutive coordinates,

(m) Bowditch's Correction (m)

Adjusted Consecutive coordinates,

m

Departure (

Di ) Latitude ( Li )

Departure,

dij

Latitude,

l ij Departure Latitude

AB 372.222 0° 42' 4.547 372.194 0.375 0.231 4.922 372.425

BC 164.988 94° 42' 164.576 -11.653 0.166 0.102 164.742 -11.551

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CD 242.438 183° 04' -12.970 -242.091 0.244 0.151 -12.726 -241.94

DA 197.145 232° 51' -157.136 -119.056 0.198 0.122 -156.938 -118.934

L =

976.793 dD = -0.983 dL = -0.606 = 0.983 = 0.606 = 0.000 = 0.000

6. Open and Closed Traverse

A traverse is a series of connected lines whose lengths and directions are known. A closed traverse is one enclosing a defined area and having a common point for its beginning to end (For Example a close property boundary). An open traverse is one which does not close on the point of the beginning (For example: the line center survey of a highway, railroad, etc). All topgraphical surveys should have a skeleton or network of traverses to serve as horizontal control. To plot a traverse you must have a bearing (Direction) and Length of line (For example: line length from A to B is North 50 degrees 0 degrees East). On a plotting table the reading might look like this (AB=N50 00E X 550.00') Closed Traverse: Boundry is closed

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Open traverse: Boundry is not closed.

UNIT III: LEVELLING

1. Types of Levels

Instruments

The instrument primarily used for leveling is the (engineer's) level in association with a

graduated rod known as leveling rod or leveling staff.

Level

A schematic diagram of an engineer's level is shown in Figure. An engineer's level primarily

consists of a telescope mounted upon a level bar which is rigidly fastened to the spindle. Inside

the tube of the telescope, there are objective and eye piece lens at the either end of the tube. A

diaphragm fitted with cross hairs is present near the eye piece end. A focussing screw is attached

with the telescope. A level tube housing a sensitive plate bubble is attached to the telescope (or

to the level bar) and parallel to it. The spindle fits into a cone-shaped bearing of the leveling

head. The leveling head consists of tribrach and trivet with three foot screws known as leveling

screws in between. The trivet is attached to a tripod stand.

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Functions of Salient Parts

Telescope : used to sight a staff placed at desired station and to read staff reading distinctly.

Diaphragm : holds the cross hairs (fitted with it).

Eye piece : magnifies the image formed in the plane of the diaphragm and thus to read staff

during leveling.

Level Tube : used to make the axis of the telescope horizontal and thus the line of sight.

Leveling screws : to adjust instrument (level) so that the line of sight is horizontal for any

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orientation of the telescope.

Tripod stand : to fix the instrument (level) at a convenient height of an observer

Dumpy Level

A dumpy level is most suitable when from one setting of the instrument, elevations of several

points are to be determined.

(a) (b)

Two Types of Dumpy Levels

Distinctive Features of an Dumpy Level

The optical axis of the telescope of a dumpy is placed perpendicular to the axis of the centre

spindle. The axis of its level tube is permanently placed so that it lies in the same vertical plane

as the optical axis

IOP Level

A IOP level is most suitable when only few readings are to be taken from one setting of the

instrument.

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IOP Level

Distinctive Features of an IOP Level

The telescope is mounted on a transverse fulcrum at the vertical axis fitted with a micrometer

screw at the eye-piece end of the telescope.

Instrument is leveled using circular spirit level. The sensitive plate-bubble is to be leveled using

micrometer screw, at the time of taking measurement. Thus, the line of sight is made horizontal

quickly, even though the instrument as a whole may not be exactly level.

Digital level

There are fundamentally two types of automatic levels.

First, the optical one whose distinguishing feature is self-leveling i.e., the instruments gets

approximately leveled by means of a circular spirit level and then it maintains a horizontal line of

sight of its own.

Second, the digital levels whose distinguishing features are automatic leveling, reading and

recording .

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Digital Level

The chief features of a digital level are:

A CCD (Charged coupled device) at the plane of diaphragm. It captures an image of the

rod and processes it resulting in a rod reading and a distance to the rod.

A data collector which keeps the level notes, performs checks and keeps a record of every

rod reading and elevation automatically.

A bar-coded rod having a scale represented through a series of bars of different widths.

Bars are spaced constantly or variably. The spacing and width of the bars denote the

code.

Advantages of digital levels include the speed of leveling, the virtual elimination of rod reading

and calculation errors and the accuracy in reading rod.

Limitation of digital level lies in its range. Beyond a certain limit it is to be used in “manual

mode”.

2. Levelling Staff

Leveling Staff

It is a self-reading graduated wooden rod having rectangular cross section. The lower end of the

rod is shod with metal to protect it from wear and usually point of zero measurement from which

the graduations are numbered. Staff are either solid (having single piece of 3 meter height) or

folding staff (of 4 meter height into two or three pieces) . The least count of a leveling staff is 5

mm.

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Single Piece 3 m staff

Folded 4 m staff

Temporary Adjustment of Level

At each set up of a level instrument, temporary adjustment is required to be carried out prior to

any staff observation. It involves some well defined operations which are required to be carried

out in proper sequence.

Temporary Adjustment of a Dumpy Level

The temporary adjustment of a dumpy level consists of Setting , Leveling and Focusing .

During Setting, the tripod stand is set up at a convenient height having its head horizontal

(through eye estimation). The instrument is then fixed on the head by rotating the lower part of

the instrument with right hand and holding firmly the upper part with left hand. Before fixing,

the leveling screws are required to be brought in between the tribrach and trivet. The bull's eye

bubble (circular bubble), if present, is then brought to the centre by adjusting the tripod legs.

Next, Leveling of the instrument is done to make the vertical axis of the instrument truly

vertical. It is achieved by carrying out the following steps:

Step 1: The level tube is brought parallel to any two of the foot screws, by rotating the upper part

of the instrument.

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Step 2: The bubble is brought to the centre of the level tube by rotating both the foot screws

either inward or outward. (The bubble moves in the same direction as the left thumb.)

Step 3: The level tube is then brought over the third foot screw again by rotating the upper part

of the instrument.

Step 4: The bubble is then again brought to the centre of the level tube by rotating the third foot

screw either inward or outward.

Step 5: Repeat Step 1 by rotating the upper part of the instrument in the same quadrant of the

circle and then Step 2.

Step 6: Repeat Step 3 by rotating the upper part of the instrument in the same quadrant of the

circle and then Step 4.

Step 7: Repeat Steps 5 and 6, till the bubble remains central in both the positions.

Step 8: By rotating the upper part of the instrument through 180 ° , the level tube is brought

parallel to first two foot screws in reverse order. The bubble will remain in the centre if the

instrument is in permanent adjustment.

Focusing is required to be done in order to form image through objective lens at the plane of the

diaphragm and to view the clear image of the object through eye-piece. This is being carried out

by removing parallax by proper focusing of objective and eye-piece. For focusing the eye-piece,

the telescope is first pointed towards the sky. Then the ring of eye-piece is turned either in or out

until the cross-hairs are seen sharp and distinct. Focusing of eye-piece depends on the vision of

observer and thus required whenever there is a change in observer. For focusing the objective,

the telescope is first pointed towards the object. Then, the focusing screw is turned until the

image of the object appears clear and sharp and there is no relative movement between the image

and the cross-hairs. This is required to be done before taking any observation.

Temporary Adjustment of an IOP Level

Temporary adjustment of a tilting level requires the same operations as in case of a dumpy level

except the operations involved in leveling. During leveling, first the IOP instrument is leveled

roughly with the leveling screws till the circular bubble is in the centre. Then, the bubble of the

level tube is brought to the centre by using the tilting screw. In case of IOP level, the bubble is

required to be leveled using tilting screw before each reading is taken.

Exercise

1 Why levels are usually called as “spirit level”?

2 Explain the importance of level tube in a levelling instrument.

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3 Explain the chief feature of a digital level.

4 State the differences in the temporary adjustment of a dumpy level and an IOP level

5 State the difference between a dumpy level and a digital level.

3. Measurements and Recording

Basic Principle of Leveling

The fundamental principle of leveling lies in finding out the separation of level lines passing

through a point of known elevation (B.M.) and that through an unknown point (whose elevation

is required to be determined).

Let X represents a point of known elevation (Hx) or a B.M. and Y be a point whose elevation is

required to be determined. To find out the unknown elevation of Y, a level is set up at L in

between X and Y. A leveling staff is first held at X and a reading hx is observed, by sighting the

staff (held vertical to the line of sight of the level). The staff reading at Y, say hy is then

observed. The elevation of the point Y (say Hy) is thus given by Hx + (hx ~ hy) i.e., known

elevation (Hx ) added to the separation of level lines (hx ~ hy) passing through the points.

Methods of Leveling

Direct Leveling : Direct measurement, precise, most commonly used; types:

Simple leveling : One set up of level. To find elevation of points.

Differential leveling : Numbers of set-ups of level. To find elevation of non-intervisible points.

Fly leveling : Low precision, to find/check approximate level, generally used during

reconnaissance survey.

Precise leveling : Precise form of differential leveling.

Profile leveling : finding of elevation along a line and its cross section.

Reciprocal leveling : Along a river or pond. Two level simultaneously used, one at either end.

Indirect or Trigonometric Leveling : By measuring vertical angles and horizontal distance;

Less precise.

Stadia Leveling : Using tacheometric principles.

Barometric Leveling : Based on atmospheric pressure difference; Using altimeter; Very rough

estimation.

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Differential Leveling

Applied to determine the elevation of point which is some distant apart from B.M i.e., the

unknown elevation of a point cannot be determined in a single set up of an instrument. Thus, in

this method, instrument gets setup number of times to observe reading along a route in between

observed points. For each set up, staff readings are taken back to a point of known elevation

(first sight from the B.M and forward to a point of unknown elevation) final sight to the terminal

station.

Procedure

Let us consider a station B whose elevation is to be established with reference to a B.M station

A, quite a distant apart. In establishing the station B as B.M., differential leveling is carried out

starting from A and terminating at B. In order to carry out the leveling, first the instrument is set

up at some location, say I1 , in such a way that backsight reading taken on A can be read clearly.

The staffman is then directed to move forward towards B and choose a point, say S1 which is

firm and stable. It is preferable that the distance of S1 from I1be the same as that of station A

from I1. After proper selection of the point S1, staff is held to take the foresight reading for this

instrument set up. The instrument is then shifted to some other position in forward direction, say

I2 towards B and take the backsight reading on S1. Thus, point S1 is used as a turning point. From

I2 foresight reading is taken to another well chosen (as followed in S1) turning point S2. Finally,

from I3 backsight is taken on S2 and last sight at the terminal point B.

Field Book

A field book, also called level book is being used for taking down each staff reading during

leveling and subsequently, used for finding out the elevation of points/ stations. There are two

types of level books (Table.1 and Table 2). Usually, level book contains columns of both the

types together (Table 3) and it is for a surveyor to use only the relevant columns only.

Table 1 Level book note for Rise and Fall method

Staff Reading Difference in Elevation Elevation

Points B.S (m) F.S.(m) Rise (m) Fall (m) R.L (m) Remark

A 2.365 100.000 B.M.

S 1 0.685 1.235 1.130 101.130 T.P.1

S2 1.745 3.570 2.885 98.245 T.P. 2

B 2.340 0.595 97.650

Table 2 Level book note for Height of instrument method

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Staff Reading Height of Instrument

(m) R.L. (m) Remarks

Points B.S (m) F.S.(m)

A 2.365 102.365 100.000 B.M.

S 1 0.685 1.235 101.815 101.130 T.P.1

S2 3.570 98.245 T.P.2

B 2.340 97.650

Table 3 Field book for Reduction of level

Staff Reading (m) Difference in

elevation (m) H.I (m) R.L. (m) Remarks

Points B.S. I.S. F.S. Rise Fall

A 2.365 102.365 100.000 B.M.

S 1 0.685 1.235 1.130 101.815 101.130 T.P.1

S2 1.745 3.570 2.885 99.990 98.245 T.P. 2

B 2.340 0.595 102.365 97.650

4.795 7.145 3.480 101.815

Reduction of Level

The observed staff readings as noted in a level book are further required to be manipulated to

find out the elevation of points. The operation is known as reduction of level. There are two

methods for reduction of levels:

1. Rise and Fall method and

2. Height of instrument method.

Rise and Fall Method

For the same set up of an instrument, Staff reading is more at a lower point and less for a higher

point. Thus, staff readings provide information regarding relative rise and fall of terrain points.

This provides the basics behind rise and fall method for finding out elevation of unknown points.

When the instrument is at I1, the staff reading at A (2.365m) is more than that at S1 which

indicates that there is a rise from station A to S1 and accordingly the difference between them

(1.130m) is entered under the rise column in Table 1. To find the elevation of S1 ( 101.130m),

the rise (1.130m) has been added to the elevation of A (100.0m). For instrument set up at I2 , S1

has been treated as a point of known elevation and considered for backsight (having reading

0.685m) . Foresight is taken at S2 and read as 3.570m i.e, S2 is at lower than S1 . Thus, there is a

fall from S1 a nd S2 and there difference (2.885m) is entered under the fall column in Table 1. To

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find the elevation of S2 ( 98.245m), the fall (2.885m) has been subtracted from the elevation of

S1 (101.130m). In this way, elevation of points are calculated by Rise and Fall method.

Table 1 Level book note for Rise and Fall method

Staff Reading Difference in Elevation Elevation

Points B.S (m) F.S.(m) Rise (m) Fall (m) R.L (m) Remark

A 2.365 100.000 B.M.

S 1 0.685 1.235 1.130 101.130 T.P.1

S2 1.745 3.570 2.885 98.245 T.P. 2

B 2.340 0.595 97.650

Height of Instrument Method

In any particular set up of an instrument height of instrument, which is the elevation of the line

of sight, is constant. The elevation of unknown points can be obtained by subtracting the staff

readings at the desired points from the height of instrument. This is the basic behind the height of

instrument method for reduction of level.

When the instrument is at I1, the staff reading observed at A is 2.365m. The elevation of the line

of sight i.e., the height of instrument is 102.365m obtained by adding the elevation of A

(100.0m) with the staff reading observed at A (2.365m). The elevation of S1 (101.130m) is

determined by subtracting its foresight reading (1.235m) from the the height of instrument

(102.365m) when the instrument is at I1 . Next, the instrument is set up at I2. S1 is considered as a

point of known elevation and backsight reading ( 0.685m) is taken . The height of the instrument

(101.815 m) is then calculated by adding backsight reading ( 0.685m) with the elevation (R.L.)

of point S1 (101.130m). Foresight is taken at S2 and its elevation (98.245m) is determined by

subtracting the foresight (3.570m) from the height of the instrument (101.815 m). In this way,

elevation of points are calculated by Height of instrument method.

Table 2 Level book note for Height of instrument method

Staff Reading Height of Instrument

(m) R.L. (m) Remarks

Points B.S (m) F.S.(m)

A 2.365 102.365 100.000 B.M.

S 1 0.685 1.235 101.815 101.130 T.P.1

S2 3.570 98.245 T.P.2

B 2.340 97.650

Example

Ex1 Data from a differential leveling have been found in the order of B.S., F.S..... etc. starting

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with the initial reading on B.M. (elevation 150.485 m) are as follows : 1.205, 1.860, 0.125,

1.915, 0.395, 2.615, 0.880, 1.760, 1.960, 0.920, 2.595, 0.915, 2.255, 0.515, 2.305, 1.170. The

final reading closes on B.M.. Put the data in a complete field note form and carry out reduction

of level by Rise and Fall method. All units are in meters.

Solution :

B.S. (m) F.S. (m) Rise (m) Fall (m) Elevation (m) Remark

1.205 150.485 B.M.

0.125 1.860 0.655 149.830

0.395 1.915 1.7290 148.040

0.880 2.615 2.220 145.820

1.960 1.760 0.880 144.940

2.595 0.920 1.040 145.980

2.255 0.915 1.680 147.660

2.305 0.515 1.740 149.450

1.170 1.135 150.535 B.M.

Arithmetic Check for Reduction of Level

In case of Rise and Fall method for Reduction of level, following arithmetic checks are applied

to verify calculations.

B.S. - F.S. = Rise - Fall = Last R.L. - First R.L.

With reference to Table 13.3:

B.S. - F.S. = 4.795 - 7.145 = - 2.350

Rise - Fall. = 1.130 - 3.480 = - 2.350

Last R.L. - First R.L.= 97.650 - 100.000 = -2.350

Table 3 Field book for Reduction of level

Staff Reading (m) Difference in

elevation (m) H.I (m) R.L. (m) Remarks

Points B.S. I.S. F.S. Rise Fall

A 2.365 102.365 100.000 B.M.

S 1 0.685 1.235 1.130 101.815 101.130 T.P.1

S2 1.745 3.570 2.885 99.990 98.245 T.P.2

B 2.340 0.595 102.365 97.650

4.795 7.145 3.480 101.815

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Example

Ex Carry out the arithmetic checks for Reduction of level of Ex13-1.

Solution :

B.S. = 11.720 m; F.S. = 11.670 m

Therefore B.S - F.S. = 0.050 m

Rise = 5.595 m; Fall = 5.545 m

Therefore Rise - Fall = 0.050 m

Last R.L. - First R.L. = 150.535 - 150.485 = 0.050 m.

B.S - F.S. = Rise - Fall = Last R.L. - First R.L.

Example

Ex Complete the differential-level notes and determine the error of closure of the level circuit

and adjust the elevations of B.M.2 and B.M.3 assuming that the error is constant per set up.

Level book note for Level Net

Staff Reading Height of Instrument

(m)

R.L. (m)

Points B.S (m) F.S.(m)

B.M.1 2.125

T.P.1 1.830 2.945

T.P.2 2.100 3.225

T.P.3 1.650 3.605

B.M.2 2.365 2.805

T.P.4 2.885 2.530

T.P.5 3.065 2.350

B.M.3 3.855 1.100

T.P.6 3.270 1.660

T.P.7 3.865 2.110

B.M.1 3.455

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Solution :

Staff Reading Height of Instrument

(m)

R.L. (m)

Points B.S (m) F.S.(m)

B.M.1 2.125 102.125 100.000

T.P.1 1.830 2.945 101.010 99.18

T.P.2 2.100 3.225 99.885 97.785

T.P.3 1.650 3.605 97.93 96.280

B.M.2 2.365 2.805 97.49 95.125

T.P.4 2.885 2.530 97.845 94.960

T.P.5 3.065 2.350 98.56 95.495

B.M.3 3.855 1.100 101.315 97.46

T.P.6 3.270 1.660 102.925 99.655

T.P.7 3.865 2.110 104.680 100.815

B.M.1 3.455 101.225

Error of closure = 101.225 - 100 = + 1.225 m

There are ten (10) set up for the instrument. Thus for each set up, there is an error of 0.1225 m.

Therefore correction for each set up = - 0.1225 m

Adjusted elevation of B.M.2 = 95.125 - 4 x .1225 = 94.635 m

Adjusted elevation of B.M. 3 = 97.46 - 7 x .1225 = 96.603 m

Exercise

Ex.1 State and explain the basic principle of levelling.

Ex.2 Enumerate the difference between rise and fall method (of reduction of level) and height of

instrument method.

Ex.3 Data from a differential leveling have been found in the order of B.S., F.S..... etc. starting

with the initial reading on B.M. (elevation 150.485 m) are as follows : 1.205, 1.860, 0.125,

1.915, 0.395, 2.615, 0.880, 1.760, 1.960, 0.920, 2.595, 0.915, 2.255, 0.515, 2.305, 1.170. The

final reading closes on B.M.. Put the data in a complete field note form and carry out reduction

of level by Height of instrument method. All units are in meters.

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4. Reciprocal leveling

Reciprocal Leveling

To find accurate relative elevations of two widely separated intervisible points (between which

levels cannot be set), reciprocal leveling is being used.

To find the difference in elevation between two points, say X and Y , a level is set up at L near X

and readings (X1 and Y1) are observed with staff on both X and Y respectively. The level is then

set up near Y and staff readings (Y2 and X2 ) are taken respectively to the near and distant points.

If the differences in the set of observations are not same, then the observations are fraught with

errors. The errors may arise out of the curvature of the earth or intervening atmosphere

(associated with variation in temperature and refraction) or instrument (due to error in

collimation) or any combination of these.

The true difference in elevation and errors associated with observation, if any, can be found as

follows:

Let the true difference in elevation between the points be h and the total error be e. Assuming,

no error on observation of staff near the level (as the distance is very small)

Then, h = X1 ~ (Y1 - e) [From first set of observation]

and h = (X2 - e) ~ Y2 [From second set of observation]

Thus, the true difference in elevation between any two points can be obtained by taking the mean

of the two differences in observation.

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Thus, total error in observations can be obtained by taking the difference of the two differences

in observation. The total error consist of error due to curvature of the earth, atmospheric errors

(due to temperature and refraction) and instrumental errors (due to error in collimation) etc.

Example

Ex1 In order to transfer reduced level across a canyon, a reciprocal leveling campaign was

conducted. Simultaneous readings were observed using two levels one at each side of the

canyon. Each of the levels are having same magnifying power and sensitiveness of level tube.

With instruments interchanged during leveling operation yielded the following average readings:

Instrument

station

Average near

readings, meter

Average distant,

readings, meter

R.L of X = 101.345 m

Distance, XY = 1.025Km

e curvature = 0.0785 XY 2

X 1.780 2.345

Y 2.435 1.870

Find out the R.L. of unknown point. Comment on the errors associated with observations.

Solution :

The difference in elevation between X and Y is

= 0.565 m (Y lower than X)

R.L. of Y (unknown Point) = R.L. of X - h = 101.345 - 0.565 = 100.780 m

Since two leveling rods are used and the elapsed time between reading in a set observation is

little, the error due to change in atmospheric condition can be neglected. Moreover, since

readings were taken with instruments interchanged, instrumental errors get cancelled between

different set of observation. As the observations are repeated and averages of the readings have

been considered for further calculation, it is expected that error associated with observation is

minimized thus removed. Only error present in the observation is that associated with the

curvature of the earth.

Trigonometric Leveling

For rapid leveling or leveling in rolling ground or for inaccessible points, trigonometric method

of leveling is being used. In this method, theodolite (an instrument which can measure angle) is

being generally used as an instrument for taking different measurements.

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Let us consider two stations T and X on rolling ground whose difference in elevation is required

to be determined by trigonometric method of leveling. At T, a theodolite instrument is set up. TT

' is the height of the instrument above the point T (to be recorded at the time of observation). A

leveling staff is held at X. At the vertical angle of elevation of the actual line of sight , let x1 is

the observed staff reading. The difference in level between T and X is given by

where xt' xh is deviation of the horizontal line of sight due to curvature of the earth and refraction

of light (given by 0.0675 T' x h2 ). xh x1 is T' x1 sin or T' x h tan , T' x1 is the inclined distance

from the instrument to the staff and T' xh is the horizontal distance between the points, x1 X is the

staff reading at X.

Examples

Ex In order to eliminate the uncertainty due to refraction, observations for vertical angle are

made at both ends of the line as close in point of time as possible. The vertical angle at the lower

of the two peaks to the upper peak is +3° 02' 05"?. The reciprocal vertical angle at the upper peak

is - 3° 12' 55"?. The height of instrument are kept to be same in all observation. The slope

distance between two mountain peaks determined by EDM measurement is 21,345m. Compute

the difference in elevations between the two peaks.

Solution :

Average vertical angle = (3° 02' 05" + 3° 12' 55") / 2 = 6° 15' 00 "

Difference in elevation = 21.345 sin 3° 07' 30 " + 0.0675 (21.345 cos 3° 07' 30 ")2

= (1.163 + 30.662) m

= 31.825 m

Exercise

1The following reciprocal levels were taken on two stations P and Q:

Instrument

station

Average near

readings, meter

Average distant,

readings, meter

R.L of P = 101.345 m

Distance, PQ = 1645 Km

P 2.165 3.810

Q 2.335 0.910

Determine the elevation of Q and the error due to refraction when the collimation error is 0.003m

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downward per 100m.

2 In order to reduce the error in measurement of vertical angle a set of measurements are taken

and find the average angle as 9° 02' 05? form a height of instrument as 1.565m to a target height

2.165m. If the elevation of the instrument station is 189.250m above mean sea level, find the

elevation of staff station. Assume any data, if required.

5. Curvature and Refraction Correction

Error due to Earth's Curvature & Refraction

The combined error due to curvature and refraction (ecomb ) is thus given by

ecomb = 0.0675 D2 m where D is the distance in km

It is finally subtractive in nature as the combined effect provides increase in staff reading. Let x l

x a represents the combined error due to curvature and refraction in Figure, it is AL .

In most ordinary leveling operation, the line of sight is rarely more than 2 meter above the

ground (where the variation in temperature causes substantial uncertainties in the refraction

index of air). Fortunately, most lines of sights in leveling are relatively short (< 30 m) and B.S.

& F.S. are balanced. Consequently, curvature and refraction corrections are relatively small thus

insignificant except for precise leveling.

Exercise

Ex.1 A surveyor standing on seashore can just see the top of a ship through the telescope of a

levelling instrument. The height of the line of sight at instrument location is 1.65 meter above

msl and the top of ship is 50 meter above sea level. How far is the ship from the surveyor?

The following notes refer to the reciprocal levels taken with one level:

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Instrument Station Staff Readings on Remarks

Near Station Further station

P 1.03 1.630 Distance PQ = 800 m

Q 2.74 0.950 R.L. of P = 450 m

Find (i) the true R.L. of Q;

combined correction for curvature and refraction

the error in collimation adjustment of the instrument.

UNIT IV- CONTOURS

1. Properties of Contours

Contour

A contour is defined as an imaginary line of constant elevation on the ground surface. It can also

be defined as the line of intersection of a level surface with the ground surface. For example, the

line of intersection of the watersurface of a still lake or pond with the surrounding ground

represents a contour line.

Definition

A line joining points of equal elevations is called a contour line. It facilitates depiction of the

relief of terrain in a two dimensional plan or map

Contour Interval

The difference in elevation between successive contour lines on a given map is fixed. This

vertical distance between any two contour lines in a map is called the contour interval (C.I.) of

the map. Figure 1(a) shows contour interval of 1m whereas Figure 1(b) shows 10m.

The choice of suitable contour interval in a map depends upon four principal considerations.

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These are:

Nature of the Terrain

Nature of Terrain

The contour interval depends upon the nature of the terrain (Table 1). For flat ground, a small

contour interval is chosen whereas for undulating and broken ground, greater contour interval is

adopted.

Table 1 Contour Interval ( CI) for different types of Survey

Sl. No Purpose of survey Scale CI (m)

1 Building site 1/1000 or less 0.2 to 0.5

2 Town planning,

reservoir etc. 1/5,000 to 1/10,000 0.5 to 2

3 Location Survey,

earthwork, etc. 1/10,000 to 1/20,000 1 to 3

Scale of the Map

Scale of the Map

The contour interval normally varies inversely to the scale of the map i.e., if the scale of map is

large, the contour interval is considered to be small and vice versa (Table 2).

Table 2 CI for different scales and types of Ground

SI.NO Map Scale Type of

Terrain CI(m)

1

Large

(1:1000 or

less)

Flat 0.2 to 0.5

Rolling 0.5 to 1

Hilly 1 to 2

2

Intermediate

(1:1000 to

1: 10,000)

Flat 0.5 to 1.5

Rolling 1.5 to 2

Hilly 2 to 3

3

Small

(1: 10,000

or more)

Flat 1 to 3

Rolling 3 to 5

Hilly 5 to 10

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Accuracy

Accuracy

Accuracy need of surveying work also decide the contour interval. Surveying for detailed

design work or for earthwork calculations demands high accuracy and thus a small contour

interval is used. But in case of location surveys where the desired accuracy is less, higher

contour interval should be used.

Time of Cost

Time and Cost

If the contour interval is small, greater time and funds will be required in the field survey, in

reduction and in plotting the map. If the time and funds available are limited, the contour

interval may be kept large.

Horizontal Equivalent

The horizontal distance between two points on two consecutive contour lines for a given slope is

known as horizontal equivalent. For example, in Figure 1 (b) having contour interval 10m, the

horizontal equivalent in a slope of 1 in 5 would be 50 m. Thus, horizontal equivalent depends

upon the slope of the ground and required grade for construction of a road, canal and contour

interval.

Characteristics of Contour

The principal characteristics of contour lines which help in plotting or reading a contour map are

as follows:

1. The variation of vertical distance between any two contour lines is assumed to be

uniform.

2. The horizontal distance between any two contour lines indicates the amount of slope and

varies inversely on the amount of slope. Thus, contours are spaced equally for uniform

slope ; closely for steep slope contours and widely for moderate slope .

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3. The steepest slope of terrain at any point on a contour is represented along the normal of

the contour at that point . They are perpendicular to ridge and valley lines where they

cross such lines.

4. Contours do not pass through permanent structures such as buildings .

5. Contours of different elevations cannot cross each other (caves and overhanging cliffs are

the exceptions).

6. Contours of different elevations cannot unite to form one contour (vertical cliff is an

exception).

7. Contour lines cannot begin or end on the plan.

8. A contour line must close itself but need not be necessarily within the limits of the map.

9. A closed contour line on a map represents either depression or hill . A set of ring contours

with higher values inside, depicts a hill whereas the lower value inside, depicts a

depression (without an outlet).

10. Contours deflect uphill at valley lines and downhill at ridge lines. Contour lines in U-

shape cross a ridge and in V-shape cross a valley at right angles. The concavity in

contour lines is towards higher ground in the case of ridge and towards lower ground in

the case of valley.

11. Contours do not have sharp turnings.

2. Plotting of Contours

Contouring

The method of establishing / plotting contours in a plan or map is known as contouring. It

requires planimetric position of the points and drawing of contours from elevations of the plotted

points. Contouring involves providing of vertical control for location of points on the contours

and horizontal control for planimetric plotting of points. Thus, contouring depends upon the

instruments used (to determine the horizontal as well as vertical position of points). In general,

the field methods of contouring may be divided into two classes:

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Direct methods

Direct Method

In the direct method, the contour to be plotted is actually traced on the ground. Points which

happen to fall on a desired contour are only surveyed, plotted and finally joined to obtain the

particular contour. This method is slow and tedious and thus used for large scale maps, small

contour interval and at high degree of precision. Direct method of contouring can be employed

using Level and Staff as follows:

Vertical control : In this method, a benchmark is required in the project area. The level is set

up on any commanding position and back sight is taken on the bench mark. Let the back sight

reading on the bench mark be 1.485 m. If the reduced level of the bench mark is 100 m, the

height of instrument would be 100 + 1.485 = 101.485 m. To locate the contour of 100.5 m

value, the staff man is directed to occupy the position on the ground where the staff reading is

101.485 -100.500 = 0.985 m. Mark all such positions on the ground where the staff reading

would be 0.985 m by inserting pegs. Similarly locate the points where the staff reading would

be 101.485 -101 = 0.485 m for 101m contour. The contour of 101.5 m cannot be set from this

setting of the instrument because the height of instrument for this setting of the instrument is

only 101.485 m. Therefore, locating contours of higher value, the instrument has to be shifted to

some other suitable position. Establish a forward station on a firm ground and take fore sight on

it. This point acts as a point of known elevation, for shifting the position of the instrument to

another position, from where the work proceeds in the similar manner till the entire area is

contoured.

Horizontal control : The horizontal control is generally provided by method of plane table

surveying or locating the positions of points by other details in which will be discussed in later

module .

Indirect methods

Indirect Methods

In this method, points are located in the field, generally as corners of well-shaped geometrical

figures such as squares, rectangles, and spot levels are determined. Elevations of desired

contours are interpolated in between spot levels and contour lines are drawn by joining points of

equal elevation.

Indirect methods are less expensive, less time consuming and less tedious as compared to the

direct method. These methods are commonly employed in small scale surveys of large areas or

during mapping of irregular surface or steep slope. There are two different ways usually

employed for indirect method of contouring:

Grid method and

Radial line method

A Comparison between Direct and Indirect Methods of Contouring

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Direct Method Indirect Method

1 Very accurate but slow and tedious Not very accurate but quicker and less

tedious.

2 Expensive Reasonable cost

3

Appropriate for small projects

requiring high accuracy, e.g., layout

of building, factory, structural

foundations, etc.

Suitable for large projects requiring

moderate to low accuracy, e.g., layout of

highway, railway, canal, etc.

4 More suitable for low undulating

terrain. Suitable for hilly terrain.

5 Calculations need to be carried out in

thefield Calculation in the field is not mandatory.

6 After contouring, calculation cannot

be checked.

Calculations can be checked as and when

needed

Drawing of Contours

Points of desired elevation, at which contours are desired to be drawn, are interpolated in

between observed points. Then, contours are drawn by joining points of equal elevation by

smooth curves keeping in mind the principal characteristics of contour. They are then inked in,

preferably in brown to distinguish them from other features. The contour value is written down

in a gap in the line provided for the purpose. Every fifth contour is drawn bolder to make it

distinguishable from the rest.

Exercise

Ex.1 On the basis od spot elevations in meters given in Fig. 1 draw contours at 20 m interval.

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Exercise Figure -1

Ex.2 Fig. 2 shows the same area with stream courses in addition to the spot elevations. Draw the

contours, in this case also, at 20 m interval.

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Exercise Figure 2

3. Uses of Contours

Nature of Ground

To visualize the nature of ground along a cross section of interest, a line say XY is being

considered through the contour map . The intersection points between the line and contours are

projected at different elevations of the contours are projected and joined by smooth curve. The

smooth curve depicts the nature of the ground surface along XY.

To Locate Route

Contour map provides useful information for locating a route at a given gradient such as

highway, canal, sewer line etc.

Let it be required to locate a route from P to Q at an upward gradient of 1 in 100. The contour

map of the area is available at a contour interval of 5 meter at a scale of 1:10000. The horizontal

equivalent will therefore be equal to 100 meter. Then with centre at P with a radius of 2 cm draw

an arc to cut the next higher contour, say at q. With q as centre, mark the next higher contour by

an arc of radius 2 cm say at r. Similarly, other points such as s,t,u…. etc are obtained and joining

the points provides the location of route. (Figure 2)

Intervisibility between Stations

When the intervisibility between two points can not be ascertained by inspection of the area, it

can be determined using contour map. The intervisibility is determined by drawing a line joining

the stations / points say PQ and plot the elevations of the points and contours intersected by PQ

as shown in Figure 3. If the intervening ground is found to be above A'B' line, the intervisibility

is obstructed. In the figure, the ground is obstructing the line of sight.

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To Determine Catchment Area or Drainage Area

The catchment area of a river is determined by using contour map. The watershed line which

indicates the drainage basin of a river passes through the ridges and saddles of the terrain

around the river. Thus, it is always perpendicular to the contour lines. The catchment area

contained between the watershed line and the river outlet is then measured with a planimeter

(Figure 4).

Storage capacity of a Reservoir

The storage capacity of a reservoir is determined from contour map. The contour line indicating

the full reservoir level (F.R.L) is drawn on the contour map. The area enclosed between

successive contours are measured by planimeter (Figure 5). The volume of water between F.R.L

and the river bed is finally estimated by using either Trapezoidal formula or Prismoidal formula.

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4. Measurement of Drainage and Volume of Reservoir

Examples

Ex.1 In a hydro-electric project, the reservoir provides a storage of 5.9 million cubic meter

between the lowest draw down and the top water level. The areas contained within the stated

contours and the upstream face of the dam are as follows :

Contour (m) 200 195 190 185 180 175 170 165

Area (104 sq m) 44 34 28 23 20 16 11 8

If the R.L. of the lowest draw down is 167 m, find the reduced level of water at the full storage

capacity of the reservoir.

Solution :

The area contained in lowest draw down level i.e. at 167 m is as follows :

Given, contour interval = 5 m

The area contained between 165 m and 170 m level is (11 - 8) x 104 = 3 x 104 sq m

i.e., For a height of 5 m, difference in area = 3 x 104 sq m

Therefore between 165 m and 167 m, i.e. for a height drift of 2 m, the area difference

= 1.2 x 104 sq m

The area contained in 167 m contour = (8 + 1.2 ) x 104 sq m = 9.2x 104 sq m

Now from given and calculated data and using trapezoidal rule

Contour Area contained

(104)

Volume contained

between (104)

Volume contained

by (104)

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167 9.2

30.3

170 11.0 30.3

67.5

175 16.0 97.8

90.0

180 20.0 187.8

107.5

185 23.0 295.3

127.5

190 28.0 422.8

155.0

195 34.0 577.8

195.0

200 44.0 772.8

So, at full storage capacity, the height of water level lies between 195 m and 200 m.

The volume of water beyond 195 m height is

(5.9 x 106 - 5.778 x 106) = 1.22 x 105 cu.m

Let h be the height of water level above 195 m height. Then area contained in (195 + h) m

contour is

= 34 x 104 +

The volume between 195 m and (195 + h) m contour is

or, h2 + 34 h -12.2 = 0

Solving, we get h = 0.355 m

Thus the reduced level of water at the full reservoir capacity is (195 + 0.355) = 195.355 m

Exercise

Ex.1 The areas enclosed by contours on the upstream face of dam in a hydro-electric project as

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Contour (m) 800 790 780 770 760 750 740 730

Area (hectares) 31.41 26.74 24.89 22.23 19.37 17.74 12.91 5.35

The lowest draw down level is 733 m. compute the full reservoir capacity.

UNIT V- MEASUREMENT OF AREA BY PLANIMETER

A linear planimeter. Wheels permit measurement of long areas without restriction

Polar Planimeter

The working of the linear planimeter may be explained by measuring the area of a rectangle

ABCD (see image). Moving with the pointer from A to B the arm EM moves through the yellow

parallelogram, with area equal to PQ×EM. This area is also equal to the area of the parallelogram

A"ABB". The measuring wheel measures the distance PQ (perpendicular to EM). Moving from

C to D the arm EM moves through the green parallelogram, with area equal to the area of the

rectangle D"DCC". The measuring wheel now moves in the opposite direction, subtracting this

reading from the former. The movements along BC and DA are the same but opposite, so they

cancel each other with no net effect on the reading of the wheel. The net result is the measuring

of the difference of the yellow and green areas, which is the area of ABCD.

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The images show the principles of a linear and a polar planimeter. The pointer M at one end of

the planimeter follows the contour C of the surface S to be measured. For the linear planimeter

the movement of the "elbow" E is restricted to the y-axis. For the polar planimeter the "elbow" is

connected to an arm with its other endpoint O at a fixed position. Connected to the arm ME is the

measuring wheel with its axis of rotation parallel to ME. A movement of the arm ME can be

decomposed into a movement perpendicular to ME, causing the wheel to rotate, and a movement

parallel to ME, causing the wheel to skid, with no contribution

to its reading.

Linear Planimeter Polar Planimeter

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BUILDING MATERIALS:-

UNIT-I: BRICKS

1. Constituents of a good brick earth:

Bricks are the most commonly used construction material. Bricks are prepared by moulding clay

in rectangular blocks of uniform size and then drying and burning these blocks.

Silica

o Brick earth should contain about 50 to % of silica.

o It is responsible for preventing cracking, shrinking and warping of raw bricks.

o It also affects the durability of bricks.

o If present in excess, then it destroys the cohesion between particles and the brick becomes

brittle.

Alumina

o Good brick earth should contain about 20% to 30% of alumina.

o It is responsible for plasticity characteristic of earth, which is important in moulding operation.

o If present in excess, then the raw brick shrink and warp during drying.

Lime

o The percentage of lime should be in the range of 5% to 10% in a good brick earth.

o It prevents shrinkage of bricks on drying.

o It causes silica in clay to melt on burning and thus helps to bind it.

o Excess of lime causes the brick to melt and brick looses its shape.

Iron oxide

o A good brick earth should contain about 5% to 7% of iron oxide.

o It gives red colour to the bricks.

o It improves impermeability and durability.

o It gives strength and hardness.

o If present in excess, then the colour of brick becomes dark blue or blakish.

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o If the quantity of iron oxide is comparatively less, the brick becomes yellowish in colour.

Magnesia

o Good brick earth should contain less a small quantity of magnesia about1%)

o Magnesium in brick earth imparts yellow tint to the brick.

o It is responsible for reducing shrinkage

o Excess of magnesia leads to the decay of bricks. Harmful Ingredients in Brick:

Undesirable Ingredients in Bricks

Lime

o A small quantity of lime is required in brick earth. But if present in excess, it causes the brick

to melt and hence brick loses its shape.

o If lime is present in the form of lumps, then it is converted into quick lime after burning. This

quick lime slakes and expands in presence of moisture, causing splitting of bricks into pieces.

Iron pyrites

o The presence of iron pyrites in brick earth causes the brick to get crystallized and disintegrated

during burning, because of the oxidation of the iron pyrits.

o Pyrites discolourise the bricks.

Alkalis

o These are exist in the brick earth in the form of soda and potash. It acts as a flux in the kiln

during burning and it causes bricks to fuse, twist and warp. Because of this, bricks are melted

and they loose their shape.

o The alkalis remaining in bricks will absorb moisture from the atmosphere, when bricks are

used in masonry. With the passage of time, the moisture gets evaporated leaving grey or white

deposits on the wall surface (known as efflorescence). This white patch affects the appearance of

the building structure.

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Pebbles

o Pebbles in brick earth create problem during mixing operation of earth. It prevents uniform and

through mixing of clay, which results in weak and porous bricks

o Bricks containing pebbles will not break into shapes as per requirements.

Vegetation and Organic Matter: The presence of vegetation and organic matter in brick earth

assists in burning. But if such matter is not completely burnt, the bricks become porous. This is

due to the fact that the gasses will be evolved during the burning of the carbonaceous matter and

it will result in the formation of small pores.

2. Manufacturing of Bricks

Manufacturing of bricks In the process of manufacturing bricks, the following distinct operations

are involved.

• Preparation of clay

The clay for brick is prepared in the following order.

• Unsoiling : The top layer of the soil, about 200mm in depth, is taken out and thrown away. The

clay in top soil is full of impurities and hence it is to be rejected for the purpose of preparing

bricks.

• Digging : The clay is then dug out from the ground. It is spread on the levelled ground, just a

little deeper than the general level. The height of heaps of clay is about 600mm to 1200mm.

• Cleaning : The clay as obtained in the process of digging should be cleaned of stones, pebbles,

vegetable matters. If these particles are in excess, the clay is to be washed and screened. Such a

process naturally will prove to be troublesome and expensive.

• Weathering : The clay is then exposed to atmosphere for softening and mellowing. The period

varies from few weeks to full season.

• Blending : The clay is made loose and any ingredient to be added to it , is spread out at its top.

The blending indicates intimate or harmonious mixing. It is carried out by taking a small amount

of clay every time and turning it up and down in vertical direction. The blending makes clay fit

for the next stage of tempering.

• Tempering : In the process of tempering, the clay is brought to a proper degree of hardness and

it is made fit for the next operation of moulding .Kneaded or pressed under the feet of man or

cattle .The tempering should be done exhaustively to obtain homogeneous mass of clay of

uniform character. For manufacturing good bricks on a large scale, tempering is done in pug

mill. A typical pug mill capable of tempering sufficient earth for a daily output of about 15000 to

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20000 bricks. A pug mill consists of a conical iron tub with cover at its top .It is fixed on a

timber base which is made by fixing two wooden planks at right angle to each other. The bottom

of tub is covered except for the hole to take out pugged earth. The diameter of pug mill at bottom

is about 800mm and that at top is about 1 m. The provision is made in top cover to place clay

inside pug mill .A vertical shaft with horizontal arms is provided at center of iron tub. The small

wedge-shaped knives of steel are fixed at arms. The long arms are fixed at vertical shaft to attach

a pair of bullocks .The ramp is provided to collect the pugged clay .The height of pug mill is

about 2m. Its depth below ground is 600m to800mm lessen the rise of the barrow run and to

throw out the tempered clay conveniently. In the beginning, the hole for pugged clay is closed

and clay with water is placed in pug mill from the top. When vertical shaft is rotated by a pair of

bullock, the clay is thoroughly mixed up by the action of horizontal arms and knives and

homogeneous mass is formed. The rotation of vertical shaft can also be achieved by using steam,

diesel or electrical power. When clay has been sufficiently pugged, the hole at the bottom of the

tub, is opened out and pugged earth is taken out from the ramp by barrow i.e. a small cart with

wheels for next operation of moulding. The pug mill is then kept moving and feeding of clay

from top and taking out of pugged clay from bottom are done simultaneously. If tempering is

properly carried out, the good brick earth can then be rolled without breaking in small threads of

3mm diameter.

A Pug Mill

• Moulding

• Drying

• Burning

Moulding: The clay which is prepared as above is then sent for the text operation of moulding.

Following are two types of moulding:

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i. Hand Moulding

ii. Machine Moulding

Hand moulding: In hand moulding, the bricks are moulded by hand i.e.; manually. It is adopted

where manpower is cheap and is readily available for the manufacturing process of bricks on a

small scale. The moulds are rectangular boxes which are open at top and bottom. They may be

of wood or steel. It should be be prepared from well-seasoned wood. The longer sides are kept

slightly projecting to serve as handles. The strips of brass or steel are sometimes fixed on the

edges of wooden moulds to make them more durable. It is prepared from the combination of

steel plate and channel. It may even be prepared from steel angles and plates. The thickness of

steel mould is 6mm.They is used for manufacturing bricks on a large scale. The steel moulds are

more durable than wooden one and turn out bricks of uniform size. The bricks shrink during

drying and burning .Hence the moulds are therefore made larger than burnt bricks (812%). The

bricks prepared by hand moulding are of two types: Ground moulded and Table moulded

Ground moulded bricks: The ground is first made level and fine sand is sprinkled over it. The

mould is dipped in water and placed over the ground. The lump of tempered clay is taken and is

dashed is the mould. The clay is pressed in the mould in such a way that it fills all the corners of

mould. The surplus clay is removed by wooden strike or framed with wire. A strike is a piece of

wood or metal with a sharp edge. It is to be dipped in water every time. The mould is then lifted

up and raw brick ids left on the ground. The mould is dipped in water and it is placed just near

the previous brick to prepare another brick. The process is repeated till the ground is covered

with raw bricks. The lower faces of ground moulded bricks are rough and it is not possible to

place frog on such bricks. A frog is mark of depth about 10mm to 20mm which is placed on raw

brick during moulding. It serves two purposes.

1.It indicates the trade name of the manufacturer

2.In brick work, the bricks are laid with frog uppermost. It thus affords a key for mortar when the

next brick is placed over it.

The ground moulded bricks of better quality and with frogs on their surface are made by using a

pair of pallet boards and a wooden block. A pallet is a piece of thin wood. The block is bigger

than the mould and it has projection of about 6mm height on its surface. The dimensions of

projection correspond to internal dimensions of mould. The design of impression or frog is made

on this block. The wooden block is also known as the moulding block or stock board.

The mould is placed to fit in the projection of wooden block and clay is then dashed inside the

mould. A pallet is placed on the top and the whole thing is then turn upside down. The mould is

taken out and placed over the raw brick and it is conveyed to the drying sheds. The bricks are

placed to stand on their longer sides in drying sheds and pallet boards are brought back for using

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them again. As the bricks are laid on edge, they occupy less space and they dry quicker and

better.

Table Moulded Bricks:

i) The process of moulding of bricks is just similar as above. But in this case, the

mould stands near a table size 2m x 1m. The bricks are moulded on the table

and send for further process of drying.

ii) However the efficiency of the moulder gradually decreases because of

standing at some place for a longer duration. The cost of brick is also

increases when table moulding is adopted.

Machine Moulding:

This type of moulding is carried out by two processes:

i) Plastic clay machine

ii) Dry clay machine

Plastic Clay Moulding

i) Such machine consists of a rectangular opening having length and width is equal to an

ordinary bricks. The pugged clay is placed in the machine and it comes out through the

rectangular opening.

ii) These are cut into strips by the wire fixed at the frame. The arrangement is made in such

a way that the strips thickness is equal to that of the bricks are obtained. So it is also

called as WIRE CUT BRICKS.

Dry Clay Machine moulding

i)In these machines, the strong clay is finally converted in to powered form. A small quantity of

water is then added to form a stiff plastic paste.

ii) Such paste is placed in mould and pressed by machine to form dry and well-shaped bricks.

They do not require the process of drying.

Drying

The damp bricks, if brunt, are likely to be cracked and distorted. Hence the moulded bricks are

dried before they are taken for the next operation of burning. For the drying the bricks are laid

longitudinally in the stacks of width equal to two bricks, A stack consists of ten or eight tiers.

The bricks are laid along and across the stock in alternate layers. All the bricks are placed on

edges. The bricks are allowed to dry until the bricks are become leather hard of moisture content

about 2%.

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Burning

Bricks are burned at high temperature to gain the strength, durability, density and red color

appearance. All the water is removed at the temperature of 650 degrees but they are burnt at an

temperature of about 1100 degrees because the fusing of sand and lime takes place at this

temperature and chemical bonding takes between these materials after the temperature is cooled

down resulting in the hard and dense mass.

Bricks are not burnt above this temperature because it will result in the melting of the bricks and

will result in a distorted shape and a very hard mass when cooled which will not be workable

while brickwork. Bricks can be burnt using the following methods:

(a) Clamp Burning

(b) Kiln Burning

Clamp Burning:

Clamp is a temporary structure generally constructed over the ground with a height of about 4 to

6 m. It is employed when the demand of the bricks is lower scale and when it is not a monsoon

season. This is generally trapezoidal in plan whose shorter edge among the parallel sides is

below the ground and then the surface raising constantly at about 15 degrees to reach the other

parallel edge over the ground. A vertical brick and mud wall is constructed at the lower edge to

support the stack of the brick. First layer of fuel is laid as the bottom most layer with the coal,

wood and other locally available material like cow dung and husk. Another layer of about 4 to 5

rows of bricks is laid and then again a fuel layer is laid over it. The thickness of the fuel layer

goes on with the height of the clamp.

After these alternate layers of the bricks and fuel the top surface is covered with the mud so as to

preserve the heat.Fire is ignited at the bottom, once fire is started it is kept under fire by itself for

one or two months and same time period is needed for the cooling of the bricks.

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Disadvantages of Clamp burning:

1. Bricks at the bottom are over-burnt while at the top are under-burnt.

2. Bricks lose their shape, and reason may be their descending downward once the fuel layer is

burnt.

3. This method cannot employ for the manufacturing of large number of bricks and it is costly in

terms of fuel because large amount of heat is wasted.

4. It cannot be employed in monsoon season.

Kiln Burning:

Kiln is a large oven used for the burning of bricks. Generally coal and other locally available

materials like wood, cow dung etc. can be used as fuel. They are of two types:

• Intermittent Kilns.

• Continuous Kilns.

Fig of a typical kiln

Intermittent Kilns:

These are also the periodic kind of kilns, because in such kilns only one process can take place at

one time. Various major processes which takes place in the kilns are: Loading, unloading,

Cooling, and Burning of bricks.

There are two kind of intermittent kilns: (i) Up-draught Intermittent Kilns (ii) Down draught

Intermittent Kilns

Down draught kilns are more efficient because the heat is utilized more by moving the hot gases

in the larger area of the kiln. In up draught kilns the hot gases are released after they rise up to

chimney entrance.

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Continuous Kilns:

These kilns are called continuous because all the processes of loading, unloading, cooling,

heating, pre-heating take place simultaneously. They are used when the bricks are demanded in

larger scale and in short time. Bricks burning are completed in one day, so it is a fast method of

burning.

There are two well-known continuous kilns:

Bull's Trench Kiln: Bull’s trench kiln consists of a rectangular, circular or oval plan shape. They

are constructed below the ground level by excavating a trench of the required width for the given

capacity of brick manufacturing. This Trench is divided generally in 12 chambers so that 2

numbers of cycles of brick burning can take place at the same time for the larger production of

the bricks. Or it may happen that one cycle is carried out at one time in all the 12 chambers by

using a single process in the 2-3 chambers at the same time. The structure is under-ground so the

heat is conserved to a large extent so it is more efficient. Once fire is started it constantly travels

from one chamber to the other chamber, while other operations like loading, unloading, cooling,

burning and preheating taking place simultaneously. Such kilns are generally constructed to have

a manufacturing capacity of about 20,000 bricks per day. The drawback of this kiln is that there

is not a permanent roof, so it is not easy to manufacture the bricks in the monsoon seasons.

Hoffman's Kiln: The main difference between the Bull's trench kiln and the Hoffman kilns are:

1. Hoffman's kiln is an over the ground structure while Bull's Trench Kiln is an underground

structure.

2.Hoffman's kiln have a permanent roof while Bull's trench Kiln do not have so it former can be

used in 12 months a year to manufacture bricks but later is stopped in the monsoon season.

Hoffman's kiln is generally circular in plan, and is constructed over the ground. The whole

structure is divided into the 12 chambers and the entire processes takes place simultaneously like

in Bull's trench Kiln.

3. Classification of Bricks

Classification of Bricks as per common practice

Bricks, which are used in construction works, are burnt bricks. They are classified into four

categories on the basis of its manufacturing and preparation, as given below.

1. First class bricks

2. Second class bricks

3. Third class bricks

4. Fourth class bricks

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First Class Bricks: These bricks are table moulded and of standard shape and they are burnt in

kilns. The surface and edges of the bricks are sharp, square, smooth and straight. They comply

with all the qualities of good bricks. These bricks are used for superior work of permanent

nature.

Second Class Bricks: These bricks are ground moulded and they are burnt in kilns. The surface

of these bricks is somewhat rough and shape is also slightly irregular. These bricks may have

hair cracks and their edges may not be sharp and uniform. These bricks are commonly used at

places where brick work is to be provided with a coat of plaster.

Third Class Bricks: These bricks are ground moulded and they are burnt in clamps. These

bricks are not hard and they have rough surfaces with irregular and distorted edges. These bricks

give dull sound when struck together. They are used for unimportant and temporary structures

and at places where rainfall is not heavy.

Fourth Class Bricks: These are over burnt bricks with irregular shape and dark colour. These

bricks are used as aggregate for concrete in foundations, floors, roads etc., because of the fact

that the over burnt bricks have a compact structure and hence they are sometimes found to be

stronger than even the first class bricks.

Classification of Bricks as per constituent materials

There are various types of bricks used in masonry.

• Common Burnt Clay Bricks

• Sand Lime Bricks (Calcium Silicate Bricks)

• Engineering Bricks

• Concrete Bricks

• Fly ash Clay Bricks

Common Burnt Clay Bricks

Common burnt clay bricks are formed by pressing in moulds. Then these bricks are dried and

fired in a kiln. Common burnt clay bricks are used in general work with no special attractive

appearances. When these bricks are used in walls, they require plastering or rendering.

Sand Lime Bricks

Sand lime bricks are made by mixing sand, fly ash and lime followed by a chemical process

during wet mixing. The mix is then moulded under pressure forming the brick. These bricks can

offer advantages over clay bricks such as: their colour appearance is grey instead of the regular

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reddish colour. Their shape is uniform and presents a smoother finish that doesn’t require

plastering. These bricks offer excellent strength as a load-bearing member.

Engineering Bricks

Engineering bricks are bricks manufactured at extremely high temperatures, forming a dense and

strong brick, allowing the brick to limit strength and water absorption. Engineering bricks offer

excellent load bearing capacity damp-proof characteristics and chemical resisting properties.

Concrete Bricks

Concrete bricks are made from solid concrete. Concrete bricks are usually placed in facades,

fences, and provide an excellent aesthetic presence. These bricks can be manufactured to provide

different colours as pigmented during its production.

Fly Ash Clay Bricks

Fly ash clay bricks are manufactured with clay and fly ash, at about 1,000 degrees C. Some

studies have shown that these bricks tend to fail poor produce pop-outs, when bricks come into

contact with moisture and water, causing the bricks to expand.

4. Test on Bricks

To know the quality of bricks following 7 tests can be performed. In these tests some are

performed in laboratory and the rest are on field.

• Compressive strength test - This test is done to know the compressive strength of brick. It is

also called crushing strength of brick. Generally 5 specimens of bricks are taken to laboratory for

testing and tested one by one. In this test a brick specimen is put on crushing machine and

applied pressure till it breaks. The ultimate pressure at which brick is crushed is taken into

account. All five brick specimens are tested one by one and average result is taken as brick’s

compressive/crushing strength.

• Water Absorption test - In this test bricks are weighed in dry condition and let them immersed

in fresh water for 24 hours. After 24 hours of immersion those are taken out from water and wipe

out with cloth. Then brick is weighed in wet condition. The difference between weights is the

water absorbed by brick. The percentage of water absorption is then calculated. The less water

absorbed by brick the greater its quality. Good quality brick doesn’t absorb more than 20% water

of its own weight.

• Efflorescence test - The presence of alkalis in bricks is harmful and they form a grey or white

layer on brick surface by absorbing moisture. To find out the presence of alkalis in bricks this

test is performed. In this test a brick is immersed in fresh water for 24 hours and then it’s taken

out from water and allowed to dry in shade. If the whitish layer is not visible on surface it proofs

that absence of alkalis in brick. If the whitish layer visible about 10% of brick surface then the

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presence of alkalis is in acceptable range. If that is about 50% of surface then it is moderate. If

the alkalis’ presence is over 50% then the brick is severely affected by alkalis.

• Hardness test - In this test a scratch is made on brick surface with a hard thing. If that doesn’t

left any impression on brick then that is good quality brick.

• Size, Shape and Colour test - In this test randomly collected 20 bricks are staked along

lengthwise, width wise and height wise and then those are measured to know the variation of

sizes as per standard. Bricks are closely viewed to check if its edges are sharp and straight and

uniform in shape. A good quality brick should have bright and uniform colour throughout.

• Soundness test - In this test two bricks are held by both hands and struck with one another. If

the bricks give clear metallic ringing sound and don’t break then those are good quality bricks.

• Structure test - In this test a brick is broken or a broken brick is collected and closely observed.

If there are any flows, cracks or holes present on that broken face then that isn’t good quality

brick.

UNIT II- CEMENT

1. Introduction and Use of Cement

Cement is a binder, a substance that sets and hardens and can bind other materials together.

Cements used in construction can be characterized as being either hydraulic or non-hydraulic,

depending upon the ability of the cement to be used in the presence of water. Non-hydraulic

cement will not set in wet conditions or underwater, rather it sets as it dries and reacts with

carbon dioxide in the air. It can be attacked by some aggressive chemicals after setting.

Hydraulic cement is made by replacing some of the cement in a mix with activated aluminium

silicates, pozzolanas, such as fly ash. The chemical reaction results in hydrates that are not very

water-soluble and so are quite durable in water and safe from chemical attack. This allows

setting in wet condition or underwater and further protects the hardened material from chemical

attack (e.g., Portland cement).

Use

1. Cement mortar for Masonry work, plaster and pointing etc.

2. Concrete for laying floors, roofs and constructing lintels, beams, weather-shed, stairs,

pillars etc.

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3. Construction for important engineering structures such as bridge, culverts, dams, tunnels,

light house, clocks, etc.

4. Construction of water, wells, tennis courts, septic tanks, lamp posts, telephone cabins etc.

5. Making joint for joints, pipes, etc.

6. Manufacturing of precast pipes, garden seats, artistically designed wens, flower posts,

etc.

7. Preparation of foundation, water tight floors, footpaths, etc.

2. Types of Cements

Many types of cements are available in markets with different compositions and for use in

different environmental conditions and specialized applications. A list of some commonly used

cement is described in this section:

Portland cement

Ordinary Portland cement is the most common type of cement in general use around the world.

This cement is made by heating limestone (calcium carbonate) with small quantities of other

materials (such as clay)to 1450°C in a kiln, in a process known as calcination, whereby a

molecule of carbon dioxide is liberated from the calcium carbonate to form calcium oxide, or

quicklime, which is then blended with the other materials that have been included in the mix.

The resulting hard substance, called 'clinker', is then ground with a small amount of gypsum into

a powder to make 'Ordinary Portland Cement'(often referred to as OPC). Portland cement is a

basic ingredient of concrete, mortar and most non-specialty grout. The most common use for

Portland cement is in the production of concrete. Concrete is a composite material consisting of

aggregate (gravel and sand), cement, and water. As a construction material, concrete can be cast

in almost any shape desired, and once hardened, can become a structural (load bearing) element.

Portland cement may be grey or white.

• This type of cement use in construction when there is no exposure to sulphates in the soil

or ground water.

• Lime saturation Factor is limited between i.e. 0.66 to 1.02.

• Free lime-cause the Cement to be unsound.

• Percentage of (AL2O3/Fe2O3) is not less than 0.66.

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• Insoluble residue not more than 1.5%.

• Percentage of SO3 limited by 2.5% when C3A < 7% and not more than 3% when C3A

>7%.

• Loss of ignition -4%(max)

• Percentage of Mg0-5% (max.)

• Fineness -not less than 2250 cm2/g.

Rapid hardening Portland cement

• It is firmer than Ordinary Portland Cement

• It contains more C3S are less C2S than the ordinary Portland cement.

• Its 3 days strength is same as 7 days strength of ordinary Portland cement.

Low heat Portland cement

• Heat generated in ordinary Portland cement at the end of 3days 80 cal/gm. While in low

heat cement it is about 50cal/gm of cement.

• It has low percentage of C3A and relatively more C2S and less C3S than O.P. Cement.

• Reduce and delay the heat of hydration. British standard ( B S. 1370 : 1974 ) limit the

heat of hydration of this cement.

Sulphate resisting Portland cement

• Maximum C3A content by 3.5% and minimum fineness by 2500 cm'/g.

• Firmer than ordinary pot land cement.

• Sulphate forms the sulpha-aluminates which have expensive properties and so causes

disintegration of concrete.

Sulphate resisting Portland cement

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• For this cement, the silage as obtained from blast furnace is used

• The clinkers of cement are ground with about 60 to 65 percent of slag.

• Its strength in early days is less and hence it required longer curing period. It proves to be

economical as slag, which is a Waste product, is used in its manufactures.

Pozzolanic cement

• As per Indian standard, the proportions of Pozzolana may be 10 to 25 % by weight. e.g.

Burnt clay, shale, Fly ash.

• This Cement has higher resistance to chemical agencies and to sea water because of

absence of lime.

• It evolves less heat and initial strength is less but final strength is 28 days onward equal

to ordinary Portland cement.

• It possesses less resistance to the erosion and weathering action.

• It imparts higher degree of water tightness and it is cheap.

White Portland cement

• Grey colour of O.P. cement is due to presence of Iron Oxide. Hence in White Cement

Fe,,O, is limited to 1 %. Sodium Alumina Ferrite (Crinoline) NavAlF6 is added to act as

flux in the absence of Iron-Oxide. •:

• It is quick drying, possesses high strength and has superior aesthetic values and it also

cost lee than ordinary Cement because of specific requirements imposed upon the raw

materials and the manufacturing process.

• White Cement are used in Swimming pools, for painting garden furniture, moulding

sculptures and statues etc.

Coloured Portland

• The Cement of desired colour may be obtained by mixing mineral pigments with

ordinary Cement.

• The amount of colouring material may vary from 5 to 10 percent. If this percentage

exceeds 10percent, the strength of cements is affected.

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• The iron Oxide in different proportions gives brown, red or yellow colour. The

coloured Cement are widely used for finishing of floors, window sill slabs, stair

treads etc.

Expansive cement

This type of cement is produced by adding an expanding medium like sulphoaluminate and a

stabilizing agent to the ordinary cement.

• The expanding cement is used for the construction of water retaining structures and

for repairing the damaged concrete surfaces.

High alumina cement

• This cement is produced by grilling clinkers formed by calcining bauxite and lime. It

can stand high temper lures.

• If evolves great heat during setting. It is therefore not affected by frost.

3. Composition of Cement clinker

The various constituents combine in burning and form cement clinker. The compounds formed

in the burning process have the properties of setting and hardening in the presence of water.

They are known as Bogue compounds after the name of Bogue who identified them. These

compounds are as follows: Alite (Tricalcium silicate or C3S), Belite (Dicalcium silicate or C2S),

Celite (Tricalciumalluminate or C3A) and Felite (Tetracalciumalumino ferrite or C4AF).

Tricalcium silicate

It is supposed to be the best cementing material and is well burnt cement. It is about 25-50%

(normally about 40 per cent) of cement. It renders the clinker easier to grind, increases resistance

to freezing and thawing, hydrates rapidly generating high heat and develops an early hardness

and strength. However, raising of C3S content beyond the specified limits increases the heat of

hydration and solubility of cement in water. The hydrolysis of C3S is mainly responsible for 7

day strength and hardness. The rate of hydrolysis of C3S and the character of gel developed are

the main causes of the hardness and early strength of cement paste. The heat of hydration is 500

J/g.

Dicalcium silicate

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It constitutes about 25-40% (normally about 32 per cent) of cement. It hydrates and hardens

slowly and takes long time to add to the strength (after a year or more). It imparts resistance to

chemical attack. Rising of C2S content renders clinker harder to grind, reduces early strength,

decreases resistance to freezing and thawing at early ages and decreases heat of hydration. The

hydrolysis of C2S proceeds slowly. At early ages, less than a month, C 2S has little influence on

strength and hardness. While after one year, its contribution to the strength and hardness is

proportionately almost equal to C3S. The heat of hydration is 260 J/g.

Tricalciumalluminate

It is about 5-11% (normally about 10.5 per cent) of cement. It rapidly reacts with water and is

responsible for flash set of finely grounded clinker. The rapidity of action is regulated by the

addition of 2-3% of gypsum at the time of grinding cement. Tricalciumalluminate is responsible

for the initial set, high heat of hydration and has greater tendency to volume changes causing

cracking. Raising the C3A content reduces the setting time, weakens resistance to sulphate attack

and lowers the ultimate strength, heat of hydration and contraction during air hardening. The

heat of hydration of 865 J/g.

Tetracalciumalumino ferrite

It constitutes about 8–14% (normally about 9 per cent) of cement. It isresponsible for flash set

but generates less heat. It has poorest cementing value. Raising theC4AF content reduces the

strength slightly. The heat of hydration is 420 J/g.

4. Hydration of Cement

In the anhydrous state, four main types of minerals are normally present: Alite, Belite, Celite and

Felite. Also present are small amounts of clinker sulfate (sulfates of sodium, potassium and

calcium) and gypsum, which was added when the clinker was ground up to produce the familiar

grey powder.

When water is added, the reactions which occur are mostly exothermic, that is, the reactions

generate heat. We can get an indication of the rate at which the minerals are reacting by

monitoring the rate at which heat is evolved using a technique called conduction

calorimetry.Almost immediately on adding water some of the clinker sulphates and gypsum

dissolve producing an alkaline, sulfate-rich, solution. Soon after mixing, the (C3A) phase (the

most reactive of the four main clinker minerals) reacts with the water to form an aluminate-rich

gel (Stage I on the heat evolution curve above). The gel reacts with sulfate in solution to form

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small rod-like crystals of ettringite. (C3A) reaction is with water is strongly exothermic but does

not last long, typically only a few minutes, and is followed by a period of a few hours of

relatively low heat evolution. This is called the dormant, or induction period (Stage II).The first

part of the dormant period, up to perhaps half-way through, corresponds to when concrete can be

placed. As the dormant period progresses, the paste becomes too stiff to be workable. At the end

of the dormant period, the Alite and Belite in the cement start to react, with the formation of

calcium silicate hydrate and calcium hydroxide. This corresponds to the main period of hydration

(Stage III), during which time concrete strengths increase. The individual grains react from the

surface inwards, and the anhydrous particles become smaller. (C3A) hydration also continues, as

fresh crystals become accessible to water. The period of maximum heat evolution occurs

typically between about 10 and 20 hours after mixing and then gradually tails off. In a mix

containing OPC only, most of the strength gain has occurred within about a month. Where OPC

has been partly-replaced by other materials, such as fly ash, strength growth may occur more

slowly and continue for several months or even a year. Ferrite reaction also starts quickly as

water is added, but then slows down, probably because a layer of iron hydroxide gel forms,

coating the ferrite and acting as a barrier, preventing further reaction.

Products of Hydration: During Hydration process several hydrated compounds are formed

most important of which are, Calcium silicate hydrate, calcium hydroxide and calcium

aluminium hydrates which is important for strength gain.

Calcium silicate hydrate:

This is not only the most abundant reaction product, occupying about 50% of the paste volume,

but it is also responsible for most of the engineering properties of cement paste. It is often

abbreviated, using cement chemists' notation, to "C-S-H," the dashes indicating that no strict

ratio of SiO2 to CaO is inferred. C-S-H forms a continuous layer that binds together the original

cement particles into a cohesive whole which results in its strong bonding capacity. The Si/Ca

ratio is somewhat variable but typically approximately 0.45-0.50 in hydrated Portland cement

but up to perhaps about 0.6 if slag or fly ash or micro silica is present, depending on the

proportions.

Calcium hydroxide:

The other products of hydration of C3S and C2S are calcium hydroxide. In contrast to the C-S-

H, the calcium hydroxide is a compound with distinctive hexagonal prism morphology. It

constitutes 20 to 25 per cent of the volume of solids in the hydrated paste. The lack of durability

of concrete is on account of the presence of calcium hydroxide. The calcium hydroxide also

reacts with sulphates present in soils or water to form calcium sulphate which further reacts with

C3A and cause deterioration of concrete. This is known as sulphate attack. To reduce the

quantity of Ca (OH)2 in concrete and to overcome its bad effects by converting it into

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cementitious product is an advancement in concrete technology. The use of blending materials

such as fly ash, silica fume and such other pozzolanic materials are the steps to overcome bad

effect of Ca(OH)2 in concrete. However, Ca(OH)2 is alkaline in nature due to which it resists

corrosion in steel.

Calcium aluminium hydrates:

These are formed due to hydration of C3A compounds. The hydrated aluminates do not

contribute anything to the strength of concrete. On the other hand, their presence is harmful to

the durability of concrete particularly where the concrete is likely to be attacked by sulphates. As

it hydrates very fast it may contribute a little to the early strength.

5. Various tests on cement:

Basically two types of tests are under taken for assessing the quality of cement. These are either

field test or lab tests. The current section describes these tests in details.

Field test:

There are four field tests may be carried out to as certain roughly the quality of cement.There are

four types of field tests to access the colour, physical property, and strength of the cement as

described below.

Colour

• The colour of cement should be uniform.

• It should be typical cement colour i.e. grey colour with a light greenish shade.

Physical properties

• Cement should feel smooth when touched between fingers.

• If hand is inserted in a bag or heap of cement, it should feel cool.

Presence of lumps

• Cement should be free from lumps.

• For a moisture content of about 5 to 8%,this increase of volume may be much as 20 to 40

%,depending upon the grading of sand.

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Strength

• A thick paste of cement with water is made on a piece of thick glass and it is kept under

water for 24 hours.It should set and not crack.

Laboratory tests:

Six laboratory tests are conducted mainly for assessing the quality of cement. These are: fineness, compressive strength, consistency, setting time, soundness and tensile strength.

Fineness

• This test is carried out to check proper grinding of cement.

• The fineness of cement particles may be determined either by sieve test or permeability

apparatus test.

• In sieve test ,the cement weighing 100 gm. is taken and it is continuously passed for 15

minutes through standard BIS sieve no. 9.The residue is then weighed and this weight

should not be more than 10% of original weight.

• In permeability apparatus test, specific area of cement particles is calculated. This test is

better than sieve test. The specific surface acts as a measure of the frequency of particles

of average size.

Compressive strength

• This test is carried out to determine the compressive strength of cement.

• The mortar of cement and sand is prepared in ratio 1:3.

• Water is added to mortar in water cement ratio 0.4.

• The mortar is placed in moulds. The test specimens are in the form of cubes and the

moulds are of metals. For 70.6 mm and 76 mm cubes ,the cement required is 185gm and

235 gm. respectively.

• Then the mortar is compacted in vibrating machine for 2 minutes and the moulds are

placed in a damp cabin for 24 hours.

• The specimens are removed from the moulds and they are submerged in clean water for

curing.

• The cubes are then tested in compression testing machine at the end of 3days and 7 days.

Thus compressive strength was found out.

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Consistency

• The purpose of this test is to determine the percentage of water required for preparing

cement pastes for other tests.

• Take 300 gm of cement and add 30 percent by weight or 90 gm of water to it.

• Mix water and cement thoroughly.

• Fill the mould of Vicat apparatus and the gauging time should be 3.75 to 4.25 minutes.

• Vicat apparatus consists of a needle is attached a movable rod with an indicator attached

to it.

• There are three attachments: square needle, plunger and needle with annular collar.

• The plunger is attached to the movable rod. the plunger is gently lowered on the paste in

the mould.

• The settlement of plunger is noted. If the penetration is between 5 mm to 7 mm from the

bottom of mould, the water added is correct. If not process is repeated with different

percentages of water till the desired penetration is obtained.

Setting time

• This test is used to detect the deterioration of cement due to storage. The test is

performed to find out initial setting time and final setting time.

• Cement mixed with water and cement paste is filled in the Vicat mould.

• Square needle is attached to moving rod of Vicat apparatus.

• The needle is quickly released and it is allowed to penetrate the cement paste. In the

beginning the needle penetrates completely. The procedure is repeated at regular intervals

till the needle does not penetrate completely.(upto 5mm from bottom)

• Initial setting time =<30min for ordinary Portland cement and 60 min for low heat

cement.

• The cement paste is prepared as above and it is filled in the Vicat mould.

• The needle with annular collar is attached to the moving rod of the Vicat apparatus.

• The needle is gently released. The time at which the needle makes an impression on test

block and the collar fails to do so is noted.

• Final setting time is the difference between the time at which water was added to cement

and time as recorded in previous step, and it is =<10hours.

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Soundness

• The purpose of this test is to detect the presence of uncombined lime in the cement.

• The cement paste is prepared.

• The mould is placed and it is filled by cement paste.

• It is covered at top by another glass plate. A small weight is placed at top and the whole

assembly is submerged in water for 24 hours.

• The distance between the points of indicator is noted. The mould is again placed in water

and heat is applied in such a way that boiling point of water is reached in about 30

minutes. The boiling of water is continued for one hour.

• The mould is removed from water and it is allowed to cool down.

• The distance between the points of indicator is again measured. The difference between

the two readings indicates the expansion of cement and it should not exceed 10 mm.

Tensile strength

• This test was formerly used to have an indirect indication of compressive strength of

cement.

• The mortar of sand and cement is prepared.

• The water is added to the mortar.

• The mortar is placed in briquette moulds. The mould is filled with mortar and then a

small heap of mortar is formed at its top. It is beaten down by a standard spatula till water

appears on the surface. Same procedure is repeated for the other face of briquette.

• The briquettes are kept in a damp for 24 hours and carefully removed from the moulds.

• The briquettes are tested in a testing machine at the end of 3 and 7 days and average is

found out.

UNIT-III CONCRETE AND MORTAR MATERIALS

1. Introduction

Concrete is a composite material composed mainly of water, aggregate, and cement. Often,

additives and reinforcements are included in the mixture to achieve the desired physical

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properties of the finished material. When these ingredients are mixed together, they form a fluid

mass that is easily molded into shape. Over time, the cement forms a hard matrix which binds the

rest of the ingredients together into a durable stone-like material with many uses.

The aim is to mix these materials in measured amounts to make concrete that is easy to:

Transport, place, compact, finish and which will set, and harden, to give a strong and durable

product. The amount of each material (ie cement, water and aggregates) affects the properties of

hardened concrete.

2. Production of concrete

A good quality concrete is essentially a homogeneous mixture of cement, coarse and fine

aggregates and water which consolidates into a hard mass due to chemical action between the

cement and water. Each of the four constituents has a specific function. The coarser aggregate

acts as a filler. The fine aggregate fills up the voids between the paste and the coarse aggregate.

The cement in conjunction with water acts as a binder. The mobility of the mixture is aided by

the cement paste, fines and nowadays, increasingly by the use of admixtures. The stages of

concrete production are: Batching or measurement of materials, Mixing, Transporting, Placing,

Compacting, Curing and Finishing.

Batching

It is the process of measuring concrete mix ingredients either by volume or by mass and

introducing them into the mixture. Traditionally batching is done by volume but most

specifications require that batching be done by mass rather than volume. The proportions of

various ingredients are determined by proper mix design.

A concrete mix is designed to produce concrete that can be easily placed at the lowest cost. The

concrete must be workable and cohesive when plastic, then set and harden to give strong and

durable concrete. The mix design must consider the environment that the concrete will be in; ie

exposure to sea water, trucks, cars, forklifts, foot traffic or extremes of hot and cold.

Proportioning concrete is a mixture of cement, water, coarse and fine aggregates and admixtures.

The proportion of each material in the mixture affects the properties of the final hardened

concrete. These proportions are best measured by weight. Measurement by volume is not as

accurate, but is suitable for minor projects.Cement content: as the cement content increases, so

does strength and durability. Therefore to increase the strength, increase the cement content of a

mix. Water Content: adding more water to a mix gives a weaker hardened concrete. Always use

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as little water as possible, only enough to make the mix workable. Water to cement ratio: as the

water to cement ratio increases, the strength and durability of hardened concrete decreases. To

increase the strength and durability of concrete, decrease the water-cement ratio. Aggregates: too

much fine aggregate gives a sticky mix. Too much coarse aggregate gives a harsh or boney mix.

Mixing: concrete must be mixed so the cement, water, aggregates and admixtures blend into an

even mix. Concrete is normally mixed by machine. Machine mixing can be done on-site or be a

pre-mixed concrete company. Pre-mixed concrete is batched (proportioned) at the plant to the

job requirements. Truck mixing the materials are normally added to the trucks at batching plants

and mixed for required time and speed at the plant. The trucks drum continues to rotate to agitate

the concrete as it is delivered to the site. Site mixing when site mixing begin by loading a

measured amount of coarse aggregate into the mixer drum. Add the sand before the cement, both

in measured amounts.

Mixing

The mixing operation consists of rotation or stirring, the objective being to coat the surface the

all aggregate particles with cement paste, and to blind all the ingredients of the concrete into a

uniform mass; this uniformity must not be disturbed by the process of discharging from the

mixer. The mixing may done by manually or by mechanical means like, Batch mixer, Tilting

drum mixer, Non tilting drum mixer, Pan type mixer, Dual drum mixer or Continuous mixers.

There are no general rules on the order of feeding the ingredients into the mixer as this

depend on the properties of the mixer and mix. Usually a small quantity of water is fed first,

followed by all the solids materials. If possible greater part of the water should also be fed

during the same time, the remainder being added after the solids. However, when using very dry

mixes in drum mixers it is necessary to feed the coarse aggregate just after the small initial water

feed in order to ensure that the aggregate surface is sufficiently wetted.

3. Compaction

The operation of placing and compaction are interdependent and are carried out simultaneously.

They are most important for the purpose of ensuring the requirements of strength,

impermeability and durability of hardened concrete in the actual structure. As for as placing is

concerned, the main objective is to deposit the concrete as close as possible to its final position

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so that segregation is avoided and the concrete can be fully compacted. The aim of good concrete

placing can be stated quite simply.It is to get the concrete into position at a speed, and in a

condition, that allow it to be compacted properly. To achieve proper placing following rules

should be kept in mind:

1. The concrete should be placed in uniform layers, not in large heaps or sloping layers.

2. The thickness of the layer should be compatible with the method of vibration so that

entrapped air can be removed from the bottom of each layer.

3. The rate of placing and of compaction should be equal. If you proceed too slowly, the

mix could stiffen so that it is no longer sufficiently workable. On no account should

water ever be added to concrete that is setting. On the other hand, if you go too quickly,

you might race ahead of the compacting gang, making it impossible for them to do their

job properly.

4. Each layer should be fully compacted before placing the next one, and each subsequent

layer should be placed whilst the underlying layer is still plastic so that monolithic

construction is achieved.

5. Collision between concrete and formwork or reinforcement should be avoided.

6. For deep sections, a long down pipe ensures accuracy of location of concrete and

minimum segregation. You must be able to see that the placing is proceeding correctly,

so lighting should be available for large, deep sections, and thin walls and columns.

Once the concrete has been placed, it is ready to be compacted. The purpose of compaction is to

get rid of the air voids that are trapped in loose concrete.

It is important to compact the concrete fully because: Air voids reduce the strength of the

concrete. For every 1% of entrapped air, the strength falls by somewhere between 5 and 7%.

This means that concrete containing a mere 5% air voids due to incomplete compaction can lose

as much as one third of its strength. Air voids increase concrete's permeability. That in turn

reduces its durability. If the concrete is not dense and impermeable, it will not be watertight. It

will be less able to withstand aggressive liquids and its exposed surfaces will weather badly.

Moisture and air are more likely to penetrate to the reinforcement causing it to rust. Air voids

impair contact between the mix and reinforcement (and, indeed, any other embedded metals).

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The required bond will not be achieved and the reinforced member will not be as strong as it

should be. Air voids produce blemishes on struck surfaces. For instance, blowholes and

honeycombing might occur. There are two methods for compaction which includes: vibration by

vibrators or by tamping using tamping rods.

4. Curing

Curing is the process of making the concrete surfaces wet for a certain time period after placing

the concrete so as to promote the hardening of cement. This process consists of controlling the

temperature and the movement of moisture from and into the concrete.

Curing of concrete is done for the following purposes. Curing is the process of controlling the

rate of moisture loss from concrete to ensure an uninterrupted hydration of Portland cement after

concrete has been placed and finished in its final position. Curing also helps maintain an

adequate temperature of concrete in its early stages, as this directly affects the rate of hydration

of cement and eventually the strength gain of concrete or mortars.

Curing of concrete must be done as soon as possible after placement and finishing and must

continue for a reasonable period of time, for the concrete to achieve its desired strength and

durability. Uniform temperature should be maintained throughout the concrete depth to avoid

thermal shrinkage cracks.Material properties are directly related to micro-structure. Curing

assists the cement hydration reaction to progress steadily and develops calcium silicate hydrate

gel, which binds aggregates leading to a rock solid mass, makes concrete denser, decreases the

porosity and enhances the physical and mechanical properties of concrete.

Some other purposes of curing can be summed up as: curing protects the concrete surfaces from

sun and wind, the process of curing increase the strength of the structure, the presence of water is

essential to cause the chemical action which accompanies the setting of concrete. Generally there

is adequate quantity of water at the time of mixing to cause the hardening of concrete, but it is

necessary to retain water until the concrete is fully hardened.

If curing is efficient, the strength of concrete gradually increases with age. This increase in

strength is sudden and rapid in early stages and it continues slowly for an indefinite period. By

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proper curing, the durability and impermeability of concrete are increased and shrinkage is

reduced. The resistance of concrete to abrasion is considerably increased by proper curing.

Curing period:

For ordinary Portland cement, the curing period is about 7 days to 14 days. If rapid hardening

cement is used the curing period can be considerably reduced.

Disadvantages of improper curing:

Following are the disadvantages of improper curing of concrete:

The chances of ingress of chlorides and atmospheric chemicals are very high. The compressive

and flexural strengths are lowered. The cracks are developed due to plastic shrinkage, drying

shrinkage and thermal effects. The durability decreases due to higher permeability. The frost and

weathering resistances are decreased. The rate of carbonation increases. The surfaces are coated

with sand and dust and it leads to lower the abrasion resistance. The disadvantages are more

prominent in those parts of surfaces which are directly exposed or which have large surfaces

compared to depth such as roads, canal, bridges, cooling towers, chimneys etc.

Factors affecting evaporation of water from concrete:

The evaporation of water depends upon the following 4 factors: Air temperature, Fresh concrete

temperature, Relative humidity and Wind velocity.

From the above mentioned factors it can be concluded environment directly influences the

process of evaporation, hence only the fresh concrete temperature can be monitored or

supervised by the concrete technologists. The evaporation of water in the first few hours can

leave very low amount of water in the concrete hydration, this leads to various shrinkage cracks.

Under normal condition the average loss of water varies from 2.5 to 10 N per m2 per hour. The

major loss occurs in the top 50 mm layer over a period of 3 hours, the loss could be about 5% of

the total volume of that layer.

Methods of curing:

While selecting any mode of curing the following two factors are considered:

• The loss of water should be prevented.

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• The temperature should be kept minimum for dissipation of heat of hydration.

Methods of curing can be categorized into the following:

Water curing- preventing the moisture loss from the concrete surface by continuously wetting the

exposed surface of concrete.

Membrane curing- minimizing moisture loss from concrete surface by covering it with an

impermeable membrane.

Steam curing- keeping the surface moist and raising the temperature of concrete to accelerate the

rate of strength gain.

Water curing is of the following types:

Ponding: most inexpensive and common method of curing flat slabs, roofs, pavements etc. A

dike around the edge of the slab is erected and water is filled to create a shallow pond. Care must

be taken to ensure that the water in the pond does not dry up, as it may lead to an alternate

drying and wetting condition.

Sprinkling: fogging and mist curing- using a fine spray or fog or moist of water to the concrete

can be efficient method of supplying water to concrete during hot weather, which helps to reduce

the temperature of concrete.

Wet coverings: water absorbent fabrics may be used to maintain water on concrete surfaces.

They must be continuously kept moist so as to prevent the fabrics from absorbing water from the

body of concrete, due to capillary action.

Impermeable membrane curing is of following types:-

Formwork: leaving the form work in place during the early age of concrete is an efficient

method of curing.

Plastic sheeting: plastic sheets form an effective barrier to control the moisture losses from the

surface of concrete, provided they are secured properly and protected from damage. The

efficiency of this system can be enhanced by flooding the concrete surface with water, under the

plastic sheet.

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Membrane curing compounds: Curing compounds are wax, acrylic and water based liquids are

spread over the freshly finished concrete to form an impermeable membrane that minimizes the

loss of moisture from the concrete surfaces. These are cost effective methods of curing where

standard curing procedures are difficult to adopt. When applied to cure concrete the time of the

application is critical for maximum effectiveness. Too early application dilutes the membrane,

whereas too late application results in being absorbed into

the concrete. They must be applied when the free water on the surface has evaporated. For

concrete with low w/c ratio, this is not a suitable process.

Steam curing: Steam curing is the process of accelerating the early hardening of concrete and

mortars by exposing it to steam and humidity. These types of curing systems are adopted for

railway sleepers, concrete blocks, pipes, manhole covers, poles etc. Precast iron is cured by this

method under pressure. Curing in hot and cold weather requires additional attention.

Hot weather: During hot weather, concrete must be protected from excessive drying and from

direct wind and sun. Curing materials which reflect sunlight to reduce concrete temperature must

be used.

Cold weather: Some problems associated with temperature below 400C are:

• Freezing of concrete before strength is developed.

• Slow development of concrete strength.

• Thermal stresses induced by the cooling of warm concrete to cooler ambient

temperatures

Chemical curing: In this method water is sprinkled over the surface, after adding certain amount

of some hygroscopic material (e.g. sodium chloride or calcium chloride). The hygroscopic

materials absorb moisture from the atmosphere and thus keep the surface damp.

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Alternating current curing: Concrete can be cured by passing alternating current through freshly

laid concrete.

5. Water cement ratio and compressive strength

A cement of average composition requires about 25% of water by mass for chemical reaction. In

addition, an amount of water is needed to fill the gel pores. Nearly 100 years ago, Duff Abrams

discovered the direct relationship between water-to-cement ratio and strength, i.e., lesser the

water used higher the strength of the concrete, since too much water leaves lots of pores in the

cement past. According to Abram’s law, the strength of fully compacted concrete at a given age

and normal temperature is inversely proportional to the water – cement ratio. Here the water-

cement ratio is the relative weight of water to the cement in the mixture. For most applications,

water-to-cement ratio should be between 0.4 and 0.5 lower for lower permeability and higher

strength. In concrete, the trade off, of course, is with workability, since very low water content

result in very stiff mixtures that are difficult to place.

6. Worability

Workability is one of the physical parameters of concrete which affects the strength and

durability as well as the cost of labor and appearance of the finished product. Concrete is said to

be workable when it is easily placed and compacted homogeneously i.e. without bleeding or

Segregation. Unworkable concrete needs more work or effort to be compacted in place, also

honeycombs &/or pockets may also be visible in finished concrete. Definition of Workability

“The property of fresh concrete which is indicated by the amount of useful internal work

required to fully compact the concrete without bleeding or segregation in the finished product.”

Factors affecting workability:

• Water content in the concrete mix

• Amount of cement & its Properties

• Aggregate Grading (Size Distribution)

• Nature of Aggregate Particles (Shape, Surface Texture, Porosity etc.)

• Temperature of the concrete mix

• Humidity of the environment

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• Mode of compaction

• Method of placement of concrete

• Method of transmission of concrete

How to improve the workability of concrete

• Increase water/cement ratio

• Increase size of aggregate

• Use well-rounded and smooth aggregate instead of irregular shape

• Increase the mixing time

• Increase the mixing temperature

• Use non-porous and saturated aggregate

• With addition of air-entraining mixtures

Workability tests:

There are 4 types of tests for workability. They are slump test, compacting factor test, flow test,

and Vee bee test

Slump test

The slump test result is a slump of the behavior of a compacted inverted cone of concrete under

the action of gravity. It measures the consistency or the wetness of concrete. Metal mould, in the

shape of the frustum of a cone, open at both ends, and provided with the handle, top internal

diameter 4 in (102 mm), and bottom internal diameter 8 in (203 mm) with a height of 1 ft (305

mm). A 2 ft (610 mm) long bullet nosed metal rod, (16 mm) in diameter. Apparatus Required:

Compacting Factor apparatus, Trowels, Graduated cylinder, Balance and Tamping rod and iron

bucket.

The test is carried out using a mould known as a slump cone. The cone is placed on a hard non-

absorbent surface. This cone is filled with fresh concrete in three stages, each time it is tamped

using a rod of standard dimensions. At the end of the third stage, concrete is struck off flush to

the top of the mould. The mould is carefully lifted vertically upwards, so as not to disturb the

concrete cone. Concrete subsides. This subsidence is termed as slump, and is measured in to the

nearest 5 mm if the slump is <100 mm and measured to the nearest 10 mm if the slump is >100

mm.The slumped concrete takes various shapes, and according to the profile of slumped

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concrete, the slump is termed as true slump, shear slump or collapse slump. If a shear or collapse

slump is achieved, a fresh sample should be taken and the test repeated. A collapse slump is an

indication of too wet a mix. Only a true slump is of any use in the test. A collapse slump will

generally mean that the mix is too wet or that it is a high workability mix, for which slump test is

not appropriate. Very dry mixes; having slump 0 – 25 mm are used in road making, low

workability mixes; having slump 10 – 40 mm are used for foundations with light reinforcement,

medium workability mixes; 50 - 90 for normal reinforced concrete placed with vibration, high

workability concrete; > 100 mm.

This test is usually used in laboratory and determines the workability of fresh concrete when size

is about 40 mm maximum. The test is carried out as per specification of IS: 1199-1959.

Compacting factor test:

Steps for performing the experiment:

• keep the apparatus on the ground and apply grease on the inner surface of the cylinders.

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• Measure the mass as w1 kg by weighing the cylinder accurately and fix the cylinder on

the base in such a way that the central points of hoppers and cylinder lie on one vertical

line and cover the cylinder with a plate.

• For each 5 kg of aggregate mixes are to be prepared with water-cement ratio by weight

with 2.5 kg sand and 1.25 kg of cement and then add required amount of water

thoroughly until and unless concrete appears to be homogeneous.

• With the help of hand scoop without compacting fill the freshly mixed concrete in upper

hopper part gently and carefully and within two minutes release the trap door so that the

concrete may fall into the lower hopper such that it bring the concrete into standard

compaction.

• Fall the concrete to into the cylinder by bringing the concrete into standard Compaction

immediately after the concrete has come to rest and open the trap door of lower hopper

and then remove the excess concrete above the top of the cylinder by a pair of trowels,

one in each hand will blades horizontal slide them from the opposite edges of the mould

inward to the center with a sawing motion.

• Clean the cylinder from all sides properly. Find the mass of partially compacted concrete

thus filled in the cylinder and say it W2 kg. After this refill the cylinder with the same

sample of concrete in approximately 50 mm layers, by vibrating each layer heavily so as

to expel all the air and obtain full compaction of the Concrete.

• Struck off level the concrete and weigh and cylinder filled with fully compacted concrete.

Let the mass be W3 kg.

• Calculate compaction factor by using the formula: C.F = W2 – W1 / W3 – W1

Flow Table Test:

The flow table test or flow test is a method to determine the consistence of fresh concrete.

Flow table with a grip and a hinge, 70 centimeters (28 in) square. Abrams cone, open at the top

and at the bottom - 30 centimeters (12 in) high, 17 centimeters (6.7 in) top diameter, 25

centimeters (9.8 in) base diameter. Water bucket and broom for wetting the flow table. Tamping

rod-60 centimeters (24 in) long. Conducting the test: The flow-table is wetted. The cone is

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placed in the center of the flow-table and filled with fresh concrete in two equal layers. Each

layer is tamped 10 times with tamping rod. Wait 30 seconds before lifting the cone. The cone is

lifted, allowing the concrete to flow. The flow-table is then lifted up 40mm and then dropped 15

times, causing the concrete to flow. After this the diameter of the concrete is measured.

Vee-Bee Test:

This test is useful for concrete having low and very low workability. In this test the concrete is

moulded into a cone in a cylinder container and the entire set up is mounted on a vibrating table.

When vibrator starts, concrete placed on the cone starts to occupy the cylindrical container by

the way of getting remoulded. Remolding is complete when the concrete surface becomes

horizontal. The time required for completion of remoulding since start of vibrator is measured

and denoted as Vee-bee seconds. This provides a measure for workability. Lesser is the Vee-bee

seconds more is the workability.

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