Unit 3

UNIT-3
LEVELLING AND APPLICATIONS
D.PARTHIBAN/AP-CIVIL

LEVELLING
 Leveling is a branch of surveying in civil engineering to
measure levels of different points with respect to a fixed
point such as elevation of a building, height of one point
from ground etc.
(Or)
 The art of determining the relative heights of points on
the surface of the earth is termed as “leveling.”
 https://www.youtube.com/watch?v=_SiSn_tcXZA
 https://www.youtube.com/watch?v=O09f2dnghgE
 https://www.youtube.com/watch?v=wgtb40Tg1vY
 https://www.youtube.com/watch?v=kB2msiRuk68

Types of Leveling in Surveying
 Direct leveling
 Trigonometric leveling
 Barometric leveling
 Stadia leveling

Direct Leveling
1. It is the most commonly used method of leveling. In
this method, measurements are observed directly
from leveling instrument.
2. Based on the observation points and instrument
positions direct leveling is divided into different
types as follows:
Simple leveling
Differential leveling
Fly leveling
Profile leveling
Precise leveling
Reciprocal leveling

Simple Leveling
• It is a simple and basic form of leveling in which the leveling
instrument is placed between the points which elevation is to
be find.
• Leveling rods are placed at that points and sighted them
through leveling instrument.
• It is performed only when the points are nearer to each other
without any obstacles.

Differential Leveling
• Differential leveling is performed when the distance between
two points is more.
• In this process, number of inter stations are located and
instrument is shifted to each station and observed the elevation
of inter station points.
• Finally difference between original two points is determined.

Fly Leveling
• Fly leveling is conducted when the benchmark is very far from
the work station.
• In such case, a temporary bench mark is located at the work
station which is located based on the original benchmark.
• Even it is not highly precise it is used for determining
approximate level.

Profile Leveling
• Profile leveling is generally adopted to find elevation of points
along a line such as for road, rails or rivers etc.
• In this case, readings of intermediate stations are taken and
reduced level of each station is found. From this cross section
of the alignment is drawn.

Reciprocal Leveling
• When it is not possible to locate the leveling instrument in between the
inter visible points, reciprocal leveling is performed.
• This case appears in case of ponds or rivers etc. in case of reciprocal
leveling, instrument is set nearer to 1st station and sighted towards
2nd station.

Trigonometric Leveling
• The process of leveling in which the elevation of point or the
difference between points is measured from the observed horizontal
distances and vertical angles in the field is called trigonometric
leveling.
• In this method, trigonometric relations are used to find the elevation
of a point from angle and horizontal distance so, it is called as
trigonometric leveling. It is also called as indirect leveling.

Barometric Leveling
• Barometer is an instrument used to measure atmosphere at any
altitude. So, in this method of leveling, atmospheric pressure at two
different points is observed, based on which the vertical difference
between two points is determined.
• It is a rough estimation and used rarely

Stadia Leveling
• It is a modified form of trigonometric leveling in which
Tacheometer principle is used to determine the elevation of
point.
• In this case the line of sight is inclined from the horizontal.
• It is more accurate and suitable for surveying in hilly terrains.

Types of Levels Used in Leveling
• To perform leveling, we need some level instruments to focus
or to read the object. Nowadays, the technology also
introduced in surveying and so many easy measuring
instruments are designed. Here we discuss about the different
levels used in leveling.
• Following are the types of different levels used for leveling in
surveying:

Dumpy Level
• Dumpy level is the most commonly used instrument in
leveling.
• In this level the telescope is restricted against movement in
its horizontal plane and telescope is fixed to its support.
• A bubble tube is provided on the top of the telescope.
• But however, the leveling head can be rotated in horizontal
plane with the telescope.
• The telescope is internal focusing telescope is a metal tube
contains four main parts as given below.
 Objective lens
 Negative lens
 Diaphragm
 Eye-piece

Objective Lens
– Objective lens should be made as the combination of crown glass and flint
glass.
– Because of this some defects like spherical aberration and chromatic
aberration can be eliminated.
– A thin layer coating which has smaller refractive index than glass is provided
on the objective lens to reduce the loss due to reflection.
Negative Lens
– Negative lens located co axial to the objective lens. So, the optical axis for both
lenses is same.
Eyepiece
– Eyepiece lens enable the ability to sight the object together with cross hairs.
– The image seen through eye piece is magnified and inverted.
– Some eyepieces erect the image into normal view and those are called as
erecting eyepieces.

Diaphragm
• Diaphragm is fitted inside the main tube which contains cross hairs
(vertical and horizontal) and these are adjusted by capstan headed screws.
• The cross hairs are made of dark metal as filament wires which are inserted
in diaphragm ring in exact position.
• For stadia leveling purposes, extra two horizontal cross hairs are provided
above and below the horizontalwire.

Y Level
• Y level or Wye-level consists y-shaped frames which supports the
telescope.
• Telescope cane be removed from the y-shaped supports by releasing clamp
screws provided.
• These y-shaped frames are arranged to vertical spindle which helps to
cause the rotation of telescope.
• Compared to dumpy level, adjustments can be rapidly tested in y- level.
But, there may be a chance of frictional wear of open parts of level.

Tilting Level
• Tilting level consist a telescope which enabled for the horizontal
rotation as well as rotation about 4 degree in its vertical plane.
• Centering of bubble can be easily done in this type of level.
• But, for every setup bubble is to be centered with the help of tilting
screw.
• The main advantage of tilting level is it is useful when the few
observations are to be taken with one setup of level.

Automatic Level
• Automatic level is like the dumpy level.
• In this case the telescope is fixed to its supports.
• Circular spirit can be attached to the side of the
telescope for approximate leveling.
• For more accurate leveling, compensator is attached
inside the telescope.
• Compensator can help the instrument to level
automatically.
• Compensator is also called as stabilizer which consists
two fixed prisms and it creates an optical path between
eye piece and objective.
• Due to the action of gravity, the compensator results the
optical system to swing into exact position of line of
sight automatically.
• But before the process of leveling, compensator should
be checked.
• To check the compensator, just move the foot screws
slightly if the leveling staff reading remains constant
then compensator is perfect.
• If it is not constant, then tap the telescope gently to free
the compensator. Automatic level is also called as self-
adjusting level.

Uses of leveling
• To prepare a contour map for fixing sites for reservoirs, dams,
barrages, etc. and
• to fix the alignment of roads, railways, irrigation canals, and so
on.
• To determine the altitudes of different important points on a
hill or to know the reduced levels of different points on or
below the surfaces of the earth.
• To prepare a longitudinal section and cross sections of a
project in order to determine the volumes of earth.
• To prepare a layout map for water supply , sanitary or
drainage scheme

Important Terms in Leveling.
• Level Surface
A level surface is defined as a curve surface which at
each point is perpendicular to the direction of gravity the
point.
• Level Line
A line lying in a level surface is known as level line.
• Horizontal line
A horizontal plane through a point is the plane normal
to the direction of gravity at that point. It is tangential to the
level surface at the point.
• Vertical line
The vertical line at a point is the direction of gravity
(i.e., towards the centre of the earth) as indicated by a plumb
line.

• Datum
Datum is any surface to which elevations are referred the mean sea
level afford a convenient datum world over and elevations are commonly
given as so much above or below sea level.
• Mean Sea Level
Mean sea level is the average height of the sea for all stages of the
tides. At any particular place it is derived by averaging the hourly tide heights
over a long period of 19 years.
• Reduced Level (RL)
The vertical distance of a point above or below the datum line is
known as the reduced level of the point
• Line of collimation
It is the imaginary line passing through the intersection of the cross
hair at the diaphragm and the optical centre of the object glass and its
continuation. It is also known as the line of sight.
• Height of instrument
When the leveling instrument is properly leveled. The RL of the line
of collimation is known as the height of instrument. This is obtained by adding
the BS reading to the RL of the BM

Bench Mark
• Bench mark is a relatively permanent point reference whose
elevation with respect to some assumed datum is known.
• There are four type of bench mark
– GTS (Great trigonometrical Survey)
– Permanent Bench Mark
– Arbitrary Bench Mark
– Temporary Bench Mark

• GTS (Great trigonometricalSurvey)
GTS bench marks were established throughout the country to a high
degree of precision by the survey of India during their Great trigonometrical
Survey.
Their plan positions and elevations with respect to the standard
datum- mean sea level at Karachi. Are tabulated in the catalogue published by
them.
• Permanent Bench Mark
Permanent bench marks are fixed reference points established by the
government organization or agencies such as the Public Works Department in
certain states from the standardsbench mark.
Conspicuous points on culverts, bridges, and buildings are normally
chosen.
• Change Points
A staff station on which a fore sight before shifting the instrument is
called a change Points or turningpoint.

• Arbitrary Bench Mark
Arbitrary Bench Mark are reference pointswhose elevations are Arbitrary
assumed.
• Temporary Bench Mark
Temporary Bench Mark is established at the end of a day’s work so that it
can be continuedlater with reference of them.
Firm points such as parts of permanent objects are used. (Man Made)
• Fore Sight
The last sight taken before shifting the instrument to a different station is
foresight.
• Back Sight
The first sight taken after setting up the instrument at a point is the back
sight.
• Intermediatesight
Once the back sight is taken at any instrument station, the surveyor is
bale to determine the level of any number of pointsof interest within range before
the fore sight is taken on a chosen point and the instrument is shifted.

Fundamental Lines of a Level
• There are three fundamental lines in a level instrument figure.
These are
– Vertical axis
– Axis of the level tube
– Line of sight

Adjustments of level
Temporary adjustments or station adjustment
– The adjustment mad easy at ever set up of the level before the staff reading are
taken are known as temporary adjustment.
– The temporary adjustments for a level consist of the following
1) Setting Up
– Fixing the instrument on the stand
– Leveling the instrument approximately by leg adjustment.
2) Leveling Up
– The purpose of leveling is to make the vertical axis truly vertical.
– The manner of leveling the instrument by the plate levels depends upon
whether there are three leveling screws.
3) Elimination of Parallax
Parallax is a condition arising when the image formed by the objective is not
in the plane of the cross hair.
It is by focusing the eye piece and by focusing the objective to bring the
image of the object in the plane of the crosshair.

b) Permanent Adjustment of Dumpy Level
If any fundamental relation is found to be disturbed in a
dumpy level, the crosshairs and level tube are adjusted so that the
fundamental relations get satisfied.
The reference line for the adjustments in dumpy level is
the vertical line which remains fixed in direction, as it depends
upon the direction of gravity.
– 1. Axis of the Level Tube is Perpendicular to the Vertical
axis
– 2. Horizontal Cross Hair Should Lie in a Plane
Perpendicular to the Vertical axis
– 3. The Line of Sight is Parallel to the axis of the Bubble
Tube

Calculation of Levels
• 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. Height of instrument method.
– 2. Rise and Fall method and

Height of collimation 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.

• 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.

Compare between Collimation and
Rise & Fall System

Errors, Mistakes and Precautions in
Leveling
Types of Errors
– a) Instrumental Errors
– b) Personal Errors
– c) Errors due to Natural Causes
– d) Error due to Earths Curvature & Refraction

Contouring
• 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 water surface of a
still lake or pond with the surrounding ground represents a
contour line.
• https://www.youtube.com/watch?v=4i_6eToM3X8
• https://www.youtube.com/watch?v=WB3_thGjEeU

What is Contour Interval?
• A contour interval in surveying is the
vertical distance or the difference in the
elevation between the two contour lines in
a topographical map.
• Usually there are different contour
intervals for the different maps.
• Considering the size of the area to be
mapped, contour intervals are assumed.
• In every map, on the right-hand bottom
side, the contour interval is specified.
• When the contour interval is not specified
in the map, it can be calculated as
explained in the following sections.
• The commonly used contour interval is 20
feet for a 1:24,000 map scale.

Uses of Contour Intervals in Surveying
• When a large area is to be mapped in small piece of paper contour intervals
are used.
• A higher contour interval is used for a large area and small contour interval
for small area.
• In a large map, index contour lines are less to keep it simple to read the
map easily.
• In this case, to find out the intermediate points elevation, contour intervals
are used.
• Earthwork estimations for any type of structure like bridges, dams or roads
can be found out with the help of contour intervals in a map.
• As contour intervals are for the calculation of vertical elevation of an area,
same way to calculate the horizontal distance it is termed as Horizontal
Equivalent.
• The horizontal distance between two points on two consecutive contour
lines for a given slope is known as horizontal equivalent.

Contour Lines
• In cartography(the science, skill, or work of making maps),
contour lines are an imaginary line of a terrain that joins the
point of equal elevation above a given level, such as mean sea
level or benchmark.

Characteristics of Contour Lines in
Surveying
Following are the characteristics of contour lines in surveying for
reading contour maps:
 No two lines meet on intersect each other in any case.
 All lines close themselves within the map boundaries or outside it.
 If the contour lines are very close to each other, this indicates steep
slope.
 If the contour lines are at very large distance to each other, this
indicates a gentle slope.
 If the closed lines have higher elevation in the center then it
represents the hill or mountain.
 If the closed line have increasing elevation as we move away, then it
represents a pond or a depression in the ground profile.
 In a single contour line, at any point the elevation is same.

Methods of Contour Surveying
There are two methods of contour surveying:
– Direct method
– Indirect method

Direct Method of Contouring
• It consists in finding vertical and horizontal controls of the points which lie on the selected
contour line.
• For vertical control levelling instrument is commonly used.
• A level is set on a commanding position in the area after taking fly levels from the nearby bench
mark.
• The plane of collimation/height of instrument is found and the required staff reading for a
contour line is calculated.
• The instrument man asks staff man to move up and down in the area till the required staff
reading is found.
• A surveyor establishes the horizontal control of that point using his instruments.
• After that instrument man directs the staff man to another point where the same staff reading can
be found.
• It is followed by establishing horizontal control.
• Thus, several points are established on a contour line on one or two contour lines and suitably
noted down.
• Plane table survey is ideally suited for this work.
• After required points are established from the instrument setting, the instrument is shifted to
another point to cover more area.
• The level and survey instrument need not be shifted at the same time.
• It is better if both are nearby to communicate easily.
• This method is slow, tedious but accurate. It is suitable for small areasD.PARTHIBAN/AP-CIVIL

Indirect Method of Contouring
• In this method, levels are taken at some selected
points and their levels are reduced.
• Thus in this method horizontal control is established
first and then the levels of those points found.
• After locating the points on the plan, reduced levels
are marked and contour lines are interpolated between
the selected points.
• For selecting points any of the following methods can
be used:
– Method of squares
– Method of cross-section
– Radial line method

Method of Squares
• In this method area is divided into a number of squares and all grid points
are marked
• Commonly used size of square varies from 5 m × 5 m to 20 m × 20 m.
• Levels of all grid pointsare established by levelling.
• Then grid square is plottedon the drawing sheet.
• Reduced levels of grid points marked and contour lines are drawn by
interpolation.

Method of Cross-Section
• In this method cross-sectional points are taken at
regular interval.
• By levelling the reduced level of all those points
are established.
• The points are marked on the drawing sheets,
their reduced levels (RL) are marked and contour
lines interpolated.
• Figure shows a typical planningof this work.
• The spacing of cross-section dependsupon the
natureof the ground, scale of the map and the
contourinterval required.
• It varies from 20 m to 100 m.
• Closer intervals are required if ground level
varies abruptly.
• The cross- sectional line need not be always be at
right angles to the main line.
• This method is ideally suited for road and
railway projects.

Radial Line Method
• In this method several radial lines are taken
from a point in the area.
• The direction of each line is noted.
• On these lines at selected distances points
are marked and levels determined.
• This method is ideally suited for hilly areas.
• In this survey theodolite with tacheometry
facility is commonly used.
• For interpolating contour points between
the two points any one of the following
method may be used:
– (a) Estimation
– (b) Arithmetic calculation
– (c) Mechanical or graphical method.

Contour Maps and Its Uses
• A contour maps consists of contour lines which are
imaginary lines connecting points of equal
elevation.
• Such lines are drawn on the plan of an area after
establishing reduced levels of several points in the
area.
• The contour lines in an area are drawn keeping
difference in elevation of between two consecutive
lines constant.
• For example, the contour map in fig. 1 shows
contours in an area with contour interval of 1 m.
• On contour lines the level of lines is also written.

Characteristics of Contour Maps
The contours maps have the following
characteristics:
 Contour lines must close, not necessarily in
the limits of the plan.
 Widely spaced contour indicates flat surface.
 Closely spaced contour indicates steep ground.
 Equally spaced contour indicates uniform
slope.
 Irregular contours indicate uneven surface.
 Approximately concentric closed contours
with decreasing values towards centre (Fig. 1)
indicate a pond.
 Approximately concentric closed contours
with increasing values towards centre indicate
hills.

• Contour lines with U-shape with
convexity towards lower ground
indicate ridge (Fig. 2).
• Contour lines with V-shaped with
convexity towards higher ground
indicate valley (Fig.3).
• Contour lines generally do not meet
or intersect each other.
• If contour lines are meeting in some
portion, it shows existence of a
vertical cliff (Fig. 4).
• If contour lines cross each other, it
shows existence of overhanging
cliffs or a cave (Fig. 5).

Uses of Contour Maps
Contour maps are extremely useful for various engineering works:
• A civil engineer studies the contours and finds out the nature of the
ground to identify. Suitable site for the project works to be taken up.
• By drawing the section in the plan, it is possible to find out profile
of the ground along that line. It helps in finding out depth of cutting
and filling, if formation level of road/railway is decided.
• Intervisibility of any two points can be found by drawing profile of
the ground along that line.
• The routes of the railway, road, canal or sewer lines can be decided
so as to minimize and balance earthworks.
• Catchment area and hence quantity of water flow at any point of
nalla or river can be found. This study is very important in locating
bunds, dams and also to find out flood levels.
• From the contours, it is possible to determine the capacity of a
reservoir.

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