Course Code: EIS MAS2 M09 0919
Applying basic leveling
procedures
Developed by : Ashenafi .s ( BSC)
Amhara Technical and Vocational Enterprise Development Bureau
Woldia Poly Technic College
2014/15 Academic year
Table of Contents
Chapter One ............................................................................................................................................... 3
1.
INTRODUCTION TO SURVEYING ........................................................................................... 3
1.1.
Basic definitions..................................................................................................................... 3
1.2.
Classification of surveying .................................................................................................... 3
1.3.
Classification of Surveying Based on Nature of the Field ................................................. 3
1.4.
Classification of Surveying Based on Purpose.................................................................... 4
1.5.
Classification based on instruments .................................................................................... 4
1.6.
Stages of surveying works ...................................................................................................... 4
1.6.
Basic measurements in surveying ........................................................................................ 5
1.7.
Reference systems .................................................................................................................. 7
Chapter two ............................................................................................................................................. 13
2.
Set up and use leveling Device ( Leveling) .................................................................................. 13
2.1.
Introduction to leveling....................................................................................................... 13
2.2.
Use of leveling ...................................................................................................................... 13
2.3.
Definition of basic terms ..................................................................................................... 14
2.4.
Equipments used in leveling ............................................................................................... 15
2.5.
Precautions in leveling ........................................................................................................ 22
2.6.
Preparing level for work ..................................................................................................... 25
2.6.
Classification of levelling ....................................................................................................... 28
2.7.
Principle of leveling ............................................................................................................. 31
2.8.
Errors in levelling works ....................................................................................................... 37
2.9.
Errors in leveling................................................................................................................... 37
Chapter three ........................................................................................................................................... 41
3.
Clean up ........................................................................................................................................ 41
3.1.
Clean work area .................................................................................................................. 41
3.2.
Dispose, Reuse and Recycle waste materials .................................................................... 41
3.3.
Maintained Of Plant, Tools And Equipment.................................................................... 41
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Amhara Technical and Vocational Enterprise Development Bureau
Woldia Poly Technic College
2014/15 Academic year
Chapter One
1. INTRODUCTION TO SURVEYING
1.1.
Basic definitions
Surveying may be defined as the science of determining the position, in three dimensions, of natural
and man-made features on or beneath the surface of the Earth. These features may then be represented
in analog form as a contoured map, plan or chart, or in digital form as a three dimensional mathematical
model stored in the computer.
The objective of surveying is the preparation of plans and maps of the areas. In the absence of accurate
maps, it is impossible to layout the alignment of road, railways, canals, transmission power lines etc.
1.2.
Classification of surveying
Surveying is primarily divided in to two parts.
Plane Surveying
Geodetic Surveying
Plane Surveying - is type of surveying which assumes that the Earth is flat (plane), which is the most
commonly practiced form of surveying. Curvature is ignored and calculations are performed using the
formulas of plane trigonometry and the properties of plane geometry. These may be considered
accurate for limited areas. These are mostly used in any engineering work like highway, canal, and
bridge etc. It consists primarily of locating the positions of features on the ground (or fairly close to it)
and all height are referenced to the mean surface of the earth (mean sea level). If the area that you are
covering with your survey is less than about 250 km2, the assumption of a flat earth is valid for most
standards of measurement in 2-D. Larger areas cause the systematic errors caused by the flat Earth
assumption to become apparent in the measurements.
Geodetic Surveying is type of surveying which consider the shape of the earth as spherical or ellipsoid
of revolution. As in plane surveying all height are referenced to the surface of mean ellipsoid or mean
sea level (MSL). For the sake of plotting on the paper map their projection length is calculated and
curvature correction is applied for every length. Geodetic surveys are precise over large areas.
Example: If the distance between two points A & B on the earth surface is to be measured. The distance
or length of line connecting these two points is treated as arc.
1.3.
Classification of Surveying Based on Nature of the Field
Surveying is classified in to three parts according to their field
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2014/15 Academic year
1. Land Surveying
A. Topographical Surveying:- This kind of surveying is to show the topography of mountain,
terrain, river, water bodies, and roads. It is three dimensional. Topographical maps are used to
select routes, crossing for bridges, canals, and dams.
B. Cadastral Surveying: - The main aim of these surveying is to fix boundary lines, calculation of
the area of land properties and preparation of revenue map for the state. This surveying is
generally plotted to large scale than topographical surveying.
C. City Surveying: - This surveying is carried out for the construction of roads, parks, water
supply for any developing township.
2. Hydrographic Surveys: - This survey deals with the surveying of mapping of large water bodies
for the purpose of navigation and construction of harbor works etc. Example: Hydrographic Survey
of Lake Tana.
3. Astronomical Surveys:-These Survey which are carried out for determining the absolute location
i.e. latitude of different place on the earth surface and direction of line on the surface of the earth by
making observation to heavenly bodies i.e. stars & Sun.
1.4.
I.
Classification of Surveying Based on Purpose
Engineering Surveying- for the execution of engineering works such as roads, railways, dams.
II.
Mine Survey- for the control of underground workings for mineral extraction.
III.
Geological Survey- for determining different strata in the earth
IV.
Military survey - for determining points of strategic importance
V.
Archeological Survey
1.5.
Classification based on instruments
According to the instruments used Surveying is classified in to:
Chain Surveying / distance measuring
Theodolite Surveying
Compass Surveying
Tacheometer Surveying
Plane table Surveying
Photogrammetric Surveying etc
1.6.
i.
Stages of surveying works
Planning, analysis and decision – no. of crew, measuring instrument, measurement methods,
and time of measurement has to be planned.
ii.
Care and adjustment of instrument – surveying requires experience in handling the
equipment used in field and office works. For example, while taking out the instrument from
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the box, do not lift it by the telescope or with hands under the horizontal circle plate. It should
be lifted by placing the hands under the leveling base.
iii.
Field works- consists of the measurement of angles and distances and the keeping of record of
what has been done in the form of field notes. Field note includes numeric values, sketches and
explanatory notes.
iv.
Office works- consists of data processing, drafting computing and designing.
v.
Setting out works – Marking the required points and sections using peg on the field.
1.6.
Basic measurements in surveying
Surveying basically consists of the following four measurements:
1. Horizontal distance: A horizontal distance is measured in a horizontal plane. If a distance is
measured along a slope, it is reduced to its horizontal equivalent.
2. Vertical distance: A vertical distance is measured along the direction of gravity at that point.
The vertical distances are measured to determine the difference in elevations (height) of the
various points.
3. Horizontal angle: A horizontal angle is measured between two lines in a plane that is horizontal
at that point.
4. Vertical angle: A vertical angle is measured between two lines in a plane that is vertical at a
point
1.6.1. Units of measurement
Generally measurements are classified in to two parts.
Linear measurement
Angular measurement
The system most commonly used in distance and angle measurements are in system international (SI).
Table 1.1 Basic units and their abbreviations
Quantity
Length
Mass
Time
SI unit
Meter
Kilogram
Second
Abbreviation
m
Kg
S
Other units derived from the SI units by directly multiplying itself or by multiplying each other.
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Table 1.2 Derived quantity and their units
Quantity
Area
Velocity
Acceleration Force
Pressure
Volume
SI unit
m2
m/s
m/s 2
Kg.( m/s 2 )
M3
Kg. m/s 2
Table 1.3 Prefix and their meanings
Term
Prefix
Dec hect
Killo Mega
Giga
Ter
Deci
Cent
Mill Micro Nan
a
i
i
Pico
Hector
a
o
101
10 2
10 3
10 6
10 9
1012 10-1
10-2
10-3
10-6
10-9
10-12
102
Da
h
K
M
G
T
c
m
μ
n
p
h
d
o
There are three systems used for plane angle measurements, namely the sexagestimal, the centesimal
and radiant (arc units).
Sexagestimal units are used in many parts of the world and measure angles in degrees, minute and
seconds of arc. A circle is divided into 360 equal degrees, so that a right angle is 90. Degrees may be
further divided into minutes and seconds. But parts of a degree are now frequently referred to
decimally. For instance seven and a half degrees is now usually written 7.5°.
Radian units are another unit of angle measurement used in most software’s, consider the unit circle (a
circle of radius 1) whose centre is the vertex of the angle in question. Then the angle cuts off an arc of
the circle, and the length of that arc is the radian measure of the angle. It is easy to convert between
degree measurement and radian measurement. The circumference of the entire circle is 2 ( is about
3.14159), so it follows that 360° equals 2 radians. Hence, 1° equals /180 radians and 1 radian equal
180/ degrees. 1 radian = 57.2957 degrees, 1 degree = 60’= 3600 ‘’= 0.0174532 radians.
Centesimal system is common in Europe and measure angles in gons (g). Half circle π rad = 180 ° =
200 gon
1 gon=100cgon =1000mgon In surveying, the reciprocals of π/180 ° or π/200 gon are used so often that
the symbol ρ has been introduced as:
180 °/ π = ρ (o) or 200/ π = ρ (gon)
Other Less frequently used SI Units
Pressure - The SI unit of pressure is Pascal (pa) which is equal to the 1 N forces acting on 1 m 2 area.
P= F/A
1pa = 10.5 bar = 10.2 milibar
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Conversation of units
A. Conversation of length
1 inch = 2.54 cm
1 mile = 1.6093 km
1 foot = 0.3048 m
B. Conversation of area
1 sq in = 6.4516 sq cm
1 sq mile = 2.59 sq km
1 sq ft = 0.0929 sq m
C. Conversation of volume
1 cu in = 16.387 cu cm
1 cu ft = 0.0283 cu m
D. Conversation of angles
1 gon = 9/10 deg
1 deg = 10/9 gon
Temperature – Basic unit of temperature is Kelvin. 0K or 0 Kelvin is the point at which no heat
energy exists in a substance, and is called absolute zero. There are also other units for temperature,
namely, Celsius and Fahrenheit .The relationship between all are shown below.
Degrees Kelvin = Degrees Celsius + 273
Degrees Fahrenheit =9/5 *(Degree Celsius) + 32
1.7.
Reference systems
Every measurement in surveying needs reference surface as well as datum to locate a point coordinate.
The reference surface should also be defined to measure the height of a point above it. Reference
Surfaces are surfaces relative to which the measurement is taken and the coordinates or the relative
position of points are determined. Reference surfaces can be local or global depends up on the required
application.
Geoid (mean sea level) is mean equpotential surface of the earth's gravity field, which is used as a
reference for height measurement in leveling. Geoid can be local or global.
Ellipsoid is mathematical surface obtained by revolving an ellipse about the earth’s polar axis. It is a
geometric reference surface that closely approximates the geoid and used by surveyors for the
computation of geodetic and rectangular coordinates. E.g. Clark 1880, WGS 84.
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Figure 1.1 Geoid, Reference Ellipsoid and Topography
Datum is a reference from which measurements are made. In surveying, a datum is a collection of
constants, physical models, orientation and origin of, and it is used to define the coordinate system.
Horizontal datum’s are used for describing a point on the earth's surface, in latitude and longitude or
another coordinate system. Vertical datum’s measure elevations or depths. E.g. Adindan and WGS 84
datums. Basically coordinate system can be 2-D or 3-D, in 3-D coordinate systems the position of a
point would be determined in terms of x, y, z or Ф, λ, h. In case of 2-D only x, y or Ф, λ determine the
location of a point.
Types of Coordinates
1. 3-D Cartesian (rectangular) coordinates - The system has its origin at the mass-centre of the
Earth with the X- and Y-axes in the plane of the equator. The X-axis passes through the
meridian of Greenwich, and the Z-axis coincides with the Earth's axis of rotation. The three
axes are mutually orthogonal and form a right-handed system. Geocentric coordinates can be
used to define a position on the surface of the Earth.
Figure 1.2 Geocentric Cartesian coordinates system
2. 2-D Cartesian coordinates - flat map has only two dimensions: width (left to right) and length
(bottom to top). Transforming the three dimensional Earth into a two-dimensional map is
subject of map projections and coordinate transformations. Here, like in several other
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cartographic applications, two dimensional Cartesian coordinates (x, y), also known as planar
rectangular coordinates, are used to describe the location of any point in a map plane,
unambiguously. It is a system of intersecting perpendicular lines, which contains two principal
axes, called the X- axis (Easting) and Y-axis (Northing). The intersection of the X- and Y-axis
forms the origin. The plane is marked at intervals by equally spaced coordinate lines, called the
map grid. Giving two numerical coordinates x and y for point P, one can now precisely and
objectively specify any location P on the map. Grid on a map represents lines having constant
2D Cartesian coordinates (x,y). It is almost always a rectangular system and is used on large
and medium scale maps to enable detailed calculations and positioning.
Figure 1.3 2-D Cartesian coordinate system
3. 2-D Polar coordinates (α,d) – the coordinate system in which the position of a point in 2-D
determined in forms of the distance d from the origin to the point and the angle a between a
fixed (or zero) direction and the direction to the point. The angle α is called azimuth or
bearing and is measured in a clockwise direction. It is given in angular units while the distance
d is expressed in length units.
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Figure 1.4 Polar coordinate system
The transformation of polar coordinates (α,d) into Cartesian coordinates (x,y) is done when field
measurements, angular and distance measurements are transformed into map coordinates. The equation
for this transformation is:
The inverse equation is:
A more realistic case makes use of a translation and a rotation to transform one system to the other.
4. 2-D Geographic coordinates-are the most widely used global coordinate system consists of
lines of geographic latitude (φ) and longitude (λ). Lines of equal latitude are called parallels.
They form circles on the surface of the ellipsoid. Lines of equal longitude are called meridians
and they form ellipses (meridian ellipses) on the ellipsoid. Both lines form the graticule when
projected onto a map plane. Note that the concept of geographic coordinates can also be applied
to a sphere as the reference surface. Geographic coordinates are also known as Geodetic
coordinates.
Figure 1.5 Geographic coordinate system
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The latitude (φ) of a point P is the angle between the ellipsoidal normal through P and the equatorial
plane. Latitude is zero on the equator and increases towards the two poles to maximum values of +90
(90°N) at the North Pole and - 90° (90°S) at the South Pole.
The longitude (λ) is the angle between the meridian ellipse which passes through Greenwich and the
meridian ellipse containing the point in question. It is measured in the equatorial plane from the
meridian of Greenwich (λ = 0°) either eastwards through λ = + 180° (180°E) or westwards through λ =
-180° (180°W).
5. 3-D geographic coordinates (ϕ, λ, h) are obtained by introducing the ellipsoidal height h to the
system. The ellipsoidal height (h) of a point is the vertical distance of the point in question
above the ellipsoid. It is measured in distance units along the ellipsoidal normal from the point
to the ellipsoid surface. 3D geographic coordinates can be used to define a position on the
surface of the Earth.
Figure 1.6 3-D Geographic coordinates
6. Plans and Maps
Plan is the graphical representation, to some scale, of the features on, near or below the surface of the
earth as projected on a horizontal plane which is represented by plane of the paper on which the plan is
drawn. However since the surface of the earth is curved and the paper of the plan or map is plane, no
part of the surface can be represented on such maps without distortion. In plane surveying the areas
involved are small; the earth’s surface may be regarded as plane and hence map is constructed by
orthographic projection without measurable distortion.
The representation is called a map if the scale is small while it is called a plan if the scale is large. On a
plan, generally only horizontal distances and directions are shown. On topographic map, however the
vertical distances are also represented by contour lines, hachure or other systems.
7. Scale of the Map
Scale is the fixed ration between the distances between points on a map to ground.
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Engineer’s scale – "1 Map Unit = X Land Units" 1cm = 100m
Representative fraction – ‘1 map unit is equivalent to 24,000 land units’ 1/24,000
Graphical Scale – line subdivided into plan distance corresponding to convenient units of
length on the ground.
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Chapter two
2. Set up and use leveling Device ( Leveling)
2.1.
Introduction to leveling
This chapter describes the various height procedures used to obtain the elevation of points of interest
above or below a reference datum. The most commonly used reference datum is mean sea level (MSL).
There is no such thing as a common global MSL, as it varies from place to place depending on local
conditions. It is important therefore that MSL is clearly defined wherever it is used. The engineer is, in
the main, more concerned with the relative height of one point above or below another, in order to
ascertain the difference in height of the two points, rather than a direct relationship to MSL. It is not
unusual,
therefore, on small local schemes, to adopt a purely arbitrary reference datum. This could take the form
of a permanent, stable position or mark, allocated such a value that the level of any point on the site
would not be negative. For example, if the reference mark was allocated a value of 0.000 m, then a
ground point 10 m lower would have a negative value, minus 10.000 m. However, if the reference
value was 100.000 m, then the level of the ground point in question would be 90.000 m. As minus signs
in front of a number can be misinterpreted, erased or simply forgotten about, they should, wherever
possible, be avoided.
The vertical height of a point above or below a reference datum is referred to as the reduced level or
simply the level of a point. Reduced levels are used in practically all aspects of construction: to produce
ground contours on a plan; to enable the optimum design of road, railway or canal gradients; to
facilitate ground modelling for accurate volumetric calculations. Indeed, there is scarcely any aspect of
construction that is not dependent on the relative levels of ground points.
Leveling is the most widely used method for obtaining the elevations of ground points relative to a
reference datum and is usually carried out as a separate procedure from that used for fixing plan metric
position. Leveling involves the measurement of vertical distance relative to a horizontal line of sight.
Hence it requires a graduated staff for the vertical measurements and an instrument that will provide a
horizontal line of sight.
2.2.
Use of leveling
Leveling is widely employed to accrue data fore mapping engineering design and construction. leveling
results are used to ;
a) Design high way, rail way canals having slope which best confirm to existing topography.
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b) Lay out construction projects according to planned elevation.
c) Calculate volume of earth work
d) Investigate drainage characteristics of an area.
e) Develop maps showing the general configurations of the ground.
2.3.
Definition of basic terms
1. Datum:- A datum is any reference surface to which the elevation (vertical distance) of a
points are referred. The most commonly used datum is that of mean sea level.
2.
Elevation: - Elevation is the vertical distance of a points above or below on assumed
datum (level surface).
3. Leveling:- The process or methods of determining the vertical distance of a points relative
to on assumed level surface.
4.
Level line:- is the surface of which it has a constant height relative to mean sea level.
5. Horizontal line:- this is a line which is tangential to the level line or a line which is normal
to direction of gravitas
Figure 2.1 Horizontal and level lines
6. Bench Mark (BM):- are permanent reference points or marks at which their elevation
(reduced level) has been accurately determined by leveling from other permanent BM.
7.
Reduced level (RL):- is the height above or below a reference datum- similar to elevation.
8. Temporary bench mark (TBM):- are marks let up on stable points near construction sites
which all leveling operation on that particular site will be referred.
9.
Back sight (BS):- is the staff reading taken on points of known elevation as a BM or a
turning points.
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10. Fore Sights (FS):- is the staff reading on points whose elevation is to be determined as a
turning points. It is the last staff reading denoting the shifting of the instruments.
11. Intermediate sights (IS):- any other staff reading taken on a points at unknown elevation
from the same set up of the level. All sights b/n BS & FS are IS.
12. Turning points (TP):- is a point denoting the shifting at the level. It is the point on which
the back a fore sight are taken.
13. Station:- is a points of which whose elevation is to be determined.
14. Height of instruments:- is the elevation of plane of collimation (plane of sight) where the
instruments is correctly leveled.
15. Level book; any leveling work is recorded in a book ruled in suitable line and columns a
good arrangements to have columns for reading on reductions on the left page. The right
page is reserved for notes and sketches. The back sight, intermediate sight and foresight
require separate columns are normally provided for station, identification, measured
distance are remarked.
2.4.
Equipments used in leveling
Basically equipments are needed, Level, Leveling staff, Tripod, Staff bubble.
1) Levels: A level is basically a telescope attached to an accurate leveling device, set upon a tripod
so that it can rotate horizontally through 360°. The following figure shows the level and its
components.
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2) Tripod: The tripod consists of three legs and a head where the level instrument is mounted. The
tripod could be of aluminum or wood material. When leveling the level instrument, the tripod
head must be set approximately level beforehand by adjusting the tripod legs.
3) Leveling staff: The leveling staff is a box section of aluminum or wood, which will extend to 3
or 5 m in height by telescoping, hinging or addition of sections. One face has a graduated scale
attached for reading with the cross-hairs of the level telescope.
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4) Staff bubbles: These are generally a small circular bubble on an angle plate which is held
against one corner of the staff to ensure that the staff is held in a vertical position. If the staff is
not held vertical, the reading will be too large and may be significantly in error.
5) Tape: to measure height of instruments
Taping over Level Ground
If Taping is done on fairly smooth and level ground where there is little underbrush the tape can rest on
the ground. The taping party consists of the head tape man and the rear tape man. The head tape- man
leaves one taping pin with the rear tape man for counting purposes and perhaps to mark the starting
point. The head tape - man takes the zero end of the tape and walks down the line toward the other end.
When the 50 - m end the tape reaches the rear tape - man, the rear tape - man calls “ tape” or “chain” to
stop the head tape - man. The rear tape - man holds the 50 – m mark at the starting point and aligns the
head tape - man ( using hand and perhaps voice signals) on the range pole which has been set behind
the ending point. Ordinarily, this “eyes ball” alignment of the tape is satisfactory, but use of the transit
is safer and will result in better precision. Sometime there are places along a line where the tape - man
cannot see the end point and there may be positions where they cannot see the signals of the instrument
- man. For such cases it is necessary to set intermediate line points before the taping can be started.
It is necessary to pull the tape firmly. This can be done by wrapping the leather thong at the end of the
tape around the hand or by holding a taping pin that has been slipped through the eye at the end of the
tape, or by using a clamp. When the rear tape - man has the 50 – m mark at the starting point and has
satisfactorily aligned the head tape - man, he or she calls “ all right” or some other such signal. The
head tape - man pulls the tape tightly and sticks a taping pin in the ground at right angles to the tape
down to the pavement or the point may be marked with a colored lumber crayon, called keel.
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The rear tape - man picks up a taping pin and the head tape - man pulls the tape down the line, and
process is repeated for the next 50 m. It will be noticed that the number of hundreds of feet which have
been measured at any time equals the number of taping pins that the rear tape - man has in his or her
possession. After 500 m has been measured, the head tape - man will have used his eleventh pin and he
calls “ tally “ or some equivalent word so that the rear tape - man will return the taping pins and they
can start on the next 500 ms.
When the end of the line is reached, the distance from the last taping pin to the end point will normally
be a fractional part of the tape. For older tapes, the first meter of the tape (from 0 to 1m) is usually
divided into tenths, as shown in figure below. The head tape - man holds this part of the tape over the
end point while the rear tape - man moves the tapes backward or forward until he has a full foot mark at
the taping pin.
The rear tape - man reads and calls out the foot mark, say 72 m and the head tape - man reads from the
tape end the number of tenths end perhaps estimates to the nearest hundredth, say 0.46, and calls this
out. This value is subtracted from 72 m to give 71. 54 m and the number of hundreds of meters
measured before is added. These numbers and the subtraction should be called out so that the math can
be checked by each partner.
For the newer steel tapes with the extra divided meter, the procedure is almost identical except that the
rear tape - man would. For example just described, hold the 71 m mark at the taping pin in the ground.
He or she would call out 71 and the head tape - man would read and call out plus 54 hundredths, giving
the same total of 71.54 ms.
A comment seems warranted here about practical significant figures as they apply to taping. If ordinary
taping is being done and the total distance obtained for this line is 2771.34 ms the 4 at the end is
ridiculous and the distance should be recorded as 2771.3 or even 2771 ms because the work is just not
done that precisely.
Taping along sloping ground or over underbrush
When sloping distances are to be measured, there are three taping methods that can be used:
The tape may be horizontally The tape may be held along the slope: the slope determined and a
correction made to obtain the horizontal distance The sloping distance may be taped: A vertical angle
measured for each slope, and the horizontal distance later computed. The latter method is sometime
referred to as dynamic taping.
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Note: There are three types of level
•
Tilting
•
Automatic
•
digital
1. Dumpy Level:
This level was commonly used in surveying work until the last few decades. Although these excellent,
sturdy, and long – lasting devices have very largely been replaced with more modern instruments, they
are discussed at some length here to help the student understand leveling.
Originally, the dumpy level had an inverting eyepiece and as a result was shorter (thus the name
“Dumpy”) than its predecessors with the same magnification power. A typical Dumpy level with its
various parts is shown below. Its major components are its telescope, level tube, and leveling head,
these and other parts are indicating in the figure.
It has the following advantages
i.
Simpler construction with fewer movable parts
ii.
Fewer adjustment to be made
iii.
Longer life of the adjustment
SETTING UP OF THE DUMPY LEVEL:
1. Release the clamp screw of the instrument
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2. Hold the instrument in the right hand and fix it on the tripod by turning round only the lower
part with the left hand.
3.
Screw the instrument firmly and bring all the foot screws to the center of its run.
4. Spread the tripod legs well apart and fix any two legs firmly into the ground by pressing
them with the hand.
5. Move the third leg to up or down until the main bubble is approximately in the center.
6. Then move the third leg in or out until the bubbles of the cross-level is approximately in the
center.
7.
Fix the third leg firmly when the bubbles are approximately in the centers of their run.
LEVELLING UP:
1) Place the telescope parallel to a pair of foot screws.
2) Bring the bubble to the center of its run by turning the foot screws equally either both
inwards and both outwards.
3) Turn the telescope through 90º, so that it lies over the third foot screw.
4) Turn this third foot screw so that the bubble comes to the center of its run.
5) Turn the telescope through and check whether the bubble remains central.
ELIMINATION OF PARALLAX:
1. Remove the lid from the object glass.
2.
Hold a sheet of white paper in front of the object glass.
3.
Move the eyepiece right or left until the cross hairs are distinctly visible.
4. Direct the telescope towards the staff.
5. Turn the focusing screw until a clear and sharp image is formed in the plane of the cross hairs.
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2. Tilting Level:
A tilting level is one whose telescope can be tilted or rotated about its horizontal axis. The instrument
can be leveled quickly and approximately by mean of a bull’s eye or circular eye level. With the
telescope pointed at the level rod, the surveyor rotates a tilting knob that moves the telescope through a
small vertical angle until the telescope is level.
The line of sight is should be parallel to the axis of the telescope, when the bubble of the sprit level is
central and the amount of tilt can be controlled or adjusted with the help of tilting
screw. A tilting level is shown in figure below.
3.
Automatic or Self – leveling Level:
Automatic levels are the standard instruments used by today’s surveyor. This type of level (an example
of which is shown in figure below) is very easy to set up and to use and is available with almost any
desired range of precision.
They are usually satisfactory for second - order leveling and may be satisfactory for first order
Leveling, if an optical micrometer is used. The automatic level has a small circular spirit level called
bull’s eye and then the instrument itself automatically does the fine leveling. For the best operation of
the automatic level it is necessary to centre this bubble carefully and keep it in good adjustment, as will
be described later.
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The advantage of this instrument are ;
It can be level within a short period of time
It shows an erect image through the telescope.
2.5.
Precautions in leveling
• before starting to take the staff readings with a level , the following precautions must be taken;
1) The level
a.
The normal height of instrument at any set up must be about 1.50m only.
b.
The level must be set up on a firm ground and the tripod pressed firmly in to the ground.
c.
The level must never be disturbed in any set up.
d.
The permanent adjustment of a level is ensured when its line of sight is horizontal.
e.
The eye piece must be focused until a distinct vision of the cross- hairs of the diaphragm is
obtained.
2) The Staff
• the staff must be held vertical
• The ground on which the staffs are held shall be firm
• The leveling staffs are used to determine the amount by which the point where staff is held is
above or below the line of sight.
• The leveling staffs are made of wood or aluminum and marked with graduations in meters and
decimals or feet and decimals. The leveling staffs may be classified into two categories:
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a) Self Reading Staff- It is read by the level man through the telescope. The self Reading staff can be
further divided into three categories.
i) Solid Staff
ii) Folding Staff
iii)
Telescopic Staff
b) Target Staff (Philadelphia Rod)-The staff contains the movable target. It is set by the staff man at
the position indicated by signals from the level man. The reading of the staff is read by the staff
man.
Figure 2.1 Leveling staff
Figure 2.2 Tilting level
Checking systems of staff reading
Inside the telescope , we have four lines
1. Vertical line- is used for by secting the staff
2. Middle cross-hair- is used for calculating H
3.
Upper & lower cross-hair- is used for checking systems
The distance are obtained by applying a very simple formula
SD = U – L x 100
SD = U – M x 200
SD = M – L x 200
The cross-hair are cheeked with by applying the formula
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(U+L) = (M*2)
(U-M) = (M-L)
Let’s see an example: We’ve got the follow reading on the staff:
U = 0.873
M = 0.679
L = 0.485
The distance are calculated as:
SD = U – L x 100 = 0.873 – 0.485 x 100 = 38.3
SD = U – M x 200 = 0.873 – 0.679 x 200 = 38.3
SD = M – L x 200 = 0.679– 0.485 x 200 = 38.3
Checking the staff reading
(U+L) = (M*2)
(U-M) = (M-L)
(0.873+0.485) = (0.679*2)
(0.873-0.679) = (0.679-0.485)
1.358 = 1.358
0.194 = 0.194
The tripod
The tripod, is used to support the instrument at about eye height over survey marks. Some
manufacturers use the same tripod for both their levels and their theodolite, but some theodolites
require special tripods.
The tripod should be set up in the same way as for the level, except that since it is used to measure
angles at a point, it must normally be set up with the top plate centered over a ground survey mark. It is
important to ensure that there are no loose tripod fittings which might allow the tripod head to twist or
turn in use.
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In some jobs, it is necessary to place the theodolite on top of a wall or pillar and in these circumstances
a special base-plate (or wall plate or trivet) is used instead of a tripod.
•
It is a three leg stand; it is used for the purpose of providing support for the instrument and
secures the instrument by the fasting screw.
•
It is made up of wood and aluminum tripods
•
There are two mode of tripods
Extension leg tripod
Fixed leg tripod
2.6.
Preparing level for work
It consists of adjustments in each station as detailed below.
A. Setting up: Since the level is not to be set at any fixed point, the setting up of a level is many
simples as compared to other instruments. While locating the level, the ground point should be so
chosen that
The instrument is not too low or too high to facilitate reading on a benchmark
The back sight distance and the foresight distance should be approximately equal. Setting up
includes fixing the instrument and approximately leveling by leg adjustment.
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B. Fixing the instrument over tripod: The clamp screw of the instrument is released. The level is
held in the right hand. It is fixed on the tripod by turning round the lower part with the left hand and
is firmly screwed over the tripod.
C. Leg adjustment: The instrument is placed at a convenient height with the tripod legs spread well
apart and so adjusted that the tripod head is as nearly horizontal as can be judged by the eye. Fix
any two legs of the tripod firmly into the ground and move the third leg right or left in
circumferential direction until the main bubble is approximately in the centre. The third leg is then
pushed in the ground.
D. Leveling Up: It is the fine adjustment of level using bubble tube.
• Turn the instrument until the axis of the spirit level is parallel with the line of any 2 foot screws.
• The screws are held by the thumb and forefinger of each hand and turned equally and
simultaneously in the opposite direction until the bubble has moved to the central position.
The bubble is now centralized.
Left thumb rule:
The bubble is always moving along the bubble tube towards the direction of
movement of the left thumb.
The telescope has to be turned through 180º or 200 Grad. If the spirit level is adjusted correctly
the bubble has to stay in the central position. If it does not, the bubble moves a distance of "a"
(see figure 3) away from the central position. Read the amount of "a" (number of divisions on
the bubble tube) and correct half the error "a/2" (see figure 3). The bubble takes up now the
mean position.
•
Keep in mind the mean position!
The telescope is now turned through 90º or100 Grad. The bubble is brought to the mean
position by turning the remaining screw.
If the whole process has been done correctly, the bubble should remain in the same position
(mean position) wherever the telescope is turned.
If the bubble does not remain in the same position, start again by bringing the bubble in the
central position and repeat the process
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The bubble is now exactly centered and leveled and the survey can be started.
E. Elimination of parallax: It consists of focusing the eye piece and objective of the level. A)
Focusing the eye piece: This operation is done to make the cross hairs appear distinct and clearly
visible. The following steps are involved.
1.
The telescope is directed skywards or a sheet of white paper is held in front of the objective.
2. The eye piece is moved in or out till the cross hairs appear distinct.
F. Focusing the objective: This operation is done to bring the image of the object in the plane of the
cross hairs. The following steps are involved.
1. The telescope is directed towards the staff.
2. The focusing screw is turned until the image appears clear and sharp.
Diaphragm
In side surveying instrument telescope, there is a diaphragm which cares the cross- hairs or
lines.
27
There are several type of cross- hairs , these are ;
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2.6.
2014/15 Academic year
Classification of levelling
The difference in elevation may be determined by any one of the following methods.
1. Simple levelling
2. Trigonometrically levelling
3.
Differential levelling
4. Profile levelling
1. simple levellingIt is the simplest operation in leveling, when it is required to find the difference
in elevation between two points, both of which are visible from a single position of the level.
If the two points are visible from a single set up of the level, the instrument is set up
approximately mid-way b/n the two points.
Let us assume that the elevation of station A, from a given datum is known & that the elevation
of a second datum point B, is to be determined from the same reference datum.
Figure
•
Let the readings at A (HA) and B (HB) is 1.26m and 1.85m respectively at the staff readings at
B is grater than at A.
•
In levelling, a d/ce in elevation is always computed by subtracting the second staff reading
from the first one.
Difference in elevation = HA – HB
= 2.324-1.838
= 0.486
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The ground at B is at a higher elevation than that A Elevation of B = Elevation of A + (HA – HB)
= 210.852 +0.486m
= 211.340m
2. Trigonometric levelling
It is the process of levelling in which the elevations of points are computed from the vertical
angle and horizontal distance measured in the field.
Let be required the height of the building by measuring trigonometrically. inorder to minimize
the effect of instrument error on the vertical angle to be measured , set the theodolite such that
its distance from the building is measured.
The theodolite is set up at ‘A’ and levelled , the vertical angle Ø to the top of the building is
measured , the horizontal distance ‘D’ from the centre of the telescope to point ‘E’ is
measured either by a tape or stadia method.
From ∆BCD = DC = d *tanØ
The height of building = EC=AB+ d *tanØ
EXAMPLE ,
Ø = 20º 25' 30"
d = 15m
AB= 1.680m
The height of building = EC=AB+ d *tanØ
= 1.680+15*tan20º 25' 30"
= 7.266m
3. Differential levelling
Determining the difference in elevation between two or more points without any regard to
the alignment of the points is called differential leveling. It is used when
a. Two points are at large distance apart
b. The difference in elevation between the two points is large and
c. Some obstacles intervene between the points
It is the most efficient performed by a party of five persons.
1) Instrument man
2) Umbrella man
3) Note keeper
4) Two staff man
In this particular case , three instruments set ups are needed to determine the deference of elevation
b/n A&E,
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a.
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Instrument stet up I
from this set up only ‘BS’ on A & ‘FS’ on B can be read , the line of sight pierce the ground at
F and subsequently reading on staff held at ‘C’ can not be obtained . Consequently ‘B’
becomes a turning point (TP).
Let us now fined the difference in elevation between A&E, from the staff readings.
Back sight to A = 0.886m
Fore sight toB = 1.209m
Difference (A-B) = -0.323m
/ fall in elevation/
b. Instrument stet up I2
Back sight to B = 0.886m
Intermediate sight to C =1.943m
Difference (B-C) = +1.486m
/ rise in elevation/
Intermediate sight to C =0.457m
Fore sight to D = 0.714m
Difference (A-B) = -0.257m
/ fall in elevation/
c. Instrument stet up I3
Back sight to D = 0.200m
Fore sight to E = 1.857m
Difference (A-B) = -1.657m
/ fall in elevation/
Difference in elevation
The difference of level b/n A&E is given by the algebraic sum of the difference of levels of stations
A&B,B&C,C&D,D&E or equals the difference b/n the sum of the back sight and fore sight (∑BS,∑FS).
∑BS = 0.886+1.943+0.200 = 3.029m
∑FS = 1.209+0.714+1.857 = 3.780m
(∑BS - ∑FS). = -0.757 / fall/
∑fall = 0.323+0.257+1.657 = 2.237m
∑rise = 1.486m
∑rise - ∑fall = -0.751m /fall/
(∑BS - ∑FS) = (∑rise - ∑fall) = -0.751m
If the elevation of A is known , that of E,is
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Elevation of E = elevation of A + (∑BS - ∑FS)
= 1959.925+ (-0.571)
= 1959.174m
2.7.
Principle of leveling
The instruments are set up and correctly leveling in order to make the line of sight through the
telescope horizontal. If the telescope is turned through 3600 a horizontal plane of sight is swept out
vertical measurements from this plane, using graduated leveling staff enable the relative portion of the
ground points to be ascertained. Consider fig below.
With the instruments set up approximately midway between ground points A & B. If the reduced level
(RL) of points A is known and equals to 100,000m above a certain reference datum then the reading at
3.00m on vertically herd staff at A gives the reduced level of horizontal line of sights as 103,000m.
This sights on to A is termed as back sights (BS) and reduced level of the line of sights is called height
of plane at collimations (HPC)
Thus,
RL = (103.000 – 1.000) = 102.000 m
RLA + BS = HPC = Height of plane of collimation
The reading of 1,000m on to staff a B is called foresight (FS) and shows the ground point B to be 1,000
below HPC therefore its RL = (103,000 – 1,000) = 102,000m Then this is the basic concept of leveling
which is then developed in to following leveling.
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Let RL be reduced level
R = Staff reading. Then
RLC = TBM
RLD = RLC + (RC – RD)
RLE = RLC + (RC – RE)
RLF = RLE + (RE – RF)
RLG = RLE + (RE – RG)
2.7.1. Rise and fall
The basic concept of rise and fall is illustrated by the above fig.
Let RLC = TRM = 100, 000m above BM
The line of sight from the instruments at A is truly horizontal. It can be seen that the higher reading of
D i.e 2.50 indicates that it is lower than C (TBM).
This can be written
1.5 – 2.50 = -1.0 indicated fall from C to D
Similarly from C to E
1.5 – 0.5 = +1.0 indicating the rise from C to E.
If the reduced level of TBM = RLC then
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RLD = RLC + (RC – RD) but RC – RD = fall
= 100.00 – 1 = 99.00
RLD = RLC + fall
RLE = RLC + (RC – RE)
But RC – RE = Rise
= 100 + 1 = 101
RLE = RLC + rise
This method of reducing staff reading gives system of booking known as rise and fall method.
2.7.2. Method of booking
The following pints may be kept in view in entering the staff readings I a level field book.
1) The readings should be entered in the respective columns and in the orde
r of their observations.
2) The first entry in a serious is always a back sight and the last one always
a foresight.
3) The back sight and fore sight of the change point should be written in the
same horizontal line.
4) The elevation of the line of sight should be written in the same horizontal
line opposite the back sig
5) Bench marks, change points and other important points should be briefly,
but accurately described in the remarks column and their sketches drawn
on the left hand side of the page.
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Level book
Observer______________ instrument_____________________project____________
Date__________________ page___________________
point
Back sight
BM-1
a
1
Intermediate
sight
Fore sight
b
2
Height
difference
elevation
remark
known
Bench
mark
a-b
d
BM-2
C
b-c
E
d-e
There are two methods of booking in the field for leveling.
1. Rise & fall method
2. Height of collimation method.
Method – 1 Rise and fall methods
The readings are booked in a level book which is specially printed for the purpose as shown in
the following table
Staff Position BS
C
IS
FS
Rise
Fall
1.5
D
2.5
E
2
F
1
0.5
2
2.5
G
3.0
Sum
34
3.5
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2
RL
Remark
100
T. B. M.
99
101
0.5
100.5
0.5
100
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The reductions of these readings are carried out in the same book. Each reading entered on different
line in the applicable column except where the points, where a foresight and back sight occupy the
same line. Note The very important check must be applied to the reductions.
∑ BS − ∑ FS = ∑ Rise − ∑ Fall = Last RL − First RL
It follows from the above that the first two check should be carried out and verified before working out
the reduced level.
Method – 2 Height of plane of collimation method
The height of plane of collimation methods sometimes called height of instruments. The height of
collimation is obtained by adding the staff reading, which must be back sight, to know RL of the points
on which the staff stands. All other reading are deducted from the height of collimation until the
instruments setting is changed. Where upon the new height of collimation is determined by adding the
back sight to the RL of the change points.
Evidently, height of instrument above a datum its reduced level of A (1958.488) plus the staff
reading at that point. HI = reduced level of A + staff reading at A
= 1958.488 + 0.458
= 1958.946m
Setting p1 : HI = RL of A + BS at A = 1958.488 + 0.458 = 1958.946m
RL of A= HI - FS at B = 1958.946 – 0.995
= 1957.951m
Setting p2 : HI = RL of B + BS at B = 1957.951+ 1.650 = 1959.601m
RL of C= HI - IS at C = 1959.601– 0.922
RL of D= HI - FS at D = 1959.601 – 1.550
Setting : HI = RL of D + BS at D = 1958.046+ 2.000
= 1958.769m
= 1958.046m
= 1960.046m
RL of E = HI - IS at E = 1960.046– 0.758
= 1959.288m
RL of F= HI - FS at F = 1959.0.46 – 0.952
= 1959.094m
Arithmetic check
i. First RL – last RL = 1958.488 -1959.094 = -0.606m, the mines sign denotes that the last station
is a higher level than the BM.
ii. (ΣBS - ΣFS) = (0.458+1.650+2.000)-(0.945+1.555+0.952) = 0.606m, the mines sign denotes
that the last station is a higher level than the BM.
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Line
1
2
3
4
5
6
BS
0.458
1.650
Staff reading
IS
Staff
station
A
B
C
D
E
F
FS
0.995
0.922
2.000
1.555
0.758
0.952
∑4.108
(∑BS - ∑FS) = (First RL – last RL)
HI
1958.946
1959.601
1960.046
2014/15 Academic year
RL
1958.488
1957.951
1958.679
1958.046
1959.288
1959.094
remark
BM
TP
TP
∑3.502
= 0.606m
The reading and Computed values are booked is a level books which is specifically printed for this
purpose.
Staff Position
BS
C
1.5
D
IS
FS
HPC
RL
Remark
101.5
100
T. B. M.
2.5
E
2
F
99
0.5
103
2.5
G
3.5
C. P.
100.5
3.0
Sum
101
100
3.5
Note: The arithmetic check to be applied to this system of booking are
(All except the first) = (each HPC) * (No. IS and FSs deducted from it) - (FS + IS) This second
check is cumbersome and is often ignored so that as consequence, the intermediate RL are
unchecked. In this case, errors could go unchecked (compared with rise and fall method where
errors in all RLs are detected). Reduction is easier in height or collimation method (or height of
instrument method) as sometimes called leveling are taken from each position of instruments.
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2.7.3. Misclosure, Limits and its distribution
Misclosure in leveling can only be assessed by
Connecting the leveling back to the BM from which it started
Connecting in to another BM of known and ground elevation.
A Common Criteria used to assess the misclosure (E) is
Where n = No of instrument setup
M = Constant is mm (± 5)
OR
E = 15mm*D where D is the total distance in Km if E is within the misclosure, it has to be
contributed equally to all set up
2.8.
Errors in levelling works
Objectives
Students will be able to:
1. Explain the most frequently error made in levelling works regarding the error source.
2. Explain the steps to take for minimizing such errors.
2.9.
Errors in leveling
According to the error source, these may be classified as
1. instrumental,
2. natural, and
3. Personal.
Errors can be reduced by careful adjustment, by establishing standard field procedures.
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2.9.1.
2014/15 Academic year
Instrumental errors:
Instrumental errors are further divided in to errors pertaining to the level, bubble, tripod, and staff.
Collimation error: The error occurs if the line of the sight is not truly horizontal when the tubular
bubble is centered i.e the line of sight is inclined up or down from the horizontal.
A. The level
this is the most common series instrumental error, the essential
requirement in sprit leveling is that the line of collimation must be
horizontal
When the level is the perfect adjustment, the line of sight is parallel to the
bubble line is horizontal, when the bubble is centered.
The error of collimation can be eliminated by
38
i.
By equalizing the back sight & fore sight distance
ii.
By perfect adjustment & the bubble is centered.
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B. The bubble
The bubble may be under sensitive, over sensitive, or it may be have irregular curvature.
An under
sensitive bubble may come to rest in the center even, when the bubble axis is not horizontal.
C. The tripod: Loose joints must always be tightened before taking any readings.
D. The staff : The graduations of the staff must be checked an invar tape or a good graduation scale.
2.9.2. Natural errors:
The effect of curvature of the earth and atmospheric refraction makes cause for natural errors.
During high wind, precise leveling work can not be taken because of the vibration of staff and
bubble. Avoid loose, muddy and swampy areas of plot for placing instrument and level as far as
possible.
2.9.3. Personal error /error of manipulation/
- Error of manipulation is further divided into the following;
A) careless leveling up of the instrument
When the instrument is set up it must be preferably leveled. The hand should not rest on the telescope.
B) Non- centrality of the bubble
Before taking reading, the instrument man must cheek the bubble in the center of the tube.
After reading, it must once again be checked to see that it has remained in the center.
C) the staff not being held vertical
The staff should always be held quite vertical
Non – verticality of the staff either away or towards the leveler –leads to greater readings. The error
increases as the readings grow larger and larger.
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Woldia Poly Technic College
EVELLING BOOK
Observer: _________________ Instrument: ______________ Project: ___________
Point
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Back sight Intermediat Fore Sight
e Sight
Applying basic leveling procedures
Fall
Rise
Reduce Remark
Level
| EIS MAS2 M09 0919
2014/15 Academic year
Amhara Technical and Vocational Enterprise Development Bureau
Woldia Poly Technic College
2014/15 Academic year
Chapter three
3. Clean up
3.1.
Clean work area
When you complete any task on a building site, you must clear your work area to ensure the safety and
convenience of your workmates, other construction teams and the public. This process includes:
recycling or disposing of any waste material
cleaning, maintaining and storing equipment
safely filing or storing plans, documents and records
cleaning up the area.
3.2.
Dispose, Reuse and Recycle waste materials
o Disposing Removing and destroying or storing damaged, used or other unwanted domestic,
agricultural or industrial products and substances
o Recycling means turning an item into raw materials which can be used again, usually for a
completely new product. This is an energy consuming procedure.
o Reusing refers to using an object as it is without treatment. This reduces pollution and waste, thus
making it a more sustainable process.
There are laws which outline how waste materials should be dealt with and large fines can be issued if
they are not followed. Companies and contractors usually develop policies and procedures to make sure
that everyone on the building site complies with these requirements.
Therefore, Waste that cannot be reused or recycled in some form eventually finds its way to disposal.
This disposal includes landfills, but an increasing number of municipalities have elected to divert waste
into resource recovery. These recovery methods use the waste to generate electricity or produce raw
materials for industry.
3.3.
Maintained Of Plant, Tools And Equipment
Tools must be checked, maintained or, if necessary, repaired when a job is completed to ensure they:
Remain In A Good Working Condition
Are Safe To Use ?
Are Ready For The Next Project?
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Applying basic leveling procedures
| EIS MAS2 M09 0919
Amhara Technical and Vocational Enterprise Development Bureau
Woldia Poly Technic College
2014/15 Academic year
Regular maintenance helps to preserve the quality of the tools, keep them safe and extend their life.
Doing a little maintenance each time you complete a job or project can prevent costly and time
consuming repairs or replacement.
You should complete the following procedures as routine maintenance at the end of every task;
1. Wipe all tools to clear away dust or debris, and remove substances like grease or sap.
2.
Pay particular attention to tools that have been used in wet or damp conditions.
3. They should be cleaned with an oily rag to prevent rust and, if rust exists, it should
4. Be removed with steel wool or a wire brush.
5.
Sharpen blades and replace damaged or worn components.
6. Lubricate moving or adjustable parts of tools to allow smooth, continuous operation. Lubrication
reduces friction between moving parts, helps them to last longer and makes the machine more
energy efficient.
7.
Store tools and equipment properly so that they are protected against weather and theft, easy to
find when needed and not a hazard to yourself, other workers or members of the public.
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Applying basic leveling procedures
| EIS MAS2 M09 0919