Lecture_3_The Principles of Levelling_fec6a71b84edc28ee2998f7ced9ddf68.pdf
1. Survey Engineering 1
Lecture 3
The principles of Levelling
Prepared by Lecturer. Razhan Sherwan M.Saleem
Technical Engineering College
Highway Engineering Dept.
October 2022
3. Questions
1.What is Levelling and why we use levelling?
2.What is Datum, Elevation and Benchmark?
3.How to set up a level instrument?
4.What are the tools used in levelling?
3
4. Introduction
Levelling is a branch of surveying which deals with the measurement
of relative heights of different points on, above or below the surface of the
earth. Thus in levelling, the measurements (elevations) are taken in the
vertical plane.
Simpler Definition
Levelling is the process used to determine a difference in elevation
between two points.
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5. Objectives of levelling
➢To find the elevation of a given point with respect to some
assumed reference line called datum.
➢To establish new vertical control (BM or TBM)
➢To determine the heights of discrete points
➢To provide spot heights or contours on a plan
➢To provide data for road cross-sections or volumes of
earthworks
➢To provide a level or inclined plane in the setting out of
construction works
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6. Terms used in levelling
Levelling is defined as “an art of determining the
relative height of different points on, above or below the
surface”.
Level surface: It is the surface parallel to the mean
spheroidal surface of
the earth.
Level line : Line lying
on level surface.
Horizontal plane
Horizontal line
It is a straight line
tangential to level line.
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7. Terms used in levelling 2
Datum “It is an arbitrary level surface from which elevation
of points may be referred.
Mean Sea Level is the average height of sea for all stages
of tides it is derived by averaging the hourly tide height.
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8. Terms used in levelling 3
Elevation or Reduced level (RL) It is height or depth of
any point above or below any datum.
Bench Mark (B.M.) It is a fixed reference point of known
elevation with respect to
datum.
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9. Terms used in levelling 4
Line of collimation It is a line joining the intersection of
cross hairs of diaphragm to the optical centre of object
glass and its continuation. It is also known as line of sight.
Height of instrument (HI) It is the elevation of line of
collimation with respect to datum
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10. Terms used in levelling 5
Back sight (B.S) It is a staff reading taken at a known
elevation. It is the first staff reading taken after setup of
instrument.
Fore sight( F.S.) It is the last staff reading taken denoting
the shifting of the instrument.
Intermediate sight.(I.S.) It is staff reading taken on a point
whose elevation is to be determined. All staff reading
between B.S. and F.S. are Intermediate sight.
Change Point or turning point(TP): It is a point on which
both fore and back sight are taken.
Station: A point where the levelling staff is kept.
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13. Types of level
1. Dumpy level
2. Tilting level
3. Wye level
4. Automatic level
5. Digital Level
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14. 1-Dumpy Level
The Dumpy level is a simple, compact and stable instrument. The
telescope is rigidly fixed to its supports. Hence it cannot be rotated
about horizontal axis.
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15. 2-Tilting Level
This tilting is a fairly large and heavy instrument featuring a long telescope
with a three foot screw levelling system.
The telescope is supported at its centre by a pivot and may be tilted (up
and down) by turning the "tilting screw"
This tilting screw enables the telescope to be precisely levelled before
each staff reading, without altering the height of the telescope. The screw
carries a graduated drum working against an index, and indicating different
gradients.
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16. 3-Wye level
Wye level The essential difference between wye level and
other levels is that in wye level the telescope is carried by two
vertical wye supports. The telescope can be rotated, moved or
even raised in wyes.
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17. 4-Automatic level
Automatic level: It is also known as self aligning level. It is a
recent development. The fundamental difference between auto
level and other levels is that the levelling is not manually but it is
levelled automatically. It is achieved by inclination
compensating device.
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18. Automatic Level
The automatic level has a compensator mechanism that uses a
combination of fixed prisms or mirrors and a moving prism suspended
on a pendulum to give a horizontal reference. When correctly set up the
compensator will ensure that the ray of light through the centre of the
reticule is exactly horizontal.
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20. 5-Digital Level
Digital Levels: Similar to automatic level, but uses a bar code
staff, read automatically by the instrument.
➢ Push-button technique
➢ No reading errors, special staff
➢ Readings are stored and analyzed digitally
➢ Uses Barcode staffs
➢ Internal storage of data
➢ Download to the computer
➢ Automated height computation + adjustment
➢ No feeling for quality anymore
➢ You frequently need power plugs
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21. Tripod
2- Tripod: is a portable three-legged frame, used as a platform
for supporting the weight and maintaining the stability of level
instrument.
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22. Staff
3-Staff (rod): Is a wooden or metal ruler one side runway to meters and
centimeters. And is a ruler of solid wood 2 , 3 , 4 , 5 meters in length and
usually 4 meters .
Types of staff
a) E type:
• 10 equal divisions (1cm each)
• Even metres in BLACK
Odd metres in RED
01
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23. b) Invar staff
• Body of invar staff made of rigid aluminium profile with
anodised surface.
• Invar tape seated in protected
groove of staff profile and tensioned
by soft spring to compensate
extension coefficient of staff profile.
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24. C) Barcode Staff
• The Barcode staff has a 2 and 3m length and two circular
bubbles along with two attached handles for secure
positioning.
• This type of staff use only with digital level
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25. Set up Level Instrument
1-Temporary Adjustment
2- Permanent Adjustment.
Temporary Adjustments of a level:
These adjustments are performed at every setup of instrument.
• Setting up of level instrument
• Levelling of telescope
• Focusing of the eye peace
• Focusing of object glass
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26. TEMPORARY ADJUSTMENTS
Setting up the level This includes
• A) Fixing the instrument on tripod
• B) Levelling the instrument approximately by Tripod
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27. TEMPORARY ADJUSTMENTS
Levelling of telescope
A) Place the telescope parallel to a pair of
foot screw then hold the foot screws
between thumb and first finger and turn
them either inward or outward until the
longitudinal bubble comes in the centre.
B)Turn the telescope through 90 0 so that it
lies parallel to third foot screw, turn the
screw until the bubble comes in the centre.
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28. Trivet base/ tribach
Thumbscrews
Spirit
Level
Direction of bubble
movement
Direction of left
thumb Movement
Direction of bubble
movement
Direction of left
thumb Movement
The direction of
telescope
The direction of
telescope
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29. Focusing the eye piece
To focus the eye piece, hold a white paper in front of object glass, and
move the eye piece in or out till the cross hair are distinctly seen.
Focusing of object glass
Direct the telescope to the levelling staff and on looking through the
telescope, turn the focusing screw till the image appears clear and
sharp.
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30. Reading a Staff
• Read the [m], [dm] & [cm]
• Estimate the [mm]
• Check yourself for frequent
used numbers (2/3) (1/2) or
(7/8)
2.20
2.152
1.95
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33. Staff Bubble
• Keep the pole upright
– Any tilt will disturb your readings
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34. Change Plate
• For long survey lines
• Allows change of instruments
– Best is a metal change plate
– Screws e.g. at fences
– Sharp stones or nails
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35. Survey Markers
• Gives you a fixed point
– Should be of good quality
– Should be long-term
– Preferable in bedrock, settled buildings, or bridges
– Do not use fences or walls
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36. “Today a reader, tomorrow a leader”
(Margaret Fuller)
Then end of lecture
