Soil and water conservation engineering- Dumpy level- Setting, Observation and tabulation of readings- Civil engineering- Agricultural engineering

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Dumpy level- Setting, observation and tabulation of readings

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Dumpy Level:
The dumpy level is an optical surveying leveling instrument consisting a telescope
tube firmly secured in two collars fixed by adjusting screws to the stage by the vertical spindle.
The telescope of dumpy level can rotate only in a horizontal plane. Relative
elevation of different points of a surveying land is determined with dumpy level.

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Advantages of Dumpy Level Survey:
The dumpy level is a widely used surveying instrument in surveying. The advantages
which have made the dumpy level so popular is given below.
•Simple construction with fewer movable parts.
•Fewer adjustments to be made.
•Due to the rigidity of dumpy levels, it retains its two adjustment for a long time.
•High optical power.

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Disadvantages of Dumpy Level Survey:
There are few limitation or disadvantages of dumpy level. These limitations are given below.
•Civil Engineers may find it difficult in making accurate measurements.
•Difficulty in using.

6. 1.Telescope
2.Eye-Piece
3.Ray Shade
4.Objective End
5.Longitudinal Bubble
6.Focusing Screws
7.Foot Screws
8.Upper parallel Plate
9.Diaphragm Adjusting Screws
10.Bubble Tube Adjusting Screws
11.Transverse Bubble Tube
12.Foot Plate
Following are the main parts of dumpy level instrument.
Parts of Dumpy Level:

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Procedure:
The art of determining the relative heights of points on the surface of the earth is termed as levelling. A level is
employed for this purpose with a metric staff
The dumpy level mainly consists of a base plate, telescope, and bubble tube. The base plate consists of 3 foot
screws which are operated simultaneously in or out to bring the bubble tube to centre. The instrument has to be temporarily
adjusted at each setting before taking the staff reading. The operations involved in the temporary adjustments are:
1. Setting the instrument
2. Leveling the instrument
3. Elimination of parallax

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Setting up the level :
Fixing the instrument on the tripod and also approximate levelling by leg adjustment.
Levelling up the instrument:
Accurate leveling is done with the help of foot screws and by using plate levels. Leveling up the instrument is to make its
vertical axis truly vertical.
Elimination of parallax :
If the image formed by the objective does not lie in the plane of the cross hairs, there will be a shift in the image due to
shift of the eye. Such displacement of image is termed as parallax.
Parallax is removed in two stages.
1) Focusing the eye for distinct vision of cross hairs.
2) Focusing the objective ‐ image is formed in the plane of cross hairs.

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Methods of Levelling:
1. Height of Collimation Method
2. Rise and Fall Method
1. Collimation Method:
It consist of finding the elevation of the plane of collimation ( H.I.) for every set up of the
instrument, and then obtaining the reduced level of point with reference to the respective plane of collimation.
1. Elevation of plane of collimation for the first set of the level determined by adding back side to
R.L. of B.M.
2. The R.L. of intermediate point and first change point are then obtained by starching the staff
reading taken on respective point (IS & FS) from the elation of the plane collimation. [H.I.]

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3. When the instrument is shifted to the second position a new plane collimation is set up. The elevation of this plane is
obtained by adding B.S. taken on the C.P. From the second position of the level to the R.L. C.P. The R.L. of successive point and second C.P. are
found by subtract these staff reading from the elevation of second plane of collimation.
 This method is simple and Reduction of levels is easy.
 Visualization is not necessary regarding the nature of the ground.
 There is no check for intermediate sight readings
 This method is generally used where more number of readings can be taken with less number of change points for constructional work and
profile leveling.

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Back sight (1) Inter sight (2) Fore sight (3) HC
(4)
RL
(5)
Remarks
(6)
0.500 100.500 100.00 Bench mark, P
0.750 0.890 100.450 99.700 CP1
0.650 1.250 99.850 99.200 CP1
1.300 98.550 Station Q
1.900 3.350 1.450
Arithmetical check
Sum of B.S. – sum of F.S. = last R.L. – First R.L.
Result:
The difference in elevation between stations P & Q,,
100.000 – 98.550 = 1.450 m

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2. Rise and Fall Method:
It consists of determining the difference of elevation between consecutive points by comparing each point after the first that
immediately preceding it. The difference between there staff reading indicates a rise fall according to the staff reading at the point. The R.L is then
found adding the rise to, or subtracting the fall from the reduced level of preceding point.
 This method is complicated and is not easy to carry out and Reduction of levels takes more time.
 Visualization is necessary regarding the nature of the ground.
 Complete check is there for all readings.
 This method is preferable for check levelling where number of change points are more.

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Back sight (1) Inter sight (2) Fore sight (3) Rise
(4)
Fall
(5)
RL
(6)
Remarks
(7)
2.150 100.00 Back bearing on P
1.64 1.650 0.500 100.500 CP1
2.345 0.700 99.800 Inter
1.965 0.380 100.180 CP2
1.425 1.825 0.400 99.780 Station
5.220 5.440 0.880 1.100 0.220
Arithmetic check
Sum of B.S. – sum of F. S. = sum of rise – sum of fall = last R. L. – first R.L.
Result:
The difference in elevation between the given station =

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