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Surveying experiment
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American University of Sharjah Instructor: Riyad Temam School of Engineering Office: EB2 - 048 Civil Engineering Department Tel: 065154003 P. O. Box 26666 e-mail: [email protected] Sharjah, UAE Course: CVE 242
EXPERIMENT # 4
DIFFERENTIAL LEVEL OPERATIONS
Objectives:
1. Acquaint the student with the Automatic levels.
2. To teach the student how to check for collimation errors using the Two-Peg test.
3. Train the students on using different types of levels.
4. Teach the students how to perform the leveling using the height of instrument method.
5. Teach the students on determining the differential level and the reduced level between two
points.
6. Teach the students how to check for errors in leveling readings.
Equipment: 1. Automatic level (Figure 2) 2. Tripod 3. Level rod/staff (Figure 3) Overview
In this lab, the reduced level of the floor in front of the AUS Library building (Bench mark) is
known to be 100.00 m, you are asked to:
1. Determine the reduced level of the floor at the main entrance of the Library building –
station 1.
2. Determine the reduced level of the floor at the passageway between the Main building
and the Library building – station 3.
3. Determine the reduced level of the floor at the entrance of Engineering Building 1
(EB1) – station 4.
4. Determine the differential level between the floor at the entrance of the Library
building and the floor level at the entrance of EB1.
5. Check for any arithmetic errors and closure errors for your measurements by performing a
closed survey (finishing the survey by returning back to the initial point)
Methodology:
1. To check for the collimation error, do the following steps:
a. Setup the level midway between two stations spaced at L (30-40 m apart).
b. Read staff on each station and calculate true height difference (δhT) between them.
c. Move the level about L/10 = 3-4 m beyond one of the stations.
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d. Read off on each station again and calculate the apparent height difference (δhA).
e. If δhT = δhA → Instrument is OK. Else, calculate the collimation error
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f. Check e with the acceptable limits (1 mm per 20 m according to Uren and Price, and 4
mm per 50 m according to Wimpey).
2. Set up the instrument in a position between the first two stations in the site making sure that
the line of sight is unimpeded between them.
3. Level the instrument using the leveling screws.
4. Take your back sight to the benchmark and then take a foresight and Intermediate
foresights (if required) onto the next station/s.
5. Keep the staff in this position while you move your instrument to the next setup point.
6. From your new setup, take a back sight onto the last station (turning point) before resuming
with your foresight to the next station again.
7. When all required levels are taken, close on the benchmark.
8. Complete your field book according to the prescribed format.
9. Find and explain any accidental and systematic errors as appropriate.
10. Report the RL of the entrance to EB1, the entrance to the Library building and the
difference in elevation between the two points.
11. What is the size of your closure error?
To calculate the reduced level of any point
HI = RL of a point with known elevation + BS
RL of new point = HI – IFS or HI – FS
Where HI is height of instrument
RL is reduced level ( elevation)
BS is back sight reading
IFS is intermediate foresight reading
FS is foresight reading
To check for any arithmetic errors
(Last level - first level) = (ΣBS- ΣFS)
Lab Handout prepared by : Arshi Faridi
Modified by : Riyad Temam
References:
1. W.R. Hudson, Charles Pilson, Athar Saeed “Engineering Measurements Laboratory
Text”, Department of Civil Engineering, The University of Texas at Austin.
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BM
1
3
4
C
B
A2
Key
BS Stations
IFS Automatic level
FS
EB2EB1
Library Building
Library Building
2. William Irvine “Surveying for Construction”.
Figure 1a: schematic plan of the area showing the movement of the level.
Figure 1b: Elevation of the area when the level is moved between stations.
DATA / CALCULATIONS
Station Back Sight (BS)
Intermediate Foresight
(IFS)
Foresight (FS)
HI Reduced Level
Remarks
B.M. 100.00
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Figure 2: Automatic level.
Figure 3: Staff
