Leveling Survey (Longitudinal and Cross-section)
Learning Outcome
By the end of this practical work students should be able to:
1.
Setup level equipment
Setup level equipment
2.
Take back sight, intermediate sight and fore sight reading
Take back sight, intermediate sight and fore sight reading
3.
Make correct booking
Make correct booking
4.
Calculate reduced level of all the point taken
Calculate reduced level of all the point taken
5.
Perform correction to the reduced level
Perform correction to the reduced level
6.
Plot a longitudinal profile and cross section with a suitable
scale
Plot a longitudinal profile and cross section with a suitable
scale
Theory
Leveling is the art of determining relative height or elevations
of different points on the earth surface. The elevation of a point has been
defined as its vertical distance above and below a given reference level
surface and usually a mean sea level. The leveling work can be carried out by
using direct method or indirect method. The main equipment needed to carry out
leveling works is level and staffs. The elevation of the point is calculated
using Height of Collimation Method or by using Rise and Fall Method. The final
works of the leveling is to transform the numerical data into graphic form
either in map or drawing.
of different points on the earth surface. The elevation of a point has been
defined as its vertical distance above and below a given reference level
surface and usually a mean sea level. The leveling work can be carried out by
using direct method or indirect method. The main equipment needed to carry out
leveling works is level and staffs. The elevation of the point is calculated
using Height of Collimation Method or by using Rise and Fall Method. The final
works of the leveling is to transform the numerical data into graphic form
either in map or drawing.
Equipment
1. level
Automatic level is used to compare points on the surface of the earth and
series of heights observed must be relative to a plane called datum. Automatic
level is a device that gives a truly horizontal line. The telescope of this
instrument need only be approximately level and the compensating device,
usually a pendulum system inside the telescope corrects for the residual
mislevelment. This instrument has no bubble tube; therefore preliminary
leveling is carried out using the conventional three-screw leveling head and a
small target bubble mounted on the tribach which brings the collimation to
within 10’ of the horizontal. A prismatic compensator fitted between the
eyepiece and the objective lens make correction of slight tilt automatically.
Automatic level is used to compare points on the surface of the earth and
series of heights observed must be relative to a plane called datum. Automatic
level is a device that gives a truly horizontal line. The telescope of this
instrument need only be approximately level and the compensating device,
usually a pendulum system inside the telescope corrects for the residual
mislevelment. This instrument has no bubble tube; therefore preliminary
leveling is carried out using the conventional three-screw leveling head and a
small target bubble mounted on the tribach which brings the collimation to
within 10’ of the horizontal. A prismatic compensator fitted between the
eyepiece and the objective lens make correction of slight tilt automatically.
2. Leveling staff
The staff used for ordinary leveling work is sectional and
assemble either telescopically or by slotting one another vertically. Most
modern designs are manufactured in an aluminum alloy BS4484:Part1:1969 requires
length of 3 m, 4m or 5m extension. The graduations are in the form of an E or F
shape and the graduations in the 100mm interval.
assemble either telescopically or by slotting one another vertically. Most
modern designs are manufactured in an aluminum alloy BS4484:Part1:1969 requires
length of 3 m, 4m or 5m extension. The graduations are in the form of an E or F
shape and the graduations in the 100mm interval.
3. Staff bubble
An instrument to ensure the staff is erected vertically. It is
place at the side of the staff.
place at the side of the staff.
4. Tapes
Tape is made of synthetic material, glass fiber or linen. The
length of the tape is 10m, 20, 30m and 50m are generally available. The tape is
graduated at every 5mm and figures every 100mm. the first and the last meter
lengths are graduated in millimeters. Whole meter figures are shown in red at
every meter.
length of the tape is 10m, 20, 30m and 50m are generally available. The tape is
graduated at every 5mm and figures every 100mm. the first and the last meter
lengths are graduated in millimeters. Whole meter figures are shown in red at
every meter.
Procedures
·
Longitudinal leveling (60m length)
Longitudinal leveling (60m length)
1.
The suitable position for the level to be set up is selected
The suitable position for the level to be set up is selected
2.
The level is set up. The temporary adjustment is made
The level is set up. The temporary adjustment is made
3.
The staff is placed at the bench mark and the reading is taken
The staff is placed at the bench mark and the reading is taken
4.
The reading is noted in the form provided
The reading is noted in the form provided
5.
Another staff is placed at the distance of 7.5m from the first
staff
Another staff is placed at the distance of 7.5m from the first
staff
6.
The reading of second staff is taken and is noted as the
intermediate sight
The reading of second staff is taken and is noted as the
intermediate sight
7.
A distance of 7.5m is measured and the third staff position is
placed. The reading is noted in the field sheet as an intermediate sight
A distance of 7.5m is measured and the third staff position is
placed. The reading is noted in the field sheet as an intermediate sight
8.
Step 5 to 7 is repeated until the staff cannot be read. The last
reading of the staff before the level is moved is noted in the column
foresight. The staff at the foresight position must not move until the back
sight reading is taken
Step 5 to 7 is repeated until the staff cannot be read. The last
reading of the staff before the level is moved is noted in the column
foresight. The staff at the foresight position must not move until the back
sight reading is taken
9.
The level is moved to new suitable position and the temporary
adjustment is made
The level is moved to new suitable position and the temporary
adjustment is made
10.
The back sight reading is taken
The back sight reading is taken
11.
A cross section reading is taken at every 15m
A cross section reading is taken at every 15m
12.
Steps 5 to 10 are repeated until the work is completed
Steps 5 to 10 are repeated until the work is completed
13.
A fly level is performed back to the benchmark
A fly level is performed back to the benchmark
14.
The HOC and the reduced level of all the staff positions is
calculate
The HOC and the reduced level of all the staff positions is
calculate
15.
The longitudinal and cross section profile of the road is
plotted
The longitudinal and cross section profile of the road is
plotted
·
Cross section leveling (0m, 40m, 80m, 120m, 160m and 200m)
Cross section leveling (0m, 40m, 80m, 120m, 160m and 200m)
1.
Five staff positions is selected perpendicular to the
longitudinal line at position A, B, C, D and E
Five staff positions is selected perpendicular to the
longitudinal line at position A, B, C, D and E
2.
The staff is placed at point A and the reading is taken
The staff is placed at point A and the reading is taken
3.
The reading is entered as intermediate sight if the level is
still not being moved from the previous position
The reading is entered as intermediate sight if the level is
still not being moved from the previous position
4.
Taking reading for points B, C, D and E is continued
Taking reading for points B, C, D and E is continued
5.
After completed cross section leveling, taking the longitudinal
leveling is continued until completed
After completed cross section leveling, taking the longitudinal
leveling is continued until completed
Conclusion
From this practical, we were able to setup the compass survey
stations and their equipment correctly. We have taken the reading of three
points of static things that have at our location from station A. There are
3.25m, 1.80m and 3.35m from station A
stations and their equipment correctly. We have taken the reading of three
points of static things that have at our location from station A. There are
3.25m, 1.80m and 3.35m from station A
We have calculated the misclosure as mentioned in the local
attraction method table. The corrected bearing and the final bearing is
determined by followed the correct steps
attraction method table. The corrected bearing and the final bearing is
determined by followed the correct steps
Discussion and Recommendations
1.
Avoid taking measurement near magnetic sources such as hand
phone, watch, electric cable and etc
Avoid taking measurement near magnetic sources such as hand
phone, watch, electric cable and etc
2.
Make sure the bubbles are properly level
Make sure the bubbles are properly level
3.
Triple check with the work and reading
Triple check with the work and reading
4.
Make sure the plum bob properly centered over the peg
Make sure the plum bob properly centered over the peg
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