Leveling Assignment
Leveling Assignment
Leveling Assignment
UJOODHA Yashveer
ID: 1110917
Introduction
Levelling is an observational technique that allows the computation of the
relative heights of points above or below some plane of reference called the
levelling datum. It can be also defined as a means by which surveyors can
determine the elevation of points, using other known points as references.
Levelling is perhaps the most basic of surveying operations and forms an
important fundamental part of almost every surveying project.
Basics of levelling
In levelling, the surveyor looks back (BS) to a point of known elevation to
determine the elevation of his or her instrument (EI). The surveyor then looks
forward (FS) to a point of unknown elevation and determines the elevation of
that point using the elevation of his or her instrument (EI) and the value on
the level rod read through the levels telescope.
Once the elevation of a point is determined, that point can be used for
determining the elevations of other points.
Aim
To determine the relative height, that is the height at the Food Technology
Laboratory (TBM), with respect to a known point (BM2, near the CITS
building).
Levelling
UJOODHA Yashveer
ID: 1110917
Levelling
UJOODHA Yashveer
ID: 1110917
4. Change plate
5. Measuring tape
Levelling
UJOODHA Yashveer
ID: 1110917
Levelling
UJOODHA Yashveer
ID: 1110917
Methodology
To begin with, an overall view of the area is noted, that is the
weather conditions, the path to go through the area.
The staff is hold by 1 member on the change plate at BM2 while
another one sets the apparatus at a distance from BM and reads
the level. A 3rd member checks the reading and the value is
recorded as the first back sight value. Furthermore the
corresponding remarks are also noted.
The staff holder changes position and the reading in the level is
noted by the booker. This new value is the fore sight value.
Note: no inter sight have been taken.
The steps are repeated at different place until the TBM is reached
and the survey ends back to the BM2.
All the readings are recorded in a clear and tabular form as
shown below and checks are carried out each time in order to
minimize errors.
Back sight
Inter sight
Fore sight
Rise
Fall
Redd level
Remarks
Levelling
UJOODHA Yashveer
ID: 1110917
Survey: Local
survey
Observer:
Group1
Booker: Group1
Back
sight
Inter
sight
Fore sight
Rise
Fall
1.315
0.545
1.840
0.525
1.390
1.440
0.895
1.190
1.570
0.180
1.120
3.510
2.320
1.092
1.092
0.028
2.710
0.240
0.852
1.939
2.642
1.185
1.565
1.525
0.374
1.675
1.800
0.842
B=15.6
18
1.380
0.295
F=15.62 R=3.91
2 6
-15.618
0.004
F=3.9
20
-3.916
0.004
Red'd level
Remarks
BM2 ( near
312.200 CITS)
CP (parking
311.675 lot)
CP (grey
310.780 building)
CP (building in
310.600 rocks)
CP (asphalt
308.280 road)
TBM (food
308.308 tech lab)
CP (asphalt
309.160 road)
CP (parking
310.685 lot)
311.059 CP ( turn)
CP ( asphalt
311.901 road)
BM2 ( near
312.196 CITS)
312.200
-312.196
0.004
Levelling
UJOODHA Yashveer
ID: 1110917
Collimation error
In a properly adjusted level the line of the sight will be perfectly horizontal
when the bubble of the spirit level is central. As the length of the sight
increases, the error e increases. The effect of the error can be eliminated by
making the back sight and fore sight equal in length.
Levelling
UJOODHA Yashveer
ID: 1110917
The test for this error, the Two- peg test, should be carried out prior to
important levelling work.
1.
Set out and mark on the ground (with wooden pegs driven into the
earth, or roofing nails in tar) two point some 30m apart. Set up the level
exactly mid-way (within 0.5m) between them:
Levelling
UJOODHA Yashveer
ID: 1110917
Take measurements of back sight and foresight for this first setup. The
height difference h1 will be free of the effects of collimation error:
h1 = b1 - f1 = (b + sb.) - (f + sf.)
= b - f + .(sb - sf)
= b - f
2.
(because sb = sf )
Next, move the level to a position just beyond the fore staff position
(about 5m):
Then repeat the readings. In this case, sb = 35m and sf = 5m. Then:
h2 = b2 - f2 = (b + sb.) - (f + sf.)
= b - f + .(sb - sf)
b - f
(because sb sf)
Levelling
3.
UJOODHA Yashveer
ID: 1110917
b b2 -
s b - sf
30
. h 2 - h1 b 2 . h 2 - h1
sb
35
In the case of older levels with tubular bubbles the adjustment consists of
tilting the level using the levelling screws until the desired staff reading
appears on the cross-hair. Then the adjusting screws on the tubular level
are adjusted until the bubble is level. For modern levels with automatic
compensators the adjustment involves moving the cross-hairs vertically
using their adjusting screws until the desired reading is obtained.
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