FIELD WORK (Leveling)
REPORT
Site Surveying (QSB 1813)
Dixon Cheong (0310356)
Adrian Ng (0314516)
Erving Tiong (0306613)
Lee Chee Ming (0308958)
CONTENTS P/G
1. Introduction
2. Objective
3.Equipment
4.Results
5.Discussion
6. Conclusion
Introduction
Leveling
Leveling may be the art of determining the relative heights or elevations of points are objects on the earth’s surface. It deals with measurements in a vertical plan. Leveling is the measurement of geodetic height using an optical leveling instrument and a level staff or rod having a numbered scale. Common leveling instruments include the spirit level, the dumpy level, the digital level, and the laser level.
Leveling Procedure
A typical procedure is to set up the instrument within 100 metres (110 yards) of a point of known or assumed elevation. A rod or staff is held vertical on that point and the instrument is used manually or automatically to read the rod scale. This gives the height of the instrument above the starting (backsight) point and allows the height of the instrument (H.I.) above the datum to be computed. The rod is then held on an
unknown point and a reading is taken in the same manner, allowing the elevation of the new (foresight) point to be computed. The procedure is repeated until the destination point is reached.
Definition of terms used in levelling:
A bench mark (B.M) :
- It is fixed reference point of known elevation.
The line of collimation:
- It is the line joining the intersection of cross hairs of the optical center of the object glass. It is also called the line of sight.
An axis of the telescope:
- It is a line joining the optical center of the object glass to the center of the eye piece.
Foresight:
- (Also called a foresight reading) It is a staff (or rod) reading on a point whose elevation is to be determined or on a change point. It is also termed as minus sight. It is the last staff reading denoting the shifting of the instrument.
An Intermediate sight (I.S):
- It is any other staff reading taken on appoint of unknown elevation from the same set up of the level. All sights taken between the back sight and the fore sight and the foresight are intermediate sights.
A Station:
- It is a point whose elevation is to be determined. It may be noted that it is a point where the staff is held not the point where they leveled is set up.
Objective
To determine the relative heights of different objects on or below the surface of the earth and to determine the undulation of the ground surface.
To prepare a contour map for fixing sites for reservoirs dams, barrages etc… and to fix the alignment of roads, railways, irrigation canals, and so on.
To determine the altitudes of different important points on a hill or to know the reduce levels of different points on or below the surface of the earth.
To prepare a longitudinal section and cross-section of a project (roads, railways, irrigation cannel, etc) in order to determine the volume of the earth work
Equipment For Levelling
Levelling Staff
A levelling staff usually shows an ”E” pattern drawing on the staff. When using telescope to get a reading, the “E” shape pattern makes it easier to read the reading.(Davis, 1966) Every meter is using an alternating colour to enable people to differentiate the length, normally the colour used is red and black. (Davis, 1966).
Every 10 cm is a number, showing (in meters to one decimal) the height of the bottom of what appears to be a stylised E (even numbers) or 3 (odd numbers), 5 cm high. The stems of the E or 3 and the gaps between then are each 10mm high. This 10mm increment continues up to the next 10cm mark.
To read the staff, take the number shown below the reticle. Count the number of whole 10mm increments between the whole number and the reticle. Then estimate the number of mm between the last whole 10mm block and the centre of the reticle.
Tripod
The figure which is located above is called a tripod, which is used to hold the dumpy level. The tripod is design in such a way that is stable and it helps to give a much more accurate reading. The legs of the tripod are adjustable, so it can also be used on uneven ground. There are screws to tighten the legs after it is adjusted.
\Staff Bubble
Basically the Staff Bubble is used to check whether the levelling staff is held vertically and not slanting in any other direction. By using the Staff Bubble, it can help reduce error with the measuring/calculation and etc. When the bubble is somewhere in the circle, it means it is in the centre and it is not slanting.
Dumpy Level
A dumpy level, builder's auto level, levelling instrument, or automatic level is an optical instrument used to establish or check points in the same horizontal plane. It is used
in surveying and building to transfer, measure, or set horizontal levels. It looks like a telescope and the way of using it is almost the same. Usually it is set-up on a tripod. A levelling staff or rod is needed when calculating the level plan using automatic level. There are three adjustable screws under the dumpy level, which is used to adjust the automatic level to horizontal. Staff bubble is used to determine the horizontality of the automatic level.
Using a Dumpy level is kind of easy. What you have to do is firstly, set up a tripod which is flat and try to make it as level as the ground, then place the dumpy level on top of the tripod and screw it on. After that, you got to adjust the bubble which is inside the staff bubble into the centre of the circle.
Plumb-bob
A plumb-bob is shaped like a fat bullet which is attached to a string and the tip of
the plumb-bob is used as a reference point. The plumb-bob is usually heavy and it
is tied from under the dumpy level and it is left hanging to the bottom as low as
possible. By using the plumb-bob, it helps by showing the exact position or the
mark of the position which the dumpy level is placed. It also helps maintain the
height of the instrument.
RESULTS
BS
FS
RISE
FALL
RL
REMARKS
1.294
100.000
BM
1.525
1.504
0.210
99.790
TP1
1.635
1.437
0.088
99.878
TP2
1.313
1.516
0.119
99.997
TP3
3.140
1.414
0.101
99.896
TP4
1.599
1.572
1.568
101.464
TP5
1.456
1.498
0.101
101.565
TP6
1.445
1.386
0.070
101.635
TP7
1.479
3.973
2.528
99.107
TP8
1.437
1.421
0.058
99.165
TP9
1.291
0.146
99.311
BM
16.323
17.012
2.150
2.839
Checking:
∑BS-∑FS= 16.323-17.012= -0.689
∑RISE-∑FALL= 2.150-2.839= -0.689
End RL-First RL= 99.311-100.000= -0.689
Misclosure:
100.000-99.311= 0.689
Distribution of error:
0.689÷9= 0.0766
ADJUSTMENT
ADJUSTED RL
0.000
100.000
0.077
99.867
0.153
100.031
0.230
100.227
0.306
100.202
0.383
101.847
0.460
102.025
0.536
102.171
0.613
99.720
0.689
99.854
0.689
100.000
Discussion
1. At first there was a slight difference between the final RL and the initial RL,
this is due to some errors like parallax error or the uneven ground which the
equipment is set up on.
2. After that, in order to right the wrong, first we had to do the checkings by
finding the difference between the total value of backsight and the total
value of foresight, difference between the total value of rise and fall and the
difference between the final RL and the initial RL.
3. If the checkings are all the same, then we had to find the misclosure by
deducting the actual RL and the measured RL.
4. The next step is to distribute the error by the number of set ups. In this case,
there were 9 set ups. For instance,
-the first set up: (0.689÷9)x 1
-second set up :(0.689÷9)x2
-third set up :(0.689÷9)x3
5. Since the checkings are negative, the adjustment should be added in to the
RL.
Conclusion
Leveling is to determine the difference in height between two points in an area.
The main purpose of leveling is to design the highways, railroad, sewers,
watersupply system and provides grade lines on the existing topography. Besides
that, leveling can also lay out the construction projects according to the planned
elevations and enables to calculate the volume of earthworks. Leveling requires
equipment such as leveling staff, tripod, auto level meter, staff bubble and
measuring tape.
Leveling method is now widely used in construction sites. Leveling is an
inexpensive, simple and accurate method for measuring height. Besides
construction site, leveling are also used for measurements of rivers or lake.
References
1. McCormack, AJ. "Setting out Auto-levels & Lasers." Pavingexpert. N.p., 1997. Web. 28 Nov. 2013. <http://www.pavingexpert.com/setout04.html>.
2. Wong, Khai Jee. "Levelling." Site Surveying. Taylor's Lakeside University, Subang Jaya. 11 Sept. 2013. Lecture.
3. Nosek, Aaron. "Long Tape." Make Your Mark. Keson, 1968. Web. 28 Nov. 2013. <http://www.keson.com/products/Measuring/Long-Tapes.aspx>.
4. Retrieved from http://www.agriinfo.in/?page=topic&superid=8&topicid=54 5. Retrieved from http://en.wikipedia.org/wiki/Levelling
