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steps of surveying
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ASSIGNMENT Two | MAY 17TH 2015
NADIM EL HINDI 20082422 ARP554 | Surveying & Field Surveying | Elias Abi Rizk
SPRING 2015 | FAAD | NOTRE DAME UNIVERSITY
Surveying and Field Surveying
Field Surveying
1
Leveling: Aims Of This Report
Aims of this Report:
-Heights, datums and bench marks
-Levelling equipment
-Field procedure for levelling
-Calculating reduced levels
-Sources of error in levelling
-Other levelling methods
Levelling how heights are defined: - Engineering surveying involves the measurement
of three quantities; heights, angles and distances. - Levelling is the process of measuring heights. - It is possible when levelling to measure heights with an accuracy of millimeters - Heights can also be measured using total stations, handheld lasers and GPS devices. - However, levelling offers an inexpensive,
simple and accurate method for measuring
heights, and it is widely used in
construction sites. - Any method of measuring the heights of
points above or below the ground using
an agreed datum. - These reference points are present in all
construction sites and has an arbitrary height
assigned to the point. Most construction sites
will have several of these benchmarks, and if
they have heights based on an arbitrary datum,
they are known as Temporary Bench Marks.
Figure: Some of the leveling equipments
Figure: Reading the height
Figure: How heights are defined
Field Surveying
2
Heights:
Heights are defined using horizontal and vertical lines. The
figure beside shows a plumb-bob suspended at point P, the
direction of gravity along the plumb-line defines the
vertical at point P. A horizontal or level line is any line at
right angles to this point.
For site work, any horizontal line can be chosen as
a datum for heights and for levelling. The height of
a point is measured along the vertical above or
below the chosen datum. The height of a point
relative to a datum is known as its reduced level
(RL).
Curved Surfaces:
Level (or horizontal) lines are always at right angles to the
direction of gravity. The direction of gravity is generally towards
the center of the earth. Over large areas, as the Earth is curved,
level surfaces will also be curved. For these, a height difference
is measured along a vertical between two curved level surfaces.
Leveling Ruler:
Levelling involves measuring vertical distances with reference to
a horizontal plane or surface. To do this, a levelling ruler is
needed to measure vertical distances and an instrument known
as a level machine that is required to define the horizontal
plane.
Many types of Leveling rulers are used with varying lengths and
different markings. The E-type face is commonly used in the UK
and Ireland. This can be read directly to 0.01m and by
estimation to the nearest mm. The ruler must be held vertically
a circular bubble is fitted to help with this.
Figure: Plumb bob suspended to define the vertical line
Figure: leveling in Curved Surfaces
Figure: Leveling Ruler and Level Machine
Field Surveying
3
Level Machine Details:
1. Focusing screw
2. Eyepiece
3. Foot screw
4. Horizontal circle
5. Base plate
6. Tangent screw
7. Circular bubble
8. Collimator (sight)
9. Object lens
The Main Features of the Telescope:
1.Object lens
2.Focusing screw
3.Focusing lens
4.Diaphragm
5.Eyepiece
The object lens, focusing lens, diaphragm and eye piece are all
mounted on an optical axis called the line of collimation or the
line of sight.
This is an imaginary line which joins the optical center of the
object lens to the center of the cross hairs.
When looking through the eye piece of the surveying telescope,
a set of lines called the cross hairs can be seen. These are used
for taking measurements from the staff. These cross hairs are
etched on a small sheet of glass known as the diaphragm.
To make the telescope work, the image of the staff is brought to
a focus in the plane of the diaphragm using the focusing screw.
The eyepiece is rotated so that the cross hairs are in focus and
its focal point is also in the plane of the diaphragm. When
looking into the telescope an observer will now see a magnified
image of the levelling staff focused against the cross hairs.
Figure: Level machine annotations
Figure: Telescope annotations
Figure: Object Lens
Field Surveying
4
The Steps of Leveling:
The following steps are taken when using a level to measure
heights:
1.Set up the tripod
- Loosen screws of tripod legs, pull out to required length and
tighten screws.
- In order to guarantee a firm foothold sufficiently press the
tripod legs into the ground. When pressing the legs into the
ground note that the force must be applied along the legs.
- Check all screws and bolts for correct fit.
- When setting up the tripod pay attention to a horizontal
position of the tripod plate. Minor inclinations of the tripod can
be corrected with the footscrews of the tribrach.
2.Attach Level on tripod
- Place level onto tripod head. Tighten central fixing screw of
tripod.
- Turn footscrews A and B simultaneously in opposite
directions until bubble is in the centre (on the imaginary
"T").
- Turn the instrument 90 and then turn the foot screw C
until bubble is centred.
3.Center instrument over a ground point
If you want to centre an instrument over a ground point:
- Attach plumb bob and arrange the tripod in such way that
the plummet is over the point.
- For fine adjustment loosen central fixing screw slightly and
shift instrument parallel on tripod until the plummet is exactly
over the point.
- Tighten central fixing screw.
Figure: Set up the tripod
Figure: Attach Level on tripod
Figure: Center instrument over a ground point
Field Surveying
5
4. Focusing telescope
- Aim telescope against a bright background (e.g. white
paper).
- Turn eyepiece until reticule is sharp-focused and deep
black. Now the eyepiece is adapted to your eye.
- Aim telescope on staff using the coarse aiming device.
- Turn focusing knob until image of staff is sharply focused.
5. Levelling staffs (rods) and accessories
There are many types of staffs, with names that identify the
form of the graduations and other characteristics. Staffs can be
one piece, but most of them are sectional and adjust the length
by telescoping..
The metric staff has major numbered graduations in meters and
tenths of meters (there is a tiny decimal point between the
numbers). Our staves have an ''E'' shape mark (or its mirror
image) with horizontal spaces between them of 10 mm.
When viewed through an instrument's telescope, the observer
can easily visually interpolate a 10 mm mark to a quarter of its
height, giving a reading accuracy of 2.5 mm. On one side of the
rod, the colors of the markings alternate between red and black
with each meter of length.
The Black arrows indicate where to push to extend the staff to
its full length.
6.Staff Reading
The figure beside shows three different staff readings:
It is easy to read (b) and (c) because the cross-hair is exactly on a
mark division. The reading for (a) is between 1.630 and 1.640. To
assess the mm reading you have to estimate where the position
of the cross-hair is. For (a) the reading is 1.636. The millimeter
reading is to be estimated and can very between 1 mm.
Figure: Focusing Telescope
Figure: Levelling Staffs
Figure: Staff Reading
Field Surveying
6
Points l Fwd distance l Back distance l Mean l Error l Accuracy A l x l y l (x+y)/2 l x-y l ( x-y)/ratio A 1 l x 1 l y 1 l (x+y)/2 l x-y l ( x-y)/ratio A 2 l x2 l y2 l (x+y)/2 l x-y l ( x-y)/ratio
A 3 l x3 l y3 l (x+y)/2 l x-y l ( x-y)/ratio
A 4 l x 4 l y4 l (x+y)/2 l x-y l ( x-y)/ratio
B l x5 l y5 l (x+y)/2 l x-y l ( x-y)/ratio
Field Results:
Points l First Trial l Points l Second Trial
A-A1 l 9m l A-A1 l 7m
A1-A2 l 9m l A1-A2 l 9m
A2-A3 l 9m l A2-A3 l 9m
A3-A4 l 10m l A3-A4 l 7m
A4-A5 l 12m l A4-A5 l 9m
A5-B l 13.40m l A5-A6 l 10m
Total l 62.40m l A6-A7 l 11.40m
Total l 62.40m
Field shots:
Figure: Level Machine
Figure: Level Machine on Tripod + Levelling Staff
Figure: Focusing Level Machine + Centering the bubble to maintain horizontality
Field Surveying
7
Figure: Measuring Distance by the tape
Field Surveying
8