Two Peg test need to carry out before we start the levelling job to ensure the instrument in good condition 1.0 Aim
Peg Test is a surveying operation carried out to determine if the leveling bubble (bubble axis) and telescope line-of-sight ( line of collimation )are parallel.
3.1 Level and Tripod ( 1 set)
3.2 Staff ( 2 sets )
3.3 Staff bubble (2 sets )
3.4 Tape ( 1 set )
4.5 Each group will be required to perform a peg test to check the instrument. 4.6 All person in the group should recorded the result of the peg test in their own field book. 4.7 Two point some 60 m apart are set out and marked the ground (with wooden pegs driven into the earth, or roofing nails in tar) 4.8 The instrument are set up midway between two pegs [figure 3.1] 4.9 The staff are read on each peg (back sight and foresight), and the height difference are calculated. 4.10 The instrument are moved about L/10 = 6m beyond one of the pegs (normally fore staff position). [figure 3.2] 4.11 The staff are read on each peg again, and the height difference are calculated.
I. First, we need to measure by tape 30m from point C to point A and B. Choose flat area for this test and observe the staff A and B.
II. After that, the auto level move to point D where is about L/10 meter. L is total length from point A to B. Jot down the Staff A and B reading.
III. Do camparison between 2 set of readings
4.0 Observation Data and Analysis
| Reading Staff B (s1)| Reading Staff B (s2)| Height difference=m| First set up| 1.325| 1.325| 0|
| Reading Staff B (s1’)| Reading Staff B (s2’)| Height difference=m’| Second set up| 1.388| 1.390| 0.002|
5.12 if m=m’ then the instrument is ok!
5.13 If NOT then the error is
e= (S1-S2) – (S1’ – S2’ ) / L mm/m
=(1.325-1,325) – (1.390-1.388)
=0.002m @ 2 mm
The error is called collimation error.
5.14 Acceptable error : 1mm per 20 mm
Therefore, because the length,L is 60m the acceptable collimation error is should be 3mm or less. So, because the collimation error is 2 mm the instrument is in a good condition.
LEVELLING (Establish TBM)
The definition of levelling is measurement process to determine the difference between high points on the earth referred to the datum level by using staff. Surveying based on measuring two quantities, height and distance. Measuring of linear distance horizontal and vertical distance. Levelling is the procedure for determining differences in elevation points that are some distance from each other. An elevation is the vertical distance above or below a reference datum. Elevation can be determined using the levelling techniques. Vertical distance measurement is called “levelling” includes procedures that determine.
* To get the difference height between two point.
* Built Bench Mark and Temporary Bench Mark for several construction projects.
* To get the cross-section and longitudinal section to show the profile of soil especially for passage project. With that all the preparation will be done.
* To produce contour map for a location of construction.
* For works of setting out.
* Mark the slope of location for the several reasons such as a stream of water and other else.
Levelling or leveling is the measurement of geodetic height using a levelling instrument and a level staff. Difference levelling is the process used to determine a difference in elevation between two points. A level is an instrument with a telescope that can be levelled with a spirit bubble. The optical line of sight forms a horizontal plane, which is at the same elevation as the telescope crosshair. By reading a graduated rod held vertically on a point of known...