How To Surveying and levelling of Longitudinal Section Or Profile Section.

Object- Main object of the longitudinal levelling or profile is to determine the undulation of the ground surface along the predetermined line at regular interval. It is used in the center line of road, railway, pipeline, canal, curve setting, finding the gradient of the proposed road. It is consist of a series of single line in chaining direction.

REQUIREMENTS- (a) Bench Mark near the chain line.
(b) Surveying and levelling instruments.
(c) Drawing materials or software.
Benchmark- Require one benchmark near the chain line for determining reduced level.
Benchmark:- A benchmark (B.M) is a fixed reference point of known
elevation.
There are four types of benchmark.:-
(i) G.T.S Benchmarks are established with very high precision 100 km intervals of all over the country their position and elevations above standard datum. They are also shown in the G.T.S map.

(II) Permanent benchmark:- Permanent benchmarks are established between the G.T.S benchmark at the interval of the 10 km by government agencies. The position of benchmark clearly defined on such as top of proper wall, A Bridge or A culvert, or any permanent structure.

(iii) Temporary Bench Mark:- Temporary benchmarks are reference points established at the end of day work. The work when resumed is continued with reference to these benchmark.

(iv) Arbitrary BenchMark:- They are the reference points whose elevations are arbitrarily assumed. They are used in small levelling operations.
(b) Surveying and levelling instruments:- two types of instrument require for longitudinal levelling.
(ii) For distance and bearing measurement (i) For measure elevation.
(iii) For above first, generally, use - For distance chain or tape and forbearing theodolite or compass,
But nowadays large scale of electronic and digital modern instrument available in surveying and levelling field. Advantage of using modern type of instrument saves time, labour and cost.

Square, pen, pencil or any survey software etc,

Procedure:-

Image of center line
The ABC be the centre line of the road. Mark the points on the ground at required intervals Establish the two T.B.M near the A and the B side to check works.Set the instrument right side of the line AB and make carefully temporary adjustment Kept The staff is vertical on T.B.M nearly A. Read and book first staff reading as a backside reading and book in backside column in level book. Take the staff reading on the marked points on the ground. Booked the Staffs reading as intermediate side in the level book. According to the nature of the ground change point (C.P) make both sides of Centre line and booked in the level book as a foresight. set the instrument on L2 and L3 both side of Centre line. After completing the take reading. Work should be closed on nearest theT.B.M
for check purpose.

Image position of staff point and instrument station

Calculation and booking of the longitudinal levelling

Drawing of longitudinal (PROFILE )section

The following points should be born in mind at the levelling.
1. The back sight and fore side distance should be equal approximately.
2. The position of important features, such as nalla, river, road etc should locate their actual
dimension.

The drawing also draw by survey software.