CiIvil Surveying - Survey Adjustments

**SURVEY
ADJUSTMENTS**

**1.
****Permanent Bench mark: **

These are established by different government departments like
PWD, Railways, Irrigation etc., The RL of these points are determined with
reference to G.T.S Benchmarks. Points on rocks, culvert, gate, pillars etc.

**2.
****Temporary Bench mark: **

These are established temporarily whenever required. These are
generally chosen to close the day's work
and to start the next days. Points on roofs, walls, basements etc

**3.
****Arbitrary Bench Mark: **

When the
RL of some fixed Points are assumed, they are termed a arbitrary Bench mark

**4.
****Extension of baseline: **

The length of baseline is usually not greater than 10 to 20
km. As it is not a often possible to sewed a favorable sight for a longer base.
They usually practice is therefore to use short base & Extend it by means.
Of forming well conditioned triangles.

**5.
****Trigonometrical levelling: **

Trigonometrical levelling is the process of determining the
differences of elevation of the given station from observed vertical angles and
known distance.

**6.
****Axis Signal correction : **

If the height of the signed is not the same as that of height
of the instrument axis above the station, a correction known as the axis signal
correction or eye & objective correction is to be applied.

**7.
****Geodetic Surveying : **

In this surveying, the shape of the earth is taken into
account and all the lines lying in the surface are curved lines. It is used for
area greater than 250km^{2}. It is accurate. It is conducted by great
geometrical survey of India.

**8.
****Baseline : **

The Base line is laid down with great accuracy of measurement
& alignment as it forms the basis for the computations of triangulation
system the length

of the
base line depends upon the grades of the triangulation.

**9.
****Laplace Station : **

At certain station, astronomical observations for
azimuth & longitude are also made on the station is called Laplace station
.

**10. Triangulation :**

Triangulation is nothing but the system consists of not of
interconnected triangles. In this method, knowing the length of one side and
three angles, the length of other two sides of each triangle can be computed.

**11. Signals :**

A Signal any object such as a pole target erected at a station
upon which a sight is taken by a observer at another station.

**12. Satellite Station :**

A subsidiary station is established as near the true or
principal station as possible, the station so established is called a satellite
station or eccentric station or false station.

**13. Reduction to centre:**

If the true station were occupied by computing the corrections
and apply them algebraically to the observed values is generally known as
reduction of centre.

**14. Base net:**

A series
of triangles connecting the baseline to the main triangulation is called base
net.

**15. Bench marking :**

It is a
fined reference point of known elevation.

**16. ****Types of
Bench Mark: **

Great
Trigonometric survey Bench mark

Permanent
Bench mark

Arbitrary
Bench mark

Temporary
Bench mark

**17. Equipments used for base line measurement:**

Marking stakes or tripod Straining device Supporting stakes or
tripod Steel tape

**18. Methods used to measure baseline**

Rigid bar
method

Wheeler's
method

Jaderin's method

Hunter's short
base method

Tacheometric
method

**19. ****Two types
of Trigonometrically leveling: **

Plane Trigonometrical levelling Geodetic Trigonometrical
levelling

**20. ****Apparatus
used in Baseline: **

Rigid
Bars

Flexible
apparatus

**21. Corrections made while calculation of true
length**

Correction
for absolute length

Correction
for temperature

Correction
for pull or tension

Correction
for Sag

Correction
for Slope

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