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What is Benchmark in Surveying

Techno Upendra

what- is- the-bench -mark-in-surveying
spheroidal surface of  the earth

1.  Level Surface:- A level surface is any surface parallel to the mean spherical surface of the earth. Every point of level surface Is equidistant from the center of the earth. It is normal to the plumb line at all points.
2. A level line is a line in a surface. It is normal to the plumb line at all points.
3. A horizontal line is any line lying in the horizontal plane. It is a straight line tangential to a level line.
4.  A vertical line at any point is a line normal to the level surface.
example. Plumb line.
what -is- the -bench -mark- in -surveying
Datum surface

5. A datum line is any arbitrarily assumed level line from which vertical distances are measured.
6. The elevation of a point is its vertical distance above or below the datum.

7. The difference in elevation between two points is the vertical distance between the level surfaces passing through the two points.

8. Benchmarks are fixed references points. Which has known reduced level from reference to the datum line
Benchmarks are generally four types.
what- is-the- bench- mark- in- surveying

A. GTS Benchmark:- Great Trigonometry Survey  Benchmark is covered whole of country at large intervals.
It is done by the main survey department of the country. In India, it is done by a survey of India department.
In this benchmark is determined by the use of vertical angle and horizontal distance with considering combined correction due to curvature and ref erection. The article angles are measured with theodolite and horizontal distance are measured or computed from the triangulation method.The GTS
Bench mark base is Karachi.
what- is- the- bench -mark- in- surveying
permanent bench mark

B. Permanent Benchmark:- The RL of permanent bench is determined by reference to GTS bench mark and determined by government department .ex PWD, Railway etc. It is kept on permanent structure. For this leveling work is completed by fly leveling.
what- is- the- bench -mark- in- surveying
Auto level.

C. Temporary Benchmark :- these bench  mark established of end of work for next day to start work.
these are kept on non disturbed object.

D. Arbitrary  bench mark:- these bench mark are established for assumed R.L . This is used in small leveling work.

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