What is Surveying and Types Of Survey ? Explain Classification of Survey In Civil Engineering

SURVEYING

* Surveying is the art of making measurement of objects on, above or beneath the ground to show their

relative positions on paper.

* The earth is an oblate spheroid, the length of equatorial axis being 12,756.75 km and polar axis

12,713.80 km.

* The gravitational force is always directed towards the centre of the earth and the plumb line is

known as vertical line. The line perpendicular to vertical is the horizontal line.

* All lines lying on the earth’s surface are curved lines and all triangles are spherical triangles.

However, the length of an arc of 1.2 km on earth’s mean surface is only 1 mm more than the

straight line connecting those two points.

* If the area to be surveyed is small, the curvature of earth may be neglected and all plumb lines

treated as the parallel to each other. All triangles in survey are treated as plane triangles.

* The survey in which earth’s curvature is considered is called Geodetic Surveying and the survey in

which earth’s curvature is neglected is called Plane Surveying.

Classification

1. On the basis of nature of the field

(a) Land survey:

(i) Topographic survey

(ii) Cadastral survey

(iii) City survey

(b) Marine or hydrographic survey

(c) Astronomical survey

2. On the basis of object of survey

(a) Engineering survey:

(i) Reconnaissance survey

(ii) Preliminary survey

(iii) Location survey

(b) Military survey

(c) Mine survey

(d) Geological survey

(e) Archaeological survey

3. On the basis of instruments used

(a) Chain survey

(b) Compass survey

(c) Plane table survey

(d) Theodolite survey

(e) Tacheometric survey

(f) Modern surveying

(g) Photographic and aerial surveying

4. Classification on the basis of methods employed

(a) Triangulation

(b) Traversing

Scales

* If 1 mm on the paper represents 1 m on the ground, then the scale is

1 mm = 1 m

or 1 : 1000

or representative factor (RF) = .

* The scale of a map is considered

(i) Large, if it is greater than 1 mm = 1 m. (i.e., RF > 1/1000)

(ii) Intermediate if RF =

(iii) Small if RF = or less

* Scales recommended for some of the works are

(i) Building sites: RF = or less

(ii) Town planning schemes: RF =

(iii) Cadastral maps: RF =

(iv) Route surveys: RF = .

* Types of graphical scales:

1. Plain scale 2. Diagonal scale.

In plain scale only units and tenths can be shown whereas in diagonal scales, it is possible to

show units, tenths and hundredths.

* Vernier is a device to measure the fractional part of smallest division on main scale. Types of

vernier scales are

(i) Direct (ii) Retrograde

In both cases least count =

where d = value of smallest division on the main scale

and n = number of divisions on the vernier

.There are special forms of verniers also

(i) Double vernier

(ii) Double folded vernier

(iii) Extended verniers

* In any map graphical scale as well as RF should be shown, since paper may shrink and actual length

may be more than what it shows. In such case

Shrinkage factor =

* Methods of locating a point in plain survey.

(i) By linear measurements

(ii) By linear and angular measurements

(iii) By angular measurements only

* Principles of surveying:

(i) Work from whole to part

(ii) Take extra care in fixing positions of new control points, i.e., have check lines and tie lines.

* The Survey of India is the oldest department of Government of India. It was established in 1767 by

East India Company. Its headquarters is in Dehradun and has got 18 Directorates. They have

prepared topographic map of the whole country and have established GTS (Great Topographic

Survey) bench marks at several places all over the country. The entire area covered by India is

divided into 4° × 4° longitude and latitude and each grid is numbered. Each grid is further divided

into 1° × 1° longitude and they are numbered. The scale used for 4° × 4° grid map is 1 : 25000 and

the scale for 1° × 1° grids is 1 : 50,000. The 1° × 1° grid is further divided in 15¢ × 15¢ grids and

the scale used are 1 : 50,000 to 1 : 25,000.