Surveying and Principles of Surveying

Surveying

The practice of measuring angles and distances on the ground so that they can be accurately plotted on a map

Principles of Surveying

The fundamental principles upon which the surveying is being carried out are

•         Working from whole to part.

•         After deciding the position of any point, its reference must be kept from at least two permanent objects or stations whose position have already been well defined.

The purpose of working from whole to part is

•         to localise the errors and

•         to control the accumulation of errors

Classifications of Surveying

Based on the purpose (for which surveying is being conducted), Surveying has been classified into:

•Control surveying : To establish horizontal and vertical positions of control points.

•Land surveying : To determine the boundaries and areas of parcels of land, also known as property survey, boundary survey or cadastral survey.

•Topographic survey : To prepare a plan/ map of a region which includes natural as well as and man-made features including elevation.

•Engineering survey : To collect requisite data for planning, design and execution of engineering projects. Three broad steps are

1)  Reconnaissance survey : To explore site conditions and availability of infrastructures.

2) Preliminary survey : To collect adequate data to prepare plan / map of area to be used for planning and design.

3)   Location survey : To set out work on the ground for actual construction / execution of the project.

•Route survey : To plan, design, and laying out of route such as highways, railways, canals, pipelines, and other linear projects.

•Construction surveys : Surveys which are required for establishment of points, lines, grades, and for staking out engineering works (after the plans have been prepared and the structural design has been done).

•Astronomic surveys : To determine the  latitude, longitude (of the observation station) and azimuth (of a line through observation station) from astronomical observation.

•Mine surveys : To carry out surveying specific for opencast and underground mining purposes

Chain Survey

Chain survey is the simplest method of surveying. In this survey only measurements are taken in the field, and the rest work, such as plotting calculation etc. are done in the office. This is most suitable adapted to small plane areas with very few details. If carefully done, it gives quite accurate results. The necessary requirements for field work are chain, tape, ranging rod, arrows and some time cross staff.

Survey Station:

Survey stations are of two kinds

1.    Main Stations

2.    Subsidiary or tie

Main Stations:

Main stations are the end of the lines, which command the boundaries of the survey, and the lines joining the main stations re called the main survey line or the chain lines.

Subsidiary or the tie stations:

Subsidiary or the tie stations are the point selected on the main survey lines, where it is necessary to locate the interior detail such as fences, hedges, building etc.

Tie or subsidiary lines:

A tie line joints two fixed points on the main survey lines. It helps to checking the accuracy of surveying and to locate the interior details. The position of each tie line should be close to some features, such as paths, building etc.

Base Lines:

It is main and longest line, which passes approximately through the centre of the field. All the other measurements to show the details of the work are taken with respect of this line.

Check Line:

A check line also termed as a proof line is a line joining the apex of a triangle to some fixed points on any two sides of a triangle. A check line is measured to check the accuracy of the framework. The length of a check line, as measured on the ground should agree with its length on the plan.

Offsets:

These are the lateral measurements from the base line to fix the positions of the different objects of the work with respect to base line. These are generally set at right angle offsets. It can also be drawn with the help of a tape. There are two kinds of offsets:

1) Perpendicular offsets, and

2) Oblique offsets.

The measurements are taken at right angle to the survey line called perpendicular or right angled offsets.

The measurements which are not made at right angles to the survey line are called oblique offsets or tie line offsets.

Procedure in chain survey:

1. Reconnaissance:

The preliminary inspection of the area to be surveyed is called reconnaissance. The surveyor inspects the area to be surveyed, survey or prepares index sketch or key plan.

2. Marking Station:

Surveyor fixes up the required no stations at places from where maximum possible stations are possible.

3. Then he selects the way for passing the main line, which should be horizontal and clean as possible and should pass approximately through the centre of work.

4. Then ranging roads are fixed on the stations.

5. After fixing the stations, chaining could be started.

6. Make ranging wherever necessary.

7. Measure the change and offset.

8. Enter in the field the book.