Explain types of surveys for railway track

The various surveys which are carried out during the construction of railway track can be divided into three parts:

1. Reconnaissance survey
2. Preliminary survey
3. Final survey

1. Reconnaissance survey:  This survey is the first survey which is carried out before the construction of any project. This survey is done when the place of construction is newly selected and has been never previously surveyed for any project.

The main purpose of the reconnaissance survey is;

1. To obtain basic knowledge of the land and construction project.
2. To obtain all the featured details of the land and its capabilities.
3. To obtain the multiple ways to complete the project and calculate the most efficient among them.

A reconnaissance survey collects information regarding the following:

1. General characteristics of the land
2. Local industries, land, forest, and the cultivated area around the construction site.
3. General conditions of the locality such as population density, distribution, nature of people, etc.
4. The number of imports and exports, their origin and destination and also their distribution.
5. Possibilities of new development schemes.
6. Surface formation of the ground.
7. Nature of the soil
8. Any river or lake in that part of the land.
9. Any hill or natural landmark in that part of the land.

Instruments used for reconnaissance survey:

Prismatic compass, Pedometer, Binocular telescope etc.

2. Preliminary survey:  This survey is done to finalise the most efficient and effective way to complete the task of construction.

The main purpose of the preliminary survey is;

1. To determine the greater accuracy in the cost estimation of the railway line involving the cost of removing the obstruction.
2. To determine the best way to proceed with the work most economically and effectively.
3. In a preliminary survey, a detailed map is prepared and cost estimation of every work is calculated and on the behalf of that the most economical, efficient and effective way is chosen for the construction o railway line.
4. This survey is carried out with great precision.

Instruments used for the preliminary survey:

Plane table, Dumpy level, Prismatic compass, Tachometer etc.

3. Final survey: Final survey is used for locating the centre line for the construction of the railway line. Based on that centre line, the detailed survey is carried out along the path selected as the most economical and effective way for the construction of the railway line.

As soon as the final survey is completed, the construction work is executed.

Instruments used for the Final survey:

Theodolite, Steel tape, etc.