Different Engineering Surveys for Highway Alignment

Before finalizing highway alignment of any highway project, different types of engineering surveys are to be carried out. 

This different surveys are,

1. Map Study 
2. Reconnaissance 
3. Preliminary Survey 
4. Final and Detailed Survey 

What is Map Study ?

 By using topographic map of the particular area most likely routes of the road can be suggested. Number of possible alignments are drawn on map considering maximum utilization and avoiding obstructions like as rivers, hills, valleys etc.

Alignment should be such that, It should pass through minimum number of obstructions and alignment should be crossing maximum number of population area (for utilization purpose). Approximated location of bridges site for crossing rivers, avoiding bend of river, if any.

In short map study gives the rough guidance of the different routes.

Reconnaissance :

The second most important stage of survey for highway alignment is reconnaissance, it is carried out to examine the general character of the area for deciding the most feasible routes for detailed studies. It is done by visiting at site location for detailing of features like Valleys, Ponds, Lakes, Marshy Land, Ridge, Any permanent structures etc, which are not available in the map. The details like as approximate values of gradient, length of gradient and radius of curve of alternate alignments and also the number and type of cross drainage structures, maximum flood level and natural ground water level along the probable routes collected during reconnaissance.

Preliminary Survey :        

The main purpose of this survey is to survey the various alternate alignments proposed after the reconnaissance and the collect all the necessary physical information and details of topography, drainage and soil. It also includes all types of surveys i.e. Topographical Survey, Leveling, Chain Survey, Drainage Survey, Traffic Study, Soil Investigation etc. The comparison between different proposals in view of the requirements of a good alignment and finalise the best alignment from all consideration. 

In short Preliminary Survey is simply means analysis of reconnaissance and finalizing the best highway alignment.

Final and Detailed Survey :

The alignment finalized after the preliminary survey is to be first located on the field by established the centre line.This is done accurately by using instruments. The final route selected after the preliminary survey is surveyed and located on the ground. Also data for finalised highway alignment should be elaborated and prepared for Planning, Design, Material Estimate, Cost Estimation etc finally DPR is prepared.