What is reconnaisance survey

It’s a brief and rudimentary examination of the area between the projected alignment’s terminal stops. The survey portions capture extra information quickly using just relatively simple instruments such as an Abney level, a tangent clinometer, and so on. All relevant data not available on the map is gathered and recorded. A few alternate alignments may be chosen for further examination when the details obtained during the reconnaissance are studied.

The following are the details to be collected during reconnaissance:

i) Permanent structures and other barriers along the path that are not visible on the map, such as valleys, ponds, lakes, marshy areas, ridges, and hills.
ii) The number and kind of cross drainage structures, the greatest flood level, and the average groundwater level along the most likely pathways are all factors to consider.
iii) Approximate gradient values, gradient lengths, and curve radius of alternate alignments.
iv) Type of soil along the routes
v) Construction material sources the alignment proposed after analysis may be revised or even modified completely based on the information gathered during the reconnaissance.

What is the function of soil as a highway subgrade?

• Maintaining the subgrade above the highest groundwater level
• To avoid pavement damage caused by surface water from adjacent land
• To reduce the chance of capillary water harming the pavement layers.
• Maintaining the highway’s design standards in terms of vertical alignment