Before a high way alignment is finalized in a high way project the basic activities have to be carried out. The surveys may be completed in four activities. The first three activities considered all possible alternate alignments as discussed in various requirements. The fourth stage is meant for the detail survey of the selected alignments.
The major activities are:
– map study
– Reconnaissance survey
– Preliminary survey
– Final location and detailed survey
When the question of constructing new alignment is raised due to public demand or some strategic reason a primary investigation is carried out to examine whether this road is necessary. The following points are to be kept in mind at the time of such investigations.
1. Total population benefited by the project
2. Number of villages, towns, industrial places etc to be connected
3. Agricultural products, industrial products, minerals etc are likely to be conveyed through the proposed road and thus help the development of trade in the country.
4. Prospect of tourism, if any etc.
If the topographic map of the area to be surveyed is available, it is possible to suggest the possible alignments of the road. The main feature like rivers, hills and valleys are also shown on those maps. That is the need of careful study of such maps that is found on the area alignment is supposed. And it is help full to have an idea of several possible alternate routes so that further details of those may be studied latter at the site. The probable alignment can be located on the map from the following details available on the map.
I- Alignment avoiding valley, ponds or lakes.
II- when the road has to cross a raw of hills, possibility of crossing through pass.
III- approximate location of bridge site for crossing rivers, avoiding bend of the river, if any.
IV- when a road is to be connected between two stations, one of the top & the other on the foot of hill then alternate routes can be suggested.
While making map study the following points should be considered
1. The proposed alignment should connect the sufficient number of villages, towns.
2. The alignment should be taken in such away that unnecessary cutting banking should be avoided.
3. If the alignment crosses the river, it should do so perpendicularly through the shortest width of the river.
Reconnaissance survey is the key to any project and the most important in the work of survey, and it is the first inspection about the area, after the inspection one has got some idea regarding the mental map about the terrain and features of the ground. Having said this reconnaissance is the third stage of surveys for high way location, and it is important to examine the general character of the area for deciding the most feasible routes for detailed studies. A field survey party may be inspecting a fairly broad stretch of land along the proposed alternative routes of the map in the field. During reconnaissance,
A. The distance along the alignment are measured approximately by facing
B. The objects and nature of ground on both sides of alignment, up to 50m are noted on the field book
C. Obstacles like religious places or valuable structures, if any should be suitably crossed over.
D. All other important points like rail way crossing, canal crossing etc should be noted.
There are two aspects of reconnaissance survey. These are:
• Office reconnaissance
• Field work report
I-Office based Analysis
The first step in reconnaissance survey is to collect the best possible available maps of the area under investigation, such as the surveyed maps and aerial photographs. (For this Ethiopian mapping authority and city administration) the area under investigation should be examined in detail and very carefully.
If it is a route surveying keeping in the general photography of the territory in the mind various possible routes may be marked on these maps in pencil and the area under consideration should be examined in detail by going over the various proposed routes. And some more relevant information can be also be marked on the map.
ii Field based Observations
The 2nd aspect of reconnaissance survey is field observations. This includes rapid observation of height, distance and gradients which are made with an aroid barometer (in high hills) clinometers in low undulations, pedometer paling, etc.
The directions are fixed by observing magnetic bearings using a magnetic compass. The reconnaissance survey should begin at one of the end stations and precede in general direction of the other.
In general a reconnaissance survey should be containing the following information.
1- Map and photographs of the area and accurate topographic of the area under investigation.
2- Approximate valet gradient
3- Length of the gradient and radius of curves of alternate alignment.
4- Number and type of cross droning structure and maximum flood level.
5- Boil invest action of the area that argument is proposed.
6- The terror type of the area.
7- Bovey of road construction material availability
8- Amount of expected earth work.
9- The approximate cost of construction.