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Understanding Engineering Surveying, (Alignment and Route Location). Steps/Procedure

In the course of road construction, before finalizing the Alignment of our highways, there are generally four (4) guidelines for the Alignment and the Route Location also known as the Engineering Surveying of the highway that must be carried out. These include

  1.     Desk Study Or Map Study  
  2.    Reconnaissance (Recce) Survey 
  3.    Preliminary Survey
  4.   Final Survey (Location Survey)


  1.  Desk Study or Map Study:-

           STEPS:
                                 i.      Get the topographic map of area (if available), the likely intended route of the road   may be marked on it.
                               ii.      Study all available information in the office for contours, ponds, valleys, lakes, mountain pass, bridge etc.
                              iii.    Study town planning master plan drawing if available
                             iv.      Also you can Study the Aerial photographs and remote sensing imagery of the area (if available) they are great source of information on topography, terrain, drainage etc.


      2     Reconnaissance Survey:-
             
     After desk study, Reconnaissance Survey is next, it start with a field inspection by walk or driving  or both and necessary information should be collected.it can be conducted in the following  

procedures:
                                 i.            Detail of route vis-à-vis topography of the area, whether its hilly or rolling or plain
                               ii.            Length of the road along various alternatives
                              iii.            Bridging requirements (number, length etc.)
                             iv.            Geometrics: 
·         Gradients that are feasible, specify the extent of deviation if any,
·         Curves and hair pin bends, etc.
                               v.            Right of way available
                             vi.            Existing means of communication i.e. car track, path, mule path etc.
                            vii.            Terrains and soil conditions i.e.
·         Geology of the area
·         Drainage characteristics of the area including area susceptible to flooding
·         General elevation of the road
·         Location of sand dunes.
·         Type and extent of vegetation, etc.
                          viii.            Climatic condition
                             ix.            Facilities/Resources



         3.      Preliminary Survey:

This is a relatively large scale investigation conducted to collect all physical information       which affects the proposed location of the new highway. During this phase of survey, the topographic   features and other features like houses, places of worships, etc. are tied to the transverse line. Longitudinal sections and cross-sections are taken and bench marks established. This data form the basis for determination of final center line of the road.

Procedures:
                                 i.            It starts with the running of a traverse along the selected route, adhering as far as possible to the probable final center line of the road, in difficult situations, a secondary transverse may be introduced.
N.B: Transverse consists of a series of straight lines with their distances and intermediate angles measured very carefully.
                               ii.            Transverse should be done with theodolite and all angles measured with double reversal method. The distance along the transverse line should be measured with metallic tape or chain.
                              iii.            Physical features like buildings, monuments, place of worships, schools rail line etc. that are likely to be affected by the project should be located by means of offsets measured from the transverse line.
                             iv.            Leveling work should be kept to the minimum. Generally, fly levels at 50m intervals, and at all intermediate breaks in ground should be taken along the transverse line.


      4.     Final Survey (Location Survey)
 
The purpose is to fix the center line of the road or selected alignment in the field and to collect additional data for the preparation of the drawings. if preliminary survey is properly done,final survey data collection will be limited

Procedure:
 
         i.            Staking (pegging) out the final center line of the road by means of a continuous transit survey
·         Process whereby the center line of the road as determined in the design office, is translated on the ground by means of a continuous transit survey and staking or pegging of the center line as survey proceed, fixed at 50m intervals in plain and rolling terrain, hilly, 20m intervals. All angles measured with theodolite

       ii.            Detailing leveling
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