Saturday, May 25, 2019

Professional Road Alignment Survey: Technical Norms and Specifications for

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Road Alignment Survey

 1. Carry out reconnaissance survey and alignment selection of a road corridor about 700m or more.

2. Starting and end point of road, location of bridge site will be provided at the site.

3. Road alignment selection i.e. IP selection shall be carried out considering the obligatory
points, permissible gradient, bridge site, balancing cut and fill, shape of the valley and cross drainage, lateral slopes, geometry of horizontal and vertical curves, etc.

4. Alignment must not be selected beyond 12% gradient of the existing ground surface.

5. Radius of the horizontal curve should not less than 12 m while assuming the radius of the
horizontal curve, select the radius in the multiple of 5 or 10.

6. Point of commencement (T1) and point of tangency (T2) must not be located within the
bridge axis. Start and finish of curves must be totally outside the bridge axis end points.

7. Avoid subsequent reverse curve in road alignment.

8. Deflection angle should not be greater than 90
9. Two successive curves must not be overlapped.

10. Measure Bearing of the starting leg. To compute bearing of next leg, record deflection   angle with respect to preceding leg.

11. Setting out of horizontal curve is not necessary for  less than 3 degree deflection angle but compute the chainage as usual manner

12. Theodolite team shall carry out the detailed survey of the road alignment. Theodolite team will mark pegging at 15m interval along the centre line of road and at curve points BC, MC and EC for longitudinal section as well as X-section. Set horizontal curve by fixing BC, MC and EC. Theodolite team should fill up three field book (FB) separately such as tacheometry FB, horizontal curve FB and detail sketch.

13. Carry out levelling survey for longitudinal section along the centre line at 15 m interval, at abrupt change point and at the curve point BC, MC and EC. Establish TBM at approximately 500m interval and near cross drainage. Close the levelling survey and check the RL at job site immediately. Permissible error of closure for levelling must not be greater than
±25 (K)^0.5 mm.

14. Perform cross section survey either by levelling instrument or by levelling staff and tape along the road alignment at 15m interval and at abrupt change of the topography as established by the theodolite team. During the field survey, draw neat and clean free hand dimensional the cross section. Coverage width of the cross section must not be less than 10mm on  either side (left and right) from proposed centre line of the road and at 5m regular interval as well as other salient points from centre line.

15. Prepare a road corridor plan in 1:500 scale showing 5m formation width, 20m right of way (corridor width 10m left and 10m right) from proposed centre line, location of intersection point (IP), geometry of horizontal curve with chainages of BC, MC, EC chainages of drainages, chainages of centre line details and other details such as vegetation, forest, cultivation, barren land etc.

16. Draw longitudinal section of road centre line [horizontal scale 1:1000, Vertical axis 1:100]. Draw the working profile i.e. formation level assuming balancing of cut and fill in between economical haul distances. Draw cross section [horizontal scale vertical scale 1:100] of existing ground surface and show the formation level and width (5m) assuming side slope 2:1 in filling and 1.5:1 in cutting. (H:V)

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