setting out simple circular curve - rankine's method of tangential deflection angles or single theodolite method

Aim:

To setout the simple curve by single theodolite method.

Instruments required:

Theodolite, Ranging rods, chain, arrows and pegs

*Principle:*

*Deflection angle:* The angle between the back tangent and the chord joining the point of commencement of the curve and the other point on the curve

Procedure:

1. Prepare a table of deflection angles for the first subchord,normal chord and last subchord.

2. Set up a theodolite over T

_{1}. Direct the telescope to bisect the point of intersection(B), with both plates clamped to zero.3. Release the vernier plate and set angle 1 on the vernier using

4. Point the zero end of the tape at T

_{1}and an arrow held at a distance C_{1}along it and swing the tape around T_{1}till the arrow is bisected by the cross hairs to fix point A.5. Set the deflection angle .

where, d

_{2}= 1718.9 x C_{2}/R min., so the line of sight is along T_{1}B6. With zero end of the tape pinned at A and an arrow held at distance AB = C

_{2}along it and swing the tape around A till the arrow is bisected by the cross hairs thus fixing the point B.7. Repeat steps 5 and 6 till the last point T

_{2}is reached.

*Check:* The last point so located must coincide with the point of tangency (T

_{2}) fixed independently by measurements from the point of intersection.Result:

The given simple curve is thus set out.

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