Setting out simple circular curve-

Two theodolite method

Aim:

To set out the simple curve by two theodolite method.

Instruments Required :

Two Theodolites and Ranging rods.

Principle: The angle between the target and the chord is equal to the angle which that chord subtends in opposite segment.

Given : Chainage of the curve , angle of intersection and Radius of curve (R).

Procedure :

1. Prepare a table of deflection angle for the first sub chord, Normal chord and last sub chord .

2. Set up one theodolite over T

_{1}and another over T_{2}.3. Direct the instrument at T

_{1}to the ranging rod at the point of intersection B and bisect it.4. Direct the instrument at T

_{2}to the first target point T_{1}and bisect it.5. Set the verniers of both the theodolites to read zero.

6. Set the first deflection angle (D

_{1}) on both theodolites so that the telescopes are in the direction of T_{1}D and T_{2}D respectively.7. Move the ranging rod until it is bisected by the cross hairs of both the theodolites to locate the point D on the curve .

8. Set the second value of deflection angle on both the theodolites and repeat the step 7 above to get the location of E.

9. Continue the process for obtaining the locations of other points in a similar manner.

Calculation :

*Given :*

Chainage at B, R, f

BT

_{1}= BT_{2}= R tan f/2 T

_{1}T_{2}= 2R sin f/2Length of curve T

_{1}T_{2}= pRChainage at T

_{1}= Chainage at B – T_{1}BChainage at T

_{2}= Chainage at T_{1}+ T_{1}T_{2}Divide the length of the curve into normal Chords(30m) and subchord (C

_{1},C_{2})

*Deflection angles :* First subchord = 1718.9

Normal chord = 1718.9

Last subchord = 1718.9

Result :

The given simple curve is thus set out.

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