2. Setting Out a Simple Curve on the Ground by Offset From the Tangent

Setting out a Simple Curve on the Ground by Offset from the Tangent

After the field operations, the students should know the method of laying out a simple curve by offset from the tangent and applied it to set out the curve on the ground.

3.1. 3.2. 3.3. 3.4.

Theodolite/Total Theodolite/Total Station with Tripod Steel Tape Range Poles/Stadia Rods Marker (Chalk)

4.1. 4.1.1. Prior to the field operations, prepare the necessary survey data in setting out the simple curve, such as: a.Length a. Length of the curves (L c) b.Length b. Length of the tangent distance (T) c.Length c. Length of the long Chord (L) d.Station d.Station PC e.Station e.Station PI f.Station f.Station PT g.Intersection g. Intersection angle (I) h.Radius h. Radius of the curve (R) i.Degree i. Degree of the curve (D, using arc basis) j.Deflection j.Deflection angle k.Possible k. Possible number of full stations and plus stations l.Components l. Components of Y and X and Y ’ and X ’ for the backward and forward tangents, respectively. 4.1.2. During the field operation, set and level the instrument over the intersection of the tangents (PI) and take a back azimuth shot on the back tangent then measure the necessary distance from the occupied station to locate 1st vertex. 4.1.3. Measure a tangent distance T from the vertex to locate and set a hub at PC. 4.1.4. Swing the instrument towards the direction of the forward tangent and measure the distance to locate the 2 nd vertex. 1

4.1.5. Measure the tangent distance T from that vertex to locate and set out station PT. 4.1.6. Set the 1st full station of the curve by tracing the point on the ground from PC. Measure a distance Y (for the 1 st station) along the backward tangent and from this point measure the corresponding distance X perpendicular to the said tangent. Mark this point on the ground as 1 st station. 4.1.7. Follow the same process for the next full stations and plus station. 4.1.8. Set the last full station of the curve by tracing the point on the ground from PT. Measure a distance Y’ (for the last full station) along the forward tangent and from this point measure the corresponding distance X’ perpendicular to the said tangent. Mark this point on the ground as last full station. 4.1.9. Follow the same process for the foregoing full stations and plus station. 4.1.10. After marking all the points on the ground, set out the simple curve by connecting the points smoothly using a marker. Take photographs for documentation.

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Table 6-1

Survey data for the Simple Curve (Offset from the Backward Tangent) STATION Y X

Table 6-2

Survey data for the Simple Curve (Offset from the Forward Tangent) STATION Y’ X’

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