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Which of the following obstacles is during setting out of curve ?
P.I is inaccessible
P.C and P.T are inaccessible
In chaining occurs
All of the above
All of the above
During the field setting out of circular curves in surveying, field conditions like obstacles, dense vegetation, steep terrain, or water bodies often prevent direct measurements. Common obstacles include cases where the Point of Intersection (P.I) is inaccessible, the Point of Curve (P.C) or Point of Tangency (P.T) are inaccessible, or chaining along the curve line is obstructed.
During the field setting out of circular curves in surveying, field conditions like obstacles, dense vegetation, steep terrain, or water bodies often prevent direct measurements. Common obstacles include cases where the Point of Intersection (P.I) is inaccessible, the Point of Curve (P.C) or Point of Tangency (P.T) are inaccessible, or chaining along the curve line is obstructed.
T=Rtan(2╬ФтАЛ) тАФ Tangent length calculation
L = \frac{\pi R \Delta}{180┬░ тАФ Length of curve
╬┤nтАЛ=1718.9├ЧRCnтАЛтАЛ тАФ Deflection angle in minutes for chord CnтАЛ
When obstacles occur, indirect surveying methods are applied using geometry and trigonometric relationships. For an inaccessible P.I, auxiliary points are marked on tangents to form a triangle and calculate the deflection angle ╬Ф. When P.C or P.T is inaccessible, layout is performed using offset methods from tangents or intermediate points, or by calculating modified deflection angles.
When P.I is inaccessible, two auxiliary points A and B are selected on the rear and forward tangents respectively.
When P.C is inaccessible, curve setting starts from an intermediate point or uses long chord offsets.
When chaining occurs across an obstacle (e.g., river), offset methods or triangular surveying are used to pass the obstacle.
Indirect methods permit accurate curve setting even in harsh topography.
Theodolite and total station methods significantly reduce manual field errors around obstacles.
Requires additional auxiliary measurements and calculations in the field.
Higher risk of cumulative error if auxiliary baseline measurements are inaccurate.
Highway alignment through mountainous regions or built-up urban zones.
Railway track location across river crossings and forest terrain.
Option A: P.I (Point of Intersection) is inaccessible when it falls in a lake, deep canyon, or inside a building structure.
Option B: P.C (Point of Curve) and P.T (Point of Tangency) can be inaccessible due to localized terrain obstructions.
Option C: Chaining obstacles occur when physical obstructions (like rivers or marshland) cross the curve line.
D is correct тАФ All listed conditions represent common physical obstacles encountered while setting out simple circular curves in field surveying.
For competitive exams like GATE/ESE, always remember that when P.I is inaccessible, the deflection angle ╬Ф=╬▒+╬▓, where ╬▒ and ╬▓ are internal angles of the triangle formed with the auxiliary line.
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