JNTU B.Tech II SURVEYING AND GEOMATICS Previous Question Paper (March - 2021 - R18)

Chain surveying is the simplest method of surveying, where only linear measurements are made in the field using a chain or tape. It is primarily suitable for small areas with open ground and simple details.

The essential instruments used in chain surveying include:

• Metric Chain: Used for measuring distances, typically 20m or 30m long.
• Tape: Metallic or steel tapes for accurate measurement of offsets.
• Arrows: Used to mark the end of each chain length on the ground.
• Ranging Rods: Used to mark positions and ensure straight lines.
• Cross Staff/Optical Square: Used for setting out right angles to take offsets.
• Pegs: Wooden stakes used to mark survey stations.
• Field Book: For recording measurements and sketches.

The field execution involves the following steps:

1. Reconnaissance: An initial inspection of the area to identify survey stations and plan the layout of the main survey lines.
2. Station Marking: Fixing survey stations at strategic points using pegs or ranging rods.
3. Ranging: Establishing intermediate points on the survey line to ensure a straight path between stations.
4. Chaining: Measuring the length of the main survey lines and recording them in the field book.
5. Offsetting: Taking lateral measurements from the main survey line to locate details like buildings, fences, or trees. Offsets can be perpendicular or oblique.

A neat sketch would depict a main survey line (base line) connecting two stations, with perpendicular offsets measured to various features on either side of the line, recorded systematically in the field book using a double-line or single-line entry system.

To determine the correct magnetic bearings, we must first calculate the observed included angles and check for local attraction. The difference between forward bearing (FB) and back bearing (BB) should be 180° for a station free from local attraction.

1. Calculation of observed included angles:

Sum of interior angles = 140° + 131° + 120° 55' + 99° 15' + 50° 05' = 541° 15'. The theoretical sum for a pentagon is (5-2) × 180° = 540°. The error is +1° 15'. Correction per angle = -1° 15' / 5 = -15'.

2. Corrected interior angles:

• A: 50° 05' - 15' = 49° 50'
• B: 140° 00' - 15' = 139° 45'
• C: 131° 00' - 15' = 130° 45'
• D: 120° 55' - 15' = 120° 40'
• E: 99° 15' - 15' = 99° 00'

3. Corrected bearings (starting from line AB as correct):