Chain surveying, It is a method of Surveying in which no angles are measured but the only linear measurement is taken in the field by using a chain or tape measure. It measures a series of straight lines on the ground with a chain or tape measure and all fixed points relative to the line of traverse either by right angles (offsets) or tie lines.
Equipment used in chain surveying.
- The chain is made up of steel wire which is divided into links and togs (rings) to facilitate folding.
- It is sometimes used as a unit of measurement
- It has brass handles at both ends for easy handling. The link is 0.2m or 200mm in diameter.
- The length is 20m or 30m.
- Steel tape
- Linear tape
A tape is made from fiberglass or a steel strip and is 10m, 20m or 30m in length graduated in 10mm divisions and numbered at each 100mm (10) divisions It is used for measuring short distances
iii. Ranging poles
are made up of wood or light metal and measure about 2m long at the top. The equipment has steel shades on its legs so it can be stuck into the ground. Ranging poles are painted red and white so that they can be easily seen even from a distance. They are used for making stations.
Arrows are made of steel wire of diameter 4mm and their ends are bent into a circle where red cloth is tied to facilitate visibility. They are used for showing points on the ground. They are also used for counting the number of chains while measuring a chain line.
Pegs are made of wood 40 mm square by 50 cm long and are used for permanently marking positions during survey
vi. Surveyors’ band
The surveyor’s band is made of a steel strip which is rolled into a metal frame with a winding handle. It is 30m, 50m or 100m long. Is used in projects where more accuracy measurement is required.
vii. Cross staff
The cross staff is made of metal or wood with eye slips at right angles and is used to measure right angles from the line of traverse
Notebooks are used during field work to record data obtained. The notebook should be of good quality and 150 mm x100 mm in size
ix.A hard pencil and a rubber Hard pencils are used for drawing in the field and a rubber is used to erase mistakes or errors which are made. A pencil should be HB or HHB.
Methods and procedures involved in chain survey
- A survey team involves three people, the leading chainman or leader, the follower and the booker.
- The chain is thrown to extend it and disentangle any knots
- The leader takes ten arrows and a ranging rod, and the follower takes a ranging rod
- The follower erects his ranging rod/pole at the first base point and places a brass handle of the chain against the ranging rod.
- A leader straightens the chain and inserts an arrow at end of the brass handle. Offsets and tie lines can now be taken.
- The leader drags the chain so that the follower’s end is on the leader’s arrow; the follower moves to another point and places his ranging pole behind the arrow. This procedure is then repeated.
The importance and usefulness of chain surveying
- It is suitable for small areas of fairly open ground.
- It is used to fill in details on a map whose large features have been surveyed by other methods.
- It is used in mapping small areas of flat or near-flat ground and associated objects, for example paths, roads and railways.
- It is used in adding detail to existing plans or large maps.