Chain surveying is the sort of surveying in which only linear measurements are selected in the jobsite.
This type of surveying is undertaken for surveys of small span to specify the boundaries of plot of land to detect the existing features on them.
Chain surveying is the simplest form of survey in which surveying area is segregated into a number of triangles and the sides of different triangles are calculated directly in the field through a chain or a tape and no angular measurements are chosen. Chain is most recommended for initial survey process.
Chains stands for the measuring devices which are applied in surveying. These are produced with the 100 links of 4mm galvanized mild steel wire. These links are attached with 3 circular or oval wire rings. These rings make the chains flexible.
The chain comprised of several small segments to manage or study the measurements.
At the ends chain contains brass handle with swivel joint to simplify the process for rolling or unrolling the chain devoid of twisting and knots.
At each 10th link is arranged with a total of one teeth, 20th link with a total of two teeth and so on till 40th link. With these arrangements, the reading of measurements can be taken efficiently.
At the center of the chain, there is a circular talley used for easy reading.
Chain surveying devices: 1. Chain, 2. Tape, 3. Arrows, 4. Ranging Rods, 5. Offset Staff, 6. Optical Square
Types of Chains utilized in Surveying - The chains are categorized as follow depending on the length of the chain:
Metric chains, Steel band or Band chain, Gunter’s chain or surveyor’s chain, Engineer’s chain, Revenue chain
Benefits of chains :-
a. The chains can be read easily and instantly b. They can resist wear and tear c. They can be repaired in the jobsite without any difficulty
d. There is no requirement to adjust measuring tape e. This type of survey work is very effective for a small plain ground. f. It needs simple instruments. g. Plotting of maps is very simple and trouble-free.
Drawbacks of chain:
a. They are heavy and take long time to open or fold. b. They turn to be longer or shorter because of repeated use. c. If measurement is done in suspension the chain sags greatly. d. Error in measurement may occur because of temperature, sagging and marking. e. Requires more manpower to complete the layout.
This type of surveying is recommended for undulation land where chaining operation is tiresome and prone to errors. This method should not be undertaken for a crowded city containing a huge numbers of buildings and obstacles since it cannot be separated into well-conditioned triangles. As for instance route surveying.
For conducting the survey work of a road, irrigation canal, railways, water and sewer lines, tunneling etc., this method is not suitable at all.
